8373114: Redundant MethodCounters in the preimage generated by training run

src/hotspot/share/cds/archiveBuilder.cpp

@@ -559,7 +559,18 @@ ArchiveBuilder::FollowMode ArchiveBuilder::get_follow_mode(MetaspaceClosure::Ref
              ref->msotype() == MetaspaceObj::KlassTrainingDataType ||
              ref->msotype() == MetaspaceObj::MethodTrainingDataType ||
              ref->msotype() == MetaspaceObj::CompileTrainingDataType) {
-    return (TrainingData::need_data() || TrainingData::assembling_data()) ? make_a_copy : set_to_null;
+    if (TrainingData::need_data() || TrainingData::assembling_data()) {
+      // Only add MethodCounters that are reachable via MethodTrainingData,
+      // i.e. MethodCounters associated with a valid MethodTrainingData.
+      if (ref->msotype() == MetaspaceObj::MethodCountersType) {
+        MethodCounters* mcs = (MethodCounters*)obj;
+        return mcs->has_valid_method_training_data() ? make_a_copy : set_to_null;
+      } else {
+        return make_a_copy;
+      }
+    } else {
+      return set_to_null;
+    }
   } else if (ref->msotype() == MetaspaceObj::AdapterHandlerEntryType) {
     return CDSConfig::is_dumping_adapters() ? make_a_copy : set_to_null;
   } else {

src/hotspot/share/oops/methodCounters.cpp

@@ -95,6 +95,12 @@ void MethodCounters::restore_unshareable_info(TRAPS) {
 }
 #endif // INCLUDE_CDS
 
+bool MethodCounters::has_valid_method_training_data() {
+  Metadata* mtd = method_training_data();
+  Metadata* mts = method_training_data_sentinel();
+  return mtd != mts;
+}
+
 void MethodCounters::print_on(outputStream* st) const {
   assert(is_methodCounters(), "should be method counters");
   st->print("method counters");

src/hotspot/share/oops/methodCounters.hpp

@@ -165,6 +165,8 @@ class MethodCounters : public Metadata {
     return false;
   }
 
+  bool has_valid_method_training_data();
+
 #if INCLUDE_CDS
   void remove_unshareable_info();
   void restore_unshareable_info(TRAPS);

src/hotspot/share/oops/trainingData.cpp

@@ -119,7 +119,7 @@ void TrainingData::verify() {
 
 MethodTrainingData* MethodTrainingData::make(const methodHandle& method, bool null_if_not_found, bool use_cache) {
   MethodTrainingData* mtd = nullptr;
-  if (!have_data() && !need_data()) {
+  if ((!have_data() && !need_data()) || (assembling_data() && !CDSConfig::is_at_aot_safepoint())) {
     return mtd;
   }
   // Try grabbing the cached value first.