[cxx-mem-model] alternate fetch operations

[Andrew MacLeod <amacleod at redhat dot com>]

Mail started bouncing from gcc-patches a couple of days ago, trying with 
some new thunderbird settings.  No idea why it just started, I haven't 
changed anything...

 anyway:
------------------------

The __sync_mem_fetch_{add,sub,and,xor,or} routines perform the operation 
atomically, and return the value that was in memory before the operation 
was performed.  As I was working on switching the c++ wrappers to use 
these new routines, I discovered we also need the versions which return 
the *result* of the operation atomically.

I implemented them initially to add a flag to indicate whether we wanted 
the value before or after the operation, but in actual practice it was a 
bit awkward to use and I was not happy with it. Instead, I simply reused 
as much internal code as I could, and added new __sync routines.

The names for the previous set implies the fetch is done before the 
operation, so the new ones simply drop the fetch and simply use the 
operation name. I found sync_mem_op_fetch slightly less clear.  the new 
routines documentation looks like:

   TYPE __sync_mem_add (TYPE *ptr, TYPE val, int memmodel)
   TYPE __sync_mem_sub (TYPE *ptr, TYPE val, int memmodel)
   TYPE __sync_mem_and (TYPE *ptr, TYPE val, int memmodel)
   TYPE __sync_mem_xor (TYPE *ptr, TYPE val, int memmodel)
   TYPE __sync_mem_or (TYPE *ptr, TYPE val, int memmodel)
         These builtins perform the operation suggested by the name, and
         return the result of the operation. That is,

              { *ptr OP= val; return *ptr; }

         All memory models are valid.

I also decided to change the testcases around (again).  I merged all the 
different fetch_op tests into one, and added all the new tests.  now 
there is simply 5 tests files sync-mem-op-[1-5].c to test all these 
routines for (1)char, (2)short, (3)int, (4)long long, and (5)__int128_t.

Bootstrapped and no new regressions on x86-64.  (I am re-verifying 
overnight however).  OK for the branch?

Andrew

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