From 94f7d7ec6ebef49a50da777fd71db3d03ee03aa0 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Wed, 4 Mar 2020 15:34:05 +0000 Subject: [PATCH] libstdc++: Fix comment on __memcpyable The discussion of iterator_traits::value_type and the example with three tempalte arguments related to an earlier version of the patch, not the one committed. Also improve the comment on __memcmpable. * include/bits/cpp_type_traits.h (__memcpyable): Fix comment. --- libstdc++-v3/ChangeLog | 4 ++++ libstdc++-v3/include/bits/cpp_type_traits.h | 11 +++++++---- 2 files changed, 11 insertions(+), 4 deletions(-) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index ff8ae64d477..df3b040abca 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,7 @@ +2020-03-04 Jonathan Wakely + + * include/bits/cpp_type_traits.h (__memcpyable): Fix comment. + 2020-03-04 Patrick Palka PR libstdc++/94017 diff --git a/libstdc++-v3/include/bits/cpp_type_traits.h b/libstdc++-v3/include/bits/cpp_type_traits.h index fac6e4bbea2..979ad9c2c69 100644 --- a/libstdc++-v3/include/bits/cpp_type_traits.h +++ b/libstdc++-v3/include/bits/cpp_type_traits.h @@ -429,10 +429,9 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3) enum { __value = __is_trivially_copyable(_Tp) }; }; - // Cannot use memcpy/memmove/memcmp on volatile types, but before C++20 - // iterator_traits::value_type is volatile T and so the - // partial specializations below match for volatile-qualified pointers - // e.g. __memcpyable. + // Cannot use memcpy/memmove/memcmp on volatile types even if they are + // trivially copyable, so ensure __memcpyable + // and similar will be false. template struct __is_nonvolatile_trivially_copyable { @@ -457,6 +456,10 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3) { }; // Whether two iterator types can be used with memcmp. + // This trait only says it's well-formed to use memcmp, not that it + // gives the right answer for a given algorithm. So for example, std::equal + // needs to add additional checks that the types are integers or pointers, + // because other trivially copyable types can overload operator==. template struct __memcmpable { -- 2.30.2