Wasmtime GitHub notifications bot (Aug 24 2022 at 17:32): Wasmtime GitHub notifications bot (Aug 24 2022 at 17:32):elliottt opened PR #4772 from trevor/x64-shuffle to main:
- Lower shuffle in ISLE
- Add a shuffle test that produces zeros
- Add a TODO for the use of vpermi2b
- Lower swizzle in ISLE
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Wasmtime GitHub notifications bot (Aug 24 2022 at 17:38):elliottt edited PR #4772 from trevor/x64-shuffle to main:
Lower
shuffleandswizzlein ISLE.This PR surfaced a bug with the lowering of
shufflewhen avx512vl and avx512vbmi are enabled: we usevpermi2bas the implementation, but panic if the immediate shuffle mask contains any out-of-bounds values. The behavior when the avx512 extensions are not present is that out-of-bounds values are turned into0in the result.I plan to fix this immediately in a follow-up PR, and have added a TODO that identifies the problem in the x64 lower.isle.
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Wasmtime GitHub notifications bot (Aug 24 2022 at 17:38):elliottt has marked PR #4772 as ready for review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:39):elliottt updated PR #4772 from trevor/x64-shuffle to main.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:41):elliottt edited PR #4772 from trevor/x64-shuffle to main:
Lower
shuffleandswizzlein ISLE.This PR surfaced a bug with the lowering of
shufflewhen avx512vl and avx512vbmi are enabled: we usevpermi2bas the implementation, but panic if the immediate shuffle mask contains any out-of-bounds values. The behavior when the avx512 extensions are not present is that out-of-bounds values are turned into0in the result.I've resolved this by detecting when the shuffle immediate has out-of-bounds indices in the avx512-enabled lowering, and generating an additional mask to zero out the lanes where those indices occur.
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Wasmtime GitHub notifications bot (Aug 24 2022 at 18:44):elliottt updated PR #4772 from trevor/x64-shuffle to main.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:45):elliottt submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:45):elliottt created PR review comment:
Here's the case where the mask wasn't necessary, thus no
andpsinstruction was generated.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:45):elliottt submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:45):elliottt created PR review comment:
Here's a case where the mask was necessary, so the
andpson line 38 is necessary.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:46):elliottt submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:46):elliottt created PR review comment:
This test already passed for the non-avx512 lowering, and this PR allows it to pass when avx512 is available as well.
Wasmtime GitHub notifications bot (Aug 24 2022 at 18:46):elliottt edited PR review comment.
Wasmtime GitHub notifications bot (Aug 24 2022 at 19:13):elliottt edited PR #4772 from trevor/x64-shuffle to main:
Lower
shuffleandswizzlein ISLE.This PR surfaced a bug with the lowering of
shufflewhen avx512vl and avx512vbmi are enabled: we usevpermi2bas the implementation, but panic if the immediate shuffle mask contains any out-of-bounds values. The behavior when the avx512 extensions are not present is that out-of-bounds values are turned into0in the result.I've resolved this by detecting when the shuffle immediate has out-of-bounds indices in the avx512-enabled lowering, and generating an additional mask to zero out the lanes where those indices occur. This brings the avx512 case into line with the semantics of the
shuffleop: https://github.com/bytecodealliance/wasmtime/blob/94bcbe844612306c136193f41f5cbdeec45a42ec/cranelift/codegen/meta/src/shared/instructions.rs#L1495-L1498<!--
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Wasmtime GitHub notifications bot (Aug 24 2022 at 19:31):elliottt submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 19:31):elliottt created PR review comment:
I'm a little unhappy about this, but we don't have an encoding for xmm instructions that have three arguments currently.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:37):cfallin submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:37):cfallin created PR review comment:
could we say what that behavior is and/or mention "CLIF-level shuffle" here? otherwise it's a bit unclear if one doesn't already have the context I think.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:37):cfallin submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:37):cfallin created PR review comment:
Excellent -- it sounds like you've tested on avx512 hardware?
(As an aside, it might be nice to think about ways to use qemu to get us AVX512 testing in CI, if the GitHub Actions host doesn't natively have it. @abrown any thoughts on that?)
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:37):cfallin created PR review comment:
Here we're relying on implicit firing-order heuristics (the above rule before this one, specifically
perm_from_mask...extractor beforemaskvariable binding); I think tests below should ensure this works properly but just wanted to call it out to be sure.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:37):cfallin created PR review comment:
Yeah, we can definitely add such a thing later, and should I think; we'll get to this as part of our "no more mod operands" cleanup on regalloc operands, if not before.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:37):cfallin created PR review comment:
s/shuffle/swizzle/ ?
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:55):elliottt created PR review comment:
I have -- my laptop has those extensions :D
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:55):elliottt submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:56):elliottt submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:56):elliottt created PR review comment:
Thanks for catching that!
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:59):elliottt created PR review comment:
Yep, we should have enough test coverage to catch problems with these two: there are precise-output tests for both rules.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:59):elliottt submitted PR review.
Wasmtime GitHub notifications bot (Aug 24 2022 at 20:59):elliottt updated PR #4772 from trevor/x64-shuffle to main.
Wasmtime GitHub notifications bot (Aug 24 2022 at 21:12):elliottt updated PR #4772 from trevor/x64-shuffle to main.
Wasmtime GitHub notifications bot (Aug 24 2022 at 21:30):elliottt has enabled auto merge for PR #4772.
Wasmtime GitHub notifications bot (Aug 24 2022 at 21:49):elliottt merged PR #4772.
Last updated: Dec 23 2024 at 12:05 UTC