Extending Temporary buffer for rvalues

[Christopher Jefferson <caj at cs dot st-andrews dot ac dot uk>]

I wanted to post this patch separate from my other work, as it might  
be controversial (but hopefully isn't).

This patch changes _Temporary_buffer so that rather than using  
uninitalised_fill_n,  it 'moves' the first value from the range being  
sorted along the uninitalised range, then back to where it started.

This isn't slow -- we already special case PODs so there isn't really  
any opportunity for the compiler to change the code into a memset or  
something similar.

I believe also the code is fine from the point of view of correctness.  
One problem is that if one of these constructors throws, the '*first'  
value is lost. However, if any constructor throws once the main body  
of the algorithm has begun, values could still be lost before, even in  
C++03, so I do not believe this harms the algorithm.

If this patch is acceptable, then the rest of the C++0x changes to  
sort are, I believe, non-contraversal.

If this patch is OK, you are welcome to apply this patch as is, or  
wait for a large patch which subsumes it.

Thanks, Chris

Attachment: temporary_buffer_rvalue.patch
Description: Binary data

2009-08-26  Chris Jefferson  <chris@bubblescope.net>

        * include/bits/stl_tempbuf.h  
(_Temporary_buffer::_Temporary_buffer) :
	Extend to work with move-only types.
	* testsuite/25_algorithm/stable_sort/mem_check.cc : New
	* testsuite/util/testsuite_hooks.h : Add operator< to copy_tracker.