Stream: git-wasmtime

Topic: wasmtime / PR #5846 x64: Add more `fma` instruction lower...

Wasmtime GitHub notifications bot (Feb 21 2023 at 14:25):

alexcrichton opened PR #5846 from improve-fma to main:

The relaxed-simd proposal for WebAssembly adds a fused-multiply-add operation for v128 types so I was poking around at Cranelift's existing support for its fma instruction. I was also poking around at the x86_64 ISA's offerings for the FMA operation and ended up with this PR that improves the lowering of the fma instruction on the x64 backend in a number of ways:

• A libcall-based fallback is now provided for f32x4 and f64x2 types in preparation for eventual support of the relaxed-simd proposal. These encodings are horribly slow, but it's expected that if FMA semantics must be guaranteed then it's the best that can be done without the fma feature. Otherwise it'll be up to producers (e.g. Wasmtime embedders) whether wasm-level FMA operations should be FMA or multiply-then-add.

• In addition to the existing vfmadd213* instructions opcodes were added for vfmadd132*. The 132 variant is selected based on which argument can have a sinkable load.

• Any argument in the fma CLIF instruction can now have a sinkable_load and it'll generate a single FMA instruction.

• All vfnmadd* opcodes were added as well. These are pattern-matched where one of the arguments to the CLIF instruction is an fneg. I opted to not add a new CLIF instruction here since it seemed like pattern matching was easy enough but I'm also not intimately familiar with the semantics here so if that's the preferred approach I can do that too.

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Wasmtime GitHub notifications bot (Feb 21 2023 at 19:58):

abrown submitted PR review.

Wasmtime GitHub notifications bot (Feb 21 2023 at 20:33):

alexcrichton updated PR #5846 from improve-fma to main.

Wasmtime GitHub notifications bot (Feb 21 2023 at 20:38):

alexcrichton has enabled auto merge for PR #5846.

Wasmtime GitHub notifications bot (Feb 21 2023 at 21:35):

alexcrichton merged PR #5846.

Last updated: Dec 23 2024 at 13:07 UTC