[Bug middle-end/53676] [4.7 regression] empty loop is not always removed now

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53676

--- Comment #15 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-08-22 09:17:10 UTC ---
(In reply to comment #14)
> (In reply to comment #13)
> > No, it's only the commit referenced in this PR.  No optimization regressions
> > warrant a backport as they always come with the risk of regressing something
> > worse than performance.  Trivial restoring of old behavior might be worth
> > backporting but the patch introduces a completely new non-trivial transform
> > into a core analysis engine that is shared among many passes.
> 
> FWIW, it seems to me that small patches, even non-trivial ones, should be
> candidates for back-porting after they've been on the trunk or on a later
> release branch for a reasonable period of time. E.g. after 3 months on the GCC
> 4.8 trunk and with no resulting bugs reported, this patch should be considered
> for back-porting IMHO.

Testing coverage during stage1 isn't very good IMHO, so we should wait at
least until we enter stage3.  But again, patch size isn't a good metric, it is
the coverage that counts - for this patch, changing SCEV analysis in a
non-trivial way is very intrusive.