[RFC / CFT] PR c++/66192 - Remove TARGET_RELAXED_ORDERING and use load acquires.

[Ramana Radhakrishnan]

On 22/05/15 14:40, Jason Merrill wrote:
> On 05/22/2015 07:23 AM, Ramana Radhakrishnan wrote:
>> +  /* Load the guard value only through an atomic acquire load.  */
>> +  guard = build_atomic_load (guard, MEMMODEL_ACQUIRE);
>> +
>>     /* Check to see if the GUARD is zero.  */
>>     guard = get_guard_bits (guard);
>
> I wonder if these calls should be reversed, to express that we're only
> trying to atomically load a byte (on non-ARM targets)?
>

I'm not sure about the impact on other non-ARM targets without some more 
investigation.

>> +  tree orig_src = src;
>> +  tree t, addr, val;
>> +  unsigned int size;
>> +  int fncode;
>> +
>> +  size = tree_to_uhwi (TYPE_SIZE_UNIT (TREE_TYPE (src)));
>> +
>> +  fncode = BUILT_IN_ATOMIC_LOAD_N + exact_log2 (size) + 1;
>> +  t = builtin_decl_implicit ((enum built_in_function) fncode);
>> +
>> +  addr = build1 (ADDR_EXPR, ptr_type, src);
>> +  val = build_call_expr (t, 2, addr, mem_model);
>> +
>> +  /* First reinterpret the loaded bits in the original type of the load,
>> +     then convert to the expected result type.  */
>> +  t = fold_build1 (VIEW_CONVERT_EXPR, TREE_TYPE (src), val);
>> +  return convert (TREE_TYPE (orig_src), t);
>
> I don't see anything that changes src here.

Sorry 'bout that. Will fix in the next spin depending on comments from 
others.

I take it that you are happy with the patch otherwise ...

regards
Ramana

>
> Jason
>