[Bug tree-optimization/53465] [4.7 regression] wrong code with -O1 -ftree-vrp

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53465

--- Comment #5 from rguenther at suse dot de <rguenther at suse dot de> 2012-05-24 07:57:58 UTC ---
On Thu, 24 May 2012, jakub at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53465
> 
> --- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-05-24 07:42:26 UTC ---
> Dropping all might pessimize some code (of course, this is VR_UNDEFINED, so the
> question is if we need to care that much about broken code), like:
> int
> foo (int x, int y)
> {
>   int z;
>   if (x <= 3)
>     return 7;
>   if (y)
>     z = x;
>   return z == x;
> }
> 
> where the equivalence could be very well kept.  Or
> int
> foo (int y)
> {
>   int z;
>   int x = bar ();
>   if (x <= 3)
>     return 7;
>   if (y)
>     z = x;
>   return z == x;
> }
> 
> In both cases the x_3 in the equivalence bitmap dominates the PHI stmt (in one
> case it is the default parm def, in the second case not).  vrp_meet would
> probably need to be called with gimple stmt in that case on which the meet
> happens.
> 
> Anyway, if you think it is overkill, we can just drop the equivalences
> altogether.

I indeed think this is overkill, definitely for the 4.7 branch.

Richard.