1 //===- SparsePropagation.h - Sparse Conditional Property Propagation ------===//
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 an abstract sparse conditional propagation algorithm,
11 // modeled after SCCP, but with a customizable lattice function.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_ANALYSIS_SPARSEPROPAGATION_H
16 #define LLVM_ANALYSIS_SPARSEPROPAGATION_H
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/Support/Debug.h"
22 #define DEBUG_TYPE "sparseprop"
26 /// A template for translating between LLVM Values and LatticeKeys. Clients must
27 /// provide a specialization of LatticeKeyInfo for their LatticeKey type.
28 template <class LatticeKey> struct LatticeKeyInfo {
29 // static inline Value *getValueFromLatticeKey(LatticeKey Key);
30 // static inline LatticeKey getLatticeKeyFromValue(Value *V);
33 template <class LatticeKey, class LatticeVal,
34 class KeyInfo = LatticeKeyInfo<LatticeKey>>
37 /// AbstractLatticeFunction - This class is implemented by the dataflow instance
38 /// to specify what the lattice values are and how they handle merges etc. This
39 /// gives the client the power to compute lattice values from instructions,
40 /// constants, etc. The current requirement is that lattice values must be
41 /// copyable. At the moment, nothing tries to avoid copying. Additionally,
42 /// lattice keys must be able to be used as keys of a mapping data structure.
43 /// Internally, the generic solver currently uses a DenseMap to map lattice keys
44 /// to lattice values. If the lattice key is a non-standard type, a
45 /// specialization of DenseMapInfo must be provided.
46 template <class LatticeKey, class LatticeVal> class AbstractLatticeFunction {
48 LatticeVal UndefVal, OverdefinedVal, UntrackedVal;
51 AbstractLatticeFunction(LatticeVal undefVal, LatticeVal overdefinedVal,
52 LatticeVal untrackedVal) {
54 OverdefinedVal = overdefinedVal;
55 UntrackedVal = untrackedVal;
58 virtual ~AbstractLatticeFunction() = default;
60 LatticeVal getUndefVal() const { return UndefVal; }
61 LatticeVal getOverdefinedVal() const { return OverdefinedVal; }
62 LatticeVal getUntrackedVal() const { return UntrackedVal; }
64 /// IsUntrackedValue - If the specified LatticeKey is obviously uninteresting
65 /// to the analysis (i.e., it would always return UntrackedVal), this
66 /// function can return true to avoid pointless work.
67 virtual bool IsUntrackedValue(LatticeKey Key) { return false; }
69 /// ComputeLatticeVal - Compute and return a LatticeVal corresponding to the
71 virtual LatticeVal ComputeLatticeVal(LatticeKey Key) {
72 return getOverdefinedVal();
75 /// IsSpecialCasedPHI - Given a PHI node, determine whether this PHI node is
76 /// one that the we want to handle through ComputeInstructionState.
77 virtual bool IsSpecialCasedPHI(PHINode *PN) { return false; }
79 /// MergeValues - Compute and return the merge of the two specified lattice
80 /// values. Merging should only move one direction down the lattice to
81 /// guarantee convergence (toward overdefined).
82 virtual LatticeVal MergeValues(LatticeVal X, LatticeVal Y) {
83 return getOverdefinedVal(); // always safe, never useful.
86 /// ComputeInstructionState - Compute the LatticeKeys that change as a result
87 /// of executing instruction \p I. Their associated LatticeVals are store in
90 ComputeInstructionState(Instruction &I,
91 DenseMap<LatticeKey, LatticeVal> &ChangedValues,
92 SparseSolver<LatticeKey, LatticeVal> &SS) = 0;
94 /// PrintLatticeVal - Render the given LatticeVal to the specified stream.
95 virtual void PrintLatticeVal(LatticeVal LV, raw_ostream &OS);
97 /// PrintLatticeKey - Render the given LatticeKey to the specified stream.
98 virtual void PrintLatticeKey(LatticeKey Key, raw_ostream &OS);
100 /// GetValueFromLatticeVal - If the given LatticeVal is representable as an
101 /// LLVM value, return it; otherwise, return nullptr. If a type is given, the
102 /// returned value must have the same type. This function is used by the
103 /// generic solver in attempting to resolve branch and switch conditions.
104 virtual Value *GetValueFromLatticeVal(LatticeVal LV, Type *Ty = nullptr) {
109 /// SparseSolver - This class is a general purpose solver for Sparse Conditional
110 /// Propagation with a programmable lattice function.
111 template <class LatticeKey, class LatticeVal, class KeyInfo>
114 /// LatticeFunc - This is the object that knows the lattice and how to
115 /// compute transfer functions.
116 AbstractLatticeFunction<LatticeKey, LatticeVal> *LatticeFunc;
118 /// ValueState - Holds the LatticeVals associated with LatticeKeys.
119 DenseMap<LatticeKey, LatticeVal> ValueState;
121 /// BBExecutable - Holds the basic blocks that are executable.
122 SmallPtrSet<BasicBlock *, 16> BBExecutable;
124 /// ValueWorkList - Holds values that should be processed.
125 SmallVector<Value *, 64> ValueWorkList;
127 /// BBWorkList - Holds basic blocks that should be processed.
128 SmallVector<BasicBlock *, 64> BBWorkList;
130 using Edge = std::pair<BasicBlock *, BasicBlock *>;
132 /// KnownFeasibleEdges - Entries in this set are edges which have already had
133 /// PHI nodes retriggered.
134 std::set<Edge> KnownFeasibleEdges;
137 explicit SparseSolver(
138 AbstractLatticeFunction<LatticeKey, LatticeVal> *Lattice)
139 : LatticeFunc(Lattice) {}
140 SparseSolver(const SparseSolver &) = delete;
141 SparseSolver &operator=(const SparseSolver &) = delete;
143 /// Solve - Solve for constants and executable blocks.
146 void Print(raw_ostream &OS) const;
148 /// getExistingValueState - Return the LatticeVal object corresponding to the
149 /// given value from the ValueState map. If the value is not in the map,
150 /// UntrackedVal is returned, unlike the getValueState method.
151 LatticeVal getExistingValueState(LatticeKey Key) const {
152 auto I = ValueState.find(Key);
153 return I != ValueState.end() ? I->second : LatticeFunc->getUntrackedVal();
156 /// getValueState - Return the LatticeVal object corresponding to the given
157 /// value from the ValueState map. If the value is not in the map, its state
159 LatticeVal getValueState(LatticeKey Key);
161 /// isEdgeFeasible - Return true if the control flow edge from the 'From'
162 /// basic block to the 'To' basic block is currently feasible. If
163 /// AggressiveUndef is true, then this treats values with unknown lattice
164 /// values as undefined. This is generally only useful when solving the
165 /// lattice, not when querying it.
166 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To,
167 bool AggressiveUndef = false);
169 /// isBlockExecutable - Return true if there are any known feasible
170 /// edges into the basic block. This is generally only useful when
171 /// querying the lattice.
172 bool isBlockExecutable(BasicBlock *BB) const {
173 return BBExecutable.count(BB);
176 /// MarkBlockExecutable - This method can be used by clients to mark all of
177 /// the blocks that are known to be intrinsically live in the processed unit.
178 void MarkBlockExecutable(BasicBlock *BB);
181 /// UpdateState - When the state of some LatticeKey is potentially updated to
182 /// the given LatticeVal, this function notices and adds the LLVM value
183 /// corresponding the key to the work list, if needed.
184 void UpdateState(LatticeKey Key, LatticeVal LV);
186 /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
187 /// work list if it is not already executable.
188 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest);
190 /// getFeasibleSuccessors - Return a vector of booleans to indicate which
191 /// successors are reachable from a given terminator instruction.
192 void getFeasibleSuccessors(TerminatorInst &TI, SmallVectorImpl<bool> &Succs,
193 bool AggressiveUndef);
195 void visitInst(Instruction &I);
196 void visitPHINode(PHINode &I);
197 void visitTerminatorInst(TerminatorInst &TI);
200 //===----------------------------------------------------------------------===//
201 // AbstractLatticeFunction Implementation
202 //===----------------------------------------------------------------------===//
204 template <class LatticeKey, class LatticeVal>
205 void AbstractLatticeFunction<LatticeKey, LatticeVal>::PrintLatticeVal(
206 LatticeVal V, raw_ostream &OS) {
209 else if (V == OverdefinedVal)
211 else if (V == UntrackedVal)
214 OS << "unknown lattice value";
217 template <class LatticeKey, class LatticeVal>
218 void AbstractLatticeFunction<LatticeKey, LatticeVal>::PrintLatticeKey(
219 LatticeKey Key, raw_ostream &OS) {
220 OS << "unknown lattice key";
223 //===----------------------------------------------------------------------===//
224 // SparseSolver Implementation
225 //===----------------------------------------------------------------------===//
227 template <class LatticeKey, class LatticeVal, class KeyInfo>
229 SparseSolver<LatticeKey, LatticeVal, KeyInfo>::getValueState(LatticeKey Key) {
230 auto I = ValueState.find(Key);
231 if (I != ValueState.end())
232 return I->second; // Common case, in the map
234 if (LatticeFunc->IsUntrackedValue(Key))
235 return LatticeFunc->getUntrackedVal();
236 LatticeVal LV = LatticeFunc->ComputeLatticeVal(Key);
238 // If this value is untracked, don't add it to the map.
239 if (LV == LatticeFunc->getUntrackedVal())
241 return ValueState[Key] = LV;
244 template <class LatticeKey, class LatticeVal, class KeyInfo>
245 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::UpdateState(LatticeKey Key,
247 auto I = ValueState.find(Key);
248 if (I != ValueState.end() && I->second == LV)
249 return; // No change.
251 // Update the state of the given LatticeKey and add its corresponding LLVM
252 // value to the work list.
253 ValueState[Key] = LV;
254 if (Value *V = KeyInfo::getValueFromLatticeKey(Key))
255 ValueWorkList.push_back(V);
258 template <class LatticeKey, class LatticeVal, class KeyInfo>
259 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::MarkBlockExecutable(
261 if (!BBExecutable.insert(BB).second)
263 DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n");
264 BBWorkList.push_back(BB); // Add the block to the work list!
267 template <class LatticeKey, class LatticeVal, class KeyInfo>
268 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::markEdgeExecutable(
269 BasicBlock *Source, BasicBlock *Dest) {
270 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
271 return; // This edge is already known to be executable!
273 DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName() << " -> "
274 << Dest->getName() << "\n");
276 if (BBExecutable.count(Dest)) {
277 // The destination is already executable, but we just made an edge
278 // feasible that wasn't before. Revisit the PHI nodes in the block
279 // because they have potentially new operands.
280 for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
281 visitPHINode(*cast<PHINode>(I));
283 MarkBlockExecutable(Dest);
287 template <class LatticeKey, class LatticeVal, class KeyInfo>
288 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::getFeasibleSuccessors(
289 TerminatorInst &TI, SmallVectorImpl<bool> &Succs, bool AggressiveUndef) {
290 Succs.resize(TI.getNumSuccessors());
291 if (TI.getNumSuccessors() == 0)
294 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
295 if (BI->isUnconditional()) {
303 getValueState(KeyInfo::getLatticeKeyFromValue(BI->getCondition()));
305 BCValue = getExistingValueState(
306 KeyInfo::getLatticeKeyFromValue(BI->getCondition()));
308 if (BCValue == LatticeFunc->getOverdefinedVal() ||
309 BCValue == LatticeFunc->getUntrackedVal()) {
310 // Overdefined condition variables can branch either way.
311 Succs[0] = Succs[1] = true;
315 // If undefined, neither is feasible yet.
316 if (BCValue == LatticeFunc->getUndefVal())
320 dyn_cast_or_null<Constant>(LatticeFunc->GetValueFromLatticeVal(
321 BCValue, BI->getCondition()->getType()));
322 if (!C || !isa<ConstantInt>(C)) {
323 // Non-constant values can go either way.
324 Succs[0] = Succs[1] = true;
328 // Constant condition variables mean the branch can only go a single way
329 Succs[C->isNullValue()] = true;
333 if (TI.isExceptional()) {
334 Succs.assign(Succs.size(), true);
338 if (isa<IndirectBrInst>(TI)) {
339 Succs.assign(Succs.size(), true);
343 SwitchInst &SI = cast<SwitchInst>(TI);
346 SCValue = getValueState(KeyInfo::getLatticeKeyFromValue(SI.getCondition()));
348 SCValue = getExistingValueState(
349 KeyInfo::getLatticeKeyFromValue(SI.getCondition()));
351 if (SCValue == LatticeFunc->getOverdefinedVal() ||
352 SCValue == LatticeFunc->getUntrackedVal()) {
353 // All destinations are executable!
354 Succs.assign(TI.getNumSuccessors(), true);
358 // If undefined, neither is feasible yet.
359 if (SCValue == LatticeFunc->getUndefVal())
362 Constant *C = dyn_cast_or_null<Constant>(LatticeFunc->GetValueFromLatticeVal(
363 SCValue, SI.getCondition()->getType()));
364 if (!C || !isa<ConstantInt>(C)) {
365 // All destinations are executable!
366 Succs.assign(TI.getNumSuccessors(), true);
369 SwitchInst::CaseHandle Case = *SI.findCaseValue(cast<ConstantInt>(C));
370 Succs[Case.getSuccessorIndex()] = true;
373 template <class LatticeKey, class LatticeVal, class KeyInfo>
374 bool SparseSolver<LatticeKey, LatticeVal, KeyInfo>::isEdgeFeasible(
375 BasicBlock *From, BasicBlock *To, bool AggressiveUndef) {
376 SmallVector<bool, 16> SuccFeasible;
377 TerminatorInst *TI = From->getTerminator();
378 getFeasibleSuccessors(*TI, SuccFeasible, AggressiveUndef);
380 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
381 if (TI->getSuccessor(i) == To && SuccFeasible[i])
387 template <class LatticeKey, class LatticeVal, class KeyInfo>
388 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitTerminatorInst(
389 TerminatorInst &TI) {
390 SmallVector<bool, 16> SuccFeasible;
391 getFeasibleSuccessors(TI, SuccFeasible, true);
393 BasicBlock *BB = TI.getParent();
395 // Mark all feasible successors executable...
396 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
398 markEdgeExecutable(BB, TI.getSuccessor(i));
401 template <class LatticeKey, class LatticeVal, class KeyInfo>
402 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitPHINode(PHINode &PN) {
403 // The lattice function may store more information on a PHINode than could be
404 // computed from its incoming values. For example, SSI form stores its sigma
405 // functions as PHINodes with a single incoming value.
406 if (LatticeFunc->IsSpecialCasedPHI(&PN)) {
407 DenseMap<LatticeKey, LatticeVal> ChangedValues;
408 LatticeFunc->ComputeInstructionState(PN, ChangedValues, *this);
409 for (auto &ChangedValue : ChangedValues)
410 if (ChangedValue.second != LatticeFunc->getUntrackedVal())
411 UpdateState(ChangedValue.first, ChangedValue.second);
415 LatticeKey Key = KeyInfo::getLatticeKeyFromValue(&PN);
416 LatticeVal PNIV = getValueState(Key);
417 LatticeVal Overdefined = LatticeFunc->getOverdefinedVal();
419 // If this value is already overdefined (common) just return.
420 if (PNIV == Overdefined || PNIV == LatticeFunc->getUntrackedVal())
421 return; // Quick exit
423 // Super-extra-high-degree PHI nodes are unlikely to ever be interesting,
424 // and slow us down a lot. Just mark them overdefined.
425 if (PN.getNumIncomingValues() > 64) {
426 UpdateState(Key, Overdefined);
430 // Look at all of the executable operands of the PHI node. If any of them
431 // are overdefined, the PHI becomes overdefined as well. Otherwise, ask the
432 // transfer function to give us the merge of the incoming values.
433 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
434 // If the edge is not yet known to be feasible, it doesn't impact the PHI.
435 if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent(), true))
438 // Merge in this value.
440 getValueState(KeyInfo::getLatticeKeyFromValue(PN.getIncomingValue(i)));
442 PNIV = LatticeFunc->MergeValues(PNIV, OpVal);
444 if (PNIV == Overdefined)
445 break; // Rest of input values don't matter.
448 // Update the PHI with the compute value, which is the merge of the inputs.
449 UpdateState(Key, PNIV);
452 template <class LatticeKey, class LatticeVal, class KeyInfo>
453 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitInst(Instruction &I) {
454 // PHIs are handled by the propagation logic, they are never passed into the
455 // transfer functions.
456 if (PHINode *PN = dyn_cast<PHINode>(&I))
457 return visitPHINode(*PN);
459 // Otherwise, ask the transfer function what the result is. If this is
460 // something that we care about, remember it.
461 DenseMap<LatticeKey, LatticeVal> ChangedValues;
462 LatticeFunc->ComputeInstructionState(I, ChangedValues, *this);
463 for (auto &ChangedValue : ChangedValues)
464 if (ChangedValue.second != LatticeFunc->getUntrackedVal())
465 UpdateState(ChangedValue.first, ChangedValue.second);
467 if (TerminatorInst *TI = dyn_cast<TerminatorInst>(&I))
468 visitTerminatorInst(*TI);
471 template <class LatticeKey, class LatticeVal, class KeyInfo>
472 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::Solve() {
473 // Process the work lists until they are empty!
474 while (!BBWorkList.empty() || !ValueWorkList.empty()) {
475 // Process the value work list.
476 while (!ValueWorkList.empty()) {
477 Value *V = ValueWorkList.back();
478 ValueWorkList.pop_back();
480 DEBUG(dbgs() << "\nPopped off V-WL: " << *V << "\n");
482 // "V" got into the work list because it made a transition. See if any
483 // users are both live and in need of updating.
484 for (User *U : V->users())
485 if (Instruction *Inst = dyn_cast<Instruction>(U))
486 if (BBExecutable.count(Inst->getParent())) // Inst is executable?
490 // Process the basic block work list.
491 while (!BBWorkList.empty()) {
492 BasicBlock *BB = BBWorkList.back();
493 BBWorkList.pop_back();
495 DEBUG(dbgs() << "\nPopped off BBWL: " << *BB);
497 // Notify all instructions in this basic block that they are newly
499 for (Instruction &I : *BB)
505 template <class LatticeKey, class LatticeVal, class KeyInfo>
506 void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::Print(
507 raw_ostream &OS) const {
508 if (ValueState.empty())
514 OS << "ValueState:\n";
515 for (auto &Entry : ValueState) {
516 std::tie(Key, LV) = Entry;
517 if (LV == LatticeFunc->getUntrackedVal())
520 LatticeFunc->PrintLatticeVal(LV, OS);
522 LatticeFunc->PrintLatticeKey(Key, OS);
526 } // end namespace llvm
530 #endif // LLVM_ANALYSIS_SPARSEPROPAGATION_H