"Casting" boolean vectors back to integer vectors

[birkenfeld]

When translating routines from C intrinsics to Rust, conceptually boolean vectors are freely mixed with non-boolean ones.

To get back from boolean to its representation you currently have to do b.select(splat(-1), splat(0)) or similar while on the instruction level it's a no-op. It already optimizes back to a no-op, but would it make sense to have a shorthand for coding it?

[wickerwaka]

I ran into something similar porting some code from C. Another common pattern is doing bitwise operations on floating point values, such as XOR-ing each lane with 0x80000000 in order to flip the sign bit.

It's not clear from the documentation what to_u32, to_i32 and to_f32 do, they just say they lanes are "converted". Looking at the code it uses the simd_cast intrinsic, which is also ambiguous. It was only through experiment and/or looking at the disassembly that you can see what is actually happening.

It seems like the work currently done by these to_ methods would be more idiomatic if they were implemented using the From and Into traits. Then a direct cast without conversion could be implemented as as_f32, as_i32, etc methods at perform an unsafe mem::transmute.