Fix PR 16728

[Benjamin Kosnik]

>When copying a pointer into another, we should also merge the flow
>sensitive information.  This first showed up on tree-cleanup-branch with
>the more aggressive copy propagator.  I'm rather surprised that it had
>never showed up on mainline.

Sweet. This had been broken for three months. Now it's possible to run
the full performance testsuites on mainline...

>The original test is only run with 'make check-performance' on
>libstdc++.  I'd like to move/copy this test into the regular 'make
>check', but I don't know my way around libstdc++/testsuite.  Could one
>of the libstdc++ folks give me a pointer?  Where could I put this test? 
>It's a runtime test that needs '-O2 -pthread' to run.

So is the test for this going to live in libstdc++? Dunno. I suppose
you'd add the smallest possible test that broke somewhere (where?), like
the testsuite/thread tests that get run all the time.

thanks again.

-benjamin