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.
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();
sequence_buffer(_Sequence& __s)
: _M_prefix(&__s), _M_buf_count(0) { }
+ // Non-const "copy" modifies the parameter - yuck
sequence_buffer&
operator=(sequence_buffer& __x)
{
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)
{
--- /dev/null
+// { 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" );
+}