http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50904
--- Comment #37 from rguenther at suse dot de <rguenther at suse dot de> 2011-12-05 08:18:00 UTC --- On Fri, 2 Dec 2011, burnus at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50904 > > --- Comment #34 from Tobias Burnus <burnus at gcc dot gnu.org> 2011-12-02 > 17:06:57 UTC --- [...] > * * * > > Back to the comment 0 issue: I still do not quite understand what the double > evaluation (on tree level) of __builtin_pow in > D.1959_82 = ((D.2115_81)); > D.1960_83 = __builtin_pow (D.1959_82, 2.0e+0); > D.1978_168 = __builtin_pow (D.2115_81, 2.0e+0); > has to do with the -Ofast slow down. If I have understood it correctly, on > tree > level, there is no reason for it while the slow-down happens on RTL level. Indeed I can find no other difference on the tree level (thus, no invariant motion missed optimization that isn't present with both -f[no-]protect-parens). > That -fprotect-parens makes it faster is a mere coincidence. Is that a > correct rough > summary? Yes. Thus, I think if at the RTL level we see a missed invariant motion then this is a RTL level bug (esp. if it only triggers with -fno-protect-parens). Richard.
