1 //===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass performs global value numbering to eliminate fully redundant
11 // instructions. It also performs simple dead load elimination.
13 // Note that this pass does the value numbering itself; it does not use the
14 // ValueNumbering analysis passes.
16 //===----------------------------------------------------------------------===//
18 #define DEBUG_TYPE "gvn"
19 #include "llvm/Transforms/Scalar.h"
20 #include "llvm/BasicBlock.h"
21 #include "llvm/Constants.h"
22 #include "llvm/DerivedTypes.h"
23 #include "llvm/GlobalVariable.h"
24 #include "llvm/Function.h"
25 #include "llvm/IntrinsicInst.h"
26 #include "llvm/LLVMContext.h"
27 #include "llvm/Operator.h"
28 #include "llvm/Value.h"
29 #include "llvm/ADT/DenseMap.h"
30 #include "llvm/ADT/DepthFirstIterator.h"
31 #include "llvm/ADT/PostOrderIterator.h"
32 #include "llvm/ADT/SmallPtrSet.h"
33 #include "llvm/ADT/SmallVector.h"
34 #include "llvm/ADT/Statistic.h"
35 #include "llvm/Analysis/AliasAnalysis.h"
36 #include "llvm/Analysis/ConstantFolding.h"
37 #include "llvm/Analysis/Dominators.h"
38 #include "llvm/Analysis/Loads.h"
39 #include "llvm/Analysis/MemoryBuiltins.h"
40 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
41 #include "llvm/Analysis/PHITransAddr.h"
42 #include "llvm/Support/CFG.h"
43 #include "llvm/Support/CommandLine.h"
44 #include "llvm/Support/Debug.h"
45 #include "llvm/Support/ErrorHandling.h"
46 #include "llvm/Support/GetElementPtrTypeIterator.h"
47 #include "llvm/Support/IRBuilder.h"
48 #include "llvm/Support/raw_ostream.h"
49 #include "llvm/Target/TargetData.h"
50 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
51 #include "llvm/Transforms/Utils/Local.h"
52 #include "llvm/Transforms/Utils/SSAUpdater.h"
55 STATISTIC(NumGVNInstr, "Number of instructions deleted");
56 STATISTIC(NumGVNLoad, "Number of loads deleted");
57 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
58 STATISTIC(NumGVNBlocks, "Number of blocks merged");
59 STATISTIC(NumPRELoad, "Number of loads PRE'd");
61 static cl::opt<bool> EnablePRE("enable-pre",
62 cl::init(true), cl::Hidden);
63 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
64 static cl::opt<bool> EnableFullLoadPRE("enable-full-load-pre", cl::init(false));
66 //===----------------------------------------------------------------------===//
68 //===----------------------------------------------------------------------===//
70 /// This class holds the mapping between values and value numbers. It is used
71 /// as an efficient mechanism to determine the expression-wise equivalence of
75 enum ExpressionOpcode {
76 ADD = Instruction::Add,
77 FADD = Instruction::FAdd,
78 SUB = Instruction::Sub,
79 FSUB = Instruction::FSub,
80 MUL = Instruction::Mul,
81 FMUL = Instruction::FMul,
82 UDIV = Instruction::UDiv,
83 SDIV = Instruction::SDiv,
84 FDIV = Instruction::FDiv,
85 UREM = Instruction::URem,
86 SREM = Instruction::SRem,
87 FREM = Instruction::FRem,
88 SHL = Instruction::Shl,
89 LSHR = Instruction::LShr,
90 ASHR = Instruction::AShr,
91 AND = Instruction::And,
93 XOR = Instruction::Xor,
94 TRUNC = Instruction::Trunc,
95 ZEXT = Instruction::ZExt,
96 SEXT = Instruction::SExt,
97 FPTOUI = Instruction::FPToUI,
98 FPTOSI = Instruction::FPToSI,
99 UITOFP = Instruction::UIToFP,
100 SITOFP = Instruction::SIToFP,
101 FPTRUNC = Instruction::FPTrunc,
102 FPEXT = Instruction::FPExt,
103 PTRTOINT = Instruction::PtrToInt,
104 INTTOPTR = Instruction::IntToPtr,
105 BITCAST = Instruction::BitCast,
106 ICMPEQ, ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
107 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
108 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
109 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
110 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
111 SHUFFLE, SELECT, GEP, CALL, CONSTANT,
112 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE };
114 ExpressionOpcode opcode;
116 SmallVector<uint32_t, 4> varargs;
120 Expression(ExpressionOpcode o) : opcode(o) { }
122 bool operator==(const Expression &other) const {
123 if (opcode != other.opcode)
125 else if (opcode == EMPTY || opcode == TOMBSTONE)
127 else if (type != other.type)
129 else if (function != other.function)
132 if (varargs.size() != other.varargs.size())
135 for (size_t i = 0; i < varargs.size(); ++i)
136 if (varargs[i] != other.varargs[i])
143 /*bool operator!=(const Expression &other) const {
144 return !(*this == other);
150 DenseMap<Value*, uint32_t> valueNumbering;
151 DenseMap<Expression, uint32_t> expressionNumbering;
153 MemoryDependenceAnalysis* MD;
156 uint32_t nextValueNumber;
158 Expression::ExpressionOpcode getOpcode(CmpInst* C);
159 Expression create_expression(BinaryOperator* BO);
160 Expression create_expression(CmpInst* C);
161 Expression create_expression(ShuffleVectorInst* V);
162 Expression create_expression(ExtractElementInst* C);
163 Expression create_expression(InsertElementInst* V);
164 Expression create_expression(SelectInst* V);
165 Expression create_expression(CastInst* C);
166 Expression create_expression(GetElementPtrInst* G);
167 Expression create_expression(CallInst* C);
168 Expression create_expression(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);
179 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
180 AliasAnalysis *getAliasAnalysis() const { return AA; }
181 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
182 void setDomTree(DominatorTree* D) { DT = D; }
183 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
184 void verifyRemoved(const Value *) const;
189 template <> struct DenseMapInfo<Expression> {
190 static inline Expression getEmptyKey() {
191 return Expression(Expression::EMPTY);
194 static inline Expression getTombstoneKey() {
195 return Expression(Expression::TOMBSTONE);
198 static unsigned getHashValue(const Expression e) {
199 unsigned hash = e.opcode;
201 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
202 (unsigned)((uintptr_t)e.type >> 9));
204 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
205 E = e.varargs.end(); I != E; ++I)
206 hash = *I + hash * 37;
208 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
209 (unsigned)((uintptr_t)e.function >> 9)) +
214 static bool isEqual(const Expression &LHS, const Expression &RHS) {
220 struct isPodLike<Expression> { static const bool value = true; };
224 //===----------------------------------------------------------------------===//
225 // ValueTable Internal Functions
226 //===----------------------------------------------------------------------===//
228 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
229 if (isa<ICmpInst>(C)) {
230 switch (C->getPredicate()) {
231 default: // THIS SHOULD NEVER HAPPEN
232 llvm_unreachable("Comparison with unknown predicate?");
233 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
234 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
235 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
236 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
237 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
238 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
239 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
240 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
241 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
242 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
245 switch (C->getPredicate()) {
246 default: // THIS SHOULD NEVER HAPPEN
247 llvm_unreachable("Comparison with unknown predicate?");
248 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
249 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
250 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
251 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
252 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
253 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
254 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
255 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
256 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
257 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
258 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
259 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
260 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
261 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
266 Expression ValueTable::create_expression(CallInst* C) {
269 e.type = C->getType();
270 e.function = C->getCalledFunction();
271 e.opcode = Expression::CALL;
274 for (CallInst::op_iterator I = CS.arg_begin(), E = CS.arg_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->getNumArgOperands() != C->getNumArgOperands()) {
451 valueNumbering[C] = nextValueNumber;
452 return nextValueNumber++;
455 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
456 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
457 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(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->getNumArgOperands() != C->getNumArgOperands()) {
508 valueNumbering[C] = nextValueNumber;
509 return nextValueNumber++;
511 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
512 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
513 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(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 INITIALIZE_PASS(GVN, "gvn", "Global Value Numbering", false, false);
719 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
721 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
722 E = d.end(); I != E; ++I) {
723 errs() << I->first << "\n";
729 static bool isSafeReplacement(PHINode* p, Instruction *inst) {
730 if (!isa<PHINode>(inst))
733 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
735 if (PHINode* use_phi = dyn_cast<PHINode>(*UI))
736 if (use_phi->getParent() == inst->getParent())
742 Value *GVN::CollapsePhi(PHINode *PN) {
743 Value *ConstVal = PN->hasConstantValue(DT);
744 if (!ConstVal) return 0;
746 Instruction *Inst = dyn_cast<Instruction>(ConstVal);
750 if (DT->dominates(Inst, PN))
751 if (isSafeReplacement(PN, Inst))
756 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
757 /// we're analyzing is fully available in the specified block. As we go, keep
758 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
759 /// map is actually a tri-state map with the following values:
760 /// 0) we know the block *is not* fully available.
761 /// 1) we know the block *is* fully available.
762 /// 2) we do not know whether the block is fully available or not, but we are
763 /// currently speculating that it will be.
764 /// 3) we are speculating for this block and have used that to speculate for
766 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
767 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
768 // Optimistically assume that the block is fully available and check to see
769 // if we already know about this block in one lookup.
770 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
771 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
773 // If the entry already existed for this block, return the precomputed value.
775 // If this is a speculative "available" value, mark it as being used for
776 // speculation of other blocks.
777 if (IV.first->second == 2)
778 IV.first->second = 3;
779 return IV.first->second != 0;
782 // Otherwise, see if it is fully available in all predecessors.
783 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
785 // If this block has no predecessors, it isn't live-in here.
787 goto SpeculationFailure;
789 for (; PI != PE; ++PI)
790 // If the value isn't fully available in one of our predecessors, then it
791 // isn't fully available in this block either. Undo our previous
792 // optimistic assumption and bail out.
793 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
794 goto SpeculationFailure;
798 // SpeculationFailure - If we get here, we found out that this is not, after
799 // all, a fully-available block. We have a problem if we speculated on this and
800 // used the speculation to mark other blocks as available.
802 char &BBVal = FullyAvailableBlocks[BB];
804 // If we didn't speculate on this, just return with it set to false.
810 // If we did speculate on this value, we could have blocks set to 1 that are
811 // incorrect. Walk the (transitive) successors of this block and mark them as
813 SmallVector<BasicBlock*, 32> BBWorklist;
814 BBWorklist.push_back(BB);
817 BasicBlock *Entry = BBWorklist.pop_back_val();
818 // Note that this sets blocks to 0 (unavailable) if they happen to not
819 // already be in FullyAvailableBlocks. This is safe.
820 char &EntryVal = FullyAvailableBlocks[Entry];
821 if (EntryVal == 0) continue; // Already unavailable.
823 // Mark as unavailable.
826 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
827 BBWorklist.push_back(*I);
828 } while (!BBWorklist.empty());
834 /// CanCoerceMustAliasedValueToLoad - Return true if
835 /// CoerceAvailableValueToLoadType will succeed.
836 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
838 const TargetData &TD) {
839 // If the loaded or stored value is an first class array or struct, don't try
840 // to transform them. We need to be able to bitcast to integer.
841 if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
842 StoredVal->getType()->isStructTy() ||
843 StoredVal->getType()->isArrayTy())
846 // The store has to be at least as big as the load.
847 if (TD.getTypeSizeInBits(StoredVal->getType()) <
848 TD.getTypeSizeInBits(LoadTy))
855 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
856 /// then a load from a must-aliased pointer of a different type, try to coerce
857 /// the stored value. LoadedTy is the type of the load we want to replace and
858 /// InsertPt is the place to insert new instructions.
860 /// If we can't do it, return null.
861 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
862 const Type *LoadedTy,
863 Instruction *InsertPt,
864 const TargetData &TD) {
865 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
868 const Type *StoredValTy = StoredVal->getType();
870 uint64_t StoreSize = TD.getTypeStoreSizeInBits(StoredValTy);
871 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
873 // If the store and reload are the same size, we can always reuse it.
874 if (StoreSize == LoadSize) {
875 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) {
876 // Pointer to Pointer -> use bitcast.
877 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
880 // Convert source pointers to integers, which can be bitcast.
881 if (StoredValTy->isPointerTy()) {
882 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
883 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
886 const Type *TypeToCastTo = LoadedTy;
887 if (TypeToCastTo->isPointerTy())
888 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
890 if (StoredValTy != TypeToCastTo)
891 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
893 // Cast to pointer if the load needs a pointer type.
894 if (LoadedTy->isPointerTy())
895 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
900 // If the loaded value is smaller than the available value, then we can
901 // extract out a piece from it. If the available value is too small, then we
902 // can't do anything.
903 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
905 // Convert source pointers to integers, which can be manipulated.
906 if (StoredValTy->isPointerTy()) {
907 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
908 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
911 // Convert vectors and fp to integer, which can be manipulated.
912 if (!StoredValTy->isIntegerTy()) {
913 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
914 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
917 // If this is a big-endian system, we need to shift the value down to the low
918 // bits so that a truncate will work.
919 if (TD.isBigEndian()) {
920 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
921 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
924 // Truncate the integer to the right size now.
925 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
926 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
928 if (LoadedTy == NewIntTy)
931 // If the result is a pointer, inttoptr.
932 if (LoadedTy->isPointerTy())
933 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
935 // Otherwise, bitcast.
936 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
939 /// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
940 /// be expressed as a base pointer plus a constant offset. Return the base and
941 /// offset to the caller.
942 static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
943 const TargetData &TD) {
944 Operator *PtrOp = dyn_cast<Operator>(Ptr);
945 if (PtrOp == 0) return Ptr;
947 // Just look through bitcasts.
948 if (PtrOp->getOpcode() == Instruction::BitCast)
949 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
951 // If this is a GEP with constant indices, we can look through it.
952 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
953 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
955 gep_type_iterator GTI = gep_type_begin(GEP);
956 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
958 ConstantInt *OpC = cast<ConstantInt>(*I);
959 if (OpC->isZero()) continue;
961 // Handle a struct and array indices which add their offset to the pointer.
962 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
963 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
965 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
966 Offset += OpC->getSExtValue()*Size;
970 // Re-sign extend from the pointer size if needed to get overflow edge cases
972 unsigned PtrSize = TD.getPointerSizeInBits();
974 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
976 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
980 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
981 /// memdep query of a load that ends up being a clobbering memory write (store,
982 /// memset, memcpy, memmove). This means that the write *may* provide bits used
983 /// by the load but we can't be sure because the pointers don't mustalias.
985 /// Check this case to see if there is anything more we can do before we give
986 /// up. This returns -1 if we have to give up, or a byte number in the stored
987 /// value of the piece that feeds the load.
988 static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
990 uint64_t WriteSizeInBits,
991 const TargetData &TD) {
992 // If the loaded or stored value is an first class array or struct, don't try
993 // to transform them. We need to be able to bitcast to integer.
994 if (LoadTy->isStructTy() || LoadTy->isArrayTy())
997 int64_t StoreOffset = 0, LoadOffset = 0;
998 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
1000 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
1001 if (StoreBase != LoadBase)
1004 // If the load and store are to the exact same address, they should have been
1005 // a must alias. AA must have gotten confused.
1006 // FIXME: Study to see if/when this happens. One case is forwarding a memset
1007 // to a load from the base of the memset.
1009 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";
1019 // If the load and store don't overlap at all, the store doesn't provide
1020 // anything to the load. In this case, they really don't alias at all, AA
1021 // must have gotten confused.
1022 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
1023 // remove this check, as it is duplicated with what we have below.
1024 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
1026 if ((WriteSizeInBits & 7) | (LoadSize & 7))
1028 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
1032 bool isAAFailure = false;
1033 if (StoreOffset < LoadOffset)
1034 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
1036 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
1040 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"
1041 << "Base = " << *StoreBase << "\n"
1042 << "Store Ptr = " << *WritePtr << "\n"
1043 << "Store Offs = " << StoreOffset << "\n"
1044 << "Load Ptr = " << *LoadPtr << "\n";
1050 // If the Load isn't completely contained within the stored bits, we don't
1051 // have all the bits to feed it. We could do something crazy in the future
1052 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1054 if (StoreOffset > LoadOffset ||
1055 StoreOffset+StoreSize < LoadOffset+LoadSize)
1058 // Okay, we can do this transformation. Return the number of bytes into the
1059 // store that the load is.
1060 return LoadOffset-StoreOffset;
1063 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1064 /// memdep query of a load that ends up being a clobbering store.
1065 static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr,
1067 const TargetData &TD) {
1068 // Cannot handle reading from store of first-class aggregate yet.
1069 if (DepSI->getOperand(0)->getType()->isStructTy() ||
1070 DepSI->getOperand(0)->getType()->isArrayTy())
1073 Value *StorePtr = DepSI->getPointerOperand();
1074 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType());
1075 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1076 StorePtr, StoreSize, TD);
1079 static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr,
1081 const TargetData &TD) {
1082 // If the mem operation is a non-constant size, we can't handle it.
1083 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1084 if (SizeCst == 0) return -1;
1085 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1087 // If this is memset, we just need to see if the offset is valid in the size
1089 if (MI->getIntrinsicID() == Intrinsic::memset)
1090 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1093 // If we have a memcpy/memmove, the only case we can handle is if this is a
1094 // copy from constant memory. In that case, we can read directly from the
1096 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1098 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1099 if (Src == 0) return -1;
1101 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1102 if (GV == 0 || !GV->isConstant()) return -1;
1104 // See if the access is within the bounds of the transfer.
1105 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1106 MI->getDest(), MemSizeInBits, TD);
1110 // Otherwise, see if we can constant fold a load from the constant with the
1111 // offset applied as appropriate.
1112 Src = ConstantExpr::getBitCast(Src,
1113 llvm::Type::getInt8PtrTy(Src->getContext()));
1114 Constant *OffsetCst =
1115 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1116 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1117 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1118 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1124 /// GetStoreValueForLoad - This function is called when we have a
1125 /// memdep query of a load that ends up being a clobbering store. This means
1126 /// that the store *may* provide bits used by the load but we can't be sure
1127 /// because the pointers don't mustalias. Check this case to see if there is
1128 /// anything more we can do before we give up.
1129 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1131 Instruction *InsertPt, const TargetData &TD){
1132 LLVMContext &Ctx = SrcVal->getType()->getContext();
1134 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8;
1135 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8;
1137 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1139 // Compute which bits of the stored value are being used by the load. Convert
1140 // to an integer type to start with.
1141 if (SrcVal->getType()->isPointerTy())
1142 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp");
1143 if (!SrcVal->getType()->isIntegerTy())
1144 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1147 // Shift the bits to the least significant depending on endianness.
1149 if (TD.isLittleEndian())
1150 ShiftAmt = Offset*8;
1152 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1155 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp");
1157 if (LoadSize != StoreSize)
1158 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1161 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1164 /// GetMemInstValueForLoad - This function is called when we have a
1165 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1166 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1167 const Type *LoadTy, Instruction *InsertPt,
1168 const TargetData &TD){
1169 LLVMContext &Ctx = LoadTy->getContext();
1170 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1172 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1174 // We know that this method is only called when the mem transfer fully
1175 // provides the bits for the load.
1176 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1177 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1178 // independently of what the offset is.
1179 Value *Val = MSI->getValue();
1181 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1183 Value *OneElt = Val;
1185 // Splat the value out to the right number of bits.
1186 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1187 // If we can double the number of bytes set, do it.
1188 if (NumBytesSet*2 <= LoadSize) {
1189 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1190 Val = Builder.CreateOr(Val, ShVal);
1195 // Otherwise insert one byte at a time.
1196 Value *ShVal = Builder.CreateShl(Val, 1*8);
1197 Val = Builder.CreateOr(OneElt, ShVal);
1201 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1204 // Otherwise, this is a memcpy/memmove from a constant global.
1205 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1206 Constant *Src = cast<Constant>(MTI->getSource());
1208 // Otherwise, see if we can constant fold a load from the constant with the
1209 // offset applied as appropriate.
1210 Src = ConstantExpr::getBitCast(Src,
1211 llvm::Type::getInt8PtrTy(Src->getContext()));
1212 Constant *OffsetCst =
1213 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1214 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1215 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1216 return ConstantFoldLoadFromConstPtr(Src, &TD);
1221 struct AvailableValueInBlock {
1222 /// BB - The basic block in question.
1225 SimpleVal, // A simple offsetted value that is accessed.
1226 MemIntrin // A memory intrinsic which is loaded from.
1229 /// V - The value that is live out of the block.
1230 PointerIntPair<Value *, 1, ValType> Val;
1232 /// Offset - The byte offset in Val that is interesting for the load query.
1235 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1236 unsigned Offset = 0) {
1237 AvailableValueInBlock Res;
1239 Res.Val.setPointer(V);
1240 Res.Val.setInt(SimpleVal);
1241 Res.Offset = Offset;
1245 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1246 unsigned Offset = 0) {
1247 AvailableValueInBlock Res;
1249 Res.Val.setPointer(MI);
1250 Res.Val.setInt(MemIntrin);
1251 Res.Offset = Offset;
1255 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1256 Value *getSimpleValue() const {
1257 assert(isSimpleValue() && "Wrong accessor");
1258 return Val.getPointer();
1261 MemIntrinsic *getMemIntrinValue() const {
1262 assert(!isSimpleValue() && "Wrong accessor");
1263 return cast<MemIntrinsic>(Val.getPointer());
1266 /// MaterializeAdjustedValue - Emit code into this block to adjust the value
1267 /// defined here to the specified type. This handles various coercion cases.
1268 Value *MaterializeAdjustedValue(const Type *LoadTy,
1269 const TargetData *TD) const {
1271 if (isSimpleValue()) {
1272 Res = getSimpleValue();
1273 if (Res->getType() != LoadTy) {
1274 assert(TD && "Need target data to handle type mismatch case");
1275 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(),
1278 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1279 << *getSimpleValue() << '\n'
1280 << *Res << '\n' << "\n\n\n");
1283 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset,
1284 LoadTy, BB->getTerminator(), *TD);
1285 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1286 << " " << *getMemIntrinValue() << '\n'
1287 << *Res << '\n' << "\n\n\n");
1295 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1296 /// construct SSA form, allowing us to eliminate LI. This returns the value
1297 /// that should be used at LI's definition site.
1298 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1299 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1300 const TargetData *TD,
1301 const DominatorTree &DT,
1302 AliasAnalysis *AA) {
1303 // Check for the fully redundant, dominating load case. In this case, we can
1304 // just use the dominating value directly.
1305 if (ValuesPerBlock.size() == 1 &&
1306 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent()))
1307 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD);
1309 // Otherwise, we have to construct SSA form.
1310 SmallVector<PHINode*, 8> NewPHIs;
1311 SSAUpdater SSAUpdate(&NewPHIs);
1312 SSAUpdate.Initialize(LI->getType(), LI->getName());
1314 const Type *LoadTy = LI->getType();
1316 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1317 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1318 BasicBlock *BB = AV.BB;
1320 if (SSAUpdate.HasValueForBlock(BB))
1323 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD));
1326 // Perform PHI construction.
1327 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1329 // If new PHI nodes were created, notify alias analysis.
1330 if (V->getType()->isPointerTy())
1331 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1332 AA->copyValue(LI, NewPHIs[i]);
1337 static bool isLifetimeStart(const Instruction *Inst) {
1338 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1339 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1343 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1344 /// non-local by performing PHI construction.
1345 bool GVN::processNonLocalLoad(LoadInst *LI,
1346 SmallVectorImpl<Instruction*> &toErase) {
1347 // Find the non-local dependencies of the load.
1348 SmallVector<NonLocalDepResult, 64> Deps;
1349 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
1351 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: "
1352 // << Deps.size() << *LI << '\n');
1354 // If we had to process more than one hundred blocks to find the
1355 // dependencies, this load isn't worth worrying about. Optimizing
1356 // it will be too expensive.
1357 if (Deps.size() > 100)
1360 // If we had a phi translation failure, we'll have a single entry which is a
1361 // clobber in the current block. Reject this early.
1362 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) {
1364 dbgs() << "GVN: non-local load ";
1365 WriteAsOperand(dbgs(), LI);
1366 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n';
1371 // Filter out useless results (non-locals, etc). Keep track of the blocks
1372 // where we have a value available in repl, also keep track of whether we see
1373 // dependencies that produce an unknown value for the load (such as a call
1374 // that could potentially clobber the load).
1375 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1376 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1378 const TargetData *TD = 0;
1380 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1381 BasicBlock *DepBB = Deps[i].getBB();
1382 MemDepResult DepInfo = Deps[i].getResult();
1384 if (DepInfo.isClobber()) {
1385 // The address being loaded in this non-local block may not be the same as
1386 // the pointer operand of the load if PHI translation occurs. Make sure
1387 // to consider the right address.
1388 Value *Address = Deps[i].getAddress();
1390 // If the dependence is to a store that writes to a superset of the bits
1391 // read by the load, we can extract the bits we need for the load from the
1393 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1395 TD = getAnalysisIfAvailable<TargetData>();
1396 if (TD && Address) {
1397 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1400 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1401 DepSI->getOperand(0),
1408 // If the clobbering value is a memset/memcpy/memmove, see if we can
1409 // forward a value on from it.
1410 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1412 TD = getAnalysisIfAvailable<TargetData>();
1413 if (TD && Address) {
1414 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1417 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1424 UnavailableBlocks.push_back(DepBB);
1428 Instruction *DepInst = DepInfo.getInst();
1430 // Loading the allocation -> undef.
1431 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1432 // Loading immediately after lifetime begin -> undef.
1433 isLifetimeStart(DepInst)) {
1434 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1435 UndefValue::get(LI->getType())));
1439 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1440 // Reject loads and stores that are to the same address but are of
1441 // different types if we have to.
1442 if (S->getOperand(0)->getType() != LI->getType()) {
1444 TD = getAnalysisIfAvailable<TargetData>();
1446 // If the stored value is larger or equal to the loaded value, we can
1448 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0),
1449 LI->getType(), *TD)) {
1450 UnavailableBlocks.push_back(DepBB);
1455 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1460 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1461 // If the types mismatch and we can't handle it, reject reuse of the load.
1462 if (LD->getType() != LI->getType()) {
1464 TD = getAnalysisIfAvailable<TargetData>();
1466 // If the stored value is larger or equal to the loaded value, we can
1468 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1469 UnavailableBlocks.push_back(DepBB);
1473 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD));
1477 UnavailableBlocks.push_back(DepBB);
1481 // If we have no predecessors that produce a known value for this load, exit
1483 if (ValuesPerBlock.empty()) return false;
1485 // If all of the instructions we depend on produce a known value for this
1486 // load, then it is fully redundant and we can use PHI insertion to compute
1487 // its value. Insert PHIs and remove the fully redundant value now.
1488 if (UnavailableBlocks.empty()) {
1489 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1491 // Perform PHI construction.
1492 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1493 VN.getAliasAnalysis());
1494 LI->replaceAllUsesWith(V);
1496 if (isa<PHINode>(V))
1498 if (V->getType()->isPointerTy())
1499 MD->invalidateCachedPointerInfo(V);
1501 toErase.push_back(LI);
1506 if (!EnablePRE || !EnableLoadPRE)
1509 // Okay, we have *some* definitions of the value. This means that the value
1510 // is available in some of our (transitive) predecessors. Lets think about
1511 // doing PRE of this load. This will involve inserting a new load into the
1512 // predecessor when it's not available. We could do this in general, but
1513 // prefer to not increase code size. As such, we only do this when we know
1514 // that we only have to insert *one* load (which means we're basically moving
1515 // the load, not inserting a new one).
1517 SmallPtrSet<BasicBlock *, 4> Blockers;
1518 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1519 Blockers.insert(UnavailableBlocks[i]);
1521 // Lets find first basic block with more than one predecessor. Walk backwards
1522 // through predecessors if needed.
1523 BasicBlock *LoadBB = LI->getParent();
1524 BasicBlock *TmpBB = LoadBB;
1526 bool isSinglePred = false;
1527 bool allSingleSucc = true;
1528 while (TmpBB->getSinglePredecessor()) {
1529 isSinglePred = true;
1530 TmpBB = TmpBB->getSinglePredecessor();
1531 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1533 if (Blockers.count(TmpBB))
1536 // If any of these blocks has more than one successor (i.e. if the edge we
1537 // just traversed was critical), then there are other paths through this
1538 // block along which the load may not be anticipated. Hoisting the load
1539 // above this block would be adding the load to execution paths along
1540 // which it was not previously executed.
1541 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1548 // FIXME: It is extremely unclear what this loop is doing, other than
1549 // artificially restricting loadpre.
1552 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1553 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1554 if (AV.isSimpleValue())
1555 // "Hot" Instruction is in some loop (because it dominates its dep.
1557 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1558 if (DT->dominates(LI, I)) {
1564 // We are interested only in "hot" instructions. We don't want to do any
1565 // mis-optimizations here.
1570 // Check to see how many predecessors have the loaded value fully
1572 DenseMap<BasicBlock*, Value*> PredLoads;
1573 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1574 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1575 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1576 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1577 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1579 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit;
1580 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1582 BasicBlock *Pred = *PI;
1583 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) {
1586 PredLoads[Pred] = 0;
1588 if (Pred->getTerminator()->getNumSuccessors() != 1) {
1589 if (isa<IndirectBrInst>(Pred->getTerminator())) {
1590 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
1591 << Pred->getName() << "': " << *LI << '\n');
1594 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB);
1595 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
1598 if (!NeedToSplit.empty()) {
1599 toSplit.append(NeedToSplit.begin(), NeedToSplit.end());
1603 // Decide whether PRE is profitable for this load.
1604 unsigned NumUnavailablePreds = PredLoads.size();
1605 assert(NumUnavailablePreds != 0 &&
1606 "Fully available value should be eliminated above!");
1607 if (!EnableFullLoadPRE) {
1608 // If this load is unavailable in multiple predecessors, reject it.
1609 // FIXME: If we could restructure the CFG, we could make a common pred with
1610 // all the preds that don't have an available LI and insert a new load into
1612 if (NumUnavailablePreds != 1)
1616 // Check if the load can safely be moved to all the unavailable predecessors.
1617 bool CanDoPRE = true;
1618 SmallVector<Instruction*, 8> NewInsts;
1619 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1620 E = PredLoads.end(); I != E; ++I) {
1621 BasicBlock *UnavailablePred = I->first;
1623 // Do PHI translation to get its value in the predecessor if necessary. The
1624 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1626 // If all preds have a single successor, then we know it is safe to insert
1627 // the load on the pred (?!?), so we can insert code to materialize the
1628 // pointer if it is not available.
1629 PHITransAddr Address(LI->getOperand(0), TD);
1631 if (allSingleSucc) {
1632 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1635 Address.PHITranslateValue(LoadBB, UnavailablePred, DT);
1636 LoadPtr = Address.getAddr();
1639 // If we couldn't find or insert a computation of this phi translated value,
1642 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1643 << *LI->getOperand(0) << "\n");
1648 // Make sure it is valid to move this load here. We have to watch out for:
1649 // @1 = getelementptr (i8* p, ...
1650 // test p and branch if == 0
1652 // It is valid to have the getelementptr before the test, even if p can be 0,
1653 // as getelementptr only does address arithmetic.
1654 // If we are not pushing the value through any multiple-successor blocks
1655 // we do not have this case. Otherwise, check that the load is safe to
1656 // put anywhere; this can be improved, but should be conservatively safe.
1657 if (!allSingleSucc &&
1658 // FIXME: REEVALUTE THIS.
1659 !isSafeToLoadUnconditionally(LoadPtr,
1660 UnavailablePred->getTerminator(),
1661 LI->getAlignment(), TD)) {
1666 I->second = LoadPtr;
1670 while (!NewInsts.empty())
1671 NewInsts.pop_back_val()->eraseFromParent();
1675 // Okay, we can eliminate this load by inserting a reload in the predecessor
1676 // and using PHI construction to get the value in the other predecessors, do
1678 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1679 DEBUG(if (!NewInsts.empty())
1680 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
1681 << *NewInsts.back() << '\n');
1683 // Assign value numbers to the new instructions.
1684 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1685 // FIXME: We really _ought_ to insert these value numbers into their
1686 // parent's availability map. However, in doing so, we risk getting into
1687 // ordering issues. If a block hasn't been processed yet, we would be
1688 // marking a value as AVAIL-IN, which isn't what we intend.
1689 VN.lookup_or_add(NewInsts[i]);
1692 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1693 E = PredLoads.end(); I != E; ++I) {
1694 BasicBlock *UnavailablePred = I->first;
1695 Value *LoadPtr = I->second;
1697 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1699 UnavailablePred->getTerminator());
1701 // Add the newly created load.
1702 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
1704 MD->invalidateCachedPointerInfo(LoadPtr);
1705 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
1708 // Perform PHI construction.
1709 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1710 VN.getAliasAnalysis());
1711 LI->replaceAllUsesWith(V);
1712 if (isa<PHINode>(V))
1714 if (V->getType()->isPointerTy())
1715 MD->invalidateCachedPointerInfo(V);
1717 toErase.push_back(LI);
1722 /// processLoad - Attempt to eliminate a load, first by eliminating it
1723 /// locally, and then attempting non-local elimination if that fails.
1724 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1728 if (L->isVolatile())
1731 // ... to a pointer that has been loaded from before...
1732 MemDepResult Dep = MD->getDependency(L);
1734 // If the value isn't available, don't do anything!
1735 if (Dep.isClobber()) {
1736 // Check to see if we have something like this:
1737 // store i32 123, i32* %P
1738 // %A = bitcast i32* %P to i8*
1739 // %B = gep i8* %A, i32 1
1742 // We could do that by recognizing if the clobber instructions are obviously
1743 // a common base + constant offset, and if the previous store (or memset)
1744 // completely covers this load. This sort of thing can happen in bitfield
1746 Value *AvailVal = 0;
1747 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1748 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1749 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1750 L->getPointerOperand(),
1753 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset,
1754 L->getType(), L, *TD);
1757 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1758 // a value on from it.
1759 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1760 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1761 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1762 L->getPointerOperand(),
1765 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1770 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1771 << *AvailVal << '\n' << *L << "\n\n\n");
1773 // Replace the load!
1774 L->replaceAllUsesWith(AvailVal);
1775 if (AvailVal->getType()->isPointerTy())
1776 MD->invalidateCachedPointerInfo(AvailVal);
1778 toErase.push_back(L);
1784 // fast print dep, using operator<< on instruction would be too slow
1785 dbgs() << "GVN: load ";
1786 WriteAsOperand(dbgs(), L);
1787 Instruction *I = Dep.getInst();
1788 dbgs() << " is clobbered by " << *I << '\n';
1793 // If it is defined in another block, try harder.
1794 if (Dep.isNonLocal())
1795 return processNonLocalLoad(L, toErase);
1797 Instruction *DepInst = Dep.getInst();
1798 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1799 Value *StoredVal = DepSI->getOperand(0);
1801 // The store and load are to a must-aliased pointer, but they may not
1802 // actually have the same type. See if we know how to reuse the stored
1803 // value (depending on its type).
1804 const TargetData *TD = 0;
1805 if (StoredVal->getType() != L->getType()) {
1806 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1807 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1812 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1813 << '\n' << *L << "\n\n\n");
1820 L->replaceAllUsesWith(StoredVal);
1821 if (StoredVal->getType()->isPointerTy())
1822 MD->invalidateCachedPointerInfo(StoredVal);
1824 toErase.push_back(L);
1829 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1830 Value *AvailableVal = DepLI;
1832 // The loads are of a must-aliased pointer, but they may not actually have
1833 // the same type. See if we know how to reuse the previously loaded value
1834 // (depending on its type).
1835 const TargetData *TD = 0;
1836 if (DepLI->getType() != L->getType()) {
1837 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1838 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1839 if (AvailableVal == 0)
1842 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1843 << "\n" << *L << "\n\n\n");
1850 L->replaceAllUsesWith(AvailableVal);
1851 if (DepLI->getType()->isPointerTy())
1852 MD->invalidateCachedPointerInfo(DepLI);
1854 toErase.push_back(L);
1859 // If this load really doesn't depend on anything, then we must be loading an
1860 // undef value. This can happen when loading for a fresh allocation with no
1861 // intervening stores, for example.
1862 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1863 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1865 toErase.push_back(L);
1870 // If this load occurs either right after a lifetime begin,
1871 // then the loaded value is undefined.
1872 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1873 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1874 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1876 toErase.push_back(L);
1885 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1886 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1887 if (I == localAvail.end())
1890 ValueNumberScope *Locals = I->second;
1892 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num);
1893 if (I != Locals->table.end())
1895 Locals = Locals->parent;
1902 /// processInstruction - When calculating availability, handle an instruction
1903 /// by inserting it into the appropriate sets
1904 bool GVN::processInstruction(Instruction *I,
1905 SmallVectorImpl<Instruction*> &toErase) {
1906 // Ignore dbg info intrinsics.
1907 if (isa<DbgInfoIntrinsic>(I))
1910 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1911 bool Changed = processLoad(LI, toErase);
1914 unsigned Num = VN.lookup_or_add(LI);
1915 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI));
1921 uint32_t NextNum = VN.getNextUnusedValueNumber();
1922 unsigned Num = VN.lookup_or_add(I);
1924 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1925 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1927 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1930 Value *BranchCond = BI->getCondition();
1931 uint32_t CondVN = VN.lookup_or_add(BranchCond);
1933 BasicBlock *TrueSucc = BI->getSuccessor(0);
1934 BasicBlock *FalseSucc = BI->getSuccessor(1);
1936 if (TrueSucc->getSinglePredecessor())
1937 localAvail[TrueSucc]->table[CondVN] =
1938 ConstantInt::getTrue(TrueSucc->getContext());
1939 if (FalseSucc->getSinglePredecessor())
1940 localAvail[FalseSucc]->table[CondVN] =
1941 ConstantInt::getFalse(TrueSucc->getContext());
1945 // Allocations are always uniquely numbered, so we can save time and memory
1946 // by fast failing them.
1947 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1948 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1952 // Collapse PHI nodes
1953 if (PHINode* p = dyn_cast<PHINode>(I)) {
1954 Value *constVal = CollapsePhi(p);
1957 p->replaceAllUsesWith(constVal);
1958 if (MD && constVal->getType()->isPointerTy())
1959 MD->invalidateCachedPointerInfo(constVal);
1962 toErase.push_back(p);
1964 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1967 // If the number we were assigned was a brand new VN, then we don't
1968 // need to do a lookup to see if the number already exists
1969 // somewhere in the domtree: it can't!
1970 } else if (Num == NextNum) {
1971 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1973 // Perform fast-path value-number based elimination of values inherited from
1975 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1978 I->replaceAllUsesWith(repl);
1979 if (MD && repl->getType()->isPointerTy())
1980 MD->invalidateCachedPointerInfo(repl);
1981 toErase.push_back(I);
1985 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1991 /// runOnFunction - This is the main transformation entry point for a function.
1992 bool GVN::runOnFunction(Function& F) {
1994 MD = &getAnalysis<MemoryDependenceAnalysis>();
1995 DT = &getAnalysis<DominatorTree>();
1996 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
2000 bool Changed = false;
2001 bool ShouldContinue = true;
2003 // Merge unconditional branches, allowing PRE to catch more
2004 // optimization opportunities.
2005 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
2006 BasicBlock *BB = FI;
2008 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
2009 if (removedBlock) ++NumGVNBlocks;
2011 Changed |= removedBlock;
2014 unsigned Iteration = 0;
2016 while (ShouldContinue) {
2017 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
2018 ShouldContinue = iterateOnFunction(F);
2019 if (splitCriticalEdges())
2020 ShouldContinue = true;
2021 Changed |= ShouldContinue;
2026 bool PREChanged = true;
2027 while (PREChanged) {
2028 PREChanged = performPRE(F);
2029 Changed |= PREChanged;
2032 // FIXME: Should perform GVN again after PRE does something. PRE can move
2033 // computations into blocks where they become fully redundant. Note that
2034 // we can't do this until PRE's critical edge splitting updates memdep.
2035 // Actually, when this happens, we should just fully integrate PRE into GVN.
2037 cleanupGlobalSets();
2043 bool GVN::processBlock(BasicBlock *BB) {
2044 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
2045 // incrementing BI before processing an instruction).
2046 SmallVector<Instruction*, 8> toErase;
2047 bool ChangedFunction = false;
2049 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2051 ChangedFunction |= processInstruction(BI, toErase);
2052 if (toErase.empty()) {
2057 // If we need some instructions deleted, do it now.
2058 NumGVNInstr += toErase.size();
2060 // Avoid iterator invalidation.
2061 bool AtStart = BI == BB->begin();
2065 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2066 E = toErase.end(); I != E; ++I) {
2067 DEBUG(dbgs() << "GVN removed: " << **I << '\n');
2068 if (MD) MD->removeInstruction(*I);
2069 (*I)->eraseFromParent();
2070 DEBUG(verifyRemoved(*I));
2080 return ChangedFunction;
2083 /// performPRE - Perform a purely local form of PRE that looks for diamond
2084 /// control flow patterns and attempts to perform simple PRE at the join point.
2085 bool GVN::performPRE(Function &F) {
2086 bool Changed = false;
2087 DenseMap<BasicBlock*, Value*> predMap;
2088 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2089 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2090 BasicBlock *CurrentBlock = *DI;
2092 // Nothing to PRE in the entry block.
2093 if (CurrentBlock == &F.getEntryBlock()) continue;
2095 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2096 BE = CurrentBlock->end(); BI != BE; ) {
2097 Instruction *CurInst = BI++;
2099 if (isa<AllocaInst>(CurInst) ||
2100 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2101 CurInst->getType()->isVoidTy() ||
2102 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2103 isa<DbgInfoIntrinsic>(CurInst))
2106 // We don't currently value number ANY inline asm calls.
2107 if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
2108 if (CallI->isInlineAsm())
2111 uint32_t ValNo = VN.lookup(CurInst);
2113 // Look for the predecessors for PRE opportunities. We're
2114 // only trying to solve the basic diamond case, where
2115 // a value is computed in the successor and one predecessor,
2116 // but not the other. We also explicitly disallow cases
2117 // where the successor is its own predecessor, because they're
2118 // more complicated to get right.
2119 unsigned NumWith = 0;
2120 unsigned NumWithout = 0;
2121 BasicBlock *PREPred = 0;
2124 for (pred_iterator PI = pred_begin(CurrentBlock),
2125 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2126 BasicBlock *P = *PI;
2127 // We're not interested in PRE where the block is its
2128 // own predecessor, or in blocks with predecessors
2129 // that are not reachable.
2130 if (P == CurrentBlock) {
2133 } else if (!localAvail.count(P)) {
2138 DenseMap<uint32_t, Value*>::iterator predV =
2139 localAvail[P]->table.find(ValNo);
2140 if (predV == localAvail[P]->table.end()) {
2143 } else if (predV->second == CurInst) {
2146 predMap[P] = predV->second;
2151 // Don't do PRE when it might increase code size, i.e. when
2152 // we would need to insert instructions in more than one pred.
2153 if (NumWithout != 1 || NumWith == 0)
2156 // Don't do PRE across indirect branch.
2157 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2160 // We can't do PRE safely on a critical edge, so instead we schedule
2161 // the edge to be split and perform the PRE the next time we iterate
2163 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
2164 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2165 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2169 // Instantiate the expression in the predecessor that lacked it.
2170 // Because we are going top-down through the block, all value numbers
2171 // will be available in the predecessor by the time we need them. Any
2172 // that weren't originally present will have been instantiated earlier
2174 Instruction *PREInstr = CurInst->clone();
2175 bool success = true;
2176 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2177 Value *Op = PREInstr->getOperand(i);
2178 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2181 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
2182 PREInstr->setOperand(i, V);
2189 // Fail out if we encounter an operand that is not available in
2190 // the PRE predecessor. This is typically because of loads which
2191 // are not value numbered precisely.
2194 DEBUG(verifyRemoved(PREInstr));
2198 PREInstr->insertBefore(PREPred->getTerminator());
2199 PREInstr->setName(CurInst->getName() + ".pre");
2200 predMap[PREPred] = PREInstr;
2201 VN.add(PREInstr, ValNo);
2204 // Update the availability map to include the new instruction.
2205 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr));
2207 // Create a PHI to make the value available in this block.
2208 PHINode* Phi = PHINode::Create(CurInst->getType(),
2209 CurInst->getName() + ".pre-phi",
2210 CurrentBlock->begin());
2211 for (pred_iterator PI = pred_begin(CurrentBlock),
2212 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2213 BasicBlock *P = *PI;
2214 Phi->addIncoming(predMap[P], P);
2218 localAvail[CurrentBlock]->table[ValNo] = Phi;
2220 CurInst->replaceAllUsesWith(Phi);
2221 if (MD && Phi->getType()->isPointerTy())
2222 MD->invalidateCachedPointerInfo(Phi);
2225 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
2226 if (MD) MD->removeInstruction(CurInst);
2227 CurInst->eraseFromParent();
2228 DEBUG(verifyRemoved(CurInst));
2233 if (splitCriticalEdges())
2239 /// splitCriticalEdges - Split critical edges found during the previous
2240 /// iteration that may enable further optimization.
2241 bool GVN::splitCriticalEdges() {
2242 if (toSplit.empty())
2245 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
2246 SplitCriticalEdge(Edge.first, Edge.second, this);
2247 } while (!toSplit.empty());
2248 if (MD) MD->invalidateCachedPredecessors();
2252 /// iterateOnFunction - Executes one iteration of GVN
2253 bool GVN::iterateOnFunction(Function &F) {
2254 cleanupGlobalSets();
2256 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2257 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
2259 localAvail[DI->getBlock()] =
2260 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
2262 localAvail[DI->getBlock()] = new ValueNumberScope(0);
2265 // Top-down walk of the dominator tree
2266 bool Changed = false;
2268 // Needed for value numbering with phi construction to work.
2269 ReversePostOrderTraversal<Function*> RPOT(&F);
2270 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2271 RE = RPOT.end(); RI != RE; ++RI)
2272 Changed |= processBlock(*RI);
2274 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2275 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2276 Changed |= processBlock(DI->getBlock());
2282 void GVN::cleanupGlobalSets() {
2285 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
2286 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
2291 /// verifyRemoved - Verify that the specified instruction does not occur in our
2292 /// internal data structures.
2293 void GVN::verifyRemoved(const Instruction *Inst) const {
2294 VN.verifyRemoved(Inst);
2296 // Walk through the value number scope to make sure the instruction isn't
2297 // ferreted away in it.
2298 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
2299 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
2300 const ValueNumberScope *VNS = I->second;
2303 for (DenseMap<uint32_t, Value*>::const_iterator
2304 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
2305 assert(II->second != Inst && "Inst still in value numbering scope!");