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Subject: [Bug middle-end/38474] compile time explosion in
 dataflow_set_preserve_mem_locs at -O3
Date: Thu, 29 Apr 2021 08:04:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D38474

--- Comment #101 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:c57a8aea0c3ab8394f7dbfa417ee27b4613f63b7

commit r12-280-gc57a8aea0c3ab8394f7dbfa417ee27b4613f63b7
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Apr 29 08:32:00 2021 +0200

    middle-end/38474 - speedup PTA constraint solving

    In testcases like PR38474 and PR99912 we're seeing very slow
    PTA solving.  One can observe an excessive amount of forwarding,
    mostly during sd constraint solving.  The way we solve the graph
    does not avoid forwarding the same bits through multiple paths,
    and especially when such alternate path involves ESCAPED as
    intermediate this causes the ESCAPED solution to be expanded
    in receivers.

    The following adds heuristic to add_graph_edge which adds
    forwarding edges but also guards the initial solution forwarding
    (which is the expensive part) to detect the case of ESCAPED
    receiving the same set and the destination already containing
    ESCAPED.

    This speeds up the PTA solving process by more than 50%.

    2021-04-29  Richard Biener  <rguenther@suse.de>

            PR middle-end/38474
            * tree-ssa-structalias.c (add_graph_edge): Avoid direct
            forwarding when indirect forwarding through ESCAPED
            alread happens.=