[llvm-bugs] [Bug 25808] [InstCombine] canonicalize extractelement reductions with shuffles

via llvm-bugs llvm-bugs at lists.llvm.org
Thu Jan 10 10:28:50 PST 2019


Sanjay Patel <spatel+llvm at rotateright.com> changed:

           What    |Removed                     |Added
             Status|CONFIRMED                   |RESOLVED
         Resolution|---                         |FIXED

--- Comment #9 from Sanjay Patel <spatel+llvm at rotateright.com> ---
(In reply to Simon Pilgrim from comment #8)
> Resolve this? Reduction costs have been tidied up a lot in the past year,
> allowing the SLP to vectorize this to a reduction pattern, even on sse2
> targets.

Yes, that's probably better than trying to do this in instcombine. We're still
unable to create arbitrary shuffles in instcombine because we don't know what
kind of target support there exists to back that up.

For x86, I think we get the expected codegen for all targets, including a
horizontal math op if that's desirable.

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