Stream: git-wasmtime

Topic: wasmtime / issue #5636 riscv64: improve unordered compari...

Wasmtime GitHub notifications bot (Jan 26 2023 at 01:28):

elliottt commented on issue #5636:

Very nice! It wasn't obvious to me, until I went and stared at the definition of FloatCC in cranelift/codegen/src/ir/condcodes.rs, that you can always eliminate the "UnorderedOr" conditions by inverting the condition code. I can't think of a case where this could make the generated code worse, and clearly it makes it substantially better in some cases, at least on this target.

I only noticed this because of how bad the fcmp test on riscv64 got when I removed brz :sweat_smile:

I wonder if we'll want to write any generic egraph optimization rules based on this observation...

I think that's worth investigating, though looking through the lowerings for fcmp on our other backends, none are as expensive as riscv64 when there are unordered comparisons involved.

Last updated: Dec 23 2024 at 12:05 UTC