8015244: G1: Verification after a full GC is incorrectly placed.

Summary: In a full GC, move the verification after the GC to after RSet rebuilding. Verify RSet entries during a full GC under control of a flag.
Reviewed-by: tschatzl, brutisso

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

@@ -1417,8 +1417,6 @@ bool G1CollectedHeap::do_collection(bool explicit_gc,
 
       MemoryService::track_memory_usage();
 
-      verify_after_gc();
-
       assert(!ref_processor_stw()->discovery_enabled(), "Postcondition");
       ref_processor_stw()->verify_no_references_recorded();
 
@@ -1521,6 +1519,8 @@ bool G1CollectedHeap::do_collection(bool explicit_gc,
       _hrs.verify_optional();
       verify_region_sets_optional();
 
+      verify_after_gc();
+
       // Start a new incremental collection set for the next pause
       assert(g1_policy()->collection_set() == NULL, "must be");
       g1_policy()->start_incremental_cset_building();

src/share/vm/gc_implementation/g1/g1RemSet.cpp

@@ -736,7 +736,7 @@ void G1RemSet::print_summary_info(G1RemSetSummary * summary, const char * header
 void G1RemSet::prepare_for_verify() {
   if (G1HRRSFlushLogBuffersOnVerify &&
       (VerifyBeforeGC || VerifyAfterGC)
-      &&  !_g1->full_collection()) {
+      &&  (!_g1->full_collection() || G1VerifyRSetsDuringFullGC)) {
     cleanupHRRS();
     _g1->set_refine_cte_cl_concurrency(false);
     if (SafepointSynchronize::is_at_safepoint()) {

src/share/vm/gc_implementation/g1/g1_globals.hpp

@@ -329,7 +329,11 @@
                                                                             \
   develop(bool, G1EvacuationFailureALotDuringMixedGC, true,                 \
           "Force use of evacuation failure handling during mixed "          \
-          "evacuation pauses")
+          "evacuation pauses")                                              \
+                                                                            \
+  diagnostic(bool, G1VerifyRSetsDuringFullGC, false,                        \
+             "If true, perform verification of each heap region's "         \
+             "remembered set when verifying the heap during a full GC.")
 
 G1_FLAGS(DECLARE_DEVELOPER_FLAG, DECLARE_PD_DEVELOPER_FLAG, DECLARE_PRODUCT_FLAG, DECLARE_PD_PRODUCT_FLAG, DECLARE_DIAGNOSTIC_FLAG, DECLARE_EXPERIMENTAL_FLAG, DECLARE_NOTPRODUCT_FLAG, DECLARE_MANAGEABLE_FLAG, DECLARE_PRODUCT_RW_FLAG)
 

src/share/vm/gc_implementation/g1/heapRegion.cpp

@@ -139,7 +139,7 @@ public:
         _n_failures++;
       }
 
-      if (!_g1h->full_collection()) {
+      if (!_g1h->full_collection() || G1VerifyRSetsDuringFullGC) {
         HeapRegion* from = _g1h->heap_region_containing((HeapWord*)p);
         HeapRegion* to   = _g1h->heap_region_containing(obj);
         if (from != NULL && to != NULL &&