forked from OSchip/llvm-project
525 lines
17 KiB
C++
525 lines
17 KiB
C++
//===- InstructionCombining.cpp - Combine multiple instructions -------------=//
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//
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// InstructionCombining - Combine instructions to form fewer, simple
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// instructions. This pass does not modify the CFG, and has a tendancy to
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// make instructions dead, so a subsequent DIE pass is useful. This pass is
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// where algebraic simplification happens.
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//
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// This pass combines things like:
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// %Y = add int 1, %X
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// %Z = add int 1, %Y
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// into:
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// %Z = add int 2, %X
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//
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// This is a simple worklist driven algorithm.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar/InstructionCombining.h"
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#include "llvm/ConstantHandling.h"
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#include "llvm/iMemory.h"
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#include "llvm/iOther.h"
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#include "llvm/iOperators.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/InstIterator.h"
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#include "llvm/Support/InstVisitor.h"
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#include "../TransformInternals.h"
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namespace {
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class InstCombiner : public FunctionPass,
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public InstVisitor<InstCombiner, Instruction*> {
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// Worklist of all of the instructions that need to be simplified.
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std::vector<Instruction*> WorkList;
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void AddUsesToWorkList(Instruction *I) {
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// The instruction was simplified, add all users of the instruction to
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// the work lists because they might get more simplified now...
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//
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for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
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UI != UE; ++UI)
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WorkList.push_back(cast<Instruction>(*UI));
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}
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public:
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const char *getPassName() const { return "Instruction Combining"; }
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virtual bool runOnFunction(Function *F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.preservesCFG();
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}
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// Visitation implementation - Implement instruction combining for different
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// instruction types. The semantics are as follows:
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// Return Value:
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// null - No change was made
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// I - Change was made, I is still valid
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// otherwise - Change was made, replace I with returned instruction
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//
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Instruction *visitNot(UnaryOperator *I);
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Instruction *visitAdd(BinaryOperator *I);
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Instruction *visitSub(BinaryOperator *I);
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Instruction *visitMul(BinaryOperator *I);
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Instruction *visitDiv(BinaryOperator *I);
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Instruction *visitRem(BinaryOperator *I);
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Instruction *visitAnd(BinaryOperator *I);
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Instruction *visitOr (BinaryOperator *I);
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Instruction *visitXor(BinaryOperator *I);
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Instruction *visitSetCondInst(BinaryOperator *I);
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Instruction *visitShiftInst(Instruction *I);
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Instruction *visitCastInst(CastInst *CI);
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Instruction *visitGetElementPtrInst(GetElementPtrInst *GEP);
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Instruction *visitMemAccessInst(MemAccessInst *MAI);
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// visitInstruction - Specify what to return for unhandled instructions...
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Instruction *visitInstruction(Instruction *I) { return 0; }
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};
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}
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Instruction *InstCombiner::visitNot(UnaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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// not (not X) = X
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if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(0)))
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if (Op->getOpcode() == Instruction::Not) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op->getOperand(0));
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return I;
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}
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return 0;
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}
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// Make sure that this instruction has a constant on the right hand side if it
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// has any constant arguments. If not, fix it an return true.
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//
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static bool SimplifyBinOp(BinaryOperator *I) {
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if (isa<Constant>(I->getOperand(0)) && !isa<Constant>(I->getOperand(1)))
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return !I->swapOperands();
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return false;
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}
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// dyn_castNegInst - Given a 'sub' instruction, return the RHS of the
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// instruction if the LHS is a constant zero (which is the 'negate' form).
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//
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static inline Value *dyn_castNegInst(Value *V) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I || I->getOpcode() != Instruction::Sub) return 0;
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if (I->getOperand(0) == Constant::getNullValue(I->getType()))
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return I->getOperand(1);
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return 0;
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}
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Instruction *InstCombiner::visitAdd(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead add instructions...
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bool Changed = SimplifyBinOp(I);
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Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
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// Eliminate 'add int %X, 0'
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if (I->getType()->isIntegral() &&
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RHS == Constant::getNullValue(I->getType())) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(LHS);
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return I;
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}
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// -B + A --> A - B
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if (Value *V = dyn_castNegInst(LHS))
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return BinaryOperator::create(Instruction::Sub, RHS, LHS);
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// A + -B --> A - B
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if (Value *V = dyn_castNegInst(RHS))
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return BinaryOperator::create(Instruction::Sub, LHS, RHS);
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// Simplify add instructions with a constant RHS...
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if (Constant *Op2 = dyn_cast<Constant>(RHS)) {
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if (BinaryOperator *ILHS = dyn_cast<BinaryOperator>(LHS)) {
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if (ILHS->getOpcode() == Instruction::Add &&
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isa<Constant>(ILHS->getOperand(1))) {
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// Fold:
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// %Y = add int %X, 1
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// %Z = add int %Y, 1
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// into:
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// %Z = add int %X, 2
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//
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if (Constant *Val = *Op2 + *cast<Constant>(ILHS->getOperand(1))) {
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I->setOperand(0, ILHS->getOperand(0));
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I->setOperand(1, Val);
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return I;
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}
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}
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}
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}
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return Changed ? I : 0;
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}
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Instruction *InstCombiner::visitSub(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead add instructions...
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Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
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if (Op0 == Op1) { // sub X, X -> 0
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
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return I;
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}
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// If this is a subtract instruction with a constant RHS, convert it to an add
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// instruction of a negative constant
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//
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if (Constant *Op2 = dyn_cast<Constant>(Op1))
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if (Constant *RHS = *Constant::getNullValue(I->getType()) - *Op2) // 0 - RHS
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return BinaryOperator::create(Instruction::Add, Op0, RHS, I->getName());
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// If this is a 'C = -B', check to see if 'B = -A', so that C = A...
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if (Op0 == Constant::getNullValue(I->getType()))
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if (Value *V = dyn_castNegInst(Op1)) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(V);
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return I;
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}
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return 0;
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}
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Instruction *InstCombiner::visitMul(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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bool Changed = SimplifyBinOp(I);
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Value *Op1 = I->getOperand(0);
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// Simplify add instructions with a constant RHS...
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if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(1))) {
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if (I->getType()->isIntegral() && cast<ConstantInt>(Op2)->equalsInt(1)){
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// Eliminate 'mul int %X, 1'
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op1);
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return I;
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} else if (I->getType()->isIntegral() &&
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cast<ConstantInt>(Op2)->equalsInt(2)) {
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// Convert 'mul int %X, 2' to 'add int %X, %X'
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return BinaryOperator::create(Instruction::Add, Op1, Op1, I->getName());
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} else if (Op2->isNullValue()) {
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// Eliminate 'mul int %X, 0'
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op2); // Set this value to zero directly
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return I;
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}
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}
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return Changed ? I : 0;
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}
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Instruction *InstCombiner::visitDiv(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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// div X, 1 == X
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if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1)))
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if (RHS->equalsInt(1)) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(I->getOperand(0));
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return I;
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}
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return 0;
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}
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Instruction *InstCombiner::visitRem(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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// rem X, 1 == 0
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if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1)))
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if (RHS->equalsInt(1)) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
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return I;
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}
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return 0;
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}
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static Constant *getMaxValue(const Type *Ty) {
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assert(Ty == Type::BoolTy || Ty->isIntegral());
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if (Ty == Type::BoolTy)
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return ConstantBool::True;
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// Calculate -1 casted to the right type...
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unsigned TypeBits = Ty->getPrimitiveSize()*8;
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uint64_t Val = (uint64_t)-1LL; // All ones
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Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
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if (Ty->isSigned())
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return ConstantSInt::get(Ty, (int64_t)Val);
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else if (Ty->isUnsigned())
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return ConstantUInt::get(Ty, Val);
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return 0;
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}
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Instruction *InstCombiner::visitAnd(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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bool Changed = SimplifyBinOp(I);
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Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
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// and X, X = X and X, 0 == 0
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if (Op0 == Op1 || Op1 == Constant::getNullValue(I->getType())) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op1);
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return I;
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}
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// and X, -1 == X
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if (Constant *RHS = dyn_cast<Constant>(Op1))
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if (RHS == getMaxValue(I->getType())) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op0);
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return I;
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}
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return Changed ? I : 0;
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}
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Instruction *InstCombiner::visitOr(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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bool Changed = SimplifyBinOp(I);
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Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
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// or X, X = X or X, 0 == X
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if (Op0 == Op1 || Op1 == Constant::getNullValue(I->getType())) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op0);
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return I;
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}
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// or X, -1 == -1
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if (Constant *RHS = dyn_cast<Constant>(Op1))
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if (RHS == getMaxValue(I->getType())) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op1);
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return I;
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}
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return Changed ? I : 0;
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}
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Instruction *InstCombiner::visitXor(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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bool Changed = SimplifyBinOp(I);
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Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
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// xor X, X = 0
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if (Op0 == Op1) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
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return I;
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}
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// xor X, 0 == X
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if (Op1 == Constant::getNullValue(I->getType())) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op0);
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return I;
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}
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return Changed ? I : 0;
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}
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Instruction *InstCombiner::visitSetCondInst(BinaryOperator *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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bool Changed = SimplifyBinOp(I);
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// setcc X, X
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if (I->getOperand(0) == I->getOperand(1)) {
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bool NewVal = I->getOpcode() == Instruction::SetEQ ||
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I->getOpcode() == Instruction::SetGE ||
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I->getOpcode() == Instruction::SetLE;
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(ConstantBool::get(NewVal));
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return I;
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}
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return Changed ? I : 0;
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}
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Instruction *InstCombiner::visitShiftInst(Instruction *I) {
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if (I->use_empty()) return 0; // Don't fix dead instructions...
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assert(I->getOperand(1)->getType() == Type::UByteTy);
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Value *Op0 = I->getOperand(0), *Op1 = I->getOperand(1);
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// shl X, 0 == X and shr X, 0 == X
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// shl 0, X == 0 and shr 0, X == 0
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if (Op1 == Constant::getNullValue(Type::UByteTy) ||
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Op0 == Constant::getNullValue(Op0->getType())) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Op0);
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return I;
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}
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// shl int X, 32 = 0 and shr sbyte Y, 9 = 0, ... just don't eliminate shr of
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// a signed value.
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//
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if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
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unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
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if (CUI->getValue() >= TypeBits &&
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!(Op0->getType()->isSigned() && I->getOpcode() == Instruction::Shr)) {
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AddUsesToWorkList(I); // Add all modified instrs to worklist
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I->replaceAllUsesWith(Constant::getNullValue(Op0->getType()));
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return I;
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}
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}
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return 0;
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}
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// isEliminableCastOfCast - Return true if it is valid to eliminate the CI
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// instruction.
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//
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static inline bool isEliminableCastOfCast(const CastInst *CI,
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const CastInst *CSrc) {
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assert(CI->getOperand(0) == CSrc);
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const Type *SrcTy = CSrc->getOperand(0)->getType();
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const Type *MidTy = CSrc->getType();
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const Type *DstTy = CI->getType();
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// It is legal to eliminate the instruction if casting A->B->A
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if (SrcTy == DstTy) return true;
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// Allow free casting and conversion of sizes as long as the sign doesn't
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// change...
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if (SrcTy->isSigned() == MidTy->isSigned() &&
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MidTy->isSigned() == DstTy->isSigned())
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return true;
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// Otherwise, we cannot succeed. Specifically we do not want to allow things
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// like: short -> ushort -> uint, because this can create wrong results if
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// the input short is negative!
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//
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return false;
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}
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// CastInst simplification
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//
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Instruction *InstCombiner::visitCastInst(CastInst *CI) {
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// If the user is casting a value to the same type, eliminate this cast
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// instruction...
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if (CI->getType() == CI->getOperand(0)->getType() && !CI->use_empty()) {
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AddUsesToWorkList(CI); // Add all modified instrs to worklist
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CI->replaceAllUsesWith(CI->getOperand(0));
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return CI;
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}
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// If casting the result of another cast instruction, try to eliminate this
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// one!
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//
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if (CastInst *CSrc = dyn_cast<CastInst>(CI->getOperand(0)))
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if (isEliminableCastOfCast(CI, CSrc)) {
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// This instruction now refers directly to the cast's src operand. This
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// has a good chance of making CSrc dead.
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CI->setOperand(0, CSrc->getOperand(0));
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return CI;
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}
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return 0;
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}
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Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst *GEP) {
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// Is it getelementptr %P, uint 0
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// If so, elminate the noop.
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if (GEP->getNumOperands() == 2 && !GEP->use_empty() &&
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GEP->getOperand(1) == Constant::getNullValue(Type::UIntTy)) {
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AddUsesToWorkList(GEP); // Add all modified instrs to worklist
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GEP->replaceAllUsesWith(GEP->getOperand(0));
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return GEP;
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}
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return visitMemAccessInst(GEP);
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}
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// Combine Indices - If the source pointer to this mem access instruction is a
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// getelementptr instruction, combine the indices of the GEP into this
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// instruction
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//
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Instruction *InstCombiner::visitMemAccessInst(MemAccessInst *MAI) {
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GetElementPtrInst *Src =
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dyn_cast<GetElementPtrInst>(MAI->getPointerOperand());
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if (!Src) return 0;
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std::vector<Value *> Indices;
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// Only special case we have to watch out for is pointer arithmetic on the
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// 0th index of MAI.
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unsigned FirstIdx = MAI->getFirstIndexOperandNumber();
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if (FirstIdx == MAI->getNumOperands() ||
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(FirstIdx == MAI->getNumOperands()-1 &&
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MAI->getOperand(FirstIdx) == ConstantUInt::get(Type::UIntTy, 0))) {
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// Replace the index list on this MAI with the index on the getelementptr
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Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
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} else if (*MAI->idx_begin() == ConstantUInt::get(Type::UIntTy, 0)) {
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// Otherwise we can do the fold if the first index of the GEP is a zero
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Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
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Indices.insert(Indices.end(), MAI->idx_begin()+1, MAI->idx_end());
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}
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if (Indices.empty()) return 0; // Can't do the fold?
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switch (MAI->getOpcode()) {
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case Instruction::GetElementPtr:
|
|
return new GetElementPtrInst(Src->getOperand(0), Indices, MAI->getName());
|
|
case Instruction::Load:
|
|
return new LoadInst(Src->getOperand(0), Indices, MAI->getName());
|
|
case Instruction::Store:
|
|
return new StoreInst(MAI->getOperand(0), Src->getOperand(0), Indices);
|
|
default:
|
|
assert(0 && "Unknown memaccessinst!");
|
|
break;
|
|
}
|
|
abort();
|
|
return 0;
|
|
}
|
|
|
|
|
|
bool InstCombiner::runOnFunction(Function *F) {
|
|
bool Changed = false;
|
|
|
|
WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
|
|
|
|
while (!WorkList.empty()) {
|
|
Instruction *I = WorkList.back(); // Get an instruction from the worklist
|
|
WorkList.pop_back();
|
|
|
|
// Now that we have an instruction, try combining it to simplify it...
|
|
Instruction *Result = visit(I);
|
|
if (Result) {
|
|
// Should we replace the old instruction with a new one?
|
|
if (Result != I)
|
|
ReplaceInstWithInst(I, Result);
|
|
|
|
WorkList.push_back(Result);
|
|
AddUsesToWorkList(Result);
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
Pass *createInstructionCombiningPass() {
|
|
return new InstCombiner();
|
|
}
|