1 //===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass performs global value numbering to eliminate fully redundant
11 // instructions. It also performs simple dead load elimination.
13 // Note that this pass does the value numbering itself; it does not use the
14 // ValueNumbering analysis passes.
16 //===----------------------------------------------------------------------===//
18 #define DEBUG_TYPE "gvn"
19 #include "llvm/Transforms/Scalar.h"
20 #include "llvm/BasicBlock.h"
21 #include "llvm/Constants.h"
22 #include "llvm/DerivedTypes.h"
23 #include "llvm/Function.h"
24 #include "llvm/IntrinsicInst.h"
25 #include "llvm/LLVMContext.h"
26 #include "llvm/Value.h"
27 #include "llvm/ADT/DenseMap.h"
28 #include "llvm/ADT/DepthFirstIterator.h"
29 #include "llvm/ADT/PostOrderIterator.h"
30 #include "llvm/ADT/SmallPtrSet.h"
31 #include "llvm/ADT/SmallVector.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "llvm/Analysis/Dominators.h"
34 #include "llvm/Analysis/AliasAnalysis.h"
35 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
36 #include "llvm/Support/CFG.h"
37 #include "llvm/Support/CommandLine.h"
38 #include "llvm/Support/Compiler.h"
39 #include "llvm/Support/Debug.h"
40 #include "llvm/Support/ErrorHandling.h"
41 #include "llvm/Support/raw_ostream.h"
42 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
43 #include "llvm/Transforms/Utils/Local.h"
47 STATISTIC(NumGVNInstr, "Number of instructions deleted");
48 STATISTIC(NumGVNLoad, "Number of loads deleted");
49 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
50 STATISTIC(NumGVNBlocks, "Number of blocks merged");
51 STATISTIC(NumPRELoad, "Number of loads PRE'd");
53 static cl::opt<bool> EnablePRE("enable-pre",
54 cl::init(true), cl::Hidden);
55 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
57 //===----------------------------------------------------------------------===//
59 //===----------------------------------------------------------------------===//
61 /// This class holds the mapping between values and value numbers. It is used
62 /// as an efficient mechanism to determine the expression-wise equivalence of
65 struct VISIBILITY_HIDDEN Expression {
66 enum ExpressionOpcode { ADD, FADD, SUB, FSUB, MUL, FMUL,
67 UDIV, SDIV, FDIV, UREM, SREM,
68 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
69 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
70 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
71 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
72 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
73 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
74 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
75 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
76 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
79 ExpressionOpcode opcode;
84 SmallVector<uint32_t, 4> varargs;
88 Expression(ExpressionOpcode o) : opcode(o) { }
90 bool operator==(const Expression &other) const {
91 if (opcode != other.opcode)
93 else if (opcode == EMPTY || opcode == TOMBSTONE)
95 else if (type != other.type)
97 else if (function != other.function)
99 else if (firstVN != other.firstVN)
101 else if (secondVN != other.secondVN)
103 else if (thirdVN != other.thirdVN)
106 if (varargs.size() != other.varargs.size())
109 for (size_t i = 0; i < varargs.size(); ++i)
110 if (varargs[i] != other.varargs[i])
117 bool operator!=(const Expression &other) const {
118 return !(*this == other);
122 class VISIBILITY_HIDDEN ValueTable {
124 DenseMap<Value*, uint32_t> valueNumbering;
125 DenseMap<Expression, uint32_t> expressionNumbering;
127 MemoryDependenceAnalysis* MD;
130 uint32_t nextValueNumber;
132 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
133 Expression::ExpressionOpcode getOpcode(CmpInst* C);
134 Expression::ExpressionOpcode getOpcode(CastInst* C);
135 Expression create_expression(BinaryOperator* BO);
136 Expression create_expression(CmpInst* C);
137 Expression create_expression(ShuffleVectorInst* V);
138 Expression create_expression(ExtractElementInst* C);
139 Expression create_expression(InsertElementInst* V);
140 Expression create_expression(SelectInst* V);
141 Expression create_expression(CastInst* C);
142 Expression create_expression(GetElementPtrInst* G);
143 Expression create_expression(CallInst* C);
144 Expression create_expression(Constant* C);
146 ValueTable() : nextValueNumber(1) { }
147 uint32_t lookup_or_add(Value* V);
148 uint32_t lookup(Value* V) const;
149 void add(Value* V, uint32_t num);
151 void erase(Value* v);
153 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
154 AliasAnalysis *getAliasAnalysis() const { return AA; }
155 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
156 void setDomTree(DominatorTree* D) { DT = D; }
157 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
158 void verifyRemoved(const Value *) const;
163 template <> struct DenseMapInfo<Expression> {
164 static inline Expression getEmptyKey() {
165 return Expression(Expression::EMPTY);
168 static inline Expression getTombstoneKey() {
169 return Expression(Expression::TOMBSTONE);
172 static unsigned getHashValue(const Expression e) {
173 unsigned hash = e.opcode;
175 hash = e.firstVN + hash * 37;
176 hash = e.secondVN + hash * 37;
177 hash = e.thirdVN + hash * 37;
179 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
180 (unsigned)((uintptr_t)e.type >> 9)) +
183 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
184 E = e.varargs.end(); I != E; ++I)
185 hash = *I + hash * 37;
187 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
188 (unsigned)((uintptr_t)e.function >> 9)) +
193 static bool isEqual(const Expression &LHS, const Expression &RHS) {
196 static bool isPod() { return true; }
200 //===----------------------------------------------------------------------===//
201 // ValueTable Internal Functions
202 //===----------------------------------------------------------------------===//
203 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
204 switch(BO->getOpcode()) {
205 default: // THIS SHOULD NEVER HAPPEN
206 llvm_unreachable("Binary operator with unknown opcode?");
207 case Instruction::Add: return Expression::ADD;
208 case Instruction::FAdd: return Expression::FADD;
209 case Instruction::Sub: return Expression::SUB;
210 case Instruction::FSub: return Expression::FSUB;
211 case Instruction::Mul: return Expression::MUL;
212 case Instruction::FMul: return Expression::FMUL;
213 case Instruction::UDiv: return Expression::UDIV;
214 case Instruction::SDiv: return Expression::SDIV;
215 case Instruction::FDiv: return Expression::FDIV;
216 case Instruction::URem: return Expression::UREM;
217 case Instruction::SRem: return Expression::SREM;
218 case Instruction::FRem: return Expression::FREM;
219 case Instruction::Shl: return Expression::SHL;
220 case Instruction::LShr: return Expression::LSHR;
221 case Instruction::AShr: return Expression::ASHR;
222 case Instruction::And: return Expression::AND;
223 case Instruction::Or: return Expression::OR;
224 case Instruction::Xor: return Expression::XOR;
228 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
229 if (isa<ICmpInst>(C)) {
230 switch (C->getPredicate()) {
231 default: // THIS SHOULD NEVER HAPPEN
232 llvm_unreachable("Comparison with unknown predicate?");
233 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
234 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
235 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
236 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
237 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
238 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
239 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
240 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
241 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
242 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
245 switch (C->getPredicate()) {
246 default: // THIS SHOULD NEVER HAPPEN
247 llvm_unreachable("Comparison with unknown predicate?");
248 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
249 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
250 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
251 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
252 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
253 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
254 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
255 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
256 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
257 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
258 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
259 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
260 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
261 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
266 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
267 switch(C->getOpcode()) {
268 default: // THIS SHOULD NEVER HAPPEN
269 llvm_unreachable("Cast operator with unknown opcode?");
270 case Instruction::Trunc: return Expression::TRUNC;
271 case Instruction::ZExt: return Expression::ZEXT;
272 case Instruction::SExt: return Expression::SEXT;
273 case Instruction::FPToUI: return Expression::FPTOUI;
274 case Instruction::FPToSI: return Expression::FPTOSI;
275 case Instruction::UIToFP: return Expression::UITOFP;
276 case Instruction::SIToFP: return Expression::SITOFP;
277 case Instruction::FPTrunc: return Expression::FPTRUNC;
278 case Instruction::FPExt: return Expression::FPEXT;
279 case Instruction::PtrToInt: return Expression::PTRTOINT;
280 case Instruction::IntToPtr: return Expression::INTTOPTR;
281 case Instruction::BitCast: return Expression::BITCAST;
285 Expression ValueTable::create_expression(CallInst* C) {
288 e.type = C->getType();
292 e.function = C->getCalledFunction();
293 e.opcode = Expression::CALL;
295 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
297 e.varargs.push_back(lookup_or_add(*I));
302 Expression ValueTable::create_expression(BinaryOperator* BO) {
305 e.firstVN = lookup_or_add(BO->getOperand(0));
306 e.secondVN = lookup_or_add(BO->getOperand(1));
309 e.type = BO->getType();
310 e.opcode = getOpcode(BO);
315 Expression ValueTable::create_expression(CmpInst* C) {
318 e.firstVN = lookup_or_add(C->getOperand(0));
319 e.secondVN = lookup_or_add(C->getOperand(1));
322 e.type = C->getType();
323 e.opcode = getOpcode(C);
328 Expression ValueTable::create_expression(CastInst* C) {
331 e.firstVN = lookup_or_add(C->getOperand(0));
335 e.type = C->getType();
336 e.opcode = getOpcode(C);
341 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
344 e.firstVN = lookup_or_add(S->getOperand(0));
345 e.secondVN = lookup_or_add(S->getOperand(1));
346 e.thirdVN = lookup_or_add(S->getOperand(2));
348 e.type = S->getType();
349 e.opcode = Expression::SHUFFLE;
354 Expression ValueTable::create_expression(ExtractElementInst* E) {
357 e.firstVN = lookup_or_add(E->getOperand(0));
358 e.secondVN = lookup_or_add(E->getOperand(1));
361 e.type = E->getType();
362 e.opcode = Expression::EXTRACT;
367 Expression ValueTable::create_expression(InsertElementInst* I) {
370 e.firstVN = lookup_or_add(I->getOperand(0));
371 e.secondVN = lookup_or_add(I->getOperand(1));
372 e.thirdVN = lookup_or_add(I->getOperand(2));
374 e.type = I->getType();
375 e.opcode = Expression::INSERT;
380 Expression ValueTable::create_expression(SelectInst* I) {
383 e.firstVN = lookup_or_add(I->getCondition());
384 e.secondVN = lookup_or_add(I->getTrueValue());
385 e.thirdVN = lookup_or_add(I->getFalseValue());
387 e.type = I->getType();
388 e.opcode = Expression::SELECT;
393 Expression ValueTable::create_expression(GetElementPtrInst* G) {
396 e.firstVN = lookup_or_add(G->getPointerOperand());
400 e.type = G->getType();
401 e.opcode = Expression::GEP;
403 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
405 e.varargs.push_back(lookup_or_add(*I));
410 //===----------------------------------------------------------------------===//
411 // ValueTable External Functions
412 //===----------------------------------------------------------------------===//
414 /// add - Insert a value into the table with a specified value number.
415 void ValueTable::add(Value* V, uint32_t num) {
416 valueNumbering.insert(std::make_pair(V, num));
419 /// lookup_or_add - Returns the value number for the specified value, assigning
420 /// it a new number if it did not have one before.
421 uint32_t ValueTable::lookup_or_add(Value* V) {
422 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
423 if (VI != valueNumbering.end())
426 if (CallInst* C = dyn_cast<CallInst>(V)) {
427 if (AA->doesNotAccessMemory(C)) {
428 Expression e = create_expression(C);
430 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
431 if (EI != expressionNumbering.end()) {
432 valueNumbering.insert(std::make_pair(V, EI->second));
435 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
436 valueNumbering.insert(std::make_pair(V, nextValueNumber));
438 return nextValueNumber++;
440 } else if (AA->onlyReadsMemory(C)) {
441 Expression e = create_expression(C);
443 if (expressionNumbering.find(e) == expressionNumbering.end()) {
444 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
445 valueNumbering.insert(std::make_pair(V, nextValueNumber));
446 return nextValueNumber++;
449 MemDepResult local_dep = MD->getDependency(C);
451 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
452 valueNumbering.insert(std::make_pair(V, nextValueNumber));
453 return nextValueNumber++;
456 if (local_dep.isDef()) {
457 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
459 if (local_cdep->getNumOperands() != C->getNumOperands()) {
460 valueNumbering.insert(std::make_pair(V, nextValueNumber));
461 return nextValueNumber++;
464 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
465 uint32_t c_vn = lookup_or_add(C->getOperand(i));
466 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
468 valueNumbering.insert(std::make_pair(V, nextValueNumber));
469 return nextValueNumber++;
473 uint32_t v = lookup_or_add(local_cdep);
474 valueNumbering.insert(std::make_pair(V, v));
479 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
480 MD->getNonLocalCallDependency(CallSite(C));
481 // FIXME: call/call dependencies for readonly calls should return def, not
482 // clobber! Move the checking logic to MemDep!
485 // Check to see if we have a single dominating call instruction that is
487 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
488 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
489 // Ignore non-local dependencies.
490 if (I->second.isNonLocal())
493 // We don't handle non-depedencies. If we already have a call, reject
494 // instruction dependencies.
495 if (I->second.isClobber() || cdep != 0) {
500 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
501 // FIXME: All duplicated with non-local case.
502 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
503 cdep = NonLocalDepCall;
512 valueNumbering.insert(std::make_pair(V, nextValueNumber));
513 return nextValueNumber++;
516 if (cdep->getNumOperands() != C->getNumOperands()) {
517 valueNumbering.insert(std::make_pair(V, nextValueNumber));
518 return nextValueNumber++;
520 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
521 uint32_t c_vn = lookup_or_add(C->getOperand(i));
522 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
524 valueNumbering.insert(std::make_pair(V, nextValueNumber));
525 return nextValueNumber++;
529 uint32_t v = lookup_or_add(cdep);
530 valueNumbering.insert(std::make_pair(V, v));
534 valueNumbering.insert(std::make_pair(V, nextValueNumber));
535 return nextValueNumber++;
537 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
538 Expression e = create_expression(BO);
540 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
541 if (EI != expressionNumbering.end()) {
542 valueNumbering.insert(std::make_pair(V, EI->second));
545 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
546 valueNumbering.insert(std::make_pair(V, nextValueNumber));
548 return nextValueNumber++;
550 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
551 Expression e = create_expression(C);
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 (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
564 Expression e = create_expression(U);
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 (ExtractElementInst* U = dyn_cast<ExtractElementInst>(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 (InsertElementInst* U = dyn_cast<InsertElementInst>(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 (SelectInst* U = dyn_cast<SelectInst>(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 (CastInst* U = dyn_cast<CastInst>(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 (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(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++;
642 valueNumbering.insert(std::make_pair(V, nextValueNumber));
643 return nextValueNumber++;
647 /// lookup - Returns the value number of the specified value. Fails if
648 /// the value has not yet been numbered.
649 uint32_t ValueTable::lookup(Value* V) const {
650 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
651 assert(VI != valueNumbering.end() && "Value not numbered?");
655 /// clear - Remove all entries from the ValueTable
656 void ValueTable::clear() {
657 valueNumbering.clear();
658 expressionNumbering.clear();
662 /// erase - Remove a value from the value numbering
663 void ValueTable::erase(Value* V) {
664 valueNumbering.erase(V);
667 /// verifyRemoved - Verify that the value is removed from all internal data
669 void ValueTable::verifyRemoved(const Value *V) const {
670 for (DenseMap<Value*, uint32_t>::iterator
671 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
672 assert(I->first != V && "Inst still occurs in value numbering map!");
676 //===----------------------------------------------------------------------===//
678 //===----------------------------------------------------------------------===//
681 struct VISIBILITY_HIDDEN ValueNumberScope {
682 ValueNumberScope* parent;
683 DenseMap<uint32_t, Value*> table;
685 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
691 class VISIBILITY_HIDDEN GVN : public FunctionPass {
692 bool runOnFunction(Function &F);
694 static char ID; // Pass identification, replacement for typeid
695 GVN() : FunctionPass(&ID) { }
698 MemoryDependenceAnalysis *MD;
702 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
704 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
708 // This transformation requires dominator postdominator info
709 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
710 AU.addRequired<DominatorTree>();
711 AU.addRequired<MemoryDependenceAnalysis>();
712 AU.addRequired<AliasAnalysis>();
714 AU.addPreserved<DominatorTree>();
715 AU.addPreserved<AliasAnalysis>();
719 // FIXME: eliminate or document these better
720 bool processLoad(LoadInst* L,
721 SmallVectorImpl<Instruction*> &toErase);
722 bool processInstruction(Instruction* I,
723 SmallVectorImpl<Instruction*> &toErase);
724 bool processNonLocalLoad(LoadInst* L,
725 SmallVectorImpl<Instruction*> &toErase);
726 bool processBlock(BasicBlock* BB);
727 Value *GetValueForBlock(BasicBlock *BB, Instruction* orig,
728 DenseMap<BasicBlock*, Value*> &Phis,
729 bool top_level = false);
730 void dump(DenseMap<uint32_t, Value*>& d);
731 bool iterateOnFunction(Function &F);
732 Value* CollapsePhi(PHINode* p);
733 bool performPRE(Function& F);
734 Value* lookupNumber(BasicBlock* BB, uint32_t num);
735 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno);
736 void cleanupGlobalSets();
737 void verifyRemoved(const Instruction *I) const;
743 // createGVNPass - The public interface to this file...
744 FunctionPass *llvm::createGVNPass() { return new GVN(); }
746 static RegisterPass<GVN> X("gvn",
747 "Global Value Numbering");
749 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
751 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
752 E = d.end(); I != E; ++I) {
753 printf("%d\n", I->first);
759 static bool isSafeReplacement(PHINode* p, Instruction* inst) {
760 if (!isa<PHINode>(inst))
763 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
765 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
766 if (use_phi->getParent() == inst->getParent())
772 Value* GVN::CollapsePhi(PHINode* p) {
773 Value* constVal = p->hasConstantValue();
774 if (!constVal) return 0;
776 Instruction* inst = dyn_cast<Instruction>(constVal);
780 if (DT->dominates(inst, p))
781 if (isSafeReplacement(p, inst))
786 /// GetValueForBlock - Get the value to use within the specified basic block.
787 /// available values are in Phis.
788 Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig,
789 DenseMap<BasicBlock*, Value*> &Phis,
792 // If we have already computed this value, return the previously computed val.
793 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
794 if (V != Phis.end() && !top_level) return V->second;
796 // If the block is unreachable, just return undef, since this path
797 // can't actually occur at runtime.
798 if (!DT->isReachableFromEntry(BB))
799 return Phis[BB] = UndefValue::get(orig->getType());
801 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
802 Value *ret = GetValueForBlock(Pred, orig, Phis);
807 // Get the number of predecessors of this block so we can reserve space later.
808 // If there is already a PHI in it, use the #preds from it, otherwise count.
809 // Getting it from the PHI is constant time.
811 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
812 NumPreds = ExistingPN->getNumIncomingValues();
814 NumPreds = std::distance(pred_begin(BB), pred_end(BB));
816 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
817 // now, then get values to fill in the incoming values for the PHI.
818 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
820 PN->reserveOperandSpace(NumPreds);
822 Phis.insert(std::make_pair(BB, PN));
824 // Fill in the incoming values for the block.
825 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
826 Value* val = GetValueForBlock(*PI, orig, Phis);
827 PN->addIncoming(val, *PI);
830 VN.getAliasAnalysis()->copyValue(orig, PN);
832 // Attempt to collapse PHI nodes that are trivially redundant
833 Value* v = CollapsePhi(PN);
835 // Cache our phi construction results
836 if (LoadInst* L = dyn_cast<LoadInst>(orig))
837 phiMap[L->getPointerOperand()].insert(PN);
839 phiMap[orig].insert(PN);
844 PN->replaceAllUsesWith(v);
845 if (isa<PointerType>(v->getType()))
846 MD->invalidateCachedPointerInfo(v);
848 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
849 E = Phis.end(); I != E; ++I)
853 DEBUG(errs() << "GVN removed: " << *PN << '\n');
854 MD->removeInstruction(PN);
855 PN->eraseFromParent();
856 DEBUG(verifyRemoved(PN));
862 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
863 /// we're analyzing is fully available in the specified block. As we go, keep
864 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
865 /// map is actually a tri-state map with the following values:
866 /// 0) we know the block *is not* fully available.
867 /// 1) we know the block *is* fully available.
868 /// 2) we do not know whether the block is fully available or not, but we are
869 /// currently speculating that it will be.
870 /// 3) we are speculating for this block and have used that to speculate for
872 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
873 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
874 // Optimistically assume that the block is fully available and check to see
875 // if we already know about this block in one lookup.
876 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
877 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
879 // If the entry already existed for this block, return the precomputed value.
881 // If this is a speculative "available" value, mark it as being used for
882 // speculation of other blocks.
883 if (IV.first->second == 2)
884 IV.first->second = 3;
885 return IV.first->second != 0;
888 // Otherwise, see if it is fully available in all predecessors.
889 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
891 // If this block has no predecessors, it isn't live-in here.
893 goto SpeculationFailure;
895 for (; PI != PE; ++PI)
896 // If the value isn't fully available in one of our predecessors, then it
897 // isn't fully available in this block either. Undo our previous
898 // optimistic assumption and bail out.
899 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
900 goto SpeculationFailure;
904 // SpeculationFailure - If we get here, we found out that this is not, after
905 // all, a fully-available block. We have a problem if we speculated on this and
906 // used the speculation to mark other blocks as available.
908 char &BBVal = FullyAvailableBlocks[BB];
910 // If we didn't speculate on this, just return with it set to false.
916 // If we did speculate on this value, we could have blocks set to 1 that are
917 // incorrect. Walk the (transitive) successors of this block and mark them as
919 SmallVector<BasicBlock*, 32> BBWorklist;
920 BBWorklist.push_back(BB);
922 while (!BBWorklist.empty()) {
923 BasicBlock *Entry = BBWorklist.pop_back_val();
924 // Note that this sets blocks to 0 (unavailable) if they happen to not
925 // already be in FullyAvailableBlocks. This is safe.
926 char &EntryVal = FullyAvailableBlocks[Entry];
927 if (EntryVal == 0) continue; // Already unavailable.
929 // Mark as unavailable.
932 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
933 BBWorklist.push_back(*I);
939 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
940 /// non-local by performing PHI construction.
941 bool GVN::processNonLocalLoad(LoadInst *LI,
942 SmallVectorImpl<Instruction*> &toErase) {
943 // Find the non-local dependencies of the load.
944 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
945 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
947 //DEBUG(errs() << "INVESTIGATING NONLOCAL LOAD: "
948 // << Deps.size() << *LI << '\n');
950 // If we had to process more than one hundred blocks to find the
951 // dependencies, this load isn't worth worrying about. Optimizing
952 // it will be too expensive.
953 if (Deps.size() > 100)
956 // If we had a phi translation failure, we'll have a single entry which is a
957 // clobber in the current block. Reject this early.
958 if (Deps.size() == 1 && Deps[0].second.isClobber()) {
960 errs() << "GVN: non-local load ";
961 WriteAsOperand(errs(), LI);
962 errs() << " is clobbered by " << *Deps[0].second.getInst() << '\n';
967 // Filter out useless results (non-locals, etc). Keep track of the blocks
968 // where we have a value available in repl, also keep track of whether we see
969 // dependencies that produce an unknown value for the load (such as a call
970 // that could potentially clobber the load).
971 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
972 SmallVector<BasicBlock*, 16> UnavailableBlocks;
974 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
975 BasicBlock *DepBB = Deps[i].first;
976 MemDepResult DepInfo = Deps[i].second;
978 if (DepInfo.isClobber()) {
979 UnavailableBlocks.push_back(DepBB);
983 Instruction *DepInst = DepInfo.getInst();
985 // Loading the allocation -> undef.
986 if (isa<AllocationInst>(DepInst)) {
987 ValuesPerBlock.push_back(std::make_pair(DepBB,
988 UndefValue::get(LI->getType())));
992 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
993 // Reject loads and stores that are to the same address but are of
995 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
996 // of bitfield access, it would be interesting to optimize for it at some
998 if (S->getOperand(0)->getType() != LI->getType()) {
999 UnavailableBlocks.push_back(DepBB);
1003 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
1005 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
1006 if (LD->getType() != LI->getType()) {
1007 UnavailableBlocks.push_back(DepBB);
1010 ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
1012 UnavailableBlocks.push_back(DepBB);
1017 // If we have no predecessors that produce a known value for this load, exit
1019 if (ValuesPerBlock.empty()) return false;
1021 // If all of the instructions we depend on produce a known value for this
1022 // load, then it is fully redundant and we can use PHI insertion to compute
1023 // its value. Insert PHIs and remove the fully redundant value now.
1024 if (UnavailableBlocks.empty()) {
1025 // Use cached PHI construction information from previous runs
1026 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1027 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
1028 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1030 if ((*I)->getParent() == LI->getParent()) {
1031 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD #1: " << *LI << '\n');
1032 LI->replaceAllUsesWith(*I);
1033 if (isa<PointerType>((*I)->getType()))
1034 MD->invalidateCachedPointerInfo(*I);
1035 toErase.push_back(LI);
1040 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1043 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1045 DenseMap<BasicBlock*, Value*> BlockReplValues;
1046 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1047 // Perform PHI construction.
1048 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1049 LI->replaceAllUsesWith(v);
1051 if (isa<PHINode>(v))
1053 if (isa<PointerType>(v->getType()))
1054 MD->invalidateCachedPointerInfo(v);
1055 toErase.push_back(LI);
1060 if (!EnablePRE || !EnableLoadPRE)
1063 // Okay, we have *some* definitions of the value. This means that the value
1064 // is available in some of our (transitive) predecessors. Lets think about
1065 // doing PRE of this load. This will involve inserting a new load into the
1066 // predecessor when it's not available. We could do this in general, but
1067 // prefer to not increase code size. As such, we only do this when we know
1068 // that we only have to insert *one* load (which means we're basically moving
1069 // the load, not inserting a new one).
1071 SmallPtrSet<BasicBlock *, 4> Blockers;
1072 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1073 Blockers.insert(UnavailableBlocks[i]);
1075 // Lets find first basic block with more than one predecessor. Walk backwards
1076 // through predecessors if needed.
1077 BasicBlock *LoadBB = LI->getParent();
1078 BasicBlock *TmpBB = LoadBB;
1080 bool isSinglePred = false;
1081 bool allSingleSucc = true;
1082 while (TmpBB->getSinglePredecessor()) {
1083 isSinglePred = true;
1084 TmpBB = TmpBB->getSinglePredecessor();
1085 if (!TmpBB) // If haven't found any, bail now.
1087 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1089 if (Blockers.count(TmpBB))
1091 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1092 allSingleSucc = false;
1098 // If we have a repl set with LI itself in it, this means we have a loop where
1099 // at least one of the values is LI. Since this means that we won't be able
1100 // to eliminate LI even if we insert uses in the other predecessors, we will
1101 // end up increasing code size. Reject this by scanning for LI.
1102 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1103 if (ValuesPerBlock[i].second == LI)
1108 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1109 if (Instruction *I = dyn_cast<Instruction>(ValuesPerBlock[i].second))
1110 // "Hot" Instruction is in some loop (because it dominates its dep.
1112 if (DT->dominates(LI, I)) {
1117 // We are interested only in "hot" instructions. We don't want to do any
1118 // mis-optimizations here.
1123 // Okay, we have some hope :). Check to see if the loaded value is fully
1124 // available in all but one predecessor.
1125 // FIXME: If we could restructure the CFG, we could make a common pred with
1126 // all the preds that don't have an available LI and insert a new load into
1128 BasicBlock *UnavailablePred = 0;
1130 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1131 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1132 FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
1133 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1134 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1136 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1138 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1141 // If this load is not available in multiple predecessors, reject it.
1142 if (UnavailablePred && UnavailablePred != *PI)
1144 UnavailablePred = *PI;
1147 assert(UnavailablePred != 0 &&
1148 "Fully available value should be eliminated above!");
1150 // If the loaded pointer is PHI node defined in this block, do PHI translation
1151 // to get its value in the predecessor.
1152 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
1154 // Make sure the value is live in the predecessor. If it was defined by a
1155 // non-PHI instruction in this block, we don't know how to recompute it above.
1156 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
1157 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
1158 DEBUG(errs() << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
1159 << *LPInst << '\n' << *LI << "\n");
1163 // We don't currently handle critical edges :(
1164 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1165 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1166 << UnavailablePred->getName() << "': " << *LI << '\n');
1170 // Make sure it is valid to move this load here. We have to watch out for:
1171 // @1 = getelementptr (i8* p, ...
1172 // test p and branch if == 0
1174 // It is valid to have the getelementptr before the test, even if p can be 0,
1175 // as getelementptr only does address arithmetic.
1176 // If we are not pushing the value through any multiple-successor blocks
1177 // we do not have this case. Otherwise, check that the load is safe to
1178 // put anywhere; this can be improved, but should be conservatively safe.
1179 if (!allSingleSucc &&
1180 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator()))
1183 // Okay, we can eliminate this load by inserting a reload in the predecessor
1184 // and using PHI construction to get the value in the other predecessors, do
1186 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1188 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1190 UnavailablePred->getTerminator());
1192 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1193 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1195 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1197 DenseMap<BasicBlock*, Value*> BlockReplValues;
1198 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1199 BlockReplValues[UnavailablePred] = NewLoad;
1201 // Perform PHI construction.
1202 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1203 LI->replaceAllUsesWith(v);
1204 if (isa<PHINode>(v))
1206 if (isa<PointerType>(v->getType()))
1207 MD->invalidateCachedPointerInfo(v);
1208 toErase.push_back(LI);
1213 /// processLoad - Attempt to eliminate a load, first by eliminating it
1214 /// locally, and then attempting non-local elimination if that fails.
1215 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1216 if (L->isVolatile())
1219 Value* pointer = L->getPointerOperand();
1221 // ... to a pointer that has been loaded from before...
1222 MemDepResult dep = MD->getDependency(L);
1224 // If the value isn't available, don't do anything!
1225 if (dep.isClobber()) {
1227 // fast print dep, using operator<< on instruction would be too slow
1228 errs() << "GVN: load ";
1229 WriteAsOperand(errs(), L);
1230 Instruction *I = dep.getInst();
1231 errs() << " is clobbered by " << *I << '\n';
1236 // If it is defined in another block, try harder.
1237 if (dep.isNonLocal())
1238 return processNonLocalLoad(L, toErase);
1240 Instruction *DepInst = dep.getInst();
1241 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1242 // Only forward substitute stores to loads of the same type.
1243 // FIXME: Could do better!
1244 if (DepSI->getPointerOperand()->getType() != pointer->getType())
1248 L->replaceAllUsesWith(DepSI->getOperand(0));
1249 if (isa<PointerType>(DepSI->getOperand(0)->getType()))
1250 MD->invalidateCachedPointerInfo(DepSI->getOperand(0));
1251 toErase.push_back(L);
1256 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1257 // Only forward substitute stores to loads of the same type.
1258 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
1259 if (DepLI->getType() != L->getType())
1263 L->replaceAllUsesWith(DepLI);
1264 if (isa<PointerType>(DepLI->getType()))
1265 MD->invalidateCachedPointerInfo(DepLI);
1266 toErase.push_back(L);
1271 // If this load really doesn't depend on anything, then we must be loading an
1272 // undef value. This can happen when loading for a fresh allocation with no
1273 // intervening stores, for example.
1274 if (isa<AllocationInst>(DepInst)) {
1275 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1276 toErase.push_back(L);
1284 Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1285 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1286 if (I == localAvail.end())
1289 ValueNumberScope* locals = I->second;
1292 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1293 if (I != locals->table.end())
1296 locals = locals->parent;
1302 /// AttemptRedundancyElimination - If the "fast path" of redundancy elimination
1303 /// by inheritance from the dominator fails, see if we can perform phi
1304 /// construction to eliminate the redundancy.
1305 Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) {
1306 BasicBlock* BaseBlock = orig->getParent();
1308 SmallPtrSet<BasicBlock*, 4> Visited;
1309 SmallVector<BasicBlock*, 8> Stack;
1310 Stack.push_back(BaseBlock);
1312 DenseMap<BasicBlock*, Value*> Results;
1314 // Walk backwards through our predecessors, looking for instances of the
1315 // value number we're looking for. Instances are recorded in the Results
1316 // map, which is then used to perform phi construction.
1317 while (!Stack.empty()) {
1318 BasicBlock* Current = Stack.back();
1321 // If we've walked all the way to a proper dominator, then give up. Cases
1322 // where the instance is in the dominator will have been caught by the fast
1323 // path, and any cases that require phi construction further than this are
1324 // probably not worth it anyways. Note that this is a SIGNIFICANT compile
1325 // time improvement.
1326 if (DT->properlyDominates(Current, orig->getParent())) return 0;
1328 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA =
1329 localAvail.find(Current);
1330 if (LA == localAvail.end()) return 0;
1331 DenseMap<uint32_t, Value*>::iterator V = LA->second->table.find(valno);
1333 if (V != LA->second->table.end()) {
1334 // Found an instance, record it.
1335 Results.insert(std::make_pair(Current, V->second));
1339 // If we reach the beginning of the function, then give up.
1340 if (pred_begin(Current) == pred_end(Current))
1343 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current);
1345 if (Visited.insert(*PI))
1346 Stack.push_back(*PI);
1349 // If we didn't find instances, give up. Otherwise, perform phi construction.
1350 if (Results.size() == 0)
1353 return GetValueForBlock(BaseBlock, orig, Results, true);
1356 /// processInstruction - When calculating availability, handle an instruction
1357 /// by inserting it into the appropriate sets
1358 bool GVN::processInstruction(Instruction *I,
1359 SmallVectorImpl<Instruction*> &toErase) {
1360 if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1361 bool changed = processLoad(L, toErase);
1364 unsigned num = VN.lookup_or_add(L);
1365 localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1371 uint32_t nextNum = VN.getNextUnusedValueNumber();
1372 unsigned num = VN.lookup_or_add(I);
1374 if (BranchInst* BI = dyn_cast<BranchInst>(I)) {
1375 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1377 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1380 Value* branchCond = BI->getCondition();
1381 uint32_t condVN = VN.lookup_or_add(branchCond);
1383 BasicBlock* trueSucc = BI->getSuccessor(0);
1384 BasicBlock* falseSucc = BI->getSuccessor(1);
1386 if (trueSucc->getSinglePredecessor())
1387 localAvail[trueSucc]->table[condVN] =
1388 ConstantInt::getTrue(trueSucc->getContext());
1389 if (falseSucc->getSinglePredecessor())
1390 localAvail[falseSucc]->table[condVN] =
1391 ConstantInt::getFalse(trueSucc->getContext());
1395 // Allocations are always uniquely numbered, so we can save time and memory
1396 // by fast failing them.
1397 } else if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
1398 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1402 // Collapse PHI nodes
1403 if (PHINode* p = dyn_cast<PHINode>(I)) {
1404 Value* constVal = CollapsePhi(p);
1407 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1409 PI->second.erase(p);
1411 p->replaceAllUsesWith(constVal);
1412 if (isa<PointerType>(constVal->getType()))
1413 MD->invalidateCachedPointerInfo(constVal);
1416 toErase.push_back(p);
1418 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1421 // If the number we were assigned was a brand new VN, then we don't
1422 // need to do a lookup to see if the number already exists
1423 // somewhere in the domtree: it can't!
1424 } else if (num == nextNum) {
1425 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1427 // Perform fast-path value-number based elimination of values inherited from
1429 } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1432 I->replaceAllUsesWith(repl);
1433 if (isa<PointerType>(repl->getType()))
1434 MD->invalidateCachedPointerInfo(repl);
1435 toErase.push_back(I);
1439 // Perform slow-pathvalue-number based elimination with phi construction.
1440 } else if (Value* repl = AttemptRedundancyElimination(I, num)) {
1443 I->replaceAllUsesWith(repl);
1444 if (isa<PointerType>(repl->getType()))
1445 MD->invalidateCachedPointerInfo(repl);
1446 toErase.push_back(I);
1450 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1456 /// runOnFunction - This is the main transformation entry point for a function.
1457 bool GVN::runOnFunction(Function& F) {
1458 MD = &getAnalysis<MemoryDependenceAnalysis>();
1459 DT = &getAnalysis<DominatorTree>();
1460 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1464 bool changed = false;
1465 bool shouldContinue = true;
1467 // Merge unconditional branches, allowing PRE to catch more
1468 // optimization opportunities.
1469 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1470 BasicBlock* BB = FI;
1472 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1473 if (removedBlock) NumGVNBlocks++;
1475 changed |= removedBlock;
1478 unsigned Iteration = 0;
1480 while (shouldContinue) {
1481 DEBUG(errs() << "GVN iteration: " << Iteration << "\n");
1482 shouldContinue = iterateOnFunction(F);
1483 changed |= shouldContinue;
1488 bool PREChanged = true;
1489 while (PREChanged) {
1490 PREChanged = performPRE(F);
1491 changed |= PREChanged;
1494 // FIXME: Should perform GVN again after PRE does something. PRE can move
1495 // computations into blocks where they become fully redundant. Note that
1496 // we can't do this until PRE's critical edge splitting updates memdep.
1497 // Actually, when this happens, we should just fully integrate PRE into GVN.
1499 cleanupGlobalSets();
1505 bool GVN::processBlock(BasicBlock* BB) {
1506 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1507 // incrementing BI before processing an instruction).
1508 SmallVector<Instruction*, 8> toErase;
1509 bool changed_function = false;
1511 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1513 changed_function |= processInstruction(BI, toErase);
1514 if (toErase.empty()) {
1519 // If we need some instructions deleted, do it now.
1520 NumGVNInstr += toErase.size();
1522 // Avoid iterator invalidation.
1523 bool AtStart = BI == BB->begin();
1527 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1528 E = toErase.end(); I != E; ++I) {
1529 DEBUG(errs() << "GVN removed: " << **I << '\n');
1530 MD->removeInstruction(*I);
1531 (*I)->eraseFromParent();
1532 DEBUG(verifyRemoved(*I));
1542 return changed_function;
1545 /// performPRE - Perform a purely local form of PRE that looks for diamond
1546 /// control flow patterns and attempts to perform simple PRE at the join point.
1547 bool GVN::performPRE(Function& F) {
1548 bool Changed = false;
1549 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1550 DenseMap<BasicBlock*, Value*> predMap;
1551 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1552 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1553 BasicBlock* CurrentBlock = *DI;
1555 // Nothing to PRE in the entry block.
1556 if (CurrentBlock == &F.getEntryBlock()) continue;
1558 for (BasicBlock::iterator BI = CurrentBlock->begin(),
1559 BE = CurrentBlock->end(); BI != BE; ) {
1560 Instruction *CurInst = BI++;
1562 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
1563 isa<PHINode>(CurInst) ||
1564 (CurInst->getType() == Type::getVoidTy(F.getContext())) ||
1565 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
1566 isa<DbgInfoIntrinsic>(CurInst))
1569 uint32_t valno = VN.lookup(CurInst);
1571 // Look for the predecessors for PRE opportunities. We're
1572 // only trying to solve the basic diamond case, where
1573 // a value is computed in the successor and one predecessor,
1574 // but not the other. We also explicitly disallow cases
1575 // where the successor is its own predecessor, because they're
1576 // more complicated to get right.
1577 unsigned numWith = 0;
1578 unsigned numWithout = 0;
1579 BasicBlock* PREPred = 0;
1582 for (pred_iterator PI = pred_begin(CurrentBlock),
1583 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1584 // We're not interested in PRE where the block is its
1585 // own predecessor, on in blocks with predecessors
1586 // that are not reachable.
1587 if (*PI == CurrentBlock) {
1590 } else if (!localAvail.count(*PI)) {
1595 DenseMap<uint32_t, Value*>::iterator predV =
1596 localAvail[*PI]->table.find(valno);
1597 if (predV == localAvail[*PI]->table.end()) {
1600 } else if (predV->second == CurInst) {
1603 predMap[*PI] = predV->second;
1608 // Don't do PRE when it might increase code size, i.e. when
1609 // we would need to insert instructions in more than one pred.
1610 if (numWithout != 1 || numWith == 0)
1613 // We can't do PRE safely on a critical edge, so instead we schedule
1614 // the edge to be split and perform the PRE the next time we iterate
1616 unsigned succNum = 0;
1617 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1619 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
1624 if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1625 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1629 // Instantiate the expression the in predecessor that lacked it.
1630 // Because we are going top-down through the block, all value numbers
1631 // will be available in the predecessor by the time we need them. Any
1632 // that weren't original present will have been instantiated earlier
1634 Instruction* PREInstr = CurInst->clone(CurInst->getContext());
1635 bool success = true;
1636 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
1637 Value *Op = PREInstr->getOperand(i);
1638 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
1641 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
1642 PREInstr->setOperand(i, V);
1649 // Fail out if we encounter an operand that is not available in
1650 // the PRE predecessor. This is typically because of loads which
1651 // are not value numbered precisely.
1654 DEBUG(verifyRemoved(PREInstr));
1658 PREInstr->insertBefore(PREPred->getTerminator());
1659 PREInstr->setName(CurInst->getName() + ".pre");
1660 predMap[PREPred] = PREInstr;
1661 VN.add(PREInstr, valno);
1664 // Update the availability map to include the new instruction.
1665 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1667 // Create a PHI to make the value available in this block.
1668 PHINode* Phi = PHINode::Create(CurInst->getType(),
1669 CurInst->getName() + ".pre-phi",
1670 CurrentBlock->begin());
1671 for (pred_iterator PI = pred_begin(CurrentBlock),
1672 PE = pred_end(CurrentBlock); PI != PE; ++PI)
1673 Phi->addIncoming(predMap[*PI], *PI);
1676 localAvail[CurrentBlock]->table[valno] = Phi;
1678 CurInst->replaceAllUsesWith(Phi);
1679 if (isa<PointerType>(Phi->getType()))
1680 MD->invalidateCachedPointerInfo(Phi);
1683 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n');
1684 MD->removeInstruction(CurInst);
1685 CurInst->eraseFromParent();
1686 DEBUG(verifyRemoved(CurInst));
1691 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1692 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1693 SplitCriticalEdge(I->first, I->second, this);
1695 return Changed || toSplit.size();
1698 /// iterateOnFunction - Executes one iteration of GVN
1699 bool GVN::iterateOnFunction(Function &F) {
1700 cleanupGlobalSets();
1702 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1703 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
1705 localAvail[DI->getBlock()] =
1706 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
1708 localAvail[DI->getBlock()] = new ValueNumberScope(0);
1711 // Top-down walk of the dominator tree
1712 bool changed = false;
1714 // Needed for value numbering with phi construction to work.
1715 ReversePostOrderTraversal<Function*> RPOT(&F);
1716 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
1717 RE = RPOT.end(); RI != RE; ++RI)
1718 changed |= processBlock(*RI);
1720 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1721 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
1722 changed |= processBlock(DI->getBlock());
1728 void GVN::cleanupGlobalSets() {
1732 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1733 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
1738 /// verifyRemoved - Verify that the specified instruction does not occur in our
1739 /// internal data structures.
1740 void GVN::verifyRemoved(const Instruction *Inst) const {
1741 VN.verifyRemoved(Inst);
1743 // Walk through the PHI map to make sure the instruction isn't hiding in there
1745 for (PhiMapType::iterator
1746 I = phiMap.begin(), E = phiMap.end(); I != E; ++I) {
1747 assert(I->first != Inst && "Inst is still a key in PHI map!");
1749 for (SmallPtrSet<Instruction*, 4>::iterator
1750 II = I->second.begin(), IE = I->second.end(); II != IE; ++II) {
1751 assert(*II != Inst && "Inst is still a value in PHI map!");
1755 // Walk through the value number scope to make sure the instruction isn't
1756 // ferreted away in it.
1757 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1758 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
1759 const ValueNumberScope *VNS = I->second;
1762 for (DenseMap<uint32_t, Value*>::iterator
1763 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
1764 assert(II->second != Inst && "Inst still in value numbering scope!");