[Bug target/123116] sbb cst is not produced with direct cond_expr expansion

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123116

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Andrew Pinski <pinskia@gcc.gnu.org>:

https://gcc.gnu.org/g:4204d3c46581bff5461e7b837e8bd3e1f2c24a2e

commit r16-6152-g4204d3c46581bff5461e7b837e8bd3e1f2c24a2e
Author: Andrew Pinski <andrew.pinski@oss.qualcomm.com>
Date:   Sat Dec 13 20:48:51 2025 -0800

    final_cleanup: Don't create forwarder blocks for degenerate_phis that are
ifconvertable [PR123111]

    So it turns out creating a forwarder block in some cases causes a
regression.
    The rtl ifcvt does like the case were the middle bb does not have a single
predecessor.
    So in some cases ifcvt does not happen any more. So the way to fix this
    is not to create a forwarder block for those edges which causes out of ssa
to
    create a middle bb which has the constant or the copy in it.

    I tried to do a simple ifcvt on the gimple level with the last phiopt but
    that introduces regressions as then `v += cmp - 43;` is not optimized
    and produces an extra subtraction. This is the best workaround I could come
up
    with until that is fixed. I filed PR 123116 for that issue.

    Bootstrapped and tested on x86_64-linux-gnu.

            PR tree-optimization/123111
    gcc/ChangeLog:

            * tree-cfg.cc (ifconvertable_edge): New function.
            (make_forwarders_with_degenerate_phis): Add skip_ifcvtable
argument,
            check ifconvertable_edge if skip_ifcvtable is true.
            * tree-cfg.h (make_forwarders_with_degenerate_phis): New argument
            with default of false.
            * tree-cfgcleanup.cc (execute_cleanup_cfg_post_optimizing): Update
            argument to make_forwarders_with_degenerate_phis.

    Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>