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

[Jan Vesely]

On Tue, 2014-11-25 at 19:08 -0500, Jan Vesely wrote:
> 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.

Ping

was that answer not good enough, or do I need to bug someone else to
review this patch?

jan

> 
> > 
> > -Matt
> 

-- 
Jan Vesely <jan.vesely at rutgers.edu>
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