8294059: Serial: Refactor GenCollectedHeap::collect

Reviewed-by: sjohanss, tschatzl

src/hotspot/share/gc/shared/genCollectedHeap.cpp

@@ -813,29 +813,7 @@ bool GenCollectedHeap::no_allocs_since_save_marks() {
 }
 
 // public collection interfaces
-
 void GenCollectedHeap::collect(GCCause::Cause cause) {
-  if ((cause == GCCause::_wb_young_gc) ||
-      (cause == GCCause::_gc_locker)) {
-    // Young collection for WhiteBox or GCLocker.
-    collect(cause, YoungGen);
-  } else {
-#ifdef ASSERT
-  if (cause == GCCause::_scavenge_alot) {
-    // Young collection only.
-    collect(cause, YoungGen);
-  } else {
-    // Stop-the-world full collection.
-    collect(cause, OldGen);
-  }
-#else
-    // Stop-the-world full collection.
-    collect(cause, OldGen);
-#endif
-  }
-}
-
-void GenCollectedHeap::collect(GCCause::Cause cause, GenerationType max_generation) {
   // The caller doesn't have the Heap_lock
   assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");
 
@@ -853,6 +831,14 @@ void GenCollectedHeap::collect(GCCause::Cause cause, GenerationType max_generati
     return;
   }
 
+  bool should_run_young_gc =  (cause == GCCause::_wb_young_gc)
+                           || (cause == GCCause::_gc_locker)
+                DEBUG_ONLY(|| (cause == GCCause::_scavenge_alot));
+
+  const GenerationType max_generation = should_run_young_gc
+                                      ? YoungGen
+                                      : OldGen;
+
   VM_GenCollectFull op(gc_count_before, full_gc_count_before,
                        cause, max_generation);
   VMThread::execute(&op);

src/hotspot/share/gc/shared/genCollectedHeap.hpp

@@ -186,10 +186,6 @@ public:
   // supports. Caller does not hold the Heap_lock on entry.
   virtual void collect(GCCause::Cause cause);
 
-  // Perform a full collection of generations up to and including max_generation.
-  // Mostly used for testing purposes. Caller does not hold the Heap_lock on entry.
-  void collect(GCCause::Cause cause, GenerationType max_generation);
-
   // Returns "TRUE" iff "p" points into the committed areas of the heap.
   // The methods is_in() and is_in_youngest() may be expensive to compute
   // in general, so, to prevent their inadvertent use in product jvm's, we