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/Instructions.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"
43 STATISTIC(NumGVNInstr, "Number of instructions deleted");
44 STATISTIC(NumGVNLoad, "Number of loads deleted");
45 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
46 STATISTIC(NumGVNBlocks, "Number of blocks merged");
47 STATISTIC(NumPRELoad, "Number of loads PRE'd");
49 static cl::opt<bool> EnablePRE("enable-pre",
50 cl::init(true), cl::Hidden);
51 cl::opt<bool> EnableLoadPRE("enable-load-pre"/*, cl::init(true)*/);
53 //===----------------------------------------------------------------------===//
55 //===----------------------------------------------------------------------===//
57 /// This class holds the mapping between values and value numbers. It is used
58 /// as an efficient mechanism to determine the expression-wise equivalence of
61 struct VISIBILITY_HIDDEN Expression {
62 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
63 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
64 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
65 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
66 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
67 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
68 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
69 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
70 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
71 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
74 ExpressionOpcode opcode;
79 SmallVector<uint32_t, 4> varargs;
83 Expression(ExpressionOpcode o) : opcode(o) { }
85 bool operator==(const Expression &other) const {
86 if (opcode != other.opcode)
88 else if (opcode == EMPTY || opcode == TOMBSTONE)
90 else if (type != other.type)
92 else if (function != other.function)
94 else if (firstVN != other.firstVN)
96 else if (secondVN != other.secondVN)
98 else if (thirdVN != other.thirdVN)
101 if (varargs.size() != other.varargs.size())
104 for (size_t i = 0; i < varargs.size(); ++i)
105 if (varargs[i] != other.varargs[i])
112 bool operator!=(const Expression &other) const {
113 if (opcode != other.opcode)
115 else if (opcode == EMPTY || opcode == TOMBSTONE)
117 else if (type != other.type)
119 else if (function != other.function)
121 else if (firstVN != other.firstVN)
123 else if (secondVN != other.secondVN)
125 else if (thirdVN != other.thirdVN)
128 if (varargs.size() != other.varargs.size())
131 for (size_t i = 0; i < varargs.size(); ++i)
132 if (varargs[i] != other.varargs[i])
140 class VISIBILITY_HIDDEN ValueTable {
142 DenseMap<Value*, uint32_t> valueNumbering;
143 DenseMap<Expression, uint32_t> expressionNumbering;
145 MemoryDependenceAnalysis* MD;
148 uint32_t nextValueNumber;
150 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
151 Expression::ExpressionOpcode getOpcode(CmpInst* C);
152 Expression::ExpressionOpcode getOpcode(CastInst* C);
153 Expression create_expression(BinaryOperator* BO);
154 Expression create_expression(CmpInst* C);
155 Expression create_expression(ShuffleVectorInst* V);
156 Expression create_expression(ExtractElementInst* C);
157 Expression create_expression(InsertElementInst* V);
158 Expression create_expression(SelectInst* V);
159 Expression create_expression(CastInst* C);
160 Expression create_expression(GetElementPtrInst* G);
161 Expression create_expression(CallInst* C);
162 Expression create_expression(Constant* C);
164 ValueTable() : nextValueNumber(1) { }
165 uint32_t lookup_or_add(Value* V);
166 uint32_t lookup(Value* V) const;
167 void add(Value* V, uint32_t num);
169 void erase(Value* v);
171 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
172 AliasAnalysis *getAliasAnalysis() const { return AA; }
173 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
174 void setDomTree(DominatorTree* D) { DT = D; }
175 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
176 void verifyRemoved(const Value *) const;
181 template <> struct DenseMapInfo<Expression> {
182 static inline Expression getEmptyKey() {
183 return Expression(Expression::EMPTY);
186 static inline Expression getTombstoneKey() {
187 return Expression(Expression::TOMBSTONE);
190 static unsigned getHashValue(const Expression e) {
191 unsigned hash = e.opcode;
193 hash = e.firstVN + hash * 37;
194 hash = e.secondVN + hash * 37;
195 hash = e.thirdVN + hash * 37;
197 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
198 (unsigned)((uintptr_t)e.type >> 9)) +
201 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
202 E = e.varargs.end(); I != E; ++I)
203 hash = *I + hash * 37;
205 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
206 (unsigned)((uintptr_t)e.function >> 9)) +
211 static bool isEqual(const Expression &LHS, const Expression &RHS) {
214 static bool isPod() { return true; }
218 //===----------------------------------------------------------------------===//
219 // ValueTable Internal Functions
220 //===----------------------------------------------------------------------===//
221 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
222 switch(BO->getOpcode()) {
223 default: // THIS SHOULD NEVER HAPPEN
224 assert(0 && "Binary operator with unknown opcode?");
225 case Instruction::Add: return Expression::ADD;
226 case Instruction::Sub: return Expression::SUB;
227 case Instruction::Mul: return Expression::MUL;
228 case Instruction::UDiv: return Expression::UDIV;
229 case Instruction::SDiv: return Expression::SDIV;
230 case Instruction::FDiv: return Expression::FDIV;
231 case Instruction::URem: return Expression::UREM;
232 case Instruction::SRem: return Expression::SREM;
233 case Instruction::FRem: return Expression::FREM;
234 case Instruction::Shl: return Expression::SHL;
235 case Instruction::LShr: return Expression::LSHR;
236 case Instruction::AShr: return Expression::ASHR;
237 case Instruction::And: return Expression::AND;
238 case Instruction::Or: return Expression::OR;
239 case Instruction::Xor: return Expression::XOR;
243 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
244 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
245 switch (C->getPredicate()) {
246 default: // THIS SHOULD NEVER HAPPEN
247 assert(0 && "Comparison with unknown predicate?");
248 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
249 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
250 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
251 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
252 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
253 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
254 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
255 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
256 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
257 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
260 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
261 switch (C->getPredicate()) {
262 default: // THIS SHOULD NEVER HAPPEN
263 assert(0 && "Comparison with unknown predicate?");
264 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
265 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
266 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
267 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
268 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
269 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
270 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
271 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
272 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
273 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
274 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
275 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
276 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
277 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
281 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
282 switch(C->getOpcode()) {
283 default: // THIS SHOULD NEVER HAPPEN
284 assert(0 && "Cast operator with unknown opcode?");
285 case Instruction::Trunc: return Expression::TRUNC;
286 case Instruction::ZExt: return Expression::ZEXT;
287 case Instruction::SExt: return Expression::SEXT;
288 case Instruction::FPToUI: return Expression::FPTOUI;
289 case Instruction::FPToSI: return Expression::FPTOSI;
290 case Instruction::UIToFP: return Expression::UITOFP;
291 case Instruction::SIToFP: return Expression::SITOFP;
292 case Instruction::FPTrunc: return Expression::FPTRUNC;
293 case Instruction::FPExt: return Expression::FPEXT;
294 case Instruction::PtrToInt: return Expression::PTRTOINT;
295 case Instruction::IntToPtr: return Expression::INTTOPTR;
296 case Instruction::BitCast: return Expression::BITCAST;
300 Expression ValueTable::create_expression(CallInst* C) {
303 e.type = C->getType();
307 e.function = C->getCalledFunction();
308 e.opcode = Expression::CALL;
310 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
312 e.varargs.push_back(lookup_or_add(*I));
317 Expression ValueTable::create_expression(BinaryOperator* BO) {
320 e.firstVN = lookup_or_add(BO->getOperand(0));
321 e.secondVN = lookup_or_add(BO->getOperand(1));
324 e.type = BO->getType();
325 e.opcode = getOpcode(BO);
330 Expression ValueTable::create_expression(CmpInst* C) {
333 e.firstVN = lookup_or_add(C->getOperand(0));
334 e.secondVN = lookup_or_add(C->getOperand(1));
337 e.type = C->getType();
338 e.opcode = getOpcode(C);
343 Expression ValueTable::create_expression(CastInst* C) {
346 e.firstVN = lookup_or_add(C->getOperand(0));
350 e.type = C->getType();
351 e.opcode = getOpcode(C);
356 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
359 e.firstVN = lookup_or_add(S->getOperand(0));
360 e.secondVN = lookup_or_add(S->getOperand(1));
361 e.thirdVN = lookup_or_add(S->getOperand(2));
363 e.type = S->getType();
364 e.opcode = Expression::SHUFFLE;
369 Expression ValueTable::create_expression(ExtractElementInst* E) {
372 e.firstVN = lookup_or_add(E->getOperand(0));
373 e.secondVN = lookup_or_add(E->getOperand(1));
376 e.type = E->getType();
377 e.opcode = Expression::EXTRACT;
382 Expression ValueTable::create_expression(InsertElementInst* I) {
385 e.firstVN = lookup_or_add(I->getOperand(0));
386 e.secondVN = lookup_or_add(I->getOperand(1));
387 e.thirdVN = lookup_or_add(I->getOperand(2));
389 e.type = I->getType();
390 e.opcode = Expression::INSERT;
395 Expression ValueTable::create_expression(SelectInst* I) {
398 e.firstVN = lookup_or_add(I->getCondition());
399 e.secondVN = lookup_or_add(I->getTrueValue());
400 e.thirdVN = lookup_or_add(I->getFalseValue());
402 e.type = I->getType();
403 e.opcode = Expression::SELECT;
408 Expression ValueTable::create_expression(GetElementPtrInst* G) {
411 e.firstVN = lookup_or_add(G->getPointerOperand());
415 e.type = G->getType();
416 e.opcode = Expression::GEP;
418 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
420 e.varargs.push_back(lookup_or_add(*I));
425 //===----------------------------------------------------------------------===//
426 // ValueTable External Functions
427 //===----------------------------------------------------------------------===//
429 /// add - Insert a value into the table with a specified value number.
430 void ValueTable::add(Value* V, uint32_t num) {
431 valueNumbering.insert(std::make_pair(V, num));
434 /// lookup_or_add - Returns the value number for the specified value, assigning
435 /// it a new number if it did not have one before.
436 uint32_t ValueTable::lookup_or_add(Value* V) {
437 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
438 if (VI != valueNumbering.end())
441 if (CallInst* C = dyn_cast<CallInst>(V)) {
442 if (AA->doesNotAccessMemory(C)) {
443 Expression e = create_expression(C);
445 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
446 if (EI != expressionNumbering.end()) {
447 valueNumbering.insert(std::make_pair(V, EI->second));
450 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
451 valueNumbering.insert(std::make_pair(V, nextValueNumber));
453 return nextValueNumber++;
455 } else if (AA->onlyReadsMemory(C)) {
456 Expression e = create_expression(C);
458 if (expressionNumbering.find(e) == expressionNumbering.end()) {
459 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
460 valueNumbering.insert(std::make_pair(V, nextValueNumber));
461 return nextValueNumber++;
464 MemDepResult local_dep = MD->getDependency(C);
466 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
467 valueNumbering.insert(std::make_pair(V, nextValueNumber));
468 return nextValueNumber++;
471 if (local_dep.isDef()) {
472 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
474 if (local_cdep->getNumOperands() != C->getNumOperands()) {
475 valueNumbering.insert(std::make_pair(V, nextValueNumber));
476 return nextValueNumber++;
479 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
480 uint32_t c_vn = lookup_or_add(C->getOperand(i));
481 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
483 valueNumbering.insert(std::make_pair(V, nextValueNumber));
484 return nextValueNumber++;
488 uint32_t v = lookup_or_add(local_cdep);
489 valueNumbering.insert(std::make_pair(V, v));
494 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
495 MD->getNonLocalCallDependency(CallSite(C));
496 // FIXME: call/call dependencies for readonly calls should return def, not
497 // clobber! Move the checking logic to MemDep!
500 // Check to see if we have a single dominating call instruction that is
502 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
503 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
504 // Ignore non-local dependencies.
505 if (I->second.isNonLocal())
508 // We don't handle non-depedencies. If we already have a call, reject
509 // instruction dependencies.
510 if (I->second.isClobber() || cdep != 0) {
515 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
516 // FIXME: All duplicated with non-local case.
517 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
518 cdep = NonLocalDepCall;
527 valueNumbering.insert(std::make_pair(V, nextValueNumber));
528 return nextValueNumber++;
531 if (cdep->getNumOperands() != C->getNumOperands()) {
532 valueNumbering.insert(std::make_pair(V, nextValueNumber));
533 return nextValueNumber++;
535 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
536 uint32_t c_vn = lookup_or_add(C->getOperand(i));
537 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
539 valueNumbering.insert(std::make_pair(V, nextValueNumber));
540 return nextValueNumber++;
544 uint32_t v = lookup_or_add(cdep);
545 valueNumbering.insert(std::make_pair(V, v));
549 valueNumbering.insert(std::make_pair(V, nextValueNumber));
550 return nextValueNumber++;
552 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
553 Expression e = create_expression(BO);
555 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
556 if (EI != expressionNumbering.end()) {
557 valueNumbering.insert(std::make_pair(V, EI->second));
560 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
561 valueNumbering.insert(std::make_pair(V, nextValueNumber));
563 return nextValueNumber++;
565 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
566 Expression e = create_expression(C);
568 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
569 if (EI != expressionNumbering.end()) {
570 valueNumbering.insert(std::make_pair(V, EI->second));
573 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
574 valueNumbering.insert(std::make_pair(V, nextValueNumber));
576 return nextValueNumber++;
578 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
579 Expression e = create_expression(U);
581 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
582 if (EI != expressionNumbering.end()) {
583 valueNumbering.insert(std::make_pair(V, EI->second));
586 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
587 valueNumbering.insert(std::make_pair(V, nextValueNumber));
589 return nextValueNumber++;
591 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
592 Expression e = create_expression(U);
594 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
595 if (EI != expressionNumbering.end()) {
596 valueNumbering.insert(std::make_pair(V, EI->second));
599 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
600 valueNumbering.insert(std::make_pair(V, nextValueNumber));
602 return nextValueNumber++;
604 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
605 Expression e = create_expression(U);
607 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
608 if (EI != expressionNumbering.end()) {
609 valueNumbering.insert(std::make_pair(V, EI->second));
612 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
613 valueNumbering.insert(std::make_pair(V, nextValueNumber));
615 return nextValueNumber++;
617 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
618 Expression e = create_expression(U);
620 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
621 if (EI != expressionNumbering.end()) {
622 valueNumbering.insert(std::make_pair(V, EI->second));
625 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
626 valueNumbering.insert(std::make_pair(V, nextValueNumber));
628 return nextValueNumber++;
630 } else if (CastInst* U = dyn_cast<CastInst>(V)) {
631 Expression e = create_expression(U);
633 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
634 if (EI != expressionNumbering.end()) {
635 valueNumbering.insert(std::make_pair(V, EI->second));
638 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
639 valueNumbering.insert(std::make_pair(V, nextValueNumber));
641 return nextValueNumber++;
643 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
644 Expression e = create_expression(U);
646 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
647 if (EI != expressionNumbering.end()) {
648 valueNumbering.insert(std::make_pair(V, EI->second));
651 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
652 valueNumbering.insert(std::make_pair(V, nextValueNumber));
654 return nextValueNumber++;
657 valueNumbering.insert(std::make_pair(V, nextValueNumber));
658 return nextValueNumber++;
662 /// lookup - Returns the value number of the specified value. Fails if
663 /// the value has not yet been numbered.
664 uint32_t ValueTable::lookup(Value* V) const {
665 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
666 assert(VI != valueNumbering.end() && "Value not numbered?");
670 /// clear - Remove all entries from the ValueTable
671 void ValueTable::clear() {
672 valueNumbering.clear();
673 expressionNumbering.clear();
677 /// erase - Remove a value from the value numbering
678 void ValueTable::erase(Value* V) {
679 valueNumbering.erase(V);
682 /// verifyRemoved - Verify that the value is removed from all internal data
684 void ValueTable::verifyRemoved(const Value *V) const {
685 for (DenseMap<Value*, uint32_t>::iterator
686 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
687 assert(I->first != V && "Inst still occurs in value numbering map!");
691 //===----------------------------------------------------------------------===//
693 //===----------------------------------------------------------------------===//
696 struct VISIBILITY_HIDDEN ValueNumberScope {
697 ValueNumberScope* parent;
698 DenseMap<uint32_t, Value*> table;
700 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
706 class VISIBILITY_HIDDEN GVN : public FunctionPass {
707 bool runOnFunction(Function &F);
709 static char ID; // Pass identification, replacement for typeid
710 GVN() : FunctionPass(&ID) { }
713 MemoryDependenceAnalysis *MD;
717 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
719 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
723 // This transformation requires dominator postdominator info
724 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
725 AU.addRequired<DominatorTree>();
726 AU.addRequired<MemoryDependenceAnalysis>();
727 AU.addRequired<AliasAnalysis>();
729 AU.addPreserved<DominatorTree>();
730 AU.addPreserved<AliasAnalysis>();
734 // FIXME: eliminate or document these better
735 bool processLoad(LoadInst* L,
736 SmallVectorImpl<Instruction*> &toErase);
737 bool processInstruction(Instruction* I,
738 SmallVectorImpl<Instruction*> &toErase);
739 bool processNonLocalLoad(LoadInst* L,
740 SmallVectorImpl<Instruction*> &toErase);
741 bool processBlock(BasicBlock* BB);
742 Value *GetValueForBlock(BasicBlock *BB, Instruction* orig,
743 DenseMap<BasicBlock*, Value*> &Phis,
744 bool top_level = false);
745 void dump(DenseMap<uint32_t, Value*>& d);
746 bool iterateOnFunction(Function &F);
747 Value* CollapsePhi(PHINode* p);
748 bool isSafeReplacement(PHINode* p, Instruction* inst);
749 bool performPRE(Function& F);
750 Value* lookupNumber(BasicBlock* BB, uint32_t num);
751 bool mergeBlockIntoPredecessor(BasicBlock* BB);
752 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno);
753 void cleanupGlobalSets();
754 void verifyRemoved(const Instruction *I) const;
760 // createGVNPass - The public interface to this file...
761 FunctionPass *llvm::createGVNPass() { return new GVN(); }
763 static RegisterPass<GVN> X("gvn",
764 "Global Value Numbering");
766 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
768 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
769 E = d.end(); I != E; ++I) {
770 printf("%d\n", I->first);
776 Value* GVN::CollapsePhi(PHINode* p) {
777 Value* constVal = p->hasConstantValue();
778 if (!constVal) return 0;
780 Instruction* inst = dyn_cast<Instruction>(constVal);
784 if (DT->dominates(inst, p))
785 if (isSafeReplacement(p, inst))
790 bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
791 if (!isa<PHINode>(inst))
794 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
796 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
797 if (use_phi->getParent() == inst->getParent())
803 /// GetValueForBlock - Get the value to use within the specified basic block.
804 /// available values are in Phis.
805 Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig,
806 DenseMap<BasicBlock*, Value*> &Phis,
809 // If we have already computed this value, return the previously computed val.
810 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
811 if (V != Phis.end() && !top_level) return V->second;
813 // If the block is unreachable, just return undef, since this path
814 // can't actually occur at runtime.
815 if (!DT->isReachableFromEntry(BB))
816 return Phis[BB] = UndefValue::get(orig->getType());
818 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
819 Value *ret = GetValueForBlock(Pred, orig, Phis);
824 // Get the number of predecessors of this block so we can reserve space later.
825 // If there is already a PHI in it, use the #preds from it, otherwise count.
826 // Getting it from the PHI is constant time.
828 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
829 NumPreds = ExistingPN->getNumIncomingValues();
831 NumPreds = std::distance(pred_begin(BB), pred_end(BB));
833 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
834 // now, then get values to fill in the incoming values for the PHI.
835 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
837 PN->reserveOperandSpace(NumPreds);
839 Phis.insert(std::make_pair(BB, PN));
841 // Fill in the incoming values for the block.
842 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
843 Value* val = GetValueForBlock(*PI, orig, Phis);
844 PN->addIncoming(val, *PI);
847 VN.getAliasAnalysis()->copyValue(orig, PN);
849 // Attempt to collapse PHI nodes that are trivially redundant
850 Value* v = CollapsePhi(PN);
852 // Cache our phi construction results
853 if (LoadInst* L = dyn_cast<LoadInst>(orig))
854 phiMap[L->getPointerOperand()].insert(PN);
856 phiMap[orig].insert(PN);
861 PN->replaceAllUsesWith(v);
862 if (isa<PointerType>(v->getType()))
863 MD->invalidateCachedPointerInfo(v);
865 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
866 E = Phis.end(); I != E; ++I)
870 DEBUG(cerr << "GVN removed: " << *PN);
871 MD->removeInstruction(PN);
872 PN->eraseFromParent();
873 DEBUG(verifyRemoved(PN));
879 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
880 /// we're analyzing is fully available in the specified block. As we go, keep
881 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
882 /// map is actually a tri-state map with the following values:
883 /// 0) we know the block *is not* fully available.
884 /// 1) we know the block *is* fully available.
885 /// 2) we do not know whether the block is fully available or not, but we are
886 /// currently speculating that it will be.
887 /// 3) we are speculating for this block and have used that to speculate for
889 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
890 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
891 // Optimistically assume that the block is fully available and check to see
892 // if we already know about this block in one lookup.
893 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
894 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
896 // If the entry already existed for this block, return the precomputed value.
898 // If this is a speculative "available" value, mark it as being used for
899 // speculation of other blocks.
900 if (IV.first->second == 2)
901 IV.first->second = 3;
902 return IV.first->second != 0;
905 // Otherwise, see if it is fully available in all predecessors.
906 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
908 // If this block has no predecessors, it isn't live-in here.
910 goto SpeculationFailure;
912 for (; PI != PE; ++PI)
913 // If the value isn't fully available in one of our predecessors, then it
914 // isn't fully available in this block either. Undo our previous
915 // optimistic assumption and bail out.
916 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
917 goto SpeculationFailure;
921 // SpeculationFailure - If we get here, we found out that this is not, after
922 // all, a fully-available block. We have a problem if we speculated on this and
923 // used the speculation to mark other blocks as available.
925 char &BBVal = FullyAvailableBlocks[BB];
927 // If we didn't speculate on this, just return with it set to false.
933 // If we did speculate on this value, we could have blocks set to 1 that are
934 // incorrect. Walk the (transitive) successors of this block and mark them as
936 SmallVector<BasicBlock*, 32> BBWorklist;
937 BBWorklist.push_back(BB);
939 while (!BBWorklist.empty()) {
940 BasicBlock *Entry = BBWorklist.pop_back_val();
941 // Note that this sets blocks to 0 (unavailable) if they happen to not
942 // already be in FullyAvailableBlocks. This is safe.
943 char &EntryVal = FullyAvailableBlocks[Entry];
944 if (EntryVal == 0) continue; // Already unavailable.
946 // Mark as unavailable.
949 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
950 BBWorklist.push_back(*I);
956 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
957 /// non-local by performing PHI construction.
958 bool GVN::processNonLocalLoad(LoadInst *LI,
959 SmallVectorImpl<Instruction*> &toErase) {
960 // Find the non-local dependencies of the load.
961 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
962 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
964 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
966 // If we had to process more than one hundred blocks to find the
967 // dependencies, this load isn't worth worrying about. Optimizing
968 // it will be too expensive.
969 if (Deps.size() > 100)
972 // If we had a phi translation failure, we'll have a single entry which is a
973 // clobber in the current block. Reject this early.
974 if (Deps.size() == 1 && Deps[0].second.isClobber())
977 // Filter out useless results (non-locals, etc). Keep track of the blocks
978 // where we have a value available in repl, also keep track of whether we see
979 // dependencies that produce an unknown value for the load (such as a call
980 // that could potentially clobber the load).
981 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
982 SmallVector<BasicBlock*, 16> UnavailableBlocks;
984 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
985 BasicBlock *DepBB = Deps[i].first;
986 MemDepResult DepInfo = Deps[i].second;
988 if (DepInfo.isClobber()) {
989 UnavailableBlocks.push_back(DepBB);
993 Instruction *DepInst = DepInfo.getInst();
995 // Loading the allocation -> undef.
996 if (isa<AllocationInst>(DepInst)) {
997 ValuesPerBlock.push_back(std::make_pair(DepBB,
998 UndefValue::get(LI->getType())));
1002 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
1003 // Reject loads and stores that are to the same address but are of
1005 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
1006 // of bitfield access, it would be interesting to optimize for it at some
1008 if (S->getOperand(0)->getType() != LI->getType()) {
1009 UnavailableBlocks.push_back(DepBB);
1013 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
1015 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
1016 if (LD->getType() != LI->getType()) {
1017 UnavailableBlocks.push_back(DepBB);
1020 ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
1022 UnavailableBlocks.push_back(DepBB);
1027 // If we have no predecessors that produce a known value for this load, exit
1029 if (ValuesPerBlock.empty()) return false;
1031 // If all of the instructions we depend on produce a known value for this
1032 // load, then it is fully redundant and we can use PHI insertion to compute
1033 // its value. Insert PHIs and remove the fully redundant value now.
1034 if (UnavailableBlocks.empty()) {
1035 // Use cached PHI construction information from previous runs
1036 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1037 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
1038 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1040 if ((*I)->getParent() == LI->getParent()) {
1041 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
1042 LI->replaceAllUsesWith(*I);
1043 if (isa<PointerType>((*I)->getType()))
1044 MD->invalidateCachedPointerInfo(*I);
1045 toErase.push_back(LI);
1050 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1053 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
1055 DenseMap<BasicBlock*, Value*> BlockReplValues;
1056 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1057 // Perform PHI construction.
1058 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1059 LI->replaceAllUsesWith(v);
1061 if (!isa<GlobalValue>(v))
1063 if (isa<PointerType>(v->getType()))
1064 MD->invalidateCachedPointerInfo(v);
1065 toErase.push_back(LI);
1070 if (!EnablePRE || !EnableLoadPRE)
1073 // Okay, we have *some* definitions of the value. This means that the value
1074 // is available in some of our (transitive) predecessors. Lets think about
1075 // doing PRE of this load. This will involve inserting a new load into the
1076 // predecessor when it's not available. We could do this in general, but
1077 // prefer to not increase code size. As such, we only do this when we know
1078 // that we only have to insert *one* load (which means we're basically moving
1079 // the load, not inserting a new one).
1081 // Everything we do here is based on local predecessors of LI's block. If it
1082 // only has one predecessor, bail now.
1083 BasicBlock *LoadBB = LI->getParent();
1084 if (LoadBB->getSinglePredecessor())
1087 // If we have a repl set with LI itself in it, this means we have a loop where
1088 // at least one of the values is LI. Since this means that we won't be able
1089 // to eliminate LI even if we insert uses in the other predecessors, we will
1090 // end up increasing code size. Reject this by scanning for LI.
1091 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1092 if (ValuesPerBlock[i].second == LI)
1095 // Okay, we have some hope :). Check to see if the loaded value is fully
1096 // available in all but one predecessor.
1097 // FIXME: If we could restructure the CFG, we could make a common pred with
1098 // all the preds that don't have an available LI and insert a new load into
1100 BasicBlock *UnavailablePred = 0;
1102 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1103 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1104 FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
1105 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1106 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1108 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1110 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1113 // If this load is not available in multiple predecessors, reject it.
1114 if (UnavailablePred && UnavailablePred != *PI)
1116 UnavailablePred = *PI;
1119 assert(UnavailablePred != 0 &&
1120 "Fully available value should be eliminated above!");
1122 // If the loaded pointer is PHI node defined in this block, do PHI translation
1123 // to get its value in the predecessor.
1124 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
1126 // Make sure the value is live in the predecessor. If it was defined by a
1127 // non-PHI instruction in this block, we don't know how to recompute it above.
1128 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
1129 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
1130 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
1131 << *LPInst << *LI << "\n");
1135 // We don't currently handle critical edges :(
1136 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1137 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1138 << UnavailablePred->getName() << "': " << *LI);
1142 // Okay, we can eliminate this load by inserting a reload in the predecessor
1143 // and using PHI construction to get the value in the other predecessors, do
1145 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
1147 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1149 UnavailablePred->getTerminator());
1151 DenseMap<BasicBlock*, Value*> BlockReplValues;
1152 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1153 BlockReplValues[UnavailablePred] = NewLoad;
1155 // Perform PHI construction.
1156 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1157 LI->replaceAllUsesWith(v);
1158 if (!isa<GlobalValue>(v))
1160 if (isa<PointerType>(v->getType()))
1161 MD->invalidateCachedPointerInfo(v);
1162 toErase.push_back(LI);
1167 /// processLoad - Attempt to eliminate a load, first by eliminating it
1168 /// locally, and then attempting non-local elimination if that fails.
1169 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1170 if (L->isVolatile())
1173 Value* pointer = L->getPointerOperand();
1175 // ... to a pointer that has been loaded from before...
1176 MemDepResult dep = MD->getDependency(L);
1178 // If the value isn't available, don't do anything!
1179 if (dep.isClobber())
1182 // If it is defined in another block, try harder.
1183 if (dep.isNonLocal())
1184 return processNonLocalLoad(L, toErase);
1186 Instruction *DepInst = dep.getInst();
1187 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1188 // Only forward substitute stores to loads of the same type.
1189 // FIXME: Could do better!
1190 if (DepSI->getPointerOperand()->getType() != pointer->getType())
1194 L->replaceAllUsesWith(DepSI->getOperand(0));
1195 if (isa<PointerType>(DepSI->getOperand(0)->getType()))
1196 MD->invalidateCachedPointerInfo(DepSI->getOperand(0));
1197 toErase.push_back(L);
1202 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1203 // Only forward substitute stores to loads of the same type.
1204 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
1205 if (DepLI->getType() != L->getType())
1209 L->replaceAllUsesWith(DepLI);
1210 if (isa<PointerType>(DepLI->getType()))
1211 MD->invalidateCachedPointerInfo(DepLI);
1212 toErase.push_back(L);
1217 // If this load really doesn't depend on anything, then we must be loading an
1218 // undef value. This can happen when loading for a fresh allocation with no
1219 // intervening stores, for example.
1220 if (isa<AllocationInst>(DepInst)) {
1221 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1222 toErase.push_back(L);
1230 Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1231 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1232 if (I == localAvail.end())
1235 ValueNumberScope* locals = I->second;
1238 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1239 if (I != locals->table.end())
1242 locals = locals->parent;
1248 /// AttemptRedundancyElimination - If the "fast path" of redundancy elimination
1249 /// by inheritance from the dominator fails, see if we can perform phi
1250 /// construction to eliminate the redundancy.
1251 Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) {
1252 BasicBlock* BaseBlock = orig->getParent();
1254 SmallPtrSet<BasicBlock*, 4> Visited;
1255 SmallVector<BasicBlock*, 8> Stack;
1256 Stack.push_back(BaseBlock);
1258 DenseMap<BasicBlock*, Value*> Results;
1260 // Walk backwards through our predecessors, looking for instances of the
1261 // value number we're looking for. Instances are recorded in the Results
1262 // map, which is then used to perform phi construction.
1263 while (!Stack.empty()) {
1264 BasicBlock* Current = Stack.back();
1267 // If we've walked all the way to a proper dominator, then give up. Cases
1268 // where the instance is in the dominator will have been caught by the fast
1269 // path, and any cases that require phi construction further than this are
1270 // probably not worth it anyways. Note that this is a SIGNIFICANT compile
1271 // time improvement.
1272 if (DT->properlyDominates(Current, orig->getParent())) return 0;
1274 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA =
1275 localAvail.find(Current);
1276 if (LA == localAvail.end()) return 0;
1277 DenseMap<unsigned, Value*>::iterator V = LA->second->table.find(valno);
1279 if (V != LA->second->table.end()) {
1280 // Found an instance, record it.
1281 Results.insert(std::make_pair(Current, V->second));
1285 // If we reach the beginning of the function, then give up.
1286 if (pred_begin(Current) == pred_end(Current))
1289 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current);
1291 if (Visited.insert(*PI))
1292 Stack.push_back(*PI);
1295 // If we didn't find instances, give up. Otherwise, perform phi construction.
1296 if (Results.size() == 0)
1299 return GetValueForBlock(BaseBlock, orig, Results, true);
1302 /// processInstruction - When calculating availability, handle an instruction
1303 /// by inserting it into the appropriate sets
1304 bool GVN::processInstruction(Instruction *I,
1305 SmallVectorImpl<Instruction*> &toErase) {
1306 if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1307 bool changed = processLoad(L, toErase);
1310 unsigned num = VN.lookup_or_add(L);
1311 localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1317 uint32_t nextNum = VN.getNextUnusedValueNumber();
1318 unsigned num = VN.lookup_or_add(I);
1320 // Allocations are always uniquely numbered, so we can save time and memory
1321 // by fast failing them.
1322 if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
1323 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1327 // Collapse PHI nodes
1328 if (PHINode* p = dyn_cast<PHINode>(I)) {
1329 Value* constVal = CollapsePhi(p);
1332 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1334 PI->second.erase(p);
1336 p->replaceAllUsesWith(constVal);
1337 if (isa<PointerType>(constVal->getType()))
1338 MD->invalidateCachedPointerInfo(constVal);
1339 toErase.push_back(p);
1341 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1344 // If the number we were assigned was a brand new VN, then we don't
1345 // need to do a lookup to see if the number already exists
1346 // somewhere in the domtree: it can't!
1347 } else if (num == nextNum) {
1348 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1350 // Perform fast-path value-number based elimination of values inherited from
1352 } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1355 I->replaceAllUsesWith(repl);
1356 if (isa<PointerType>(repl->getType()))
1357 MD->invalidateCachedPointerInfo(repl);
1358 toErase.push_back(I);
1362 // Perform slow-pathvalue-number based elimination with phi construction.
1363 } else if (Value* repl = AttemptRedundancyElimination(I, num)) {
1366 I->replaceAllUsesWith(repl);
1367 if (isa<PointerType>(repl->getType()))
1368 MD->invalidateCachedPointerInfo(repl);
1369 toErase.push_back(I);
1373 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1379 // GVN::runOnFunction - This is the main transformation entry point for a
1382 bool GVN::runOnFunction(Function& F) {
1383 MD = &getAnalysis<MemoryDependenceAnalysis>();
1384 DT = &getAnalysis<DominatorTree>();
1385 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1389 bool changed = false;
1390 bool shouldContinue = true;
1392 // Merge unconditional branches, allowing PRE to catch more
1393 // optimization opportunities.
1394 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1395 BasicBlock* BB = FI;
1397 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1398 if (removedBlock) NumGVNBlocks++;
1400 changed |= removedBlock;
1403 unsigned Iteration = 0;
1405 while (shouldContinue) {
1406 DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
1407 shouldContinue = iterateOnFunction(F);
1408 changed |= shouldContinue;
1413 bool PREChanged = true;
1414 while (PREChanged) {
1415 PREChanged = performPRE(F);
1416 changed |= PREChanged;
1419 // FIXME: Should perform GVN again after PRE does something. PRE can move
1420 // computations into blocks where they become fully redundant. Note that
1421 // we can't do this until PRE's critical edge splitting updates memdep.
1422 // Actually, when this happens, we should just fully integrate PRE into GVN.
1424 cleanupGlobalSets();
1430 bool GVN::processBlock(BasicBlock* BB) {
1431 DomTreeNode* DTN = DT->getNode(BB);
1432 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1433 // incrementing BI before processing an instruction).
1434 SmallVector<Instruction*, 8> toErase;
1435 bool changed_function = false;
1439 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]);
1441 localAvail[BB] = new ValueNumberScope(0);
1443 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1445 changed_function |= processInstruction(BI, toErase);
1446 if (toErase.empty()) {
1451 // If we need some instructions deleted, do it now.
1452 NumGVNInstr += toErase.size();
1454 // Avoid iterator invalidation.
1455 bool AtStart = BI == BB->begin();
1459 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1460 E = toErase.end(); I != E; ++I) {
1461 DEBUG(cerr << "GVN removed: " << **I);
1462 MD->removeInstruction(*I);
1463 (*I)->eraseFromParent();
1464 DEBUG(verifyRemoved(*I));
1474 return changed_function;
1477 /// performPRE - Perform a purely local form of PRE that looks for diamond
1478 /// control flow patterns and attempts to perform simple PRE at the join point.
1479 bool GVN::performPRE(Function& F) {
1480 bool Changed = false;
1481 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1482 DenseMap<BasicBlock*, Value*> predMap;
1483 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1484 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1485 BasicBlock* CurrentBlock = *DI;
1487 // Nothing to PRE in the entry block.
1488 if (CurrentBlock == &F.getEntryBlock()) continue;
1490 for (BasicBlock::iterator BI = CurrentBlock->begin(),
1491 BE = CurrentBlock->end(); BI != BE; ) {
1492 Instruction *CurInst = BI++;
1494 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
1495 isa<PHINode>(CurInst) || CurInst->mayReadFromMemory() ||
1496 CurInst->mayWriteToMemory())
1499 uint32_t valno = VN.lookup(CurInst);
1501 // Look for the predecessors for PRE opportunities. We're
1502 // only trying to solve the basic diamond case, where
1503 // a value is computed in the successor and one predecessor,
1504 // but not the other. We also explicitly disallow cases
1505 // where the successor is its own predecessor, because they're
1506 // more complicated to get right.
1507 unsigned numWith = 0;
1508 unsigned numWithout = 0;
1509 BasicBlock* PREPred = 0;
1512 for (pred_iterator PI = pred_begin(CurrentBlock),
1513 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1514 // We're not interested in PRE where the block is its
1515 // own predecessor, on in blocks with predecessors
1516 // that are not reachable.
1517 if (*PI == CurrentBlock) {
1520 } else if (!localAvail.count(*PI)) {
1525 DenseMap<uint32_t, Value*>::iterator predV =
1526 localAvail[*PI]->table.find(valno);
1527 if (predV == localAvail[*PI]->table.end()) {
1530 } else if (predV->second == CurInst) {
1533 predMap[*PI] = predV->second;
1538 // Don't do PRE when it might increase code size, i.e. when
1539 // we would need to insert instructions in more than one pred.
1540 if (numWithout != 1 || numWith == 0)
1543 // We can't do PRE safely on a critical edge, so instead we schedule
1544 // the edge to be split and perform the PRE the next time we iterate
1546 unsigned succNum = 0;
1547 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1549 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
1554 if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1555 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1559 // Instantiate the expression the in predecessor that lacked it.
1560 // Because we are going top-down through the block, all value numbers
1561 // will be available in the predecessor by the time we need them. Any
1562 // that weren't original present will have been instantiated earlier
1564 Instruction* PREInstr = CurInst->clone();
1565 bool success = true;
1566 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
1567 Value *Op = PREInstr->getOperand(i);
1568 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
1571 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
1572 PREInstr->setOperand(i, V);
1579 // Fail out if we encounter an operand that is not available in
1580 // the PRE predecessor. This is typically because of loads which
1581 // are not value numbered precisely.
1587 PREInstr->insertBefore(PREPred->getTerminator());
1588 PREInstr->setName(CurInst->getName() + ".pre");
1589 predMap[PREPred] = PREInstr;
1590 VN.add(PREInstr, valno);
1593 // Update the availability map to include the new instruction.
1594 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1596 // Create a PHI to make the value available in this block.
1597 PHINode* Phi = PHINode::Create(CurInst->getType(),
1598 CurInst->getName() + ".pre-phi",
1599 CurrentBlock->begin());
1600 for (pred_iterator PI = pred_begin(CurrentBlock),
1601 PE = pred_end(CurrentBlock); PI != PE; ++PI)
1602 Phi->addIncoming(predMap[*PI], *PI);
1605 localAvail[CurrentBlock]->table[valno] = Phi;
1607 CurInst->replaceAllUsesWith(Phi);
1608 if (isa<PointerType>(Phi->getType()))
1609 MD->invalidateCachedPointerInfo(Phi);
1612 DEBUG(cerr << "GVN PRE removed: " << *CurInst);
1613 MD->removeInstruction(CurInst);
1614 CurInst->eraseFromParent();
1615 DEBUG(verifyRemoved(CurInst));
1620 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1621 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1622 SplitCriticalEdge(I->first, I->second, this);
1624 return Changed || toSplit.size();
1627 // iterateOnFunction - Executes one iteration of GVN
1628 bool GVN::iterateOnFunction(Function &F) {
1629 cleanupGlobalSets();
1631 // Top-down walk of the dominator tree
1632 bool changed = false;
1634 // Needed for value numbering with phi construction to work.
1635 ReversePostOrderTraversal<Function*> RPOT(&F);
1636 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
1637 RE = RPOT.end(); RI != RE; ++RI)
1638 changed |= processBlock(*RI);
1640 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1641 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
1642 changed |= processBlock(DI->getBlock());
1648 void GVN::cleanupGlobalSets() {
1652 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1653 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
1658 /// verifyRemoved - Verify that the specified instruction does not occur in our
1659 /// internal data structures.
1660 void GVN::verifyRemoved(const Instruction *I) const {
1661 VN.verifyRemoved(I);