RFR: 8075930: AARCH64: Use FP Register in C2

[Andrew Haley]

On 26/03/15 09:32, Zoltán Majó wrote:
> Hi Andrew,
> 
> 
> On 03/26/2015 10:27 AM, Andrew Haley wrote:
>> On 25/03/15 14:08, Andrew Dinn wrote:
>>> On 25/03/15 13:28, Zoltán Majó wrote:
>>>> On 03/25/2015 02:02 PM, Edward Nevill wrote:
>>>>> The aarch64 C2 compiler makes no use of the FP register even though
>>>>> this register is saved on entry and restored on exit and is therefore
>>>>> always available for allocation.
>>>> It seems to me that the C2 compiler currently saves the SP into FP on
>>>> method handle invokes. This functionality is encoded by
>>>> aarch64_enc_java_handle_call in aarch64.ad. C1 does the same (see usages
>>>> of FrameMap::method_handle_invoke_SP_save_opr()).
>>> Yes, that's correct. aarch64_enc_java_handle relies on having FP
>>> available to save SP. So, it looks like this fix will break that.
>>
>> I'm surprised it matters.  If FP is live around a handle call I would
>> have thought it would be spilled onto the stack.
> 
> It seems to me that FP is currently not allocatable on aarch64.

It seems that way to me too.  That's what we want to change.

Andrew.