RFR: 8280872: Reorder code cache segments to improve code density [v2]

[Evgeny Astigeevich]

On Thu, 3 Mar 2022 12:07:54 GMT, Boris Ulasevich <bulasevich at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/icBuffer_aarch64.cpp line 55:
>> 
>>> 53:   Label l;
>>> 54:   __ ldr(rscratch2, l);
>>> 55:   __ far_jump(ExternalAddress(entry_point), NULL, rscratch1, true);
>> 
>> This complicates `assemble_ic_buffer_code`. You need to know `far_jump` implementation, especially the generation of  NOPs. I understand why we need those NOPs.
>> Do we have calls of non-nmethod code here?
>
> Yes, there are entry points from both non_method and method segments.

I suggest the following code:

int inst_count = __ far_jump(ExternalAddress(entry_point));
// IC stub code size is not expected to vary depending on target address.
// We use NOPs to make the size equal to ic_stub_code_size.
for (int i = 3 + inst_count; i < ic_stub_code_size(); ++i) {
  __ nop();
}

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PR: https://git.openjdk.java.net/jdk/pull/7517