riscv64: Improve pattern matching rules for FMA #8596
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This commit reworks our FMA pattern matching to be slightly less verbose. It additionally adds the `(fma x (splat y) z)` pattern for vectors, which can be proven to be equivalent to `(splat x)`. Co-Authored-By: Jamey Sharp <jsharp@fastly.com>
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Redirecting to @jameysharp since it seems like he has more context here. |
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May 12, 2024
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Fantastic, I love that this worked out, and I really appreciate the effort you put into using Alive2 to check which of my guesses were correct. Too bad about signed zeroes…
By the way, this motivated me to write up #8599, which would make this kind of pattern easier to write someday.
| (rule 1 (is_fneg (fneg x)) (IsFneg.Result 1 x)) | ||
| (rule 0 (is_fneg x) (IsFneg.Result 0 x)) | ||
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| (rule 1 (lower (has_type ty (fma x_src y_src z_src))) |
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Interesting, why does this rule need a priority?
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Oops, it shouldn't. I was debugging some stuff and forgot to remove it.
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👋 Hey,
This PR reworks our FMA pattern matching to be slightly less verbose using the suggestions provided by @jameysharp on #8588 (comment).
It additionally adds the
(fma x (splat y) z)pattern for vectors, which can be proven to be equivalent to(fma y (splat x) z). See #8588 (comment). I've only added ISA tests for these patterns since it turns out they are already present in the SIMD FMA runtests.I think all of the patterns matched here are sound although I can't formally prove all of them. This comment #8588 (comment) describes most of the validations that I did.