RFR: 8257423: [PPC64] Support -XX:-UseInlineCaches

[Martin Doerr]

On Tue, 1 Dec 2020 17:10:52 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> The JVM currently runs into Unimplemented() when using -XX:-UseInlineCaches in C2 code (postalloc_expand_java_dynamic_call_sched).
>> I'd like to enable the existing code in postalloc_expand_java_dynamic_call_sched and fix MachCallDynamicJavaNode::ret_addr_offset() and MacroAssembler::instr_size_for_decode_klass_not_null().
>> I suggest to use scratch emit to determine the size, because there are too many cases and emitting it once is fast.
>
> Hi Martin,
> 
> this looks good to my non-compiler-eyes. 
> 
> Cheers, Thomas

Thanks for reviewing it!

> src/hotspot/cpu/ppc/macroAssembler_ppc.cpp line 3168:
> 
>> 3166:       int code_size = 8 * BytesPerInstWord;
>> 3167:       CodeBuffer cb("decode_klass_not_null scratch buffer", code_size, 0);
>> 3168:       MacroAssembler* a = new MacroAssembler(&cb);
> 
> Idle thought: if this is done frequently, maybe MacroAssembler could have a "dry run" mode with no attached CodeBuffer, just counting instructions.

The scratch emit is only executed during the first call. Afterwards, the computed_size is just returned and we don't call the CodeBuffer constructor any more.

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PR: https://git.openjdk.java.net/jdk/pull/1521