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"
31 class InstCombiner : public FunctionPass,
32 public InstVisitor<InstCombiner, Instruction*> {
33 // Worklist of all of the instructions that need to be simplified.
34 std::vector<Instruction*> WorkList;
36 void AddUsesToWorkList(Instruction *I) {
37 // The instruction was simplified, add all users of the instruction to
38 // the work lists because they might get more simplified now...
40 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
42 WorkList.push_back(cast<Instruction>(*UI));
46 const char *getPassName() const { return "Instruction Combining"; }
48 virtual bool runOnFunction(Function *F);
50 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
54 // Visitation implementation - Implement instruction combining for different
55 // instruction types. The semantics are as follows:
57 // null - No change was made
58 // I - Change was made, I is still valid
59 // otherwise - Change was made, replace I with returned instruction
61 Instruction *visitNot(UnaryOperator *I);
62 Instruction *visitAdd(BinaryOperator *I);
63 Instruction *visitSub(BinaryOperator *I);
64 Instruction *visitMul(BinaryOperator *I);
65 Instruction *visitDiv(BinaryOperator *I);
66 Instruction *visitRem(BinaryOperator *I);
67 Instruction *visitAnd(BinaryOperator *I);
68 Instruction *visitOr (BinaryOperator *I);
69 Instruction *visitXor(BinaryOperator *I);
70 Instruction *visitSetCondInst(BinaryOperator *I);
71 Instruction *visitShiftInst(Instruction *I);
72 Instruction *visitCastInst(CastInst *CI);
73 Instruction *visitPHINode(PHINode *PN);
74 Instruction *visitGetElementPtrInst(GetElementPtrInst *GEP);
75 Instruction *visitMemAccessInst(MemAccessInst *MAI);
77 // visitInstruction - Specify what to return for unhandled instructions...
78 Instruction *visitInstruction(Instruction *I) { return 0; }
83 Instruction *InstCombiner::visitNot(UnaryOperator *I) {
84 if (I->use_empty()) return 0; // Don't fix dead instructions...
87 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(0)))
88 if (Op->getOpcode() == Instruction::Not) {
89 AddUsesToWorkList(I); // Add all modified instrs to worklist
90 I->replaceAllUsesWith(Op->getOperand(0));
97 // Make sure that this instruction has a constant on the right hand side if it
98 // has any constant arguments. If not, fix it an return true.
100 static bool SimplifyBinOp(BinaryOperator *I) {
101 if (isa<Constant>(I->getOperand(0)) && !isa<Constant>(I->getOperand(1)))
102 return !I->swapOperands();
106 // dyn_castNegInst - Given a 'sub' instruction, return the RHS of the
107 // instruction if the LHS is a constant zero (which is the 'negate' form).
109 static inline Value *dyn_castNegInst(Value *V) {
110 Instruction *I = dyn_cast<Instruction>(V);
111 if (!I || I->getOpcode() != Instruction::Sub) return 0;
113 if (I->getOperand(0) == Constant::getNullValue(I->getType()))
114 return I->getOperand(1);
118 Instruction *InstCombiner::visitAdd(BinaryOperator *I) {
119 if (I->use_empty()) return 0; // Don't fix dead add instructions...
120 bool Changed = SimplifyBinOp(I);
121 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
123 // Eliminate 'add int %X, 0'
124 if (I->getType()->isIntegral() &&
125 RHS == Constant::getNullValue(I->getType())) {
126 AddUsesToWorkList(I); // Add all modified instrs to worklist
127 I->replaceAllUsesWith(LHS);
132 if (Value *V = dyn_castNegInst(LHS))
133 return BinaryOperator::create(Instruction::Sub, RHS, V);
136 if (Value *V = dyn_castNegInst(RHS))
137 return BinaryOperator::create(Instruction::Sub, LHS, V);
139 // Simplify add instructions with a constant RHS...
140 if (Constant *Op2 = dyn_cast<Constant>(RHS)) {
141 if (BinaryOperator *ILHS = dyn_cast<BinaryOperator>(LHS)) {
142 if (ILHS->getOpcode() == Instruction::Add &&
143 isa<Constant>(ILHS->getOperand(1))) {
145 // %Y = add int %X, 1
146 // %Z = add int %Y, 1
148 // %Z = add int %X, 2
150 if (Constant *Val = *Op2 + *cast<Constant>(ILHS->getOperand(1))) {
151 I->setOperand(0, ILHS->getOperand(0));
152 I->setOperand(1, Val);
159 return Changed ? I : 0;
162 Instruction *InstCombiner::visitSub(BinaryOperator *I) {
163 if (I->use_empty()) return 0; // Don't fix dead add instructions...
164 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
166 if (Op0 == Op1) { // sub X, X -> 0
167 AddUsesToWorkList(I); // Add all modified instrs to worklist
168 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
172 // If this is a subtract instruction with a constant RHS, convert it to an add
173 // instruction of a negative constant
175 if (Constant *Op2 = dyn_cast<Constant>(Op1))
176 if (Constant *RHS = *Constant::getNullValue(I->getType()) - *Op2) // 0 - RHS
177 return BinaryOperator::create(Instruction::Add, Op0, RHS, I->getName());
179 // If this is a 'C = x-B', check to see if 'B = -A', so that C = x+A...
180 if (Value *V = dyn_castNegInst(Op1))
181 return BinaryOperator::create(Instruction::Add, Op0, V);
183 // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression is
184 // not used by anyone else...
186 if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1))
187 if (Op1I->use_size() == 1) {
188 // Swap the two operands of the subexpr...
189 Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
190 Op1I->setOperand(0, IIOp1);
191 Op1I->setOperand(1, IIOp0);
193 // Create the new top level add instruction...
194 return BinaryOperator::create(Instruction::Add, Op0, Op1);
199 Instruction *InstCombiner::visitMul(BinaryOperator *I) {
200 if (I->use_empty()) return 0; // Don't fix dead instructions...
201 bool Changed = SimplifyBinOp(I);
202 Value *Op1 = I->getOperand(0);
204 // Simplify add instructions with a constant RHS...
205 if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(1))) {
206 if (I->getType()->isIntegral() && cast<ConstantInt>(Op2)->equalsInt(1)){
207 // Eliminate 'mul int %X, 1'
208 AddUsesToWorkList(I); // Add all modified instrs to worklist
209 I->replaceAllUsesWith(Op1);
212 } else if (I->getType()->isIntegral() &&
213 cast<ConstantInt>(Op2)->equalsInt(2)) {
214 // Convert 'mul int %X, 2' to 'add int %X, %X'
215 return BinaryOperator::create(Instruction::Add, Op1, Op1, I->getName());
217 } else if (Op2->isNullValue()) {
218 // Eliminate 'mul int %X, 0'
219 AddUsesToWorkList(I); // Add all modified instrs to worklist
220 I->replaceAllUsesWith(Op2); // Set this value to zero directly
225 return Changed ? I : 0;
229 Instruction *InstCombiner::visitDiv(BinaryOperator *I) {
230 if (I->use_empty()) return 0; // Don't fix dead instructions...
233 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1)))
234 if (RHS->equalsInt(1)) {
235 AddUsesToWorkList(I); // Add all modified instrs to worklist
236 I->replaceAllUsesWith(I->getOperand(0));
243 Instruction *InstCombiner::visitRem(BinaryOperator *I) {
244 if (I->use_empty()) return 0; // Don't fix dead instructions...
247 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1)))
248 if (RHS->equalsInt(1)) {
249 AddUsesToWorkList(I); // Add all modified instrs to worklist
250 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
256 static Constant *getMaxValue(const Type *Ty) {
257 assert(Ty == Type::BoolTy || Ty->isIntegral());
258 if (Ty == Type::BoolTy)
259 return ConstantBool::True;
262 return ConstantSInt::get(Ty, -1);
263 else if (Ty->isUnsigned()) {
264 // Calculate -1 casted to the right type...
265 unsigned TypeBits = Ty->getPrimitiveSize()*8;
266 uint64_t Val = (uint64_t)-1LL; // All ones
267 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
268 return ConstantUInt::get(Ty, Val);
274 Instruction *InstCombiner::visitAnd(BinaryOperator *I) {
275 if (I->use_empty()) return 0; // Don't fix dead instructions...
276 bool Changed = SimplifyBinOp(I);
277 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
279 // and X, X = X and X, 0 == 0
280 if (Op0 == Op1 || Op1 == Constant::getNullValue(I->getType())) {
281 AddUsesToWorkList(I); // Add all modified instrs to worklist
282 I->replaceAllUsesWith(Op1);
287 if (Constant *RHS = dyn_cast<Constant>(Op1))
288 if (RHS == getMaxValue(I->getType())) {
289 AddUsesToWorkList(I); // Add all modified instrs to worklist
290 I->replaceAllUsesWith(Op0);
294 return Changed ? I : 0;
299 Instruction *InstCombiner::visitOr(BinaryOperator *I) {
300 if (I->use_empty()) return 0; // Don't fix dead instructions...
301 bool Changed = SimplifyBinOp(I);
302 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
304 // or X, X = X or X, 0 == X
305 if (Op0 == Op1 || Op1 == Constant::getNullValue(I->getType())) {
306 AddUsesToWorkList(I); // Add all modified instrs to worklist
307 I->replaceAllUsesWith(Op0);
312 if (Constant *RHS = dyn_cast<Constant>(Op1))
313 if (RHS == getMaxValue(I->getType())) {
314 AddUsesToWorkList(I); // Add all modified instrs to worklist
315 I->replaceAllUsesWith(Op1);
319 return Changed ? I : 0;
324 Instruction *InstCombiner::visitXor(BinaryOperator *I) {
325 if (I->use_empty()) return 0; // Don't fix dead instructions...
326 bool Changed = SimplifyBinOp(I);
327 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
331 AddUsesToWorkList(I); // Add all modified instrs to worklist
332 I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
337 if (Op1 == Constant::getNullValue(I->getType())) {
338 AddUsesToWorkList(I); // Add all modified instrs to worklist
339 I->replaceAllUsesWith(Op0);
343 return Changed ? I : 0;
346 Instruction *InstCombiner::visitSetCondInst(BinaryOperator *I) {
347 if (I->use_empty()) return 0; // Don't fix dead instructions...
348 bool Changed = SimplifyBinOp(I);
351 if (I->getOperand(0) == I->getOperand(1)) {
352 bool NewVal = I->getOpcode() == Instruction::SetEQ ||
353 I->getOpcode() == Instruction::SetGE ||
354 I->getOpcode() == Instruction::SetLE;
355 AddUsesToWorkList(I); // Add all modified instrs to worklist
356 I->replaceAllUsesWith(ConstantBool::get(NewVal));
360 return Changed ? I : 0;
365 Instruction *InstCombiner::visitShiftInst(Instruction *I) {
366 if (I->use_empty()) return 0; // Don't fix dead instructions...
367 assert(I->getOperand(1)->getType() == Type::UByteTy);
368 Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
370 // shl X, 0 == X and shr X, 0 == X
371 // shl 0, X == 0 and shr 0, X == 0
372 if (Op1 == Constant::getNullValue(Type::UByteTy) ||
373 Op0 == Constant::getNullValue(Op0->getType())) {
374 AddUsesToWorkList(I); // Add all modified instrs to worklist
375 I->replaceAllUsesWith(Op0);
379 // shl int X, 32 = 0 and shr sbyte Y, 9 = 0, ... just don't eliminate shr of
382 if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
383 unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
384 if (CUI->getValue() >= TypeBits &&
385 !(Op0->getType()->isSigned() && I->getOpcode() == Instruction::Shr)) {
386 AddUsesToWorkList(I); // Add all modified instrs to worklist
387 I->replaceAllUsesWith(Constant::getNullValue(Op0->getType()));
395 // isEliminableCastOfCast - Return true if it is valid to eliminate the CI
398 static inline bool isEliminableCastOfCast(const CastInst *CI,
399 const CastInst *CSrc) {
400 assert(CI->getOperand(0) == CSrc);
401 const Type *SrcTy = CSrc->getOperand(0)->getType();
402 const Type *MidTy = CSrc->getType();
403 const Type *DstTy = CI->getType();
405 // It is legal to eliminate the instruction if casting A->B->A
406 if (SrcTy == DstTy) return true;
408 // Allow free casting and conversion of sizes as long as the sign doesn't
410 if (SrcTy->isSigned() == MidTy->isSigned() &&
411 MidTy->isSigned() == DstTy->isSigned())
414 // Otherwise, we cannot succeed. Specifically we do not want to allow things
415 // like: short -> ushort -> uint, because this can create wrong results if
416 // the input short is negative!
422 // CastInst simplification
424 Instruction *InstCombiner::visitCastInst(CastInst *CI) {
425 if (CI->use_empty()) return 0; // Don't fix dead instructions...
427 // If the user is casting a value to the same type, eliminate this cast
429 if (CI->getType() == CI->getOperand(0)->getType() && !CI->use_empty()) {
430 AddUsesToWorkList(CI); // Add all modified instrs to worklist
431 CI->replaceAllUsesWith(CI->getOperand(0));
436 // If casting the result of another cast instruction, try to eliminate this
439 if (CastInst *CSrc = dyn_cast<CastInst>(CI->getOperand(0)))
440 if (isEliminableCastOfCast(CI, CSrc)) {
441 // This instruction now refers directly to the cast's src operand. This
442 // has a good chance of making CSrc dead.
443 CI->setOperand(0, CSrc->getOperand(0));
451 // PHINode simplification
453 Instruction *InstCombiner::visitPHINode(PHINode *PN) {
454 if (PN->use_empty()) return 0; // Don't fix dead instructions...
456 // If the PHI node only has one incoming value, eliminate the PHI node...
457 if (PN->getNumIncomingValues() == 1) {
458 AddUsesToWorkList(PN); // Add all modified instrs to worklist
459 PN->replaceAllUsesWith(PN->getIncomingValue(0));
467 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst *GEP) {
468 // Is it getelementptr %P, uint 0
469 // If so, elminate the noop.
470 if (GEP->getNumOperands() == 2 && !GEP->use_empty() &&
471 GEP->getOperand(1) == Constant::getNullValue(Type::UIntTy)) {
472 AddUsesToWorkList(GEP); // Add all modified instrs to worklist
473 GEP->replaceAllUsesWith(GEP->getOperand(0));
477 return visitMemAccessInst(GEP);
481 // Combine Indices - If the source pointer to this mem access instruction is a
482 // getelementptr instruction, combine the indices of the GEP into this
485 Instruction *InstCombiner::visitMemAccessInst(MemAccessInst *MAI) {
486 GetElementPtrInst *Src =
487 dyn_cast<GetElementPtrInst>(MAI->getPointerOperand());
490 std::vector<Value *> Indices;
492 // Only special case we have to watch out for is pointer arithmetic on the
494 unsigned FirstIdx = MAI->getFirstIndexOperandNumber();
495 if (FirstIdx == MAI->getNumOperands() ||
496 (FirstIdx == MAI->getNumOperands()-1 &&
497 MAI->getOperand(FirstIdx) == ConstantUInt::get(Type::UIntTy, 0))) {
498 // Replace the index list on this MAI with the index on the getelementptr
499 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
500 } else if (*MAI->idx_begin() == ConstantUInt::get(Type::UIntTy, 0)) {
501 // Otherwise we can do the fold if the first index of the GEP is a zero
502 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
503 Indices.insert(Indices.end(), MAI->idx_begin()+1, MAI->idx_end());
506 if (Indices.empty()) return 0; // Can't do the fold?
508 switch (MAI->getOpcode()) {
509 case Instruction::GetElementPtr:
510 return new GetElementPtrInst(Src->getOperand(0), Indices, MAI->getName());
511 case Instruction::Load:
512 return new LoadInst(Src->getOperand(0), Indices, MAI->getName());
513 case Instruction::Store:
514 return new StoreInst(MAI->getOperand(0), Src->getOperand(0), Indices);
516 assert(0 && "Unknown memaccessinst!");
524 bool InstCombiner::runOnFunction(Function *F) {
525 bool Changed = false;
527 WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
529 while (!WorkList.empty()) {
530 Instruction *I = WorkList.back(); // Get an instruction from the worklist
533 // Now that we have an instruction, try combining it to simplify it...
534 Instruction *Result = visit(I);
536 // Should we replace the old instruction with a new one?
538 ReplaceInstWithInst(I, Result);
540 WorkList.push_back(Result);
541 AddUsesToWorkList(Result);
549 Pass *createInstructionCombiningPass() {
550 return new InstCombiner();