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[PATCH] PR libstdc++/69724 avoid temporary in std::thread construction

From: Jonathan Wakely <jwakely at redhat dot com>
To: libstdc++ at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
Date: Tue, 14 May 2019 13:01:38 +0100
Subject: [PATCH] PR libstdc++/69724 avoid temporary in std::thread construction

The std::thread constructor creates (and then moves) an unnecessary
temporary copy of each argument. Optimize it to only make the one copy
that is required.

	PR libstdc++/69724
	* include/std/thread (thread::_State_impl, thread::_S_make_state):
	Replace single _Callable parameter with variadic _Args pack, to
	forward them directly to the tuple of decayed copies.
	* testsuite/30_threads/thread/cons/69724.cc: New test.

Tested powerpc64le-linux, committed to trunk.

I'll leave the bug report open as I want to do a similar optimization
for std::async's DECAY_COPY as well.

Attachment: patch.txt
Description: Text document

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