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) {
193 static bool isPod() { return true; }
197 //===----------------------------------------------------------------------===//
198 // ValueTable Internal Functions
199 //===----------------------------------------------------------------------===//
200 Expression::ExpressionOpcode ValueTable::getOpcode(BinaryOperator* BO) {
201 switch(BO->getOpcode()) {
202 default: // THIS SHOULD NEVER HAPPEN
203 llvm_unreachable("Binary operator with unknown opcode?");
204 case Instruction::Add: return Expression::ADD;
205 case Instruction::FAdd: return Expression::FADD;
206 case Instruction::Sub: return Expression::SUB;
207 case Instruction::FSub: return Expression::FSUB;
208 case Instruction::Mul: return Expression::MUL;
209 case Instruction::FMul: return Expression::FMUL;
210 case Instruction::UDiv: return Expression::UDIV;
211 case Instruction::SDiv: return Expression::SDIV;
212 case Instruction::FDiv: return Expression::FDIV;
213 case Instruction::URem: return Expression::UREM;
214 case Instruction::SRem: return Expression::SREM;
215 case Instruction::FRem: return Expression::FREM;
216 case Instruction::Shl: return Expression::SHL;
217 case Instruction::LShr: return Expression::LSHR;
218 case Instruction::AShr: return Expression::ASHR;
219 case Instruction::And: return Expression::AND;
220 case Instruction::Or: return Expression::OR;
221 case Instruction::Xor: return Expression::XOR;
225 Expression::ExpressionOpcode ValueTable::getOpcode(CmpInst* C) {
226 if (isa<ICmpInst>(C)) {
227 switch (C->getPredicate()) {
228 default: // THIS SHOULD NEVER HAPPEN
229 llvm_unreachable("Comparison with unknown predicate?");
230 case ICmpInst::ICMP_EQ: return Expression::ICMPEQ;
231 case ICmpInst::ICMP_NE: return Expression::ICMPNE;
232 case ICmpInst::ICMP_UGT: return Expression::ICMPUGT;
233 case ICmpInst::ICMP_UGE: return Expression::ICMPUGE;
234 case ICmpInst::ICMP_ULT: return Expression::ICMPULT;
235 case ICmpInst::ICMP_ULE: return Expression::ICMPULE;
236 case ICmpInst::ICMP_SGT: return Expression::ICMPSGT;
237 case ICmpInst::ICMP_SGE: return Expression::ICMPSGE;
238 case ICmpInst::ICMP_SLT: return Expression::ICMPSLT;
239 case ICmpInst::ICMP_SLE: return Expression::ICMPSLE;
242 switch (C->getPredicate()) {
243 default: // THIS SHOULD NEVER HAPPEN
244 llvm_unreachable("Comparison with unknown predicate?");
245 case FCmpInst::FCMP_OEQ: return Expression::FCMPOEQ;
246 case FCmpInst::FCMP_OGT: return Expression::FCMPOGT;
247 case FCmpInst::FCMP_OGE: return Expression::FCMPOGE;
248 case FCmpInst::FCMP_OLT: return Expression::FCMPOLT;
249 case FCmpInst::FCMP_OLE: return Expression::FCMPOLE;
250 case FCmpInst::FCMP_ONE: return Expression::FCMPONE;
251 case FCmpInst::FCMP_ORD: return Expression::FCMPORD;
252 case FCmpInst::FCMP_UNO: return Expression::FCMPUNO;
253 case FCmpInst::FCMP_UEQ: return Expression::FCMPUEQ;
254 case FCmpInst::FCMP_UGT: return Expression::FCMPUGT;
255 case FCmpInst::FCMP_UGE: return Expression::FCMPUGE;
256 case FCmpInst::FCMP_ULT: return Expression::FCMPULT;
257 case FCmpInst::FCMP_ULE: return Expression::FCMPULE;
258 case FCmpInst::FCMP_UNE: return Expression::FCMPUNE;
263 Expression::ExpressionOpcode ValueTable::getOpcode(CastInst* C) {
264 switch(C->getOpcode()) {
265 default: // THIS SHOULD NEVER HAPPEN
266 llvm_unreachable("Cast operator with unknown opcode?");
267 case Instruction::Trunc: return Expression::TRUNC;
268 case Instruction::ZExt: return Expression::ZEXT;
269 case Instruction::SExt: return Expression::SEXT;
270 case Instruction::FPToUI: return Expression::FPTOUI;
271 case Instruction::FPToSI: return Expression::FPTOSI;
272 case Instruction::UIToFP: return Expression::UITOFP;
273 case Instruction::SIToFP: return Expression::SITOFP;
274 case Instruction::FPTrunc: return Expression::FPTRUNC;
275 case Instruction::FPExt: return Expression::FPEXT;
276 case Instruction::PtrToInt: return Expression::PTRTOINT;
277 case Instruction::IntToPtr: return Expression::INTTOPTR;
278 case Instruction::BitCast: return Expression::BITCAST;
282 Expression ValueTable::create_expression(CallInst* C) {
285 e.type = C->getType();
286 e.function = C->getCalledFunction();
287 e.opcode = Expression::CALL;
289 for (CallInst::op_iterator I = C->op_begin()+1, E = C->op_end();
291 e.varargs.push_back(lookup_or_add(*I));
296 Expression ValueTable::create_expression(BinaryOperator* BO) {
298 e.varargs.push_back(lookup_or_add(BO->getOperand(0)));
299 e.varargs.push_back(lookup_or_add(BO->getOperand(1)));
301 e.type = BO->getType();
302 e.opcode = getOpcode(BO);
307 Expression ValueTable::create_expression(CmpInst* C) {
310 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
311 e.varargs.push_back(lookup_or_add(C->getOperand(1)));
313 e.type = C->getType();
314 e.opcode = getOpcode(C);
319 Expression ValueTable::create_expression(CastInst* C) {
322 e.varargs.push_back(lookup_or_add(C->getOperand(0)));
324 e.type = C->getType();
325 e.opcode = getOpcode(C);
330 Expression ValueTable::create_expression(ShuffleVectorInst* S) {
333 e.varargs.push_back(lookup_or_add(S->getOperand(0)));
334 e.varargs.push_back(lookup_or_add(S->getOperand(1)));
335 e.varargs.push_back(lookup_or_add(S->getOperand(2)));
337 e.type = S->getType();
338 e.opcode = Expression::SHUFFLE;
343 Expression ValueTable::create_expression(ExtractElementInst* E) {
346 e.varargs.push_back(lookup_or_add(E->getOperand(0)));
347 e.varargs.push_back(lookup_or_add(E->getOperand(1)));
349 e.type = E->getType();
350 e.opcode = Expression::EXTRACT;
355 Expression ValueTable::create_expression(InsertElementInst* I) {
358 e.varargs.push_back(lookup_or_add(I->getOperand(0)));
359 e.varargs.push_back(lookup_or_add(I->getOperand(1)));
360 e.varargs.push_back(lookup_or_add(I->getOperand(2)));
362 e.type = I->getType();
363 e.opcode = Expression::INSERT;
368 Expression ValueTable::create_expression(SelectInst* I) {
371 e.varargs.push_back(lookup_or_add(I->getCondition()));
372 e.varargs.push_back(lookup_or_add(I->getTrueValue()));
373 e.varargs.push_back(lookup_or_add(I->getFalseValue()));
375 e.type = I->getType();
376 e.opcode = Expression::SELECT;
381 Expression ValueTable::create_expression(GetElementPtrInst* G) {
384 e.varargs.push_back(lookup_or_add(G->getPointerOperand()));
386 e.type = G->getType();
387 e.opcode = Expression::GEP;
389 for (GetElementPtrInst::op_iterator I = G->idx_begin(), E = G->idx_end();
391 e.varargs.push_back(lookup_or_add(*I));
396 Expression ValueTable::create_expression(ExtractValueInst* E) {
399 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
400 for (ExtractValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
402 e.varargs.push_back(*II);
404 e.type = E->getType();
405 e.opcode = Expression::EXTRACTVALUE;
410 Expression ValueTable::create_expression(InsertValueInst* E) {
413 e.varargs.push_back(lookup_or_add(E->getAggregateOperand()));
414 e.varargs.push_back(lookup_or_add(E->getInsertedValueOperand()));
415 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
417 e.varargs.push_back(*II);
419 e.type = E->getType();
420 e.opcode = Expression::INSERTVALUE;
425 //===----------------------------------------------------------------------===//
426 // ValueTable External Functions
427 //===----------------------------------------------------------------------===//
429 /// add - Insert a value into the table with a specified value number.
430 void ValueTable::add(Value *V, uint32_t num) {
431 valueNumbering.insert(std::make_pair(V, num));
434 uint32_t ValueTable::lookup_or_add_call(CallInst* C) {
435 if (AA->doesNotAccessMemory(C)) {
436 Expression exp = create_expression(C);
437 uint32_t& e = expressionNumbering[exp];
438 if (!e) e = nextValueNumber++;
439 valueNumbering[C] = e;
441 } else if (AA->onlyReadsMemory(C)) {
442 Expression exp = create_expression(C);
443 uint32_t& e = expressionNumbering[exp];
445 e = nextValueNumber++;
446 valueNumbering[C] = e;
450 e = nextValueNumber++;
451 valueNumbering[C] = e;
455 MemDepResult local_dep = MD->getDependency(C);
457 if (!local_dep.isDef() && !local_dep.isNonLocal()) {
458 valueNumbering[C] = nextValueNumber;
459 return nextValueNumber++;
462 if (local_dep.isDef()) {
463 CallInst* local_cdep = cast<CallInst>(local_dep.getInst());
465 if (local_cdep->getNumOperands() != C->getNumOperands()) {
466 valueNumbering[C] = nextValueNumber;
467 return nextValueNumber++;
470 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
471 uint32_t c_vn = lookup_or_add(C->getOperand(i));
472 uint32_t cd_vn = lookup_or_add(local_cdep->getOperand(i));
474 valueNumbering[C] = nextValueNumber;
475 return nextValueNumber++;
479 uint32_t v = lookup_or_add(local_cdep);
480 valueNumbering[C] = v;
485 const MemoryDependenceAnalysis::NonLocalDepInfo &deps =
486 MD->getNonLocalCallDependency(CallSite(C));
487 // FIXME: call/call dependencies for readonly calls should return def, not
488 // clobber! Move the checking logic to MemDep!
491 // Check to see if we have a single dominating call instruction that is
493 for (unsigned i = 0, e = deps.size(); i != e; ++i) {
494 const NonLocalDepEntry *I = &deps[i];
495 // Ignore non-local dependencies.
496 if (I->getResult().isNonLocal())
499 // We don't handle non-depedencies. If we already have a call, reject
500 // instruction dependencies.
501 if (I->getResult().isClobber() || cdep != 0) {
506 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst());
507 // FIXME: All duplicated with non-local case.
508 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){
509 cdep = NonLocalDepCall;
518 valueNumbering[C] = nextValueNumber;
519 return nextValueNumber++;
522 if (cdep->getNumOperands() != C->getNumOperands()) {
523 valueNumbering[C] = nextValueNumber;
524 return nextValueNumber++;
526 for (unsigned i = 1; i < C->getNumOperands(); ++i) {
527 uint32_t c_vn = lookup_or_add(C->getOperand(i));
528 uint32_t cd_vn = lookup_or_add(cdep->getOperand(i));
530 valueNumbering[C] = nextValueNumber;
531 return nextValueNumber++;
535 uint32_t v = lookup_or_add(cdep);
536 valueNumbering[C] = v;
540 valueNumbering[C] = nextValueNumber;
541 return nextValueNumber++;
545 /// lookup_or_add - Returns the value number for the specified value, assigning
546 /// it a new number if it did not have one before.
547 uint32_t ValueTable::lookup_or_add(Value *V) {
548 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
549 if (VI != valueNumbering.end())
552 if (!isa<Instruction>(V)) {
553 valueNumbering[V] = nextValueNumber;
554 return nextValueNumber++;
557 Instruction* I = cast<Instruction>(V);
559 switch (I->getOpcode()) {
560 case Instruction::Call:
561 return lookup_or_add_call(cast<CallInst>(I));
562 case Instruction::Add:
563 case Instruction::FAdd:
564 case Instruction::Sub:
565 case Instruction::FSub:
566 case Instruction::Mul:
567 case Instruction::FMul:
568 case Instruction::UDiv:
569 case Instruction::SDiv:
570 case Instruction::FDiv:
571 case Instruction::URem:
572 case Instruction::SRem:
573 case Instruction::FRem:
574 case Instruction::Shl:
575 case Instruction::LShr:
576 case Instruction::AShr:
577 case Instruction::And:
578 case Instruction::Or :
579 case Instruction::Xor:
580 exp = create_expression(cast<BinaryOperator>(I));
582 case Instruction::ICmp:
583 case Instruction::FCmp:
584 exp = create_expression(cast<CmpInst>(I));
586 case Instruction::Trunc:
587 case Instruction::ZExt:
588 case Instruction::SExt:
589 case Instruction::FPToUI:
590 case Instruction::FPToSI:
591 case Instruction::UIToFP:
592 case Instruction::SIToFP:
593 case Instruction::FPTrunc:
594 case Instruction::FPExt:
595 case Instruction::PtrToInt:
596 case Instruction::IntToPtr:
597 case Instruction::BitCast:
598 exp = create_expression(cast<CastInst>(I));
600 case Instruction::Select:
601 exp = create_expression(cast<SelectInst>(I));
603 case Instruction::ExtractElement:
604 exp = create_expression(cast<ExtractElementInst>(I));
606 case Instruction::InsertElement:
607 exp = create_expression(cast<InsertElementInst>(I));
609 case Instruction::ShuffleVector:
610 exp = create_expression(cast<ShuffleVectorInst>(I));
612 case Instruction::ExtractValue:
613 exp = create_expression(cast<ExtractValueInst>(I));
615 case Instruction::InsertValue:
616 exp = create_expression(cast<InsertValueInst>(I));
618 case Instruction::GetElementPtr:
619 exp = create_expression(cast<GetElementPtrInst>(I));
622 valueNumbering[V] = nextValueNumber;
623 return nextValueNumber++;
626 uint32_t& e = expressionNumbering[exp];
627 if (!e) e = nextValueNumber++;
628 valueNumbering[V] = e;
632 /// lookup - Returns the value number of the specified value. Fails if
633 /// the value has not yet been numbered.
634 uint32_t ValueTable::lookup(Value *V) const {
635 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
636 assert(VI != valueNumbering.end() && "Value not numbered?");
640 /// clear - Remove all entries from the ValueTable
641 void ValueTable::clear() {
642 valueNumbering.clear();
643 expressionNumbering.clear();
647 /// erase - Remove a value from the value numbering
648 void ValueTable::erase(Value *V) {
649 valueNumbering.erase(V);
652 /// verifyRemoved - Verify that the value is removed from all internal data
654 void ValueTable::verifyRemoved(const Value *V) const {
655 for (DenseMap<Value*, uint32_t>::const_iterator
656 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
657 assert(I->first != V && "Inst still occurs in value numbering map!");
661 //===----------------------------------------------------------------------===//
663 //===----------------------------------------------------------------------===//
666 struct ValueNumberScope {
667 ValueNumberScope* parent;
668 DenseMap<uint32_t, Value*> table;
670 ValueNumberScope(ValueNumberScope* p) : parent(p) { }
676 class GVN : public FunctionPass {
677 bool runOnFunction(Function &F);
679 static char ID; // Pass identification, replacement for typeid
680 explicit GVN(bool nopre = false, bool noloads = false)
681 : FunctionPass(&ID), NoPRE(nopre), NoLoads(noloads), MD(0) { }
686 MemoryDependenceAnalysis *MD;
690 DenseMap<BasicBlock*, ValueNumberScope*> localAvail;
692 // This transformation requires dominator postdominator info
693 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
694 AU.addRequired<DominatorTree>();
696 AU.addRequired<MemoryDependenceAnalysis>();
697 AU.addRequired<AliasAnalysis>();
699 AU.addPreserved<DominatorTree>();
700 AU.addPreserved<AliasAnalysis>();
704 // FIXME: eliminate or document these better
705 bool processLoad(LoadInst* L,
706 SmallVectorImpl<Instruction*> &toErase);
707 bool processInstruction(Instruction *I,
708 SmallVectorImpl<Instruction*> &toErase);
709 bool processNonLocalLoad(LoadInst* L,
710 SmallVectorImpl<Instruction*> &toErase);
711 bool processBlock(BasicBlock *BB);
712 void dump(DenseMap<uint32_t, Value*>& d);
713 bool iterateOnFunction(Function &F);
714 Value *CollapsePhi(PHINode* p);
715 bool performPRE(Function& F);
716 Value *lookupNumber(BasicBlock *BB, uint32_t num);
717 void cleanupGlobalSets();
718 void verifyRemoved(const Instruction *I) const;
724 // createGVNPass - The public interface to this file...
725 FunctionPass *llvm::createGVNPass(bool NoPRE, bool NoLoads) {
726 return new GVN(NoPRE, NoLoads);
729 static RegisterPass<GVN> X("gvn",
730 "Global Value Numbering");
732 void GVN::dump(DenseMap<uint32_t, Value*>& d) {
734 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(),
735 E = d.end(); I != E; ++I) {
736 printf("%d\n", I->first);
742 static bool isSafeReplacement(PHINode* p, Instruction *inst) {
743 if (!isa<PHINode>(inst))
746 for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
748 if (PHINode* use_phi = dyn_cast<PHINode>(UI))
749 if (use_phi->getParent() == inst->getParent())
755 Value *GVN::CollapsePhi(PHINode *PN) {
756 Value *ConstVal = PN->hasConstantValue(DT);
757 if (!ConstVal) return 0;
759 Instruction *Inst = dyn_cast<Instruction>(ConstVal);
763 if (DT->dominates(Inst, PN))
764 if (isSafeReplacement(PN, Inst))
769 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
770 /// we're analyzing is fully available in the specified block. As we go, keep
771 /// track of which blocks we know are fully alive in FullyAvailableBlocks. This
772 /// map is actually a tri-state map with the following values:
773 /// 0) we know the block *is not* fully available.
774 /// 1) we know the block *is* fully available.
775 /// 2) we do not know whether the block is fully available or not, but we are
776 /// currently speculating that it will be.
777 /// 3) we are speculating for this block and have used that to speculate for
779 static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
780 DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
781 // Optimistically assume that the block is fully available and check to see
782 // if we already know about this block in one lookup.
783 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
784 FullyAvailableBlocks.insert(std::make_pair(BB, 2));
786 // If the entry already existed for this block, return the precomputed value.
788 // If this is a speculative "available" value, mark it as being used for
789 // speculation of other blocks.
790 if (IV.first->second == 2)
791 IV.first->second = 3;
792 return IV.first->second != 0;
795 // Otherwise, see if it is fully available in all predecessors.
796 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
798 // If this block has no predecessors, it isn't live-in here.
800 goto SpeculationFailure;
802 for (; PI != PE; ++PI)
803 // If the value isn't fully available in one of our predecessors, then it
804 // isn't fully available in this block either. Undo our previous
805 // optimistic assumption and bail out.
806 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
807 goto SpeculationFailure;
811 // SpeculationFailure - If we get here, we found out that this is not, after
812 // all, a fully-available block. We have a problem if we speculated on this and
813 // used the speculation to mark other blocks as available.
815 char &BBVal = FullyAvailableBlocks[BB];
817 // If we didn't speculate on this, just return with it set to false.
823 // If we did speculate on this value, we could have blocks set to 1 that are
824 // incorrect. Walk the (transitive) successors of this block and mark them as
826 SmallVector<BasicBlock*, 32> BBWorklist;
827 BBWorklist.push_back(BB);
829 while (!BBWorklist.empty()) {
830 BasicBlock *Entry = BBWorklist.pop_back_val();
831 // Note that this sets blocks to 0 (unavailable) if they happen to not
832 // already be in FullyAvailableBlocks. This is safe.
833 char &EntryVal = FullyAvailableBlocks[Entry];
834 if (EntryVal == 0) continue; // Already unavailable.
836 // Mark as unavailable.
839 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
840 BBWorklist.push_back(*I);
847 /// CanCoerceMustAliasedValueToLoad - Return true if
848 /// CoerceAvailableValueToLoadType will succeed.
849 static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal,
851 const TargetData &TD) {
852 // If the loaded or stored value is an first class array or struct, don't try
853 // to transform them. We need to be able to bitcast to integer.
854 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy) ||
855 isa<StructType>(StoredVal->getType()) ||
856 isa<ArrayType>(StoredVal->getType()))
859 // The store has to be at least as big as the load.
860 if (TD.getTypeSizeInBits(StoredVal->getType()) <
861 TD.getTypeSizeInBits(LoadTy))
868 /// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and
869 /// then a load from a must-aliased pointer of a different type, try to coerce
870 /// the stored value. LoadedTy is the type of the load we want to replace and
871 /// InsertPt is the place to insert new instructions.
873 /// If we can't do it, return null.
874 static Value *CoerceAvailableValueToLoadType(Value *StoredVal,
875 const Type *LoadedTy,
876 Instruction *InsertPt,
877 const TargetData &TD) {
878 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD))
881 const Type *StoredValTy = StoredVal->getType();
883 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy);
884 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy);
886 // If the store and reload are the same size, we can always reuse it.
887 if (StoreSize == LoadSize) {
888 if (isa<PointerType>(StoredValTy) && isa<PointerType>(LoadedTy)) {
889 // Pointer to Pointer -> use bitcast.
890 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt);
893 // Convert source pointers to integers, which can be bitcast.
894 if (isa<PointerType>(StoredValTy)) {
895 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
896 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
899 const Type *TypeToCastTo = LoadedTy;
900 if (isa<PointerType>(TypeToCastTo))
901 TypeToCastTo = TD.getIntPtrType(StoredValTy->getContext());
903 if (StoredValTy != TypeToCastTo)
904 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt);
906 // Cast to pointer if the load needs a pointer type.
907 if (isa<PointerType>(LoadedTy))
908 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt);
913 // If the loaded value is smaller than the available value, then we can
914 // extract out a piece from it. If the available value is too small, then we
915 // can't do anything.
916 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail");
918 // Convert source pointers to integers, which can be manipulated.
919 if (isa<PointerType>(StoredValTy)) {
920 StoredValTy = TD.getIntPtrType(StoredValTy->getContext());
921 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt);
924 // Convert vectors and fp to integer, which can be manipulated.
925 if (!isa<IntegerType>(StoredValTy)) {
926 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize);
927 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt);
930 // If this is a big-endian system, we need to shift the value down to the low
931 // bits so that a truncate will work.
932 if (TD.isBigEndian()) {
933 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize);
934 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt);
937 // Truncate the integer to the right size now.
938 const Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize);
939 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt);
941 if (LoadedTy == NewIntTy)
944 // If the result is a pointer, inttoptr.
945 if (isa<PointerType>(LoadedTy))
946 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt);
948 // Otherwise, bitcast.
949 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt);
952 /// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
953 /// be expressed as a base pointer plus a constant offset. Return the base and
954 /// offset to the caller.
955 static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
956 const TargetData &TD) {
957 Operator *PtrOp = dyn_cast<Operator>(Ptr);
958 if (PtrOp == 0) return Ptr;
960 // Just look through bitcasts.
961 if (PtrOp->getOpcode() == Instruction::BitCast)
962 return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
964 // If this is a GEP with constant indices, we can look through it.
965 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
966 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
968 gep_type_iterator GTI = gep_type_begin(GEP);
969 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
971 ConstantInt *OpC = cast<ConstantInt>(*I);
972 if (OpC->isZero()) continue;
974 // Handle a struct and array indices which add their offset to the pointer.
975 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
976 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
978 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
979 Offset += OpC->getSExtValue()*Size;
983 // Re-sign extend from the pointer size if needed to get overflow edge cases
985 unsigned PtrSize = TD.getPointerSizeInBits();
987 Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
989 return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
993 /// AnalyzeLoadFromClobberingWrite - This function is called when we have a
994 /// memdep query of a load that ends up being a clobbering memory write (store,
995 /// memset, memcpy, memmove). This means that the write *may* provide bits used
996 /// by the load but we can't be sure because the pointers don't mustalias.
998 /// Check this case to see if there is anything more we can do before we give
999 /// up. This returns -1 if we have to give up, or a byte number in the stored
1000 /// value of the piece that feeds the load.
1001 static int AnalyzeLoadFromClobberingWrite(const Type *LoadTy, Value *LoadPtr,
1003 uint64_t WriteSizeInBits,
1004 const TargetData &TD) {
1005 // If the loaded or stored value is an first class array or struct, don't try
1006 // to transform them. We need to be able to bitcast to integer.
1007 if (isa<StructType>(LoadTy) || isa<ArrayType>(LoadTy))
1010 int64_t StoreOffset = 0, LoadOffset = 0;
1011 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
1013 GetBaseWithConstantOffset(LoadPtr, LoadOffset, TD);
1014 if (StoreBase != LoadBase)
1017 // If the load and store are to the exact same address, they should have been
1018 // a must alias. AA must have gotten confused.
1019 // FIXME: Study to see if/when this happens.
1020 if (LoadOffset == StoreOffset) {
1022 errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
1023 << "Base = " << *StoreBase << "\n"
1024 << "Store Ptr = " << *WritePtr << "\n"
1025 << "Store Offs = " << StoreOffset << "\n"
1026 << "Load Ptr = " << *LoadPtr << "\n"
1027 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n";
1033 // If the load and store don't overlap at all, the store doesn't provide
1034 // anything to the load. In this case, they really don't alias at all, AA
1035 // must have gotten confused.
1036 // FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
1037 // remove this check, as it is duplicated with what we have below.
1038 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy);
1040 if ((WriteSizeInBits & 7) | (LoadSize & 7))
1042 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes.
1046 bool isAAFailure = false;
1047 if (StoreOffset < LoadOffset) {
1048 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
1050 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
1054 errs() << "STORE LOAD DEP WITH COMMON BASE:\n"
1055 << "Base = " << *StoreBase << "\n"
1056 << "Store Ptr = " << *WritePtr << "\n"
1057 << "Store Offs = " << StoreOffset << "\n"
1058 << "Load Ptr = " << *L->getPointerOperand() << "\n"
1059 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n";
1060 errs() << "'" << L->getParent()->getParent()->getName() << "'"
1067 // If the Load isn't completely contained within the stored bits, we don't
1068 // have all the bits to feed it. We could do something crazy in the future
1069 // (issue a smaller load then merge the bits in) but this seems unlikely to be
1071 if (StoreOffset > LoadOffset ||
1072 StoreOffset+StoreSize < LoadOffset+LoadSize)
1075 // Okay, we can do this transformation. Return the number of bytes into the
1076 // store that the load is.
1077 return LoadOffset-StoreOffset;
1080 /// AnalyzeLoadFromClobberingStore - This function is called when we have a
1081 /// memdep query of a load that ends up being a clobbering store.
1082 static int AnalyzeLoadFromClobberingStore(const Type *LoadTy, Value *LoadPtr,
1084 const TargetData &TD) {
1085 // Cannot handle reading from store of first-class aggregate yet.
1086 if (isa<StructType>(DepSI->getOperand(0)->getType()) ||
1087 isa<ArrayType>(DepSI->getOperand(0)->getType()))
1090 Value *StorePtr = DepSI->getPointerOperand();
1091 uint64_t StoreSize = TD.getTypeSizeInBits(StorePtr->getType());
1092 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1093 StorePtr, StoreSize, TD);
1096 static int AnalyzeLoadFromClobberingMemInst(const Type *LoadTy, Value *LoadPtr,
1098 const TargetData &TD) {
1099 // If the mem operation is a non-constant size, we can't handle it.
1100 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1101 if (SizeCst == 0) return -1;
1102 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1104 // If this is memset, we just need to see if the offset is valid in the size
1106 if (MI->getIntrinsicID() == Intrinsic::memset)
1107 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(),
1110 // If we have a memcpy/memmove, the only case we can handle is if this is a
1111 // copy from constant memory. In that case, we can read directly from the
1113 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1115 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1116 if (Src == 0) return -1;
1118 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1119 if (GV == 0 || !GV->isConstant()) return -1;
1121 // See if the access is within the bounds of the transfer.
1122 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr,
1123 MI->getDest(), MemSizeInBits, TD);
1127 // Otherwise, see if we can constant fold a load from the constant with the
1128 // offset applied as appropriate.
1129 Src = ConstantExpr::getBitCast(Src,
1130 llvm::Type::getInt8PtrTy(Src->getContext()));
1131 Constant *OffsetCst =
1132 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1133 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1134 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1135 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1141 /// GetStoreValueForLoad - This function is called when we have a
1142 /// memdep query of a load that ends up being a clobbering store. This means
1143 /// that the store *may* provide bits used by the load but we can't be sure
1144 /// because the pointers don't mustalias. Check this case to see if there is
1145 /// anything more we can do before we give up.
1146 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1148 Instruction *InsertPt, const TargetData &TD){
1149 LLVMContext &Ctx = SrcVal->getType()->getContext();
1151 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8;
1152 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1154 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1156 // Compute which bits of the stored value are being used by the load. Convert
1157 // to an integer type to start with.
1158 if (isa<PointerType>(SrcVal->getType()))
1159 SrcVal = Builder.CreatePtrToInt(SrcVal, TD.getIntPtrType(Ctx), "tmp");
1160 if (!isa<IntegerType>(SrcVal->getType()))
1161 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1164 // Shift the bits to the least significant depending on endianness.
1166 if (TD.isLittleEndian())
1167 ShiftAmt = Offset*8;
1169 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1172 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt, "tmp");
1174 if (LoadSize != StoreSize)
1175 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1178 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1181 /// GetMemInstValueForLoad - This function is called when we have a
1182 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1183 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1184 const Type *LoadTy, Instruction *InsertPt,
1185 const TargetData &TD){
1186 LLVMContext &Ctx = LoadTy->getContext();
1187 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1189 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1191 // We know that this method is only called when the mem transfer fully
1192 // provides the bits for the load.
1193 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1194 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1195 // independently of what the offset is.
1196 Value *Val = MSI->getValue();
1198 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1200 Value *OneElt = Val;
1202 // Splat the value out to the right number of bits.
1203 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1204 // If we can double the number of bytes set, do it.
1205 if (NumBytesSet*2 <= LoadSize) {
1206 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1207 Val = Builder.CreateOr(Val, ShVal);
1212 // Otherwise insert one byte at a time.
1213 Value *ShVal = Builder.CreateShl(Val, 1*8);
1214 Val = Builder.CreateOr(OneElt, ShVal);
1218 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1221 // Otherwise, this is a memcpy/memmove from a constant global.
1222 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1223 Constant *Src = cast<Constant>(MTI->getSource());
1225 // Otherwise, see if we can constant fold a load from the constant with the
1226 // offset applied as appropriate.
1227 Src = ConstantExpr::getBitCast(Src,
1228 llvm::Type::getInt8PtrTy(Src->getContext()));
1229 Constant *OffsetCst =
1230 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1231 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1232 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1233 return ConstantFoldLoadFromConstPtr(Src, &TD);
1238 struct AvailableValueInBlock {
1239 /// BB - The basic block in question.
1242 SimpleVal, // A simple offsetted value that is accessed.
1243 MemIntrin // A memory intrinsic which is loaded from.
1246 /// V - The value that is live out of the block.
1247 PointerIntPair<Value *, 1, ValType> Val;
1249 /// Offset - The byte offset in Val that is interesting for the load query.
1252 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1253 unsigned Offset = 0) {
1254 AvailableValueInBlock Res;
1256 Res.Val.setPointer(V);
1257 Res.Val.setInt(SimpleVal);
1258 Res.Offset = Offset;
1262 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1263 unsigned Offset = 0) {
1264 AvailableValueInBlock Res;
1266 Res.Val.setPointer(MI);
1267 Res.Val.setInt(MemIntrin);
1268 Res.Offset = Offset;
1272 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1273 Value *getSimpleValue() const {
1274 assert(isSimpleValue() && "Wrong accessor");
1275 return Val.getPointer();
1278 MemIntrinsic *getMemIntrinValue() const {
1279 assert(!isSimpleValue() && "Wrong accessor");
1280 return cast<MemIntrinsic>(Val.getPointer());
1284 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1285 /// construct SSA form, allowing us to eliminate LI. This returns the value
1286 /// that should be used at LI's definition site.
1287 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1288 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1289 const TargetData *TD,
1290 AliasAnalysis *AA) {
1291 SmallVector<PHINode*, 8> NewPHIs;
1292 SSAUpdater SSAUpdate(&NewPHIs);
1293 SSAUpdate.Initialize(LI);
1295 const Type *LoadTy = LI->getType();
1297 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1298 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1299 BasicBlock *BB = AV.BB;
1301 if (SSAUpdate.HasValueForBlock(BB))
1304 unsigned Offset = AV.Offset;
1306 Value *AvailableVal;
1307 if (AV.isSimpleValue()) {
1308 AvailableVal = AV.getSimpleValue();
1309 if (AvailableVal->getType() != LoadTy) {
1310 assert(TD && "Need target data to handle type mismatch case");
1311 AvailableVal = GetStoreValueForLoad(AvailableVal, Offset, LoadTy,
1312 BB->getTerminator(), *TD);
1314 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1315 << *AV.getSimpleValue() << '\n'
1316 << *AvailableVal << '\n' << "\n\n\n");
1319 AvailableVal = GetMemInstValueForLoad(AV.getMemIntrinValue(), Offset,
1320 LoadTy, BB->getTerminator(), *TD);
1321 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1322 << " " << *AV.getMemIntrinValue() << '\n'
1323 << *AvailableVal << '\n' << "\n\n\n");
1325 SSAUpdate.AddAvailableValue(BB, AvailableVal);
1328 // Perform PHI construction.
1329 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1331 // If new PHI nodes were created, notify alias analysis.
1332 if (isa<PointerType>(V->getType()))
1333 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1334 AA->copyValue(LI, NewPHIs[i]);
1339 static bool isLifetimeStart(Instruction *Inst) {
1340 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1341 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1345 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1346 /// non-local by performing PHI construction.
1347 bool GVN::processNonLocalLoad(LoadInst *LI,
1348 SmallVectorImpl<Instruction*> &toErase) {
1349 // Find the non-local dependencies of the load.
1350 SmallVector<NonLocalDepEntry, 64> Deps;
1351 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
1353 //DEBUG(errs() << "INVESTIGATING NONLOCAL LOAD: "
1354 // << Deps.size() << *LI << '\n');
1356 // If we had to process more than one hundred blocks to find the
1357 // dependencies, this load isn't worth worrying about. Optimizing
1358 // it will be too expensive.
1359 if (Deps.size() > 100)
1362 // If we had a phi translation failure, we'll have a single entry which is a
1363 // clobber in the current block. Reject this early.
1364 if (Deps.size() == 1 && Deps[0].getResult().isClobber()) {
1366 errs() << "GVN: non-local load ";
1367 WriteAsOperand(errs(), LI);
1368 errs() << " is clobbered by " << *Deps[0].getResult().getInst() << '\n';
1373 // Filter out useless results (non-locals, etc). Keep track of the blocks
1374 // where we have a value available in repl, also keep track of whether we see
1375 // dependencies that produce an unknown value for the load (such as a call
1376 // that could potentially clobber the load).
1377 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1378 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1380 const TargetData *TD = 0;
1382 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1383 BasicBlock *DepBB = Deps[i].getBB();
1384 MemDepResult DepInfo = Deps[i].getResult();
1386 if (DepInfo.isClobber()) {
1387 // The address being loaded in this non-local block may not be the same as
1388 // the pointer operand of the load if PHI translation occurs. Make sure
1389 // to consider the right address.
1390 Value *Address = Deps[i].getAddress();
1392 // If the dependence is to a store that writes to a superset of the bits
1393 // read by the load, we can extract the bits we need for the load from the
1395 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1397 TD = getAnalysisIfAvailable<TargetData>();
1398 if (TD && Address) {
1399 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address,
1402 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1403 DepSI->getOperand(0),
1410 // If the clobbering value is a memset/memcpy/memmove, see if we can
1411 // forward a value on from it.
1412 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1414 TD = getAnalysisIfAvailable<TargetData>();
1415 if (TD && Address) {
1416 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address,
1419 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1426 UnavailableBlocks.push_back(DepBB);
1430 Instruction *DepInst = DepInfo.getInst();
1432 // Loading the allocation -> undef.
1433 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1434 // Loading immediately after lifetime begin -> undef.
1435 isLifetimeStart(DepInst)) {
1436 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1437 UndefValue::get(LI->getType())));
1441 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1442 // Reject loads and stores that are to the same address but are of
1443 // different types if we have to.
1444 if (S->getOperand(0)->getType() != LI->getType()) {
1446 TD = getAnalysisIfAvailable<TargetData>();
1448 // If the stored value is larger or equal to the loaded value, we can
1450 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0),
1451 LI->getType(), *TD)) {
1452 UnavailableBlocks.push_back(DepBB);
1457 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1462 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1463 // If the types mismatch and we can't handle it, reject reuse of the load.
1464 if (LD->getType() != LI->getType()) {
1466 TD = getAnalysisIfAvailable<TargetData>();
1468 // If the stored value is larger or equal to the loaded value, we can
1470 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1471 UnavailableBlocks.push_back(DepBB);
1475 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD));
1479 UnavailableBlocks.push_back(DepBB);
1483 // If we have no predecessors that produce a known value for this load, exit
1485 if (ValuesPerBlock.empty()) return false;
1487 // If all of the instructions we depend on produce a known value for this
1488 // load, then it is fully redundant and we can use PHI insertion to compute
1489 // its value. Insert PHIs and remove the fully redundant value now.
1490 if (UnavailableBlocks.empty()) {
1491 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1493 // Perform PHI construction.
1494 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD,
1495 VN.getAliasAnalysis());
1496 LI->replaceAllUsesWith(V);
1498 if (isa<PHINode>(V))
1500 if (isa<PointerType>(V->getType()))
1501 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) // If haven't found any, bail now.
1534 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1536 if (Blockers.count(TmpBB))
1538 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1539 allSingleSucc = false;
1545 // If we have a repl set with LI itself in it, this means we have a loop where
1546 // at least one of the values is LI. Since this means that we won't be able
1547 // to eliminate LI even if we insert uses in the other predecessors, we will
1548 // end up increasing code size. Reject this by scanning for LI.
1549 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1550 if (ValuesPerBlock[i].isSimpleValue() &&
1551 ValuesPerBlock[i].getSimpleValue() == LI)
1554 // FIXME: It is extremely unclear what this loop is doing, other than
1555 // artificially restricting loadpre.
1558 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1559 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1560 if (AV.isSimpleValue())
1561 // "Hot" Instruction is in some loop (because it dominates its dep.
1563 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1564 if (DT->dominates(LI, I)) {
1570 // We are interested only in "hot" instructions. We don't want to do any
1571 // mis-optimizations here.
1576 // Okay, we have some hope :). Check to see if the loaded value is fully
1577 // available in all but one predecessor.
1578 // FIXME: If we could restructure the CFG, we could make a common pred with
1579 // all the preds that don't have an available LI and insert a new load into
1581 BasicBlock *UnavailablePred = 0;
1583 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1584 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1585 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1586 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1587 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1589 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1591 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1594 // If this load is not available in multiple predecessors, reject it.
1595 if (UnavailablePred && UnavailablePred != *PI)
1597 UnavailablePred = *PI;
1600 assert(UnavailablePred != 0 &&
1601 "Fully available value should be eliminated above!");
1603 // We don't currently handle critical edges :(
1604 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1605 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1606 << UnavailablePred->getName() << "': " << *LI << '\n');
1610 // Do PHI translation to get its value in the predecessor if necessary. The
1611 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1613 SmallVector<Instruction*, 8> NewInsts;
1615 // If all preds have a single successor, then we know it is safe to insert the
1616 // load on the pred (?!?), so we can insert code to materialize the pointer if
1617 // it is not available.
1618 PHITransAddr Address(LI->getOperand(0), TD);
1620 if (allSingleSucc) {
1621 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1624 Address.PHITranslateValue(LoadBB, UnavailablePred);
1625 LoadPtr = Address.getAddr();
1627 // Make sure the value is live in the predecessor.
1628 if (Instruction *Inst = dyn_cast_or_null<Instruction>(LoadPtr))
1629 if (!DT->dominates(Inst->getParent(), UnavailablePred))
1633 // If we couldn't find or insert a computation of this phi translated value,
1636 assert(NewInsts.empty() && "Shouldn't insert insts on failure");
1637 DEBUG(errs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1638 << *LI->getOperand(0) << "\n");
1642 // Assign value numbers to these new instructions.
1643 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1644 // FIXME: We really _ought_ to insert these value numbers into their
1645 // parent's availability map. However, in doing so, we risk getting into
1646 // ordering issues. If a block hasn't been processed yet, we would be
1647 // marking a value as AVAIL-IN, which isn't what we intend.
1648 VN.lookup_or_add(NewInsts[i]);
1651 // Make sure it is valid to move this load here. We have to watch out for:
1652 // @1 = getelementptr (i8* p, ...
1653 // test p and branch if == 0
1655 // It is valid to have the getelementptr before the test, even if p can be 0,
1656 // as getelementptr only does address arithmetic.
1657 // If we are not pushing the value through any multiple-successor blocks
1658 // we do not have this case. Otherwise, check that the load is safe to
1659 // put anywhere; this can be improved, but should be conservatively safe.
1660 if (!allSingleSucc &&
1661 // FIXME: REEVALUTE THIS.
1662 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) {
1663 assert(NewInsts.empty() && "Should not have inserted instructions");
1667 // Okay, we can eliminate this load by inserting a reload in the predecessor
1668 // and using PHI construction to get the value in the other predecessors, do
1670 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1671 DEBUG(if (!NewInsts.empty())
1672 errs() << "INSERTED " << NewInsts.size() << " INSTS: "
1673 << *NewInsts.back() << '\n');
1675 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1677 UnavailablePred->getTerminator());
1679 // Add the newly created load.
1680 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,NewLoad));
1682 // Perform PHI construction.
1683 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD,
1684 VN.getAliasAnalysis());
1685 LI->replaceAllUsesWith(V);
1686 if (isa<PHINode>(V))
1688 if (isa<PointerType>(V->getType()))
1689 MD->invalidateCachedPointerInfo(V);
1690 toErase.push_back(LI);
1695 /// processLoad - Attempt to eliminate a load, first by eliminating it
1696 /// locally, and then attempting non-local elimination if that fails.
1697 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1701 if (L->isVolatile())
1704 // ... to a pointer that has been loaded from before...
1705 MemDepResult Dep = MD->getDependency(L);
1707 // If the value isn't available, don't do anything!
1708 if (Dep.isClobber()) {
1709 // Check to see if we have something like this:
1710 // store i32 123, i32* %P
1711 // %A = bitcast i32* %P to i8*
1712 // %B = gep i8* %A, i32 1
1715 // We could do that by recognizing if the clobber instructions are obviously
1716 // a common base + constant offset, and if the previous store (or memset)
1717 // completely covers this load. This sort of thing can happen in bitfield
1719 Value *AvailVal = 0;
1720 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1721 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1722 int Offset = AnalyzeLoadFromClobberingStore(L->getType(),
1723 L->getPointerOperand(),
1726 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset,
1727 L->getType(), L, *TD);
1730 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1731 // a value on from it.
1732 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1733 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1734 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(),
1735 L->getPointerOperand(),
1738 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1743 DEBUG(errs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1744 << *AvailVal << '\n' << *L << "\n\n\n");
1746 // Replace the load!
1747 L->replaceAllUsesWith(AvailVal);
1748 if (isa<PointerType>(AvailVal->getType()))
1749 MD->invalidateCachedPointerInfo(AvailVal);
1750 toErase.push_back(L);
1756 // fast print dep, using operator<< on instruction would be too slow
1757 errs() << "GVN: load ";
1758 WriteAsOperand(errs(), L);
1759 Instruction *I = Dep.getInst();
1760 errs() << " is clobbered by " << *I << '\n';
1765 // If it is defined in another block, try harder.
1766 if (Dep.isNonLocal())
1767 return processNonLocalLoad(L, toErase);
1769 Instruction *DepInst = Dep.getInst();
1770 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1771 Value *StoredVal = DepSI->getOperand(0);
1773 // The store and load are to a must-aliased pointer, but they may not
1774 // actually have the same type. See if we know how to reuse the stored
1775 // value (depending on its type).
1776 const TargetData *TD = 0;
1777 if (StoredVal->getType() != L->getType()) {
1778 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1779 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1784 DEBUG(errs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1785 << '\n' << *L << "\n\n\n");
1792 L->replaceAllUsesWith(StoredVal);
1793 if (isa<PointerType>(StoredVal->getType()))
1794 MD->invalidateCachedPointerInfo(StoredVal);
1795 toErase.push_back(L);
1800 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1801 Value *AvailableVal = DepLI;
1803 // The loads are of a must-aliased pointer, but they may not actually have
1804 // the same type. See if we know how to reuse the previously loaded value
1805 // (depending on its type).
1806 const TargetData *TD = 0;
1807 if (DepLI->getType() != L->getType()) {
1808 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1809 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1810 if (AvailableVal == 0)
1813 DEBUG(errs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1814 << "\n" << *L << "\n\n\n");
1821 L->replaceAllUsesWith(AvailableVal);
1822 if (isa<PointerType>(DepLI->getType()))
1823 MD->invalidateCachedPointerInfo(DepLI);
1824 toErase.push_back(L);
1829 // If this load really doesn't depend on anything, then we must be loading an
1830 // undef value. This can happen when loading for a fresh allocation with no
1831 // intervening stores, for example.
1832 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1833 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1834 toErase.push_back(L);
1839 // If this load occurs either right after a lifetime begin,
1840 // then the loaded value is undefined.
1841 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1842 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1843 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1844 toErase.push_back(L);
1853 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1854 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1855 if (I == localAvail.end())
1858 ValueNumberScope *Locals = I->second;
1860 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num);
1861 if (I != Locals->table.end())
1863 Locals = Locals->parent;
1870 /// processInstruction - When calculating availability, handle an instruction
1871 /// by inserting it into the appropriate sets
1872 bool GVN::processInstruction(Instruction *I,
1873 SmallVectorImpl<Instruction*> &toErase) {
1874 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1875 bool Changed = processLoad(LI, toErase);
1878 unsigned Num = VN.lookup_or_add(LI);
1879 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI));
1885 uint32_t NextNum = VN.getNextUnusedValueNumber();
1886 unsigned Num = VN.lookup_or_add(I);
1888 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1889 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1891 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1894 Value *BranchCond = BI->getCondition();
1895 uint32_t CondVN = VN.lookup_or_add(BranchCond);
1897 BasicBlock *TrueSucc = BI->getSuccessor(0);
1898 BasicBlock *FalseSucc = BI->getSuccessor(1);
1900 if (TrueSucc->getSinglePredecessor())
1901 localAvail[TrueSucc]->table[CondVN] =
1902 ConstantInt::getTrue(TrueSucc->getContext());
1903 if (FalseSucc->getSinglePredecessor())
1904 localAvail[FalseSucc]->table[CondVN] =
1905 ConstantInt::getFalse(TrueSucc->getContext());
1909 // Allocations are always uniquely numbered, so we can save time and memory
1910 // by fast failing them.
1911 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1912 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1916 // Collapse PHI nodes
1917 if (PHINode* p = dyn_cast<PHINode>(I)) {
1918 Value *constVal = CollapsePhi(p);
1921 p->replaceAllUsesWith(constVal);
1922 if (MD && isa<PointerType>(constVal->getType()))
1923 MD->invalidateCachedPointerInfo(constVal);
1926 toErase.push_back(p);
1928 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1931 // If the number we were assigned was a brand new VN, then we don't
1932 // need to do a lookup to see if the number already exists
1933 // somewhere in the domtree: it can't!
1934 } else if (Num == NextNum) {
1935 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1937 // Perform fast-path value-number based elimination of values inherited from
1939 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1942 I->replaceAllUsesWith(repl);
1943 if (MD && isa<PointerType>(repl->getType()))
1944 MD->invalidateCachedPointerInfo(repl);
1945 toErase.push_back(I);
1949 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1955 /// runOnFunction - This is the main transformation entry point for a function.
1956 bool GVN::runOnFunction(Function& F) {
1958 MD = &getAnalysis<MemoryDependenceAnalysis>();
1959 DT = &getAnalysis<DominatorTree>();
1960 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1964 bool Changed = false;
1965 bool ShouldContinue = true;
1967 // Merge unconditional branches, allowing PRE to catch more
1968 // optimization opportunities.
1969 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1970 BasicBlock *BB = FI;
1972 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1973 if (removedBlock) NumGVNBlocks++;
1975 Changed |= removedBlock;
1978 unsigned Iteration = 0;
1980 while (ShouldContinue) {
1981 DEBUG(errs() << "GVN iteration: " << Iteration << "\n");
1982 ShouldContinue = iterateOnFunction(F);
1983 Changed |= ShouldContinue;
1988 bool PREChanged = true;
1989 while (PREChanged) {
1990 PREChanged = performPRE(F);
1991 Changed |= PREChanged;
1994 // FIXME: Should perform GVN again after PRE does something. PRE can move
1995 // computations into blocks where they become fully redundant. Note that
1996 // we can't do this until PRE's critical edge splitting updates memdep.
1997 // Actually, when this happens, we should just fully integrate PRE into GVN.
1999 cleanupGlobalSets();
2005 bool GVN::processBlock(BasicBlock *BB) {
2006 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
2007 // incrementing BI before processing an instruction).
2008 SmallVector<Instruction*, 8> toErase;
2009 bool ChangedFunction = false;
2011 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
2013 ChangedFunction |= processInstruction(BI, toErase);
2014 if (toErase.empty()) {
2019 // If we need some instructions deleted, do it now.
2020 NumGVNInstr += toErase.size();
2022 // Avoid iterator invalidation.
2023 bool AtStart = BI == BB->begin();
2027 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2028 E = toErase.end(); I != E; ++I) {
2029 DEBUG(errs() << "GVN removed: " << **I << '\n');
2030 if (MD) MD->removeInstruction(*I);
2031 (*I)->eraseFromParent();
2032 DEBUG(verifyRemoved(*I));
2042 return ChangedFunction;
2045 /// performPRE - Perform a purely local form of PRE that looks for diamond
2046 /// control flow patterns and attempts to perform simple PRE at the join point.
2047 bool GVN::performPRE(Function &F) {
2048 bool Changed = false;
2049 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
2050 DenseMap<BasicBlock*, Value*> predMap;
2051 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2052 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2053 BasicBlock *CurrentBlock = *DI;
2055 // Nothing to PRE in the entry block.
2056 if (CurrentBlock == &F.getEntryBlock()) continue;
2058 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2059 BE = CurrentBlock->end(); BI != BE; ) {
2060 Instruction *CurInst = BI++;
2062 if (isa<AllocaInst>(CurInst) ||
2063 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2064 CurInst->getType()->isVoidTy() ||
2065 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2066 isa<DbgInfoIntrinsic>(CurInst))
2069 uint32_t ValNo = VN.lookup(CurInst);
2071 // Look for the predecessors for PRE opportunities. We're
2072 // only trying to solve the basic diamond case, where
2073 // a value is computed in the successor and one predecessor,
2074 // but not the other. We also explicitly disallow cases
2075 // where the successor is its own predecessor, because they're
2076 // more complicated to get right.
2077 unsigned NumWith = 0;
2078 unsigned NumWithout = 0;
2079 BasicBlock *PREPred = 0;
2082 for (pred_iterator PI = pred_begin(CurrentBlock),
2083 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2084 // We're not interested in PRE where the block is its
2085 // own predecessor, on in blocks with predecessors
2086 // that are not reachable.
2087 if (*PI == CurrentBlock) {
2090 } else if (!localAvail.count(*PI)) {
2095 DenseMap<uint32_t, Value*>::iterator predV =
2096 localAvail[*PI]->table.find(ValNo);
2097 if (predV == localAvail[*PI]->table.end()) {
2100 } else if (predV->second == CurInst) {
2103 predMap[*PI] = predV->second;
2108 // Don't do PRE when it might increase code size, i.e. when
2109 // we would need to insert instructions in more than one pred.
2110 if (NumWithout != 1 || NumWith == 0)
2113 // Don't do PRE across indirect branch.
2114 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2117 // We can't do PRE safely on a critical edge, so instead we schedule
2118 // the edge to be split and perform the PRE the next time we iterate
2120 unsigned SuccNum = 0;
2121 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
2123 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
2128 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2129 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2133 // Instantiate the expression the in predecessor that lacked it.
2134 // Because we are going top-down through the block, all value numbers
2135 // will be available in the predecessor by the time we need them. Any
2136 // that weren't original present will have been instantiated earlier
2138 Instruction *PREInstr = CurInst->clone();
2139 bool success = true;
2140 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2141 Value *Op = PREInstr->getOperand(i);
2142 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2145 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
2146 PREInstr->setOperand(i, V);
2153 // Fail out if we encounter an operand that is not available in
2154 // the PRE predecessor. This is typically because of loads which
2155 // are not value numbered precisely.
2158 DEBUG(verifyRemoved(PREInstr));
2162 PREInstr->insertBefore(PREPred->getTerminator());
2163 PREInstr->setName(CurInst->getName() + ".pre");
2164 predMap[PREPred] = PREInstr;
2165 VN.add(PREInstr, ValNo);
2168 // Update the availability map to include the new instruction.
2169 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr));
2171 // Create a PHI to make the value available in this block.
2172 PHINode* Phi = PHINode::Create(CurInst->getType(),
2173 CurInst->getName() + ".pre-phi",
2174 CurrentBlock->begin());
2175 for (pred_iterator PI = pred_begin(CurrentBlock),
2176 PE = pred_end(CurrentBlock); PI != PE; ++PI)
2177 Phi->addIncoming(predMap[*PI], *PI);
2180 localAvail[CurrentBlock]->table[ValNo] = Phi;
2182 CurInst->replaceAllUsesWith(Phi);
2183 if (MD && isa<PointerType>(Phi->getType()))
2184 MD->invalidateCachedPointerInfo(Phi);
2187 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n');
2188 if (MD) MD->removeInstruction(CurInst);
2189 CurInst->eraseFromParent();
2190 DEBUG(verifyRemoved(CurInst));
2195 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
2196 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
2197 SplitCriticalEdge(I->first, I->second, this);
2199 return Changed || toSplit.size();
2202 /// iterateOnFunction - Executes one iteration of GVN
2203 bool GVN::iterateOnFunction(Function &F) {
2204 cleanupGlobalSets();
2206 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2207 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
2209 localAvail[DI->getBlock()] =
2210 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
2212 localAvail[DI->getBlock()] = new ValueNumberScope(0);
2215 // Top-down walk of the dominator tree
2216 bool Changed = false;
2218 // Needed for value numbering with phi construction to work.
2219 ReversePostOrderTraversal<Function*> RPOT(&F);
2220 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2221 RE = RPOT.end(); RI != RE; ++RI)
2222 Changed |= processBlock(*RI);
2224 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2225 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2226 Changed |= processBlock(DI->getBlock());
2232 void GVN::cleanupGlobalSets() {
2235 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
2236 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
2241 /// verifyRemoved - Verify that the specified instruction does not occur in our
2242 /// internal data structures.
2243 void GVN::verifyRemoved(const Instruction *Inst) const {
2244 VN.verifyRemoved(Inst);
2246 // Walk through the value number scope to make sure the instruction isn't
2247 // ferreted away in it.
2248 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
2249 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
2250 const ValueNumberScope *VNS = I->second;
2253 for (DenseMap<uint32_t, Value*>::const_iterator
2254 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
2255 assert(II->second != Inst && "Inst still in value numbering scope!");