Performance of Scope.getSymbolsByName()

[Ron Shapiro]

Hi,

I'm observing a particularly bizarre compilation. It's a single file with
annotation processing, and the type that is being compiled and processed
has ~1000 declared and inherited methods combined. The total compilation is
3 minutes, but 65% of the entire compilation is spent in 3 methods:
Check.checkOverrideClashes(), Resolve.findInheritedMemberType(),
and Resolve.findField().

Looking at profiles, it looks like getSymbolsByName() is the major culprit
here. I initially thought the reason was that there were far too many
overloads (this type had >600 overloads...) and that that was causing a bad
regression for the pseudo-hashmap that ScopeImpl uses. However, renaming
the methods did not alleviate the build pain and these methods continue to
be taking long amounts of time.

I was wondering what could be done to improve the performance of this code.
It seemed to me that something like a Map<Name, List<Symbol>> could be a
reasonable+modern replacement for this table, which would naturally have a
fast getSymbolsForName() implementation. I'm having some trouble
implementing it correctly, and I believe it's partially related to not
fully understanding some of the semantics of the class.

Does what I wrote make sense to anyone, and maybe spark a lightbulb?

I'm trying to put together a repro in case that helps, but I'm not 100%
sure I even understand what the regression case is.

Thanks for you help!
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