1 //===---- NewGVN.cpp - Global Value Numbering Pass --------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 /// This file implements the new LLVM's Global Value Numbering pass.
11 /// GVN partitions values computed by a function into congruence classes.
12 /// Values ending up in the same congruence class are guaranteed to be the same
13 /// for every execution of the program. In that respect, congruency is a
14 /// compile-time approximation of equivalence of values at runtime.
15 /// The algorithm implemented here uses a sparse formulation and it's based
16 /// on the ideas described in the paper:
17 /// "A Sparse Algorithm for Predicated Global Value Numbering" from
20 /// A brief overview of the algorithm: The algorithm is essentially the same as
21 /// the standard RPO value numbering algorithm (a good reference is the paper
22 /// "SCC based value numbering" by L. Taylor Simpson) with one major difference:
23 /// The RPO algorithm proceeds, on every iteration, to process every reachable
24 /// block and every instruction in that block. This is because the standard RPO
25 /// algorithm does not track what things have the same value number, it only
26 /// tracks what the value number of a given operation is (the mapping is
27 /// operation -> value number). Thus, when a value number of an operation
28 /// changes, it must reprocess everything to ensure all uses of a value number
29 /// get updated properly. In constrast, the sparse algorithm we use *also*
30 /// tracks what operations have a given value number (IE it also tracks the
31 /// reverse mapping from value number -> operations with that value number), so
32 /// that it only needs to reprocess the instructions that are affected when
33 /// something's value number changes. The vast majority of complexity and code
34 /// in this file is devoted to tracking what value numbers could change for what
35 /// instructions when various things happen. The rest of the algorithm is
36 /// devoted to performing symbolic evaluation, forward propagation, and
37 /// simplification of operations based on the value numbers deduced so far
39 /// In order to make the GVN mostly-complete, we use a technique derived from
40 /// "Detection of Redundant Expressions: A Complete and Polynomial-time
41 /// Algorithm in SSA" by R.R. Pai. The source of incompleteness in most SSA
42 /// based GVN algorithms is related to their inability to detect equivalence
43 /// between phi of ops (IE phi(a+b, c+d)) and op of phis (phi(a,c) + phi(b, d)).
44 /// We resolve this issue by generating the equivalent "phi of ops" form for
45 /// each op of phis we see, in a way that only takes polynomial time to resolve.
47 /// We also do not perform elimination by using any published algorithm. All
48 /// published algorithms are O(Instructions). Instead, we use a technique that
49 /// is O(number of operations with the same value number), enabling us to skip
50 /// trying to eliminate things that have unique value numbers.
51 //===----------------------------------------------------------------------===//
53 #include "llvm/Transforms/Scalar/NewGVN.h"
54 #include "llvm/ADT/BitVector.h"
55 #include "llvm/ADT/DenseMap.h"
56 #include "llvm/ADT/DenseSet.h"
57 #include "llvm/ADT/DepthFirstIterator.h"
58 #include "llvm/ADT/Hashing.h"
59 #include "llvm/ADT/MapVector.h"
60 #include "llvm/ADT/PostOrderIterator.h"
61 #include "llvm/ADT/STLExtras.h"
62 #include "llvm/ADT/SmallPtrSet.h"
63 #include "llvm/ADT/SmallSet.h"
64 #include "llvm/ADT/Statistic.h"
65 #include "llvm/ADT/TinyPtrVector.h"
66 #include "llvm/Analysis/AliasAnalysis.h"
67 #include "llvm/Analysis/AssumptionCache.h"
68 #include "llvm/Analysis/CFG.h"
69 #include "llvm/Analysis/CFGPrinter.h"
70 #include "llvm/Analysis/ConstantFolding.h"
71 #include "llvm/Analysis/GlobalsModRef.h"
72 #include "llvm/Analysis/InstructionSimplify.h"
73 #include "llvm/Analysis/MemoryBuiltins.h"
74 #include "llvm/Analysis/MemoryLocation.h"
75 #include "llvm/Analysis/MemorySSA.h"
76 #include "llvm/Analysis/TargetLibraryInfo.h"
77 #include "llvm/IR/DataLayout.h"
78 #include "llvm/IR/Dominators.h"
79 #include "llvm/IR/GlobalVariable.h"
80 #include "llvm/IR/IRBuilder.h"
81 #include "llvm/IR/IntrinsicInst.h"
82 #include "llvm/IR/LLVMContext.h"
83 #include "llvm/IR/Metadata.h"
84 #include "llvm/IR/PatternMatch.h"
85 #include "llvm/IR/Type.h"
86 #include "llvm/Support/Allocator.h"
87 #include "llvm/Support/CommandLine.h"
88 #include "llvm/Support/Debug.h"
89 #include "llvm/Support/DebugCounter.h"
90 #include "llvm/Transforms/Scalar.h"
91 #include "llvm/Transforms/Scalar/GVNExpression.h"
92 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
93 #include "llvm/Transforms/Utils/Local.h"
94 #include "llvm/Transforms/Utils/PredicateInfo.h"
95 #include "llvm/Transforms/Utils/VNCoercion.h"
97 #include <unordered_map>
100 using namespace llvm;
101 using namespace PatternMatch;
102 using namespace llvm::GVNExpression;
103 using namespace llvm::VNCoercion;
104 #define DEBUG_TYPE "newgvn"
106 STATISTIC(NumGVNInstrDeleted, "Number of instructions deleted");
107 STATISTIC(NumGVNBlocksDeleted, "Number of blocks deleted");
108 STATISTIC(NumGVNOpsSimplified, "Number of Expressions simplified");
109 STATISTIC(NumGVNPhisAllSame, "Number of PHIs whos arguments are all the same");
110 STATISTIC(NumGVNMaxIterations,
111 "Maximum Number of iterations it took to converge GVN");
112 STATISTIC(NumGVNLeaderChanges, "Number of leader changes");
113 STATISTIC(NumGVNSortedLeaderChanges, "Number of sorted leader changes");
114 STATISTIC(NumGVNAvoidedSortedLeaderChanges,
115 "Number of avoided sorted leader changes");
116 STATISTIC(NumGVNDeadStores, "Number of redundant/dead stores eliminated");
117 STATISTIC(NumGVNPHIOfOpsCreated, "Number of PHI of ops created");
118 STATISTIC(NumGVNPHIOfOpsEliminations,
119 "Number of things eliminated using PHI of ops");
120 DEBUG_COUNTER(VNCounter, "newgvn-vn",
121 "Controls which instructions are value numbered")
122 DEBUG_COUNTER(PHIOfOpsCounter, "newgvn-phi",
123 "Controls which instructions we create phi of ops for")
124 // Currently store defining access refinement is too slow due to basicaa being
125 // egregiously slow. This flag lets us keep it working while we work on this
127 static cl::opt<bool> EnableStoreRefinement("enable-store-refinement",
128 cl::init(false), cl::Hidden);
130 //===----------------------------------------------------------------------===//
132 //===----------------------------------------------------------------------===//
136 namespace GVNExpression {
137 Expression::~Expression() = default;
138 BasicExpression::~BasicExpression() = default;
139 CallExpression::~CallExpression() = default;
140 LoadExpression::~LoadExpression() = default;
141 StoreExpression::~StoreExpression() = default;
142 AggregateValueExpression::~AggregateValueExpression() = default;
143 PHIExpression::~PHIExpression() = default;
147 // Tarjan's SCC finding algorithm with Nuutila's improvements
148 // SCCIterator is actually fairly complex for the simple thing we want.
149 // It also wants to hand us SCC's that are unrelated to the phi node we ask
150 // about, and have us process them there or risk redoing work.
151 // Graph traits over a filter iterator also doesn't work that well here.
152 // This SCC finder is specialized to walk use-def chains, and only follows
154 // not generic values (arguments, etc).
157 TarjanSCC() : Components(1) {}
159 void Start(const Instruction *Start) {
160 if (Root.lookup(Start) == 0)
164 const SmallPtrSetImpl<const Value *> &getComponentFor(const Value *V) const {
165 unsigned ComponentID = ValueToComponent.lookup(V);
167 assert(ComponentID > 0 &&
168 "Asking for a component for a value we never processed");
169 return Components[ComponentID];
173 void FindSCC(const Instruction *I) {
175 // Store the DFS Number we had before it possibly gets incremented.
176 unsigned int OurDFS = DFSNum;
177 for (auto &Op : I->operands()) {
178 if (auto *InstOp = dyn_cast<Instruction>(Op)) {
179 if (Root.lookup(Op) == 0)
181 if (!InComponent.count(Op))
182 Root[I] = std::min(Root.lookup(I), Root.lookup(Op));
185 // See if we really were the root of a component, by seeing if we still have
186 // our DFSNumber. If we do, we are the root of the component, and we have
187 // completed a component. If we do not, we are not the root of a component,
188 // and belong on the component stack.
189 if (Root.lookup(I) == OurDFS) {
190 unsigned ComponentID = Components.size();
191 Components.resize(Components.size() + 1);
192 auto &Component = Components.back();
194 DEBUG(dbgs() << "Component root is " << *I << "\n");
195 InComponent.insert(I);
196 ValueToComponent[I] = ComponentID;
197 // Pop a component off the stack and label it.
198 while (!Stack.empty() && Root.lookup(Stack.back()) >= OurDFS) {
199 auto *Member = Stack.back();
200 DEBUG(dbgs() << "Component member is " << *Member << "\n");
201 Component.insert(Member);
202 InComponent.insert(Member);
203 ValueToComponent[Member] = ComponentID;
207 // Part of a component, push to stack
211 unsigned int DFSNum = 1;
212 SmallPtrSet<const Value *, 8> InComponent;
213 DenseMap<const Value *, unsigned int> Root;
214 SmallVector<const Value *, 8> Stack;
215 // Store the components as vector of ptr sets, because we need the topo order
216 // of SCC's, but not individual member order
217 SmallVector<SmallPtrSet<const Value *, 8>, 8> Components;
218 DenseMap<const Value *, unsigned> ValueToComponent;
220 // Congruence classes represent the set of expressions/instructions
221 // that are all the same *during some scope in the function*.
222 // That is, because of the way we perform equality propagation, and
223 // because of memory value numbering, it is not correct to assume
224 // you can willy-nilly replace any member with any other at any
225 // point in the function.
227 // For any Value in the Member set, it is valid to replace any dominated member
230 // Every congruence class has a leader, and the leader is used to symbolize
231 // instructions in a canonical way (IE every operand of an instruction that is a
232 // member of the same congruence class will always be replaced with leader
233 // during symbolization). To simplify symbolization, we keep the leader as a
234 // constant if class can be proved to be a constant value. Otherwise, the
235 // leader is the member of the value set with the smallest DFS number. Each
236 // congruence class also has a defining expression, though the expression may be
237 // null. If it exists, it can be used for forward propagation and reassociation
240 // For memory, we also track a representative MemoryAccess, and a set of memory
241 // members for MemoryPhis (which have no real instructions). Note that for
242 // memory, it seems tempting to try to split the memory members into a
243 // MemoryCongruenceClass or something. Unfortunately, this does not work
244 // easily. The value numbering of a given memory expression depends on the
245 // leader of the memory congruence class, and the leader of memory congruence
246 // class depends on the value numbering of a given memory expression. This
247 // leads to wasted propagation, and in some cases, missed optimization. For
248 // example: If we had value numbered two stores together before, but now do not,
249 // we move them to a new value congruence class. This in turn will move at one
250 // of the memorydefs to a new memory congruence class. Which in turn, affects
251 // the value numbering of the stores we just value numbered (because the memory
252 // congruence class is part of the value number). So while theoretically
253 // possible to split them up, it turns out to be *incredibly* complicated to get
254 // it to work right, because of the interdependency. While structurally
255 // slightly messier, it is algorithmically much simpler and faster to do what we
256 // do here, and track them both at once in the same class.
257 // Note: The default iterators for this class iterate over values
258 class CongruenceClass {
260 using MemberType = Value;
261 using MemberSet = SmallPtrSet<MemberType *, 4>;
262 using MemoryMemberType = MemoryPhi;
263 using MemoryMemberSet = SmallPtrSet<const MemoryMemberType *, 2>;
265 explicit CongruenceClass(unsigned ID) : ID(ID) {}
266 CongruenceClass(unsigned ID, Value *Leader, const Expression *E)
267 : ID(ID), RepLeader(Leader), DefiningExpr(E) {}
268 unsigned getID() const { return ID; }
269 // True if this class has no members left. This is mainly used for assertion
270 // purposes, and for skipping empty classes.
271 bool isDead() const {
272 // If it's both dead from a value perspective, and dead from a memory
273 // perspective, it's really dead.
274 return empty() && memory_empty();
277 Value *getLeader() const { return RepLeader; }
278 void setLeader(Value *Leader) { RepLeader = Leader; }
279 const std::pair<Value *, unsigned int> &getNextLeader() const {
282 void resetNextLeader() { NextLeader = {nullptr, ~0}; }
284 void addPossibleNextLeader(std::pair<Value *, unsigned int> LeaderPair) {
285 if (LeaderPair.second < NextLeader.second)
286 NextLeader = LeaderPair;
289 Value *getStoredValue() const { return RepStoredValue; }
290 void setStoredValue(Value *Leader) { RepStoredValue = Leader; }
291 const MemoryAccess *getMemoryLeader() const { return RepMemoryAccess; }
292 void setMemoryLeader(const MemoryAccess *Leader) { RepMemoryAccess = Leader; }
294 // Forward propagation info
295 const Expression *getDefiningExpr() const { return DefiningExpr; }
298 bool empty() const { return Members.empty(); }
299 unsigned size() const { return Members.size(); }
300 MemberSet::const_iterator begin() const { return Members.begin(); }
301 MemberSet::const_iterator end() const { return Members.end(); }
302 void insert(MemberType *M) { Members.insert(M); }
303 void erase(MemberType *M) { Members.erase(M); }
304 void swap(MemberSet &Other) { Members.swap(Other); }
307 bool memory_empty() const { return MemoryMembers.empty(); }
308 unsigned memory_size() const { return MemoryMembers.size(); }
309 MemoryMemberSet::const_iterator memory_begin() const {
310 return MemoryMembers.begin();
312 MemoryMemberSet::const_iterator memory_end() const {
313 return MemoryMembers.end();
315 iterator_range<MemoryMemberSet::const_iterator> memory() const {
316 return make_range(memory_begin(), memory_end());
318 void memory_insert(const MemoryMemberType *M) { MemoryMembers.insert(M); }
319 void memory_erase(const MemoryMemberType *M) { MemoryMembers.erase(M); }
322 unsigned getStoreCount() const { return StoreCount; }
323 void incStoreCount() { ++StoreCount; }
324 void decStoreCount() {
325 assert(StoreCount != 0 && "Store count went negative");
329 // True if this class has no memory members.
330 bool definesNoMemory() const { return StoreCount == 0 && memory_empty(); }
332 // Return true if two congruence classes are equivalent to each other. This
334 // that every field but the ID number and the dead field are equivalent.
335 bool isEquivalentTo(const CongruenceClass *Other) const {
341 if (std::tie(StoreCount, RepLeader, RepStoredValue, RepMemoryAccess) !=
342 std::tie(Other->StoreCount, Other->RepLeader, Other->RepStoredValue,
343 Other->RepMemoryAccess))
345 if (DefiningExpr != Other->DefiningExpr)
346 if (!DefiningExpr || !Other->DefiningExpr ||
347 *DefiningExpr != *Other->DefiningExpr)
349 // We need some ordered set
350 std::set<Value *> AMembers(Members.begin(), Members.end());
351 std::set<Value *> BMembers(Members.begin(), Members.end());
352 return AMembers == BMembers;
357 // Representative leader.
358 Value *RepLeader = nullptr;
359 // The most dominating leader after our current leader, because the member set
360 // is not sorted and is expensive to keep sorted all the time.
361 std::pair<Value *, unsigned int> NextLeader = {nullptr, ~0U};
362 // If this is represented by a store, the value of the store.
363 Value *RepStoredValue = nullptr;
364 // If this class contains MemoryDefs or MemoryPhis, this is the leading memory
366 const MemoryAccess *RepMemoryAccess = nullptr;
367 // Defining Expression.
368 const Expression *DefiningExpr = nullptr;
369 // Actual members of this class.
371 // This is the set of MemoryPhis that exist in the class. MemoryDefs and
372 // MemoryUses have real instructions representing them, so we only need to
373 // track MemoryPhis here.
374 MemoryMemberSet MemoryMembers;
375 // Number of stores in this congruence class.
376 // This is used so we can detect store equivalence changes properly.
381 template <> struct DenseMapInfo<const Expression *> {
382 static const Expression *getEmptyKey() {
383 auto Val = static_cast<uintptr_t>(-1);
384 Val <<= PointerLikeTypeTraits<const Expression *>::NumLowBitsAvailable;
385 return reinterpret_cast<const Expression *>(Val);
387 static const Expression *getTombstoneKey() {
388 auto Val = static_cast<uintptr_t>(~1U);
389 Val <<= PointerLikeTypeTraits<const Expression *>::NumLowBitsAvailable;
390 return reinterpret_cast<const Expression *>(Val);
392 static unsigned getHashValue(const Expression *E) {
393 return static_cast<unsigned>(E->getComputedHash());
395 static bool isEqual(const Expression *LHS, const Expression *RHS) {
398 if (LHS == getTombstoneKey() || RHS == getTombstoneKey() ||
399 LHS == getEmptyKey() || RHS == getEmptyKey())
401 // Compare hashes before equality. This is *not* what the hashtable does,
402 // since it is computing it modulo the number of buckets, whereas we are
403 // using the full hash keyspace. Since the hashes are precomputed, this
404 // check is *much* faster than equality.
405 if (LHS->getComputedHash() != RHS->getComputedHash())
410 } // end namespace llvm
416 const TargetLibraryInfo *TLI;
419 MemorySSAWalker *MSSAWalker;
420 const DataLayout &DL;
421 std::unique_ptr<PredicateInfo> PredInfo;
423 // These are the only two things the create* functions should have
424 // side-effects on due to allocating memory.
425 mutable BumpPtrAllocator ExpressionAllocator;
426 mutable ArrayRecycler<Value *> ArgRecycler;
427 mutable TarjanSCC SCCFinder;
428 const SimplifyQuery SQ;
430 // Number of function arguments, used by ranking
431 unsigned int NumFuncArgs;
433 // RPOOrdering of basic blocks
434 DenseMap<const DomTreeNode *, unsigned> RPOOrdering;
436 // Congruence class info.
438 // This class is called INITIAL in the paper. It is the class everything
439 // startsout in, and represents any value. Being an optimistic analysis,
440 // anything in the TOP class has the value TOP, which is indeterminate and
441 // equivalent to everything.
442 CongruenceClass *TOPClass;
443 std::vector<CongruenceClass *> CongruenceClasses;
444 unsigned NextCongruenceNum;
447 DenseMap<Value *, CongruenceClass *> ValueToClass;
448 DenseMap<Value *, const Expression *> ValueToExpression;
449 // Value PHI handling, used to make equivalence between phi(op, op) and
451 // These mappings just store various data that would normally be part of the
453 DenseSet<const Instruction *> PHINodeUses;
454 // Map a temporary instruction we created to a parent block.
455 DenseMap<const Value *, BasicBlock *> TempToBlock;
456 // Map between the temporary phis we created and the real instructions they
457 // are known equivalent to.
458 DenseMap<const Value *, PHINode *> RealToTemp;
459 // In order to know when we should re-process instructions that have
460 // phi-of-ops, we track the set of expressions that they needed as
461 // leaders. When we discover new leaders for those expressions, we process the
462 // associated phi-of-op instructions again in case they have changed. The
463 // other way they may change is if they had leaders, and those leaders
464 // disappear. However, at the point they have leaders, there are uses of the
465 // relevant operands in the created phi node, and so they will get reprocessed
466 // through the normal user marking we perform.
467 mutable DenseMap<const Value *, SmallPtrSet<Value *, 2>> AdditionalUsers;
468 DenseMap<const Expression *, SmallPtrSet<Instruction *, 2>>
469 ExpressionToPhiOfOps;
470 // Map from basic block to the temporary operations we created
471 DenseMap<const BasicBlock *, SmallVector<PHINode *, 8>> PHIOfOpsPHIs;
472 // Map from temporary operation to MemoryAccess.
473 DenseMap<const Instruction *, MemoryUseOrDef *> TempToMemory;
474 // Set of all temporary instructions we created.
475 DenseSet<Instruction *> AllTempInstructions;
477 // Mapping from predicate info we used to the instructions we used it with.
478 // In order to correctly ensure propagation, we must keep track of what
479 // comparisons we used, so that when the values of the comparisons change, we
480 // propagate the information to the places we used the comparison.
481 mutable DenseMap<const Value *, SmallPtrSet<Instruction *, 2>>
483 // the same reasoning as PredicateToUsers. When we skip MemoryAccesses for
484 // stores, we no longer can rely solely on the def-use chains of MemorySSA.
485 mutable DenseMap<const MemoryAccess *, SmallPtrSet<MemoryAccess *, 2>>
488 // A table storing which memorydefs/phis represent a memory state provably
489 // equivalent to another memory state.
490 // We could use the congruence class machinery, but the MemoryAccess's are
491 // abstract memory states, so they can only ever be equivalent to each other,
492 // and not to constants, etc.
493 DenseMap<const MemoryAccess *, CongruenceClass *> MemoryAccessToClass;
495 // We could, if we wanted, build MemoryPhiExpressions and
496 // MemoryVariableExpressions, etc, and value number them the same way we value
497 // number phi expressions. For the moment, this seems like overkill. They
498 // can only exist in one of three states: they can be TOP (equal to
499 // everything), Equivalent to something else, or unique. Because we do not
500 // create expressions for them, we need to simulate leader change not just
501 // when they change class, but when they change state. Note: We can do the
502 // same thing for phis, and avoid having phi expressions if we wanted, We
503 // should eventually unify in one direction or the other, so this is a little
504 // bit of an experiment in which turns out easier to maintain.
505 enum MemoryPhiState { MPS_Invalid, MPS_TOP, MPS_Equivalent, MPS_Unique };
506 DenseMap<const MemoryPhi *, MemoryPhiState> MemoryPhiState;
508 enum InstCycleState { ICS_Unknown, ICS_CycleFree, ICS_Cycle };
509 mutable DenseMap<const Instruction *, InstCycleState> InstCycleState;
510 // Expression to class mapping.
511 using ExpressionClassMap = DenseMap<const Expression *, CongruenceClass *>;
512 ExpressionClassMap ExpressionToClass;
514 // We have a single expression that represents currently DeadExpressions.
515 // For dead expressions we can prove will stay dead, we mark them with
516 // DFS number zero. However, it's possible in the case of phi nodes
517 // for us to assume/prove all arguments are dead during fixpointing.
518 // We use DeadExpression for that case.
519 DeadExpression *SingletonDeadExpression = nullptr;
521 // Which values have changed as a result of leader changes.
522 SmallPtrSet<Value *, 8> LeaderChanges;
524 // Reachability info.
525 using BlockEdge = BasicBlockEdge;
526 DenseSet<BlockEdge> ReachableEdges;
527 SmallPtrSet<const BasicBlock *, 8> ReachableBlocks;
529 // This is a bitvector because, on larger functions, we may have
530 // thousands of touched instructions at once (entire blocks,
531 // instructions with hundreds of uses, etc). Even with optimization
532 // for when we mark whole blocks as touched, when this was a
533 // SmallPtrSet or DenseSet, for some functions, we spent >20% of all
534 // the time in GVN just managing this list. The bitvector, on the
535 // other hand, efficiently supports test/set/clear of both
536 // individual and ranges, as well as "find next element" This
537 // enables us to use it as a worklist with essentially 0 cost.
538 BitVector TouchedInstructions;
540 DenseMap<const BasicBlock *, std::pair<unsigned, unsigned>> BlockInstRange;
543 // Debugging for how many times each block and instruction got processed.
544 DenseMap<const Value *, unsigned> ProcessedCount;
548 // This contains a mapping from Instructions to DFS numbers.
549 // The numbering starts at 1. An instruction with DFS number zero
550 // means that the instruction is dead.
551 DenseMap<const Value *, unsigned> InstrDFS;
553 // This contains the mapping DFS numbers to instructions.
554 SmallVector<Value *, 32> DFSToInstr;
557 SmallPtrSet<Instruction *, 8> InstructionsToErase;
560 NewGVN(Function &F, DominatorTree *DT, AssumptionCache *AC,
561 TargetLibraryInfo *TLI, AliasAnalysis *AA, MemorySSA *MSSA,
562 const DataLayout &DL)
563 : F(F), DT(DT), TLI(TLI), AA(AA), MSSA(MSSA), DL(DL),
564 PredInfo(make_unique<PredicateInfo>(F, *DT, *AC)), SQ(DL, TLI, DT, AC) {
569 // Expression handling.
570 const Expression *createExpression(Instruction *) const;
571 const Expression *createBinaryExpression(unsigned, Type *, Value *,
573 PHIExpression *createPHIExpression(Instruction *, bool &HasBackEdge,
574 bool &OriginalOpsConstant) const;
575 const DeadExpression *createDeadExpression() const;
576 const VariableExpression *createVariableExpression(Value *) const;
577 const ConstantExpression *createConstantExpression(Constant *) const;
578 const Expression *createVariableOrConstant(Value *V) const;
579 const UnknownExpression *createUnknownExpression(Instruction *) const;
580 const StoreExpression *createStoreExpression(StoreInst *,
581 const MemoryAccess *) const;
582 LoadExpression *createLoadExpression(Type *, Value *, LoadInst *,
583 const MemoryAccess *) const;
584 const CallExpression *createCallExpression(CallInst *,
585 const MemoryAccess *) const;
586 const AggregateValueExpression *
587 createAggregateValueExpression(Instruction *) const;
588 bool setBasicExpressionInfo(Instruction *, BasicExpression *) const;
590 // Congruence class handling.
591 CongruenceClass *createCongruenceClass(Value *Leader, const Expression *E) {
592 auto *result = new CongruenceClass(NextCongruenceNum++, Leader, E);
593 CongruenceClasses.emplace_back(result);
597 CongruenceClass *createMemoryClass(MemoryAccess *MA) {
598 auto *CC = createCongruenceClass(nullptr, nullptr);
599 CC->setMemoryLeader(MA);
602 CongruenceClass *ensureLeaderOfMemoryClass(MemoryAccess *MA) {
603 auto *CC = getMemoryClass(MA);
604 if (CC->getMemoryLeader() != MA)
605 CC = createMemoryClass(MA);
609 CongruenceClass *createSingletonCongruenceClass(Value *Member) {
610 CongruenceClass *CClass = createCongruenceClass(Member, nullptr);
611 CClass->insert(Member);
612 ValueToClass[Member] = CClass;
615 void initializeCongruenceClasses(Function &F);
616 const Expression *makePossiblePhiOfOps(Instruction *,
617 SmallPtrSetImpl<Value *> &);
618 void addPhiOfOps(PHINode *Op, BasicBlock *BB, Instruction *ExistingValue);
620 // Value number an Instruction or MemoryPhi.
621 void valueNumberMemoryPhi(MemoryPhi *);
622 void valueNumberInstruction(Instruction *);
624 // Symbolic evaluation.
625 const Expression *checkSimplificationResults(Expression *, Instruction *,
627 const Expression *performSymbolicEvaluation(Value *,
628 SmallPtrSetImpl<Value *> &) const;
629 const Expression *performSymbolicLoadCoercion(Type *, Value *, LoadInst *,
631 MemoryAccess *) const;
632 const Expression *performSymbolicLoadEvaluation(Instruction *) const;
633 const Expression *performSymbolicStoreEvaluation(Instruction *) const;
634 const Expression *performSymbolicCallEvaluation(Instruction *) const;
635 const Expression *performSymbolicPHIEvaluation(Instruction *) const;
636 const Expression *performSymbolicAggrValueEvaluation(Instruction *) const;
637 const Expression *performSymbolicCmpEvaluation(Instruction *) const;
638 const Expression *performSymbolicPredicateInfoEvaluation(Instruction *) const;
640 // Congruence finding.
641 bool someEquivalentDominates(const Instruction *, const Instruction *) const;
642 Value *lookupOperandLeader(Value *) const;
643 void performCongruenceFinding(Instruction *, const Expression *);
644 void moveValueToNewCongruenceClass(Instruction *, const Expression *,
645 CongruenceClass *, CongruenceClass *);
646 void moveMemoryToNewCongruenceClass(Instruction *, MemoryAccess *,
647 CongruenceClass *, CongruenceClass *);
648 Value *getNextValueLeader(CongruenceClass *) const;
649 const MemoryAccess *getNextMemoryLeader(CongruenceClass *) const;
650 bool setMemoryClass(const MemoryAccess *From, CongruenceClass *To);
651 CongruenceClass *getMemoryClass(const MemoryAccess *MA) const;
652 const MemoryAccess *lookupMemoryLeader(const MemoryAccess *) const;
653 bool isMemoryAccessTOP(const MemoryAccess *) const;
656 unsigned int getRank(const Value *) const;
657 bool shouldSwapOperands(const Value *, const Value *) const;
659 // Reachability handling.
660 void updateReachableEdge(BasicBlock *, BasicBlock *);
661 void processOutgoingEdges(TerminatorInst *, BasicBlock *);
662 Value *findConditionEquivalence(Value *) const;
666 void convertClassToDFSOrdered(const CongruenceClass &,
667 SmallVectorImpl<ValueDFS> &,
668 DenseMap<const Value *, unsigned int> &,
669 SmallPtrSetImpl<Instruction *> &) const;
670 void convertClassToLoadsAndStores(const CongruenceClass &,
671 SmallVectorImpl<ValueDFS> &) const;
673 bool eliminateInstructions(Function &);
674 void replaceInstruction(Instruction *, Value *);
675 void markInstructionForDeletion(Instruction *);
676 void deleteInstructionsInBlock(BasicBlock *);
677 Value *findPhiOfOpsLeader(const Expression *E, const BasicBlock *BB) const;
679 // New instruction creation.
680 void handleNewInstruction(Instruction *){};
682 // Various instruction touch utilities
683 template <typename Map, typename KeyType, typename Func>
684 void for_each_found(Map &, const KeyType &, Func);
685 template <typename Map, typename KeyType>
686 void touchAndErase(Map &, const KeyType &);
687 void markUsersTouched(Value *);
688 void markMemoryUsersTouched(const MemoryAccess *);
689 void markMemoryDefTouched(const MemoryAccess *);
690 void markPredicateUsersTouched(Instruction *);
691 void markValueLeaderChangeTouched(CongruenceClass *CC);
692 void markMemoryLeaderChangeTouched(CongruenceClass *CC);
693 void markPhiOfOpsChanged(const Expression *E);
694 void addPredicateUsers(const PredicateBase *, Instruction *) const;
695 void addMemoryUsers(const MemoryAccess *To, MemoryAccess *U) const;
696 void addAdditionalUsers(Value *To, Value *User) const;
698 // Main loop of value numbering
699 void iterateTouchedInstructions();
702 void cleanupTables();
703 std::pair<unsigned, unsigned> assignDFSNumbers(BasicBlock *, unsigned);
704 void updateProcessedCount(const Value *V);
705 void verifyMemoryCongruency() const;
706 void verifyIterationSettled(Function &F);
707 void verifyStoreExpressions() const;
708 bool singleReachablePHIPath(SmallPtrSet<const MemoryAccess *, 8> &,
709 const MemoryAccess *, const MemoryAccess *) const;
710 BasicBlock *getBlockForValue(Value *V) const;
711 void deleteExpression(const Expression *E) const;
712 MemoryUseOrDef *getMemoryAccess(const Instruction *) const;
713 MemoryAccess *getDefiningAccess(const MemoryAccess *) const;
714 MemoryPhi *getMemoryAccess(const BasicBlock *) const;
715 template <class T, class Range> T *getMinDFSOfRange(const Range &) const;
716 unsigned InstrToDFSNum(const Value *V) const {
717 assert(isa<Instruction>(V) && "This should not be used for MemoryAccesses");
718 return InstrDFS.lookup(V);
721 unsigned InstrToDFSNum(const MemoryAccess *MA) const {
722 return MemoryToDFSNum(MA);
724 Value *InstrFromDFSNum(unsigned DFSNum) { return DFSToInstr[DFSNum]; }
725 // Given a MemoryAccess, return the relevant instruction DFS number. Note:
726 // This deliberately takes a value so it can be used with Use's, which will
727 // auto-convert to Value's but not to MemoryAccess's.
728 unsigned MemoryToDFSNum(const Value *MA) const {
729 assert(isa<MemoryAccess>(MA) &&
730 "This should not be used with instructions");
731 return isa<MemoryUseOrDef>(MA)
732 ? InstrToDFSNum(cast<MemoryUseOrDef>(MA)->getMemoryInst())
733 : InstrDFS.lookup(MA);
735 bool isCycleFree(const Instruction *) const;
736 bool isBackedge(BasicBlock *From, BasicBlock *To) const;
737 // Debug counter info. When verifying, we have to reset the value numbering
738 // debug counter to the same state it started in to get the same results.
739 std::pair<int, int> StartingVNCounter;
741 } // end anonymous namespace
743 template <typename T>
744 static bool equalsLoadStoreHelper(const T &LHS, const Expression &RHS) {
745 if (!isa<LoadExpression>(RHS) && !isa<StoreExpression>(RHS))
747 return LHS.MemoryExpression::equals(RHS);
750 bool LoadExpression::equals(const Expression &Other) const {
751 return equalsLoadStoreHelper(*this, Other);
754 bool StoreExpression::equals(const Expression &Other) const {
755 if (!equalsLoadStoreHelper(*this, Other))
757 // Make sure that store vs store includes the value operand.
758 if (const auto *S = dyn_cast<StoreExpression>(&Other))
759 if (getStoredValue() != S->getStoredValue())
764 // Determine if the edge From->To is a backedge
765 bool NewGVN::isBackedge(BasicBlock *From, BasicBlock *To) const {
768 auto *FromDTN = DT->getNode(From);
769 auto *ToDTN = DT->getNode(To);
770 return RPOOrdering.lookup(FromDTN) >= RPOOrdering.lookup(ToDTN);
774 static std::string getBlockName(const BasicBlock *B) {
775 return DOTGraphTraits<const Function *>::getSimpleNodeLabel(B, nullptr);
779 // Get a MemoryAccess for an instruction, fake or real.
780 MemoryUseOrDef *NewGVN::getMemoryAccess(const Instruction *I) const {
781 auto *Result = MSSA->getMemoryAccess(I);
782 return Result ? Result : TempToMemory.lookup(I);
785 // Get a MemoryPhi for a basic block. These are all real.
786 MemoryPhi *NewGVN::getMemoryAccess(const BasicBlock *BB) const {
787 return MSSA->getMemoryAccess(BB);
790 // Get the basic block from an instruction/memory value.
791 BasicBlock *NewGVN::getBlockForValue(Value *V) const {
792 if (auto *I = dyn_cast<Instruction>(V)) {
793 auto *Parent = I->getParent();
796 Parent = TempToBlock.lookup(V);
797 assert(Parent && "Every fake instruction should have a block");
801 auto *MP = dyn_cast<MemoryPhi>(V);
802 assert(MP && "Should have been an instruction or a MemoryPhi");
803 return MP->getBlock();
806 // Delete a definitely dead expression, so it can be reused by the expression
807 // allocator. Some of these are not in creation functions, so we have to accept
809 void NewGVN::deleteExpression(const Expression *E) const {
810 assert(isa<BasicExpression>(E));
811 auto *BE = cast<BasicExpression>(E);
812 const_cast<BasicExpression *>(BE)->deallocateOperands(ArgRecycler);
813 ExpressionAllocator.Deallocate(E);
815 PHIExpression *NewGVN::createPHIExpression(Instruction *I, bool &HasBackedge,
816 bool &OriginalOpsConstant) const {
817 BasicBlock *PHIBlock = getBlockForValue(I);
818 auto *PN = cast<PHINode>(I);
820 new (ExpressionAllocator) PHIExpression(PN->getNumOperands(), PHIBlock);
822 E->allocateOperands(ArgRecycler, ExpressionAllocator);
823 E->setType(I->getType());
824 E->setOpcode(I->getOpcode());
826 // NewGVN assumes the operands of a PHI node are in a consistent order across
827 // PHIs. LLVM doesn't seem to always guarantee this. While we need to fix
828 // this in LLVM at some point we don't want GVN to find wrong congruences.
829 // Therefore, here we sort uses in predecessor order.
830 // We're sorting the values by pointer. In theory this might be cause of
831 // non-determinism, but here we don't rely on the ordering for anything
832 // significant, e.g. we don't create new instructions based on it so we're
834 SmallVector<const Use *, 4> PHIOperands;
835 for (const Use &U : PN->operands())
836 PHIOperands.push_back(&U);
837 std::sort(PHIOperands.begin(), PHIOperands.end(),
838 [&](const Use *U1, const Use *U2) {
839 return PN->getIncomingBlock(*U1) < PN->getIncomingBlock(*U2);
842 // Filter out unreachable phi operands.
843 auto Filtered = make_filter_range(PHIOperands, [&](const Use *U) {
846 if (!ReachableEdges.count({PN->getIncomingBlock(*U), PHIBlock}))
848 // Things in TOPClass are equivalent to everything.
849 if (ValueToClass.lookup(*U) == TOPClass)
853 std::transform(Filtered.begin(), Filtered.end(), op_inserter(E),
854 [&](const Use *U) -> Value * {
855 auto *BB = PN->getIncomingBlock(*U);
856 HasBackedge = HasBackedge || isBackedge(BB, PHIBlock);
857 OriginalOpsConstant =
858 OriginalOpsConstant && isa<Constant>(*U);
859 return lookupOperandLeader(*U);
864 // Set basic expression info (Arguments, type, opcode) for Expression
865 // E from Instruction I in block B.
866 bool NewGVN::setBasicExpressionInfo(Instruction *I, BasicExpression *E) const {
867 bool AllConstant = true;
868 if (auto *GEP = dyn_cast<GetElementPtrInst>(I))
869 E->setType(GEP->getSourceElementType());
871 E->setType(I->getType());
872 E->setOpcode(I->getOpcode());
873 E->allocateOperands(ArgRecycler, ExpressionAllocator);
875 // Transform the operand array into an operand leader array, and keep track of
876 // whether all members are constant.
877 std::transform(I->op_begin(), I->op_end(), op_inserter(E), [&](Value *O) {
878 auto Operand = lookupOperandLeader(O);
879 AllConstant = AllConstant && isa<Constant>(Operand);
886 const Expression *NewGVN::createBinaryExpression(unsigned Opcode, Type *T,
889 auto *E = new (ExpressionAllocator) BasicExpression(2);
892 E->setOpcode(Opcode);
893 E->allocateOperands(ArgRecycler, ExpressionAllocator);
894 if (Instruction::isCommutative(Opcode)) {
895 // Ensure that commutative instructions that only differ by a permutation
896 // of their operands get the same value number by sorting the operand value
897 // numbers. Since all commutative instructions have two operands it is more
898 // efficient to sort by hand rather than using, say, std::sort.
899 if (shouldSwapOperands(Arg1, Arg2))
900 std::swap(Arg1, Arg2);
902 E->op_push_back(lookupOperandLeader(Arg1));
903 E->op_push_back(lookupOperandLeader(Arg2));
905 Value *V = SimplifyBinOp(Opcode, E->getOperand(0), E->getOperand(1), SQ);
906 if (const Expression *SimplifiedE = checkSimplificationResults(E, nullptr, V))
911 // Take a Value returned by simplification of Expression E/Instruction
912 // I, and see if it resulted in a simpler expression. If so, return
914 // TODO: Once finished, this should not take an Instruction, we only
915 // use it for printing.
916 const Expression *NewGVN::checkSimplificationResults(Expression *E,
921 if (auto *C = dyn_cast<Constant>(V)) {
923 DEBUG(dbgs() << "Simplified " << *I << " to "
924 << " constant " << *C << "\n");
925 NumGVNOpsSimplified++;
926 assert(isa<BasicExpression>(E) &&
927 "We should always have had a basic expression here");
929 return createConstantExpression(C);
930 } else if (isa<Argument>(V) || isa<GlobalVariable>(V)) {
932 DEBUG(dbgs() << "Simplified " << *I << " to "
933 << " variable " << *V << "\n");
935 return createVariableExpression(V);
938 CongruenceClass *CC = ValueToClass.lookup(V);
939 if (CC && CC->getDefiningExpr()) {
940 // If we simplified to something else, we need to communicate
941 // that we're users of the value we simplified to.
943 // Don't add temporary instructions to the user lists.
944 if (!AllTempInstructions.count(I))
945 addAdditionalUsers(V, I);
949 DEBUG(dbgs() << "Simplified " << *I << " to "
950 << " expression " << *CC->getDefiningExpr() << "\n");
951 NumGVNOpsSimplified++;
953 return CC->getDefiningExpr();
958 const Expression *NewGVN::createExpression(Instruction *I) const {
959 auto *E = new (ExpressionAllocator) BasicExpression(I->getNumOperands());
961 bool AllConstant = setBasicExpressionInfo(I, E);
963 if (I->isCommutative()) {
964 // Ensure that commutative instructions that only differ by a permutation
965 // of their operands get the same value number by sorting the operand value
966 // numbers. Since all commutative instructions have two operands it is more
967 // efficient to sort by hand rather than using, say, std::sort.
968 assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!");
969 if (shouldSwapOperands(E->getOperand(0), E->getOperand(1)))
970 E->swapOperands(0, 1);
973 // Perform simplificaiton
974 // TODO: Right now we only check to see if we get a constant result.
975 // We may get a less than constant, but still better, result for
980 // We should handle this by simply rewriting the expression.
981 if (auto *CI = dyn_cast<CmpInst>(I)) {
982 // Sort the operand value numbers so x<y and y>x get the same value
984 CmpInst::Predicate Predicate = CI->getPredicate();
985 if (shouldSwapOperands(E->getOperand(0), E->getOperand(1))) {
986 E->swapOperands(0, 1);
987 Predicate = CmpInst::getSwappedPredicate(Predicate);
989 E->setOpcode((CI->getOpcode() << 8) | Predicate);
990 // TODO: 25% of our time is spent in SimplifyCmpInst with pointer operands
991 assert(I->getOperand(0)->getType() == I->getOperand(1)->getType() &&
992 "Wrong types on cmp instruction");
993 assert((E->getOperand(0)->getType() == I->getOperand(0)->getType() &&
994 E->getOperand(1)->getType() == I->getOperand(1)->getType()));
996 SimplifyCmpInst(Predicate, E->getOperand(0), E->getOperand(1), SQ);
997 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
999 } else if (isa<SelectInst>(I)) {
1000 if (isa<Constant>(E->getOperand(0)) ||
1001 E->getOperand(0) == E->getOperand(1)) {
1002 assert(E->getOperand(1)->getType() == I->getOperand(1)->getType() &&
1003 E->getOperand(2)->getType() == I->getOperand(2)->getType());
1004 Value *V = SimplifySelectInst(E->getOperand(0), E->getOperand(1),
1005 E->getOperand(2), SQ);
1006 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1009 } else if (I->isBinaryOp()) {
1011 SimplifyBinOp(E->getOpcode(), E->getOperand(0), E->getOperand(1), SQ);
1012 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1014 } else if (auto *BI = dyn_cast<BitCastInst>(I)) {
1016 SimplifyCastInst(BI->getOpcode(), BI->getOperand(0), BI->getType(), SQ);
1017 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1019 } else if (isa<GetElementPtrInst>(I)) {
1020 Value *V = SimplifyGEPInst(
1021 E->getType(), ArrayRef<Value *>(E->op_begin(), E->op_end()), SQ);
1022 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1024 } else if (AllConstant) {
1025 // We don't bother trying to simplify unless all of the operands
1027 // TODO: There are a lot of Simplify*'s we could call here, if we
1028 // wanted to. The original motivating case for this code was a
1029 // zext i1 false to i8, which we don't have an interface to
1030 // simplify (IE there is no SimplifyZExt).
1032 SmallVector<Constant *, 8> C;
1033 for (Value *Arg : E->operands())
1034 C.emplace_back(cast<Constant>(Arg));
1036 if (Value *V = ConstantFoldInstOperands(I, C, DL, TLI))
1037 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1043 const AggregateValueExpression *
1044 NewGVN::createAggregateValueExpression(Instruction *I) const {
1045 if (auto *II = dyn_cast<InsertValueInst>(I)) {
1046 auto *E = new (ExpressionAllocator)
1047 AggregateValueExpression(I->getNumOperands(), II->getNumIndices());
1048 setBasicExpressionInfo(I, E);
1049 E->allocateIntOperands(ExpressionAllocator);
1050 std::copy(II->idx_begin(), II->idx_end(), int_op_inserter(E));
1052 } else if (auto *EI = dyn_cast<ExtractValueInst>(I)) {
1053 auto *E = new (ExpressionAllocator)
1054 AggregateValueExpression(I->getNumOperands(), EI->getNumIndices());
1055 setBasicExpressionInfo(EI, E);
1056 E->allocateIntOperands(ExpressionAllocator);
1057 std::copy(EI->idx_begin(), EI->idx_end(), int_op_inserter(E));
1060 llvm_unreachable("Unhandled type of aggregate value operation");
1063 const DeadExpression *NewGVN::createDeadExpression() const {
1064 // DeadExpression has no arguments and all DeadExpression's are the same,
1065 // so we only need one of them.
1066 return SingletonDeadExpression;
1069 const VariableExpression *NewGVN::createVariableExpression(Value *V) const {
1070 auto *E = new (ExpressionAllocator) VariableExpression(V);
1071 E->setOpcode(V->getValueID());
1075 const Expression *NewGVN::createVariableOrConstant(Value *V) const {
1076 if (auto *C = dyn_cast<Constant>(V))
1077 return createConstantExpression(C);
1078 return createVariableExpression(V);
1081 const ConstantExpression *NewGVN::createConstantExpression(Constant *C) const {
1082 auto *E = new (ExpressionAllocator) ConstantExpression(C);
1083 E->setOpcode(C->getValueID());
1087 const UnknownExpression *NewGVN::createUnknownExpression(Instruction *I) const {
1088 auto *E = new (ExpressionAllocator) UnknownExpression(I);
1089 E->setOpcode(I->getOpcode());
1093 const CallExpression *
1094 NewGVN::createCallExpression(CallInst *CI, const MemoryAccess *MA) const {
1095 // FIXME: Add operand bundles for calls.
1097 new (ExpressionAllocator) CallExpression(CI->getNumOperands(), CI, MA);
1098 setBasicExpressionInfo(CI, E);
1102 // Return true if some equivalent of instruction Inst dominates instruction U.
1103 bool NewGVN::someEquivalentDominates(const Instruction *Inst,
1104 const Instruction *U) const {
1105 auto *CC = ValueToClass.lookup(Inst);
1106 // This must be an instruction because we are only called from phi nodes
1107 // in the case that the value it needs to check against is an instruction.
1109 // The most likely candiates for dominance are the leader and the next leader.
1110 // The leader or nextleader will dominate in all cases where there is an
1111 // equivalent that is higher up in the dom tree.
1112 // We can't *only* check them, however, because the
1113 // dominator tree could have an infinite number of non-dominating siblings
1114 // with instructions that are in the right congruence class.
1119 // Instruction U could be in H, with equivalents in every other sibling.
1120 // Depending on the rpo order picked, the leader could be the equivalent in
1121 // any of these siblings.
1124 if (DT->dominates(cast<Instruction>(CC->getLeader()), U))
1126 if (CC->getNextLeader().first &&
1127 DT->dominates(cast<Instruction>(CC->getNextLeader().first), U))
1129 return llvm::any_of(*CC, [&](const Value *Member) {
1130 return Member != CC->getLeader() &&
1131 DT->dominates(cast<Instruction>(Member), U);
1135 // See if we have a congruence class and leader for this operand, and if so,
1136 // return it. Otherwise, return the operand itself.
1137 Value *NewGVN::lookupOperandLeader(Value *V) const {
1138 CongruenceClass *CC = ValueToClass.lookup(V);
1140 // Everything in TOP is represented by undef, as it can be any value.
1141 // We do have to make sure we get the type right though, so we can't set the
1142 // RepLeader to undef.
1144 return UndefValue::get(V->getType());
1145 return CC->getStoredValue() ? CC->getStoredValue() : CC->getLeader();
1151 const MemoryAccess *NewGVN::lookupMemoryLeader(const MemoryAccess *MA) const {
1152 auto *CC = getMemoryClass(MA);
1153 assert(CC->getMemoryLeader() &&
1154 "Every MemoryAccess should be mapped to a congruence class with a "
1155 "representative memory access");
1156 return CC->getMemoryLeader();
1159 // Return true if the MemoryAccess is really equivalent to everything. This is
1160 // equivalent to the lattice value "TOP" in most lattices. This is the initial
1161 // state of all MemoryAccesses.
1162 bool NewGVN::isMemoryAccessTOP(const MemoryAccess *MA) const {
1163 return getMemoryClass(MA) == TOPClass;
1166 LoadExpression *NewGVN::createLoadExpression(Type *LoadType, Value *PointerOp,
1168 const MemoryAccess *MA) const {
1170 new (ExpressionAllocator) LoadExpression(1, LI, lookupMemoryLeader(MA));
1171 E->allocateOperands(ArgRecycler, ExpressionAllocator);
1172 E->setType(LoadType);
1174 // Give store and loads same opcode so they value number together.
1176 E->op_push_back(PointerOp);
1178 E->setAlignment(LI->getAlignment());
1180 // TODO: Value number heap versions. We may be able to discover
1181 // things alias analysis can't on it's own (IE that a store and a
1182 // load have the same value, and thus, it isn't clobbering the load).
1186 const StoreExpression *
1187 NewGVN::createStoreExpression(StoreInst *SI, const MemoryAccess *MA) const {
1188 auto *StoredValueLeader = lookupOperandLeader(SI->getValueOperand());
1189 auto *E = new (ExpressionAllocator)
1190 StoreExpression(SI->getNumOperands(), SI, StoredValueLeader, MA);
1191 E->allocateOperands(ArgRecycler, ExpressionAllocator);
1192 E->setType(SI->getValueOperand()->getType());
1194 // Give store and loads same opcode so they value number together.
1196 E->op_push_back(lookupOperandLeader(SI->getPointerOperand()));
1198 // TODO: Value number heap versions. We may be able to discover
1199 // things alias analysis can't on it's own (IE that a store and a
1200 // load have the same value, and thus, it isn't clobbering the load).
1204 const Expression *NewGVN::performSymbolicStoreEvaluation(Instruction *I) const {
1205 // Unlike loads, we never try to eliminate stores, so we do not check if they
1206 // are simple and avoid value numbering them.
1207 auto *SI = cast<StoreInst>(I);
1208 auto *StoreAccess = getMemoryAccess(SI);
1209 // Get the expression, if any, for the RHS of the MemoryDef.
1210 const MemoryAccess *StoreRHS = StoreAccess->getDefiningAccess();
1211 if (EnableStoreRefinement)
1212 StoreRHS = MSSAWalker->getClobberingMemoryAccess(StoreAccess);
1213 // If we bypassed the use-def chains, make sure we add a use.
1214 if (StoreRHS != StoreAccess->getDefiningAccess())
1215 addMemoryUsers(StoreRHS, StoreAccess);
1216 StoreRHS = lookupMemoryLeader(StoreRHS);
1217 // If we are defined by ourselves, use the live on entry def.
1218 if (StoreRHS == StoreAccess)
1219 StoreRHS = MSSA->getLiveOnEntryDef();
1221 if (SI->isSimple()) {
1222 // See if we are defined by a previous store expression, it already has a
1223 // value, and it's the same value as our current store. FIXME: Right now, we
1224 // only do this for simple stores, we should expand to cover memcpys, etc.
1225 const auto *LastStore = createStoreExpression(SI, StoreRHS);
1226 const auto *LastCC = ExpressionToClass.lookup(LastStore);
1227 // Basically, check if the congruence class the store is in is defined by a
1228 // store that isn't us, and has the same value. MemorySSA takes care of
1229 // ensuring the store has the same memory state as us already.
1230 // The RepStoredValue gets nulled if all the stores disappear in a class, so
1231 // we don't need to check if the class contains a store besides us.
1233 LastCC->getStoredValue() == lookupOperandLeader(SI->getValueOperand()))
1235 deleteExpression(LastStore);
1236 // Also check if our value operand is defined by a load of the same memory
1237 // location, and the memory state is the same as it was then (otherwise, it
1238 // could have been overwritten later. See test32 in
1239 // transforms/DeadStoreElimination/simple.ll).
1241 dyn_cast<LoadInst>(lookupOperandLeader(SI->getValueOperand()))) {
1242 if ((lookupOperandLeader(LI->getPointerOperand()) ==
1243 lookupOperandLeader(SI->getPointerOperand())) &&
1244 (lookupMemoryLeader(getMemoryAccess(LI)->getDefiningAccess()) ==
1246 return createStoreExpression(SI, StoreRHS);
1250 // If the store is not equivalent to anything, value number it as a store that
1251 // produces a unique memory state (instead of using it's MemoryUse, we use
1253 return createStoreExpression(SI, StoreAccess);
1256 // See if we can extract the value of a loaded pointer from a load, a store, or
1257 // a memory instruction.
1259 NewGVN::performSymbolicLoadCoercion(Type *LoadType, Value *LoadPtr,
1260 LoadInst *LI, Instruction *DepInst,
1261 MemoryAccess *DefiningAccess) const {
1262 assert((!LI || LI->isSimple()) && "Not a simple load");
1263 if (auto *DepSI = dyn_cast<StoreInst>(DepInst)) {
1264 // Can't forward from non-atomic to atomic without violating memory model.
1265 // Also don't need to coerce if they are the same type, we will just
1267 if (LI->isAtomic() > DepSI->isAtomic() ||
1268 LoadType == DepSI->getValueOperand()->getType())
1270 int Offset = analyzeLoadFromClobberingStore(LoadType, LoadPtr, DepSI, DL);
1272 if (auto *C = dyn_cast<Constant>(
1273 lookupOperandLeader(DepSI->getValueOperand()))) {
1274 DEBUG(dbgs() << "Coercing load from store " << *DepSI << " to constant "
1276 return createConstantExpression(
1277 getConstantStoreValueForLoad(C, Offset, LoadType, DL));
1281 } else if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1282 // Can't forward from non-atomic to atomic without violating memory model.
1283 if (LI->isAtomic() > DepLI->isAtomic())
1285 int Offset = analyzeLoadFromClobberingLoad(LoadType, LoadPtr, DepLI, DL);
1287 // We can coerce a constant load into a load
1288 if (auto *C = dyn_cast<Constant>(lookupOperandLeader(DepLI)))
1289 if (auto *PossibleConstant =
1290 getConstantLoadValueForLoad(C, Offset, LoadType, DL)) {
1291 DEBUG(dbgs() << "Coercing load from load " << *LI << " to constant "
1292 << *PossibleConstant << "\n");
1293 return createConstantExpression(PossibleConstant);
1297 } else if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInst)) {
1298 int Offset = analyzeLoadFromClobberingMemInst(LoadType, LoadPtr, DepMI, DL);
1300 if (auto *PossibleConstant =
1301 getConstantMemInstValueForLoad(DepMI, Offset, LoadType, DL)) {
1302 DEBUG(dbgs() << "Coercing load from meminst " << *DepMI
1303 << " to constant " << *PossibleConstant << "\n");
1304 return createConstantExpression(PossibleConstant);
1309 // All of the below are only true if the loaded pointer is produced
1310 // by the dependent instruction.
1311 if (LoadPtr != lookupOperandLeader(DepInst) &&
1312 !AA->isMustAlias(LoadPtr, DepInst))
1314 // If this load really doesn't depend on anything, then we must be loading an
1315 // undef value. This can happen when loading for a fresh allocation with no
1316 // intervening stores, for example. Note that this is only true in the case
1317 // that the result of the allocation is pointer equal to the load ptr.
1318 if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI)) {
1319 return createConstantExpression(UndefValue::get(LoadType));
1321 // If this load occurs either right after a lifetime begin,
1322 // then the loaded value is undefined.
1323 else if (auto *II = dyn_cast<IntrinsicInst>(DepInst)) {
1324 if (II->getIntrinsicID() == Intrinsic::lifetime_start)
1325 return createConstantExpression(UndefValue::get(LoadType));
1327 // If this load follows a calloc (which zero initializes memory),
1328 // then the loaded value is zero
1329 else if (isCallocLikeFn(DepInst, TLI)) {
1330 return createConstantExpression(Constant::getNullValue(LoadType));
1336 const Expression *NewGVN::performSymbolicLoadEvaluation(Instruction *I) const {
1337 auto *LI = cast<LoadInst>(I);
1339 // We can eliminate in favor of non-simple loads, but we won't be able to
1340 // eliminate the loads themselves.
1341 if (!LI->isSimple())
1344 Value *LoadAddressLeader = lookupOperandLeader(LI->getPointerOperand());
1345 // Load of undef is undef.
1346 if (isa<UndefValue>(LoadAddressLeader))
1347 return createConstantExpression(UndefValue::get(LI->getType()));
1348 MemoryAccess *OriginalAccess = getMemoryAccess(I);
1349 MemoryAccess *DefiningAccess =
1350 MSSAWalker->getClobberingMemoryAccess(OriginalAccess);
1352 if (!MSSA->isLiveOnEntryDef(DefiningAccess)) {
1353 if (auto *MD = dyn_cast<MemoryDef>(DefiningAccess)) {
1354 Instruction *DefiningInst = MD->getMemoryInst();
1355 // If the defining instruction is not reachable, replace with undef.
1356 if (!ReachableBlocks.count(DefiningInst->getParent()))
1357 return createConstantExpression(UndefValue::get(LI->getType()));
1358 // This will handle stores and memory insts. We only do if it the
1359 // defining access has a different type, or it is a pointer produced by
1360 // certain memory operations that cause the memory to have a fixed value
1361 // (IE things like calloc).
1362 if (const auto *CoercionResult =
1363 performSymbolicLoadCoercion(LI->getType(), LoadAddressLeader, LI,
1364 DefiningInst, DefiningAccess))
1365 return CoercionResult;
1369 const Expression *E = createLoadExpression(LI->getType(), LoadAddressLeader,
1370 LI, DefiningAccess);
1375 NewGVN::performSymbolicPredicateInfoEvaluation(Instruction *I) const {
1376 auto *PI = PredInfo->getPredicateInfoFor(I);
1380 DEBUG(dbgs() << "Found predicate info from instruction !\n");
1382 auto *PWC = dyn_cast<PredicateWithCondition>(PI);
1386 auto *CopyOf = I->getOperand(0);
1387 auto *Cond = PWC->Condition;
1389 // If this a copy of the condition, it must be either true or false depending
1390 // on the predicate info type and edge
1391 if (CopyOf == Cond) {
1392 // We should not need to add predicate users because the predicate info is
1393 // already a use of this operand.
1394 if (isa<PredicateAssume>(PI))
1395 return createConstantExpression(ConstantInt::getTrue(Cond->getType()));
1396 if (auto *PBranch = dyn_cast<PredicateBranch>(PI)) {
1397 if (PBranch->TrueEdge)
1398 return createConstantExpression(ConstantInt::getTrue(Cond->getType()));
1399 return createConstantExpression(ConstantInt::getFalse(Cond->getType()));
1401 if (auto *PSwitch = dyn_cast<PredicateSwitch>(PI))
1402 return createConstantExpression(cast<Constant>(PSwitch->CaseValue));
1405 // Not a copy of the condition, so see what the predicates tell us about this
1406 // value. First, though, we check to make sure the value is actually a copy
1407 // of one of the condition operands. It's possible, in certain cases, for it
1408 // to be a copy of a predicateinfo copy. In particular, if two branch
1409 // operations use the same condition, and one branch dominates the other, we
1410 // will end up with a copy of a copy. This is currently a small deficiency in
1411 // predicateinfo. What will end up happening here is that we will value
1412 // number both copies the same anyway.
1414 // Everything below relies on the condition being a comparison.
1415 auto *Cmp = dyn_cast<CmpInst>(Cond);
1419 if (CopyOf != Cmp->getOperand(0) && CopyOf != Cmp->getOperand(1)) {
1420 DEBUG(dbgs() << "Copy is not of any condition operands!\n");
1423 Value *FirstOp = lookupOperandLeader(Cmp->getOperand(0));
1424 Value *SecondOp = lookupOperandLeader(Cmp->getOperand(1));
1425 bool SwappedOps = false;
1427 if (shouldSwapOperands(FirstOp, SecondOp)) {
1428 std::swap(FirstOp, SecondOp);
1431 CmpInst::Predicate Predicate =
1432 SwappedOps ? Cmp->getSwappedPredicate() : Cmp->getPredicate();
1434 if (isa<PredicateAssume>(PI)) {
1435 // If the comparison is true when the operands are equal, then we know the
1436 // operands are equal, because assumes must always be true.
1437 if (CmpInst::isTrueWhenEqual(Predicate)) {
1438 addPredicateUsers(PI, I);
1439 addAdditionalUsers(Cmp->getOperand(0), I);
1440 return createVariableOrConstant(FirstOp);
1443 if (const auto *PBranch = dyn_cast<PredicateBranch>(PI)) {
1444 // If we are *not* a copy of the comparison, we may equal to the other
1445 // operand when the predicate implies something about equality of
1446 // operations. In particular, if the comparison is true/false when the
1447 // operands are equal, and we are on the right edge, we know this operation
1448 // is equal to something.
1449 if ((PBranch->TrueEdge && Predicate == CmpInst::ICMP_EQ) ||
1450 (!PBranch->TrueEdge && Predicate == CmpInst::ICMP_NE)) {
1451 addPredicateUsers(PI, I);
1452 addAdditionalUsers(Cmp->getOperand(0), I);
1453 return createVariableOrConstant(FirstOp);
1455 // Handle the special case of floating point.
1456 if (((PBranch->TrueEdge && Predicate == CmpInst::FCMP_OEQ) ||
1457 (!PBranch->TrueEdge && Predicate == CmpInst::FCMP_UNE)) &&
1458 isa<ConstantFP>(FirstOp) && !cast<ConstantFP>(FirstOp)->isZero()) {
1459 addPredicateUsers(PI, I);
1460 addAdditionalUsers(Cmp->getOperand(0), I);
1461 return createConstantExpression(cast<Constant>(FirstOp));
1467 // Evaluate read only and pure calls, and create an expression result.
1468 const Expression *NewGVN::performSymbolicCallEvaluation(Instruction *I) const {
1469 auto *CI = cast<CallInst>(I);
1470 if (auto *II = dyn_cast<IntrinsicInst>(I)) {
1471 // Instrinsics with the returned attribute are copies of arguments.
1472 if (auto *ReturnedValue = II->getReturnedArgOperand()) {
1473 if (II->getIntrinsicID() == Intrinsic::ssa_copy)
1474 if (const auto *Result = performSymbolicPredicateInfoEvaluation(I))
1476 return createVariableOrConstant(ReturnedValue);
1479 if (AA->doesNotAccessMemory(CI)) {
1480 return createCallExpression(CI, TOPClass->getMemoryLeader());
1481 } else if (AA->onlyReadsMemory(CI)) {
1482 MemoryAccess *DefiningAccess = MSSAWalker->getClobberingMemoryAccess(CI);
1483 return createCallExpression(CI, DefiningAccess);
1488 // Retrieve the memory class for a given MemoryAccess.
1489 CongruenceClass *NewGVN::getMemoryClass(const MemoryAccess *MA) const {
1491 auto *Result = MemoryAccessToClass.lookup(MA);
1492 assert(Result && "Should have found memory class");
1496 // Update the MemoryAccess equivalence table to say that From is equal to To,
1497 // and return true if this is different from what already existed in the table.
1498 bool NewGVN::setMemoryClass(const MemoryAccess *From,
1499 CongruenceClass *NewClass) {
1501 "Every MemoryAccess should be getting mapped to a non-null class");
1502 DEBUG(dbgs() << "Setting " << *From);
1503 DEBUG(dbgs() << " equivalent to congruence class ");
1504 DEBUG(dbgs() << NewClass->getID() << " with current MemoryAccess leader ");
1505 DEBUG(dbgs() << *NewClass->getMemoryLeader() << "\n");
1507 auto LookupResult = MemoryAccessToClass.find(From);
1508 bool Changed = false;
1509 // If it's already in the table, see if the value changed.
1510 if (LookupResult != MemoryAccessToClass.end()) {
1511 auto *OldClass = LookupResult->second;
1512 if (OldClass != NewClass) {
1513 // If this is a phi, we have to handle memory member updates.
1514 if (auto *MP = dyn_cast<MemoryPhi>(From)) {
1515 OldClass->memory_erase(MP);
1516 NewClass->memory_insert(MP);
1517 // This may have killed the class if it had no non-memory members
1518 if (OldClass->getMemoryLeader() == From) {
1519 if (OldClass->definesNoMemory()) {
1520 OldClass->setMemoryLeader(nullptr);
1522 OldClass->setMemoryLeader(getNextMemoryLeader(OldClass));
1523 DEBUG(dbgs() << "Memory class leader change for class "
1524 << OldClass->getID() << " to "
1525 << *OldClass->getMemoryLeader()
1526 << " due to removal of a memory member " << *From
1528 markMemoryLeaderChangeTouched(OldClass);
1532 // It wasn't equivalent before, and now it is.
1533 LookupResult->second = NewClass;
1541 // Determine if a instruction is cycle-free. That means the values in the
1542 // instruction don't depend on any expressions that can change value as a result
1543 // of the instruction. For example, a non-cycle free instruction would be v =
1545 bool NewGVN::isCycleFree(const Instruction *I) const {
1546 // In order to compute cycle-freeness, we do SCC finding on the instruction,
1547 // and see what kind of SCC it ends up in. If it is a singleton, it is
1548 // cycle-free. If it is not in a singleton, it is only cycle free if the
1549 // other members are all phi nodes (as they do not compute anything, they are
1551 auto ICS = InstCycleState.lookup(I);
1552 if (ICS == ICS_Unknown) {
1554 auto &SCC = SCCFinder.getComponentFor(I);
1555 // It's cycle free if it's size 1 or or the SCC is *only* phi nodes.
1556 if (SCC.size() == 1)
1557 InstCycleState.insert({I, ICS_CycleFree});
1560 llvm::all_of(SCC, [](const Value *V) { return isa<PHINode>(V); });
1561 ICS = AllPhis ? ICS_CycleFree : ICS_Cycle;
1562 for (auto *Member : SCC)
1563 if (auto *MemberPhi = dyn_cast<PHINode>(Member))
1564 InstCycleState.insert({MemberPhi, ICS});
1567 if (ICS == ICS_Cycle)
1572 // Evaluate PHI nodes symbolically, and create an expression result.
1573 const Expression *NewGVN::performSymbolicPHIEvaluation(Instruction *I) const {
1574 // Resolve irreducible and reducible phi cycles.
1575 // FIXME: This is hopefully a temporary solution while we resolve the issues
1576 // with fixpointing self-cycles. It currently should be "guaranteed" to be
1577 // correct, but non-optimal. The SCCFinder does not, for example, take
1578 // reachability of arguments into account, etc.
1580 bool CanOptimize = true;
1581 SmallPtrSet<Value *, 8> OuterOps;
1583 auto &Component = SCCFinder.getComponentFor(I);
1584 for (auto *Member : Component) {
1585 if (!isa<PHINode>(Member)) {
1586 CanOptimize = false;
1589 for (auto &PHIOp : cast<PHINode>(Member)->operands())
1590 if (!isa<PHINode>(PHIOp) || !Component.count(cast<PHINode>(PHIOp)))
1591 OuterOps.insert(PHIOp);
1593 if (CanOptimize && OuterOps.size() == 1) {
1594 DEBUG(dbgs() << "Resolving cyclic phi to value " << *(*OuterOps.begin())
1596 return createVariableOrConstant(*OuterOps.begin());
1598 // True if one of the incoming phi edges is a backedge.
1599 bool HasBackedge = false;
1600 // All constant tracks the state of whether all the *original* phi operands
1601 // This is really shorthand for "this phi cannot cycle due to forward
1602 // change in value of the phi is guaranteed not to later change the value of
1603 // the phi. IE it can't be v = phi(undef, v+1)
1604 bool AllConstant = true;
1606 cast<PHIExpression>(createPHIExpression(I, HasBackedge, AllConstant));
1607 // We match the semantics of SimplifyPhiNode from InstructionSimplify here.
1608 // See if all arguments are the same.
1609 // We track if any were undef because they need special handling.
1610 bool HasUndef = false;
1611 auto Filtered = make_filter_range(E->operands(), [&](Value *Arg) {
1612 if (isa<UndefValue>(Arg)) {
1618 // If we are left with no operands, it's dead.
1619 if (Filtered.begin() == Filtered.end()) {
1620 // If it has undef at this point, it means there are no-non-undef arguments,
1621 // and thus, the value of the phi node must be undef.
1623 DEBUG(dbgs() << "PHI Node " << *I
1624 << " has no non-undef arguments, valuing it as undef\n");
1625 return createConstantExpression(UndefValue::get(I->getType()));
1628 DEBUG(dbgs() << "No arguments of PHI node " << *I << " are live\n");
1629 deleteExpression(E);
1630 return createDeadExpression();
1632 unsigned NumOps = 0;
1633 Value *AllSameValue = *(Filtered.begin());
1635 // Can't use std::equal here, sadly, because filter.begin moves.
1636 if (llvm::all_of(Filtered, [&](Value *Arg) {
1638 return Arg == AllSameValue;
1640 // In LLVM's non-standard representation of phi nodes, it's possible to have
1641 // phi nodes with cycles (IE dependent on other phis that are .... dependent
1642 // on the original phi node), especially in weird CFG's where some arguments
1643 // are unreachable, or uninitialized along certain paths. This can cause
1644 // infinite loops during evaluation. We work around this by not trying to
1645 // really evaluate them independently, but instead using a variable
1646 // expression to say if one is equivalent to the other.
1647 // We also special case undef, so that if we have an undef, we can't use the
1648 // common value unless it dominates the phi block.
1650 // If we have undef and at least one other value, this is really a
1651 // multivalued phi, and we need to know if it's cycle free in order to
1652 // evaluate whether we can ignore the undef. The other parts of this are
1653 // just shortcuts. If there is no backedge, or all operands are
1654 // constants, or all operands are ignored but the undef, it also must be
1656 if (!AllConstant && HasBackedge && NumOps > 0 &&
1657 !isa<UndefValue>(AllSameValue) && !isCycleFree(I))
1660 // Only have to check for instructions
1661 if (auto *AllSameInst = dyn_cast<Instruction>(AllSameValue))
1662 if (!someEquivalentDominates(AllSameInst, I))
1666 NumGVNPhisAllSame++;
1667 DEBUG(dbgs() << "Simplified PHI node " << *I << " to " << *AllSameValue
1669 deleteExpression(E);
1670 return createVariableOrConstant(AllSameValue);
1676 NewGVN::performSymbolicAggrValueEvaluation(Instruction *I) const {
1677 if (auto *EI = dyn_cast<ExtractValueInst>(I)) {
1678 auto *II = dyn_cast<IntrinsicInst>(EI->getAggregateOperand());
1679 if (II && EI->getNumIndices() == 1 && *EI->idx_begin() == 0) {
1680 unsigned Opcode = 0;
1681 // EI might be an extract from one of our recognised intrinsics. If it
1682 // is we'll synthesize a semantically equivalent expression instead on
1683 // an extract value expression.
1684 switch (II->getIntrinsicID()) {
1685 case Intrinsic::sadd_with_overflow:
1686 case Intrinsic::uadd_with_overflow:
1687 Opcode = Instruction::Add;
1689 case Intrinsic::ssub_with_overflow:
1690 case Intrinsic::usub_with_overflow:
1691 Opcode = Instruction::Sub;
1693 case Intrinsic::smul_with_overflow:
1694 case Intrinsic::umul_with_overflow:
1695 Opcode = Instruction::Mul;
1702 // Intrinsic recognized. Grab its args to finish building the
1704 assert(II->getNumArgOperands() == 2 &&
1705 "Expect two args for recognised intrinsics.");
1706 return createBinaryExpression(
1707 Opcode, EI->getType(), II->getArgOperand(0), II->getArgOperand(1));
1712 return createAggregateValueExpression(I);
1714 const Expression *NewGVN::performSymbolicCmpEvaluation(Instruction *I) const {
1715 auto *CI = dyn_cast<CmpInst>(I);
1716 // See if our operands are equal to those of a previous predicate, and if so,
1717 // if it implies true or false.
1718 auto Op0 = lookupOperandLeader(CI->getOperand(0));
1719 auto Op1 = lookupOperandLeader(CI->getOperand(1));
1720 auto OurPredicate = CI->getPredicate();
1721 if (shouldSwapOperands(Op0, Op1)) {
1722 std::swap(Op0, Op1);
1723 OurPredicate = CI->getSwappedPredicate();
1726 // Avoid processing the same info twice
1727 const PredicateBase *LastPredInfo = nullptr;
1728 // See if we know something about the comparison itself, like it is the target
1730 auto *CmpPI = PredInfo->getPredicateInfoFor(I);
1731 if (dyn_cast_or_null<PredicateAssume>(CmpPI))
1732 return createConstantExpression(ConstantInt::getTrue(CI->getType()));
1735 // This condition does not depend on predicates, no need to add users
1736 if (CI->isTrueWhenEqual())
1737 return createConstantExpression(ConstantInt::getTrue(CI->getType()));
1738 else if (CI->isFalseWhenEqual())
1739 return createConstantExpression(ConstantInt::getFalse(CI->getType()));
1742 // NOTE: Because we are comparing both operands here and below, and using
1743 // previous comparisons, we rely on fact that predicateinfo knows to mark
1744 // comparisons that use renamed operands as users of the earlier comparisons.
1745 // It is *not* enough to just mark predicateinfo renamed operands as users of
1746 // the earlier comparisons, because the *other* operand may have changed in a
1747 // previous iteration.
1750 // %b.0 = ssa.copy(%b)
1752 // icmp slt %c, %b.0
1754 // %c and %a may start out equal, and thus, the code below will say the second
1755 // %icmp is false. c may become equal to something else, and in that case the
1756 // %second icmp *must* be reexamined, but would not if only the renamed
1757 // %operands are considered users of the icmp.
1759 // *Currently* we only check one level of comparisons back, and only mark one
1760 // level back as touched when changes appen . If you modify this code to look
1761 // back farther through comparisons, you *must* mark the appropriate
1762 // comparisons as users in PredicateInfo.cpp, or you will cause bugs. See if
1763 // we know something just from the operands themselves
1765 // See if our operands have predicate info, so that we may be able to derive
1766 // something from a previous comparison.
1767 for (const auto &Op : CI->operands()) {
1768 auto *PI = PredInfo->getPredicateInfoFor(Op);
1769 if (const auto *PBranch = dyn_cast_or_null<PredicateBranch>(PI)) {
1770 if (PI == LastPredInfo)
1774 // TODO: Along the false edge, we may know more things too, like icmp of
1775 // same operands is false.
1776 // TODO: We only handle actual comparison conditions below, not and/or.
1777 auto *BranchCond = dyn_cast<CmpInst>(PBranch->Condition);
1780 auto *BranchOp0 = lookupOperandLeader(BranchCond->getOperand(0));
1781 auto *BranchOp1 = lookupOperandLeader(BranchCond->getOperand(1));
1782 auto BranchPredicate = BranchCond->getPredicate();
1783 if (shouldSwapOperands(BranchOp0, BranchOp1)) {
1784 std::swap(BranchOp0, BranchOp1);
1785 BranchPredicate = BranchCond->getSwappedPredicate();
1787 if (BranchOp0 == Op0 && BranchOp1 == Op1) {
1788 if (PBranch->TrueEdge) {
1789 // If we know the previous predicate is true and we are in the true
1790 // edge then we may be implied true or false.
1791 if (CmpInst::isImpliedTrueByMatchingCmp(BranchPredicate,
1793 addPredicateUsers(PI, I);
1794 return createConstantExpression(
1795 ConstantInt::getTrue(CI->getType()));
1798 if (CmpInst::isImpliedFalseByMatchingCmp(BranchPredicate,
1800 addPredicateUsers(PI, I);
1801 return createConstantExpression(
1802 ConstantInt::getFalse(CI->getType()));
1806 // Just handle the ne and eq cases, where if we have the same
1807 // operands, we may know something.
1808 if (BranchPredicate == OurPredicate) {
1809 addPredicateUsers(PI, I);
1810 // Same predicate, same ops,we know it was false, so this is false.
1811 return createConstantExpression(
1812 ConstantInt::getFalse(CI->getType()));
1813 } else if (BranchPredicate ==
1814 CmpInst::getInversePredicate(OurPredicate)) {
1815 addPredicateUsers(PI, I);
1816 // Inverse predicate, we know the other was false, so this is true.
1817 return createConstantExpression(
1818 ConstantInt::getTrue(CI->getType()));
1824 // Create expression will take care of simplifyCmpInst
1825 return createExpression(I);
1828 // Return true if V is a value that will always be available (IE can
1829 // be placed anywhere) in the function. We don't do globals here
1830 // because they are often worse to put in place.
1831 // TODO: Separate cost from availability
1832 static bool alwaysAvailable(Value *V) {
1833 return isa<Constant>(V) || isa<Argument>(V);
1836 // Substitute and symbolize the value before value numbering.
1838 NewGVN::performSymbolicEvaluation(Value *V,
1839 SmallPtrSetImpl<Value *> &Visited) const {
1840 const Expression *E = nullptr;
1841 if (auto *C = dyn_cast<Constant>(V))
1842 E = createConstantExpression(C);
1843 else if (isa<Argument>(V) || isa<GlobalVariable>(V)) {
1844 E = createVariableExpression(V);
1846 // TODO: memory intrinsics.
1847 // TODO: Some day, we should do the forward propagation and reassociation
1848 // parts of the algorithm.
1849 auto *I = cast<Instruction>(V);
1850 switch (I->getOpcode()) {
1851 case Instruction::ExtractValue:
1852 case Instruction::InsertValue:
1853 E = performSymbolicAggrValueEvaluation(I);
1855 case Instruction::PHI:
1856 E = performSymbolicPHIEvaluation(I);
1858 case Instruction::Call:
1859 E = performSymbolicCallEvaluation(I);
1861 case Instruction::Store:
1862 E = performSymbolicStoreEvaluation(I);
1864 case Instruction::Load:
1865 E = performSymbolicLoadEvaluation(I);
1867 case Instruction::BitCast: {
1868 E = createExpression(I);
1870 case Instruction::ICmp:
1871 case Instruction::FCmp: {
1872 E = performSymbolicCmpEvaluation(I);
1874 case Instruction::Add:
1875 case Instruction::FAdd:
1876 case Instruction::Sub:
1877 case Instruction::FSub:
1878 case Instruction::Mul:
1879 case Instruction::FMul:
1880 case Instruction::UDiv:
1881 case Instruction::SDiv:
1882 case Instruction::FDiv:
1883 case Instruction::URem:
1884 case Instruction::SRem:
1885 case Instruction::FRem:
1886 case Instruction::Shl:
1887 case Instruction::LShr:
1888 case Instruction::AShr:
1889 case Instruction::And:
1890 case Instruction::Or:
1891 case Instruction::Xor:
1892 case Instruction::Trunc:
1893 case Instruction::ZExt:
1894 case Instruction::SExt:
1895 case Instruction::FPToUI:
1896 case Instruction::FPToSI:
1897 case Instruction::UIToFP:
1898 case Instruction::SIToFP:
1899 case Instruction::FPTrunc:
1900 case Instruction::FPExt:
1901 case Instruction::PtrToInt:
1902 case Instruction::IntToPtr:
1903 case Instruction::Select:
1904 case Instruction::ExtractElement:
1905 case Instruction::InsertElement:
1906 case Instruction::ShuffleVector:
1907 case Instruction::GetElementPtr:
1908 E = createExpression(I);
1917 // Look up a container in a map, and then call a function for each thing in the
1919 template <typename Map, typename KeyType, typename Func>
1920 void NewGVN::for_each_found(Map &M, const KeyType &Key, Func F) {
1921 const auto Result = M.find_as(Key);
1922 if (Result != M.end())
1923 for (typename Map::mapped_type::value_type Mapped : Result->second)
1927 // Look up a container of values/instructions in a map, and touch all the
1928 // instructions in the container. Then erase value from the map.
1929 template <typename Map, typename KeyType>
1930 void NewGVN::touchAndErase(Map &M, const KeyType &Key) {
1931 const auto Result = M.find_as(Key);
1932 if (Result != M.end()) {
1933 for (const typename Map::mapped_type::value_type Mapped : Result->second)
1934 TouchedInstructions.set(InstrToDFSNum(Mapped));
1939 void NewGVN::addAdditionalUsers(Value *To, Value *User) const {
1940 if (isa<Instruction>(To))
1941 AdditionalUsers[To].insert(User);
1944 void NewGVN::markUsersTouched(Value *V) {
1945 // Now mark the users as touched.
1946 for (auto *User : V->users()) {
1947 assert(isa<Instruction>(User) && "Use of value not within an instruction?");
1948 TouchedInstructions.set(InstrToDFSNum(User));
1950 touchAndErase(AdditionalUsers, V);
1953 void NewGVN::addMemoryUsers(const MemoryAccess *To, MemoryAccess *U) const {
1954 DEBUG(dbgs() << "Adding memory user " << *U << " to " << *To << "\n");
1955 MemoryToUsers[To].insert(U);
1958 void NewGVN::markMemoryDefTouched(const MemoryAccess *MA) {
1959 TouchedInstructions.set(MemoryToDFSNum(MA));
1962 void NewGVN::markMemoryUsersTouched(const MemoryAccess *MA) {
1963 if (isa<MemoryUse>(MA))
1965 for (auto U : MA->users())
1966 TouchedInstructions.set(MemoryToDFSNum(U));
1967 touchAndErase(MemoryToUsers, MA);
1970 // Add I to the set of users of a given predicate.
1971 void NewGVN::addPredicateUsers(const PredicateBase *PB, Instruction *I) const {
1972 // Don't add temporary instructions to the user lists.
1973 if (AllTempInstructions.count(I))
1976 if (auto *PBranch = dyn_cast<PredicateBranch>(PB))
1977 PredicateToUsers[PBranch->Condition].insert(I);
1978 else if (auto *PAssume = dyn_cast<PredicateBranch>(PB))
1979 PredicateToUsers[PAssume->Condition].insert(I);
1982 // Touch all the predicates that depend on this instruction.
1983 void NewGVN::markPredicateUsersTouched(Instruction *I) {
1984 touchAndErase(PredicateToUsers, I);
1987 // Mark users affected by a memory leader change.
1988 void NewGVN::markMemoryLeaderChangeTouched(CongruenceClass *CC) {
1989 for (auto M : CC->memory())
1990 markMemoryDefTouched(M);
1993 // Touch the instructions that need to be updated after a congruence class has a
1994 // leader change, and mark changed values.
1995 void NewGVN::markValueLeaderChangeTouched(CongruenceClass *CC) {
1996 for (auto M : *CC) {
1997 if (auto *I = dyn_cast<Instruction>(M))
1998 TouchedInstructions.set(InstrToDFSNum(I));
1999 LeaderChanges.insert(M);
2003 // Give a range of things that have instruction DFS numbers, this will return
2004 // the member of the range with the smallest dfs number.
2005 template <class T, class Range>
2006 T *NewGVN::getMinDFSOfRange(const Range &R) const {
2007 std::pair<T *, unsigned> MinDFS = {nullptr, ~0U};
2008 for (const auto X : R) {
2009 auto DFSNum = InstrToDFSNum(X);
2010 if (DFSNum < MinDFS.second)
2011 MinDFS = {X, DFSNum};
2013 return MinDFS.first;
2016 // This function returns the MemoryAccess that should be the next leader of
2017 // congruence class CC, under the assumption that the current leader is going to
2019 const MemoryAccess *NewGVN::getNextMemoryLeader(CongruenceClass *CC) const {
2020 // TODO: If this ends up to slow, we can maintain a next memory leader like we
2021 // do for regular leaders.
2022 // Make sure there will be a leader to find
2023 assert(!CC->definesNoMemory() && "Can't get next leader if there is none");
2024 if (CC->getStoreCount() > 0) {
2025 if (auto *NL = dyn_cast_or_null<StoreInst>(CC->getNextLeader().first))
2026 return getMemoryAccess(NL);
2027 // Find the store with the minimum DFS number.
2028 auto *V = getMinDFSOfRange<Value>(make_filter_range(
2029 *CC, [&](const Value *V) { return isa<StoreInst>(V); }));
2030 return getMemoryAccess(cast<StoreInst>(V));
2032 assert(CC->getStoreCount() == 0);
2034 // Given our assertion, hitting this part must mean
2035 // !OldClass->memory_empty()
2036 if (CC->memory_size() == 1)
2037 return *CC->memory_begin();
2038 return getMinDFSOfRange<const MemoryPhi>(CC->memory());
2041 // This function returns the next value leader of a congruence class, under the
2042 // assumption that the current leader is going away. This should end up being
2043 // the next most dominating member.
2044 Value *NewGVN::getNextValueLeader(CongruenceClass *CC) const {
2045 // We don't need to sort members if there is only 1, and we don't care about
2046 // sorting the TOP class because everything either gets out of it or is
2049 if (CC->size() == 1 || CC == TOPClass) {
2050 return *(CC->begin());
2051 } else if (CC->getNextLeader().first) {
2052 ++NumGVNAvoidedSortedLeaderChanges;
2053 return CC->getNextLeader().first;
2055 ++NumGVNSortedLeaderChanges;
2056 // NOTE: If this ends up to slow, we can maintain a dual structure for
2057 // member testing/insertion, or keep things mostly sorted, and sort only
2058 // here, or use SparseBitVector or ....
2059 return getMinDFSOfRange<Value>(*CC);
2063 // Move a MemoryAccess, currently in OldClass, to NewClass, including updates to
2064 // the memory members, etc for the move.
2066 // The invariants of this function are:
2068 // I must be moving to NewClass from OldClass The StoreCount of OldClass and
2069 // NewClass is expected to have been updated for I already if it is is a store.
2070 // The OldClass memory leader has not been updated yet if I was the leader.
2071 void NewGVN::moveMemoryToNewCongruenceClass(Instruction *I,
2072 MemoryAccess *InstMA,
2073 CongruenceClass *OldClass,
2074 CongruenceClass *NewClass) {
2075 // If the leader is I, and we had a represenative MemoryAccess, it should
2076 // be the MemoryAccess of OldClass.
2077 assert((!InstMA || !OldClass->getMemoryLeader() ||
2078 OldClass->getLeader() != I ||
2079 OldClass->getMemoryLeader() == InstMA) &&
2080 "Representative MemoryAccess mismatch");
2081 // First, see what happens to the new class
2082 if (!NewClass->getMemoryLeader()) {
2083 // Should be a new class, or a store becoming a leader of a new class.
2084 assert(NewClass->size() == 1 ||
2085 (isa<StoreInst>(I) && NewClass->getStoreCount() == 1));
2086 NewClass->setMemoryLeader(InstMA);
2087 // Mark it touched if we didn't just create a singleton
2088 DEBUG(dbgs() << "Memory class leader change for class " << NewClass->getID()
2089 << " due to new memory instruction becoming leader\n");
2090 markMemoryLeaderChangeTouched(NewClass);
2092 setMemoryClass(InstMA, NewClass);
2093 // Now, fixup the old class if necessary
2094 if (OldClass->getMemoryLeader() == InstMA) {
2095 if (!OldClass->definesNoMemory()) {
2096 OldClass->setMemoryLeader(getNextMemoryLeader(OldClass));
2097 DEBUG(dbgs() << "Memory class leader change for class "
2098 << OldClass->getID() << " to "
2099 << *OldClass->getMemoryLeader()
2100 << " due to removal of old leader " << *InstMA << "\n");
2101 markMemoryLeaderChangeTouched(OldClass);
2103 OldClass->setMemoryLeader(nullptr);
2107 // Move a value, currently in OldClass, to be part of NewClass
2108 // Update OldClass and NewClass for the move (including changing leaders, etc).
2109 void NewGVN::moveValueToNewCongruenceClass(Instruction *I, const Expression *E,
2110 CongruenceClass *OldClass,
2111 CongruenceClass *NewClass) {
2112 if (I == OldClass->getNextLeader().first)
2113 OldClass->resetNextLeader();
2116 NewClass->insert(I);
2118 if (NewClass->getLeader() != I)
2119 NewClass->addPossibleNextLeader({I, InstrToDFSNum(I)});
2120 // Handle our special casing of stores.
2121 if (auto *SI = dyn_cast<StoreInst>(I)) {
2122 OldClass->decStoreCount();
2123 // Okay, so when do we want to make a store a leader of a class?
2124 // If we have a store defined by an earlier load, we want the earlier load
2125 // to lead the class.
2126 // If we have a store defined by something else, we want the store to lead
2127 // the class so everything else gets the "something else" as a value.
2128 // If we have a store as the single member of the class, we want the store
2130 if (NewClass->getStoreCount() == 0 && !NewClass->getStoredValue()) {
2131 // If it's a store expression we are using, it means we are not equivalent
2132 // to something earlier.
2133 if (auto *SE = dyn_cast<StoreExpression>(E)) {
2134 NewClass->setStoredValue(SE->getStoredValue());
2135 markValueLeaderChangeTouched(NewClass);
2136 // Shift the new class leader to be the store
2137 DEBUG(dbgs() << "Changing leader of congruence class "
2138 << NewClass->getID() << " from " << *NewClass->getLeader()
2139 << " to " << *SI << " because store joined class\n");
2140 // If we changed the leader, we have to mark it changed because we don't
2141 // know what it will do to symbolic evlauation.
2142 NewClass->setLeader(SI);
2144 // We rely on the code below handling the MemoryAccess change.
2146 NewClass->incStoreCount();
2148 // True if there is no memory instructions left in a class that had memory
2149 // instructions before.
2151 // If it's not a memory use, set the MemoryAccess equivalence
2152 auto *InstMA = dyn_cast_or_null<MemoryDef>(getMemoryAccess(I));
2154 moveMemoryToNewCongruenceClass(I, InstMA, OldClass, NewClass);
2155 ValueToClass[I] = NewClass;
2156 // See if we destroyed the class or need to swap leaders.
2157 if (OldClass->empty() && OldClass != TOPClass) {
2158 if (OldClass->getDefiningExpr()) {
2159 DEBUG(dbgs() << "Erasing expression " << *OldClass->getDefiningExpr()
2160 << " from table\n");
2161 ExpressionToClass.erase(OldClass->getDefiningExpr());
2163 } else if (OldClass->getLeader() == I) {
2164 // When the leader changes, the value numbering of
2165 // everything may change due to symbolization changes, so we need to
2167 DEBUG(dbgs() << "Value class leader change for class " << OldClass->getID()
2169 ++NumGVNLeaderChanges;
2170 // Destroy the stored value if there are no more stores to represent it.
2171 // Note that this is basically clean up for the expression removal that
2172 // happens below. If we remove stores from a class, we may leave it as a
2173 // class of equivalent memory phis.
2174 if (OldClass->getStoreCount() == 0) {
2175 if (OldClass->getStoredValue())
2176 OldClass->setStoredValue(nullptr);
2178 OldClass->setLeader(getNextValueLeader(OldClass));
2179 OldClass->resetNextLeader();
2180 markValueLeaderChangeTouched(OldClass);
2184 // For a given expression, mark the phi of ops instructions that could have
2185 // changed as a result.
2186 void NewGVN::markPhiOfOpsChanged(const Expression *E) {
2187 touchAndErase(ExpressionToPhiOfOps, E);
2190 // Perform congruence finding on a given value numbering expression.
2191 void NewGVN::performCongruenceFinding(Instruction *I, const Expression *E) {
2192 // This is guaranteed to return something, since it will at least find
2195 CongruenceClass *IClass = ValueToClass.lookup(I);
2196 assert(IClass && "Should have found a IClass");
2197 // Dead classes should have been eliminated from the mapping.
2198 assert(!IClass->isDead() && "Found a dead class");
2200 CongruenceClass *EClass = nullptr;
2201 if (const auto *VE = dyn_cast<VariableExpression>(E)) {
2202 EClass = ValueToClass.lookup(VE->getVariableValue());
2203 } else if (isa<DeadExpression>(E)) {
2207 auto lookupResult = ExpressionToClass.insert({E, nullptr});
2209 // If it's not in the value table, create a new congruence class.
2210 if (lookupResult.second) {
2211 CongruenceClass *NewClass = createCongruenceClass(nullptr, E);
2212 auto place = lookupResult.first;
2213 place->second = NewClass;
2215 // Constants and variables should always be made the leader.
2216 if (const auto *CE = dyn_cast<ConstantExpression>(E)) {
2217 NewClass->setLeader(CE->getConstantValue());
2218 } else if (const auto *SE = dyn_cast<StoreExpression>(E)) {
2219 StoreInst *SI = SE->getStoreInst();
2220 NewClass->setLeader(SI);
2221 NewClass->setStoredValue(SE->getStoredValue());
2222 // The RepMemoryAccess field will be filled in properly by the
2223 // moveValueToNewCongruenceClass call.
2225 NewClass->setLeader(I);
2227 assert(!isa<VariableExpression>(E) &&
2228 "VariableExpression should have been handled already");
2231 DEBUG(dbgs() << "Created new congruence class for " << *I
2232 << " using expression " << *E << " at " << NewClass->getID()
2233 << " and leader " << *(NewClass->getLeader()));
2234 if (NewClass->getStoredValue())
2235 DEBUG(dbgs() << " and stored value " << *(NewClass->getStoredValue()));
2236 DEBUG(dbgs() << "\n");
2238 EClass = lookupResult.first->second;
2239 if (isa<ConstantExpression>(E))
2240 assert((isa<Constant>(EClass->getLeader()) ||
2241 (EClass->getStoredValue() &&
2242 isa<Constant>(EClass->getStoredValue()))) &&
2243 "Any class with a constant expression should have a "
2246 assert(EClass && "Somehow don't have an eclass");
2248 assert(!EClass->isDead() && "We accidentally looked up a dead class");
2251 bool ClassChanged = IClass != EClass;
2252 bool LeaderChanged = LeaderChanges.erase(I);
2253 if (ClassChanged || LeaderChanged) {
2254 DEBUG(dbgs() << "New class " << EClass->getID() << " for expression " << *E
2257 moveValueToNewCongruenceClass(I, E, IClass, EClass);
2258 markPhiOfOpsChanged(E);
2261 markUsersTouched(I);
2262 if (MemoryAccess *MA = getMemoryAccess(I))
2263 markMemoryUsersTouched(MA);
2264 if (auto *CI = dyn_cast<CmpInst>(I))
2265 markPredicateUsersTouched(CI);
2267 // If we changed the class of the store, we want to ensure nothing finds the
2268 // old store expression. In particular, loads do not compare against stored
2269 // value, so they will find old store expressions (and associated class
2270 // mappings) if we leave them in the table.
2271 if (ClassChanged && isa<StoreInst>(I)) {
2272 auto *OldE = ValueToExpression.lookup(I);
2273 // It could just be that the old class died. We don't want to erase it if we
2274 // just moved classes.
2275 if (OldE && isa<StoreExpression>(OldE) && *E != *OldE)
2276 ExpressionToClass.erase(OldE);
2278 ValueToExpression[I] = E;
2281 // Process the fact that Edge (from, to) is reachable, including marking
2282 // any newly reachable blocks and instructions for processing.
2283 void NewGVN::updateReachableEdge(BasicBlock *From, BasicBlock *To) {
2284 // Check if the Edge was reachable before.
2285 if (ReachableEdges.insert({From, To}).second) {
2286 // If this block wasn't reachable before, all instructions are touched.
2287 if (ReachableBlocks.insert(To).second) {
2288 DEBUG(dbgs() << "Block " << getBlockName(To) << " marked reachable\n");
2289 const auto &InstRange = BlockInstRange.lookup(To);
2290 TouchedInstructions.set(InstRange.first, InstRange.second);
2292 DEBUG(dbgs() << "Block " << getBlockName(To)
2293 << " was reachable, but new edge {" << getBlockName(From)
2294 << "," << getBlockName(To) << "} to it found\n");
2296 // We've made an edge reachable to an existing block, which may
2297 // impact predicates. Otherwise, only mark the phi nodes as touched, as
2298 // they are the only thing that depend on new edges. Anything using their
2299 // values will get propagated to if necessary.
2300 if (MemoryAccess *MemPhi = getMemoryAccess(To))
2301 TouchedInstructions.set(InstrToDFSNum(MemPhi));
2303 auto BI = To->begin();
2304 while (isa<PHINode>(BI)) {
2305 TouchedInstructions.set(InstrToDFSNum(&*BI));
2308 for_each_found(PHIOfOpsPHIs, To, [&](const PHINode *I) {
2309 TouchedInstructions.set(InstrToDFSNum(I));
2315 // Given a predicate condition (from a switch, cmp, or whatever) and a block,
2316 // see if we know some constant value for it already.
2317 Value *NewGVN::findConditionEquivalence(Value *Cond) const {
2318 auto Result = lookupOperandLeader(Cond);
2319 if (isa<Constant>(Result))
2324 // Process the outgoing edges of a block for reachability.
2325 void NewGVN::processOutgoingEdges(TerminatorInst *TI, BasicBlock *B) {
2326 // Evaluate reachability of terminator instruction.
2328 if ((BR = dyn_cast<BranchInst>(TI)) && BR->isConditional()) {
2329 Value *Cond = BR->getCondition();
2330 Value *CondEvaluated = findConditionEquivalence(Cond);
2331 if (!CondEvaluated) {
2332 if (auto *I = dyn_cast<Instruction>(Cond)) {
2333 const Expression *E = createExpression(I);
2334 if (const auto *CE = dyn_cast<ConstantExpression>(E)) {
2335 CondEvaluated = CE->getConstantValue();
2337 } else if (isa<ConstantInt>(Cond)) {
2338 CondEvaluated = Cond;
2342 BasicBlock *TrueSucc = BR->getSuccessor(0);
2343 BasicBlock *FalseSucc = BR->getSuccessor(1);
2344 if (CondEvaluated && (CI = dyn_cast<ConstantInt>(CondEvaluated))) {
2346 DEBUG(dbgs() << "Condition for Terminator " << *TI
2347 << " evaluated to true\n");
2348 updateReachableEdge(B, TrueSucc);
2349 } else if (CI->isZero()) {
2350 DEBUG(dbgs() << "Condition for Terminator " << *TI
2351 << " evaluated to false\n");
2352 updateReachableEdge(B, FalseSucc);
2355 updateReachableEdge(B, TrueSucc);
2356 updateReachableEdge(B, FalseSucc);
2358 } else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
2359 // For switches, propagate the case values into the case
2362 // Remember how many outgoing edges there are to every successor.
2363 SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
2365 Value *SwitchCond = SI->getCondition();
2366 Value *CondEvaluated = findConditionEquivalence(SwitchCond);
2367 // See if we were able to turn this switch statement into a constant.
2368 if (CondEvaluated && isa<ConstantInt>(CondEvaluated)) {
2369 auto *CondVal = cast<ConstantInt>(CondEvaluated);
2370 // We should be able to get case value for this.
2371 auto Case = *SI->findCaseValue(CondVal);
2372 if (Case.getCaseSuccessor() == SI->getDefaultDest()) {
2373 // We proved the value is outside of the range of the case.
2374 // We can't do anything other than mark the default dest as reachable,
2376 updateReachableEdge(B, SI->getDefaultDest());
2379 // Now get where it goes and mark it reachable.
2380 BasicBlock *TargetBlock = Case.getCaseSuccessor();
2381 updateReachableEdge(B, TargetBlock);
2383 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
2384 BasicBlock *TargetBlock = SI->getSuccessor(i);
2385 ++SwitchEdges[TargetBlock];
2386 updateReachableEdge(B, TargetBlock);
2390 // Otherwise this is either unconditional, or a type we have no
2391 // idea about. Just mark successors as reachable.
2392 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
2393 BasicBlock *TargetBlock = TI->getSuccessor(i);
2394 updateReachableEdge(B, TargetBlock);
2397 // This also may be a memory defining terminator, in which case, set it
2398 // equivalent only to itself.
2400 auto *MA = getMemoryAccess(TI);
2401 if (MA && !isa<MemoryUse>(MA)) {
2402 auto *CC = ensureLeaderOfMemoryClass(MA);
2403 if (setMemoryClass(MA, CC))
2404 markMemoryUsersTouched(MA);
2409 void NewGVN::addPhiOfOps(PHINode *Op, BasicBlock *BB,
2410 Instruction *ExistingValue) {
2411 InstrDFS[Op] = InstrToDFSNum(ExistingValue);
2412 AllTempInstructions.insert(Op);
2413 PHIOfOpsPHIs[BB].push_back(Op);
2414 TempToBlock[Op] = BB;
2416 RealToTemp[ExistingValue] = Op;
2419 static bool okayForPHIOfOps(const Instruction *I) {
2420 return isa<BinaryOperator>(I) || isa<SelectInst>(I) || isa<CmpInst>(I) ||
2424 // When we see an instruction that is an op of phis, generate the equivalent phi
2427 NewGVN::makePossiblePhiOfOps(Instruction *I,
2428 SmallPtrSetImpl<Value *> &Visited) {
2429 if (!okayForPHIOfOps(I))
2432 if (!Visited.insert(I).second)
2434 // For now, we require the instruction be cycle free because we don't
2435 // *always* create a phi of ops for instructions that could be done as phi
2436 // of ops, we only do it if we think it is useful. If we did do it all the
2437 // time, we could remove the cycle free check.
2438 if (!isCycleFree(I))
2441 unsigned IDFSNum = InstrToDFSNum(I);
2442 SmallPtrSet<const Value *, 8> ProcessedPHIs;
2443 // TODO: We don't do phi translation on memory accesses because it's
2444 // complicated. For a load, we'd need to be able to simulate a new memoryuse,
2445 // which we don't have a good way of doing ATM.
2446 auto *MemAccess = getMemoryAccess(I);
2447 // If the memory operation is defined by a memory operation this block that
2448 // isn't a MemoryPhi, transforming the pointer backwards through a scalar phi
2449 // can't help, as it would still be killed by that memory operation.
2450 if (MemAccess && !isa<MemoryPhi>(MemAccess->getDefiningAccess()) &&
2451 MemAccess->getDefiningAccess()->getBlock() == I->getParent())
2454 // Convert op of phis to phi of ops
2455 for (auto &Op : I->operands()) {
2456 // TODO: We can't handle expressions that must be recursively translated
2460 // g = f + phi of something
2461 // To properly make a phi of ops for g, we'd have to properly translate and
2462 // use the instruction for f. We should add this by splitting out the
2463 // instruction creation we do below.
2464 if (isa<Instruction>(Op) && PHINodeUses.count(cast<Instruction>(Op)))
2466 if (!isa<PHINode>(Op))
2468 auto *OpPHI = cast<PHINode>(Op);
2469 // No point in doing this for one-operand phis.
2470 if (OpPHI->getNumOperands() == 1)
2472 if (!DebugCounter::shouldExecute(PHIOfOpsCounter))
2474 SmallVector<std::pair<Value *, BasicBlock *>, 4> Ops;
2475 auto *PHIBlock = getBlockForValue(OpPHI);
2476 for (auto PredBB : OpPHI->blocks()) {
2477 Value *FoundVal = nullptr;
2478 // We could just skip unreachable edges entirely but it's tricky to do
2479 // with rewriting existing phi nodes.
2480 if (ReachableEdges.count({PredBB, PHIBlock})) {
2481 // Clone the instruction, create an expression from it, and see if we
2483 Instruction *ValueOp = I->clone();
2485 TempToMemory.insert({ValueOp, MemAccess});
2487 for (auto &Op : ValueOp->operands()) {
2488 Op = Op->DoPHITranslation(PHIBlock, PredBB);
2489 // When this operand changes, it could change whether there is a
2490 // leader for us or not.
2491 addAdditionalUsers(Op, I);
2493 // Make sure it's marked as a temporary instruction.
2494 AllTempInstructions.insert(ValueOp);
2495 // and make sure anything that tries to add it's DFS number is
2496 // redirected to the instruction we are making a phi of ops
2498 InstrDFS.insert({ValueOp, IDFSNum});
2499 const Expression *E = performSymbolicEvaluation(ValueOp, Visited);
2500 InstrDFS.erase(ValueOp);
2501 AllTempInstructions.erase(ValueOp);
2502 ValueOp->deleteValue();
2504 TempToMemory.erase(ValueOp);
2507 FoundVal = findPhiOfOpsLeader(E, PredBB);
2509 ExpressionToPhiOfOps[E].insert(I);
2512 if (auto *SI = dyn_cast<StoreInst>(FoundVal))
2513 FoundVal = SI->getValueOperand();
2515 DEBUG(dbgs() << "Skipping phi of ops operand for incoming block "
2516 << getBlockName(PredBB)
2517 << " because the block is unreachable\n");
2518 FoundVal = UndefValue::get(I->getType());
2521 Ops.push_back({FoundVal, PredBB});
2522 DEBUG(dbgs() << "Found phi of ops operand " << *FoundVal << " in "
2523 << getBlockName(PredBB) << "\n");
2525 auto *ValuePHI = RealToTemp.lookup(I);
2526 bool NewPHI = false;
2528 ValuePHI = PHINode::Create(I->getType(), OpPHI->getNumOperands());
2529 addPhiOfOps(ValuePHI, PHIBlock, I);
2531 NumGVNPHIOfOpsCreated++;
2534 for (auto PHIOp : Ops)
2535 ValuePHI->addIncoming(PHIOp.first, PHIOp.second);
2538 for (auto PHIOp : Ops) {
2539 ValuePHI->setIncomingValue(i, PHIOp.first);
2540 ValuePHI->setIncomingBlock(i, PHIOp.second);
2545 DEBUG(dbgs() << "Created phi of ops " << *ValuePHI << " for " << *I
2547 return performSymbolicEvaluation(ValuePHI, Visited);
2552 // The algorithm initially places the values of the routine in the TOP
2553 // congruence class. The leader of TOP is the undetermined value `undef`.
2554 // When the algorithm has finished, values still in TOP are unreachable.
2555 void NewGVN::initializeCongruenceClasses(Function &F) {
2556 NextCongruenceNum = 0;
2558 // Note that even though we use the live on entry def as a representative
2559 // MemoryAccess, it is *not* the same as the actual live on entry def. We
2560 // have no real equivalemnt to undef for MemoryAccesses, and so we really
2561 // should be checking whether the MemoryAccess is top if we want to know if it
2562 // is equivalent to everything. Otherwise, what this really signifies is that
2563 // the access "it reaches all the way back to the beginning of the function"
2565 // Initialize all other instructions to be in TOP class.
2566 TOPClass = createCongruenceClass(nullptr, nullptr);
2567 TOPClass->setMemoryLeader(MSSA->getLiveOnEntryDef());
2568 // The live on entry def gets put into it's own class
2569 MemoryAccessToClass[MSSA->getLiveOnEntryDef()] =
2570 createMemoryClass(MSSA->getLiveOnEntryDef());
2572 for (auto DTN : nodes(DT)) {
2573 BasicBlock *BB = DTN->getBlock();
2574 // All MemoryAccesses are equivalent to live on entry to start. They must
2575 // be initialized to something so that initial changes are noticed. For
2576 // the maximal answer, we initialize them all to be the same as
2578 auto *MemoryBlockDefs = MSSA->getBlockDefs(BB);
2579 if (MemoryBlockDefs)
2580 for (const auto &Def : *MemoryBlockDefs) {
2581 MemoryAccessToClass[&Def] = TOPClass;
2582 auto *MD = dyn_cast<MemoryDef>(&Def);
2583 // Insert the memory phis into the member list.
2585 const MemoryPhi *MP = cast<MemoryPhi>(&Def);
2586 TOPClass->memory_insert(MP);
2587 MemoryPhiState.insert({MP, MPS_TOP});
2590 if (MD && isa<StoreInst>(MD->getMemoryInst()))
2591 TOPClass->incStoreCount();
2593 for (auto &I : *BB) {
2594 // TODO: Move to helper
2595 if (isa<PHINode>(&I))
2596 for (auto *U : I.users())
2597 if (auto *UInst = dyn_cast<Instruction>(U))
2598 if (InstrToDFSNum(UInst) != 0 && okayForPHIOfOps(UInst))
2599 PHINodeUses.insert(UInst);
2600 // Don't insert void terminators into the class. We don't value number
2601 // them, and they just end up sitting in TOP.
2602 if (isa<TerminatorInst>(I) && I.getType()->isVoidTy())
2604 TOPClass->insert(&I);
2605 ValueToClass[&I] = TOPClass;
2609 // Initialize arguments to be in their own unique congruence classes
2610 for (auto &FA : F.args())
2611 createSingletonCongruenceClass(&FA);
2614 void NewGVN::cleanupTables() {
2615 for (unsigned i = 0, e = CongruenceClasses.size(); i != e; ++i) {
2616 DEBUG(dbgs() << "Congruence class " << CongruenceClasses[i]->getID()
2617 << " has " << CongruenceClasses[i]->size() << " members\n");
2618 // Make sure we delete the congruence class (probably worth switching to
2619 // a unique_ptr at some point.
2620 delete CongruenceClasses[i];
2621 CongruenceClasses[i] = nullptr;
2624 // Destroy the value expressions
2625 SmallVector<Instruction *, 8> TempInst(AllTempInstructions.begin(),
2626 AllTempInstructions.end());
2627 AllTempInstructions.clear();
2629 // We have to drop all references for everything first, so there are no uses
2630 // left as we delete them.
2631 for (auto *I : TempInst) {
2632 I->dropAllReferences();
2635 while (!TempInst.empty()) {
2636 auto *I = TempInst.back();
2637 TempInst.pop_back();
2641 ValueToClass.clear();
2642 ArgRecycler.clear(ExpressionAllocator);
2643 ExpressionAllocator.Reset();
2644 CongruenceClasses.clear();
2645 ExpressionToClass.clear();
2646 ValueToExpression.clear();
2648 AdditionalUsers.clear();
2649 ExpressionToPhiOfOps.clear();
2650 TempToBlock.clear();
2651 TempToMemory.clear();
2652 PHIOfOpsPHIs.clear();
2653 ReachableBlocks.clear();
2654 ReachableEdges.clear();
2656 ProcessedCount.clear();
2659 InstructionsToErase.clear();
2661 BlockInstRange.clear();
2662 TouchedInstructions.clear();
2663 MemoryAccessToClass.clear();
2664 PredicateToUsers.clear();
2665 MemoryToUsers.clear();
2668 // Assign local DFS number mapping to instructions, and leave space for Value
2670 std::pair<unsigned, unsigned> NewGVN::assignDFSNumbers(BasicBlock *B,
2672 unsigned End = Start;
2673 if (MemoryAccess *MemPhi = getMemoryAccess(B)) {
2674 InstrDFS[MemPhi] = End++;
2675 DFSToInstr.emplace_back(MemPhi);
2678 // Then the real block goes next.
2679 for (auto &I : *B) {
2680 // There's no need to call isInstructionTriviallyDead more than once on
2681 // an instruction. Therefore, once we know that an instruction is dead
2682 // we change its DFS number so that it doesn't get value numbered.
2683 if (isInstructionTriviallyDead(&I, TLI)) {
2685 DEBUG(dbgs() << "Skipping trivially dead instruction " << I << "\n");
2686 markInstructionForDeletion(&I);
2689 InstrDFS[&I] = End++;
2690 DFSToInstr.emplace_back(&I);
2693 // All of the range functions taken half-open ranges (open on the end side).
2694 // So we do not subtract one from count, because at this point it is one
2695 // greater than the last instruction.
2696 return std::make_pair(Start, End);
2699 void NewGVN::updateProcessedCount(const Value *V) {
2701 if (ProcessedCount.count(V) == 0) {
2702 ProcessedCount.insert({V, 1});
2704 ++ProcessedCount[V];
2705 assert(ProcessedCount[V] < 100 &&
2706 "Seem to have processed the same Value a lot");
2710 // Evaluate MemoryPhi nodes symbolically, just like PHI nodes
2711 void NewGVN::valueNumberMemoryPhi(MemoryPhi *MP) {
2712 // If all the arguments are the same, the MemoryPhi has the same value as the
2713 // argument. Filter out unreachable blocks and self phis from our operands.
2714 // TODO: We could do cycle-checking on the memory phis to allow valueizing for
2715 // self-phi checking.
2716 const BasicBlock *PHIBlock = MP->getBlock();
2717 auto Filtered = make_filter_range(MP->operands(), [&](const Use &U) {
2718 return cast<MemoryAccess>(U) != MP &&
2719 !isMemoryAccessTOP(cast<MemoryAccess>(U)) &&
2720 ReachableEdges.count({MP->getIncomingBlock(U), PHIBlock});
2722 // If all that is left is nothing, our memoryphi is undef. We keep it as
2723 // InitialClass. Note: The only case this should happen is if we have at
2724 // least one self-argument.
2725 if (Filtered.begin() == Filtered.end()) {
2726 if (setMemoryClass(MP, TOPClass))
2727 markMemoryUsersTouched(MP);
2731 // Transform the remaining operands into operand leaders.
2732 // FIXME: mapped_iterator should have a range version.
2733 auto LookupFunc = [&](const Use &U) {
2734 return lookupMemoryLeader(cast<MemoryAccess>(U));
2736 auto MappedBegin = map_iterator(Filtered.begin(), LookupFunc);
2737 auto MappedEnd = map_iterator(Filtered.end(), LookupFunc);
2739 // and now check if all the elements are equal.
2740 // Sadly, we can't use std::equals since these are random access iterators.
2741 const auto *AllSameValue = *MappedBegin;
2743 bool AllEqual = std::all_of(
2744 MappedBegin, MappedEnd,
2745 [&AllSameValue](const MemoryAccess *V) { return V == AllSameValue; });
2748 DEBUG(dbgs() << "Memory Phi value numbered to " << *AllSameValue << "\n");
2750 DEBUG(dbgs() << "Memory Phi value numbered to itself\n");
2751 // If it's equal to something, it's in that class. Otherwise, it has to be in
2752 // a class where it is the leader (other things may be equivalent to it, but
2753 // it needs to start off in its own class, which means it must have been the
2754 // leader, and it can't have stopped being the leader because it was never
2756 CongruenceClass *CC =
2757 AllEqual ? getMemoryClass(AllSameValue) : ensureLeaderOfMemoryClass(MP);
2758 auto OldState = MemoryPhiState.lookup(MP);
2759 assert(OldState != MPS_Invalid && "Invalid memory phi state");
2760 auto NewState = AllEqual ? MPS_Equivalent : MPS_Unique;
2761 MemoryPhiState[MP] = NewState;
2762 if (setMemoryClass(MP, CC) || OldState != NewState)
2763 markMemoryUsersTouched(MP);
2766 // Value number a single instruction, symbolically evaluating, performing
2767 // congruence finding, and updating mappings.
2768 void NewGVN::valueNumberInstruction(Instruction *I) {
2769 DEBUG(dbgs() << "Processing instruction " << *I << "\n");
2770 if (!I->isTerminator()) {
2771 const Expression *Symbolized = nullptr;
2772 SmallPtrSet<Value *, 2> Visited;
2773 if (DebugCounter::shouldExecute(VNCounter)) {
2774 Symbolized = performSymbolicEvaluation(I, Visited);
2775 // Make a phi of ops if necessary
2776 if (Symbolized && !isa<ConstantExpression>(Symbolized) &&
2777 !isa<VariableExpression>(Symbolized) && PHINodeUses.count(I)) {
2778 auto *PHIE = makePossiblePhiOfOps(I, Visited);
2784 // Mark the instruction as unused so we don't value number it again.
2787 // If we couldn't come up with a symbolic expression, use the unknown
2789 if (Symbolized == nullptr)
2790 Symbolized = createUnknownExpression(I);
2791 performCongruenceFinding(I, Symbolized);
2793 // Handle terminators that return values. All of them produce values we
2794 // don't currently understand. We don't place non-value producing
2795 // terminators in a class.
2796 if (!I->getType()->isVoidTy()) {
2797 auto *Symbolized = createUnknownExpression(I);
2798 performCongruenceFinding(I, Symbolized);
2800 processOutgoingEdges(dyn_cast<TerminatorInst>(I), I->getParent());
2804 // Check if there is a path, using single or equal argument phi nodes, from
2806 bool NewGVN::singleReachablePHIPath(
2807 SmallPtrSet<const MemoryAccess *, 8> &Visited, const MemoryAccess *First,
2808 const MemoryAccess *Second) const {
2809 if (First == Second)
2811 if (MSSA->isLiveOnEntryDef(First))
2814 // This is not perfect, but as we're just verifying here, we can live with
2815 // the loss of precision. The real solution would be that of doing strongly
2816 // connected component finding in this routine, and it's probably not worth
2817 // the complexity for the time being. So, we just keep a set of visited
2818 // MemoryAccess and return true when we hit a cycle.
2819 if (Visited.count(First))
2821 Visited.insert(First);
2823 const auto *EndDef = First;
2824 for (auto *ChainDef : optimized_def_chain(First)) {
2825 if (ChainDef == Second)
2827 if (MSSA->isLiveOnEntryDef(ChainDef))
2831 auto *MP = cast<MemoryPhi>(EndDef);
2832 auto ReachableOperandPred = [&](const Use &U) {
2833 return ReachableEdges.count({MP->getIncomingBlock(U), MP->getBlock()});
2835 auto FilteredPhiArgs =
2836 make_filter_range(MP->operands(), ReachableOperandPred);
2837 SmallVector<const Value *, 32> OperandList;
2838 std::copy(FilteredPhiArgs.begin(), FilteredPhiArgs.end(),
2839 std::back_inserter(OperandList));
2840 bool Okay = OperandList.size() == 1;
2843 std::equal(OperandList.begin(), OperandList.end(), OperandList.begin());
2845 return singleReachablePHIPath(Visited, cast<MemoryAccess>(OperandList[0]),
2850 // Verify the that the memory equivalence table makes sense relative to the
2851 // congruence classes. Note that this checking is not perfect, and is currently
2852 // subject to very rare false negatives. It is only useful for
2853 // testing/debugging.
2854 void NewGVN::verifyMemoryCongruency() const {
2856 // Verify that the memory table equivalence and memory member set match
2857 for (const auto *CC : CongruenceClasses) {
2858 if (CC == TOPClass || CC->isDead())
2860 if (CC->getStoreCount() != 0) {
2861 assert((CC->getStoredValue() || !isa<StoreInst>(CC->getLeader())) &&
2862 "Any class with a store as a leader should have a "
2863 "representative stored value");
2864 assert(CC->getMemoryLeader() &&
2865 "Any congruence class with a store should have a "
2866 "representative access");
2869 if (CC->getMemoryLeader())
2870 assert(MemoryAccessToClass.lookup(CC->getMemoryLeader()) == CC &&
2871 "Representative MemoryAccess does not appear to be reverse "
2873 for (auto M : CC->memory())
2874 assert(MemoryAccessToClass.lookup(M) == CC &&
2875 "Memory member does not appear to be reverse mapped properly");
2878 // Anything equivalent in the MemoryAccess table should be in the same
2879 // congruence class.
2881 // Filter out the unreachable and trivially dead entries, because they may
2882 // never have been updated if the instructions were not processed.
2883 auto ReachableAccessPred =
2884 [&](const std::pair<const MemoryAccess *, CongruenceClass *> Pair) {
2885 bool Result = ReachableBlocks.count(Pair.first->getBlock());
2886 if (!Result || MSSA->isLiveOnEntryDef(Pair.first) ||
2887 MemoryToDFSNum(Pair.first) == 0)
2889 if (auto *MemDef = dyn_cast<MemoryDef>(Pair.first))
2890 return !isInstructionTriviallyDead(MemDef->getMemoryInst());
2892 // We could have phi nodes which operands are all trivially dead,
2893 // so we don't process them.
2894 if (auto *MemPHI = dyn_cast<MemoryPhi>(Pair.first)) {
2895 for (auto &U : MemPHI->incoming_values()) {
2896 if (Instruction *I = dyn_cast<Instruction>(U.get())) {
2897 if (!isInstructionTriviallyDead(I))
2907 auto Filtered = make_filter_range(MemoryAccessToClass, ReachableAccessPred);
2908 for (auto KV : Filtered) {
2909 if (auto *FirstMUD = dyn_cast<MemoryUseOrDef>(KV.first)) {
2910 auto *SecondMUD = dyn_cast<MemoryUseOrDef>(KV.second->getMemoryLeader());
2911 if (FirstMUD && SecondMUD) {
2912 SmallPtrSet<const MemoryAccess *, 8> VisitedMAS;
2913 assert((singleReachablePHIPath(VisitedMAS, FirstMUD, SecondMUD) ||
2914 ValueToClass.lookup(FirstMUD->getMemoryInst()) ==
2915 ValueToClass.lookup(SecondMUD->getMemoryInst())) &&
2916 "The instructions for these memory operations should have "
2917 "been in the same congruence class or reachable through"
2918 "a single argument phi");
2920 } else if (auto *FirstMP = dyn_cast<MemoryPhi>(KV.first)) {
2921 // We can only sanely verify that MemoryDefs in the operand list all have
2923 auto ReachableOperandPred = [&](const Use &U) {
2924 return ReachableEdges.count(
2925 {FirstMP->getIncomingBlock(U), FirstMP->getBlock()}) &&
2929 // All arguments should in the same class, ignoring unreachable arguments
2930 auto FilteredPhiArgs =
2931 make_filter_range(FirstMP->operands(), ReachableOperandPred);
2932 SmallVector<const CongruenceClass *, 16> PhiOpClasses;
2933 std::transform(FilteredPhiArgs.begin(), FilteredPhiArgs.end(),
2934 std::back_inserter(PhiOpClasses), [&](const Use &U) {
2935 const MemoryDef *MD = cast<MemoryDef>(U);
2936 return ValueToClass.lookup(MD->getMemoryInst());
2938 assert(std::equal(PhiOpClasses.begin(), PhiOpClasses.end(),
2939 PhiOpClasses.begin()) &&
2940 "All MemoryPhi arguments should be in the same class");
2946 // Verify that the sparse propagation we did actually found the maximal fixpoint
2947 // We do this by storing the value to class mapping, touching all instructions,
2948 // and redoing the iteration to see if anything changed.
2949 void NewGVN::verifyIterationSettled(Function &F) {
2951 DEBUG(dbgs() << "Beginning iteration verification\n");
2952 if (DebugCounter::isCounterSet(VNCounter))
2953 DebugCounter::setCounterValue(VNCounter, StartingVNCounter);
2955 // Note that we have to store the actual classes, as we may change existing
2956 // classes during iteration. This is because our memory iteration propagation
2957 // is not perfect, and so may waste a little work. But it should generate
2958 // exactly the same congruence classes we have now, with different IDs.
2959 std::map<const Value *, CongruenceClass> BeforeIteration;
2961 for (auto &KV : ValueToClass) {
2962 if (auto *I = dyn_cast<Instruction>(KV.first))
2963 // Skip unused/dead instructions.
2964 if (InstrToDFSNum(I) == 0)
2966 BeforeIteration.insert({KV.first, *KV.second});
2969 TouchedInstructions.set();
2970 TouchedInstructions.reset(0);
2971 iterateTouchedInstructions();
2972 DenseSet<std::pair<const CongruenceClass *, const CongruenceClass *>>
2974 for (const auto &KV : ValueToClass) {
2975 if (auto *I = dyn_cast<Instruction>(KV.first))
2976 // Skip unused/dead instructions.
2977 if (InstrToDFSNum(I) == 0)
2979 // We could sink these uses, but i think this adds a bit of clarity here as
2980 // to what we are comparing.
2981 auto *BeforeCC = &BeforeIteration.find(KV.first)->second;
2982 auto *AfterCC = KV.second;
2983 // Note that the classes can't change at this point, so we memoize the set
2985 if (!EqualClasses.count({BeforeCC, AfterCC})) {
2986 assert(BeforeCC->isEquivalentTo(AfterCC) &&
2987 "Value number changed after main loop completed!");
2988 EqualClasses.insert({BeforeCC, AfterCC});
2994 // Verify that for each store expression in the expression to class mapping,
2995 // only the latest appears, and multiple ones do not appear.
2996 // Because loads do not use the stored value when doing equality with stores,
2997 // if we don't erase the old store expressions from the table, a load can find
2998 // a no-longer valid StoreExpression.
2999 void NewGVN::verifyStoreExpressions() const {
3001 DenseSet<std::pair<const Value *, const Value *>> StoreExpressionSet;
3002 for (const auto &KV : ExpressionToClass) {
3003 if (auto *SE = dyn_cast<StoreExpression>(KV.first)) {
3004 // Make sure a version that will conflict with loads is not already there
3006 StoreExpressionSet.insert({SE->getOperand(0), SE->getMemoryLeader()});
3007 assert(Res.second &&
3008 "Stored expression conflict exists in expression table");
3009 auto *ValueExpr = ValueToExpression.lookup(SE->getStoreInst());
3010 assert(ValueExpr && ValueExpr->equals(*SE) &&
3011 "StoreExpression in ExpressionToClass is not latest "
3012 "StoreExpression for value");
3018 // This is the main value numbering loop, it iterates over the initial touched
3019 // instruction set, propagating value numbers, marking things touched, etc,
3020 // until the set of touched instructions is completely empty.
3021 void NewGVN::iterateTouchedInstructions() {
3022 unsigned int Iterations = 0;
3023 // Figure out where touchedinstructions starts
3024 int FirstInstr = TouchedInstructions.find_first();
3025 // Nothing set, nothing to iterate, just return.
3026 if (FirstInstr == -1)
3028 const BasicBlock *LastBlock = getBlockForValue(InstrFromDFSNum(FirstInstr));
3029 while (TouchedInstructions.any()) {
3031 // Walk through all the instructions in all the blocks in RPO.
3032 // TODO: As we hit a new block, we should push and pop equalities into a
3033 // table lookupOperandLeader can use, to catch things PredicateInfo
3034 // might miss, like edge-only equivalences.
3035 for (unsigned InstrNum : TouchedInstructions.set_bits()) {
3037 // This instruction was found to be dead. We don't bother looking
3039 if (InstrNum == 0) {
3040 TouchedInstructions.reset(InstrNum);
3044 Value *V = InstrFromDFSNum(InstrNum);
3045 const BasicBlock *CurrBlock = getBlockForValue(V);
3047 // If we hit a new block, do reachability processing.
3048 if (CurrBlock != LastBlock) {
3049 LastBlock = CurrBlock;
3050 bool BlockReachable = ReachableBlocks.count(CurrBlock);
3051 const auto &CurrInstRange = BlockInstRange.lookup(CurrBlock);
3053 // If it's not reachable, erase any touched instructions and move on.
3054 if (!BlockReachable) {
3055 TouchedInstructions.reset(CurrInstRange.first, CurrInstRange.second);
3056 DEBUG(dbgs() << "Skipping instructions in block "
3057 << getBlockName(CurrBlock)
3058 << " because it is unreachable\n");
3061 updateProcessedCount(CurrBlock);
3064 if (auto *MP = dyn_cast<MemoryPhi>(V)) {
3065 DEBUG(dbgs() << "Processing MemoryPhi " << *MP << "\n");
3066 valueNumberMemoryPhi(MP);
3067 } else if (auto *I = dyn_cast<Instruction>(V)) {
3068 valueNumberInstruction(I);
3070 llvm_unreachable("Should have been a MemoryPhi or Instruction");
3072 updateProcessedCount(V);
3073 // Reset after processing (because we may mark ourselves as touched when
3074 // we propagate equalities).
3075 TouchedInstructions.reset(InstrNum);
3078 NumGVNMaxIterations = std::max(NumGVNMaxIterations.getValue(), Iterations);
3081 // This is the main transformation entry point.
3082 bool NewGVN::runGVN() {
3083 if (DebugCounter::isCounterSet(VNCounter))
3084 StartingVNCounter = DebugCounter::getCounterValue(VNCounter);
3085 bool Changed = false;
3086 NumFuncArgs = F.arg_size();
3087 MSSAWalker = MSSA->getWalker();
3088 SingletonDeadExpression = new (ExpressionAllocator) DeadExpression();
3090 // Count number of instructions for sizing of hash tables, and come
3091 // up with a global dfs numbering for instructions.
3092 unsigned ICount = 1;
3093 // Add an empty instruction to account for the fact that we start at 1
3094 DFSToInstr.emplace_back(nullptr);
3095 // Note: We want ideal RPO traversal of the blocks, which is not quite the
3096 // same as dominator tree order, particularly with regard whether backedges
3097 // get visited first or second, given a block with multiple successors.
3098 // If we visit in the wrong order, we will end up performing N times as many
3100 // The dominator tree does guarantee that, for a given dom tree node, it's
3101 // parent must occur before it in the RPO ordering. Thus, we only need to sort
3103 ReversePostOrderTraversal<Function *> RPOT(&F);
3104 unsigned Counter = 0;
3105 for (auto &B : RPOT) {
3106 auto *Node = DT->getNode(B);
3107 assert(Node && "RPO and Dominator tree should have same reachability");
3108 RPOOrdering[Node] = ++Counter;
3110 // Sort dominator tree children arrays into RPO.
3111 for (auto &B : RPOT) {
3112 auto *Node = DT->getNode(B);
3113 if (Node->getChildren().size() > 1)
3114 std::sort(Node->begin(), Node->end(),
3115 [&](const DomTreeNode *A, const DomTreeNode *B) {
3116 return RPOOrdering[A] < RPOOrdering[B];
3120 // Now a standard depth first ordering of the domtree is equivalent to RPO.
3121 for (auto DTN : depth_first(DT->getRootNode())) {
3122 BasicBlock *B = DTN->getBlock();
3123 const auto &BlockRange = assignDFSNumbers(B, ICount);
3124 BlockInstRange.insert({B, BlockRange});
3125 ICount += BlockRange.second - BlockRange.first;
3127 initializeCongruenceClasses(F);
3129 TouchedInstructions.resize(ICount);
3130 // Ensure we don't end up resizing the expressionToClass map, as
3131 // that can be quite expensive. At most, we have one expression per
3133 ExpressionToClass.reserve(ICount);
3135 // Initialize the touched instructions to include the entry block.
3136 const auto &InstRange = BlockInstRange.lookup(&F.getEntryBlock());
3137 TouchedInstructions.set(InstRange.first, InstRange.second);
3138 DEBUG(dbgs() << "Block " << getBlockName(&F.getEntryBlock())
3139 << " marked reachable\n");
3140 ReachableBlocks.insert(&F.getEntryBlock());
3142 iterateTouchedInstructions();
3143 verifyMemoryCongruency();
3144 verifyIterationSettled(F);
3145 verifyStoreExpressions();
3147 Changed |= eliminateInstructions(F);
3149 // Delete all instructions marked for deletion.
3150 for (Instruction *ToErase : InstructionsToErase) {
3151 if (!ToErase->use_empty())
3152 ToErase->replaceAllUsesWith(UndefValue::get(ToErase->getType()));
3154 if (ToErase->getParent())
3155 ToErase->eraseFromParent();
3158 // Delete all unreachable blocks.
3159 auto UnreachableBlockPred = [&](const BasicBlock &BB) {
3160 return !ReachableBlocks.count(&BB);
3163 for (auto &BB : make_filter_range(F, UnreachableBlockPred)) {
3164 DEBUG(dbgs() << "We believe block " << getBlockName(&BB)
3165 << " is unreachable\n");
3166 deleteInstructionsInBlock(&BB);
3174 struct NewGVN::ValueDFS {
3178 // Only one of Def and U will be set.
3179 // The bool in the Def tells us whether the Def is the stored value of a
3181 PointerIntPair<Value *, 1, bool> Def;
3183 bool operator<(const ValueDFS &Other) const {
3184 // It's not enough that any given field be less than - we have sets
3185 // of fields that need to be evaluated together to give a proper ordering.
3186 // For example, if you have;
3191 // We want the second to be less than the first, but if we just go field
3192 // by field, we will get to Val 0 < Val 50 and say the first is less than
3193 // the second. We only want it to be less than if the DFS orders are equal.
3195 // Each LLVM instruction only produces one value, and thus the lowest-level
3196 // differentiator that really matters for the stack (and what we use as as a
3197 // replacement) is the local dfs number.
3198 // Everything else in the structure is instruction level, and only affects
3199 // the order in which we will replace operands of a given instruction.
3201 // For a given instruction (IE things with equal dfsin, dfsout, localnum),
3202 // the order of replacement of uses does not matter.
3206 // When you hit b, you will have two valuedfs with the same dfsin, out, and
3208 // The .val will be the same as well.
3209 // The .u's will be different.
3210 // You will replace both, and it does not matter what order you replace them
3211 // in (IE whether you replace operand 2, then operand 1, or operand 1, then
3213 // Similarly for the case of same dfsin, dfsout, localnum, but different
3218 // in c, we will a valuedfs for a, and one for b,with everything the same
3220 // It does not matter what order we replace these operands in.
3221 // You will always end up with the same IR, and this is guaranteed.
3222 return std::tie(DFSIn, DFSOut, LocalNum, Def, U) <
3223 std::tie(Other.DFSIn, Other.DFSOut, Other.LocalNum, Other.Def,
3228 // This function converts the set of members for a congruence class from values,
3229 // to sets of defs and uses with associated DFS info. The total number of
3230 // reachable uses for each value is stored in UseCount, and instructions that
3232 // dead (have no non-dead uses) are stored in ProbablyDead.
3233 void NewGVN::convertClassToDFSOrdered(
3234 const CongruenceClass &Dense, SmallVectorImpl<ValueDFS> &DFSOrderedSet,
3235 DenseMap<const Value *, unsigned int> &UseCounts,
3236 SmallPtrSetImpl<Instruction *> &ProbablyDead) const {
3237 for (auto D : Dense) {
3238 // First add the value.
3239 BasicBlock *BB = getBlockForValue(D);
3240 // Constants are handled prior to ever calling this function, so
3241 // we should only be left with instructions as members.
3242 assert(BB && "Should have figured out a basic block for value");
3244 DomTreeNode *DomNode = DT->getNode(BB);
3245 VDDef.DFSIn = DomNode->getDFSNumIn();
3246 VDDef.DFSOut = DomNode->getDFSNumOut();
3247 // If it's a store, use the leader of the value operand, if it's always
3248 // available, or the value operand. TODO: We could do dominance checks to
3249 // find a dominating leader, but not worth it ATM.
3250 if (auto *SI = dyn_cast<StoreInst>(D)) {
3251 auto Leader = lookupOperandLeader(SI->getValueOperand());
3252 if (alwaysAvailable(Leader)) {
3253 VDDef.Def.setPointer(Leader);
3255 VDDef.Def.setPointer(SI->getValueOperand());
3256 VDDef.Def.setInt(true);
3259 VDDef.Def.setPointer(D);
3261 assert(isa<Instruction>(D) &&
3262 "The dense set member should always be an instruction");
3263 Instruction *Def = cast<Instruction>(D);
3264 VDDef.LocalNum = InstrToDFSNum(D);
3265 DFSOrderedSet.push_back(VDDef);
3266 // If there is a phi node equivalent, add it
3267 if (auto *PN = RealToTemp.lookup(Def)) {
3269 dyn_cast_or_null<PHIExpression>(ValueToExpression.lookup(Def));
3271 VDDef.Def.setInt(false);
3272 VDDef.Def.setPointer(PN);
3274 DFSOrderedSet.push_back(VDDef);
3278 unsigned int UseCount = 0;
3279 // Now add the uses.
3280 for (auto &U : Def->uses()) {
3281 if (auto *I = dyn_cast<Instruction>(U.getUser())) {
3282 // Don't try to replace into dead uses
3283 if (InstructionsToErase.count(I))
3286 // Put the phi node uses in the incoming block.
3288 if (auto *P = dyn_cast<PHINode>(I)) {
3289 IBlock = P->getIncomingBlock(U);
3290 // Make phi node users appear last in the incoming block
3292 VDUse.LocalNum = InstrDFS.size() + 1;
3294 IBlock = getBlockForValue(I);
3295 VDUse.LocalNum = InstrToDFSNum(I);
3298 // Skip uses in unreachable blocks, as we're going
3300 if (ReachableBlocks.count(IBlock) == 0)
3303 DomTreeNode *DomNode = DT->getNode(IBlock);
3304 VDUse.DFSIn = DomNode->getDFSNumIn();
3305 VDUse.DFSOut = DomNode->getDFSNumOut();
3308 DFSOrderedSet.emplace_back(VDUse);
3312 // If there are no uses, it's probably dead (but it may have side-effects,
3313 // so not definitely dead. Otherwise, store the number of uses so we can
3314 // track if it becomes dead later).
3316 ProbablyDead.insert(Def);
3318 UseCounts[Def] = UseCount;
3322 // This function converts the set of members for a congruence class from values,
3323 // to the set of defs for loads and stores, with associated DFS info.
3324 void NewGVN::convertClassToLoadsAndStores(
3325 const CongruenceClass &Dense,
3326 SmallVectorImpl<ValueDFS> &LoadsAndStores) const {
3327 for (auto D : Dense) {
3328 if (!isa<LoadInst>(D) && !isa<StoreInst>(D))
3331 BasicBlock *BB = getBlockForValue(D);
3333 DomTreeNode *DomNode = DT->getNode(BB);
3334 VD.DFSIn = DomNode->getDFSNumIn();
3335 VD.DFSOut = DomNode->getDFSNumOut();
3336 VD.Def.setPointer(D);
3338 // If it's an instruction, use the real local dfs number.
3339 if (auto *I = dyn_cast<Instruction>(D))
3340 VD.LocalNum = InstrToDFSNum(I);
3342 llvm_unreachable("Should have been an instruction");
3344 LoadsAndStores.emplace_back(VD);
3348 static void patchReplacementInstruction(Instruction *I, Value *Repl) {
3349 auto *ReplInst = dyn_cast<Instruction>(Repl);
3353 // Patch the replacement so that it is not more restrictive than the value
3355 // Note that if 'I' is a load being replaced by some operation,
3356 // for example, by an arithmetic operation, then andIRFlags()
3357 // would just erase all math flags from the original arithmetic
3358 // operation, which is clearly not wanted and not needed.
3359 if (!isa<LoadInst>(I))
3360 ReplInst->andIRFlags(I);
3362 // FIXME: If both the original and replacement value are part of the
3363 // same control-flow region (meaning that the execution of one
3364 // guarantees the execution of the other), then we can combine the
3365 // noalias scopes here and do better than the general conservative
3366 // answer used in combineMetadata().
3368 // In general, GVN unifies expressions over different control-flow
3369 // regions, and so we need a conservative combination of the noalias
3371 static const unsigned KnownIDs[] = {
3372 LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
3373 LLVMContext::MD_noalias, LLVMContext::MD_range,
3374 LLVMContext::MD_fpmath, LLVMContext::MD_invariant_load,
3375 LLVMContext::MD_invariant_group};
3376 combineMetadata(ReplInst, I, KnownIDs);
3379 static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) {
3380 patchReplacementInstruction(I, Repl);
3381 I->replaceAllUsesWith(Repl);
3384 void NewGVN::deleteInstructionsInBlock(BasicBlock *BB) {
3385 DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
3386 ++NumGVNBlocksDeleted;
3388 // Delete the instructions backwards, as it has a reduced likelihood of having
3389 // to update as many def-use and use-def chains. Start after the terminator.
3390 auto StartPoint = BB->rbegin();
3392 // Note that we explicitly recalculate BB->rend() on each iteration,
3393 // as it may change when we remove the first instruction.
3394 for (BasicBlock::reverse_iterator I(StartPoint); I != BB->rend();) {
3395 Instruction &Inst = *I++;
3396 if (!Inst.use_empty())
3397 Inst.replaceAllUsesWith(UndefValue::get(Inst.getType()));
3398 if (isa<LandingPadInst>(Inst))
3401 Inst.eraseFromParent();
3402 ++NumGVNInstrDeleted;
3404 // Now insert something that simplifycfg will turn into an unreachable.
3405 Type *Int8Ty = Type::getInt8Ty(BB->getContext());
3406 new StoreInst(UndefValue::get(Int8Ty),
3407 Constant::getNullValue(Int8Ty->getPointerTo()),
3408 BB->getTerminator());
3411 void NewGVN::markInstructionForDeletion(Instruction *I) {
3412 DEBUG(dbgs() << "Marking " << *I << " for deletion\n");
3413 InstructionsToErase.insert(I);
3416 void NewGVN::replaceInstruction(Instruction *I, Value *V) {
3418 DEBUG(dbgs() << "Replacing " << *I << " with " << *V << "\n");
3419 patchAndReplaceAllUsesWith(I, V);
3420 // We save the actual erasing to avoid invalidating memory
3421 // dependencies until we are done with everything.
3422 markInstructionForDeletion(I);
3427 // This is a stack that contains both the value and dfs info of where
3428 // that value is valid.
3429 class ValueDFSStack {
3431 Value *back() const { return ValueStack.back(); }
3432 std::pair<int, int> dfs_back() const { return DFSStack.back(); }
3434 void push_back(Value *V, int DFSIn, int DFSOut) {
3435 ValueStack.emplace_back(V);
3436 DFSStack.emplace_back(DFSIn, DFSOut);
3438 bool empty() const { return DFSStack.empty(); }
3439 bool isInScope(int DFSIn, int DFSOut) const {
3442 return DFSIn >= DFSStack.back().first && DFSOut <= DFSStack.back().second;
3445 void popUntilDFSScope(int DFSIn, int DFSOut) {
3447 // These two should always be in sync at this point.
3448 assert(ValueStack.size() == DFSStack.size() &&
3449 "Mismatch between ValueStack and DFSStack");
3451 !DFSStack.empty() &&
3452 !(DFSIn >= DFSStack.back().first && DFSOut <= DFSStack.back().second)) {
3453 DFSStack.pop_back();
3454 ValueStack.pop_back();
3459 SmallVector<Value *, 8> ValueStack;
3460 SmallVector<std::pair<int, int>, 8> DFSStack;
3464 // Given a value and a basic block we are trying to see if it is available in,
3465 // see if the value has a leader available in that block.
3466 Value *NewGVN::findPhiOfOpsLeader(const Expression *E,
3467 const BasicBlock *BB) const {
3468 // It would already be constant if we could make it constant
3469 if (auto *CE = dyn_cast<ConstantExpression>(E))
3470 return CE->getConstantValue();
3471 if (auto *VE = dyn_cast<VariableExpression>(E))
3472 return VE->getVariableValue();
3474 auto *CC = ExpressionToClass.lookup(E);
3477 if (alwaysAvailable(CC->getLeader()))
3478 return CC->getLeader();
3480 for (auto Member : *CC) {
3481 auto *MemberInst = dyn_cast<Instruction>(Member);
3482 // Anything that isn't an instruction is always available.
3485 // If we are looking for something in the same block as the member, it must
3486 // be a leader because this function is looking for operands for a phi node.
3487 if (MemberInst->getParent() == BB ||
3488 DT->dominates(MemberInst->getParent(), BB)) {
3495 bool NewGVN::eliminateInstructions(Function &F) {
3496 // This is a non-standard eliminator. The normal way to eliminate is
3497 // to walk the dominator tree in order, keeping track of available
3498 // values, and eliminating them. However, this is mildly
3499 // pointless. It requires doing lookups on every instruction,
3500 // regardless of whether we will ever eliminate it. For
3501 // instructions part of most singleton congruence classes, we know we
3502 // will never eliminate them.
3504 // Instead, this eliminator looks at the congruence classes directly, sorts
3505 // them into a DFS ordering of the dominator tree, and then we just
3506 // perform elimination straight on the sets by walking the congruence
3507 // class member uses in order, and eliminate the ones dominated by the
3508 // last member. This is worst case O(E log E) where E = number of
3509 // instructions in a single congruence class. In theory, this is all
3510 // instructions. In practice, it is much faster, as most instructions are
3511 // either in singleton congruence classes or can't possibly be eliminated
3512 // anyway (if there are no overlapping DFS ranges in class).
3513 // When we find something not dominated, it becomes the new leader
3514 // for elimination purposes.
3515 // TODO: If we wanted to be faster, We could remove any members with no
3516 // overlapping ranges while sorting, as we will never eliminate anything
3517 // with those members, as they don't dominate anything else in our set.
3519 bool AnythingReplaced = false;
3521 // Since we are going to walk the domtree anyway, and we can't guarantee the
3522 // DFS numbers are updated, we compute some ourselves.
3523 DT->updateDFSNumbers();
3525 // Go through all of our phi nodes, and kill the arguments associated with
3526 // unreachable edges.
3527 auto ReplaceUnreachablePHIArgs = [&](PHINode &PHI, BasicBlock *BB) {
3528 for (auto &Operand : PHI.incoming_values())
3529 if (!ReachableEdges.count({PHI.getIncomingBlock(Operand), BB})) {
3530 DEBUG(dbgs() << "Replacing incoming value of " << PHI << " for block "
3531 << getBlockName(PHI.getIncomingBlock(Operand))
3532 << " with undef due to it being unreachable\n");
3533 Operand.set(UndefValue::get(PHI.getType()));
3536 SmallPtrSet<BasicBlock *, 8> BlocksWithPhis;
3538 if ((!B.empty() && isa<PHINode>(*B.begin())) ||
3539 (PHIOfOpsPHIs.find(&B) != PHIOfOpsPHIs.end()))
3540 BlocksWithPhis.insert(&B);
3541 DenseMap<const BasicBlock *, unsigned> ReachablePredCount;
3542 for (auto KV : ReachableEdges)
3543 ReachablePredCount[KV.getEnd()]++;
3544 for (auto *BB : BlocksWithPhis)
3545 // TODO: It would be faster to use getNumIncomingBlocks() on a phi node in
3546 // the block and subtract the pred count, but it's more complicated.
3547 if (ReachablePredCount.lookup(BB) !=
3548 std::distance(pred_begin(BB), pred_end(BB))) {
3549 for (auto II = BB->begin(); isa<PHINode>(II); ++II) {
3550 auto &PHI = cast<PHINode>(*II);
3551 ReplaceUnreachablePHIArgs(PHI, BB);
3553 for_each_found(PHIOfOpsPHIs, BB, [&](PHINode *PHI) {
3554 ReplaceUnreachablePHIArgs(*PHI, BB);
3558 // Map to store the use counts
3559 DenseMap<const Value *, unsigned int> UseCounts;
3560 for (auto *CC : reverse(CongruenceClasses)) {
3561 DEBUG(dbgs() << "Eliminating in congruence class " << CC->getID() << "\n");
3562 // Track the equivalent store info so we can decide whether to try
3563 // dead store elimination.
3564 SmallVector<ValueDFS, 8> PossibleDeadStores;
3565 SmallPtrSet<Instruction *, 8> ProbablyDead;
3566 if (CC->isDead() || CC->empty())
3568 // Everything still in the TOP class is unreachable or dead.
3569 if (CC == TOPClass) {
3570 for (auto M : *CC) {
3571 auto *VTE = ValueToExpression.lookup(M);
3572 if (VTE && isa<DeadExpression>(VTE))
3573 markInstructionForDeletion(cast<Instruction>(M));
3574 assert((!ReachableBlocks.count(cast<Instruction>(M)->getParent()) ||
3575 InstructionsToErase.count(cast<Instruction>(M))) &&
3576 "Everything in TOP should be unreachable or dead at this "
3582 assert(CC->getLeader() && "We should have had a leader");
3583 // If this is a leader that is always available, and it's a
3584 // constant or has no equivalences, just replace everything with
3585 // it. We then update the congruence class with whatever members
3588 CC->getStoredValue() ? CC->getStoredValue() : CC->getLeader();
3589 if (alwaysAvailable(Leader)) {
3590 CongruenceClass::MemberSet MembersLeft;
3591 for (auto M : *CC) {
3593 // Void things have no uses we can replace.
3594 if (Member == Leader || !isa<Instruction>(Member) ||
3595 Member->getType()->isVoidTy()) {
3596 MembersLeft.insert(Member);
3599 DEBUG(dbgs() << "Found replacement " << *(Leader) << " for " << *Member
3601 auto *I = cast<Instruction>(Member);
3602 assert(Leader != I && "About to accidentally remove our leader");
3603 replaceInstruction(I, Leader);
3604 AnythingReplaced = true;
3606 CC->swap(MembersLeft);
3608 // If this is a singleton, we can skip it.
3609 if (CC->size() != 1 || RealToTemp.lookup(Leader)) {
3610 // This is a stack because equality replacement/etc may place
3611 // constants in the middle of the member list, and we want to use
3612 // those constant values in preference to the current leader, over
3613 // the scope of those constants.
3614 ValueDFSStack EliminationStack;
3616 // Convert the members to DFS ordered sets and then merge them.
3617 SmallVector<ValueDFS, 8> DFSOrderedSet;
3618 convertClassToDFSOrdered(*CC, DFSOrderedSet, UseCounts, ProbablyDead);
3620 // Sort the whole thing.
3621 std::sort(DFSOrderedSet.begin(), DFSOrderedSet.end());
3622 for (auto &VD : DFSOrderedSet) {
3623 int MemberDFSIn = VD.DFSIn;
3624 int MemberDFSOut = VD.DFSOut;
3625 Value *Def = VD.Def.getPointer();
3626 bool FromStore = VD.Def.getInt();
3628 // We ignore void things because we can't get a value from them.
3629 if (Def && Def->getType()->isVoidTy())
3631 auto *DefInst = dyn_cast_or_null<Instruction>(Def);
3632 if (DefInst && AllTempInstructions.count(DefInst)) {
3633 auto *PN = cast<PHINode>(DefInst);
3635 // If this is a value phi and that's the expression we used, insert
3636 // it into the program
3637 // remove from temp instruction list.
3638 AllTempInstructions.erase(PN);
3639 auto *DefBlock = getBlockForValue(Def);
3640 DEBUG(dbgs() << "Inserting fully real phi of ops" << *Def
3642 << getBlockName(getBlockForValue(Def)) << "\n");
3643 PN->insertBefore(&DefBlock->front());
3645 NumGVNPHIOfOpsEliminations++;
3648 if (EliminationStack.empty()) {
3649 DEBUG(dbgs() << "Elimination Stack is empty\n");
3651 DEBUG(dbgs() << "Elimination Stack Top DFS numbers are ("
3652 << EliminationStack.dfs_back().first << ","
3653 << EliminationStack.dfs_back().second << ")\n");
3656 DEBUG(dbgs() << "Current DFS numbers are (" << MemberDFSIn << ","
3657 << MemberDFSOut << ")\n");
3658 // First, we see if we are out of scope or empty. If so,
3659 // and there equivalences, we try to replace the top of
3660 // stack with equivalences (if it's on the stack, it must
3661 // not have been eliminated yet).
3662 // Then we synchronize to our current scope, by
3663 // popping until we are back within a DFS scope that
3664 // dominates the current member.
3665 // Then, what happens depends on a few factors
3666 // If the stack is now empty, we need to push
3667 // If we have a constant or a local equivalence we want to
3668 // start using, we also push.
3669 // Otherwise, we walk along, processing members who are
3670 // dominated by this scope, and eliminate them.
3671 bool ShouldPush = Def && EliminationStack.empty();
3673 !EliminationStack.isInScope(MemberDFSIn, MemberDFSOut);
3675 if (OutOfScope || ShouldPush) {
3676 // Sync to our current scope.
3677 EliminationStack.popUntilDFSScope(MemberDFSIn, MemberDFSOut);
3678 bool ShouldPush = Def && EliminationStack.empty();
3680 EliminationStack.push_back(Def, MemberDFSIn, MemberDFSOut);
3684 // Skip the Def's, we only want to eliminate on their uses. But mark
3685 // dominated defs as dead.
3687 // For anything in this case, what and how we value number
3688 // guarantees that any side-effets that would have occurred (ie
3689 // throwing, etc) can be proven to either still occur (because it's
3690 // dominated by something that has the same side-effects), or never
3691 // occur. Otherwise, we would not have been able to prove it value
3692 // equivalent to something else. For these things, we can just mark
3693 // it all dead. Note that this is different from the "ProbablyDead"
3694 // set, which may not be dominated by anything, and thus, are only
3695 // easy to prove dead if they are also side-effect free. Note that
3696 // because stores are put in terms of the stored value, we skip
3697 // stored values here. If the stored value is really dead, it will
3698 // still be marked for deletion when we process it in its own class.
3699 if (!EliminationStack.empty() && Def != EliminationStack.back() &&
3700 isa<Instruction>(Def) && !FromStore)
3701 markInstructionForDeletion(cast<Instruction>(Def));
3704 // At this point, we know it is a Use we are trying to possibly
3707 assert(isa<Instruction>(U->get()) &&
3708 "Current def should have been an instruction");
3709 assert(isa<Instruction>(U->getUser()) &&
3710 "Current user should have been an instruction");
3712 // If the thing we are replacing into is already marked to be dead,
3713 // this use is dead. Note that this is true regardless of whether
3714 // we have anything dominating the use or not. We do this here
3715 // because we are already walking all the uses anyway.
3716 Instruction *InstUse = cast<Instruction>(U->getUser());
3717 if (InstructionsToErase.count(InstUse)) {
3718 auto &UseCount = UseCounts[U->get()];
3719 if (--UseCount == 0) {
3720 ProbablyDead.insert(cast<Instruction>(U->get()));
3724 // If we get to this point, and the stack is empty we must have a use
3725 // with nothing we can use to eliminate this use, so just skip it.
3726 if (EliminationStack.empty())
3729 Value *DominatingLeader = EliminationStack.back();
3731 auto *II = dyn_cast<IntrinsicInst>(DominatingLeader);
3732 if (II && II->getIntrinsicID() == Intrinsic::ssa_copy)
3733 DominatingLeader = II->getOperand(0);
3735 // Don't replace our existing users with ourselves.
3736 if (U->get() == DominatingLeader)
3738 DEBUG(dbgs() << "Found replacement " << *DominatingLeader << " for "
3739 << *U->get() << " in " << *(U->getUser()) << "\n");
3741 // If we replaced something in an instruction, handle the patching of
3742 // metadata. Skip this if we are replacing predicateinfo with its
3743 // original operand, as we already know we can just drop it.
3744 auto *ReplacedInst = cast<Instruction>(U->get());
3745 auto *PI = PredInfo->getPredicateInfoFor(ReplacedInst);
3746 if (!PI || DominatingLeader != PI->OriginalOp)
3747 patchReplacementInstruction(ReplacedInst, DominatingLeader);
3748 U->set(DominatingLeader);
3749 // This is now a use of the dominating leader, which means if the
3750 // dominating leader was dead, it's now live!
3751 auto &LeaderUseCount = UseCounts[DominatingLeader];
3752 // It's about to be alive again.
3753 if (LeaderUseCount == 0 && isa<Instruction>(DominatingLeader))
3754 ProbablyDead.erase(cast<Instruction>(DominatingLeader));
3755 if (LeaderUseCount == 0 && II)
3756 ProbablyDead.insert(II);
3758 AnythingReplaced = true;
3763 // At this point, anything still in the ProbablyDead set is actually dead if
3764 // would be trivially dead.
3765 for (auto *I : ProbablyDead)
3766 if (wouldInstructionBeTriviallyDead(I))
3767 markInstructionForDeletion(I);
3769 // Cleanup the congruence class.
3770 CongruenceClass::MemberSet MembersLeft;
3771 for (auto *Member : *CC)
3772 if (!isa<Instruction>(Member) ||
3773 !InstructionsToErase.count(cast<Instruction>(Member)))
3774 MembersLeft.insert(Member);
3775 CC->swap(MembersLeft);
3777 // If we have possible dead stores to look at, try to eliminate them.
3778 if (CC->getStoreCount() > 0) {
3779 convertClassToLoadsAndStores(*CC, PossibleDeadStores);
3780 std::sort(PossibleDeadStores.begin(), PossibleDeadStores.end());
3781 ValueDFSStack EliminationStack;
3782 for (auto &VD : PossibleDeadStores) {
3783 int MemberDFSIn = VD.DFSIn;
3784 int MemberDFSOut = VD.DFSOut;
3785 Instruction *Member = cast<Instruction>(VD.Def.getPointer());
3786 if (EliminationStack.empty() ||
3787 !EliminationStack.isInScope(MemberDFSIn, MemberDFSOut)) {
3788 // Sync to our current scope.
3789 EliminationStack.popUntilDFSScope(MemberDFSIn, MemberDFSOut);
3790 if (EliminationStack.empty()) {
3791 EliminationStack.push_back(Member, MemberDFSIn, MemberDFSOut);
3795 // We already did load elimination, so nothing to do here.
3796 if (isa<LoadInst>(Member))
3798 assert(!EliminationStack.empty());
3799 Instruction *Leader = cast<Instruction>(EliminationStack.back());
3801 assert(DT->dominates(Leader->getParent(), Member->getParent()));
3802 // Member is dominater by Leader, and thus dead
3803 DEBUG(dbgs() << "Marking dead store " << *Member
3804 << " that is dominated by " << *Leader << "\n");
3805 markInstructionForDeletion(Member);
3811 return AnythingReplaced;
3814 // This function provides global ranking of operations so that we can place them
3815 // in a canonical order. Note that rank alone is not necessarily enough for a
3816 // complete ordering, as constants all have the same rank. However, generally,
3817 // we will simplify an operation with all constants so that it doesn't matter
3818 // what order they appear in.
3819 unsigned int NewGVN::getRank(const Value *V) const {
3820 // Prefer constants to undef to anything else
3821 // Undef is a constant, have to check it first.
3822 // Prefer smaller constants to constantexprs
3823 if (isa<ConstantExpr>(V))
3825 if (isa<UndefValue>(V))
3827 if (isa<Constant>(V))
3829 else if (auto *A = dyn_cast<Argument>(V))
3830 return 3 + A->getArgNo();
3832 // Need to shift the instruction DFS by number of arguments + 3 to account for
3833 // the constant and argument ranking above.
3834 unsigned Result = InstrToDFSNum(V);
3836 return 4 + NumFuncArgs + Result;
3837 // Unreachable or something else, just return a really large number.
3841 // This is a function that says whether two commutative operations should
3842 // have their order swapped when canonicalizing.
3843 bool NewGVN::shouldSwapOperands(const Value *A, const Value *B) const {
3844 // Because we only care about a total ordering, and don't rewrite expressions
3845 // in this order, we order by rank, which will give a strict weak ordering to
3846 // everything but constants, and then we order by pointer address.
3847 return std::make_pair(getRank(A), A) > std::make_pair(getRank(B), B);
3851 class NewGVNLegacyPass : public FunctionPass {
3853 static char ID; // Pass identification, replacement for typeid.
3854 NewGVNLegacyPass() : FunctionPass(ID) {
3855 initializeNewGVNLegacyPassPass(*PassRegistry::getPassRegistry());
3857 bool runOnFunction(Function &F) override;
3860 void getAnalysisUsage(AnalysisUsage &AU) const override {
3861 AU.addRequired<AssumptionCacheTracker>();
3862 AU.addRequired<DominatorTreeWrapperPass>();
3863 AU.addRequired<TargetLibraryInfoWrapperPass>();
3864 AU.addRequired<MemorySSAWrapperPass>();
3865 AU.addRequired<AAResultsWrapperPass>();
3866 AU.addPreserved<DominatorTreeWrapperPass>();
3867 AU.addPreserved<GlobalsAAWrapperPass>();
3872 bool NewGVNLegacyPass::runOnFunction(Function &F) {
3873 if (skipFunction(F))
3875 return NewGVN(F, &getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
3876 &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F),
3877 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
3878 &getAnalysis<AAResultsWrapperPass>().getAAResults(),
3879 &getAnalysis<MemorySSAWrapperPass>().getMSSA(),
3880 F.getParent()->getDataLayout())
3884 INITIALIZE_PASS_BEGIN(NewGVNLegacyPass, "newgvn", "Global Value Numbering",
3886 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
3887 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
3888 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
3889 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
3890 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
3891 INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
3892 INITIALIZE_PASS_END(NewGVNLegacyPass, "newgvn", "Global Value Numbering", false,
3895 char NewGVNLegacyPass::ID = 0;
3897 // createGVNPass - The public interface to this file.
3898 FunctionPass *llvm::createNewGVNPass() { return new NewGVNLegacyPass(); }
3900 PreservedAnalyses NewGVNPass::run(Function &F, AnalysisManager<Function> &AM) {
3901 // Apparently the order in which we get these results matter for
3902 // the old GVN (see Chandler's comment in GVN.cpp). I'll keep
3903 // the same order here, just in case.
3904 auto &AC = AM.getResult<AssumptionAnalysis>(F);
3905 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
3906 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
3907 auto &AA = AM.getResult<AAManager>(F);
3908 auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
3910 NewGVN(F, &DT, &AC, &TLI, &AA, &MSSA, F.getParent()->getDataLayout())
3913 return PreservedAnalyses::all();
3914 PreservedAnalyses PA;
3915 PA.preserve<DominatorTreeAnalysis>();
3916 PA.preserve<GlobalsAA>();