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* Add ability to eliminate a bunch of different cascading cast variations
* Allow elimination of getelementptr X, uint 0 (which is a noop) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2428 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -61,6 +61,7 @@ namespace {
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Instruction *visitSub(BinaryOperator *I);
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Instruction *visitMul(BinaryOperator *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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@ -163,18 +164,75 @@ Instruction *InstCombiner::visitMul(BinaryOperator *I) {
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}
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// CastInst simplification - If the user is casting a value to the same type,
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// eliminate this cast instruction...
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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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