diff options
Diffstat (limited to 'llvm/lib/Transforms/InstCombine')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp | 21 |
1 files changed, 12 insertions, 9 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp index 00feb01de40..4b1705ca69c 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -1524,25 +1524,28 @@ Instruction *InstCombiner::foldICmpAndShift(ICmpInst &Cmp, BinaryOperator *And, const APInt *C3; if (match(Shift->getOperand(1), m_APInt(C3))) { bool CanFold = false; - if (ShiftOpcode == Instruction::AShr) { - // There may be some constraints that make this possible, but nothing - // simple has been discovered yet. - CanFold = false; - } else if (ShiftOpcode == Instruction::Shl) { + if (ShiftOpcode == Instruction::Shl) { // For a left shift, we can fold if the comparison is not signed. We can // also fold a signed comparison if the mask value and comparison value // are not negative. These constraints may not be obvious, but we can // prove that they are correct using an SMT solver. if (!Cmp.isSigned() || (!C2.isNegative() && !C1.isNegative())) CanFold = true; - } else if (ShiftOpcode == Instruction::LShr) { + } else { + bool IsAshr = ShiftOpcode == Instruction::AShr; // For a logical right shift, we can fold if the comparison is not signed. // We can also fold a signed comparison if the shifted mask value and the // shifted comparison value are not negative. These constraints may not be // obvious, but we can prove that they are correct using an SMT solver. - if (!Cmp.isSigned() || - (!C2.shl(*C3).isNegative() && !C1.shl(*C3).isNegative())) - CanFold = true; + // For an arithmetic shift right we can do the same, if we ensure + // the And doesn't use any bits being shifted in. Normally these would + // be turned into lshr by SimplifyDemandedBits, but not if there is an + // additional user. + if (!IsAshr || (C2.shl(*C3).lshr(*C3) == C2)) { + if (!Cmp.isSigned() || + (!C2.shl(*C3).isNegative() && !C1.shl(*C3).isNegative())) + CanFold = true; + } } if (CanFold) { |
