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SelectionDAG: Add KnownBits and SignBits computation for EXTRACT_ELEMENT

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v2: use getZExtValue
    add missing break
    codestyle

v3: add few more comments

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Matt Arsenault <Matthew.Arsenault@amd.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226880 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jan Vesely 2015-01-22 23:42:41 +00:00
parent cd0d34f1a3
commit 3ff611bb38
1 changed files with 30 additions and 0 deletions
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30
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -2344,6 +2344,21 @@ void SelectionDAG::computeKnownBits(SDValue Op, APInt &KnownZero,
KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
break;
}
case ISD::EXTRACT_ELEMENT: {
computeKnownBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
const unsigned Index =
cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
const unsigned BitWidth = Op.getValueType().getSizeInBits();
// Remove low part of known bits mask
KnownZero = KnownZero.getHiBits(KnownZero.getBitWidth() - Index * BitWidth);
KnownOne = KnownOne.getHiBits(KnownOne.getBitWidth() - Index * BitWidth);
// Remove high part of known bit mask
KnownZero = KnownZero.trunc(BitWidth);
KnownOne = KnownOne.trunc(BitWidth);
break;
}
case ISD::FrameIndex:
case ISD::TargetFrameIndex:
if (unsigned Align = InferPtrAlignment(Op)) {
@ -2543,6 +2558,21 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const{
// FIXME: it's tricky to do anything useful for this, but it is an important
// case for targets like X86.
break;
case ISD::EXTRACT_ELEMENT: {
const int KnownSign = ComputeNumSignBits(Op.getOperand(0), Depth+1);
const int BitWidth = Op.getValueType().getSizeInBits();
const int Items =
Op.getOperand(0).getValueType().getSizeInBits() / BitWidth;
// Get reverse index (starting from 1), Op1 value indexes elements from
// little end. Sign starts at big end.
const int rIndex = Items - 1 -
cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
// If the sign portion ends in our element the substraction gives correct
// result. Otherwise it gives either negative or > bitwidth result
return std::max(std::min(KnownSign - rIndex * BitWidth, BitWidth), 0);
}
}
// If we are looking at the loaded value of the SDNode.