[PATCH][X86] Add target specific combine rules to fold SSE/AVX/AVX2 blend intrinsics.

[Craig Topper]

I believe we can remove the intrinsics and have AutoUpgrade.cpp convert
them to the correct IR. I think Chris told me a while back that intrinsic
upgrading in AutoUpgrade would have to stay until 4.0.


On Thu, May 15, 2014 at 1:45 PM, Alex Rosenberg <alexr at leftfield.org> wrote:

> After r208664, most of those patch is dead code since Clang no longer
> generates these intrinsics except the blendv variants. We have to keep the
> intrinsics as is until the next release because they may exist in IR, but
> we should remove unused ones when possible.
>
> Also, it seems to me that this kind of folding belongs in InstCombine
> since it enables other optimizations and does not generate new shuffles.
> The only benefit here to SelectionDAG is carrying code for X86 intrinsics
> in non-X86 builds of LLVM. In this case, the code is small, so I'd still
> favor InstCombine.
>
> Alex
>
> > On May 15, 2014, at 8:26 AM, Andrea Di Biagio <andrea.dibiagio at gmail.com>
> wrote:
> >
> > Thanks Nadav!
> >
> > Committed revision 208895.
> >
> >> On Thu, May 15, 2014 at 4:04 PM, Nadav Rotem <nrotem at apple.com> wrote:
> >> LGTM.  Thanks Andrea.
> >>
> >>> On May 15, 2014, at 7:41, Andrea Di Biagio <andrea.dibiagio at gmail.com>
> wrote:
> >>>
> >>> Hi,
> >>>
> >>> This patch teaches the x86 backend how to fold SSE4.1/AVX/AVX2 blend
> >>> intrinsics in the following trivial cases:
> >>> 1)  fold (blend A, A, Mask) -> A;
> >>> 2)  fold (blend A, B, <allZeros>) -> A;
> >>> 3) fold (blend A, B, <allOnes>) -> B;
> >>>
> >>> Added two new tests to verify that the new folding rules work for all
> >>> the optimized blend intrinsics.
> >>>
> >>> Please let me know if ok to submit.
> >>>
> >>> Thanks,
> >>> Andrea Di Biagio
> >>> <patch-combine-x86-blend.diff>
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-- 
~Craig
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