[Bug c++/94695] Implement -Wrange-loop-analysis

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94695

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:c51e31a06f2c740c55852a683aa7ffdc20417362

commit r11-5234-gc51e31a06f2c740c55852a683aa7ffdc20417362
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon Nov 9 21:15:33 2020 -0500

    c++: Extend -Wrange-loop-construct for binding-to-temp [PR94695]

    This patch finishes the second half of -Wrange-loop-construct I promised
    to implement: it warns when a loop variable in a range-based for-loop is
    initialized with a value of a different type resulting in a copy.  For
    instance:

      int arr[10];
      for (const double &x : arr) { ... }

    where in every iteration we have to create and destroy a temporary value
    of type double, to which we bind the reference.  This could negatively
    impact performance.

    As per Clang, this doesn't warn when the range returns a copy, hence the
    glvalue_p check.

    gcc/ChangeLog:

            PR c++/94695
            * doc/invoke.texi: Update the -Wrange-loop-construct description.

    gcc/cp/ChangeLog:

            PR c++/94695
            * parser.c (warn_for_range_copy): Warn when the loop variable is
            initialized with a value of a different type resulting in a copy.

    gcc/testsuite/ChangeLog:

            PR c++/94695
            * g++.dg/warn/Wrange-loop-construct2.C: New test.