[Bug middle-end/108789] __builtin_(add|mul|sub)_overflow methods generate duplicate operations if both operands are const which in turn causes wrong code due to overlapping arguments

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108789

--- Comment #6 from GCC 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:b8e28381cb5c0cddfe5201faf799d8b27f5d7d6c

commit r15-1009-gb8e28381cb5c0cddfe5201faf799d8b27f5d7d6c
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jun 4 12:28:01 2024 +0200

    builtins: Force SAVE_EXPR for __builtin_{add,sub,mul}_overflow and
__builtin{add,sub}c [PR108789]

    The following testcase is miscompiled, because we use save_expr
    on the .{ADD,SUB,MUL}_OVERFLOW call we are creating, but if the first
    two operands are not INTEGER_CSTs (in that case we just fold it right away)
    but are TREE_READONLY/!TREE_SIDE_EFFECTS, save_expr doesn't actually
    create a SAVE_EXPR at all and so we lower it to
    *arg2 = REALPART_EXPR (.ADD_OVERFLOW (arg0, arg1)), \
    IMAGPART_EXPR (.ADD_OVERFLOW (arg0, arg1))
    which evaluates the ifn twice and just hope it will be CSEd back.
    As *arg2 aliases *arg0, that is not the case.
    The builtins are really never const/pure as they store into what
    the third arguments points to, so after handling the
INTEGER_CST+INTEGER_CST
    case, I think we should just always use SAVE_EXPR.  Just building SAVE_EXPR
    by hand and setting TREE_SIDE_EFFECTS on it doesn't work, because
    c_fully_fold optimizes it away again, so the following patch marks the
    ifn calls as TREE_SIDE_EFFECTS (but doesn't do it for the
    __builtin_{add,sub,mul}_overflow_p case which were designed for use
    especially in constant expressions and don't really evaluate the
    realpart side, so we don't really need a SAVE_EXPR in that case).

    2024-06-04  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/108789
            * builtins.cc (fold_builtin_arith_overflow): For ovf_only,
            don't call save_expr and don't build REALPART_EXPR, otherwise
            set TREE_SIDE_EFFECTS on call before calling save_expr.
            (fold_builtin_addc_subc): Set TREE_SIDE_EFFECTS on call before
            calling save_expr.

            * gcc.c-torture/execute/pr108789.c: New test.