1 //===-- PredicateSimplifier.cpp - Path Sensitive Simplifier -----------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Nick Lewycky and is distributed under the
6 // University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===------------------------------------------------------------------===//
10 // Path-sensitive optimizer. In a branch where x == y, replace uses of
11 // x with y. Permits further optimization, such as the elimination of
12 // the unreachable call:
14 // void test(int *p, int *q)
20 // foo(); // unreachable
23 //===------------------------------------------------------------------===//
25 // This optimization works by substituting %q for %p when protected by a
26 // conditional that assures us of that fact. Properties are stored as
27 // relationships between two values.
29 //===------------------------------------------------------------------===//
31 #define DEBUG_TYPE "predsimplify"
32 #include "llvm/Transforms/Scalar.h"
33 #include "llvm/Constants.h"
34 #include "llvm/DerivedTypes.h"
35 #include "llvm/Instructions.h"
36 #include "llvm/Pass.h"
37 #include "llvm/ADT/Statistic.h"
38 #include "llvm/ADT/STLExtras.h"
39 #include "llvm/Analysis/Dominators.h"
40 #include "llvm/Support/CFG.h"
41 #include "llvm/Support/Debug.h"
42 #include "llvm/Support/InstVisitor.h"
46 typedef DominatorTree::Node DTNodeType;
50 NumVarsReplaced("predsimplify", "Number of argument substitutions");
52 NumInstruction("predsimplify", "Number of instructions removed");
56 /// Similar to EquivalenceClasses, this stores the set of equivalent
57 /// types. Beyond EquivalenceClasses, it allows us to specify which
58 /// element will act as leader.
59 template<typename ElemTy>
60 class VISIBILITY_HIDDEN Synonyms {
61 std::map<ElemTy, unsigned> mapping;
62 std::vector<ElemTy> leaders;
66 typedef unsigned iterator;
67 typedef const unsigned const_iterator;
69 Synonyms(PropertySet *PS) : PS(PS) {}
74 return leaders.empty();
77 iterator findLeader(ElemTy e) {
78 typename std::map<ElemTy, unsigned>::iterator MI = mapping.find(e);
79 if (MI == mapping.end()) return 0;
84 const_iterator findLeader(ElemTy e) const {
85 typename std::map<ElemTy, unsigned>::const_iterator MI =
87 if (MI == mapping.end()) return 0;
92 ElemTy &getLeader(iterator I) {
93 assert(I && I <= leaders.size() && "Illegal leader to get.");
97 const ElemTy &getLeader(const_iterator I) const {
98 assert(I && I <= leaders.size() && "Illegal leaders to get.");
103 void debug(std::ostream &os) const {
104 for (unsigned i = 1, e = leaders.size()+1; i != e; ++i) {
105 os << i << ". " << *getLeader(i) << ": [";
106 for (std::map<Value *, unsigned>::const_iterator
107 I = mapping.begin(), E = mapping.end(); I != E; ++I) {
108 if ((*I).second == i && (*I).first != leaders[i-1]) {
109 os << *(*I).first << " ";
119 /// Combine two sets referring to the same element, inserting the
120 /// elements as needed. Returns a valid iterator iff two already
121 /// existing disjoint synonym sets were combined. The iterator
122 /// points to the no longer existing element.
123 iterator unionSets(ElemTy E1, ElemTy E2);
125 /// Returns an iterator pointing to the synonym set containing
126 /// element e. If none exists, a new one is created and returned.
127 iterator findOrInsert(ElemTy e) {
128 iterator I = findLeader(e);
131 leaders.push_back(e);
138 /// Represents the set of equivalent Value*s and provides insertion
139 /// and fast lookup. Also stores the set of inequality relationships.
141 /// Returns true if V1 is a better choice than V2.
142 bool compare(Value *V1, Value *V2) const {
143 if (isa<Constant>(V1)) {
144 if (!isa<Constant>(V2)) {
147 } else if (isa<Argument>(V1)) {
148 if (!isa<Constant>(V2) && !isa<Argument>(V2)) {
152 if (Instruction *I1 = dyn_cast<Instruction>(V1)) {
153 if (Instruction *I2 = dyn_cast<Instruction>(V2)) {
154 BasicBlock *BB1 = I1->getParent(),
155 *BB2 = I2->getParent();
157 for (BasicBlock::const_iterator I = BB1->begin(), E = BB1->end();
159 if (&*I == I1) return true;
160 if (&*I == I2) return false;
162 assert(0 && "Instructions not found in parent BasicBlock?");
164 return DT->getNode(BB1)->properlyDominates(DT->getNode(BB2));
172 /// Choose the canonical Value in a synonym set.
173 /// Leaves the more canonical choice in V1.
174 void order(Value *&V1, Value *&V2) const {
175 if (compare(V2, V1)) std::swap(V1, V2);
178 PropertySet(DominatorTree *DT) : union_find(this), DT(DT) {}
180 Synonyms<Value *> union_find;
182 typedef std::vector<Property>::iterator PropertyIterator;
183 typedef std::vector<Property>::const_iterator ConstPropertyIterator;
184 typedef Synonyms<Value *>::iterator SynonymIterator;
191 Value *canonicalize(Value *V) const {
192 Value *C = lookup(V);
196 Value *lookup(Value *V) const {
197 SynonymIterator SI = union_find.findLeader(V);
198 if (!SI) return NULL;
199 return union_find.getLeader(SI);
203 return union_find.empty();
206 void addEqual(Value *V1, Value *V2) {
207 // If %x = 0. and %y = -0., seteq %x, %y is true, but
208 // copysign(%x) is not the same as copysign(%y).
209 if (V1->getType()->isFloatingPoint()) return;
212 if (isa<Constant>(V2)) return; // refuse to set false == true.
214 SynonymIterator deleted = union_find.unionSets(V1, V2);
216 SynonymIterator replacement = union_find.findLeader(V1);
218 for (PropertyIterator I = Properties.begin(), E = Properties.end();
220 if (I->I1 == deleted) I->I1 = replacement;
221 else if (I->I1 > deleted) --I->I1;
222 if (I->I2 == deleted) I->I2 = replacement;
223 else if (I->I2 > deleted) --I->I2;
226 addImpliedProperties(EQ, V1, V2);
229 void addNotEqual(Value *V1, Value *V2) {
230 // If %x = NAN then seteq %x, %x is false.
231 if (V1->getType()->isFloatingPoint()) return;
233 // For example, %x = setne int 0, 0 causes "0 != 0".
234 if (isa<Constant>(V1) && isa<Constant>(V2)) return;
236 if (findProperty(NE, V1, V2) != Properties.end())
240 SynonymIterator I1 = union_find.findOrInsert(V1),
241 I2 = union_find.findOrInsert(V2);
243 // Technically this means that the block is unreachable.
244 if (I1 == I2) return;
246 Properties.push_back(Property(NE, I1, I2));
247 addImpliedProperties(NE, V1, V2);
250 PropertyIterator findProperty(Ops Opcode, Value *V1, Value *V2) {
251 assert(Opcode != EQ && "Can't findProperty on EQ."
252 "Use the lookup method instead.");
254 SynonymIterator I1 = union_find.findLeader(V1),
255 I2 = union_find.findLeader(V2);
256 if (!I1 || !I2) return Properties.end();
259 find(Properties.begin(), Properties.end(), Property(Opcode, I1, I2));
262 ConstPropertyIterator
263 findProperty(Ops Opcode, Value *V1, Value *V2) const {
264 assert(Opcode != EQ && "Can't findProperty on EQ."
265 "Use the lookup method instead.");
267 SynonymIterator I1 = union_find.findLeader(V1),
268 I2 = union_find.findLeader(V2);
269 if (!I1 || !I2) return Properties.end();
272 find(Properties.begin(), Properties.end(), Property(Opcode, I1, I2));
276 // Represents Head OP [Tail1, Tail2, ...]
277 // For example: %x != %a, %x != %b.
278 struct VISIBILITY_HIDDEN Property {
279 typedef SynonymIterator Iter;
281 Property(Ops opcode, Iter i1, Iter i2)
282 : Opcode(opcode), I1(i1), I2(i2)
283 { assert(opcode != EQ && "Equality belongs in the synonym set, "
284 "not a property."); }
286 bool operator==(const Property &P) const {
287 return (Opcode == P.Opcode) &&
288 ((I1 == P.I1 && I2 == P.I2) ||
289 (I1 == P.I2 && I2 == P.I1));
296 void add(Ops Opcode, Value *V1, Value *V2, bool invert) {
299 if (invert) addNotEqual(V1, V2);
300 else addEqual(V1, V2);
303 if (invert) addEqual(V1, V2);
304 else addNotEqual(V1, V2);
307 assert(0 && "Unknown property opcode.");
311 // Finds the properties implied by an equivalence and adds them too.
312 // Example: ("seteq %a, %b", true, EQ) --> (%a, %b, EQ)
313 // ("seteq %a, %b", false, EQ) --> (%a, %b, NE)
314 void addImpliedProperties(Ops Opcode, Value *V1, Value *V2) {
317 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V2)) {
318 switch (BO->getOpcode()) {
319 case Instruction::SetEQ:
320 if (ConstantBool *V1CB = dyn_cast<ConstantBool>(V1))
321 add(Opcode, BO->getOperand(0), BO->getOperand(1),!V1CB->getValue());
323 case Instruction::SetNE:
324 if (ConstantBool *V1CB = dyn_cast<ConstantBool>(V1))
325 add(Opcode, BO->getOperand(0), BO->getOperand(1), V1CB->getValue());
327 case Instruction::SetLT:
328 case Instruction::SetGT:
329 if (V1 == ConstantBool::getTrue())
330 add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
332 case Instruction::SetLE:
333 case Instruction::SetGE:
334 if (V1 == ConstantBool::getFalse())
335 add(Opcode, BO->getOperand(0), BO->getOperand(1), true);
337 case Instruction::And:
338 if (V1 == ConstantBool::getTrue()) {
339 add(Opcode, V1, BO->getOperand(0), false);
340 add(Opcode, V1, BO->getOperand(1), false);
343 case Instruction::Or:
344 if (V1 == ConstantBool::getFalse()) {
345 add(Opcode, V1, BO->getOperand(0), false);
346 add(Opcode, V1, BO->getOperand(1), false);
349 case Instruction::Xor:
350 if (V1 == ConstantBool::getTrue()) {
351 if (BO->getOperand(0) == V1)
352 add(Opcode, ConstantBool::getFalse(), BO->getOperand(1), false);
353 if (BO->getOperand(1) == V1)
354 add(Opcode, ConstantBool::getFalse(), BO->getOperand(0), false);
356 if (V1 == ConstantBool::getFalse()) {
357 if (BO->getOperand(0) == ConstantBool::getTrue())
358 add(Opcode, ConstantBool::getTrue(), BO->getOperand(1), false);
359 if (BO->getOperand(1) == ConstantBool::getTrue())
360 add(Opcode, ConstantBool::getTrue(), BO->getOperand(0), false);
366 } else if (SelectInst *SI = dyn_cast<SelectInst>(V2)) {
367 if (Opcode != EQ && Opcode != NE) return;
369 ConstantBool *True = ConstantBool::get(Opcode==EQ),
370 *False = ConstantBool::get(Opcode!=EQ);
372 if (V1 == SI->getTrueValue())
373 addEqual(SI->getCondition(), True);
374 else if (V1 == SI->getFalseValue())
375 addEqual(SI->getCondition(), False);
376 else if (Opcode == EQ)
377 assert("Result of select not equal to either value.");
384 void debug(std::ostream &os) const {
385 static const char *OpcodeTable[] = { "EQ", "NE" };
387 union_find.debug(os);
388 for (std::vector<Property>::const_iterator I = Properties.begin(),
389 E = Properties.end(); I != E; ++I) {
390 os << (*I).I1 << " " << OpcodeTable[(*I).Opcode] << " "
397 std::vector<Property> Properties;
400 /// PredicateSimplifier - This class is a simplifier that replaces
401 /// one equivalent variable with another. It also tracks what
402 /// can't be equal and will solve setcc instructions when possible.
403 class PredicateSimplifier : public FunctionPass {
405 bool runOnFunction(Function &F);
406 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
409 /// Backwards - Try to replace the Use of the instruction with
410 /// something simpler. This resolves a value by walking backwards
411 /// through its definition and the operands of that definition to
412 /// see if any values can now be solved for with the properties
413 /// that are in effect now, but weren't at definition time.
414 class Backwards : public InstVisitor<Backwards, Value &> {
415 friend class InstVisitor<Backwards, Value &>;
416 const PropertySet &KP;
418 Value &visitSetCondInst(SetCondInst &SCI);
419 Value &visitBinaryOperator(BinaryOperator &BO);
420 Value &visitSelectInst(SelectInst &SI);
421 Value &visitInstruction(Instruction &I);
424 explicit Backwards(const PropertySet &KP) : KP(KP) {}
426 Value *resolve(Value *V);
429 /// Forwards - Adds new properties into PropertySet and uses them to
430 /// simplify instructions. Because new properties sometimes apply to
431 /// a transition from one BasicBlock to another, this will use the
432 /// PredicateSimplifier::proceedToSuccessor(s) interface to enter the
433 /// basic block with the new PropertySet.
434 class Forwards : public InstVisitor<Forwards> {
435 friend class InstVisitor<Forwards>;
436 PredicateSimplifier *PS;
440 Forwards(PredicateSimplifier *PS, PropertySet &KP) : PS(PS), KP(KP) {}
442 // Tries to simplify each Instruction and add new properties to
443 // the PropertySet. Returns true if it erase the instruction.
444 //void visitInstruction(Instruction *I);
446 void visitTerminatorInst(TerminatorInst &TI);
447 void visitBranchInst(BranchInst &BI);
448 void visitSwitchInst(SwitchInst &SI);
450 void visitAllocaInst(AllocaInst &AI);
451 void visitLoadInst(LoadInst &LI);
452 void visitStoreInst(StoreInst &SI);
453 void visitBinaryOperator(BinaryOperator &BO);
456 // Used by terminator instructions to proceed from the current basic
457 // block to the next. Verifies that "current" dominates "next",
458 // then calls visitBasicBlock.
459 void proceedToSuccessors(PropertySet &CurrentPS, BasicBlock *Current);
460 void proceedToSuccessor(PropertySet &Properties, BasicBlock *Next);
462 // Visits each instruction in the basic block.
463 void visitBasicBlock(BasicBlock *Block, PropertySet &KnownProperties);
465 // Tries to simplify each Instruction and add new properties to
467 void visitInstruction(Instruction *I, PropertySet &);
473 RegisterPass<PredicateSimplifier> X("predsimplify",
474 "Predicate Simplifier");
476 template <typename ElemTy>
477 typename Synonyms<ElemTy>::iterator
478 Synonyms<ElemTy>::unionSets(ElemTy E1, ElemTy E2) {
481 iterator I1 = findLeader(E1),
484 if (!I1 && !I2) { // neither entry is in yet
485 leaders.push_back(E1);
494 std::swap(getLeader(I2), E1);
503 if (I1 == I2) return 0;
505 // This is the case where we have two sets, [%a1, %a2, %a3] and
506 // [%p1, %p2, %p3] and someone says that %a2 == %p3. We need to
507 // combine the two synsets.
511 for (std::map<Value *, unsigned>::iterator I = mapping.begin(),
512 E = mapping.end(); I != E; ++I) {
513 if (I->second == I2) I->second = I1;
514 else if (I->second > I2) --I->second;
517 leaders.erase(leaders.begin() + I2 - 1);
523 FunctionPass *llvm::createPredicateSimplifierPass() {
524 return new PredicateSimplifier();
527 bool PredicateSimplifier::runOnFunction(Function &F) {
528 DT = &getAnalysis<DominatorTree>();
531 PropertySet KnownProperties(DT);
532 visitBasicBlock(DT->getRootNode()->getBlock(), KnownProperties);
536 void PredicateSimplifier::getAnalysisUsage(AnalysisUsage &AU) const {
537 AU.addRequiredID(BreakCriticalEdgesID);
538 AU.addRequired<DominatorTree>();
539 AU.setPreservesCFG();
540 AU.addPreservedID(BreakCriticalEdgesID);
543 Value &PredicateSimplifier::Backwards::visitSetCondInst(SetCondInst &SCI) {
544 Value &vBO = visitBinaryOperator(SCI);
545 if (&vBO != &SCI) return vBO;
547 Value *SCI0 = resolve(SCI.getOperand(0)),
548 *SCI1 = resolve(SCI.getOperand(1));
550 PropertySet::ConstPropertyIterator NE =
551 KP.findProperty(PropertySet::NE, SCI0, SCI1);
553 if (NE != KP.Properties.end()) {
554 switch (SCI.getOpcode()) {
555 case Instruction::SetEQ: return *ConstantBool::getFalse();
556 case Instruction::SetNE: return *ConstantBool::getTrue();
557 case Instruction::SetLE:
558 case Instruction::SetGE:
559 case Instruction::SetLT:
560 case Instruction::SetGT:
563 assert(0 && "Unknown opcode in SetCondInst.");
570 Value &PredicateSimplifier::Backwards::visitBinaryOperator(BinaryOperator &BO) {
571 Value *V = KP.canonicalize(&BO);
572 if (V != &BO) return *V;
574 Value *lhs = resolve(BO.getOperand(0)),
575 *rhs = resolve(BO.getOperand(1));
577 ConstantIntegral *CI1 = dyn_cast<ConstantIntegral>(lhs),
578 *CI2 = dyn_cast<ConstantIntegral>(rhs);
580 if (CI1 && CI2) return *ConstantExpr::get(BO.getOpcode(), CI1, CI2);
585 Value &PredicateSimplifier::Backwards::visitSelectInst(SelectInst &SI) {
586 Value *V = KP.canonicalize(&SI);
587 if (V != &SI) return *V;
589 Value *Condition = resolve(SI.getCondition());
590 if (ConstantBool *CB = dyn_cast<ConstantBool>(Condition))
591 return *resolve(CB->getValue() ? SI.getTrueValue() : SI.getFalseValue());
595 Value &PredicateSimplifier::Backwards::visitInstruction(Instruction &I) {
596 return *KP.canonicalize(&I);
599 Value *PredicateSimplifier::Backwards::resolve(Value *V) {
600 if (isa<Constant>(V) || isa<BasicBlock>(V) || KP.empty()) return V;
602 if (Instruction *I = dyn_cast<Instruction>(V)) return &visit(*I);
603 return KP.canonicalize(V);
606 void PredicateSimplifier::visitBasicBlock(BasicBlock *BB,
607 PropertySet &KnownProperties) {
608 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
609 visitInstruction(I++, KnownProperties);
613 void PredicateSimplifier::visitInstruction(Instruction *I,
614 PropertySet &KnownProperties) {
615 // Try to replace the whole instruction.
616 Backwards resolve(KnownProperties);
617 Value *V = resolve.resolve(I);
621 DEBUG(std::cerr << "Removing " << *I);
622 I->replaceAllUsesWith(V);
623 I->eraseFromParent();
627 // Try to substitute operands.
628 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
629 Value *Oper = I->getOperand(i);
630 Value *V = resolve.resolve(Oper);
634 DEBUG(std::cerr << "Resolving " << *I);
636 DEBUG(std::cerr << "into " << *I);
640 Forwards visit(this, KnownProperties);
644 void PredicateSimplifier::proceedToSuccessors(PropertySet &KP,
645 BasicBlock *BBCurrent) {
646 DTNodeType *Current = DT->getNode(BBCurrent);
647 for (DTNodeType::iterator I = Current->begin(), E = Current->end();
649 PropertySet Copy(KP);
650 visitBasicBlock((*I)->getBlock(), Copy);
654 void PredicateSimplifier::proceedToSuccessor(PropertySet &KP, BasicBlock *BB) {
655 visitBasicBlock(BB, KP);
658 void PredicateSimplifier::Forwards::visitTerminatorInst(TerminatorInst &TI) {
659 PS->proceedToSuccessors(KP, TI.getParent());
662 void PredicateSimplifier::Forwards::visitBranchInst(BranchInst &BI) {
663 BasicBlock *BB = BI.getParent();
665 if (BI.isUnconditional()) {
666 PS->proceedToSuccessors(KP, BB);
670 Value *Condition = BI.getCondition();
672 BasicBlock *TrueDest = BI.getSuccessor(0),
673 *FalseDest = BI.getSuccessor(1);
675 if (isa<ConstantBool>(Condition) || TrueDest == FalseDest) {
676 PS->proceedToSuccessors(KP, BB);
680 DTNodeType *Node = PS->DT->getNode(BB);
681 for (DTNodeType::iterator I = Node->begin(), E = Node->end(); I != E; ++I) {
682 BasicBlock *Dest = (*I)->getBlock();
683 PropertySet DestProperties(KP);
685 if (Dest == TrueDest)
686 DestProperties.addEqual(ConstantBool::getTrue(), Condition);
687 else if (Dest == FalseDest)
688 DestProperties.addEqual(ConstantBool::getFalse(), Condition);
690 PS->proceedToSuccessor(DestProperties, Dest);
694 void PredicateSimplifier::Forwards::visitSwitchInst(SwitchInst &SI) {
695 Value *Condition = SI.getCondition();
697 // Set the EQProperty in each of the cases BBs,
698 // and the NEProperties in the default BB.
699 PropertySet DefaultProperties(KP);
701 DTNodeType *Node = PS->DT->getNode(SI.getParent());
702 for (DTNodeType::iterator I = Node->begin(), E = Node->end(); I != E; ++I) {
703 BasicBlock *BB = (*I)->getBlock();
705 PropertySet BBProperties(KP);
706 if (BB == SI.getDefaultDest()) {
707 for (unsigned i = 1, e = SI.getNumCases(); i < e; ++i)
708 if (SI.getSuccessor(i) != BB)
709 BBProperties.addNotEqual(Condition, SI.getCaseValue(i));
710 } else if (ConstantInt *CI = SI.findCaseDest(BB)) {
711 BBProperties.addEqual(Condition, CI);
713 PS->proceedToSuccessor(BBProperties, BB);
717 void PredicateSimplifier::Forwards::visitAllocaInst(AllocaInst &AI) {
718 KP.addNotEqual(Constant::getNullValue(AI.getType()), &AI);
721 void PredicateSimplifier::Forwards::visitLoadInst(LoadInst &LI) {
722 Value *Ptr = LI.getPointerOperand();
723 KP.addNotEqual(Constant::getNullValue(Ptr->getType()), Ptr);
726 void PredicateSimplifier::Forwards::visitStoreInst(StoreInst &SI) {
727 Value *Ptr = SI.getPointerOperand();
728 KP.addNotEqual(Constant::getNullValue(Ptr->getType()), Ptr);
731 void PredicateSimplifier::Forwards::visitBinaryOperator(BinaryOperator &BO) {
732 Instruction::BinaryOps ops = BO.getOpcode();
735 case Instruction::Div:
736 case Instruction::Rem: {
737 Value *Divisor = BO.getOperand(1);
738 KP.addNotEqual(Constant::getNullValue(Divisor->getType()), Divisor);