https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64058
--- Comment #10 from rguenther at suse dot de <rguenther at suse dot de> --- On March 8, 2016 8:39:34 PM GMT+01:00, law at redhat dot com <gcc-bugzi...@gcc.gnu.org> wrote: >https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64058 > >--- Comment #9 from Jeffrey A. Law <law at redhat dot com> --- >So if I take my code to renumber SSA_NAMES so they they're consistent >irrespective how SSA_NAMEs were recycled and apply that on top of >r216304 and >r216305 the net result is I get the same code from those two compilers. > >That argues that ultimately this is another case of SSA_NAME_VERSION >differences causing coalescing to make different decisions in a >semi-random way >which leads to random performance changes. > >That means this BZ and 68654 are likely manifestations of the same >underlying >issue. > >I'm still having some problems with getting consistent results across a >larger >codebase comparing before/after the SSA_NAME freelist flushing change, >so >clearly something isn't getting renumbered properly. But it's >promising. How is renumbering promising if it doesn't address the underlying randomness in the coalescing decision?
