[Bug c++/96780] debuginfo for std::move and std::forward isn't useful

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96780

--- Comment #16 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:e55c5e24b97ad8ddc44588da18e894c139e02c0a

commit r12-7668-ge55c5e24b97ad8ddc44588da18e894c139e02c0a
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Mar 16 08:25:54 2022 -0400

    c++: fold calls to std::move/forward [PR96780]

    A well-formed call to std::move/forward is equivalent to a cast, but the
    former being a function call means the compiler generates debug info,
    which persists even after the call gets inlined, for an operation that's
    never interesting to debug.

    This patch addresses this problem by folding calls to std::move/forward
    and other cast-like functions into simple casts as part of the frontend's
    general expression folding routine.  This behavior is controlled by a
    new flag -ffold-simple-inlines, and otherwise by -fno-inline, so that
    users can enable this folding with -O0 (which implies -fno-inline).

    After this patch with -O2 and a non-checking compiler, debug info size
    for some testcases from range-v3 and cmcstl2 decreases by as much as ~10%
    and overall compile time and memory usage decreases by ~2%.

            PR c++/96780

    gcc/ChangeLog:

            * doc/invoke.texi (C++ Dialect Options): Document
            -ffold-simple-inlines.

    gcc/c-family/ChangeLog:

            * c.opt: Add -ffold-simple-inlines.

    gcc/cp/ChangeLog:

            * cp-gimplify.cc (cp_fold) <case CALL_EXPR>: Fold calls to
            std::move/forward and other cast-like functions into simple
            casts.

    gcc/testsuite/ChangeLog:

            * g++.dg/opt/pr96780.C: New test.