1 //===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass performs global value numbering to eliminate fully redundant
11 // instructions. It also performs simple dead load elimination.
13 // Note that this pass does the value numbering itself; it does not use the
14 // ValueNumbering analysis passes.
16 //===----------------------------------------------------------------------===//
18 #define DEBUG_TYPE "gvn"
19 #include "llvm/Transforms/Scalar.h"
20 #include "llvm/BasicBlock.h"
21 #include "llvm/Constants.h"
22 #include "llvm/DerivedTypes.h"
23 #include "llvm/Function.h"
24 #include "llvm/IntrinsicInst.h"
25 #include "llvm/Value.h"
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/DepthFirstIterator.h"
28 #include "llvm/ADT/PostOrderIterator.h"
29 #include "llvm/ADT/SmallPtrSet.h"
30 #include "llvm/ADT/SmallVector.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/Analysis/Dominators.h"
33 #include "llvm/Analysis/AliasAnalysis.h"
34 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
35 #include "llvm/Support/CFG.h"
36 #include "llvm/Support/CommandLine.h"
37 #include "llvm/Support/Compiler.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
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 return !(*this == other);
117 class VISIBILITY_HIDDEN ValueTable {
119 DenseMap<Value*, uint32_t> valueNumbering;
120 DenseMap<Expression, uint32_t> expressionNumbering;
122 MemoryDependenceAnalysis* MD;
125 uint32_t nextValueNumber;
127 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
128 Expression::ExpressionOpcode getOpcode(CmpInst* C);
129 Expression::ExpressionOpcode getOpcode(CastInst* C);
130 Expression create_expression(BinaryOperator* BO);
131 Expression create_expression(CmpInst* C);
132 Expression create_expression(ShuffleVectorInst* V);
133 Expression create_expression(ExtractElementInst* C);
134 Expression create_expression(InsertElementInst* V);
135 Expression create_expression(SelectInst* V);
136 Expression create_expression(CastInst* C);
137 Expression create_expression(GetElementPtrInst* G);
138 Expression create_expression(CallInst* C);
139 Expression create_expression(Constant* C);
141 ValueTable() : nextValueNumber(1) { }
142 uint32_t lookup_or_add(Value* V);
143 uint32_t lookup(Value* V) const;
144 void add(Value* V, uint32_t num);
146 void erase(Value* v);
148 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
149 AliasAnalysis *getAliasAnalysis() const { return AA; }
150 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
151 void setDomTree(DominatorTree* D) { DT = D; }
152 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
153 void verifyRemoved(const Value *) const;
158 template <> struct DenseMapInfo<Expression> {
159 static inline Expression getEmptyKey() {
160 return Expression(Expression::EMPTY);
163 static inline Expression getTombstoneKey() {
164 return Expression(Expression::TOMBSTONE);
167 static unsigned getHashValue(const Expression e) {
168 unsigned hash = e.opcode;
170 hash = e.firstVN + hash * 37;
171 hash = e.secondVN + hash * 37;
172 hash = e.thirdVN + hash * 37;
174 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
175 (unsigned)((uintptr_t)e.type >> 9)) +
178 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
179 E = e.varargs.end(); I != E; ++I)
180 hash = *I + hash * 37;
182 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
183 (unsigned)((uintptr_t)e.function >> 9)) +
188 static bool isEqual(const Expression &LHS, const Expression &RHS) {
191 static bool isPod() { return true; }
195 //===----------------------------------------------------------------------===//
196 // ValueTable Internal Functions
197 //===----------------------------------------------------------------------===//
198 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
199 switch(BO->getOpcode()) {
200 default: // THIS SHOULD NEVER HAPPEN
201 assert(0 && "Binary operator with unknown opcode?");
202 case Instruction::Add: return Expression::ADD;
203 case Instruction::Sub: return Expression::SUB;
204 case Instruction::Mul: return Expression::MUL;
205 case Instruction::UDiv: return Expression::UDIV;
206 case Instruction::SDiv: return Expression::SDIV;
207 case Instruction::FDiv: return Expression::FDIV;
208 case Instruction::URem: return Expression::UREM;
209 case Instruction::SRem: return Expression::SREM;
210 case Instruction::FRem: return Expression::FREM;
211 case Instruction::Shl: return Expression::SHL;
212 case Instruction::LShr: return Expression::LSHR;
213 case Instruction::AShr: return Expression::ASHR;
214 case Instruction::And: return Expression::AND;
215 case Instruction::Or: return Expression::OR;
216 case Instruction::Xor: return Expression::XOR;
220 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
221 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
222 switch (C->getPredicate()) {
223 default: // THIS SHOULD NEVER HAPPEN
224 assert(0 && "Comparison with unknown predicate?");
225 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
226 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
227 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
228 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
229 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
230 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
231 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
232 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
233 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
234 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
237 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
238 switch (C->getPredicate()) {
239 default: // THIS SHOULD NEVER HAPPEN
240 assert(0 && "Comparison with unknown predicate?");
241 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
242 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
243 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
244 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
245 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
246 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
247 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
248 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
249 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
250 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
251 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
252 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
253 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
254 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
258 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
259 switch(C->getOpcode()) {
260 default: // THIS SHOULD NEVER HAPPEN
261 assert(0 && "Cast operator with unknown opcode?");
262 case Instruction::Trunc: return Expression::TRUNC;
263 case Instruction::ZExt: return Expression::ZEXT;
264 case Instruction::SExt: return Expression::SEXT;
265 case Instruction::FPToUI: return Expression::FPTOUI;
266 case Instruction::FPToSI: return Expression::FPTOSI;
267 case Instruction::UIToFP: return Expression::UITOFP;
268 case Instruction::SIToFP: return Expression::SITOFP;
269 case Instruction::FPTrunc: return Expression::FPTRUNC;
270 case Instruction::FPExt: return Expression::FPEXT;
271 case Instruction::PtrToInt: return Expression::PTRTOINT;
272 case Instruction::IntToPtr: return Expression::INTTOPTR;
273 case Instruction::BitCast: return Expression::BITCAST;
277 Expression ValueTable::create_expression(CallInst* C) {
280 e.type = C->getType();
284 e.function = C->getCalledFunction();
285 e.opcode = Expression::CALL;
287 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
289 e.varargs.push_back(lookup_or_add(*I));
294 Expression ValueTable::create_expression(BinaryOperator* BO) {
297 e.firstVN = lookup_or_add(BO->getOperand(0));
298 e.secondVN = lookup_or_add(BO->getOperand(1));
301 e.type = BO->getType();
302 e.opcode = getOpcode(BO);
307 Expression ValueTable::create_expression(CmpInst* C) {
310 e.firstVN = lookup_or_add(C->getOperand(0));
311 e.secondVN = lookup_or_add(C->getOperand(1));
314 e.type = C->getType();
315 e.opcode = getOpcode(C);
320 Expression ValueTable::create_expression(CastInst* C) {
323 e.firstVN = lookup_or_add(C->getOperand(0));
327 e.type = C->getType();
328 e.opcode = getOpcode(C);
333 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
336 e.firstVN = lookup_or_add(S->getOperand(0));
337 e.secondVN = lookup_or_add(S->getOperand(1));
338 e.thirdVN = lookup_or_add(S->getOperand(2));
340 e.type = S->getType();
341 e.opcode = Expression::SHUFFLE;
346 Expression ValueTable::create_expression(ExtractElementInst* E) {
349 e.firstVN = lookup_or_add(E->getOperand(0));
350 e.secondVN = lookup_or_add(E->getOperand(1));
353 e.type = E->getType();
354 e.opcode = Expression::EXTRACT;
359 Expression ValueTable::create_expression(InsertElementInst* I) {
362 e.firstVN = lookup_or_add(I->getOperand(0));
363 e.secondVN = lookup_or_add(I->getOperand(1));
364 e.thirdVN = lookup_or_add(I->getOperand(2));
366 e.type = I->getType();
367 e.opcode = Expression::INSERT;
372 Expression ValueTable::create_expression(SelectInst* I) {
375 e.firstVN = lookup_or_add(I->getCondition());
376 e.secondVN = lookup_or_add(I->getTrueValue());
377 e.thirdVN = lookup_or_add(I->getFalseValue());
379 e.type = I->getType();
380 e.opcode = Expression::SELECT;
385 Expression ValueTable::create_expression(GetElementPtrInst* G) {
388 e.firstVN = lookup_or_add(G->getPointerOperand());
392 e.type = G->getType();
393 e.opcode = Expression::GEP;
395 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
397 e.varargs.push_back(lookup_or_add(*I));
402 //===----------------------------------------------------------------------===//
403 // ValueTable External Functions
404 //===----------------------------------------------------------------------===//
406 /// add - Insert a value into the table with a specified value number.
407 void ValueTable::add(Value* V, uint32_t num) {
408 valueNumbering.insert(std::make_pair(V, num));
411 /// lookup_or_add - Returns the value number for the specified value, assigning
412 /// it a new number if it did not have one before.
413 uint32_t ValueTable::lookup_or_add(Value* V) {
414 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
415 if (VI != valueNumbering.end())
418 if (CallInst* C = dyn_cast<CallInst>(V)) {
419 if (AA->doesNotAccessMemory(C)) {
420 Expression e = create_expression(C);
422 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
423 if (EI != expressionNumbering.end()) {
424 valueNumbering.insert(std::make_pair(V, EI->second));
427 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
428 valueNumbering.insert(std::make_pair(V, nextValueNumber));
430 return nextValueNumber++;
432 } else if (AA->onlyReadsMemory(C)) {
433 Expression e = create_expression(C);
435 if (expressionNumbering.find(e) == expressionNumbering.end()) {
436 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
437 valueNumbering.insert(std::make_pair(V, nextValueNumber));
438 return nextValueNumber++;
441 MemDepResult local_dep = MD->getDependency(C);
443 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
444 valueNumbering.insert(std::make_pair(V, nextValueNumber));
445 return nextValueNumber++;
448 if (local_dep.isDef()) {
449 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
451 if (local_cdep->getNumOperands() != C->getNumOperands()) {
452 valueNumbering.insert(std::make_pair(V, nextValueNumber));
453 return nextValueNumber++;
456 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
457 uint32_t c_vn = lookup_or_add(C->getOperand(i));
458 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
460 valueNumbering.insert(std::make_pair(V, nextValueNumber));
461 return nextValueNumber++;
465 uint32_t v = lookup_or_add(local_cdep);
466 valueNumbering.insert(std::make_pair(V, v));
471 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
472 MD->getNonLocalCallDependency(CallSite(C));
473 // FIXME: call/call dependencies for readonly calls should return def, not
474 // clobber! Move the checking logic to MemDep!
477 // Check to see if we have a single dominating call instruction that is
479 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
480 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
481 // Ignore non-local dependencies.
482 if (I->second.isNonLocal())
485 // We don't handle non-depedencies. If we already have a call, reject
486 // instruction dependencies.
487 if (I->second.isClobber() || cdep != 0) {
492 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
493 // FIXME: All duplicated with non-local case.
494 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
495 cdep = NonLocalDepCall;
504 valueNumbering.insert(std::make_pair(V, nextValueNumber));
505 return nextValueNumber++;
508 if (cdep->getNumOperands() != C->getNumOperands()) {
509 valueNumbering.insert(std::make_pair(V, nextValueNumber));
510 return nextValueNumber++;
512 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
513 uint32_t c_vn = lookup_or_add(C->getOperand(i));
514 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
516 valueNumbering.insert(std::make_pair(V, nextValueNumber));
517 return nextValueNumber++;
521 uint32_t v = lookup_or_add(cdep);
522 valueNumbering.insert(std::make_pair(V, v));
526 valueNumbering.insert(std::make_pair(V, nextValueNumber));
527 return nextValueNumber++;
529 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
530 Expression e = create_expression(BO);
532 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
533 if (EI != expressionNumbering.end()) {
534 valueNumbering.insert(std::make_pair(V, EI->second));
537 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
538 valueNumbering.insert(std::make_pair(V, nextValueNumber));
540 return nextValueNumber++;
542 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
543 Expression e = create_expression(C);
545 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
546 if (EI != expressionNumbering.end()) {
547 valueNumbering.insert(std::make_pair(V, EI->second));
550 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
551 valueNumbering.insert(std::make_pair(V, nextValueNumber));
553 return nextValueNumber++;
555 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
556 Expression e = create_expression(U);
558 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
559 if (EI != expressionNumbering.end()) {
560 valueNumbering.insert(std::make_pair(V, EI->second));
563 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
564 valueNumbering.insert(std::make_pair(V, nextValueNumber));
566 return nextValueNumber++;
568 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
569 Expression e = create_expression(U);
571 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
572 if (EI != expressionNumbering.end()) {
573 valueNumbering.insert(std::make_pair(V, EI->second));
576 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
577 valueNumbering.insert(std::make_pair(V, nextValueNumber));
579 return nextValueNumber++;
581 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
582 Expression e = create_expression(U);
584 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
585 if (EI != expressionNumbering.end()) {
586 valueNumbering.insert(std::make_pair(V, EI->second));
589 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
590 valueNumbering.insert(std::make_pair(V, nextValueNumber));
592 return nextValueNumber++;
594 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
595 Expression e = create_expression(U);
597 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
598 if (EI != expressionNumbering.end()) {
599 valueNumbering.insert(std::make_pair(V, EI->second));
602 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
603 valueNumbering.insert(std::make_pair(V, nextValueNumber));
605 return nextValueNumber++;
607 } else if (CastInst* U = dyn_cast<CastInst>(V)) {
608 Expression e = create_expression(U);
610 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
611 if (EI != expressionNumbering.end()) {
612 valueNumbering.insert(std::make_pair(V, EI->second));
615 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
616 valueNumbering.insert(std::make_pair(V, nextValueNumber));
618 return nextValueNumber++;
620 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
621 Expression e = create_expression(U);
623 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
624 if (EI != expressionNumbering.end()) {
625 valueNumbering.insert(std::make_pair(V, EI->second));
628 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
629 valueNumbering.insert(std::make_pair(V, nextValueNumber));
631 return nextValueNumber++;
634 valueNumbering.insert(std::make_pair(V, nextValueNumber));
635 return nextValueNumber++;
639 /// lookup - Returns the value number of the specified value. Fails if
640 /// the value has not yet been numbered.
641 uint32_t ValueTable::lookup(Value* V) const {
642 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
643 assert(VI != valueNumbering.end() && "Value not numbered?");
647 /// clear - Remove all entries from the ValueTable
648 void ValueTable::clear() {
649 valueNumbering.clear();
650 expressionNumbering.clear();
654 /// erase - Remove a value from the value numbering
655 void ValueTable::erase(Value* V) {
656 valueNumbering.erase(V);
659 /// verifyRemoved - Verify that the value is removed from all internal data
661 void ValueTable::verifyRemoved(const Value *V) const {
662 for (DenseMap<Value*, uint32_t>::iterator
663 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
664 assert(I->first != V && "Inst still occurs in value numbering map!");
668 //===----------------------------------------------------------------------===//
670 //===----------------------------------------------------------------------===//
673 struct VISIBILITY_HIDDEN ValueNumberScope {
674 ValueNumberScope* parent;
675 DenseMap<uint32_t, Value*> table;
677 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
683 class VISIBILITY_HIDDEN GVN : public FunctionPass {
684 bool runOnFunction(Function &F);
686 static char ID; // Pass identification, replacement for typeid
687 GVN() : FunctionPass(&ID) { }
690 MemoryDependenceAnalysis *MD;
694 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
696 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
700 // This transformation requires dominator postdominator info
701 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
702 AU.addRequired<DominatorTree>();
703 AU.addRequired<MemoryDependenceAnalysis>();
704 AU.addRequired<AliasAnalysis>();
706 AU.addPreserved<DominatorTree>();
707 AU.addPreserved<AliasAnalysis>();
711 // FIXME: eliminate or document these better
712 bool processLoad(LoadInst* L,
713 SmallVectorImpl<Instruction*> &toErase);
714 bool processInstruction(Instruction* I,
715 SmallVectorImpl<Instruction*> &toErase);
716 bool processNonLocalLoad(LoadInst* L,
717 SmallVectorImpl<Instruction*> &toErase);
718 bool processBlock(BasicBlock* BB);
719 Value *GetValueForBlock(BasicBlock *BB, Instruction* orig,
720 DenseMap<BasicBlock*, Value*> &Phis,
721 bool top_level = false);
722 void dump(DenseMap<uint32_t, Value*>& d);
723 bool iterateOnFunction(Function &F);
724 Value* CollapsePhi(PHINode* p);
725 bool isSafeReplacement(PHINode* p, Instruction* inst);
726 bool performPRE(Function& F);
727 Value* lookupNumber(BasicBlock* BB, uint32_t num);
728 bool mergeBlockIntoPredecessor(BasicBlock* BB);
729 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno);
730 void cleanupGlobalSets();
731 void verifyRemoved(const Instruction *I) const;
737 // createGVNPass - The public interface to this file...
738 FunctionPass *llvm::createGVNPass() { return new GVN(); }
740 static RegisterPass<GVN> X("gvn",
741 "Global Value Numbering");
743 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
745 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
746 E = d.end(); I != E; ++I) {
747 printf("%d\n", I->first);
753 Value* GVN::CollapsePhi(PHINode* p) {
754 Value* constVal = p->hasConstantValue();
755 if (!constVal) return 0;
757 Instruction* inst = dyn_cast<Instruction>(constVal);
761 if (DT->dominates(inst, p))
762 if (isSafeReplacement(p, inst))
767 bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
768 if (!isa<PHINode>(inst))
771 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
773 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
774 if (use_phi->getParent() == inst->getParent())
780 /// GetValueForBlock - Get the value to use within the specified basic block.
781 /// available values are in Phis.
782 Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig,
783 DenseMap<BasicBlock*, Value*> &Phis,
786 // If we have already computed this value, return the previously computed val.
787 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
788 if (V != Phis.end() && !top_level) return V->second;
790 // If the block is unreachable, just return undef, since this path
791 // can't actually occur at runtime.
792 if (!DT->isReachableFromEntry(BB))
793 return Phis[BB] = UndefValue::get(orig->getType());
795 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
796 Value *ret = GetValueForBlock(Pred, orig, Phis);
801 // Get the number of predecessors of this block so we can reserve space later.
802 // If there is already a PHI in it, use the #preds from it, otherwise count.
803 // Getting it from the PHI is constant time.
805 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
806 NumPreds = ExistingPN->getNumIncomingValues();
808 NumPreds = std::distance(pred_begin(BB), pred_end(BB));
810 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
811 // now, then get values to fill in the incoming values for the PHI.
812 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
814 PN->reserveOperandSpace(NumPreds);
816 Phis.insert(std::make_pair(BB, PN));
818 // Fill in the incoming values for the block.
819 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
820 Value* val = GetValueForBlock(*PI, orig, Phis);
821 PN->addIncoming(val, *PI);
824 VN.getAliasAnalysis()->copyValue(orig, PN);
826 // Attempt to collapse PHI nodes that are trivially redundant
827 Value* v = CollapsePhi(PN);
829 // Cache our phi construction results
830 if (LoadInst* L = dyn_cast<LoadInst>(orig))
831 phiMap[L->getPointerOperand()].insert(PN);
833 phiMap[orig].insert(PN);
838 PN->replaceAllUsesWith(v);
839 if (isa<PointerType>(v->getType()))
840 MD->invalidateCachedPointerInfo(v);
842 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
843 E = Phis.end(); I != E; ++I)
847 DEBUG(cerr << "GVN removed: " << *PN);
848 MD->removeInstruction(PN);
849 PN->eraseFromParent();
850 DEBUG(verifyRemoved(PN));
856 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
857 /// we're analyzing is fully available in the specified block. As we go, keep
858 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
859 /// map is actually a tri-state map with the following values:
860 /// 0) we know the block *is not* fully available.
861 /// 1) we know the block *is* fully available.
862 /// 2) we do not know whether the block is fully available or not, but we are
863 /// currently speculating that it will be.
864 /// 3) we are speculating for this block and have used that to speculate for
866 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
867 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
868 // Optimistically assume that the block is fully available and check to see
869 // if we already know about this block in one lookup.
870 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
871 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
873 // If the entry already existed for this block, return the precomputed value.
875 // If this is a speculative "available" value, mark it as being used for
876 // speculation of other blocks.
877 if (IV.first->second == 2)
878 IV.first->second = 3;
879 return IV.first->second != 0;
882 // Otherwise, see if it is fully available in all predecessors.
883 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
885 // If this block has no predecessors, it isn't live-in here.
887 goto SpeculationFailure;
889 for (; PI != PE; ++PI)
890 // If the value isn't fully available in one of our predecessors, then it
891 // isn't fully available in this block either. Undo our previous
892 // optimistic assumption and bail out.
893 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
894 goto SpeculationFailure;
898 // SpeculationFailure - If we get here, we found out that this is not, after
899 // all, a fully-available block. We have a problem if we speculated on this and
900 // used the speculation to mark other blocks as available.
902 char &BBVal = FullyAvailableBlocks[BB];
904 // If we didn't speculate on this, just return with it set to false.
910 // If we did speculate on this value, we could have blocks set to 1 that are
911 // incorrect. Walk the (transitive) successors of this block and mark them as
913 SmallVector<BasicBlock*, 32> BBWorklist;
914 BBWorklist.push_back(BB);
916 while (!BBWorklist.empty()) {
917 BasicBlock *Entry = BBWorklist.pop_back_val();
918 // Note that this sets blocks to 0 (unavailable) if they happen to not
919 // already be in FullyAvailableBlocks. This is safe.
920 char &EntryVal = FullyAvailableBlocks[Entry];
921 if (EntryVal == 0) continue; // Already unavailable.
923 // Mark as unavailable.
926 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
927 BBWorklist.push_back(*I);
933 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
934 /// non-local by performing PHI construction.
935 bool GVN::processNonLocalLoad(LoadInst *LI,
936 SmallVectorImpl<Instruction*> &toErase) {
937 // Find the non-local dependencies of the load.
938 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
939 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
941 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
943 // If we had to process more than one hundred blocks to find the
944 // dependencies, this load isn't worth worrying about. Optimizing
945 // it will be too expensive.
946 if (Deps.size() > 100)
949 // If we had a phi translation failure, we'll have a single entry which is a
950 // clobber in the current block. Reject this early.
951 if (Deps.size() == 1 && Deps[0].second.isClobber())
954 // Filter out useless results (non-locals, etc). Keep track of the blocks
955 // where we have a value available in repl, also keep track of whether we see
956 // dependencies that produce an unknown value for the load (such as a call
957 // that could potentially clobber the load).
958 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
959 SmallVector<BasicBlock*, 16> UnavailableBlocks;
961 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
962 BasicBlock *DepBB = Deps[i].first;
963 MemDepResult DepInfo = Deps[i].second;
965 if (DepInfo.isClobber()) {
966 UnavailableBlocks.push_back(DepBB);
970 Instruction *DepInst = DepInfo.getInst();
972 // Loading the allocation -> undef.
973 if (isa<AllocationInst>(DepInst)) {
974 ValuesPerBlock.push_back(std::make_pair(DepBB,
975 UndefValue::get(LI->getType())));
979 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
980 // Reject loads and stores that are to the same address but are of
982 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
983 // of bitfield access, it would be interesting to optimize for it at some
985 if (S->getOperand(0)->getType() != LI->getType()) {
986 UnavailableBlocks.push_back(DepBB);
990 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
992 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
993 if (LD->getType() != LI->getType()) {
994 UnavailableBlocks.push_back(DepBB);
997 ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
999 UnavailableBlocks.push_back(DepBB);
1004 // If we have no predecessors that produce a known value for this load, exit
1006 if (ValuesPerBlock.empty()) return false;
1008 // If all of the instructions we depend on produce a known value for this
1009 // load, then it is fully redundant and we can use PHI insertion to compute
1010 // its value. Insert PHIs and remove the fully redundant value now.
1011 if (UnavailableBlocks.empty()) {
1012 // Use cached PHI construction information from previous runs
1013 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1014 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
1015 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1017 if ((*I)->getParent() == LI->getParent()) {
1018 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
1019 LI->replaceAllUsesWith(*I);
1020 if (isa<PointerType>((*I)->getType()))
1021 MD->invalidateCachedPointerInfo(*I);
1022 toErase.push_back(LI);
1027 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1030 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
1032 DenseMap<BasicBlock*, Value*> BlockReplValues;
1033 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1034 // Perform PHI construction.
1035 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1036 LI->replaceAllUsesWith(v);
1038 if (isa<PHINode>(v))
1040 if (isa<PointerType>(v->getType()))
1041 MD->invalidateCachedPointerInfo(v);
1042 toErase.push_back(LI);
1047 if (!EnablePRE || !EnableLoadPRE)
1050 // Okay, we have *some* definitions of the value. This means that the value
1051 // is available in some of our (transitive) predecessors. Lets think about
1052 // doing PRE of this load. This will involve inserting a new load into the
1053 // predecessor when it's not available. We could do this in general, but
1054 // prefer to not increase code size. As such, we only do this when we know
1055 // that we only have to insert *one* load (which means we're basically moving
1056 // the load, not inserting a new one).
1058 SmallPtrSet<BasicBlock *, 4> Blockers;
1059 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1060 Blockers.insert(UnavailableBlocks[i]);
1062 // Lets find first basic block with more than one predecessor. Walk backwards
1063 // through predecessors if needed.
1064 BasicBlock *LoadBB = LI->getParent();
1065 BasicBlock *TmpBB = LoadBB;
1067 bool isSinglePred = false;
1068 while (TmpBB->getSinglePredecessor()) {
1069 isSinglePred = true;
1070 TmpBB = TmpBB->getSinglePredecessor();
1071 if (!TmpBB) // If haven't found any, bail now.
1073 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1075 if (Blockers.count(TmpBB))
1082 // If we have a repl set with LI itself in it, this means we have a loop where
1083 // at least one of the values is LI. Since this means that we won't be able
1084 // to eliminate LI even if we insert uses in the other predecessors, we will
1085 // end up increasing code size. Reject this by scanning for LI.
1086 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1087 if (ValuesPerBlock[i].second == LI)
1092 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1093 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second))
1094 // "Hot" Instruction is in some loop (because it dominates its dep.
1096 if (DT->dominates(LI, I)) {
1101 // We are interested only in "hot" instructions. We don't want to do any
1102 // mis-optimizations here.
1107 // Okay, we have some hope :). Check to see if the loaded value is fully
1108 // available in all but one predecessor.
1109 // FIXME: If we could restructure the CFG, we could make a common pred with
1110 // all the preds that don't have an available LI and insert a new load into
1112 BasicBlock *UnavailablePred = 0;
1114 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1115 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1116 FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
1117 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1118 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1120 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1122 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1125 // If this load is not available in multiple predecessors, reject it.
1126 if (UnavailablePred && UnavailablePred != *PI)
1128 UnavailablePred = *PI;
1131 assert(UnavailablePred != 0 &&
1132 "Fully available value should be eliminated above!");
1134 // If the loaded pointer is PHI node defined in this block, do PHI translation
1135 // to get its value in the predecessor.
1136 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
1138 // Make sure the value is live in the predecessor. If it was defined by a
1139 // non-PHI instruction in this block, we don't know how to recompute it above.
1140 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
1141 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
1142 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
1143 << *LPInst << *LI << "\n");
1147 // We don't currently handle critical edges :(
1148 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1149 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1150 << UnavailablePred->getName() << "': " << *LI);
1154 // Okay, we can eliminate this load by inserting a reload in the predecessor
1155 // and using PHI construction to get the value in the other predecessors, do
1157 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
1159 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1161 UnavailablePred->getTerminator());
1163 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1164 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1166 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1168 DenseMap<BasicBlock*, Value*> BlockReplValues;
1169 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1170 BlockReplValues[UnavailablePred] = NewLoad;
1172 // Perform PHI construction.
1173 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1174 LI->replaceAllUsesWith(v);
1175 if (isa<PHINode>(v))
1177 if (isa<PointerType>(v->getType()))
1178 MD->invalidateCachedPointerInfo(v);
1179 toErase.push_back(LI);
1184 /// processLoad - Attempt to eliminate a load, first by eliminating it
1185 /// locally, and then attempting non-local elimination if that fails.
1186 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1187 if (L->isVolatile())
1190 Value* pointer = L->getPointerOperand();
1192 // ... to a pointer that has been loaded from before...
1193 MemDepResult dep = MD->getDependency(L);
1195 // If the value isn't available, don't do anything!
1196 if (dep.isClobber()) {
1198 // fast print dep, using operator<< on instruction would be too slow
1199 DOUT << "GVN: load ";
1200 WriteAsOperand(*DOUT.stream(), L);
1201 Instruction *I = dep.getInst();
1202 DOUT << " is clobbered by " << *I;
1207 // If it is defined in another block, try harder.
1208 if (dep.isNonLocal())
1209 return processNonLocalLoad(L, toErase);
1211 Instruction *DepInst = dep.getInst();
1212 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1213 // Only forward substitute stores to loads of the same type.
1214 // FIXME: Could do better!
1215 if (DepSI->getPointerOperand()->getType() != pointer->getType())
1219 L->replaceAllUsesWith(DepSI->getOperand(0));
1220 if (isa<PointerType>(DepSI->getOperand(0)->getType()))
1221 MD->invalidateCachedPointerInfo(DepSI->getOperand(0));
1222 toErase.push_back(L);
1227 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1228 // Only forward substitute stores to loads of the same type.
1229 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
1230 if (DepLI->getType() != L->getType())
1234 L->replaceAllUsesWith(DepLI);
1235 if (isa<PointerType>(DepLI->getType()))
1236 MD->invalidateCachedPointerInfo(DepLI);
1237 toErase.push_back(L);
1242 // If this load really doesn't depend on anything, then we must be loading an
1243 // undef value. This can happen when loading for a fresh allocation with no
1244 // intervening stores, for example.
1245 if (isa<AllocationInst>(DepInst)) {
1246 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1247 toErase.push_back(L);
1255 Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1256 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1257 if (I == localAvail.end())
1260 ValueNumberScope* locals = I->second;
1263 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1264 if (I != locals->table.end())
1267 locals = locals->parent;
1273 /// AttemptRedundancyElimination - If the "fast path" of redundancy elimination
1274 /// by inheritance from the dominator fails, see if we can perform phi
1275 /// construction to eliminate the redundancy.
1276 Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) {
1277 BasicBlock* BaseBlock = orig->getParent();
1279 SmallPtrSet<BasicBlock*, 4> Visited;
1280 SmallVector<BasicBlock*, 8> Stack;
1281 Stack.push_back(BaseBlock);
1283 DenseMap<BasicBlock*, Value*> Results;
1285 // Walk backwards through our predecessors, looking for instances of the
1286 // value number we're looking for. Instances are recorded in the Results
1287 // map, which is then used to perform phi construction.
1288 while (!Stack.empty()) {
1289 BasicBlock* Current = Stack.back();
1292 // If we've walked all the way to a proper dominator, then give up. Cases
1293 // where the instance is in the dominator will have been caught by the fast
1294 // path, and any cases that require phi construction further than this are
1295 // probably not worth it anyways. Note that this is a SIGNIFICANT compile
1296 // time improvement.
1297 if (DT->properlyDominates(Current, orig->getParent())) return 0;
1299 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA =
1300 localAvail.find(Current);
1301 if (LA == localAvail.end()) return 0;
1302 DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno);
1304 if (V != LA->second->table.end()) {
1305 // Found an instance, record it.
1306 Results.insert(std::make_pair(Current, V->second));
1310 // If we reach the beginning of the function, then give up.
1311 if (pred_begin(Current) == pred_end(Current))
1314 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current);
1316 if (Visited.insert(*PI))
1317 Stack.push_back(*PI);
1320 // If we didn't find instances, give up. Otherwise, perform phi construction.
1321 if (Results.size() == 0)
1324 return GetValueForBlock(BaseBlock, orig, Results, true);
1327 /// processInstruction - When calculating availability, handle an instruction
1328 /// by inserting it into the appropriate sets
1329 bool GVN::processInstruction(Instruction *I,
1330 SmallVectorImpl<Instruction*> &toErase) {
1331 if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1332 bool changed = processLoad(L, toErase);
1335 unsigned num = VN.lookup_or_add(L);
1336 localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1342 uint32_t nextNum = VN.getNextUnusedValueNumber();
1343 unsigned num = VN.lookup_or_add(I);
1345 if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
1346 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1348 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1351 Value* branchCond = BI->getCondition();
1352 uint32_t condVN = VN.lookup_or_add(branchCond);
1354 BasicBlock* trueSucc = BI->getSuccessor(0);
1355 BasicBlock* falseSucc = BI->getSuccessor(1);
1357 if (trueSucc->getSinglePredecessor())
1358 localAvail[trueSucc]->table[condVN] = ConstantInt::getTrue();
1359 if (falseSucc->getSinglePredecessor())
1360 localAvail[falseSucc]->table[condVN] = ConstantInt::getFalse();
1364 // Allocations are always uniquely numbered, so we can save time and memory
1365 // by fast failing them.
1366 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
1367 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1371 // Collapse PHI nodes
1372 if (PHINode* p = dyn_cast<PHINode>(I)) {
1373 Value* constVal = CollapsePhi(p);
1376 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1378 PI->second.erase(p);
1380 p->replaceAllUsesWith(constVal);
1381 if (isa<PointerType>(constVal->getType()))
1382 MD->invalidateCachedPointerInfo(constVal);
1385 toErase.push_back(p);
1387 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1390 // If the number we were assigned was a brand new VN, then we don't
1391 // need to do a lookup to see if the number already exists
1392 // somewhere in the domtree: it can't!
1393 } else if (num == nextNum) {
1394 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1396 // Perform fast-path value-number based elimination of values inherited from
1398 } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1401 I->replaceAllUsesWith(repl);
1402 if (isa<PointerType>(repl->getType()))
1403 MD->invalidateCachedPointerInfo(repl);
1404 toErase.push_back(I);
1408 // Perform slow-pathvalue-number based elimination with phi construction.
1409 } else if (Value* repl = AttemptRedundancyElimination(I, num)) {
1412 I->replaceAllUsesWith(repl);
1413 if (isa<PointerType>(repl->getType()))
1414 MD->invalidateCachedPointerInfo(repl);
1415 toErase.push_back(I);
1419 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1425 /// runOnFunction - This is the main transformation entry point for a function.
1426 bool GVN::runOnFunction(Function& F) {
1427 MD = &getAnalysis<MemoryDependenceAnalysis>();
1428 DT = &getAnalysis<DominatorTree>();
1429 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1433 bool changed = false;
1434 bool shouldContinue = true;
1436 // Merge unconditional branches, allowing PRE to catch more
1437 // optimization opportunities.
1438 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1439 BasicBlock* BB = FI;
1441 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1442 if (removedBlock) NumGVNBlocks++;
1444 changed |= removedBlock;
1447 unsigned Iteration = 0;
1449 while (shouldContinue) {
1450 DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
1451 shouldContinue = iterateOnFunction(F);
1452 changed |= shouldContinue;
1457 bool PREChanged = true;
1458 while (PREChanged) {
1459 PREChanged = performPRE(F);
1460 changed |= PREChanged;
1463 // FIXME: Should perform GVN again after PRE does something. PRE can move
1464 // computations into blocks where they become fully redundant. Note that
1465 // we can't do this until PRE's critical edge splitting updates memdep.
1466 // Actually, when this happens, we should just fully integrate PRE into GVN.
1468 cleanupGlobalSets();
1474 bool GVN::processBlock(BasicBlock* BB) {
1475 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1476 // incrementing BI before processing an instruction).
1477 SmallVector<Instruction*, 8> toErase;
1478 bool changed_function = false;
1480 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1482 changed_function |= processInstruction(BI, toErase);
1483 if (toErase.empty()) {
1488 // If we need some instructions deleted, do it now.
1489 NumGVNInstr += toErase.size();
1491 // Avoid iterator invalidation.
1492 bool AtStart = BI == BB->begin();
1496 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1497 E = toErase.end(); I != E; ++I) {
1498 DEBUG(cerr << "GVN removed: " << **I);
1499 MD->removeInstruction(*I);
1500 (*I)->eraseFromParent();
1501 DEBUG(verifyRemoved(*I));
1511 return changed_function;
1514 /// performPRE - Perform a purely local form of PRE that looks for diamond
1515 /// control flow patterns and attempts to perform simple PRE at the join point.
1516 bool GVN::performPRE(Function& F) {
1517 bool Changed = false;
1518 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1519 DenseMap<BasicBlock*, Value*> predMap;
1520 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1521 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1522 BasicBlock* CurrentBlock = *DI;
1524 // Nothing to PRE in the entry block.
1525 if (CurrentBlock == &F.getEntryBlock()) continue;
1527 for (BasicBlock::iterator BI = CurrentBlock->begin(),
1528 BE = CurrentBlock->end(); BI != BE; ) {
1529 Instruction *CurInst = BI++;
1531 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
1532 isa<PHINode>(CurInst) || (CurInst->getType() == Type::VoidTy) ||
1533 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
1534 isa<DbgInfoIntrinsic>(CurInst))
1537 uint32_t valno = VN.lookup(CurInst);
1539 // Look for the predecessors for PRE opportunities. We're
1540 // only trying to solve the basic diamond case, where
1541 // a value is computed in the successor and one predecessor,
1542 // but not the other. We also explicitly disallow cases
1543 // where the successor is its own predecessor, because they're
1544 // more complicated to get right.
1545 unsigned numWith = 0;
1546 unsigned numWithout = 0;
1547 BasicBlock* PREPred = 0;
1550 for (pred_iterator PI = pred_begin(CurrentBlock),
1551 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1552 // We're not interested in PRE where the block is its
1553 // own predecessor, on in blocks with predecessors
1554 // that are not reachable.
1555 if (*PI == CurrentBlock) {
1558 } else if (!localAvail.count(*PI)) {
1563 DenseMap<uint32_t, Value*>::iterator predV =
1564 localAvail[*PI]->table.find(valno);
1565 if (predV == localAvail[*PI]->table.end()) {
1568 } else if (predV->second == CurInst) {
1571 predMap[*PI] = predV->second;
1576 // Don't do PRE when it might increase code size, i.e. when
1577 // we would need to insert instructions in more than one pred.
1578 if (numWithout != 1 || numWith == 0)
1581 // We can't do PRE safely on a critical edge, so instead we schedule
1582 // the edge to be split and perform the PRE the next time we iterate
1584 unsigned succNum = 0;
1585 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1587 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
1592 if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1593 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1597 // Instantiate the expression the in predecessor that lacked it.
1598 // Because we are going top-down through the block, all value numbers
1599 // will be available in the predecessor by the time we need them. Any
1600 // that weren't original present will have been instantiated earlier
1602 Instruction* PREInstr = CurInst->clone();
1603 bool success = true;
1604 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
1605 Value *Op = PREInstr->getOperand(i);
1606 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
1609 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
1610 PREInstr->setOperand(i, V);
1617 // Fail out if we encounter an operand that is not available in
1618 // the PRE predecessor. This is typically because of loads which
1619 // are not value numbered precisely.
1622 DEBUG(verifyRemoved(PREInstr));
1626 PREInstr->insertBefore(PREPred->getTerminator());
1627 PREInstr->setName(CurInst->getName() + ".pre");
1628 predMap[PREPred] = PREInstr;
1629 VN.add(PREInstr, valno);
1632 // Update the availability map to include the new instruction.
1633 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1635 // Create a PHI to make the value available in this block.
1636 PHINode* Phi = PHINode::Create(CurInst->getType(),
1637 CurInst->getName() + ".pre-phi",
1638 CurrentBlock->begin());
1639 for (pred_iterator PI = pred_begin(CurrentBlock),
1640 PE = pred_end(CurrentBlock); PI != PE; ++PI)
1641 Phi->addIncoming(predMap[*PI], *PI);
1644 localAvail[CurrentBlock]->table[valno] = Phi;
1646 CurInst->replaceAllUsesWith(Phi);
1647 if (isa<PointerType>(Phi->getType()))
1648 MD->invalidateCachedPointerInfo(Phi);
1651 DEBUG(cerr << "GVN PRE removed: " << *CurInst);
1652 MD->removeInstruction(CurInst);
1653 CurInst->eraseFromParent();
1654 DEBUG(verifyRemoved(CurInst));
1659 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1660 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1661 SplitCriticalEdge(I->first, I->second, this);
1663 return Changed || toSplit.size();
1666 /// iterateOnFunction - Executes one iteration of GVN
1667 bool GVN::iterateOnFunction(Function &F) {
1668 cleanupGlobalSets();
1670 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1671 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
1673 localAvail[DI->getBlock()] =
1674 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
1676 localAvail[DI->getBlock()] = new ValueNumberScope(0);
1679 // Top-down walk of the dominator tree
1680 bool changed = false;
1682 // Needed for value numbering with phi construction to work.
1683 ReversePostOrderTraversal<Function*> RPOT(&F);
1684 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
1685 RE = RPOT.end(); RI != RE; ++RI)
1686 changed |= processBlock(*RI);
1688 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1689 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
1690 changed |= processBlock(DI->getBlock());
1696 void GVN::cleanupGlobalSets() {
1700 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1701 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
1706 /// verifyRemoved - Verify that the specified instruction does not occur in our
1707 /// internal data structures.
1708 void GVN::verifyRemoved(const Instruction *Inst) const {
1709 VN.verifyRemoved(Inst);
1711 // Walk through the PHI map to make sure the instruction isn't hiding in there
1713 for (PhiMapType::iterator
1714 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) {
1715 assert(I->first != Inst && "Inst is still a key in PHI map!");
1717 for (SmallPtrSet<Instruction*, 4>::iterator
1718 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) {
1719 assert(*II != Inst && "Inst is still a value in PHI map!");
1723 // Walk through the value number scope to make sure the instruction isn't
1724 // ferreted away in it.
1725 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1726 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
1727 const ValueNumberScope *VNS = I->second;
1730 for (DenseMap<uint32_t, Value*>::iterator
1731 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
1732 assert(II->second != Inst && "Inst still in value numbering scope!");