diff options
Diffstat (limited to 'llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp index b40d067b281..dc0032b4f0c 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -680,6 +680,25 @@ Instruction *InstCombiner::visitLShr(BinaryOperator &I) { return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask)); } + if (match(Op0, m_SExt(m_Value(X)))) { + // Are we moving the sign bit to the low bit and widening with high zeros? + unsigned SrcTyBitWidth = X->getType()->getScalarSizeInBits(); + if (ShAmt == BitWidth - 1 && + (!Ty->isIntegerTy() || shouldChangeType(Ty, X->getType()))) { + // lshr (sext i1 X to iN), N-1 --> zext X to iN + if (SrcTyBitWidth == 1) + return new ZExtInst(X, Ty); + + // lshr (sext iM X to iN), N-1 --> zext (lshr X, M-1) to iN + if (Op0->hasOneUse()) { + Value *NewLShr = Builder->CreateLShr(X, SrcTyBitWidth - 1); + return new ZExtInst(NewLShr, Ty); + } + } + + // TODO: Convert to ashr+zext if the shift equals the extension amount. + } + if (match(Op0, m_LShr(m_Value(X), m_APInt(ShOp1)))) { unsigned AmtSum = ShAmt + ShOp1->getZExtValue(); // Oversized shifts are simplified to zero in InstSimplify. |
