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libstdc++: Fix comment on __memcpyable

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The discussion of iterator_traits<volatile T*>::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.
This commit is contained in:
Jonathan Wakely 2020-03-04 15:34:05 +00:00
parent 0b0908c1f2
commit 94f7d7ec6e
2 changed files with 11 additions and 4 deletions
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4
libstdc++-v3/ChangeLog
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@ -1,3 +1,7 @@
2020-03-04 Jonathan Wakely <jwakely@redhat.com>
* include/bits/cpp_type_traits.h (__memcpyable): Fix comment.
2020-03-04 Patrick Palka <ppalka@redhat.com>
PR libstdc++/94017

11
libstdc++-v3/include/bits/cpp_type_traits.h
View File

@ -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<volatile T*>::value_type is volatile T and so the
// partial specializations below match for volatile-qualified pointers
// e.g. __memcpyable<volatile int*, volatile int*, volatile int>.
// Cannot use memcpy/memmove/memcmp on volatile types even if they are
// trivially copyable, so ensure __memcpyable<volatile int*, volatile int*>
// and similar will be false.
template<typename _Tp>
struct __is_nonvolatile_trivially_copyable<volatile _Tp>
{
@ -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<typename _Iter1, typename _Iter2>
struct __memcmpable
{