[PATCH 2/3] SelectionDAG: Add KnownBits and SignBits computation for EXTRACT_ELEMENT
Mehdi Amini
mehdi.amini at apple.com
Thu Jan 22 13:26:34 PST 2015
Hi Jan,
Sorry, I haven’t seen your previous email. Do not hesitate to ping after 2 days without an answer.
Ok for me.
Mehdi
> On Jan 22, 2015, at 10:37 AM, Jan Vesely <jan.vesely at rutgers.edu> wrote:
>
> ping.
>
> Mehdi, is this version OK with you?
>
> jan
>
> On Wed, 2015-01-14 at 15:11 -0500, Jan Vesely wrote:
>> v2: use getZExtValue
>> add missing break
>> codestyle
>>
>> v3: add few more comments
>>
>> Signed-off-by: Jan Vesely <jan.vesely at rutgers.edu>
>> ---
>>
>> Hi Mehdi,
>>
>> I was not sure what kind of comments you had in mind, so I added few that are
>> in line with the rest of the code in those functions.
>>
>> jan
>>
>> lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 30 ++++++++++++++++++++++++++++++
>> 1 file changed, 30 insertions(+)
>>
>> diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
>> index c819516..673fbf3 100644
>> --- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
>> +++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
>> @@ -2323,6 +2323,21 @@ 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)) {
>> @@ -2522,6 +2537,21 @@ 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.
>
> --
> Jan Vesely <jan.vesely at rutgers.edu>
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