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Require fma and f16c for avx512f in std_detect #1781

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Merged
merged 1 commit into from
May 1, 2025
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Require fma and f16c for avx512f in std_detect #1781

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14 changes: 10 additions & 4 deletions crates/std_detect/src/detect/os/x86.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -106,9 +106,11 @@ pub(crate) fn detect_features() -> cache::Initializer {
{
// borrows value till the end of this scope:
let mut enable = |r, rb, f| {
if bit::test(r as usize, rb) {
let present = bit::test(r as usize, rb);
if present {
value.set(f as u32);
}
present
};

enable(proc_info_ecx, 0, Feature::sse3);
Expand All @@ -120,7 +122,7 @@ pub(crate) fn detect_features() -> cache::Initializer {
enable(proc_info_ecx, 22, Feature::movbe);
enable(proc_info_ecx, 23, Feature::popcnt);
enable(proc_info_ecx, 25, Feature::aes);
enable(proc_info_ecx, 29, Feature::f16c);
let f16c = enable(proc_info_ecx, 29, Feature::f16c);
enable(proc_info_ecx, 30, Feature::rdrand);
enable(extended_features_ebx, 18, Feature::rdseed);
enable(extended_features_ebx, 19, Feature::adx);
Expand Down Expand Up @@ -216,7 +218,7 @@ pub(crate) fn detect_features() -> cache::Initializer {
}

// FMA (uses 256-bit wide registers):
enable(proc_info_ecx, 12, Feature::fma);
let fma = enable(proc_info_ecx, 12, Feature::fma);

// And AVX/AVX2:
enable(proc_info_ecx, 28, Feature::avx);
Expand All @@ -235,7 +237,11 @@ pub(crate) fn detect_features() -> cache::Initializer {

// For AVX-512 the OS also needs to support saving/restoring
// the extended state, only then we enable AVX-512 support:
if os_avx512_support {
// Also, Rust makes `avx512f` imply `fma` and `f16c`, because
// otherwise the assembler is broken. But Intel doesn't guarantee
// that `fma` and `f16c` are available with `avx512f`, so we
// need to check for them separately.
if os_avx512_support && f16c && fma {
enable(extended_features_ebx, 16, Feature::avx512f);
enable(extended_features_ebx, 17, Feature::avx512dq);
enable(extended_features_ebx, 21, Feature::avx512ifma);
Expand Down