------- Comment #2 from ibolton at gcc dot gnu dot org  2010-09-07 13:05 -------
(In reply to comment #1)
> Created an attachment (id=21454)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21454&action=view) [edit]
> Testcase

OK.  I can see this happening on trunk, when compiled as follows:

arm-none-linux-gnueabi/obj/gcc3/gcc/cc1 -O2 pr45256.i -fdump-tree-all

The 148t.optimized dump shows exactly what has been posted above, where
effectively 32 is both added and then subtracted.

The 183r.dce dump still shows this extra work happening and the 184r.combine
dump shows that it has been optimised away.  It should be possible to do this
optimisation at the tree-level, so this bug is confirmed.

Should I check whether this happens for 4.4 and 4.5 too?


ibolton at gcc dot gnu dot org changed:

           What    |Removed                     |Added
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |missed-optimization
      Known to fail|                            |4.6.0
   Last reconfirmed|0000-00-00 00:00:00         |2010-09-07 13:05:49
               date|                            |


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