Request for comments, very slow compilation with super-overloaded methods

[Adam Domurad]

Hi, see attached sources.zip containing ArrayUtil.java & 
MethodHandle.java, taken from Groovy sourcecode.
They exhibit a case with which javac performs very badly.

Try
  javac ArrayUtil.java #Not too bad
  javac MethodHandle.java # But this takes many minutes

Note that MethodHandle references ArrayUtil, and this is auto-generated 
code.

ECJ compiles this source code in ~4 seconds.

This problem is present in JDK8 and JDK7.

      - The performance problem stems from 
com.sun.tools.javac.comp.Resolve.InapplicableSymbolsError.Candidate#equals. 
This is used during method resolution, and is performed O(n^2) times for 
'n' same-name methods. It references rather expensive methods that 
iterate over and potentially copy (eg for erasure) both argument lists, 
which can be up to 255 elements in this case.
      - MethodHandle references a method from ArrayUtil that has 255 
candidates; this is many orders of magnitude slower than it should be.

I have attached a patch that does a hackish fix, by providing a fast 
route for when method is obviously not a sub-signature of another.
The patch is mainly there as a proof-of-concept (its rather slapped on), 
hopefully someone knows a better way to fix these corner cases?

I am rather dubious about argument lists pervasively being treated as 
singly-linked lists. It makes certain operations quite costly, even 
changing the complexity of them unfavourably.

Happy hacking,
-Adam

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