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[Bug tree-optimization/65177] [5 Regression]: extend jump thread for finite state automata causes miscompilation
- From: "law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 11 Mar 2015 21:45:25 +0000
- Subject: [Bug tree-optimization/65177] [5 Regression]: extend jump thread for finite state automata causes miscompilation
- Auto-submitted: auto-generated
- References: <bug-65177-4 at http dot gcc dot gnu dot org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65177
--- Comment #15 from Jeffrey A. Law <law at redhat dot com> ---
Basically the way this works is we record the SSA_NAMEs that are being
duplicated during block copying. For any duplicated SSA_NAME, if > 1 instance
of it is live at a join point in the CFG, then update_ssa will create a PHI and
merge the values.
I can't offhand think of any reason why it wouldn't work here if the names were
properly marked. But I haven't looked at the before/after CFGs to see if
there's something unique in this case. In fact, I haven't looked at it at all
at this point.