RFR: 8280481: Duplicated stubs to interpreter for static calls

[Dingli Zhang]

On Tue, 30 Aug 2022 09:04:21 GMT, Evgeny Astigeevich <duke at openjdk.org> wrote:

> > Hi @eastig ,
> > I would like to recurring your experimental data and I would be very grateful if you could provide a small patch to help me get the result of `Saved bytes` and `Nmethods with shared stubs`.
> > Thank you!
> 
> ```
> diff --git a/src/hotspot/share/asm/codeBuffer.inline.hpp b/src/hotspot/share/asm/codeBuffer.inline.hpp
> index 045cff13f25..9af26730cbd 100644
> --- a/src/hotspot/share/asm/codeBuffer.inline.hpp
> +++ b/src/hotspot/share/asm/codeBuffer.inline.hpp
> @@ -45,6 +45,7 @@ bool emit_shared_stubs_to_interp(CodeBuffer* cb, SharedStubToInterpRequests* sha
>    };
>    shared_stub_to_interp_requests->sort(by_shared_method);
>    MacroAssembler masm(cb);
> +  bool has_shared = false;
>    for (int i = 0; i < shared_stub_to_interp_requests->length();) {
>      address stub = masm.start_a_stub(CompiledStaticCall::to_interp_stub_size());
>      if (stub == NULL) {
> @@ -53,13 +54,22 @@ bool emit_shared_stubs_to_interp(CodeBuffer* cb, SharedStubToInterpRequests* sha
>      }
> 
>      ciMethod* method = shared_stub_to_interp_requests->at(i).shared_method();
> +    int shared = 0;
>      do {
>        address caller_pc = cb->insts_begin() + shared_stub_to_interp_requests->at(i).call_offset();
>        masm.relocate(static_stub_Relocation::spec(caller_pc), relocate_format);
>        ++i;
> +      ++shared;
>      } while (i < shared_stub_to_interp_requests->length() && shared_stub_to_interp_requests->at(i).shared_method() == method);
>      masm.emit_static_call_stub();
>      masm.end_a_stub();
> +    if (UseNewCode && shared > 1) {
> +      has_shared = true;
> +      tty->print_cr("Saved: %d", (shared - 1) * CompiledStaticCall::to_interp_stub_size());
> +    }
> +  }
> +  if (has_shared) {
> +    tty->print_cr("nm_has_shared");
>    }
>    return true;
>  }
> ```
> 
> You will need to use `-XX:+UseNewCode` in your runs. `grep nm_has_shared run.log | wc -l` is a number of nmethods having a shared stub. `grep Saved: run.log | awk '{print $2}' | grep -o '[0-9]*' | paste -s -d+ - | bc` prints a number of saved bytes.

Thanks a lot, eastig!

-------------

PR: https://git.openjdk.org/jdk/pull/8816