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Subject: [Bug tree-optimization/65177] [5 Regression]: extend jump thread for finite state automata causes miscompilation
Date: Wed, 11 Mar 2015 16:27:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65177

--- Comment #14 from Sebastian Pop <spop at gcc dot gnu.org> ---
(In reply to Jeffrey A. Law from comment #13)
> But you can need updates that extend beyond the scope of the SEME I would
> think.  That was my recollection from looking at ways to minimize the number
> of blocks the renamer had to examine after threading.

You are right, we need to update all uses of ssa_names defined in the SEME.

We currently only fix all the phi nodes on all the exits of the SEME by adding
one more operand to the phis.  I think we would also need to add phi nodes for
all the definitions that we copied as now we may reach the destination of an
SEME exit through at least two paths: the original path and the copied one.

I do not know whether update_ssa has enough information to correctly add these
phi nodes.