http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53695
--- Comment #14 from rguenther at suse dot de <rguenther at suse dot de> 2012-08-23 08:10:15 UTC --- On Thu, 23 Aug 2012, stevenb.gcc at gmail dot com wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53695 > > --- Comment #12 from stevenb.gcc at gmail dot com <stevenb.gcc at gmail dot > com> 2012-08-23 07:56:13 UTC --- > > The patch is of couse a "big hammer" because it has a cost, but IMHO > > it still makes sense. > > I'm not convinced. GCC has always detected this kind of loop (even the > old non-cfg loop code recognizes this kind of loop) and it has never > caused any problems before your patch to keep the loop structure > up-to-date. To me, this means that the fix should be in the loop > updating, not in abandoning a decades-old behavior of the compiler. It's inconsistent in that it considers <header> | ^ (ab) | v | latch a loop but not <header> | ^ | (ab) v | latch and tracer "rotates" this loop by swapping dominance relationship between header and latch but not makes the non-loop magically a loop. My patch makes both not a loop.
