Require fma and f16c for avx512f in std_detect
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This was referenced Apr 24, 2025
VlaDexa
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Remove `avx512dq` and `avx512vl` implication for `avx512fp16` According to Intel, `avx512fp16` requires only `avx512bw`, but LLVM also enables `avx512vl` and `avx512dq` when `avx512fp16` is active. This is relic code, and will be fixed in LLVM soon. We should remove this from Rust too asap, especially before the stabilization of AVX512 Related: - llvm/llvm-project#136209 - rust-lang#138940 - rust-lang/stdarch#1781 - rust-lang#111137 `@rustbot` label O-x86_64 O-x86_32 A-SIMD A-target-feature T-compiler -T-libs r? `@Amanieu` **Update: the LLVM fix has been merged** cc `@rust-lang/wg-llvm` will it be possible to update the rustc llvm version to something after llvm/llvm-project#137450
Zalathar
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Remove `avx512dq` and `avx512vl` implication for `avx512fp16` According to Intel, `avx512fp16` requires only `avx512bw`, but LLVM also enables `avx512vl` and `avx512dq` when `avx512fp16` is active. This is relic code, and will be fixed in LLVM soon. We should remove this from Rust too asap, especially before the stabilization of AVX512 Related: - llvm/llvm-project#136209 - rust-lang#138940 - rust-lang/stdarch#1781 - rust-lang#111137 ``@rustbot`` label O-x86_64 O-x86_32 A-SIMD A-target-feature T-compiler -T-libs r? ``@Amanieu`` **Update: the LLVM fix has been merged** cc ``@rust-lang/wg-llvm`` will it be possible to update the rustc llvm version to something after llvm/llvm-project#137450
rust-timer
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Rollup merge of rust-lang#140389 - sayantn:avx512fp16, r=Amanieu Remove `avx512dq` and `avx512vl` implication for `avx512fp16` According to Intel, `avx512fp16` requires only `avx512bw`, but LLVM also enables `avx512vl` and `avx512dq` when `avx512fp16` is active. This is relic code, and will be fixed in LLVM soon. We should remove this from Rust too asap, especially before the stabilization of AVX512 Related: - llvm/llvm-project#136209 - rust-lang#138940 - rust-lang/stdarch#1781 - rust-lang#111137 ``@rustbot`` label O-x86_64 O-x86_32 A-SIMD A-target-feature T-compiler -T-libs r? ``@Amanieu`` **Update: the LLVM fix has been merged** cc ``@rust-lang/wg-llvm`` will it be possible to update the rustc llvm version to something after llvm/llvm-project#137450
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The target feature
avx512fimpliesavx2,fmaandf16cin rustc, but Intel only guarantees thatavx2will be there whenavx512fis present, nothing aboutfmaorf16c. This is correct behavior by rustc, and is based on how the assembler decides what encoding to use, VEX vs EVEX. So this PR simply requires thatfmaandf16cbe present when enabling any AVX512 target features, to match exactly with rustc behavior.Related:
avx512dqandavx512vlimplication foravx512fp16rust#140389