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 DCE pass is useful.
7 // This pass combines things like:
13 // This is a simple worklist driven algorithm.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Transforms/Scalar/InstructionCombining.h"
18 #include "llvm/ConstantHandling.h"
19 #include "llvm/Function.h"
20 #include "llvm/iMemory.h"
21 #include "llvm/iOther.h"
22 #include "llvm/InstrTypes.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Support/InstIterator.h"
25 #include "../TransformInternals.h"
27 static Instruction *CombineBinOp(BinaryOperator *I) {
30 // First thing we do is make sure that this instruction has a constant on the
31 // right hand side if it has any constant arguments.
33 if (isa<Constant>(I->getOperand(0)) && !isa<Constant>(I->getOperand(1)))
34 if (!I->swapOperands())
37 bool LocalChange = true;
40 Value *Op1 = I->getOperand(0);
41 if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(1))) {
42 switch (I->getOpcode()) {
43 case Instruction::Add:
44 if (I->getType()->isIntegral() && cast<ConstantInt>(Op2)->equalsInt(0)){
45 // Eliminate 'add int %X, 0'
46 I->replaceAllUsesWith(Op1); // FIXME: This breaks the worklist
51 if (Instruction *IOp1 = dyn_cast<Instruction>(Op1)) {
52 if (IOp1->getOpcode() == Instruction::Add &&
53 isa<Constant>(IOp1->getOperand(1))) {
60 // Constant fold both constants...
61 Constant *Val = *Op2 + *cast<Constant>(IOp1->getOperand(1));
64 I->setOperand(0, IOp1->getOperand(0));
65 I->setOperand(1, Val);
74 case Instruction::Mul:
75 if (I->getType()->isIntegral() && cast<ConstantInt>(Op2)->equalsInt(1)){
76 // Eliminate 'mul int %X, 1'
77 I->replaceAllUsesWith(Op1); // FIXME: This breaks the worklist
86 Changed |= LocalChange;
89 if (!Changed) return 0;
93 // Combine Indices - If the source pointer to this mem access instruction is a
94 // getelementptr instruction, combine the indices of the GEP into this
97 static Instruction *CombineIndicies(MemAccessInst *MAI) {
98 GetElementPtrInst *Src =
99 dyn_cast<GetElementPtrInst>(MAI->getPointerOperand());
102 std::vector<Value *> Indices;
104 // Only special case we have to watch out for is pointer arithmetic on the
106 unsigned FirstIdx = MAI->getFirstIndexOperandNumber();
107 if (FirstIdx == MAI->getNumOperands() ||
108 (FirstIdx == MAI->getNumOperands()-1 &&
109 MAI->getOperand(FirstIdx) == ConstantUInt::get(Type::UIntTy, 0))) {
110 // Replace the index list on this MAI with the index on the getelementptr
111 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
112 } else if (*MAI->idx_begin() == ConstantUInt::get(Type::UIntTy, 0)) {
113 // Otherwise we can do the fold if the first index of the GEP is a zero
114 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
115 Indices.insert(Indices.end(), MAI->idx_begin()+1, MAI->idx_end());
118 if (Indices.empty()) return 0; // Can't do the fold?
120 switch (MAI->getOpcode()) {
121 case Instruction::GetElementPtr:
122 return new GetElementPtrInst(Src->getOperand(0), Indices, MAI->getName());
123 case Instruction::Load:
124 return new LoadInst(Src->getOperand(0), Indices, MAI->getName());
125 case Instruction::Store:
126 return new StoreInst(MAI->getOperand(0), Src->getOperand(0), Indices);
128 assert(0 && "Unknown memaccessinst!");
135 static bool CombineInstruction(Instruction *I) {
136 Instruction *Result = 0;
137 if (BinaryOperator *BOP = dyn_cast<BinaryOperator>(I))
138 Result = CombineBinOp(BOP);
139 else if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(I))
140 Result = CombineIndicies(MAI);
141 else if (CastInst *CI = dyn_cast<CastInst>(I)) {
142 if (CI->getType() == CI->getOperand(0)->getType() && !CI->use_empty()) {
143 CI->replaceAllUsesWith(CI->getOperand(0));
149 if (!Result) return false;
150 if (Result == I) return true;
152 // If we get to here, we are to replace I with Result.
153 ReplaceInstWithInst(I, Result);
157 static bool doInstCombining(Function *M) {
158 // Start the worklist out with all of the instructions in the function in it.
159 std::vector<Instruction*> WorkList(inst_begin(M), inst_end(M));
161 while (!WorkList.empty()) {
162 Instruction *I = WorkList.back(); // Get an instruction from the worklist
165 // Now that we have an instruction, try combining it to simplify it...
166 if (CombineInstruction(I)) {
167 // The instruction was simplified, add all users of the instruction to
168 // the work lists because they might get more simplified now...
170 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
172 if (Instruction *User = dyn_cast<Instruction>(*UI))
173 WorkList.push_back(User);
181 struct InstructionCombining : public MethodPass {
182 virtual bool runOnMethod(Function *F) { return doInstCombining(F); }
186 Pass *createInstructionCombiningPass() {
187 return new InstructionCombining();