AARCH64: 8139041: Redundant DMB instructions (CORRECTED )

[Andrew Haley]

On 10/10/2015 02:00 AM, Vladimir Kozlov wrote:
> On 10/10/15 2:47 AM, Christian Thalinger wrote:
>>
>>> On Oct 9, 2015, at 5:37 AM, Andrew Haley <aph at redhat.com> wrote:
>>>
>>> Hi,
>>>
>>> On 10/09/2015 03:59 PM, Roland Westrelin wrote:
>>>
>>>>> There is a much simpler way: remove adjacent barriers in
>>>>> MacroAssembler.  Thanks to the way that the AArch64 ISA is designed,
>>>>> barriers can be merged simply by ORing them together.  Of course, this
>>>>> technique works for C1 and C2, and it adds essentially nothing to the
>>>>> compilation time.
>>>>>
>>>>> http://cr.openjdk.java.net/~aph/8139041/
>>>>>
>>>>> One thing which may be controversial is that I've added a field to
>>>>> CodeBuffer to keep track of barriers and labels.  I had to do this
>>>>> because when we're compiling there is (AFAICS) essentially nowhere
>>>>> else to keep the state.
>>
>> I don’t think it matters to have an additional field in CodeBuffer.  It’s a temporary data structure and we use much more memory for graphs.
>>
>> I would even go that far and questioning putting it under #ifdef AARCH64.
> 
> +1 that.

OK.  I'm guessing that PPC will want to use this anyway.

http://cr.openjdk.java.net/~aph/8139041-2

Andrew.