Fearless SIMD v1.0

SBCL has the right hooks. Jai probably does as well. You could build your own thing on LLVM relatively easily - so Rust _could_ do it if you gave it sufficient access to the compiler, but so could C++ or D.

SIMD bitmasks being ~0 instead of (00000001)+ is common and useful, but there's an annoying language design question in there about what type comparisons between vectors should be (if you don't have a <N x i1> as a type, say because you liked C too much). Shout out to std::vector<bool>.

There is probably interesting work in mojo for this. The library being in MLIR strongly encourages taking that sort of approach. I haven't looked at their implementation though. Happy hacking!

Pattern types could potentially maybe in the future allow for the compiler to know more details though. They are a nightly feature, and afaik only for enums, integers and pointers so far. The idea would be that you can define a custom type such as "an integer between 7 and 45" and everything else become niches for niche optimisation (e.g. for `Option<MyFunkyInt>` some of those impossible values would be used to represent the None case of the wrapping Option).

But I could envisage a future in which you could say "f64 without NaN" which would both make those available for niches and potentially tell LLVM about this. However, we are very far from any of that currently. And it might not be what you want, since you would need to add checks when you perform operations to ensure the value doesn't suddenly become a NaN. Which is way more complicated than ensuring integers don't become, say, zero. It will likely be much harder to optimise away the checks.

But I suspect you're overvaluing the potential savings. Knowing when a float is 0.0 or NaN beforehand is almost entirely impossible, except for the most trivial of cases - like when you first initialize a variable or first enter a loop. Everything after that is very hard or impossible with floats as they are.

Those cases can be const folded at compile time.

Those cases are never a measurable bottleneck.

The closest thing I know of in the realm of the optimization you're curious about is Rust NonZero* variants, but they're used for enum compression afaik.