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<p class="MsoNormal">Is there a place to encode calls to the VM in the interpreted methods other than the method prologs? </p>
<p class="MsoNormal">I've recently discovered the interpreted method adaptors which seems like a candidate, but there's
</p>
<p class="MsoNormal">no examples of the adaptors calling into the VM.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Follows is the rational as to why I'm looking for an alternative to the method prologs</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The AOTEndTrainingOnMethodEntry feature [1] introduces calls from java methods into the
</p>
<p class="MsoNormal">VM (upcalls) when specific methods are entered. The methods are identified via a pattern in a
</p>
<p class="MsoNormal">similar manner to the CompileOnly option.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Following the initial PR review we’re looking at removing the knowledge of this AOT feature from
</p>
<p class="MsoNormal">the compilers/interpreter and introducing a more generic system (RuntimeUpcalls) that can be
</p>
<p class="MsoNormal">used by other parts of the VM [2]. In building out the RuntimeUpcalls system we've come across
</p>
<p class="MsoNormal">an inefficiency that isn't an immediate problem for this feature, but should another feature use this
</p>
<p class="MsoNormal">new system then it's less than optimal.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Interpreted code uses a shared method prolog (there are 8 variants for 'regular' methods [more
</p>
<p class="MsoNormal">for some special math/zip methods]), the AOTEndTrainingOnMethodEntry feature introduces a
</p>
<p class="MsoNormal">further 5 prolog types. When there is a single upcall (eg. AOTEndTrainingOnMethodEntry) to the VM
</p>
<p class="MsoNormal">everything is efficient.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The inefficiency issue arises as soon as there are two or more upcalls; which upcalls relate to
</p>
<p class="MsoNormal">which methods is contained within the RuntimeUpcalls system. When the interpreter examines
</p>
<p class="MsoNormal">the method flags they only indicate whether there are any upcalls (but not how many or which ones).
</p>
<p class="MsoNormal">As the interpreter can't encode which upcalls should be called in the prolog (without an explosion
</p>
<p class="MsoNormal">of new runtime generated prologs), it needs to call the RuntimeUpcalls system which in turn iterates</p>
<p class="MsoNormal">over the upcalls and calls the appropriate ones; the problem is that during that iteration the methods
</p>
<p class="MsoNormal">need to be compared against the pattern. So we either pay a memory cost to cache the method to
</p>
<p class="MsoNormal">upcall relationships or we pay a performance cost to repeatedly test the method against the pattern.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This is not a problem for C1 and C2 as we pay this cost only when the methods are compiled and
</p>
<p class="MsoNormal">create the multiple upcalls in those methods, eliminating the need for pattern matching by the
</p>
<p class="MsoNormal">RuntimeUpcalls system during method execution</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks in advance </p>
<p class="MsoNormal">Mat</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[1] <a href="https://github.com/openjdk/leyden/pull/21">https://github.com/openjdk/leyden/pull/21</a></p>
<p class="MsoNormal">[2] <a href="https://github.com/macarte/leyden/pull/2">https://github.com/macarte/leyden/pull/2</a></p>
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