RFR: 8302369: Reduce the stack size of the C1 compiler [v2]

[Dean Long]

On Wed, 15 Feb 2023 06:52:53 GMT, SUN Guoyun <duke at openjdk.org> wrote:

>> In order to reduce the minimum size lower than 2, C1 would need to determine (in advance?) if any stubs might be called.  Maybe there is a way to calculate actual frame size required based on actual stores emitted, but that seems tricky if the prologue has already been emitted.
>
> <pre><code class="cpp">
> // src/hotspot/share/c1/c1_FrameMap.cpp
> // bool FrameMap::finalize_frame(int nof_slots) { 
> 
> 191   _framesize =  align_up(in_bytes(sp_offset_for_monitor_base(0)) +              
> 192                          _num_monitors * (int)sizeof(BasicObjectLock) +         
> 193                          (int)sizeof(intptr_t) +                        // offset of deopt orig pc
> 194                          frame_pad_in_bytes,                                    
> 195                          StackAlignmentInBytes) / 4; 
> </code></pre>
> Here the value of ` (int)sizeof(intptr_t)` is 8 and the value of `StackAlignmentInBytes` is 16, so the minimum stack size of a method is guaranteed to be 16, which should ensure that CounterOverflowStub (or other stub) needs two slots(0, 1).
> But I don't understand what the addition of `(int)sizeof(intptr_t)` does here and what does `// offset of deopt orig pc` mean, do you know?

That would be to support `nmethod::orig_pc_offset()`.

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

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