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