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Re: [tree-ssa] Avoid jump threading from producing irreducible regions
> In message <20031121152630.GV12030@kam.mff.cuni.cz>, Jan Hubicka writes:
> >as discussed earlier, I believe we must avoid producing irreducible
> >loops in early stages of compilation as disabling loop optimizations for
> >no good reason can be disasterous.
> >regtested/bootstrapped i386
> >2003-11-21 Jan Hubicka <email@example.com>
> > * tree-ssa.dom.c (tree_ssa_domionator_thread_jumps): Mark back edges.
> > (thread_across_edge): Do not thread across loop headers.
> Note that the threader is run in two modes.
> The first (and the one you changed) is allowed to thread through blocks
> which begin with PHI nodes.
> The second runs as part of the dominator optimizer, but is not allowed to
> thread through a block with PHI nodes. You didn't change the behavior of
> this instance.
> [ Note I fully expect that with Andrew's changes that we'll have a single
> mode for the dominator based jump threader in the future. ]
> Anyway, I'm guessing that you don't have to worry about the second mode
> (no threading through PHIs) since loops are going to have a PHI at the
> the block which starts the natural loop. Right?
I guess so. Except for loops with no loop carried variables that are
out of interest anyway.
OK then? :)