[Bug libstdc++/94017] std::ranges::fill_n uses memset incorrectly

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94017

--- Comment #1 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:712b182a8bc2d7510d7a2fbede43bf134c539f25

commit r10-7006-g712b182a8bc2d7510d7a2fbede43bf134c539f25
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Mar 3 16:16:05 2020 -0500

    libstdc++: Fix incorrect use of memset in ranges::fill_n (PR 94017)

    When deciding whether to perform the memset optimization in ranges::fill_n,
we
    were crucially neglecting to check that the output pointer's value type is
a
    byte type.  This patch adds such a check to the problematic condition in
    ranges::fill_n.

    At the same time, this patch relaxes the overly conservative
    __is_byte<_Tp>::__value check that requires the fill type be a byte type. 
It's
    overly conservative because it means we won't enable the memset
optimization in
    the following example

      char c[100];
      ranges::fill(c, 37);

    because the fill type is deduced to be int here.  Rather than requiring
that the
    fill type be a byte type, it seems safe to just require the fill type be an
    integral type, which is what this patch does.

    libstdc++-v3/ChangeLog:

        PR libstdc++/94017
        * include/bits/ranges_algobase.h (__fill_n_fn::operator()): Refine
        condition for when to use memset, making sure to additionally check
that
        the output pointer's value type is a non-volatile byte type.  Instead
of
        requiring that the fill type is a byte type, just require that it's an
        integral type.
        * testsuite/20_util/specialized_algorithms/uninitialized_fill/94017.cc:
        New test.
        *
testsuite/20_util/specialized_algorithms/uninitialized_fill_n/94017.cc:
        New test.
        * testsuite/25_algorithms/fill/94013.cc: Uncomment part that was
blocked
        by PR 94017.
        * testsuite/25_algorithms/fill/94017.cc: New test.
        * testsuite/25_algorithms/fill_n/94017.cc: New test.