calebzulawski
Trouble using x86-64-v4, clarifying current support (nightly)
Sorry if this is because the flags are not supported in Rust, but I am trying to use multiversion on our Xeons with AV512 and the special "simd" target didn't work (only dispatches to AVX2 unless I compile the whole binary for the AVX512 target), so I tried it manually:
error: unknown x86 target feature: lahfsahf
--> src/path/to/mod.rs:435:38
|
435 | #[cfg_attr(feature = "multiversion", multiversion::multiversion(targets("x86_64+avx2","x86_64/x86-64-v4")))]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: this error originates in the macro `std::arch::is_x86_feature_detected` which comes from the expansion of the attribute macro `multiversion::multiversion` (in Nightly builds, run with -Z macro-backtrace for more info)
I'm on nightly, so adding an extra, contingent compiler feature is not a problem, albeit I'm not sure what I would add to fix this.
This also affects "x86_64/x86-64-v2" level on stable, rustc v1.90.0, multiversion v0.8.0:
error: unknown x86 target feature: lahfsahf
--> src/twiddles.rs:189:1
|
189 | / #[multiversion::multiversion(
190 | | targets("x86_64+avx512f+avx512bw+avx512cd+avx512dq+avx512vl", // x86_64-v4
191 | | "x86_64/x86-64-v2", // x86_64-v2
... |
198 | | ))]
| |___^
|
= note: this error originates in the macro `std::arch::is_x86_feature_detected` which comes from the expansion of the attribute macro `multiversion::multiversion` (in Nightly builds, run with -Z macro-backtrace for more info)
I'm not totally sure what the best way to handle this is. Specifying a CPU is a convenient shortcut but simply filtering out unsupported features could result in undefined behavior. It's unlikely, but for example you could use asm! or call an external function that uses the filtered out feature.
