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PR 101923 points out that the unconditional swap in the std::function move constructor makes it slower than copying an empty std::function. The copy constructor has to check for the empty case before doing anything, and that makes it very fast for the empty case. Adding the same check to the move constructor avoids copying the _Any_data POD when we don't need to. We can also inline the effects of swap, by copying each member and then zeroing the pointer members. This makes moving an empty object at least as fast as copying an empty object. Signed-off-by: Jonathan Wakely <jwakely@redhat.com> libstdc++-v3/ChangeLog: PR libstdc++/101923 * include/bits/std_function.h (function(function&&)): Check for non-empty parameter before doing any work. |
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file: libstdc++-v3/README New users may wish to point their web browsers to the file index.html in the 'doc/html' subdirectory. It contains brief building instructions and notes on how to configure the library in interesting ways.