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/InstructionSimplify.h"
39 #include "llvm/Analysis/Loads.h"
40 #include "llvm/Analysis/MemoryBuiltins.h"
41 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
42 #include "llvm/Analysis/PHITransAddr.h"
43 #include "llvm/Support/Allocator.h"
44 #include "llvm/Support/CFG.h"
45 #include "llvm/Support/CommandLine.h"
46 #include "llvm/Support/Debug.h"
47 #include "llvm/Support/ErrorHandling.h"
48 #include "llvm/Support/GetElementPtrTypeIterator.h"
49 #include "llvm/Support/IRBuilder.h"
50 #include "llvm/Support/raw_ostream.h"
51 #include "llvm/Target/TargetData.h"
52 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
53 #include "llvm/Transforms/Utils/Local.h"
54 #include "llvm/Transforms/Utils/SSAUpdater.h"
58 STATISTIC(NumGVNInstr, "Number of instructions deleted");
59 STATISTIC(NumGVNLoad, "Number of loads deleted");
60 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
61 STATISTIC(NumGVNBlocks, "Number of blocks merged");
62 STATISTIC(NumPRELoad, "Number of loads PRE'd");
64 static cl::opt<bool> EnablePRE("enable-pre",
65 cl::init(true), cl::Hidden);
66 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
68 //===----------------------------------------------------------------------===//
70 //===----------------------------------------------------------------------===//
72 /// This class holds the mapping between values and value numbers. It is used
73 /// as an efficient mechanism to determine the expression-wise equivalence of
77 enum ExpressionOpcode {
78 ADD = Instruction::Add,
79 FADD = Instruction::FAdd,
80 SUB = Instruction::Sub,
81 FSUB = Instruction::FSub,
82 MUL = Instruction::Mul,
83 FMUL = Instruction::FMul,
84 UDIV = Instruction::UDiv,
85 SDIV = Instruction::SDiv,
86 FDIV = Instruction::FDiv,
87 UREM = Instruction::URem,
88 SREM = Instruction::SRem,
89 FREM = Instruction::FRem,
90 SHL = Instruction::Shl,
91 LSHR = Instruction::LShr,
92 ASHR = Instruction::AShr,
93 AND = Instruction::And,
95 XOR = Instruction::Xor,
96 TRUNC = Instruction::Trunc,
97 ZEXT = Instruction::ZExt,
98 SEXT = Instruction::SExt,
99 FPTOUI = Instruction::FPToUI,
100 FPTOSI = Instruction::FPToSI,
101 UITOFP = Instruction::UIToFP,
102 SITOFP = Instruction::SIToFP,
103 FPTRUNC = Instruction::FPTrunc,
104 FPEXT = Instruction::FPExt,
105 PTRTOINT = Instruction::PtrToInt,
106 INTTOPTR = Instruction::IntToPtr,
107 BITCAST = Instruction::BitCast,
108 ICMPEQ, ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
109 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
110 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
111 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
112 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
113 SHUFFLE, SELECT, GEP, CALL, CONSTANT,
114 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE };
116 ExpressionOpcode opcode;
118 SmallVector<uint32_t, 4> varargs;
122 Expression(ExpressionOpcode o) : opcode(o) { }
124 bool operator==(const Expression &other) const {
125 if (opcode != other.opcode)
127 else if (opcode == EMPTY || opcode == TOMBSTONE)
129 else if (type != other.type)
131 else if (function != other.function)
134 if (varargs.size() != other.varargs.size())
137 for (size_t i = 0; i < varargs.size(); ++i)
138 if (varargs[i] != other.varargs[i])
145 /*bool operator!=(const Expression &other) const {
146 return !(*this == other);
152 DenseMap<Value*, uint32_t> valueNumbering;
153 DenseMap<Expression, uint32_t> expressionNumbering;
155 MemoryDependenceAnalysis* MD;
158 uint32_t nextValueNumber;
160 Expression::ExpressionOpcode getOpcode(CmpInst* C);
161 Expression create_expression(BinaryOperator* BO);
162 Expression create_expression(CmpInst* C);
163 Expression create_expression(ShuffleVectorInst* V);
164 Expression create_expression(ExtractElementInst* C);
165 Expression create_expression(InsertElementInst* V);
166 Expression create_expression(SelectInst* V);
167 Expression create_expression(CastInst* C);
168 Expression create_expression(GetElementPtrInst* G);
169 Expression create_expression(CallInst* C);
170 Expression create_expression(ExtractValueInst* C);
171 Expression create_expression(InsertValueInst* C);
173 uint32_t lookup_or_add_call(CallInst* C);
175 ValueTable() : nextValueNumber(1) { }
176 uint32_t lookup_or_add(Value *V);
177 uint32_t lookup(Value *V) const;
178 void add(Value *V, uint32_t num);
180 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) {
669 initializeGVNPass(*PassRegistry::getPassRegistry());
674 MemoryDependenceAnalysis *MD;
676 const TargetData* TD;
680 /// NumberTable - A mapping from value numers to lists of Value*'s that
681 /// have that value number. Use lookupNumber to query it.
682 DenseMap<uint32_t, std::pair<Value*, void*> > NumberTable;
683 BumpPtrAllocator TableAllocator;
685 /// insert_table - Push a new Value to the NumberTable onto the list for
686 /// its value number.
687 void insert_table(uint32_t N, Value *V) {
688 std::pair<Value*, void*>& Curr = NumberTable[N];
694 std::pair<Value*, void*>* Node =
695 TableAllocator.Allocate<std::pair<Value*, void*> >();
697 Node->second = Curr.second;
701 /// erase_table - Scan the list of values corresponding to a given value
702 /// number, and remove the given value if encountered.
703 void erase_table(uint32_t N, Value *V) {
704 std::pair<Value*, void*>* Prev = 0;
705 std::pair<Value*, void*>* Curr = &NumberTable[N];
707 while (Curr->first != V) {
709 Curr = static_cast<std::pair<Value*, void*>*>(Curr->second);
713 Prev->second = Curr->second;
718 std::pair<Value*, void*>* Next =
719 static_cast<std::pair<Value*, void*>*>(Curr->second);
720 Curr->first = Next->first;
721 Curr->second = Next->second;
726 // List of critical edges to be split between iterations.
727 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
729 // This transformation requires dominator postdominator info
730 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
731 AU.addRequired<DominatorTree>();
733 AU.addRequired<MemoryDependenceAnalysis>();
734 AU.addRequired<AliasAnalysis>();
736 AU.addPreserved<DominatorTree>();
737 AU.addPreserved<AliasAnalysis>();
741 // FIXME: eliminate or document these better
742 bool processLoad(LoadInst* L,
743 SmallVectorImpl<Instruction*> &toErase);
744 bool processInstruction(Instruction *I,
745 SmallVectorImpl<Instruction*> &toErase);
746 bool processNonLocalLoad(LoadInst* L,
747 SmallVectorImpl<Instruction*> &toErase);
748 bool processBlock(BasicBlock *BB);
749 void dump(DenseMap<uint32_t, Value*>& d);
750 bool iterateOnFunction(Function &F);
751 bool performPRE(Function& F);
752 Value *lookupNumber(BasicBlock *BB, uint32_t num);
753 void cleanupGlobalSets();
754 void verifyRemoved(const Instruction *I) const;
755 bool splitCriticalEdges();
761 // createGVNPass - The public interface to this file...
762 FunctionPass *llvm::createGVNPass(bool NoLoads) {
763 return new GVN(NoLoads);
766 INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false)
767 INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)
768 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
769 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
770 INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false)
772 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
774 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
775 E = d.end(); I != E; ++I) {
776 errs() << I->first << "\n";
782 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
783 /// we're analyzing is fully available in the specified block. As we go, keep
784 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
785 /// map is actually a tri-state map with the following values:
786 /// 0) we know the block *is not* fully available.
787 /// 1) we know the block *is* fully available.
788 /// 2) we do not know whether the block is fully available or not, but we are
789 /// currently speculating that it will be.
790 /// 3) we are speculating for this block and have used that to speculate for
792 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
793 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
794 // Optimistically assume that the block is fully available and check to see
795 // if we already know about this block in one lookup.
796 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
797 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
799 // If the entry already existed for this block, return the precomputed value.
801 // If this is a speculative "available" value, mark it as being used for
802 // speculation of other blocks.
803 if (IV.first->second == 2)
804 IV.first->second = 3;
805 return IV.first->second != 0;
808 // Otherwise, see if it is fully available in all predecessors.
809 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
811 // If this block has no predecessors, it isn't live-in here.
813 goto SpeculationFailure;
815 for (; PI != PE; ++PI)
816 // If the value isn't fully available in one of our predecessors, then it
817 // isn't fully available in this block either. Undo our previous
818 // optimistic assumption and bail out.
819 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
820 goto SpeculationFailure;
824 // SpeculationFailure - If we get here, we found out that this is not, after
825 // all, a fully-available block. We have a problem if we speculated on this and
826 // used the speculation to mark other blocks as available.
828 char &BBVal = FullyAvailableBlocks[BB];
830 // If we didn't speculate on this, just return with it set to false.
836 // If we did speculate on this value, we could have blocks set to 1 that are
837 // incorrect. Walk the (transitive) successors of this block and mark them as
839 SmallVector<BasicBlock*, 32> BBWorklist;
840 BBWorklist.push_back(BB);
843 BasicBlock *Entry = BBWorklist.pop_back_val();
844 // Note that this sets blocks to 0 (unavailable) if they happen to not
845 // already be in FullyAvailableBlocks. This is safe.
846 char &EntryVal = FullyAvailableBlocks[Entry];
847 if (EntryVal == 0) continue; // Already unavailable.
849 // Mark as unavailable.
852 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
853 BBWorklist.push_back(*I);
854 } while (!BBWorklist.empty());
860 /// CanCoerceMustAliasedValueToLoad - Return true if
861 /// CoerceAvailableValueToLoadType will succeed.
862 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
864 const TargetData &TD) {
865 // If the loaded or stored value is an first class array or struct, don't try
866 // to transform them. We need to be able to bitcast to integer.
867 if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
868 StoredVal->getType()->isStructTy() ||
869 StoredVal->getType()->isArrayTy())
872 // The store has to be at least as big as the load.
873 if (TD.getTypeSizeInBits(StoredVal->getType()) <
874 TD.getTypeSizeInBits(LoadTy))
881 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
882 /// then a load from a must-aliased pointer of a different type, try to coerce
883 /// the stored value. LoadedTy is the type of the load we want to replace and
884 /// InsertPt is the place to insert new instructions.
886 /// If we can't do it, return null.
887 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
888 const Type *LoadedTy,
889 Instruction *InsertPt,
890 const TargetData &TD) {
891 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
894 const Type *StoredValTy = StoredVal->getType();
896 uint64_t StoreSize = TD.getTypeStoreSizeInBits(StoredValTy);
897 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
899 // If the store and reload are the same size, we can always reuse it.
900 if (StoreSize == LoadSize) {
901 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) {
902 // Pointer to Pointer -> use bitcast.
903 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
906 // Convert source pointers to integers, which can be bitcast.
907 if (StoredValTy->isPointerTy()) {
908 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
909 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
912 const Type *TypeToCastTo = LoadedTy;
913 if (TypeToCastTo->isPointerTy())
914 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
916 if (StoredValTy != TypeToCastTo)
917 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
919 // Cast to pointer if the load needs a pointer type.
920 if (LoadedTy->isPointerTy())
921 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
926 // If the loaded value is smaller than the available value, then we can
927 // extract out a piece from it. If the available value is too small, then we
928 // can't do anything.
929 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
931 // Convert source pointers to integers, which can be manipulated.
932 if (StoredValTy->isPointerTy()) {
933 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
934 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
937 // Convert vectors and fp to integer, which can be manipulated.
938 if (!StoredValTy->isIntegerTy()) {
939 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
940 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
943 // If this is a big-endian system, we need to shift the value down to the low
944 // bits so that a truncate will work.
945 if (TD.isBigEndian()) {
946 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
947 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
950 // Truncate the integer to the right size now.
951 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
952 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
954 if (LoadedTy == NewIntTy)
957 // If the result is a pointer, inttoptr.
958 if (LoadedTy->isPointerTy())
959 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
961 // Otherwise, bitcast.
962 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
965 /// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
966 /// be expressed as a base pointer plus a constant offset. Return the base and
967 /// offset to the caller.
968 static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
969 const TargetData &TD) {
970 Operator *PtrOp = dyn_cast<Operator>(Ptr);
971 if (PtrOp == 0) return Ptr;
973 // Just look through bitcasts.
974 if (PtrOp->getOpcode() == Instruction::BitCast)
975 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
977 // If this is a GEP with constant indices, we can look through it.
978 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
979 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
981 gep_type_iterator GTI = gep_type_begin(GEP);
982 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
984 ConstantInt *OpC = cast<ConstantInt>(*I);
985 if (OpC->isZero()) continue;
987 // Handle a struct and array indices which add their offset to the pointer.
988 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
989 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
991 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
992 Offset += OpC->getSExtValue()*Size;
996 // Re-sign extend from the pointer size if needed to get overflow edge cases
998 unsigned PtrSize = TD.getPointerSizeInBits();
1000 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
1002 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
1006 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
1007 /// memdep query of a load that ends up being a clobbering memory write (store,
1008 /// memset, memcpy, memmove). This means that the write *may* provide bits used
1009 /// by the load but we can't be sure because the pointers don't mustalias.
1011 /// Check this case to see if there is anything more we can do before we give
1012 /// up. This returns -1 if we have to give up, or a byte number in the stored
1013 /// value of the piece that feeds the load.
1014 static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
1016 uint64_t WriteSizeInBits,
1017 const TargetData &TD) {
1018 // If the loaded or stored value is an first class array or struct, don't try
1019 // to transform them. We need to be able to bitcast to integer.
1020 if (LoadTy->isStructTy() || LoadTy->isArrayTy())
1023 int64_t StoreOffset = 0, LoadOffset = 0;
1024 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
1026 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
1027 if (StoreBase != LoadBase)
1030 // If the load and store are to the exact same address, they should have been
1031 // a must alias. AA must have gotten confused.
1032 // FIXME: Study to see if/when this happens. One case is forwarding a memset
1033 // to a load from the base of the memset.
1035 if (LoadOffset == StoreOffset) {
1036 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
1037 << "Base = " << *StoreBase << "\n"
1038 << "Store Ptr = " << *WritePtr << "\n"
1039 << "Store Offs = " << StoreOffset << "\n"
1040 << "Load Ptr = " << *LoadPtr << "\n";
1045 // If the load and store don't overlap at all, the store doesn't provide
1046 // anything to the load. In this case, they really don't alias at all, AA
1047 // must have gotten confused.
1048 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
1049 // remove this check, as it is duplicated with what we have below.
1050 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
1052 if ((WriteSizeInBits & 7) | (LoadSize & 7))
1054 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
1058 bool isAAFailure = false;
1059 if (StoreOffset < LoadOffset)
1060 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
1062 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
1066 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"
1067 << "Base = " << *StoreBase << "\n"
1068 << "Store Ptr = " << *WritePtr << "\n"
1069 << "Store Offs = " << StoreOffset << "\n"
1070 << "Load Ptr = " << *LoadPtr << "\n";
1076 // If the Load isn't completely contained within the stored bits, we don't
1077 // have all the bits to feed it. We could do something crazy in the future
1078 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1080 if (StoreOffset > LoadOffset ||
1081 StoreOffset+StoreSize < LoadOffset+LoadSize)
1084 // Okay, we can do this transformation. Return the number of bytes into the
1085 // store that the load is.
1086 return LoadOffset-StoreOffset;
1089 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1090 /// memdep query of a load that ends up being a clobbering store.
1091 static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr,
1093 const TargetData &TD) {
1094 // Cannot handle reading from store of first-class aggregate yet.
1095 if (DepSI->getValueOperand()->getType()->isStructTy() ||
1096 DepSI->getValueOperand()->getType()->isArrayTy())
1099 Value *StorePtr = DepSI->getPointerOperand();
1100 uint64_t StoreSize =TD.getTypeSizeInBits(DepSI->getValueOperand()->getType());
1101 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1102 StorePtr, StoreSize, TD);
1105 static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr,
1107 const TargetData &TD) {
1108 // If the mem operation is a non-constant size, we can't handle it.
1109 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1110 if (SizeCst == 0) return -1;
1111 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1113 // If this is memset, we just need to see if the offset is valid in the size
1115 if (MI->getIntrinsicID() == Intrinsic::memset)
1116 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1119 // If we have a memcpy/memmove, the only case we can handle is if this is a
1120 // copy from constant memory. In that case, we can read directly from the
1122 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1124 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1125 if (Src == 0) return -1;
1127 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1128 if (GV == 0 || !GV->isConstant()) return -1;
1130 // See if the access is within the bounds of the transfer.
1131 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1132 MI->getDest(), MemSizeInBits, TD);
1136 // Otherwise, see if we can constant fold a load from the constant with the
1137 // offset applied as appropriate.
1138 Src = ConstantExpr::getBitCast(Src,
1139 llvm::Type::getInt8PtrTy(Src->getContext()));
1140 Constant *OffsetCst =
1141 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1142 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1143 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1144 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1150 /// GetStoreValueForLoad - This function is called when we have a
1151 /// memdep query of a load that ends up being a clobbering store. This means
1152 /// that the store *may* provide bits used by the load but we can't be sure
1153 /// because the pointers don't mustalias. Check this case to see if there is
1154 /// anything more we can do before we give up.
1155 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1157 Instruction *InsertPt, const TargetData &TD){
1158 LLVMContext &Ctx = SrcVal->getType()->getContext();
1160 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8;
1161 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8;
1163 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1165 // Compute which bits of the stored value are being used by the load. Convert
1166 // to an integer type to start with.
1167 if (SrcVal->getType()->isPointerTy())
1168 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp");
1169 if (!SrcVal->getType()->isIntegerTy())
1170 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1173 // Shift the bits to the least significant depending on endianness.
1175 if (TD.isLittleEndian())
1176 ShiftAmt = Offset*8;
1178 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1181 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp");
1183 if (LoadSize != StoreSize)
1184 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1187 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1190 /// GetMemInstValueForLoad - This function is called when we have a
1191 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1192 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1193 const Type *LoadTy, Instruction *InsertPt,
1194 const TargetData &TD){
1195 LLVMContext &Ctx = LoadTy->getContext();
1196 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1198 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1200 // We know that this method is only called when the mem transfer fully
1201 // provides the bits for the load.
1202 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1203 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1204 // independently of what the offset is.
1205 Value *Val = MSI->getValue();
1207 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1209 Value *OneElt = Val;
1211 // Splat the value out to the right number of bits.
1212 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1213 // If we can double the number of bytes set, do it.
1214 if (NumBytesSet*2 <= LoadSize) {
1215 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1216 Val = Builder.CreateOr(Val, ShVal);
1221 // Otherwise insert one byte at a time.
1222 Value *ShVal = Builder.CreateShl(Val, 1*8);
1223 Val = Builder.CreateOr(OneElt, ShVal);
1227 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1230 // Otherwise, this is a memcpy/memmove from a constant global.
1231 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1232 Constant *Src = cast<Constant>(MTI->getSource());
1234 // Otherwise, see if we can constant fold a load from the constant with the
1235 // offset applied as appropriate.
1236 Src = ConstantExpr::getBitCast(Src,
1237 llvm::Type::getInt8PtrTy(Src->getContext()));
1238 Constant *OffsetCst =
1239 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1240 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1241 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1242 return ConstantFoldLoadFromConstPtr(Src, &TD);
1247 struct AvailableValueInBlock {
1248 /// BB - The basic block in question.
1251 SimpleVal, // A simple offsetted value that is accessed.
1252 MemIntrin // A memory intrinsic which is loaded from.
1255 /// V - The value that is live out of the block.
1256 PointerIntPair<Value *, 1, ValType> Val;
1258 /// Offset - The byte offset in Val that is interesting for the load query.
1261 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1262 unsigned Offset = 0) {
1263 AvailableValueInBlock Res;
1265 Res.Val.setPointer(V);
1266 Res.Val.setInt(SimpleVal);
1267 Res.Offset = Offset;
1271 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1272 unsigned Offset = 0) {
1273 AvailableValueInBlock Res;
1275 Res.Val.setPointer(MI);
1276 Res.Val.setInt(MemIntrin);
1277 Res.Offset = Offset;
1281 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1282 Value *getSimpleValue() const {
1283 assert(isSimpleValue() && "Wrong accessor");
1284 return Val.getPointer();
1287 MemIntrinsic *getMemIntrinValue() const {
1288 assert(!isSimpleValue() && "Wrong accessor");
1289 return cast<MemIntrinsic>(Val.getPointer());
1292 /// MaterializeAdjustedValue - Emit code into this block to adjust the value
1293 /// defined here to the specified type. This handles various coercion cases.
1294 Value *MaterializeAdjustedValue(const Type *LoadTy,
1295 const TargetData *TD) const {
1297 if (isSimpleValue()) {
1298 Res = getSimpleValue();
1299 if (Res->getType() != LoadTy) {
1300 assert(TD && "Need target data to handle type mismatch case");
1301 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(),
1304 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1305 << *getSimpleValue() << '\n'
1306 << *Res << '\n' << "\n\n\n");
1309 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset,
1310 LoadTy, BB->getTerminator(), *TD);
1311 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1312 << " " << *getMemIntrinValue() << '\n'
1313 << *Res << '\n' << "\n\n\n");
1321 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1322 /// construct SSA form, allowing us to eliminate LI. This returns the value
1323 /// that should be used at LI's definition site.
1324 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1325 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1326 const TargetData *TD,
1327 const DominatorTree &DT,
1328 AliasAnalysis *AA) {
1329 // Check for the fully redundant, dominating load case. In this case, we can
1330 // just use the dominating value directly.
1331 if (ValuesPerBlock.size() == 1 &&
1332 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent()))
1333 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD);
1335 // Otherwise, we have to construct SSA form.
1336 SmallVector<PHINode*, 8> NewPHIs;
1337 SSAUpdater SSAUpdate(&NewPHIs);
1338 SSAUpdate.Initialize(LI->getType(), LI->getName());
1340 const Type *LoadTy = LI->getType();
1342 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1343 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1344 BasicBlock *BB = AV.BB;
1346 if (SSAUpdate.HasValueForBlock(BB))
1349 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD));
1352 // Perform PHI construction.
1353 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1355 // If new PHI nodes were created, notify alias analysis.
1356 if (V->getType()->isPointerTy())
1357 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1358 AA->copyValue(LI, NewPHIs[i]);
1363 static bool isLifetimeStart(const Instruction *Inst) {
1364 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1365 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1369 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1370 /// non-local by performing PHI construction.
1371 bool GVN::processNonLocalLoad(LoadInst *LI,
1372 SmallVectorImpl<Instruction*> &toErase) {
1373 // Find the non-local dependencies of the load.
1374 SmallVector<NonLocalDepResult, 64> Deps;
1375 AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI);
1376 MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps);
1377 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: "
1378 // << Deps.size() << *LI << '\n');
1380 // If we had to process more than one hundred blocks to find the
1381 // dependencies, this load isn't worth worrying about. Optimizing
1382 // it will be too expensive.
1383 if (Deps.size() > 100)
1386 // If we had a phi translation failure, we'll have a single entry which is a
1387 // clobber in the current block. Reject this early.
1388 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) {
1390 dbgs() << "GVN: non-local load ";
1391 WriteAsOperand(dbgs(), LI);
1392 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n';
1397 // Filter out useless results (non-locals, etc). Keep track of the blocks
1398 // where we have a value available in repl, also keep track of whether we see
1399 // dependencies that produce an unknown value for the load (such as a call
1400 // that could potentially clobber the load).
1401 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1402 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1404 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1405 BasicBlock *DepBB = Deps[i].getBB();
1406 MemDepResult DepInfo = Deps[i].getResult();
1408 if (DepInfo.isClobber()) {
1409 // The address being loaded in this non-local block may not be the same as
1410 // the pointer operand of the load if PHI translation occurs. Make sure
1411 // to consider the right address.
1412 Value *Address = Deps[i].getAddress();
1414 // If the dependence is to a store that writes to a superset of the bits
1415 // read by the load, we can extract the bits we need for the load from the
1417 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1418 if (TD && Address) {
1419 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1422 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1423 DepSI->getValueOperand(),
1430 // If the clobbering value is a memset/memcpy/memmove, see if we can
1431 // forward a value on from it.
1432 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1433 if (TD && Address) {
1434 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1437 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1444 UnavailableBlocks.push_back(DepBB);
1448 Instruction *DepInst = DepInfo.getInst();
1450 // Loading the allocation -> undef.
1451 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1452 // Loading immediately after lifetime begin -> undef.
1453 isLifetimeStart(DepInst)) {
1454 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1455 UndefValue::get(LI->getType())));
1459 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1460 // Reject loads and stores that are to the same address but are of
1461 // different types if we have to.
1462 if (S->getValueOperand()->getType() != LI->getType()) {
1463 // If the stored value is larger or equal to the loaded value, we can
1465 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(),
1466 LI->getType(), *TD)) {
1467 UnavailableBlocks.push_back(DepBB);
1472 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1473 S->getValueOperand()));
1477 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1478 // If the types mismatch and we can't handle it, reject reuse of the load.
1479 if (LD->getType() != LI->getType()) {
1480 // If the stored value is larger or equal to the loaded value, we can
1482 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1483 UnavailableBlocks.push_back(DepBB);
1487 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD));
1491 UnavailableBlocks.push_back(DepBB);
1495 // If we have no predecessors that produce a known value for this load, exit
1497 if (ValuesPerBlock.empty()) return false;
1499 // If all of the instructions we depend on produce a known value for this
1500 // load, then it is fully redundant and we can use PHI insertion to compute
1501 // its value. Insert PHIs and remove the fully redundant value now.
1502 if (UnavailableBlocks.empty()) {
1503 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1505 // Perform PHI construction.
1506 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1507 VN.getAliasAnalysis());
1508 LI->replaceAllUsesWith(V);
1510 if (isa<PHINode>(V))
1512 if (V->getType()->isPointerTy())
1513 MD->invalidateCachedPointerInfo(V);
1515 toErase.push_back(LI);
1520 if (!EnablePRE || !EnableLoadPRE)
1523 // Okay, we have *some* definitions of the value. This means that the value
1524 // is available in some of our (transitive) predecessors. Lets think about
1525 // doing PRE of this load. This will involve inserting a new load into the
1526 // predecessor when it's not available. We could do this in general, but
1527 // prefer to not increase code size. As such, we only do this when we know
1528 // that we only have to insert *one* load (which means we're basically moving
1529 // the load, not inserting a new one).
1531 SmallPtrSet<BasicBlock *, 4> Blockers;
1532 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1533 Blockers.insert(UnavailableBlocks[i]);
1535 // Lets find first basic block with more than one predecessor. Walk backwards
1536 // through predecessors if needed.
1537 BasicBlock *LoadBB = LI->getParent();
1538 BasicBlock *TmpBB = LoadBB;
1540 bool isSinglePred = false;
1541 bool allSingleSucc = true;
1542 while (TmpBB->getSinglePredecessor()) {
1543 isSinglePred = true;
1544 TmpBB = TmpBB->getSinglePredecessor();
1545 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1547 if (Blockers.count(TmpBB))
1550 // If any of these blocks has more than one successor (i.e. if the edge we
1551 // just traversed was critical), then there are other paths through this
1552 // block along which the load may not be anticipated. Hoisting the load
1553 // above this block would be adding the load to execution paths along
1554 // which it was not previously executed.
1555 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1562 // FIXME: It is extremely unclear what this loop is doing, other than
1563 // artificially restricting loadpre.
1566 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1567 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1568 if (AV.isSimpleValue())
1569 // "Hot" Instruction is in some loop (because it dominates its dep.
1571 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1572 if (DT->dominates(LI, I)) {
1578 // We are interested only in "hot" instructions. We don't want to do any
1579 // mis-optimizations here.
1584 // Check to see how many predecessors have the loaded value fully
1586 DenseMap<BasicBlock*, Value*> PredLoads;
1587 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1588 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1589 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1590 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1591 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1593 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit;
1594 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1596 BasicBlock *Pred = *PI;
1597 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) {
1600 PredLoads[Pred] = 0;
1602 if (Pred->getTerminator()->getNumSuccessors() != 1) {
1603 if (isa<IndirectBrInst>(Pred->getTerminator())) {
1604 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
1605 << Pred->getName() << "': " << *LI << '\n');
1608 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB);
1609 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
1612 if (!NeedToSplit.empty()) {
1613 toSplit.append(NeedToSplit.begin(), NeedToSplit.end());
1617 // Decide whether PRE is profitable for this load.
1618 unsigned NumUnavailablePreds = PredLoads.size();
1619 assert(NumUnavailablePreds != 0 &&
1620 "Fully available value should be eliminated above!");
1622 // If this load is unavailable in multiple predecessors, reject it.
1623 // FIXME: If we could restructure the CFG, we could make a common pred with
1624 // all the preds that don't have an available LI and insert a new load into
1626 if (NumUnavailablePreds != 1)
1629 // Check if the load can safely be moved to all the unavailable predecessors.
1630 bool CanDoPRE = true;
1631 SmallVector<Instruction*, 8> NewInsts;
1632 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1633 E = PredLoads.end(); I != E; ++I) {
1634 BasicBlock *UnavailablePred = I->first;
1636 // Do PHI translation to get its value in the predecessor if necessary. The
1637 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1639 // If all preds have a single successor, then we know it is safe to insert
1640 // the load on the pred (?!?), so we can insert code to materialize the
1641 // pointer if it is not available.
1642 PHITransAddr Address(LI->getPointerOperand(), TD);
1644 if (allSingleSucc) {
1645 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1648 Address.PHITranslateValue(LoadBB, UnavailablePred, DT);
1649 LoadPtr = Address.getAddr();
1652 // If we couldn't find or insert a computation of this phi translated value,
1655 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1656 << *LI->getPointerOperand() << "\n");
1661 // Make sure it is valid to move this load here. We have to watch out for:
1662 // @1 = getelementptr (i8* p, ...
1663 // test p and branch if == 0
1665 // It is valid to have the getelementptr before the test, even if p can be 0,
1666 // as getelementptr only does address arithmetic.
1667 // If we are not pushing the value through any multiple-successor blocks
1668 // we do not have this case. Otherwise, check that the load is safe to
1669 // put anywhere; this can be improved, but should be conservatively safe.
1670 if (!allSingleSucc &&
1671 // FIXME: REEVALUTE THIS.
1672 !isSafeToLoadUnconditionally(LoadPtr,
1673 UnavailablePred->getTerminator(),
1674 LI->getAlignment(), TD)) {
1679 I->second = LoadPtr;
1683 while (!NewInsts.empty())
1684 NewInsts.pop_back_val()->eraseFromParent();
1688 // Okay, we can eliminate this load by inserting a reload in the predecessor
1689 // and using PHI construction to get the value in the other predecessors, do
1691 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1692 DEBUG(if (!NewInsts.empty())
1693 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
1694 << *NewInsts.back() << '\n');
1696 // Assign value numbers to the new instructions.
1697 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1698 // FIXME: We really _ought_ to insert these value numbers into their
1699 // parent's availability map. However, in doing so, we risk getting into
1700 // ordering issues. If a block hasn't been processed yet, we would be
1701 // marking a value as AVAIL-IN, which isn't what we intend.
1702 VN.lookup_or_add(NewInsts[i]);
1705 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1706 E = PredLoads.end(); I != E; ++I) {
1707 BasicBlock *UnavailablePred = I->first;
1708 Value *LoadPtr = I->second;
1710 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1712 UnavailablePred->getTerminator());
1714 // Add the newly created load.
1715 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
1717 MD->invalidateCachedPointerInfo(LoadPtr);
1718 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
1721 // Perform PHI construction.
1722 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1723 VN.getAliasAnalysis());
1724 LI->replaceAllUsesWith(V);
1725 if (isa<PHINode>(V))
1727 if (V->getType()->isPointerTy())
1728 MD->invalidateCachedPointerInfo(V);
1730 toErase.push_back(LI);
1735 /// processLoad - Attempt to eliminate a load, first by eliminating it
1736 /// locally, and then attempting non-local elimination if that fails.
1737 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1741 if (L->isVolatile())
1744 // ... to a pointer that has been loaded from before...
1745 MemDepResult Dep = MD->getDependency(L);
1747 // If the value isn't available, don't do anything!
1748 if (Dep.isClobber()) {
1749 // Check to see if we have something like this:
1750 // store i32 123, i32* %P
1751 // %A = bitcast i32* %P to i8*
1752 // %B = gep i8* %A, i32 1
1755 // We could do that by recognizing if the clobber instructions are obviously
1756 // a common base + constant offset, and if the previous store (or memset)
1757 // completely covers this load. This sort of thing can happen in bitfield
1759 Value *AvailVal = 0;
1760 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1762 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1763 L->getPointerOperand(),
1766 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset,
1767 L->getType(), L, *TD);
1770 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1771 // a value on from it.
1772 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1774 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1775 L->getPointerOperand(),
1778 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1783 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1784 << *AvailVal << '\n' << *L << "\n\n\n");
1786 // Replace the load!
1787 L->replaceAllUsesWith(AvailVal);
1788 if (AvailVal->getType()->isPointerTy())
1789 MD->invalidateCachedPointerInfo(AvailVal);
1791 toErase.push_back(L);
1797 // fast print dep, using operator<< on instruction would be too slow
1798 dbgs() << "GVN: load ";
1799 WriteAsOperand(dbgs(), L);
1800 Instruction *I = Dep.getInst();
1801 dbgs() << " is clobbered by " << *I << '\n';
1806 // If it is defined in another block, try harder.
1807 if (Dep.isNonLocal())
1808 return processNonLocalLoad(L, toErase);
1810 Instruction *DepInst = Dep.getInst();
1811 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1812 Value *StoredVal = DepSI->getValueOperand();
1814 // The store and load are to a must-aliased pointer, but they may not
1815 // actually have the same type. See if we know how to reuse the stored
1816 // value (depending on its type).
1817 if (StoredVal->getType() != L->getType()) {
1819 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1824 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1825 << '\n' << *L << "\n\n\n");
1832 L->replaceAllUsesWith(StoredVal);
1833 if (StoredVal->getType()->isPointerTy())
1834 MD->invalidateCachedPointerInfo(StoredVal);
1836 toErase.push_back(L);
1841 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1842 Value *AvailableVal = DepLI;
1844 // The loads are of a must-aliased pointer, but they may not actually have
1845 // the same type. See if we know how to reuse the previously loaded value
1846 // (depending on its type).
1847 if (DepLI->getType() != L->getType()) {
1849 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1850 if (AvailableVal == 0)
1853 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1854 << "\n" << *L << "\n\n\n");
1861 L->replaceAllUsesWith(AvailableVal);
1862 if (DepLI->getType()->isPointerTy())
1863 MD->invalidateCachedPointerInfo(DepLI);
1865 toErase.push_back(L);
1870 // If this load really doesn't depend on anything, then we must be loading an
1871 // undef value. This can happen when loading for a fresh allocation with no
1872 // intervening stores, for example.
1873 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1874 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1876 toErase.push_back(L);
1881 // If this load occurs either right after a lifetime begin,
1882 // then the loaded value is undefined.
1883 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1884 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1885 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1887 toErase.push_back(L);
1896 // lookupNumber - In order to find a leader for a given value number at a
1897 // specific basic block, we first obtain the list of all Values for that number,
1898 // and then scan the list to find one whose block dominates the block in
1899 // question. This is fast because dominator tree queries consist of only
1900 // a few comparisons of DFS numbers.
1901 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1902 std::pair<Value*, void*> Vals = NumberTable[num];
1903 if (!Vals.first) return 0;
1904 Instruction *Inst = dyn_cast<Instruction>(Vals.first);
1905 if (!Inst) return Vals.first;
1906 BasicBlock *Parent = Inst->getParent();
1907 if (DT->dominates(Parent, BB))
1910 std::pair<Value*, void*>* Next =
1911 static_cast<std::pair<Value*, void*>*>(Vals.second);
1913 Instruction *CurrInst = dyn_cast<Instruction>(Next->first);
1914 if (!CurrInst) return Next->first;
1916 BasicBlock *Parent = CurrInst->getParent();
1917 if (DT->dominates(Parent, BB))
1920 Next = static_cast<std::pair<Value*, void*>*>(Next->second);
1927 /// processInstruction - When calculating availability, handle an instruction
1928 /// by inserting it into the appropriate sets
1929 bool GVN::processInstruction(Instruction *I,
1930 SmallVectorImpl<Instruction*> &toErase) {
1931 // Ignore dbg info intrinsics.
1932 if (isa<DbgInfoIntrinsic>(I))
1935 // If the instruction can be easily simplified then do so now in preference
1936 // to value numbering it. Value numbering often exposes redundancies, for
1937 // example if it determines that %y is equal to %x then the instruction
1938 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify.
1939 if (Value *V = SimplifyInstruction(I, TD, DT)) {
1940 I->replaceAllUsesWith(V);
1941 if (MD && V->getType()->isPointerTy())
1942 MD->invalidateCachedPointerInfo(V);
1944 toErase.push_back(I);
1948 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1949 bool Changed = processLoad(LI, toErase);
1952 unsigned Num = VN.lookup_or_add(LI);
1953 insert_table(Num, LI);
1959 uint32_t NextNum = VN.getNextUnusedValueNumber();
1960 unsigned Num = VN.lookup_or_add(I);
1962 // Allocations are always uniquely numbered, so we can save time and memory
1963 // by fast failing them.
1964 if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1965 insert_table(Num, I);
1969 if (isa<PHINode>(I)) {
1970 insert_table(Num, I);
1972 // If the number we were assigned was a brand new VN, then we don't
1973 // need to do a lookup to see if the number already exists
1974 // somewhere in the domtree: it can't!
1975 } else if (Num == NextNum) {
1976 insert_table(Num, I);
1978 // Perform fast-path value-number based elimination of values inherited from
1980 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1983 I->replaceAllUsesWith(repl);
1984 if (MD && repl->getType()->isPointerTy())
1985 MD->invalidateCachedPointerInfo(repl);
1986 toErase.push_back(I);
1990 insert_table(Num, I);
1996 /// runOnFunction - This is the main transformation entry point for a function.
1997 bool GVN::runOnFunction(Function& F) {
1999 MD = &getAnalysis<MemoryDependenceAnalysis>();
2000 DT = &getAnalysis<DominatorTree>();
2001 TD = getAnalysisIfAvailable<TargetData>();
2002 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
2006 bool Changed = false;
2007 bool ShouldContinue = true;
2009 // Merge unconditional branches, allowing PRE to catch more
2010 // optimization opportunities.
2011 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
2012 BasicBlock *BB = FI;
2014 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
2015 if (removedBlock) ++NumGVNBlocks;
2017 Changed |= removedBlock;
2020 unsigned Iteration = 0;
2022 while (ShouldContinue) {
2023 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
2024 ShouldContinue = iterateOnFunction(F);
2025 if (splitCriticalEdges())
2026 ShouldContinue = true;
2027 Changed |= ShouldContinue;
2032 bool PREChanged = true;
2033 while (PREChanged) {
2034 PREChanged = performPRE(F);
2035 Changed |= PREChanged;
2038 // FIXME: Should perform GVN again after PRE does something. PRE can move
2039 // computations into blocks where they become fully redundant. Note that
2040 // we can't do this until PRE's critical edge splitting updates memdep.
2041 // Actually, when this happens, we should just fully integrate PRE into GVN.
2043 cleanupGlobalSets();
2049 bool GVN::processBlock(BasicBlock *BB) {
2050 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
2051 // incrementing BI before processing an instruction).
2052 SmallVector<Instruction*, 8> toErase;
2053 bool ChangedFunction = false;
2055 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2057 ChangedFunction |= processInstruction(BI, toErase);
2058 if (toErase.empty()) {
2063 // If we need some instructions deleted, do it now.
2064 NumGVNInstr += toErase.size();
2066 // Avoid iterator invalidation.
2067 bool AtStart = BI == BB->begin();
2071 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2072 E = toErase.end(); I != E; ++I) {
2073 DEBUG(dbgs() << "GVN removed: " << **I << '\n');
2074 if (MD) MD->removeInstruction(*I);
2075 (*I)->eraseFromParent();
2076 DEBUG(verifyRemoved(*I));
2086 return ChangedFunction;
2089 /// performPRE - Perform a purely local form of PRE that looks for diamond
2090 /// control flow patterns and attempts to perform simple PRE at the join point.
2091 bool GVN::performPRE(Function &F) {
2092 bool Changed = false;
2093 DenseMap<BasicBlock*, Value*> predMap;
2094 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2095 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2096 BasicBlock *CurrentBlock = *DI;
2098 // Nothing to PRE in the entry block.
2099 if (CurrentBlock == &F.getEntryBlock()) continue;
2101 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2102 BE = CurrentBlock->end(); BI != BE; ) {
2103 Instruction *CurInst = BI++;
2105 if (isa<AllocaInst>(CurInst) ||
2106 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2107 CurInst->getType()->isVoidTy() ||
2108 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2109 isa<DbgInfoIntrinsic>(CurInst))
2112 // We don't currently value number ANY inline asm calls.
2113 if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
2114 if (CallI->isInlineAsm())
2117 uint32_t ValNo = VN.lookup(CurInst);
2119 // Look for the predecessors for PRE opportunities. We're
2120 // only trying to solve the basic diamond case, where
2121 // a value is computed in the successor and one predecessor,
2122 // but not the other. We also explicitly disallow cases
2123 // where the successor is its own predecessor, because they're
2124 // more complicated to get right.
2125 unsigned NumWith = 0;
2126 unsigned NumWithout = 0;
2127 BasicBlock *PREPred = 0;
2130 for (pred_iterator PI = pred_begin(CurrentBlock),
2131 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2132 BasicBlock *P = *PI;
2133 // We're not interested in PRE where the block is its
2134 // own predecessor, or in blocks with predecessors
2135 // that are not reachable.
2136 if (P == CurrentBlock) {
2139 } else if (!DT->dominates(&F.getEntryBlock(), P)) {
2144 Value* predV = lookupNumber(P, ValNo);
2148 } else if (predV == CurInst) {
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 insert_table(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 BasicBlock *P = *PI;
2219 Phi->addIncoming(predMap[P], P);
2223 insert_table(ValNo, Phi);
2225 CurInst->replaceAllUsesWith(Phi);
2226 if (MD && Phi->getType()->isPointerTy())
2227 MD->invalidateCachedPointerInfo(Phi);
2229 erase_table(ValNo, CurInst);
2231 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
2232 if (MD) MD->removeInstruction(CurInst);
2233 CurInst->eraseFromParent();
2234 DEBUG(verifyRemoved(CurInst));
2239 if (splitCriticalEdges())
2245 /// splitCriticalEdges - Split critical edges found during the previous
2246 /// iteration that may enable further optimization.
2247 bool GVN::splitCriticalEdges() {
2248 if (toSplit.empty())
2251 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
2252 SplitCriticalEdge(Edge.first, Edge.second, this);
2253 } while (!toSplit.empty());
2254 if (MD) MD->invalidateCachedPredecessors();
2258 /// iterateOnFunction - Executes one iteration of GVN
2259 bool GVN::iterateOnFunction(Function &F) {
2260 cleanupGlobalSets();
2262 // Top-down walk of the dominator tree
2263 bool Changed = false;
2265 // Needed for value numbering with phi construction to work.
2266 ReversePostOrderTraversal<Function*> RPOT(&F);
2267 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2268 RE = RPOT.end(); RI != RE; ++RI)
2269 Changed |= processBlock(*RI);
2271 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2272 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2273 Changed |= processBlock(DI->getBlock());
2279 void GVN::cleanupGlobalSets() {
2281 NumberTable.clear();
2282 TableAllocator.Reset();
2285 /// verifyRemoved - Verify that the specified instruction does not occur in our
2286 /// internal data structures.
2287 void GVN::verifyRemoved(const Instruction *Inst) const {
2288 VN.verifyRemoved(Inst);
2290 // Walk through the value number scope to make sure the instruction isn't
2291 // ferreted away in it.
2292 for (DenseMap<uint32_t, std::pair<Value*, void*> >::const_iterator
2293 I = NumberTable.begin(), E = NumberTable.end(); I != E; ++I) {
2294 std::pair<Value*, void*> const * Node = &I->second;
2295 assert(Node->first != Inst && "Inst still in value numbering scope!");
2297 while (Node->second) {
2298 Node = static_cast<std::pair<Value*, void*>*>(Node->second);
2299 assert(Node->first != Inst && "Inst still in value numbering scope!");