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/GlobalVariable.h"
24 #include "llvm/Function.h"
25 #include "llvm/IntrinsicInst.h"
26 #include "llvm/LLVMContext.h"
27 #include "llvm/Operator.h"
28 #include "llvm/Value.h"
29 #include "llvm/ADT/DenseMap.h"
30 #include "llvm/ADT/DepthFirstIterator.h"
31 #include "llvm/ADT/PostOrderIterator.h"
32 #include "llvm/ADT/SmallPtrSet.h"
33 #include "llvm/ADT/SmallVector.h"
34 #include "llvm/ADT/Statistic.h"
35 #include "llvm/Analysis/AliasAnalysis.h"
36 #include "llvm/Analysis/ConstantFolding.h"
37 #include "llvm/Analysis/Dominators.h"
38 #include "llvm/Analysis/Loads.h"
39 #include "llvm/Analysis/MemoryBuiltins.h"
40 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
41 #include "llvm/Analysis/PHITransAddr.h"
42 #include "llvm/Support/CFG.h"
43 #include "llvm/Support/CommandLine.h"
44 #include "llvm/Support/Debug.h"
45 #include "llvm/Support/ErrorHandling.h"
46 #include "llvm/Support/GetElementPtrTypeIterator.h"
47 #include "llvm/Support/IRBuilder.h"
48 #include "llvm/Support/raw_ostream.h"
49 #include "llvm/Target/TargetData.h"
50 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
51 #include "llvm/Transforms/Utils/Local.h"
52 #include "llvm/Transforms/Utils/SSAUpdater.h"
55 STATISTIC(NumGVNInstr, "Number of instructions deleted");
56 STATISTIC(NumGVNLoad, "Number of loads deleted");
57 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
58 STATISTIC(NumGVNBlocks, "Number of blocks merged");
59 STATISTIC(NumPRELoad, "Number of loads PRE'd");
61 static cl::opt<bool> EnablePRE("enable-pre",
62 cl::init(true), cl::Hidden);
63 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
64 static cl::opt<bool> EnableFullLoadPRE("enable-full-load-pre", cl::init(false));
66 //===----------------------------------------------------------------------===//
68 //===----------------------------------------------------------------------===//
70 /// This class holds the mapping between values and value numbers. It is used
71 /// as an efficient mechanism to determine the expression-wise equivalence of
75 enum ExpressionOpcode {
76 ADD = Instruction::Add,
77 FADD = Instruction::FAdd,
78 SUB = Instruction::Sub,
79 FSUB = Instruction::FSub,
80 MUL = Instruction::Mul,
81 FMUL = Instruction::FMul,
82 UDIV = Instruction::UDiv,
83 SDIV = Instruction::SDiv,
84 FDIV = Instruction::FDiv,
85 UREM = Instruction::URem,
86 SREM = Instruction::SRem,
87 FREM = Instruction::FRem,
88 SHL = Instruction::Shl,
89 LSHR = Instruction::LShr,
90 ASHR = Instruction::AShr,
91 AND = Instruction::And,
93 XOR = Instruction::Xor,
94 TRUNC = Instruction::Trunc,
95 ZEXT = Instruction::ZExt,
96 SEXT = Instruction::SExt,
97 FPTOUI = Instruction::FPToUI,
98 FPTOSI = Instruction::FPToSI,
99 UITOFP = Instruction::UIToFP,
100 SITOFP = Instruction::SIToFP,
101 FPTRUNC = Instruction::FPTrunc,
102 FPEXT = Instruction::FPExt,
103 PTRTOINT = Instruction::PtrToInt,
104 INTTOPTR = Instruction::IntToPtr,
105 BITCAST = Instruction::BitCast,
106 ICMPEQ, ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
107 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
108 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
109 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
110 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
111 SHUFFLE, SELECT, GEP, CALL, CONSTANT,
112 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE };
114 ExpressionOpcode opcode;
116 SmallVector<uint32_t, 4> varargs;
120 Expression(ExpressionOpcode o) : opcode(o) { }
122 bool operator==(const Expression &other) const {
123 if (opcode != other.opcode)
125 else if (opcode == EMPTY || opcode == TOMBSTONE)
127 else if (type != other.type)
129 else if (function != other.function)
132 if (varargs.size() != other.varargs.size())
135 for (size_t i = 0; i < varargs.size(); ++i)
136 if (varargs[i] != other.varargs[i])
143 bool operator!=(const Expression &other) const {
144 return !(*this == other);
150 DenseMap<Value*, uint32_t> valueNumbering;
151 DenseMap<Expression, uint32_t> expressionNumbering;
153 MemoryDependenceAnalysis* MD;
156 uint32_t nextValueNumber;
158 Expression::ExpressionOpcode getOpcode(CmpInst* C);
159 Expression create_expression(BinaryOperator* BO);
160 Expression create_expression(CmpInst* C);
161 Expression create_expression(ShuffleVectorInst* V);
162 Expression create_expression(ExtractElementInst* C);
163 Expression create_expression(InsertElementInst* V);
164 Expression create_expression(SelectInst* V);
165 Expression create_expression(CastInst* C);
166 Expression create_expression(GetElementPtrInst* G);
167 Expression create_expression(CallInst* C);
168 Expression create_expression(Constant* C);
169 Expression create_expression(ExtractValueInst* C);
170 Expression create_expression(InsertValueInst* C);
172 uint32_t lookup_or_add_call(CallInst* C);
174 ValueTable() : nextValueNumber(1) { }
175 uint32_t lookup_or_add(Value *V);
176 uint32_t lookup(Value *V) const;
177 void add(Value *V, uint32_t num);
179 void erase(Value *v);
181 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
182 AliasAnalysis *getAliasAnalysis() const { return AA; }
183 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
184 void setDomTree(DominatorTree* D) { DT = D; }
185 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
186 void verifyRemoved(const Value *) const;
191 template <> struct DenseMapInfo<Expression> {
192 static inline Expression getEmptyKey() {
193 return Expression(Expression::EMPTY);
196 static inline Expression getTombstoneKey() {
197 return Expression(Expression::TOMBSTONE);
200 static unsigned getHashValue(const Expression e) {
201 unsigned hash = e.opcode;
203 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
204 (unsigned)((uintptr_t)e.type >> 9));
206 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
207 E = e.varargs.end(); I != E; ++I)
208 hash = *I + hash * 37;
210 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
211 (unsigned)((uintptr_t)e.function >> 9)) +
216 static bool isEqual(const Expression &LHS, const Expression &RHS) {
222 struct isPodLike<Expression> { static const bool value = true; };
226 //===----------------------------------------------------------------------===//
227 // ValueTable Internal Functions
228 //===----------------------------------------------------------------------===//
230 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
231 if (isa<ICmpInst>(C)) {
232 switch (C->getPredicate()) {
233 default: // THIS SHOULD NEVER HAPPEN
234 llvm_unreachable("Comparison with unknown predicate?");
235 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
236 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
237 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
238 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
239 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
240 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
241 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
242 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
243 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
244 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
247 switch (C->getPredicate()) {
248 default: // THIS SHOULD NEVER HAPPEN
249 llvm_unreachable("Comparison with unknown predicate?");
250 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
251 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
252 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
253 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
254 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
255 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
256 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
257 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
258 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
259 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
260 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
261 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
262 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
263 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
268 Expression ValueTable::create_expression(CallInst* C) {
271 e.type = C->getType();
272 e.function = C->getCalledFunction();
273 e.opcode = Expression::CALL;
276 for (CallInst::op_iterator I = CS.arg_begin(), E = CS.arg_end();
278 e.varargs.push_back(lookup_or_add(*I));
283 Expression ValueTable::create_expression(BinaryOperator* BO) {
285 e.varargs.push_back(lookup_or_add(BO->getOperand(0)));
286 e.varargs.push_back(lookup_or_add(BO->getOperand(1)));
288 e.type = BO->getType();
289 e.opcode = static_cast<Expression::ExpressionOpcode>(BO->getOpcode());
294 Expression ValueTable::create_expression(CmpInst* C) {
297 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
298 e.varargs.push_back(lookup_or_add(C->getOperand(1)));
300 e.type = C->getType();
301 e.opcode = getOpcode(C);
306 Expression ValueTable::create_expression(CastInst* C) {
309 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
311 e.type = C->getType();
312 e.opcode = static_cast<Expression::ExpressionOpcode>(C->getOpcode());
317 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
320 e.varargs.push_back(lookup_or_add(S->getOperand(0)));
321 e.varargs.push_back(lookup_or_add(S->getOperand(1)));
322 e.varargs.push_back(lookup_or_add(S->getOperand(2)));
324 e.type = S->getType();
325 e.opcode = Expression::SHUFFLE;
330 Expression ValueTable::create_expression(ExtractElementInst* E) {
333 e.varargs.push_back(lookup_or_add(E->getOperand(0)));
334 e.varargs.push_back(lookup_or_add(E->getOperand(1)));
336 e.type = E->getType();
337 e.opcode = Expression::EXTRACT;
342 Expression ValueTable::create_expression(InsertElementInst* I) {
345 e.varargs.push_back(lookup_or_add(I->getOperand(0)));
346 e.varargs.push_back(lookup_or_add(I->getOperand(1)));
347 e.varargs.push_back(lookup_or_add(I->getOperand(2)));
349 e.type = I->getType();
350 e.opcode = Expression::INSERT;
355 Expression ValueTable::create_expression(SelectInst* I) {
358 e.varargs.push_back(lookup_or_add(I->getCondition()));
359 e.varargs.push_back(lookup_or_add(I->getTrueValue()));
360 e.varargs.push_back(lookup_or_add(I->getFalseValue()));
362 e.type = I->getType();
363 e.opcode = Expression::SELECT;
368 Expression ValueTable::create_expression(GetElementPtrInst* G) {
371 e.varargs.push_back(lookup_or_add(G->getPointerOperand()));
373 e.type = G->getType();
374 e.opcode = Expression::GEP;
376 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
378 e.varargs.push_back(lookup_or_add(*I));
383 Expression ValueTable::create_expression(ExtractValueInst* E) {
386 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
387 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
389 e.varargs.push_back(*II);
391 e.type = E->getType();
392 e.opcode = Expression::EXTRACTVALUE;
397 Expression ValueTable::create_expression(InsertValueInst* E) {
400 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
401 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand()));
402 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
404 e.varargs.push_back(*II);
406 e.type = E->getType();
407 e.opcode = Expression::INSERTVALUE;
412 //===----------------------------------------------------------------------===//
413 // ValueTable External Functions
414 //===----------------------------------------------------------------------===//
416 /// add - Insert a value into the table with a specified value number.
417 void ValueTable::add(Value *V, uint32_t num) {
418 valueNumbering.insert(std::make_pair(V, num));
421 uint32_t ValueTable::lookup_or_add_call(CallInst* C) {
422 if (AA->doesNotAccessMemory(C)) {
423 Expression exp = create_expression(C);
424 uint32_t& e = expressionNumbering[exp];
425 if (!e) e = nextValueNumber++;
426 valueNumbering[C] = e;
428 } else if (AA->onlyReadsMemory(C)) {
429 Expression exp = create_expression(C);
430 uint32_t& e = expressionNumbering[exp];
432 e = nextValueNumber++;
433 valueNumbering[C] = e;
437 e = nextValueNumber++;
438 valueNumbering[C] = e;
442 MemDepResult local_dep = MD->getDependency(C);
444 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
445 valueNumbering[C] = nextValueNumber;
446 return nextValueNumber++;
449 if (local_dep.isDef()) {
450 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
452 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) {
453 valueNumbering[C] = nextValueNumber;
454 return nextValueNumber++;
457 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
458 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
459 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i));
461 valueNumbering[C] = nextValueNumber;
462 return nextValueNumber++;
466 uint32_t v = lookup_or_add(local_cdep);
467 valueNumbering[C] = v;
472 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
473 MD->getNonLocalCallDependency(CallSite(C));
474 // FIXME: call/call dependencies for readonly calls should return def, not
475 // clobber! Move the checking logic to MemDep!
478 // Check to see if we have a single dominating call instruction that is
480 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
481 const NonLocalDepEntry *I = &deps[i];
482 // Ignore non-local dependencies.
483 if (I->getResult().isNonLocal())
486 // We don't handle non-depedencies. If we already have a call, reject
487 // instruction dependencies.
488 if (I->getResult().isClobber() || cdep != 0) {
493 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
494 // FIXME: All duplicated with non-local case.
495 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
496 cdep = NonLocalDepCall;
505 valueNumbering[C] = nextValueNumber;
506 return nextValueNumber++;
509 if (cdep->getNumArgOperands() != C->getNumArgOperands()) {
510 valueNumbering[C] = nextValueNumber;
511 return nextValueNumber++;
513 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
514 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
515 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i));
517 valueNumbering[C] = nextValueNumber;
518 return nextValueNumber++;
522 uint32_t v = lookup_or_add(cdep);
523 valueNumbering[C] = v;
527 valueNumbering[C] = nextValueNumber;
528 return nextValueNumber++;
532 /// lookup_or_add - Returns the value number for the specified value, assigning
533 /// it a new number if it did not have one before.
534 uint32_t ValueTable::lookup_or_add(Value *V) {
535 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
536 if (VI != valueNumbering.end())
539 if (!isa<Instruction>(V)) {
540 valueNumbering[V] = nextValueNumber;
541 return nextValueNumber++;
544 Instruction* I = cast<Instruction>(V);
546 switch (I->getOpcode()) {
547 case Instruction::Call:
548 return lookup_or_add_call(cast<CallInst>(I));
549 case Instruction::Add:
550 case Instruction::FAdd:
551 case Instruction::Sub:
552 case Instruction::FSub:
553 case Instruction::Mul:
554 case Instruction::FMul:
555 case Instruction::UDiv:
556 case Instruction::SDiv:
557 case Instruction::FDiv:
558 case Instruction::URem:
559 case Instruction::SRem:
560 case Instruction::FRem:
561 case Instruction::Shl:
562 case Instruction::LShr:
563 case Instruction::AShr:
564 case Instruction::And:
565 case Instruction::Or :
566 case Instruction::Xor:
567 exp = create_expression(cast<BinaryOperator>(I));
569 case Instruction::ICmp:
570 case Instruction::FCmp:
571 exp = create_expression(cast<CmpInst>(I));
573 case Instruction::Trunc:
574 case Instruction::ZExt:
575 case Instruction::SExt:
576 case Instruction::FPToUI:
577 case Instruction::FPToSI:
578 case Instruction::UIToFP:
579 case Instruction::SIToFP:
580 case Instruction::FPTrunc:
581 case Instruction::FPExt:
582 case Instruction::PtrToInt:
583 case Instruction::IntToPtr:
584 case Instruction::BitCast:
585 exp = create_expression(cast<CastInst>(I));
587 case Instruction::Select:
588 exp = create_expression(cast<SelectInst>(I));
590 case Instruction::ExtractElement:
591 exp = create_expression(cast<ExtractElementInst>(I));
593 case Instruction::InsertElement:
594 exp = create_expression(cast<InsertElementInst>(I));
596 case Instruction::ShuffleVector:
597 exp = create_expression(cast<ShuffleVectorInst>(I));
599 case Instruction::ExtractValue:
600 exp = create_expression(cast<ExtractValueInst>(I));
602 case Instruction::InsertValue:
603 exp = create_expression(cast<InsertValueInst>(I));
605 case Instruction::GetElementPtr:
606 exp = create_expression(cast<GetElementPtrInst>(I));
609 valueNumbering[V] = nextValueNumber;
610 return nextValueNumber++;
613 uint32_t& e = expressionNumbering[exp];
614 if (!e) e = nextValueNumber++;
615 valueNumbering[V] = e;
619 /// lookup - Returns the value number of the specified value. Fails if
620 /// the value has not yet been numbered.
621 uint32_t ValueTable::lookup(Value *V) const {
622 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
623 assert(VI != valueNumbering.end() && "Value not numbered?");
627 /// clear - Remove all entries from the ValueTable
628 void ValueTable::clear() {
629 valueNumbering.clear();
630 expressionNumbering.clear();
634 /// erase - Remove a value from the value numbering
635 void ValueTable::erase(Value *V) {
636 valueNumbering.erase(V);
639 /// verifyRemoved - Verify that the value is removed from all internal data
641 void ValueTable::verifyRemoved(const Value *V) const {
642 for (DenseMap<Value*, uint32_t>::const_iterator
643 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
644 assert(I->first != V && "Inst still occurs in value numbering map!");
648 //===----------------------------------------------------------------------===//
650 //===----------------------------------------------------------------------===//
653 struct ValueNumberScope {
654 ValueNumberScope* parent;
655 DenseMap<uint32_t, Value*> table;
657 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
663 class GVN : public FunctionPass {
664 bool runOnFunction(Function &F);
666 static char ID; // Pass identification, replacement for typeid
667 explicit GVN(bool noloads = false)
668 : FunctionPass(&ID), NoLoads(noloads), MD(0) { }
672 MemoryDependenceAnalysis *MD;
676 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
678 // List of critical edges to be split between iterations.
679 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
681 // This transformation requires dominator postdominator info
682 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
683 AU.addRequired<DominatorTree>();
685 AU.addRequired<MemoryDependenceAnalysis>();
686 AU.addRequired<AliasAnalysis>();
688 AU.addPreserved<DominatorTree>();
689 AU.addPreserved<AliasAnalysis>();
693 // FIXME: eliminate or document these better
694 bool processLoad(LoadInst* L,
695 SmallVectorImpl<Instruction*> &toErase);
696 bool processInstruction(Instruction *I,
697 SmallVectorImpl<Instruction*> &toErase);
698 bool processNonLocalLoad(LoadInst* L,
699 SmallVectorImpl<Instruction*> &toErase);
700 bool processBlock(BasicBlock *BB);
701 void dump(DenseMap<uint32_t, Value*>& d);
702 bool iterateOnFunction(Function &F);
703 Value *CollapsePhi(PHINode* p);
704 bool performPRE(Function& F);
705 Value *lookupNumber(BasicBlock *BB, uint32_t num);
706 void cleanupGlobalSets();
707 void verifyRemoved(const Instruction *I) const;
708 bool splitCriticalEdges();
714 // createGVNPass - The public interface to this file...
715 FunctionPass *llvm::createGVNPass(bool NoLoads) {
716 return new GVN(NoLoads);
719 static RegisterPass<GVN> X("gvn",
720 "Global Value Numbering");
722 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
724 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
725 E = d.end(); I != E; ++I) {
726 errs() << I->first << "\n";
732 static bool isSafeReplacement(PHINode* p, Instruction *inst) {
733 if (!isa<PHINode>(inst))
736 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
738 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
739 if (use_phi->getParent() == inst->getParent())
745 Value *GVN::CollapsePhi(PHINode *PN) {
746 Value *ConstVal = PN->hasConstantValue(DT);
747 if (!ConstVal) return 0;
749 Instruction *Inst = dyn_cast<Instruction>(ConstVal);
753 if (DT->dominates(Inst, PN))
754 if (isSafeReplacement(PN, Inst))
759 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
760 /// we're analyzing is fully available in the specified block. As we go, keep
761 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
762 /// map is actually a tri-state map with the following values:
763 /// 0) we know the block *is not* fully available.
764 /// 1) we know the block *is* fully available.
765 /// 2) we do not know whether the block is fully available or not, but we are
766 /// currently speculating that it will be.
767 /// 3) we are speculating for this block and have used that to speculate for
769 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
770 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
771 // Optimistically assume that the block is fully available and check to see
772 // if we already know about this block in one lookup.
773 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
774 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
776 // If the entry already existed for this block, return the precomputed value.
778 // If this is a speculative "available" value, mark it as being used for
779 // speculation of other blocks.
780 if (IV.first->second == 2)
781 IV.first->second = 3;
782 return IV.first->second != 0;
785 // Otherwise, see if it is fully available in all predecessors.
786 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
788 // If this block has no predecessors, it isn't live-in here.
790 goto SpeculationFailure;
792 for (; PI != PE; ++PI)
793 // If the value isn't fully available in one of our predecessors, then it
794 // isn't fully available in this block either. Undo our previous
795 // optimistic assumption and bail out.
796 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
797 goto SpeculationFailure;
801 // SpeculationFailure - If we get here, we found out that this is not, after
802 // all, a fully-available block. We have a problem if we speculated on this and
803 // used the speculation to mark other blocks as available.
805 char &BBVal = FullyAvailableBlocks[BB];
807 // If we didn't speculate on this, just return with it set to false.
813 // If we did speculate on this value, we could have blocks set to 1 that are
814 // incorrect. Walk the (transitive) successors of this block and mark them as
816 SmallVector<BasicBlock*, 32> BBWorklist;
817 BBWorklist.push_back(BB);
820 BasicBlock *Entry = BBWorklist.pop_back_val();
821 // Note that this sets blocks to 0 (unavailable) if they happen to not
822 // already be in FullyAvailableBlocks. This is safe.
823 char &EntryVal = FullyAvailableBlocks[Entry];
824 if (EntryVal == 0) continue; // Already unavailable.
826 // Mark as unavailable.
829 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
830 BBWorklist.push_back(*I);
831 } while (!BBWorklist.empty());
837 /// CanCoerceMustAliasedValueToLoad - Return true if
838 /// CoerceAvailableValueToLoadType will succeed.
839 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
841 const TargetData &TD) {
842 // If the loaded or stored value is an first class array or struct, don't try
843 // to transform them. We need to be able to bitcast to integer.
844 if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
845 StoredVal->getType()->isStructTy() ||
846 StoredVal->getType()->isArrayTy())
849 // The store has to be at least as big as the load.
850 if (TD.getTypeSizeInBits(StoredVal->getType()) <
851 TD.getTypeSizeInBits(LoadTy))
858 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
859 /// then a load from a must-aliased pointer of a different type, try to coerce
860 /// the stored value. LoadedTy is the type of the load we want to replace and
861 /// InsertPt is the place to insert new instructions.
863 /// If we can't do it, return null.
864 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
865 const Type *LoadedTy,
866 Instruction *InsertPt,
867 const TargetData &TD) {
868 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
871 const Type *StoredValTy = StoredVal->getType();
873 uint64_t StoreSize = TD.getTypeStoreSizeInBits(StoredValTy);
874 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
876 // If the store and reload are the same size, we can always reuse it.
877 if (StoreSize == LoadSize) {
878 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) {
879 // Pointer to Pointer -> use bitcast.
880 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
883 // Convert source pointers to integers, which can be bitcast.
884 if (StoredValTy->isPointerTy()) {
885 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
886 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
889 const Type *TypeToCastTo = LoadedTy;
890 if (TypeToCastTo->isPointerTy())
891 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
893 if (StoredValTy != TypeToCastTo)
894 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
896 // Cast to pointer if the load needs a pointer type.
897 if (LoadedTy->isPointerTy())
898 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
903 // If the loaded value is smaller than the available value, then we can
904 // extract out a piece from it. If the available value is too small, then we
905 // can't do anything.
906 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
908 // Convert source pointers to integers, which can be manipulated.
909 if (StoredValTy->isPointerTy()) {
910 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
911 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
914 // Convert vectors and fp to integer, which can be manipulated.
915 if (!StoredValTy->isIntegerTy()) {
916 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
917 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
920 // If this is a big-endian system, we need to shift the value down to the low
921 // bits so that a truncate will work.
922 if (TD.isBigEndian()) {
923 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
924 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
927 // Truncate the integer to the right size now.
928 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
929 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
931 if (LoadedTy == NewIntTy)
934 // If the result is a pointer, inttoptr.
935 if (LoadedTy->isPointerTy())
936 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
938 // Otherwise, bitcast.
939 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
942 /// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
943 /// be expressed as a base pointer plus a constant offset. Return the base and
944 /// offset to the caller.
945 static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
946 const TargetData &TD) {
947 Operator *PtrOp = dyn_cast<Operator>(Ptr);
948 if (PtrOp == 0) return Ptr;
950 // Just look through bitcasts.
951 if (PtrOp->getOpcode() == Instruction::BitCast)
952 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
954 // If this is a GEP with constant indices, we can look through it.
955 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
956 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
958 gep_type_iterator GTI = gep_type_begin(GEP);
959 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
961 ConstantInt *OpC = cast<ConstantInt>(*I);
962 if (OpC->isZero()) continue;
964 // Handle a struct and array indices which add their offset to the pointer.
965 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
966 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
968 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
969 Offset += OpC->getSExtValue()*Size;
973 // Re-sign extend from the pointer size if needed to get overflow edge cases
975 unsigned PtrSize = TD.getPointerSizeInBits();
977 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
979 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
983 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
984 /// memdep query of a load that ends up being a clobbering memory write (store,
985 /// memset, memcpy, memmove). This means that the write *may* provide bits used
986 /// by the load but we can't be sure because the pointers don't mustalias.
988 /// Check this case to see if there is anything more we can do before we give
989 /// up. This returns -1 if we have to give up, or a byte number in the stored
990 /// value of the piece that feeds the load.
991 static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
993 uint64_t WriteSizeInBits,
994 const TargetData &TD) {
995 // If the loaded or stored value is an first class array or struct, don't try
996 // to transform them. We need to be able to bitcast to integer.
997 if (LoadTy->isStructTy() || LoadTy->isArrayTy())
1000 int64_t StoreOffset = 0, LoadOffset = 0;
1001 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
1003 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
1004 if (StoreBase != LoadBase)
1007 // If the load and store are to the exact same address, they should have been
1008 // a must alias. AA must have gotten confused.
1009 // FIXME: Study to see if/when this happens. One case is forwarding a memset
1010 // to a load from the base of the memset.
1012 if (LoadOffset == StoreOffset) {
1013 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
1014 << "Base = " << *StoreBase << "\n"
1015 << "Store Ptr = " << *WritePtr << "\n"
1016 << "Store Offs = " << StoreOffset << "\n"
1017 << "Load Ptr = " << *LoadPtr << "\n";
1022 // If the load and store don't overlap at all, the store doesn't provide
1023 // anything to the load. In this case, they really don't alias at all, AA
1024 // must have gotten confused.
1025 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
1026 // remove this check, as it is duplicated with what we have below.
1027 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
1029 if ((WriteSizeInBits & 7) | (LoadSize & 7))
1031 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
1035 bool isAAFailure = false;
1036 if (StoreOffset < LoadOffset)
1037 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
1039 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
1043 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"
1044 << "Base = " << *StoreBase << "\n"
1045 << "Store Ptr = " << *WritePtr << "\n"
1046 << "Store Offs = " << StoreOffset << "\n"
1047 << "Load Ptr = " << *LoadPtr << "\n";
1053 // If the Load isn't completely contained within the stored bits, we don't
1054 // have all the bits to feed it. We could do something crazy in the future
1055 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1057 if (StoreOffset > LoadOffset ||
1058 StoreOffset+StoreSize < LoadOffset+LoadSize)
1061 // Okay, we can do this transformation. Return the number of bytes into the
1062 // store that the load is.
1063 return LoadOffset-StoreOffset;
1066 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1067 /// memdep query of a load that ends up being a clobbering store.
1068 static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr,
1070 const TargetData &TD) {
1071 // Cannot handle reading from store of first-class aggregate yet.
1072 if (DepSI->getOperand(0)->getType()->isStructTy() ||
1073 DepSI->getOperand(0)->getType()->isArrayTy())
1076 Value *StorePtr = DepSI->getPointerOperand();
1077 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType());
1078 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1079 StorePtr, StoreSize, TD);
1082 static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr,
1084 const TargetData &TD) {
1085 // If the mem operation is a non-constant size, we can't handle it.
1086 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1087 if (SizeCst == 0) return -1;
1088 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1090 // If this is memset, we just need to see if the offset is valid in the size
1092 if (MI->getIntrinsicID() == Intrinsic::memset)
1093 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1096 // If we have a memcpy/memmove, the only case we can handle is if this is a
1097 // copy from constant memory. In that case, we can read directly from the
1099 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1101 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1102 if (Src == 0) return -1;
1104 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1105 if (GV == 0 || !GV->isConstant()) return -1;
1107 // See if the access is within the bounds of the transfer.
1108 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1109 MI->getDest(), MemSizeInBits, TD);
1113 // Otherwise, see if we can constant fold a load from the constant with the
1114 // offset applied as appropriate.
1115 Src = ConstantExpr::getBitCast(Src,
1116 llvm::Type::getInt8PtrTy(Src->getContext()));
1117 Constant *OffsetCst =
1118 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1119 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1120 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1121 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1127 /// GetStoreValueForLoad - This function is called when we have a
1128 /// memdep query of a load that ends up being a clobbering store. This means
1129 /// that the store *may* provide bits used by the load but we can't be sure
1130 /// because the pointers don't mustalias. Check this case to see if there is
1131 /// anything more we can do before we give up.
1132 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1134 Instruction *InsertPt, const TargetData &TD){
1135 LLVMContext &Ctx = SrcVal->getType()->getContext();
1137 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8;
1138 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8;
1140 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1142 // Compute which bits of the stored value are being used by the load. Convert
1143 // to an integer type to start with.
1144 if (SrcVal->getType()->isPointerTy())
1145 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp");
1146 if (!SrcVal->getType()->isIntegerTy())
1147 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1150 // Shift the bits to the least significant depending on endianness.
1152 if (TD.isLittleEndian())
1153 ShiftAmt = Offset*8;
1155 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1158 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp");
1160 if (LoadSize != StoreSize)
1161 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1164 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1167 /// GetMemInstValueForLoad - This function is called when we have a
1168 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1169 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1170 const Type *LoadTy, Instruction *InsertPt,
1171 const TargetData &TD){
1172 LLVMContext &Ctx = LoadTy->getContext();
1173 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1175 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1177 // We know that this method is only called when the mem transfer fully
1178 // provides the bits for the load.
1179 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1180 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1181 // independently of what the offset is.
1182 Value *Val = MSI->getValue();
1184 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1186 Value *OneElt = Val;
1188 // Splat the value out to the right number of bits.
1189 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1190 // If we can double the number of bytes set, do it.
1191 if (NumBytesSet*2 <= LoadSize) {
1192 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1193 Val = Builder.CreateOr(Val, ShVal);
1198 // Otherwise insert one byte at a time.
1199 Value *ShVal = Builder.CreateShl(Val, 1*8);
1200 Val = Builder.CreateOr(OneElt, ShVal);
1204 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1207 // Otherwise, this is a memcpy/memmove from a constant global.
1208 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1209 Constant *Src = cast<Constant>(MTI->getSource());
1211 // Otherwise, see if we can constant fold a load from the constant with the
1212 // offset applied as appropriate.
1213 Src = ConstantExpr::getBitCast(Src,
1214 llvm::Type::getInt8PtrTy(Src->getContext()));
1215 Constant *OffsetCst =
1216 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1217 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1218 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1219 return ConstantFoldLoadFromConstPtr(Src, &TD);
1224 struct AvailableValueInBlock {
1225 /// BB - The basic block in question.
1228 SimpleVal, // A simple offsetted value that is accessed.
1229 MemIntrin // A memory intrinsic which is loaded from.
1232 /// V - The value that is live out of the block.
1233 PointerIntPair<Value *, 1, ValType> Val;
1235 /// Offset - The byte offset in Val that is interesting for the load query.
1238 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1239 unsigned Offset = 0) {
1240 AvailableValueInBlock Res;
1242 Res.Val.setPointer(V);
1243 Res.Val.setInt(SimpleVal);
1244 Res.Offset = Offset;
1248 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1249 unsigned Offset = 0) {
1250 AvailableValueInBlock Res;
1252 Res.Val.setPointer(MI);
1253 Res.Val.setInt(MemIntrin);
1254 Res.Offset = Offset;
1258 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1259 Value *getSimpleValue() const {
1260 assert(isSimpleValue() && "Wrong accessor");
1261 return Val.getPointer();
1264 MemIntrinsic *getMemIntrinValue() const {
1265 assert(!isSimpleValue() && "Wrong accessor");
1266 return cast<MemIntrinsic>(Val.getPointer());
1269 /// MaterializeAdjustedValue - Emit code into this block to adjust the value
1270 /// defined here to the specified type. This handles various coercion cases.
1271 Value *MaterializeAdjustedValue(const Type *LoadTy,
1272 const TargetData *TD) const {
1274 if (isSimpleValue()) {
1275 Res = getSimpleValue();
1276 if (Res->getType() != LoadTy) {
1277 assert(TD && "Need target data to handle type mismatch case");
1278 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(),
1281 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1282 << *getSimpleValue() << '\n'
1283 << *Res << '\n' << "\n\n\n");
1286 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset,
1287 LoadTy, BB->getTerminator(), *TD);
1288 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1289 << " " << *getMemIntrinValue() << '\n'
1290 << *Res << '\n' << "\n\n\n");
1298 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1299 /// construct SSA form, allowing us to eliminate LI. This returns the value
1300 /// that should be used at LI's definition site.
1301 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1302 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1303 const TargetData *TD,
1304 const DominatorTree &DT,
1305 AliasAnalysis *AA) {
1306 // Check for the fully redundant, dominating load case. In this case, we can
1307 // just use the dominating value directly.
1308 if (ValuesPerBlock.size() == 1 &&
1309 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent()))
1310 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD);
1312 // Otherwise, we have to construct SSA form.
1313 SmallVector<PHINode*, 8> NewPHIs;
1314 SSAUpdater SSAUpdate(&NewPHIs);
1315 SSAUpdate.Initialize(LI);
1317 const Type *LoadTy = LI->getType();
1319 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1320 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1321 BasicBlock *BB = AV.BB;
1323 if (SSAUpdate.HasValueForBlock(BB))
1326 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD));
1329 // Perform PHI construction.
1330 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1332 // If new PHI nodes were created, notify alias analysis.
1333 if (V->getType()->isPointerTy())
1334 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1335 AA->copyValue(LI, NewPHIs[i]);
1340 static bool isLifetimeStart(const Instruction *Inst) {
1341 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1342 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1346 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1347 /// non-local by performing PHI construction.
1348 bool GVN::processNonLocalLoad(LoadInst *LI,
1349 SmallVectorImpl<Instruction*> &toErase) {
1350 // Find the non-local dependencies of the load.
1351 SmallVector<NonLocalDepResult, 64> Deps;
1352 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
1354 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: "
1355 // << Deps.size() << *LI << '\n');
1357 // If we had to process more than one hundred blocks to find the
1358 // dependencies, this load isn't worth worrying about. Optimizing
1359 // it will be too expensive.
1360 if (Deps.size() > 100)
1363 // If we had a phi translation failure, we'll have a single entry which is a
1364 // clobber in the current block. Reject this early.
1365 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) {
1367 dbgs() << "GVN: non-local load ";
1368 WriteAsOperand(dbgs(), LI);
1369 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n';
1374 // Filter out useless results (non-locals, etc). Keep track of the blocks
1375 // where we have a value available in repl, also keep track of whether we see
1376 // dependencies that produce an unknown value for the load (such as a call
1377 // that could potentially clobber the load).
1378 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1379 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1381 const TargetData *TD = 0;
1383 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1384 BasicBlock *DepBB = Deps[i].getBB();
1385 MemDepResult DepInfo = Deps[i].getResult();
1387 if (DepInfo.isClobber()) {
1388 // The address being loaded in this non-local block may not be the same as
1389 // the pointer operand of the load if PHI translation occurs. Make sure
1390 // to consider the right address.
1391 Value *Address = Deps[i].getAddress();
1393 // If the dependence is to a store that writes to a superset of the bits
1394 // read by the load, we can extract the bits we need for the load from the
1396 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1398 TD = getAnalysisIfAvailable<TargetData>();
1399 if (TD && Address) {
1400 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1403 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1404 DepSI->getOperand(0),
1411 // If the clobbering value is a memset/memcpy/memmove, see if we can
1412 // forward a value on from it.
1413 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1415 TD = getAnalysisIfAvailable<TargetData>();
1416 if (TD && Address) {
1417 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1420 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1427 UnavailableBlocks.push_back(DepBB);
1431 Instruction *DepInst = DepInfo.getInst();
1433 // Loading the allocation -> undef.
1434 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1435 // Loading immediately after lifetime begin -> undef.
1436 isLifetimeStart(DepInst)) {
1437 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1438 UndefValue::get(LI->getType())));
1442 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1443 // Reject loads and stores that are to the same address but are of
1444 // different types if we have to.
1445 if (S->getOperand(0)->getType() != LI->getType()) {
1447 TD = getAnalysisIfAvailable<TargetData>();
1449 // If the stored value is larger or equal to the loaded value, we can
1451 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0),
1452 LI->getType(), *TD)) {
1453 UnavailableBlocks.push_back(DepBB);
1458 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1463 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1464 // If the types mismatch and we can't handle it, reject reuse of the load.
1465 if (LD->getType() != LI->getType()) {
1467 TD = getAnalysisIfAvailable<TargetData>();
1469 // If the stored value is larger or equal to the loaded value, we can
1471 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1472 UnavailableBlocks.push_back(DepBB);
1476 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD));
1480 UnavailableBlocks.push_back(DepBB);
1484 // If we have no predecessors that produce a known value for this load, exit
1486 if (ValuesPerBlock.empty()) return false;
1488 // If all of the instructions we depend on produce a known value for this
1489 // load, then it is fully redundant and we can use PHI insertion to compute
1490 // its value. Insert PHIs and remove the fully redundant value now.
1491 if (UnavailableBlocks.empty()) {
1492 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1494 // Perform PHI construction.
1495 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1496 VN.getAliasAnalysis());
1497 LI->replaceAllUsesWith(V);
1499 if (isa<PHINode>(V))
1501 if (V->getType()->isPointerTy())
1502 MD->invalidateCachedPointerInfo(V);
1504 toErase.push_back(LI);
1509 if (!EnablePRE || !EnableLoadPRE)
1512 // Okay, we have *some* definitions of the value. This means that the value
1513 // is available in some of our (transitive) predecessors. Lets think about
1514 // doing PRE of this load. This will involve inserting a new load into the
1515 // predecessor when it's not available. We could do this in general, but
1516 // prefer to not increase code size. As such, we only do this when we know
1517 // that we only have to insert *one* load (which means we're basically moving
1518 // the load, not inserting a new one).
1520 SmallPtrSet<BasicBlock *, 4> Blockers;
1521 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1522 Blockers.insert(UnavailableBlocks[i]);
1524 // Lets find first basic block with more than one predecessor. Walk backwards
1525 // through predecessors if needed.
1526 BasicBlock *LoadBB = LI->getParent();
1527 BasicBlock *TmpBB = LoadBB;
1529 bool isSinglePred = false;
1530 bool allSingleSucc = true;
1531 while (TmpBB->getSinglePredecessor()) {
1532 isSinglePred = true;
1533 TmpBB = TmpBB->getSinglePredecessor();
1534 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1536 if (Blockers.count(TmpBB))
1538 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1539 allSingleSucc = false;
1545 // If we have a repl set with LI itself in it, this means we have a loop where
1546 // at least one of the values is LI. Since this means that we won't be able
1547 // to eliminate LI even if we insert uses in the other predecessors, we will
1548 // end up increasing code size. Reject this by scanning for LI.
1549 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1550 if (ValuesPerBlock[i].isSimpleValue() &&
1551 ValuesPerBlock[i].getSimpleValue() == LI) {
1552 // Skip cases where LI is the only definition, even for EnableFullLoadPRE.
1553 if (!EnableFullLoadPRE || e == 1)
1558 // FIXME: It is extremely unclear what this loop is doing, other than
1559 // artificially restricting loadpre.
1562 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1563 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1564 if (AV.isSimpleValue())
1565 // "Hot" Instruction is in some loop (because it dominates its dep.
1567 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1568 if (DT->dominates(LI, I)) {
1574 // We are interested only in "hot" instructions. We don't want to do any
1575 // mis-optimizations here.
1580 // Check to see how many predecessors have the loaded value fully
1582 DenseMap<BasicBlock*, Value*> PredLoads;
1583 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1584 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1585 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1586 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1587 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1589 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit;
1590 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1592 BasicBlock *Pred = *PI;
1593 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) {
1596 PredLoads[Pred] = 0;
1598 if (Pred->getTerminator()->getNumSuccessors() != 1) {
1599 if (isa<IndirectBrInst>(Pred->getTerminator())) {
1600 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
1601 << Pred->getName() << "': " << *LI << '\n');
1604 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB);
1605 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
1608 if (!NeedToSplit.empty()) {
1609 toSplit.append(NeedToSplit.begin(), NeedToSplit.end());
1613 // Decide whether PRE is profitable for this load.
1614 unsigned NumUnavailablePreds = PredLoads.size();
1615 assert(NumUnavailablePreds != 0 &&
1616 "Fully available value should be eliminated above!");
1617 if (!EnableFullLoadPRE) {
1618 // If this load is unavailable in multiple predecessors, reject it.
1619 // FIXME: If we could restructure the CFG, we could make a common pred with
1620 // all the preds that don't have an available LI and insert a new load into
1622 if (NumUnavailablePreds != 1)
1626 // Check if the load can safely be moved to all the unavailable predecessors.
1627 bool CanDoPRE = true;
1628 SmallVector<Instruction*, 8> NewInsts;
1629 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1630 E = PredLoads.end(); I != E; ++I) {
1631 BasicBlock *UnavailablePred = I->first;
1633 // Do PHI translation to get its value in the predecessor if necessary. The
1634 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1636 // If all preds have a single successor, then we know it is safe to insert
1637 // the load on the pred (?!?), so we can insert code to materialize the
1638 // pointer if it is not available.
1639 PHITransAddr Address(LI->getOperand(0), TD);
1641 if (allSingleSucc) {
1642 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1645 Address.PHITranslateValue(LoadBB, UnavailablePred, DT);
1646 LoadPtr = Address.getAddr();
1649 // If we couldn't find or insert a computation of this phi translated value,
1652 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1653 << *LI->getOperand(0) << "\n");
1658 // Make sure it is valid to move this load here. We have to watch out for:
1659 // @1 = getelementptr (i8* p, ...
1660 // test p and branch if == 0
1662 // It is valid to have the getelementptr before the test, even if p can be 0,
1663 // as getelementptr only does address arithmetic.
1664 // If we are not pushing the value through any multiple-successor blocks
1665 // we do not have this case. Otherwise, check that the load is safe to
1666 // put anywhere; this can be improved, but should be conservatively safe.
1667 if (!allSingleSucc &&
1668 // FIXME: REEVALUTE THIS.
1669 !isSafeToLoadUnconditionally(LoadPtr,
1670 UnavailablePred->getTerminator(),
1671 LI->getAlignment(), TD)) {
1676 I->second = LoadPtr;
1680 while (!NewInsts.empty())
1681 NewInsts.pop_back_val()->eraseFromParent();
1685 // Okay, we can eliminate this load by inserting a reload in the predecessor
1686 // and using PHI construction to get the value in the other predecessors, do
1688 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1689 DEBUG(if (!NewInsts.empty())
1690 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
1691 << *NewInsts.back() << '\n');
1693 // Assign value numbers to the new instructions.
1694 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1695 // FIXME: We really _ought_ to insert these value numbers into their
1696 // parent's availability map. However, in doing so, we risk getting into
1697 // ordering issues. If a block hasn't been processed yet, we would be
1698 // marking a value as AVAIL-IN, which isn't what we intend.
1699 VN.lookup_or_add(NewInsts[i]);
1702 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1703 E = PredLoads.end(); I != E; ++I) {
1704 BasicBlock *UnavailablePred = I->first;
1705 Value *LoadPtr = I->second;
1707 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1709 UnavailablePred->getTerminator());
1711 // Add the newly created load.
1712 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
1714 MD->invalidateCachedPointerInfo(LoadPtr);
1715 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
1718 // Perform PHI construction.
1719 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1720 VN.getAliasAnalysis());
1721 LI->replaceAllUsesWith(V);
1722 if (isa<PHINode>(V))
1724 if (V->getType()->isPointerTy())
1725 MD->invalidateCachedPointerInfo(V);
1727 toErase.push_back(LI);
1732 /// processLoad - Attempt to eliminate a load, first by eliminating it
1733 /// locally, and then attempting non-local elimination if that fails.
1734 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1738 if (L->isVolatile())
1741 // ... to a pointer that has been loaded from before...
1742 MemDepResult Dep = MD->getDependency(L);
1744 // If the value isn't available, don't do anything!
1745 if (Dep.isClobber()) {
1746 // Check to see if we have something like this:
1747 // store i32 123, i32* %P
1748 // %A = bitcast i32* %P to i8*
1749 // %B = gep i8* %A, i32 1
1752 // We could do that by recognizing if the clobber instructions are obviously
1753 // a common base + constant offset, and if the previous store (or memset)
1754 // completely covers this load. This sort of thing can happen in bitfield
1756 Value *AvailVal = 0;
1757 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1758 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1759 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1760 L->getPointerOperand(),
1763 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset,
1764 L->getType(), L, *TD);
1767 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1768 // a value on from it.
1769 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1770 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1771 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1772 L->getPointerOperand(),
1775 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1780 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1781 << *AvailVal << '\n' << *L << "\n\n\n");
1783 // Replace the load!
1784 L->replaceAllUsesWith(AvailVal);
1785 if (AvailVal->getType()->isPointerTy())
1786 MD->invalidateCachedPointerInfo(AvailVal);
1788 toErase.push_back(L);
1794 // fast print dep, using operator<< on instruction would be too slow
1795 dbgs() << "GVN: load ";
1796 WriteAsOperand(dbgs(), L);
1797 Instruction *I = Dep.getInst();
1798 dbgs() << " is clobbered by " << *I << '\n';
1803 // If it is defined in another block, try harder.
1804 if (Dep.isNonLocal())
1805 return processNonLocalLoad(L, toErase);
1807 Instruction *DepInst = Dep.getInst();
1808 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1809 Value *StoredVal = DepSI->getOperand(0);
1811 // The store and load are to a must-aliased pointer, but they may not
1812 // actually have the same type. See if we know how to reuse the stored
1813 // value (depending on its type).
1814 const TargetData *TD = 0;
1815 if (StoredVal->getType() != L->getType()) {
1816 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1817 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1822 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1823 << '\n' << *L << "\n\n\n");
1830 L->replaceAllUsesWith(StoredVal);
1831 if (StoredVal->getType()->isPointerTy())
1832 MD->invalidateCachedPointerInfo(StoredVal);
1834 toErase.push_back(L);
1839 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1840 Value *AvailableVal = DepLI;
1842 // The loads are of a must-aliased pointer, but they may not actually have
1843 // the same type. See if we know how to reuse the previously loaded value
1844 // (depending on its type).
1845 const TargetData *TD = 0;
1846 if (DepLI->getType() != L->getType()) {
1847 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1848 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1849 if (AvailableVal == 0)
1852 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1853 << "\n" << *L << "\n\n\n");
1860 L->replaceAllUsesWith(AvailableVal);
1861 if (DepLI->getType()->isPointerTy())
1862 MD->invalidateCachedPointerInfo(DepLI);
1864 toErase.push_back(L);
1869 // If this load really doesn't depend on anything, then we must be loading an
1870 // undef value. This can happen when loading for a fresh allocation with no
1871 // intervening stores, for example.
1872 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1873 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1875 toErase.push_back(L);
1880 // If this load occurs either right after a lifetime begin,
1881 // then the loaded value is undefined.
1882 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1883 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1884 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1886 toErase.push_back(L);
1895 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1896 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1897 if (I == localAvail.end())
1900 ValueNumberScope *Locals = I->second;
1902 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num);
1903 if (I != Locals->table.end())
1905 Locals = Locals->parent;
1912 /// processInstruction - When calculating availability, handle an instruction
1913 /// by inserting it into the appropriate sets
1914 bool GVN::processInstruction(Instruction *I,
1915 SmallVectorImpl<Instruction*> &toErase) {
1916 // Ignore dbg info intrinsics.
1917 if (isa<DbgInfoIntrinsic>(I))
1920 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1921 bool Changed = processLoad(LI, toErase);
1924 unsigned Num = VN.lookup_or_add(LI);
1925 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI));
1931 uint32_t NextNum = VN.getNextUnusedValueNumber();
1932 unsigned Num = VN.lookup_or_add(I);
1934 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1935 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1937 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1940 Value *BranchCond = BI->getCondition();
1941 uint32_t CondVN = VN.lookup_or_add(BranchCond);
1943 BasicBlock *TrueSucc = BI->getSuccessor(0);
1944 BasicBlock *FalseSucc = BI->getSuccessor(1);
1946 if (TrueSucc->getSinglePredecessor())
1947 localAvail[TrueSucc]->table[CondVN] =
1948 ConstantInt::getTrue(TrueSucc->getContext());
1949 if (FalseSucc->getSinglePredecessor())
1950 localAvail[FalseSucc]->table[CondVN] =
1951 ConstantInt::getFalse(TrueSucc->getContext());
1955 // Allocations are always uniquely numbered, so we can save time and memory
1956 // by fast failing them.
1957 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1958 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1962 // Collapse PHI nodes
1963 if (PHINode* p = dyn_cast<PHINode>(I)) {
1964 Value *constVal = CollapsePhi(p);
1967 p->replaceAllUsesWith(constVal);
1968 if (MD && constVal->getType()->isPointerTy())
1969 MD->invalidateCachedPointerInfo(constVal);
1972 toErase.push_back(p);
1974 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1977 // If the number we were assigned was a brand new VN, then we don't
1978 // need to do a lookup to see if the number already exists
1979 // somewhere in the domtree: it can't!
1980 } else if (Num == NextNum) {
1981 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1983 // Perform fast-path value-number based elimination of values inherited from
1985 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1988 I->replaceAllUsesWith(repl);
1989 if (MD && repl->getType()->isPointerTy())
1990 MD->invalidateCachedPointerInfo(repl);
1991 toErase.push_back(I);
1995 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
2001 /// runOnFunction - This is the main transformation entry point for a function.
2002 bool GVN::runOnFunction(Function& F) {
2004 MD = &getAnalysis<MemoryDependenceAnalysis>();
2005 DT = &getAnalysis<DominatorTree>();
2006 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
2010 bool Changed = false;
2011 bool ShouldContinue = true;
2013 // Merge unconditional branches, allowing PRE to catch more
2014 // optimization opportunities.
2015 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
2016 BasicBlock *BB = FI;
2018 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
2019 if (removedBlock) ++NumGVNBlocks;
2021 Changed |= removedBlock;
2024 unsigned Iteration = 0;
2026 while (ShouldContinue) {
2027 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
2028 ShouldContinue = iterateOnFunction(F);
2029 if (splitCriticalEdges())
2030 ShouldContinue = true;
2031 Changed |= ShouldContinue;
2036 bool PREChanged = true;
2037 while (PREChanged) {
2038 PREChanged = performPRE(F);
2039 Changed |= PREChanged;
2042 // FIXME: Should perform GVN again after PRE does something. PRE can move
2043 // computations into blocks where they become fully redundant. Note that
2044 // we can't do this until PRE's critical edge splitting updates memdep.
2045 // Actually, when this happens, we should just fully integrate PRE into GVN.
2047 cleanupGlobalSets();
2053 bool GVN::processBlock(BasicBlock *BB) {
2054 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
2055 // incrementing BI before processing an instruction).
2056 SmallVector<Instruction*, 8> toErase;
2057 bool ChangedFunction = false;
2059 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2061 ChangedFunction |= processInstruction(BI, toErase);
2062 if (toErase.empty()) {
2067 // If we need some instructions deleted, do it now.
2068 NumGVNInstr += toErase.size();
2070 // Avoid iterator invalidation.
2071 bool AtStart = BI == BB->begin();
2075 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2076 E = toErase.end(); I != E; ++I) {
2077 DEBUG(dbgs() << "GVN removed: " << **I << '\n');
2078 if (MD) MD->removeInstruction(*I);
2079 (*I)->eraseFromParent();
2080 DEBUG(verifyRemoved(*I));
2090 return ChangedFunction;
2093 /// performPRE - Perform a purely local form of PRE that looks for diamond
2094 /// control flow patterns and attempts to perform simple PRE at the join point.
2095 bool GVN::performPRE(Function &F) {
2096 bool Changed = false;
2097 DenseMap<BasicBlock*, Value*> predMap;
2098 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2099 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2100 BasicBlock *CurrentBlock = *DI;
2102 // Nothing to PRE in the entry block.
2103 if (CurrentBlock == &F.getEntryBlock()) continue;
2105 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2106 BE = CurrentBlock->end(); BI != BE; ) {
2107 Instruction *CurInst = BI++;
2109 if (isa<AllocaInst>(CurInst) ||
2110 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2111 CurInst->getType()->isVoidTy() ||
2112 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2113 isa<DbgInfoIntrinsic>(CurInst))
2116 uint32_t ValNo = VN.lookup(CurInst);
2118 // Look for the predecessors for PRE opportunities. We're
2119 // only trying to solve the basic diamond case, where
2120 // a value is computed in the successor and one predecessor,
2121 // but not the other. We also explicitly disallow cases
2122 // where the successor is its own predecessor, because they're
2123 // more complicated to get right.
2124 unsigned NumWith = 0;
2125 unsigned NumWithout = 0;
2126 BasicBlock *PREPred = 0;
2129 for (pred_iterator PI = pred_begin(CurrentBlock),
2130 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2131 BasicBlock *P = *PI;
2132 // We're not interested in PRE where the block is its
2133 // own predecessor, or in blocks with predecessors
2134 // that are not reachable.
2135 if (P == CurrentBlock) {
2138 } else if (!localAvail.count(P)) {
2143 DenseMap<uint32_t, Value*>::iterator predV =
2144 localAvail[P]->table.find(ValNo);
2145 if (predV == localAvail[P]->table.end()) {
2148 } else if (predV->second == CurInst) {
2151 predMap[P] = predV->second;
2156 // Don't do PRE when it might increase code size, i.e. when
2157 // we would need to insert instructions in more than one pred.
2158 if (NumWithout != 1 || NumWith == 0)
2161 // Don't do PRE across indirect branch.
2162 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2165 // We can't do PRE safely on a critical edge, so instead we schedule
2166 // the edge to be split and perform the PRE the next time we iterate
2168 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
2169 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2170 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2174 // Instantiate the expression in the predecessor that lacked it.
2175 // Because we are going top-down through the block, all value numbers
2176 // will be available in the predecessor by the time we need them. Any
2177 // that weren't originally present will have been instantiated earlier
2179 Instruction *PREInstr = CurInst->clone();
2180 bool success = true;
2181 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2182 Value *Op = PREInstr->getOperand(i);
2183 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2186 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
2187 PREInstr->setOperand(i, V);
2194 // Fail out if we encounter an operand that is not available in
2195 // the PRE predecessor. This is typically because of loads which
2196 // are not value numbered precisely.
2199 DEBUG(verifyRemoved(PREInstr));
2203 PREInstr->insertBefore(PREPred->getTerminator());
2204 PREInstr->setName(CurInst->getName() + ".pre");
2205 predMap[PREPred] = PREInstr;
2206 VN.add(PREInstr, ValNo);
2209 // Update the availability map to include the new instruction.
2210 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr));
2212 // Create a PHI to make the value available in this block.
2213 PHINode* Phi = PHINode::Create(CurInst->getType(),
2214 CurInst->getName() + ".pre-phi",
2215 CurrentBlock->begin());
2216 for (pred_iterator PI = pred_begin(CurrentBlock),
2217 PE = pred_end(CurrentBlock); PI != PE; ++PI)
2218 Phi->addIncoming(predMap[*PI], *PI);
2221 localAvail[CurrentBlock]->table[ValNo] = Phi;
2223 CurInst->replaceAllUsesWith(Phi);
2224 if (MD && Phi->getType()->isPointerTy())
2225 MD->invalidateCachedPointerInfo(Phi);
2228 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
2229 if (MD) MD->removeInstruction(CurInst);
2230 CurInst->eraseFromParent();
2231 DEBUG(verifyRemoved(CurInst));
2236 if (splitCriticalEdges())
2242 /// splitCriticalEdges - Split critical edges found during the previous
2243 /// iteration that may enable further optimization.
2244 bool GVN::splitCriticalEdges() {
2245 if (toSplit.empty())
2248 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
2249 SplitCriticalEdge(Edge.first, Edge.second, this);
2250 } while (!toSplit.empty());
2251 if (MD) MD->invalidateCachedPredecessors();
2255 /// iterateOnFunction - Executes one iteration of GVN
2256 bool GVN::iterateOnFunction(Function &F) {
2257 cleanupGlobalSets();
2259 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2260 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
2262 localAvail[DI->getBlock()] =
2263 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
2265 localAvail[DI->getBlock()] = new ValueNumberScope(0);
2268 // Top-down walk of the dominator tree
2269 bool Changed = false;
2271 // Needed for value numbering with phi construction to work.
2272 ReversePostOrderTraversal<Function*> RPOT(&F);
2273 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2274 RE = RPOT.end(); RI != RE; ++RI)
2275 Changed |= processBlock(*RI);
2277 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2278 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2279 Changed |= processBlock(DI->getBlock());
2285 void GVN::cleanupGlobalSets() {
2288 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
2289 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
2294 /// verifyRemoved - Verify that the specified instruction does not occur in our
2295 /// internal data structures.
2296 void GVN::verifyRemoved(const Instruction *Inst) const {
2297 VN.verifyRemoved(Inst);
2299 // Walk through the value number scope to make sure the instruction isn't
2300 // ferreted away in it.
2301 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
2302 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
2303 const ValueNumberScope *VNS = I->second;
2306 for (DenseMap<uint32_t, Value*>::const_iterator
2307 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
2308 assert(II->second != Inst && "Inst still in value numbering scope!");