RFR: 8073093: AARCH64: C2 generates poor code for ByteBuffer accesses

[Vladimir Kozlov]

There was discussion should we remove such barriers or not because they 
create memory operations ordering which could be different if we remove 
them.

To eliminate them we need to add 'precedent' edge to store's membar as 
we do, for example, for loads:

   if (field->is_volatile()) {
     // Memory barrier includes bogus read of value to force load BEFORE 
membar
     insert_mem_bar(Op_MemBarAcquire, ld);
   }

MemBarNode::Ideal() will do elimination.

Regards,
Vladimir

On 2/17/15 10:58 AM, Andrew Haley wrote:
> On 02/17/2015 06:42 PM, John Rose wrote:
>> The remaining store fence is probably a bug.  A store fence for scalarized (lifted-out-of-memory) final fields should go away, since the fields are not actually stored in heap memory.
>
> After inlining how would escape analysis know that the store fence is
> associated with final fields rather than, say, an explicit
> Unsafe.storeFence() ?
>
> Andrew.
>