[Bug middle-end/57748] [4.7/4.8/4.9 Regression] ICE when expanding assignment to unaligned zero-sized array

[bernd.edlinger at hotmail dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57748

--- Comment #41 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to rguenther@suse.de from comment #40)
> The issue is that we added the movmisaling-on-component-ref path
> for _correctness_ reasons.  Now, if all misaligned accesses end up
> being expanded using BLKmode moves then it probably works ok (but
> then they are going to be horribly inefficent and wouldn't have
> triggered the movmisaling path anyway ...).
> 
> But I'm willing to make the experiment - we've got plenty (well ...)
> time to watch out for fallout of this change (and it does simplify
> code, something I always like ;))

Ok, then I'll commit part 1 later in the evening.

>From my experiments I've learned that when expanding a
mov_optab instead of a movmisalign_optab the backend
looks at the MEM_ALIGN() info of both sides and based on that
information either a movdqa or movdqu is expanded. And
in the example that you mentioned, apparently the MEM_ALIGN
must be wrong.