RFR: 8302369: Reduce the stack size of the C1 compiler

[SUN Guoyun]

On Wed, 15 Feb 2023 00:32:30 GMT, Dean Long <dlong at openjdk.org> wrote:

>> The current fact is that C1 uses more stack space than the C2 compiler, taking method `java.lang.Object::<init>`as an example on the x86_64 platform , the stack size used is 48 bytes for C1 compiler, while only 16 bytes is used for C2 compiler.
>> 
>> ========== C1-compiled nmethod =====
>> 0x00007f93311cc747: push %rbp
>> 0x00007f93311cc748: sub $0x30,%rsp // stack sizes is 48 bytes
>> 
>> 
>> ========== C2-compiled nmethod =======
>>     pushq rbp # Save rbp
>>     subq rsp, #16 # Create frame //stack sizes is 16 bytes
>> 
>> After this patch, the C1 compiler will use less stack space. also taking method `java.lang.Object::<init>`as an example on the x86_64 platform , the stack size used is 16 bytes, which is the same as C2 compiler.
>> 
>> ========== C1-compiled nmethod =====
>> 0x00007f80491ce647:   push   %rbp
>> 0x00007f80491ce648:   sub    $0x10,%rsp   //stack sizes is 16 bytes
>
> I suspect this change is too simplistic and the change to use <= instead of < only works because stubs only use slots 0 and 1 and max_stack() has an extra slot added for JSR292.

Thank you all for the review and @dean-long explanation, I don't understand the compiler well, I'll check it again.

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PR: https://git.openjdk.org/jdk/pull/12548