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/Value.h"
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/DepthFirstIterator.h"
28 #include "llvm/ADT/PostOrderIterator.h"
29 #include "llvm/ADT/SmallPtrSet.h"
30 #include "llvm/ADT/SmallVector.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/Analysis/Dominators.h"
33 #include "llvm/Analysis/AliasAnalysis.h"
34 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
35 #include "llvm/Support/CFG.h"
36 #include "llvm/Support/CommandLine.h"
37 #include "llvm/Support/Compiler.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
40 #include "llvm/Transforms/Utils/Local.h"
44 STATISTIC(NumGVNInstr, "Number of instructions deleted");
45 STATISTIC(NumGVNLoad, "Number of loads deleted");
46 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
47 STATISTIC(NumGVNBlocks, "Number of blocks merged");
48 STATISTIC(NumPRELoad, "Number of loads PRE'd");
50 static cl::opt<bool> EnablePRE("enable-pre",
51 cl::init(true), cl::Hidden);
52 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
54 //===----------------------------------------------------------------------===//
56 //===----------------------------------------------------------------------===//
58 /// This class holds the mapping between values and value numbers. It is used
59 /// as an efficient mechanism to determine the expression-wise equivalence of
62 struct VISIBILITY_HIDDEN Expression {
63 enum ExpressionOpcode { ADD, FADD, SUB, FSUB, MUL, FMUL,
64 UDIV, SDIV, FDIV, UREM, SREM,
65 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
66 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
67 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
68 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
69 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
70 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
71 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
72 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
73 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
76 ExpressionOpcode opcode;
81 SmallVector<uint32_t, 4> varargs;
85 Expression(ExpressionOpcode o) : opcode(o) { }
87 bool operator==(const Expression &other) const {
88 if (opcode != other.opcode)
90 else if (opcode == EMPTY || opcode == TOMBSTONE)
92 else if (type != other.type)
94 else if (function != other.function)
96 else if (firstVN != other.firstVN)
98 else if (secondVN != other.secondVN)
100 else if (thirdVN != other.thirdVN)
103 if (varargs.size() != other.varargs.size())
106 for (size_t i = 0; i < varargs.size(); ++i)
107 if (varargs[i] != other.varargs[i])
114 bool operator!=(const Expression &other) const {
115 return !(*this == other);
119 class VISIBILITY_HIDDEN ValueTable {
121 DenseMap<Value*, uint32_t> valueNumbering;
122 DenseMap<Expression, uint32_t> expressionNumbering;
124 MemoryDependenceAnalysis* MD;
127 uint32_t nextValueNumber;
129 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
130 Expression::ExpressionOpcode getOpcode(CmpInst* C);
131 Expression::ExpressionOpcode getOpcode(CastInst* C);
132 Expression create_expression(BinaryOperator* BO);
133 Expression create_expression(CmpInst* C);
134 Expression create_expression(ShuffleVectorInst* V);
135 Expression create_expression(ExtractElementInst* C);
136 Expression create_expression(InsertElementInst* V);
137 Expression create_expression(SelectInst* V);
138 Expression create_expression(CastInst* C);
139 Expression create_expression(GetElementPtrInst* G);
140 Expression create_expression(CallInst* C);
141 Expression create_expression(Constant* C);
143 ValueTable() : nextValueNumber(1) { }
144 uint32_t lookup_or_add(Value* V);
145 uint32_t lookup(Value* V) const;
146 void add(Value* V, uint32_t num);
148 void erase(Value* v);
150 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
151 AliasAnalysis *getAliasAnalysis() const { return AA; }
152 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
153 void setDomTree(DominatorTree* D) { DT = D; }
154 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
155 void verifyRemoved(const Value *) const;
160 template <> struct DenseMapInfo<Expression> {
161 static inline Expression getEmptyKey() {
162 return Expression(Expression::EMPTY);
165 static inline Expression getTombstoneKey() {
166 return Expression(Expression::TOMBSTONE);
169 static unsigned getHashValue(const Expression e) {
170 unsigned hash = e.opcode;
172 hash = e.firstVN + hash * 37;
173 hash = e.secondVN + hash * 37;
174 hash = e.thirdVN + hash * 37;
176 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
177 (unsigned)((uintptr_t)e.type >> 9)) +
180 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
181 E = e.varargs.end(); I != E; ++I)
182 hash = *I + hash * 37;
184 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
185 (unsigned)((uintptr_t)e.function >> 9)) +
190 static bool isEqual(const Expression &LHS, const Expression &RHS) {
193 static bool isPod() { return true; }
197 //===----------------------------------------------------------------------===//
198 // ValueTable Internal Functions
199 //===----------------------------------------------------------------------===//
200 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
201 switch(BO->getOpcode()) {
202 default: // THIS SHOULD NEVER HAPPEN
203 assert(0 && "Binary operator with unknown opcode?");
204 case Instruction::Add: return Expression::ADD;
205 case Instruction::FAdd: return Expression::FADD;
206 case Instruction::Sub: return Expression::SUB;
207 case Instruction::FSub: return Expression::FSUB;
208 case Instruction::Mul: return Expression::MUL;
209 case Instruction::FMul: return Expression::FMUL;
210 case Instruction::UDiv: return Expression::UDIV;
211 case Instruction::SDiv: return Expression::SDIV;
212 case Instruction::FDiv: return Expression::FDIV;
213 case Instruction::URem: return Expression::UREM;
214 case Instruction::SRem: return Expression::SREM;
215 case Instruction::FRem: return Expression::FREM;
216 case Instruction::Shl: return Expression::SHL;
217 case Instruction::LShr: return Expression::LSHR;
218 case Instruction::AShr: return Expression::ASHR;
219 case Instruction::And: return Expression::AND;
220 case Instruction::Or: return Expression::OR;
221 case Instruction::Xor: return Expression::XOR;
225 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
226 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
227 switch (C->getPredicate()) {
228 default: // THIS SHOULD NEVER HAPPEN
229 assert(0 && "Comparison with unknown predicate?");
230 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
231 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
232 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
233 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
234 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
235 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
236 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
237 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
238 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
239 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
242 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
243 switch (C->getPredicate()) {
244 default: // THIS SHOULD NEVER HAPPEN
245 assert(0 && "Comparison with unknown predicate?");
246 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
247 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
248 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
249 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
250 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
251 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
252 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
253 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
254 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
255 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
256 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
257 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
258 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
259 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
263 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
264 switch(C->getOpcode()) {
265 default: // THIS SHOULD NEVER HAPPEN
266 assert(0 && "Cast operator with unknown opcode?");
267 case Instruction::Trunc: return Expression::TRUNC;
268 case Instruction::ZExt: return Expression::ZEXT;
269 case Instruction::SExt: return Expression::SEXT;
270 case Instruction::FPToUI: return Expression::FPTOUI;
271 case Instruction::FPToSI: return Expression::FPTOSI;
272 case Instruction::UIToFP: return Expression::UITOFP;
273 case Instruction::SIToFP: return Expression::SITOFP;
274 case Instruction::FPTrunc: return Expression::FPTRUNC;
275 case Instruction::FPExt: return Expression::FPEXT;
276 case Instruction::PtrToInt: return Expression::PTRTOINT;
277 case Instruction::IntToPtr: return Expression::INTTOPTR;
278 case Instruction::BitCast: return Expression::BITCAST;
282 Expression ValueTable::create_expression(CallInst* C) {
285 e.type = C->getType();
289 e.function = C->getCalledFunction();
290 e.opcode = Expression::CALL;
292 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
294 e.varargs.push_back(lookup_or_add(*I));
299 Expression ValueTable::create_expression(BinaryOperator* BO) {
302 e.firstVN = lookup_or_add(BO->getOperand(0));
303 e.secondVN = lookup_or_add(BO->getOperand(1));
306 e.type = BO->getType();
307 e.opcode = getOpcode(BO);
312 Expression ValueTable::create_expression(CmpInst* C) {
315 e.firstVN = lookup_or_add(C->getOperand(0));
316 e.secondVN = lookup_or_add(C->getOperand(1));
319 e.type = C->getType();
320 e.opcode = getOpcode(C);
325 Expression ValueTable::create_expression(CastInst* C) {
328 e.firstVN = lookup_or_add(C->getOperand(0));
332 e.type = C->getType();
333 e.opcode = getOpcode(C);
338 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
341 e.firstVN = lookup_or_add(S->getOperand(0));
342 e.secondVN = lookup_or_add(S->getOperand(1));
343 e.thirdVN = lookup_or_add(S->getOperand(2));
345 e.type = S->getType();
346 e.opcode = Expression::SHUFFLE;
351 Expression ValueTable::create_expression(ExtractElementInst* E) {
354 e.firstVN = lookup_or_add(E->getOperand(0));
355 e.secondVN = lookup_or_add(E->getOperand(1));
358 e.type = E->getType();
359 e.opcode = Expression::EXTRACT;
364 Expression ValueTable::create_expression(InsertElementInst* I) {
367 e.firstVN = lookup_or_add(I->getOperand(0));
368 e.secondVN = lookup_or_add(I->getOperand(1));
369 e.thirdVN = lookup_or_add(I->getOperand(2));
371 e.type = I->getType();
372 e.opcode = Expression::INSERT;
377 Expression ValueTable::create_expression(SelectInst* I) {
380 e.firstVN = lookup_or_add(I->getCondition());
381 e.secondVN = lookup_or_add(I->getTrueValue());
382 e.thirdVN = lookup_or_add(I->getFalseValue());
384 e.type = I->getType();
385 e.opcode = Expression::SELECT;
390 Expression ValueTable::create_expression(GetElementPtrInst* G) {
393 e.firstVN = lookup_or_add(G->getPointerOperand());
397 e.type = G->getType();
398 e.opcode = Expression::GEP;
400 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
402 e.varargs.push_back(lookup_or_add(*I));
407 //===----------------------------------------------------------------------===//
408 // ValueTable External Functions
409 //===----------------------------------------------------------------------===//
411 /// add - Insert a value into the table with a specified value number.
412 void ValueTable::add(Value* V, uint32_t num) {
413 valueNumbering.insert(std::make_pair(V, num));
416 /// lookup_or_add - Returns the value number for the specified value, assigning
417 /// it a new number if it did not have one before.
418 uint32_t ValueTable::lookup_or_add(Value* V) {
419 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
420 if (VI != valueNumbering.end())
423 if (CallInst* C = dyn_cast<CallInst>(V)) {
424 if (AA->doesNotAccessMemory(C)) {
425 Expression e = create_expression(C);
427 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
428 if (EI != expressionNumbering.end()) {
429 valueNumbering.insert(std::make_pair(V, EI->second));
432 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
433 valueNumbering.insert(std::make_pair(V, nextValueNumber));
435 return nextValueNumber++;
437 } else if (AA->onlyReadsMemory(C)) {
438 Expression e = create_expression(C);
440 if (expressionNumbering.find(e) == expressionNumbering.end()) {
441 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
442 valueNumbering.insert(std::make_pair(V, nextValueNumber));
443 return nextValueNumber++;
446 MemDepResult local_dep = MD->getDependency(C);
448 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
449 valueNumbering.insert(std::make_pair(V, nextValueNumber));
450 return nextValueNumber++;
453 if (local_dep.isDef()) {
454 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
456 if (local_cdep->getNumOperands() != C->getNumOperands()) {
457 valueNumbering.insert(std::make_pair(V, nextValueNumber));
458 return nextValueNumber++;
461 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
462 uint32_t c_vn = lookup_or_add(C->getOperand(i));
463 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
465 valueNumbering.insert(std::make_pair(V, nextValueNumber));
466 return nextValueNumber++;
470 uint32_t v = lookup_or_add(local_cdep);
471 valueNumbering.insert(std::make_pair(V, v));
476 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
477 MD->getNonLocalCallDependency(CallSite(C));
478 // FIXME: call/call dependencies for readonly calls should return def, not
479 // clobber! Move the checking logic to MemDep!
482 // Check to see if we have a single dominating call instruction that is
484 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
485 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
486 // Ignore non-local dependencies.
487 if (I->second.isNonLocal())
490 // We don't handle non-depedencies. If we already have a call, reject
491 // instruction dependencies.
492 if (I->second.isClobber() || cdep != 0) {
497 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
498 // FIXME: All duplicated with non-local case.
499 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
500 cdep = NonLocalDepCall;
509 valueNumbering.insert(std::make_pair(V, nextValueNumber));
510 return nextValueNumber++;
513 if (cdep->getNumOperands() != C->getNumOperands()) {
514 valueNumbering.insert(std::make_pair(V, nextValueNumber));
515 return nextValueNumber++;
517 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
518 uint32_t c_vn = lookup_or_add(C->getOperand(i));
519 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
521 valueNumbering.insert(std::make_pair(V, nextValueNumber));
522 return nextValueNumber++;
526 uint32_t v = lookup_or_add(cdep);
527 valueNumbering.insert(std::make_pair(V, v));
531 valueNumbering.insert(std::make_pair(V, nextValueNumber));
532 return nextValueNumber++;
534 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
535 Expression e = create_expression(BO);
537 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
538 if (EI != expressionNumbering.end()) {
539 valueNumbering.insert(std::make_pair(V, EI->second));
542 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
543 valueNumbering.insert(std::make_pair(V, nextValueNumber));
545 return nextValueNumber++;
547 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
548 Expression e = create_expression(C);
550 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
551 if (EI != expressionNumbering.end()) {
552 valueNumbering.insert(std::make_pair(V, EI->second));
555 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
556 valueNumbering.insert(std::make_pair(V, nextValueNumber));
558 return nextValueNumber++;
560 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
561 Expression e = create_expression(U);
563 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
564 if (EI != expressionNumbering.end()) {
565 valueNumbering.insert(std::make_pair(V, EI->second));
568 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
569 valueNumbering.insert(std::make_pair(V, nextValueNumber));
571 return nextValueNumber++;
573 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
574 Expression e = create_expression(U);
576 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
577 if (EI != expressionNumbering.end()) {
578 valueNumbering.insert(std::make_pair(V, EI->second));
581 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
582 valueNumbering.insert(std::make_pair(V, nextValueNumber));
584 return nextValueNumber++;
586 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
587 Expression e = create_expression(U);
589 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
590 if (EI != expressionNumbering.end()) {
591 valueNumbering.insert(std::make_pair(V, EI->second));
594 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
595 valueNumbering.insert(std::make_pair(V, nextValueNumber));
597 return nextValueNumber++;
599 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
600 Expression e = create_expression(U);
602 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
603 if (EI != expressionNumbering.end()) {
604 valueNumbering.insert(std::make_pair(V, EI->second));
607 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
608 valueNumbering.insert(std::make_pair(V, nextValueNumber));
610 return nextValueNumber++;
612 } else if (CastInst* U = dyn_cast<CastInst>(V)) {
613 Expression e = create_expression(U);
615 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
616 if (EI != expressionNumbering.end()) {
617 valueNumbering.insert(std::make_pair(V, EI->second));
620 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
621 valueNumbering.insert(std::make_pair(V, nextValueNumber));
623 return nextValueNumber++;
625 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
626 Expression e = create_expression(U);
628 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
629 if (EI != expressionNumbering.end()) {
630 valueNumbering.insert(std::make_pair(V, EI->second));
633 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
634 valueNumbering.insert(std::make_pair(V, nextValueNumber));
636 return nextValueNumber++;
639 valueNumbering.insert(std::make_pair(V, nextValueNumber));
640 return nextValueNumber++;
644 /// lookup - Returns the value number of the specified value. Fails if
645 /// the value has not yet been numbered.
646 uint32_t ValueTable::lookup(Value* V) const {
647 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
648 assert(VI != valueNumbering.end() && "Value not numbered?");
652 /// clear - Remove all entries from the ValueTable
653 void ValueTable::clear() {
654 valueNumbering.clear();
655 expressionNumbering.clear();
659 /// erase - Remove a value from the value numbering
660 void ValueTable::erase(Value* V) {
661 valueNumbering.erase(V);
664 /// verifyRemoved - Verify that the value is removed from all internal data
666 void ValueTable::verifyRemoved(const Value *V) const {
667 for (DenseMap<Value*, uint32_t>::iterator
668 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
669 assert(I->first != V && "Inst still occurs in value numbering map!");
673 //===----------------------------------------------------------------------===//
675 //===----------------------------------------------------------------------===//
678 struct VISIBILITY_HIDDEN ValueNumberScope {
679 ValueNumberScope* parent;
680 DenseMap<uint32_t, Value*> table;
682 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
688 class VISIBILITY_HIDDEN GVN : public FunctionPass {
689 bool runOnFunction(Function &F);
691 static char ID; // Pass identification, replacement for typeid
692 GVN() : FunctionPass(&ID) { }
695 MemoryDependenceAnalysis *MD;
699 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
701 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
705 // This transformation requires dominator postdominator info
706 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
707 AU.addRequired<DominatorTree>();
708 AU.addRequired<MemoryDependenceAnalysis>();
709 AU.addRequired<AliasAnalysis>();
711 AU.addPreserved<DominatorTree>();
712 AU.addPreserved<AliasAnalysis>();
716 // FIXME: eliminate or document these better
717 bool processLoad(LoadInst* L,
718 SmallVectorImpl<Instruction*> &toErase);
719 bool processInstruction(Instruction* I,
720 SmallVectorImpl<Instruction*> &toErase);
721 bool processNonLocalLoad(LoadInst* L,
722 SmallVectorImpl<Instruction*> &toErase);
723 bool processBlock(BasicBlock* BB);
724 Value *GetValueForBlock(BasicBlock *BB, Instruction* orig,
725 DenseMap<BasicBlock*, Value*> &Phis,
726 bool top_level = false);
727 void dump(DenseMap<uint32_t, Value*>& d);
728 bool iterateOnFunction(Function &F);
729 Value* CollapsePhi(PHINode* p);
730 bool isSafeReplacement(PHINode* p, Instruction* inst);
731 bool performPRE(Function& F);
732 Value* lookupNumber(BasicBlock* BB, uint32_t num);
733 bool mergeBlockIntoPredecessor(BasicBlock* BB);
734 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno);
735 void cleanupGlobalSets();
736 void verifyRemoved(const Instruction *I) const;
742 // createGVNPass - The public interface to this file...
743 FunctionPass *llvm::createGVNPass() { return new GVN(); }
745 static RegisterPass<GVN> X("gvn",
746 "Global Value Numbering");
748 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
750 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
751 E = d.end(); I != E; ++I) {
752 printf("%d\n", I->first);
758 Value* GVN::CollapsePhi(PHINode* p) {
759 Value* constVal = p->hasConstantValue();
760 if (!constVal) return 0;
762 Instruction* inst = dyn_cast<Instruction>(constVal);
766 if (DT->dominates(inst, p))
767 if (isSafeReplacement(p, inst))
772 bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
773 if (!isa<PHINode>(inst))
776 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
778 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
779 if (use_phi->getParent() == inst->getParent())
785 /// GetValueForBlock - Get the value to use within the specified basic block.
786 /// available values are in Phis.
787 Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig,
788 DenseMap<BasicBlock*, Value*> &Phis,
791 // If we have already computed this value, return the previously computed val.
792 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
793 if (V != Phis.end() && !top_level) return V->second;
795 // If the block is unreachable, just return undef, since this path
796 // can't actually occur at runtime.
797 if (!DT->isReachableFromEntry(BB))
798 return Phis[BB] = UndefValue::get(orig->getType());
800 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
801 Value *ret = GetValueForBlock(Pred, orig, Phis);
806 // Get the number of predecessors of this block so we can reserve space later.
807 // If there is already a PHI in it, use the #preds from it, otherwise count.
808 // Getting it from the PHI is constant time.
810 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
811 NumPreds = ExistingPN->getNumIncomingValues();
813 NumPreds = std::distance(pred_begin(BB), pred_end(BB));
815 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
816 // now, then get values to fill in the incoming values for the PHI.
817 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
819 PN->reserveOperandSpace(NumPreds);
821 Phis.insert(std::make_pair(BB, PN));
823 // Fill in the incoming values for the block.
824 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
825 Value* val = GetValueForBlock(*PI, orig, Phis);
826 PN->addIncoming(val, *PI);
829 VN.getAliasAnalysis()->copyValue(orig, PN);
831 // Attempt to collapse PHI nodes that are trivially redundant
832 Value* v = CollapsePhi(PN);
834 // Cache our phi construction results
835 if (LoadInst* L = dyn_cast<LoadInst>(orig))
836 phiMap[L->getPointerOperand()].insert(PN);
838 phiMap[orig].insert(PN);
843 PN->replaceAllUsesWith(v);
844 if (isa<PointerType>(v->getType()))
845 MD->invalidateCachedPointerInfo(v);
847 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
848 E = Phis.end(); I != E; ++I)
852 DEBUG(cerr << "GVN removed: " << *PN);
853 MD->removeInstruction(PN);
854 PN->eraseFromParent();
855 DEBUG(verifyRemoved(PN));
861 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
862 /// we're analyzing is fully available in the specified block. As we go, keep
863 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
864 /// map is actually a tri-state map with the following values:
865 /// 0) we know the block *is not* fully available.
866 /// 1) we know the block *is* fully available.
867 /// 2) we do not know whether the block is fully available or not, but we are
868 /// currently speculating that it will be.
869 /// 3) we are speculating for this block and have used that to speculate for
871 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
872 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
873 // Optimistically assume that the block is fully available and check to see
874 // if we already know about this block in one lookup.
875 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
876 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
878 // If the entry already existed for this block, return the precomputed value.
880 // If this is a speculative "available" value, mark it as being used for
881 // speculation of other blocks.
882 if (IV.first->second == 2)
883 IV.first->second = 3;
884 return IV.first->second != 0;
887 // Otherwise, see if it is fully available in all predecessors.
888 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
890 // If this block has no predecessors, it isn't live-in here.
892 goto SpeculationFailure;
894 for (; PI != PE; ++PI)
895 // If the value isn't fully available in one of our predecessors, then it
896 // isn't fully available in this block either. Undo our previous
897 // optimistic assumption and bail out.
898 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
899 goto SpeculationFailure;
903 // SpeculationFailure - If we get here, we found out that this is not, after
904 // all, a fully-available block. We have a problem if we speculated on this and
905 // used the speculation to mark other blocks as available.
907 char &BBVal = FullyAvailableBlocks[BB];
909 // If we didn't speculate on this, just return with it set to false.
915 // If we did speculate on this value, we could have blocks set to 1 that are
916 // incorrect. Walk the (transitive) successors of this block and mark them as
918 SmallVector<BasicBlock*, 32> BBWorklist;
919 BBWorklist.push_back(BB);
921 while (!BBWorklist.empty()) {
922 BasicBlock *Entry = BBWorklist.pop_back_val();
923 // Note that this sets blocks to 0 (unavailable) if they happen to not
924 // already be in FullyAvailableBlocks. This is safe.
925 char &EntryVal = FullyAvailableBlocks[Entry];
926 if (EntryVal == 0) continue; // Already unavailable.
928 // Mark as unavailable.
931 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
932 BBWorklist.push_back(*I);
938 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
939 /// non-local by performing PHI construction.
940 bool GVN::processNonLocalLoad(LoadInst *LI,
941 SmallVectorImpl<Instruction*> &toErase) {
942 // Find the non-local dependencies of the load.
943 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
944 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
946 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
948 // If we had to process more than one hundred blocks to find the
949 // dependencies, this load isn't worth worrying about. Optimizing
950 // it will be too expensive.
951 if (Deps.size() > 100)
954 // If we had a phi translation failure, we'll have a single entry which is a
955 // clobber in the current block. Reject this early.
956 if (Deps.size() == 1 && Deps[0].second.isClobber()) {
958 DOUT << "GVN: non-local load ";
959 WriteAsOperand(*DOUT.stream(), LI);
960 DOUT << " is clobbered by " << *Deps[0].second.getInst();
965 // Filter out useless results (non-locals, etc). Keep track of the blocks
966 // where we have a value available in repl, also keep track of whether we see
967 // dependencies that produce an unknown value for the load (such as a call
968 // that could potentially clobber the load).
969 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
970 SmallVector<BasicBlock*, 16> UnavailableBlocks;
972 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
973 BasicBlock *DepBB = Deps[i].first;
974 MemDepResult DepInfo = Deps[i].second;
976 if (DepInfo.isClobber()) {
977 UnavailableBlocks.push_back(DepBB);
981 Instruction *DepInst = DepInfo.getInst();
983 // Loading the allocation -> undef.
984 if (isa<AllocationInst>(DepInst)) {
985 ValuesPerBlock.push_back(std::make_pair(DepBB,
986 UndefValue::get(LI->getType())));
990 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
991 // Reject loads and stores that are to the same address but are of
993 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
994 // of bitfield access, it would be interesting to optimize for it at some
996 if (S->getOperand(0)->getType() != LI->getType()) {
997 UnavailableBlocks.push_back(DepBB);
1001 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
1003 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
1004 if (LD->getType() != LI->getType()) {
1005 UnavailableBlocks.push_back(DepBB);
1008 ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
1010 UnavailableBlocks.push_back(DepBB);
1015 // If we have no predecessors that produce a known value for this load, exit
1017 if (ValuesPerBlock.empty()) return false;
1019 // If all of the instructions we depend on produce a known value for this
1020 // load, then it is fully redundant and we can use PHI insertion to compute
1021 // its value. Insert PHIs and remove the fully redundant value now.
1022 if (UnavailableBlocks.empty()) {
1023 // Use cached PHI construction information from previous runs
1024 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1025 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
1026 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1028 if ((*I)->getParent() == LI->getParent()) {
1029 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
1030 LI->replaceAllUsesWith(*I);
1031 if (isa<PointerType>((*I)->getType()))
1032 MD->invalidateCachedPointerInfo(*I);
1033 toErase.push_back(LI);
1038 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1041 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
1043 DenseMap<BasicBlock*, Value*> BlockReplValues;
1044 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1045 // Perform PHI construction.
1046 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1047 LI->replaceAllUsesWith(v);
1049 if (isa<PHINode>(v))
1051 if (isa<PointerType>(v->getType()))
1052 MD->invalidateCachedPointerInfo(v);
1053 toErase.push_back(LI);
1058 if (!EnablePRE || !EnableLoadPRE)
1061 // Okay, we have *some* definitions of the value. This means that the value
1062 // is available in some of our (transitive) predecessors. Lets think about
1063 // doing PRE of this load. This will involve inserting a new load into the
1064 // predecessor when it's not available. We could do this in general, but
1065 // prefer to not increase code size. As such, we only do this when we know
1066 // that we only have to insert *one* load (which means we're basically moving
1067 // the load, not inserting a new one).
1069 SmallPtrSet<BasicBlock *, 4> Blockers;
1070 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1071 Blockers.insert(UnavailableBlocks[i]);
1073 // Lets find first basic block with more than one predecessor. Walk backwards
1074 // through predecessors if needed.
1075 BasicBlock *LoadBB = LI->getParent();
1076 BasicBlock *TmpBB = LoadBB;
1078 bool isSinglePred = false;
1079 bool allSingleSucc = true;
1080 while (TmpBB->getSinglePredecessor()) {
1081 isSinglePred = true;
1082 TmpBB = TmpBB->getSinglePredecessor();
1083 if (!TmpBB) // If haven't found any, bail now.
1085 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1087 if (Blockers.count(TmpBB))
1089 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1090 allSingleSucc = false;
1096 // If we have a repl set with LI itself in it, this means we have a loop where
1097 // at least one of the values is LI. Since this means that we won't be able
1098 // to eliminate LI even if we insert uses in the other predecessors, we will
1099 // end up increasing code size. Reject this by scanning for LI.
1100 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1101 if (ValuesPerBlock[i].second == LI)
1106 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1107 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second))
1108 // "Hot" Instruction is in some loop (because it dominates its dep.
1110 if (DT->dominates(LI, I)) {
1115 // We are interested only in "hot" instructions. We don't want to do any
1116 // mis-optimizations here.
1121 // Okay, we have some hope :). Check to see if the loaded value is fully
1122 // available in all but one predecessor.
1123 // FIXME: If we could restructure the CFG, we could make a common pred with
1124 // all the preds that don't have an available LI and insert a new load into
1126 BasicBlock *UnavailablePred = 0;
1128 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1129 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1130 FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
1131 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1132 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1134 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1136 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1139 // If this load is not available in multiple predecessors, reject it.
1140 if (UnavailablePred && UnavailablePred != *PI)
1142 UnavailablePred = *PI;
1145 assert(UnavailablePred != 0 &&
1146 "Fully available value should be eliminated above!");
1148 // If the loaded pointer is PHI node defined in this block, do PHI translation
1149 // to get its value in the predecessor.
1150 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
1152 // Make sure the value is live in the predecessor. If it was defined by a
1153 // non-PHI instruction in this block, we don't know how to recompute it above.
1154 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
1155 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
1156 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
1157 << *LPInst << *LI << "\n");
1161 // We don't currently handle critical edges :(
1162 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1163 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1164 << UnavailablePred->getName() << "': " << *LI);
1168 // Make sure it is valid to move this load here. We have to watch out for:
1169 // @1 = getelementptr (i8* p, ...
1170 // test p and branch if == 0
1172 // It is valid to have the getelementptr before the test, even if p can be 0,
1173 // as getelementptr only does address arithmetic.
1174 // If we are not pushing the value through any multiple-successor blocks
1175 // we do not have this case. Otherwise, check that the load is safe to
1176 // put anywhere; this can be improved, but should be conservatively safe.
1177 if (!allSingleSucc &&
1178 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator()))
1181 // Okay, we can eliminate this load by inserting a reload in the predecessor
1182 // and using PHI construction to get the value in the other predecessors, do
1184 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
1186 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1188 UnavailablePred->getTerminator());
1190 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1191 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1193 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1195 DenseMap<BasicBlock*, Value*> BlockReplValues;
1196 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1197 BlockReplValues[UnavailablePred] = NewLoad;
1199 // Perform PHI construction.
1200 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1201 LI->replaceAllUsesWith(v);
1202 if (isa<PHINode>(v))
1204 if (isa<PointerType>(v->getType()))
1205 MD->invalidateCachedPointerInfo(v);
1206 toErase.push_back(LI);
1211 /// processLoad - Attempt to eliminate a load, first by eliminating it
1212 /// locally, and then attempting non-local elimination if that fails.
1213 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1214 if (L->isVolatile())
1217 Value* pointer = L->getPointerOperand();
1219 // ... to a pointer that has been loaded from before...
1220 MemDepResult dep = MD->getDependency(L);
1222 // If the value isn't available, don't do anything!
1223 if (dep.isClobber()) {
1225 // fast print dep, using operator<< on instruction would be too slow
1226 DOUT << "GVN: load ";
1227 WriteAsOperand(*DOUT.stream(), L);
1228 Instruction *I = dep.getInst();
1229 DOUT << " is clobbered by " << *I;
1234 // If it is defined in another block, try harder.
1235 if (dep.isNonLocal())
1236 return processNonLocalLoad(L, toErase);
1238 Instruction *DepInst = dep.getInst();
1239 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1240 // Only forward substitute stores to loads of the same type.
1241 // FIXME: Could do better!
1242 if (DepSI->getPointerOperand()->getType() != pointer->getType())
1246 L->replaceAllUsesWith(DepSI->getOperand(0));
1247 if (isa<PointerType>(DepSI->getOperand(0)->getType()))
1248 MD->invalidateCachedPointerInfo(DepSI->getOperand(0));
1249 toErase.push_back(L);
1254 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1255 // Only forward substitute stores to loads of the same type.
1256 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
1257 if (DepLI->getType() != L->getType())
1261 L->replaceAllUsesWith(DepLI);
1262 if (isa<PointerType>(DepLI->getType()))
1263 MD->invalidateCachedPointerInfo(DepLI);
1264 toErase.push_back(L);
1269 // If this load really doesn't depend on anything, then we must be loading an
1270 // undef value. This can happen when loading for a fresh allocation with no
1271 // intervening stores, for example.
1272 if (isa<AllocationInst>(DepInst)) {
1273 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1274 toErase.push_back(L);
1282 Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1283 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1284 if (I == localAvail.end())
1287 ValueNumberScope* locals = I->second;
1290 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1291 if (I != locals->table.end())
1294 locals = locals->parent;
1300 /// AttemptRedundancyElimination - If the "fast path" of redundancy elimination
1301 /// by inheritance from the dominator fails, see if we can perform phi
1302 /// construction to eliminate the redundancy.
1303 Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) {
1304 BasicBlock* BaseBlock = orig->getParent();
1306 SmallPtrSet<BasicBlock*, 4> Visited;
1307 SmallVector<BasicBlock*, 8> Stack;
1308 Stack.push_back(BaseBlock);
1310 DenseMap<BasicBlock*, Value*> Results;
1312 // Walk backwards through our predecessors, looking for instances of the
1313 // value number we're looking for. Instances are recorded in the Results
1314 // map, which is then used to perform phi construction.
1315 while (!Stack.empty()) {
1316 BasicBlock* Current = Stack.back();
1319 // If we've walked all the way to a proper dominator, then give up. Cases
1320 // where the instance is in the dominator will have been caught by the fast
1321 // path, and any cases that require phi construction further than this are
1322 // probably not worth it anyways. Note that this is a SIGNIFICANT compile
1323 // time improvement.
1324 if (DT->properlyDominates(Current, orig->getParent())) return 0;
1326 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA =
1327 localAvail.find(Current);
1328 if (LA == localAvail.end()) return 0;
1329 DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno);
1331 if (V != LA->second->table.end()) {
1332 // Found an instance, record it.
1333 Results.insert(std::make_pair(Current, V->second));
1337 // If we reach the beginning of the function, then give up.
1338 if (pred_begin(Current) == pred_end(Current))
1341 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current);
1343 if (Visited.insert(*PI))
1344 Stack.push_back(*PI);
1347 // If we didn't find instances, give up. Otherwise, perform phi construction.
1348 if (Results.size() == 0)
1351 return GetValueForBlock(BaseBlock, orig, Results, true);
1354 /// processInstruction - When calculating availability, handle an instruction
1355 /// by inserting it into the appropriate sets
1356 bool GVN::processInstruction(Instruction *I,
1357 SmallVectorImpl<Instruction*> &toErase) {
1358 if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1359 bool changed = processLoad(L, toErase);
1362 unsigned num = VN.lookup_or_add(L);
1363 localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1369 uint32_t nextNum = VN.getNextUnusedValueNumber();
1370 unsigned num = VN.lookup_or_add(I);
1372 if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
1373 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1375 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1378 Value* branchCond = BI->getCondition();
1379 uint32_t condVN = VN.lookup_or_add(branchCond);
1381 BasicBlock* trueSucc = BI->getSuccessor(0);
1382 BasicBlock* falseSucc = BI->getSuccessor(1);
1384 if (trueSucc->getSinglePredecessor())
1385 localAvail[trueSucc]->table[condVN] = ConstantInt::getTrue();
1386 if (falseSucc->getSinglePredecessor())
1387 localAvail[falseSucc]->table[condVN] = ConstantInt::getFalse();
1391 // Allocations are always uniquely numbered, so we can save time and memory
1392 // by fast failing them.
1393 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
1394 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1398 // Collapse PHI nodes
1399 if (PHINode* p = dyn_cast<PHINode>(I)) {
1400 Value* constVal = CollapsePhi(p);
1403 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1405 PI->second.erase(p);
1407 p->replaceAllUsesWith(constVal);
1408 if (isa<PointerType>(constVal->getType()))
1409 MD->invalidateCachedPointerInfo(constVal);
1412 toErase.push_back(p);
1414 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1417 // If the number we were assigned was a brand new VN, then we don't
1418 // need to do a lookup to see if the number already exists
1419 // somewhere in the domtree: it can't!
1420 } else if (num == nextNum) {
1421 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1423 // Perform fast-path value-number based elimination of values inherited from
1425 } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1428 I->replaceAllUsesWith(repl);
1429 if (isa<PointerType>(repl->getType()))
1430 MD->invalidateCachedPointerInfo(repl);
1431 toErase.push_back(I);
1435 // Perform slow-pathvalue-number based elimination with phi construction.
1436 } else if (Value* repl = AttemptRedundancyElimination(I, num)) {
1439 I->replaceAllUsesWith(repl);
1440 if (isa<PointerType>(repl->getType()))
1441 MD->invalidateCachedPointerInfo(repl);
1442 toErase.push_back(I);
1446 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1452 /// runOnFunction - This is the main transformation entry point for a function.
1453 bool GVN::runOnFunction(Function& F) {
1454 MD = &getAnalysis<MemoryDependenceAnalysis>();
1455 DT = &getAnalysis<DominatorTree>();
1456 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1460 bool changed = false;
1461 bool shouldContinue = true;
1463 // Merge unconditional branches, allowing PRE to catch more
1464 // optimization opportunities.
1465 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1466 BasicBlock* BB = FI;
1468 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1469 if (removedBlock) NumGVNBlocks++;
1471 changed |= removedBlock;
1474 unsigned Iteration = 0;
1476 while (shouldContinue) {
1477 DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
1478 shouldContinue = iterateOnFunction(F);
1479 changed |= shouldContinue;
1484 bool PREChanged = true;
1485 while (PREChanged) {
1486 PREChanged = performPRE(F);
1487 changed |= PREChanged;
1490 // FIXME: Should perform GVN again after PRE does something. PRE can move
1491 // computations into blocks where they become fully redundant. Note that
1492 // we can't do this until PRE's critical edge splitting updates memdep.
1493 // Actually, when this happens, we should just fully integrate PRE into GVN.
1495 cleanupGlobalSets();
1501 bool GVN::processBlock(BasicBlock* BB) {
1502 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1503 // incrementing BI before processing an instruction).
1504 SmallVector<Instruction*, 8> toErase;
1505 bool changed_function = false;
1507 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1509 changed_function |= processInstruction(BI, toErase);
1510 if (toErase.empty()) {
1515 // If we need some instructions deleted, do it now.
1516 NumGVNInstr += toErase.size();
1518 // Avoid iterator invalidation.
1519 bool AtStart = BI == BB->begin();
1523 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1524 E = toErase.end(); I != E; ++I) {
1525 DEBUG(cerr << "GVN removed: " << **I);
1526 MD->removeInstruction(*I);
1527 (*I)->eraseFromParent();
1528 DEBUG(verifyRemoved(*I));
1538 return changed_function;
1541 /// performPRE - Perform a purely local form of PRE that looks for diamond
1542 /// control flow patterns and attempts to perform simple PRE at the join point.
1543 bool GVN::performPRE(Function& F) {
1544 bool Changed = false;
1545 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1546 DenseMap<BasicBlock*, Value*> predMap;
1547 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1548 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1549 BasicBlock* CurrentBlock = *DI;
1551 // Nothing to PRE in the entry block.
1552 if (CurrentBlock == &F.getEntryBlock()) continue;
1554 for (BasicBlock::iterator BI = CurrentBlock->begin(),
1555 BE = CurrentBlock->end(); BI != BE; ) {
1556 Instruction *CurInst = BI++;
1558 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
1559 isa<PHINode>(CurInst) || (CurInst->getType() == Type::VoidTy) ||
1560 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
1561 isa<DbgInfoIntrinsic>(CurInst))
1564 uint32_t valno = VN.lookup(CurInst);
1566 // Look for the predecessors for PRE opportunities. We're
1567 // only trying to solve the basic diamond case, where
1568 // a value is computed in the successor and one predecessor,
1569 // but not the other. We also explicitly disallow cases
1570 // where the successor is its own predecessor, because they're
1571 // more complicated to get right.
1572 unsigned numWith = 0;
1573 unsigned numWithout = 0;
1574 BasicBlock* PREPred = 0;
1577 for (pred_iterator PI = pred_begin(CurrentBlock),
1578 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1579 // We're not interested in PRE where the block is its
1580 // own predecessor, on in blocks with predecessors
1581 // that are not reachable.
1582 if (*PI == CurrentBlock) {
1585 } else if (!localAvail.count(*PI)) {
1590 DenseMap<uint32_t, Value*>::iterator predV =
1591 localAvail[*PI]->table.find(valno);
1592 if (predV == localAvail[*PI]->table.end()) {
1595 } else if (predV->second == CurInst) {
1598 predMap[*PI] = predV->second;
1603 // Don't do PRE when it might increase code size, i.e. when
1604 // we would need to insert instructions in more than one pred.
1605 if (numWithout != 1 || numWith == 0)
1608 // We can't do PRE safely on a critical edge, so instead we schedule
1609 // the edge to be split and perform the PRE the next time we iterate
1611 unsigned succNum = 0;
1612 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1614 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
1619 if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1620 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1624 // Instantiate the expression the in predecessor that lacked it.
1625 // Because we are going top-down through the block, all value numbers
1626 // will be available in the predecessor by the time we need them. Any
1627 // that weren't original present will have been instantiated earlier
1629 Instruction* PREInstr = CurInst->clone();
1630 bool success = true;
1631 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
1632 Value *Op = PREInstr->getOperand(i);
1633 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
1636 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
1637 PREInstr->setOperand(i, V);
1644 // Fail out if we encounter an operand that is not available in
1645 // the PRE predecessor. This is typically because of loads which
1646 // are not value numbered precisely.
1649 DEBUG(verifyRemoved(PREInstr));
1653 PREInstr->insertBefore(PREPred->getTerminator());
1654 PREInstr->setName(CurInst->getName() + ".pre");
1655 predMap[PREPred] = PREInstr;
1656 VN.add(PREInstr, valno);
1659 // Update the availability map to include the new instruction.
1660 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1662 // Create a PHI to make the value available in this block.
1663 PHINode* Phi = PHINode::Create(CurInst->getType(),
1664 CurInst->getName() + ".pre-phi",
1665 CurrentBlock->begin());
1666 for (pred_iterator PI = pred_begin(CurrentBlock),
1667 PE = pred_end(CurrentBlock); PI != PE; ++PI)
1668 Phi->addIncoming(predMap[*PI], *PI);
1671 localAvail[CurrentBlock]->table[valno] = Phi;
1673 CurInst->replaceAllUsesWith(Phi);
1674 if (isa<PointerType>(Phi->getType()))
1675 MD->invalidateCachedPointerInfo(Phi);
1678 DEBUG(cerr << "GVN PRE removed: " << *CurInst);
1679 MD->removeInstruction(CurInst);
1680 CurInst->eraseFromParent();
1681 DEBUG(verifyRemoved(CurInst));
1686 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1687 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1688 SplitCriticalEdge(I->first, I->second, this);
1690 return Changed || toSplit.size();
1693 /// iterateOnFunction - Executes one iteration of GVN
1694 bool GVN::iterateOnFunction(Function &F) {
1695 cleanupGlobalSets();
1697 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1698 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
1700 localAvail[DI->getBlock()] =
1701 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
1703 localAvail[DI->getBlock()] = new ValueNumberScope(0);
1706 // Top-down walk of the dominator tree
1707 bool changed = false;
1709 // Needed for value numbering with phi construction to work.
1710 ReversePostOrderTraversal<Function*> RPOT(&F);
1711 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
1712 RE = RPOT.end(); RI != RE; ++RI)
1713 changed |= processBlock(*RI);
1715 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1716 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
1717 changed |= processBlock(DI->getBlock());
1723 void GVN::cleanupGlobalSets() {
1727 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1728 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
1733 /// verifyRemoved - Verify that the specified instruction does not occur in our
1734 /// internal data structures.
1735 void GVN::verifyRemoved(const Instruction *Inst) const {
1736 VN.verifyRemoved(Inst);
1738 // Walk through the PHI map to make sure the instruction isn't hiding in there
1740 for (PhiMapType::iterator
1741 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) {
1742 assert(I->first != Inst && "Inst is still a key in PHI map!");
1744 for (SmallPtrSet<Instruction*, 4>::iterator
1745 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) {
1746 assert(*II != Inst && "Inst is still a value in PHI map!");
1750 // Walk through the value number scope to make sure the instruction isn't
1751 // ferreted away in it.
1752 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1753 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
1754 const ValueNumberScope *VNS = I->second;
1757 for (DenseMap<uint32_t, Value*>::iterator
1758 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
1759 assert(II->second != Inst && "Inst still in value numbering scope!");