[llvm-dev] [FPEnv] FNEG instruction (original) (raw)

Cameron McInally via llvm-dev llvm-dev at lists.llvm.org
Wed Sep 26 08:42:08 PDT 2018

On Wed, Sep 26, 2018 at 9:32 AM Sanjay Patel <spatel at rotateright.com> wrote:

On Tue, Sep 25, 2018 at 7:47 PM Cameron McInally <cameron.mcinally at nyu.edu> wrote:

This is the first time I'm looking at foldShuffledBinop(...), so maybe a naive question, but why not do similar shuffle canonicalizations on unary (or ternary) operations? That may be a better fix in the long run. AFAIK, all of the math/logic folding that we do currently is on binary operators because all of the instructions have that form: http://llvm.org/docs/LangRef.html#instruction-reference As discussed, we fake the unary neg/not/fneg as binops. Excluding control-flow, the only unary instructions are casts, and I don't see any ternary or higher math ops other than intrinsics.

Digressing a bit...

That sounds like a bug, not a feature. Casts/converts, rounds, abs, other libm functions, fmas, compares, and probably more can be masked. If intermixed shuffles are preventing combines on those, intrinsics or not, that isn't ideal. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20180926/6deec4ac/attachment.html>

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