[Bug middle-end/51752] New: trans-mem: publication safety violated

[torvald at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51752

             Bug #: 51752
           Summary: trans-mem: publication safety violated
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: torvald@gcc.gnu.org


Created attachment 26238
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26238
publication safety test

Publication safety refers to transactions being able to safely publish data by
setting something like a shared flag (e.g., "data=23; __transaction_atomic {
flag = 1; }").  For that to work, programmers must access the data only if the
flag is true.  Second, the compiler must preserve program order in this case
and is not allowed to reorder the two loads (i.e., load data before loading the
flag).  Otherwise, there will be a race condition and the data load can return
an inconsistent value.

The attached test shows that this isn't working currently (e.g., look at
149t.optimized, the load of data is moved to out of the loop and before the
"flag" loads).