Bug 53822

Created attachment 29322 [details]
patchSmall.diff

"IdentityStack.containsAll(Collection coll)" has a similar performance
problem as the previously fixed Bug 53622 (for
"VectorSet.retainAll(Collection coll)").  The problem is that
"containsAll(Collection coll)" performs "this.contains(e.next())",
which is slow because "this" is an IdentityStack, i.e., a Vector, and
therefore "contains" is linear.

I attached a patch (patchSmall.diff) similar to the one used by Jesse
Glick in Bug 53622.  I attached an improved patch (patchFull.diff)
that builds the IdentityHashMap lazily, which gives slightly better
performance than patchSmall.diff (which builds IdentityHashMap
eagerly).  I also attached a test that exposes this problem.  For this
test, patchSmall.diff provides a 676X speedup on my machine.

To run the test, just do:

$ java Test

The output for the un-patched version is:
Time is 17572

The output for the patched version is:
Time is 26