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));
65 //===----------------------------------------------------------------------===//
67 //===----------------------------------------------------------------------===//
69 /// This class holds the mapping between values and value numbers. It is used
70 /// as an efficient mechanism to determine the expression-wise equivalence of
74 enum ExpressionOpcode {
75 ADD = Instruction::Add,
76 FADD = Instruction::FAdd,
77 SUB = Instruction::Sub,
78 FSUB = Instruction::FSub,
79 MUL = Instruction::Mul,
80 FMUL = Instruction::FMul,
81 UDIV = Instruction::UDiv,
82 SDIV = Instruction::SDiv,
83 FDIV = Instruction::FDiv,
84 UREM = Instruction::URem,
85 SREM = Instruction::SRem,
86 FREM = Instruction::FRem,
87 SHL = Instruction::Shl,
88 LSHR = Instruction::LShr,
89 ASHR = Instruction::AShr,
90 AND = Instruction::And,
92 XOR = Instruction::Xor,
93 TRUNC = Instruction::Trunc,
94 ZEXT = Instruction::ZExt,
95 SEXT = Instruction::SExt,
96 FPTOUI = Instruction::FPToUI,
97 FPTOSI = Instruction::FPToSI,
98 UITOFP = Instruction::UIToFP,
99 SITOFP = Instruction::SIToFP,
100 FPTRUNC = Instruction::FPTrunc,
101 FPEXT = Instruction::FPExt,
102 PTRTOINT = Instruction::PtrToInt,
103 INTTOPTR = Instruction::IntToPtr,
104 BITCAST = Instruction::BitCast,
105 ICMPEQ, ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
106 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
107 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
108 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
109 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
110 SHUFFLE, SELECT, GEP, CALL, CONSTANT,
111 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE };
113 ExpressionOpcode opcode;
115 SmallVector<uint32_t, 4> varargs;
119 Expression(ExpressionOpcode o) : opcode(o) { }
121 bool operator==(const Expression &other) const {
122 if (opcode != other.opcode)
124 else if (opcode == EMPTY || opcode == TOMBSTONE)
126 else if (type != other.type)
128 else if (function != other.function)
131 if (varargs.size() != other.varargs.size())
134 for (size_t i = 0; i < varargs.size(); ++i)
135 if (varargs[i] != other.varargs[i])
142 /*bool operator!=(const Expression &other) const {
143 return !(*this == other);
149 DenseMap<Value*, uint32_t> valueNumbering;
150 DenseMap<Expression, uint32_t> expressionNumbering;
152 MemoryDependenceAnalysis* MD;
155 uint32_t nextValueNumber;
157 Expression::ExpressionOpcode getOpcode(CmpInst* C);
158 Expression create_expression(BinaryOperator* BO);
159 Expression create_expression(CmpInst* C);
160 Expression create_expression(ShuffleVectorInst* V);
161 Expression create_expression(ExtractElementInst* C);
162 Expression create_expression(InsertElementInst* V);
163 Expression create_expression(SelectInst* V);
164 Expression create_expression(CastInst* C);
165 Expression create_expression(GetElementPtrInst* G);
166 Expression create_expression(CallInst* C);
167 Expression create_expression(ExtractValueInst* C);
168 Expression create_expression(InsertValueInst* C);
170 uint32_t lookup_or_add_call(CallInst* C);
172 ValueTable() : nextValueNumber(1) { }
173 uint32_t lookup_or_add(Value *V);
174 uint32_t lookup(Value *V) const;
175 void add(Value *V, uint32_t num);
177 void erase(Value *v);
178 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
179 AliasAnalysis *getAliasAnalysis() const { return AA; }
180 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
181 void setDomTree(DominatorTree* D) { DT = D; }
182 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
183 void verifyRemoved(const Value *) const;
188 template <> struct DenseMapInfo<Expression> {
189 static inline Expression getEmptyKey() {
190 return Expression(Expression::EMPTY);
193 static inline Expression getTombstoneKey() {
194 return Expression(Expression::TOMBSTONE);
197 static unsigned getHashValue(const Expression e) {
198 unsigned hash = e.opcode;
200 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
201 (unsigned)((uintptr_t)e.type >> 9));
203 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
204 E = e.varargs.end(); I != E; ++I)
205 hash = *I + hash * 37;
207 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
208 (unsigned)((uintptr_t)e.function >> 9)) +
213 static bool isEqual(const Expression &LHS, const Expression &RHS) {
219 struct isPodLike<Expression> { static const bool value = true; };
223 //===----------------------------------------------------------------------===//
224 // ValueTable Internal Functions
225 //===----------------------------------------------------------------------===//
227 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
228 if (isa<ICmpInst>(C)) {
229 switch (C->getPredicate()) {
230 default: // THIS SHOULD NEVER HAPPEN
231 llvm_unreachable("Comparison with unknown predicate?");
232 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
233 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
234 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
235 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
236 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
237 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
238 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
239 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
240 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
241 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
244 switch (C->getPredicate()) {
245 default: // THIS SHOULD NEVER HAPPEN
246 llvm_unreachable("Comparison with unknown predicate?");
247 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
248 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
249 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
250 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
251 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
252 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
253 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
254 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
255 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
256 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
257 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
258 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
259 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
260 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
265 Expression ValueTable::create_expression(CallInst* C) {
268 e.type = C->getType();
269 e.function = C->getCalledFunction();
270 e.opcode = Expression::CALL;
273 for (CallInst::op_iterator I = CS.arg_begin(), E = CS.arg_end();
275 e.varargs.push_back(lookup_or_add(*I));
280 Expression ValueTable::create_expression(BinaryOperator* BO) {
282 e.varargs.push_back(lookup_or_add(BO->getOperand(0)));
283 e.varargs.push_back(lookup_or_add(BO->getOperand(1)));
285 e.type = BO->getType();
286 e.opcode = static_cast<Expression::ExpressionOpcode>(BO->getOpcode());
291 Expression ValueTable::create_expression(CmpInst* C) {
294 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
295 e.varargs.push_back(lookup_or_add(C->getOperand(1)));
297 e.type = C->getType();
298 e.opcode = getOpcode(C);
303 Expression ValueTable::create_expression(CastInst* C) {
306 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
308 e.type = C->getType();
309 e.opcode = static_cast<Expression::ExpressionOpcode>(C->getOpcode());
314 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
317 e.varargs.push_back(lookup_or_add(S->getOperand(0)));
318 e.varargs.push_back(lookup_or_add(S->getOperand(1)));
319 e.varargs.push_back(lookup_or_add(S->getOperand(2)));
321 e.type = S->getType();
322 e.opcode = Expression::SHUFFLE;
327 Expression ValueTable::create_expression(ExtractElementInst* E) {
330 e.varargs.push_back(lookup_or_add(E->getOperand(0)));
331 e.varargs.push_back(lookup_or_add(E->getOperand(1)));
333 e.type = E->getType();
334 e.opcode = Expression::EXTRACT;
339 Expression ValueTable::create_expression(InsertElementInst* I) {
342 e.varargs.push_back(lookup_or_add(I->getOperand(0)));
343 e.varargs.push_back(lookup_or_add(I->getOperand(1)));
344 e.varargs.push_back(lookup_or_add(I->getOperand(2)));
346 e.type = I->getType();
347 e.opcode = Expression::INSERT;
352 Expression ValueTable::create_expression(SelectInst* I) {
355 e.varargs.push_back(lookup_or_add(I->getCondition()));
356 e.varargs.push_back(lookup_or_add(I->getTrueValue()));
357 e.varargs.push_back(lookup_or_add(I->getFalseValue()));
359 e.type = I->getType();
360 e.opcode = Expression::SELECT;
365 Expression ValueTable::create_expression(GetElementPtrInst* G) {
368 e.varargs.push_back(lookup_or_add(G->getPointerOperand()));
370 e.type = G->getType();
371 e.opcode = Expression::GEP;
373 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
375 e.varargs.push_back(lookup_or_add(*I));
380 Expression ValueTable::create_expression(ExtractValueInst* E) {
383 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
384 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
386 e.varargs.push_back(*II);
388 e.type = E->getType();
389 e.opcode = Expression::EXTRACTVALUE;
394 Expression ValueTable::create_expression(InsertValueInst* E) {
397 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
398 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand()));
399 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
401 e.varargs.push_back(*II);
403 e.type = E->getType();
404 e.opcode = Expression::INSERTVALUE;
409 //===----------------------------------------------------------------------===//
410 // ValueTable External Functions
411 //===----------------------------------------------------------------------===//
413 /// add - Insert a value into the table with a specified value number.
414 void ValueTable::add(Value *V, uint32_t num) {
415 valueNumbering.insert(std::make_pair(V, num));
418 uint32_t ValueTable::lookup_or_add_call(CallInst* C) {
419 if (AA->doesNotAccessMemory(C)) {
420 Expression exp = create_expression(C);
421 uint32_t& e = expressionNumbering[exp];
422 if (!e) e = nextValueNumber++;
423 valueNumbering[C] = e;
425 } else if (AA->onlyReadsMemory(C)) {
426 Expression exp = create_expression(C);
427 uint32_t& e = expressionNumbering[exp];
429 e = nextValueNumber++;
430 valueNumbering[C] = e;
434 e = nextValueNumber++;
435 valueNumbering[C] = e;
439 MemDepResult local_dep = MD->getDependency(C);
441 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
442 valueNumbering[C] = nextValueNumber;
443 return nextValueNumber++;
446 if (local_dep.isDef()) {
447 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
449 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) {
450 valueNumbering[C] = nextValueNumber;
451 return nextValueNumber++;
454 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
455 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
456 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i));
458 valueNumbering[C] = nextValueNumber;
459 return nextValueNumber++;
463 uint32_t v = lookup_or_add(local_cdep);
464 valueNumbering[C] = v;
469 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
470 MD->getNonLocalCallDependency(CallSite(C));
471 // FIXME: call/call dependencies for readonly calls should return def, not
472 // clobber! Move the checking logic to MemDep!
475 // Check to see if we have a single dominating call instruction that is
477 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
478 const NonLocalDepEntry *I = &deps[i];
479 // Ignore non-local dependencies.
480 if (I->getResult().isNonLocal())
483 // We don't handle non-depedencies. If we already have a call, reject
484 // instruction dependencies.
485 if (I->getResult().isClobber() || cdep != 0) {
490 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
491 // FIXME: All duplicated with non-local case.
492 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
493 cdep = NonLocalDepCall;
502 valueNumbering[C] = nextValueNumber;
503 return nextValueNumber++;
506 if (cdep->getNumArgOperands() != C->getNumArgOperands()) {
507 valueNumbering[C] = nextValueNumber;
508 return nextValueNumber++;
510 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
511 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
512 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i));
514 valueNumbering[C] = nextValueNumber;
515 return nextValueNumber++;
519 uint32_t v = lookup_or_add(cdep);
520 valueNumbering[C] = v;
524 valueNumbering[C] = nextValueNumber;
525 return nextValueNumber++;
529 /// lookup_or_add - Returns the value number for the specified value, assigning
530 /// it a new number if it did not have one before.
531 uint32_t ValueTable::lookup_or_add(Value *V) {
532 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
533 if (VI != valueNumbering.end())
536 if (!isa<Instruction>(V)) {
537 valueNumbering[V] = nextValueNumber;
538 return nextValueNumber++;
541 Instruction* I = cast<Instruction>(V);
543 switch (I->getOpcode()) {
544 case Instruction::Call:
545 return lookup_or_add_call(cast<CallInst>(I));
546 case Instruction::Add:
547 case Instruction::FAdd:
548 case Instruction::Sub:
549 case Instruction::FSub:
550 case Instruction::Mul:
551 case Instruction::FMul:
552 case Instruction::UDiv:
553 case Instruction::SDiv:
554 case Instruction::FDiv:
555 case Instruction::URem:
556 case Instruction::SRem:
557 case Instruction::FRem:
558 case Instruction::Shl:
559 case Instruction::LShr:
560 case Instruction::AShr:
561 case Instruction::And:
562 case Instruction::Or :
563 case Instruction::Xor:
564 exp = create_expression(cast<BinaryOperator>(I));
566 case Instruction::ICmp:
567 case Instruction::FCmp:
568 exp = create_expression(cast<CmpInst>(I));
570 case Instruction::Trunc:
571 case Instruction::ZExt:
572 case Instruction::SExt:
573 case Instruction::FPToUI:
574 case Instruction::FPToSI:
575 case Instruction::UIToFP:
576 case Instruction::SIToFP:
577 case Instruction::FPTrunc:
578 case Instruction::FPExt:
579 case Instruction::PtrToInt:
580 case Instruction::IntToPtr:
581 case Instruction::BitCast:
582 exp = create_expression(cast<CastInst>(I));
584 case Instruction::Select:
585 exp = create_expression(cast<SelectInst>(I));
587 case Instruction::ExtractElement:
588 exp = create_expression(cast<ExtractElementInst>(I));
590 case Instruction::InsertElement:
591 exp = create_expression(cast<InsertElementInst>(I));
593 case Instruction::ShuffleVector:
594 exp = create_expression(cast<ShuffleVectorInst>(I));
596 case Instruction::ExtractValue:
597 exp = create_expression(cast<ExtractValueInst>(I));
599 case Instruction::InsertValue:
600 exp = create_expression(cast<InsertValueInst>(I));
602 case Instruction::GetElementPtr:
603 exp = create_expression(cast<GetElementPtrInst>(I));
606 valueNumbering[V] = nextValueNumber;
607 return nextValueNumber++;
610 uint32_t& e = expressionNumbering[exp];
611 if (!e) e = nextValueNumber++;
612 valueNumbering[V] = e;
616 /// lookup - Returns the value number of the specified value. Fails if
617 /// the value has not yet been numbered.
618 uint32_t ValueTable::lookup(Value *V) const {
619 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
620 assert(VI != valueNumbering.end() && "Value not numbered?");
624 /// clear - Remove all entries from the ValueTable
625 void ValueTable::clear() {
626 valueNumbering.clear();
627 expressionNumbering.clear();
631 /// erase - Remove a value from the value numbering
632 void ValueTable::erase(Value *V) {
633 valueNumbering.erase(V);
636 /// verifyRemoved - Verify that the value is removed from all internal data
638 void ValueTable::verifyRemoved(const Value *V) const {
639 for (DenseMap<Value*, uint32_t>::const_iterator
640 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
641 assert(I->first != V && "Inst still occurs in value numbering map!");
645 //===----------------------------------------------------------------------===//
647 //===----------------------------------------------------------------------===//
650 struct ValueNumberScope {
651 ValueNumberScope* parent;
652 DenseMap<uint32_t, Value*> table;
654 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
660 class GVN : public FunctionPass {
661 bool runOnFunction(Function &F);
663 static char ID; // Pass identification, replacement for typeid
664 explicit GVN(bool noloads = false)
665 : FunctionPass(ID), NoLoads(noloads), MD(0) { }
669 MemoryDependenceAnalysis *MD;
673 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
675 // List of critical edges to be split between iterations.
676 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
678 // This transformation requires dominator postdominator info
679 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
680 AU.addRequired<DominatorTree>();
682 AU.addRequired<MemoryDependenceAnalysis>();
683 AU.addRequired<AliasAnalysis>();
685 AU.addPreserved<DominatorTree>();
686 AU.addPreserved<AliasAnalysis>();
690 // FIXME: eliminate or document these better
691 bool processLoad(LoadInst* L,
692 SmallVectorImpl<Instruction*> &toErase);
693 bool processInstruction(Instruction *I,
694 SmallVectorImpl<Instruction*> &toErase);
695 bool processNonLocalLoad(LoadInst* L,
696 SmallVectorImpl<Instruction*> &toErase);
697 bool processBlock(BasicBlock *BB);
698 void dump(DenseMap<uint32_t, Value*>& d);
699 bool iterateOnFunction(Function &F);
700 Value *CollapsePhi(PHINode* p);
701 bool performPRE(Function& F);
702 Value *lookupNumber(BasicBlock *BB, uint32_t num);
703 void cleanupGlobalSets();
704 void verifyRemoved(const Instruction *I) const;
705 bool splitCriticalEdges();
711 // createGVNPass - The public interface to this file...
712 FunctionPass *llvm::createGVNPass(bool NoLoads) {
713 return new GVN(NoLoads);
716 INITIALIZE_PASS(GVN, "gvn", "Global Value Numbering", false, false)
718 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
720 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
721 E = d.end(); I != E; ++I) {
722 errs() << I->first << "\n";
728 static bool isSafeReplacement(PHINode* p, Instruction *inst) {
729 if (!isa<PHINode>(inst))
732 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
734 if (PHINode* use_phi = dyn_cast<PHINode>(*UI))
735 if (use_phi->getParent() == inst->getParent())
741 Value *GVN::CollapsePhi(PHINode *PN) {
742 Value *ConstVal = PN->hasConstantValue(DT);
743 if (!ConstVal) return 0;
745 Instruction *Inst = dyn_cast<Instruction>(ConstVal);
749 if (DT->dominates(Inst, PN))
750 if (isSafeReplacement(PN, Inst))
755 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
756 /// we're analyzing is fully available in the specified block. As we go, keep
757 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
758 /// map is actually a tri-state map with the following values:
759 /// 0) we know the block *is not* fully available.
760 /// 1) we know the block *is* fully available.
761 /// 2) we do not know whether the block is fully available or not, but we are
762 /// currently speculating that it will be.
763 /// 3) we are speculating for this block and have used that to speculate for
765 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
766 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
767 // Optimistically assume that the block is fully available and check to see
768 // if we already know about this block in one lookup.
769 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
770 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
772 // If the entry already existed for this block, return the precomputed value.
774 // If this is a speculative "available" value, mark it as being used for
775 // speculation of other blocks.
776 if (IV.first->second == 2)
777 IV.first->second = 3;
778 return IV.first->second != 0;
781 // Otherwise, see if it is fully available in all predecessors.
782 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
784 // If this block has no predecessors, it isn't live-in here.
786 goto SpeculationFailure;
788 for (; PI != PE; ++PI)
789 // If the value isn't fully available in one of our predecessors, then it
790 // isn't fully available in this block either. Undo our previous
791 // optimistic assumption and bail out.
792 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
793 goto SpeculationFailure;
797 // SpeculationFailure - If we get here, we found out that this is not, after
798 // all, a fully-available block. We have a problem if we speculated on this and
799 // used the speculation to mark other blocks as available.
801 char &BBVal = FullyAvailableBlocks[BB];
803 // If we didn't speculate on this, just return with it set to false.
809 // If we did speculate on this value, we could have blocks set to 1 that are
810 // incorrect. Walk the (transitive) successors of this block and mark them as
812 SmallVector<BasicBlock*, 32> BBWorklist;
813 BBWorklist.push_back(BB);
816 BasicBlock *Entry = BBWorklist.pop_back_val();
817 // Note that this sets blocks to 0 (unavailable) if they happen to not
818 // already be in FullyAvailableBlocks. This is safe.
819 char &EntryVal = FullyAvailableBlocks[Entry];
820 if (EntryVal == 0) continue; // Already unavailable.
822 // Mark as unavailable.
825 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
826 BBWorklist.push_back(*I);
827 } while (!BBWorklist.empty());
833 /// CanCoerceMustAliasedValueToLoad - Return true if
834 /// CoerceAvailableValueToLoadType will succeed.
835 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
837 const TargetData &TD) {
838 // If the loaded or stored value is an first class array or struct, don't try
839 // to transform them. We need to be able to bitcast to integer.
840 if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
841 StoredVal->getType()->isStructTy() ||
842 StoredVal->getType()->isArrayTy())
845 // The store has to be at least as big as the load.
846 if (TD.getTypeSizeInBits(StoredVal->getType()) <
847 TD.getTypeSizeInBits(LoadTy))
854 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
855 /// then a load from a must-aliased pointer of a different type, try to coerce
856 /// the stored value. LoadedTy is the type of the load we want to replace and
857 /// InsertPt is the place to insert new instructions.
859 /// If we can't do it, return null.
860 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
861 const Type *LoadedTy,
862 Instruction *InsertPt,
863 const TargetData &TD) {
864 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
867 const Type *StoredValTy = StoredVal->getType();
869 uint64_t StoreSize = TD.getTypeStoreSizeInBits(StoredValTy);
870 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
872 // If the store and reload are the same size, we can always reuse it.
873 if (StoreSize == LoadSize) {
874 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) {
875 // Pointer to Pointer -> use bitcast.
876 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
879 // Convert source pointers to integers, which can be bitcast.
880 if (StoredValTy->isPointerTy()) {
881 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
882 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
885 const Type *TypeToCastTo = LoadedTy;
886 if (TypeToCastTo->isPointerTy())
887 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
889 if (StoredValTy != TypeToCastTo)
890 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
892 // Cast to pointer if the load needs a pointer type.
893 if (LoadedTy->isPointerTy())
894 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
899 // If the loaded value is smaller than the available value, then we can
900 // extract out a piece from it. If the available value is too small, then we
901 // can't do anything.
902 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
904 // Convert source pointers to integers, which can be manipulated.
905 if (StoredValTy->isPointerTy()) {
906 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
907 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
910 // Convert vectors and fp to integer, which can be manipulated.
911 if (!StoredValTy->isIntegerTy()) {
912 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
913 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
916 // If this is a big-endian system, we need to shift the value down to the low
917 // bits so that a truncate will work.
918 if (TD.isBigEndian()) {
919 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
920 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
923 // Truncate the integer to the right size now.
924 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
925 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
927 if (LoadedTy == NewIntTy)
930 // If the result is a pointer, inttoptr.
931 if (LoadedTy->isPointerTy())
932 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
934 // Otherwise, bitcast.
935 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
938 /// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
939 /// be expressed as a base pointer plus a constant offset. Return the base and
940 /// offset to the caller.
941 static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
942 const TargetData &TD) {
943 Operator *PtrOp = dyn_cast<Operator>(Ptr);
944 if (PtrOp == 0) return Ptr;
946 // Just look through bitcasts.
947 if (PtrOp->getOpcode() == Instruction::BitCast)
948 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
950 // If this is a GEP with constant indices, we can look through it.
951 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
952 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
954 gep_type_iterator GTI = gep_type_begin(GEP);
955 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
957 ConstantInt *OpC = cast<ConstantInt>(*I);
958 if (OpC->isZero()) continue;
960 // Handle a struct and array indices which add their offset to the pointer.
961 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
962 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
964 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
965 Offset += OpC->getSExtValue()*Size;
969 // Re-sign extend from the pointer size if needed to get overflow edge cases
971 unsigned PtrSize = TD.getPointerSizeInBits();
973 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
975 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
979 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
980 /// memdep query of a load that ends up being a clobbering memory write (store,
981 /// memset, memcpy, memmove). This means that the write *may* provide bits used
982 /// by the load but we can't be sure because the pointers don't mustalias.
984 /// Check this case to see if there is anything more we can do before we give
985 /// up. This returns -1 if we have to give up, or a byte number in the stored
986 /// value of the piece that feeds the load.
987 static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
989 uint64_t WriteSizeInBits,
990 const TargetData &TD) {
991 // If the loaded or stored value is an first class array or struct, don't try
992 // to transform them. We need to be able to bitcast to integer.
993 if (LoadTy->isStructTy() || LoadTy->isArrayTy())
996 int64_t StoreOffset = 0, LoadOffset = 0;
997 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
999 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
1000 if (StoreBase != LoadBase)
1003 // If the load and store are to the exact same address, they should have been
1004 // a must alias. AA must have gotten confused.
1005 // FIXME: Study to see if/when this happens. One case is forwarding a memset
1006 // to a load from the base of the memset.
1008 if (LoadOffset == StoreOffset) {
1009 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
1010 << "Base = " << *StoreBase << "\n"
1011 << "Store Ptr = " << *WritePtr << "\n"
1012 << "Store Offs = " << StoreOffset << "\n"
1013 << "Load Ptr = " << *LoadPtr << "\n";
1018 // If the load and store don't overlap at all, the store doesn't provide
1019 // anything to the load. In this case, they really don't alias at all, AA
1020 // must have gotten confused.
1021 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
1022 // remove this check, as it is duplicated with what we have below.
1023 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
1025 if ((WriteSizeInBits & 7) | (LoadSize & 7))
1027 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
1031 bool isAAFailure = false;
1032 if (StoreOffset < LoadOffset)
1033 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
1035 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
1039 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"
1040 << "Base = " << *StoreBase << "\n"
1041 << "Store Ptr = " << *WritePtr << "\n"
1042 << "Store Offs = " << StoreOffset << "\n"
1043 << "Load Ptr = " << *LoadPtr << "\n";
1049 // If the Load isn't completely contained within the stored bits, we don't
1050 // have all the bits to feed it. We could do something crazy in the future
1051 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1053 if (StoreOffset > LoadOffset ||
1054 StoreOffset+StoreSize < LoadOffset+LoadSize)
1057 // Okay, we can do this transformation. Return the number of bytes into the
1058 // store that the load is.
1059 return LoadOffset-StoreOffset;
1062 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1063 /// memdep query of a load that ends up being a clobbering store.
1064 static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr,
1066 const TargetData &TD) {
1067 // Cannot handle reading from store of first-class aggregate yet.
1068 if (DepSI->getOperand(0)->getType()->isStructTy() ||
1069 DepSI->getOperand(0)->getType()->isArrayTy())
1072 Value *StorePtr = DepSI->getPointerOperand();
1073 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType());
1074 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1075 StorePtr, StoreSize, TD);
1078 static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr,
1080 const TargetData &TD) {
1081 // If the mem operation is a non-constant size, we can't handle it.
1082 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1083 if (SizeCst == 0) return -1;
1084 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1086 // If this is memset, we just need to see if the offset is valid in the size
1088 if (MI->getIntrinsicID() == Intrinsic::memset)
1089 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1092 // If we have a memcpy/memmove, the only case we can handle is if this is a
1093 // copy from constant memory. In that case, we can read directly from the
1095 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1097 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1098 if (Src == 0) return -1;
1100 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1101 if (GV == 0 || !GV->isConstant()) return -1;
1103 // See if the access is within the bounds of the transfer.
1104 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1105 MI->getDest(), MemSizeInBits, TD);
1109 // Otherwise, see if we can constant fold a load from the constant with the
1110 // offset applied as appropriate.
1111 Src = ConstantExpr::getBitCast(Src,
1112 llvm::Type::getInt8PtrTy(Src->getContext()));
1113 Constant *OffsetCst =
1114 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1115 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1116 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1117 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1123 /// GetStoreValueForLoad - This function is called when we have a
1124 /// memdep query of a load that ends up being a clobbering store. This means
1125 /// that the store *may* provide bits used by the load but we can't be sure
1126 /// because the pointers don't mustalias. Check this case to see if there is
1127 /// anything more we can do before we give up.
1128 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1130 Instruction *InsertPt, const TargetData &TD){
1131 LLVMContext &Ctx = SrcVal->getType()->getContext();
1133 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8;
1134 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8;
1136 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1138 // Compute which bits of the stored value are being used by the load. Convert
1139 // to an integer type to start with.
1140 if (SrcVal->getType()->isPointerTy())
1141 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp");
1142 if (!SrcVal->getType()->isIntegerTy())
1143 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1146 // Shift the bits to the least significant depending on endianness.
1148 if (TD.isLittleEndian())
1149 ShiftAmt = Offset*8;
1151 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1154 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp");
1156 if (LoadSize != StoreSize)
1157 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1160 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1163 /// GetMemInstValueForLoad - This function is called when we have a
1164 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1165 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1166 const Type *LoadTy, Instruction *InsertPt,
1167 const TargetData &TD){
1168 LLVMContext &Ctx = LoadTy->getContext();
1169 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1171 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1173 // We know that this method is only called when the mem transfer fully
1174 // provides the bits for the load.
1175 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1176 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1177 // independently of what the offset is.
1178 Value *Val = MSI->getValue();
1180 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1182 Value *OneElt = Val;
1184 // Splat the value out to the right number of bits.
1185 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1186 // If we can double the number of bytes set, do it.
1187 if (NumBytesSet*2 <= LoadSize) {
1188 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1189 Val = Builder.CreateOr(Val, ShVal);
1194 // Otherwise insert one byte at a time.
1195 Value *ShVal = Builder.CreateShl(Val, 1*8);
1196 Val = Builder.CreateOr(OneElt, ShVal);
1200 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1203 // Otherwise, this is a memcpy/memmove from a constant global.
1204 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1205 Constant *Src = cast<Constant>(MTI->getSource());
1207 // Otherwise, see if we can constant fold a load from the constant with the
1208 // offset applied as appropriate.
1209 Src = ConstantExpr::getBitCast(Src,
1210 llvm::Type::getInt8PtrTy(Src->getContext()));
1211 Constant *OffsetCst =
1212 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1213 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1214 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1215 return ConstantFoldLoadFromConstPtr(Src, &TD);
1220 struct AvailableValueInBlock {
1221 /// BB - The basic block in question.
1224 SimpleVal, // A simple offsetted value that is accessed.
1225 MemIntrin // A memory intrinsic which is loaded from.
1228 /// V - The value that is live out of the block.
1229 PointerIntPair<Value *, 1, ValType> Val;
1231 /// Offset - The byte offset in Val that is interesting for the load query.
1234 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1235 unsigned Offset = 0) {
1236 AvailableValueInBlock Res;
1238 Res.Val.setPointer(V);
1239 Res.Val.setInt(SimpleVal);
1240 Res.Offset = Offset;
1244 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1245 unsigned Offset = 0) {
1246 AvailableValueInBlock Res;
1248 Res.Val.setPointer(MI);
1249 Res.Val.setInt(MemIntrin);
1250 Res.Offset = Offset;
1254 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1255 Value *getSimpleValue() const {
1256 assert(isSimpleValue() && "Wrong accessor");
1257 return Val.getPointer();
1260 MemIntrinsic *getMemIntrinValue() const {
1261 assert(!isSimpleValue() && "Wrong accessor");
1262 return cast<MemIntrinsic>(Val.getPointer());
1265 /// MaterializeAdjustedValue - Emit code into this block to adjust the value
1266 /// defined here to the specified type. This handles various coercion cases.
1267 Value *MaterializeAdjustedValue(const Type *LoadTy,
1268 const TargetData *TD) const {
1270 if (isSimpleValue()) {
1271 Res = getSimpleValue();
1272 if (Res->getType() != LoadTy) {
1273 assert(TD && "Need target data to handle type mismatch case");
1274 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(),
1277 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1278 << *getSimpleValue() << '\n'
1279 << *Res << '\n' << "\n\n\n");
1282 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset,
1283 LoadTy, BB->getTerminator(), *TD);
1284 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1285 << " " << *getMemIntrinValue() << '\n'
1286 << *Res << '\n' << "\n\n\n");
1294 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1295 /// construct SSA form, allowing us to eliminate LI. This returns the value
1296 /// that should be used at LI's definition site.
1297 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1298 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1299 const TargetData *TD,
1300 const DominatorTree &DT,
1301 AliasAnalysis *AA) {
1302 // Check for the fully redundant, dominating load case. In this case, we can
1303 // just use the dominating value directly.
1304 if (ValuesPerBlock.size() == 1 &&
1305 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent()))
1306 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD);
1308 // Otherwise, we have to construct SSA form.
1309 SmallVector<PHINode*, 8> NewPHIs;
1310 SSAUpdater SSAUpdate(&NewPHIs);
1311 SSAUpdate.Initialize(LI->getType(), LI->getName());
1313 const Type *LoadTy = LI->getType();
1315 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1316 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1317 BasicBlock *BB = AV.BB;
1319 if (SSAUpdate.HasValueForBlock(BB))
1322 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD));
1325 // Perform PHI construction.
1326 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1328 // If new PHI nodes were created, notify alias analysis.
1329 if (V->getType()->isPointerTy())
1330 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1331 AA->copyValue(LI, NewPHIs[i]);
1336 static bool isLifetimeStart(const Instruction *Inst) {
1337 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1338 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1342 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1343 /// non-local by performing PHI construction.
1344 bool GVN::processNonLocalLoad(LoadInst *LI,
1345 SmallVectorImpl<Instruction*> &toErase) {
1346 // Find the non-local dependencies of the load.
1347 SmallVector<NonLocalDepResult, 64> Deps;
1348 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
1350 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: "
1351 // << Deps.size() << *LI << '\n');
1353 // If we had to process more than one hundred blocks to find the
1354 // dependencies, this load isn't worth worrying about. Optimizing
1355 // it will be too expensive.
1356 if (Deps.size() > 100)
1359 // If we had a phi translation failure, we'll have a single entry which is a
1360 // clobber in the current block. Reject this early.
1361 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) {
1363 dbgs() << "GVN: non-local load ";
1364 WriteAsOperand(dbgs(), LI);
1365 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n';
1370 // Filter out useless results (non-locals, etc). Keep track of the blocks
1371 // where we have a value available in repl, also keep track of whether we see
1372 // dependencies that produce an unknown value for the load (such as a call
1373 // that could potentially clobber the load).
1374 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1375 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1377 const TargetData *TD = 0;
1379 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1380 BasicBlock *DepBB = Deps[i].getBB();
1381 MemDepResult DepInfo = Deps[i].getResult();
1383 if (DepInfo.isClobber()) {
1384 // The address being loaded in this non-local block may not be the same as
1385 // the pointer operand of the load if PHI translation occurs. Make sure
1386 // to consider the right address.
1387 Value *Address = Deps[i].getAddress();
1389 // If the dependence is to a store that writes to a superset of the bits
1390 // read by the load, we can extract the bits we need for the load from the
1392 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1394 TD = getAnalysisIfAvailable<TargetData>();
1395 if (TD && Address) {
1396 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1399 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1400 DepSI->getOperand(0),
1407 // If the clobbering value is a memset/memcpy/memmove, see if we can
1408 // forward a value on from it.
1409 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1411 TD = getAnalysisIfAvailable<TargetData>();
1412 if (TD && Address) {
1413 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1416 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1423 UnavailableBlocks.push_back(DepBB);
1427 Instruction *DepInst = DepInfo.getInst();
1429 // Loading the allocation -> undef.
1430 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1431 // Loading immediately after lifetime begin -> undef.
1432 isLifetimeStart(DepInst)) {
1433 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1434 UndefValue::get(LI->getType())));
1438 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1439 // Reject loads and stores that are to the same address but are of
1440 // different types if we have to.
1441 if (S->getOperand(0)->getType() != LI->getType()) {
1443 TD = getAnalysisIfAvailable<TargetData>();
1445 // If the stored value is larger or equal to the loaded value, we can
1447 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0),
1448 LI->getType(), *TD)) {
1449 UnavailableBlocks.push_back(DepBB);
1454 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1459 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1460 // If the types mismatch and we can't handle it, reject reuse of the load.
1461 if (LD->getType() != LI->getType()) {
1463 TD = getAnalysisIfAvailable<TargetData>();
1465 // If the stored value is larger or equal to the loaded value, we can
1467 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1468 UnavailableBlocks.push_back(DepBB);
1472 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD));
1476 UnavailableBlocks.push_back(DepBB);
1480 // If we have no predecessors that produce a known value for this load, exit
1482 if (ValuesPerBlock.empty()) return false;
1484 // If all of the instructions we depend on produce a known value for this
1485 // load, then it is fully redundant and we can use PHI insertion to compute
1486 // its value. Insert PHIs and remove the fully redundant value now.
1487 if (UnavailableBlocks.empty()) {
1488 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1490 // Perform PHI construction.
1491 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1492 VN.getAliasAnalysis());
1493 LI->replaceAllUsesWith(V);
1495 if (isa<PHINode>(V))
1497 if (V->getType()->isPointerTy())
1498 MD->invalidateCachedPointerInfo(V);
1500 toErase.push_back(LI);
1505 if (!EnablePRE || !EnableLoadPRE)
1508 // Okay, we have *some* definitions of the value. This means that the value
1509 // is available in some of our (transitive) predecessors. Lets think about
1510 // doing PRE of this load. This will involve inserting a new load into the
1511 // predecessor when it's not available. We could do this in general, but
1512 // prefer to not increase code size. As such, we only do this when we know
1513 // that we only have to insert *one* load (which means we're basically moving
1514 // the load, not inserting a new one).
1516 SmallPtrSet<BasicBlock *, 4> Blockers;
1517 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1518 Blockers.insert(UnavailableBlocks[i]);
1520 // Lets find first basic block with more than one predecessor. Walk backwards
1521 // through predecessors if needed.
1522 BasicBlock *LoadBB = LI->getParent();
1523 BasicBlock *TmpBB = LoadBB;
1525 bool isSinglePred = false;
1526 bool allSingleSucc = true;
1527 while (TmpBB->getSinglePredecessor()) {
1528 isSinglePred = true;
1529 TmpBB = TmpBB->getSinglePredecessor();
1530 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1532 if (Blockers.count(TmpBB))
1535 // If any of these blocks has more than one successor (i.e. if the edge we
1536 // just traversed was critical), then there are other paths through this
1537 // block along which the load may not be anticipated. Hoisting the load
1538 // above this block would be adding the load to execution paths along
1539 // which it was not previously executed.
1540 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1547 // FIXME: It is extremely unclear what this loop is doing, other than
1548 // artificially restricting loadpre.
1551 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1552 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1553 if (AV.isSimpleValue())
1554 // "Hot" Instruction is in some loop (because it dominates its dep.
1556 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1557 if (DT->dominates(LI, I)) {
1563 // We are interested only in "hot" instructions. We don't want to do any
1564 // mis-optimizations here.
1569 // Check to see how many predecessors have the loaded value fully
1571 DenseMap<BasicBlock*, Value*> PredLoads;
1572 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1573 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1574 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1575 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1576 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1578 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit;
1579 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1581 BasicBlock *Pred = *PI;
1582 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) {
1585 PredLoads[Pred] = 0;
1587 if (Pred->getTerminator()->getNumSuccessors() != 1) {
1588 if (isa<IndirectBrInst>(Pred->getTerminator())) {
1589 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
1590 << Pred->getName() << "': " << *LI << '\n');
1593 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB);
1594 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
1597 if (!NeedToSplit.empty()) {
1598 toSplit.append(NeedToSplit.begin(), NeedToSplit.end());
1602 // Decide whether PRE is profitable for this load.
1603 unsigned NumUnavailablePreds = PredLoads.size();
1604 assert(NumUnavailablePreds != 0 &&
1605 "Fully available value should be eliminated above!");
1607 // If this load is unavailable in multiple predecessors, reject it.
1608 // FIXME: If we could restructure the CFG, we could make a common pred with
1609 // all the preds that don't have an available LI and insert a new load into
1611 if (NumUnavailablePreds != 1)
1614 // Check if the load can safely be moved to all the unavailable predecessors.
1615 bool CanDoPRE = true;
1616 SmallVector<Instruction*, 8> NewInsts;
1617 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1618 E = PredLoads.end(); I != E; ++I) {
1619 BasicBlock *UnavailablePred = I->first;
1621 // Do PHI translation to get its value in the predecessor if necessary. The
1622 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1624 // If all preds have a single successor, then we know it is safe to insert
1625 // the load on the pred (?!?), so we can insert code to materialize the
1626 // pointer if it is not available.
1627 PHITransAddr Address(LI->getOperand(0), TD);
1629 if (allSingleSucc) {
1630 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1633 Address.PHITranslateValue(LoadBB, UnavailablePred, DT);
1634 LoadPtr = Address.getAddr();
1637 // If we couldn't find or insert a computation of this phi translated value,
1640 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1641 << *LI->getOperand(0) << "\n");
1646 // Make sure it is valid to move this load here. We have to watch out for:
1647 // @1 = getelementptr (i8* p, ...
1648 // test p and branch if == 0
1650 // It is valid to have the getelementptr before the test, even if p can be 0,
1651 // as getelementptr only does address arithmetic.
1652 // If we are not pushing the value through any multiple-successor blocks
1653 // we do not have this case. Otherwise, check that the load is safe to
1654 // put anywhere; this can be improved, but should be conservatively safe.
1655 if (!allSingleSucc &&
1656 // FIXME: REEVALUTE THIS.
1657 !isSafeToLoadUnconditionally(LoadPtr,
1658 UnavailablePred->getTerminator(),
1659 LI->getAlignment(), TD)) {
1664 I->second = LoadPtr;
1668 while (!NewInsts.empty())
1669 NewInsts.pop_back_val()->eraseFromParent();
1673 // Okay, we can eliminate this load by inserting a reload in the predecessor
1674 // and using PHI construction to get the value in the other predecessors, do
1676 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1677 DEBUG(if (!NewInsts.empty())
1678 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
1679 << *NewInsts.back() << '\n');
1681 // Assign value numbers to the new instructions.
1682 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1683 // FIXME: We really _ought_ to insert these value numbers into their
1684 // parent's availability map. However, in doing so, we risk getting into
1685 // ordering issues. If a block hasn't been processed yet, we would be
1686 // marking a value as AVAIL-IN, which isn't what we intend.
1687 VN.lookup_or_add(NewInsts[i]);
1690 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1691 E = PredLoads.end(); I != E; ++I) {
1692 BasicBlock *UnavailablePred = I->first;
1693 Value *LoadPtr = I->second;
1695 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1697 UnavailablePred->getTerminator());
1699 // Add the newly created load.
1700 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
1702 MD->invalidateCachedPointerInfo(LoadPtr);
1703 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
1706 // Perform PHI construction.
1707 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1708 VN.getAliasAnalysis());
1709 LI->replaceAllUsesWith(V);
1710 if (isa<PHINode>(V))
1712 if (V->getType()->isPointerTy())
1713 MD->invalidateCachedPointerInfo(V);
1715 toErase.push_back(LI);
1720 /// processLoad - Attempt to eliminate a load, first by eliminating it
1721 /// locally, and then attempting non-local elimination if that fails.
1722 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1726 if (L->isVolatile())
1729 // ... to a pointer that has been loaded from before...
1730 MemDepResult Dep = MD->getDependency(L);
1732 // If the value isn't available, don't do anything!
1733 if (Dep.isClobber()) {
1734 // Check to see if we have something like this:
1735 // store i32 123, i32* %P
1736 // %A = bitcast i32* %P to i8*
1737 // %B = gep i8* %A, i32 1
1740 // We could do that by recognizing if the clobber instructions are obviously
1741 // a common base + constant offset, and if the previous store (or memset)
1742 // completely covers this load. This sort of thing can happen in bitfield
1744 Value *AvailVal = 0;
1745 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1746 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1747 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1748 L->getPointerOperand(),
1751 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset,
1752 L->getType(), L, *TD);
1755 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1756 // a value on from it.
1757 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1758 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1759 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1760 L->getPointerOperand(),
1763 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1768 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1769 << *AvailVal << '\n' << *L << "\n\n\n");
1771 // Replace the load!
1772 L->replaceAllUsesWith(AvailVal);
1773 if (AvailVal->getType()->isPointerTy())
1774 MD->invalidateCachedPointerInfo(AvailVal);
1776 toErase.push_back(L);
1782 // fast print dep, using operator<< on instruction would be too slow
1783 dbgs() << "GVN: load ";
1784 WriteAsOperand(dbgs(), L);
1785 Instruction *I = Dep.getInst();
1786 dbgs() << " is clobbered by " << *I << '\n';
1791 // If it is defined in another block, try harder.
1792 if (Dep.isNonLocal())
1793 return processNonLocalLoad(L, toErase);
1795 Instruction *DepInst = Dep.getInst();
1796 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1797 Value *StoredVal = DepSI->getOperand(0);
1799 // The store and load are to a must-aliased pointer, but they may not
1800 // actually have the same type. See if we know how to reuse the stored
1801 // value (depending on its type).
1802 const TargetData *TD = 0;
1803 if (StoredVal->getType() != L->getType()) {
1804 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1805 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1810 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1811 << '\n' << *L << "\n\n\n");
1818 L->replaceAllUsesWith(StoredVal);
1819 if (StoredVal->getType()->isPointerTy())
1820 MD->invalidateCachedPointerInfo(StoredVal);
1822 toErase.push_back(L);
1827 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1828 Value *AvailableVal = DepLI;
1830 // The loads are of a must-aliased pointer, but they may not actually have
1831 // the same type. See if we know how to reuse the previously loaded value
1832 // (depending on its type).
1833 const TargetData *TD = 0;
1834 if (DepLI->getType() != L->getType()) {
1835 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1836 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1837 if (AvailableVal == 0)
1840 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1841 << "\n" << *L << "\n\n\n");
1848 L->replaceAllUsesWith(AvailableVal);
1849 if (DepLI->getType()->isPointerTy())
1850 MD->invalidateCachedPointerInfo(DepLI);
1852 toErase.push_back(L);
1857 // If this load really doesn't depend on anything, then we must be loading an
1858 // undef value. This can happen when loading for a fresh allocation with no
1859 // intervening stores, for example.
1860 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1861 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1863 toErase.push_back(L);
1868 // If this load occurs either right after a lifetime begin,
1869 // then the loaded value is undefined.
1870 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1871 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1872 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1874 toErase.push_back(L);
1883 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1884 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1885 if (I == localAvail.end())
1888 ValueNumberScope *Locals = I->second;
1890 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num);
1891 if (I != Locals->table.end())
1893 Locals = Locals->parent;
1900 /// processInstruction - When calculating availability, handle an instruction
1901 /// by inserting it into the appropriate sets
1902 bool GVN::processInstruction(Instruction *I,
1903 SmallVectorImpl<Instruction*> &toErase) {
1904 // Ignore dbg info intrinsics.
1905 if (isa<DbgInfoIntrinsic>(I))
1908 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1909 bool Changed = processLoad(LI, toErase);
1912 unsigned Num = VN.lookup_or_add(LI);
1913 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI));
1919 uint32_t NextNum = VN.getNextUnusedValueNumber();
1920 unsigned Num = VN.lookup_or_add(I);
1922 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1923 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1925 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1928 Value *BranchCond = BI->getCondition();
1929 uint32_t CondVN = VN.lookup_or_add(BranchCond);
1931 BasicBlock *TrueSucc = BI->getSuccessor(0);
1932 BasicBlock *FalseSucc = BI->getSuccessor(1);
1934 if (TrueSucc->getSinglePredecessor())
1935 localAvail[TrueSucc]->table[CondVN] =
1936 ConstantInt::getTrue(TrueSucc->getContext());
1937 if (FalseSucc->getSinglePredecessor())
1938 localAvail[FalseSucc]->table[CondVN] =
1939 ConstantInt::getFalse(TrueSucc->getContext());
1943 // Allocations are always uniquely numbered, so we can save time and memory
1944 // by fast failing them.
1945 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1946 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1950 // Collapse PHI nodes
1951 if (PHINode* p = dyn_cast<PHINode>(I)) {
1952 Value *constVal = CollapsePhi(p);
1955 p->replaceAllUsesWith(constVal);
1956 if (MD && constVal->getType()->isPointerTy())
1957 MD->invalidateCachedPointerInfo(constVal);
1960 toErase.push_back(p);
1962 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1965 // If the number we were assigned was a brand new VN, then we don't
1966 // need to do a lookup to see if the number already exists
1967 // somewhere in the domtree: it can't!
1968 } else if (Num == NextNum) {
1969 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1971 // Perform fast-path value-number based elimination of values inherited from
1973 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1976 I->replaceAllUsesWith(repl);
1977 if (MD && repl->getType()->isPointerTy())
1978 MD->invalidateCachedPointerInfo(repl);
1979 toErase.push_back(I);
1983 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1989 /// runOnFunction - This is the main transformation entry point for a function.
1990 bool GVN::runOnFunction(Function& F) {
1992 MD = &getAnalysis<MemoryDependenceAnalysis>();
1993 DT = &getAnalysis<DominatorTree>();
1994 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1998 bool Changed = false;
1999 bool ShouldContinue = true;
2001 // Merge unconditional branches, allowing PRE to catch more
2002 // optimization opportunities.
2003 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
2004 BasicBlock *BB = FI;
2006 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
2007 if (removedBlock) ++NumGVNBlocks;
2009 Changed |= removedBlock;
2012 unsigned Iteration = 0;
2014 while (ShouldContinue) {
2015 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
2016 ShouldContinue = iterateOnFunction(F);
2017 if (splitCriticalEdges())
2018 ShouldContinue = true;
2019 Changed |= ShouldContinue;
2024 bool PREChanged = true;
2025 while (PREChanged) {
2026 PREChanged = performPRE(F);
2027 Changed |= PREChanged;
2030 // FIXME: Should perform GVN again after PRE does something. PRE can move
2031 // computations into blocks where they become fully redundant. Note that
2032 // we can't do this until PRE's critical edge splitting updates memdep.
2033 // Actually, when this happens, we should just fully integrate PRE into GVN.
2035 cleanupGlobalSets();
2041 bool GVN::processBlock(BasicBlock *BB) {
2042 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
2043 // incrementing BI before processing an instruction).
2044 SmallVector<Instruction*, 8> toErase;
2045 bool ChangedFunction = false;
2047 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2049 ChangedFunction |= processInstruction(BI, toErase);
2050 if (toErase.empty()) {
2055 // If we need some instructions deleted, do it now.
2056 NumGVNInstr += toErase.size();
2058 // Avoid iterator invalidation.
2059 bool AtStart = BI == BB->begin();
2063 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2064 E = toErase.end(); I != E; ++I) {
2065 DEBUG(dbgs() << "GVN removed: " << **I << '\n');
2066 if (MD) MD->removeInstruction(*I);
2067 (*I)->eraseFromParent();
2068 DEBUG(verifyRemoved(*I));
2078 return ChangedFunction;
2081 /// performPRE - Perform a purely local form of PRE that looks for diamond
2082 /// control flow patterns and attempts to perform simple PRE at the join point.
2083 bool GVN::performPRE(Function &F) {
2084 bool Changed = false;
2085 DenseMap<BasicBlock*, Value*> predMap;
2086 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2087 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2088 BasicBlock *CurrentBlock = *DI;
2090 // Nothing to PRE in the entry block.
2091 if (CurrentBlock == &F.getEntryBlock()) continue;
2093 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2094 BE = CurrentBlock->end(); BI != BE; ) {
2095 Instruction *CurInst = BI++;
2097 if (isa<AllocaInst>(CurInst) ||
2098 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2099 CurInst->getType()->isVoidTy() ||
2100 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2101 isa<DbgInfoIntrinsic>(CurInst))
2104 // We don't currently value number ANY inline asm calls.
2105 if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
2106 if (CallI->isInlineAsm())
2109 uint32_t ValNo = VN.lookup(CurInst);
2111 // Look for the predecessors for PRE opportunities. We're
2112 // only trying to solve the basic diamond case, where
2113 // a value is computed in the successor and one predecessor,
2114 // but not the other. We also explicitly disallow cases
2115 // where the successor is its own predecessor, because they're
2116 // more complicated to get right.
2117 unsigned NumWith = 0;
2118 unsigned NumWithout = 0;
2119 BasicBlock *PREPred = 0;
2122 for (pred_iterator PI = pred_begin(CurrentBlock),
2123 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2124 BasicBlock *P = *PI;
2125 // We're not interested in PRE where the block is its
2126 // own predecessor, or in blocks with predecessors
2127 // that are not reachable.
2128 if (P == CurrentBlock) {
2131 } else if (!localAvail.count(P)) {
2136 DenseMap<uint32_t, Value*>::iterator predV =
2137 localAvail[P]->table.find(ValNo);
2138 if (predV == localAvail[P]->table.end()) {
2141 } else if (predV->second == CurInst) {
2144 predMap[P] = predV->second;
2149 // Don't do PRE when it might increase code size, i.e. when
2150 // we would need to insert instructions in more than one pred.
2151 if (NumWithout != 1 || NumWith == 0)
2154 // Don't do PRE across indirect branch.
2155 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2158 // We can't do PRE safely on a critical edge, so instead we schedule
2159 // the edge to be split and perform the PRE the next time we iterate
2161 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
2162 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2163 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2167 // Instantiate the expression in the predecessor that lacked it.
2168 // Because we are going top-down through the block, all value numbers
2169 // will be available in the predecessor by the time we need them. Any
2170 // that weren't originally present will have been instantiated earlier
2172 Instruction *PREInstr = CurInst->clone();
2173 bool success = true;
2174 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2175 Value *Op = PREInstr->getOperand(i);
2176 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2179 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
2180 PREInstr->setOperand(i, V);
2187 // Fail out if we encounter an operand that is not available in
2188 // the PRE predecessor. This is typically because of loads which
2189 // are not value numbered precisely.
2192 DEBUG(verifyRemoved(PREInstr));
2196 PREInstr->insertBefore(PREPred->getTerminator());
2197 PREInstr->setName(CurInst->getName() + ".pre");
2198 predMap[PREPred] = PREInstr;
2199 VN.add(PREInstr, ValNo);
2202 // Update the availability map to include the new instruction.
2203 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr));
2205 // Create a PHI to make the value available in this block.
2206 PHINode* Phi = PHINode::Create(CurInst->getType(),
2207 CurInst->getName() + ".pre-phi",
2208 CurrentBlock->begin());
2209 for (pred_iterator PI = pred_begin(CurrentBlock),
2210 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2211 BasicBlock *P = *PI;
2212 Phi->addIncoming(predMap[P], P);
2216 localAvail[CurrentBlock]->table[ValNo] = Phi;
2218 CurInst->replaceAllUsesWith(Phi);
2219 if (MD && Phi->getType()->isPointerTy())
2220 MD->invalidateCachedPointerInfo(Phi);
2223 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
2224 if (MD) MD->removeInstruction(CurInst);
2225 CurInst->eraseFromParent();
2226 DEBUG(verifyRemoved(CurInst));
2231 if (splitCriticalEdges())
2237 /// splitCriticalEdges - Split critical edges found during the previous
2238 /// iteration that may enable further optimization.
2239 bool GVN::splitCriticalEdges() {
2240 if (toSplit.empty())
2243 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
2244 SplitCriticalEdge(Edge.first, Edge.second, this);
2245 } while (!toSplit.empty());
2246 if (MD) MD->invalidateCachedPredecessors();
2250 /// iterateOnFunction - Executes one iteration of GVN
2251 bool GVN::iterateOnFunction(Function &F) {
2252 cleanupGlobalSets();
2254 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2255 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
2257 localAvail[DI->getBlock()] =
2258 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
2260 localAvail[DI->getBlock()] = new ValueNumberScope(0);
2263 // Top-down walk of the dominator tree
2264 bool Changed = false;
2266 // Needed for value numbering with phi construction to work.
2267 ReversePostOrderTraversal<Function*> RPOT(&F);
2268 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2269 RE = RPOT.end(); RI != RE; ++RI)
2270 Changed |= processBlock(*RI);
2272 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2273 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2274 Changed |= processBlock(DI->getBlock());
2280 void GVN::cleanupGlobalSets() {
2283 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
2284 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
2289 /// verifyRemoved - Verify that the specified instruction does not occur in our
2290 /// internal data structures.
2291 void GVN::verifyRemoved(const Instruction *Inst) const {
2292 VN.verifyRemoved(Inst);
2294 // Walk through the value number scope to make sure the instruction isn't
2295 // ferreted away in it.
2296 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
2297 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
2298 const ValueNumberScope *VNS = I->second;
2301 for (DenseMap<uint32_t, Value*>::const_iterator
2302 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
2303 assert(II->second != Inst && "Inst still in value numbering scope!");