From da60588402e8913f5b7ec40945d4170d0c4ffaf5 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Sun, 19 Dec 2010 20:38:28 +0000 Subject: [PATCH] teach MaskedValueIsZero how to analyze ADDE. This is enough to teach it that ADDE(0,0) is known 0 except the low bit, for example. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122191 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp index 988ccd6a96f..019c9feb993 100644 --- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp +++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp @@ -1956,7 +1956,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask, } } // fall through - case ISD::ADD: { + case ISD::ADD: + case ISD::ADDE: { // Output known-0 bits are known if clear or set in both the low clear bits // common to both LHS & RHS. For example, 8+(X<<3) is known to have the // low 3 bits clear. @@ -1971,7 +1972,17 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask, KnownZeroOut = std::min(KnownZeroOut, KnownZero2.countTrailingOnes()); - KnownZero |= APInt::getLowBitsSet(BitWidth, KnownZeroOut); + if (Op.getOpcode() == ISD::ADD) { + KnownZero |= APInt::getLowBitsSet(BitWidth, KnownZeroOut); + return; + } + + // With ADDE, a carry bit may be added in, so we can only use this + // information if we know (at least) that the low two bits are clear. We + // then return to the caller that the low bit is unknown but that other bits + // are known zero. + if (KnownZeroOut >= 2) // ADDE + KnownZero |= APInt::getBitsSet(BitWidth, 1, KnownZeroOut); return; } case ISD::SREM: -- 2.34.1