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/SmallPtrSet.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/ADT/Statistic.h"
31 #include "llvm/Analysis/Dominators.h"
32 #include "llvm/Analysis/AliasAnalysis.h"
33 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
34 #include "llvm/Support/CFG.h"
35 #include "llvm/Support/CommandLine.h"
36 #include "llvm/Support/Compiler.h"
37 #include "llvm/Support/Debug.h"
38 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
42 STATISTIC(NumGVNInstr, "Number of instructions deleted");
43 STATISTIC(NumGVNLoad, "Number of loads deleted");
44 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
45 STATISTIC(NumGVNBlocks, "Number of blocks merged");
46 STATISTIC(NumPRELoad, "Number of loads PRE'd");
48 static cl::opt<bool> EnablePRE("enable-pre",
49 cl::init(true), cl::Hidden);
50 cl::opt<bool> EnableLoadPRE("enable-load-pre"/*, cl::init(true)*/);
52 //===----------------------------------------------------------------------===//
54 //===----------------------------------------------------------------------===//
56 /// This class holds the mapping between values and value numbers. It is used
57 /// as an efficient mechanism to determine the expression-wise equivalence of
60 struct VISIBILITY_HIDDEN Expression {
61 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
62 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
63 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
64 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
65 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
66 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
67 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
68 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
69 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
70 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
73 ExpressionOpcode opcode;
78 SmallVector<uint32_t, 4> varargs;
82 Expression(ExpressionOpcode o) : opcode(o) { }
84 bool operator==(const Expression &other) const {
85 if (opcode != other.opcode)
87 else if (opcode == EMPTY || opcode == TOMBSTONE)
89 else if (type != other.type)
91 else if (function != other.function)
93 else if (firstVN != other.firstVN)
95 else if (secondVN != other.secondVN)
97 else if (thirdVN != other.thirdVN)
100 if (varargs.size() != other.varargs.size())
103 for (size_t i = 0; i < varargs.size(); ++i)
104 if (varargs[i] != other.varargs[i])
111 bool operator!=(const Expression &other) const {
112 if (opcode != other.opcode)
114 else if (opcode == EMPTY || opcode == TOMBSTONE)
116 else if (type != other.type)
118 else if (function != other.function)
120 else if (firstVN != other.firstVN)
122 else if (secondVN != other.secondVN)
124 else if (thirdVN != other.thirdVN)
127 if (varargs.size() != other.varargs.size())
130 for (size_t i = 0; i < varargs.size(); ++i)
131 if (varargs[i] != other.varargs[i])
139 class VISIBILITY_HIDDEN ValueTable {
141 DenseMap<Value*, uint32_t> valueNumbering;
142 DenseMap<Expression, uint32_t> expressionNumbering;
144 MemoryDependenceAnalysis* MD;
147 uint32_t nextValueNumber;
149 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
150 Expression::ExpressionOpcode getOpcode(CmpInst* C);
151 Expression::ExpressionOpcode getOpcode(CastInst* C);
152 Expression create_expression(BinaryOperator* BO);
153 Expression create_expression(CmpInst* C);
154 Expression create_expression(ShuffleVectorInst* V);
155 Expression create_expression(ExtractElementInst* C);
156 Expression create_expression(InsertElementInst* V);
157 Expression create_expression(SelectInst* V);
158 Expression create_expression(CastInst* C);
159 Expression create_expression(GetElementPtrInst* G);
160 Expression create_expression(CallInst* C);
161 Expression create_expression(Constant* C);
163 ValueTable() : nextValueNumber(1) { }
164 uint32_t lookup_or_add(Value* V);
165 uint32_t lookup(Value* V) const;
166 void add(Value* V, uint32_t num);
168 void erase(Value* v);
170 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
171 AliasAnalysis *getAliasAnalysis() const { return AA; }
172 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
173 void setDomTree(DominatorTree* D) { DT = D; }
174 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
179 template <> struct DenseMapInfo<Expression> {
180 static inline Expression getEmptyKey() {
181 return Expression(Expression::EMPTY);
184 static inline Expression getTombstoneKey() {
185 return Expression(Expression::TOMBSTONE);
188 static unsigned getHashValue(const Expression e) {
189 unsigned hash = e.opcode;
191 hash = e.firstVN + hash * 37;
192 hash = e.secondVN + hash * 37;
193 hash = e.thirdVN + hash * 37;
195 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
196 (unsigned)((uintptr_t)e.type >> 9)) +
199 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
200 E = e.varargs.end(); I != E; ++I)
201 hash = *I + hash * 37;
203 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
204 (unsigned)((uintptr_t)e.function >> 9)) +
209 static bool isEqual(const Expression &LHS, const Expression &RHS) {
212 static bool isPod() { return true; }
216 //===----------------------------------------------------------------------===//
217 // ValueTable Internal Functions
218 //===----------------------------------------------------------------------===//
219 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
220 switch(BO->getOpcode()) {
221 default: // THIS SHOULD NEVER HAPPEN
222 assert(0 && "Binary operator with unknown opcode?");
223 case Instruction::Add: return Expression::ADD;
224 case Instruction::Sub: return Expression::SUB;
225 case Instruction::Mul: return Expression::MUL;
226 case Instruction::UDiv: return Expression::UDIV;
227 case Instruction::SDiv: return Expression::SDIV;
228 case Instruction::FDiv: return Expression::FDIV;
229 case Instruction::URem: return Expression::UREM;
230 case Instruction::SRem: return Expression::SREM;
231 case Instruction::FRem: return Expression::FREM;
232 case Instruction::Shl: return Expression::SHL;
233 case Instruction::LShr: return Expression::LSHR;
234 case Instruction::AShr: return Expression::ASHR;
235 case Instruction::And: return Expression::AND;
236 case Instruction::Or: return Expression::OR;
237 case Instruction::Xor: return Expression::XOR;
241 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
242 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
243 switch (C->getPredicate()) {
244 default: // THIS SHOULD NEVER HAPPEN
245 assert(0 && "Comparison with unknown predicate?");
246 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
247 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
248 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
249 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
250 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
251 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
252 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
253 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
254 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
255 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
258 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
259 switch (C->getPredicate()) {
260 default: // THIS SHOULD NEVER HAPPEN
261 assert(0 && "Comparison with unknown predicate?");
262 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
263 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
264 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
265 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
266 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
267 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
268 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
269 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
270 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
271 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
272 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
273 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
274 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
275 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
279 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
280 switch(C->getOpcode()) {
281 default: // THIS SHOULD NEVER HAPPEN
282 assert(0 && "Cast operator with unknown opcode?");
283 case Instruction::Trunc: return Expression::TRUNC;
284 case Instruction::ZExt: return Expression::ZEXT;
285 case Instruction::SExt: return Expression::SEXT;
286 case Instruction::FPToUI: return Expression::FPTOUI;
287 case Instruction::FPToSI: return Expression::FPTOSI;
288 case Instruction::UIToFP: return Expression::UITOFP;
289 case Instruction::SIToFP: return Expression::SITOFP;
290 case Instruction::FPTrunc: return Expression::FPTRUNC;
291 case Instruction::FPExt: return Expression::FPEXT;
292 case Instruction::PtrToInt: return Expression::PTRTOINT;
293 case Instruction::IntToPtr: return Expression::INTTOPTR;
294 case Instruction::BitCast: return Expression::BITCAST;
298 Expression ValueTable::create_expression(CallInst* C) {
301 e.type = C->getType();
305 e.function = C->getCalledFunction();
306 e.opcode = Expression::CALL;
308 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
310 e.varargs.push_back(lookup_or_add(*I));
315 Expression ValueTable::create_expression(BinaryOperator* BO) {
318 e.firstVN = lookup_or_add(BO->getOperand(0));
319 e.secondVN = lookup_or_add(BO->getOperand(1));
322 e.type = BO->getType();
323 e.opcode = getOpcode(BO);
328 Expression ValueTable::create_expression(CmpInst* C) {
331 e.firstVN = lookup_or_add(C->getOperand(0));
332 e.secondVN = lookup_or_add(C->getOperand(1));
335 e.type = C->getType();
336 e.opcode = getOpcode(C);
341 Expression ValueTable::create_expression(CastInst* C) {
344 e.firstVN = lookup_or_add(C->getOperand(0));
348 e.type = C->getType();
349 e.opcode = getOpcode(C);
354 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
357 e.firstVN = lookup_or_add(S->getOperand(0));
358 e.secondVN = lookup_or_add(S->getOperand(1));
359 e.thirdVN = lookup_or_add(S->getOperand(2));
361 e.type = S->getType();
362 e.opcode = Expression::SHUFFLE;
367 Expression ValueTable::create_expression(ExtractElementInst* E) {
370 e.firstVN = lookup_or_add(E->getOperand(0));
371 e.secondVN = lookup_or_add(E->getOperand(1));
374 e.type = E->getType();
375 e.opcode = Expression::EXTRACT;
380 Expression ValueTable::create_expression(InsertElementInst* I) {
383 e.firstVN = lookup_or_add(I->getOperand(0));
384 e.secondVN = lookup_or_add(I->getOperand(1));
385 e.thirdVN = lookup_or_add(I->getOperand(2));
387 e.type = I->getType();
388 e.opcode = Expression::INSERT;
393 Expression ValueTable::create_expression(SelectInst* I) {
396 e.firstVN = lookup_or_add(I->getCondition());
397 e.secondVN = lookup_or_add(I->getTrueValue());
398 e.thirdVN = lookup_or_add(I->getFalseValue());
400 e.type = I->getType();
401 e.opcode = Expression::SELECT;
406 Expression ValueTable::create_expression(GetElementPtrInst* G) {
409 e.firstVN = lookup_or_add(G->getPointerOperand());
413 e.type = G->getType();
414 e.opcode = Expression::GEP;
416 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
418 e.varargs.push_back(lookup_or_add(*I));
423 //===----------------------------------------------------------------------===//
424 // ValueTable External Functions
425 //===----------------------------------------------------------------------===//
427 /// add - Insert a value into the table with a specified value number.
428 void ValueTable::add(Value* V, uint32_t num) {
429 valueNumbering.insert(std::make_pair(V, num));
432 /// lookup_or_add - Returns the value number for the specified value, assigning
433 /// it a new number if it did not have one before.
434 uint32_t ValueTable::lookup_or_add(Value* V) {
435 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
436 if (VI != valueNumbering.end())
439 if (CallInst* C = dyn_cast<CallInst>(V)) {
440 if (AA->doesNotAccessMemory(C)) {
441 Expression e = create_expression(C);
443 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
444 if (EI != expressionNumbering.end()) {
445 valueNumbering.insert(std::make_pair(V, EI->second));
448 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
449 valueNumbering.insert(std::make_pair(V, nextValueNumber));
451 return nextValueNumber++;
453 } else if (AA->onlyReadsMemory(C)) {
454 Expression e = create_expression(C);
456 if (expressionNumbering.find(e) == expressionNumbering.end()) {
457 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
458 valueNumbering.insert(std::make_pair(V, nextValueNumber));
459 return nextValueNumber++;
462 MemDepResult local_dep = MD->getDependency(C);
464 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
465 valueNumbering.insert(std::make_pair(V, nextValueNumber));
466 return nextValueNumber++;
469 if (local_dep.isDef()) {
470 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
472 if (local_cdep->getNumOperands() != C->getNumOperands()) {
473 valueNumbering.insert(std::make_pair(V, nextValueNumber));
474 return nextValueNumber++;
477 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
478 uint32_t c_vn = lookup_or_add(C->getOperand(i));
479 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
481 valueNumbering.insert(std::make_pair(V, nextValueNumber));
482 return nextValueNumber++;
486 uint32_t v = lookup_or_add(local_cdep);
487 valueNumbering.insert(std::make_pair(V, v));
492 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
493 MD->getNonLocalDependency(C);
494 // FIXME: call/call dependencies for readonly calls should return def, not
495 // clobber! Move the checking logic to MemDep!
498 // Check to see if we have a single dominating call instruction that is
500 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
501 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
502 // Ignore non-local dependencies.
503 if (I->second.isNonLocal())
506 // We don't handle non-depedencies. If we already have a call, reject
507 // instruction dependencies.
508 if (I->second.isClobber() || cdep != 0) {
513 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
514 // FIXME: All duplicated with non-local case.
515 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
516 cdep = NonLocalDepCall;
525 valueNumbering.insert(std::make_pair(V, nextValueNumber));
526 return nextValueNumber++;
529 if (cdep->getNumOperands() != C->getNumOperands()) {
530 valueNumbering.insert(std::make_pair(V, nextValueNumber));
531 return nextValueNumber++;
533 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
534 uint32_t c_vn = lookup_or_add(C->getOperand(i));
535 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
537 valueNumbering.insert(std::make_pair(V, nextValueNumber));
538 return nextValueNumber++;
542 uint32_t v = lookup_or_add(cdep);
543 valueNumbering.insert(std::make_pair(V, v));
547 valueNumbering.insert(std::make_pair(V, nextValueNumber));
548 return nextValueNumber++;
550 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
551 Expression e = create_expression(BO);
553 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
554 if (EI != expressionNumbering.end()) {
555 valueNumbering.insert(std::make_pair(V, EI->second));
558 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
559 valueNumbering.insert(std::make_pair(V, nextValueNumber));
561 return nextValueNumber++;
563 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
564 Expression e = create_expression(C);
566 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
567 if (EI != expressionNumbering.end()) {
568 valueNumbering.insert(std::make_pair(V, EI->second));
571 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
572 valueNumbering.insert(std::make_pair(V, nextValueNumber));
574 return nextValueNumber++;
576 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
577 Expression e = create_expression(U);
579 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
580 if (EI != expressionNumbering.end()) {
581 valueNumbering.insert(std::make_pair(V, EI->second));
584 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
585 valueNumbering.insert(std::make_pair(V, nextValueNumber));
587 return nextValueNumber++;
589 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
590 Expression e = create_expression(U);
592 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
593 if (EI != expressionNumbering.end()) {
594 valueNumbering.insert(std::make_pair(V, EI->second));
597 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
598 valueNumbering.insert(std::make_pair(V, nextValueNumber));
600 return nextValueNumber++;
602 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
603 Expression e = create_expression(U);
605 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
606 if (EI != expressionNumbering.end()) {
607 valueNumbering.insert(std::make_pair(V, EI->second));
610 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
611 valueNumbering.insert(std::make_pair(V, nextValueNumber));
613 return nextValueNumber++;
615 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
616 Expression e = create_expression(U);
618 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
619 if (EI != expressionNumbering.end()) {
620 valueNumbering.insert(std::make_pair(V, EI->second));
623 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
624 valueNumbering.insert(std::make_pair(V, nextValueNumber));
626 return nextValueNumber++;
628 } else if (CastInst* U = dyn_cast<CastInst>(V)) {
629 Expression e = create_expression(U);
631 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
632 if (EI != expressionNumbering.end()) {
633 valueNumbering.insert(std::make_pair(V, EI->second));
636 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
637 valueNumbering.insert(std::make_pair(V, nextValueNumber));
639 return nextValueNumber++;
641 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
642 Expression e = create_expression(U);
644 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
645 if (EI != expressionNumbering.end()) {
646 valueNumbering.insert(std::make_pair(V, EI->second));
649 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
650 valueNumbering.insert(std::make_pair(V, nextValueNumber));
652 return nextValueNumber++;
655 valueNumbering.insert(std::make_pair(V, nextValueNumber));
656 return nextValueNumber++;
660 /// lookup - Returns the value number of the specified value. Fails if
661 /// the value has not yet been numbered.
662 uint32_t ValueTable::lookup(Value* V) const {
663 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
664 assert(VI != valueNumbering.end() && "Value not numbered?");
668 /// clear - Remove all entries from the ValueTable
669 void ValueTable::clear() {
670 valueNumbering.clear();
671 expressionNumbering.clear();
675 /// erase - Remove a value from the value numbering
676 void ValueTable::erase(Value* V) {
677 valueNumbering.erase(V);
680 //===----------------------------------------------------------------------===//
682 //===----------------------------------------------------------------------===//
685 struct VISIBILITY_HIDDEN ValueNumberScope {
686 ValueNumberScope* parent;
687 DenseMap<uint32_t, Value*> table;
689 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
695 class VISIBILITY_HIDDEN GVN : public FunctionPass {
696 bool runOnFunction(Function &F);
698 static char ID; // Pass identification, replacement for typeid
699 GVN() : FunctionPass(&ID) { }
702 MemoryDependenceAnalysis *MD;
706 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
708 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
712 // This transformation requires dominator postdominator info
713 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
714 AU.addRequired<DominatorTree>();
715 AU.addRequired<MemoryDependenceAnalysis>();
716 AU.addRequired<AliasAnalysis>();
718 AU.addPreserved<DominatorTree>();
719 AU.addPreserved<AliasAnalysis>();
723 // FIXME: eliminate or document these better
724 bool processLoad(LoadInst* L,
725 SmallVectorImpl<Instruction*> &toErase);
726 bool processInstruction(Instruction* I,
727 SmallVectorImpl<Instruction*> &toErase);
728 bool processNonLocalLoad(LoadInst* L,
729 SmallVectorImpl<Instruction*> &toErase);
730 bool processBlock(DomTreeNode* DTN);
731 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
732 DenseMap<BasicBlock*, Value*> &Phis,
733 bool top_level = false);
734 void dump(DenseMap<uint32_t, Value*>& d);
735 bool iterateOnFunction(Function &F);
736 Value* CollapsePhi(PHINode* p);
737 bool isSafeReplacement(PHINode* p, Instruction* inst);
738 bool performPRE(Function& F);
739 Value* lookupNumber(BasicBlock* BB, uint32_t num);
740 bool mergeBlockIntoPredecessor(BasicBlock* BB);
741 void cleanupGlobalSets();
747 // createGVNPass - The public interface to this file...
748 FunctionPass *llvm::createGVNPass() { return new GVN(); }
750 static RegisterPass<GVN> X("gvn",
751 "Global Value Numbering");
753 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
755 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
756 E = d.end(); I != E; ++I) {
757 printf("%d\n", I->first);
763 Value* GVN::CollapsePhi(PHINode* p) {
764 Value* constVal = p->hasConstantValue();
765 if (!constVal) return 0;
767 Instruction* inst = dyn_cast<Instruction>(constVal);
771 if (DT->dominates(inst, p))
772 if (isSafeReplacement(p, inst))
777 bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
778 if (!isa<PHINode>(inst))
781 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
783 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
784 if (use_phi->getParent() == inst->getParent())
790 /// GetValueForBlock - Get the value to use within the specified basic block.
791 /// available values are in Phis.
792 Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
793 DenseMap<BasicBlock*, Value*> &Phis,
796 // If we have already computed this value, return the previously computed val.
797 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
798 if (V != Phis.end() && !top_level) return V->second;
800 // If the block is unreachable, just return undef, since this path
801 // can't actually occur at runtime.
802 if (!DT->isReachableFromEntry(BB))
803 return Phis[BB] = UndefValue::get(orig->getType());
805 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
806 Value *ret = GetValueForBlock(Pred, orig, Phis);
811 // Get the number of predecessors of this block so we can reserve space later.
812 // If there is already a PHI in it, use the #preds from it, otherwise count.
813 // Getting it from the PHI is constant time.
815 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
816 NumPreds = ExistingPN->getNumIncomingValues();
818 NumPreds = std::distance(pred_begin(BB), pred_end(BB));
820 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
821 // now, then get values to fill in the incoming values for the PHI.
822 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
824 PN->reserveOperandSpace(NumPreds);
826 Phis.insert(std::make_pair(BB, PN));
828 // Fill in the incoming values for the block.
829 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
830 Value* val = GetValueForBlock(*PI, orig, Phis);
831 PN->addIncoming(val, *PI);
834 VN.getAliasAnalysis()->copyValue(orig, PN);
836 // Attempt to collapse PHI nodes that are trivially redundant
837 Value* v = CollapsePhi(PN);
839 // Cache our phi construction results
840 phiMap[orig->getPointerOperand()].insert(PN);
844 PN->replaceAllUsesWith(v);
846 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
847 E = Phis.end(); I != E; ++I)
851 DEBUG(cerr << "GVN removed: " << *PN);
852 MD->removeInstruction(PN);
853 PN->eraseFromParent();
859 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
860 /// we're analyzing is fully available in the specified block. As we go, keep
861 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
862 /// map is actually a tri-state map with the following values:
863 /// 0) we know the block *is not* fully available.
864 /// 1) we know the block *is* fully available.
865 /// 2) we do not know whether the block is fully available or not, but we are
866 /// currently speculating that it will be.
867 /// 3) we are speculating for this block and have used that to speculate for
869 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
870 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
871 // Optimistically assume that the block is fully available and check to see
872 // if we already know about this block in one lookup.
873 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
874 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
876 // If the entry already existed for this block, return the precomputed value.
878 // If this is a speculative "available" value, mark it as being used for
879 // speculation of other blocks.
880 if (IV.first->second == 2)
881 IV.first->second = 3;
882 return IV.first->second != 0;
885 // Otherwise, see if it is fully available in all predecessors.
886 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
888 // If this block has no predecessors, it isn't live-in here.
890 goto SpeculationFailure;
892 for (; PI != PE; ++PI)
893 // If the value isn't fully available in one of our predecessors, then it
894 // isn't fully available in this block either. Undo our previous
895 // optimistic assumption and bail out.
896 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
897 goto SpeculationFailure;
901 // SpeculationFailure - If we get here, we found out that this is not, after
902 // all, a fully-available block. We have a problem if we speculated on this and
903 // used the speculation to mark other blocks as available.
905 char &BBVal = FullyAvailableBlocks[BB];
907 // If we didn't speculate on this, just return with it set to false.
913 // If we did speculate on this value, we could have blocks set to 1 that are
914 // incorrect. Walk the (transitive) successors of this block and mark them as
916 SmallVector<BasicBlock*, 32> BBWorklist;
917 BBWorklist.push_back(BB);
919 while (!BBWorklist.empty()) {
920 BasicBlock *Entry = BBWorklist.pop_back_val();
921 // Note that this sets blocks to 0 (unavailable) if they happen to not
922 // already be in FullyAvailableBlocks. This is safe.
923 char &EntryVal = FullyAvailableBlocks[Entry];
924 if (EntryVal == 0) continue; // Already unavailable.
926 // Mark as unavailable.
929 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
930 BBWorklist.push_back(*I);
936 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
937 /// non-local by performing PHI construction.
938 bool GVN::processNonLocalLoad(LoadInst *LI,
939 SmallVectorImpl<Instruction*> &toErase) {
940 // Find the non-local dependencies of the load.
941 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
942 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
944 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
946 // If we had to process more than one hundred blocks to find the
947 // dependencies, this load isn't worth worrying about. Optimizing
948 // it will be too expensive.
949 if (Deps.size() > 100)
952 // Filter out useless results (non-locals, etc). Keep track of the blocks
953 // where we have a value available in repl, also keep track of whether we see
954 // dependencies that produce an unknown value for the load (such as a call
955 // that could potentially clobber the load).
956 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
957 SmallVector<BasicBlock*, 16> UnavailableBlocks;
959 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
960 BasicBlock *DepBB = Deps[i].first;
961 MemDepResult DepInfo = Deps[i].second;
963 if (DepInfo.isClobber()) {
964 UnavailableBlocks.push_back(DepBB);
968 Instruction *DepInst = DepInfo.getInst();
970 // Loading the allocation -> undef.
971 if (isa<AllocationInst>(DepInst)) {
972 ValuesPerBlock.push_back(std::make_pair(DepBB,
973 UndefValue::get(LI->getType())));
977 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
978 // Reject loads and stores that are to the same address but are of
980 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
981 // of bitfield access, it would be interesting to optimize for it at some
983 if (S->getOperand(0)->getType() != LI->getType()) {
984 UnavailableBlocks.push_back(DepBB);
988 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
990 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
991 if (LD->getType() != LI->getType()) {
992 UnavailableBlocks.push_back(DepBB);
995 ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
997 UnavailableBlocks.push_back(DepBB);
1002 // If we have no predecessors that produce a known value for this load, exit
1004 if (ValuesPerBlock.empty()) return false;
1006 // If all of the instructions we depend on produce a known value for this
1007 // load, then it is fully redundant and we can use PHI insertion to compute
1008 // its value. Insert PHIs and remove the fully redundant value now.
1009 if (UnavailableBlocks.empty()) {
1010 // Use cached PHI construction information from previous runs
1011 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1012 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
1013 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1015 if ((*I)->getParent() == LI->getParent()) {
1016 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
1017 LI->replaceAllUsesWith(*I);
1018 toErase.push_back(LI);
1023 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1026 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
1028 DenseMap<BasicBlock*, Value*> BlockReplValues;
1029 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1030 // Perform PHI construction.
1031 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1032 LI->replaceAllUsesWith(v);
1033 toErase.push_back(LI);
1038 if (!EnablePRE || !EnableLoadPRE)
1041 // Okay, we have *some* definitions of the value. This means that the value
1042 // is available in some of our (transitive) predecessors. Lets think about
1043 // doing PRE of this load. This will involve inserting a new load into the
1044 // predecessor when it's not available. We could do this in general, but
1045 // prefer to not increase code size. As such, we only do this when we know
1046 // that we only have to insert *one* load (which means we're basically moving
1047 // the load, not inserting a new one).
1049 // Everything we do here is based on local predecessors of LI's block. If it
1050 // only has one predecessor, bail now.
1051 BasicBlock *LoadBB = LI->getParent();
1052 if (LoadBB->getSinglePredecessor())
1055 // If we have a repl set with LI itself in it, this means we have a loop where
1056 // at least one of the values is LI. Since this means that we won't be able
1057 // to eliminate LI even if we insert uses in the other predecessors, we will
1058 // end up increasing code size. Reject this by scanning for LI.
1059 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1060 if (ValuesPerBlock[i].second == LI)
1063 // Okay, we have some hope :). Check to see if the loaded value is fully
1064 // available in all but one predecessor.
1065 // FIXME: If we could restructure the CFG, we could make a common pred with
1066 // all the preds that don't have an available LI and insert a new load into
1068 BasicBlock *UnavailablePred = 0;
1070 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1071 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1072 FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
1073 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1074 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1076 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1078 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1081 // If this load is not available in multiple predecessors, reject it.
1082 if (UnavailablePred && UnavailablePred != *PI)
1084 UnavailablePred = *PI;
1087 assert(UnavailablePred != 0 &&
1088 "Fully available value should be eliminated above!");
1090 // If the loaded pointer is PHI node defined in this block, do PHI translation
1091 // to get its value in the predecessor.
1092 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
1094 // Make sure the value is live in the predecessor. If it was defined by a
1095 // non-PHI instruction in this block, we don't know how to recompute it above.
1096 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
1097 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
1098 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
1099 << *LPInst << *LI << "\n");
1103 // We don't currently handle critical edges :(
1104 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1105 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1106 << UnavailablePred->getName() << "': " << *LI);
1110 // Okay, we can eliminate this load by inserting a reload in the predecessor
1111 // and using PHI construction to get the value in the other predecessors, do
1113 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
1115 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1117 UnavailablePred->getTerminator());
1119 DenseMap<BasicBlock*, Value*> BlockReplValues;
1120 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1121 BlockReplValues[UnavailablePred] = NewLoad;
1123 // Perform PHI construction.
1124 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1125 LI->replaceAllUsesWith(v);
1127 toErase.push_back(LI);
1132 /// processLoad - Attempt to eliminate a load, first by eliminating it
1133 /// locally, and then attempting non-local elimination if that fails.
1134 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1135 if (L->isVolatile())
1138 Value* pointer = L->getPointerOperand();
1140 // ... to a pointer that has been loaded from before...
1141 MemDepResult dep = MD->getDependency(L);
1143 // If the value isn't available, don't do anything!
1144 if (dep.isClobber())
1147 // If it is defined in another block, try harder.
1148 if (dep.isNonLocal())
1149 return processNonLocalLoad(L, toErase);
1151 Instruction *DepInst = dep.getInst();
1152 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1153 // Only forward substitute stores to loads of the same type.
1154 // FIXME: Could do better!
1155 if (DepSI->getPointerOperand()->getType() != pointer->getType())
1159 L->replaceAllUsesWith(DepSI->getOperand(0));
1160 toErase.push_back(L);
1165 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1166 // Only forward substitute stores to loads of the same type.
1167 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
1168 if (DepLI->getType() != L->getType())
1172 L->replaceAllUsesWith(DepLI);
1173 toErase.push_back(L);
1178 // If this load really doesn't depend on anything, then we must be loading an
1179 // undef value. This can happen when loading for a fresh allocation with no
1180 // intervening stores, for example.
1181 if (isa<AllocationInst>(DepInst)) {
1182 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1183 toErase.push_back(L);
1191 Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1192 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1193 if (I == localAvail.end())
1196 ValueNumberScope* locals = I->second;
1199 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1200 if (I != locals->table.end())
1203 locals = locals->parent;
1209 /// processInstruction - When calculating availability, handle an instruction
1210 /// by inserting it into the appropriate sets
1211 bool GVN::processInstruction(Instruction *I,
1212 SmallVectorImpl<Instruction*> &toErase) {
1213 if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1214 bool changed = processLoad(L, toErase);
1217 unsigned num = VN.lookup_or_add(L);
1218 localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1224 uint32_t nextNum = VN.getNextUnusedValueNumber();
1225 unsigned num = VN.lookup_or_add(I);
1227 // Allocations are always uniquely numbered, so we can save time and memory
1228 // by fast failing them.
1229 if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
1230 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1234 // Collapse PHI nodes
1235 if (PHINode* p = dyn_cast<PHINode>(I)) {
1236 Value* constVal = CollapsePhi(p);
1239 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1241 PI->second.erase(p);
1243 p->replaceAllUsesWith(constVal);
1244 toErase.push_back(p);
1246 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1249 // If the number we were assigned was a brand new VN, then we don't
1250 // need to do a lookup to see if the number already exists
1251 // somewhere in the domtree: it can't!
1252 } else if (num == nextNum) {
1253 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1255 // Perform value-number based elimination
1256 } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1259 I->replaceAllUsesWith(repl);
1260 toErase.push_back(I);
1263 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1269 // GVN::runOnFunction - This is the main transformation entry point for a
1272 bool GVN::runOnFunction(Function& F) {
1273 MD = &getAnalysis<MemoryDependenceAnalysis>();
1274 DT = &getAnalysis<DominatorTree>();
1275 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1279 bool changed = false;
1280 bool shouldContinue = true;
1282 // Merge unconditional branches, allowing PRE to catch more
1283 // optimization opportunities.
1284 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1285 BasicBlock* BB = FI;
1287 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1288 if (removedBlock) NumGVNBlocks++;
1290 changed |= removedBlock;
1293 unsigned Iteration = 0;
1295 while (shouldContinue) {
1296 DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
1297 shouldContinue = iterateOnFunction(F);
1298 changed |= shouldContinue;
1303 bool PREChanged = true;
1304 while (PREChanged) {
1305 PREChanged = performPRE(F);
1306 changed |= PREChanged;
1309 // FIXME: Should perform GVN again after PRE does something. PRE can move
1310 // computations into blocks where they become fully redundant. Note that
1311 // we can't do this until PRE's critical edge splitting updates memdep.
1312 // Actually, when this happens, we should just fully integrate PRE into GVN.
1314 cleanupGlobalSets();
1320 bool GVN::processBlock(DomTreeNode* DTN) {
1321 BasicBlock* BB = DTN->getBlock();
1322 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1323 // incrementing BI before processing an instruction).
1324 SmallVector<Instruction*, 8> toErase;
1325 bool changed_function = false;
1329 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]);
1331 localAvail[BB] = new ValueNumberScope(0);
1333 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1335 changed_function |= processInstruction(BI, toErase);
1336 if (toErase.empty()) {
1341 // If we need some instructions deleted, do it now.
1342 NumGVNInstr += toErase.size();
1344 // Avoid iterator invalidation.
1345 bool AtStart = BI == BB->begin();
1349 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1350 E = toErase.end(); I != E; ++I) {
1351 DEBUG(cerr << "GVN removed: " << **I);
1352 MD->removeInstruction(*I);
1353 (*I)->eraseFromParent();
1363 return changed_function;
1366 /// performPRE - Perform a purely local form of PRE that looks for diamond
1367 /// control flow patterns and attempts to perform simple PRE at the join point.
1368 bool GVN::performPRE(Function& F) {
1369 bool Changed = false;
1370 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1371 DenseMap<BasicBlock*, Value*> predMap;
1372 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1373 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1374 BasicBlock* CurrentBlock = *DI;
1376 // Nothing to PRE in the entry block.
1377 if (CurrentBlock == &F.getEntryBlock()) continue;
1379 for (BasicBlock::iterator BI = CurrentBlock->begin(),
1380 BE = CurrentBlock->end(); BI != BE; ) {
1381 Instruction *CurInst = BI++;
1383 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
1384 isa<PHINode>(CurInst) || CurInst->mayReadFromMemory() ||
1385 CurInst->mayWriteToMemory())
1388 uint32_t valno = VN.lookup(CurInst);
1390 // Look for the predecessors for PRE opportunities. We're
1391 // only trying to solve the basic diamond case, where
1392 // a value is computed in the successor and one predecessor,
1393 // but not the other. We also explicitly disallow cases
1394 // where the successor is its own predecessor, because they're
1395 // more complicated to get right.
1396 unsigned numWith = 0;
1397 unsigned numWithout = 0;
1398 BasicBlock* PREPred = 0;
1401 for (pred_iterator PI = pred_begin(CurrentBlock),
1402 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1403 // We're not interested in PRE where the block is its
1404 // own predecessor, on in blocks with predecessors
1405 // that are not reachable.
1406 if (*PI == CurrentBlock) {
1409 } else if (!localAvail.count(*PI)) {
1414 DenseMap<uint32_t, Value*>::iterator predV =
1415 localAvail[*PI]->table.find(valno);
1416 if (predV == localAvail[*PI]->table.end()) {
1419 } else if (predV->second == CurInst) {
1422 predMap[*PI] = predV->second;
1427 // Don't do PRE when it might increase code size, i.e. when
1428 // we would need to insert instructions in more than one pred.
1429 if (numWithout != 1 || numWith == 0)
1432 // We can't do PRE safely on a critical edge, so instead we schedule
1433 // the edge to be split and perform the PRE the next time we iterate
1435 unsigned succNum = 0;
1436 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1438 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
1443 if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1444 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1448 // Instantiate the expression the in predecessor that lacked it.
1449 // Because we are going top-down through the block, all value numbers
1450 // will be available in the predecessor by the time we need them. Any
1451 // that weren't original present will have been instantiated earlier
1453 Instruction* PREInstr = CurInst->clone();
1454 bool success = true;
1455 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
1456 Value *Op = PREInstr->getOperand(i);
1457 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
1460 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
1461 PREInstr->setOperand(i, V);
1468 // Fail out if we encounter an operand that is not available in
1469 // the PRE predecessor. This is typically because of loads which
1470 // are not value numbered precisely.
1476 PREInstr->insertBefore(PREPred->getTerminator());
1477 PREInstr->setName(CurInst->getName() + ".pre");
1478 predMap[PREPred] = PREInstr;
1479 VN.add(PREInstr, valno);
1482 // Update the availability map to include the new instruction.
1483 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1485 // Create a PHI to make the value available in this block.
1486 PHINode* Phi = PHINode::Create(CurInst->getType(),
1487 CurInst->getName() + ".pre-phi",
1488 CurrentBlock->begin());
1489 for (pred_iterator PI = pred_begin(CurrentBlock),
1490 PE = pred_end(CurrentBlock); PI != PE; ++PI)
1491 Phi->addIncoming(predMap[*PI], *PI);
1494 localAvail[CurrentBlock]->table[valno] = Phi;
1496 CurInst->replaceAllUsesWith(Phi);
1499 DEBUG(cerr << "GVN PRE removed: " << *CurInst);
1500 MD->removeInstruction(CurInst);
1501 CurInst->eraseFromParent();
1506 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1507 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1508 SplitCriticalEdge(I->first, I->second, this);
1510 return Changed || toSplit.size();
1513 // iterateOnFunction - Executes one iteration of GVN
1514 bool GVN::iterateOnFunction(Function &F) {
1515 cleanupGlobalSets();
1517 // Top-down walk of the dominator tree
1518 bool changed = false;
1519 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1520 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
1521 changed |= processBlock(*DI);
1526 void GVN::cleanupGlobalSets() {
1530 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1531 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)