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/Function.h"
24 #include "llvm/IntrinsicInst.h"
25 #include "llvm/LLVMContext.h"
26 #include "llvm/Operator.h"
27 #include "llvm/Value.h"
28 #include "llvm/ADT/DenseMap.h"
29 #include "llvm/ADT/DepthFirstIterator.h"
30 #include "llvm/ADT/PostOrderIterator.h"
31 #include "llvm/ADT/SmallPtrSet.h"
32 #include "llvm/ADT/SmallVector.h"
33 #include "llvm/ADT/Statistic.h"
34 #include "llvm/Analysis/AliasAnalysis.h"
35 #include "llvm/Analysis/ConstantFolding.h"
36 #include "llvm/Analysis/Dominators.h"
37 #include "llvm/Analysis/MemoryBuiltins.h"
38 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
39 #include "llvm/Analysis/PHITransAddr.h"
40 #include "llvm/Support/CFG.h"
41 #include "llvm/Support/CommandLine.h"
42 #include "llvm/Support/Debug.h"
43 #include "llvm/Support/ErrorHandling.h"
44 #include "llvm/Support/GetElementPtrTypeIterator.h"
45 #include "llvm/Support/IRBuilder.h"
46 #include "llvm/Support/raw_ostream.h"
47 #include "llvm/Target/TargetData.h"
48 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
49 #include "llvm/Transforms/Utils/Local.h"
50 #include "llvm/Transforms/Utils/SSAUpdater.h"
54 STATISTIC(NumGVNInstr, "Number of instructions deleted");
55 STATISTIC(NumGVNLoad, "Number of loads deleted");
56 STATISTIC(NumGVNPRE, "Number of instructions PRE'd");
57 STATISTIC(NumGVNBlocks, "Number of blocks merged");
58 STATISTIC(NumPRELoad, "Number of loads PRE'd");
60 static cl::opt<bool> EnablePRE("enable-pre",
61 cl::init(true), cl::Hidden);
62 static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true));
64 //===----------------------------------------------------------------------===//
66 //===----------------------------------------------------------------------===//
68 /// This class holds the mapping between values and value numbers. It is used
69 /// as an efficient mechanism to determine the expression-wise equivalence of
73 enum ExpressionOpcode { ADD, FADD, SUB, FSUB, MUL, FMUL,
74 UDIV, SDIV, FDIV, UREM, SREM,
75 FREM, SHL, LSHR, ASHR, AND, OR, XOR, ICMPEQ,
76 ICMPNE, ICMPUGT, ICMPUGE, ICMPULT, ICMPULE,
77 ICMPSGT, ICMPSGE, ICMPSLT, ICMPSLE, FCMPOEQ,
78 FCMPOGT, FCMPOGE, FCMPOLT, FCMPOLE, FCMPONE,
79 FCMPORD, FCMPUNO, FCMPUEQ, FCMPUGT, FCMPUGE,
80 FCMPULT, FCMPULE, FCMPUNE, EXTRACT, INSERT,
81 SHUFFLE, SELECT, TRUNC, ZEXT, SEXT, FPTOUI,
82 FPTOSI, UITOFP, SITOFP, FPTRUNC, FPEXT,
83 PTRTOINT, INTTOPTR, BITCAST, GEP, CALL, CONSTANT,
84 INSERTVALUE, EXTRACTVALUE, EMPTY, TOMBSTONE };
86 ExpressionOpcode opcode;
88 SmallVector<uint32_t, 4> varargs;
92 Expression(ExpressionOpcode o) : opcode(o) { }
94 bool operator==(const Expression &other) const {
95 if (opcode != other.opcode)
97 else if (opcode == EMPTY || opcode == TOMBSTONE)
99 else if (type != other.type)
101 else if (function != other.function)
104 if (varargs.size() != other.varargs.size())
107 for (size_t i = 0; i < varargs.size(); ++i)
108 if (varargs[i] != other.varargs[i])
115 bool operator!=(const Expression &other) const {
116 return !(*this == other);
122 DenseMap<Value*, uint32_t> valueNumbering;
123 DenseMap<Expression, uint32_t> expressionNumbering;
125 MemoryDependenceAnalysis* MD;
128 uint32_t nextValueNumber;
130 Expression::ExpressionOpcode getOpcode(BinaryOperator* BO);
131 Expression::ExpressionOpcode getOpcode(CmpInst* C);
132 Expression::ExpressionOpcode getOpcode(CastInst* C);
133 Expression create_expression(BinaryOperator* BO);
134 Expression create_expression(CmpInst* C);
135 Expression create_expression(ShuffleVectorInst* V);
136 Expression create_expression(ExtractElementInst* C);
137 Expression create_expression(InsertElementInst* V);
138 Expression create_expression(SelectInst* V);
139 Expression create_expression(CastInst* C);
140 Expression create_expression(GetElementPtrInst* G);
141 Expression create_expression(CallInst* C);
142 Expression create_expression(Constant* C);
143 Expression create_expression(ExtractValueInst* C);
144 Expression create_expression(InsertValueInst* C);
146 uint32_t lookup_or_add_call(CallInst* C);
148 ValueTable() : nextValueNumber(1) { }
149 uint32_t lookup_or_add(Value *V);
150 uint32_t lookup(Value *V) const;
151 void add(Value *V, uint32_t num);
153 void erase(Value *v);
155 void setAliasAnalysis(AliasAnalysis* A) { AA = A; }
156 AliasAnalysis *getAliasAnalysis() const { return AA; }
157 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; }
158 void setDomTree(DominatorTree* D) { DT = D; }
159 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
160 void verifyRemoved(const Value *) const;
165 template <> struct DenseMapInfo<Expression> {
166 static inline Expression getEmptyKey() {
167 return Expression(Expression::EMPTY);
170 static inline Expression getTombstoneKey() {
171 return Expression(Expression::TOMBSTONE);
174 static unsigned getHashValue(const Expression e) {
175 unsigned hash = e.opcode;
177 hash = ((unsigned)((uintptr_t)e.type >> 4) ^
178 (unsigned)((uintptr_t)e.type >> 9));
180 for (SmallVector<uint32_t, 4>::const_iterator I = e.varargs.begin(),
181 E = e.varargs.end(); I != E; ++I)
182 hash = *I + hash * 37;
184 hash = ((unsigned)((uintptr_t)e.function >> 4) ^
185 (unsigned)((uintptr_t)e.function >> 9)) +
190 static bool isEqual(const Expression &LHS, const Expression &RHS) {
196 struct isPodLike<Expression> { static const bool value = true; };
200 //===----------------------------------------------------------------------===//
201 // ValueTable Internal Functions
202 //===----------------------------------------------------------------------===//
203 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
204 switch(BO->getOpcode()) {
205 default: // THIS SHOULD NEVER HAPPEN
206 llvm_unreachable("Binary operator with unknown opcode?");
207 case Instruction::Add: return Expression::ADD;
208 case Instruction::FAdd: return Expression::FADD;
209 case Instruction::Sub: return Expression::SUB;
210 case Instruction::FSub: return Expression::FSUB;
211 case Instruction::Mul: return Expression::MUL;
212 case Instruction::FMul: return Expression::FMUL;
213 case Instruction::UDiv: return Expression::UDIV;
214 case Instruction::SDiv: return Expression::SDIV;
215 case Instruction::FDiv: return Expression::FDIV;
216 case Instruction::URem: return Expression::UREM;
217 case Instruction::SRem: return Expression::SREM;
218 case Instruction::FRem: return Expression::FREM;
219 case Instruction::Shl: return Expression::SHL;
220 case Instruction::LShr: return Expression::LSHR;
221 case Instruction::AShr: return Expression::ASHR;
222 case Instruction::And: return Expression::AND;
223 case Instruction::Or: return Expression::OR;
224 case Instruction::Xor: return Expression::XOR;
228 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
229 if (isa<ICmpInst>(C)) {
230 switch (C->getPredicate()) {
231 default: // THIS SHOULD NEVER HAPPEN
232 llvm_unreachable("Comparison with unknown predicate?");
233 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
234 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
235 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
236 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
237 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
238 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
239 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
240 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
241 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
242 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
245 switch (C->getPredicate()) {
246 default: // THIS SHOULD NEVER HAPPEN
247 llvm_unreachable("Comparison with unknown predicate?");
248 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
249 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
250 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
251 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
252 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
253 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
254 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
255 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
256 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
257 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
258 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
259 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
260 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
261 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
266 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
267 switch(C->getOpcode()) {
268 default: // THIS SHOULD NEVER HAPPEN
269 llvm_unreachable("Cast operator with unknown opcode?");
270 case Instruction::Trunc: return Expression::TRUNC;
271 case Instruction::ZExt: return Expression::ZEXT;
272 case Instruction::SExt: return Expression::SEXT;
273 case Instruction::FPToUI: return Expression::FPTOUI;
274 case Instruction::FPToSI: return Expression::FPTOSI;
275 case Instruction::UIToFP: return Expression::UITOFP;
276 case Instruction::SIToFP: return Expression::SITOFP;
277 case Instruction::FPTrunc: return Expression::FPTRUNC;
278 case Instruction::FPExt: return Expression::FPEXT;
279 case Instruction::PtrToInt: return Expression::PTRTOINT;
280 case Instruction::IntToPtr: return Expression::INTTOPTR;
281 case Instruction::BitCast: return Expression::BITCAST;
285 Expression ValueTable::create_expression(CallInst* C) {
288 e.type = C->getType();
289 e.function = C->getCalledFunction();
290 e.opcode = Expression::CALL;
292 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
294 e.varargs.push_back(lookup_or_add(*I));
299 Expression ValueTable::create_expression(BinaryOperator* BO) {
301 e.varargs.push_back(lookup_or_add(BO->getOperand(0)));
302 e.varargs.push_back(lookup_or_add(BO->getOperand(1)));
304 e.type = BO->getType();
305 e.opcode = getOpcode(BO);
310 Expression ValueTable::create_expression(CmpInst* C) {
313 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
314 e.varargs.push_back(lookup_or_add(C->getOperand(1)));
316 e.type = C->getType();
317 e.opcode = getOpcode(C);
322 Expression ValueTable::create_expression(CastInst* C) {
325 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
327 e.type = C->getType();
328 e.opcode = getOpcode(C);
333 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
336 e.varargs.push_back(lookup_or_add(S->getOperand(0)));
337 e.varargs.push_back(lookup_or_add(S->getOperand(1)));
338 e.varargs.push_back(lookup_or_add(S->getOperand(2)));
340 e.type = S->getType();
341 e.opcode = Expression::SHUFFLE;
346 Expression ValueTable::create_expression(ExtractElementInst* E) {
349 e.varargs.push_back(lookup_or_add(E->getOperand(0)));
350 e.varargs.push_back(lookup_or_add(E->getOperand(1)));
352 e.type = E->getType();
353 e.opcode = Expression::EXTRACT;
358 Expression ValueTable::create_expression(InsertElementInst* I) {
361 e.varargs.push_back(lookup_or_add(I->getOperand(0)));
362 e.varargs.push_back(lookup_or_add(I->getOperand(1)));
363 e.varargs.push_back(lookup_or_add(I->getOperand(2)));
365 e.type = I->getType();
366 e.opcode = Expression::INSERT;
371 Expression ValueTable::create_expression(SelectInst* I) {
374 e.varargs.push_back(lookup_or_add(I->getCondition()));
375 e.varargs.push_back(lookup_or_add(I->getTrueValue()));
376 e.varargs.push_back(lookup_or_add(I->getFalseValue()));
378 e.type = I->getType();
379 e.opcode = Expression::SELECT;
384 Expression ValueTable::create_expression(GetElementPtrInst* G) {
387 e.varargs.push_back(lookup_or_add(G->getPointerOperand()));
389 e.type = G->getType();
390 e.opcode = Expression::GEP;
392 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
394 e.varargs.push_back(lookup_or_add(*I));
399 Expression ValueTable::create_expression(ExtractValueInst* E) {
402 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
403 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
405 e.varargs.push_back(*II);
407 e.type = E->getType();
408 e.opcode = Expression::EXTRACTVALUE;
413 Expression ValueTable::create_expression(InsertValueInst* E) {
416 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
417 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand()));
418 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
420 e.varargs.push_back(*II);
422 e.type = E->getType();
423 e.opcode = Expression::INSERTVALUE;
428 //===----------------------------------------------------------------------===//
429 // ValueTable External Functions
430 //===----------------------------------------------------------------------===//
432 /// add - Insert a value into the table with a specified value number.
433 void ValueTable::add(Value *V, uint32_t num) {
434 valueNumbering.insert(std::make_pair(V, num));
437 uint32_t ValueTable::lookup_or_add_call(CallInst* C) {
438 if (AA->doesNotAccessMemory(C)) {
439 Expression exp = create_expression(C);
440 uint32_t& e = expressionNumbering[exp];
441 if (!e) e = nextValueNumber++;
442 valueNumbering[C] = e;
444 } else if (AA->onlyReadsMemory(C)) {
445 Expression exp = create_expression(C);
446 uint32_t& e = expressionNumbering[exp];
448 e = nextValueNumber++;
449 valueNumbering[C] = e;
453 e = nextValueNumber++;
454 valueNumbering[C] = e;
458 MemDepResult local_dep = MD->getDependency(C);
460 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
461 valueNumbering[C] = nextValueNumber;
462 return nextValueNumber++;
465 if (local_dep.isDef()) {
466 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
468 if (local_cdep->getNumOperands() != C->getNumOperands()) {
469 valueNumbering[C] = nextValueNumber;
470 return nextValueNumber++;
473 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
474 uint32_t c_vn = lookup_or_add(C->getOperand(i));
475 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
477 valueNumbering[C] = nextValueNumber;
478 return nextValueNumber++;
482 uint32_t v = lookup_or_add(local_cdep);
483 valueNumbering[C] = v;
488 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
489 MD->getNonLocalCallDependency(CallSite(C));
490 // FIXME: call/call dependencies for readonly calls should return def, not
491 // clobber! Move the checking logic to MemDep!
494 // Check to see if we have a single dominating call instruction that is
496 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
497 const NonLocalDepEntry *I = &deps[i];
498 // Ignore non-local dependencies.
499 if (I->getResult().isNonLocal())
502 // We don't handle non-depedencies. If we already have a call, reject
503 // instruction dependencies.
504 if (I->getResult().isClobber() || cdep != 0) {
509 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
510 // FIXME: All duplicated with non-local case.
511 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
512 cdep = NonLocalDepCall;
521 valueNumbering[C] = nextValueNumber;
522 return nextValueNumber++;
525 if (cdep->getNumOperands() != C->getNumOperands()) {
526 valueNumbering[C] = nextValueNumber;
527 return nextValueNumber++;
529 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
530 uint32_t c_vn = lookup_or_add(C->getOperand(i));
531 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
533 valueNumbering[C] = nextValueNumber;
534 return nextValueNumber++;
538 uint32_t v = lookup_or_add(cdep);
539 valueNumbering[C] = v;
543 valueNumbering[C] = nextValueNumber;
544 return nextValueNumber++;
548 /// lookup_or_add - Returns the value number for the specified value, assigning
549 /// it a new number if it did not have one before.
550 uint32_t ValueTable::lookup_or_add(Value *V) {
551 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
552 if (VI != valueNumbering.end())
555 if (!isa<Instruction>(V)) {
556 valueNumbering[V] = nextValueNumber;
557 return nextValueNumber++;
560 Instruction* I = cast<Instruction>(V);
562 switch (I->getOpcode()) {
563 case Instruction::Call:
564 return lookup_or_add_call(cast<CallInst>(I));
565 case Instruction::Add:
566 case Instruction::FAdd:
567 case Instruction::Sub:
568 case Instruction::FSub:
569 case Instruction::Mul:
570 case Instruction::FMul:
571 case Instruction::UDiv:
572 case Instruction::SDiv:
573 case Instruction::FDiv:
574 case Instruction::URem:
575 case Instruction::SRem:
576 case Instruction::FRem:
577 case Instruction::Shl:
578 case Instruction::LShr:
579 case Instruction::AShr:
580 case Instruction::And:
581 case Instruction::Or :
582 case Instruction::Xor:
583 exp = create_expression(cast<BinaryOperator>(I));
585 case Instruction::ICmp:
586 case Instruction::FCmp:
587 exp = create_expression(cast<CmpInst>(I));
589 case Instruction::Trunc:
590 case Instruction::ZExt:
591 case Instruction::SExt:
592 case Instruction::FPToUI:
593 case Instruction::FPToSI:
594 case Instruction::UIToFP:
595 case Instruction::SIToFP:
596 case Instruction::FPTrunc:
597 case Instruction::FPExt:
598 case Instruction::PtrToInt:
599 case Instruction::IntToPtr:
600 case Instruction::BitCast:
601 exp = create_expression(cast<CastInst>(I));
603 case Instruction::Select:
604 exp = create_expression(cast<SelectInst>(I));
606 case Instruction::ExtractElement:
607 exp = create_expression(cast<ExtractElementInst>(I));
609 case Instruction::InsertElement:
610 exp = create_expression(cast<InsertElementInst>(I));
612 case Instruction::ShuffleVector:
613 exp = create_expression(cast<ShuffleVectorInst>(I));
615 case Instruction::ExtractValue:
616 exp = create_expression(cast<ExtractValueInst>(I));
618 case Instruction::InsertValue:
619 exp = create_expression(cast<InsertValueInst>(I));
621 case Instruction::GetElementPtr:
622 exp = create_expression(cast<GetElementPtrInst>(I));
625 valueNumbering[V] = nextValueNumber;
626 return nextValueNumber++;
629 uint32_t& e = expressionNumbering[exp];
630 if (!e) e = nextValueNumber++;
631 valueNumbering[V] = e;
635 /// lookup - Returns the value number of the specified value. Fails if
636 /// the value has not yet been numbered.
637 uint32_t ValueTable::lookup(Value *V) const {
638 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
639 assert(VI != valueNumbering.end() && "Value not numbered?");
643 /// clear - Remove all entries from the ValueTable
644 void ValueTable::clear() {
645 valueNumbering.clear();
646 expressionNumbering.clear();
650 /// erase - Remove a value from the value numbering
651 void ValueTable::erase(Value *V) {
652 valueNumbering.erase(V);
655 /// verifyRemoved - Verify that the value is removed from all internal data
657 void ValueTable::verifyRemoved(const Value *V) const {
658 for (DenseMap<Value*, uint32_t>::const_iterator
659 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
660 assert(I->first != V && "Inst still occurs in value numbering map!");
664 //===----------------------------------------------------------------------===//
666 //===----------------------------------------------------------------------===//
669 struct ValueNumberScope {
670 ValueNumberScope* parent;
671 DenseMap<uint32_t, Value*> table;
673 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
679 class GVN : public FunctionPass {
680 bool runOnFunction(Function &F);
682 static char ID; // Pass identification, replacement for typeid
683 explicit GVN(bool nopre = false, bool noloads = false)
684 : FunctionPass(&ID), NoPRE(nopre), NoLoads(noloads), MD(0) { }
689 MemoryDependenceAnalysis *MD;
693 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
695 // This transformation requires dominator postdominator info
696 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
697 AU.addRequired<DominatorTree>();
699 AU.addRequired<MemoryDependenceAnalysis>();
700 AU.addRequired<AliasAnalysis>();
702 AU.addPreserved<DominatorTree>();
703 AU.addPreserved<AliasAnalysis>();
707 // FIXME: eliminate or document these better
708 bool processLoad(LoadInst* L,
709 SmallVectorImpl<Instruction*> &toErase);
710 bool processInstruction(Instruction *I,
711 SmallVectorImpl<Instruction*> &toErase);
712 bool processNonLocalLoad(LoadInst* L,
713 SmallVectorImpl<Instruction*> &toErase);
714 bool processBlock(BasicBlock *BB);
715 void dump(DenseMap<uint32_t, Value*>& d);
716 bool iterateOnFunction(Function &F);
717 Value *CollapsePhi(PHINode* p);
718 bool performPRE(Function& F);
719 Value *lookupNumber(BasicBlock *BB, uint32_t num);
720 void cleanupGlobalSets();
721 void verifyRemoved(const Instruction *I) const;
727 // createGVNPass - The public interface to this file...
728 FunctionPass *llvm::createGVNPass(bool NoPRE, bool NoLoads) {
729 return new GVN(NoPRE, NoLoads);
732 static RegisterPass<GVN> X("gvn",
733 "Global Value Numbering");
735 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
737 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
738 E = d.end(); I != E; ++I) {
739 printf("%d\n", I->first);
745 static bool isSafeReplacement(PHINode* p, Instruction *inst) {
746 if (!isa<PHINode>(inst))
749 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
751 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
752 if (use_phi->getParent() == inst->getParent())
758 Value *GVN::CollapsePhi(PHINode *PN) {
759 Value *ConstVal = PN->hasConstantValue(DT);
760 if (!ConstVal) return 0;
762 Instruction *Inst = dyn_cast<Instruction>(ConstVal);
766 if (DT->dominates(Inst, PN))
767 if (isSafeReplacement(PN, Inst))
772 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
773 /// we're analyzing is fully available in the specified block. As we go, keep
774 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
775 /// map is actually a tri-state map with the following values:
776 /// 0) we know the block *is not* fully available.
777 /// 1) we know the block *is* fully available.
778 /// 2) we do not know whether the block is fully available or not, but we are
779 /// currently speculating that it will be.
780 /// 3) we are speculating for this block and have used that to speculate for
782 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
783 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
784 // Optimistically assume that the block is fully available and check to see
785 // if we already know about this block in one lookup.
786 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
787 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
789 // If the entry already existed for this block, return the precomputed value.
791 // If this is a speculative "available" value, mark it as being used for
792 // speculation of other blocks.
793 if (IV.first->second == 2)
794 IV.first->second = 3;
795 return IV.first->second != 0;
798 // Otherwise, see if it is fully available in all predecessors.
799 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
801 // If this block has no predecessors, it isn't live-in here.
803 goto SpeculationFailure;
805 for (; PI != PE; ++PI)
806 // If the value isn't fully available in one of our predecessors, then it
807 // isn't fully available in this block either. Undo our previous
808 // optimistic assumption and bail out.
809 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
810 goto SpeculationFailure;
814 // SpeculationFailure - If we get here, we found out that this is not, after
815 // all, a fully-available block. We have a problem if we speculated on this and
816 // used the speculation to mark other blocks as available.
818 char &BBVal = FullyAvailableBlocks[BB];
820 // If we didn't speculate on this, just return with it set to false.
826 // If we did speculate on this value, we could have blocks set to 1 that are
827 // incorrect. Walk the (transitive) successors of this block and mark them as
829 SmallVector<BasicBlock*, 32> BBWorklist;
830 BBWorklist.push_back(BB);
832 while (!BBWorklist.empty()) {
833 BasicBlock *Entry = BBWorklist.pop_back_val();
834 // Note that this sets blocks to 0 (unavailable) if they happen to not
835 // already be in FullyAvailableBlocks. This is safe.
836 char &EntryVal = FullyAvailableBlocks[Entry];
837 if (EntryVal == 0) continue; // Already unavailable.
839 // Mark as unavailable.
842 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
843 BBWorklist.push_back(*I);
850 /// CanCoerceMustAliasedValueToLoad - Return true if
851 /// CoerceAvailableValueToLoadType will succeed.
852 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
854 const TargetData &TD) {
855 // If the loaded or stored value is an first class array or struct, don't try
856 // to transform them. We need to be able to bitcast to integer.
857 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy) ||
858 isa<StructType>(StoredVal->getType()) ||
859 isa<ArrayType>(StoredVal->getType()))
862 // The store has to be at least as big as the load.
863 if (TD.getTypeSizeInBits(StoredVal->getType()) <
864 TD.getTypeSizeInBits(LoadTy))
871 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
872 /// then a load from a must-aliased pointer of a different type, try to coerce
873 /// the stored value. LoadedTy is the type of the load we want to replace and
874 /// InsertPt is the place to insert new instructions.
876 /// If we can't do it, return null.
877 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
878 const Type *LoadedTy,
879 Instruction *InsertPt,
880 const TargetData &TD) {
881 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
884 const Type *StoredValTy = StoredVal->getType();
886 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy);
887 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
889 // If the store and reload are the same size, we can always reuse it.
890 if (StoreSize == LoadSize) {
891 if (isa<PointerType>(StoredValTy) && isa<PointerType>(LoadedTy)) {
892 // Pointer to Pointer -> use bitcast.
893 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
896 // Convert source pointers to integers, which can be bitcast.
897 if (isa<PointerType>(StoredValTy)) {
898 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
899 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
902 const Type *TypeToCastTo = LoadedTy;
903 if (isa<PointerType>(TypeToCastTo))
904 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
906 if (StoredValTy != TypeToCastTo)
907 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
909 // Cast to pointer if the load needs a pointer type.
910 if (isa<PointerType>(LoadedTy))
911 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
916 // If the loaded value is smaller than the available value, then we can
917 // extract out a piece from it. If the available value is too small, then we
918 // can't do anything.
919 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
921 // Convert source pointers to integers, which can be manipulated.
922 if (isa<PointerType>(StoredValTy)) {
923 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
924 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
927 // Convert vectors and fp to integer, which can be manipulated.
928 if (!isa<IntegerType>(StoredValTy)) {
929 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
930 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
933 // If this is a big-endian system, we need to shift the value down to the low
934 // bits so that a truncate will work.
935 if (TD.isBigEndian()) {
936 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
937 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
940 // Truncate the integer to the right size now.
941 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
942 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
944 if (LoadedTy == NewIntTy)
947 // If the result is a pointer, inttoptr.
948 if (isa<PointerType>(LoadedTy))
949 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
951 // Otherwise, bitcast.
952 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
955 /// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
956 /// be expressed as a base pointer plus a constant offset. Return the base and
957 /// offset to the caller.
958 static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
959 const TargetData &TD) {
960 Operator *PtrOp = dyn_cast<Operator>(Ptr);
961 if (PtrOp == 0) return Ptr;
963 // Just look through bitcasts.
964 if (PtrOp->getOpcode() == Instruction::BitCast)
965 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
967 // If this is a GEP with constant indices, we can look through it.
968 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
969 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
971 gep_type_iterator GTI = gep_type_begin(GEP);
972 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
974 ConstantInt *OpC = cast<ConstantInt>(*I);
975 if (OpC->isZero()) continue;
977 // Handle a struct and array indices which add their offset to the pointer.
978 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
979 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
981 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
982 Offset += OpC->getSExtValue()*Size;
986 // Re-sign extend from the pointer size if needed to get overflow edge cases
988 unsigned PtrSize = TD.getPointerSizeInBits();
990 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
992 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
996 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
997 /// memdep query of a load that ends up being a clobbering memory write (store,
998 /// memset, memcpy, memmove). This means that the write *may* provide bits used
999 /// by the load but we can't be sure because the pointers don't mustalias.
1001 /// Check this case to see if there is anything more we can do before we give
1002 /// up. This returns -1 if we have to give up, or a byte number in the stored
1003 /// value of the piece that feeds the load.
1004 static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
1006 uint64_t WriteSizeInBits,
1007 const TargetData &TD) {
1008 // If the loaded or stored value is an first class array or struct, don't try
1009 // to transform them. We need to be able to bitcast to integer.
1010 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy))
1013 int64_t StoreOffset = 0, LoadOffset = 0;
1014 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
1016 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
1017 if (StoreBase != LoadBase)
1020 // If the load and store are to the exact same address, they should have been
1021 // a must alias. AA must have gotten confused.
1022 // FIXME: Study to see if/when this happens.
1023 if (LoadOffset == StoreOffset) {
1025 errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
1026 << "Base = " << *StoreBase << "\n"
1027 << "Store Ptr = " << *WritePtr << "\n"
1028 << "Store Offs = " << StoreOffset << "\n"
1029 << "Load Ptr = " << *LoadPtr << "\n";
1035 // If the load and store don't overlap at all, the store doesn't provide
1036 // anything to the load. In this case, they really don't alias at all, AA
1037 // must have gotten confused.
1038 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
1039 // remove this check, as it is duplicated with what we have below.
1040 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
1042 if ((WriteSizeInBits & 7) | (LoadSize & 7))
1044 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
1048 bool isAAFailure = false;
1049 if (StoreOffset < LoadOffset) {
1050 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
1052 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
1056 errs() << "STORE LOAD DEP WITH COMMON BASE:\n"
1057 << "Base = " << *StoreBase << "\n"
1058 << "Store Ptr = " << *WritePtr << "\n"
1059 << "Store Offs = " << StoreOffset << "\n"
1060 << "Load Ptr = " << *LoadPtr << "\n";
1066 // If the Load isn't completely contained within the stored bits, we don't
1067 // have all the bits to feed it. We could do something crazy in the future
1068 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1070 if (StoreOffset > LoadOffset ||
1071 StoreOffset+StoreSize < LoadOffset+LoadSize)
1074 // Okay, we can do this transformation. Return the number of bytes into the
1075 // store that the load is.
1076 return LoadOffset-StoreOffset;
1079 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1080 /// memdep query of a load that ends up being a clobbering store.
1081 static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr,
1083 const TargetData &TD) {
1084 // Cannot handle reading from store of first-class aggregate yet.
1085 if (isa<StructType>(DepSI->getOperand(0)->getType()) ||
1086 isa<ArrayType>(DepSI->getOperand(0)->getType()))
1089 Value *StorePtr = DepSI->getPointerOperand();
1090 uint64_t StoreSize = TD.getTypeSizeInBits(DepSI->getOperand(0)->getType());
1091 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1092 StorePtr, StoreSize, TD);
1095 static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr,
1097 const TargetData &TD) {
1098 // If the mem operation is a non-constant size, we can't handle it.
1099 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1100 if (SizeCst == 0) return -1;
1101 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1103 // If this is memset, we just need to see if the offset is valid in the size
1105 if (MI->getIntrinsicID() == Intrinsic::memset)
1106 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1109 // If we have a memcpy/memmove, the only case we can handle is if this is a
1110 // copy from constant memory. In that case, we can read directly from the
1112 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1114 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1115 if (Src == 0) return -1;
1117 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1118 if (GV == 0 || !GV->isConstant()) return -1;
1120 // See if the access is within the bounds of the transfer.
1121 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1122 MI->getDest(), MemSizeInBits, TD);
1126 // Otherwise, see if we can constant fold a load from the constant with the
1127 // offset applied as appropriate.
1128 Src = ConstantExpr::getBitCast(Src,
1129 llvm::Type::getInt8PtrTy(Src->getContext()));
1130 Constant *OffsetCst =
1131 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1132 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1133 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1134 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1140 /// GetStoreValueForLoad - This function is called when we have a
1141 /// memdep query of a load that ends up being a clobbering store. This means
1142 /// that the store *may* provide bits used by the load but we can't be sure
1143 /// because the pointers don't mustalias. Check this case to see if there is
1144 /// anything more we can do before we give up.
1145 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1147 Instruction *InsertPt, const TargetData &TD){
1148 LLVMContext &Ctx = SrcVal->getType()->getContext();
1150 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8;
1151 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1153 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1155 // Compute which bits of the stored value are being used by the load. Convert
1156 // to an integer type to start with.
1157 if (isa<PointerType>(SrcVal->getType()))
1158 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp");
1159 if (!isa<IntegerType>(SrcVal->getType()))
1160 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1163 // Shift the bits to the least significant depending on endianness.
1165 if (TD.isLittleEndian())
1166 ShiftAmt = Offset*8;
1168 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1171 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp");
1173 if (LoadSize != StoreSize)
1174 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1177 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1180 /// GetMemInstValueForLoad - This function is called when we have a
1181 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1182 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1183 const Type *LoadTy, Instruction *InsertPt,
1184 const TargetData &TD){
1185 LLVMContext &Ctx = LoadTy->getContext();
1186 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1188 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1190 // We know that this method is only called when the mem transfer fully
1191 // provides the bits for the load.
1192 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1193 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1194 // independently of what the offset is.
1195 Value *Val = MSI->getValue();
1197 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1199 Value *OneElt = Val;
1201 // Splat the value out to the right number of bits.
1202 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1203 // If we can double the number of bytes set, do it.
1204 if (NumBytesSet*2 <= LoadSize) {
1205 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1206 Val = Builder.CreateOr(Val, ShVal);
1211 // Otherwise insert one byte at a time.
1212 Value *ShVal = Builder.CreateShl(Val, 1*8);
1213 Val = Builder.CreateOr(OneElt, ShVal);
1217 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1220 // Otherwise, this is a memcpy/memmove from a constant global.
1221 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1222 Constant *Src = cast<Constant>(MTI->getSource());
1224 // Otherwise, see if we can constant fold a load from the constant with the
1225 // offset applied as appropriate.
1226 Src = ConstantExpr::getBitCast(Src,
1227 llvm::Type::getInt8PtrTy(Src->getContext()));
1228 Constant *OffsetCst =
1229 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1230 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1231 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1232 return ConstantFoldLoadFromConstPtr(Src, &TD);
1237 struct AvailableValueInBlock {
1238 /// BB - The basic block in question.
1241 SimpleVal, // A simple offsetted value that is accessed.
1242 MemIntrin // A memory intrinsic which is loaded from.
1245 /// V - The value that is live out of the block.
1246 PointerIntPair<Value *, 1, ValType> Val;
1248 /// Offset - The byte offset in Val that is interesting for the load query.
1251 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1252 unsigned Offset = 0) {
1253 AvailableValueInBlock Res;
1255 Res.Val.setPointer(V);
1256 Res.Val.setInt(SimpleVal);
1257 Res.Offset = Offset;
1261 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1262 unsigned Offset = 0) {
1263 AvailableValueInBlock Res;
1265 Res.Val.setPointer(MI);
1266 Res.Val.setInt(MemIntrin);
1267 Res.Offset = Offset;
1271 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1272 Value *getSimpleValue() const {
1273 assert(isSimpleValue() && "Wrong accessor");
1274 return Val.getPointer();
1277 MemIntrinsic *getMemIntrinValue() const {
1278 assert(!isSimpleValue() && "Wrong accessor");
1279 return cast<MemIntrinsic>(Val.getPointer());
1283 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1284 /// construct SSA form, allowing us to eliminate LI. This returns the value
1285 /// that should be used at LI's definition site.
1286 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1287 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1288 const TargetData *TD,
1289 AliasAnalysis *AA) {
1290 SmallVector<PHINode*, 8> NewPHIs;
1291 SSAUpdater SSAUpdate(&NewPHIs);
1292 SSAUpdate.Initialize(LI);
1294 const Type *LoadTy = LI->getType();
1296 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1297 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1298 BasicBlock *BB = AV.BB;
1300 if (SSAUpdate.HasValueForBlock(BB))
1303 unsigned Offset = AV.Offset;
1305 Value *AvailableVal;
1306 if (AV.isSimpleValue()) {
1307 AvailableVal = AV.getSimpleValue();
1308 if (AvailableVal->getType() != LoadTy) {
1309 assert(TD && "Need target data to handle type mismatch case");
1310 AvailableVal = GetStoreValueForLoad(AvailableVal, Offset, LoadTy,
1311 BB->getTerminator(), *TD);
1313 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1314 << *AV.getSimpleValue() << '\n'
1315 << *AvailableVal << '\n' << "\n\n\n");
1318 AvailableVal = GetMemInstValueForLoad(AV.getMemIntrinValue(), Offset,
1319 LoadTy, BB->getTerminator(), *TD);
1320 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1321 << " " << *AV.getMemIntrinValue() << '\n'
1322 << *AvailableVal << '\n' << "\n\n\n");
1324 SSAUpdate.AddAvailableValue(BB, AvailableVal);
1327 // Perform PHI construction.
1328 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1330 // If new PHI nodes were created, notify alias analysis.
1331 if (isa<PointerType>(V->getType()))
1332 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1333 AA->copyValue(LI, NewPHIs[i]);
1338 static bool isLifetimeStart(Instruction *Inst) {
1339 if (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<NonLocalDepEntry, 64> Deps;
1350 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
1352 //DEBUG(errs() << "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 errs() << "GVN: non-local load ";
1366 WriteAsOperand(errs(), LI);
1367 errs() << " 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(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1492 // Perform PHI construction.
1493 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD,
1494 VN.getAliasAnalysis());
1495 LI->replaceAllUsesWith(V);
1497 if (isa<PHINode>(V))
1499 if (isa<PointerType>(V->getType()))
1500 MD->invalidateCachedPointerInfo(V);
1501 toErase.push_back(LI);
1506 if (!EnablePRE || !EnableLoadPRE)
1509 // Okay, we have *some* definitions of the value. This means that the value
1510 // is available in some of our (transitive) predecessors. Lets think about
1511 // doing PRE of this load. This will involve inserting a new load into the
1512 // predecessor when it's not available. We could do this in general, but
1513 // prefer to not increase code size. As such, we only do this when we know
1514 // that we only have to insert *one* load (which means we're basically moving
1515 // the load, not inserting a new one).
1517 SmallPtrSet<BasicBlock *, 4> Blockers;
1518 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1519 Blockers.insert(UnavailableBlocks[i]);
1521 // Lets find first basic block with more than one predecessor. Walk backwards
1522 // through predecessors if needed.
1523 BasicBlock *LoadBB = LI->getParent();
1524 BasicBlock *TmpBB = LoadBB;
1526 bool isSinglePred = false;
1527 bool allSingleSucc = true;
1528 while (TmpBB->getSinglePredecessor()) {
1529 isSinglePred = true;
1530 TmpBB = TmpBB->getSinglePredecessor();
1531 if (!TmpBB) // If haven't found any, bail now.
1533 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1535 if (Blockers.count(TmpBB))
1537 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1538 allSingleSucc = false;
1544 // If we have a repl set with LI itself in it, this means we have a loop where
1545 // at least one of the values is LI. Since this means that we won't be able
1546 // to eliminate LI even if we insert uses in the other predecessors, we will
1547 // end up increasing code size. Reject this by scanning for LI.
1548 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1549 if (ValuesPerBlock[i].isSimpleValue() &&
1550 ValuesPerBlock[i].getSimpleValue() == LI)
1553 // FIXME: It is extremely unclear what this loop is doing, other than
1554 // artificially restricting loadpre.
1557 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1558 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1559 if (AV.isSimpleValue())
1560 // "Hot" Instruction is in some loop (because it dominates its dep.
1562 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1563 if (DT->dominates(LI, I)) {
1569 // We are interested only in "hot" instructions. We don't want to do any
1570 // mis-optimizations here.
1575 // Okay, we have some hope :). Check to see if the loaded value is fully
1576 // available in all but one predecessor.
1577 // FIXME: If we could restructure the CFG, we could make a common pred with
1578 // all the preds that don't have an available LI and insert a new load into
1580 BasicBlock *UnavailablePred = 0;
1582 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1583 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1584 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1585 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1586 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1588 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1590 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1593 // If this load is not available in multiple predecessors, reject it.
1594 if (UnavailablePred && UnavailablePred != *PI)
1596 UnavailablePred = *PI;
1599 assert(UnavailablePred != 0 &&
1600 "Fully available value should be eliminated above!");
1602 // We don't currently handle critical edges :(
1603 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1604 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1605 << UnavailablePred->getName() << "': " << *LI << '\n');
1609 // Do PHI translation to get its value in the predecessor if necessary. The
1610 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1612 SmallVector<Instruction*, 8> NewInsts;
1614 // If all preds have a single successor, then we know it is safe to insert the
1615 // load on the pred (?!?), so we can insert code to materialize the pointer if
1616 // it is not available.
1617 PHITransAddr Address(LI->getOperand(0), TD);
1619 if (allSingleSucc) {
1620 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1623 Address.PHITranslateValue(LoadBB, UnavailablePred);
1624 LoadPtr = Address.getAddr();
1626 // Make sure the value is live in the predecessor.
1627 if (Instruction *Inst = dyn_cast_or_null<Instruction>(LoadPtr))
1628 if (!DT->dominates(Inst->getParent(), UnavailablePred))
1632 // If we couldn't find or insert a computation of this phi translated value,
1635 assert(NewInsts.empty() && "Shouldn't insert insts on failure");
1636 DEBUG(errs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1637 << *LI->getOperand(0) << "\n");
1641 // Assign value numbers to these new instructions.
1642 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1643 // FIXME: We really _ought_ to insert these value numbers into their
1644 // parent's availability map. However, in doing so, we risk getting into
1645 // ordering issues. If a block hasn't been processed yet, we would be
1646 // marking a value as AVAIL-IN, which isn't what we intend.
1647 VN.lookup_or_add(NewInsts[i]);
1650 // Make sure it is valid to move this load here. We have to watch out for:
1651 // @1 = getelementptr (i8* p, ...
1652 // test p and branch if == 0
1654 // It is valid to have the getelementptr before the test, even if p can be 0,
1655 // as getelementptr only does address arithmetic.
1656 // If we are not pushing the value through any multiple-successor blocks
1657 // we do not have this case. Otherwise, check that the load is safe to
1658 // put anywhere; this can be improved, but should be conservatively safe.
1659 if (!allSingleSucc &&
1660 // FIXME: REEVALUTE THIS.
1661 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) {
1662 assert(NewInsts.empty() && "Should not have inserted instructions");
1666 // Okay, we can eliminate this load by inserting a reload in the predecessor
1667 // and using PHI construction to get the value in the other predecessors, do
1669 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1670 DEBUG(if (!NewInsts.empty())
1671 errs() << "INSERTED " << NewInsts.size() << " INSTS: "
1672 << *NewInsts.back() << '\n');
1674 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1676 UnavailablePred->getTerminator());
1678 // Add the newly created load.
1679 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,NewLoad));
1681 // Perform PHI construction.
1682 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD,
1683 VN.getAliasAnalysis());
1684 LI->replaceAllUsesWith(V);
1685 if (isa<PHINode>(V))
1687 if (isa<PointerType>(V->getType()))
1688 MD->invalidateCachedPointerInfo(V);
1689 toErase.push_back(LI);
1694 /// processLoad - Attempt to eliminate a load, first by eliminating it
1695 /// locally, and then attempting non-local elimination if that fails.
1696 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1700 if (L->isVolatile())
1703 // ... to a pointer that has been loaded from before...
1704 MemDepResult Dep = MD->getDependency(L);
1706 // If the value isn't available, don't do anything!
1707 if (Dep.isClobber()) {
1708 // Check to see if we have something like this:
1709 // store i32 123, i32* %P
1710 // %A = bitcast i32* %P to i8*
1711 // %B = gep i8* %A, i32 1
1714 // We could do that by recognizing if the clobber instructions are obviously
1715 // a common base + constant offset, and if the previous store (or memset)
1716 // completely covers this load. This sort of thing can happen in bitfield
1718 Value *AvailVal = 0;
1719 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1720 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1721 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1722 L->getPointerOperand(),
1725 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset,
1726 L->getType(), L, *TD);
1729 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1730 // a value on from it.
1731 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1732 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1733 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1734 L->getPointerOperand(),
1737 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1742 DEBUG(errs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1743 << *AvailVal << '\n' << *L << "\n\n\n");
1745 // Replace the load!
1746 L->replaceAllUsesWith(AvailVal);
1747 if (isa<PointerType>(AvailVal->getType()))
1748 MD->invalidateCachedPointerInfo(AvailVal);
1749 toErase.push_back(L);
1755 // fast print dep, using operator<< on instruction would be too slow
1756 errs() << "GVN: load ";
1757 WriteAsOperand(errs(), L);
1758 Instruction *I = Dep.getInst();
1759 errs() << " is clobbered by " << *I << '\n';
1764 // If it is defined in another block, try harder.
1765 if (Dep.isNonLocal())
1766 return processNonLocalLoad(L, toErase);
1768 Instruction *DepInst = Dep.getInst();
1769 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1770 Value *StoredVal = DepSI->getOperand(0);
1772 // The store and load are to a must-aliased pointer, but they may not
1773 // actually have the same type. See if we know how to reuse the stored
1774 // value (depending on its type).
1775 const TargetData *TD = 0;
1776 if (StoredVal->getType() != L->getType()) {
1777 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1778 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1783 DEBUG(errs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1784 << '\n' << *L << "\n\n\n");
1791 L->replaceAllUsesWith(StoredVal);
1792 if (isa<PointerType>(StoredVal->getType()))
1793 MD->invalidateCachedPointerInfo(StoredVal);
1794 toErase.push_back(L);
1799 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1800 Value *AvailableVal = DepLI;
1802 // The loads are of a must-aliased pointer, but they may not actually have
1803 // the same type. See if we know how to reuse the previously loaded value
1804 // (depending on its type).
1805 const TargetData *TD = 0;
1806 if (DepLI->getType() != L->getType()) {
1807 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1808 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1809 if (AvailableVal == 0)
1812 DEBUG(errs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1813 << "\n" << *L << "\n\n\n");
1820 L->replaceAllUsesWith(AvailableVal);
1821 if (isa<PointerType>(DepLI->getType()))
1822 MD->invalidateCachedPointerInfo(DepLI);
1823 toErase.push_back(L);
1828 // If this load really doesn't depend on anything, then we must be loading an
1829 // undef value. This can happen when loading for a fresh allocation with no
1830 // intervening stores, for example.
1831 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1832 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1833 toErase.push_back(L);
1838 // If this load occurs either right after a lifetime begin,
1839 // then the loaded value is undefined.
1840 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1841 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1842 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1843 toErase.push_back(L);
1852 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1853 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1854 if (I == localAvail.end())
1857 ValueNumberScope *Locals = I->second;
1859 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num);
1860 if (I != Locals->table.end())
1862 Locals = Locals->parent;
1869 /// processInstruction - When calculating availability, handle an instruction
1870 /// by inserting it into the appropriate sets
1871 bool GVN::processInstruction(Instruction *I,
1872 SmallVectorImpl<Instruction*> &toErase) {
1873 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1874 bool Changed = processLoad(LI, toErase);
1877 unsigned Num = VN.lookup_or_add(LI);
1878 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI));
1884 uint32_t NextNum = VN.getNextUnusedValueNumber();
1885 unsigned Num = VN.lookup_or_add(I);
1887 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1888 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1890 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1893 Value *BranchCond = BI->getCondition();
1894 uint32_t CondVN = VN.lookup_or_add(BranchCond);
1896 BasicBlock *TrueSucc = BI->getSuccessor(0);
1897 BasicBlock *FalseSucc = BI->getSuccessor(1);
1899 if (TrueSucc->getSinglePredecessor())
1900 localAvail[TrueSucc]->table[CondVN] =
1901 ConstantInt::getTrue(TrueSucc->getContext());
1902 if (FalseSucc->getSinglePredecessor())
1903 localAvail[FalseSucc]->table[CondVN] =
1904 ConstantInt::getFalse(TrueSucc->getContext());
1908 // Allocations are always uniquely numbered, so we can save time and memory
1909 // by fast failing them.
1910 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1911 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1915 // Collapse PHI nodes
1916 if (PHINode* p = dyn_cast<PHINode>(I)) {
1917 Value *constVal = CollapsePhi(p);
1920 p->replaceAllUsesWith(constVal);
1921 if (MD && isa<PointerType>(constVal->getType()))
1922 MD->invalidateCachedPointerInfo(constVal);
1925 toErase.push_back(p);
1927 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1930 // If the number we were assigned was a brand new VN, then we don't
1931 // need to do a lookup to see if the number already exists
1932 // somewhere in the domtree: it can't!
1933 } else if (Num == NextNum) {
1934 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1936 // Perform fast-path value-number based elimination of values inherited from
1938 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1941 I->replaceAllUsesWith(repl);
1942 if (MD && isa<PointerType>(repl->getType()))
1943 MD->invalidateCachedPointerInfo(repl);
1944 toErase.push_back(I);
1948 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1954 /// runOnFunction - This is the main transformation entry point for a function.
1955 bool GVN::runOnFunction(Function& F) {
1957 MD = &getAnalysis<MemoryDependenceAnalysis>();
1958 DT = &getAnalysis<DominatorTree>();
1959 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1963 bool Changed = false;
1964 bool ShouldContinue = true;
1966 // Merge unconditional branches, allowing PRE to catch more
1967 // optimization opportunities.
1968 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1969 BasicBlock *BB = FI;
1971 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1972 if (removedBlock) NumGVNBlocks++;
1974 Changed |= removedBlock;
1977 unsigned Iteration = 0;
1979 while (ShouldContinue) {
1980 DEBUG(errs() << "GVN iteration: " << Iteration << "\n");
1981 ShouldContinue = iterateOnFunction(F);
1982 Changed |= ShouldContinue;
1987 bool PREChanged = true;
1988 while (PREChanged) {
1989 PREChanged = performPRE(F);
1990 Changed |= PREChanged;
1993 // FIXME: Should perform GVN again after PRE does something. PRE can move
1994 // computations into blocks where they become fully redundant. Note that
1995 // we can't do this until PRE's critical edge splitting updates memdep.
1996 // Actually, when this happens, we should just fully integrate PRE into GVN.
1998 cleanupGlobalSets();
2004 bool GVN::processBlock(BasicBlock *BB) {
2005 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
2006 // incrementing BI before processing an instruction).
2007 SmallVector<Instruction*, 8> toErase;
2008 bool ChangedFunction = false;
2010 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2012 ChangedFunction |= processInstruction(BI, toErase);
2013 if (toErase.empty()) {
2018 // If we need some instructions deleted, do it now.
2019 NumGVNInstr += toErase.size();
2021 // Avoid iterator invalidation.
2022 bool AtStart = BI == BB->begin();
2026 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2027 E = toErase.end(); I != E; ++I) {
2028 DEBUG(errs() << "GVN removed: " << **I << '\n');
2029 if (MD) MD->removeInstruction(*I);
2030 (*I)->eraseFromParent();
2031 DEBUG(verifyRemoved(*I));
2041 return ChangedFunction;
2044 /// performPRE - Perform a purely local form of PRE that looks for diamond
2045 /// control flow patterns and attempts to perform simple PRE at the join point.
2046 bool GVN::performPRE(Function &F) {
2047 bool Changed = false;
2048 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
2049 DenseMap<BasicBlock*, Value*> predMap;
2050 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2051 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2052 BasicBlock *CurrentBlock = *DI;
2054 // Nothing to PRE in the entry block.
2055 if (CurrentBlock == &F.getEntryBlock()) continue;
2057 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2058 BE = CurrentBlock->end(); BI != BE; ) {
2059 Instruction *CurInst = BI++;
2061 if (isa<AllocaInst>(CurInst) ||
2062 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2063 CurInst->getType()->isVoidTy() ||
2064 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2065 isa<DbgInfoIntrinsic>(CurInst))
2068 uint32_t ValNo = VN.lookup(CurInst);
2070 // Look for the predecessors for PRE opportunities. We're
2071 // only trying to solve the basic diamond case, where
2072 // a value is computed in the successor and one predecessor,
2073 // but not the other. We also explicitly disallow cases
2074 // where the successor is its own predecessor, because they're
2075 // more complicated to get right.
2076 unsigned NumWith = 0;
2077 unsigned NumWithout = 0;
2078 BasicBlock *PREPred = 0;
2081 for (pred_iterator PI = pred_begin(CurrentBlock),
2082 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2083 // We're not interested in PRE where the block is its
2084 // own predecessor, on in blocks with predecessors
2085 // that are not reachable.
2086 if (*PI == CurrentBlock) {
2089 } else if (!localAvail.count(*PI)) {
2094 DenseMap<uint32_t, Value*>::iterator predV =
2095 localAvail[*PI]->table.find(ValNo);
2096 if (predV == localAvail[*PI]->table.end()) {
2099 } else if (predV->second == CurInst) {
2102 predMap[*PI] = predV->second;
2107 // Don't do PRE when it might increase code size, i.e. when
2108 // we would need to insert instructions in more than one pred.
2109 if (NumWithout != 1 || NumWith == 0)
2112 // Don't do PRE across indirect branch.
2113 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2116 // We can't do PRE safely on a critical edge, so instead we schedule
2117 // the edge to be split and perform the PRE the next time we iterate
2119 unsigned SuccNum = 0;
2120 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
2122 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
2127 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2128 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2132 // Instantiate the expression the in predecessor that lacked it.
2133 // Because we are going top-down through the block, all value numbers
2134 // will be available in the predecessor by the time we need them. Any
2135 // that weren't original present will have been instantiated earlier
2137 Instruction *PREInstr = CurInst->clone();
2138 bool success = true;
2139 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2140 Value *Op = PREInstr->getOperand(i);
2141 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2144 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
2145 PREInstr->setOperand(i, V);
2152 // Fail out if we encounter an operand that is not available in
2153 // the PRE predecessor. This is typically because of loads which
2154 // are not value numbered precisely.
2157 DEBUG(verifyRemoved(PREInstr));
2161 PREInstr->insertBefore(PREPred->getTerminator());
2162 PREInstr->setName(CurInst->getName() + ".pre");
2163 predMap[PREPred] = PREInstr;
2164 VN.add(PREInstr, ValNo);
2167 // Update the availability map to include the new instruction.
2168 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr));
2170 // Create a PHI to make the value available in this block.
2171 PHINode* Phi = PHINode::Create(CurInst->getType(),
2172 CurInst->getName() + ".pre-phi",
2173 CurrentBlock->begin());
2174 for (pred_iterator PI = pred_begin(CurrentBlock),
2175 PE = pred_end(CurrentBlock); PI != PE; ++PI)
2176 Phi->addIncoming(predMap[*PI], *PI);
2179 localAvail[CurrentBlock]->table[ValNo] = Phi;
2181 CurInst->replaceAllUsesWith(Phi);
2182 if (MD && isa<PointerType>(Phi->getType()))
2183 MD->invalidateCachedPointerInfo(Phi);
2186 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n');
2187 if (MD) MD->removeInstruction(CurInst);
2188 CurInst->eraseFromParent();
2189 DEBUG(verifyRemoved(CurInst));
2194 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
2195 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
2196 SplitCriticalEdge(I->first, I->second, this);
2198 return Changed || toSplit.size();
2201 /// iterateOnFunction - Executes one iteration of GVN
2202 bool GVN::iterateOnFunction(Function &F) {
2203 cleanupGlobalSets();
2205 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2206 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
2208 localAvail[DI->getBlock()] =
2209 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
2211 localAvail[DI->getBlock()] = new ValueNumberScope(0);
2214 // Top-down walk of the dominator tree
2215 bool Changed = false;
2217 // Needed for value numbering with phi construction to work.
2218 ReversePostOrderTraversal<Function*> RPOT(&F);
2219 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2220 RE = RPOT.end(); RI != RE; ++RI)
2221 Changed |= processBlock(*RI);
2223 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2224 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2225 Changed |= processBlock(DI->getBlock());
2231 void GVN::cleanupGlobalSets() {
2234 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
2235 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
2240 /// verifyRemoved - Verify that the specified instruction does not occur in our
2241 /// internal data structures.
2242 void GVN::verifyRemoved(const Instruction *Inst) const {
2243 VN.verifyRemoved(Inst);
2245 // Walk through the value number scope to make sure the instruction isn't
2246 // ferreted away in it.
2247 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
2248 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
2249 const ValueNumberScope *VNS = I->second;
2252 for (DenseMap<uint32_t, Value*>::const_iterator
2253 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
2254 assert(II->second != Inst && "Inst still in value numbering scope!");