6888898: CMS: ReduceInitialCardMarks unsafe in the presence of cms precleaning

6889757: G1: enable card mark elision for initializing writes from compiled code (ReduceInitialCardMarks)

Defer the (compiler-elided) card-mark upon a slow-path allocation until after the store  and before the next subsequent safepoint; G1 now answers yes to can_elide_tlab_write_barriers().

Reviewed-by: jcoomes, kvn, never

hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp

@@ -314,41 +314,6 @@ bool ParallelScavengeHeap::is_in_reserved(const void* p) const {
   return false;
 }
 
-// Static method
-bool ParallelScavengeHeap::is_in_young(oop* p) {
-  ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
-  assert(heap->kind() == CollectedHeap::ParallelScavengeHeap,
-                                            "Must be ParallelScavengeHeap");
-
-  PSYoungGen* young_gen = heap->young_gen();
-
-  if (young_gen->is_in_reserved(p)) {
-    return true;
-  }
-
-  return false;
-}
-
-// Static method
-bool ParallelScavengeHeap::is_in_old_or_perm(oop* p) {
-  ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
-  assert(heap->kind() == CollectedHeap::ParallelScavengeHeap,
-                                            "Must be ParallelScavengeHeap");
-
-  PSOldGen* old_gen = heap->old_gen();
-  PSPermGen* perm_gen = heap->perm_gen();
-
-  if (old_gen->is_in_reserved(p)) {
-    return true;
-  }
-
-  if (perm_gen->is_in_reserved(p)) {
-    return true;
-  }
-
-  return false;
-}
-
 // There are two levels of allocation policy here.
 //
 // When an allocation request fails, the requesting thread must invoke a VM
@@ -764,6 +729,13 @@ void ParallelScavengeHeap::resize_all_tlabs() {
   CollectedHeap::resize_all_tlabs();
 }
 
+bool ParallelScavengeHeap::can_elide_initializing_store_barrier(oop new_obj) {
+  // We don't need barriers for stores to objects in the
+  // young gen and, a fortiori, for initializing stores to
+  // objects therein.
+  return is_in_young(new_obj);
+}
+
 // This method is used by System.gc() and JVMTI.
 void ParallelScavengeHeap::collect(GCCause::Cause cause) {
   assert(!Heap_lock->owned_by_self(),

hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp

@@ -129,8 +129,8 @@ class ParallelScavengeHeap : public CollectedHeap {
     return perm_gen()->is_in(p);
   }
 
-  static bool is_in_young(oop *p);        // reserved part
-  static bool is_in_old_or_perm(oop *p);  // reserved part
+  inline bool is_in_young(oop p);        // reserved part
+  inline bool is_in_old_or_perm(oop p);  // reserved part
 
   // Memory allocation.   "gc_time_limit_was_exceeded" will
   // be set to true if the adaptive size policy determine that
@@ -191,6 +191,10 @@ class ParallelScavengeHeap : public CollectedHeap {
     return true;
   }
 
+  // Return true if we don't we need a store barrier for
+  // initializing stores to an object at this address.
+  virtual bool can_elide_initializing_store_barrier(oop new_obj);
+
   // Can a compiler elide a store barrier when it writes
   // a permanent oop into the heap?  Applies when the compiler
   // is storing x to the heap, where x->is_perm() is true.

hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.inline.hpp

@@ -41,3 +41,11 @@ inline void ParallelScavengeHeap::invoke_full_gc(bool maximum_compaction)
     PSMarkSweep::invoke(maximum_compaction);
   }
 }
+
+inline bool ParallelScavengeHeap::is_in_young(oop p) {
+  return young_gen()->is_in_reserved(p);
+}
+
+inline bool ParallelScavengeHeap::is_in_old_or_perm(oop p) {
+  return old_gen()->is_in_reserved(p) || perm_gen()->is_in_reserved(p);
+}