Support vectors with fewer than 8 elements for simd_select_bitmask Resolves the issue raised here: https://github.com/rust-lang/stdarch/issues/310#issuecomment-693730094
The codegen
crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc dev guide.