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

[Denghui Dong]

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

src/hotspot/share/c1/c1_LinearScan.cpp line 5755:

> 5753: bool LinearScanWalker::no_allocation_possible(Interval* cur) {
> 5754: #ifdef X86
> 5755: #ifndef _LP64

rbp is callee-saved, so the following logic doesn't work. That'll slow down the allocation.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18167#discussion_r1524251207