1 //===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
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 pass performs global value numbering to eliminate fully redundant
11 // instructions. It also performs simple dead load elimination.
13 // Note that this pass does the value numbering itself; it does not use the
14 // ValueNumbering analysis passes.
16 //===----------------------------------------------------------------------===//
18 #define DEBUG_TYPE "gvn"
19 #include "llvm/Transforms/Scalar.h"
20 #include "llvm/BasicBlock.h"
21 #include "llvm/Constants.h"
22 #include "llvm/DerivedTypes.h"
23 #include "llvm/Function.h"
24 #include "llvm/IntrinsicInst.h"
25 #include "llvm/LLVMContext.h"
26 #include "llvm/Value.h"
27 #include "llvm/ADT/DenseMap.h"
28 #include "llvm/ADT/DepthFirstIterator.h"
29 #include "llvm/ADT/PostOrderIterator.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/SmallVector.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Analysis/Dominators.h"
34 #include "llvm/Analysis/AliasAnalysis.h"
35 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
36 #include "llvm/Support/CFG.h"
37 #include "llvm/Support/CommandLine.h"
38 #include "llvm/Support/Compiler.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/ErrorHandling.h"
41 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
42 #include "llvm/Transforms/Utils/Local.h"
46 STATISTIC(NumGVNInstr, "Number of instructions deleted");
47 STATISTIC(NumGVNLoad, "Number of loads deleted");
48 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
49 STATISTIC(NumGVNBlocks, "Number of blocks merged");
50 STATISTIC(NumPRELoad, "Number of loads PRE'd");
52 static cl::opt<bool> EnablePRE("enable-pre",
53 cl::init(true), cl::Hidden);
54 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
56 //===----------------------------------------------------------------------===//
58 //===----------------------------------------------------------------------===//
60 /// This class holds the mapping between values and value numbers. It is used
61 /// as an efficient mechanism to determine the expression-wise equivalence of
64 struct VISIBILITY_HIDDEN Expression {
65 enum ExpressionOpcode { ADD, FADD, SUB, FSUB, MUL, FMUL,
66 UDIV, SDIV, FDIV, UREM, SREM,
67 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
68 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
69 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
70 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
71 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
72 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
73 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
74 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
75 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
78 ExpressionOpcode opcode;
83 SmallVector<uint32_t, 4> varargs;
87 Expression(ExpressionOpcode o) : opcode(o) { }
89 bool operator==(const Expression &other) const {
90 if (opcode != other.opcode)
92 else if (opcode == EMPTY || opcode == TOMBSTONE)
94 else if (type != other.type)
96 else if (function != other.function)
98 else if (firstVN != other.firstVN)
100 else if (secondVN != other.secondVN)
102 else if (thirdVN != other.thirdVN)
105 if (varargs.size() != other.varargs.size())
108 for (size_t i = 0; i < varargs.size(); ++i)
109 if (varargs[i] != other.varargs[i])
116 bool operator!=(const Expression &other) const {
117 return !(*this == other);
121 class VISIBILITY_HIDDEN ValueTable {
123 DenseMap<Value*, uint32_t> valueNumbering;
124 DenseMap<Expression, uint32_t> expressionNumbering;
126 MemoryDependenceAnalysis* MD;
129 uint32_t nextValueNumber;
131 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
132 Expression::ExpressionOpcode getOpcode(CmpInst* C);
133 Expression::ExpressionOpcode getOpcode(CastInst* C);
134 Expression create_expression(BinaryOperator* BO);
135 Expression create_expression(CmpInst* C);
136 Expression create_expression(ShuffleVectorInst* V);
137 Expression create_expression(ExtractElementInst* C);
138 Expression create_expression(InsertElementInst* V);
139 Expression create_expression(SelectInst* V);
140 Expression create_expression(CastInst* C);
141 Expression create_expression(GetElementPtrInst* G);
142 Expression create_expression(CallInst* C);
143 Expression create_expression(Constant* C);
145 ValueTable() : nextValueNumber(1) { }
146 uint32_t lookup_or_add(Value* V);
147 uint32_t lookup(Value* V) const;
148 void add(Value* V, uint32_t num);
150 void erase(Value* v);
152 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
153 AliasAnalysis *getAliasAnalysis() const { return AA; }
154 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
155 void setDomTree(DominatorTree* D) { DT = D; }
156 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
157 void verifyRemoved(const Value *) const;
162 template <> struct DenseMapInfo<Expression> {
163 static inline Expression getEmptyKey() {
164 return Expression(Expression::EMPTY);
167 static inline Expression getTombstoneKey() {
168 return Expression(Expression::TOMBSTONE);
171 static unsigned getHashValue(const Expression e) {
172 unsigned hash = e.opcode;
174 hash = e.firstVN + hash * 37;
175 hash = e.secondVN + hash * 37;
176 hash = e.thirdVN + hash * 37;
178 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
179 (unsigned)((uintptr_t)e.type >> 9)) +
182 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
183 E = e.varargs.end(); I != E; ++I)
184 hash = *I + hash * 37;
186 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
187 (unsigned)((uintptr_t)e.function >> 9)) +
192 static bool isEqual(const Expression &LHS, const Expression &RHS) {
195 static bool isPod() { return true; }
199 //===----------------------------------------------------------------------===//
200 // ValueTable Internal Functions
201 //===----------------------------------------------------------------------===//
202 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
203 switch(BO->getOpcode()) {
204 default: // THIS SHOULD NEVER HAPPEN
205 llvm_unreachable("Binary operator with unknown opcode?");
206 case Instruction::Add: return Expression::ADD;
207 case Instruction::FAdd: return Expression::FADD;
208 case Instruction::Sub: return Expression::SUB;
209 case Instruction::FSub: return Expression::FSUB;
210 case Instruction::Mul: return Expression::MUL;
211 case Instruction::FMul: return Expression::FMUL;
212 case Instruction::UDiv: return Expression::UDIV;
213 case Instruction::SDiv: return Expression::SDIV;
214 case Instruction::FDiv: return Expression::FDIV;
215 case Instruction::URem: return Expression::UREM;
216 case Instruction::SRem: return Expression::SREM;
217 case Instruction::FRem: return Expression::FREM;
218 case Instruction::Shl: return Expression::SHL;
219 case Instruction::LShr: return Expression::LSHR;
220 case Instruction::AShr: return Expression::ASHR;
221 case Instruction::And: return Expression::AND;
222 case Instruction::Or: return Expression::OR;
223 case Instruction::Xor: return Expression::XOR;
227 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
228 if (isa<ICmpInst>(C)) {
229 switch (C->getPredicate()) {
230 default: // THIS SHOULD NEVER HAPPEN
231 llvm_unreachable("Comparison with unknown predicate?");
232 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
233 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
234 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
235 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
236 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
237 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
238 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
239 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
240 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
241 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
244 switch (C->getPredicate()) {
245 default: // THIS SHOULD NEVER HAPPEN
246 llvm_unreachable("Comparison with unknown predicate?");
247 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
248 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
249 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
250 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
251 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
252 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
253 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
254 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
255 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
256 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
257 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
258 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
259 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
260 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
265 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
266 switch(C->getOpcode()) {
267 default: // THIS SHOULD NEVER HAPPEN
268 llvm_unreachable("Cast operator with unknown opcode?");
269 case Instruction::Trunc: return Expression::TRUNC;
270 case Instruction::ZExt: return Expression::ZEXT;
271 case Instruction::SExt: return Expression::SEXT;
272 case Instruction::FPToUI: return Expression::FPTOUI;
273 case Instruction::FPToSI: return Expression::FPTOSI;
274 case Instruction::UIToFP: return Expression::UITOFP;
275 case Instruction::SIToFP: return Expression::SITOFP;
276 case Instruction::FPTrunc: return Expression::FPTRUNC;
277 case Instruction::FPExt: return Expression::FPEXT;
278 case Instruction::PtrToInt: return Expression::PTRTOINT;
279 case Instruction::IntToPtr: return Expression::INTTOPTR;
280 case Instruction::BitCast: return Expression::BITCAST;
284 Expression ValueTable::create_expression(CallInst* C) {
287 e.type = C->getType();
291 e.function = C->getCalledFunction();
292 e.opcode = Expression::CALL;
294 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
296 e.varargs.push_back(lookup_or_add(*I));
301 Expression ValueTable::create_expression(BinaryOperator* BO) {
304 e.firstVN = lookup_or_add(BO->getOperand(0));
305 e.secondVN = lookup_or_add(BO->getOperand(1));
308 e.type = BO->getType();
309 e.opcode = getOpcode(BO);
314 Expression ValueTable::create_expression(CmpInst* C) {
317 e.firstVN = lookup_or_add(C->getOperand(0));
318 e.secondVN = lookup_or_add(C->getOperand(1));
321 e.type = C->getType();
322 e.opcode = getOpcode(C);
327 Expression ValueTable::create_expression(CastInst* C) {
330 e.firstVN = lookup_or_add(C->getOperand(0));
334 e.type = C->getType();
335 e.opcode = getOpcode(C);
340 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
343 e.firstVN = lookup_or_add(S->getOperand(0));
344 e.secondVN = lookup_or_add(S->getOperand(1));
345 e.thirdVN = lookup_or_add(S->getOperand(2));
347 e.type = S->getType();
348 e.opcode = Expression::SHUFFLE;
353 Expression ValueTable::create_expression(ExtractElementInst* E) {
356 e.firstVN = lookup_or_add(E->getOperand(0));
357 e.secondVN = lookup_or_add(E->getOperand(1));
360 e.type = E->getType();
361 e.opcode = Expression::EXTRACT;
366 Expression ValueTable::create_expression(InsertElementInst* I) {
369 e.firstVN = lookup_or_add(I->getOperand(0));
370 e.secondVN = lookup_or_add(I->getOperand(1));
371 e.thirdVN = lookup_or_add(I->getOperand(2));
373 e.type = I->getType();
374 e.opcode = Expression::INSERT;
379 Expression ValueTable::create_expression(SelectInst* I) {
382 e.firstVN = lookup_or_add(I->getCondition());
383 e.secondVN = lookup_or_add(I->getTrueValue());
384 e.thirdVN = lookup_or_add(I->getFalseValue());
386 e.type = I->getType();
387 e.opcode = Expression::SELECT;
392 Expression ValueTable::create_expression(GetElementPtrInst* G) {
395 e.firstVN = lookup_or_add(G->getPointerOperand());
399 e.type = G->getType();
400 e.opcode = Expression::GEP;
402 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
404 e.varargs.push_back(lookup_or_add(*I));
409 //===----------------------------------------------------------------------===//
410 // ValueTable External Functions
411 //===----------------------------------------------------------------------===//
413 /// add - Insert a value into the table with a specified value number.
414 void ValueTable::add(Value* V, uint32_t num) {
415 valueNumbering.insert(std::make_pair(V, num));
418 /// lookup_or_add - Returns the value number for the specified value, assigning
419 /// it a new number if it did not have one before.
420 uint32_t ValueTable::lookup_or_add(Value* V) {
421 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
422 if (VI != valueNumbering.end())
425 if (CallInst* C = dyn_cast<CallInst>(V)) {
426 if (AA->doesNotAccessMemory(C)) {
427 Expression e = create_expression(C);
429 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
430 if (EI != expressionNumbering.end()) {
431 valueNumbering.insert(std::make_pair(V, EI->second));
434 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
435 valueNumbering.insert(std::make_pair(V, nextValueNumber));
437 return nextValueNumber++;
439 } else if (AA->onlyReadsMemory(C)) {
440 Expression e = create_expression(C);
442 if (expressionNumbering.find(e) == expressionNumbering.end()) {
443 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
444 valueNumbering.insert(std::make_pair(V, nextValueNumber));
445 return nextValueNumber++;
448 MemDepResult local_dep = MD->getDependency(C);
450 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
451 valueNumbering.insert(std::make_pair(V, nextValueNumber));
452 return nextValueNumber++;
455 if (local_dep.isDef()) {
456 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
458 if (local_cdep->getNumOperands() != C->getNumOperands()) {
459 valueNumbering.insert(std::make_pair(V, nextValueNumber));
460 return nextValueNumber++;
463 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
464 uint32_t c_vn = lookup_or_add(C->getOperand(i));
465 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
467 valueNumbering.insert(std::make_pair(V, nextValueNumber));
468 return nextValueNumber++;
472 uint32_t v = lookup_or_add(local_cdep);
473 valueNumbering.insert(std::make_pair(V, v));
478 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
479 MD->getNonLocalCallDependency(CallSite(C));
480 // FIXME: call/call dependencies for readonly calls should return def, not
481 // clobber! Move the checking logic to MemDep!
484 // Check to see if we have a single dominating call instruction that is
486 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
487 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
488 // Ignore non-local dependencies.
489 if (I->second.isNonLocal())
492 // We don't handle non-depedencies. If we already have a call, reject
493 // instruction dependencies.
494 if (I->second.isClobber() || cdep != 0) {
499 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
500 // FIXME: All duplicated with non-local case.
501 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
502 cdep = NonLocalDepCall;
511 valueNumbering.insert(std::make_pair(V, nextValueNumber));
512 return nextValueNumber++;
515 if (cdep->getNumOperands() != C->getNumOperands()) {
516 valueNumbering.insert(std::make_pair(V, nextValueNumber));
517 return nextValueNumber++;
519 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
520 uint32_t c_vn = lookup_or_add(C->getOperand(i));
521 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
523 valueNumbering.insert(std::make_pair(V, nextValueNumber));
524 return nextValueNumber++;
528 uint32_t v = lookup_or_add(cdep);
529 valueNumbering.insert(std::make_pair(V, v));
533 valueNumbering.insert(std::make_pair(V, nextValueNumber));
534 return nextValueNumber++;
536 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
537 Expression e = create_expression(BO);
539 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
540 if (EI != expressionNumbering.end()) {
541 valueNumbering.insert(std::make_pair(V, EI->second));
544 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
545 valueNumbering.insert(std::make_pair(V, nextValueNumber));
547 return nextValueNumber++;
549 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
550 Expression e = create_expression(C);
552 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
553 if (EI != expressionNumbering.end()) {
554 valueNumbering.insert(std::make_pair(V, EI->second));
557 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
558 valueNumbering.insert(std::make_pair(V, nextValueNumber));
560 return nextValueNumber++;
562 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
563 Expression e = create_expression(U);
565 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
566 if (EI != expressionNumbering.end()) {
567 valueNumbering.insert(std::make_pair(V, EI->second));
570 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
571 valueNumbering.insert(std::make_pair(V, nextValueNumber));
573 return nextValueNumber++;
575 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
576 Expression e = create_expression(U);
578 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
579 if (EI != expressionNumbering.end()) {
580 valueNumbering.insert(std::make_pair(V, EI->second));
583 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
584 valueNumbering.insert(std::make_pair(V, nextValueNumber));
586 return nextValueNumber++;
588 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
589 Expression e = create_expression(U);
591 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
592 if (EI != expressionNumbering.end()) {
593 valueNumbering.insert(std::make_pair(V, EI->second));
596 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
597 valueNumbering.insert(std::make_pair(V, nextValueNumber));
599 return nextValueNumber++;
601 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
602 Expression e = create_expression(U);
604 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
605 if (EI != expressionNumbering.end()) {
606 valueNumbering.insert(std::make_pair(V, EI->second));
609 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
610 valueNumbering.insert(std::make_pair(V, nextValueNumber));
612 return nextValueNumber++;
614 } else if (CastInst* U = dyn_cast<CastInst>(V)) {
615 Expression e = create_expression(U);
617 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
618 if (EI != expressionNumbering.end()) {
619 valueNumbering.insert(std::make_pair(V, EI->second));
622 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
623 valueNumbering.insert(std::make_pair(V, nextValueNumber));
625 return nextValueNumber++;
627 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
628 Expression e = create_expression(U);
630 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
631 if (EI != expressionNumbering.end()) {
632 valueNumbering.insert(std::make_pair(V, EI->second));
635 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
636 valueNumbering.insert(std::make_pair(V, nextValueNumber));
638 return nextValueNumber++;
641 valueNumbering.insert(std::make_pair(V, nextValueNumber));
642 return nextValueNumber++;
646 /// lookup - Returns the value number of the specified value. Fails if
647 /// the value has not yet been numbered.
648 uint32_t ValueTable::lookup(Value* V) const {
649 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
650 assert(VI != valueNumbering.end() && "Value not numbered?");
654 /// clear - Remove all entries from the ValueTable
655 void ValueTable::clear() {
656 valueNumbering.clear();
657 expressionNumbering.clear();
661 /// erase - Remove a value from the value numbering
662 void ValueTable::erase(Value* V) {
663 valueNumbering.erase(V);
666 /// verifyRemoved - Verify that the value is removed from all internal data
668 void ValueTable::verifyRemoved(const Value *V) const {
669 for (DenseMap<Value*, uint32_t>::iterator
670 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
671 assert(I->first != V && "Inst still occurs in value numbering map!");
675 //===----------------------------------------------------------------------===//
677 //===----------------------------------------------------------------------===//
680 struct VISIBILITY_HIDDEN ValueNumberScope {
681 ValueNumberScope* parent;
682 DenseMap<uint32_t, Value*> table;
684 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
690 class VISIBILITY_HIDDEN GVN : public FunctionPass {
691 bool runOnFunction(Function &F);
693 static char ID; // Pass identification, replacement for typeid
694 GVN() : FunctionPass(&ID) { }
697 MemoryDependenceAnalysis *MD;
701 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
703 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
707 // This transformation requires dominator postdominator info
708 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
709 AU.addRequired<DominatorTree>();
710 AU.addRequired<MemoryDependenceAnalysis>();
711 AU.addRequired<AliasAnalysis>();
713 AU.addPreserved<DominatorTree>();
714 AU.addPreserved<AliasAnalysis>();
718 // FIXME: eliminate or document these better
719 bool processLoad(LoadInst* L,
720 SmallVectorImpl<Instruction*> &toErase);
721 bool processInstruction(Instruction* I,
722 SmallVectorImpl<Instruction*> &toErase);
723 bool processNonLocalLoad(LoadInst* L,
724 SmallVectorImpl<Instruction*> &toErase);
725 bool processBlock(BasicBlock* BB);
726 Value *GetValueForBlock(BasicBlock *BB, Instruction* orig,
727 DenseMap<BasicBlock*, Value*> &Phis,
728 bool top_level = false);
729 void dump(DenseMap<uint32_t, Value*>& d);
730 bool iterateOnFunction(Function &F);
731 Value* CollapsePhi(PHINode* p);
732 bool isSafeReplacement(PHINode* p, Instruction* inst);
733 bool performPRE(Function& F);
734 Value* lookupNumber(BasicBlock* BB, uint32_t num);
735 bool mergeBlockIntoPredecessor(BasicBlock* BB);
736 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno);
737 void cleanupGlobalSets();
738 void verifyRemoved(const Instruction *I) const;
744 // createGVNPass - The public interface to this file...
745 FunctionPass *llvm::createGVNPass() { return new GVN(); }
747 static RegisterPass<GVN> X("gvn",
748 "Global Value Numbering");
750 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
752 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
753 E = d.end(); I != E; ++I) {
754 printf("%d\n", I->first);
760 Value* GVN::CollapsePhi(PHINode* p) {
761 Value* constVal = p->hasConstantValue();
762 if (!constVal) return 0;
764 Instruction* inst = dyn_cast<Instruction>(constVal);
768 if (DT->dominates(inst, p))
769 if (isSafeReplacement(p, inst))
774 bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
775 if (!isa<PHINode>(inst))
778 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
780 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
781 if (use_phi->getParent() == inst->getParent())
787 /// GetValueForBlock - Get the value to use within the specified basic block.
788 /// available values are in Phis.
789 Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig,
790 DenseMap<BasicBlock*, Value*> &Phis,
793 // If we have already computed this value, return the previously computed val.
794 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
795 if (V != Phis.end() && !top_level) return V->second;
797 // If the block is unreachable, just return undef, since this path
798 // can't actually occur at runtime.
799 if (!DT->isReachableFromEntry(BB))
800 return Phis[BB] = Context->getUndef(orig->getType());
802 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
803 Value *ret = GetValueForBlock(Pred, orig, Phis);
808 // Get the number of predecessors of this block so we can reserve space later.
809 // If there is already a PHI in it, use the #preds from it, otherwise count.
810 // Getting it from the PHI is constant time.
812 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
813 NumPreds = ExistingPN->getNumIncomingValues();
815 NumPreds = std::distance(pred_begin(BB), pred_end(BB));
817 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
818 // now, then get values to fill in the incoming values for the PHI.
819 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
821 PN->reserveOperandSpace(NumPreds);
823 Phis.insert(std::make_pair(BB, PN));
825 // Fill in the incoming values for the block.
826 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
827 Value* val = GetValueForBlock(*PI, orig, Phis);
828 PN->addIncoming(val, *PI);
831 VN.getAliasAnalysis()->copyValue(orig, PN);
833 // Attempt to collapse PHI nodes that are trivially redundant
834 Value* v = CollapsePhi(PN);
836 // Cache our phi construction results
837 if (LoadInst* L = dyn_cast<LoadInst>(orig))
838 phiMap[L->getPointerOperand()].insert(PN);
840 phiMap[orig].insert(PN);
845 PN->replaceAllUsesWith(v);
846 if (isa<PointerType>(v->getType()))
847 MD->invalidateCachedPointerInfo(v);
849 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
850 E = Phis.end(); I != E; ++I)
854 DEBUG(cerr << "GVN removed: " << *PN);
855 MD->removeInstruction(PN);
856 PN->eraseFromParent();
857 DEBUG(verifyRemoved(PN));
863 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
864 /// we're analyzing is fully available in the specified block. As we go, keep
865 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
866 /// map is actually a tri-state map with the following values:
867 /// 0) we know the block *is not* fully available.
868 /// 1) we know the block *is* fully available.
869 /// 2) we do not know whether the block is fully available or not, but we are
870 /// currently speculating that it will be.
871 /// 3) we are speculating for this block and have used that to speculate for
873 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
874 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
875 // Optimistically assume that the block is fully available and check to see
876 // if we already know about this block in one lookup.
877 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
878 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
880 // If the entry already existed for this block, return the precomputed value.
882 // If this is a speculative "available" value, mark it as being used for
883 // speculation of other blocks.
884 if (IV.first->second == 2)
885 IV.first->second = 3;
886 return IV.first->second != 0;
889 // Otherwise, see if it is fully available in all predecessors.
890 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
892 // If this block has no predecessors, it isn't live-in here.
894 goto SpeculationFailure;
896 for (; PI != PE; ++PI)
897 // If the value isn't fully available in one of our predecessors, then it
898 // isn't fully available in this block either. Undo our previous
899 // optimistic assumption and bail out.
900 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
901 goto SpeculationFailure;
905 // SpeculationFailure - If we get here, we found out that this is not, after
906 // all, a fully-available block. We have a problem if we speculated on this and
907 // used the speculation to mark other blocks as available.
909 char &BBVal = FullyAvailableBlocks[BB];
911 // If we didn't speculate on this, just return with it set to false.
917 // If we did speculate on this value, we could have blocks set to 1 that are
918 // incorrect. Walk the (transitive) successors of this block and mark them as
920 SmallVector<BasicBlock*, 32> BBWorklist;
921 BBWorklist.push_back(BB);
923 while (!BBWorklist.empty()) {
924 BasicBlock *Entry = BBWorklist.pop_back_val();
925 // Note that this sets blocks to 0 (unavailable) if they happen to not
926 // already be in FullyAvailableBlocks. This is safe.
927 char &EntryVal = FullyAvailableBlocks[Entry];
928 if (EntryVal == 0) continue; // Already unavailable.
930 // Mark as unavailable.
933 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
934 BBWorklist.push_back(*I);
940 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
941 /// non-local by performing PHI construction.
942 bool GVN::processNonLocalLoad(LoadInst *LI,
943 SmallVectorImpl<Instruction*> &toErase) {
944 // Find the non-local dependencies of the load.
945 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
946 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
948 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
950 // If we had to process more than one hundred blocks to find the
951 // dependencies, this load isn't worth worrying about. Optimizing
952 // it will be too expensive.
953 if (Deps.size() > 100)
956 // If we had a phi translation failure, we'll have a single entry which is a
957 // clobber in the current block. Reject this early.
958 if (Deps.size() == 1 && Deps[0].second.isClobber()) {
960 DOUT << "GVN: non-local load ";
961 WriteAsOperand(*DOUT.stream(), LI);
962 DOUT << " is clobbered by " << *Deps[0].second.getInst();
967 // Filter out useless results (non-locals, etc). Keep track of the blocks
968 // where we have a value available in repl, also keep track of whether we see
969 // dependencies that produce an unknown value for the load (such as a call
970 // that could potentially clobber the load).
971 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
972 SmallVector<BasicBlock*, 16> UnavailableBlocks;
974 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
975 BasicBlock *DepBB = Deps[i].first;
976 MemDepResult DepInfo = Deps[i].second;
978 if (DepInfo.isClobber()) {
979 UnavailableBlocks.push_back(DepBB);
983 Instruction *DepInst = DepInfo.getInst();
985 // Loading the allocation -> undef.
986 if (isa<AllocationInst>(DepInst)) {
987 ValuesPerBlock.push_back(std::make_pair(DepBB,
988 Context->getUndef(LI->getType())));
992 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
993 // Reject loads and stores that are to the same address but are of
995 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
996 // of bitfield access, it would be interesting to optimize for it at some
998 if (S->getOperand(0)->getType() != LI->getType()) {
999 UnavailableBlocks.push_back(DepBB);
1003 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
1005 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
1006 if (LD->getType() != LI->getType()) {
1007 UnavailableBlocks.push_back(DepBB);
1010 ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
1012 UnavailableBlocks.push_back(DepBB);
1017 // If we have no predecessors that produce a known value for this load, exit
1019 if (ValuesPerBlock.empty()) return false;
1021 // If all of the instructions we depend on produce a known value for this
1022 // load, then it is fully redundant and we can use PHI insertion to compute
1023 // its value. Insert PHIs and remove the fully redundant value now.
1024 if (UnavailableBlocks.empty()) {
1025 // Use cached PHI construction information from previous runs
1026 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1027 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
1028 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1030 if ((*I)->getParent() == LI->getParent()) {
1031 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
1032 LI->replaceAllUsesWith(*I);
1033 if (isa<PointerType>((*I)->getType()))
1034 MD->invalidateCachedPointerInfo(*I);
1035 toErase.push_back(LI);
1040 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1043 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
1045 DenseMap<BasicBlock*, Value*> BlockReplValues;
1046 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1047 // Perform PHI construction.
1048 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1049 LI->replaceAllUsesWith(v);
1051 if (isa<PHINode>(v))
1053 if (isa<PointerType>(v->getType()))
1054 MD->invalidateCachedPointerInfo(v);
1055 toErase.push_back(LI);
1060 if (!EnablePRE || !EnableLoadPRE)
1063 // Okay, we have *some* definitions of the value. This means that the value
1064 // is available in some of our (transitive) predecessors. Lets think about
1065 // doing PRE of this load. This will involve inserting a new load into the
1066 // predecessor when it's not available. We could do this in general, but
1067 // prefer to not increase code size. As such, we only do this when we know
1068 // that we only have to insert *one* load (which means we're basically moving
1069 // the load, not inserting a new one).
1071 SmallPtrSet<BasicBlock *, 4> Blockers;
1072 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1073 Blockers.insert(UnavailableBlocks[i]);
1075 // Lets find first basic block with more than one predecessor. Walk backwards
1076 // through predecessors if needed.
1077 BasicBlock *LoadBB = LI->getParent();
1078 BasicBlock *TmpBB = LoadBB;
1080 bool isSinglePred = false;
1081 bool allSingleSucc = true;
1082 while (TmpBB->getSinglePredecessor()) {
1083 isSinglePred = true;
1084 TmpBB = TmpBB->getSinglePredecessor();
1085 if (!TmpBB) // If haven't found any, bail now.
1087 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1089 if (Blockers.count(TmpBB))
1091 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1092 allSingleSucc = false;
1098 // If we have a repl set with LI itself in it, this means we have a loop where
1099 // at least one of the values is LI. Since this means that we won't be able
1100 // to eliminate LI even if we insert uses in the other predecessors, we will
1101 // end up increasing code size. Reject this by scanning for LI.
1102 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1103 if (ValuesPerBlock[i].second == LI)
1108 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1109 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second))
1110 // "Hot" Instruction is in some loop (because it dominates its dep.
1112 if (DT->dominates(LI, I)) {
1117 // We are interested only in "hot" instructions. We don't want to do any
1118 // mis-optimizations here.
1123 // Okay, we have some hope :). Check to see if the loaded value is fully
1124 // available in all but one predecessor.
1125 // FIXME: If we could restructure the CFG, we could make a common pred with
1126 // all the preds that don't have an available LI and insert a new load into
1128 BasicBlock *UnavailablePred = 0;
1130 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1131 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1132 FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
1133 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1134 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1136 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1138 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1141 // If this load is not available in multiple predecessors, reject it.
1142 if (UnavailablePred && UnavailablePred != *PI)
1144 UnavailablePred = *PI;
1147 assert(UnavailablePred != 0 &&
1148 "Fully available value should be eliminated above!");
1150 // If the loaded pointer is PHI node defined in this block, do PHI translation
1151 // to get its value in the predecessor.
1152 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
1154 // Make sure the value is live in the predecessor. If it was defined by a
1155 // non-PHI instruction in this block, we don't know how to recompute it above.
1156 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
1157 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
1158 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
1159 << *LPInst << *LI << "\n");
1163 // We don't currently handle critical edges :(
1164 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1165 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1166 << UnavailablePred->getName() << "': " << *LI);
1170 // Make sure it is valid to move this load here. We have to watch out for:
1171 // @1 = getelementptr (i8* p, ...
1172 // test p and branch if == 0
1174 // It is valid to have the getelementptr before the test, even if p can be 0,
1175 // as getelementptr only does address arithmetic.
1176 // If we are not pushing the value through any multiple-successor blocks
1177 // we do not have this case. Otherwise, check that the load is safe to
1178 // put anywhere; this can be improved, but should be conservatively safe.
1179 if (!allSingleSucc &&
1180 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator()))
1183 // Okay, we can eliminate this load by inserting a reload in the predecessor
1184 // and using PHI construction to get the value in the other predecessors, do
1186 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
1188 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1190 UnavailablePred->getTerminator());
1192 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1193 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1195 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1197 DenseMap<BasicBlock*, Value*> BlockReplValues;
1198 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1199 BlockReplValues[UnavailablePred] = NewLoad;
1201 // Perform PHI construction.
1202 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1203 LI->replaceAllUsesWith(v);
1204 if (isa<PHINode>(v))
1206 if (isa<PointerType>(v->getType()))
1207 MD->invalidateCachedPointerInfo(v);
1208 toErase.push_back(LI);
1213 /// processLoad - Attempt to eliminate a load, first by eliminating it
1214 /// locally, and then attempting non-local elimination if that fails.
1215 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1216 if (L->isVolatile())
1219 Value* pointer = L->getPointerOperand();
1221 // ... to a pointer that has been loaded from before...
1222 MemDepResult dep = MD->getDependency(L);
1224 // If the value isn't available, don't do anything!
1225 if (dep.isClobber()) {
1227 // fast print dep, using operator<< on instruction would be too slow
1228 DOUT << "GVN: load ";
1229 WriteAsOperand(*DOUT.stream(), L);
1230 Instruction *I = dep.getInst();
1231 DOUT << " is clobbered by " << *I;
1236 // If it is defined in another block, try harder.
1237 if (dep.isNonLocal())
1238 return processNonLocalLoad(L, toErase);
1240 Instruction *DepInst = dep.getInst();
1241 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1242 // Only forward substitute stores to loads of the same type.
1243 // FIXME: Could do better!
1244 if (DepSI->getPointerOperand()->getType() != pointer->getType())
1248 L->replaceAllUsesWith(DepSI->getOperand(0));
1249 if (isa<PointerType>(DepSI->getOperand(0)->getType()))
1250 MD->invalidateCachedPointerInfo(DepSI->getOperand(0));
1251 toErase.push_back(L);
1256 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1257 // Only forward substitute stores to loads of the same type.
1258 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
1259 if (DepLI->getType() != L->getType())
1263 L->replaceAllUsesWith(DepLI);
1264 if (isa<PointerType>(DepLI->getType()))
1265 MD->invalidateCachedPointerInfo(DepLI);
1266 toErase.push_back(L);
1271 // If this load really doesn't depend on anything, then we must be loading an
1272 // undef value. This can happen when loading for a fresh allocation with no
1273 // intervening stores, for example.
1274 if (isa<AllocationInst>(DepInst)) {
1275 L->replaceAllUsesWith(Context->getUndef(L->getType()));
1276 toErase.push_back(L);
1284 Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1285 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1286 if (I == localAvail.end())
1289 ValueNumberScope* locals = I->second;
1292 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1293 if (I != locals->table.end())
1296 locals = locals->parent;
1302 /// AttemptRedundancyElimination - If the "fast path" of redundancy elimination
1303 /// by inheritance from the dominator fails, see if we can perform phi
1304 /// construction to eliminate the redundancy.
1305 Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) {
1306 BasicBlock* BaseBlock = orig->getParent();
1308 SmallPtrSet<BasicBlock*, 4> Visited;
1309 SmallVector<BasicBlock*, 8> Stack;
1310 Stack.push_back(BaseBlock);
1312 DenseMap<BasicBlock*, Value*> Results;
1314 // Walk backwards through our predecessors, looking for instances of the
1315 // value number we're looking for. Instances are recorded in the Results
1316 // map, which is then used to perform phi construction.
1317 while (!Stack.empty()) {
1318 BasicBlock* Current = Stack.back();
1321 // If we've walked all the way to a proper dominator, then give up. Cases
1322 // where the instance is in the dominator will have been caught by the fast
1323 // path, and any cases that require phi construction further than this are
1324 // probably not worth it anyways. Note that this is a SIGNIFICANT compile
1325 // time improvement.
1326 if (DT->properlyDominates(Current, orig->getParent())) return 0;
1328 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA =
1329 localAvail.find(Current);
1330 if (LA == localAvail.end()) return 0;
1331 DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno);
1333 if (V != LA->second->table.end()) {
1334 // Found an instance, record it.
1335 Results.insert(std::make_pair(Current, V->second));
1339 // If we reach the beginning of the function, then give up.
1340 if (pred_begin(Current) == pred_end(Current))
1343 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current);
1345 if (Visited.insert(*PI))
1346 Stack.push_back(*PI);
1349 // If we didn't find instances, give up. Otherwise, perform phi construction.
1350 if (Results.size() == 0)
1353 return GetValueForBlock(BaseBlock, orig, Results, true);
1356 /// processInstruction - When calculating availability, handle an instruction
1357 /// by inserting it into the appropriate sets
1358 bool GVN::processInstruction(Instruction *I,
1359 SmallVectorImpl<Instruction*> &toErase) {
1360 if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1361 bool changed = processLoad(L, toErase);
1364 unsigned num = VN.lookup_or_add(L);
1365 localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1371 uint32_t nextNum = VN.getNextUnusedValueNumber();
1372 unsigned num = VN.lookup_or_add(I);
1374 if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
1375 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1377 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1380 Value* branchCond = BI->getCondition();
1381 uint32_t condVN = VN.lookup_or_add(branchCond);
1383 BasicBlock* trueSucc = BI->getSuccessor(0);
1384 BasicBlock* falseSucc = BI->getSuccessor(1);
1386 if (trueSucc->getSinglePredecessor())
1387 localAvail[trueSucc]->table[condVN] = Context->getConstantIntTrue();
1388 if (falseSucc->getSinglePredecessor())
1389 localAvail[falseSucc]->table[condVN] = Context->getConstantIntFalse();
1393 // Allocations are always uniquely numbered, so we can save time and memory
1394 // by fast failing them.
1395 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
1396 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1400 // Collapse PHI nodes
1401 if (PHINode* p = dyn_cast<PHINode>(I)) {
1402 Value* constVal = CollapsePhi(p);
1405 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1407 PI->second.erase(p);
1409 p->replaceAllUsesWith(constVal);
1410 if (isa<PointerType>(constVal->getType()))
1411 MD->invalidateCachedPointerInfo(constVal);
1414 toErase.push_back(p);
1416 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1419 // If the number we were assigned was a brand new VN, then we don't
1420 // need to do a lookup to see if the number already exists
1421 // somewhere in the domtree: it can't!
1422 } else if (num == nextNum) {
1423 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1425 // Perform fast-path value-number based elimination of values inherited from
1427 } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1430 I->replaceAllUsesWith(repl);
1431 if (isa<PointerType>(repl->getType()))
1432 MD->invalidateCachedPointerInfo(repl);
1433 toErase.push_back(I);
1437 // Perform slow-pathvalue-number based elimination with phi construction.
1438 } else if (Value* repl = AttemptRedundancyElimination(I, num)) {
1441 I->replaceAllUsesWith(repl);
1442 if (isa<PointerType>(repl->getType()))
1443 MD->invalidateCachedPointerInfo(repl);
1444 toErase.push_back(I);
1448 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1454 /// runOnFunction - This is the main transformation entry point for a function.
1455 bool GVN::runOnFunction(Function& F) {
1456 MD = &getAnalysis<MemoryDependenceAnalysis>();
1457 DT = &getAnalysis<DominatorTree>();
1458 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1462 bool changed = false;
1463 bool shouldContinue = true;
1465 // Merge unconditional branches, allowing PRE to catch more
1466 // optimization opportunities.
1467 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1468 BasicBlock* BB = FI;
1470 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1471 if (removedBlock) NumGVNBlocks++;
1473 changed |= removedBlock;
1476 unsigned Iteration = 0;
1478 while (shouldContinue) {
1479 DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
1480 shouldContinue = iterateOnFunction(F);
1481 changed |= shouldContinue;
1486 bool PREChanged = true;
1487 while (PREChanged) {
1488 PREChanged = performPRE(F);
1489 changed |= PREChanged;
1492 // FIXME: Should perform GVN again after PRE does something. PRE can move
1493 // computations into blocks where they become fully redundant. Note that
1494 // we can't do this until PRE's critical edge splitting updates memdep.
1495 // Actually, when this happens, we should just fully integrate PRE into GVN.
1497 cleanupGlobalSets();
1503 bool GVN::processBlock(BasicBlock* BB) {
1504 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1505 // incrementing BI before processing an instruction).
1506 SmallVector<Instruction*, 8> toErase;
1507 bool changed_function = false;
1509 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1511 changed_function |= processInstruction(BI, toErase);
1512 if (toErase.empty()) {
1517 // If we need some instructions deleted, do it now.
1518 NumGVNInstr += toErase.size();
1520 // Avoid iterator invalidation.
1521 bool AtStart = BI == BB->begin();
1525 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1526 E = toErase.end(); I != E; ++I) {
1527 DEBUG(cerr << "GVN removed: " << **I);
1528 MD->removeInstruction(*I);
1529 (*I)->eraseFromParent();
1530 DEBUG(verifyRemoved(*I));
1540 return changed_function;
1543 /// performPRE - Perform a purely local form of PRE that looks for diamond
1544 /// control flow patterns and attempts to perform simple PRE at the join point.
1545 bool GVN::performPRE(Function& F) {
1546 bool Changed = false;
1547 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1548 DenseMap<BasicBlock*, Value*> predMap;
1549 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1550 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1551 BasicBlock* CurrentBlock = *DI;
1553 // Nothing to PRE in the entry block.
1554 if (CurrentBlock == &F.getEntryBlock()) continue;
1556 for (BasicBlock::iterator BI = CurrentBlock->begin(),
1557 BE = CurrentBlock->end(); BI != BE; ) {
1558 Instruction *CurInst = BI++;
1560 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
1561 isa<PHINode>(CurInst) || (CurInst->getType() == Type::VoidTy) ||
1562 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
1563 isa<DbgInfoIntrinsic>(CurInst))
1566 uint32_t valno = VN.lookup(CurInst);
1568 // Look for the predecessors for PRE opportunities. We're
1569 // only trying to solve the basic diamond case, where
1570 // a value is computed in the successor and one predecessor,
1571 // but not the other. We also explicitly disallow cases
1572 // where the successor is its own predecessor, because they're
1573 // more complicated to get right.
1574 unsigned numWith = 0;
1575 unsigned numWithout = 0;
1576 BasicBlock* PREPred = 0;
1579 for (pred_iterator PI = pred_begin(CurrentBlock),
1580 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1581 // We're not interested in PRE where the block is its
1582 // own predecessor, on in blocks with predecessors
1583 // that are not reachable.
1584 if (*PI == CurrentBlock) {
1587 } else if (!localAvail.count(*PI)) {
1592 DenseMap<uint32_t, Value*>::iterator predV =
1593 localAvail[*PI]->table.find(valno);
1594 if (predV == localAvail[*PI]->table.end()) {
1597 } else if (predV->second == CurInst) {
1600 predMap[*PI] = predV->second;
1605 // Don't do PRE when it might increase code size, i.e. when
1606 // we would need to insert instructions in more than one pred.
1607 if (numWithout != 1 || numWith == 0)
1610 // We can't do PRE safely on a critical edge, so instead we schedule
1611 // the edge to be split and perform the PRE the next time we iterate
1613 unsigned succNum = 0;
1614 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1616 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
1621 if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1622 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1626 // Instantiate the expression the in predecessor that lacked it.
1627 // Because we are going top-down through the block, all value numbers
1628 // will be available in the predecessor by the time we need them. Any
1629 // that weren't original present will have been instantiated earlier
1631 Instruction* PREInstr = CurInst->clone(*Context);
1632 bool success = true;
1633 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
1634 Value *Op = PREInstr->getOperand(i);
1635 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
1638 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
1639 PREInstr->setOperand(i, V);
1646 // Fail out if we encounter an operand that is not available in
1647 // the PRE predecessor. This is typically because of loads which
1648 // are not value numbered precisely.
1651 DEBUG(verifyRemoved(PREInstr));
1655 PREInstr->insertBefore(PREPred->getTerminator());
1656 PREInstr->setName(CurInst->getName() + ".pre");
1657 predMap[PREPred] = PREInstr;
1658 VN.add(PREInstr, valno);
1661 // Update the availability map to include the new instruction.
1662 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1664 // Create a PHI to make the value available in this block.
1665 PHINode* Phi = PHINode::Create(CurInst->getType(),
1666 CurInst->getName() + ".pre-phi",
1667 CurrentBlock->begin());
1668 for (pred_iterator PI = pred_begin(CurrentBlock),
1669 PE = pred_end(CurrentBlock); PI != PE; ++PI)
1670 Phi->addIncoming(predMap[*PI], *PI);
1673 localAvail[CurrentBlock]->table[valno] = Phi;
1675 CurInst->replaceAllUsesWith(Phi);
1676 if (isa<PointerType>(Phi->getType()))
1677 MD->invalidateCachedPointerInfo(Phi);
1680 DEBUG(cerr << "GVN PRE removed: " << *CurInst);
1681 MD->removeInstruction(CurInst);
1682 CurInst->eraseFromParent();
1683 DEBUG(verifyRemoved(CurInst));
1688 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1689 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1690 SplitCriticalEdge(I->first, I->second, this);
1692 return Changed || toSplit.size();
1695 /// iterateOnFunction - Executes one iteration of GVN
1696 bool GVN::iterateOnFunction(Function &F) {
1697 cleanupGlobalSets();
1699 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1700 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
1702 localAvail[DI->getBlock()] =
1703 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
1705 localAvail[DI->getBlock()] = new ValueNumberScope(0);
1708 // Top-down walk of the dominator tree
1709 bool changed = false;
1711 // Needed for value numbering with phi construction to work.
1712 ReversePostOrderTraversal<Function*> RPOT(&F);
1713 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
1714 RE = RPOT.end(); RI != RE; ++RI)
1715 changed |= processBlock(*RI);
1717 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1718 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
1719 changed |= processBlock(DI->getBlock());
1725 void GVN::cleanupGlobalSets() {
1729 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1730 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
1735 /// verifyRemoved - Verify that the specified instruction does not occur in our
1736 /// internal data structures.
1737 void GVN::verifyRemoved(const Instruction *Inst) const {
1738 VN.verifyRemoved(Inst);
1740 // Walk through the PHI map to make sure the instruction isn't hiding in there
1742 for (PhiMapType::iterator
1743 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) {
1744 assert(I->first != Inst && "Inst is still a key in PHI map!");
1746 for (SmallPtrSet<Instruction*, 4>::iterator
1747 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) {
1748 assert(*II != Inst && "Inst is still a value in PHI map!");
1752 // Walk through the value number scope to make sure the instruction isn't
1753 // ferreted away in it.
1754 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1755 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
1756 const ValueNumberScope *VNS = I->second;
1759 for (DenseMap<uint32_t, Value*>::iterator
1760 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
1761 assert(II->second != Inst && "Inst still in value numbering scope!");