RFR: 8327661: C1: Make RBP allocatable on x64 when PreserveFramePointer is disabled [v3]

[Dean Long]

On Wed, 13 Mar 2024 06:49:30 GMT, Denghui Dong <ddong at openjdk.org> wrote:

>> Hi,
>> 
>> Could I have a review of this change that makes RBP allocatable in c1 register allocation when PreserveFramePointer is not enabled.
>> 
>> There seems no reason that RBP cannot be used. Although the performance of c1 jit code is not very critical, in my opinion, this change will not add overhead of compilation. So maybe it is acceptable.
>> 
>> I am not very sure if I have changed all the places that should be.
>> 
>> Testing: fastdebug tier1-4 on Linux x64
>
> Denghui Dong has updated the pull request incrementally with one additional commit since the last revision:
> 
>   delete jmh

Yes, the risk / reward ratio on this seems borderline.  Even of arm32 or x86_32, where there are fewer registers, it's not clear how much using FP in C1 would help.

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PR Comment: https://git.openjdk.org/jdk/pull/18167#issuecomment-2111188367