I think embedded is one of the specific buckets.

You target the compiler your client uses for their platform. There is very little choice there.

Even then you're probably better off using something safer that transpiles to C.

”Transpiles to c” - how do you generally optimize single line performance hotspots in that case?

I don't see why that would make any difference? The generated C code is just a build artifact in this case, similar to IRs often used by compilers internally. You don't think about e.g. gcc IR when you optimize hotspots in code written in C, though - you just look at the C source and the generated asm code. If you have, say, Zig transpiling to C (which it can do with `-ofmt=c`), you'd similarly look at the Zig source and the generated asm code.