On 10/1/21 4:46 PM, Brett Okken wrote:
The current pure Java implementation does two things: it provides a fallback
for pure-interpreter JVMs and it provides the reader with a simple
implementation.
I'm not at all sure we'd want a complex implementation.
I thought this might be the case.
Having said that, if I were looking at a faster pure Java version of
this logic, I'd look at MethodHandles.byteArrayViewVarHandle().
I considered that, but had 2 concerns:
1. creating potential dependency/initialization order issues
2. creating/managing a constant VarHandle that would never be used
with normal compiler behavior
Also, interpreter-only VMs are likely to be pessimized by Var/MethodHandles, as they would not be
able to fold a lot of code (e.g. checks) on the hotpaths. I have seen this after SHA-2 was rewritten
to use byteViews (that one was done for simplicity, rather than directly for performance, I think).
Optimizing this does not seem worth it, in my opinion. The only reason to do this would be showing
that it improves the interpreter performance so much it improves startup until compilers are coming
up with the optimized code.
--
Thanks,
-Aleksey
