[Bug middle-end/79173] add-with-carry and subtract-with-borrow support (x86_64 and others)

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79173

--- Comment #25 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:f8f68c4ca622a24c2e8cf2b5f2f9fdcd47a7b369

commit r14-2001-gf8f68c4ca622a24c2e8cf2b5f2f9fdcd47a7b369
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jun 20 20:17:41 2023 +0200

    tree-ssa-math-opts: Small uaddc/usubc pattern matching improvement
[PR79173]

    In the following testcase we fail to pattern recognize the least
significant
    .UADDC call.  The reason is that arg3 in that case is
      _3 = .ADD_OVERFLOW (...);
      _2 = __imag__ _3;
      _1 = _2 != 0;
      arg3 = (unsigned long) _1;
    and while before the changes arg3 has a single use in some .ADD_OVERFLOW
    later on, we add a .UADDC call next to it (and gsi_remove/gsi_replace only
    what is strictly necessary and leave quite a few dead stmts around which
    next DCE cleans up) and so it all of sudden isn't used just once, but twice
    (.ADD_OVERFLOW and .UADDC) and so uaddc_cast fails.  While we could tweak
    uaddc_cast and not require has_single_use in these uses, there is also
    no vrp that would figure out that because __imag__ _3 is in [0, 1] range,
    it can just use arg3 = __imag__ _3; and drop the comparison and cast.

    We already search if either arg2 or arg3 is ultimately set from __imag__
    of .{{ADD,SUB}_OVERFLOW,U{ADD,SUB}C} call, so the following patch just
    remembers the lhs of __imag__ from that case and uses it later.

    2023-06-20  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/79173
            * tree-ssa-math-opts.cc (match_uaddc_usubc): Remember lhs of
            IMAGPART_EXPR of arg2/arg3 and use that as arg3 if it has the right
            type.

            * g++.target/i386/pr79173-1.C: New test.