RFR: 8253740: [PPC64] Minor interpreter cleanup

[Martin Doerr]

On Tue, 29 Sep 2020 00:02:44 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Template interpreter on PPC64 can be cleaned up after JDK-8253540:
>> unlock_object has a parameter check_for_exceptions which is now unused.
>> 
>> In addition to that, restore_interpreter_state is redundant after
>> call_VM(R4_ARG2, CAST_FROM_FN_PTR(address, InterpreterRuntime::member_name_arg_or_null) because it's already included
>> in call_VM.
>> https://bugs.openjdk.java.net/browse/JDK-8253740
>
> This looks good but I also noticed that ppc and s390 pass an extra parameter to InterpreterRuntime::monitorenter() also.

That's an interesting point: call_VM(monitorenter) uses check_for_exceptions=true on PPC64 and
check_for_exceptions=false on s390. check_for_exceptions=true is default, so it's equivalent to omitting the explicit
parameter. So PPC64 is implemented like x86 in this matter. Seems like we have optimized the exception check out for
s390. This should be valid because monitorenter uses JRT_ENTRY_NO_ASYNC and doesn't throw any exception. Note that the
JIT compiler's version uses assert(!HAS_PENDING_EXCEPTION, "Should have no exception here") in
SharedRuntime::monitor_enter_helper. I think we could assert that in the interpreter's version and use
check_for_exceptions=false on all platforms. It's probably not worth optimizing this, but maybe it'd be a good
simplification wrt. complexity and readability of the gererated assembly code. But that's a bit out of scope for this
issue.

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PR: https://git.openjdk.java.net/jdk/pull/385