From adc149549dc08f4f864ab2ce737016264ea3a919 Mon Sep 17 00:00:00 2001 From: Zhou Sheng Date: Wed, 14 Mar 2007 09:07:33 +0000 Subject: [PATCH] ShiftAmt might equal to zero. Handle this situation. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35094 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/InstructionCombining.cpp | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index e072d966a7b..1e5b7ec3ca2 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -1997,7 +1997,8 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, APInt DemandedMask, RHSKnownZero <<= ShiftAmt; RHSKnownOne <<= ShiftAmt; // low bits known zero. - RHSKnownZero |= APInt::getAllOnesValue(ShiftAmt).zextOrCopy(BitWidth); + if (ShiftAmt) + RHSKnownZero |= APInt::getAllOnesValue(ShiftAmt).zextOrCopy(BitWidth); } break; case Instruction::LShr: @@ -2013,14 +2014,16 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, APInt DemandedMask, return true; assert((RHSKnownZero & RHSKnownOne) == 0 && "Bits known to be one AND zero?"); - // Compute the new bits that are at the top now. - APInt HighBits(APInt::getAllOnesValue(ShiftAmt).zextOrCopy(BitWidth).shl( - BitWidth - ShiftAmt)); RHSKnownZero &= TypeMask; RHSKnownOne &= TypeMask; RHSKnownZero = APIntOps::lshr(RHSKnownZero, ShiftAmt); RHSKnownOne = APIntOps::lshr(RHSKnownOne, ShiftAmt); - RHSKnownZero |= HighBits; // high bits known zero. + if (ShiftAmt) { + // Compute the new bits that are at the top now. + APInt HighBits(APInt::getAllOnesValue(BitWidth).shl( + BitWidth - ShiftAmt)); + RHSKnownZero |= HighBits; // high bits known zero. + } } break; case Instruction::AShr: @@ -2048,8 +2051,7 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, APInt DemandedMask, assert((RHSKnownZero & RHSKnownOne) == 0 && "Bits known to be one AND zero?"); // Compute the new bits that are at the top now. - APInt HighBits(APInt::getAllOnesValue(ShiftAmt).zextOrCopy(BitWidth).shl( - BitWidth - ShiftAmt)); + APInt HighBits(APInt::getAllOnesValue(BitWidth).shl(BitWidth - ShiftAmt)); RHSKnownZero &= TypeMask; RHSKnownOne &= TypeMask; RHSKnownZero = APIntOps::lshr(RHSKnownZero, ShiftAmt);