http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49847
--- Comment #33 from rguenther at suse dot de <rguenther at suse dot de> --- On Sun, 16 Feb 2014, law at redhat dot com wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49847 > > --- Comment #32 from Jeffrey A. Law <law at redhat dot com> --- > The problem we're seeing is with the cc0-setter and cc0-user in different > blocks, they're separated by a NOTE_BASIC_BLOCK. > > That causes CSE to blow up because it expects that the cc0-setter and > cc0-user are always consecutive. While we're just seeing the failure in > CSE right now, I'm sure there's a ton of places that assume the > setter/user are inseparable as that has been the documented form for ~20 > years. > > From rtl.texi: > > The instruction setting the > condition code must be adjacent to the instruction using the condition > code; only @code{note} insns may separate them. > > > We either need to relax that and audit all the HAVE_cc0 code to ensure it > doesn't make that assumption, or we need to somehow restore the property that > the setter and user are inseparable. I think relaxing this constraint and allowing the cc0-setter and cc0-user be separated by a fallthru-edge should be allowed (and make sure that bb-reorder later doesn't separate the BBs)
