[Bug middle-end/50251] [4.7 Regression] Revision 178353 caused many test failures

[vries at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50251

--- Comment #3 from vries at gcc dot gnu.org 2011-09-01 13:06:45 UTC ---
Created attachment 25162
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25162
optimized dump

1. The alloca in main is transformed into this declaration:

  <unnamed-unsigned:8> D.2129[24];

and accessed like this:

  iftmp.6_13 = MEM[symbol: D.2129, index: ivtmp.30_31, step: 4, 
                   offset: 4294967292B];

  MEM[symbol: D.2129, index: ivtmp.30_31, step: 4, offset: 0B] = D.2105_15;

  D.2099_18 = MEM[(int *)&D.2129][5]{lb: 0 sz: 4};

  MEM[symbol: D.2129, index: ivtmp.30_31, step: 4, offset: 0B] = 0;


2. __builtin_stack_restore/__builtin_stack_restore in main are not optimized
away, because the restored value is potentially used. The restored value is the
same as the current value, so the restore is redundant, but that's not checked
in optimize_stack_restore.

   saved_stack.3_5 = __builtin_stack_save ();

  __builtin_stack_restore (saved_stack.3_5);