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.
380 struct HashedExpression;
382 template <> struct DenseMapInfo<const Expression *> {
383 static const Expression *getEmptyKey() {
384 auto Val = static_cast<uintptr_t>(-1);
385 Val <<= PointerLikeTypeTraits<const Expression *>::NumLowBitsAvailable;
386 return reinterpret_cast<const Expression *>(Val);
388 static const Expression *getTombstoneKey() {
389 auto Val = static_cast<uintptr_t>(~1U);
390 Val <<= PointerLikeTypeTraits<const Expression *>::NumLowBitsAvailable;
391 return reinterpret_cast<const Expression *>(Val);
393 static unsigned getHashValue(const Expression *E) {
394 return static_cast<unsigned>(E->getHashValue());
396 static unsigned getHashValue(const HashedExpression &HE);
397 static bool isEqual(const HashedExpression &LHS, const Expression *RHS);
398 static bool isEqual(const Expression *LHS, const Expression *RHS) {
401 if (LHS == getTombstoneKey() || RHS == getTombstoneKey() ||
402 LHS == getEmptyKey() || RHS == getEmptyKey())
407 } // end namespace llvm
409 // This is just a wrapper around Expression that computes the hash value once at
410 // creation time. Hash values for an Expression can't change once they are
411 // inserted into the DenseMap (it breaks DenseMap), so they must be immutable at
412 // that point anyway.
413 struct HashedExpression {
416 HashedExpression(const Expression *E)
417 : E(E), HashVal(DenseMapInfo<const Expression *>::getHashValue(E)) {}
421 DenseMapInfo<const Expression *>::getHashValue(const HashedExpression &HE) {
424 bool DenseMapInfo<const Expression *>::isEqual(const HashedExpression &LHS,
425 const Expression *RHS) {
426 return isEqual(LHS.E, RHS);
433 const TargetLibraryInfo *TLI;
436 MemorySSAWalker *MSSAWalker;
437 const DataLayout &DL;
438 std::unique_ptr<PredicateInfo> PredInfo;
440 // These are the only two things the create* functions should have
441 // side-effects on due to allocating memory.
442 mutable BumpPtrAllocator ExpressionAllocator;
443 mutable ArrayRecycler<Value *> ArgRecycler;
444 mutable TarjanSCC SCCFinder;
445 const SimplifyQuery SQ;
447 // Number of function arguments, used by ranking
448 unsigned int NumFuncArgs;
450 // RPOOrdering of basic blocks
451 DenseMap<const DomTreeNode *, unsigned> RPOOrdering;
453 // Congruence class info.
455 // This class is called INITIAL in the paper. It is the class everything
456 // startsout in, and represents any value. Being an optimistic analysis,
457 // anything in the TOP class has the value TOP, which is indeterminate and
458 // equivalent to everything.
459 CongruenceClass *TOPClass;
460 std::vector<CongruenceClass *> CongruenceClasses;
461 unsigned NextCongruenceNum;
464 DenseMap<Value *, CongruenceClass *> ValueToClass;
465 DenseMap<Value *, const Expression *> ValueToExpression;
466 // Value PHI handling, used to make equivalence between phi(op, op) and
468 // These mappings just store various data that would normally be part of the
470 DenseSet<const Instruction *> PHINodeUses;
471 // Map a temporary instruction we created to a parent block.
472 DenseMap<const Value *, BasicBlock *> TempToBlock;
473 // Map between the temporary phis we created and the real instructions they
474 // are known equivalent to.
475 DenseMap<const Value *, PHINode *> RealToTemp;
476 // In order to know when we should re-process instructions that have
477 // phi-of-ops, we track the set of expressions that they needed as
478 // leaders. When we discover new leaders for those expressions, we process the
479 // associated phi-of-op instructions again in case they have changed. The
480 // other way they may change is if they had leaders, and those leaders
481 // disappear. However, at the point they have leaders, there are uses of the
482 // relevant operands in the created phi node, and so they will get reprocessed
483 // through the normal user marking we perform.
484 mutable DenseMap<const Value *, SmallPtrSet<Value *, 2>> AdditionalUsers;
485 DenseMap<const Expression *, SmallPtrSet<Instruction *, 2>>
486 ExpressionToPhiOfOps;
487 // Map from basic block to the temporary operations we created
488 DenseMap<const BasicBlock *, SmallVector<PHINode *, 8>> PHIOfOpsPHIs;
489 // Map from temporary operation to MemoryAccess.
490 DenseMap<const Instruction *, MemoryUseOrDef *> TempToMemory;
491 // Set of all temporary instructions we created.
492 DenseSet<Instruction *> AllTempInstructions;
494 // Mapping from predicate info we used to the instructions we used it with.
495 // In order to correctly ensure propagation, we must keep track of what
496 // comparisons we used, so that when the values of the comparisons change, we
497 // propagate the information to the places we used the comparison.
498 mutable DenseMap<const Value *, SmallPtrSet<Instruction *, 2>>
500 // the same reasoning as PredicateToUsers. When we skip MemoryAccesses for
501 // stores, we no longer can rely solely on the def-use chains of MemorySSA.
502 mutable DenseMap<const MemoryAccess *, SmallPtrSet<MemoryAccess *, 2>>
505 // A table storing which memorydefs/phis represent a memory state provably
506 // equivalent to another memory state.
507 // We could use the congruence class machinery, but the MemoryAccess's are
508 // abstract memory states, so they can only ever be equivalent to each other,
509 // and not to constants, etc.
510 DenseMap<const MemoryAccess *, CongruenceClass *> MemoryAccessToClass;
512 // We could, if we wanted, build MemoryPhiExpressions and
513 // MemoryVariableExpressions, etc, and value number them the same way we value
514 // number phi expressions. For the moment, this seems like overkill. They
515 // can only exist in one of three states: they can be TOP (equal to
516 // everything), Equivalent to something else, or unique. Because we do not
517 // create expressions for them, we need to simulate leader change not just
518 // when they change class, but when they change state. Note: We can do the
519 // same thing for phis, and avoid having phi expressions if we wanted, We
520 // should eventually unify in one direction or the other, so this is a little
521 // bit of an experiment in which turns out easier to maintain.
522 enum MemoryPhiState { MPS_Invalid, MPS_TOP, MPS_Equivalent, MPS_Unique };
523 DenseMap<const MemoryPhi *, MemoryPhiState> MemoryPhiState;
525 enum InstCycleState { ICS_Unknown, ICS_CycleFree, ICS_Cycle };
526 mutable DenseMap<const Instruction *, InstCycleState> InstCycleState;
527 // Expression to class mapping.
528 using ExpressionClassMap = DenseMap<const Expression *, CongruenceClass *>;
529 ExpressionClassMap ExpressionToClass;
531 // We have a single expression that represents currently DeadExpressions.
532 // For dead expressions we can prove will stay dead, we mark them with
533 // DFS number zero. However, it's possible in the case of phi nodes
534 // for us to assume/prove all arguments are dead during fixpointing.
535 // We use DeadExpression for that case.
536 DeadExpression *SingletonDeadExpression = nullptr;
538 // Which values have changed as a result of leader changes.
539 SmallPtrSet<Value *, 8> LeaderChanges;
541 // Reachability info.
542 using BlockEdge = BasicBlockEdge;
543 DenseSet<BlockEdge> ReachableEdges;
544 SmallPtrSet<const BasicBlock *, 8> ReachableBlocks;
546 // This is a bitvector because, on larger functions, we may have
547 // thousands of touched instructions at once (entire blocks,
548 // instructions with hundreds of uses, etc). Even with optimization
549 // for when we mark whole blocks as touched, when this was a
550 // SmallPtrSet or DenseSet, for some functions, we spent >20% of all
551 // the time in GVN just managing this list. The bitvector, on the
552 // other hand, efficiently supports test/set/clear of both
553 // individual and ranges, as well as "find next element" This
554 // enables us to use it as a worklist with essentially 0 cost.
555 BitVector TouchedInstructions;
557 DenseMap<const BasicBlock *, std::pair<unsigned, unsigned>> BlockInstRange;
560 // Debugging for how many times each block and instruction got processed.
561 DenseMap<const Value *, unsigned> ProcessedCount;
565 // This contains a mapping from Instructions to DFS numbers.
566 // The numbering starts at 1. An instruction with DFS number zero
567 // means that the instruction is dead.
568 DenseMap<const Value *, unsigned> InstrDFS;
570 // This contains the mapping DFS numbers to instructions.
571 SmallVector<Value *, 32> DFSToInstr;
574 SmallPtrSet<Instruction *, 8> InstructionsToErase;
577 NewGVN(Function &F, DominatorTree *DT, AssumptionCache *AC,
578 TargetLibraryInfo *TLI, AliasAnalysis *AA, MemorySSA *MSSA,
579 const DataLayout &DL)
580 : F(F), DT(DT), TLI(TLI), AA(AA), MSSA(MSSA), DL(DL),
581 PredInfo(make_unique<PredicateInfo>(F, *DT, *AC)), SQ(DL, TLI, DT, AC) {
586 // Expression handling.
587 const Expression *createExpression(Instruction *) const;
588 const Expression *createBinaryExpression(unsigned, Type *, Value *,
590 PHIExpression *createPHIExpression(Instruction *, bool &HasBackEdge,
591 bool &OriginalOpsConstant) const;
592 const DeadExpression *createDeadExpression() const;
593 const VariableExpression *createVariableExpression(Value *) const;
594 const ConstantExpression *createConstantExpression(Constant *) const;
595 const Expression *createVariableOrConstant(Value *V) const;
596 const UnknownExpression *createUnknownExpression(Instruction *) const;
597 const StoreExpression *createStoreExpression(StoreInst *,
598 const MemoryAccess *) const;
599 LoadExpression *createLoadExpression(Type *, Value *, LoadInst *,
600 const MemoryAccess *) const;
601 const CallExpression *createCallExpression(CallInst *,
602 const MemoryAccess *) const;
603 const AggregateValueExpression *
604 createAggregateValueExpression(Instruction *) const;
605 bool setBasicExpressionInfo(Instruction *, BasicExpression *) const;
607 // Congruence class handling.
608 CongruenceClass *createCongruenceClass(Value *Leader, const Expression *E) {
609 auto *result = new CongruenceClass(NextCongruenceNum++, Leader, E);
610 CongruenceClasses.emplace_back(result);
614 CongruenceClass *createMemoryClass(MemoryAccess *MA) {
615 auto *CC = createCongruenceClass(nullptr, nullptr);
616 CC->setMemoryLeader(MA);
619 CongruenceClass *ensureLeaderOfMemoryClass(MemoryAccess *MA) {
620 auto *CC = getMemoryClass(MA);
621 if (CC->getMemoryLeader() != MA)
622 CC = createMemoryClass(MA);
626 CongruenceClass *createSingletonCongruenceClass(Value *Member) {
627 CongruenceClass *CClass = createCongruenceClass(Member, nullptr);
628 CClass->insert(Member);
629 ValueToClass[Member] = CClass;
632 void initializeCongruenceClasses(Function &F);
633 const Expression *makePossiblePhiOfOps(Instruction *, bool,
634 SmallPtrSetImpl<Value *> &);
635 void addPhiOfOps(PHINode *Op, BasicBlock *BB, Instruction *ExistingValue);
637 // Value number an Instruction or MemoryPhi.
638 void valueNumberMemoryPhi(MemoryPhi *);
639 void valueNumberInstruction(Instruction *);
641 // Symbolic evaluation.
642 const Expression *checkSimplificationResults(Expression *, Instruction *,
644 const Expression *performSymbolicEvaluation(Value *,
645 SmallPtrSetImpl<Value *> &) const;
646 const Expression *performSymbolicLoadCoercion(Type *, Value *, LoadInst *,
648 MemoryAccess *) const;
649 const Expression *performSymbolicLoadEvaluation(Instruction *) const;
650 const Expression *performSymbolicStoreEvaluation(Instruction *) const;
651 const Expression *performSymbolicCallEvaluation(Instruction *) const;
652 const Expression *performSymbolicPHIEvaluation(Instruction *) const;
653 const Expression *performSymbolicAggrValueEvaluation(Instruction *) const;
654 const Expression *performSymbolicCmpEvaluation(Instruction *) const;
655 const Expression *performSymbolicPredicateInfoEvaluation(Instruction *) const;
657 // Congruence finding.
658 bool someEquivalentDominates(const Instruction *, const Instruction *) const;
659 Value *lookupOperandLeader(Value *) const;
660 void performCongruenceFinding(Instruction *, const Expression *);
661 void moveValueToNewCongruenceClass(Instruction *, const Expression *,
662 CongruenceClass *, CongruenceClass *);
663 void moveMemoryToNewCongruenceClass(Instruction *, MemoryAccess *,
664 CongruenceClass *, CongruenceClass *);
665 Value *getNextValueLeader(CongruenceClass *) const;
666 const MemoryAccess *getNextMemoryLeader(CongruenceClass *) const;
667 bool setMemoryClass(const MemoryAccess *From, CongruenceClass *To);
668 CongruenceClass *getMemoryClass(const MemoryAccess *MA) const;
669 const MemoryAccess *lookupMemoryLeader(const MemoryAccess *) const;
670 bool isMemoryAccessTOP(const MemoryAccess *) const;
673 unsigned int getRank(const Value *) const;
674 bool shouldSwapOperands(const Value *, const Value *) const;
676 // Reachability handling.
677 void updateReachableEdge(BasicBlock *, BasicBlock *);
678 void processOutgoingEdges(TerminatorInst *, BasicBlock *);
679 Value *findConditionEquivalence(Value *) const;
683 void convertClassToDFSOrdered(const CongruenceClass &,
684 SmallVectorImpl<ValueDFS> &,
685 DenseMap<const Value *, unsigned int> &,
686 SmallPtrSetImpl<Instruction *> &) const;
687 void convertClassToLoadsAndStores(const CongruenceClass &,
688 SmallVectorImpl<ValueDFS> &) const;
690 bool eliminateInstructions(Function &);
691 void replaceInstruction(Instruction *, Value *);
692 void markInstructionForDeletion(Instruction *);
693 void deleteInstructionsInBlock(BasicBlock *);
694 Value *findPhiOfOpsLeader(const Expression *E, const BasicBlock *BB) const;
696 // New instruction creation.
697 void handleNewInstruction(Instruction *){};
699 // Various instruction touch utilities
700 template <typename Map, typename KeyType, typename Func>
701 void for_each_found(Map &, const KeyType &, Func);
702 template <typename Map, typename KeyType>
703 void touchAndErase(Map &, const KeyType &);
704 void markUsersTouched(Value *);
705 void markMemoryUsersTouched(const MemoryAccess *);
706 void markMemoryDefTouched(const MemoryAccess *);
707 void markPredicateUsersTouched(Instruction *);
708 void markValueLeaderChangeTouched(CongruenceClass *CC);
709 void markMemoryLeaderChangeTouched(CongruenceClass *CC);
710 void markPhiOfOpsChanged(const HashedExpression &HE);
711 void addPredicateUsers(const PredicateBase *, Instruction *) const;
712 void addMemoryUsers(const MemoryAccess *To, MemoryAccess *U) const;
713 void addAdditionalUsers(Value *To, Value *User) const;
715 // Main loop of value numbering
716 void iterateTouchedInstructions();
719 void cleanupTables();
720 std::pair<unsigned, unsigned> assignDFSNumbers(BasicBlock *, unsigned);
721 void updateProcessedCount(const Value *V);
722 void verifyMemoryCongruency() const;
723 void verifyIterationSettled(Function &F);
724 void verifyStoreExpressions() const;
725 bool singleReachablePHIPath(SmallPtrSet<const MemoryAccess *, 8> &,
726 const MemoryAccess *, const MemoryAccess *) const;
727 BasicBlock *getBlockForValue(Value *V) const;
728 void deleteExpression(const Expression *E) const;
729 MemoryUseOrDef *getMemoryAccess(const Instruction *) const;
730 MemoryAccess *getDefiningAccess(const MemoryAccess *) const;
731 MemoryPhi *getMemoryAccess(const BasicBlock *) const;
732 template <class T, class Range> T *getMinDFSOfRange(const Range &) const;
733 unsigned InstrToDFSNum(const Value *V) const {
734 assert(isa<Instruction>(V) && "This should not be used for MemoryAccesses");
735 return InstrDFS.lookup(V);
738 unsigned InstrToDFSNum(const MemoryAccess *MA) const {
739 return MemoryToDFSNum(MA);
741 Value *InstrFromDFSNum(unsigned DFSNum) { return DFSToInstr[DFSNum]; }
742 // Given a MemoryAccess, return the relevant instruction DFS number. Note:
743 // This deliberately takes a value so it can be used with Use's, which will
744 // auto-convert to Value's but not to MemoryAccess's.
745 unsigned MemoryToDFSNum(const Value *MA) const {
746 assert(isa<MemoryAccess>(MA) &&
747 "This should not be used with instructions");
748 return isa<MemoryUseOrDef>(MA)
749 ? InstrToDFSNum(cast<MemoryUseOrDef>(MA)->getMemoryInst())
750 : InstrDFS.lookup(MA);
752 bool isCycleFree(const Instruction *) const;
753 bool isBackedge(BasicBlock *From, BasicBlock *To) const;
754 // Debug counter info. When verifying, we have to reset the value numbering
755 // debug counter to the same state it started in to get the same results.
756 std::pair<int, int> StartingVNCounter;
758 } // end anonymous namespace
760 template <typename T>
761 static bool equalsLoadStoreHelper(const T &LHS, const Expression &RHS) {
762 if (!isa<LoadExpression>(RHS) && !isa<StoreExpression>(RHS))
764 return LHS.MemoryExpression::equals(RHS);
767 bool LoadExpression::equals(const Expression &Other) const {
768 return equalsLoadStoreHelper(*this, Other);
771 bool StoreExpression::equals(const Expression &Other) const {
772 if (!equalsLoadStoreHelper(*this, Other))
774 // Make sure that store vs store includes the value operand.
775 if (const auto *S = dyn_cast<StoreExpression>(&Other))
776 if (getStoredValue() != S->getStoredValue())
781 // Determine if the edge From->To is a backedge
782 bool NewGVN::isBackedge(BasicBlock *From, BasicBlock *To) const {
785 auto *FromDTN = DT->getNode(From);
786 auto *ToDTN = DT->getNode(To);
787 return RPOOrdering.lookup(FromDTN) >= RPOOrdering.lookup(ToDTN);
791 static std::string getBlockName(const BasicBlock *B) {
792 return DOTGraphTraits<const Function *>::getSimpleNodeLabel(B, nullptr);
796 // Get a MemoryAccess for an instruction, fake or real.
797 MemoryUseOrDef *NewGVN::getMemoryAccess(const Instruction *I) const {
798 auto *Result = MSSA->getMemoryAccess(I);
799 return Result ? Result : TempToMemory.lookup(I);
802 // Get a MemoryPhi for a basic block. These are all real.
803 MemoryPhi *NewGVN::getMemoryAccess(const BasicBlock *BB) const {
804 return MSSA->getMemoryAccess(BB);
807 // Get the basic block from an instruction/memory value.
808 BasicBlock *NewGVN::getBlockForValue(Value *V) const {
809 if (auto *I = dyn_cast<Instruction>(V)) {
810 auto *Parent = I->getParent();
813 Parent = TempToBlock.lookup(V);
814 assert(Parent && "Every fake instruction should have a block");
818 auto *MP = dyn_cast<MemoryPhi>(V);
819 assert(MP && "Should have been an instruction or a MemoryPhi");
820 return MP->getBlock();
823 // Delete a definitely dead expression, so it can be reused by the expression
824 // allocator. Some of these are not in creation functions, so we have to accept
826 void NewGVN::deleteExpression(const Expression *E) const {
827 assert(isa<BasicExpression>(E));
828 auto *BE = cast<BasicExpression>(E);
829 const_cast<BasicExpression *>(BE)->deallocateOperands(ArgRecycler);
830 ExpressionAllocator.Deallocate(E);
832 PHIExpression *NewGVN::createPHIExpression(Instruction *I, bool &HasBackedge,
833 bool &OriginalOpsConstant) const {
834 BasicBlock *PHIBlock = getBlockForValue(I);
835 auto *PN = cast<PHINode>(I);
837 new (ExpressionAllocator) PHIExpression(PN->getNumOperands(), PHIBlock);
839 E->allocateOperands(ArgRecycler, ExpressionAllocator);
840 E->setType(I->getType());
841 E->setOpcode(I->getOpcode());
843 // NewGVN assumes the operands of a PHI node are in a consistent order across
844 // PHIs. LLVM doesn't seem to always guarantee this. While we need to fix
845 // this in LLVM at some point we don't want GVN to find wrong congruences.
846 // Therefore, here we sort uses in predecessor order.
847 // We're sorting the values by pointer. In theory this might be cause of
848 // non-determinism, but here we don't rely on the ordering for anything
849 // significant, e.g. we don't create new instructions based on it so we're
851 SmallVector<const Use *, 4> PHIOperands;
852 for (const Use &U : PN->operands())
853 PHIOperands.push_back(&U);
854 std::sort(PHIOperands.begin(), PHIOperands.end(),
855 [&](const Use *U1, const Use *U2) {
856 return PN->getIncomingBlock(*U1) < PN->getIncomingBlock(*U2);
859 // Filter out unreachable phi operands.
860 auto Filtered = make_filter_range(PHIOperands, [&](const Use *U) {
861 return ReachableEdges.count({PN->getIncomingBlock(*U), PHIBlock});
863 std::transform(Filtered.begin(), Filtered.end(), op_inserter(E),
864 [&](const Use *U) -> Value * {
865 auto *BB = PN->getIncomingBlock(*U);
866 HasBackedge = HasBackedge || isBackedge(BB, PHIBlock);
867 OriginalOpsConstant =
868 OriginalOpsConstant && isa<Constant>(*U);
869 // Use nullptr to distinguish between things that were
870 // originally self-defined and those that have an operand
871 // leader that is self-defined.
874 // Things in TOPClass are equivalent to everything.
875 if (ValueToClass.lookup(*U) == TOPClass)
877 return lookupOperandLeader(*U);
882 // Set basic expression info (Arguments, type, opcode) for Expression
883 // E from Instruction I in block B.
884 bool NewGVN::setBasicExpressionInfo(Instruction *I, BasicExpression *E) const {
885 bool AllConstant = true;
886 if (auto *GEP = dyn_cast<GetElementPtrInst>(I))
887 E->setType(GEP->getSourceElementType());
889 E->setType(I->getType());
890 E->setOpcode(I->getOpcode());
891 E->allocateOperands(ArgRecycler, ExpressionAllocator);
893 // Transform the operand array into an operand leader array, and keep track of
894 // whether all members are constant.
895 std::transform(I->op_begin(), I->op_end(), op_inserter(E), [&](Value *O) {
896 auto Operand = lookupOperandLeader(O);
897 AllConstant = AllConstant && isa<Constant>(Operand);
904 const Expression *NewGVN::createBinaryExpression(unsigned Opcode, Type *T,
907 auto *E = new (ExpressionAllocator) BasicExpression(2);
910 E->setOpcode(Opcode);
911 E->allocateOperands(ArgRecycler, ExpressionAllocator);
912 if (Instruction::isCommutative(Opcode)) {
913 // Ensure that commutative instructions that only differ by a permutation
914 // of their operands get the same value number by sorting the operand value
915 // numbers. Since all commutative instructions have two operands it is more
916 // efficient to sort by hand rather than using, say, std::sort.
917 if (shouldSwapOperands(Arg1, Arg2))
918 std::swap(Arg1, Arg2);
920 E->op_push_back(lookupOperandLeader(Arg1));
921 E->op_push_back(lookupOperandLeader(Arg2));
923 Value *V = SimplifyBinOp(Opcode, E->getOperand(0), E->getOperand(1), SQ);
924 if (const Expression *SimplifiedE = checkSimplificationResults(E, nullptr, V))
929 // Take a Value returned by simplification of Expression E/Instruction
930 // I, and see if it resulted in a simpler expression. If so, return
932 // TODO: Once finished, this should not take an Instruction, we only
933 // use it for printing.
934 const Expression *NewGVN::checkSimplificationResults(Expression *E,
939 if (auto *C = dyn_cast<Constant>(V)) {
941 DEBUG(dbgs() << "Simplified " << *I << " to "
942 << " constant " << *C << "\n");
943 NumGVNOpsSimplified++;
944 assert(isa<BasicExpression>(E) &&
945 "We should always have had a basic expression here");
947 return createConstantExpression(C);
948 } else if (isa<Argument>(V) || isa<GlobalVariable>(V)) {
950 DEBUG(dbgs() << "Simplified " << *I << " to "
951 << " variable " << *V << "\n");
953 return createVariableExpression(V);
956 CongruenceClass *CC = ValueToClass.lookup(V);
957 if (CC && CC->getDefiningExpr()) {
959 DEBUG(dbgs() << "Simplified " << *I << " to "
960 << " expression " << *CC->getDefiningExpr() << "\n");
961 NumGVNOpsSimplified++;
963 return CC->getDefiningExpr();
968 const Expression *NewGVN::createExpression(Instruction *I) const {
969 auto *E = new (ExpressionAllocator) BasicExpression(I->getNumOperands());
971 bool AllConstant = setBasicExpressionInfo(I, E);
973 if (I->isCommutative()) {
974 // Ensure that commutative instructions that only differ by a permutation
975 // of their operands get the same value number by sorting the operand value
976 // numbers. Since all commutative instructions have two operands it is more
977 // efficient to sort by hand rather than using, say, std::sort.
978 assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!");
979 if (shouldSwapOperands(E->getOperand(0), E->getOperand(1)))
980 E->swapOperands(0, 1);
983 // Perform simplificaiton
984 // TODO: Right now we only check to see if we get a constant result.
985 // We may get a less than constant, but still better, result for
990 // We should handle this by simply rewriting the expression.
991 if (auto *CI = dyn_cast<CmpInst>(I)) {
992 // Sort the operand value numbers so x<y and y>x get the same value
994 CmpInst::Predicate Predicate = CI->getPredicate();
995 if (shouldSwapOperands(E->getOperand(0), E->getOperand(1))) {
996 E->swapOperands(0, 1);
997 Predicate = CmpInst::getSwappedPredicate(Predicate);
999 E->setOpcode((CI->getOpcode() << 8) | Predicate);
1000 // TODO: 25% of our time is spent in SimplifyCmpInst with pointer operands
1001 assert(I->getOperand(0)->getType() == I->getOperand(1)->getType() &&
1002 "Wrong types on cmp instruction");
1003 assert((E->getOperand(0)->getType() == I->getOperand(0)->getType() &&
1004 E->getOperand(1)->getType() == I->getOperand(1)->getType()));
1006 SimplifyCmpInst(Predicate, E->getOperand(0), E->getOperand(1), SQ);
1007 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1009 } else if (isa<SelectInst>(I)) {
1010 if (isa<Constant>(E->getOperand(0)) ||
1011 E->getOperand(0) == E->getOperand(1)) {
1012 assert(E->getOperand(1)->getType() == I->getOperand(1)->getType() &&
1013 E->getOperand(2)->getType() == I->getOperand(2)->getType());
1014 Value *V = SimplifySelectInst(E->getOperand(0), E->getOperand(1),
1015 E->getOperand(2), SQ);
1016 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1019 } else if (I->isBinaryOp()) {
1021 SimplifyBinOp(E->getOpcode(), E->getOperand(0), E->getOperand(1), SQ);
1022 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1024 } else if (auto *BI = dyn_cast<BitCastInst>(I)) {
1026 SimplifyCastInst(BI->getOpcode(), BI->getOperand(0), BI->getType(), SQ);
1027 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1029 } else if (isa<GetElementPtrInst>(I)) {
1030 Value *V = SimplifyGEPInst(
1031 E->getType(), ArrayRef<Value *>(E->op_begin(), E->op_end()), SQ);
1032 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1034 } else if (AllConstant) {
1035 // We don't bother trying to simplify unless all of the operands
1037 // TODO: There are a lot of Simplify*'s we could call here, if we
1038 // wanted to. The original motivating case for this code was a
1039 // zext i1 false to i8, which we don't have an interface to
1040 // simplify (IE there is no SimplifyZExt).
1042 SmallVector<Constant *, 8> C;
1043 for (Value *Arg : E->operands())
1044 C.emplace_back(cast<Constant>(Arg));
1046 if (Value *V = ConstantFoldInstOperands(I, C, DL, TLI))
1047 if (const Expression *SimplifiedE = checkSimplificationResults(E, I, V))
1053 const AggregateValueExpression *
1054 NewGVN::createAggregateValueExpression(Instruction *I) const {
1055 if (auto *II = dyn_cast<InsertValueInst>(I)) {
1056 auto *E = new (ExpressionAllocator)
1057 AggregateValueExpression(I->getNumOperands(), II->getNumIndices());
1058 setBasicExpressionInfo(I, E);
1059 E->allocateIntOperands(ExpressionAllocator);
1060 std::copy(II->idx_begin(), II->idx_end(), int_op_inserter(E));
1062 } else if (auto *EI = dyn_cast<ExtractValueInst>(I)) {
1063 auto *E = new (ExpressionAllocator)
1064 AggregateValueExpression(I->getNumOperands(), EI->getNumIndices());
1065 setBasicExpressionInfo(EI, E);
1066 E->allocateIntOperands(ExpressionAllocator);
1067 std::copy(EI->idx_begin(), EI->idx_end(), int_op_inserter(E));
1070 llvm_unreachable("Unhandled type of aggregate value operation");
1073 const DeadExpression *NewGVN::createDeadExpression() const {
1074 // DeadExpression has no arguments and all DeadExpression's are the same,
1075 // so we only need one of them.
1076 return SingletonDeadExpression;
1079 const VariableExpression *NewGVN::createVariableExpression(Value *V) const {
1080 auto *E = new (ExpressionAllocator) VariableExpression(V);
1081 E->setOpcode(V->getValueID());
1085 const Expression *NewGVN::createVariableOrConstant(Value *V) const {
1086 if (auto *C = dyn_cast<Constant>(V))
1087 return createConstantExpression(C);
1088 return createVariableExpression(V);
1091 const ConstantExpression *NewGVN::createConstantExpression(Constant *C) const {
1092 auto *E = new (ExpressionAllocator) ConstantExpression(C);
1093 E->setOpcode(C->getValueID());
1097 const UnknownExpression *NewGVN::createUnknownExpression(Instruction *I) const {
1098 auto *E = new (ExpressionAllocator) UnknownExpression(I);
1099 E->setOpcode(I->getOpcode());
1103 const CallExpression *
1104 NewGVN::createCallExpression(CallInst *CI, const MemoryAccess *MA) const {
1105 // FIXME: Add operand bundles for calls.
1107 new (ExpressionAllocator) CallExpression(CI->getNumOperands(), CI, MA);
1108 setBasicExpressionInfo(CI, E);
1112 // Return true if some equivalent of instruction Inst dominates instruction U.
1113 bool NewGVN::someEquivalentDominates(const Instruction *Inst,
1114 const Instruction *U) const {
1115 auto *CC = ValueToClass.lookup(Inst);
1116 // This must be an instruction because we are only called from phi nodes
1117 // in the case that the value it needs to check against is an instruction.
1119 // The most likely candiates for dominance are the leader and the next leader.
1120 // The leader or nextleader will dominate in all cases where there is an
1121 // equivalent that is higher up in the dom tree.
1122 // We can't *only* check them, however, because the
1123 // dominator tree could have an infinite number of non-dominating siblings
1124 // with instructions that are in the right congruence class.
1129 // Instruction U could be in H, with equivalents in every other sibling.
1130 // Depending on the rpo order picked, the leader could be the equivalent in
1131 // any of these siblings.
1134 if (DT->dominates(cast<Instruction>(CC->getLeader()), U))
1136 if (CC->getNextLeader().first &&
1137 DT->dominates(cast<Instruction>(CC->getNextLeader().first), U))
1139 return llvm::any_of(*CC, [&](const Value *Member) {
1140 return Member != CC->getLeader() &&
1141 DT->dominates(cast<Instruction>(Member), U);
1145 // See if we have a congruence class and leader for this operand, and if so,
1146 // return it. Otherwise, return the operand itself.
1147 Value *NewGVN::lookupOperandLeader(Value *V) const {
1148 CongruenceClass *CC = ValueToClass.lookup(V);
1150 // Everything in TOP is represented by undef, as it can be any value.
1151 // We do have to make sure we get the type right though, so we can't set the
1152 // RepLeader to undef.
1154 return UndefValue::get(V->getType());
1155 return CC->getStoredValue() ? CC->getStoredValue() : CC->getLeader();
1161 const MemoryAccess *NewGVN::lookupMemoryLeader(const MemoryAccess *MA) const {
1162 auto *CC = getMemoryClass(MA);
1163 assert(CC->getMemoryLeader() &&
1164 "Every MemoryAccess should be mapped to a congruence class with a "
1165 "representative memory access");
1166 return CC->getMemoryLeader();
1169 // Return true if the MemoryAccess is really equivalent to everything. This is
1170 // equivalent to the lattice value "TOP" in most lattices. This is the initial
1171 // state of all MemoryAccesses.
1172 bool NewGVN::isMemoryAccessTOP(const MemoryAccess *MA) const {
1173 return getMemoryClass(MA) == TOPClass;
1176 LoadExpression *NewGVN::createLoadExpression(Type *LoadType, Value *PointerOp,
1178 const MemoryAccess *MA) const {
1180 new (ExpressionAllocator) LoadExpression(1, LI, lookupMemoryLeader(MA));
1181 E->allocateOperands(ArgRecycler, ExpressionAllocator);
1182 E->setType(LoadType);
1184 // Give store and loads same opcode so they value number together.
1186 E->op_push_back(PointerOp);
1188 E->setAlignment(LI->getAlignment());
1190 // TODO: Value number heap versions. We may be able to discover
1191 // things alias analysis can't on it's own (IE that a store and a
1192 // load have the same value, and thus, it isn't clobbering the load).
1196 const StoreExpression *
1197 NewGVN::createStoreExpression(StoreInst *SI, const MemoryAccess *MA) const {
1198 auto *StoredValueLeader = lookupOperandLeader(SI->getValueOperand());
1199 auto *E = new (ExpressionAllocator)
1200 StoreExpression(SI->getNumOperands(), SI, StoredValueLeader, MA);
1201 E->allocateOperands(ArgRecycler, ExpressionAllocator);
1202 E->setType(SI->getValueOperand()->getType());
1204 // Give store and loads same opcode so they value number together.
1206 E->op_push_back(lookupOperandLeader(SI->getPointerOperand()));
1208 // TODO: Value number heap versions. We may be able to discover
1209 // things alias analysis can't on it's own (IE that a store and a
1210 // load have the same value, and thus, it isn't clobbering the load).
1214 const Expression *NewGVN::performSymbolicStoreEvaluation(Instruction *I) const {
1215 // Unlike loads, we never try to eliminate stores, so we do not check if they
1216 // are simple and avoid value numbering them.
1217 auto *SI = cast<StoreInst>(I);
1218 auto *StoreAccess = getMemoryAccess(SI);
1219 // Get the expression, if any, for the RHS of the MemoryDef.
1220 const MemoryAccess *StoreRHS = StoreAccess->getDefiningAccess();
1221 if (EnableStoreRefinement)
1222 StoreRHS = MSSAWalker->getClobberingMemoryAccess(StoreAccess);
1223 // If we bypassed the use-def chains, make sure we add a use.
1224 if (StoreRHS != StoreAccess->getDefiningAccess())
1225 addMemoryUsers(StoreRHS, StoreAccess);
1226 StoreRHS = lookupMemoryLeader(StoreRHS);
1227 // If we are defined by ourselves, use the live on entry def.
1228 if (StoreRHS == StoreAccess)
1229 StoreRHS = MSSA->getLiveOnEntryDef();
1231 if (SI->isSimple()) {
1232 // See if we are defined by a previous store expression, it already has a
1233 // value, and it's the same value as our current store. FIXME: Right now, we
1234 // only do this for simple stores, we should expand to cover memcpys, etc.
1235 const auto *LastStore = createStoreExpression(SI, StoreRHS);
1236 const auto *LastCC = ExpressionToClass.lookup(LastStore);
1237 // Basically, check if the congruence class the store is in is defined by a
1238 // store that isn't us, and has the same value. MemorySSA takes care of
1239 // ensuring the store has the same memory state as us already.
1240 // The RepStoredValue gets nulled if all the stores disappear in a class, so
1241 // we don't need to check if the class contains a store besides us.
1243 LastCC->getStoredValue() == lookupOperandLeader(SI->getValueOperand()))
1245 deleteExpression(LastStore);
1246 // Also check if our value operand is defined by a load of the same memory
1247 // location, and the memory state is the same as it was then (otherwise, it
1248 // could have been overwritten later. See test32 in
1249 // transforms/DeadStoreElimination/simple.ll).
1251 dyn_cast<LoadInst>(lookupOperandLeader(SI->getValueOperand()))) {
1252 if ((lookupOperandLeader(LI->getPointerOperand()) ==
1253 lookupOperandLeader(SI->getPointerOperand())) &&
1254 (lookupMemoryLeader(getMemoryAccess(LI)->getDefiningAccess()) ==
1256 return createStoreExpression(SI, StoreRHS);
1260 // If the store is not equivalent to anything, value number it as a store that
1261 // produces a unique memory state (instead of using it's MemoryUse, we use
1263 return createStoreExpression(SI, StoreAccess);
1266 // See if we can extract the value of a loaded pointer from a load, a store, or
1267 // a memory instruction.
1269 NewGVN::performSymbolicLoadCoercion(Type *LoadType, Value *LoadPtr,
1270 LoadInst *LI, Instruction *DepInst,
1271 MemoryAccess *DefiningAccess) const {
1272 assert((!LI || LI->isSimple()) && "Not a simple load");
1273 if (auto *DepSI = dyn_cast<StoreInst>(DepInst)) {
1274 // Can't forward from non-atomic to atomic without violating memory model.
1275 // Also don't need to coerce if they are the same type, we will just
1277 if (LI->isAtomic() > DepSI->isAtomic() ||
1278 LoadType == DepSI->getValueOperand()->getType())
1280 int Offset = analyzeLoadFromClobberingStore(LoadType, LoadPtr, DepSI, DL);
1282 if (auto *C = dyn_cast<Constant>(
1283 lookupOperandLeader(DepSI->getValueOperand()))) {
1284 DEBUG(dbgs() << "Coercing load from store " << *DepSI << " to constant "
1286 return createConstantExpression(
1287 getConstantStoreValueForLoad(C, Offset, LoadType, DL));
1291 } else if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1292 // Can't forward from non-atomic to atomic without violating memory model.
1293 if (LI->isAtomic() > DepLI->isAtomic())
1295 int Offset = analyzeLoadFromClobberingLoad(LoadType, LoadPtr, DepLI, DL);
1297 // We can coerce a constant load into a load
1298 if (auto *C = dyn_cast<Constant>(lookupOperandLeader(DepLI)))
1299 if (auto *PossibleConstant =
1300 getConstantLoadValueForLoad(C, Offset, LoadType, DL)) {
1301 DEBUG(dbgs() << "Coercing load from load " << *LI << " to constant "
1302 << *PossibleConstant << "\n");
1303 return createConstantExpression(PossibleConstant);
1307 } else if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInst)) {
1308 int Offset = analyzeLoadFromClobberingMemInst(LoadType, LoadPtr, DepMI, DL);
1310 if (auto *PossibleConstant =
1311 getConstantMemInstValueForLoad(DepMI, Offset, LoadType, DL)) {
1312 DEBUG(dbgs() << "Coercing load from meminst " << *DepMI
1313 << " to constant " << *PossibleConstant << "\n");
1314 return createConstantExpression(PossibleConstant);
1319 // All of the below are only true if the loaded pointer is produced
1320 // by the dependent instruction.
1321 if (LoadPtr != lookupOperandLeader(DepInst) &&
1322 !AA->isMustAlias(LoadPtr, DepInst))
1324 // If this load really doesn't depend on anything, then we must be loading an
1325 // undef value. This can happen when loading for a fresh allocation with no
1326 // intervening stores, for example. Note that this is only true in the case
1327 // that the result of the allocation is pointer equal to the load ptr.
1328 if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI)) {
1329 return createConstantExpression(UndefValue::get(LoadType));
1331 // If this load occurs either right after a lifetime begin,
1332 // then the loaded value is undefined.
1333 else if (auto *II = dyn_cast<IntrinsicInst>(DepInst)) {
1334 if (II->getIntrinsicID() == Intrinsic::lifetime_start)
1335 return createConstantExpression(UndefValue::get(LoadType));
1337 // If this load follows a calloc (which zero initializes memory),
1338 // then the loaded value is zero
1339 else if (isCallocLikeFn(DepInst, TLI)) {
1340 return createConstantExpression(Constant::getNullValue(LoadType));
1346 const Expression *NewGVN::performSymbolicLoadEvaluation(Instruction *I) const {
1347 auto *LI = cast<LoadInst>(I);
1349 // We can eliminate in favor of non-simple loads, but we won't be able to
1350 // eliminate the loads themselves.
1351 if (!LI->isSimple())
1354 Value *LoadAddressLeader = lookupOperandLeader(LI->getPointerOperand());
1355 // Load of undef is undef.
1356 if (isa<UndefValue>(LoadAddressLeader))
1357 return createConstantExpression(UndefValue::get(LI->getType()));
1358 MemoryAccess *OriginalAccess = getMemoryAccess(I);
1359 MemoryAccess *DefiningAccess =
1360 MSSAWalker->getClobberingMemoryAccess(OriginalAccess);
1362 if (!MSSA->isLiveOnEntryDef(DefiningAccess)) {
1363 if (auto *MD = dyn_cast<MemoryDef>(DefiningAccess)) {
1364 Instruction *DefiningInst = MD->getMemoryInst();
1365 // If the defining instruction is not reachable, replace with undef.
1366 if (!ReachableBlocks.count(DefiningInst->getParent()))
1367 return createConstantExpression(UndefValue::get(LI->getType()));
1368 // This will handle stores and memory insts. We only do if it the
1369 // defining access has a different type, or it is a pointer produced by
1370 // certain memory operations that cause the memory to have a fixed value
1371 // (IE things like calloc).
1372 if (const auto *CoercionResult =
1373 performSymbolicLoadCoercion(LI->getType(), LoadAddressLeader, LI,
1374 DefiningInst, DefiningAccess))
1375 return CoercionResult;
1379 const Expression *E = createLoadExpression(LI->getType(), LoadAddressLeader,
1380 LI, DefiningAccess);
1385 NewGVN::performSymbolicPredicateInfoEvaluation(Instruction *I) const {
1386 auto *PI = PredInfo->getPredicateInfoFor(I);
1390 DEBUG(dbgs() << "Found predicate info from instruction !\n");
1392 auto *PWC = dyn_cast<PredicateWithCondition>(PI);
1396 auto *CopyOf = I->getOperand(0);
1397 auto *Cond = PWC->Condition;
1399 // If this a copy of the condition, it must be either true or false depending
1400 // on the predicate info type and edge
1401 if (CopyOf == Cond) {
1402 // We should not need to add predicate users because the predicate info is
1403 // already a use of this operand.
1404 if (isa<PredicateAssume>(PI))
1405 return createConstantExpression(ConstantInt::getTrue(Cond->getType()));
1406 if (auto *PBranch = dyn_cast<PredicateBranch>(PI)) {
1407 if (PBranch->TrueEdge)
1408 return createConstantExpression(ConstantInt::getTrue(Cond->getType()));
1409 return createConstantExpression(ConstantInt::getFalse(Cond->getType()));
1411 if (auto *PSwitch = dyn_cast<PredicateSwitch>(PI))
1412 return createConstantExpression(cast<Constant>(PSwitch->CaseValue));
1415 // Not a copy of the condition, so see what the predicates tell us about this
1416 // value. First, though, we check to make sure the value is actually a copy
1417 // of one of the condition operands. It's possible, in certain cases, for it
1418 // to be a copy of a predicateinfo copy. In particular, if two branch
1419 // operations use the same condition, and one branch dominates the other, we
1420 // will end up with a copy of a copy. This is currently a small deficiency in
1421 // predicateinfo. What will end up happening here is that we will value
1422 // number both copies the same anyway.
1424 // Everything below relies on the condition being a comparison.
1425 auto *Cmp = dyn_cast<CmpInst>(Cond);
1429 if (CopyOf != Cmp->getOperand(0) && CopyOf != Cmp->getOperand(1)) {
1430 DEBUG(dbgs() << "Copy is not of any condition operands!\n");
1433 Value *FirstOp = lookupOperandLeader(Cmp->getOperand(0));
1434 Value *SecondOp = lookupOperandLeader(Cmp->getOperand(1));
1435 bool SwappedOps = false;
1437 if (shouldSwapOperands(FirstOp, SecondOp)) {
1438 std::swap(FirstOp, SecondOp);
1441 CmpInst::Predicate Predicate =
1442 SwappedOps ? Cmp->getSwappedPredicate() : Cmp->getPredicate();
1444 if (isa<PredicateAssume>(PI)) {
1445 // If the comparison is true when the operands are equal, then we know the
1446 // operands are equal, because assumes must always be true.
1447 if (CmpInst::isTrueWhenEqual(Predicate)) {
1448 addPredicateUsers(PI, I);
1449 addAdditionalUsers(Cmp->getOperand(0), I);
1450 return createVariableOrConstant(FirstOp);
1453 if (const auto *PBranch = dyn_cast<PredicateBranch>(PI)) {
1454 // If we are *not* a copy of the comparison, we may equal to the other
1455 // operand when the predicate implies something about equality of
1456 // operations. In particular, if the comparison is true/false when the
1457 // operands are equal, and we are on the right edge, we know this operation
1458 // is equal to something.
1459 if ((PBranch->TrueEdge && Predicate == CmpInst::ICMP_EQ) ||
1460 (!PBranch->TrueEdge && Predicate == CmpInst::ICMP_NE)) {
1461 addPredicateUsers(PI, I);
1462 addAdditionalUsers(Cmp->getOperand(0), I);
1463 return createVariableOrConstant(FirstOp);
1465 // Handle the special case of floating point.
1466 if (((PBranch->TrueEdge && Predicate == CmpInst::FCMP_OEQ) ||
1467 (!PBranch->TrueEdge && Predicate == CmpInst::FCMP_UNE)) &&
1468 isa<ConstantFP>(FirstOp) && !cast<ConstantFP>(FirstOp)->isZero()) {
1469 addPredicateUsers(PI, I);
1470 addAdditionalUsers(Cmp->getOperand(0), I);
1471 return createConstantExpression(cast<Constant>(FirstOp));
1477 // Evaluate read only and pure calls, and create an expression result.
1478 const Expression *NewGVN::performSymbolicCallEvaluation(Instruction *I) const {
1479 auto *CI = cast<CallInst>(I);
1480 if (auto *II = dyn_cast<IntrinsicInst>(I)) {
1481 // Instrinsics with the returned attribute are copies of arguments.
1482 if (auto *ReturnedValue = II->getReturnedArgOperand()) {
1483 if (II->getIntrinsicID() == Intrinsic::ssa_copy)
1484 if (const auto *Result = performSymbolicPredicateInfoEvaluation(I))
1486 return createVariableOrConstant(ReturnedValue);
1489 if (AA->doesNotAccessMemory(CI)) {
1490 return createCallExpression(CI, TOPClass->getMemoryLeader());
1491 } else if (AA->onlyReadsMemory(CI)) {
1492 MemoryAccess *DefiningAccess = MSSAWalker->getClobberingMemoryAccess(CI);
1493 return createCallExpression(CI, DefiningAccess);
1498 // Retrieve the memory class for a given MemoryAccess.
1499 CongruenceClass *NewGVN::getMemoryClass(const MemoryAccess *MA) const {
1501 auto *Result = MemoryAccessToClass.lookup(MA);
1502 assert(Result && "Should have found memory class");
1506 // Update the MemoryAccess equivalence table to say that From is equal to To,
1507 // and return true if this is different from what already existed in the table.
1508 bool NewGVN::setMemoryClass(const MemoryAccess *From,
1509 CongruenceClass *NewClass) {
1511 "Every MemoryAccess should be getting mapped to a non-null class");
1512 DEBUG(dbgs() << "Setting " << *From);
1513 DEBUG(dbgs() << " equivalent to congruence class ");
1514 DEBUG(dbgs() << NewClass->getID() << " with current MemoryAccess leader ");
1515 DEBUG(dbgs() << *NewClass->getMemoryLeader() << "\n");
1517 auto LookupResult = MemoryAccessToClass.find(From);
1518 bool Changed = false;
1519 // If it's already in the table, see if the value changed.
1520 if (LookupResult != MemoryAccessToClass.end()) {
1521 auto *OldClass = LookupResult->second;
1522 if (OldClass != NewClass) {
1523 // If this is a phi, we have to handle memory member updates.
1524 if (auto *MP = dyn_cast<MemoryPhi>(From)) {
1525 OldClass->memory_erase(MP);
1526 NewClass->memory_insert(MP);
1527 // This may have killed the class if it had no non-memory members
1528 if (OldClass->getMemoryLeader() == From) {
1529 if (OldClass->definesNoMemory()) {
1530 OldClass->setMemoryLeader(nullptr);
1532 OldClass->setMemoryLeader(getNextMemoryLeader(OldClass));
1533 DEBUG(dbgs() << "Memory class leader change for class "
1534 << OldClass->getID() << " to "
1535 << *OldClass->getMemoryLeader()
1536 << " due to removal of a memory member " << *From
1538 markMemoryLeaderChangeTouched(OldClass);
1542 // It wasn't equivalent before, and now it is.
1543 LookupResult->second = NewClass;
1551 // Determine if a instruction is cycle-free. That means the values in the
1552 // instruction don't depend on any expressions that can change value as a result
1553 // of the instruction. For example, a non-cycle free instruction would be v =
1555 bool NewGVN::isCycleFree(const Instruction *I) const {
1556 // In order to compute cycle-freeness, we do SCC finding on the instruction,
1557 // and see what kind of SCC it ends up in. If it is a singleton, it is
1558 // cycle-free. If it is not in a singleton, it is only cycle free if the
1559 // other members are all phi nodes (as they do not compute anything, they are
1561 auto ICS = InstCycleState.lookup(I);
1562 if (ICS == ICS_Unknown) {
1564 auto &SCC = SCCFinder.getComponentFor(I);
1565 // It's cycle free if it's size 1 or or the SCC is *only* phi nodes.
1566 if (SCC.size() == 1)
1567 InstCycleState.insert({I, ICS_CycleFree});
1570 llvm::all_of(SCC, [](const Value *V) { return isa<PHINode>(V); });
1571 ICS = AllPhis ? ICS_CycleFree : ICS_Cycle;
1572 for (auto *Member : SCC)
1573 if (auto *MemberPhi = dyn_cast<PHINode>(Member))
1574 InstCycleState.insert({MemberPhi, ICS});
1577 if (ICS == ICS_Cycle)
1582 // Evaluate PHI nodes symbolically, and create an expression result.
1583 const Expression *NewGVN::performSymbolicPHIEvaluation(Instruction *I) const {
1584 // True if one of the incoming phi edges is a backedge.
1585 bool HasBackedge = false;
1586 // All constant tracks the state of whether all the *original* phi operands
1587 // This is really shorthand for "this phi cannot cycle due to forward
1588 // change in value of the phi is guaranteed not to later change the value of
1589 // the phi. IE it can't be v = phi(undef, v+1)
1590 bool AllConstant = true;
1592 cast<PHIExpression>(createPHIExpression(I, HasBackedge, AllConstant));
1593 // We match the semantics of SimplifyPhiNode from InstructionSimplify here.
1594 // See if all arguments are the same.
1595 // We track if any were undef because they need special handling.
1596 bool HasUndef = false;
1597 bool CycleFree = isCycleFree(I);
1598 auto Filtered = make_filter_range(E->operands(), [&](Value *Arg) {
1601 // Original self-operands are already eliminated during expression creation.
1602 // We can only eliminate value-wise self-operands if it's cycle
1603 // free. Otherwise, eliminating the operand can cause our value to change,
1604 // which can cause us to not eliminate the operand, which changes the value
1605 // back to what it was before, cycling forever.
1606 if (CycleFree && Arg == I)
1608 if (isa<UndefValue>(Arg)) {
1614 // If we are left with no operands, it's dead.
1615 if (Filtered.begin() == Filtered.end()) {
1616 DEBUG(dbgs() << "No arguments of PHI node " << *I << " are live\n");
1617 deleteExpression(E);
1618 return createDeadExpression();
1620 unsigned NumOps = 0;
1621 Value *AllSameValue = *(Filtered.begin());
1623 // Can't use std::equal here, sadly, because filter.begin moves.
1624 if (llvm::all_of(Filtered, [&](Value *Arg) {
1626 return Arg == AllSameValue;
1628 // In LLVM's non-standard representation of phi nodes, it's possible to have
1629 // phi nodes with cycles (IE dependent on other phis that are .... dependent
1630 // on the original phi node), especially in weird CFG's where some arguments
1631 // are unreachable, or uninitialized along certain paths. This can cause
1632 // infinite loops during evaluation. We work around this by not trying to
1633 // really evaluate them independently, but instead using a variable
1634 // expression to say if one is equivalent to the other.
1635 // We also special case undef, so that if we have an undef, we can't use the
1636 // common value unless it dominates the phi block.
1638 // If we have undef and at least one other value, this is really a
1639 // multivalued phi, and we need to know if it's cycle free in order to
1640 // evaluate whether we can ignore the undef. The other parts of this are
1641 // just shortcuts. If there is no backedge, or all operands are
1642 // constants, or all operands are ignored but the undef, it also must be
1644 if (!AllConstant && HasBackedge && NumOps > 0 &&
1645 !isa<UndefValue>(AllSameValue) && !CycleFree)
1648 // Only have to check for instructions
1649 if (auto *AllSameInst = dyn_cast<Instruction>(AllSameValue))
1650 if (!someEquivalentDominates(AllSameInst, I))
1654 NumGVNPhisAllSame++;
1655 DEBUG(dbgs() << "Simplified PHI node " << *I << " to " << *AllSameValue
1657 deleteExpression(E);
1658 return createVariableOrConstant(AllSameValue);
1664 NewGVN::performSymbolicAggrValueEvaluation(Instruction *I) const {
1665 if (auto *EI = dyn_cast<ExtractValueInst>(I)) {
1666 auto *II = dyn_cast<IntrinsicInst>(EI->getAggregateOperand());
1667 if (II && EI->getNumIndices() == 1 && *EI->idx_begin() == 0) {
1668 unsigned Opcode = 0;
1669 // EI might be an extract from one of our recognised intrinsics. If it
1670 // is we'll synthesize a semantically equivalent expression instead on
1671 // an extract value expression.
1672 switch (II->getIntrinsicID()) {
1673 case Intrinsic::sadd_with_overflow:
1674 case Intrinsic::uadd_with_overflow:
1675 Opcode = Instruction::Add;
1677 case Intrinsic::ssub_with_overflow:
1678 case Intrinsic::usub_with_overflow:
1679 Opcode = Instruction::Sub;
1681 case Intrinsic::smul_with_overflow:
1682 case Intrinsic::umul_with_overflow:
1683 Opcode = Instruction::Mul;
1690 // Intrinsic recognized. Grab its args to finish building the
1692 assert(II->getNumArgOperands() == 2 &&
1693 "Expect two args for recognised intrinsics.");
1694 return createBinaryExpression(
1695 Opcode, EI->getType(), II->getArgOperand(0), II->getArgOperand(1));
1700 return createAggregateValueExpression(I);
1702 const Expression *NewGVN::performSymbolicCmpEvaluation(Instruction *I) const {
1703 auto *CI = dyn_cast<CmpInst>(I);
1704 // See if our operands are equal to those of a previous predicate, and if so,
1705 // if it implies true or false.
1706 auto Op0 = lookupOperandLeader(CI->getOperand(0));
1707 auto Op1 = lookupOperandLeader(CI->getOperand(1));
1708 auto OurPredicate = CI->getPredicate();
1709 if (shouldSwapOperands(Op0, Op1)) {
1710 std::swap(Op0, Op1);
1711 OurPredicate = CI->getSwappedPredicate();
1714 // Avoid processing the same info twice
1715 const PredicateBase *LastPredInfo = nullptr;
1716 // See if we know something about the comparison itself, like it is the target
1718 auto *CmpPI = PredInfo->getPredicateInfoFor(I);
1719 if (dyn_cast_or_null<PredicateAssume>(CmpPI))
1720 return createConstantExpression(ConstantInt::getTrue(CI->getType()));
1723 // This condition does not depend on predicates, no need to add users
1724 if (CI->isTrueWhenEqual())
1725 return createConstantExpression(ConstantInt::getTrue(CI->getType()));
1726 else if (CI->isFalseWhenEqual())
1727 return createConstantExpression(ConstantInt::getFalse(CI->getType()));
1730 // NOTE: Because we are comparing both operands here and below, and using
1731 // previous comparisons, we rely on fact that predicateinfo knows to mark
1732 // comparisons that use renamed operands as users of the earlier comparisons.
1733 // It is *not* enough to just mark predicateinfo renamed operands as users of
1734 // the earlier comparisons, because the *other* operand may have changed in a
1735 // previous iteration.
1738 // %b.0 = ssa.copy(%b)
1740 // icmp slt %c, %b.0
1742 // %c and %a may start out equal, and thus, the code below will say the second
1743 // %icmp is false. c may become equal to something else, and in that case the
1744 // %second icmp *must* be reexamined, but would not if only the renamed
1745 // %operands are considered users of the icmp.
1747 // *Currently* we only check one level of comparisons back, and only mark one
1748 // level back as touched when changes appen . If you modify this code to look
1749 // back farther through comparisons, you *must* mark the appropriate
1750 // comparisons as users in PredicateInfo.cpp, or you will cause bugs. See if
1751 // we know something just from the operands themselves
1753 // See if our operands have predicate info, so that we may be able to derive
1754 // something from a previous comparison.
1755 for (const auto &Op : CI->operands()) {
1756 auto *PI = PredInfo->getPredicateInfoFor(Op);
1757 if (const auto *PBranch = dyn_cast_or_null<PredicateBranch>(PI)) {
1758 if (PI == LastPredInfo)
1762 // TODO: Along the false edge, we may know more things too, like icmp of
1763 // same operands is false.
1764 // TODO: We only handle actual comparison conditions below, not and/or.
1765 auto *BranchCond = dyn_cast<CmpInst>(PBranch->Condition);
1768 auto *BranchOp0 = lookupOperandLeader(BranchCond->getOperand(0));
1769 auto *BranchOp1 = lookupOperandLeader(BranchCond->getOperand(1));
1770 auto BranchPredicate = BranchCond->getPredicate();
1771 if (shouldSwapOperands(BranchOp0, BranchOp1)) {
1772 std::swap(BranchOp0, BranchOp1);
1773 BranchPredicate = BranchCond->getSwappedPredicate();
1775 if (BranchOp0 == Op0 && BranchOp1 == Op1) {
1776 if (PBranch->TrueEdge) {
1777 // If we know the previous predicate is true and we are in the true
1778 // edge then we may be implied true or false.
1779 if (CmpInst::isImpliedTrueByMatchingCmp(BranchPredicate,
1781 addPredicateUsers(PI, I);
1782 return createConstantExpression(
1783 ConstantInt::getTrue(CI->getType()));
1786 if (CmpInst::isImpliedFalseByMatchingCmp(BranchPredicate,
1788 addPredicateUsers(PI, I);
1789 return createConstantExpression(
1790 ConstantInt::getFalse(CI->getType()));
1794 // Just handle the ne and eq cases, where if we have the same
1795 // operands, we may know something.
1796 if (BranchPredicate == OurPredicate) {
1797 addPredicateUsers(PI, I);
1798 // Same predicate, same ops,we know it was false, so this is false.
1799 return createConstantExpression(
1800 ConstantInt::getFalse(CI->getType()));
1801 } else if (BranchPredicate ==
1802 CmpInst::getInversePredicate(OurPredicate)) {
1803 addPredicateUsers(PI, I);
1804 // Inverse predicate, we know the other was false, so this is true.
1805 return createConstantExpression(
1806 ConstantInt::getTrue(CI->getType()));
1812 // Create expression will take care of simplifyCmpInst
1813 return createExpression(I);
1816 // Return true if V is a value that will always be available (IE can
1817 // be placed anywhere) in the function. We don't do globals here
1818 // because they are often worse to put in place.
1819 // TODO: Separate cost from availability
1820 static bool alwaysAvailable(Value *V) {
1821 return isa<Constant>(V) || isa<Argument>(V);
1824 // Substitute and symbolize the value before value numbering.
1826 NewGVN::performSymbolicEvaluation(Value *V,
1827 SmallPtrSetImpl<Value *> &Visited) const {
1828 const Expression *E = nullptr;
1829 if (auto *C = dyn_cast<Constant>(V))
1830 E = createConstantExpression(C);
1831 else if (isa<Argument>(V) || isa<GlobalVariable>(V)) {
1832 E = createVariableExpression(V);
1834 // TODO: memory intrinsics.
1835 // TODO: Some day, we should do the forward propagation and reassociation
1836 // parts of the algorithm.
1837 auto *I = cast<Instruction>(V);
1838 switch (I->getOpcode()) {
1839 case Instruction::ExtractValue:
1840 case Instruction::InsertValue:
1841 E = performSymbolicAggrValueEvaluation(I);
1843 case Instruction::PHI:
1844 E = performSymbolicPHIEvaluation(I);
1846 case Instruction::Call:
1847 E = performSymbolicCallEvaluation(I);
1849 case Instruction::Store:
1850 E = performSymbolicStoreEvaluation(I);
1852 case Instruction::Load:
1853 E = performSymbolicLoadEvaluation(I);
1855 case Instruction::BitCast: {
1856 E = createExpression(I);
1858 case Instruction::ICmp:
1859 case Instruction::FCmp: {
1860 E = performSymbolicCmpEvaluation(I);
1862 case Instruction::Add:
1863 case Instruction::FAdd:
1864 case Instruction::Sub:
1865 case Instruction::FSub:
1866 case Instruction::Mul:
1867 case Instruction::FMul:
1868 case Instruction::UDiv:
1869 case Instruction::SDiv:
1870 case Instruction::FDiv:
1871 case Instruction::URem:
1872 case Instruction::SRem:
1873 case Instruction::FRem:
1874 case Instruction::Shl:
1875 case Instruction::LShr:
1876 case Instruction::AShr:
1877 case Instruction::And:
1878 case Instruction::Or:
1879 case Instruction::Xor:
1880 case Instruction::Trunc:
1881 case Instruction::ZExt:
1882 case Instruction::SExt:
1883 case Instruction::FPToUI:
1884 case Instruction::FPToSI:
1885 case Instruction::UIToFP:
1886 case Instruction::SIToFP:
1887 case Instruction::FPTrunc:
1888 case Instruction::FPExt:
1889 case Instruction::PtrToInt:
1890 case Instruction::IntToPtr:
1891 case Instruction::Select:
1892 case Instruction::ExtractElement:
1893 case Instruction::InsertElement:
1894 case Instruction::ShuffleVector:
1895 case Instruction::GetElementPtr:
1896 E = createExpression(I);
1905 // Look up a container in a map, and then call a function for each thing in the
1907 template <typename Map, typename KeyType, typename Func>
1908 void NewGVN::for_each_found(Map &M, const KeyType &Key, Func F) {
1909 const auto Result = M.find_as(Key);
1910 if (Result != M.end())
1911 for (typename Map::mapped_type::value_type Mapped : Result->second)
1915 // Look up a container of values/instructions in a map, and touch all the
1916 // instructions in the container. Then erase value from the map.
1917 template <typename Map, typename KeyType>
1918 void NewGVN::touchAndErase(Map &M, const KeyType &Key) {
1919 const auto Result = M.find_as(Key);
1920 if (Result != M.end()) {
1921 for (const typename Map::mapped_type::value_type Mapped : Result->second)
1922 TouchedInstructions.set(InstrToDFSNum(Mapped));
1927 void NewGVN::addAdditionalUsers(Value *To, Value *User) const {
1928 AdditionalUsers[To].insert(User);
1931 void NewGVN::markUsersTouched(Value *V) {
1932 // Now mark the users as touched.
1933 for (auto *User : V->users()) {
1934 assert(isa<Instruction>(User) && "Use of value not within an instruction?");
1935 TouchedInstructions.set(InstrToDFSNum(User));
1937 touchAndErase(AdditionalUsers, V);
1940 void NewGVN::addMemoryUsers(const MemoryAccess *To, MemoryAccess *U) const {
1941 DEBUG(dbgs() << "Adding memory user " << *U << " to " << *To << "\n");
1942 MemoryToUsers[To].insert(U);
1945 void NewGVN::markMemoryDefTouched(const MemoryAccess *MA) {
1946 TouchedInstructions.set(MemoryToDFSNum(MA));
1949 void NewGVN::markMemoryUsersTouched(const MemoryAccess *MA) {
1950 if (isa<MemoryUse>(MA))
1952 for (auto U : MA->users())
1953 TouchedInstructions.set(MemoryToDFSNum(U));
1954 touchAndErase(MemoryToUsers, MA);
1957 // Add I to the set of users of a given predicate.
1958 void NewGVN::addPredicateUsers(const PredicateBase *PB, Instruction *I) const {
1959 // Don't add temporary instructions to the user lists.
1960 if (AllTempInstructions.count(I))
1963 if (auto *PBranch = dyn_cast<PredicateBranch>(PB))
1964 PredicateToUsers[PBranch->Condition].insert(I);
1965 else if (auto *PAssume = dyn_cast<PredicateBranch>(PB))
1966 PredicateToUsers[PAssume->Condition].insert(I);
1969 // Touch all the predicates that depend on this instruction.
1970 void NewGVN::markPredicateUsersTouched(Instruction *I) {
1971 touchAndErase(PredicateToUsers, I);
1974 // Mark users affected by a memory leader change.
1975 void NewGVN::markMemoryLeaderChangeTouched(CongruenceClass *CC) {
1976 for (auto M : CC->memory())
1977 markMemoryDefTouched(M);
1980 // Touch the instructions that need to be updated after a congruence class has a
1981 // leader change, and mark changed values.
1982 void NewGVN::markValueLeaderChangeTouched(CongruenceClass *CC) {
1983 for (auto M : *CC) {
1984 if (auto *I = dyn_cast<Instruction>(M))
1985 TouchedInstructions.set(InstrToDFSNum(I));
1986 LeaderChanges.insert(M);
1990 // Give a range of things that have instruction DFS numbers, this will return
1991 // the member of the range with the smallest dfs number.
1992 template <class T, class Range>
1993 T *NewGVN::getMinDFSOfRange(const Range &R) const {
1994 std::pair<T *, unsigned> MinDFS = {nullptr, ~0U};
1995 for (const auto X : R) {
1996 auto DFSNum = InstrToDFSNum(X);
1997 if (DFSNum < MinDFS.second)
1998 MinDFS = {X, DFSNum};
2000 return MinDFS.first;
2003 // This function returns the MemoryAccess that should be the next leader of
2004 // congruence class CC, under the assumption that the current leader is going to
2006 const MemoryAccess *NewGVN::getNextMemoryLeader(CongruenceClass *CC) const {
2007 // TODO: If this ends up to slow, we can maintain a next memory leader like we
2008 // do for regular leaders.
2009 // Make sure there will be a leader to find
2010 assert(!CC->definesNoMemory() && "Can't get next leader if there is none");
2011 if (CC->getStoreCount() > 0) {
2012 if (auto *NL = dyn_cast_or_null<StoreInst>(CC->getNextLeader().first))
2013 return getMemoryAccess(NL);
2014 // Find the store with the minimum DFS number.
2015 auto *V = getMinDFSOfRange<Value>(make_filter_range(
2016 *CC, [&](const Value *V) { return isa<StoreInst>(V); }));
2017 return getMemoryAccess(cast<StoreInst>(V));
2019 assert(CC->getStoreCount() == 0);
2021 // Given our assertion, hitting this part must mean
2022 // !OldClass->memory_empty()
2023 if (CC->memory_size() == 1)
2024 return *CC->memory_begin();
2025 return getMinDFSOfRange<const MemoryPhi>(CC->memory());
2028 // This function returns the next value leader of a congruence class, under the
2029 // assumption that the current leader is going away. This should end up being
2030 // the next most dominating member.
2031 Value *NewGVN::getNextValueLeader(CongruenceClass *CC) const {
2032 // We don't need to sort members if there is only 1, and we don't care about
2033 // sorting the TOP class because everything either gets out of it or is
2036 if (CC->size() == 1 || CC == TOPClass) {
2037 return *(CC->begin());
2038 } else if (CC->getNextLeader().first) {
2039 ++NumGVNAvoidedSortedLeaderChanges;
2040 return CC->getNextLeader().first;
2042 ++NumGVNSortedLeaderChanges;
2043 // NOTE: If this ends up to slow, we can maintain a dual structure for
2044 // member testing/insertion, or keep things mostly sorted, and sort only
2045 // here, or use SparseBitVector or ....
2046 return getMinDFSOfRange<Value>(*CC);
2050 // Move a MemoryAccess, currently in OldClass, to NewClass, including updates to
2051 // the memory members, etc for the move.
2053 // The invariants of this function are:
2055 // I must be moving to NewClass from OldClass The StoreCount of OldClass and
2056 // NewClass is expected to have been updated for I already if it is is a store.
2057 // The OldClass memory leader has not been updated yet if I was the leader.
2058 void NewGVN::moveMemoryToNewCongruenceClass(Instruction *I,
2059 MemoryAccess *InstMA,
2060 CongruenceClass *OldClass,
2061 CongruenceClass *NewClass) {
2062 // If the leader is I, and we had a represenative MemoryAccess, it should
2063 // be the MemoryAccess of OldClass.
2064 assert((!InstMA || !OldClass->getMemoryLeader() ||
2065 OldClass->getLeader() != I ||
2066 OldClass->getMemoryLeader() == InstMA) &&
2067 "Representative MemoryAccess mismatch");
2068 // First, see what happens to the new class
2069 if (!NewClass->getMemoryLeader()) {
2070 // Should be a new class, or a store becoming a leader of a new class.
2071 assert(NewClass->size() == 1 ||
2072 (isa<StoreInst>(I) && NewClass->getStoreCount() == 1));
2073 NewClass->setMemoryLeader(InstMA);
2074 // Mark it touched if we didn't just create a singleton
2075 DEBUG(dbgs() << "Memory class leader change for class " << NewClass->getID()
2076 << " due to new memory instruction becoming leader\n");
2077 markMemoryLeaderChangeTouched(NewClass);
2079 setMemoryClass(InstMA, NewClass);
2080 // Now, fixup the old class if necessary
2081 if (OldClass->getMemoryLeader() == InstMA) {
2082 if (!OldClass->definesNoMemory()) {
2083 OldClass->setMemoryLeader(getNextMemoryLeader(OldClass));
2084 DEBUG(dbgs() << "Memory class leader change for class "
2085 << OldClass->getID() << " to "
2086 << *OldClass->getMemoryLeader()
2087 << " due to removal of old leader " << *InstMA << "\n");
2088 markMemoryLeaderChangeTouched(OldClass);
2090 OldClass->setMemoryLeader(nullptr);
2094 // Move a value, currently in OldClass, to be part of NewClass
2095 // Update OldClass and NewClass for the move (including changing leaders, etc).
2096 void NewGVN::moveValueToNewCongruenceClass(Instruction *I, const Expression *E,
2097 CongruenceClass *OldClass,
2098 CongruenceClass *NewClass) {
2099 if (I == OldClass->getNextLeader().first)
2100 OldClass->resetNextLeader();
2103 NewClass->insert(I);
2105 if (NewClass->getLeader() != I)
2106 NewClass->addPossibleNextLeader({I, InstrToDFSNum(I)});
2107 // Handle our special casing of stores.
2108 if (auto *SI = dyn_cast<StoreInst>(I)) {
2109 OldClass->decStoreCount();
2110 // Okay, so when do we want to make a store a leader of a class?
2111 // If we have a store defined by an earlier load, we want the earlier load
2112 // to lead the class.
2113 // If we have a store defined by something else, we want the store to lead
2114 // the class so everything else gets the "something else" as a value.
2115 // If we have a store as the single member of the class, we want the store
2117 if (NewClass->getStoreCount() == 0 && !NewClass->getStoredValue()) {
2118 // If it's a store expression we are using, it means we are not equivalent
2119 // to something earlier.
2120 if (auto *SE = dyn_cast<StoreExpression>(E)) {
2121 NewClass->setStoredValue(SE->getStoredValue());
2122 markValueLeaderChangeTouched(NewClass);
2123 // Shift the new class leader to be the store
2124 DEBUG(dbgs() << "Changing leader of congruence class "
2125 << NewClass->getID() << " from " << *NewClass->getLeader()
2126 << " to " << *SI << " because store joined class\n");
2127 // If we changed the leader, we have to mark it changed because we don't
2128 // know what it will do to symbolic evlauation.
2129 NewClass->setLeader(SI);
2131 // We rely on the code below handling the MemoryAccess change.
2133 NewClass->incStoreCount();
2135 // True if there is no memory instructions left in a class that had memory
2136 // instructions before.
2138 // If it's not a memory use, set the MemoryAccess equivalence
2139 auto *InstMA = dyn_cast_or_null<MemoryDef>(getMemoryAccess(I));
2141 moveMemoryToNewCongruenceClass(I, InstMA, OldClass, NewClass);
2142 ValueToClass[I] = NewClass;
2143 // See if we destroyed the class or need to swap leaders.
2144 if (OldClass->empty() && OldClass != TOPClass) {
2145 if (OldClass->getDefiningExpr()) {
2146 DEBUG(dbgs() << "Erasing expression " << *OldClass->getDefiningExpr()
2147 << " from table\n");
2148 ExpressionToClass.erase(OldClass->getDefiningExpr());
2150 } else if (OldClass->getLeader() == I) {
2151 // When the leader changes, the value numbering of
2152 // everything may change due to symbolization changes, so we need to
2154 DEBUG(dbgs() << "Value class leader change for class " << OldClass->getID()
2156 ++NumGVNLeaderChanges;
2157 // Destroy the stored value if there are no more stores to represent it.
2158 // Note that this is basically clean up for the expression removal that
2159 // happens below. If we remove stores from a class, we may leave it as a
2160 // class of equivalent memory phis.
2161 if (OldClass->getStoreCount() == 0) {
2162 if (OldClass->getStoredValue())
2163 OldClass->setStoredValue(nullptr);
2165 OldClass->setLeader(getNextValueLeader(OldClass));
2166 OldClass->resetNextLeader();
2167 markValueLeaderChangeTouched(OldClass);
2171 // For a given expression, mark the phi of ops instructions that could have
2172 // changed as a result.
2173 void NewGVN::markPhiOfOpsChanged(const HashedExpression &HE) {
2174 touchAndErase(ExpressionToPhiOfOps, HE);
2177 // Perform congruence finding on a given value numbering expression.
2178 void NewGVN::performCongruenceFinding(Instruction *I, const Expression *E) {
2179 // This is guaranteed to return something, since it will at least find
2182 CongruenceClass *IClass = ValueToClass.lookup(I);
2183 assert(IClass && "Should have found a IClass");
2184 // Dead classes should have been eliminated from the mapping.
2185 assert(!IClass->isDead() && "Found a dead class");
2187 CongruenceClass *EClass = nullptr;
2188 HashedExpression HE(E);
2189 if (const auto *VE = dyn_cast<VariableExpression>(E)) {
2190 EClass = ValueToClass.lookup(VE->getVariableValue());
2191 } else if (isa<DeadExpression>(E)) {
2195 auto lookupResult = ExpressionToClass.insert_as({E, nullptr}, HE);
2197 // If it's not in the value table, create a new congruence class.
2198 if (lookupResult.second) {
2199 CongruenceClass *NewClass = createCongruenceClass(nullptr, E);
2200 auto place = lookupResult.first;
2201 place->second = NewClass;
2203 // Constants and variables should always be made the leader.
2204 if (const auto *CE = dyn_cast<ConstantExpression>(E)) {
2205 NewClass->setLeader(CE->getConstantValue());
2206 } else if (const auto *SE = dyn_cast<StoreExpression>(E)) {
2207 StoreInst *SI = SE->getStoreInst();
2208 NewClass->setLeader(SI);
2209 NewClass->setStoredValue(SE->getStoredValue());
2210 // The RepMemoryAccess field will be filled in properly by the
2211 // moveValueToNewCongruenceClass call.
2213 NewClass->setLeader(I);
2215 assert(!isa<VariableExpression>(E) &&
2216 "VariableExpression should have been handled already");
2219 DEBUG(dbgs() << "Created new congruence class for " << *I
2220 << " using expression " << *E << " at " << NewClass->getID()
2221 << " and leader " << *(NewClass->getLeader()));
2222 if (NewClass->getStoredValue())
2223 DEBUG(dbgs() << " and stored value " << *(NewClass->getStoredValue()));
2224 DEBUG(dbgs() << "\n");
2226 EClass = lookupResult.first->second;
2227 if (isa<ConstantExpression>(E))
2228 assert((isa<Constant>(EClass->getLeader()) ||
2229 (EClass->getStoredValue() &&
2230 isa<Constant>(EClass->getStoredValue()))) &&
2231 "Any class with a constant expression should have a "
2234 assert(EClass && "Somehow don't have an eclass");
2236 assert(!EClass->isDead() && "We accidentally looked up a dead class");
2239 bool ClassChanged = IClass != EClass;
2240 bool LeaderChanged = LeaderChanges.erase(I);
2241 if (ClassChanged || LeaderChanged) {
2242 DEBUG(dbgs() << "New class " << EClass->getID() << " for expression " << *E
2245 moveValueToNewCongruenceClass(I, E, IClass, EClass);
2246 markPhiOfOpsChanged(HE);
2249 markUsersTouched(I);
2250 if (MemoryAccess *MA = getMemoryAccess(I))
2251 markMemoryUsersTouched(MA);
2252 if (auto *CI = dyn_cast<CmpInst>(I))
2253 markPredicateUsersTouched(CI);
2255 // If we changed the class of the store, we want to ensure nothing finds the
2256 // old store expression. In particular, loads do not compare against stored
2257 // value, so they will find old store expressions (and associated class
2258 // mappings) if we leave them in the table.
2259 if (ClassChanged && isa<StoreInst>(I)) {
2260 auto *OldE = ValueToExpression.lookup(I);
2261 // It could just be that the old class died. We don't want to erase it if we
2262 // just moved classes.
2263 if (OldE && isa<StoreExpression>(OldE) && *E != *OldE)
2264 ExpressionToClass.erase(OldE);
2266 ValueToExpression[I] = E;
2269 // Process the fact that Edge (from, to) is reachable, including marking
2270 // any newly reachable blocks and instructions for processing.
2271 void NewGVN::updateReachableEdge(BasicBlock *From, BasicBlock *To) {
2272 // Check if the Edge was reachable before.
2273 if (ReachableEdges.insert({From, To}).second) {
2274 // If this block wasn't reachable before, all instructions are touched.
2275 if (ReachableBlocks.insert(To).second) {
2276 DEBUG(dbgs() << "Block " << getBlockName(To) << " marked reachable\n");
2277 const auto &InstRange = BlockInstRange.lookup(To);
2278 TouchedInstructions.set(InstRange.first, InstRange.second);
2280 DEBUG(dbgs() << "Block " << getBlockName(To)
2281 << " was reachable, but new edge {" << getBlockName(From)
2282 << "," << getBlockName(To) << "} to it found\n");
2284 // We've made an edge reachable to an existing block, which may
2285 // impact predicates. Otherwise, only mark the phi nodes as touched, as
2286 // they are the only thing that depend on new edges. Anything using their
2287 // values will get propagated to if necessary.
2288 if (MemoryAccess *MemPhi = getMemoryAccess(To))
2289 TouchedInstructions.set(InstrToDFSNum(MemPhi));
2291 auto BI = To->begin();
2292 while (isa<PHINode>(BI)) {
2293 TouchedInstructions.set(InstrToDFSNum(&*BI));
2296 for_each_found(PHIOfOpsPHIs, To, [&](const PHINode *I) {
2297 TouchedInstructions.set(InstrToDFSNum(I));
2303 // Given a predicate condition (from a switch, cmp, or whatever) and a block,
2304 // see if we know some constant value for it already.
2305 Value *NewGVN::findConditionEquivalence(Value *Cond) const {
2306 auto Result = lookupOperandLeader(Cond);
2307 if (isa<Constant>(Result))
2312 // Process the outgoing edges of a block for reachability.
2313 void NewGVN::processOutgoingEdges(TerminatorInst *TI, BasicBlock *B) {
2314 // Evaluate reachability of terminator instruction.
2316 if ((BR = dyn_cast<BranchInst>(TI)) && BR->isConditional()) {
2317 Value *Cond = BR->getCondition();
2318 Value *CondEvaluated = findConditionEquivalence(Cond);
2319 if (!CondEvaluated) {
2320 if (auto *I = dyn_cast<Instruction>(Cond)) {
2321 const Expression *E = createExpression(I);
2322 if (const auto *CE = dyn_cast<ConstantExpression>(E)) {
2323 CondEvaluated = CE->getConstantValue();
2325 } else if (isa<ConstantInt>(Cond)) {
2326 CondEvaluated = Cond;
2330 BasicBlock *TrueSucc = BR->getSuccessor(0);
2331 BasicBlock *FalseSucc = BR->getSuccessor(1);
2332 if (CondEvaluated && (CI = dyn_cast<ConstantInt>(CondEvaluated))) {
2334 DEBUG(dbgs() << "Condition for Terminator " << *TI
2335 << " evaluated to true\n");
2336 updateReachableEdge(B, TrueSucc);
2337 } else if (CI->isZero()) {
2338 DEBUG(dbgs() << "Condition for Terminator " << *TI
2339 << " evaluated to false\n");
2340 updateReachableEdge(B, FalseSucc);
2343 updateReachableEdge(B, TrueSucc);
2344 updateReachableEdge(B, FalseSucc);
2346 } else if (auto *SI = dyn_cast<SwitchInst>(TI)) {
2347 // For switches, propagate the case values into the case
2350 // Remember how many outgoing edges there are to every successor.
2351 SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
2353 Value *SwitchCond = SI->getCondition();
2354 Value *CondEvaluated = findConditionEquivalence(SwitchCond);
2355 // See if we were able to turn this switch statement into a constant.
2356 if (CondEvaluated && isa<ConstantInt>(CondEvaluated)) {
2357 auto *CondVal = cast<ConstantInt>(CondEvaluated);
2358 // We should be able to get case value for this.
2359 auto Case = *SI->findCaseValue(CondVal);
2360 if (Case.getCaseSuccessor() == SI->getDefaultDest()) {
2361 // We proved the value is outside of the range of the case.
2362 // We can't do anything other than mark the default dest as reachable,
2364 updateReachableEdge(B, SI->getDefaultDest());
2367 // Now get where it goes and mark it reachable.
2368 BasicBlock *TargetBlock = Case.getCaseSuccessor();
2369 updateReachableEdge(B, TargetBlock);
2371 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
2372 BasicBlock *TargetBlock = SI->getSuccessor(i);
2373 ++SwitchEdges[TargetBlock];
2374 updateReachableEdge(B, TargetBlock);
2378 // Otherwise this is either unconditional, or a type we have no
2379 // idea about. Just mark successors as reachable.
2380 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
2381 BasicBlock *TargetBlock = TI->getSuccessor(i);
2382 updateReachableEdge(B, TargetBlock);
2385 // This also may be a memory defining terminator, in which case, set it
2386 // equivalent only to itself.
2388 auto *MA = getMemoryAccess(TI);
2389 if (MA && !isa<MemoryUse>(MA)) {
2390 auto *CC = ensureLeaderOfMemoryClass(MA);
2391 if (setMemoryClass(MA, CC))
2392 markMemoryUsersTouched(MA);
2397 void NewGVN::addPhiOfOps(PHINode *Op, BasicBlock *BB,
2398 Instruction *ExistingValue) {
2399 InstrDFS[Op] = InstrToDFSNum(ExistingValue);
2400 AllTempInstructions.insert(Op);
2401 PHIOfOpsPHIs[BB].push_back(Op);
2402 TempToBlock[Op] = BB;
2404 RealToTemp[ExistingValue] = Op;
2407 static bool okayForPHIOfOps(const Instruction *I) {
2408 return isa<BinaryOperator>(I) || isa<SelectInst>(I) || isa<CmpInst>(I) ||
2412 // When we see an instruction that is an op of phis, generate the equivalent phi
2415 NewGVN::makePossiblePhiOfOps(Instruction *I, bool HasBackedge,
2416 SmallPtrSetImpl<Value *> &Visited) {
2417 if (!okayForPHIOfOps(I))
2420 if (!Visited.insert(I).second)
2422 // For now, we require the instruction be cycle free because we don't
2423 // *always* create a phi of ops for instructions that could be done as phi
2424 // of ops, we only do it if we think it is useful. If we did do it all the
2425 // time, we could remove the cycle free check.
2426 if (!isCycleFree(I))
2429 unsigned IDFSNum = InstrToDFSNum(I);
2430 // Pretty much all of the instructions we can convert to phi of ops over a
2431 // backedge that are adds, are really induction variables, and those are
2432 // pretty much pointless to convert. This is very coarse-grained for a
2433 // test, so if we do find some value, we can change it later.
2434 // But otherwise, what can happen is we convert the induction variable from
2440 // i = phi (0, tmpphi)
2441 // tmpphi = phi(1, tmpphi+1)
2443 // Which we don't want to happen. We could just avoid this for all non-cycle
2444 // free phis, and we made go that route.
2445 if (HasBackedge && I->getOpcode() == Instruction::Add)
2448 SmallPtrSet<const Value *, 8> ProcessedPHIs;
2449 // TODO: We don't do phi translation on memory accesses because it's
2450 // complicated. For a load, we'd need to be able to simulate a new memoryuse,
2451 // which we don't have a good way of doing ATM.
2452 auto *MemAccess = getMemoryAccess(I);
2453 // If the memory operation is defined by a memory operation this block that
2454 // isn't a MemoryPhi, transforming the pointer backwards through a scalar phi
2455 // can't help, as it would still be killed by that memory operation.
2456 if (MemAccess && !isa<MemoryPhi>(MemAccess->getDefiningAccess()) &&
2457 MemAccess->getDefiningAccess()->getBlock() == I->getParent())
2460 // Convert op of phis to phi of ops
2461 for (auto &Op : I->operands()) {
2462 if (!isa<PHINode>(Op))
2464 auto *OpPHI = cast<PHINode>(Op);
2465 // No point in doing this for one-operand phis.
2466 if (OpPHI->getNumOperands() == 1)
2468 if (!DebugCounter::shouldExecute(PHIOfOpsCounter))
2470 SmallVector<std::pair<Value *, BasicBlock *>, 4> Ops;
2471 auto *PHIBlock = getBlockForValue(OpPHI);
2472 for (auto PredBB : OpPHI->blocks()) {
2473 Value *FoundVal = nullptr;
2474 // We could just skip unreachable edges entirely but it's tricky to do
2475 // with rewriting existing phi nodes.
2476 if (ReachableEdges.count({PredBB, PHIBlock})) {
2477 // Clone the instruction, create an expression from it, and see if we
2479 Instruction *ValueOp = I->clone();
2480 auto Iter = TempToMemory.end();
2482 Iter = TempToMemory.insert({ValueOp, MemAccess}).first;
2484 for (auto &Op : ValueOp->operands()) {
2485 Op = Op->DoPHITranslation(PHIBlock, PredBB);
2486 // When this operand changes, it could change whether there is a
2487 // leader for us or not.
2488 addAdditionalUsers(Op, I);
2490 // Make sure it's marked as a temporary instruction.
2491 AllTempInstructions.insert(ValueOp);
2492 // and make sure anything that tries to add it's DFS number is
2493 // redirected to the instruction we are making a phi of ops
2495 InstrDFS.insert({ValueOp, IDFSNum});
2496 const Expression *E = performSymbolicEvaluation(ValueOp, Visited);
2497 InstrDFS.erase(ValueOp);
2498 AllTempInstructions.erase(ValueOp);
2499 ValueOp->deleteValue();
2501 TempToMemory.erase(Iter);
2504 FoundVal = findPhiOfOpsLeader(E, PredBB);
2506 ExpressionToPhiOfOps[E].insert(I);
2509 if (auto *SI = dyn_cast<StoreInst>(FoundVal))
2510 FoundVal = SI->getValueOperand();
2512 DEBUG(dbgs() << "Skipping phi of ops operand for incoming block "
2513 << getBlockName(PredBB)
2514 << " because the block is unreachable\n");
2515 FoundVal = UndefValue::get(I->getType());
2518 Ops.push_back({FoundVal, PredBB});
2519 DEBUG(dbgs() << "Found phi of ops operand " << *FoundVal << " in "
2520 << getBlockName(PredBB) << "\n");
2522 auto *ValuePHI = RealToTemp.lookup(I);
2523 bool NewPHI = false;
2525 ValuePHI = PHINode::Create(I->getType(), OpPHI->getNumOperands());
2526 addPhiOfOps(ValuePHI, PHIBlock, I);
2528 NumGVNPHIOfOpsCreated++;
2531 for (auto PHIOp : Ops)
2532 ValuePHI->addIncoming(PHIOp.first, PHIOp.second);
2535 for (auto PHIOp : Ops) {
2536 ValuePHI->setIncomingValue(i, PHIOp.first);
2537 ValuePHI->setIncomingBlock(i, PHIOp.second);
2542 DEBUG(dbgs() << "Created phi of ops " << *ValuePHI << " for " << *I
2544 return performSymbolicEvaluation(ValuePHI, Visited);
2549 // The algorithm initially places the values of the routine in the TOP
2550 // congruence class. The leader of TOP is the undetermined value `undef`.
2551 // When the algorithm has finished, values still in TOP are unreachable.
2552 void NewGVN::initializeCongruenceClasses(Function &F) {
2553 NextCongruenceNum = 0;
2555 // Note that even though we use the live on entry def as a representative
2556 // MemoryAccess, it is *not* the same as the actual live on entry def. We
2557 // have no real equivalemnt to undef for MemoryAccesses, and so we really
2558 // should be checking whether the MemoryAccess is top if we want to know if it
2559 // is equivalent to everything. Otherwise, what this really signifies is that
2560 // the access "it reaches all the way back to the beginning of the function"
2562 // Initialize all other instructions to be in TOP class.
2563 TOPClass = createCongruenceClass(nullptr, nullptr);
2564 TOPClass->setMemoryLeader(MSSA->getLiveOnEntryDef());
2565 // The live on entry def gets put into it's own class
2566 MemoryAccessToClass[MSSA->getLiveOnEntryDef()] =
2567 createMemoryClass(MSSA->getLiveOnEntryDef());
2569 for (auto DTN : nodes(DT)) {
2570 BasicBlock *BB = DTN->getBlock();
2571 // All MemoryAccesses are equivalent to live on entry to start. They must
2572 // be initialized to something so that initial changes are noticed. For
2573 // the maximal answer, we initialize them all to be the same as
2575 auto *MemoryBlockDefs = MSSA->getBlockDefs(BB);
2576 if (MemoryBlockDefs)
2577 for (const auto &Def : *MemoryBlockDefs) {
2578 MemoryAccessToClass[&Def] = TOPClass;
2579 auto *MD = dyn_cast<MemoryDef>(&Def);
2580 // Insert the memory phis into the member list.
2582 const MemoryPhi *MP = cast<MemoryPhi>(&Def);
2583 TOPClass->memory_insert(MP);
2584 MemoryPhiState.insert({MP, MPS_TOP});
2587 if (MD && isa<StoreInst>(MD->getMemoryInst()))
2588 TOPClass->incStoreCount();
2590 for (auto &I : *BB) {
2591 // TODO: Move to helper
2592 if (isa<PHINode>(&I))
2593 for (auto *U : I.users())
2594 if (auto *UInst = dyn_cast<Instruction>(U))
2595 if (InstrToDFSNum(UInst) != 0 && okayForPHIOfOps(UInst))
2596 PHINodeUses.insert(UInst);
2597 // Don't insert void terminators into the class. We don't value number
2598 // them, and they just end up sitting in TOP.
2599 if (isa<TerminatorInst>(I) && I.getType()->isVoidTy())
2601 TOPClass->insert(&I);
2602 ValueToClass[&I] = TOPClass;
2606 // Initialize arguments to be in their own unique congruence classes
2607 for (auto &FA : F.args())
2608 createSingletonCongruenceClass(&FA);
2611 void NewGVN::cleanupTables() {
2612 for (unsigned i = 0, e = CongruenceClasses.size(); i != e; ++i) {
2613 DEBUG(dbgs() << "Congruence class " << CongruenceClasses[i]->getID()
2614 << " has " << CongruenceClasses[i]->size() << " members\n");
2615 // Make sure we delete the congruence class (probably worth switching to
2616 // a unique_ptr at some point.
2617 delete CongruenceClasses[i];
2618 CongruenceClasses[i] = nullptr;
2621 // Destroy the value expressions
2622 SmallVector<Instruction *, 8> TempInst(AllTempInstructions.begin(),
2623 AllTempInstructions.end());
2624 AllTempInstructions.clear();
2626 // We have to drop all references for everything first, so there are no uses
2627 // left as we delete them.
2628 for (auto *I : TempInst) {
2629 I->dropAllReferences();
2632 while (!TempInst.empty()) {
2633 auto *I = TempInst.back();
2634 TempInst.pop_back();
2638 ValueToClass.clear();
2639 ArgRecycler.clear(ExpressionAllocator);
2640 ExpressionAllocator.Reset();
2641 CongruenceClasses.clear();
2642 ExpressionToClass.clear();
2643 ValueToExpression.clear();
2645 AdditionalUsers.clear();
2646 ExpressionToPhiOfOps.clear();
2647 TempToBlock.clear();
2648 TempToMemory.clear();
2649 PHIOfOpsPHIs.clear();
2650 ReachableBlocks.clear();
2651 ReachableEdges.clear();
2653 ProcessedCount.clear();
2656 InstructionsToErase.clear();
2658 BlockInstRange.clear();
2659 TouchedInstructions.clear();
2660 MemoryAccessToClass.clear();
2661 PredicateToUsers.clear();
2662 MemoryToUsers.clear();
2665 // Assign local DFS number mapping to instructions, and leave space for Value
2667 std::pair<unsigned, unsigned> NewGVN::assignDFSNumbers(BasicBlock *B,
2669 unsigned End = Start;
2670 if (MemoryAccess *MemPhi = getMemoryAccess(B)) {
2671 InstrDFS[MemPhi] = End++;
2672 DFSToInstr.emplace_back(MemPhi);
2675 // Then the real block goes next.
2676 for (auto &I : *B) {
2677 // There's no need to call isInstructionTriviallyDead more than once on
2678 // an instruction. Therefore, once we know that an instruction is dead
2679 // we change its DFS number so that it doesn't get value numbered.
2680 if (isInstructionTriviallyDead(&I, TLI)) {
2682 DEBUG(dbgs() << "Skipping trivially dead instruction " << I << "\n");
2683 markInstructionForDeletion(&I);
2686 InstrDFS[&I] = End++;
2687 DFSToInstr.emplace_back(&I);
2690 // All of the range functions taken half-open ranges (open on the end side).
2691 // So we do not subtract one from count, because at this point it is one
2692 // greater than the last instruction.
2693 return std::make_pair(Start, End);
2696 void NewGVN::updateProcessedCount(const Value *V) {
2698 if (ProcessedCount.count(V) == 0) {
2699 ProcessedCount.insert({V, 1});
2701 ++ProcessedCount[V];
2702 assert(ProcessedCount[V] < 100 &&
2703 "Seem to have processed the same Value a lot");
2707 // Evaluate MemoryPhi nodes symbolically, just like PHI nodes
2708 void NewGVN::valueNumberMemoryPhi(MemoryPhi *MP) {
2709 // If all the arguments are the same, the MemoryPhi has the same value as the
2710 // argument. Filter out unreachable blocks and self phis from our operands.
2711 // TODO: We could do cycle-checking on the memory phis to allow valueizing for
2712 // self-phi checking.
2713 const BasicBlock *PHIBlock = MP->getBlock();
2714 auto Filtered = make_filter_range(MP->operands(), [&](const Use &U) {
2715 return cast<MemoryAccess>(U) != MP &&
2716 !isMemoryAccessTOP(cast<MemoryAccess>(U)) &&
2717 ReachableEdges.count({MP->getIncomingBlock(U), PHIBlock});
2719 // If all that is left is nothing, our memoryphi is undef. We keep it as
2720 // InitialClass. Note: The only case this should happen is if we have at
2721 // least one self-argument.
2722 if (Filtered.begin() == Filtered.end()) {
2723 if (setMemoryClass(MP, TOPClass))
2724 markMemoryUsersTouched(MP);
2728 // Transform the remaining operands into operand leaders.
2729 // FIXME: mapped_iterator should have a range version.
2730 auto LookupFunc = [&](const Use &U) {
2731 return lookupMemoryLeader(cast<MemoryAccess>(U));
2733 auto MappedBegin = map_iterator(Filtered.begin(), LookupFunc);
2734 auto MappedEnd = map_iterator(Filtered.end(), LookupFunc);
2736 // and now check if all the elements are equal.
2737 // Sadly, we can't use std::equals since these are random access iterators.
2738 const auto *AllSameValue = *MappedBegin;
2740 bool AllEqual = std::all_of(
2741 MappedBegin, MappedEnd,
2742 [&AllSameValue](const MemoryAccess *V) { return V == AllSameValue; });
2745 DEBUG(dbgs() << "Memory Phi value numbered to " << *AllSameValue << "\n");
2747 DEBUG(dbgs() << "Memory Phi value numbered to itself\n");
2748 // If it's equal to something, it's in that class. Otherwise, it has to be in
2749 // a class where it is the leader (other things may be equivalent to it, but
2750 // it needs to start off in its own class, which means it must have been the
2751 // leader, and it can't have stopped being the leader because it was never
2753 CongruenceClass *CC =
2754 AllEqual ? getMemoryClass(AllSameValue) : ensureLeaderOfMemoryClass(MP);
2755 auto OldState = MemoryPhiState.lookup(MP);
2756 assert(OldState != MPS_Invalid && "Invalid memory phi state");
2757 auto NewState = AllEqual ? MPS_Equivalent : MPS_Unique;
2758 MemoryPhiState[MP] = NewState;
2759 if (setMemoryClass(MP, CC) || OldState != NewState)
2760 markMemoryUsersTouched(MP);
2763 // Value number a single instruction, symbolically evaluating, performing
2764 // congruence finding, and updating mappings.
2765 void NewGVN::valueNumberInstruction(Instruction *I) {
2766 DEBUG(dbgs() << "Processing instruction " << *I << "\n");
2767 if (!I->isTerminator()) {
2768 const Expression *Symbolized = nullptr;
2769 SmallPtrSet<Value *, 2> Visited;
2770 if (DebugCounter::shouldExecute(VNCounter)) {
2771 Symbolized = performSymbolicEvaluation(I, Visited);
2772 // Make a phi of ops if necessary
2773 if (Symbolized && !isa<ConstantExpression>(Symbolized) &&
2774 !isa<VariableExpression>(Symbolized) && PHINodeUses.count(I)) {
2775 // FIXME: Backedge argument
2776 auto *PHIE = makePossiblePhiOfOps(I, false, Visited);
2782 // Mark the instruction as unused so we don't value number it again.
2785 // If we couldn't come up with a symbolic expression, use the unknown
2787 if (Symbolized == nullptr)
2788 Symbolized = createUnknownExpression(I);
2789 performCongruenceFinding(I, Symbolized);
2791 // Handle terminators that return values. All of them produce values we
2792 // don't currently understand. We don't place non-value producing
2793 // terminators in a class.
2794 if (!I->getType()->isVoidTy()) {
2795 auto *Symbolized = createUnknownExpression(I);
2796 performCongruenceFinding(I, Symbolized);
2798 processOutgoingEdges(dyn_cast<TerminatorInst>(I), I->getParent());
2802 // Check if there is a path, using single or equal argument phi nodes, from
2804 bool NewGVN::singleReachablePHIPath(
2805 SmallPtrSet<const MemoryAccess *, 8> &Visited, const MemoryAccess *First,
2806 const MemoryAccess *Second) const {
2807 if (First == Second)
2809 if (MSSA->isLiveOnEntryDef(First))
2812 // This is not perfect, but as we're just verifying here, we can live with
2813 // the loss of precision. The real solution would be that of doing strongly
2814 // connected component finding in this routine, and it's probably not worth
2815 // the complexity for the time being. So, we just keep a set of visited
2816 // MemoryAccess and return true when we hit a cycle.
2817 if (Visited.count(First))
2819 Visited.insert(First);
2821 const auto *EndDef = First;
2822 for (auto *ChainDef : optimized_def_chain(First)) {
2823 if (ChainDef == Second)
2825 if (MSSA->isLiveOnEntryDef(ChainDef))
2829 auto *MP = cast<MemoryPhi>(EndDef);
2830 auto ReachableOperandPred = [&](const Use &U) {
2831 return ReachableEdges.count({MP->getIncomingBlock(U), MP->getBlock()});
2833 auto FilteredPhiArgs =
2834 make_filter_range(MP->operands(), ReachableOperandPred);
2835 SmallVector<const Value *, 32> OperandList;
2836 std::copy(FilteredPhiArgs.begin(), FilteredPhiArgs.end(),
2837 std::back_inserter(OperandList));
2838 bool Okay = OperandList.size() == 1;
2841 std::equal(OperandList.begin(), OperandList.end(), OperandList.begin());
2843 return singleReachablePHIPath(Visited, cast<MemoryAccess>(OperandList[0]),
2848 // Verify the that the memory equivalence table makes sense relative to the
2849 // congruence classes. Note that this checking is not perfect, and is currently
2850 // subject to very rare false negatives. It is only useful for
2851 // testing/debugging.
2852 void NewGVN::verifyMemoryCongruency() const {
2854 // Verify that the memory table equivalence and memory member set match
2855 for (const auto *CC : CongruenceClasses) {
2856 if (CC == TOPClass || CC->isDead())
2858 if (CC->getStoreCount() != 0) {
2859 assert((CC->getStoredValue() || !isa<StoreInst>(CC->getLeader())) &&
2860 "Any class with a store as a leader should have a "
2861 "representative stored value");
2862 assert(CC->getMemoryLeader() &&
2863 "Any congruence class with a store should have a "
2864 "representative access");
2867 if (CC->getMemoryLeader())
2868 assert(MemoryAccessToClass.lookup(CC->getMemoryLeader()) == CC &&
2869 "Representative MemoryAccess does not appear to be reverse "
2871 for (auto M : CC->memory())
2872 assert(MemoryAccessToClass.lookup(M) == CC &&
2873 "Memory member does not appear to be reverse mapped properly");
2876 // Anything equivalent in the MemoryAccess table should be in the same
2877 // congruence class.
2879 // Filter out the unreachable and trivially dead entries, because they may
2880 // never have been updated if the instructions were not processed.
2881 auto ReachableAccessPred =
2882 [&](const std::pair<const MemoryAccess *, CongruenceClass *> Pair) {
2883 bool Result = ReachableBlocks.count(Pair.first->getBlock());
2884 if (!Result || MSSA->isLiveOnEntryDef(Pair.first) ||
2885 MemoryToDFSNum(Pair.first) == 0)
2887 if (auto *MemDef = dyn_cast<MemoryDef>(Pair.first))
2888 return !isInstructionTriviallyDead(MemDef->getMemoryInst());
2890 // We could have phi nodes which operands are all trivially dead,
2891 // so we don't process them.
2892 if (auto *MemPHI = dyn_cast<MemoryPhi>(Pair.first)) {
2893 for (auto &U : MemPHI->incoming_values()) {
2894 if (Instruction *I = dyn_cast<Instruction>(U.get())) {
2895 if (!isInstructionTriviallyDead(I))
2905 auto Filtered = make_filter_range(MemoryAccessToClass, ReachableAccessPred);
2906 for (auto KV : Filtered) {
2907 if (auto *FirstMUD = dyn_cast<MemoryUseOrDef>(KV.first)) {
2908 auto *SecondMUD = dyn_cast<MemoryUseOrDef>(KV.second->getMemoryLeader());
2909 if (FirstMUD && SecondMUD) {
2910 SmallPtrSet<const MemoryAccess *, 8> VisitedMAS;
2911 assert((singleReachablePHIPath(VisitedMAS, FirstMUD, SecondMUD) ||
2912 ValueToClass.lookup(FirstMUD->getMemoryInst()) ==
2913 ValueToClass.lookup(SecondMUD->getMemoryInst())) &&
2914 "The instructions for these memory operations should have "
2915 "been in the same congruence class or reachable through"
2916 "a single argument phi");
2918 } else if (auto *FirstMP = dyn_cast<MemoryPhi>(KV.first)) {
2919 // We can only sanely verify that MemoryDefs in the operand list all have
2921 auto ReachableOperandPred = [&](const Use &U) {
2922 return ReachableEdges.count(
2923 {FirstMP->getIncomingBlock(U), FirstMP->getBlock()}) &&
2927 // All arguments should in the same class, ignoring unreachable arguments
2928 auto FilteredPhiArgs =
2929 make_filter_range(FirstMP->operands(), ReachableOperandPred);
2930 SmallVector<const CongruenceClass *, 16> PhiOpClasses;
2931 std::transform(FilteredPhiArgs.begin(), FilteredPhiArgs.end(),
2932 std::back_inserter(PhiOpClasses), [&](const Use &U) {
2933 const MemoryDef *MD = cast<MemoryDef>(U);
2934 return ValueToClass.lookup(MD->getMemoryInst());
2936 assert(std::equal(PhiOpClasses.begin(), PhiOpClasses.end(),
2937 PhiOpClasses.begin()) &&
2938 "All MemoryPhi arguments should be in the same class");
2944 // Verify that the sparse propagation we did actually found the maximal fixpoint
2945 // We do this by storing the value to class mapping, touching all instructions,
2946 // and redoing the iteration to see if anything changed.
2947 void NewGVN::verifyIterationSettled(Function &F) {
2949 DEBUG(dbgs() << "Beginning iteration verification\n");
2950 if (DebugCounter::isCounterSet(VNCounter))
2951 DebugCounter::setCounterValue(VNCounter, StartingVNCounter);
2953 // Note that we have to store the actual classes, as we may change existing
2954 // classes during iteration. This is because our memory iteration propagation
2955 // is not perfect, and so may waste a little work. But it should generate
2956 // exactly the same congruence classes we have now, with different IDs.
2957 std::map<const Value *, CongruenceClass> BeforeIteration;
2959 for (auto &KV : ValueToClass) {
2960 if (auto *I = dyn_cast<Instruction>(KV.first))
2961 // Skip unused/dead instructions.
2962 if (InstrToDFSNum(I) == 0)
2964 BeforeIteration.insert({KV.first, *KV.second});
2967 TouchedInstructions.set();
2968 TouchedInstructions.reset(0);
2969 iterateTouchedInstructions();
2970 DenseSet<std::pair<const CongruenceClass *, const CongruenceClass *>>
2972 for (const auto &KV : ValueToClass) {
2973 if (auto *I = dyn_cast<Instruction>(KV.first))
2974 // Skip unused/dead instructions.
2975 if (InstrToDFSNum(I) == 0)
2977 // We could sink these uses, but i think this adds a bit of clarity here as
2978 // to what we are comparing.
2979 auto *BeforeCC = &BeforeIteration.find(KV.first)->second;
2980 auto *AfterCC = KV.second;
2981 // Note that the classes can't change at this point, so we memoize the set
2983 if (!EqualClasses.count({BeforeCC, AfterCC})) {
2984 assert(BeforeCC->isEquivalentTo(AfterCC) &&
2985 "Value number changed after main loop completed!");
2986 EqualClasses.insert({BeforeCC, AfterCC});
2992 // Verify that for each store expression in the expression to class mapping,
2993 // only the latest appears, and multiple ones do not appear.
2994 // Because loads do not use the stored value when doing equality with stores,
2995 // if we don't erase the old store expressions from the table, a load can find
2996 // a no-longer valid StoreExpression.
2997 void NewGVN::verifyStoreExpressions() const {
2999 DenseSet<std::pair<const Value *, const Value *>> StoreExpressionSet;
3000 for (const auto &KV : ExpressionToClass) {
3001 if (auto *SE = dyn_cast<StoreExpression>(KV.first)) {
3002 // Make sure a version that will conflict with loads is not already there
3004 StoreExpressionSet.insert({SE->getOperand(0), SE->getMemoryLeader()});
3005 assert(Res.second &&
3006 "Stored expression conflict exists in expression table");
3007 auto *ValueExpr = ValueToExpression.lookup(SE->getStoreInst());
3008 assert(ValueExpr && ValueExpr->equals(*SE) &&
3009 "StoreExpression in ExpressionToClass is not latest "
3010 "StoreExpression for value");
3016 // This is the main value numbering loop, it iterates over the initial touched
3017 // instruction set, propagating value numbers, marking things touched, etc,
3018 // until the set of touched instructions is completely empty.
3019 void NewGVN::iterateTouchedInstructions() {
3020 unsigned int Iterations = 0;
3021 // Figure out where touchedinstructions starts
3022 int FirstInstr = TouchedInstructions.find_first();
3023 // Nothing set, nothing to iterate, just return.
3024 if (FirstInstr == -1)
3026 const BasicBlock *LastBlock = getBlockForValue(InstrFromDFSNum(FirstInstr));
3027 while (TouchedInstructions.any()) {
3029 // Walk through all the instructions in all the blocks in RPO.
3030 // TODO: As we hit a new block, we should push and pop equalities into a
3031 // table lookupOperandLeader can use, to catch things PredicateInfo
3032 // might miss, like edge-only equivalences.
3033 for (unsigned InstrNum : TouchedInstructions.set_bits()) {
3035 // This instruction was found to be dead. We don't bother looking
3037 if (InstrNum == 0) {
3038 TouchedInstructions.reset(InstrNum);
3042 Value *V = InstrFromDFSNum(InstrNum);
3043 const BasicBlock *CurrBlock = getBlockForValue(V);
3045 // If we hit a new block, do reachability processing.
3046 if (CurrBlock != LastBlock) {
3047 LastBlock = CurrBlock;
3048 bool BlockReachable = ReachableBlocks.count(CurrBlock);
3049 const auto &CurrInstRange = BlockInstRange.lookup(CurrBlock);
3051 // If it's not reachable, erase any touched instructions and move on.
3052 if (!BlockReachable) {
3053 TouchedInstructions.reset(CurrInstRange.first, CurrInstRange.second);
3054 DEBUG(dbgs() << "Skipping instructions in block "
3055 << getBlockName(CurrBlock)
3056 << " because it is unreachable\n");
3059 updateProcessedCount(CurrBlock);
3062 if (auto *MP = dyn_cast<MemoryPhi>(V)) {
3063 DEBUG(dbgs() << "Processing MemoryPhi " << *MP << "\n");
3064 valueNumberMemoryPhi(MP);
3065 } else if (auto *I = dyn_cast<Instruction>(V)) {
3066 valueNumberInstruction(I);
3068 llvm_unreachable("Should have been a MemoryPhi or Instruction");
3070 updateProcessedCount(V);
3071 // Reset after processing (because we may mark ourselves as touched when
3072 // we propagate equalities).
3073 TouchedInstructions.reset(InstrNum);
3076 NumGVNMaxIterations = std::max(NumGVNMaxIterations.getValue(), Iterations);
3079 // This is the main transformation entry point.
3080 bool NewGVN::runGVN() {
3081 if (DebugCounter::isCounterSet(VNCounter))
3082 StartingVNCounter = DebugCounter::getCounterValue(VNCounter);
3083 bool Changed = false;
3084 NumFuncArgs = F.arg_size();
3085 MSSAWalker = MSSA->getWalker();
3086 SingletonDeadExpression = new (ExpressionAllocator) DeadExpression();
3088 // Count number of instructions for sizing of hash tables, and come
3089 // up with a global dfs numbering for instructions.
3090 unsigned ICount = 1;
3091 // Add an empty instruction to account for the fact that we start at 1
3092 DFSToInstr.emplace_back(nullptr);
3093 // Note: We want ideal RPO traversal of the blocks, which is not quite the
3094 // same as dominator tree order, particularly with regard whether backedges
3095 // get visited first or second, given a block with multiple successors.
3096 // If we visit in the wrong order, we will end up performing N times as many
3098 // The dominator tree does guarantee that, for a given dom tree node, it's
3099 // parent must occur before it in the RPO ordering. Thus, we only need to sort
3101 ReversePostOrderTraversal<Function *> RPOT(&F);
3102 unsigned Counter = 0;
3103 for (auto &B : RPOT) {
3104 auto *Node = DT->getNode(B);
3105 assert(Node && "RPO and Dominator tree should have same reachability");
3106 RPOOrdering[Node] = ++Counter;
3108 // Sort dominator tree children arrays into RPO.
3109 for (auto &B : RPOT) {
3110 auto *Node = DT->getNode(B);
3111 if (Node->getChildren().size() > 1)
3112 std::sort(Node->begin(), Node->end(),
3113 [&](const DomTreeNode *A, const DomTreeNode *B) {
3114 return RPOOrdering[A] < RPOOrdering[B];
3118 // Now a standard depth first ordering of the domtree is equivalent to RPO.
3119 for (auto DTN : depth_first(DT->getRootNode())) {
3120 BasicBlock *B = DTN->getBlock();
3121 const auto &BlockRange = assignDFSNumbers(B, ICount);
3122 BlockInstRange.insert({B, BlockRange});
3123 ICount += BlockRange.second - BlockRange.first;
3125 initializeCongruenceClasses(F);
3127 TouchedInstructions.resize(ICount);
3128 // Ensure we don't end up resizing the expressionToClass map, as
3129 // that can be quite expensive. At most, we have one expression per
3131 ExpressionToClass.reserve(ICount);
3133 // Initialize the touched instructions to include the entry block.
3134 const auto &InstRange = BlockInstRange.lookup(&F.getEntryBlock());
3135 TouchedInstructions.set(InstRange.first, InstRange.second);
3136 DEBUG(dbgs() << "Block " << getBlockName(&F.getEntryBlock())
3137 << " marked reachable\n");
3138 ReachableBlocks.insert(&F.getEntryBlock());
3140 iterateTouchedInstructions();
3141 verifyMemoryCongruency();
3142 verifyIterationSettled(F);
3143 verifyStoreExpressions();
3145 Changed |= eliminateInstructions(F);
3147 // Delete all instructions marked for deletion.
3148 for (Instruction *ToErase : InstructionsToErase) {
3149 if (!ToErase->use_empty())
3150 ToErase->replaceAllUsesWith(UndefValue::get(ToErase->getType()));
3152 if (ToErase->getParent())
3153 ToErase->eraseFromParent();
3156 // Delete all unreachable blocks.
3157 auto UnreachableBlockPred = [&](const BasicBlock &BB) {
3158 return !ReachableBlocks.count(&BB);
3161 for (auto &BB : make_filter_range(F, UnreachableBlockPred)) {
3162 DEBUG(dbgs() << "We believe block " << getBlockName(&BB)
3163 << " is unreachable\n");
3164 deleteInstructionsInBlock(&BB);
3172 struct NewGVN::ValueDFS {
3176 // Only one of Def and U will be set.
3177 // The bool in the Def tells us whether the Def is the stored value of a
3179 PointerIntPair<Value *, 1, bool> Def;
3181 bool operator<(const ValueDFS &Other) const {
3182 // It's not enough that any given field be less than - we have sets
3183 // of fields that need to be evaluated together to give a proper ordering.
3184 // For example, if you have;
3189 // We want the second to be less than the first, but if we just go field
3190 // by field, we will get to Val 0 < Val 50 and say the first is less than
3191 // the second. We only want it to be less than if the DFS orders are equal.
3193 // Each LLVM instruction only produces one value, and thus the lowest-level
3194 // differentiator that really matters for the stack (and what we use as as a
3195 // replacement) is the local dfs number.
3196 // Everything else in the structure is instruction level, and only affects
3197 // the order in which we will replace operands of a given instruction.
3199 // For a given instruction (IE things with equal dfsin, dfsout, localnum),
3200 // the order of replacement of uses does not matter.
3204 // When you hit b, you will have two valuedfs with the same dfsin, out, and
3206 // The .val will be the same as well.
3207 // The .u's will be different.
3208 // You will replace both, and it does not matter what order you replace them
3209 // in (IE whether you replace operand 2, then operand 1, or operand 1, then
3211 // Similarly for the case of same dfsin, dfsout, localnum, but different
3216 // in c, we will a valuedfs for a, and one for b,with everything the same
3218 // It does not matter what order we replace these operands in.
3219 // You will always end up with the same IR, and this is guaranteed.
3220 return std::tie(DFSIn, DFSOut, LocalNum, Def, U) <
3221 std::tie(Other.DFSIn, Other.DFSOut, Other.LocalNum, Other.Def,
3226 // This function converts the set of members for a congruence class from values,
3227 // to sets of defs and uses with associated DFS info. The total number of
3228 // reachable uses for each value is stored in UseCount, and instructions that
3230 // dead (have no non-dead uses) are stored in ProbablyDead.
3231 void NewGVN::convertClassToDFSOrdered(
3232 const CongruenceClass &Dense, SmallVectorImpl<ValueDFS> &DFSOrderedSet,
3233 DenseMap<const Value *, unsigned int> &UseCounts,
3234 SmallPtrSetImpl<Instruction *> &ProbablyDead) const {
3235 for (auto D : Dense) {
3236 // First add the value.
3237 BasicBlock *BB = getBlockForValue(D);
3238 // Constants are handled prior to ever calling this function, so
3239 // we should only be left with instructions as members.
3240 assert(BB && "Should have figured out a basic block for value");
3242 DomTreeNode *DomNode = DT->getNode(BB);
3243 VDDef.DFSIn = DomNode->getDFSNumIn();
3244 VDDef.DFSOut = DomNode->getDFSNumOut();
3245 // If it's a store, use the leader of the value operand, if it's always
3246 // available, or the value operand. TODO: We could do dominance checks to
3247 // find a dominating leader, but not worth it ATM.
3248 if (auto *SI = dyn_cast<StoreInst>(D)) {
3249 auto Leader = lookupOperandLeader(SI->getValueOperand());
3250 if (alwaysAvailable(Leader)) {
3251 VDDef.Def.setPointer(Leader);
3253 VDDef.Def.setPointer(SI->getValueOperand());
3254 VDDef.Def.setInt(true);
3257 VDDef.Def.setPointer(D);
3259 assert(isa<Instruction>(D) &&
3260 "The dense set member should always be an instruction");
3261 Instruction *Def = cast<Instruction>(D);
3262 VDDef.LocalNum = InstrToDFSNum(D);
3263 DFSOrderedSet.push_back(VDDef);
3264 // If there is a phi node equivalent, add it
3265 if (auto *PN = RealToTemp.lookup(Def)) {
3267 dyn_cast_or_null<PHIExpression>(ValueToExpression.lookup(Def));
3269 VDDef.Def.setInt(false);
3270 VDDef.Def.setPointer(PN);
3272 DFSOrderedSet.push_back(VDDef);
3276 unsigned int UseCount = 0;
3277 // Now add the uses.
3278 for (auto &U : Def->uses()) {
3279 if (auto *I = dyn_cast<Instruction>(U.getUser())) {
3280 // Don't try to replace into dead uses
3281 if (InstructionsToErase.count(I))
3284 // Put the phi node uses in the incoming block.
3286 if (auto *P = dyn_cast<PHINode>(I)) {
3287 IBlock = P->getIncomingBlock(U);
3288 // Make phi node users appear last in the incoming block
3290 VDUse.LocalNum = InstrDFS.size() + 1;
3292 IBlock = getBlockForValue(I);
3293 VDUse.LocalNum = InstrToDFSNum(I);
3296 // Skip uses in unreachable blocks, as we're going
3298 if (ReachableBlocks.count(IBlock) == 0)
3301 DomTreeNode *DomNode = DT->getNode(IBlock);
3302 VDUse.DFSIn = DomNode->getDFSNumIn();
3303 VDUse.DFSOut = DomNode->getDFSNumOut();
3306 DFSOrderedSet.emplace_back(VDUse);
3310 // If there are no uses, it's probably dead (but it may have side-effects,
3311 // so not definitely dead. Otherwise, store the number of uses so we can
3312 // track if it becomes dead later).
3314 ProbablyDead.insert(Def);
3316 UseCounts[Def] = UseCount;
3320 // This function converts the set of members for a congruence class from values,
3321 // to the set of defs for loads and stores, with associated DFS info.
3322 void NewGVN::convertClassToLoadsAndStores(
3323 const CongruenceClass &Dense,
3324 SmallVectorImpl<ValueDFS> &LoadsAndStores) const {
3325 for (auto D : Dense) {
3326 if (!isa<LoadInst>(D) && !isa<StoreInst>(D))
3329 BasicBlock *BB = getBlockForValue(D);
3331 DomTreeNode *DomNode = DT->getNode(BB);
3332 VD.DFSIn = DomNode->getDFSNumIn();
3333 VD.DFSOut = DomNode->getDFSNumOut();
3334 VD.Def.setPointer(D);
3336 // If it's an instruction, use the real local dfs number.
3337 if (auto *I = dyn_cast<Instruction>(D))
3338 VD.LocalNum = InstrToDFSNum(I);
3340 llvm_unreachable("Should have been an instruction");
3342 LoadsAndStores.emplace_back(VD);
3346 static void patchReplacementInstruction(Instruction *I, Value *Repl) {
3347 auto *ReplInst = dyn_cast<Instruction>(Repl);
3351 // Patch the replacement so that it is not more restrictive than the value
3353 // Note that if 'I' is a load being replaced by some operation,
3354 // for example, by an arithmetic operation, then andIRFlags()
3355 // would just erase all math flags from the original arithmetic
3356 // operation, which is clearly not wanted and not needed.
3357 if (!isa<LoadInst>(I))
3358 ReplInst->andIRFlags(I);
3360 // FIXME: If both the original and replacement value are part of the
3361 // same control-flow region (meaning that the execution of one
3362 // guarantees the execution of the other), then we can combine the
3363 // noalias scopes here and do better than the general conservative
3364 // answer used in combineMetadata().
3366 // In general, GVN unifies expressions over different control-flow
3367 // regions, and so we need a conservative combination of the noalias
3369 static const unsigned KnownIDs[] = {
3370 LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
3371 LLVMContext::MD_noalias, LLVMContext::MD_range,
3372 LLVMContext::MD_fpmath, LLVMContext::MD_invariant_load,
3373 LLVMContext::MD_invariant_group};
3374 combineMetadata(ReplInst, I, KnownIDs);
3377 static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) {
3378 patchReplacementInstruction(I, Repl);
3379 I->replaceAllUsesWith(Repl);
3382 void NewGVN::deleteInstructionsInBlock(BasicBlock *BB) {
3383 DEBUG(dbgs() << " BasicBlock Dead:" << *BB);
3384 ++NumGVNBlocksDeleted;
3386 // Delete the instructions backwards, as it has a reduced likelihood of having
3387 // to update as many def-use and use-def chains. Start after the terminator.
3388 auto StartPoint = BB->rbegin();
3390 // Note that we explicitly recalculate BB->rend() on each iteration,
3391 // as it may change when we remove the first instruction.
3392 for (BasicBlock::reverse_iterator I(StartPoint); I != BB->rend();) {
3393 Instruction &Inst = *I++;
3394 if (!Inst.use_empty())
3395 Inst.replaceAllUsesWith(UndefValue::get(Inst.getType()));
3396 if (isa<LandingPadInst>(Inst))
3399 Inst.eraseFromParent();
3400 ++NumGVNInstrDeleted;
3402 // Now insert something that simplifycfg will turn into an unreachable.
3403 Type *Int8Ty = Type::getInt8Ty(BB->getContext());
3404 new StoreInst(UndefValue::get(Int8Ty),
3405 Constant::getNullValue(Int8Ty->getPointerTo()),
3406 BB->getTerminator());
3409 void NewGVN::markInstructionForDeletion(Instruction *I) {
3410 DEBUG(dbgs() << "Marking " << *I << " for deletion\n");
3411 InstructionsToErase.insert(I);
3414 void NewGVN::replaceInstruction(Instruction *I, Value *V) {
3416 DEBUG(dbgs() << "Replacing " << *I << " with " << *V << "\n");
3417 patchAndReplaceAllUsesWith(I, V);
3418 // We save the actual erasing to avoid invalidating memory
3419 // dependencies until we are done with everything.
3420 markInstructionForDeletion(I);
3425 // This is a stack that contains both the value and dfs info of where
3426 // that value is valid.
3427 class ValueDFSStack {
3429 Value *back() const { return ValueStack.back(); }
3430 std::pair<int, int> dfs_back() const { return DFSStack.back(); }
3432 void push_back(Value *V, int DFSIn, int DFSOut) {
3433 ValueStack.emplace_back(V);
3434 DFSStack.emplace_back(DFSIn, DFSOut);
3436 bool empty() const { return DFSStack.empty(); }
3437 bool isInScope(int DFSIn, int DFSOut) const {
3440 return DFSIn >= DFSStack.back().first && DFSOut <= DFSStack.back().second;
3443 void popUntilDFSScope(int DFSIn, int DFSOut) {
3445 // These two should always be in sync at this point.
3446 assert(ValueStack.size() == DFSStack.size() &&
3447 "Mismatch between ValueStack and DFSStack");
3449 !DFSStack.empty() &&
3450 !(DFSIn >= DFSStack.back().first && DFSOut <= DFSStack.back().second)) {
3451 DFSStack.pop_back();
3452 ValueStack.pop_back();
3457 SmallVector<Value *, 8> ValueStack;
3458 SmallVector<std::pair<int, int>, 8> DFSStack;
3462 // Given a value and a basic block we are trying to see if it is available in,
3463 // see if the value has a leader available in that block.
3464 Value *NewGVN::findPhiOfOpsLeader(const Expression *E,
3465 const BasicBlock *BB) const {
3466 // It would already be constant if we could make it constant
3467 if (auto *CE = dyn_cast<ConstantExpression>(E))
3468 return CE->getConstantValue();
3469 if (auto *VE = dyn_cast<VariableExpression>(E))
3470 return VE->getVariableValue();
3472 auto *CC = ExpressionToClass.lookup(E);
3475 if (alwaysAvailable(CC->getLeader()))
3476 return CC->getLeader();
3478 for (auto Member : *CC) {
3479 auto *MemberInst = dyn_cast<Instruction>(Member);
3480 // Anything that isn't an instruction is always available.
3483 // If we are looking for something in the same block as the member, it must
3484 // be a leader because this function is looking for operands for a phi node.
3485 if (MemberInst->getParent() == BB ||
3486 DT->dominates(MemberInst->getParent(), BB)) {
3493 bool NewGVN::eliminateInstructions(Function &F) {
3494 // This is a non-standard eliminator. The normal way to eliminate is
3495 // to walk the dominator tree in order, keeping track of available
3496 // values, and eliminating them. However, this is mildly
3497 // pointless. It requires doing lookups on every instruction,
3498 // regardless of whether we will ever eliminate it. For
3499 // instructions part of most singleton congruence classes, we know we
3500 // will never eliminate them.
3502 // Instead, this eliminator looks at the congruence classes directly, sorts
3503 // them into a DFS ordering of the dominator tree, and then we just
3504 // perform elimination straight on the sets by walking the congruence
3505 // class member uses in order, and eliminate the ones dominated by the
3506 // last member. This is worst case O(E log E) where E = number of
3507 // instructions in a single congruence class. In theory, this is all
3508 // instructions. In practice, it is much faster, as most instructions are
3509 // either in singleton congruence classes or can't possibly be eliminated
3510 // anyway (if there are no overlapping DFS ranges in class).
3511 // When we find something not dominated, it becomes the new leader
3512 // for elimination purposes.
3513 // TODO: If we wanted to be faster, We could remove any members with no
3514 // overlapping ranges while sorting, as we will never eliminate anything
3515 // with those members, as they don't dominate anything else in our set.
3517 bool AnythingReplaced = false;
3519 // Since we are going to walk the domtree anyway, and we can't guarantee the
3520 // DFS numbers are updated, we compute some ourselves.
3521 DT->updateDFSNumbers();
3523 // Go through all of our phi nodes, and kill the arguments associated with
3524 // unreachable edges.
3525 auto ReplaceUnreachablePHIArgs = [&](PHINode &PHI, BasicBlock *BB) {
3526 for (auto &Operand : PHI.incoming_values())
3527 if (!ReachableEdges.count({PHI.getIncomingBlock(Operand), BB})) {
3528 DEBUG(dbgs() << "Replacing incoming value of " << PHI << " for block "
3529 << getBlockName(PHI.getIncomingBlock(Operand))
3530 << " with undef due to it being unreachable\n");
3531 Operand.set(UndefValue::get(PHI.getType()));
3534 SmallPtrSet<BasicBlock *, 8> BlocksWithPhis;
3536 if ((!B.empty() && isa<PHINode>(*B.begin())) ||
3537 (PHIOfOpsPHIs.find(&B) != PHIOfOpsPHIs.end()))
3538 BlocksWithPhis.insert(&B);
3539 DenseMap<const BasicBlock *, unsigned> ReachablePredCount;
3540 for (auto KV : ReachableEdges)
3541 ReachablePredCount[KV.getEnd()]++;
3542 for (auto *BB : BlocksWithPhis)
3543 // TODO: It would be faster to use getNumIncomingBlocks() on a phi node in
3544 // the block and subtract the pred count, but it's more complicated.
3545 if (ReachablePredCount.lookup(BB) !=
3546 std::distance(pred_begin(BB), pred_end(BB))) {
3547 for (auto II = BB->begin(); isa<PHINode>(II); ++II) {
3548 auto &PHI = cast<PHINode>(*II);
3549 ReplaceUnreachablePHIArgs(PHI, BB);
3551 for_each_found(PHIOfOpsPHIs, BB, [&](PHINode *PHI) {
3552 ReplaceUnreachablePHIArgs(*PHI, BB);
3556 // Map to store the use counts
3557 DenseMap<const Value *, unsigned int> UseCounts;
3558 for (auto *CC : reverse(CongruenceClasses)) {
3559 // Track the equivalent store info so we can decide whether to try
3560 // dead store elimination.
3561 SmallVector<ValueDFS, 8> PossibleDeadStores;
3562 SmallPtrSet<Instruction *, 8> ProbablyDead;
3563 if (CC->isDead() || CC->empty())
3565 // Everything still in the TOP class is unreachable or dead.
3566 if (CC == TOPClass) {
3567 for (auto M : *CC) {
3568 auto *VTE = ValueToExpression.lookup(M);
3569 if (VTE && isa<DeadExpression>(VTE))
3570 markInstructionForDeletion(cast<Instruction>(M));
3571 assert((!ReachableBlocks.count(cast<Instruction>(M)->getParent()) ||
3572 InstructionsToErase.count(cast<Instruction>(M))) &&
3573 "Everything in TOP should be unreachable or dead at this "
3579 assert(CC->getLeader() && "We should have had a leader");
3580 // If this is a leader that is always available, and it's a
3581 // constant or has no equivalences, just replace everything with
3582 // it. We then update the congruence class with whatever members
3585 CC->getStoredValue() ? CC->getStoredValue() : CC->getLeader();
3586 if (alwaysAvailable(Leader)) {
3587 CongruenceClass::MemberSet MembersLeft;
3588 for (auto M : *CC) {
3590 // Void things have no uses we can replace.
3591 if (Member == Leader || !isa<Instruction>(Member) ||
3592 Member->getType()->isVoidTy()) {
3593 MembersLeft.insert(Member);
3596 DEBUG(dbgs() << "Found replacement " << *(Leader) << " for " << *Member
3598 auto *I = cast<Instruction>(Member);
3599 assert(Leader != I && "About to accidentally remove our leader");
3600 replaceInstruction(I, Leader);
3601 AnythingReplaced = true;
3603 CC->swap(MembersLeft);
3605 DEBUG(dbgs() << "Eliminating in congruence class " << CC->getID()
3607 // If this is a singleton, we can skip it.
3608 if (CC->size() != 1 || RealToTemp.lookup(Leader)) {
3609 // This is a stack because equality replacement/etc may place
3610 // constants in the middle of the member list, and we want to use
3611 // those constant values in preference to the current leader, over
3612 // the scope of those constants.
3613 ValueDFSStack EliminationStack;
3615 // Convert the members to DFS ordered sets and then merge them.
3616 SmallVector<ValueDFS, 8> DFSOrderedSet;
3617 convertClassToDFSOrdered(*CC, DFSOrderedSet, UseCounts, ProbablyDead);
3619 // Sort the whole thing.
3620 std::sort(DFSOrderedSet.begin(), DFSOrderedSet.end());
3621 for (auto &VD : DFSOrderedSet) {
3622 int MemberDFSIn = VD.DFSIn;
3623 int MemberDFSOut = VD.DFSOut;
3624 Value *Def = VD.Def.getPointer();
3625 bool FromStore = VD.Def.getInt();
3627 // We ignore void things because we can't get a value from them.
3628 if (Def && Def->getType()->isVoidTy())
3630 auto *DefInst = dyn_cast_or_null<Instruction>(Def);
3631 if (DefInst && AllTempInstructions.count(DefInst)) {
3632 auto *PN = cast<PHINode>(DefInst);
3634 // If this is a value phi and that's the expression we used, insert
3635 // it into the program
3636 // remove from temp instruction list.
3637 AllTempInstructions.erase(PN);
3638 auto *DefBlock = getBlockForValue(Def);
3639 DEBUG(dbgs() << "Inserting fully real phi of ops" << *Def
3641 << getBlockName(getBlockForValue(Def)) << "\n");
3642 PN->insertBefore(&DefBlock->front());
3644 NumGVNPHIOfOpsEliminations++;
3647 if (EliminationStack.empty()) {
3648 DEBUG(dbgs() << "Elimination Stack is empty\n");
3650 DEBUG(dbgs() << "Elimination Stack Top DFS numbers are ("
3651 << EliminationStack.dfs_back().first << ","
3652 << EliminationStack.dfs_back().second << ")\n");
3655 DEBUG(dbgs() << "Current DFS numbers are (" << MemberDFSIn << ","
3656 << MemberDFSOut << ")\n");
3657 // First, we see if we are out of scope or empty. If so,
3658 // and there equivalences, we try to replace the top of
3659 // stack with equivalences (if it's on the stack, it must
3660 // not have been eliminated yet).
3661 // Then we synchronize to our current scope, by
3662 // popping until we are back within a DFS scope that
3663 // dominates the current member.
3664 // Then, what happens depends on a few factors
3665 // If the stack is now empty, we need to push
3666 // If we have a constant or a local equivalence we want to
3667 // start using, we also push.
3668 // Otherwise, we walk along, processing members who are
3669 // dominated by this scope, and eliminate them.
3670 bool ShouldPush = Def && EliminationStack.empty();
3672 !EliminationStack.isInScope(MemberDFSIn, MemberDFSOut);
3674 if (OutOfScope || ShouldPush) {
3675 // Sync to our current scope.
3676 EliminationStack.popUntilDFSScope(MemberDFSIn, MemberDFSOut);
3677 bool ShouldPush = Def && EliminationStack.empty();
3679 EliminationStack.push_back(Def, MemberDFSIn, MemberDFSOut);
3683 // Skip the Def's, we only want to eliminate on their uses. But mark
3684 // dominated defs as dead.
3686 // For anything in this case, what and how we value number
3687 // guarantees that any side-effets that would have occurred (ie
3688 // throwing, etc) can be proven to either still occur (because it's
3689 // dominated by something that has the same side-effects), or never
3690 // occur. Otherwise, we would not have been able to prove it value
3691 // equivalent to something else. For these things, we can just mark
3692 // it all dead. Note that this is different from the "ProbablyDead"
3693 // set, which may not be dominated by anything, and thus, are only
3694 // easy to prove dead if they are also side-effect free. Note that
3695 // because stores are put in terms of the stored value, we skip
3696 // stored values here. If the stored value is really dead, it will
3697 // still be marked for deletion when we process it in its own class.
3698 if (!EliminationStack.empty() && Def != EliminationStack.back() &&
3699 isa<Instruction>(Def) && !FromStore)
3700 markInstructionForDeletion(cast<Instruction>(Def));
3703 // At this point, we know it is a Use we are trying to possibly
3706 assert(isa<Instruction>(U->get()) &&
3707 "Current def should have been an instruction");
3708 assert(isa<Instruction>(U->getUser()) &&
3709 "Current user should have been an instruction");
3711 // If the thing we are replacing into is already marked to be dead,
3712 // this use is dead. Note that this is true regardless of whether
3713 // we have anything dominating the use or not. We do this here
3714 // because we are already walking all the uses anyway.
3715 Instruction *InstUse = cast<Instruction>(U->getUser());
3716 if (InstructionsToErase.count(InstUse)) {
3717 auto &UseCount = UseCounts[U->get()];
3718 if (--UseCount == 0) {
3719 ProbablyDead.insert(cast<Instruction>(U->get()));
3723 // If we get to this point, and the stack is empty we must have a use
3724 // with nothing we can use to eliminate this use, so just skip it.
3725 if (EliminationStack.empty())
3728 Value *DominatingLeader = EliminationStack.back();
3730 auto *II = dyn_cast<IntrinsicInst>(DominatingLeader);
3731 if (II && II->getIntrinsicID() == Intrinsic::ssa_copy)
3732 DominatingLeader = II->getOperand(0);
3734 // Don't replace our existing users with ourselves.
3735 if (U->get() == DominatingLeader)
3737 DEBUG(dbgs() << "Found replacement " << *DominatingLeader << " for "
3738 << *U->get() << " in " << *(U->getUser()) << "\n");
3740 // If we replaced something in an instruction, handle the patching of
3741 // metadata. Skip this if we are replacing predicateinfo with its
3742 // original operand, as we already know we can just drop it.
3743 auto *ReplacedInst = cast<Instruction>(U->get());
3744 auto *PI = PredInfo->getPredicateInfoFor(ReplacedInst);
3745 if (!PI || DominatingLeader != PI->OriginalOp)
3746 patchReplacementInstruction(ReplacedInst, DominatingLeader);
3747 U->set(DominatingLeader);
3748 // This is now a use of the dominating leader, which means if the
3749 // dominating leader was dead, it's now live!
3750 auto &LeaderUseCount = UseCounts[DominatingLeader];
3751 // It's about to be alive again.
3752 if (LeaderUseCount == 0 && isa<Instruction>(DominatingLeader))
3753 ProbablyDead.erase(cast<Instruction>(DominatingLeader));
3754 if (LeaderUseCount == 0 && II)
3755 ProbablyDead.insert(II);
3757 AnythingReplaced = true;
3762 // At this point, anything still in the ProbablyDead set is actually dead if
3763 // would be trivially dead.
3764 for (auto *I : ProbablyDead)
3765 if (wouldInstructionBeTriviallyDead(I))
3766 markInstructionForDeletion(I);
3768 // Cleanup the congruence class.
3769 CongruenceClass::MemberSet MembersLeft;
3770 for (auto *Member : *CC)
3771 if (!isa<Instruction>(Member) ||
3772 !InstructionsToErase.count(cast<Instruction>(Member)))
3773 MembersLeft.insert(Member);
3774 CC->swap(MembersLeft);
3776 // If we have possible dead stores to look at, try to eliminate them.
3777 if (CC->getStoreCount() > 0) {
3778 convertClassToLoadsAndStores(*CC, PossibleDeadStores);
3779 std::sort(PossibleDeadStores.begin(), PossibleDeadStores.end());
3780 ValueDFSStack EliminationStack;
3781 for (auto &VD : PossibleDeadStores) {
3782 int MemberDFSIn = VD.DFSIn;
3783 int MemberDFSOut = VD.DFSOut;
3784 Instruction *Member = cast<Instruction>(VD.Def.getPointer());
3785 if (EliminationStack.empty() ||
3786 !EliminationStack.isInScope(MemberDFSIn, MemberDFSOut)) {
3787 // Sync to our current scope.
3788 EliminationStack.popUntilDFSScope(MemberDFSIn, MemberDFSOut);
3789 if (EliminationStack.empty()) {
3790 EliminationStack.push_back(Member, MemberDFSIn, MemberDFSOut);
3794 // We already did load elimination, so nothing to do here.
3795 if (isa<LoadInst>(Member))
3797 assert(!EliminationStack.empty());
3798 Instruction *Leader = cast<Instruction>(EliminationStack.back());
3800 assert(DT->dominates(Leader->getParent(), Member->getParent()));
3801 // Member is dominater by Leader, and thus dead
3802 DEBUG(dbgs() << "Marking dead store " << *Member
3803 << " that is dominated by " << *Leader << "\n");
3804 markInstructionForDeletion(Member);
3810 return AnythingReplaced;
3813 // This function provides global ranking of operations so that we can place them
3814 // in a canonical order. Note that rank alone is not necessarily enough for a
3815 // complete ordering, as constants all have the same rank. However, generally,
3816 // we will simplify an operation with all constants so that it doesn't matter
3817 // what order they appear in.
3818 unsigned int NewGVN::getRank(const Value *V) const {
3819 // Prefer constants to undef to anything else
3820 // Undef is a constant, have to check it first.
3821 // Prefer smaller constants to constantexprs
3822 if (isa<ConstantExpr>(V))
3824 if (isa<UndefValue>(V))
3826 if (isa<Constant>(V))
3828 else if (auto *A = dyn_cast<Argument>(V))
3829 return 3 + A->getArgNo();
3831 // Need to shift the instruction DFS by number of arguments + 3 to account for
3832 // the constant and argument ranking above.
3833 unsigned Result = InstrToDFSNum(V);
3835 return 4 + NumFuncArgs + Result;
3836 // Unreachable or something else, just return a really large number.
3840 // This is a function that says whether two commutative operations should
3841 // have their order swapped when canonicalizing.
3842 bool NewGVN::shouldSwapOperands(const Value *A, const Value *B) const {
3843 // Because we only care about a total ordering, and don't rewrite expressions
3844 // in this order, we order by rank, which will give a strict weak ordering to
3845 // everything but constants, and then we order by pointer address.
3846 return std::make_pair(getRank(A), A) > std::make_pair(getRank(B), B);
3849 class NewGVNLegacyPass : public FunctionPass {
3851 static char ID; // Pass identification, replacement for typeid.
3852 NewGVNLegacyPass() : FunctionPass(ID) {
3853 initializeNewGVNLegacyPassPass(*PassRegistry::getPassRegistry());
3855 bool runOnFunction(Function &F) override;
3858 void getAnalysisUsage(AnalysisUsage &AU) const override {
3859 AU.addRequired<AssumptionCacheTracker>();
3860 AU.addRequired<DominatorTreeWrapperPass>();
3861 AU.addRequired<TargetLibraryInfoWrapperPass>();
3862 AU.addRequired<MemorySSAWrapperPass>();
3863 AU.addRequired<AAResultsWrapperPass>();
3864 AU.addPreserved<DominatorTreeWrapperPass>();
3865 AU.addPreserved<GlobalsAAWrapperPass>();
3869 bool NewGVNLegacyPass::runOnFunction(Function &F) {
3870 if (skipFunction(F))
3872 return NewGVN(F, &getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
3873 &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F),
3874 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
3875 &getAnalysis<AAResultsWrapperPass>().getAAResults(),
3876 &getAnalysis<MemorySSAWrapperPass>().getMSSA(),
3877 F.getParent()->getDataLayout())
3881 INITIALIZE_PASS_BEGIN(NewGVNLegacyPass, "newgvn", "Global Value Numbering",
3883 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
3884 INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
3885 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
3886 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
3887 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
3888 INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
3889 INITIALIZE_PASS_END(NewGVNLegacyPass, "newgvn", "Global Value Numbering", false,
3892 char NewGVNLegacyPass::ID = 0;
3894 // createGVNPass - The public interface to this file.
3895 FunctionPass *llvm::createNewGVNPass() { return new NewGVNLegacyPass(); }
3897 PreservedAnalyses NewGVNPass::run(Function &F, AnalysisManager<Function> &AM) {
3898 // Apparently the order in which we get these results matter for
3899 // the old GVN (see Chandler's comment in GVN.cpp). I'll keep
3900 // the same order here, just in case.
3901 auto &AC = AM.getResult<AssumptionAnalysis>(F);
3902 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
3903 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
3904 auto &AA = AM.getResult<AAManager>(F);
3905 auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
3907 NewGVN(F, &DT, &AC, &TLI, &AA, &MSSA, F.getParent()->getDataLayout())
3910 return PreservedAnalyses::all();
3911 PreservedAnalyses PA;
3912 PA.preserve<DominatorTreeAnalysis>();
3913 PA.preserve<GlobalsAA>();