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 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "gvn"
17 #include "llvm/Transforms/Scalar.h"
18 #include "llvm/BasicBlock.h"
19 #include "llvm/Constants.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Function.h"
22 #include "llvm/IntrinsicInst.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/ParameterAttributes.h"
25 #include "llvm/Value.h"
26 #include "llvm/ADT/BitVector.h"
27 #include "llvm/ADT/DenseMap.h"
28 #include "llvm/ADT/DepthFirstIterator.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/Compiler.h"
37 #include "llvm/Target/TargetData.h"
40 //===----------------------------------------------------------------------===//
42 //===----------------------------------------------------------------------===//
44 /// This class holds the mapping between values and value numbers. It is used
45 /// as an efficient mechanism to determine the expression-wise equivalence of
48 struct VISIBILITY_HIDDEN Expression {
49 enum ExpressionOpcode { ADD, SUB, MUL, UDIV, SDIV, FDIV, UREM, SREM,
50 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
51 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
52 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
53 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
54 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
55 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
56 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
57 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
58 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, EMPTY,
61 ExpressionOpcode opcode;
66 SmallVector<uint32_t, 4> varargs;
70 Expression(ExpressionOpcode o) : opcode(o) { }
72 bool operator==(const Expression &other) const {
73 if (opcode != other.opcode)
75 else if (opcode == EMPTY || opcode == TOMBSTONE)
77 else if (type != other.type)
79 else if (function != other.function)
81 else if (firstVN != other.firstVN)
83 else if (secondVN != other.secondVN)
85 else if (thirdVN != other.thirdVN)
88 if (varargs.size() != other.varargs.size())
91 for (size_t i = 0; i < varargs.size(); ++i)
92 if (varargs[i] != other.varargs[i])
99 bool operator!=(const Expression &other) const {
100 if (opcode != other.opcode)
102 else if (opcode == EMPTY || opcode == TOMBSTONE)
104 else if (type != other.type)
106 else if (function != other.function)
108 else if (firstVN != other.firstVN)
110 else if (secondVN != other.secondVN)
112 else if (thirdVN != other.thirdVN)
115 if (varargs.size() != other.varargs.size())
118 for (size_t i = 0; i < varargs.size(); ++i)
119 if (varargs[i] != other.varargs[i])
127 class VISIBILITY_HIDDEN ValueTable {
129 DenseMap<Value*, uint32_t> valueNumbering;
130 DenseMap<Expression, uint32_t> expressionNumbering;
133 uint32_t nextValueNumber;
135 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
136 Expression::ExpressionOpcode getOpcode(CmpInst* C);
137 Expression::ExpressionOpcode getOpcode(CastInst* C);
138 Expression create_expression(BinaryOperator* BO);
139 Expression create_expression(CmpInst* C);
140 Expression create_expression(ShuffleVectorInst* V);
141 Expression create_expression(ExtractElementInst* C);
142 Expression create_expression(InsertElementInst* V);
143 Expression create_expression(SelectInst* V);
144 Expression create_expression(CastInst* C);
145 Expression create_expression(GetElementPtrInst* G);
146 Expression create_expression(CallInst* C);
148 ValueTable() : nextValueNumber(1) { }
149 uint32_t lookup_or_add(Value* V);
150 uint32_t lookup(Value* V) const;
151 void add(Value* V, uint32_t num);
153 void erase(Value* v);
155 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
156 uint32_t hash_operand(Value* v);
161 template <> struct DenseMapInfo<Expression> {
162 static inline Expression getEmptyKey() {
163 return Expression(Expression::EMPTY);
166 static inline Expression getTombstoneKey() {
167 return Expression(Expression::TOMBSTONE);
170 static unsigned getHashValue(const Expression e) {
171 unsigned hash = e.opcode;
173 hash = e.firstVN + hash * 37;
174 hash = e.secondVN + hash * 37;
175 hash = e.thirdVN + hash * 37;
177 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
178 (unsigned)((uintptr_t)e.type >> 9)) +
181 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
182 E = e.varargs.end(); I != E; ++I)
183 hash = *I + hash * 37;
185 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
186 (unsigned)((uintptr_t)e.function >> 9)) +
191 static bool isEqual(const Expression &LHS, const Expression &RHS) {
194 static bool isPod() { return true; }
198 //===----------------------------------------------------------------------===//
199 // ValueTable Internal Functions
200 //===----------------------------------------------------------------------===//
201 Expression::ExpressionOpcode
202 ValueTable::getOpcode(BinaryOperator* BO) {
203 switch(BO->getOpcode()) {
204 case Instruction::Add:
205 return Expression::ADD;
206 case Instruction::Sub:
207 return Expression::SUB;
208 case Instruction::Mul:
209 return Expression::MUL;
210 case Instruction::UDiv:
211 return Expression::UDIV;
212 case Instruction::SDiv:
213 return Expression::SDIV;
214 case Instruction::FDiv:
215 return Expression::FDIV;
216 case Instruction::URem:
217 return Expression::UREM;
218 case Instruction::SRem:
219 return Expression::SREM;
220 case Instruction::FRem:
221 return Expression::FREM;
222 case Instruction::Shl:
223 return Expression::SHL;
224 case Instruction::LShr:
225 return Expression::LSHR;
226 case Instruction::AShr:
227 return Expression::ASHR;
228 case Instruction::And:
229 return Expression::AND;
230 case Instruction::Or:
231 return Expression::OR;
232 case Instruction::Xor:
233 return Expression::XOR;
235 // THIS SHOULD NEVER HAPPEN
237 assert(0 && "Binary operator with unknown opcode?");
238 return Expression::ADD;
242 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
243 if (C->getOpcode() == Instruction::ICmp) {
244 switch (C->getPredicate()) {
245 case ICmpInst::ICMP_EQ:
246 return Expression::ICMPEQ;
247 case ICmpInst::ICMP_NE:
248 return Expression::ICMPNE;
249 case ICmpInst::ICMP_UGT:
250 return Expression::ICMPUGT;
251 case ICmpInst::ICMP_UGE:
252 return Expression::ICMPUGE;
253 case ICmpInst::ICMP_ULT:
254 return Expression::ICMPULT;
255 case ICmpInst::ICMP_ULE:
256 return Expression::ICMPULE;
257 case ICmpInst::ICMP_SGT:
258 return Expression::ICMPSGT;
259 case ICmpInst::ICMP_SGE:
260 return Expression::ICMPSGE;
261 case ICmpInst::ICMP_SLT:
262 return Expression::ICMPSLT;
263 case ICmpInst::ICMP_SLE:
264 return Expression::ICMPSLE;
266 // THIS SHOULD NEVER HAPPEN
268 assert(0 && "Comparison with unknown predicate?");
269 return Expression::ICMPEQ;
272 switch (C->getPredicate()) {
273 case FCmpInst::FCMP_OEQ:
274 return Expression::FCMPOEQ;
275 case FCmpInst::FCMP_OGT:
276 return Expression::FCMPOGT;
277 case FCmpInst::FCMP_OGE:
278 return Expression::FCMPOGE;
279 case FCmpInst::FCMP_OLT:
280 return Expression::FCMPOLT;
281 case FCmpInst::FCMP_OLE:
282 return Expression::FCMPOLE;
283 case FCmpInst::FCMP_ONE:
284 return Expression::FCMPONE;
285 case FCmpInst::FCMP_ORD:
286 return Expression::FCMPORD;
287 case FCmpInst::FCMP_UNO:
288 return Expression::FCMPUNO;
289 case FCmpInst::FCMP_UEQ:
290 return Expression::FCMPUEQ;
291 case FCmpInst::FCMP_UGT:
292 return Expression::FCMPUGT;
293 case FCmpInst::FCMP_UGE:
294 return Expression::FCMPUGE;
295 case FCmpInst::FCMP_ULT:
296 return Expression::FCMPULT;
297 case FCmpInst::FCMP_ULE:
298 return Expression::FCMPULE;
299 case FCmpInst::FCMP_UNE:
300 return Expression::FCMPUNE;
302 // THIS SHOULD NEVER HAPPEN
304 assert(0 && "Comparison with unknown predicate?");
305 return Expression::FCMPOEQ;
310 Expression::ExpressionOpcode
311 ValueTable::getOpcode(CastInst* C) {
312 switch(C->getOpcode()) {
313 case Instruction::Trunc:
314 return Expression::TRUNC;
315 case Instruction::ZExt:
316 return Expression::ZEXT;
317 case Instruction::SExt:
318 return Expression::SEXT;
319 case Instruction::FPToUI:
320 return Expression::FPTOUI;
321 case Instruction::FPToSI:
322 return Expression::FPTOSI;
323 case Instruction::UIToFP:
324 return Expression::UITOFP;
325 case Instruction::SIToFP:
326 return Expression::SITOFP;
327 case Instruction::FPTrunc:
328 return Expression::FPTRUNC;
329 case Instruction::FPExt:
330 return Expression::FPEXT;
331 case Instruction::PtrToInt:
332 return Expression::PTRTOINT;
333 case Instruction::IntToPtr:
334 return Expression::INTTOPTR;
335 case Instruction::BitCast:
336 return Expression::BITCAST;
338 // THIS SHOULD NEVER HAPPEN
340 assert(0 && "Cast operator with unknown opcode?");
341 return Expression::BITCAST;
345 uint32_t ValueTable::hash_operand(Value* v) {
346 if (CallInst* CI = dyn_cast<CallInst>(v))
347 if (!AA->doesNotAccessMemory(CI))
348 return nextValueNumber++;
350 return lookup_or_add(v);
353 Expression ValueTable::create_expression(CallInst* C) {
356 e.type = C->getType();
360 e.function = C->getCalledFunction();
361 e.opcode = Expression::CALL;
363 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
365 e.varargs.push_back(hash_operand(*I));
370 Expression ValueTable::create_expression(BinaryOperator* BO) {
373 e.firstVN = hash_operand(BO->getOperand(0));
374 e.secondVN = hash_operand(BO->getOperand(1));
377 e.type = BO->getType();
378 e.opcode = getOpcode(BO);
383 Expression ValueTable::create_expression(CmpInst* C) {
386 e.firstVN = hash_operand(C->getOperand(0));
387 e.secondVN = hash_operand(C->getOperand(1));
390 e.type = C->getType();
391 e.opcode = getOpcode(C);
396 Expression ValueTable::create_expression(CastInst* C) {
399 e.firstVN = hash_operand(C->getOperand(0));
403 e.type = C->getType();
404 e.opcode = getOpcode(C);
409 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
412 e.firstVN = hash_operand(S->getOperand(0));
413 e.secondVN = hash_operand(S->getOperand(1));
414 e.thirdVN = hash_operand(S->getOperand(2));
416 e.type = S->getType();
417 e.opcode = Expression::SHUFFLE;
422 Expression ValueTable::create_expression(ExtractElementInst* E) {
425 e.firstVN = hash_operand(E->getOperand(0));
426 e.secondVN = hash_operand(E->getOperand(1));
429 e.type = E->getType();
430 e.opcode = Expression::EXTRACT;
435 Expression ValueTable::create_expression(InsertElementInst* I) {
438 e.firstVN = hash_operand(I->getOperand(0));
439 e.secondVN = hash_operand(I->getOperand(1));
440 e.thirdVN = hash_operand(I->getOperand(2));
442 e.type = I->getType();
443 e.opcode = Expression::INSERT;
448 Expression ValueTable::create_expression(SelectInst* I) {
451 e.firstVN = hash_operand(I->getCondition());
452 e.secondVN = hash_operand(I->getTrueValue());
453 e.thirdVN = hash_operand(I->getFalseValue());
455 e.type = I->getType();
456 e.opcode = Expression::SELECT;
461 Expression ValueTable::create_expression(GetElementPtrInst* G) {
464 e.firstVN = hash_operand(G->getPointerOperand());
468 e.type = G->getType();
469 e.opcode = Expression::GEP;
471 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
473 e.varargs.push_back(hash_operand(*I));
478 //===----------------------------------------------------------------------===//
479 // ValueTable External Functions
480 //===----------------------------------------------------------------------===//
482 /// lookup_or_add - Returns the value number for the specified value, assigning
483 /// it a new number if it did not have one before.
484 uint32_t ValueTable::lookup_or_add(Value* V) {
485 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
486 if (VI != valueNumbering.end())
489 if (CallInst* C = dyn_cast<CallInst>(V)) {
490 if (AA->onlyReadsMemory(C)) { // includes doesNotAccessMemory
491 Expression e = create_expression(C);
493 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
494 if (EI != expressionNumbering.end()) {
495 valueNumbering.insert(std::make_pair(V, EI->second));
498 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
499 valueNumbering.insert(std::make_pair(V, nextValueNumber));
501 return nextValueNumber++;
504 valueNumbering.insert(std::make_pair(V, nextValueNumber));
505 return nextValueNumber++;
507 } else if (BinaryOperator* BO = dyn_cast<BinaryOperator>(V)) {
508 Expression e = create_expression(BO);
510 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
511 if (EI != expressionNumbering.end()) {
512 valueNumbering.insert(std::make_pair(V, EI->second));
515 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
516 valueNumbering.insert(std::make_pair(V, nextValueNumber));
518 return nextValueNumber++;
520 } else if (CmpInst* C = dyn_cast<CmpInst>(V)) {
521 Expression e = create_expression(C);
523 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
524 if (EI != expressionNumbering.end()) {
525 valueNumbering.insert(std::make_pair(V, EI->second));
528 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
529 valueNumbering.insert(std::make_pair(V, nextValueNumber));
531 return nextValueNumber++;
533 } else if (ShuffleVectorInst* U = dyn_cast<ShuffleVectorInst>(V)) {
534 Expression e = create_expression(U);
536 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
537 if (EI != expressionNumbering.end()) {
538 valueNumbering.insert(std::make_pair(V, EI->second));
541 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
542 valueNumbering.insert(std::make_pair(V, nextValueNumber));
544 return nextValueNumber++;
546 } else if (ExtractElementInst* U = dyn_cast<ExtractElementInst>(V)) {
547 Expression e = create_expression(U);
549 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
550 if (EI != expressionNumbering.end()) {
551 valueNumbering.insert(std::make_pair(V, EI->second));
554 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
555 valueNumbering.insert(std::make_pair(V, nextValueNumber));
557 return nextValueNumber++;
559 } else if (InsertElementInst* U = dyn_cast<InsertElementInst>(V)) {
560 Expression e = create_expression(U);
562 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
563 if (EI != expressionNumbering.end()) {
564 valueNumbering.insert(std::make_pair(V, EI->second));
567 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
568 valueNumbering.insert(std::make_pair(V, nextValueNumber));
570 return nextValueNumber++;
572 } else if (SelectInst* U = dyn_cast<SelectInst>(V)) {
573 Expression e = create_expression(U);
575 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
576 if (EI != expressionNumbering.end()) {
577 valueNumbering.insert(std::make_pair(V, EI->second));
580 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
581 valueNumbering.insert(std::make_pair(V, nextValueNumber));
583 return nextValueNumber++;
585 } else if (CastInst* U = dyn_cast<CastInst>(V)) {
586 Expression e = create_expression(U);
588 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
589 if (EI != expressionNumbering.end()) {
590 valueNumbering.insert(std::make_pair(V, EI->second));
593 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
594 valueNumbering.insert(std::make_pair(V, nextValueNumber));
596 return nextValueNumber++;
598 } else if (GetElementPtrInst* U = dyn_cast<GetElementPtrInst>(V)) {
599 Expression e = create_expression(U);
601 DenseMap<Expression, uint32_t>::iterator EI = expressionNumbering.find(e);
602 if (EI != expressionNumbering.end()) {
603 valueNumbering.insert(std::make_pair(V, EI->second));
606 expressionNumbering.insert(std::make_pair(e, nextValueNumber));
607 valueNumbering.insert(std::make_pair(V, nextValueNumber));
609 return nextValueNumber++;
612 valueNumbering.insert(std::make_pair(V, nextValueNumber));
613 return nextValueNumber++;
617 /// lookup - Returns the value number of the specified value. Fails if
618 /// the value has not yet been numbered.
619 uint32_t ValueTable::lookup(Value* V) const {
620 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
621 if (VI != valueNumbering.end())
624 assert(0 && "Value not numbered?");
629 /// clear - Remove all entries from the ValueTable
630 void ValueTable::clear() {
631 valueNumbering.clear();
632 expressionNumbering.clear();
636 /// erase - Remove a value from the value numbering
637 void ValueTable::erase(Value* V) {
638 valueNumbering.erase(V);
641 //===----------------------------------------------------------------------===//
642 // ValueNumberedSet Class
643 //===----------------------------------------------------------------------===//
645 class ValueNumberedSet {
647 SmallPtrSet<Value*, 8> contents;
650 ValueNumberedSet() { numbers.resize(1); }
651 ValueNumberedSet(const ValueNumberedSet& other) {
652 numbers = other.numbers;
653 contents = other.contents;
656 typedef SmallPtrSet<Value*, 8>::iterator iterator;
658 iterator begin() { return contents.begin(); }
659 iterator end() { return contents.end(); }
661 bool insert(Value* v) { return contents.insert(v); }
662 void insert(iterator I, iterator E) { contents.insert(I, E); }
663 void erase(Value* v) { contents.erase(v); }
664 unsigned count(Value* v) { return contents.count(v); }
665 size_t size() { return contents.size(); }
667 void set(unsigned i) {
668 if (i >= numbers.size())
674 void operator=(const ValueNumberedSet& other) {
675 contents = other.contents;
676 numbers = other.numbers;
679 void reset(unsigned i) {
680 if (i < numbers.size())
684 bool test(unsigned i) {
685 if (i >= numbers.size())
688 return numbers.test(i);
698 //===----------------------------------------------------------------------===//
700 //===----------------------------------------------------------------------===//
704 class VISIBILITY_HIDDEN GVN : public FunctionPass {
705 bool runOnFunction(Function &F);
707 static char ID; // Pass identification, replacement for typeid
708 GVN() : FunctionPass((intptr_t)&ID) { }
713 DenseMap<BasicBlock*, ValueNumberedSet> availableOut;
715 typedef DenseMap<Value*, SmallPtrSet<Instruction*, 4> > PhiMapType;
719 // This transformation requires dominator postdominator info
720 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
721 AU.setPreservesCFG();
722 AU.addRequired<DominatorTree>();
723 AU.addRequired<MemoryDependenceAnalysis>();
724 AU.addRequired<AliasAnalysis>();
725 AU.addRequired<TargetData>();
726 AU.addPreserved<AliasAnalysis>();
727 AU.addPreserved<MemoryDependenceAnalysis>();
728 AU.addPreserved<TargetData>();
732 // FIXME: eliminate or document these better
733 Value* find_leader(ValueNumberedSet& vals, uint32_t v) ;
734 void val_insert(ValueNumberedSet& s, Value* v);
735 bool processLoad(LoadInst* L,
736 DenseMap<Value*, LoadInst*>& lastLoad,
737 SmallVector<Instruction*, 4>& toErase);
738 bool processInstruction(Instruction* I,
739 ValueNumberedSet& currAvail,
740 DenseMap<Value*, LoadInst*>& lastSeenLoad,
741 SmallVector<Instruction*, 4>& toErase);
742 bool processNonLocalLoad(LoadInst* L,
743 SmallVector<Instruction*, 4>& toErase);
744 bool processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
745 SmallVector<Instruction*, 4>& toErase);
746 bool performReturnSlotOptzn(MemCpyInst* cpy, CallInst* C,
747 SmallVector<Instruction*, 4>& toErase);
748 Value *GetValueForBlock(BasicBlock *BB, LoadInst* orig,
749 DenseMap<BasicBlock*, Value*> &Phis,
750 bool top_level = false);
751 void dump(DenseMap<BasicBlock*, Value*>& d);
752 bool iterateOnFunction(Function &F);
753 Value* CollapsePhi(PHINode* p);
754 bool isSafeReplacement(PHINode* p, Instruction* inst);
755 bool valueHasOnlyOneUseAfter(Value* val, MemCpyInst* use,
756 Instruction* cutoff);
763 // createGVNPass - The public interface to this file...
764 FunctionPass *llvm::createGVNPass() { return new GVN(); }
766 static RegisterPass<GVN> X("gvn",
767 "Global Value Numbering");
769 STATISTIC(NumGVNInstr, "Number of instructions deleted");
770 STATISTIC(NumGVNLoad, "Number of loads deleted");
772 /// find_leader - Given a set and a value number, return the first
773 /// element of the set with that value number, or 0 if no such element
775 Value* GVN::find_leader(ValueNumberedSet& vals, uint32_t v) {
779 for (ValueNumberedSet::iterator I = vals.begin(), E = vals.end();
781 if (v == VN.lookup(*I))
784 assert(0 && "No leader found, but present bit is set?");
788 /// val_insert - Insert a value into a set only if there is not a value
789 /// with the same value number already in the set
790 void GVN::val_insert(ValueNumberedSet& s, Value* v) {
791 uint32_t num = VN.lookup(v);
796 void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
798 for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
799 E = d.end(); I != E; ++I) {
800 if (I->second == MemoryDependenceAnalysis::None)
808 Value* GVN::CollapsePhi(PHINode* p) {
809 DominatorTree &DT = getAnalysis<DominatorTree>();
810 Value* constVal = p->hasConstantValue();
813 if (Instruction* inst = dyn_cast<Instruction>(constVal)) {
814 if (DT.dominates(inst, p))
815 if (isSafeReplacement(p, inst))
825 bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
826 if (!isa<PHINode>(inst))
829 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
831 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
832 if (use_phi->getParent() == inst->getParent())
838 /// GetValueForBlock - Get the value to use within the specified basic block.
839 /// available values are in Phis.
840 Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
841 DenseMap<BasicBlock*, Value*> &Phis,
844 // If we have already computed this value, return the previously computed val.
845 DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
846 if (V != Phis.end() && !top_level) return V->second;
848 BasicBlock* singlePred = BB->getSinglePredecessor();
850 Value *ret = GetValueForBlock(singlePred, orig, Phis);
854 // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
855 // now, then get values to fill in the incoming values for the PHI.
856 PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle",
858 PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
860 if (Phis.count(BB) == 0)
861 Phis.insert(std::make_pair(BB, PN));
863 // Fill in the incoming values for the block.
864 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
865 Value* val = GetValueForBlock(*PI, orig, Phis);
867 PN->addIncoming(val, *PI);
869 AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
870 AA.copyValue(orig, PN);
872 // Attempt to collapse PHI nodes that are trivially redundant
873 Value* v = CollapsePhi(PN);
875 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
877 MD.removeInstruction(PN);
878 PN->replaceAllUsesWith(v);
880 for (DenseMap<BasicBlock*, Value*>::iterator I = Phis.begin(),
881 E = Phis.end(); I != E; ++I)
885 PN->eraseFromParent();
892 // Cache our phi construction results
893 phiMap[orig->getPointerOperand()].insert(PN);
897 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
898 /// non-local by performing PHI construction.
899 bool GVN::processNonLocalLoad(LoadInst* L,
900 SmallVector<Instruction*, 4>& toErase) {
901 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
903 // Find the non-local dependencies of the load
904 DenseMap<BasicBlock*, Value*> deps;
905 MD.getNonLocalDependency(L, deps);
907 DenseMap<BasicBlock*, Value*> repl;
909 // Filter out useless results (non-locals, etc)
910 for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
912 if (I->second == MemoryDependenceAnalysis::None) {
914 } else if (I->second == MemoryDependenceAnalysis::NonLocal) {
916 } else if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
917 if (S->getPointerOperand() == L->getPointerOperand())
918 repl[I->first] = S->getOperand(0);
921 } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
922 if (LD->getPointerOperand() == L->getPointerOperand())
930 // Use cached PHI construction information from previous runs
931 SmallPtrSet<Instruction*, 4>& p = phiMap[L->getPointerOperand()];
932 for (SmallPtrSet<Instruction*, 4>::iterator I = p.begin(), E = p.end();
934 if ((*I)->getParent() == L->getParent()) {
935 MD.removeInstruction(L);
936 L->replaceAllUsesWith(*I);
937 toErase.push_back(L);
942 repl.insert(std::make_pair((*I)->getParent(), *I));
946 // Perform PHI construction
947 SmallPtrSet<BasicBlock*, 4> visited;
948 Value* v = GetValueForBlock(L->getParent(), L, repl, true);
950 MD.removeInstruction(L);
951 L->replaceAllUsesWith(v);
952 toErase.push_back(L);
958 /// processLoad - Attempt to eliminate a load, first by eliminating it
959 /// locally, and then attempting non-local elimination if that fails.
960 bool GVN::processLoad(LoadInst* L,
961 DenseMap<Value*, LoadInst*>& lastLoad,
962 SmallVector<Instruction*, 4>& toErase) {
963 if (L->isVolatile()) {
964 lastLoad[L->getPointerOperand()] = L;
968 Value* pointer = L->getPointerOperand();
969 LoadInst*& last = lastLoad[pointer];
971 // ... to a pointer that has been loaded from before...
972 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
973 bool removedNonLocal = false;
974 Instruction* dep = MD.getDependency(L);
975 if (dep == MemoryDependenceAnalysis::NonLocal &&
976 L->getParent() != &L->getParent()->getParent()->getEntryBlock()) {
977 removedNonLocal = processNonLocalLoad(L, toErase);
979 if (!removedNonLocal)
982 return removedNonLocal;
986 bool deletedLoad = false;
988 // Walk up the dependency chain until we either find
989 // a dependency we can use, or we can't walk any further
990 while (dep != MemoryDependenceAnalysis::None &&
991 dep != MemoryDependenceAnalysis::NonLocal &&
992 (isa<LoadInst>(dep) || isa<StoreInst>(dep))) {
993 // ... that depends on a store ...
994 if (StoreInst* S = dyn_cast<StoreInst>(dep)) {
995 if (S->getPointerOperand() == pointer) {
997 MD.removeInstruction(L);
999 L->replaceAllUsesWith(S->getOperand(0));
1000 toErase.push_back(L);
1005 // Whether we removed it or not, we can't
1009 // If we don't depend on a store, and we haven't
1010 // been loaded before, bail.
1012 } else if (dep == last) {
1014 MD.removeInstruction(L);
1016 L->replaceAllUsesWith(last);
1017 toErase.push_back(L);
1023 dep = MD.getDependency(L, dep);
1027 if (dep != MemoryDependenceAnalysis::None &&
1028 dep != MemoryDependenceAnalysis::NonLocal &&
1029 isa<AllocationInst>(dep)) {
1030 // Check that this load is actually from the
1031 // allocation we found
1032 Value* v = L->getOperand(0);
1034 if (BitCastInst *BC = dyn_cast<BitCastInst>(v))
1035 v = BC->getOperand(0);
1036 else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v))
1037 v = GEP->getOperand(0);
1042 // If this load depends directly on an allocation, there isn't
1043 // anything stored there; therefore, we can optimize this load
1045 MD.removeInstruction(L);
1047 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1048 toErase.push_back(L);
1060 /// valueHasOnlyOneUse - Returns true if a value has only one use after the
1061 /// cutoff that is in the current same block and is the same as the use
1063 bool GVN::valueHasOnlyOneUseAfter(Value* val, MemCpyInst* use,
1064 Instruction* cutoff) {
1065 DominatorTree& DT = getAnalysis<DominatorTree>();
1067 SmallVector<User*, 8> useList(val->use_begin(), val->use_end());
1068 while (!useList.empty()) {
1069 User* UI = useList.back();
1072 if (isa<GetElementPtrInst>(UI) || isa<BitCastInst>(UI)) {
1074 for (User::use_iterator I = UI->use_begin(), E = UI->use_end();
1076 useList.push_back(*I);
1077 } else if (UI == use) {
1079 } else if (Instruction* inst = dyn_cast<Instruction>(UI)) {
1080 if (inst->getParent() == use->getParent() &&
1081 (inst == cutoff || !DT.dominates(cutoff, inst))) {
1092 /// performReturnSlotOptzn - takes a memcpy and a call that it depends on,
1093 /// and checks for the possibility of a return slot optimization by having
1094 /// the call write its result directly into the callees return parameter
1095 /// rather than using memcpy
1096 bool GVN::performReturnSlotOptzn(MemCpyInst* cpy, CallInst* C,
1097 SmallVector<Instruction*, 4>& toErase) {
1098 // Deliberately get the source and destination with bitcasts stripped away,
1099 // because we'll need to do type comparisons based on the underlying type.
1100 Value* cpyDest = cpy->getDest();
1101 Value* cpySrc = cpy->getSource();
1102 CallSite CS = CallSite::get(C);
1104 // Since this is a return slot optimization, we need to make sure that
1105 // the value being copied is, in fact, in a return slot. We also need to
1106 // check that the return slot parameter is marked noalias, so that we can
1107 // be sure that changing it will not cause unexpected behavior changes due
1108 // to it being accessed through a global or another parameter.
1109 if (CS.arg_size() == 0 ||
1110 cpySrc != CS.getArgument(0) ||
1111 !CS.paramHasAttr(1, ParamAttr::NoAlias | ParamAttr::StructRet))
1114 // Since we're changing the parameter to the callsite, we need to make sure
1115 // that what would be the new parameter dominates the callsite.
1116 DominatorTree& DT = getAnalysis<DominatorTree>();
1117 if (Instruction* cpyDestInst = dyn_cast<Instruction>(cpyDest))
1118 if (!DT.dominates(cpyDestInst, C))
1121 // Check that something sneaky is not happening involving casting
1122 // return slot types around.
1123 if (CS.getArgument(0)->getType() != cpyDest->getType())
1126 const PointerType* PT = cast<PointerType>(cpyDest->getType());
1128 // We can only perform the transformation if the size of the memcpy
1129 // is constant and equal to the size of the structure.
1130 ConstantInt* cpyLength = dyn_cast<ConstantInt>(cpy->getLength());
1134 TargetData& TD = getAnalysis<TargetData>();
1135 if (TD.getTypeStoreSize(PT->getElementType()) != cpyLength->getZExtValue())
1138 // For safety, we must ensure that the output parameter of the call only has
1139 // a single use, the memcpy. Otherwise this can introduce an invalid
1141 if (!valueHasOnlyOneUseAfter(CS.getArgument(0), cpy, C))
1144 // We only perform the transformation if it will be profitable.
1145 if (!valueHasOnlyOneUseAfter(cpyDest, cpy, C))
1148 // In addition to knowing that the call does not access the return slot
1149 // in some unexpected manner, which we derive from the noalias attribute,
1150 // we also need to know that it does not sneakily modify the destination
1151 // slot in the caller. We don't have parameter attributes to go by
1152 // for this one, so we just rely on AA to figure it out for us.
1153 AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
1154 if (AA.getModRefInfo(C, cpy->getRawDest(), cpyLength->getZExtValue()) !=
1155 AliasAnalysis::NoModRef)
1158 // If all the checks have passed, then we're alright to do the transformation.
1159 CS.setArgument(0, cpyDest);
1161 // Drop any cached information about the call, because we may have changed
1162 // its dependence information by changing its parameter.
1163 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1164 MD.dropInstruction(C);
1166 // Remove the memcpy
1167 MD.removeInstruction(cpy);
1168 toErase.push_back(cpy);
1173 /// processMemCpy - perform simplication of memcpy's. If we have memcpy A which
1174 /// copies X to Y, and memcpy B which copies Y to Z, then we can rewrite B to be
1175 /// a memcpy from X to Z (or potentially a memmove, depending on circumstances).
1176 /// This allows later passes to remove the first memcpy altogether.
1177 bool GVN::processMemCpy(MemCpyInst* M, MemCpyInst* MDep,
1178 SmallVector<Instruction*, 4>& toErase) {
1179 // We can only transforms memcpy's where the dest of one is the source of the
1181 if (M->getSource() != MDep->getDest())
1184 // Second, the length of the memcpy's must be the same, or the preceeding one
1185 // must be larger than the following one.
1186 ConstantInt* C1 = dyn_cast<ConstantInt>(MDep->getLength());
1187 ConstantInt* C2 = dyn_cast<ConstantInt>(M->getLength());
1191 uint64_t DepSize = C1->getValue().getZExtValue();
1192 uint64_t CpySize = C2->getValue().getZExtValue();
1194 if (DepSize < CpySize)
1197 // Finally, we have to make sure that the dest of the second does not
1198 // alias the source of the first
1199 AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
1200 if (AA.alias(M->getRawDest(), CpySize, MDep->getRawSource(), DepSize) !=
1201 AliasAnalysis::NoAlias)
1203 else if (AA.alias(M->getRawDest(), CpySize, M->getRawSource(), CpySize) !=
1204 AliasAnalysis::NoAlias)
1206 else if (AA.alias(MDep->getRawDest(), DepSize, MDep->getRawSource(), DepSize)
1207 != AliasAnalysis::NoAlias)
1210 // If all checks passed, then we can transform these memcpy's
1211 Function* MemCpyFun = Intrinsic::getDeclaration(
1212 M->getParent()->getParent()->getParent(),
1213 M->getIntrinsicID());
1215 std::vector<Value*> args;
1216 args.push_back(M->getRawDest());
1217 args.push_back(MDep->getRawSource());
1218 args.push_back(M->getLength());
1219 args.push_back(M->getAlignment());
1221 CallInst* C = new CallInst(MemCpyFun, args.begin(), args.end(), "", M);
1223 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1224 if (MD.getDependency(C) == MDep) {
1225 MD.dropInstruction(M);
1226 toErase.push_back(M);
1229 MD.removeInstruction(C);
1230 toErase.push_back(C);
1235 /// processInstruction - When calculating availability, handle an instruction
1236 /// by inserting it into the appropriate sets
1237 bool GVN::processInstruction(Instruction* I,
1238 ValueNumberedSet& currAvail,
1239 DenseMap<Value*, LoadInst*>& lastSeenLoad,
1240 SmallVector<Instruction*, 4>& toErase) {
1241 if (LoadInst* L = dyn_cast<LoadInst>(I)) {
1242 return processLoad(L, lastSeenLoad, toErase);
1243 } else if (MemCpyInst* M = dyn_cast<MemCpyInst>(I)) {
1244 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1246 // The are two possible optimizations we can do for memcpy:
1247 // a) memcpy-memcpy xform which exposes redundance for DSE
1248 // b) call-memcpy xform for sret return slot optimization
1249 Instruction* dep = MD.getDependency(M);
1250 if (dep == MemoryDependenceAnalysis::None ||
1251 dep == MemoryDependenceAnalysis::NonLocal)
1253 if (MemCpyInst *MemCpy = dyn_cast<MemCpyInst>(dep))
1254 return processMemCpy(M, MemCpy, toErase);
1255 if (CallInst* C = dyn_cast<CallInst>(dep))
1256 return performReturnSlotOptzn(M, C, toErase);
1260 unsigned num = VN.lookup_or_add(I);
1262 // Collapse PHI nodes
1263 if (PHINode* p = dyn_cast<PHINode>(I)) {
1264 Value* constVal = CollapsePhi(p);
1267 for (PhiMapType::iterator PI = phiMap.begin(), PE = phiMap.end();
1269 if (PI->second.count(p))
1270 PI->second.erase(p);
1272 p->replaceAllUsesWith(constVal);
1273 toErase.push_back(p);
1275 // Perform value-number based elimination
1276 } else if (currAvail.test(num)) {
1277 Value* repl = find_leader(currAvail, num);
1279 if (CallInst* CI = dyn_cast<CallInst>(I)) {
1280 AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
1281 if (!AA.doesNotAccessMemory(CI)) {
1282 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1283 if (cast<Instruction>(repl)->getParent() != CI->getParent() ||
1284 MD.getDependency(CI) != MD.getDependency(cast<CallInst>(repl))) {
1285 // There must be an intervening may-alias store, so nothing from
1286 // this point on will be able to be replaced with the preceding call
1287 currAvail.erase(repl);
1288 currAvail.insert(I);
1296 MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
1297 MD.removeInstruction(I);
1300 I->replaceAllUsesWith(repl);
1301 toErase.push_back(I);
1303 } else if (!I->isTerminator()) {
1305 currAvail.insert(I);
1311 // GVN::runOnFunction - This is the main transformation entry point for a
1314 bool GVN::runOnFunction(Function& F) {
1315 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1317 bool changed = false;
1318 bool shouldContinue = true;
1320 while (shouldContinue) {
1321 shouldContinue = iterateOnFunction(F);
1322 changed |= shouldContinue;
1329 // GVN::iterateOnFunction - Executes one iteration of GVN
1330 bool GVN::iterateOnFunction(Function &F) {
1331 // Clean out global sets from any previous functions
1333 availableOut.clear();
1336 bool changed_function = false;
1338 DominatorTree &DT = getAnalysis<DominatorTree>();
1340 SmallVector<Instruction*, 4> toErase;
1342 // Top-down walk of the dominator tree
1343 for (df_iterator<DomTreeNode*> DI = df_begin(DT.getRootNode()),
1344 E = df_end(DT.getRootNode()); DI != E; ++DI) {
1346 // Get the set to update for this block
1347 ValueNumberedSet& currAvail = availableOut[DI->getBlock()];
1348 DenseMap<Value*, LoadInst*> lastSeenLoad;
1350 BasicBlock* BB = DI->getBlock();
1352 // A block inherits AVAIL_OUT from its dominator
1353 if (DI->getIDom() != 0)
1354 currAvail = availableOut[DI->getIDom()->getBlock()];
1356 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1358 changed_function |= processInstruction(BI, currAvail,
1359 lastSeenLoad, toErase);
1361 NumGVNInstr += toErase.size();
1363 // Avoid iterator invalidation
1366 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
1367 E = toErase.end(); I != E; ++I) {
1368 (*I)->eraseFromParent();
1375 return changed_function;