G1 and ParallelGC (and others) have specific heap() functions that return the associated derived CollectedHeap object. These functions are all defined in .cpp files, so (most) callers will make an out of line function call, even though the implementation is pretty trivial (esp. in release builds).

At least G1 and ParallelGC have calls to these functions in relatively performance critical locations. It would be better if they were inlined, at least for these collectors.

Also, these functions are nearly identical for each collector; it would be nice to have a helper function they can all use.