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);
180 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
181 AliasAnalysis *getAliasAnalysis() const { return AA; }
182 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
183 void setDomTree(DominatorTree* D) { DT = D; }
184 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
185 void verifyRemoved(const Value *) const;
190 template <> struct DenseMapInfo<Expression> {
191 static inline Expression getEmptyKey() {
192 return Expression(Expression::EMPTY);
195 static inline Expression getTombstoneKey() {
196 return Expression(Expression::TOMBSTONE);
199 static unsigned getHashValue(const Expression e) {
200 unsigned hash = e.opcode;
202 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
203 (unsigned)((uintptr_t)e.type >> 9));
205 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
206 E = e.varargs.end(); I != E; ++I)
207 hash = *I + hash * 37;
209 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
210 (unsigned)((uintptr_t)e.function >> 9)) +
215 static bool isEqual(const Expression &LHS, const Expression &RHS) {
221 struct isPodLike<Expression> { static const bool value = true; };
225 //===----------------------------------------------------------------------===//
226 // ValueTable Internal Functions
227 //===----------------------------------------------------------------------===//
229 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
230 if (isa<ICmpInst>(C)) {
231 switch (C->getPredicate()) {
232 default: // THIS SHOULD NEVER HAPPEN
233 llvm_unreachable("Comparison with unknown predicate?");
234 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
235 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
236 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
237 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
238 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
239 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
240 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
241 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
242 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
243 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
246 switch (C->getPredicate()) {
247 default: // THIS SHOULD NEVER HAPPEN
248 llvm_unreachable("Comparison with unknown predicate?");
249 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
250 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
251 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
252 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
253 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
254 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
255 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
256 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
257 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
258 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
259 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
260 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
261 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
262 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
267 Expression ValueTable::create_expression(CallInst* C) {
270 e.type = C->getType();
271 e.function = C->getCalledFunction();
272 e.opcode = Expression::CALL;
275 for (CallInst::op_iterator I = CS.arg_begin(), E = CS.arg_end();
277 e.varargs.push_back(lookup_or_add(*I));
282 Expression ValueTable::create_expression(BinaryOperator* BO) {
284 e.varargs.push_back(lookup_or_add(BO->getOperand(0)));
285 e.varargs.push_back(lookup_or_add(BO->getOperand(1)));
287 e.type = BO->getType();
288 e.opcode = static_cast<Expression::ExpressionOpcode>(BO->getOpcode());
293 Expression ValueTable::create_expression(CmpInst* C) {
296 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
297 e.varargs.push_back(lookup_or_add(C->getOperand(1)));
299 e.type = C->getType();
300 e.opcode = getOpcode(C);
305 Expression ValueTable::create_expression(CastInst* C) {
308 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
310 e.type = C->getType();
311 e.opcode = static_cast<Expression::ExpressionOpcode>(C->getOpcode());
316 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
319 e.varargs.push_back(lookup_or_add(S->getOperand(0)));
320 e.varargs.push_back(lookup_or_add(S->getOperand(1)));
321 e.varargs.push_back(lookup_or_add(S->getOperand(2)));
323 e.type = S->getType();
324 e.opcode = Expression::SHUFFLE;
329 Expression ValueTable::create_expression(ExtractElementInst* E) {
332 e.varargs.push_back(lookup_or_add(E->getOperand(0)));
333 e.varargs.push_back(lookup_or_add(E->getOperand(1)));
335 e.type = E->getType();
336 e.opcode = Expression::EXTRACT;
341 Expression ValueTable::create_expression(InsertElementInst* I) {
344 e.varargs.push_back(lookup_or_add(I->getOperand(0)));
345 e.varargs.push_back(lookup_or_add(I->getOperand(1)));
346 e.varargs.push_back(lookup_or_add(I->getOperand(2)));
348 e.type = I->getType();
349 e.opcode = Expression::INSERT;
354 Expression ValueTable::create_expression(SelectInst* I) {
357 e.varargs.push_back(lookup_or_add(I->getCondition()));
358 e.varargs.push_back(lookup_or_add(I->getTrueValue()));
359 e.varargs.push_back(lookup_or_add(I->getFalseValue()));
361 e.type = I->getType();
362 e.opcode = Expression::SELECT;
367 Expression ValueTable::create_expression(GetElementPtrInst* G) {
370 e.varargs.push_back(lookup_or_add(G->getPointerOperand()));
372 e.type = G->getType();
373 e.opcode = Expression::GEP;
375 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
377 e.varargs.push_back(lookup_or_add(*I));
382 Expression ValueTable::create_expression(ExtractValueInst* E) {
385 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
386 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
388 e.varargs.push_back(*II);
390 e.type = E->getType();
391 e.opcode = Expression::EXTRACTVALUE;
396 Expression ValueTable::create_expression(InsertValueInst* E) {
399 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
400 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand()));
401 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
403 e.varargs.push_back(*II);
405 e.type = E->getType();
406 e.opcode = Expression::INSERTVALUE;
411 //===----------------------------------------------------------------------===//
412 // ValueTable External Functions
413 //===----------------------------------------------------------------------===//
415 /// add - Insert a value into the table with a specified value number.
416 void ValueTable::add(Value *V, uint32_t num) {
417 valueNumbering.insert(std::make_pair(V, num));
420 uint32_t ValueTable::lookup_or_add_call(CallInst* C) {
421 if (AA->doesNotAccessMemory(C)) {
422 Expression exp = create_expression(C);
423 uint32_t& e = expressionNumbering[exp];
424 if (!e) e = nextValueNumber++;
425 valueNumbering[C] = e;
427 } else if (AA->onlyReadsMemory(C)) {
428 Expression exp = create_expression(C);
429 uint32_t& e = expressionNumbering[exp];
431 e = nextValueNumber++;
432 valueNumbering[C] = e;
436 e = nextValueNumber++;
437 valueNumbering[C] = e;
441 MemDepResult local_dep = MD->getDependency(C);
443 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
444 valueNumbering[C] = nextValueNumber;
445 return nextValueNumber++;
448 if (local_dep.isDef()) {
449 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
451 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) {
452 valueNumbering[C] = nextValueNumber;
453 return nextValueNumber++;
456 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
457 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
458 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i));
460 valueNumbering[C] = nextValueNumber;
461 return nextValueNumber++;
465 uint32_t v = lookup_or_add(local_cdep);
466 valueNumbering[C] = v;
471 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
472 MD->getNonLocalCallDependency(CallSite(C));
473 // FIXME: call/call dependencies for readonly calls should return def, not
474 // clobber! Move the checking logic to MemDep!
477 // Check to see if we have a single dominating call instruction that is
479 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
480 const NonLocalDepEntry *I = &deps[i];
481 // Ignore non-local dependencies.
482 if (I->getResult().isNonLocal())
485 // We don't handle non-depedencies. If we already have a call, reject
486 // instruction dependencies.
487 if (I->getResult().isClobber() || cdep != 0) {
492 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
493 // FIXME: All duplicated with non-local case.
494 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
495 cdep = NonLocalDepCall;
504 valueNumbering[C] = nextValueNumber;
505 return nextValueNumber++;
508 if (cdep->getNumArgOperands() != C->getNumArgOperands()) {
509 valueNumbering[C] = nextValueNumber;
510 return nextValueNumber++;
512 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) {
513 uint32_t c_vn = lookup_or_add(C->getArgOperand(i));
514 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i));
516 valueNumbering[C] = nextValueNumber;
517 return nextValueNumber++;
521 uint32_t v = lookup_or_add(cdep);
522 valueNumbering[C] = v;
526 valueNumbering[C] = nextValueNumber;
527 return nextValueNumber++;
531 /// lookup_or_add - Returns the value number for the specified value, assigning
532 /// it a new number if it did not have one before.
533 uint32_t ValueTable::lookup_or_add(Value *V) {
534 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
535 if (VI != valueNumbering.end())
538 if (!isa<Instruction>(V)) {
539 valueNumbering[V] = nextValueNumber;
540 return nextValueNumber++;
543 Instruction* I = cast<Instruction>(V);
545 switch (I->getOpcode()) {
546 case Instruction::Call:
547 return lookup_or_add_call(cast<CallInst>(I));
548 case Instruction::Add:
549 case Instruction::FAdd:
550 case Instruction::Sub:
551 case Instruction::FSub:
552 case Instruction::Mul:
553 case Instruction::FMul:
554 case Instruction::UDiv:
555 case Instruction::SDiv:
556 case Instruction::FDiv:
557 case Instruction::URem:
558 case Instruction::SRem:
559 case Instruction::FRem:
560 case Instruction::Shl:
561 case Instruction::LShr:
562 case Instruction::AShr:
563 case Instruction::And:
564 case Instruction::Or :
565 case Instruction::Xor:
566 exp = create_expression(cast<BinaryOperator>(I));
568 case Instruction::ICmp:
569 case Instruction::FCmp:
570 exp = create_expression(cast<CmpInst>(I));
572 case Instruction::Trunc:
573 case Instruction::ZExt:
574 case Instruction::SExt:
575 case Instruction::FPToUI:
576 case Instruction::FPToSI:
577 case Instruction::UIToFP:
578 case Instruction::SIToFP:
579 case Instruction::FPTrunc:
580 case Instruction::FPExt:
581 case Instruction::PtrToInt:
582 case Instruction::IntToPtr:
583 case Instruction::BitCast:
584 exp = create_expression(cast<CastInst>(I));
586 case Instruction::Select:
587 exp = create_expression(cast<SelectInst>(I));
589 case Instruction::ExtractElement:
590 exp = create_expression(cast<ExtractElementInst>(I));
592 case Instruction::InsertElement:
593 exp = create_expression(cast<InsertElementInst>(I));
595 case Instruction::ShuffleVector:
596 exp = create_expression(cast<ShuffleVectorInst>(I));
598 case Instruction::ExtractValue:
599 exp = create_expression(cast<ExtractValueInst>(I));
601 case Instruction::InsertValue:
602 exp = create_expression(cast<InsertValueInst>(I));
604 case Instruction::GetElementPtr:
605 exp = create_expression(cast<GetElementPtrInst>(I));
608 valueNumbering[V] = nextValueNumber;
609 return nextValueNumber++;
612 uint32_t& e = expressionNumbering[exp];
613 if (!e) e = nextValueNumber++;
614 valueNumbering[V] = e;
618 /// lookup - Returns the value number of the specified value. Fails if
619 /// the value has not yet been numbered.
620 uint32_t ValueTable::lookup(Value *V) const {
621 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
622 assert(VI != valueNumbering.end() && "Value not numbered?");
626 /// clear - Remove all entries from the ValueTable
627 void ValueTable::clear() {
628 valueNumbering.clear();
629 expressionNumbering.clear();
633 /// erase - Remove a value from the value numbering
634 void ValueTable::erase(Value *V) {
635 valueNumbering.erase(V);
638 /// verifyRemoved - Verify that the value is removed from all internal data
640 void ValueTable::verifyRemoved(const Value *V) const {
641 for (DenseMap<Value*, uint32_t>::const_iterator
642 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
643 assert(I->first != V && "Inst still occurs in value numbering map!");
647 //===----------------------------------------------------------------------===//
649 //===----------------------------------------------------------------------===//
652 struct ValueNumberScope {
653 ValueNumberScope* parent;
654 DenseMap<uint32_t, Value*> table;
656 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
662 class GVN : public FunctionPass {
663 bool runOnFunction(Function &F);
665 static char ID; // Pass identification, replacement for typeid
666 explicit GVN(bool noloads = false)
667 : FunctionPass(ID), NoLoads(noloads), MD(0) { }
671 MemoryDependenceAnalysis *MD;
675 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
677 // List of critical edges to be split between iterations.
678 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
680 // This transformation requires dominator postdominator info
681 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
682 AU.addRequired<DominatorTree>();
684 AU.addRequired<MemoryDependenceAnalysis>();
685 AU.addRequired<AliasAnalysis>();
687 AU.addPreserved<DominatorTree>();
688 AU.addPreserved<AliasAnalysis>();
692 // FIXME: eliminate or document these better
693 bool processLoad(LoadInst* L,
694 SmallVectorImpl<Instruction*> &toErase);
695 bool processInstruction(Instruction *I,
696 SmallVectorImpl<Instruction*> &toErase);
697 bool processNonLocalLoad(LoadInst* L,
698 SmallVectorImpl<Instruction*> &toErase);
699 bool processBlock(BasicBlock *BB);
700 void dump(DenseMap<uint32_t, Value*>& d);
701 bool iterateOnFunction(Function &F);
702 Value *CollapsePhi(PHINode* p);
703 bool performPRE(Function& F);
704 Value *lookupNumber(BasicBlock *BB, uint32_t num);
705 void cleanupGlobalSets();
706 void verifyRemoved(const Instruction *I) const;
707 bool splitCriticalEdges();
713 // createGVNPass - The public interface to this file...
714 FunctionPass *llvm::createGVNPass(bool NoLoads) {
715 return new GVN(NoLoads);
718 INITIALIZE_PASS(GVN, "gvn", "Global Value Numbering", false, false);
720 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
722 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
723 E = d.end(); I != E; ++I) {
724 errs() << I->first << "\n";
730 static bool isSafeReplacement(PHINode* p, Instruction *inst) {
731 if (!isa<PHINode>(inst))
734 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
736 if (PHINode* use_phi = dyn_cast<PHINode>(*UI))
737 if (use_phi->getParent() == inst->getParent())
743 Value *GVN::CollapsePhi(PHINode *PN) {
744 Value *ConstVal = PN->hasConstantValue(DT);
745 if (!ConstVal) return 0;
747 Instruction *Inst = dyn_cast<Instruction>(ConstVal);
751 if (DT->dominates(Inst, PN))
752 if (isSafeReplacement(PN, Inst))
757 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
758 /// we're analyzing is fully available in the specified block. As we go, keep
759 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
760 /// map is actually a tri-state map with the following values:
761 /// 0) we know the block *is not* fully available.
762 /// 1) we know the block *is* fully available.
763 /// 2) we do not know whether the block is fully available or not, but we are
764 /// currently speculating that it will be.
765 /// 3) we are speculating for this block and have used that to speculate for
767 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
768 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
769 // Optimistically assume that the block is fully available and check to see
770 // if we already know about this block in one lookup.
771 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
772 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
774 // If the entry already existed for this block, return the precomputed value.
776 // If this is a speculative "available" value, mark it as being used for
777 // speculation of other blocks.
778 if (IV.first->second == 2)
779 IV.first->second = 3;
780 return IV.first->second != 0;
783 // Otherwise, see if it is fully available in all predecessors.
784 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
786 // If this block has no predecessors, it isn't live-in here.
788 goto SpeculationFailure;
790 for (; PI != PE; ++PI)
791 // If the value isn't fully available in one of our predecessors, then it
792 // isn't fully available in this block either. Undo our previous
793 // optimistic assumption and bail out.
794 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
795 goto SpeculationFailure;
799 // SpeculationFailure - If we get here, we found out that this is not, after
800 // all, a fully-available block. We have a problem if we speculated on this and
801 // used the speculation to mark other blocks as available.
803 char &BBVal = FullyAvailableBlocks[BB];
805 // If we didn't speculate on this, just return with it set to false.
811 // If we did speculate on this value, we could have blocks set to 1 that are
812 // incorrect. Walk the (transitive) successors of this block and mark them as
814 SmallVector<BasicBlock*, 32> BBWorklist;
815 BBWorklist.push_back(BB);
818 BasicBlock *Entry = BBWorklist.pop_back_val();
819 // Note that this sets blocks to 0 (unavailable) if they happen to not
820 // already be in FullyAvailableBlocks. This is safe.
821 char &EntryVal = FullyAvailableBlocks[Entry];
822 if (EntryVal == 0) continue; // Already unavailable.
824 // Mark as unavailable.
827 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
828 BBWorklist.push_back(*I);
829 } while (!BBWorklist.empty());
835 /// CanCoerceMustAliasedValueToLoad - Return true if
836 /// CoerceAvailableValueToLoadType will succeed.
837 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
839 const TargetData &TD) {
840 // If the loaded or stored value is an first class array or struct, don't try
841 // to transform them. We need to be able to bitcast to integer.
842 if (LoadTy->isStructTy() || LoadTy->isArrayTy() ||
843 StoredVal->getType()->isStructTy() ||
844 StoredVal->getType()->isArrayTy())
847 // The store has to be at least as big as the load.
848 if (TD.getTypeSizeInBits(StoredVal->getType()) <
849 TD.getTypeSizeInBits(LoadTy))
856 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
857 /// then a load from a must-aliased pointer of a different type, try to coerce
858 /// the stored value. LoadedTy is the type of the load we want to replace and
859 /// InsertPt is the place to insert new instructions.
861 /// If we can't do it, return null.
862 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
863 const Type *LoadedTy,
864 Instruction *InsertPt,
865 const TargetData &TD) {
866 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
869 const Type *StoredValTy = StoredVal->getType();
871 uint64_t StoreSize = TD.getTypeStoreSizeInBits(StoredValTy);
872 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
874 // If the store and reload are the same size, we can always reuse it.
875 if (StoreSize == LoadSize) {
876 if (StoredValTy->isPointerTy() && LoadedTy->isPointerTy()) {
877 // Pointer to Pointer -> use bitcast.
878 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
881 // Convert source pointers to integers, which can be bitcast.
882 if (StoredValTy->isPointerTy()) {
883 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
884 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
887 const Type *TypeToCastTo = LoadedTy;
888 if (TypeToCastTo->isPointerTy())
889 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
891 if (StoredValTy != TypeToCastTo)
892 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
894 // Cast to pointer if the load needs a pointer type.
895 if (LoadedTy->isPointerTy())
896 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
901 // If the loaded value is smaller than the available value, then we can
902 // extract out a piece from it. If the available value is too small, then we
903 // can't do anything.
904 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
906 // Convert source pointers to integers, which can be manipulated.
907 if (StoredValTy->isPointerTy()) {
908 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
909 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
912 // Convert vectors and fp to integer, which can be manipulated.
913 if (!StoredValTy->isIntegerTy()) {
914 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
915 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
918 // If this is a big-endian system, we need to shift the value down to the low
919 // bits so that a truncate will work.
920 if (TD.isBigEndian()) {
921 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
922 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
925 // Truncate the integer to the right size now.
926 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
927 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
929 if (LoadedTy == NewIntTy)
932 // If the result is a pointer, inttoptr.
933 if (LoadedTy->isPointerTy())
934 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
936 // Otherwise, bitcast.
937 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
940 /// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
941 /// be expressed as a base pointer plus a constant offset. Return the base and
942 /// offset to the caller.
943 static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
944 const TargetData &TD) {
945 Operator *PtrOp = dyn_cast<Operator>(Ptr);
946 if (PtrOp == 0) return Ptr;
948 // Just look through bitcasts.
949 if (PtrOp->getOpcode() == Instruction::BitCast)
950 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
952 // If this is a GEP with constant indices, we can look through it.
953 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
954 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
956 gep_type_iterator GTI = gep_type_begin(GEP);
957 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
959 ConstantInt *OpC = cast<ConstantInt>(*I);
960 if (OpC->isZero()) continue;
962 // Handle a struct and array indices which add their offset to the pointer.
963 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
964 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
966 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
967 Offset += OpC->getSExtValue()*Size;
971 // Re-sign extend from the pointer size if needed to get overflow edge cases
973 unsigned PtrSize = TD.getPointerSizeInBits();
975 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
977 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
981 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
982 /// memdep query of a load that ends up being a clobbering memory write (store,
983 /// memset, memcpy, memmove). This means that the write *may* provide bits used
984 /// by the load but we can't be sure because the pointers don't mustalias.
986 /// Check this case to see if there is anything more we can do before we give
987 /// up. This returns -1 if we have to give up, or a byte number in the stored
988 /// value of the piece that feeds the load.
989 static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
991 uint64_t WriteSizeInBits,
992 const TargetData &TD) {
993 // If the loaded or stored value is an first class array or struct, don't try
994 // to transform them. We need to be able to bitcast to integer.
995 if (LoadTy->isStructTy() || LoadTy->isArrayTy())
998 int64_t StoreOffset = 0, LoadOffset = 0;
999 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
1001 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
1002 if (StoreBase != LoadBase)
1005 // If the load and store are to the exact same address, they should have been
1006 // a must alias. AA must have gotten confused.
1007 // FIXME: Study to see if/when this happens. One case is forwarding a memset
1008 // to a load from the base of the memset.
1010 if (LoadOffset == StoreOffset) {
1011 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
1012 << "Base = " << *StoreBase << "\n"
1013 << "Store Ptr = " << *WritePtr << "\n"
1014 << "Store Offs = " << StoreOffset << "\n"
1015 << "Load Ptr = " << *LoadPtr << "\n";
1020 // If the load and store don't overlap at all, the store doesn't provide
1021 // anything to the load. In this case, they really don't alias at all, AA
1022 // must have gotten confused.
1023 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
1024 // remove this check, as it is duplicated with what we have below.
1025 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
1027 if ((WriteSizeInBits & 7) | (LoadSize & 7))
1029 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
1033 bool isAAFailure = false;
1034 if (StoreOffset < LoadOffset)
1035 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
1037 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
1041 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n"
1042 << "Base = " << *StoreBase << "\n"
1043 << "Store Ptr = " << *WritePtr << "\n"
1044 << "Store Offs = " << StoreOffset << "\n"
1045 << "Load Ptr = " << *LoadPtr << "\n";
1051 // If the Load isn't completely contained within the stored bits, we don't
1052 // have all the bits to feed it. We could do something crazy in the future
1053 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1055 if (StoreOffset > LoadOffset ||
1056 StoreOffset+StoreSize < LoadOffset+LoadSize)
1059 // Okay, we can do this transformation. Return the number of bytes into the
1060 // store that the load is.
1061 return LoadOffset-StoreOffset;
1064 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1065 /// memdep query of a load that ends up being a clobbering store.
1066 static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr,
1068 const TargetData &TD) {
1069 // Cannot handle reading from store of first-class aggregate yet.
1070 if (DepSI->getOperand(0)->getType()->isStructTy() ||
1071 DepSI->getOperand(0)->getType()->isArrayTy())
1074 Value *StorePtr = DepSI->getPointerOperand();
1075 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType());
1076 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1077 StorePtr, StoreSize, TD);
1080 static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr,
1082 const TargetData &TD) {
1083 // If the mem operation is a non-constant size, we can't handle it.
1084 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1085 if (SizeCst == 0) return -1;
1086 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1088 // If this is memset, we just need to see if the offset is valid in the size
1090 if (MI->getIntrinsicID() == Intrinsic::memset)
1091 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1094 // If we have a memcpy/memmove, the only case we can handle is if this is a
1095 // copy from constant memory. In that case, we can read directly from the
1097 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1099 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1100 if (Src == 0) return -1;
1102 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1103 if (GV == 0 || !GV->isConstant()) return -1;
1105 // See if the access is within the bounds of the transfer.
1106 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1107 MI->getDest(), MemSizeInBits, TD);
1111 // Otherwise, see if we can constant fold a load from the constant with the
1112 // offset applied as appropriate.
1113 Src = ConstantExpr::getBitCast(Src,
1114 llvm::Type::getInt8PtrTy(Src->getContext()));
1115 Constant *OffsetCst =
1116 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1117 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1118 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1119 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1125 /// GetStoreValueForLoad - This function is called when we have a
1126 /// memdep query of a load that ends up being a clobbering store. This means
1127 /// that the store *may* provide bits used by the load but we can't be sure
1128 /// because the pointers don't mustalias. Check this case to see if there is
1129 /// anything more we can do before we give up.
1130 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1132 Instruction *InsertPt, const TargetData &TD){
1133 LLVMContext &Ctx = SrcVal->getType()->getContext();
1135 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8;
1136 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8;
1138 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1140 // Compute which bits of the stored value are being used by the load. Convert
1141 // to an integer type to start with.
1142 if (SrcVal->getType()->isPointerTy())
1143 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp");
1144 if (!SrcVal->getType()->isIntegerTy())
1145 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1148 // Shift the bits to the least significant depending on endianness.
1150 if (TD.isLittleEndian())
1151 ShiftAmt = Offset*8;
1153 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1156 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp");
1158 if (LoadSize != StoreSize)
1159 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1162 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1165 /// GetMemInstValueForLoad - This function is called when we have a
1166 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1167 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1168 const Type *LoadTy, Instruction *InsertPt,
1169 const TargetData &TD){
1170 LLVMContext &Ctx = LoadTy->getContext();
1171 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1173 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1175 // We know that this method is only called when the mem transfer fully
1176 // provides the bits for the load.
1177 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1178 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1179 // independently of what the offset is.
1180 Value *Val = MSI->getValue();
1182 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1184 Value *OneElt = Val;
1186 // Splat the value out to the right number of bits.
1187 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1188 // If we can double the number of bytes set, do it.
1189 if (NumBytesSet*2 <= LoadSize) {
1190 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1191 Val = Builder.CreateOr(Val, ShVal);
1196 // Otherwise insert one byte at a time.
1197 Value *ShVal = Builder.CreateShl(Val, 1*8);
1198 Val = Builder.CreateOr(OneElt, ShVal);
1202 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1205 // Otherwise, this is a memcpy/memmove from a constant global.
1206 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1207 Constant *Src = cast<Constant>(MTI->getSource());
1209 // Otherwise, see if we can constant fold a load from the constant with the
1210 // offset applied as appropriate.
1211 Src = ConstantExpr::getBitCast(Src,
1212 llvm::Type::getInt8PtrTy(Src->getContext()));
1213 Constant *OffsetCst =
1214 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1215 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1216 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1217 return ConstantFoldLoadFromConstPtr(Src, &TD);
1222 struct AvailableValueInBlock {
1223 /// BB - The basic block in question.
1226 SimpleVal, // A simple offsetted value that is accessed.
1227 MemIntrin // A memory intrinsic which is loaded from.
1230 /// V - The value that is live out of the block.
1231 PointerIntPair<Value *, 1, ValType> Val;
1233 /// Offset - The byte offset in Val that is interesting for the load query.
1236 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1237 unsigned Offset = 0) {
1238 AvailableValueInBlock Res;
1240 Res.Val.setPointer(V);
1241 Res.Val.setInt(SimpleVal);
1242 Res.Offset = Offset;
1246 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1247 unsigned Offset = 0) {
1248 AvailableValueInBlock Res;
1250 Res.Val.setPointer(MI);
1251 Res.Val.setInt(MemIntrin);
1252 Res.Offset = Offset;
1256 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1257 Value *getSimpleValue() const {
1258 assert(isSimpleValue() && "Wrong accessor");
1259 return Val.getPointer();
1262 MemIntrinsic *getMemIntrinValue() const {
1263 assert(!isSimpleValue() && "Wrong accessor");
1264 return cast<MemIntrinsic>(Val.getPointer());
1267 /// MaterializeAdjustedValue - Emit code into this block to adjust the value
1268 /// defined here to the specified type. This handles various coercion cases.
1269 Value *MaterializeAdjustedValue(const Type *LoadTy,
1270 const TargetData *TD) const {
1272 if (isSimpleValue()) {
1273 Res = getSimpleValue();
1274 if (Res->getType() != LoadTy) {
1275 assert(TD && "Need target data to handle type mismatch case");
1276 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(),
1279 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1280 << *getSimpleValue() << '\n'
1281 << *Res << '\n' << "\n\n\n");
1284 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset,
1285 LoadTy, BB->getTerminator(), *TD);
1286 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1287 << " " << *getMemIntrinValue() << '\n'
1288 << *Res << '\n' << "\n\n\n");
1296 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1297 /// construct SSA form, allowing us to eliminate LI. This returns the value
1298 /// that should be used at LI's definition site.
1299 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1300 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1301 const TargetData *TD,
1302 const DominatorTree &DT,
1303 AliasAnalysis *AA) {
1304 // Check for the fully redundant, dominating load case. In this case, we can
1305 // just use the dominating value directly.
1306 if (ValuesPerBlock.size() == 1 &&
1307 DT.properlyDominates(ValuesPerBlock[0].BB, LI->getParent()))
1308 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), TD);
1310 // Otherwise, we have to construct SSA form.
1311 SmallVector<PHINode*, 8> NewPHIs;
1312 SSAUpdater SSAUpdate(&NewPHIs);
1313 SSAUpdate.Initialize(LI);
1315 const Type *LoadTy = LI->getType();
1317 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1318 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1319 BasicBlock *BB = AV.BB;
1321 if (SSAUpdate.HasValueForBlock(BB))
1324 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, TD));
1327 // Perform PHI construction.
1328 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1330 // If new PHI nodes were created, notify alias analysis.
1331 if (V->getType()->isPointerTy())
1332 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1333 AA->copyValue(LI, NewPHIs[i]);
1338 static bool isLifetimeStart(const Instruction *Inst) {
1339 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1340 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1344 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1345 /// non-local by performing PHI construction.
1346 bool GVN::processNonLocalLoad(LoadInst *LI,
1347 SmallVectorImpl<Instruction*> &toErase) {
1348 // Find the non-local dependencies of the load.
1349 SmallVector<NonLocalDepResult, 64> Deps;
1350 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
1352 //DEBUG(dbgs() << "INVESTIGATING NONLOCAL LOAD: "
1353 // << Deps.size() << *LI << '\n');
1355 // If we had to process more than one hundred blocks to find the
1356 // dependencies, this load isn't worth worrying about. Optimizing
1357 // it will be too expensive.
1358 if (Deps.size() > 100)
1361 // If we had a phi translation failure, we'll have a single entry which is a
1362 // clobber in the current block. Reject this early.
1363 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) {
1365 dbgs() << "GVN: non-local load ";
1366 WriteAsOperand(dbgs(), LI);
1367 dbgs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n';
1372 // Filter out useless results (non-locals, etc). Keep track of the blocks
1373 // where we have a value available in repl, also keep track of whether we see
1374 // dependencies that produce an unknown value for the load (such as a call
1375 // that could potentially clobber the load).
1376 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1377 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1379 const TargetData *TD = 0;
1381 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1382 BasicBlock *DepBB = Deps[i].getBB();
1383 MemDepResult DepInfo = Deps[i].getResult();
1385 if (DepInfo.isClobber()) {
1386 // The address being loaded in this non-local block may not be the same as
1387 // the pointer operand of the load if PHI translation occurs. Make sure
1388 // to consider the right address.
1389 Value *Address = Deps[i].getAddress();
1391 // If the dependence is to a store that writes to a superset of the bits
1392 // read by the load, we can extract the bits we need for the load from the
1394 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1396 TD = getAnalysisIfAvailable<TargetData>();
1397 if (TD && Address) {
1398 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1401 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1402 DepSI->getOperand(0),
1409 // If the clobbering value is a memset/memcpy/memmove, see if we can
1410 // forward a value on from it.
1411 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1413 TD = getAnalysisIfAvailable<TargetData>();
1414 if (TD && Address) {
1415 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1418 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1425 UnavailableBlocks.push_back(DepBB);
1429 Instruction *DepInst = DepInfo.getInst();
1431 // Loading the allocation -> undef.
1432 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1433 // Loading immediately after lifetime begin -> undef.
1434 isLifetimeStart(DepInst)) {
1435 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1436 UndefValue::get(LI->getType())));
1440 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1441 // Reject loads and stores that are to the same address but are of
1442 // different types if we have to.
1443 if (S->getOperand(0)->getType() != LI->getType()) {
1445 TD = getAnalysisIfAvailable<TargetData>();
1447 // If the stored value is larger or equal to the loaded value, we can
1449 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0),
1450 LI->getType(), *TD)) {
1451 UnavailableBlocks.push_back(DepBB);
1456 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1461 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1462 // If the types mismatch and we can't handle it, reject reuse of the load.
1463 if (LD->getType() != LI->getType()) {
1465 TD = getAnalysisIfAvailable<TargetData>();
1467 // If the stored value is larger or equal to the loaded value, we can
1469 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1470 UnavailableBlocks.push_back(DepBB);
1474 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD));
1478 UnavailableBlocks.push_back(DepBB);
1482 // If we have no predecessors that produce a known value for this load, exit
1484 if (ValuesPerBlock.empty()) return false;
1486 // If all of the instructions we depend on produce a known value for this
1487 // load, then it is fully redundant and we can use PHI insertion to compute
1488 // its value. Insert PHIs and remove the fully redundant value now.
1489 if (UnavailableBlocks.empty()) {
1490 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1492 // Perform PHI construction.
1493 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1494 VN.getAliasAnalysis());
1495 LI->replaceAllUsesWith(V);
1497 if (isa<PHINode>(V))
1499 if (V->getType()->isPointerTy())
1500 MD->invalidateCachedPointerInfo(V);
1502 toErase.push_back(LI);
1507 if (!EnablePRE || !EnableLoadPRE)
1510 // Okay, we have *some* definitions of the value. This means that the value
1511 // is available in some of our (transitive) predecessors. Lets think about
1512 // doing PRE of this load. This will involve inserting a new load into the
1513 // predecessor when it's not available. We could do this in general, but
1514 // prefer to not increase code size. As such, we only do this when we know
1515 // that we only have to insert *one* load (which means we're basically moving
1516 // the load, not inserting a new one).
1518 SmallPtrSet<BasicBlock *, 4> Blockers;
1519 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1520 Blockers.insert(UnavailableBlocks[i]);
1522 // Lets find first basic block with more than one predecessor. Walk backwards
1523 // through predecessors if needed.
1524 BasicBlock *LoadBB = LI->getParent();
1525 BasicBlock *TmpBB = LoadBB;
1527 bool isSinglePred = false;
1528 bool allSingleSucc = true;
1529 while (TmpBB->getSinglePredecessor()) {
1530 isSinglePred = true;
1531 TmpBB = TmpBB->getSinglePredecessor();
1532 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1534 if (Blockers.count(TmpBB))
1536 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1537 allSingleSucc = false;
1543 // If we have a repl set with LI itself in it, this means we have a loop where
1544 // at least one of the values is LI. Since this means that we won't be able
1545 // to eliminate LI even if we insert uses in the other predecessors, we will
1546 // end up increasing code size. Reject this by scanning for LI.
1547 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1548 if (ValuesPerBlock[i].isSimpleValue() &&
1549 ValuesPerBlock[i].getSimpleValue() == LI) {
1550 // Skip cases where LI is the only definition, even for EnableFullLoadPRE.
1551 if (!EnableFullLoadPRE || e == 1)
1556 // FIXME: It is extremely unclear what this loop is doing, other than
1557 // artificially restricting loadpre.
1560 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1561 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1562 if (AV.isSimpleValue())
1563 // "Hot" Instruction is in some loop (because it dominates its dep.
1565 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1566 if (DT->dominates(LI, I)) {
1572 // We are interested only in "hot" instructions. We don't want to do any
1573 // mis-optimizations here.
1578 // Check to see how many predecessors have the loaded value fully
1580 DenseMap<BasicBlock*, Value*> PredLoads;
1581 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1582 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1583 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1584 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1585 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1587 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> NeedToSplit;
1588 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1590 BasicBlock *Pred = *PI;
1591 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks)) {
1594 PredLoads[Pred] = 0;
1596 if (Pred->getTerminator()->getNumSuccessors() != 1) {
1597 if (isa<IndirectBrInst>(Pred->getTerminator())) {
1598 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '"
1599 << Pred->getName() << "': " << *LI << '\n');
1602 unsigned SuccNum = GetSuccessorNumber(Pred, LoadBB);
1603 NeedToSplit.push_back(std::make_pair(Pred->getTerminator(), SuccNum));
1606 if (!NeedToSplit.empty()) {
1607 toSplit.append(NeedToSplit.begin(), NeedToSplit.end());
1611 // Decide whether PRE is profitable for this load.
1612 unsigned NumUnavailablePreds = PredLoads.size();
1613 assert(NumUnavailablePreds != 0 &&
1614 "Fully available value should be eliminated above!");
1615 if (!EnableFullLoadPRE) {
1616 // If this load is unavailable in multiple predecessors, reject it.
1617 // FIXME: If we could restructure the CFG, we could make a common pred with
1618 // all the preds that don't have an available LI and insert a new load into
1620 if (NumUnavailablePreds != 1)
1624 // Check if the load can safely be moved to all the unavailable predecessors.
1625 bool CanDoPRE = true;
1626 SmallVector<Instruction*, 8> NewInsts;
1627 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1628 E = PredLoads.end(); I != E; ++I) {
1629 BasicBlock *UnavailablePred = I->first;
1631 // Do PHI translation to get its value in the predecessor if necessary. The
1632 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1634 // If all preds have a single successor, then we know it is safe to insert
1635 // the load on the pred (?!?), so we can insert code to materialize the
1636 // pointer if it is not available.
1637 PHITransAddr Address(LI->getOperand(0), TD);
1639 if (allSingleSucc) {
1640 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1643 Address.PHITranslateValue(LoadBB, UnavailablePred, DT);
1644 LoadPtr = Address.getAddr();
1647 // If we couldn't find or insert a computation of this phi translated value,
1650 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1651 << *LI->getOperand(0) << "\n");
1656 // Make sure it is valid to move this load here. We have to watch out for:
1657 // @1 = getelementptr (i8* p, ...
1658 // test p and branch if == 0
1660 // It is valid to have the getelementptr before the test, even if p can be 0,
1661 // as getelementptr only does address arithmetic.
1662 // If we are not pushing the value through any multiple-successor blocks
1663 // we do not have this case. Otherwise, check that the load is safe to
1664 // put anywhere; this can be improved, but should be conservatively safe.
1665 if (!allSingleSucc &&
1666 // FIXME: REEVALUTE THIS.
1667 !isSafeToLoadUnconditionally(LoadPtr,
1668 UnavailablePred->getTerminator(),
1669 LI->getAlignment(), TD)) {
1674 I->second = LoadPtr;
1678 while (!NewInsts.empty())
1679 NewInsts.pop_back_val()->eraseFromParent();
1683 // Okay, we can eliminate this load by inserting a reload in the predecessor
1684 // and using PHI construction to get the value in the other predecessors, do
1686 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1687 DEBUG(if (!NewInsts.empty())
1688 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: "
1689 << *NewInsts.back() << '\n');
1691 // Assign value numbers to the new instructions.
1692 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1693 // FIXME: We really _ought_ to insert these value numbers into their
1694 // parent's availability map. However, in doing so, we risk getting into
1695 // ordering issues. If a block hasn't been processed yet, we would be
1696 // marking a value as AVAIL-IN, which isn't what we intend.
1697 VN.lookup_or_add(NewInsts[i]);
1700 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(),
1701 E = PredLoads.end(); I != E; ++I) {
1702 BasicBlock *UnavailablePred = I->first;
1703 Value *LoadPtr = I->second;
1705 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1707 UnavailablePred->getTerminator());
1709 // Add the newly created load.
1710 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,
1712 MD->invalidateCachedPointerInfo(LoadPtr);
1713 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n');
1716 // Perform PHI construction.
1717 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD, *DT,
1718 VN.getAliasAnalysis());
1719 LI->replaceAllUsesWith(V);
1720 if (isa<PHINode>(V))
1722 if (V->getType()->isPointerTy())
1723 MD->invalidateCachedPointerInfo(V);
1725 toErase.push_back(LI);
1730 /// processLoad - Attempt to eliminate a load, first by eliminating it
1731 /// locally, and then attempting non-local elimination if that fails.
1732 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1736 if (L->isVolatile())
1739 // ... to a pointer that has been loaded from before...
1740 MemDepResult Dep = MD->getDependency(L);
1742 // If the value isn't available, don't do anything!
1743 if (Dep.isClobber()) {
1744 // Check to see if we have something like this:
1745 // store i32 123, i32* %P
1746 // %A = bitcast i32* %P to i8*
1747 // %B = gep i8* %A, i32 1
1750 // We could do that by recognizing if the clobber instructions are obviously
1751 // a common base + constant offset, and if the previous store (or memset)
1752 // completely covers this load. This sort of thing can happen in bitfield
1754 Value *AvailVal = 0;
1755 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1756 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1757 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1758 L->getPointerOperand(),
1761 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset,
1762 L->getType(), L, *TD);
1765 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1766 // a value on from it.
1767 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1768 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1769 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1770 L->getPointerOperand(),
1773 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1778 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1779 << *AvailVal << '\n' << *L << "\n\n\n");
1781 // Replace the load!
1782 L->replaceAllUsesWith(AvailVal);
1783 if (AvailVal->getType()->isPointerTy())
1784 MD->invalidateCachedPointerInfo(AvailVal);
1786 toErase.push_back(L);
1792 // fast print dep, using operator<< on instruction would be too slow
1793 dbgs() << "GVN: load ";
1794 WriteAsOperand(dbgs(), L);
1795 Instruction *I = Dep.getInst();
1796 dbgs() << " is clobbered by " << *I << '\n';
1801 // If it is defined in another block, try harder.
1802 if (Dep.isNonLocal())
1803 return processNonLocalLoad(L, toErase);
1805 Instruction *DepInst = Dep.getInst();
1806 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1807 Value *StoredVal = DepSI->getOperand(0);
1809 // The store and load are to a must-aliased pointer, but they may not
1810 // actually have the same type. See if we know how to reuse the stored
1811 // value (depending on its type).
1812 const TargetData *TD = 0;
1813 if (StoredVal->getType() != L->getType()) {
1814 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1815 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1820 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1821 << '\n' << *L << "\n\n\n");
1828 L->replaceAllUsesWith(StoredVal);
1829 if (StoredVal->getType()->isPointerTy())
1830 MD->invalidateCachedPointerInfo(StoredVal);
1832 toErase.push_back(L);
1837 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1838 Value *AvailableVal = DepLI;
1840 // The loads are of a must-aliased pointer, but they may not actually have
1841 // the same type. See if we know how to reuse the previously loaded value
1842 // (depending on its type).
1843 const TargetData *TD = 0;
1844 if (DepLI->getType() != L->getType()) {
1845 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1846 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1847 if (AvailableVal == 0)
1850 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1851 << "\n" << *L << "\n\n\n");
1858 L->replaceAllUsesWith(AvailableVal);
1859 if (DepLI->getType()->isPointerTy())
1860 MD->invalidateCachedPointerInfo(DepLI);
1862 toErase.push_back(L);
1867 // If this load really doesn't depend on anything, then we must be loading an
1868 // undef value. This can happen when loading for a fresh allocation with no
1869 // intervening stores, for example.
1870 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1871 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1873 toErase.push_back(L);
1878 // If this load occurs either right after a lifetime begin,
1879 // then the loaded value is undefined.
1880 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1881 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1882 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1884 toErase.push_back(L);
1893 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1894 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1895 if (I == localAvail.end())
1898 ValueNumberScope *Locals = I->second;
1900 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num);
1901 if (I != Locals->table.end())
1903 Locals = Locals->parent;
1910 /// processInstruction - When calculating availability, handle an instruction
1911 /// by inserting it into the appropriate sets
1912 bool GVN::processInstruction(Instruction *I,
1913 SmallVectorImpl<Instruction*> &toErase) {
1914 // Ignore dbg info intrinsics.
1915 if (isa<DbgInfoIntrinsic>(I))
1918 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1919 bool Changed = processLoad(LI, toErase);
1922 unsigned Num = VN.lookup_or_add(LI);
1923 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI));
1929 uint32_t NextNum = VN.getNextUnusedValueNumber();
1930 unsigned Num = VN.lookup_or_add(I);
1932 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1933 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1935 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1938 Value *BranchCond = BI->getCondition();
1939 uint32_t CondVN = VN.lookup_or_add(BranchCond);
1941 BasicBlock *TrueSucc = BI->getSuccessor(0);
1942 BasicBlock *FalseSucc = BI->getSuccessor(1);
1944 if (TrueSucc->getSinglePredecessor())
1945 localAvail[TrueSucc]->table[CondVN] =
1946 ConstantInt::getTrue(TrueSucc->getContext());
1947 if (FalseSucc->getSinglePredecessor())
1948 localAvail[FalseSucc]->table[CondVN] =
1949 ConstantInt::getFalse(TrueSucc->getContext());
1953 // Allocations are always uniquely numbered, so we can save time and memory
1954 // by fast failing them.
1955 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1956 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1960 // Collapse PHI nodes
1961 if (PHINode* p = dyn_cast<PHINode>(I)) {
1962 Value *constVal = CollapsePhi(p);
1965 p->replaceAllUsesWith(constVal);
1966 if (MD && constVal->getType()->isPointerTy())
1967 MD->invalidateCachedPointerInfo(constVal);
1970 toErase.push_back(p);
1972 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1975 // If the number we were assigned was a brand new VN, then we don't
1976 // need to do a lookup to see if the number already exists
1977 // somewhere in the domtree: it can't!
1978 } else if (Num == NextNum) {
1979 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1981 // Perform fast-path value-number based elimination of values inherited from
1983 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1986 I->replaceAllUsesWith(repl);
1987 if (MD && repl->getType()->isPointerTy())
1988 MD->invalidateCachedPointerInfo(repl);
1989 toErase.push_back(I);
1993 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1999 /// runOnFunction - This is the main transformation entry point for a function.
2000 bool GVN::runOnFunction(Function& F) {
2002 MD = &getAnalysis<MemoryDependenceAnalysis>();
2003 DT = &getAnalysis<DominatorTree>();
2004 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
2008 bool Changed = false;
2009 bool ShouldContinue = true;
2011 // Merge unconditional branches, allowing PRE to catch more
2012 // optimization opportunities.
2013 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
2014 BasicBlock *BB = FI;
2016 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
2017 if (removedBlock) ++NumGVNBlocks;
2019 Changed |= removedBlock;
2022 unsigned Iteration = 0;
2024 while (ShouldContinue) {
2025 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n");
2026 ShouldContinue = iterateOnFunction(F);
2027 if (splitCriticalEdges())
2028 ShouldContinue = true;
2029 Changed |= ShouldContinue;
2034 bool PREChanged = true;
2035 while (PREChanged) {
2036 PREChanged = performPRE(F);
2037 Changed |= PREChanged;
2040 // FIXME: Should perform GVN again after PRE does something. PRE can move
2041 // computations into blocks where they become fully redundant. Note that
2042 // we can't do this until PRE's critical edge splitting updates memdep.
2043 // Actually, when this happens, we should just fully integrate PRE into GVN.
2045 cleanupGlobalSets();
2051 bool GVN::processBlock(BasicBlock *BB) {
2052 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
2053 // incrementing BI before processing an instruction).
2054 SmallVector<Instruction*, 8> toErase;
2055 bool ChangedFunction = false;
2057 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2059 ChangedFunction |= processInstruction(BI, toErase);
2060 if (toErase.empty()) {
2065 // If we need some instructions deleted, do it now.
2066 NumGVNInstr += toErase.size();
2068 // Avoid iterator invalidation.
2069 bool AtStart = BI == BB->begin();
2073 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2074 E = toErase.end(); I != E; ++I) {
2075 DEBUG(dbgs() << "GVN removed: " << **I << '\n');
2076 if (MD) MD->removeInstruction(*I);
2077 (*I)->eraseFromParent();
2078 DEBUG(verifyRemoved(*I));
2088 return ChangedFunction;
2091 /// performPRE - Perform a purely local form of PRE that looks for diamond
2092 /// control flow patterns and attempts to perform simple PRE at the join point.
2093 bool GVN::performPRE(Function &F) {
2094 bool Changed = false;
2095 DenseMap<BasicBlock*, Value*> predMap;
2096 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2097 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2098 BasicBlock *CurrentBlock = *DI;
2100 // Nothing to PRE in the entry block.
2101 if (CurrentBlock == &F.getEntryBlock()) continue;
2103 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2104 BE = CurrentBlock->end(); BI != BE; ) {
2105 Instruction *CurInst = BI++;
2107 if (isa<AllocaInst>(CurInst) ||
2108 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2109 CurInst->getType()->isVoidTy() ||
2110 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2111 isa<DbgInfoIntrinsic>(CurInst))
2114 // We don't currently value number ANY inline asm calls.
2115 if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
2116 if (CallI->isInlineAsm())
2119 uint32_t ValNo = VN.lookup(CurInst);
2121 // Look for the predecessors for PRE opportunities. We're
2122 // only trying to solve the basic diamond case, where
2123 // a value is computed in the successor and one predecessor,
2124 // but not the other. We also explicitly disallow cases
2125 // where the successor is its own predecessor, because they're
2126 // more complicated to get right.
2127 unsigned NumWith = 0;
2128 unsigned NumWithout = 0;
2129 BasicBlock *PREPred = 0;
2132 for (pred_iterator PI = pred_begin(CurrentBlock),
2133 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2134 BasicBlock *P = *PI;
2135 // We're not interested in PRE where the block is its
2136 // own predecessor, or in blocks with predecessors
2137 // that are not reachable.
2138 if (P == CurrentBlock) {
2141 } else if (!localAvail.count(P)) {
2146 DenseMap<uint32_t, Value*>::iterator predV =
2147 localAvail[P]->table.find(ValNo);
2148 if (predV == localAvail[P]->table.end()) {
2151 } else if (predV->second == CurInst) {
2154 predMap[P] = predV->second;
2159 // Don't do PRE when it might increase code size, i.e. when
2160 // we would need to insert instructions in more than one pred.
2161 if (NumWithout != 1 || NumWith == 0)
2164 // Don't do PRE across indirect branch.
2165 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2168 // We can't do PRE safely on a critical edge, so instead we schedule
2169 // the edge to be split and perform the PRE the next time we iterate
2171 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
2172 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2173 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2177 // Instantiate the expression in the predecessor that lacked it.
2178 // Because we are going top-down through the block, all value numbers
2179 // will be available in the predecessor by the time we need them. Any
2180 // that weren't originally present will have been instantiated earlier
2182 Instruction *PREInstr = CurInst->clone();
2183 bool success = true;
2184 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2185 Value *Op = PREInstr->getOperand(i);
2186 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2189 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
2190 PREInstr->setOperand(i, V);
2197 // Fail out if we encounter an operand that is not available in
2198 // the PRE predecessor. This is typically because of loads which
2199 // are not value numbered precisely.
2202 DEBUG(verifyRemoved(PREInstr));
2206 PREInstr->insertBefore(PREPred->getTerminator());
2207 PREInstr->setName(CurInst->getName() + ".pre");
2208 predMap[PREPred] = PREInstr;
2209 VN.add(PREInstr, ValNo);
2212 // Update the availability map to include the new instruction.
2213 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr));
2215 // Create a PHI to make the value available in this block.
2216 PHINode* Phi = PHINode::Create(CurInst->getType(),
2217 CurInst->getName() + ".pre-phi",
2218 CurrentBlock->begin());
2219 for (pred_iterator PI = pred_begin(CurrentBlock),
2220 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2221 BasicBlock *P = *PI;
2222 Phi->addIncoming(predMap[P], P);
2226 localAvail[CurrentBlock]->table[ValNo] = Phi;
2228 CurInst->replaceAllUsesWith(Phi);
2229 if (MD && Phi->getType()->isPointerTy())
2230 MD->invalidateCachedPointerInfo(Phi);
2233 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
2234 if (MD) MD->removeInstruction(CurInst);
2235 CurInst->eraseFromParent();
2236 DEBUG(verifyRemoved(CurInst));
2241 if (splitCriticalEdges())
2247 /// splitCriticalEdges - Split critical edges found during the previous
2248 /// iteration that may enable further optimization.
2249 bool GVN::splitCriticalEdges() {
2250 if (toSplit.empty())
2253 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val();
2254 SplitCriticalEdge(Edge.first, Edge.second, this);
2255 } while (!toSplit.empty());
2256 if (MD) MD->invalidateCachedPredecessors();
2260 /// iterateOnFunction - Executes one iteration of GVN
2261 bool GVN::iterateOnFunction(Function &F) {
2262 cleanupGlobalSets();
2264 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2265 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
2267 localAvail[DI->getBlock()] =
2268 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
2270 localAvail[DI->getBlock()] = new ValueNumberScope(0);
2273 // Top-down walk of the dominator tree
2274 bool Changed = false;
2276 // Needed for value numbering with phi construction to work.
2277 ReversePostOrderTraversal<Function*> RPOT(&F);
2278 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2279 RE = RPOT.end(); RI != RE; ++RI)
2280 Changed |= processBlock(*RI);
2282 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2283 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2284 Changed |= processBlock(DI->getBlock());
2290 void GVN::cleanupGlobalSets() {
2293 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
2294 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
2299 /// verifyRemoved - Verify that the specified instruction does not occur in our
2300 /// internal data structures.
2301 void GVN::verifyRemoved(const Instruction *Inst) const {
2302 VN.verifyRemoved(Inst);
2304 // Walk through the value number scope to make sure the instruction isn't
2305 // ferreted away in it.
2306 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
2307 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
2308 const ValueNumberScope *VNS = I->second;
2311 for (DenseMap<uint32_t, Value*>::const_iterator
2312 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
2313 assert(II->second != Inst && "Inst still in value numbering scope!");