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With LLVM 20 the SIMD intrinsic wasm32::u8x16_sub_sat is compiled to a function call #137419

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hkratz opened this issue Feb 22, 2025 · 3 comments
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With LLVM 20 the SIMD intrinsic wasm32::u8x16_sub_sat is compiled to a function call #137419

hkratz opened this issue Feb 22, 2025 · 3 comments
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A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. A-SIMD Area: SIMD (Single Instruction Multiple Data) C-bug Category: This is a bug. O-wasm Target: WASM (WebAssembly), http://webassembly.org/

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@hkratz
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hkratz commented Feb 22, 2025 •
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The WASM SIMD intrinsic std::arch::wasm32::u8x16_sub_sat used to be compiled to the WASM instruction i8x16.sub_sat_u. Since the switch LLVM 20 (bisected) it is compiled to call llvm.wasm.sub.sat.unsigned.v16i8

Other intrinsics (e.g. saturated integer addition) do not seem to be affected.

Godbolt
@hkratz hkratz added the C-bug Category: This is a bug. label Feb 22, 2025
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Feb 22, 2025
@hkratz
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hkratz commented Feb 22, 2025 •
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@rustbot label +A-llvm +A-SIMD +O-WASM

@rustbot rustbot added A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. O-wasm Target: WASM (WebAssembly), http://webassembly.org/ A-SIMD Area: SIMD (Single Instruction Multiple Data) labels Feb 22, 2025
@nikic
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nikic commented Feb 22, 2025

This is already fixed in stdarch (rust-lang/stdarch#1719), but needs the update to be pulled in.

@nikic nikic mentioned this issue Feb 24, 2025
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GuillaumeGomez added a commit to GuillaumeGomez/rust that referenced this issue Feb 24, 2025
@GuillaumeGomez
Rollup merge of rust-lang#137527 - nikic:update-stdarch, r=Amanieu
7e51258 
Update stdarch

Update stdarch to fix rust-lang#137419. (This also pulls in a lot of other changes though).

r? `@Amanieu`
@Noratrieb Noratrieb removed the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Mar 1, 2025
@hanna-kruppe
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Fixed (by #136831?), see original godbolt link

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A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. A-SIMD Area: SIMD (Single Instruction Multiple Data) C-bug Category: This is a bug. O-wasm Target: WASM (WebAssembly), http://webassembly.org/
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Update stdarch nikic/rust
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@nikic @hanna-kruppe @hkratz @rustbot @Noratrieb