Potential missed optimization with mutable noalias

[veber-alex]

https://godbolt.org/z/9TY68vcjq

In the above code the methods on the struct that owns the array are not SIMD optimized but the methods on struct which has a reference are SIMD optimized.
On stable or with -Zmutable-noalias=off all methods are not SIMD optimized.

Is this a missed optimization or is there a real difference between owning the array and having a reference?

[veber-alex]

@rustbot label +I-slow

[nikic]

I expect the problem here is that self.data[self.ptr] += 1; could overwrite self.ptr. It would be necessary to reason about the range of the induction variable in AA to exclude the possibility.

[veber-alex]

Looks like the upgrade to LLVM 16 in Rust 1.70 fixed the first case and it's now SIMD optimized.
However the second method still has a bound check that doesn't exist in version of the code where data is borrowed.