1 //===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass performs global value numbering to eliminate fully redundant
11 // instructions. It also performs simple dead load elimination.
13 // Note that this pass does the value numbering itself, it does not use the
14 // ValueNumbering analysis passes.
16 //===----------------------------------------------------------------------===//
18 #define DEBUG_TYPE "gvn"
19 #include "llvm/Transforms/Scalar.h"
20 #include "llvm/BasicBlock.h"
21 #include "llvm/Constants.h"
22 #include "llvm/DerivedTypes.h"
23 #include "llvm/Function.h"
24 #include "llvm/Instructions.h"
25 #include "llvm/Value.h"
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/DepthFirstIterator.h"
28 #include "llvm/ADT/PostOrderIterator.h"
29 #include "llvm/ADT/SmallPtrSet.h"
30 #include "llvm/ADT/SmallVector.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/Analysis/Dominators.h"
33 #include "llvm/Analysis/AliasAnalysis.h"
34 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
35 #include "llvm/Support/CFG.h"
36 #include "llvm/Support/CommandLine.h"
37 #include "llvm/Support/Compiler.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
43 STATISTIC(NumGVNInstr, "Number of instructions deleted");
44 STATISTIC(NumGVNLoad, "Number of loads deleted");
45 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
46 STATISTIC(NumGVNBlocks, "Number of blocks merged");
47 STATISTIC(NumPRELoad, "Number of loads PRE'd");
49 static cl::opt<bool> EnablePRE("enable-pre",
50 cl::init(true), cl::Hidden);
51 cl::opt<bool> EnableLoadPRE("enable-load-pre"/*, cl::init(true)*/);
53 //===----------------------------------------------------------------------===//
55 //===----------------------------------------------------------------------===//
57 /// This class holds the mapping between values and value numbers. It is used
58 /// as an efficient mechanism to determine the expression-wise equivalence of
61 struct VISIBILITY_HIDDEN Expression {
62 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
63 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
64 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
65 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
66 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
67 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
68 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
69 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
70 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
71 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
74 ExpressionOpcode opcode;
79 SmallVector<uint32_t, 4> varargs;
83 Expression(ExpressionOpcode o) : opcode(o) { }
85 bool operator==(const Expression &other) const {
86 if (opcode != other.opcode)
88 else if (opcode == EMPTY || opcode == TOMBSTONE)
90 else if (type != other.type)
92 else if (function != other.function)
94 else if (firstVN != other.firstVN)
96 else if (secondVN != other.secondVN)
98 else if (thirdVN != other.thirdVN)
101 if (varargs.size() != other.varargs.size())
104 for (size_t i = 0; i < varargs.size(); ++i)
105 if (varargs[i] != other.varargs[i])
112 bool operator!=(const Expression &other) const {
113 if (opcode != other.opcode)
115 else if (opcode == EMPTY || opcode == TOMBSTONE)
117 else if (type != other.type)
119 else if (function != other.function)
121 else if (firstVN != other.firstVN)
123 else if (secondVN != other.secondVN)
125 else if (thirdVN != other.thirdVN)
128 if (varargs.size() != other.varargs.size())
131 for (size_t i = 0; i < varargs.size(); ++i)
132 if (varargs[i] != other.varargs[i])
140 class VISIBILITY_HIDDEN ValueTable {
142 DenseMap<Value*, uint32_t> valueNumbering;
143 DenseMap<Expression, uint32_t> expressionNumbering;
145 MemoryDependenceAnalysis* MD;
148 uint32_t nextValueNumber;
150 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
151 Expression::ExpressionOpcode getOpcode(CmpInst* C);
152 Expression::ExpressionOpcode getOpcode(CastInst* C);
153 Expression create_expression(BinaryOperator* BO);
154 Expression create_expression(CmpInst* C);
155 Expression create_expression(ShuffleVectorInst* V);
156 Expression create_expression(ExtractElementInst* C);
157 Expression create_expression(InsertElementInst* V);
158 Expression create_expression(SelectInst* V);
159 Expression create_expression(CastInst* C);
160 Expression create_expression(GetElementPtrInst* G);
161 Expression create_expression(CallInst* C);
162 Expression create_expression(Constant* C);
164 ValueTable() : nextValueNumber(1) { }
165 uint32_t lookup_or_add(Value* V);
166 uint32_t lookup(Value* V) const;
167 void add(Value* V, uint32_t num);
169 void erase(Value* v);
171 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
172 AliasAnalysis *getAliasAnalysis() const { return AA; }
173 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
174 void setDomTree(DominatorTree* D) { DT = D; }
175 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
180 template <> struct DenseMapInfo<Expression> {
181 static inline Expression getEmptyKey() {
182 return Expression(Expression::EMPTY);
185 static inline Expression getTombstoneKey() {
186 return Expression(Expression::TOMBSTONE);
189 static unsigned getHashValue(const Expression e) {
190 unsigned hash = e.opcode;
192 hash = e.firstVN + hash * 37;
193 hash = e.secondVN + hash * 37;
194 hash = e.thirdVN + hash * 37;
196 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
197 (unsigned)((uintptr_t)e.type >> 9)) +
200 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
201 E = e.varargs.end(); I != E; ++I)
202 hash = *I + hash * 37;
204 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
205 (unsigned)((uintptr_t)e.function >> 9)) +
210 static bool isEqual(const Expression &LHS, const Expression &RHS) {
213 static bool isPod() { return true; }
217 //===----------------------------------------------------------------------===//
218 // ValueTable Internal Functions
219 //===----------------------------------------------------------------------===//
220 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
221 switch(BO->getOpcode()) {
222 default: // THIS SHOULD NEVER HAPPEN
223 assert(0 && "Binary operator with unknown opcode?");
224 case Instruction::Add: return Expression::ADD;
225 case Instruction::Sub: return Expression::SUB;
226 case Instruction::Mul: return Expression::MUL;
227 case Instruction::UDiv: return Expression::UDIV;
228 case Instruction::SDiv: return Expression::SDIV;
229 case Instruction::FDiv: return Expression::FDIV;
230 case Instruction::URem: return Expression::UREM;
231 case Instruction::SRem: return Expression::SREM;
232 case Instruction::FRem: return Expression::FREM;
233 case Instruction::Shl: return Expression::SHL;
234 case Instruction::LShr: return Expression::LSHR;
235 case Instruction::AShr: return Expression::ASHR;
236 case Instruction::And: return Expression::AND;
237 case Instruction::Or: return Expression::OR;
238 case Instruction::Xor: return Expression::XOR;
242 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
243 if (isa<ICmpInst>(C) || isa<VICmpInst>(C)) {
244 switch (C->getPredicate()) {
245 default: // THIS SHOULD NEVER HAPPEN
246 assert(0 && "Comparison with unknown predicate?");
247 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
248 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
249 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
250 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
251 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
252 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
253 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
254 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
255 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
256 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
259 assert((isa<FCmpInst>(C) || isa<VFCmpInst>(C)) && "Unknown compare");
260 switch (C->getPredicate()) {
261 default: // THIS SHOULD NEVER HAPPEN
262 assert(0 && "Comparison with unknown predicate?");
263 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
264 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
265 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
266 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
267 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
268 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
269 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
270 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
271 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
272 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
273 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
274 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
275 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
276 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
280 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
281 switch(C->getOpcode()) {
282 default: // THIS SHOULD NEVER HAPPEN
283 assert(0 && "Cast operator with unknown opcode?");
284 case Instruction::Trunc: return Expression::TRUNC;
285 case Instruction::ZExt: return Expression::ZEXT;
286 case Instruction::SExt: return Expression::SEXT;
287 case Instruction::FPToUI: return Expression::FPTOUI;
288 case Instruction::FPToSI: return Expression::FPTOSI;
289 case Instruction::UIToFP: return Expression::UITOFP;
290 case Instruction::SIToFP: return Expression::SITOFP;
291 case Instruction::FPTrunc: return Expression::FPTRUNC;
292 case Instruction::FPExt: return Expression::FPEXT;
293 case Instruction::PtrToInt: return Expression::PTRTOINT;
294 case Instruction::IntToPtr: return Expression::INTTOPTR;
295 case Instruction::BitCast: return Expression::BITCAST;
299 Expression ValueTable::create_expression(CallInst* C) {
302 e.type = C->getType();
306 e.function = C->getCalledFunction();
307 e.opcode = Expression::CALL;
309 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
311 e.varargs.push_back(lookup_or_add(*I));
316 Expression ValueTable::create_expression(BinaryOperator* BO) {
319 e.firstVN = lookup_or_add(BO->getOperand(0));
320 e.secondVN = lookup_or_add(BO->getOperand(1));
323 e.type = BO->getType();
324 e.opcode = getOpcode(BO);
329 Expression ValueTable::create_expression(CmpInst* C) {
332 e.firstVN = lookup_or_add(C->getOperand(0));
333 e.secondVN = lookup_or_add(C->getOperand(1));
336 e.type = C->getType();
337 e.opcode = getOpcode(C);
342 Expression ValueTable::create_expression(CastInst* C) {
345 e.firstVN = lookup_or_add(C->getOperand(0));
349 e.type = C->getType();
350 e.opcode = getOpcode(C);
355 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
358 e.firstVN = lookup_or_add(S->getOperand(0));
359 e.secondVN = lookup_or_add(S->getOperand(1));
360 e.thirdVN = lookup_or_add(S->getOperand(2));
362 e.type = S->getType();
363 e.opcode = Expression::SHUFFLE;
368 Expression ValueTable::create_expression(ExtractElementInst* E) {
371 e.firstVN = lookup_or_add(E->getOperand(0));
372 e.secondVN = lookup_or_add(E->getOperand(1));
375 e.type = E->getType();
376 e.opcode = Expression::EXTRACT;
381 Expression ValueTable::create_expression(InsertElementInst* I) {
384 e.firstVN = lookup_or_add(I->getOperand(0));
385 e.secondVN = lookup_or_add(I->getOperand(1));
386 e.thirdVN = lookup_or_add(I->getOperand(2));
388 e.type = I->getType();
389 e.opcode = Expression::INSERT;
394 Expression ValueTable::create_expression(SelectInst* I) {
397 e.firstVN = lookup_or_add(I->getCondition());
398 e.secondVN = lookup_or_add(I->getTrueValue());
399 e.thirdVN = lookup_or_add(I->getFalseValue());
401 e.type = I->getType();
402 e.opcode = Expression::SELECT;
407 Expression ValueTable::create_expression(GetElementPtrInst* G) {
410 e.firstVN = lookup_or_add(G->getPointerOperand());
414 e.type = G->getType();
415 e.opcode = Expression::GEP;
417 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
419 e.varargs.push_back(lookup_or_add(*I));
424 //===----------------------------------------------------------------------===//
425 // ValueTable External Functions
426 //===----------------------------------------------------------------------===//
428 /// add - Insert a value into the table with a specified value number.
429 void ValueTable::add(Value* V, uint32_t num) {
430 valueNumbering.insert(std::make_pair(V, num));
433 /// lookup_or_add - Returns the value number for the specified value, assigning
434 /// it a new number if it did not have one before.
435 uint32_t ValueTable::lookup_or_add(Value* V) {
436 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
437 if (VI != valueNumbering.end())
440 if (CallInst* C = dyn_cast<CallInst>(V)) {
441 if (AA->doesNotAccessMemory(C)) {
442 Expression e = create_expression(C);
444 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
445 if (EI != expressionNumbering.end()) {
446 valueNumbering.insert(std::make_pair(V, EI->second));
449 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
450 valueNumbering.insert(std::make_pair(V, nextValueNumber));
452 return nextValueNumber++;
454 } else if (AA->onlyReadsMemory(C)) {
455 Expression e = create_expression(C);
457 if (expressionNumbering.find(e) == expressionNumbering.end()) {
458 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
459 valueNumbering.insert(std::make_pair(V, nextValueNumber));
460 return nextValueNumber++;
463 MemDepResult local_dep = MD->getDependency(C);
465 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
466 valueNumbering.insert(std::make_pair(V, nextValueNumber));
467 return nextValueNumber++;
470 if (local_dep.isDef()) {
471 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
473 if (local_cdep->getNumOperands() != C->getNumOperands()) {
474 valueNumbering.insert(std::make_pair(V, nextValueNumber));
475 return nextValueNumber++;
478 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
479 uint32_t c_vn = lookup_or_add(C->getOperand(i));
480 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
482 valueNumbering.insert(std::make_pair(V, nextValueNumber));
483 return nextValueNumber++;
487 uint32_t v = lookup_or_add(local_cdep);
488 valueNumbering.insert(std::make_pair(V, v));
493 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
494 MD->getNonLocalCallDependency(CallSite(C));
495 // FIXME: call/call dependencies for readonly calls should return def, not
496 // clobber! Move the checking logic to MemDep!
499 // Check to see if we have a single dominating call instruction that is
501 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
502 const MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
503 // Ignore non-local dependencies.
504 if (I->second.isNonLocal())
507 // We don't handle non-depedencies. If we already have a call, reject
508 // instruction dependencies.
509 if (I->second.isClobber() || cdep != 0) {
514 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
515 // FIXME: All duplicated with non-local case.
516 if (NonLocalDepCall && DT->properlyDominates(I->first, C->getParent())){
517 cdep = NonLocalDepCall;
526 valueNumbering.insert(std::make_pair(V, nextValueNumber));
527 return nextValueNumber++;
530 if (cdep->getNumOperands() != C->getNumOperands()) {
531 valueNumbering.insert(std::make_pair(V, nextValueNumber));
532 return nextValueNumber++;
534 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
535 uint32_t c_vn = lookup_or_add(C->getOperand(i));
536 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
538 valueNumbering.insert(std::make_pair(V, nextValueNumber));
539 return nextValueNumber++;
543 uint32_t v = lookup_or_add(cdep);
544 valueNumbering.insert(std::make_pair(V, v));
548 valueNumbering.insert(std::make_pair(V, nextValueNumber));
549 return nextValueNumber++;
551 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
552 Expression e = create_expression(BO);
554 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
555 if (EI != expressionNumbering.end()) {
556 valueNumbering.insert(std::make_pair(V, EI->second));
559 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
560 valueNumbering.insert(std::make_pair(V, nextValueNumber));
562 return nextValueNumber++;
564 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
565 Expression e = create_expression(C);
567 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
568 if (EI != expressionNumbering.end()) {
569 valueNumbering.insert(std::make_pair(V, EI->second));
572 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
573 valueNumbering.insert(std::make_pair(V, nextValueNumber));
575 return nextValueNumber++;
577 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
578 Expression e = create_expression(U);
580 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
581 if (EI != expressionNumbering.end()) {
582 valueNumbering.insert(std::make_pair(V, EI->second));
585 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
586 valueNumbering.insert(std::make_pair(V, nextValueNumber));
588 return nextValueNumber++;
590 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
591 Expression e = create_expression(U);
593 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
594 if (EI != expressionNumbering.end()) {
595 valueNumbering.insert(std::make_pair(V, EI->second));
598 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
599 valueNumbering.insert(std::make_pair(V, nextValueNumber));
601 return nextValueNumber++;
603 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
604 Expression e = create_expression(U);
606 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
607 if (EI != expressionNumbering.end()) {
608 valueNumbering.insert(std::make_pair(V, EI->second));
611 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
612 valueNumbering.insert(std::make_pair(V, nextValueNumber));
614 return nextValueNumber++;
616 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
617 Expression e = create_expression(U);
619 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
620 if (EI != expressionNumbering.end()) {
621 valueNumbering.insert(std::make_pair(V, EI->second));
624 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
625 valueNumbering.insert(std::make_pair(V, nextValueNumber));
627 return nextValueNumber++;
629 } else if (CastInst* U = dyn_cast<CastInst>(V)) {
630 Expression e = create_expression(U);
632 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
633 if (EI != expressionNumbering.end()) {
634 valueNumbering.insert(std::make_pair(V, EI->second));
637 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
638 valueNumbering.insert(std::make_pair(V, nextValueNumber));
640 return nextValueNumber++;
642 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
643 Expression e = create_expression(U);
645 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
646 if (EI != expressionNumbering.end()) {
647 valueNumbering.insert(std::make_pair(V, EI->second));
650 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
651 valueNumbering.insert(std::make_pair(V, nextValueNumber));
653 return nextValueNumber++;
656 valueNumbering.insert(std::make_pair(V, nextValueNumber));
657 return nextValueNumber++;
661 /// lookup - Returns the value number of the specified value. Fails if
662 /// the value has not yet been numbered.
663 uint32_t ValueTable::lookup(Value* V) const {
664 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
665 assert(VI != valueNumbering.end() && "Value not numbered?");
669 /// clear - Remove all entries from the ValueTable
670 void ValueTable::clear() {
671 valueNumbering.clear();
672 expressionNumbering.clear();
676 /// erase - Remove a value from the value numbering
677 void ValueTable::erase(Value* V) {
678 valueNumbering.erase(V);
681 //===----------------------------------------------------------------------===//
683 //===----------------------------------------------------------------------===//
686 struct VISIBILITY_HIDDEN ValueNumberScope {
687 ValueNumberScope* parent;
688 DenseMap<uint32_t, Value*> table;
690 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
696 class VISIBILITY_HIDDEN GVN : public FunctionPass {
697 bool runOnFunction(Function &F);
699 static char ID; // Pass identification, replacement for typeid
700 GVN() : FunctionPass(&ID) { }
703 MemoryDependenceAnalysis *MD;
707 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
709 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
713 // This transformation requires dominator postdominator info
714 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
715 AU.addRequired<DominatorTree>();
716 AU.addRequired<MemoryDependenceAnalysis>();
717 AU.addRequired<AliasAnalysis>();
719 AU.addPreserved<DominatorTree>();
720 AU.addPreserved<AliasAnalysis>();
724 // FIXME: eliminate or document these better
725 bool processLoad(LoadInst* L,
726 SmallVectorImpl<Instruction*> &toErase);
727 bool processInstruction(Instruction* I,
728 SmallVectorImpl<Instruction*> &toErase);
729 bool processNonLocalLoad(LoadInst* L,
730 SmallVectorImpl<Instruction*> &toErase);
731 bool processBlock(BasicBlock* BB);
732 Value *GetValueForBlock(BasicBlock *BB, Instruction* orig,
733 DenseMap<BasicBlock*, Value*> &Phis,
734 bool top_level = false);
735 void dump(DenseMap<uint32_t, Value*>& d);
736 bool iterateOnFunction(Function &F);
737 Value* CollapsePhi(PHINode* p);
738 bool isSafeReplacement(PHINode* p, Instruction* inst);
739 bool performPRE(Function& F);
740 Value* lookupNumber(BasicBlock* BB, uint32_t num);
741 bool mergeBlockIntoPredecessor(BasicBlock* BB);
742 Value* AttemptRedundancyElimination(Instruction* orig, unsigned valno);
743 void cleanupGlobalSets();
749 // createGVNPass - The public interface to this file...
750 FunctionPass *llvm::createGVNPass() { return new GVN(); }
752 static RegisterPass<GVN> X("gvn",
753 "Global Value Numbering");
755 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
757 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
758 E = d.end(); I != E; ++I) {
759 printf("%d\n", I->first);
765 Value* GVN::CollapsePhi(PHINode* p) {
766 Value* constVal = p->hasConstantValue();
767 if (!constVal) return 0;
769 Instruction* inst = dyn_cast<Instruction>(constVal);
773 if (DT->dominates(inst, p))
774 if (isSafeReplacement(p, inst))
779 bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
780 if (!isa<PHINode>(inst))
783 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
785 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
786 if (use_phi->getParent() == inst->getParent())
792 /// GetValueForBlock - Get the value to use within the specified basic block.
793 /// available values are in Phis.
794 Value *GVN::GetValueForBlock(BasicBlock *BB, Instruction* orig,
795 DenseMap<BasicBlock*, Value*> &Phis,
798 // If we have already computed this value, return the previously computed val.
799 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
800 if (V != Phis.end() && !top_level) return V->second;
802 // If the block is unreachable, just return undef, since this path
803 // can't actually occur at runtime.
804 if (!DT->isReachableFromEntry(BB))
805 return Phis[BB] = UndefValue::get(orig->getType());
807 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
808 Value *ret = GetValueForBlock(Pred, orig, Phis);
813 // Get the number of predecessors of this block so we can reserve space later.
814 // If there is already a PHI in it, use the #preds from it, otherwise count.
815 // Getting it from the PHI is constant time.
817 if (PHINode *ExistingPN = dyn_cast<PHINode>(BB->begin()))
818 NumPreds = ExistingPN->getNumIncomingValues();
820 NumPreds = std::distance(pred_begin(BB), pred_end(BB));
822 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
823 // now, then get values to fill in the incoming values for the PHI.
824 PHINode *PN = PHINode::Create(orig->getType(), orig->getName()+".rle",
826 PN->reserveOperandSpace(NumPreds);
828 Phis.insert(std::make_pair(BB, PN));
830 // Fill in the incoming values for the block.
831 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
832 Value* val = GetValueForBlock(*PI, orig, Phis);
833 PN->addIncoming(val, *PI);
836 VN.getAliasAnalysis()->copyValue(orig, PN);
838 // Attempt to collapse PHI nodes that are trivially redundant
839 Value* v = CollapsePhi(PN);
841 // Cache our phi construction results
842 if (LoadInst* L = dyn_cast<LoadInst>(orig))
843 phiMap[L->getPointerOperand()].insert(PN);
845 phiMap[orig].insert(PN);
850 PN->replaceAllUsesWith(v);
851 if (isa<PointerType>(v->getType()))
852 MD->invalidateCachedPointerInfo(v);
854 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
855 E = Phis.end(); I != E; ++I)
859 DEBUG(cerr << "GVN removed: " << *PN);
860 MD->removeInstruction(PN);
861 PN->eraseFromParent();
867 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
868 /// we're analyzing is fully available in the specified block. As we go, keep
869 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
870 /// map is actually a tri-state map with the following values:
871 /// 0) we know the block *is not* fully available.
872 /// 1) we know the block *is* fully available.
873 /// 2) we do not know whether the block is fully available or not, but we are
874 /// currently speculating that it will be.
875 /// 3) we are speculating for this block and have used that to speculate for
877 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
878 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
879 // Optimistically assume that the block is fully available and check to see
880 // if we already know about this block in one lookup.
881 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
882 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
884 // If the entry already existed for this block, return the precomputed value.
886 // If this is a speculative "available" value, mark it as being used for
887 // speculation of other blocks.
888 if (IV.first->second == 2)
889 IV.first->second = 3;
890 return IV.first->second != 0;
893 // Otherwise, see if it is fully available in all predecessors.
894 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
896 // If this block has no predecessors, it isn't live-in here.
898 goto SpeculationFailure;
900 for (; PI != PE; ++PI)
901 // If the value isn't fully available in one of our predecessors, then it
902 // isn't fully available in this block either. Undo our previous
903 // optimistic assumption and bail out.
904 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
905 goto SpeculationFailure;
909 // SpeculationFailure - If we get here, we found out that this is not, after
910 // all, a fully-available block. We have a problem if we speculated on this and
911 // used the speculation to mark other blocks as available.
913 char &BBVal = FullyAvailableBlocks[BB];
915 // If we didn't speculate on this, just return with it set to false.
921 // If we did speculate on this value, we could have blocks set to 1 that are
922 // incorrect. Walk the (transitive) successors of this block and mark them as
924 SmallVector<BasicBlock*, 32> BBWorklist;
925 BBWorklist.push_back(BB);
927 while (!BBWorklist.empty()) {
928 BasicBlock *Entry = BBWorklist.pop_back_val();
929 // Note that this sets blocks to 0 (unavailable) if they happen to not
930 // already be in FullyAvailableBlocks. This is safe.
931 char &EntryVal = FullyAvailableBlocks[Entry];
932 if (EntryVal == 0) continue; // Already unavailable.
934 // Mark as unavailable.
937 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
938 BBWorklist.push_back(*I);
944 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
945 /// non-local by performing PHI construction.
946 bool GVN::processNonLocalLoad(LoadInst *LI,
947 SmallVectorImpl<Instruction*> &toErase) {
948 // Find the non-local dependencies of the load.
949 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
950 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
952 //DEBUG(cerr << "INVESTIGATING NONLOCAL LOAD: " << Deps.size() << *LI);
954 // If we had to process more than one hundred blocks to find the
955 // dependencies, this load isn't worth worrying about. Optimizing
956 // it will be too expensive.
957 if (Deps.size() > 100)
960 // If we had a phi translation failure, we'll have a single entry which is a
961 // clobber in the current block. Reject this early.
962 if (Deps.size() == 1 && Deps[0].second.isClobber())
965 // Filter out useless results (non-locals, etc). Keep track of the blocks
966 // where we have a value available in repl, also keep track of whether we see
967 // dependencies that produce an unknown value for the load (such as a call
968 // that could potentially clobber the load).
969 SmallVector<std::pair<BasicBlock*, Value*>, 16> ValuesPerBlock;
970 SmallVector<BasicBlock*, 16> UnavailableBlocks;
972 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
973 BasicBlock *DepBB = Deps[i].first;
974 MemDepResult DepInfo = Deps[i].second;
976 if (DepInfo.isClobber()) {
977 UnavailableBlocks.push_back(DepBB);
981 Instruction *DepInst = DepInfo.getInst();
983 // Loading the allocation -> undef.
984 if (isa<AllocationInst>(DepInst)) {
985 ValuesPerBlock.push_back(std::make_pair(DepBB,
986 UndefValue::get(LI->getType())));
990 if (StoreInst* S = dyn_cast<StoreInst>(DepInst)) {
991 // Reject loads and stores that are to the same address but are of
993 // NOTE: 403.gcc does have this case (e.g. in readonly_fields_p) because
994 // of bitfield access, it would be interesting to optimize for it at some
996 if (S->getOperand(0)->getType() != LI->getType()) {
997 UnavailableBlocks.push_back(DepBB);
1001 ValuesPerBlock.push_back(std::make_pair(DepBB, S->getOperand(0)));
1003 } else if (LoadInst* LD = dyn_cast<LoadInst>(DepInst)) {
1004 if (LD->getType() != LI->getType()) {
1005 UnavailableBlocks.push_back(DepBB);
1008 ValuesPerBlock.push_back(std::make_pair(DepBB, LD));
1010 UnavailableBlocks.push_back(DepBB);
1015 // If we have no predecessors that produce a known value for this load, exit
1017 if (ValuesPerBlock.empty()) return false;
1019 // If all of the instructions we depend on produce a known value for this
1020 // load, then it is fully redundant and we can use PHI insertion to compute
1021 // its value. Insert PHIs and remove the fully redundant value now.
1022 if (UnavailableBlocks.empty()) {
1023 // Use cached PHI construction information from previous runs
1024 SmallPtrSet<Instruction*, 4> &p = phiMap[LI->getPointerOperand()];
1025 // FIXME: What does phiMap do? Are we positive it isn't getting invalidated?
1026 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
1028 if ((*I)->getParent() == LI->getParent()) {
1029 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD #1: " << *LI);
1030 LI->replaceAllUsesWith(*I);
1031 if (isa<PointerType>((*I)->getType()))
1032 MD->invalidateCachedPointerInfo(*I);
1033 toErase.push_back(LI);
1038 ValuesPerBlock.push_back(std::make_pair((*I)->getParent(), *I));
1041 DEBUG(cerr << "GVN REMOVING NONLOCAL LOAD: " << *LI);
1043 DenseMap<BasicBlock*, Value*> BlockReplValues;
1044 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1045 // Perform PHI construction.
1046 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1047 LI->replaceAllUsesWith(v);
1049 if (!isa<GlobalValue>(v))
1051 if (isa<PointerType>(v->getType()))
1052 MD->invalidateCachedPointerInfo(v);
1053 toErase.push_back(LI);
1058 if (!EnablePRE || !EnableLoadPRE)
1061 // Okay, we have *some* definitions of the value. This means that the value
1062 // is available in some of our (transitive) predecessors. Lets think about
1063 // doing PRE of this load. This will involve inserting a new load into the
1064 // predecessor when it's not available. We could do this in general, but
1065 // prefer to not increase code size. As such, we only do this when we know
1066 // that we only have to insert *one* load (which means we're basically moving
1067 // the load, not inserting a new one).
1069 // Everything we do here is based on local predecessors of LI's block. If it
1070 // only has one predecessor, bail now.
1071 BasicBlock *LoadBB = LI->getParent();
1072 if (LoadBB->getSinglePredecessor())
1075 // If we have a repl set with LI itself in it, this means we have a loop where
1076 // at least one of the values is LI. Since this means that we won't be able
1077 // to eliminate LI even if we insert uses in the other predecessors, we will
1078 // end up increasing code size. Reject this by scanning for LI.
1079 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1080 if (ValuesPerBlock[i].second == LI)
1083 // Okay, we have some hope :). Check to see if the loaded value is fully
1084 // available in all but one predecessor.
1085 // FIXME: If we could restructure the CFG, we could make a common pred with
1086 // all the preds that don't have an available LI and insert a new load into
1088 BasicBlock *UnavailablePred = 0;
1090 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1091 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1092 FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
1093 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1094 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1096 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1098 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1101 // If this load is not available in multiple predecessors, reject it.
1102 if (UnavailablePred && UnavailablePred != *PI)
1104 UnavailablePred = *PI;
1107 assert(UnavailablePred != 0 &&
1108 "Fully available value should be eliminated above!");
1110 // If the loaded pointer is PHI node defined in this block, do PHI translation
1111 // to get its value in the predecessor.
1112 Value *LoadPtr = LI->getOperand(0)->DoPHITranslation(LoadBB, UnavailablePred);
1114 // Make sure the value is live in the predecessor. If it was defined by a
1115 // non-PHI instruction in this block, we don't know how to recompute it above.
1116 if (Instruction *LPInst = dyn_cast<Instruction>(LoadPtr))
1117 if (!DT->dominates(LPInst->getParent(), UnavailablePred)) {
1118 DEBUG(cerr << "COULDN'T PRE LOAD BECAUSE PTR IS UNAVAILABLE IN PRED: "
1119 << *LPInst << *LI << "\n");
1123 // We don't currently handle critical edges :(
1124 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1125 DEBUG(cerr << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1126 << UnavailablePred->getName() << "': " << *LI);
1130 // Okay, we can eliminate this load by inserting a reload in the predecessor
1131 // and using PHI construction to get the value in the other predecessors, do
1133 DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
1135 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1137 UnavailablePred->getTerminator());
1139 DenseMap<BasicBlock*, Value*> BlockReplValues;
1140 BlockReplValues.insert(ValuesPerBlock.begin(), ValuesPerBlock.end());
1141 BlockReplValues[UnavailablePred] = NewLoad;
1143 // Perform PHI construction.
1144 Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
1145 LI->replaceAllUsesWith(v);
1146 if (!isa<GlobalValue>(v))
1148 if (isa<PointerType>(v->getType()))
1149 MD->invalidateCachedPointerInfo(v);
1150 toErase.push_back(LI);
1155 /// processLoad - Attempt to eliminate a load, first by eliminating it
1156 /// locally, and then attempting non-local elimination if that fails.
1157 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1158 if (L->isVolatile())
1161 Value* pointer = L->getPointerOperand();
1163 // ... to a pointer that has been loaded from before...
1164 MemDepResult dep = MD->getDependency(L);
1166 // If the value isn't available, don't do anything!
1167 if (dep.isClobber())
1170 // If it is defined in another block, try harder.
1171 if (dep.isNonLocal())
1172 return processNonLocalLoad(L, toErase);
1174 Instruction *DepInst = dep.getInst();
1175 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1176 // Only forward substitute stores to loads of the same type.
1177 // FIXME: Could do better!
1178 if (DepSI->getPointerOperand()->getType() != pointer->getType())
1182 L->replaceAllUsesWith(DepSI->getOperand(0));
1183 if (isa<PointerType>(DepSI->getOperand(0)->getType()))
1184 MD->invalidateCachedPointerInfo(DepSI->getOperand(0));
1185 toErase.push_back(L);
1190 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1191 // Only forward substitute stores to loads of the same type.
1192 // FIXME: Could do better! load i32 -> load i8 -> truncate on little endian.
1193 if (DepLI->getType() != L->getType())
1197 L->replaceAllUsesWith(DepLI);
1198 if (isa<PointerType>(DepLI->getType()))
1199 MD->invalidateCachedPointerInfo(DepLI);
1200 toErase.push_back(L);
1205 // If this load really doesn't depend on anything, then we must be loading an
1206 // undef value. This can happen when loading for a fresh allocation with no
1207 // intervening stores, for example.
1208 if (isa<AllocationInst>(DepInst)) {
1209 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1210 toErase.push_back(L);
1218 Value* GVN::lookupNumber(BasicBlock* BB, uint32_t num) {
1219 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1220 if (I == localAvail.end())
1223 ValueNumberScope* locals = I->second;
1226 DenseMap<uint32_t, Value*>::iterator I = locals->table.find(num);
1227 if (I != locals->table.end())
1230 locals = locals->parent;
1236 /// AttemptRedundancyElimination - If the "fast path" of redundancy elimination
1237 /// by inheritance from the dominator fails, see if we can perform phi
1238 /// construction to eliminate the redundancy.
1239 Value* GVN::AttemptRedundancyElimination(Instruction* orig, unsigned valno) {
1240 BasicBlock* BaseBlock = orig->getParent();
1242 SmallPtrSet<BasicBlock*, 4> Visited;
1243 SmallVector<BasicBlock*, 8> Stack;
1244 Stack.push_back(BaseBlock);
1246 DenseMap<BasicBlock*, Value*> Results;
1248 // Walk backwards through our predecessors, looking for instances of the
1249 // value number we're looking for. Instances are recorded in the Results
1250 // map, which is then used to perform phi construction.
1251 while (!Stack.empty()) {
1252 BasicBlock* Current = Stack.back();
1255 // If we've walked all the way to a proper dominator, then give up. Cases
1256 // where the instance is in the dominator will have been caught by the fast
1257 // path, and any cases that require phi construction further than this are
1258 // probably not worth it anyways. Note that this is a SIGNIFICANT compile
1259 // time improvement.
1260 if (DT->properlyDominates(Current, orig->getParent())) return 0;
1262 DenseMap<BasicBlock*, ValueNumberScope*>::iterator LA =
1263 localAvail.find(Current);
1264 if (LA == localAvail.end()) return 0;
1265 DenseMap<unsigned, Value*>::iterator V = LA->second->table.find(valno);
1267 if (V != LA->second->table.end()) {
1268 // Found an instance, record it.
1269 Results.insert(std::make_pair(Current, V->second));
1273 // If we reach the beginning of the function, then give up.
1274 if (pred_begin(Current) == pred_end(Current))
1277 for (pred_iterator PI = pred_begin(Current), PE = pred_end(Current);
1279 if (Visited.insert(*PI))
1280 Stack.push_back(*PI);
1283 // If we didn't find instances, give up. Otherwise, perform phi construction.
1284 if (Results.size() == 0)
1287 return GetValueForBlock(BaseBlock, orig, Results, true);
1290 /// processInstruction - When calculating availability, handle an instruction
1291 /// by inserting it into the appropriate sets
1292 bool GVN::processInstruction(Instruction *I,
1293 SmallVectorImpl<Instruction*> &toErase) {
1294 if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1295 bool changed = processLoad(L, toErase);
1298 unsigned num = VN.lookup_or_add(L);
1299 localAvail[I->getParent()]->table.insert(std::make_pair(num, L));
1305 uint32_t nextNum = VN.getNextUnusedValueNumber();
1306 unsigned num = VN.lookup_or_add(I);
1308 // Allocations are always uniquely numbered, so we can save time and memory
1309 // by fast failing them.
1310 if (isa<AllocationInst>(I) || isa<TerminatorInst>(I)) {
1311 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1315 // Collapse PHI nodes
1316 if (PHINode* p = dyn_cast<PHINode>(I)) {
1317 Value* constVal = CollapsePhi(p);
1320 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1322 PI->second.erase(p);
1324 p->replaceAllUsesWith(constVal);
1325 if (isa<PointerType>(constVal->getType()))
1326 MD->invalidateCachedPointerInfo(constVal);
1327 toErase.push_back(p);
1329 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1332 // If the number we were assigned was a brand new VN, then we don't
1333 // need to do a lookup to see if the number already exists
1334 // somewhere in the domtree: it can't!
1335 } else if (num == nextNum) {
1336 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1338 // Perform fast-path value-number based elimination of values inherited from
1340 } else if (Value* repl = lookupNumber(I->getParent(), num)) {
1343 I->replaceAllUsesWith(repl);
1344 if (isa<PointerType>(repl->getType()))
1345 MD->invalidateCachedPointerInfo(repl);
1346 toErase.push_back(I);
1350 // Perform slow-pathvalue-number based elimination with phi construction.
1351 } else if (Value* repl = AttemptRedundancyElimination(I, num)) {
1354 I->replaceAllUsesWith(repl);
1355 if (isa<PointerType>(repl->getType()))
1356 MD->invalidateCachedPointerInfo(repl);
1357 toErase.push_back(I);
1361 localAvail[I->getParent()]->table.insert(std::make_pair(num, I));
1367 // GVN::runOnFunction - This is the main transformation entry point for a
1370 bool GVN::runOnFunction(Function& F) {
1371 MD = &getAnalysis<MemoryDependenceAnalysis>();
1372 DT = &getAnalysis<DominatorTree>();
1373 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1377 bool changed = false;
1378 bool shouldContinue = true;
1380 // Merge unconditional branches, allowing PRE to catch more
1381 // optimization opportunities.
1382 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1383 BasicBlock* BB = FI;
1385 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1386 if (removedBlock) NumGVNBlocks++;
1388 changed |= removedBlock;
1391 unsigned Iteration = 0;
1393 while (shouldContinue) {
1394 DEBUG(cerr << "GVN iteration: " << Iteration << "\n");
1395 shouldContinue = iterateOnFunction(F);
1396 changed |= shouldContinue;
1401 bool PREChanged = true;
1402 while (PREChanged) {
1403 PREChanged = performPRE(F);
1404 changed |= PREChanged;
1407 // FIXME: Should perform GVN again after PRE does something. PRE can move
1408 // computations into blocks where they become fully redundant. Note that
1409 // we can't do this until PRE's critical edge splitting updates memdep.
1410 // Actually, when this happens, we should just fully integrate PRE into GVN.
1412 cleanupGlobalSets();
1418 bool GVN::processBlock(BasicBlock* BB) {
1419 DomTreeNode* DTN = DT->getNode(BB);
1420 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1421 // incrementing BI before processing an instruction).
1422 SmallVector<Instruction*, 8> toErase;
1423 bool changed_function = false;
1427 new ValueNumberScope(localAvail[DTN->getIDom()->getBlock()]);
1429 localAvail[BB] = new ValueNumberScope(0);
1431 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1433 changed_function |= processInstruction(BI, toErase);
1434 if (toErase.empty()) {
1439 // If we need some instructions deleted, do it now.
1440 NumGVNInstr += toErase.size();
1442 // Avoid iterator invalidation.
1443 bool AtStart = BI == BB->begin();
1447 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1448 E = toErase.end(); I != E; ++I) {
1449 DEBUG(cerr << "GVN removed: " << **I);
1450 MD->removeInstruction(*I);
1451 (*I)->eraseFromParent();
1461 return changed_function;
1464 /// performPRE - Perform a purely local form of PRE that looks for diamond
1465 /// control flow patterns and attempts to perform simple PRE at the join point.
1466 bool GVN::performPRE(Function& F) {
1467 bool Changed = false;
1468 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
1469 DenseMap<BasicBlock*, Value*> predMap;
1470 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
1471 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
1472 BasicBlock* CurrentBlock = *DI;
1474 // Nothing to PRE in the entry block.
1475 if (CurrentBlock == &F.getEntryBlock()) continue;
1477 for (BasicBlock::iterator BI = CurrentBlock->begin(),
1478 BE = CurrentBlock->end(); BI != BE; ) {
1479 Instruction *CurInst = BI++;
1481 if (isa<AllocationInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
1482 isa<PHINode>(CurInst) || CurInst->mayReadFromMemory() ||
1483 CurInst->mayWriteToMemory())
1486 uint32_t valno = VN.lookup(CurInst);
1488 // Look for the predecessors for PRE opportunities. We're
1489 // only trying to solve the basic diamond case, where
1490 // a value is computed in the successor and one predecessor,
1491 // but not the other. We also explicitly disallow cases
1492 // where the successor is its own predecessor, because they're
1493 // more complicated to get right.
1494 unsigned numWith = 0;
1495 unsigned numWithout = 0;
1496 BasicBlock* PREPred = 0;
1499 for (pred_iterator PI = pred_begin(CurrentBlock),
1500 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
1501 // We're not interested in PRE where the block is its
1502 // own predecessor, on in blocks with predecessors
1503 // that are not reachable.
1504 if (*PI == CurrentBlock) {
1507 } else if (!localAvail.count(*PI)) {
1512 DenseMap<uint32_t, Value*>::iterator predV =
1513 localAvail[*PI]->table.find(valno);
1514 if (predV == localAvail[*PI]->table.end()) {
1517 } else if (predV->second == CurInst) {
1520 predMap[*PI] = predV->second;
1525 // Don't do PRE when it might increase code size, i.e. when
1526 // we would need to insert instructions in more than one pred.
1527 if (numWithout != 1 || numWith == 0)
1530 // We can't do PRE safely on a critical edge, so instead we schedule
1531 // the edge to be split and perform the PRE the next time we iterate
1533 unsigned succNum = 0;
1534 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
1536 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
1541 if (isCriticalEdge(PREPred->getTerminator(), succNum)) {
1542 toSplit.push_back(std::make_pair(PREPred->getTerminator(), succNum));
1546 // Instantiate the expression the in predecessor that lacked it.
1547 // Because we are going top-down through the block, all value numbers
1548 // will be available in the predecessor by the time we need them. Any
1549 // that weren't original present will have been instantiated earlier
1551 Instruction* PREInstr = CurInst->clone();
1552 bool success = true;
1553 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
1554 Value *Op = PREInstr->getOperand(i);
1555 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
1558 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
1559 PREInstr->setOperand(i, V);
1566 // Fail out if we encounter an operand that is not available in
1567 // the PRE predecessor. This is typically because of loads which
1568 // are not value numbered precisely.
1574 PREInstr->insertBefore(PREPred->getTerminator());
1575 PREInstr->setName(CurInst->getName() + ".pre");
1576 predMap[PREPred] = PREInstr;
1577 VN.add(PREInstr, valno);
1580 // Update the availability map to include the new instruction.
1581 localAvail[PREPred]->table.insert(std::make_pair(valno, PREInstr));
1583 // Create a PHI to make the value available in this block.
1584 PHINode* Phi = PHINode::Create(CurInst->getType(),
1585 CurInst->getName() + ".pre-phi",
1586 CurrentBlock->begin());
1587 for (pred_iterator PI = pred_begin(CurrentBlock),
1588 PE = pred_end(CurrentBlock); PI != PE; ++PI)
1589 Phi->addIncoming(predMap[*PI], *PI);
1592 localAvail[CurrentBlock]->table[valno] = Phi;
1594 CurInst->replaceAllUsesWith(Phi);
1595 if (isa<PointerType>(Phi->getType()))
1596 MD->invalidateCachedPointerInfo(Phi);
1599 DEBUG(cerr << "GVN PRE removed: " << *CurInst);
1600 MD->removeInstruction(CurInst);
1601 CurInst->eraseFromParent();
1606 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
1607 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
1608 SplitCriticalEdge(I->first, I->second, this);
1610 return Changed || toSplit.size();
1613 // iterateOnFunction - Executes one iteration of GVN
1614 bool GVN::iterateOnFunction(Function &F) {
1615 cleanupGlobalSets();
1617 // Top-down walk of the dominator tree
1618 bool changed = false;
1620 // Needed for value numbering with phi construction to work.
1621 ReversePostOrderTraversal<Function*> RPOT(&F);
1622 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
1623 RE = RPOT.end(); RI != RE; ++RI)
1624 changed |= processBlock(*RI);
1626 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
1627 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
1628 changed |= processBlock(DI->getBlock());
1634 void GVN::cleanupGlobalSets() {
1638 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
1639 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)