------- 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
-fdump-rtl-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| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45256
