[Bug c++/52558] write introduction incorrect wrt the C++11 memory model

[amacleod at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52558

--- Comment #3 from Andrew Macleod <amacleod at redhat dot com> 2012-03-12 15:24:35 UTC ---
Created attachment 26881
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26881
Testcase for simulate-threads

I've modified the testcase so that it runs in gcc.dg/simulate-thread as a
pass/fail. 

Clearly it currently fails, although its interesting because at -O3 it passes
again!!  The second pass of DOM undoes the extra write!

It does fail the testsuite at -O2 as expected.
This diff can be applied to add it to simulate threads.