[Bug tree-optimization/59354] [4.8/4.9/5 Regression] Element swizzling produces invalid result with -O3

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59354

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
            Summary|[4.8/4.9/5/Regression]      |[4.8/4.9/5 Regression]
                   |Element swizzling produces  |Element swizzling produces
                   |invalid result with -O3     |invalid result with -O3

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Uroš Bizjak from comment #3)
> It looks to me that cunrolli pass is messing up element swizzling code.
> 
> bisection-friendly C testcase:
> 
> --cut here--
> void abort (void);
> 
> unsigned int a[256];
> unsigned char b[256];
> 
> int main()
> {
>   int i, z, x, y;
> 
>   for(i = 0; i < 256; i++)
>     a[i] = i % 5;
> 
>   for (z = 0; z < 16; z++)
>     for (y = 0; y < 4; y++)
>       for (x = 0; x < 4; x++)
>         b[y*64 + z*4 + x] = a[z*16 + y*4 + x];
> 
>   if (b[4] != 1)
>     abort ();
> 
>   return 0;
> }
> --cut here--

This testcase works for me on trunk now (maybe one of my recent vectorizer
fixes) but it miscompiles on the 4.9 and 4.8 branches (4.7 seems to work).

Maybe somebody can bisect what fixed it on trunk? (and confirm the bug is
indeed gone on trunk)