diff options
| -rw-r--r-- | llvm/lib/Transforms/Scalar/InstructionCombining.cpp | 22 |
1 files changed, 19 insertions, 3 deletions
diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp index 6824c345524..6cc7bbe3dc7 100644 --- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp @@ -3571,6 +3571,25 @@ Instruction *InstCombiner::visitCastInst(CastInst &CI) { return new ShiftInst(Instruction::Shl, Op0c, Op1); } break; + case Instruction::Shr: + // If this is a signed shr, and if all bits shifted in are about to be + // truncated off, turn it into an unsigned shr to allow greater + // simplifications. + if (DestBitSize < SrcBitSize && Src->getType()->isSigned() && + isa<ConstantInt>(Op1)) { + unsigned ShiftAmt = cast<ConstantUInt>(Op1)->getValue(); + if (SrcBitSize > ShiftAmt && SrcBitSize-ShiftAmt >= DestBitSize) { + // Convert to unsigned. + Value *N1 = InsertOperandCastBefore(Op0, + Op0->getType()->getUnsignedVersion(), &CI); + // Insert the new shift, which is now unsigned. + N1 = InsertNewInstBefore(new ShiftInst(Instruction::Shr, N1, + Op1, Src->getName()), CI); + return new CastInst(N1, CI.getType()); + } + } + break; + case Instruction::SetNE: if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { if (Op1C->getRawValue() == 0) { @@ -3601,9 +3620,6 @@ Instruction *InstCombiner::visitCastInst(CastInst &CI) { In = InsertNewInstBefore(new ShiftInst(Instruction::Shr, In, ConstantInt::get(Type::UByteTy, ShiftAmt), In->getName()+".lobit"), CI); - std::cerr << "In1 = " << *Op0; - std::cerr << "In2 = " << *CI.getOperand(0); - std::cerr << "In3 = " << CI; if (CI.getType() == In->getType()) return ReplaceInstUsesWith(CI, In); else |
