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/InstrTypes.h"
22 #include "llvm/Pass.h"
23 #include "llvm/Support/InstIterator.h"
24 #include "../TransformInternals.h"
26 static Instruction *CombineBinOp(BinaryOperator *I) {
29 // First thing we do is make sure that this instruction has a constant on the
30 // right hand side if it has any constant arguments.
32 if (isa<Constant>(I->getOperand(0)) && !isa<Constant>(I->getOperand(1)))
33 if (!I->swapOperands())
36 bool LocalChange = true;
39 Value *Op1 = I->getOperand(0);
40 if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(1))) {
41 switch (I->getOpcode()) {
42 case Instruction::Add:
43 if (I->getType()->isIntegral() && cast<ConstantInt>(Op2)->equalsInt(0)){
44 // Eliminate 'add int %X, 0'
45 I->replaceAllUsesWith(Op1); // FIXME: This breaks the worklist
50 if (Instruction *IOp1 = dyn_cast<Instruction>(Op1)) {
51 if (IOp1->getOpcode() == Instruction::Add &&
52 isa<Constant>(IOp1->getOperand(1))) {
59 // Constant fold both constants...
60 Constant *Val = *Op2 + *cast<Constant>(IOp1->getOperand(1));
63 I->setOperand(0, IOp1->getOperand(0));
64 I->setOperand(1, Val);
73 case Instruction::Mul:
74 if (I->getType()->isIntegral() && cast<ConstantInt>(Op2)->equalsInt(1)){
75 // Eliminate 'mul int %X, 1'
76 I->replaceAllUsesWith(Op1); // FIXME: This breaks the worklist
85 Changed |= LocalChange;
88 if (!Changed) return 0;
92 // Combine Indices - If the source pointer to this mem access instruction is a
93 // getelementptr instruction, combine the indices of the GEP into this
96 static Instruction *CombineIndicies(MemAccessInst *MAI) {
97 GetElementPtrInst *Src =
98 dyn_cast<GetElementPtrInst>(MAI->getPointerOperand());
101 std::vector<Value *> Indices;
103 // Only special case we have to watch out for is pointer arithmetic on the
105 unsigned FirstIdx = MAI->getFirstIndexOperandNumber();
106 if (FirstIdx == MAI->getNumOperands() ||
107 (FirstIdx == MAI->getNumOperands()-1 &&
108 MAI->getOperand(FirstIdx) == ConstantUInt::get(Type::UIntTy, 0))) {
109 // Replace the index list on this MAI with the index on the getelementptr
110 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
111 } else if (*MAI->idx_begin() == ConstantUInt::get(Type::UIntTy, 0)) {
112 // Otherwise we can do the fold if the first index of the GEP is a zero
113 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
114 Indices.insert(Indices.end(), MAI->idx_begin()+1, MAI->idx_end());
117 if (Indices.empty()) return 0; // Can't do the fold?
119 switch (MAI->getOpcode()) {
120 case Instruction::GetElementPtr:
121 return new GetElementPtrInst(Src->getOperand(0), Indices, MAI->getName());
122 case Instruction::Load:
123 return new LoadInst(Src->getOperand(0), Indices, MAI->getName());
124 case Instruction::Store:
125 return new StoreInst(MAI->getOperand(0), Src->getOperand(0),
126 Indices, MAI->getName());
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);
142 if (!Result) return false;
143 if (Result == I) return true;
145 // If we get to here, we are to replace I with Result.
146 ReplaceInstWithInst(I, Result);
150 static bool doInstCombining(Function *M) {
151 // Start the worklist out with all of the instructions in the function in it.
152 std::vector<Instruction*> WorkList(inst_begin(M), inst_end(M));
154 while (!WorkList.empty()) {
155 Instruction *I = WorkList.back(); // Get an instruction from the worklist
158 // Now that we have an instruction, try combining it to simplify it...
159 if (CombineInstruction(I)) {
160 // The instruction was simplified, add all users of the instruction to
161 // the work lists because they might get more simplified now...
163 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
165 if (Instruction *User = dyn_cast<Instruction>(*UI))
166 WorkList.push_back(User);
174 struct InstructionCombining : public MethodPass {
175 virtual bool runOnMethod(Function *F) { return doInstCombining(F); }
179 Pass *createInstructionCombiningPass() {
180 return new InstructionCombining();