[PATCH 2/3] SelectionDAG: Add KnownBits and SignBits computation for EXTRACT_ELEMENT

[Jan Vesely]

On Tue, 2014-11-25 at 17:37 -0500, Matt Arsenault wrote:
> > On Nov 18, 2014, at 11:06 AM, Jan Vesely <jan.vesely at rutgers.edu> wrote:
> > 
> > v2: use getZExtValue
> >    add missing break
> >    codestyle
> > 
> > Signed-off-by: Jan Vesely <jan.vesely at rutgers.edu>
> > ---
> > lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 22 ++++++++++++++++++++++
> > 1 file changed, 22 insertions(+)
> > 
> > diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
> > index 33620e7..09e0239 100644
> > --- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
> > +++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
> > @@ -2323,6 +2323,19 @@ 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();
> > +
> > +    KnownZero = KnownZero.getHiBits(KnownZero.getBitWidth() - Index * BitWidth);
> > +    KnownOne = KnownOne.getHiBits(KnownOne.getBitWidth() - Index * BitWidth);
> > +
> > +    KnownZero = KnownZero.trunc(BitWidth);
> > +    KnownOne = KnownOne.trunc(BitWidth);
> > +    break;
> > +  }
> >   case ISD::FrameIndex:
> >   case ISD::TargetFrameIndex:
> >     if (unsigned Align = InferPtrAlignment(Op)) {
> > @@ -2522,6 +2535,15 @@ 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;
> > +    const int rIndex = Items - 1 -
> > +      cast<ConstantSDNode>(Op.getOperand(1))->getZExtValue();
> > +    return std::max(std::min(KnownSign - rIndex * BitWidth, BitWidth), 0);
> > +  }
> >   }
> > 
> >   // If we are looking at the loaded value of the SDNode.
> > -- 
> > 1.9.3
> > 
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> 
> 
> These need tests. Do these really work? I remember trying to do this at
> some point, but then gave up because computeKnownBits doesn’t
> understand vectors very well

the tests are included in 3/3. this patch is needed so reduction from
i64->i32 can than be further turned into i24. Without this patch the
reduction stops at i32 and we'd need another check to do i64 to i24.

> 
> -Matt

-- 
Jan Vesely <jan.vesely at rutgers.edu>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: This is a digitally signed message part
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20141125/1c57d00b/attachment.sig>