7041789: 30% perf regression with c2/arm following 7017732

Implement a more accurate is_scavengable()

Reviewed-by: stefank, jcoomes, ysr

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -428,6 +428,37 @@ void G1CollectedHeap::stop_conc_gc_threads() {
   _cmThread->stop();
 }
 
+#ifdef ASSERT
+// A region is added to the collection set as it is retired
+// so an address p can point to a region which will be in the
+// collection set but has not yet been retired.  This method
+// therefore is only accurate during a GC pause after all
+// regions have been retired.  It is used for debugging
+// to check if an nmethod has references to objects that can
+// be move during a partial collection.  Though it can be
+// inaccurate, it is sufficient for G1 because the conservative
+// implementation of is_scavengable() for G1 will indicate that
+// all nmethods must be scanned during a partial collection.
+bool G1CollectedHeap::is_in_partial_collection(const void* p) {
+  HeapRegion* hr = heap_region_containing(p);
+  return hr != NULL && hr->in_collection_set();
+}
+#endif
+
+// Returns true if the reference points to an object that
+// can move in an incremental collecction.
+bool G1CollectedHeap::is_scavengable(const void* p) {
+  G1CollectedHeap* g1h = G1CollectedHeap::heap();
+  G1CollectorPolicy* g1p = g1h->g1_policy();
+  HeapRegion* hr = heap_region_containing(p);
+  if (hr == NULL) {
+     // perm gen (or null)
+     return false;
+  } else {
+    return !hr->isHumongous();
+  }
+}
+
 void G1CollectedHeap::check_ct_logs_at_safepoint() {
   DirtyCardQueueSet& dcqs = JavaThread::dirty_card_queue_set();
   CardTableModRefBS* ct_bs = (CardTableModRefBS*)barrier_set();