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rust-lang / stdarch

Rust's standard library vendor-specific APIs and run-time feature detection
https://doc.rust-lang.org/stable/core/arch/
Apache License 2.0
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Incorrect `target_feature` attributes #1577

Closed sayantn closed 4 weeks ago

sayantn commented 1 month ago

According to [Intel Intrinsics Guide] (https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html) the _mm256_cvtsd_f64 intrinsic should be enabled with AVX, but the rust function has target_feature AVX2. This makes it unable to inline with AVX only, but AVX cpus do have the vmovsd instruction

Amanieu commented 1 month ago

That does seem like an oversight, feel free to send a PR to fix it! Also, could you check if any similar mistakes have been made for other intrinsics?

sayantn commented 1 month ago

I could not find any more such oversights. I will send a PR.

There is also issues in x86 feature detection in Alderlake. Some Alderlake CPUs do have the "AVX512" instructions VAES, VPCLMULQDQ and GFNI, even though they do not have any other AVX512 instructions. 

rustc --print cfg --target-cpu=native

does print that these instructions are supported, but is_x86_feature_detected returns false for these features. Using these instructions return the correct result too (no SIGILL).

Amanieu commented 1 month ago

That can be fixed in the feature-detection logic for AVX512 in crates/std_detect/src/detect/os/x86.rs.