[Bug tree-optimization/18241] [4.0 Regression] linux kernel loop gets miscompiled

["rakdver at atrey dot karlin dot mff dot cuni dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From rakdver at atrey dot karlin dot mff dot cuni dot cz  2004-11-28 09:17 -------
Subject: Re:  [4.0 Regression] linux kernel loop gets miscompiled

> 
> ------- Additional Comments From pinskia at gcc dot gnu dot org  2004-11-28 01:28 -------
> Confirmed,  this looks like a jump threading bug.
> Before we have:
>  goto <bb 9> (<L10>);
> 
> <L8>:;
>   D.7815_42 = pathp_2->node;
>   tag_43 = tag_27;
>   idx_44 = idx_6;
>   D.7819_45 = D.7815_42->tags[tag_43][idx_44];
>   if (D.7819_45 != 0) goto out; else goto <L9>;
> 
> <L9>:;
>   idx_46 = idx_6 + 1;
> 
>   # idx_6 = PHI <idx_39(6), idx_46(8)>;
> <L10>:;
>   if (idx_6 == 0) goto <L8>; else goto <L11>;
> 
> 
> But after:
>  goto <bb 8> (<L10>);
> 
> <L9>:;
>   idx_46 = 1;
>   goto <bb 10> (<L15>);
> 
>   # idx_57 = PHI <0(6)>;
> <L10>:;
>   D.7815_42 = pathp_2->node;
>   tag_43 = tag_27; 
>   idx_44 = 0;   <---- this is just plainly wrong.

this seems OK to me (note the "weird" condition that
ends the loop -- this loops iterates exactly once, with idx being 0).

>   D.7819_45 = D.7815_42->tags[tag_27][0];
>   if (D.7819_45 != 0) goto out; else goto <L9>;


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18241