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| author | Jonathan Wakely <jwakely@redhat.com> | 2021-07-21 15:29:19 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2021-07-21 17:20:37 +0100 |
| commit | 8edb61420502c62fa2cccdd98876a9aa039b72a6 (patch) | |
| tree | 571f02297c927569f8aff7ad4a254fc8a4837a64 | |
| parent | e4d306cf706eef83f99d510c308eda1539d05875 (diff) | |
| download | gcc-8edb61420502c62fa2cccdd98876a9aa039b72a6.zip gcc-8edb61420502c62fa2cccdd98876a9aa039b72a6.tar.gz gcc-8edb61420502c62fa2cccdd98876a9aa039b72a6.tar.bz2 | |
libstdc++: Make __gnu_cxx::sequence_buffer move-aware [PR101542]
The PR explains that Clang trunk now selects a different constructor
when a non-const sequence_buffer is returned in a context where it
qualifies as an implicitly-movable entity. Because lookup is first
performed using an rvalue, the sequence_buffer(const sequence_buffer&)
constructor gets chosen, which makes a copy instead of a "pseudo-move"
via the sequence_buffer(sequence_buffer&) constructor. The problem isn't
seen with GCC because as noted in the r11-2412 commit log, GCC actually
implements a slightly modified rule that avoids breaking exactly this
type of code.
This patch adds a move constructor to sequence_buffer, so that implicit
or explicit moves will have the same effect, calling the
sequence_buffer(sequence_buffer&) constructor. A move assignment
operator is also added to make move assignment work similarly.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
PR libstdc++/101542
* include/ext/rope (sequence_buffer): Add move constructor and
move assignment operator.
* testsuite/ext/rope/101542.cc: New test.
| -rw-r--r-- | libstdc++-v3/include/ext/rope | 9 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/ext/rope/101542.cc | 27 |
2 files changed, 35 insertions, 1 deletions
diff --git a/libstdc++-v3/include/ext/rope b/libstdc++-v3/include/ext/rope index 81e4f23..9681dbc 100644 --- a/libstdc++-v3/include/ext/rope +++ b/libstdc++-v3/include/ext/rope @@ -203,6 +203,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION std::copy(__x._M_buffer, __x._M_buffer + __x._M_buf_count, _M_buffer); } + // Non-const "copy" modifies the parameter - yuck sequence_buffer(sequence_buffer& __x) { __x.flush(); @@ -213,6 +214,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION sequence_buffer(_Sequence& __s) : _M_prefix(&__s), _M_buf_count(0) { } + // Non-const "copy" modifies the parameter - yuck sequence_buffer& operator=(sequence_buffer& __x) { @@ -230,7 +232,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION std::copy(__x._M_buffer, __x._M_buffer + __x._M_buf_count, _M_buffer); return *this; } - + +#if __cplusplus >= 201103L + sequence_buffer(sequence_buffer&& __x) : sequence_buffer(__x) { } + sequence_buffer& operator=(sequence_buffer&& __x) { return *this = __x; } +#endif + void push_back(value_type __x) { diff --git a/libstdc++-v3/testsuite/ext/rope/101542.cc b/libstdc++-v3/testsuite/ext/rope/101542.cc new file mode 100644 index 0000000..e89f23d --- /dev/null +++ b/libstdc++-v3/testsuite/ext/rope/101542.cc @@ -0,0 +1,27 @@ +// { dg-do run { target c++11 } } +// PR libstdc++/101542 +#include <ext/rope> +#include <testsuite_hooks.h> + +template<typename T> T f(T x) { return x; } +template<typename T> T g(T x) { return std::move(x); } + +int main() +{ + std::string s; + { + __gnu_cxx::sequence_buffer<std::string> a(s); + { + __gnu_cxx::sequence_buffer<std::string> b = std::move(a); + b.push_back('h'); + b.push_back('e'); + b.push_back('l'); + b.push_back('l'); + b.push_back('o'); + + __gnu_cxx::sequence_buffer<std::string> c; + c = f(g((std::move(b)))); + } + } + VERIFY( s == "hello" ); +} |