8348853: Fold layout helper check for objects implementing non-array interfaces

Reviewed-by: thartmann, roland

Author: marc-chevalier

src/hotspot/share/ci/ciMetadata.hpp

@@ -103,7 +103,7 @@ class ciMetadata: public ciBaseObject {
 
   Metadata* constant_encoding() { return _metadata; }
 
-  bool equals(ciMetadata* obj) const { return (this == obj); }
+  bool equals(const ciMetadata* obj) const { return (this == obj); }
 
   uint hash() { return ident() * 31; } // ???
 

src/hotspot/share/opto/library_call.cpp

@@ -4305,12 +4305,7 @@ Node* LibraryCallKit::generate_array_guard_common(Node* kls, RegionNode* region,
   if (obj != nullptr && is_array_ctrl != nullptr && is_array_ctrl != top()) {
     // Keep track of the fact that 'obj' is an array to prevent
     // array specific accesses from floating above the guard.
-    Node* cast = _gvn.transform(new CastPPNode(is_array_ctrl, *obj, TypeAryPtr::BOTTOM));
-    // Check for top because in rare cases, the type system can determine that
-    // the object can't be an array but the layout helper check is not folded.
-    if (!cast->is_top()) {
-      *obj = cast;
-    }
+    *obj = _gvn.transform(new CastPPNode(is_array_ctrl, *obj, TypeAryPtr::BOTTOM));
   }
   return ctrl;
 }

src/hotspot/share/opto/memnode.cpp

@@ -2218,10 +2218,8 @@ const Type* LoadNode::Value(PhaseGVN* phase) const {
     // This will help short-circuit some reflective code.
     if (tkls->offset() == in_bytes(Klass::layout_helper_offset()) &&
         tkls->isa_instklassptr() && // not directly typed as an array
-        !tkls->is_instklassptr()->instance_klass()->is_java_lang_Object() // not the supertype of all T[] and specifically not Serializable & Cloneable
-        ) {
-      // Note:  When interfaces are reliable, we can narrow the interface
-      // test to (klass != Serializable && klass != Cloneable).
+        !tkls->is_instklassptr()->might_be_an_array() // not the supertype of all T[] (java.lang.Object) or has an interface that is not Serializable or Cloneable
+    ) {
       assert(Opcode() == Op_LoadI, "must load an int from _layout_helper");
       jint min_size = Klass::instance_layout_helper(oopDesc::header_size(), false);
       // The key property of this type is that it folds up tests

src/hotspot/share/opto/type.cpp

@@ -3685,6 +3685,12 @@ bool TypeInterfaces::singleton(void) const {
   return Type::singleton();
 }
 
+bool TypeInterfaces::has_non_array_interface() const {
+  assert(TypeAryPtr::_array_interfaces != nullptr, "How come Type::Initialize_shared wasn't called yet?");
+
+  return !TypeAryPtr::_array_interfaces->contains(this);
+}
+
 //------------------------------TypeOopPtr-------------------------------------
 TypeOopPtr::TypeOopPtr(TYPES t, PTR ptr, ciKlass* k, const TypeInterfaces* interfaces, bool xk, ciObject* o, int offset,
                        int instance_id, const TypePtr* speculative, int inline_depth)
@@ -6197,6 +6203,19 @@ template <class T1, class T2> bool TypePtr::is_java_subtype_of_helper_for_instan
   return this_one->klass()->is_subtype_of(other->klass()) && this_one->_interfaces->contains(other->_interfaces);
 }
 
+bool TypeInstKlassPtr::might_be_an_array() const {
+  if (!instance_klass()->is_java_lang_Object()) {
+    // TypeInstKlassPtr can be an array only if it is java.lang.Object: the only supertype of array types.
+    return false;
+  }
+  if (interfaces()->has_non_array_interface()) {
+    // Arrays only implement Cloneable and Serializable. If we see any other interface, [this] cannot be an array.
+    return false;
+  }
+  // Cannot prove it's not an array.
+  return true;
+}
+
 bool TypeInstKlassPtr::is_java_subtype_of_helper(const TypeKlassPtr* other, bool this_exact, bool other_exact) const {
   return TypePtr::is_java_subtype_of_helper_for_instance(this, other, this_exact, other_exact);
 }

src/hotspot/share/opto/type.hpp

@@ -943,6 +943,7 @@ class TypeInterfaces : public Type {
   const Type* xmeet(const Type* t) const;
 
   bool singleton(void) const;
+  bool has_non_array_interface() const;
 };
 
 //------------------------------TypePtr----------------------------------------
@@ -1420,6 +1421,7 @@ class TypeInstPtr : public TypeOopPtr {
 class TypeAryPtr : public TypeOopPtr {
   friend class Type;
   friend class TypePtr;
+  friend class TypeInterfaces;
 
   TypeAryPtr( PTR ptr, ciObject* o, const TypeAry *ary, ciKlass* k, bool xk,
               int offset, int instance_id, bool is_autobox_cache,
@@ -1692,6 +1694,8 @@ class TypeInstKlassPtr : public TypeKlassPtr {
     return klass()->as_instance_klass();
   }
 
+  bool might_be_an_array() const;
+
   bool is_same_java_type_as_helper(const TypeKlassPtr* other) const;
   bool is_java_subtype_of_helper(const TypeKlassPtr* other, bool this_exact, bool other_exact) const;
   bool maybe_java_subtype_of_helper(const TypeKlassPtr* other, bool this_exact, bool other_exact) const;