1 //===- InstructionCombining.cpp - Combine multiple instructions -------------=//
3 // InstructionCombining - Combine instructions to form fewer, simple
4 // instructions. This pass does not modify the CFG, and has a tendancy to
5 // make instructions dead, so a subsequent DIE pass is useful. This pass is
6 // where algebraic simplification happens.
8 // This pass combines things like:
14 // This is a simple worklist driven algorithm.
16 //===----------------------------------------------------------------------===//
18 #include "llvm/Transforms/Scalar.h"
19 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
20 #include "llvm/ConstantHandling.h"
21 #include "llvm/iMemory.h"
22 #include "llvm/iOther.h"
23 #include "llvm/iPHINode.h"
24 #include "llvm/iOperators.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Support/InstIterator.h"
27 #include "llvm/Support/InstVisitor.h"
28 #include "Support/StatisticReporter.h"
31 static Statistic<> NumCombined("instcombine\t- Number of insts combined");
34 class InstCombiner : public FunctionPass,
35 public InstVisitor<InstCombiner, Instruction*> {
36 // Worklist of all of the instructions that need to be simplified.
37 std::vector<Instruction*> WorkList;
39 void AddUsesToWorkList(Instruction *I) {
40 // The instruction was simplified, add all users of the instruction to
41 // the work lists because they might get more simplified now...
43 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
45 WorkList.push_back(cast<Instruction>(*UI));
49 const char *getPassName() const { return "Instruction Combining"; }
51 virtual bool runOnFunction(Function *F);
53 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
57 // Visitation implementation - Implement instruction combining for different
58 // instruction types. The semantics are as follows:
60 // null - No change was made
61 // I - Change was made, I is still valid
62 // otherwise - Change was made, replace I with returned instruction
64 Instruction *visitNot(UnaryOperator *I);
65 Instruction *visitAdd(BinaryOperator *I);
66 Instruction *visitSub(BinaryOperator *I);
67 Instruction *visitMul(BinaryOperator *I);
68 Instruction *visitDiv(BinaryOperator *I);
69 Instruction *visitRem(BinaryOperator *I);
70 Instruction *visitAnd(BinaryOperator *I);
71 Instruction *visitOr (BinaryOperator *I);
72 Instruction *visitXor(BinaryOperator *I);
73 Instruction *visitSetCondInst(BinaryOperator *I);
74 Instruction *visitShiftInst(Instruction *I);
75 Instruction *visitCastInst(CastInst *CI);
76 Instruction *visitPHINode(PHINode *PN);
77 Instruction *visitGetElementPtrInst(GetElementPtrInst *GEP);
78 Instruction *visitMemAccessInst(MemAccessInst *MAI);
80 // visitInstruction - Specify what to return for unhandled instructions...
81 Instruction *visitInstruction(Instruction *I) { return 0; }
86 Instruction *InstCombiner::visitNot(UnaryOperator *I) {
87 if (I->use_empty()) return 0; // Don't fix dead instructions...
90 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(0)))
91 if (Op->getOpcode() == Instruction::Not) {
92 AddUsesToWorkList(I); // Add all modified instrs to worklist
93 I->replaceAllUsesWith(Op->getOperand(0));
100 // Make sure that this instruction has a constant on the right hand side if it
101 // has any constant arguments. If not, fix it an return true.
103 static bool SimplifyBinOp(BinaryOperator *I) {
104 if (isa<Constant>(I->getOperand(0)) && !isa<Constant>(I->getOperand(1)))
105 return !I->swapOperands();
109 // dyn_castNegInst - Given a 'sub' instruction, return the RHS of the
110 // instruction if the LHS is a constant zero (which is the 'negate' form).
112 static inline Value *dyn_castNegInst(Value *V) {
113 Instruction *I = dyn_cast<Instruction>(V);
114 if (!I || I->getOpcode() != Instruction::Sub) return 0;
116 if (I->getOperand(0) == Constant::getNullValue(I->getType()))
117 return I->getOperand(1);
121 Instruction *InstCombiner::visitAdd(BinaryOperator *I) {
122 if (I->use_empty()) return 0; // Don't fix dead add instructions...
123 bool Changed = SimplifyBinOp(I);
124 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
126 // Eliminate 'add int %X, 0'
127 if (I->getType()->isIntegral() &&
128 RHS == Constant::getNullValue(I->getType())) {
129 AddUsesToWorkList(I); // Add all modified instrs to worklist
130 I->replaceAllUsesWith(LHS);
135 if (Value *V = dyn_castNegInst(LHS))
136 return BinaryOperator::create(Instruction::Sub, RHS, V);
139 if (Value *V = dyn_castNegInst(RHS))
140 return BinaryOperator::create(Instruction::Sub, LHS, V);
142 // Simplify add instructions with a constant RHS...
143 if (Constant *Op2 = dyn_cast<Constant>(RHS)) {
144 if (BinaryOperator *ILHS = dyn_cast<BinaryOperator>(LHS)) {
145 if (ILHS->getOpcode() == Instruction::Add &&
146 isa<Constant>(ILHS->getOperand(1))) {
148 // %Y = add int %X, 1
149 // %Z = add int %Y, 1
151 // %Z = add int %X, 2
153 if (Constant *Val = *Op2 + *cast<Constant>(ILHS->getOperand(1))) {
154 I->setOperand(0, ILHS->getOperand(0));
155 I->setOperand(1, Val);
162 return Changed ? I : 0;
165 Instruction *InstCombiner::visitSub(BinaryOperator *I) {
166 if (I->use_empty()) return 0; // Don't fix dead add instructions...
167 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
169 if (Op0 == Op1) { // sub X, X -> 0
170 AddUsesToWorkList(I); // Add all modified instrs to worklist
171 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
175 // If this is a subtract instruction with a constant RHS, convert it to an add
176 // instruction of a negative constant
178 if (Constant *Op2 = dyn_cast<Constant>(Op1))
179 if (Constant *RHS = *Constant::getNullValue(I->getType()) - *Op2) // 0 - RHS
180 return BinaryOperator::create(Instruction::Add, Op0, RHS, I->getName());
182 // If this is a 'C = x-B', check to see if 'B = -A', so that C = x+A...
183 if (Value *V = dyn_castNegInst(Op1))
184 return BinaryOperator::create(Instruction::Add, Op0, V);
186 // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression is
187 // not used by anyone else...
189 if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1))
190 if (Op1I->use_size() == 1 && Op1I->getOpcode() == Instruction::Sub) {
191 // Swap the two operands of the subexpr...
192 Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
193 Op1I->setOperand(0, IIOp1);
194 Op1I->setOperand(1, IIOp0);
196 // Create the new top level add instruction...
197 return BinaryOperator::create(Instruction::Add, Op0, Op1);
202 Instruction *InstCombiner::visitMul(BinaryOperator *I) {
203 if (I->use_empty()) return 0; // Don't fix dead instructions...
204 bool Changed = SimplifyBinOp(I);
205 Value *Op1 = I->getOperand(0);
207 // Simplify add instructions with a constant RHS...
208 if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(1))) {
209 if (I->getType()->isIntegral() && cast<ConstantInt>(Op2)->equalsInt(1)){
210 // Eliminate 'mul int %X, 1'
211 AddUsesToWorkList(I); // Add all modified instrs to worklist
212 I->replaceAllUsesWith(Op1);
215 } else if (I->getType()->isIntegral() &&
216 cast<ConstantInt>(Op2)->equalsInt(2)) {
217 // Convert 'mul int %X, 2' to 'add int %X, %X'
218 return BinaryOperator::create(Instruction::Add, Op1, Op1, I->getName());
220 } else if (Op2->isNullValue()) {
221 // Eliminate 'mul int %X, 0'
222 AddUsesToWorkList(I); // Add all modified instrs to worklist
223 I->replaceAllUsesWith(Op2); // Set this value to zero directly
228 return Changed ? I : 0;
232 Instruction *InstCombiner::visitDiv(BinaryOperator *I) {
233 if (I->use_empty()) return 0; // Don't fix dead instructions...
236 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1)))
237 if (RHS->equalsInt(1)) {
238 AddUsesToWorkList(I); // Add all modified instrs to worklist
239 I->replaceAllUsesWith(I->getOperand(0));
246 Instruction *InstCombiner::visitRem(BinaryOperator *I) {
247 if (I->use_empty()) return 0; // Don't fix dead instructions...
250 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1)))
251 if (RHS->equalsInt(1)) {
252 AddUsesToWorkList(I); // Add all modified instrs to worklist
253 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
259 static Constant *getMaxValue(const Type *Ty) {
260 assert(Ty == Type::BoolTy || Ty->isIntegral());
261 if (Ty == Type::BoolTy)
262 return ConstantBool::True;
265 return ConstantSInt::get(Ty, -1);
266 else if (Ty->isUnsigned()) {
267 // Calculate -1 casted to the right type...
268 unsigned TypeBits = Ty->getPrimitiveSize()*8;
269 uint64_t Val = (uint64_t)-1LL; // All ones
270 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
271 return ConstantUInt::get(Ty, Val);
277 Instruction *InstCombiner::visitAnd(BinaryOperator *I) {
278 if (I->use_empty()) return 0; // Don't fix dead instructions...
279 bool Changed = SimplifyBinOp(I);
280 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
282 // and X, X = X and X, 0 == 0
283 if (Op0 == Op1 || Op1 == Constant::getNullValue(I->getType())) {
284 AddUsesToWorkList(I); // Add all modified instrs to worklist
285 I->replaceAllUsesWith(Op1);
290 if (Constant *RHS = dyn_cast<Constant>(Op1))
291 if (RHS == getMaxValue(I->getType())) {
292 AddUsesToWorkList(I); // Add all modified instrs to worklist
293 I->replaceAllUsesWith(Op0);
297 return Changed ? I : 0;
302 Instruction *InstCombiner::visitOr(BinaryOperator *I) {
303 if (I->use_empty()) return 0; // Don't fix dead instructions...
304 bool Changed = SimplifyBinOp(I);
305 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
307 // or X, X = X or X, 0 == X
308 if (Op0 == Op1 || Op1 == Constant::getNullValue(I->getType())) {
309 AddUsesToWorkList(I); // Add all modified instrs to worklist
310 I->replaceAllUsesWith(Op0);
315 if (Constant *RHS = dyn_cast<Constant>(Op1))
316 if (RHS == getMaxValue(I->getType())) {
317 AddUsesToWorkList(I); // Add all modified instrs to worklist
318 I->replaceAllUsesWith(Op1);
322 return Changed ? I : 0;
327 Instruction *InstCombiner::visitXor(BinaryOperator *I) {
328 if (I->use_empty()) return 0; // Don't fix dead instructions...
329 bool Changed = SimplifyBinOp(I);
330 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
334 AddUsesToWorkList(I); // Add all modified instrs to worklist
335 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
340 if (Op1 == Constant::getNullValue(I->getType())) {
341 AddUsesToWorkList(I); // Add all modified instrs to worklist
342 I->replaceAllUsesWith(Op0);
346 return Changed ? I : 0;
349 // isTrueWhenEqual - Return true if the specified setcondinst instruction is
350 // true when both operands are equal...
352 static bool isTrueWhenEqual(Instruction *I) {
353 return I->getOpcode() == Instruction::SetEQ ||
354 I->getOpcode() == Instruction::SetGE ||
355 I->getOpcode() == Instruction::SetLE;
358 Instruction *InstCombiner::visitSetCondInst(BinaryOperator *I) {
359 if (I->use_empty()) return 0; // Don't fix dead instructions...
360 bool Changed = SimplifyBinOp(I);
363 if (I->getOperand(0) == I->getOperand(1)) {
364 AddUsesToWorkList(I); // Add all modified instrs to worklist
365 I->replaceAllUsesWith(ConstantBool::get(isTrueWhenEqual(I)));
369 // setcc <global*>, 0 - Global value addresses are never null!
370 if (isa<GlobalValue>(I->getOperand(0)) &&
371 isa<ConstantPointerNull>(I->getOperand(1))) {
372 AddUsesToWorkList(I); // Add all modified instrs to worklist
373 I->replaceAllUsesWith(ConstantBool::get(!isTrueWhenEqual(I)));
377 return Changed ? I : 0;
382 Instruction *InstCombiner::visitShiftInst(Instruction *I) {
383 if (I->use_empty()) return 0; // Don't fix dead instructions...
384 assert(I->getOperand(1)->getType() == Type::UByteTy);
385 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
387 // shl X, 0 == X and shr X, 0 == X
388 // shl 0, X == 0 and shr 0, X == 0
389 if (Op1 == Constant::getNullValue(Type::UByteTy) ||
390 Op0 == Constant::getNullValue(Op0->getType())) {
391 AddUsesToWorkList(I); // Add all modified instrs to worklist
392 I->replaceAllUsesWith(Op0);
396 // shl int X, 32 = 0 and shr sbyte Y, 9 = 0, ... just don't eliminate shr of
399 if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
400 unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
401 if (CUI->getValue() >= TypeBits &&
402 !(Op0->getType()->isSigned() && I->getOpcode() == Instruction::Shr)) {
403 AddUsesToWorkList(I); // Add all modified instrs to worklist
404 I->replaceAllUsesWith(Constant::getNullValue(Op0->getType()));
412 // isEliminableCastOfCast - Return true if it is valid to eliminate the CI
415 static inline bool isEliminableCastOfCast(const CastInst *CI,
416 const CastInst *CSrc) {
417 assert(CI->getOperand(0) == CSrc);
418 const Type *SrcTy = CSrc->getOperand(0)->getType();
419 const Type *MidTy = CSrc->getType();
420 const Type *DstTy = CI->getType();
422 // It is legal to eliminate the instruction if casting A->B->A
423 if (SrcTy == DstTy) return true;
425 // Allow free casting and conversion of sizes as long as the sign doesn't
427 if (SrcTy->isSigned() == MidTy->isSigned() &&
428 MidTy->isSigned() == DstTy->isSigned())
431 // Otherwise, we cannot succeed. Specifically we do not want to allow things
432 // like: short -> ushort -> uint, because this can create wrong results if
433 // the input short is negative!
439 // CastInst simplification
441 Instruction *InstCombiner::visitCastInst(CastInst *CI) {
442 if (CI->use_empty()) return 0; // Don't fix dead instructions...
444 // If the user is casting a value to the same type, eliminate this cast
446 if (CI->getType() == CI->getOperand(0)->getType() && !CI->use_empty()) {
447 AddUsesToWorkList(CI); // Add all modified instrs to worklist
448 CI->replaceAllUsesWith(CI->getOperand(0));
453 // If casting the result of another cast instruction, try to eliminate this
456 if (CastInst *CSrc = dyn_cast<CastInst>(CI->getOperand(0)))
457 if (isEliminableCastOfCast(CI, CSrc)) {
458 // This instruction now refers directly to the cast's src operand. This
459 // has a good chance of making CSrc dead.
460 CI->setOperand(0, CSrc->getOperand(0));
468 // PHINode simplification
470 Instruction *InstCombiner::visitPHINode(PHINode *PN) {
471 if (PN->use_empty()) return 0; // Don't fix dead instructions...
473 // If the PHI node only has one incoming value, eliminate the PHI node...
474 if (PN->getNumIncomingValues() == 1) {
475 AddUsesToWorkList(PN); // Add all modified instrs to worklist
476 PN->replaceAllUsesWith(PN->getIncomingValue(0));
484 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst *GEP) {
485 // Is it getelementptr %P, uint 0
486 // If so, elminate the noop.
487 if (GEP->getNumOperands() == 2 && !GEP->use_empty() &&
488 GEP->getOperand(1) == Constant::getNullValue(Type::UIntTy)) {
489 AddUsesToWorkList(GEP); // Add all modified instrs to worklist
490 GEP->replaceAllUsesWith(GEP->getOperand(0));
494 return visitMemAccessInst(GEP);
498 // Combine Indices - If the source pointer to this mem access instruction is a
499 // getelementptr instruction, combine the indices of the GEP into this
502 Instruction *InstCombiner::visitMemAccessInst(MemAccessInst *MAI) {
503 GetElementPtrInst *Src =
504 dyn_cast<GetElementPtrInst>(MAI->getPointerOperand());
507 std::vector<Value *> Indices;
509 // Only special case we have to watch out for is pointer arithmetic on the
511 unsigned FirstIdx = MAI->getFirstIndexOperandNumber();
512 if (FirstIdx == MAI->getNumOperands() ||
513 (FirstIdx == MAI->getNumOperands()-1 &&
514 MAI->getOperand(FirstIdx) == ConstantUInt::get(Type::UIntTy, 0))) {
515 // Replace the index list on this MAI with the index on the getelementptr
516 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
517 } else if (*MAI->idx_begin() == ConstantUInt::get(Type::UIntTy, 0)) {
518 // Otherwise we can do the fold if the first index of the GEP is a zero
519 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
520 Indices.insert(Indices.end(), MAI->idx_begin()+1, MAI->idx_end());
523 if (Indices.empty()) return 0; // Can't do the fold?
525 switch (MAI->getOpcode()) {
526 case Instruction::GetElementPtr:
527 return new GetElementPtrInst(Src->getOperand(0), Indices, MAI->getName());
528 case Instruction::Load:
529 return new LoadInst(Src->getOperand(0), Indices, MAI->getName());
530 case Instruction::Store:
531 return new StoreInst(MAI->getOperand(0), Src->getOperand(0), Indices);
533 assert(0 && "Unknown memaccessinst!");
541 bool InstCombiner::runOnFunction(Function *F) {
542 bool Changed = false;
544 WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
546 while (!WorkList.empty()) {
547 Instruction *I = WorkList.back(); // Get an instruction from the worklist
550 // Now that we have an instruction, try combining it to simplify it...
551 Instruction *Result = visit(I);
554 // Should we replace the old instruction with a new one?
556 // Instructions can end up on the worklist more than once. Make sure
557 // we do not process an instruction that has been deleted.
558 std::vector<Instruction*>::iterator It = std::find(WorkList.begin(),
560 while (It != WorkList.end()) {
561 It = WorkList.erase(It);
562 It = std::find(It, WorkList.end(), I);
565 ReplaceInstWithInst(I, Result);
568 WorkList.push_back(Result);
569 AddUsesToWorkList(Result);
577 Pass *createInstructionCombiningPass() {
578 return new InstCombiner();