A quick test to check which instructions are available in the x86-64-v2 target arch, for purposes of figuring out whether the feature detection that the crc32fast crate does (and some other tests that other crates to) is happening at runtime or compile-time.
Examine assembly with cargo asm --target-cpu=x86-64-v2 'test' and look for a branch (je or jne).
Results:
- sse2 is available in x86-64-v1 (default target CPU)
- sse4.1 is available in x86-64-v2
- pclmulqdq is not available even in x86-64-v4, even though in practice it seems the pclmulqdq instruction is actually available on all consumer CPUs from 2013 onwards (2010 for Intel).
- f16c for the half crate is available in x86-64-v3
Points 1 and 2 and 4 are expected based on https://en.wikipedia.org/wiki/X86-64#Microarchitecture_levels - but point 3 I wasn't sure of.
See also:
- there are some instructions for checking target features in this unfinished book on Rust SIMD
- https://doc.rust-lang.org/reference/attributes/codegen.html#the-target_feature-attribute to explicitly enable features for parts of the codebase.