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Re: [PATCH] Restrict LOOP_ALIGN to loop headers only.
Hi,
On Tue, 9 Jul 2019, Richard Biener wrote:
> >The basic block index is not a DFS index, so no, that's not a test for
> >backedge.
>
> I think in CFG RTL mode the BB index designates the order of the BBs in
> the object file? So this is a way to identify backwards jumps?
Even if it means a backwards jump (and that's not always the case, the
insns are emitted by following the NEXT_INSN links, without a CFG, and
that all happens after machine-dependend reorg, and going out of cfg
layout might link insn together even from high index BBs to low index BBs
(e.g. because of fall-through)), that's still not a backedge in the
general case. If a heuristic is enough here it might be okay, though.
OTOH, as here a CFG still exists, why not simply rely on a proper DFS
marking backedges?
Ciao,
Michael.