for review (M): 6863023: need non-perm oops in code cache for JSR 292

[John Rose]

Here is an updated webrev.  The operations of the GC relative to the  
code cache are much more explicit now:
   http://cr.openjdk.java.net/~jrose/6863023/webrev.06

This one (a) is about to pass JPRT, (b) does pass unit tests like  
GCBasher and GCOld in various stress modes, (c) does run various JRuby 
+invokedynamic benchmarks successfully.  I've been routinely testing  
with all four GC modes.

I think it's ready to go back, as soon as a GC person verifies that my  
GC-related refactorings are reasonable.  The other parts of the code  
are already reviewed.

-- John

P.S.  The two stress modes I've mostly used are are  
ScavengeRootsInCode=2 and ScavengeRootsInCode=2 with -Xcomp.  These  
modes tend to create a lot of nmethods with non-perm oops embedded.   
The default I'm going to push is ScavengeRootsInCode=0.  When  
invokedynamic is turned on by default, the flag will change to  
ScavengeRootsInCode=1, which means non-perm oops will be inserted into  
code for invokedynamic, but not for user-written Java code.