I was wrong elsewhere in this discussion. I now think the problem isn't that the original code breaks any rules/promises, but that the transformation to the second version of the code is not valid.
> So, which of the optimizations is the wrong one?
In the original function, the code compares addresses but only modifies through `x`. But since it's a static function, and since it can see all the call sites, it eliminates a test it can prove is always true. So far so good.
However, it's not valid to keep the `restrict` declarations after that rewrite. It changed a modification through `x` to a modification through `y`, so that clearly violates the promise.
> So, which of the optimizations is the wrong one?
In the original function, the code compares addresses but only modifies through `x`. But since it's a static function, and since it can see all the call sites, it eliminates a test it can prove is always true. So far so good.
However, it's not valid to keep the `restrict` declarations after that rewrite. It changed a modification through `x` to a modification through `y`, so that clearly violates the promise.