diff options
| author | Jonathan Wakely <jwakely@redhat.com> | 2021-11-17 10:23:14 +0000 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2021-11-17 17:21:25 +0000 |
| commit | 6afa1083c6ee7b31629fb0c16299b952cb17868c (patch) | |
| tree | 80ca1827605ce99fa1690f650cb3f707e857a363 | |
| parent | 054bf99841aad3869c70643b2ba2d9f85770c980 (diff) | |
| download | gcc-6afa1083c6ee7b31629fb0c16299b952cb17868c.zip gcc-6afa1083c6ee7b31629fb0c16299b952cb17868c.tar.gz gcc-6afa1083c6ee7b31629fb0c16299b952cb17868c.tar.bz2 | |
libstdc++: Set active member of union in std::string [PR103295]
Clang diagnoses that the new constexpr std::string constructors are not
usable in constant expressions, because they start to write to members
of the union without setting an active member.
This adds a new helper function which returns the address of the local
buffer after making it the active member.
This doesn't fix all problems with Clang, because it still refuses to
write to memory returned by the allocator.
libstdc++-v3/ChangeLog:
PR libstdc++/103295
* include/bits/basic_string.h (_M_use_local_data()): New
member function to make local buffer the active member.
(assign(const basic_string&)): Use it.
* include/bits/basic_string.tcc (_M_construct, reserve()):
Likewise.
| -rw-r--r-- | libstdc++-v3/include/bits/basic_string.h | 15 | ||||
| -rw-r--r-- | libstdc++-v3/include/bits/basic_string.tcc | 10 |
2 files changed, 22 insertions, 3 deletions
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h index 0b7d6c0..9d281f5 100644 --- a/libstdc++-v3/include/bits/basic_string.h +++ b/libstdc++-v3/include/bits/basic_string.h @@ -325,6 +325,19 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 _M_get_allocator() const { return _M_dataplus; } + // Ensure that _M_local_buf is the active member of the union. + __attribute__((__always_inline__)) + _GLIBCXX14_CONSTEXPR + pointer + _M_use_local_data() _GLIBCXX_NOEXCEPT + { +#if __cpp_lib_is_constant_evaluated + if (__builtin_is_constant_evaluated()) + _M_local_buf[0] = _CharT(); +#endif + return _M_local_data(); + } + private: #ifdef _GLIBCXX_DISAMBIGUATE_REPLACE_INST @@ -1487,7 +1500,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11 if (__str.size() <= _S_local_capacity) { _M_destroy(_M_allocated_capacity); - _M_data(_M_local_data()); + _M_data(_M_use_local_data()); _M_set_length(0); } else diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc index 5743770..5a51f7e 100644 --- a/libstdc++-v3/include/bits/basic_string.tcc +++ b/libstdc++-v3/include/bits/basic_string.tcc @@ -170,9 +170,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION size_type __len = 0; size_type __capacity = size_type(_S_local_capacity); + pointer __p = _M_use_local_data(); + while (__beg != __end && __len < __capacity) { - _M_data()[__len++] = *__beg; + __p[__len++] = *__beg; ++__beg; } @@ -223,6 +225,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_data(_M_create(__dnew, size_type(0))); _M_capacity(__dnew); } + else + _M_use_local_data(); // Check for out_of_range and length_error exceptions. __try @@ -247,6 +251,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _M_data(_M_create(__n, size_type(0))); _M_capacity(__n); } + else + _M_use_local_data(); if (__n) this->_S_assign(_M_data(), __n, __c); @@ -355,7 +361,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION if (__length <= size_type(_S_local_capacity)) { - this->_S_copy(_M_local_data(), _M_data(), __length + 1); + this->_S_copy(_M_use_local_data(), _M_data(), __length + 1); _M_destroy(__capacity); _M_data(_M_local_data()); } |