diff options
Diffstat (limited to 'lib/Transforms/InstCombine/InstCombineShifts.cpp')
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineShifts.cpp | 24 |
1 files changed, 19 insertions, 5 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp index fe91da1..321c91d 100644 --- a/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -404,12 +404,26 @@ Instruction *InstCombiner::visitAShr(BinaryOperator &I) { if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { // If the input is a SHL by the same constant (ashr (shl X, C), C), then we - // have a sign-extend idiom. If the input value is known to already be sign - // extended enough, delete the extension. + // have a sign-extend idiom. Value *X; - if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1))) && - ComputeNumSignBits(X) > Op1C->getZExtValue()) - return ReplaceInstUsesWith(I, X); + if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) { + // If the input value is known to already be sign extended enough, delete + // the extension. + if (ComputeNumSignBits(X) > Op1C->getZExtValue()) + return ReplaceInstUsesWith(I, X); + + // If the input is an extension from the shifted amount value, e.g. + // %x = zext i8 %A to i32 + // %y = shl i32 %x, 24 + // %z = ashr %y, 24 + // then turn this into "z = sext i8 A to i32". + if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) { + uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits(); + uint32_t DestBits = ZI->getType()->getScalarSizeInBits(); + if (Op1C->getZExtValue() == DestBits-SrcBits) + return new SExtInst(ZI->getOperand(0), ZI->getType()); + } + } } // See if we can turn a signed shr into an unsigned shr. |
