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 MemoryDependenceAnalysis::NonLocalDepEntry *I = &deps[i];
495 // Ignore non-local dependencies.
496 if (I->second.isNonLocal())
499 // We don't handle non-depedencies. If we already have a call, reject
500 // instruction dependencies.
501 if (I->second.isClobber() || cdep != 0) {
506 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->second.getInst());
507 // FIXME: All duplicated with non-local case.
508 if (NonLocalDepCall && DT->properlyDominates(I->first, 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(LoadInst *L, Value *WritePtr,
1002 uint64_t WriteSizeInBits,
1003 const TargetData &TD) {
1004 // If the loaded or stored value is an first class array or struct, don't try
1005 // to transform them. We need to be able to bitcast to integer.
1006 if (isa<StructType>(L->getType()) || isa<ArrayType>(L->getType()))
1009 int64_t StoreOffset = 0, LoadOffset = 0;
1010 Value *StoreBase = GetBaseWithConstantOffset(WritePtr, StoreOffset, TD);
1012 GetBaseWithConstantOffset(L->getPointerOperand(), LoadOffset, TD);
1013 if (StoreBase != LoadBase)
1016 // If the load and store are to the exact same address, they should have been
1017 // a must alias. AA must have gotten confused.
1018 // FIXME: Study to see if/when this happens.
1019 if (LoadOffset == StoreOffset) {
1021 errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
1022 << "Base = " << *StoreBase << "\n"
1023 << "Store Ptr = " << *WritePtr << "\n"
1024 << "Store Offs = " << StoreOffset << "\n"
1025 << "Load Ptr = " << *L->getPointerOperand() << "\n"
1026 << "Load Offs = " << LoadOffset << " - " << *L << "\n\n";
1027 errs() << "'" << L->getParent()->getParent()->getName() << "'"
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(L->getType());
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() << "'"
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(LoadInst *L, StoreInst *DepSI,
1082 const TargetData &TD) {
1083 // Cannot handle reading from store of first-class aggregate yet.
1084 if (isa<StructType>(DepSI->getOperand(0)->getType()) ||
1085 isa<ArrayType>(DepSI->getOperand(0)->getType()))
1088 Value *StorePtr = DepSI->getPointerOperand();
1089 uint64_t StoreSize = TD.getTypeSizeInBits(StorePtr->getType());
1090 return AnalyzeLoadFromClobberingWrite(L, StorePtr, StoreSize, TD);
1093 static int AnalyzeLoadFromClobberingMemInst(LoadInst *L, MemIntrinsic *MI,
1094 const TargetData &TD) {
1095 // If the mem operation is a non-constant size, we can't handle it.
1096 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
1097 if (SizeCst == 0) return -1;
1098 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
1100 // If this is memset, we just need to see if the offset is valid in the size
1102 if (MI->getIntrinsicID() == Intrinsic::memset)
1103 return AnalyzeLoadFromClobberingWrite(L, MI->getDest(), MemSizeInBits, TD);
1105 // If we have a memcpy/memmove, the only case we can handle is if this is a
1106 // copy from constant memory. In that case, we can read directly from the
1108 MemTransferInst *MTI = cast<MemTransferInst>(MI);
1110 Constant *Src = dyn_cast<Constant>(MTI->getSource());
1111 if (Src == 0) return -1;
1113 GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
1114 if (GV == 0 || !GV->isConstant()) return -1;
1116 // See if the access is within the bounds of the transfer.
1118 AnalyzeLoadFromClobberingWrite(L, MI->getDest(), MemSizeInBits, TD);
1122 // Otherwise, see if we can constant fold a load from the constant with the
1123 // offset applied as appropriate.
1124 Src = ConstantExpr::getBitCast(Src,
1125 llvm::Type::getInt8PtrTy(Src->getContext()));
1126 Constant *OffsetCst =
1127 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1128 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1129 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(L->getType()));
1130 if (ConstantFoldLoadFromConstPtr(Src, &TD))
1136 /// GetStoreValueForLoad - This function is called when we have a
1137 /// memdep query of a load that ends up being a clobbering store. This means
1138 /// that the store *may* provide bits used by the load but we can't be sure
1139 /// because the pointers don't mustalias. Check this case to see if there is
1140 /// anything more we can do before we give up.
1141 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
1143 Instruction *InsertPt, const TargetData &TD){
1144 LLVMContext &Ctx = SrcVal->getType()->getContext();
1146 uint64_t StoreSize = TD.getTypeSizeInBits(SrcVal->getType())/8;
1147 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1150 // Compute which bits of the stored value are being used by the load. Convert
1151 // to an integer type to start with.
1152 if (isa<PointerType>(SrcVal->getType()))
1153 SrcVal = new PtrToIntInst(SrcVal, TD.getIntPtrType(Ctx), "tmp", InsertPt);
1154 if (!isa<IntegerType>(SrcVal->getType()))
1155 SrcVal = new BitCastInst(SrcVal, IntegerType::get(Ctx, StoreSize*8),
1158 // Shift the bits to the least significant depending on endianness.
1160 if (TD.isLittleEndian())
1161 ShiftAmt = Offset*8;
1163 ShiftAmt = (StoreSize-LoadSize-Offset)*8;
1166 SrcVal = BinaryOperator::CreateLShr(SrcVal,
1167 ConstantInt::get(SrcVal->getType(), ShiftAmt), "tmp", InsertPt);
1169 if (LoadSize != StoreSize)
1170 SrcVal = new TruncInst(SrcVal, IntegerType::get(Ctx, LoadSize*8),
1173 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD);
1176 /// GetMemInstValueForLoad - This function is called when we have a
1177 /// memdep query of a load that ends up being a clobbering mem intrinsic.
1178 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
1179 const Type *LoadTy, Instruction *InsertPt,
1180 const TargetData &TD){
1181 LLVMContext &Ctx = LoadTy->getContext();
1182 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8;
1184 IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
1186 // We know that this method is only called when the mem transfer fully
1187 // provides the bits for the load.
1188 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
1189 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
1190 // independently of what the offset is.
1191 Value *Val = MSI->getValue();
1193 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8));
1195 Value *OneElt = Val;
1197 // Splat the value out to the right number of bits.
1198 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) {
1199 // If we can double the number of bytes set, do it.
1200 if (NumBytesSet*2 <= LoadSize) {
1201 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8);
1202 Val = Builder.CreateOr(Val, ShVal);
1207 // Otherwise insert one byte at a time.
1208 Value *ShVal = Builder.CreateShl(Val, 1*8);
1209 Val = Builder.CreateOr(OneElt, ShVal);
1213 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
1216 // Otherwise, this is a memcpy/memmove from a constant global.
1217 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
1218 Constant *Src = cast<Constant>(MTI->getSource());
1220 // Otherwise, see if we can constant fold a load from the constant with the
1221 // offset applied as appropriate.
1222 Src = ConstantExpr::getBitCast(Src,
1223 llvm::Type::getInt8PtrTy(Src->getContext()));
1224 Constant *OffsetCst =
1225 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
1226 Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
1227 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
1228 return ConstantFoldLoadFromConstPtr(Src, &TD);
1233 struct AvailableValueInBlock {
1234 /// BB - The basic block in question.
1237 SimpleVal, // A simple offsetted value that is accessed.
1238 MemIntrin // A memory intrinsic which is loaded from.
1241 /// V - The value that is live out of the block.
1242 PointerIntPair<Value *, 1, ValType> Val;
1244 /// Offset - The byte offset in Val that is interesting for the load query.
1247 static AvailableValueInBlock get(BasicBlock *BB, Value *V,
1248 unsigned Offset = 0) {
1249 AvailableValueInBlock Res;
1251 Res.Val.setPointer(V);
1252 Res.Val.setInt(SimpleVal);
1253 Res.Offset = Offset;
1257 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI,
1258 unsigned Offset = 0) {
1259 AvailableValueInBlock Res;
1261 Res.Val.setPointer(MI);
1262 Res.Val.setInt(MemIntrin);
1263 Res.Offset = Offset;
1267 bool isSimpleValue() const { return Val.getInt() == SimpleVal; }
1268 Value *getSimpleValue() const {
1269 assert(isSimpleValue() && "Wrong accessor");
1270 return Val.getPointer();
1273 MemIntrinsic *getMemIntrinValue() const {
1274 assert(!isSimpleValue() && "Wrong accessor");
1275 return cast<MemIntrinsic>(Val.getPointer());
1279 /// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock,
1280 /// construct SSA form, allowing us to eliminate LI. This returns the value
1281 /// that should be used at LI's definition site.
1282 static Value *ConstructSSAForLoadSet(LoadInst *LI,
1283 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock,
1284 const TargetData *TD,
1285 AliasAnalysis *AA) {
1286 SmallVector<PHINode*, 8> NewPHIs;
1287 SSAUpdater SSAUpdate(&NewPHIs);
1288 SSAUpdate.Initialize(LI);
1290 const Type *LoadTy = LI->getType();
1292 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1293 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1294 BasicBlock *BB = AV.BB;
1296 if (SSAUpdate.HasValueForBlock(BB))
1299 unsigned Offset = AV.Offset;
1301 Value *AvailableVal;
1302 if (AV.isSimpleValue()) {
1303 AvailableVal = AV.getSimpleValue();
1304 if (AvailableVal->getType() != LoadTy) {
1305 assert(TD && "Need target data to handle type mismatch case");
1306 AvailableVal = GetStoreValueForLoad(AvailableVal, Offset, LoadTy,
1307 BB->getTerminator(), *TD);
1309 DEBUG(errs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " "
1310 << *AV.getSimpleValue() << '\n'
1311 << *AvailableVal << '\n' << "\n\n\n");
1314 AvailableVal = GetMemInstValueForLoad(AV.getMemIntrinValue(), Offset,
1315 LoadTy, BB->getTerminator(), *TD);
1316 DEBUG(errs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset
1317 << " " << *AV.getMemIntrinValue() << '\n'
1318 << *AvailableVal << '\n' << "\n\n\n");
1320 SSAUpdate.AddAvailableValue(BB, AvailableVal);
1323 // Perform PHI construction.
1324 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
1326 // If new PHI nodes were created, notify alias analysis.
1327 if (isa<PointerType>(V->getType()))
1328 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
1329 AA->copyValue(LI, NewPHIs[i]);
1334 static bool isLifetimeStart(Instruction *Inst) {
1335 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst))
1336 return II->getIntrinsicID() == Intrinsic::lifetime_start;
1340 /// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
1341 /// non-local by performing PHI construction.
1342 bool GVN::processNonLocalLoad(LoadInst *LI,
1343 SmallVectorImpl<Instruction*> &toErase) {
1344 // Find the non-local dependencies of the load.
1345 SmallVector<MemoryDependenceAnalysis::NonLocalDepEntry, 64> Deps;
1346 MD->getNonLocalPointerDependency(LI->getOperand(0), true, LI->getParent(),
1348 //DEBUG(errs() << "INVESTIGATING NONLOCAL LOAD: "
1349 // << Deps.size() << *LI << '\n');
1351 // If we had to process more than one hundred blocks to find the
1352 // dependencies, this load isn't worth worrying about. Optimizing
1353 // it will be too expensive.
1354 if (Deps.size() > 100)
1357 // If we had a phi translation failure, we'll have a single entry which is a
1358 // clobber in the current block. Reject this early.
1359 if (Deps.size() == 1 && Deps[0].second.isClobber()) {
1361 errs() << "GVN: non-local load ";
1362 WriteAsOperand(errs(), LI);
1363 errs() << " is clobbered by " << *Deps[0].second.getInst() << '\n';
1368 // Filter out useless results (non-locals, etc). Keep track of the blocks
1369 // where we have a value available in repl, also keep track of whether we see
1370 // dependencies that produce an unknown value for the load (such as a call
1371 // that could potentially clobber the load).
1372 SmallVector<AvailableValueInBlock, 16> ValuesPerBlock;
1373 SmallVector<BasicBlock*, 16> UnavailableBlocks;
1375 const TargetData *TD = 0;
1377 for (unsigned i = 0, e = Deps.size(); i != e; ++i) {
1378 BasicBlock *DepBB = Deps[i].first;
1379 MemDepResult DepInfo = Deps[i].second;
1381 if (DepInfo.isClobber()) {
1382 // If the dependence is to a store that writes to a superset of the bits
1383 // read by the load, we can extract the bits we need for the load from the
1385 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) {
1387 TD = getAnalysisIfAvailable<TargetData>();
1389 int Offset = AnalyzeLoadFromClobberingStore(LI, DepSI, *TD);
1391 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1392 DepSI->getOperand(0),
1399 // If the clobbering value is a memset/memcpy/memmove, see if we can
1400 // forward a value on from it.
1401 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) {
1403 TD = getAnalysisIfAvailable<TargetData>();
1405 int Offset = AnalyzeLoadFromClobberingMemInst(LI, DepMI, *TD);
1407 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI,
1414 UnavailableBlocks.push_back(DepBB);
1418 Instruction *DepInst = DepInfo.getInst();
1420 // Loading the allocation -> undef.
1421 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst) ||
1422 // Loading immediately after lifetime begin -> undef.
1423 isLifetimeStart(DepInst)) {
1424 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1425 UndefValue::get(LI->getType())));
1429 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) {
1430 // Reject loads and stores that are to the same address but are of
1431 // different types if we have to.
1432 if (S->getOperand(0)->getType() != LI->getType()) {
1434 TD = getAnalysisIfAvailable<TargetData>();
1436 // If the stored value is larger or equal to the loaded value, we can
1438 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getOperand(0),
1439 LI->getType(), *TD)) {
1440 UnavailableBlocks.push_back(DepBB);
1445 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB,
1450 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) {
1451 // If the types mismatch and we can't handle it, reject reuse of the load.
1452 if (LD->getType() != LI->getType()) {
1454 TD = getAnalysisIfAvailable<TargetData>();
1456 // If the stored value is larger or equal to the loaded value, we can
1458 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){
1459 UnavailableBlocks.push_back(DepBB);
1463 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, LD));
1467 UnavailableBlocks.push_back(DepBB);
1471 // If we have no predecessors that produce a known value for this load, exit
1473 if (ValuesPerBlock.empty()) return false;
1475 // If all of the instructions we depend on produce a known value for this
1476 // load, then it is fully redundant and we can use PHI insertion to compute
1477 // its value. Insert PHIs and remove the fully redundant value now.
1478 if (UnavailableBlocks.empty()) {
1479 DEBUG(errs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n');
1481 // Perform PHI construction.
1482 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD,
1483 VN.getAliasAnalysis());
1484 LI->replaceAllUsesWith(V);
1486 if (isa<PHINode>(V))
1488 if (isa<PointerType>(V->getType()))
1489 MD->invalidateCachedPointerInfo(V);
1490 toErase.push_back(LI);
1495 if (!EnablePRE || !EnableLoadPRE)
1498 // Okay, we have *some* definitions of the value. This means that the value
1499 // is available in some of our (transitive) predecessors. Lets think about
1500 // doing PRE of this load. This will involve inserting a new load into the
1501 // predecessor when it's not available. We could do this in general, but
1502 // prefer to not increase code size. As such, we only do this when we know
1503 // that we only have to insert *one* load (which means we're basically moving
1504 // the load, not inserting a new one).
1506 SmallPtrSet<BasicBlock *, 4> Blockers;
1507 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1508 Blockers.insert(UnavailableBlocks[i]);
1510 // Lets find first basic block with more than one predecessor. Walk backwards
1511 // through predecessors if needed.
1512 BasicBlock *LoadBB = LI->getParent();
1513 BasicBlock *TmpBB = LoadBB;
1515 bool isSinglePred = false;
1516 bool allSingleSucc = true;
1517 while (TmpBB->getSinglePredecessor()) {
1518 isSinglePred = true;
1519 TmpBB = TmpBB->getSinglePredecessor();
1520 if (!TmpBB) // If haven't found any, bail now.
1522 if (TmpBB == LoadBB) // Infinite (unreachable) loop.
1524 if (Blockers.count(TmpBB))
1526 if (TmpBB->getTerminator()->getNumSuccessors() != 1)
1527 allSingleSucc = false;
1533 // If we have a repl set with LI itself in it, this means we have a loop where
1534 // at least one of the values is LI. Since this means that we won't be able
1535 // to eliminate LI even if we insert uses in the other predecessors, we will
1536 // end up increasing code size. Reject this by scanning for LI.
1537 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1538 if (ValuesPerBlock[i].isSimpleValue() &&
1539 ValuesPerBlock[i].getSimpleValue() == LI)
1542 // FIXME: It is extremely unclear what this loop is doing, other than
1543 // artificially restricting loadpre.
1546 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
1547 const AvailableValueInBlock &AV = ValuesPerBlock[i];
1548 if (AV.isSimpleValue())
1549 // "Hot" Instruction is in some loop (because it dominates its dep.
1551 if (Instruction *I = dyn_cast<Instruction>(AV.getSimpleValue()))
1552 if (DT->dominates(LI, I)) {
1558 // We are interested only in "hot" instructions. We don't want to do any
1559 // mis-optimizations here.
1564 // Okay, we have some hope :). Check to see if the loaded value is fully
1565 // available in all but one predecessor.
1566 // FIXME: If we could restructure the CFG, we could make a common pred with
1567 // all the preds that don't have an available LI and insert a new load into
1569 BasicBlock *UnavailablePred = 0;
1571 DenseMap<BasicBlock*, char> FullyAvailableBlocks;
1572 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
1573 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true;
1574 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
1575 FullyAvailableBlocks[UnavailableBlocks[i]] = false;
1577 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB);
1579 if (IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
1582 // If this load is not available in multiple predecessors, reject it.
1583 if (UnavailablePred && UnavailablePred != *PI)
1585 UnavailablePred = *PI;
1588 assert(UnavailablePred != 0 &&
1589 "Fully available value should be eliminated above!");
1591 // We don't currently handle critical edges :(
1592 if (UnavailablePred->getTerminator()->getNumSuccessors() != 1) {
1593 DEBUG(errs() << "COULD NOT PRE LOAD BECAUSE OF CRITICAL EDGE '"
1594 << UnavailablePred->getName() << "': " << *LI << '\n');
1598 // Do PHI translation to get its value in the predecessor if necessary. The
1599 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred.
1601 SmallVector<Instruction*, 8> NewInsts;
1603 // If all preds have a single successor, then we know it is safe to insert the
1604 // load on the pred (?!?), so we can insert code to materialize the pointer if
1605 // it is not available.
1606 PHITransAddr Address(LI->getOperand(0), TD);
1608 if (allSingleSucc) {
1609 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred,
1612 Address.PHITranslateValue(LoadBB, UnavailablePred);
1613 LoadPtr = Address.getAddr();
1615 // Make sure the value is live in the predecessor.
1616 if (Instruction *Inst = dyn_cast_or_null<Instruction>(LoadPtr))
1617 if (!DT->dominates(Inst->getParent(), UnavailablePred))
1621 // If we couldn't find or insert a computation of this phi translated value,
1624 assert(NewInsts.empty() && "Shouldn't insert insts on failure");
1625 DEBUG(errs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: "
1626 << *LI->getOperand(0) << "\n");
1630 // Assign value numbers to these new instructions.
1631 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) {
1632 // FIXME: We really _ought_ to insert these value numbers into their
1633 // parent's availability map. However, in doing so, we risk getting into
1634 // ordering issues. If a block hasn't been processed yet, we would be
1635 // marking a value as AVAIL-IN, which isn't what we intend.
1636 VN.lookup_or_add(NewInsts[i]);
1639 // Make sure it is valid to move this load here. We have to watch out for:
1640 // @1 = getelementptr (i8* p, ...
1641 // test p and branch if == 0
1643 // It is valid to have the getelementptr before the test, even if p can be 0,
1644 // as getelementptr only does address arithmetic.
1645 // If we are not pushing the value through any multiple-successor blocks
1646 // we do not have this case. Otherwise, check that the load is safe to
1647 // put anywhere; this can be improved, but should be conservatively safe.
1648 if (!allSingleSucc &&
1649 // FIXME: REEVALUTE THIS.
1650 !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) {
1651 assert(NewInsts.empty() && "Should not have inserted instructions");
1655 // Okay, we can eliminate this load by inserting a reload in the predecessor
1656 // and using PHI construction to get the value in the other predecessors, do
1658 DEBUG(errs() << "GVN REMOVING PRE LOAD: " << *LI << '\n');
1659 DEBUG(if (!NewInsts.empty())
1660 errs() << "INSERTED " << NewInsts.size() << " INSTS: "
1661 << *NewInsts.back() << '\n');
1663 Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
1665 UnavailablePred->getTerminator());
1667 // Add the newly created load.
1668 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,NewLoad));
1670 // Perform PHI construction.
1671 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, TD,
1672 VN.getAliasAnalysis());
1673 LI->replaceAllUsesWith(V);
1674 if (isa<PHINode>(V))
1676 if (isa<PointerType>(V->getType()))
1677 MD->invalidateCachedPointerInfo(V);
1678 toErase.push_back(LI);
1683 /// processLoad - Attempt to eliminate a load, first by eliminating it
1684 /// locally, and then attempting non-local elimination if that fails.
1685 bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
1689 if (L->isVolatile())
1692 // ... to a pointer that has been loaded from before...
1693 MemDepResult Dep = MD->getDependency(L);
1695 // If the value isn't available, don't do anything!
1696 if (Dep.isClobber()) {
1697 // Check to see if we have something like this:
1698 // store i32 123, i32* %P
1699 // %A = bitcast i32* %P to i8*
1700 // %B = gep i8* %A, i32 1
1703 // We could do that by recognizing if the clobber instructions are obviously
1704 // a common base + constant offset, and if the previous store (or memset)
1705 // completely covers this load. This sort of thing can happen in bitfield
1707 Value *AvailVal = 0;
1708 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
1709 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1710 int Offset = AnalyzeLoadFromClobberingStore(L, DepSI, *TD);
1712 AvailVal = GetStoreValueForLoad(DepSI->getOperand(0), Offset,
1713 L->getType(), L, *TD);
1716 // If the clobbering value is a memset/memcpy/memmove, see if we can forward
1717 // a value on from it.
1718 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) {
1719 if (const TargetData *TD = getAnalysisIfAvailable<TargetData>()) {
1720 int Offset = AnalyzeLoadFromClobberingMemInst(L, DepMI, *TD);
1722 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L,*TD);
1727 DEBUG(errs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n'
1728 << *AvailVal << '\n' << *L << "\n\n\n");
1730 // Replace the load!
1731 L->replaceAllUsesWith(AvailVal);
1732 if (isa<PointerType>(AvailVal->getType()))
1733 MD->invalidateCachedPointerInfo(AvailVal);
1734 toErase.push_back(L);
1740 // fast print dep, using operator<< on instruction would be too slow
1741 errs() << "GVN: load ";
1742 WriteAsOperand(errs(), L);
1743 Instruction *I = Dep.getInst();
1744 errs() << " is clobbered by " << *I << '\n';
1749 // If it is defined in another block, try harder.
1750 if (Dep.isNonLocal())
1751 return processNonLocalLoad(L, toErase);
1753 Instruction *DepInst = Dep.getInst();
1754 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) {
1755 Value *StoredVal = DepSI->getOperand(0);
1757 // The store and load are to a must-aliased pointer, but they may not
1758 // actually have the same type. See if we know how to reuse the stored
1759 // value (depending on its type).
1760 const TargetData *TD = 0;
1761 if (StoredVal->getType() != L->getType()) {
1762 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1763 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(),
1768 DEBUG(errs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal
1769 << '\n' << *L << "\n\n\n");
1776 L->replaceAllUsesWith(StoredVal);
1777 if (isa<PointerType>(StoredVal->getType()))
1778 MD->invalidateCachedPointerInfo(StoredVal);
1779 toErase.push_back(L);
1784 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) {
1785 Value *AvailableVal = DepLI;
1787 // The loads are of a must-aliased pointer, but they may not actually have
1788 // the same type. See if we know how to reuse the previously loaded value
1789 // (depending on its type).
1790 const TargetData *TD = 0;
1791 if (DepLI->getType() != L->getType()) {
1792 if ((TD = getAnalysisIfAvailable<TargetData>())) {
1793 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), L,*TD);
1794 if (AvailableVal == 0)
1797 DEBUG(errs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal
1798 << "\n" << *L << "\n\n\n");
1805 L->replaceAllUsesWith(AvailableVal);
1806 if (isa<PointerType>(DepLI->getType()))
1807 MD->invalidateCachedPointerInfo(DepLI);
1808 toErase.push_back(L);
1813 // If this load really doesn't depend on anything, then we must be loading an
1814 // undef value. This can happen when loading for a fresh allocation with no
1815 // intervening stores, for example.
1816 if (isa<AllocaInst>(DepInst) || isMalloc(DepInst)) {
1817 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1818 toErase.push_back(L);
1823 // If this load occurs either right after a lifetime begin,
1824 // then the loaded value is undefined.
1825 if (IntrinsicInst* II = dyn_cast<IntrinsicInst>(DepInst)) {
1826 if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
1827 L->replaceAllUsesWith(UndefValue::get(L->getType()));
1828 toErase.push_back(L);
1837 Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
1838 DenseMap<BasicBlock*, ValueNumberScope*>::iterator I = localAvail.find(BB);
1839 if (I == localAvail.end())
1842 ValueNumberScope *Locals = I->second;
1844 DenseMap<uint32_t, Value*>::iterator I = Locals->table.find(num);
1845 if (I != Locals->table.end())
1847 Locals = Locals->parent;
1854 /// processInstruction - When calculating availability, handle an instruction
1855 /// by inserting it into the appropriate sets
1856 bool GVN::processInstruction(Instruction *I,
1857 SmallVectorImpl<Instruction*> &toErase) {
1858 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
1859 bool Changed = processLoad(LI, toErase);
1862 unsigned Num = VN.lookup_or_add(LI);
1863 localAvail[I->getParent()]->table.insert(std::make_pair(Num, LI));
1869 uint32_t NextNum = VN.getNextUnusedValueNumber();
1870 unsigned Num = VN.lookup_or_add(I);
1872 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1873 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1875 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
1878 Value *BranchCond = BI->getCondition();
1879 uint32_t CondVN = VN.lookup_or_add(BranchCond);
1881 BasicBlock *TrueSucc = BI->getSuccessor(0);
1882 BasicBlock *FalseSucc = BI->getSuccessor(1);
1884 if (TrueSucc->getSinglePredecessor())
1885 localAvail[TrueSucc]->table[CondVN] =
1886 ConstantInt::getTrue(TrueSucc->getContext());
1887 if (FalseSucc->getSinglePredecessor())
1888 localAvail[FalseSucc]->table[CondVN] =
1889 ConstantInt::getFalse(TrueSucc->getContext());
1893 // Allocations are always uniquely numbered, so we can save time and memory
1894 // by fast failing them.
1895 } else if (isa<AllocaInst>(I) || isa<TerminatorInst>(I)) {
1896 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1900 // Collapse PHI nodes
1901 if (PHINode* p = dyn_cast<PHINode>(I)) {
1902 Value *constVal = CollapsePhi(p);
1905 p->replaceAllUsesWith(constVal);
1906 if (MD && isa<PointerType>(constVal->getType()))
1907 MD->invalidateCachedPointerInfo(constVal);
1910 toErase.push_back(p);
1912 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1915 // If the number we were assigned was a brand new VN, then we don't
1916 // need to do a lookup to see if the number already exists
1917 // somewhere in the domtree: it can't!
1918 } else if (Num == NextNum) {
1919 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1921 // Perform fast-path value-number based elimination of values inherited from
1923 } else if (Value *repl = lookupNumber(I->getParent(), Num)) {
1926 I->replaceAllUsesWith(repl);
1927 if (MD && isa<PointerType>(repl->getType()))
1928 MD->invalidateCachedPointerInfo(repl);
1929 toErase.push_back(I);
1933 localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
1939 /// runOnFunction - This is the main transformation entry point for a function.
1940 bool GVN::runOnFunction(Function& F) {
1942 MD = &getAnalysis<MemoryDependenceAnalysis>();
1943 DT = &getAnalysis<DominatorTree>();
1944 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>());
1948 bool Changed = false;
1949 bool ShouldContinue = true;
1951 // Merge unconditional branches, allowing PRE to catch more
1952 // optimization opportunities.
1953 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) {
1954 BasicBlock *BB = FI;
1956 bool removedBlock = MergeBlockIntoPredecessor(BB, this);
1957 if (removedBlock) NumGVNBlocks++;
1959 Changed |= removedBlock;
1962 unsigned Iteration = 0;
1964 while (ShouldContinue) {
1965 DEBUG(errs() << "GVN iteration: " << Iteration << "\n");
1966 ShouldContinue = iterateOnFunction(F);
1967 Changed |= ShouldContinue;
1972 bool PREChanged = true;
1973 while (PREChanged) {
1974 PREChanged = performPRE(F);
1975 Changed |= PREChanged;
1978 // FIXME: Should perform GVN again after PRE does something. PRE can move
1979 // computations into blocks where they become fully redundant. Note that
1980 // we can't do this until PRE's critical edge splitting updates memdep.
1981 // Actually, when this happens, we should just fully integrate PRE into GVN.
1983 cleanupGlobalSets();
1989 bool GVN::processBlock(BasicBlock *BB) {
1990 // FIXME: Kill off toErase by doing erasing eagerly in a helper function (and
1991 // incrementing BI before processing an instruction).
1992 SmallVector<Instruction*, 8> toErase;
1993 bool ChangedFunction = false;
1995 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
1997 ChangedFunction |= processInstruction(BI, toErase);
1998 if (toErase.empty()) {
2003 // If we need some instructions deleted, do it now.
2004 NumGVNInstr += toErase.size();
2006 // Avoid iterator invalidation.
2007 bool AtStart = BI == BB->begin();
2011 for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
2012 E = toErase.end(); I != E; ++I) {
2013 DEBUG(errs() << "GVN removed: " << **I << '\n');
2014 if (MD) MD->removeInstruction(*I);
2015 (*I)->eraseFromParent();
2016 DEBUG(verifyRemoved(*I));
2026 return ChangedFunction;
2029 /// performPRE - Perform a purely local form of PRE that looks for diamond
2030 /// control flow patterns and attempts to perform simple PRE at the join point.
2031 bool GVN::performPRE(Function &F) {
2032 bool Changed = false;
2033 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit;
2034 DenseMap<BasicBlock*, Value*> predMap;
2035 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
2036 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) {
2037 BasicBlock *CurrentBlock = *DI;
2039 // Nothing to PRE in the entry block.
2040 if (CurrentBlock == &F.getEntryBlock()) continue;
2042 for (BasicBlock::iterator BI = CurrentBlock->begin(),
2043 BE = CurrentBlock->end(); BI != BE; ) {
2044 Instruction *CurInst = BI++;
2046 if (isa<AllocaInst>(CurInst) ||
2047 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
2048 CurInst->getType()->isVoidTy() ||
2049 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
2050 isa<DbgInfoIntrinsic>(CurInst))
2053 uint32_t ValNo = VN.lookup(CurInst);
2055 // Look for the predecessors for PRE opportunities. We're
2056 // only trying to solve the basic diamond case, where
2057 // a value is computed in the successor and one predecessor,
2058 // but not the other. We also explicitly disallow cases
2059 // where the successor is its own predecessor, because they're
2060 // more complicated to get right.
2061 unsigned NumWith = 0;
2062 unsigned NumWithout = 0;
2063 BasicBlock *PREPred = 0;
2066 for (pred_iterator PI = pred_begin(CurrentBlock),
2067 PE = pred_end(CurrentBlock); PI != PE; ++PI) {
2068 // We're not interested in PRE where the block is its
2069 // own predecessor, on in blocks with predecessors
2070 // that are not reachable.
2071 if (*PI == CurrentBlock) {
2074 } else if (!localAvail.count(*PI)) {
2079 DenseMap<uint32_t, Value*>::iterator predV =
2080 localAvail[*PI]->table.find(ValNo);
2081 if (predV == localAvail[*PI]->table.end()) {
2084 } else if (predV->second == CurInst) {
2087 predMap[*PI] = predV->second;
2092 // Don't do PRE when it might increase code size, i.e. when
2093 // we would need to insert instructions in more than one pred.
2094 if (NumWithout != 1 || NumWith == 0)
2097 // Don't do PRE across indirect branch.
2098 if (isa<IndirectBrInst>(PREPred->getTerminator()))
2101 // We can't do PRE safely on a critical edge, so instead we schedule
2102 // the edge to be split and perform the PRE the next time we iterate
2104 unsigned SuccNum = 0;
2105 for (unsigned i = 0, e = PREPred->getTerminator()->getNumSuccessors();
2107 if (PREPred->getTerminator()->getSuccessor(i) == CurrentBlock) {
2112 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
2113 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
2117 // Instantiate the expression the in predecessor that lacked it.
2118 // Because we are going top-down through the block, all value numbers
2119 // will be available in the predecessor by the time we need them. Any
2120 // that weren't original present will have been instantiated earlier
2122 Instruction *PREInstr = CurInst->clone();
2123 bool success = true;
2124 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
2125 Value *Op = PREInstr->getOperand(i);
2126 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
2129 if (Value *V = lookupNumber(PREPred, VN.lookup(Op))) {
2130 PREInstr->setOperand(i, V);
2137 // Fail out if we encounter an operand that is not available in
2138 // the PRE predecessor. This is typically because of loads which
2139 // are not value numbered precisely.
2142 DEBUG(verifyRemoved(PREInstr));
2146 PREInstr->insertBefore(PREPred->getTerminator());
2147 PREInstr->setName(CurInst->getName() + ".pre");
2148 predMap[PREPred] = PREInstr;
2149 VN.add(PREInstr, ValNo);
2152 // Update the availability map to include the new instruction.
2153 localAvail[PREPred]->table.insert(std::make_pair(ValNo, PREInstr));
2155 // Create a PHI to make the value available in this block.
2156 PHINode* Phi = PHINode::Create(CurInst->getType(),
2157 CurInst->getName() + ".pre-phi",
2158 CurrentBlock->begin());
2159 for (pred_iterator PI = pred_begin(CurrentBlock),
2160 PE = pred_end(CurrentBlock); PI != PE; ++PI)
2161 Phi->addIncoming(predMap[*PI], *PI);
2164 localAvail[CurrentBlock]->table[ValNo] = Phi;
2166 CurInst->replaceAllUsesWith(Phi);
2167 if (MD && isa<PointerType>(Phi->getType()))
2168 MD->invalidateCachedPointerInfo(Phi);
2171 DEBUG(errs() << "GVN PRE removed: " << *CurInst << '\n');
2172 if (MD) MD->removeInstruction(CurInst);
2173 CurInst->eraseFromParent();
2174 DEBUG(verifyRemoved(CurInst));
2179 for (SmallVector<std::pair<TerminatorInst*, unsigned>, 4>::iterator
2180 I = toSplit.begin(), E = toSplit.end(); I != E; ++I)
2181 SplitCriticalEdge(I->first, I->second, this);
2183 return Changed || toSplit.size();
2186 /// iterateOnFunction - Executes one iteration of GVN
2187 bool GVN::iterateOnFunction(Function &F) {
2188 cleanupGlobalSets();
2190 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2191 DE = df_end(DT->getRootNode()); DI != DE; ++DI) {
2193 localAvail[DI->getBlock()] =
2194 new ValueNumberScope(localAvail[DI->getIDom()->getBlock()]);
2196 localAvail[DI->getBlock()] = new ValueNumberScope(0);
2199 // Top-down walk of the dominator tree
2200 bool Changed = false;
2202 // Needed for value numbering with phi construction to work.
2203 ReversePostOrderTraversal<Function*> RPOT(&F);
2204 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
2205 RE = RPOT.end(); RI != RE; ++RI)
2206 Changed |= processBlock(*RI);
2208 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()),
2209 DE = df_end(DT->getRootNode()); DI != DE; ++DI)
2210 Changed |= processBlock(DI->getBlock());
2216 void GVN::cleanupGlobalSets() {
2219 for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
2220 I = localAvail.begin(), E = localAvail.end(); I != E; ++I)
2225 /// verifyRemoved - Verify that the specified instruction does not occur in our
2226 /// internal data structures.
2227 void GVN::verifyRemoved(const Instruction *Inst) const {
2228 VN.verifyRemoved(Inst);
2230 // Walk through the value number scope to make sure the instruction isn't
2231 // ferreted away in it.
2232 for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
2233 I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
2234 const ValueNumberScope *VNS = I->second;
2237 for (DenseMap<uint32_t, Value*>::const_iterator
2238 II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
2239 assert(II->second != Inst && "Inst still in value numbering scope!");