[Bug middle-end/88490] Missed autovectorization when indices are different

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88490

--- Comment #5 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Fri, 14 Dec 2018, rguenther at suse dot de wrote:

> Note I do not think the C standard is sufficiently clear with regarding 
> to restrict qualified pointers loaded from memory.

I think this is where "Every access that modifies X shall be considered 
also to modify P, for the purposes of this subclause." comes in.  (See 
what I said at <https://gcc.gnu.org/ml/gcc-bugs/2005-01/msg03394.html>.)  
Modifying s->d[n][0] is considered to modify s->d[n], and so considered to 
modify s->d, and so considered to modify s.  (It's still perfectly valid 
to have n == k; what's not valid is aliasing between objects accessed via 
s->d[0] and s->d[1], for example.)