add safety for noalias on a parameter

[andrewrk]

When you call a function with pointer arguments marked as noalias, such as @memcpy, it is undefined behavior for the pointer arguments to point to the same memory. We can insert a safety check for this. It should be pretty low cost.

This should work for slices too, and it should ensure that the slices do not overlap. In order for the optimizer to potentially be able to use this information, we should probably pass slices as 2 parameters, the pointer and the length. This way we can add parameter attributes to the pointer parameter.

[BarabasGitHub]

we should probably pass slices as 2 parameters, the pointer and the length. This way we can add parameter attributes to the pointer parameter.

Can't you do a noalias on a slice? Or are slices internally passed by reference currently?

[matu3ba]

This should work for slices too, and it should ensure that the slices do not overlap. In order for the optimizer to potentially be able to use this information, we should probably pass slices as 2 parameters, the pointer and the length. This way we can add parameter attributes to the pointer parameter.

Fingers crossed that the LLVM IR does not break everything, once they enable noalias. This would also require implementing pointer provenance.