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/MemoryBuiltins.h"
39 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
40 #include "llvm/Analysis/PHITransAddr.h"
41 #include "llvm/Support/CFG.h"
42 #include "llvm/Support/CommandLine.h"
43 #include "llvm/Support/Debug.h"
44 #include "llvm/Support/ErrorHandling.h"
45 #include "llvm/Support/GetElementPtrTypeIterator.h"
46 #include "llvm/Support/IRBuilder.h"
47 #include "llvm/Support/raw_ostream.h"
48 #include "llvm/Target/TargetData.h"
49 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
50 #include "llvm/Transforms/Utils/Local.h"
51 #include "llvm/Transforms/Utils/SSAUpdater.h"
54 STATISTIC(NumGVNInstr, "Number of instructions deleted");
55 STATISTIC(NumGVNLoad, "Number of loads deleted");
56 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
57 STATISTIC(NumGVNBlocks, "Number of blocks merged");
58 STATISTIC(NumPRELoad, "Number of loads PRE'd");
60 static cl::opt<bool> EnablePRE("enable-pre",
61 cl::init(true), cl::Hidden);
62 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
63 static cl::opt<bool> EnableFullLoadPRE("enable-full-load-pre", cl::init(false));
65 //===----------------------------------------------------------------------===//
67 //===----------------------------------------------------------------------===//
69 /// This class holds the mapping between values and value numbers. It is used
70 /// as an efficient mechanism to determine the expression-wise equivalence of
74 enum ExpressionOpcode {
75 ADD = Instruction::Add,
76 FADD = Instruction::FAdd,
77 SUB = Instruction::Sub,
78 FSUB = Instruction::FSub,
79 MUL = Instruction::Mul,
80 FMUL = Instruction::FMul,
81 UDIV = Instruction::UDiv,
82 SDIV = Instruction::SDiv,
83 FDIV = Instruction::FDiv,
84 UREM = Instruction::URem,
85 SREM = Instruction::SRem,
86 FREM = Instruction::FRem,
87 SHL = Instruction::Shl,
88 LSHR = Instruction::LShr,
89 ASHR = Instruction::AShr,
90 AND = Instruction::And,
92 XOR = Instruction::Xor,
93 TRUNC = Instruction::Trunc,
94 ZEXT = Instruction::ZExt,
95 SEXT = Instruction::SExt,
96 FPTOUI = Instruction::FPToUI,
97 FPTOSI = Instruction::FPToSI,
98 UITOFP = Instruction::UIToFP,
99 SITOFP = Instruction::SIToFP,
100 FPTRUNC = Instruction::FPTrunc,
101 FPEXT = Instruction::FPExt,
102 PTRTOINT = Instruction::PtrToInt,
103 INTTOPTR = Instruction::IntToPtr,
104 BITCAST = Instruction::BitCast,
105 ICMPEQ, ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
106 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
107 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
108 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
109 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
110 SHUFFLE, SELECT, GEP, CALL, CONSTANT,
111 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE };
113 ExpressionOpcode opcode;
115 SmallVector<uint32_t, 4> varargs;
119 Expression(ExpressionOpcode o) : opcode(o) { }
121 bool operator==(const Expression &other) const {
122 if (opcode != other.opcode)
124 else if (opcode == EMPTY || opcode == TOMBSTONE)
126 else if (type != other.type)
128 else if (function != other.function)
131 if (varargs.size() != other.varargs.size())
134 for (size_t i = 0; i < varargs.size(); ++i)
135 if (varargs[i] != other.varargs[i])
142 bool operator!=(const Expression &other) const {
143 return !(*this == other);
149 DenseMap<Value*, uint32_t> valueNumbering;
150 DenseMap<Expression, uint32_t> expressionNumbering;
152 MemoryDependenceAnalysis* MD;
155 uint32_t nextValueNumber;
157 Expression::ExpressionOpcode getOpcode(CmpInst* C);
158 Expression create_expression(BinaryOperator* BO);
159 Expression create_expression(CmpInst* C);
160 Expression create_expression(ShuffleVectorInst* V);
161 Expression create_expression(ExtractElementInst* C);
162 Expression create_expression(InsertElementInst* V);
163 Expression create_expression(SelectInst* V);
164 Expression create_expression(CastInst* C);
165 Expression create_expression(GetElementPtrInst* G);
166 Expression create_expression(CallInst* C);
167 Expression create_expression(Constant* C);
168 Expression create_expression(ExtractValueInst* C);
169 Expression create_expression(InsertValueInst* C);
171 uint32_t lookup_or_add_call(CallInst* C);
173 ValueTable() : nextValueNumber(1) { }
174 uint32_t lookup_or_add(Value *V);
175 uint32_t lookup(Value *V) const;
176 void add(Value *V, uint32_t num);
178 void erase(Value *v);
180 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
181 AliasAnalysis *getAliasAnalysis() const { return AA; }
182 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
183 void setDomTree(DominatorTree* D) { DT = D; }
184 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
185 void verifyRemoved(const Value *) const;
190 template <> struct DenseMapInfo<Expression> {
191 static inline Expression getEmptyKey() {
192 return Expression(Expression::EMPTY);
195 static inline Expression getTombstoneKey() {
196 return Expression(Expression::TOMBSTONE);
199 static unsigned getHashValue(const Expression e) {
200 unsigned hash = e.opcode;
202 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
203 (unsigned)((uintptr_t)e.type >> 9));
205 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
206 E = e.varargs.end(); I != E; ++I)
207 hash = *I + hash * 37;
209 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
210 (unsigned)((uintptr_t)e.function >> 9)) +
215 static bool isEqual(const Expression &LHS, const Expression &RHS) {
221 struct isPodLike<Expression> { static const bool value = true; };
225 //===----------------------------------------------------------------------===//
226 // ValueTable Internal Functions
227 //===----------------------------------------------------------------------===//
229 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
230 if (isa<ICmpInst>(C)) {
231 switch (C->getPredicate()) {
232 default: // THIS SHOULD NEVER HAPPEN
233 llvm_unreachable("Comparison with unknown predicate?");
234 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
235 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
236 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
237 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
238 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
239 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
240 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
241 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
242 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
243 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
246 switch (C->getPredicate()) {
247 default: // THIS SHOULD NEVER HAPPEN
248 llvm_unreachable("Comparison with unknown predicate?");
249 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
250 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
251 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
252 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
253 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
254 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
255 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
256 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
257 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
258 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
259 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
260 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
261 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
262 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
267 Expression ValueTable::create_expression(CallInst* C) {
270 e.type = C->getType();
271 e.function = C->getCalledFunction();
272 e.opcode = Expression::CALL;
274 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
276 e.varargs.push_back(lookup_or_add(*I));
281 Expression ValueTable::create_expression(BinaryOperator* BO) {
283 e.varargs.push_back(lookup_or_add(BO->getOperand(0)));
284 e.varargs.push_back(lookup_or_add(BO->getOperand(1)));
286 e.type = BO->getType();
287 e.opcode = static_cast<Expression::ExpressionOpcode>(BO->getOpcode());
292 Expression ValueTable::create_expression(CmpInst* C) {
295 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
296 e.varargs.push_back(lookup_or_add(C->getOperand(1)));
298 e.type = C->getType();
299 e.opcode = getOpcode(C);
304 Expression ValueTable::create_expression(CastInst* C) {
307 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
309 e.type = C->getType();
310 e.opcode = static_cast<Expression::ExpressionOpcode>(C->getOpcode());
315 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
318 e.varargs.push_back(lookup_or_add(S->getOperand(0)));
319 e.varargs.push_back(lookup_or_add(S->getOperand(1)));
320 e.varargs.push_back(lookup_or_add(S->getOperand(2)));
322 e.type = S->getType();
323 e.opcode = Expression::SHUFFLE;
328 Expression ValueTable::create_expression(ExtractElementInst* E) {
331 e.varargs.push_back(lookup_or_add(E->getOperand(0)));
332 e.varargs.push_back(lookup_or_add(E->getOperand(1)));
334 e.type = E->getType();
335 e.opcode = Expression::EXTRACT;
340 Expression ValueTable::create_expression(InsertElementInst* I) {
343 e.varargs.push_back(lookup_or_add(I->getOperand(0)));
344 e.varargs.push_back(lookup_or_add(I->getOperand(1)));
345 e.varargs.push_back(lookup_or_add(I->getOperand(2)));
347 e.type = I->getType();
348 e.opcode = Expression::INSERT;
353 Expression ValueTable::create_expression(SelectInst* I) {
356 e.varargs.push_back(lookup_or_add(I->getCondition()));
357 e.varargs.push_back(lookup_or_add(I->getTrueValue()));
358 e.varargs.push_back(lookup_or_add(I->getFalseValue()));
360 e.type = I->getType();
361 e.opcode = Expression::SELECT;
366 Expression ValueTable::create_expression(GetElementPtrInst* G) {
369 e.varargs.push_back(lookup_or_add(G->getPointerOperand()));
371 e.type = G->getType();
372 e.opcode = Expression::GEP;
374 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
376 e.varargs.push_back(lookup_or_add(*I));
381 Expression ValueTable::create_expression(ExtractValueInst* E) {
384 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
385 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
387 e.varargs.push_back(*II);
389 e.type = E->getType();
390 e.opcode = Expression::EXTRACTVALUE;
395 Expression ValueTable::create_expression(InsertValueInst* E) {
398 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
399 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand()));
400 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
402 e.varargs.push_back(*II);
404 e.type = E->getType();
405 e.opcode = Expression::INSERTVALUE;
410 //===----------------------------------------------------------------------===//
411 // ValueTable External Functions
412 //===----------------------------------------------------------------------===//
414 /// add - Insert a value into the table with a specified value number.
415 void ValueTable::add(Value *V, uint32_t num) {
416 valueNumbering.insert(std::make_pair(V, num));
419 uint32_t ValueTable::lookup_or_add_call(CallInst* C) {
420 if (AA->doesNotAccessMemory(C)) {
421 Expression exp = create_expression(C);
422 uint32_t& e = expressionNumbering[exp];
423 if (!e) e = nextValueNumber++;
424 valueNumbering[C] = e;
426 } else if (AA->onlyReadsMemory(C)) {
427 Expression exp = create_expression(C);
428 uint32_t& e = expressionNumbering[exp];
430 e = nextValueNumber++;
431 valueNumbering[C] = e;
435 e = nextValueNumber++;
436 valueNumbering[C] = e;
440 MemDepResult local_dep = MD->getDependency(C);
442 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
443 valueNumbering[C] = nextValueNumber;
444 return nextValueNumber++;
447 if (local_dep.isDef()) {
448 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
450 if (local_cdep->getNumOperands() != C->getNumOperands()) {
451 valueNumbering[C] = nextValueNumber;
452 return nextValueNumber++;
455 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
456 uint32_t c_vn = lookup_or_add(C->getOperand(i));
457 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
459 valueNumbering[C] = nextValueNumber;
460 return nextValueNumber++;
464 uint32_t v = lookup_or_add(local_cdep);
465 valueNumbering[C] = v;
470 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
471 MD->getNonLocalCallDependency(CallSite(C));
472 // FIXME: call/call dependencies for readonly calls should return def, not
473 // clobber! Move the checking logic to MemDep!
476 // Check to see if we have a single dominating call instruction that is
478 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
479 const NonLocalDepEntry *I = &deps[i];
480 // Ignore non-local dependencies.
481 if (I->getResult().isNonLocal())
484 // We don't handle non-depedencies. If we already have a call, reject
485 // instruction dependencies.
486 if (I->getResult().isClobber() || cdep != 0) {
491 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
492 // FIXME: All duplicated with non-local case.
493 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
494 cdep = NonLocalDepCall;
503 valueNumbering[C] = nextValueNumber;
504 return nextValueNumber++;
507 if (cdep->getNumOperands() != C->getNumOperands()) {
508 valueNumbering[C] = nextValueNumber;
509 return nextValueNumber++;
511 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
512 uint32_t c_vn = lookup_or_add(C->getOperand(i));
513 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
515 valueNumbering[C] = nextValueNumber;
516 return nextValueNumber++;
520 uint32_t v = lookup_or_add(cdep);
521 valueNumbering[C] = v;
525 valueNumbering[C] = nextValueNumber;
526 return nextValueNumber++;
530 /// lookup_or_add - Returns the value number for the specified value, assigning
531 /// it a new number if it did not have one before.
532 uint32_t ValueTable::lookup_or_add(Value *V) {
533 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
534 if (VI != valueNumbering.end())
537 if (!isa<Instruction>(V)) {
538 valueNumbering[V] = nextValueNumber;
539 return nextValueNumber++;
542 Instruction* I = cast<Instruction>(V);
544 switch (I->getOpcode()) {
545 case Instruction::Call:
546 return lookup_or_add_call(cast<CallInst>(I));
547 case Instruction::Add:
548 case Instruction::FAdd:
549 case Instruction::Sub:
550 case Instruction::FSub:
551 case Instruction::Mul:
552 case Instruction::FMul:
553 case Instruction::UDiv:
554 case Instruction::SDiv:
555 case Instruction::FDiv:
556 case Instruction::URem:
557 case Instruction::SRem:
558 case Instruction::FRem:
559 case Instruction::Shl:
560 case Instruction::LShr:
561 case Instruction::AShr:
562 case Instruction::And:
563 case Instruction::Or :
564 case Instruction::Xor:
565 exp = create_expression(cast<BinaryOperator>(I));
567 case Instruction::ICmp:
568 case Instruction::FCmp:
569 exp = create_expression(cast<CmpInst>(I));
571 case Instruction::Trunc:
572 case Instruction::ZExt:
573 case Instruction::SExt:
574 case Instruction::FPToUI:
575 case Instruction::FPToSI:
576 case Instruction::UIToFP:
577 case Instruction::SIToFP:
578 case Instruction::FPTrunc:
579 case Instruction::FPExt:
580 case Instruction::PtrToInt:
581 case Instruction::IntToPtr:
582 case Instruction::BitCast:
583 exp = create_expression(cast<CastInst>(I));
585 case Instruction::Select:
586 exp = create_expression(cast<SelectInst>(I));
588 case Instruction::ExtractElement:
589 exp = create_expression(cast<ExtractElementInst>(I));
591 case Instruction::InsertElement:
592 exp = create_expression(cast<InsertElementInst>(I));
594 case Instruction::ShuffleVector:
595 exp = create_expression(cast<ShuffleVectorInst>(I));
597 case Instruction::ExtractValue:
598 exp = create_expression(cast<ExtractValueInst>(I));
600 case Instruction::InsertValue:
601 exp = create_expression(cast<InsertValueInst>(I));
603 case Instruction::GetElementPtr:
604 exp = create_expression(cast<GetElementPtrInst>(I));
607 valueNumbering[V] = nextValueNumber;
608 return nextValueNumber++;
611 uint32_t& e = expressionNumbering[exp];
612 if (!e) e = nextValueNumber++;
613 valueNumbering[V] = e;
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>::const_iterator VI = valueNumbering.find(V);
621 assert(VI != valueNumbering.end() && "Value not numbered?");
625 /// clear - Remove all entries from the ValueTable
626 void ValueTable::clear() {
627 valueNumbering.clear();
628 expressionNumbering.clear();
632 /// erase - Remove a value from the value numbering
633 void ValueTable::erase(Value *V) {
634 valueNumbering.erase(V);
637 /// verifyRemoved - Verify that the value is removed from all internal data
639 void ValueTable::verifyRemoved(const Value *V) const {
640 for (DenseMap<Value*, uint32_t>::const_iterator
641 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
642 assert(I->first != V && "Inst still occurs in value numbering map!");
646 //===----------------------------------------------------------------------===//
648 //===----------------------------------------------------------------------===//
651 struct ValueNumberScope {
652 ValueNumberScope* parent;
653 DenseMap<uint32_t, Value*> table;
655 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
661 class GVN : public FunctionPass {
662 bool runOnFunction(Function &F);
664 static char ID; // Pass identification, replacement for typeid
665 explicit GVN(bool noloads = false)
666 : FunctionPass(&ID), NoLoads(noloads), MD(0) { }
670 MemoryDependenceAnalysis *MD;
674 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
676 // List of critical edges to be split between iterations.
677 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
679 // This transformation requires dominator postdominator info
680 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
681 AU.addRequired<DominatorTree>();
683 AU.addRequired<MemoryDependenceAnalysis>();
684 AU.addRequired<AliasAnalysis>();
686 AU.addPreserved<DominatorTree>();
687 AU.addPreserved<AliasAnalysis>();
691 // FIXME: eliminate or document these better
692 bool processLoad(LoadInst* L,
693 SmallVectorImpl<Instruction*> &toErase);
694 bool processInstruction(Instruction *I,
695 SmallVectorImpl<Instruction*> &toErase);
696 bool processNonLocalLoad(LoadInst* L,
697 SmallVectorImpl<Instruction*> &toErase);
698 bool processBlock(BasicBlock *BB);
699 void dump(DenseMap<uint32_t, Value*>& d);
700 bool iterateOnFunction(Function &F);
701 Value *CollapsePhi(PHINode* p);
702 bool performPRE(Function& F);
703 Value *lookupNumber(BasicBlock *BB, uint32_t num);
704 void cleanupGlobalSets();
705 void verifyRemoved(const Instruction *I) const;
706 bool splitCriticalEdges();
712 // createGVNPass - The public interface to this file...
713 FunctionPass *llvm::createGVNPass(bool NoLoads) {
714 return new GVN(NoLoads);
717 static RegisterPass<GVN> X("gvn",
718 "Global Value Numbering");
720 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
722 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
723 E = d.end(); I != E; ++I) {
724 errs() << I->first << "\n";
730 static bool isSafeReplacement(PHINode* p, Instruction *inst) {
731 if (!isa<PHINode>(inst))
734 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
736 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
737 if (use_phi->getParent() == inst->getParent())
743 Value *GVN::CollapsePhi(PHINode *PN) {
744 Value *ConstVal = PN->hasConstantValue(DT);
745 if (!ConstVal) return 0;
747 Instruction *Inst = dyn_cast<Instruction>(ConstVal);
751 if (DT->dominates(Inst, PN))
752 if (isSafeReplacement(PN, Inst))
757 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
758 /// we're analyzing is fully available in the specified block. As we go, keep
759 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
760 /// map is actually a tri-state map with the following values:
761 /// 0) we know the block *is not* fully available.
762 /// 1) we know the block *is* fully available.
763 /// 2) we do not know whether the block is fully available or not, but we are
764 /// currently speculating that it will be.
765 /// 3) we are speculating for this block and have used that to speculate for
767 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
768 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
769 // Optimistically assume that the block is fully available and check to see
770 // if we already know about this block in one lookup.
771 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
772 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
774 // If the entry already existed for this block, return the precomputed value.
776 // If this is a speculative "available" value, mark it as being used for
777 // speculation of other blocks.
778 if (IV.first->second == 2)
779 IV.first->second = 3;
780 return IV.first->second != 0;
783 // Otherwise, see if it is fully available in all predecessors.
784 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
786 // If this block has no predecessors, it isn't live-in here.
788 goto SpeculationFailure;
790 for (; PI != PE; ++PI)
791 // If the value isn't fully available in one of our predecessors, then it
792 // isn't fully available in this block either. Undo our previous
793 // optimistic assumption and bail out.
794 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
795 goto SpeculationFailure;
799 // SpeculationFailure - If we get here, we found out that this is not, after
800 // all, a fully-available block. We have a problem if we speculated on this and
801 // used the speculation to mark other blocks as available.
803 char &BBVal = FullyAvailableBlocks[BB];
805 // If we didn't speculate on this, just return with it set to false.
811 // If we did speculate on this value, we could have blocks set to 1 that are
812 // incorrect. Walk the (transitive) successors of this block and mark them as
814 SmallVector<BasicBlock*, 32> BBWorklist;
815 BBWorklist.push_back(BB);
818 BasicBlock *Entry = BBWorklist.pop_back_val();
819 // Note that this sets blocks to 0 (unavailable) if they happen to not
820 // already be in FullyAvailableBlocks. This is safe.
821 char &EntryVal = FullyAvailableBlocks[Entry];
822 if (EntryVal == 0) continue; // Already unavailable.
824 // Mark as unavailable.
827 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
828 BBWorklist.push_back(*I);
829 } while (!BBWorklist.empty());
835 /// CanCoerceMustAliasedValueToLoad - Return true if
836 /// CoerceAvailableValueToLoadType will succeed.
837 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
839 const TargetData &TD) {
840 // If the loaded or stored value is an first class array or struct, don't try
841 // to transform them. We need to be able to bitcast to integer.
842 if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
843 StoredVal->getType()->isStructTy() ||
844 StoredVal->getType()->isArrayTy())
847 // The store has to be at least as big as the load.
848 if (TD.getTypeSizeInBits(StoredVal->getType()) <
849 TD.getTypeSizeInBits(LoadTy))
856 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
857 /// then a load from a must-aliased pointer of a different type, try to coerce
858 /// the stored value. LoadedTy is the type of the load we want to replace and
859 /// InsertPt is the place to insert new instructions.
861 /// If we can't do it, return null.
862 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
863 const Type *LoadedTy,
864 Instruction *InsertPt,
865 const TargetData &TD) {
866 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
869 const Type *StoredValTy = StoredVal->getType();
871 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy);
872 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
874 // If the store and reload are the same size, we can always reuse it.
875 if (StoreSize == LoadSize) {
876 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) {
877 // Pointer to Pointer -> use bitcast.
878 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
881 // Convert source pointers to integers, which can be bitcast.
882 if (StoredValTy->isPointerTy()) {
883 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
884 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
887 const Type *TypeToCastTo = LoadedTy;
888 if (TypeToCastTo->isPointerTy())
889 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
891 if (StoredValTy != TypeToCastTo)
892 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
894 // Cast to pointer if the load needs a pointer type.
895 if (LoadedTy->isPointerTy())
896 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
901 // If the loaded value is smaller than the available value, then we can
902 // extract out a piece from it. If the available value is too small, then we
903 // can't do anything.
904 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
906 // Convert source pointers to integers, which can be manipulated.
907 if (StoredValTy->isPointerTy()) {
908 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
909 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
912 // Convert vectors and fp to integer, which can be manipulated.
913 if (!StoredValTy->isIntegerTy()) {
914 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
915 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
918 // If this is a big-endian system, we need to shift the value down to the low
919 // bits so that a truncate will work.
920 if (TD.isBigEndian()) {
921 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
922 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
925 // Truncate the integer to the right size now.
926 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
927 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
929 if (LoadedTy == NewIntTy)
932 // If the result is a pointer, inttoptr.
933 if (LoadedTy->isPointerTy())
934 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
936 // Otherwise, bitcast.
937 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
940 /// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
941 /// be expressed as a base pointer plus a constant offset. Return the base and
942 /// offset to the caller.
943 static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
944 const TargetData &TD) {
945 Operator *PtrOp = dyn_cast<Operator>(Ptr);
946 if (PtrOp == 0) return Ptr;
948 // Just look through bitcasts.
949 if (PtrOp->getOpcode() == Instruction::BitCast)
950 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
952 // If this is a GEP with constant indices, we can look through it.
953 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
954 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
956 gep_type_iterator GTI = gep_type_begin(GEP);
957 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
959 ConstantInt *OpC = cast<ConstantInt>(*I);
960 if (OpC->isZero()) continue;
962 // Handle a struct and array indices which add their offset to the pointer.
963 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
964 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
966 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
967 Offset += OpC->getSExtValue()*Size;
971 // Re-sign extend from the pointer size if needed to get overflow edge cases
973 unsigned PtrSize = TD.getPointerSizeInBits();
975 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
977 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
981 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
982 /// memdep query of a load that ends up being a clobbering memory write (store,
983 /// memset, memcpy, memmove). This means that the write *may* provide bits used
984 /// by the load but we can't be sure because the pointers don't mustalias.
986 /// Check this case to see if there is anything more we can do before we give
987 /// up. This returns -1 if we have to give up, or a byte number in the stored
988 /// value of the piece that feeds the load.
989 static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
991 uint64_t WriteSizeInBits,
992 const TargetData &TD) {
993 // If the loaded or stored value is an first class array or struct, don't try
994 // to transform them. We need to be able to bitcast to integer.
995 if (LoadTy->isStructTy() || LoadTy->isArrayTy())
998 int64_t StoreOffset = 0, LoadOffset = 0;
999 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
1001 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
1002 if (StoreBase != LoadBase)
1005 // If the load and store are to the exact same address, they should have been
1006 // a must alias. AA must have gotten confused.
1007 // FIXME: Study to see if/when this happens.
1008 if (LoadOffset == StoreOffset) {
1010 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
1011 << "Base = " << *StoreBase << "\n"
1012 << "Store Ptr = " << *WritePtr << "\n"
1013 << "Store Offs = " << StoreOffset << "\n"
1014 << "Load Ptr = " << *LoadPtr << "\n";
1020 // If the load and store don't overlap at all, the store doesn't provide
1021 // anything to the load. In this case, they really don't alias at all, AA
1022 // must have gotten confused.
1023 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
1024 // remove this check, as it is duplicated with what we have below.
1025 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
1027 if ((WriteSizeInBits & 7) | (LoadSize & 7))
1029 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
1033 bool isAAFailure = false;
1034 if (StoreOffset < LoadOffset) {
1035 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
1037 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
1041 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"
1042 << "Base = " << *StoreBase << "\n"
1043 << "Store Ptr = " << *WritePtr << "\n"
1044 << "Store Offs = " << StoreOffset << "\n"
1045 << "Load Ptr = " << *LoadPtr << "\n";
1051 // If the Load isn't completely contained within the stored bits, we don't
1052 // have all the bits to feed it. We could do something crazy in the future
1053 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1055 if (StoreOffset > LoadOffset ||
1056 StoreOffset+StoreSize < LoadOffset+LoadSize)
1059 // Okay, we can do this transformation. Return the number of bytes into the
1060 // store that the load is.
1061 return LoadOffset-StoreOffset;
1064 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1065 /// memdep query of a load that ends up being a clobbering store.
1066 static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr,
1068 const TargetData &TD) {
1069 // Cannot handle reading from store of first-class aggregate yet.
1070 if (DepSI->getOperand(0)->getType()->isStructTy() ||
1071 DepSI->getOperand(0)->getType()->isArrayTy())
1074 Value *StorePtr = DepSI->getPointerOperand();
1075 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType());
1076 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1077 StorePtr, StoreSize, TD);
1080 static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr,
1082 const TargetData &TD) {
1083 // If the mem operation is a non-constant size, we can't handle it.
1084 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1085 if (SizeCst == 0) return -1;
1086 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1088 // If this is memset, we just need to see if the offset is valid in the size
1090 if (MI->getIntrinsicID() == Intrinsic::memset)
1091 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1094 // If we have a memcpy/memmove, the only case we can handle is if this is a
1095 // copy from constant memory. In that case, we can read directly from the
1097 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1099 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1100 if (Src == 0) return -1;
1102 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1103 if (GV == 0 || !GV->isConstant()) return -1;
1105 // See if the access is within the bounds of the transfer.
1106 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1107 MI->getDest(), MemSizeInBits, TD);
1111 // Otherwise, see if we can constant fold a load from the constant with the
1112 // offset applied as appropriate.
1113 Src = ConstantExpr::getBitCast(Src,
1114 llvm::Type::getInt8PtrTy(Src->getContext()));
1115 Constant *OffsetCst =
1116 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1117 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1118 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1119 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1125 /// GetStoreValueForLoad - This function is called when we have a
1126 /// memdep query of a load that ends up being a clobbering store. This means
1127 /// that the store *may* provide bits used by the load but we can't be sure
1128 /// because the pointers don't mustalias. Check this case to see if there is
1129 /// anything more we can do before we give up.
1130 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1132 Instruction *InsertPt, const TargetData &TD){
1133 LLVMContext &Ctx = SrcVal->getType()->getContext();
1135 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8;
1136 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1138 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1140 // Compute which bits of the stored value are being used by the load. Convert
1141 // to an integer type to start with.
1142 if (SrcVal->getType()->isPointerTy())
1143 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp");
1144 if (!SrcVal->getType()->isIntegerTy())
1145 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1148 // Shift the bits to the least significant depending on endianness.
1150 if (TD.isLittleEndian())
1151 ShiftAmt = Offset*8;
1153 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1156 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp");
1158 if (LoadSize != StoreSize)
1159 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1162 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1165 /// GetMemInstValueForLoad - This function is called when we have a
1166 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1167 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1168 const Type *LoadTy, Instruction *InsertPt,
1169 const TargetData &TD){
1170 LLVMContext &Ctx = LoadTy->getContext();
1171 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1173 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1175 // We know that this method is only called when the mem transfer fully
1176 // provides the bits for the load.
1177 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1178 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1179 // independently of what the offset is.
1180 Value *Val = MSI->getValue();
1182 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1184 Value *OneElt = Val;
1186 // Splat the value out to the right number of bits.
1187 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1188 // If we can double the number of bytes set, do it.
1189 if (NumBytesSet*2 <= LoadSize) {
1190 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1191 Val = Builder.CreateOr(Val, ShVal);
1196 // Otherwise insert one byte at a time.
1197 Value *ShVal = Builder.CreateShl(Val, 1*8);
1198 Val = Builder.CreateOr(OneElt, ShVal);
1202 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1205 // Otherwise, this is a memcpy/memmove from a constant global.
1206 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1207 Constant *Src = cast<Constant>(MTI->getSource());
1209 // Otherwise, see if we can constant fold a load from the constant with the
1210 // offset applied as appropriate.
1211 Src = ConstantExpr::getBitCast(Src,
1212 llvm::Type::getInt8PtrTy(Src->getContext()));
1213 Constant *OffsetCst =
1214 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1215 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1216 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1217 return ConstantFoldLoadFromConstPtr(Src, &TD);
1222 struct AvailableValueInBlock {
1223 /// BB - The basic block in question.
1226 SimpleVal, // A simple offsetted value that is accessed.
1227 MemIntrin // A memory intrinsic which is loaded from.
1230 /// V - The value that is live out of the block.
1231 PointerIntPair<Value *, 1, ValType> Val;
1233 /// Offset - The byte offset in Val that is interesting for the load query.
1236 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1237 unsigned Offset = 0) {
1238 AvailableValueInBlock Res;
1240 Res.Val.setPointer(V);
1241 Res.Val.setInt(SimpleVal);
1242 Res.Offset = Offset;
1246 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1247 unsigned Offset = 0) {
1248 AvailableValueInBlock Res;
1250 Res.Val.setPointer(MI);
1251 Res.Val.setInt(MemIntrin);
1252 Res.Offset = Offset;
1256 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1257 Value *getSimpleValue() const {
1258 assert(isSimpleValue() && "Wrong accessor");
1259 return Val.getPointer();
1262 MemIntrinsic *getMemIntrinValue() const {
1263 assert(!isSimpleValue() && "Wrong accessor");
1264 return cast<MemIntrinsic>(Val.getPointer());
1267 /// MaterializeAdjustedValue - Emit code into this block to adjust the value
1268 /// defined here to the specified type. This handles various coercion cases.
1269 Value *MaterializeAdjustedValue(const Type *LoadTy,
1270 const TargetData *TD) const {
1272 if (isSimpleValue()) {
1273 Res = getSimpleValue();
1274 if (Res->getType() != LoadTy) {
1275 assert(TD && "Need target data to handle type mismatch case");
1276 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(),
1279 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1280 << *getSimpleValue() << '\n'
1281 << *Res << '\n' << "\n\n\n");
1284 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset,
1285 LoadTy, BB->getTerminator(), *TD);
1286 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1287 << " " << *getMemIntrinValue() << '\n'
1288 << *Res << '\n' << "\n\n\n");
1294 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1295 /// construct SSA form, allowing us to eliminate LI. This returns the value
1296 /// that should be used at LI's definition site.
1297 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1298 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1299 const TargetData *TD,
1300 const DominatorTree &DT,
1301 AliasAnalysis *AA) {
1302 // Check for the fully redundant, dominating load case. In this case, we can
1303 // just use the dominating value directly.
1304 if (ValuesPerBlock.size() == 1 &&
1305 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent()))
1306 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD);
1308 // Otherwise, we have to construct SSA form.
1309 SmallVector<PHINode*, 8> NewPHIs;
1310 SSAUpdater SSAUpdate(&NewPHIs);
1311 SSAUpdate.Initialize(LI);
1313 const Type *LoadTy = LI->getType();
1315 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1316 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1317 BasicBlock *BB = AV.BB;
1319 if (SSAUpdate.HasValueForBlock(BB))
1322 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD));
1325 // Perform PHI construction.
1326 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1328 // If new PHI nodes were created, notify alias analysis.
1329 if (V->getType()->isPointerTy())
1330 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1331 AA->copyValue(LI, NewPHIs[i]);
1336 static bool isLifetimeStart(Instruction *Inst) {
1337 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1338 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1342 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1343 /// non-local by performing PHI construction.
1344 bool GVN::processNonLocalLoad(LoadInst *LI,
1345 SmallVectorImpl<Instruction*> &toErase) {
1346 // Find the non-local dependencies of the load.
1347 SmallVector<NonLocalDepResult, 64> Deps;
1348 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
1350 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: "
1351 // << Deps.size() << *LI << '\n');
1353 // If we had to process more than one hundred blocks to find the
1354 // dependencies, this load isn't worth worrying about. Optimizing
1355 // it will be too expensive.
1356 if (Deps.size() > 100)
1359 // If we had a phi translation failure, we'll have a single entry which is a
1360 // clobber in the current block. Reject this early.
1361 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) {
1363 dbgs() << "GVN: non-local load ";
1364 WriteAsOperand(dbgs(), LI);
1365 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n';
1370 // Filter out useless results (non-locals, etc). Keep track of the blocks
1371 // where we have a value available in repl, also keep track of whether we see
1372 // dependencies that produce an unknown value for the load (such as a call
1373 // that could potentially clobber the load).
1374 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1375 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1377 const TargetData *TD = 0;
1379 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1380 BasicBlock *DepBB = Deps[i].getBB();
1381 MemDepResult DepInfo = Deps[i].getResult();
1383 if (DepInfo.isClobber()) {
1384 // The address being loaded in this non-local block may not be the same as
1385 // the pointer operand of the load if PHI translation occurs. Make sure
1386 // to consider the right address.
1387 Value *Address = Deps[i].getAddress();
1389 // If the dependence is to a store that writes to a superset of the bits
1390 // read by the load, we can extract the bits we need for the load from the
1392 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1394 TD = getAnalysisIfAvailable<TargetData>();
1395 if (TD && Address) {
1396 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1399 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1400 DepSI->getOperand(0),
1407 // If the clobbering value is a memset/memcpy/memmove, see if we can
1408 // forward a value on from it.
1409 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1411 TD = getAnalysisIfAvailable<TargetData>();
1412 if (TD && Address) {
1413 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1416 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1423 UnavailableBlocks.push_back(DepBB);
1427 Instruction *DepInst = DepInfo.getInst();
1429 // Loading the allocation -> undef.
1430 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1431 // Loading immediately after lifetime begin -> undef.
1432 isLifetimeStart(DepInst)) {
1433 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1434 UndefValue::get(LI->getType())));
1438 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1439 // Reject loads and stores that are to the same address but are of
1440 // different types if we have to.
1441 if (S->getOperand(0)->getType() != LI->getType()) {
1443 TD = getAnalysisIfAvailable<TargetData>();
1445 // If the stored value is larger or equal to the loaded value, we can
1447 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0),
1448 LI->getType(), *TD)) {
1449 UnavailableBlocks.push_back(DepBB);
1454 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1459 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1460 // If the types mismatch and we can't handle it, reject reuse of the load.
1461 if (LD->getType() != LI->getType()) {
1463 TD = getAnalysisIfAvailable<TargetData>();
1465 // If the stored value is larger or equal to the loaded value, we can
1467 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1468 UnavailableBlocks.push_back(DepBB);
1472 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD));
1476 UnavailableBlocks.push_back(DepBB);
1480 // If we have no predecessors that produce a known value for this load, exit
1482 if (ValuesPerBlock.empty()) return false;
1484 // If all of the instructions we depend on produce a known value for this
1485 // load, then it is fully redundant and we can use PHI insertion to compute
1486 // its value. Insert PHIs and remove the fully redundant value now.
1487 if (UnavailableBlocks.empty()) {
1488 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1490 // Perform PHI construction.
1491 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1492 VN.getAliasAnalysis());
1493 LI->replaceAllUsesWith(V);
1495 if (isa<PHINode>(V))
1497 if (V->getType()->isPointerTy())
1498 MD->invalidateCachedPointerInfo(V);
1500 toErase.push_back(LI);
1505 if (!EnablePRE || !EnableLoadPRE)
1508 // Okay, we have *some* definitions of the value. This means that the value
1509 // is available in some of our (transitive) predecessors. Lets think about
1510 // doing PRE of this load. This will involve inserting a new load into the
1511 // predecessor when it's not available. We could do this in general, but
1512 // prefer to not increase code size. As such, we only do this when we know
1513 // that we only have to insert *one* load (which means we're basically moving
1514 // the load, not inserting a new one).
1516 SmallPtrSet<BasicBlock *, 4> Blockers;
1517 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1518 Blockers.insert(UnavailableBlocks[i]);
1520 // Lets find first basic block with more than one predecessor. Walk backwards
1521 // through predecessors if needed.
1522 BasicBlock *LoadBB = LI->getParent();
1523 BasicBlock *TmpBB = LoadBB;
1525 bool isSinglePred = false;
1526 bool allSingleSucc = true;
1527 while (TmpBB->getSinglePredecessor()) {
1528 isSinglePred = true;
1529 TmpBB = TmpBB->getSinglePredecessor();
1530 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1532 if (Blockers.count(TmpBB))
1534 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1535 allSingleSucc = false;
1541 // If we have a repl set with LI itself in it, this means we have a loop where
1542 // at least one of the values is LI. Since this means that we won't be able
1543 // to eliminate LI even if we insert uses in the other predecessors, we will
1544 // end up increasing code size. Reject this by scanning for LI.
1545 if (!EnableFullLoadPRE) {
1546 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1547 if (ValuesPerBlock[i].isSimpleValue() &&
1548 ValuesPerBlock[i].getSimpleValue() == LI)
1552 // FIXME: It is extremely unclear what this loop is doing, other than
1553 // artificially restricting loadpre.
1556 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1557 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1558 if (AV.isSimpleValue())
1559 // "Hot" Instruction is in some loop (because it dominates its dep.
1561 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1562 if (DT->dominates(LI, I)) {
1568 // We are interested only in "hot" instructions. We don't want to do any
1569 // mis-optimizations here.
1574 // Check to see how many predecessors have the loaded value fully
1576 DenseMap<BasicBlock*, Value*> PredLoads;
1577 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1578 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1579 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1580 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1581 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1583 bool NeedToSplitEdges = false;
1584 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1586 BasicBlock *Pred = *PI;
1587 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) {
1590 PredLoads[Pred] = 0;
1592 if (Pred->getTerminator()->getNumSuccessors() != 1) {
1593 if (isa<IndirectBrInst>(Pred->getTerminator())) {
1594 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
1595 << Pred->getName() << "': " << *LI << '\n');
1598 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB);
1599 toSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
1600 NeedToSplitEdges = true;
1603 if (NeedToSplitEdges)
1606 // Decide whether PRE is profitable for this load.
1607 unsigned NumUnavailablePreds = PredLoads.size();
1608 assert(NumUnavailablePreds != 0 &&
1609 "Fully available value should be eliminated above!");
1610 if (!EnableFullLoadPRE) {
1611 // If this load is unavailable in multiple predecessors, reject it.
1612 // FIXME: If we could restructure the CFG, we could make a common pred with
1613 // all the preds that don't have an available LI and insert a new load into
1615 if (NumUnavailablePreds != 1)
1619 // Check if the load can safely be moved to all the unavailable predecessors.
1620 bool CanDoPRE = true;
1621 SmallVector<Instruction*, 8> NewInsts;
1622 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1623 E = PredLoads.end(); I != E; ++I) {
1624 BasicBlock *UnavailablePred = I->first;
1626 // Do PHI translation to get its value in the predecessor if necessary. The
1627 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1629 // If all preds have a single successor, then we know it is safe to insert
1630 // the load on the pred (?!?), so we can insert code to materialize the
1631 // pointer if it is not available.
1632 PHITransAddr Address(LI->getOperand(0), TD);
1634 if (allSingleSucc) {
1635 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1638 Address.PHITranslateValue(LoadBB, UnavailablePred, DT);
1639 LoadPtr = Address.getAddr();
1642 // If we couldn't find or insert a computation of this phi translated value,
1645 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1646 << *LI->getOperand(0) << "\n");
1651 // Make sure it is valid to move this load here. We have to watch out for:
1652 // @1 = getelementptr (i8* p, ...
1653 // test p and branch if == 0
1655 // It is valid to have the getelementptr before the test, even if p can be 0,
1656 // as getelementptr only does address arithmetic.
1657 // If we are not pushing the value through any multiple-successor blocks
1658 // we do not have this case. Otherwise, check that the load is safe to
1659 // put anywhere; this can be improved, but should be conservatively safe.
1660 if (!allSingleSucc &&
1661 // FIXME: REEVALUTE THIS.
1662 !isSafeToLoadUnconditionally(LoadPtr,
1663 UnavailablePred->getTerminator(),
1664 LI->getAlignment(), TD)) {
1669 I->second = LoadPtr;
1673 while (!NewInsts.empty())
1674 NewInsts.pop_back_val()->eraseFromParent();
1678 // Okay, we can eliminate this load by inserting a reload in the predecessor
1679 // and using PHI construction to get the value in the other predecessors, do
1681 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1682 DEBUG(if (!NewInsts.empty())
1683 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
1684 << *NewInsts.back() << '\n');
1686 // Assign value numbers to the new instructions.
1687 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1688 // FIXME: We really _ought_ to insert these value numbers into their
1689 // parent's availability map. However, in doing so, we risk getting into
1690 // ordering issues. If a block hasn't been processed yet, we would be
1691 // marking a value as AVAIL-IN, which isn't what we intend.
1692 VN.lookup_or_add(NewInsts[i]);
1695 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1696 E = PredLoads.end(); I != E; ++I) {
1697 BasicBlock *UnavailablePred = I->first;
1698 Value *LoadPtr = I->second;
1700 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1702 UnavailablePred->getTerminator());
1704 // Add the newly created load.
1705 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
1707 MD->invalidateCachedPointerInfo(LoadPtr);
1708 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
1711 // Perform PHI construction.
1712 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1713 VN.getAliasAnalysis());
1714 LI->replaceAllUsesWith(V);
1715 if (isa<PHINode>(V))
1717 if (V->getType()->isPointerTy())
1718 MD->invalidateCachedPointerInfo(V);
1720 toErase.push_back(LI);
1725 /// processLoad - Attempt to eliminate a load, first by eliminating it
1726 /// locally, and then attempting non-local elimination if that fails.
1727 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1731 if (L->isVolatile())
1734 // ... to a pointer that has been loaded from before...
1735 MemDepResult Dep = MD->getDependency(L);
1737 // If the value isn't available, don't do anything!
1738 if (Dep.isClobber()) {
1739 // Check to see if we have something like this:
1740 // store i32 123, i32* %P
1741 // %A = bitcast i32* %P to i8*
1742 // %B = gep i8* %A, i32 1
1745 // We could do that by recognizing if the clobber instructions are obviously
1746 // a common base + constant offset, and if the previous store (or memset)
1747 // completely covers this load. This sort of thing can happen in bitfield
1749 Value *AvailVal = 0;
1750 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1751 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1752 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1753 L->getPointerOperand(),
1756 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset,
1757 L->getType(), L, *TD);
1760 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1761 // a value on from it.
1762 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1763 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1764 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1765 L->getPointerOperand(),
1768 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1773 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1774 << *AvailVal << '\n' << *L << "\n\n\n");
1776 // Replace the load!
1777 L->replaceAllUsesWith(AvailVal);
1778 if (AvailVal->getType()->isPointerTy())
1779 MD->invalidateCachedPointerInfo(AvailVal);
1781 toErase.push_back(L);
1787 // fast print dep, using operator<< on instruction would be too slow
1788 dbgs() << "GVN: load ";
1789 WriteAsOperand(dbgs(), L);
1790 Instruction *I = Dep.getInst();
1791 dbgs() << " is clobbered by " << *I << '\n';
1796 // If it is defined in another block, try harder.
1797 if (Dep.isNonLocal())
1798 return processNonLocalLoad(L, toErase);
1800 Instruction *DepInst = Dep.getInst();
1801 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1802 Value *StoredVal = DepSI->getOperand(0);
1804 // The store and load are to a must-aliased pointer, but they may not
1805 // actually have the same type. See if we know how to reuse the stored
1806 // value (depending on its type).
1807 const TargetData *TD = 0;
1808 if (StoredVal->getType() != L->getType()) {
1809 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1810 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1815 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1816 << '\n' << *L << "\n\n\n");
1823 L->replaceAllUsesWith(StoredVal);
1824 if (StoredVal->getType()->isPointerTy())
1825 MD->invalidateCachedPointerInfo(StoredVal);
1827 toErase.push_back(L);
1832 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1833 Value *AvailableVal = DepLI;
1835 // The loads are of a must-aliased pointer, but they may not actually have
1836 // the same type. See if we know how to reuse the previously loaded value
1837 // (depending on its type).
1838 const TargetData *TD = 0;
1839 if (DepLI->getType() != L->getType()) {
1840 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1841 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1842 if (AvailableVal == 0)
1845 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1846 << "\n" << *L << "\n\n\n");
1853 L->replaceAllUsesWith(AvailableVal);
1854 if (DepLI->getType()->isPointerTy())
1855 MD->invalidateCachedPointerInfo(DepLI);
1857 toErase.push_back(L);
1862 // If this load really doesn't depend on anything, then we must be loading an
1863 // undef value. This can happen when loading for a fresh allocation with no
1864 // intervening stores, for example.
1865 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1866 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1868 toErase.push_back(L);
1873 // If this load occurs either right after a lifetime begin,
1874 // then the loaded value is undefined.
1875 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1876 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1877 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1879 toErase.push_back(L);
1888 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1889 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1890 if (I == localAvail.end())
1893 ValueNumberScope *Locals = I->second;
1895 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num);
1896 if (I != Locals->table.end())
1898 Locals = Locals->parent;
1905 /// processInstruction - When calculating availability, handle an instruction
1906 /// by inserting it into the appropriate sets
1907 bool GVN::processInstruction(Instruction *I,
1908 SmallVectorImpl<Instruction*> &toErase) {
1909 // Ignore dbg info intrinsics.
1910 if (isa<DbgInfoIntrinsic>(I))
1913 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1914 bool Changed = processLoad(LI, toErase);
1917 unsigned Num = VN.lookup_or_add(LI);
1918 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI));
1924 uint32_t NextNum = VN.getNextUnusedValueNumber();
1925 unsigned Num = VN.lookup_or_add(I);
1927 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1928 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1930 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1933 Value *BranchCond = BI->getCondition();
1934 uint32_t CondVN = VN.lookup_or_add(BranchCond);
1936 BasicBlock *TrueSucc = BI->getSuccessor(0);
1937 BasicBlock *FalseSucc = BI->getSuccessor(1);
1939 if (TrueSucc->getSinglePredecessor())
1940 localAvail[TrueSucc]->table[CondVN] =
1941 ConstantInt::getTrue(TrueSucc->getContext());
1942 if (FalseSucc->getSinglePredecessor())
1943 localAvail[FalseSucc]->table[CondVN] =
1944 ConstantInt::getFalse(TrueSucc->getContext());
1948 // Allocations are always uniquely numbered, so we can save time and memory
1949 // by fast failing them.
1950 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1951 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1955 // Collapse PHI nodes
1956 if (PHINode* p = dyn_cast<PHINode>(I)) {
1957 Value *constVal = CollapsePhi(p);
1960 p->replaceAllUsesWith(constVal);
1961 if (MD && constVal->getType()->isPointerTy())
1962 MD->invalidateCachedPointerInfo(constVal);
1965 toErase.push_back(p);
1967 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1970 // If the number we were assigned was a brand new VN, then we don't
1971 // need to do a lookup to see if the number already exists
1972 // somewhere in the domtree: it can't!
1973 } else if (Num == NextNum) {
1974 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1976 // Perform fast-path value-number based elimination of values inherited from
1978 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1981 I->replaceAllUsesWith(repl);
1982 if (MD && repl->getType()->isPointerTy())
1983 MD->invalidateCachedPointerInfo(repl);
1984 toErase.push_back(I);
1988 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1994 /// runOnFunction - This is the main transformation entry point for a function.
1995 bool GVN::runOnFunction(Function& F) {
1997 MD = &getAnalysis<MemoryDependenceAnalysis>();
1998 DT = &getAnalysis<DominatorTree>();
1999 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
2003 bool Changed = false;
2004 bool ShouldContinue = true;
2006 // Merge unconditional branches, allowing PRE to catch more
2007 // optimization opportunities.
2008 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
2009 BasicBlock *BB = FI;
2011 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
2012 if (removedBlock) NumGVNBlocks++;
2014 Changed |= removedBlock;
2017 unsigned Iteration = 0;
2019 while (ShouldContinue) {
2020 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
2021 ShouldContinue = iterateOnFunction(F);
2022 if (splitCriticalEdges())
2023 ShouldContinue = true;
2024 Changed |= ShouldContinue;
2029 bool PREChanged = true;
2030 while (PREChanged) {
2031 PREChanged = performPRE(F);
2032 Changed |= PREChanged;
2035 // FIXME: Should perform GVN again after PRE does something. PRE can move
2036 // computations into blocks where they become fully redundant. Note that
2037 // we can't do this until PRE's critical edge splitting updates memdep.
2038 // Actually, when this happens, we should just fully integrate PRE into GVN.
2040 cleanupGlobalSets();
2046 bool GVN::processBlock(BasicBlock *BB) {
2047 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
2048 // incrementing BI before processing an instruction).
2049 SmallVector<Instruction*, 8> toErase;
2050 bool ChangedFunction = false;
2052 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2054 ChangedFunction |= processInstruction(BI, toErase);
2055 if (toErase.empty()) {
2060 // If we need some instructions deleted, do it now.
2061 NumGVNInstr += toErase.size();
2063 // Avoid iterator invalidation.
2064 bool AtStart = BI == BB->begin();
2068 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2069 E = toErase.end(); I != E; ++I) {
2070 DEBUG(dbgs() << "GVN removed: " << **I << '\n');
2071 if (MD) MD->removeInstruction(*I);
2072 (*I)->eraseFromParent();
2073 DEBUG(verifyRemoved(*I));
2083 return ChangedFunction;
2086 /// performPRE - Perform a purely local form of PRE that looks for diamond
2087 /// control flow patterns and attempts to perform simple PRE at the join point.
2088 bool GVN::performPRE(Function &F) {
2089 bool Changed = false;
2090 DenseMap<BasicBlock*, Value*> predMap;
2091 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2092 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2093 BasicBlock *CurrentBlock = *DI;
2095 // Nothing to PRE in the entry block.
2096 if (CurrentBlock == &F.getEntryBlock()) continue;
2098 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2099 BE = CurrentBlock->end(); BI != BE; ) {
2100 Instruction *CurInst = BI++;
2102 if (isa<AllocaInst>(CurInst) ||
2103 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2104 CurInst->getType()->isVoidTy() ||
2105 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2106 isa<DbgInfoIntrinsic>(CurInst))
2109 uint32_t ValNo = VN.lookup(CurInst);
2111 // Look for the predecessors for PRE opportunities. We're
2112 // only trying to solve the basic diamond case, where
2113 // a value is computed in the successor and one predecessor,
2114 // but not the other. We also explicitly disallow cases
2115 // where the successor is its own predecessor, because they're
2116 // more complicated to get right.
2117 unsigned NumWith = 0;
2118 unsigned NumWithout = 0;
2119 BasicBlock *PREPred = 0;
2122 for (pred_iterator PI = pred_begin(CurrentBlock),
2123 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2124 // We're not interested in PRE where the block is its
2125 // own predecessor, or in blocks with predecessors
2126 // that are not reachable.
2127 if (*PI == CurrentBlock) {
2130 } else if (!localAvail.count(*PI)) {
2135 DenseMap<uint32_t, Value*>::iterator predV =
2136 localAvail[*PI]->table.find(ValNo);
2137 if (predV == localAvail[*PI]->table.end()) {
2140 } else if (predV->second == CurInst) {
2143 predMap[*PI] = predV->second;
2148 // Don't do PRE when it might increase code size, i.e. when
2149 // we would need to insert instructions in more than one pred.
2150 if (NumWithout != 1 || NumWith == 0)
2153 // Don't do PRE across indirect branch.
2154 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2157 // We can't do PRE safely on a critical edge, so instead we schedule
2158 // the edge to be split and perform the PRE the next time we iterate
2160 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
2161 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2162 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2166 // Instantiate the expression in the predecessor that lacked it.
2167 // Because we are going top-down through the block, all value numbers
2168 // will be available in the predecessor by the time we need them. Any
2169 // that weren't originally present will have been instantiated earlier
2171 Instruction *PREInstr = CurInst->clone();
2172 bool success = true;
2173 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2174 Value *Op = PREInstr->getOperand(i);
2175 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2178 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
2179 PREInstr->setOperand(i, V);
2186 // Fail out if we encounter an operand that is not available in
2187 // the PRE predecessor. This is typically because of loads which
2188 // are not value numbered precisely.
2191 DEBUG(verifyRemoved(PREInstr));
2195 PREInstr->insertBefore(PREPred->getTerminator());
2196 PREInstr->setName(CurInst->getName() + ".pre");
2197 predMap[PREPred] = PREInstr;
2198 VN.add(PREInstr, ValNo);
2201 // Update the availability map to include the new instruction.
2202 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr));
2204 // Create a PHI to make the value available in this block.
2205 PHINode* Phi = PHINode::Create(CurInst->getType(),
2206 CurInst->getName() + ".pre-phi",
2207 CurrentBlock->begin());
2208 for (pred_iterator PI = pred_begin(CurrentBlock),
2209 PE = pred_end(CurrentBlock); PI != PE; ++PI)
2210 Phi->addIncoming(predMap[*PI], *PI);
2213 localAvail[CurrentBlock]->table[ValNo] = Phi;
2215 CurInst->replaceAllUsesWith(Phi);
2216 if (MD && Phi->getType()->isPointerTy())
2217 MD->invalidateCachedPointerInfo(Phi);
2220 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
2221 if (MD) MD->removeInstruction(CurInst);
2222 CurInst->eraseFromParent();
2223 DEBUG(verifyRemoved(CurInst));
2228 if (splitCriticalEdges())
2234 /// splitCriticalEdges - Split critical edges found during the previous
2235 /// iteration that may enable further optimization.
2236 bool GVN::splitCriticalEdges() {
2237 if (toSplit.empty())
2240 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
2241 SplitCriticalEdge(Edge.first, Edge.second, this);
2242 } while (!toSplit.empty());
2243 if (MD) MD->invalidateCachedPredecessors();
2247 /// iterateOnFunction - Executes one iteration of GVN
2248 bool GVN::iterateOnFunction(Function &F) {
2249 cleanupGlobalSets();
2251 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2252 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
2254 localAvail[DI->getBlock()] =
2255 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
2257 localAvail[DI->getBlock()] = new ValueNumberScope(0);
2260 // Top-down walk of the dominator tree
2261 bool Changed = false;
2263 // Needed for value numbering with phi construction to work.
2264 ReversePostOrderTraversal<Function*> RPOT(&F);
2265 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2266 RE = RPOT.end(); RI != RE; ++RI)
2267 Changed |= processBlock(*RI);
2269 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2270 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2271 Changed |= processBlock(DI->getBlock());
2277 void GVN::cleanupGlobalSets() {
2280 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
2281 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
2286 /// verifyRemoved - Verify that the specified instruction does not occur in our
2287 /// internal data structures.
2288 void GVN::verifyRemoved(const Instruction *Inst) const {
2289 VN.verifyRemoved(Inst);
2291 // Walk through the value number scope to make sure the instruction isn't
2292 // ferreted away in it.
2293 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
2294 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
2295 const ValueNumberScope *VNS = I->second;
2298 for (DenseMap<uint32_t, Value*>::const_iterator
2299 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
2300 assert(II->second != Inst && "Inst still in value numbering scope!");