[llvm-commits] Optimization for SIGN_EXTEND on AVX and AVX2 - please review

[Demikhovsky, Elena]

I put 2 or 3 sequential sign-extend operations.

original: v8i8 - > v8i64
new:      v8i8 -> v8i16 ->v8i32 ->v8i64

I combine load with v8i8 -> v8i16 and use VPMOVSXBW instruction.
I translate v8i16 ->v8i32 to 2 VPMOVSXWD instructions.
And then I have 4 VPMOVSXDQ for  v8i32 ->v8i64.

if I work with one SIGN_EXTEND operation with illegal types, I receive a scalar code after type legalizer.

- Elena

-----Original Message-----
From: llvm-commits-bounces at cs.uiuc.edu [mailto:llvm-commits-bounces at cs.uiuc.edu] On Behalf Of Duncan Sands
Sent: Tuesday, January 15, 2013 13:58
To: llvm-commits at cs.uiuc.edu
Subject: Re: [llvm-commits] Optimization for SIGN_EXTEND on AVX and AVX2 - please review

Hi Elena,

On 15/01/13 12:47, Demikhovsky, Elena wrote:
> I optimized the following SEXT pairs:
> v8i8 -> v8i64
> v8i8->v8i32
> v4i8 ->v4i64
> v4i16->v4i64

> Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> ===================================================================
> --- lib/CodeGen/SelectionDAG/DAGCombiner.cpp	(revision 172422)
> +++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp	(working copy)
> @@ -4298,12 +4298,13 @@
>    if (isa<ConstantSDNode>(N0))
>      return DAG.getNode(ISD::SIGN_EXTEND, N->getDebugLoc(), VT, N0);
>
> -  // fold (sext (sext x)) -> (sext x)
> -  // fold (sext (aext x)) -> (sext x)
> -  if (N0.getOpcode() == ISD::SIGN_EXTEND || N0.getOpcode() == ISD::ANY_EXTEND)
> -    return DAG.getNode(ISD::SIGN_EXTEND, N->getDebugLoc(), VT,
> -                       N0.getOperand(0));
> -
> +  if (Level >= AfterLegalizeTypes) {
> +    // fold (sext (sext x)) -> (sext x)
> +    // fold (sext (aext x)) -> (sext x)
> +    if (N0.getOpcode() == ISD::SIGN_EXTEND || N0.getOpcode() == ISD::ANY_EXTEND)
> +      return DAG.getNode(ISD::SIGN_EXTEND, N->getDebugLoc(), VT,
> +                         N0.getOperand(0));  }

why is this needed?  As the transform doesn't introduce any illegal types that weren't there already it should be safe to perform at any level.

If you are worried that it might create an illegal operation, then that is what you should check for, not the Level.

>    if (N0.getOpcode() == ISD::TRUNCATE) {
>      // fold (sext (truncate (load x))) -> (sext (smaller load x))
>      // fold (sext (truncate (srl (load x), c))) -> (sext (smaller 
> load (x+c/n)))

...

> --- lib/CodeGen/SelectionDAG/SelectionDAG.cpp	(revision 172422)
> +++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp	(working copy)
> @@ -2554,9 +2554,7 @@
>              VT.getVectorNumElements() ==
>              Operand.getValueType().getVectorNumElements()) &&
>             "Vector element count mismatch!");
> -    if (OpOpcode == ISD::SIGN_EXTEND || OpOpcode == ISD::ZERO_EXTEND)
> -      return getNode(OpOpcode, DL, VT, Operand.getNode()->getOperand(0));
> -    else if (OpOpcode == ISD::UNDEF)
> +    if (OpOpcode == ISD::UNDEF)
>        // sext(undef) = 0, because the top bits will all be the same.
>        return getConstant(0, VT);
>      break;

Likewise, why are you getting rid of this folding?

Ciao, Duncan.
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