diff options
Diffstat (limited to 'llvm/lib/Transforms')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/InstructionCombining.cpp | 43 |
1 files changed, 8 insertions, 35 deletions
diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp index dd8a63053c7..9b75ee13cb6 100644 --- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp @@ -3940,7 +3940,7 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) { if (Op1 == Constant::getNullValue(Type::UByteTy) || Op0 == Constant::getNullValue(Op0->getType())) return ReplaceInstUsesWith(I, Op0); - + if (isa<UndefValue>(Op0)) { // undef >>s X -> undef if (!isLeftShift && I.getType()->isSigned()) return ReplaceInstUsesWith(I, Op0); @@ -3989,6 +3989,13 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantUInt *Op1, bool isSignedShift = Op0->getType()->isSigned(); bool isUnsignedShift = !isSignedShift; + // See if we can simplify any instructions used by the instruction whose sole + // purpose is to compute bits we don't care about. + uint64_t KnownZero, KnownOne; + if (SimplifyDemandedBits(&I, I.getType()->getIntegralTypeMask(), + KnownZero, KnownOne)) + return &I; + // shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr // of a signed value. // @@ -4018,40 +4025,6 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantUInt *Op1, return NV; if (Op0->hasOneUse()) { - // If this is a SHL of a sign-extending cast, see if we can turn the input - // into a zero extending cast (a simple strength reduction). - if (CastInst *CI = dyn_cast<CastInst>(Op0)) { - const Type *SrcTy = CI->getOperand(0)->getType(); - if (isLeftShift && SrcTy->isInteger() && SrcTy->isSigned() && - SrcTy->getPrimitiveSizeInBits() < - CI->getType()->getPrimitiveSizeInBits()) { - // We can change it to a zero extension if we are shifting out all of - // the sign extended bits. To check this, form a mask of all of the - // sign extend bits, then shift them left and see if we have anything - // left. - Constant *Mask = ConstantIntegral::getAllOnesValue(SrcTy); // 1111 - Mask = ConstantExpr::getZeroExtend(Mask, CI->getType()); // 00001111 - Mask = ConstantExpr::getNot(Mask); // 1's in the sign bits: 11110000 - if (ConstantExpr::getShl(Mask, Op1)->isNullValue()) { - // If the shift is nuking all of the sign bits, change this to a - // zero extension cast. To do this, cast the cast input to - // unsigned, then to the requested size. - Value *CastOp = CI->getOperand(0); - Instruction *NC = - new CastInst(CastOp, CastOp->getType()->getUnsignedVersion(), - CI->getName()+".uns"); - NC = InsertNewInstBefore(NC, I); - // Finally, insert a replacement for CI. - NC = new CastInst(NC, CI->getType(), CI->getName()); - CI->setName(""); - NC = InsertNewInstBefore(NC, I); - WorkList.push_back(CI); // Delete CI later. - I.setOperand(0, NC); - return &I; // The SHL operand was modified. - } - } - } - if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) { // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C) Value *V1, *V2; |
