Merge

make/jprt.properties

@@ -54,72 +54,72 @@ jprt.sync.push=false
 # Define the Solaris platforms we want for the various releases
 jprt.my.solaris.sparc.jdk8=solaris_sparc_5.10
 jprt.my.solaris.sparc.jdk7=solaris_sparc_5.10
-jprt.my.solaris.sparc.jdk7u4=${jprt.my.solaris.sparc.jdk7}
+jprt.my.solaris.sparc.jdk7u6=${jprt.my.solaris.sparc.jdk7}
 jprt.my.solaris.sparc=${jprt.my.solaris.sparc.${jprt.tools.default.release}}
 
 jprt.my.solaris.sparcv9.jdk8=solaris_sparcv9_5.10
 jprt.my.solaris.sparcv9.jdk7=solaris_sparcv9_5.10
-jprt.my.solaris.sparcv9.jdk7u4=${jprt.my.solaris.sparcv9.jdk7}
+jprt.my.solaris.sparcv9.jdk7u6=${jprt.my.solaris.sparcv9.jdk7}
 jprt.my.solaris.sparcv9=${jprt.my.solaris.sparcv9.${jprt.tools.default.release}}
 
 jprt.my.solaris.i586.jdk8=solaris_i586_5.10
 jprt.my.solaris.i586.jdk7=solaris_i586_5.10
-jprt.my.solaris.i586.jdk7u4=${jprt.my.solaris.i586.jdk7}
+jprt.my.solaris.i586.jdk7u6=${jprt.my.solaris.i586.jdk7}
 jprt.my.solaris.i586=${jprt.my.solaris.i586.${jprt.tools.default.release}}
 
 jprt.my.solaris.x64.jdk8=solaris_x64_5.10
 jprt.my.solaris.x64.jdk7=solaris_x64_5.10
-jprt.my.solaris.x64.jdk7u4=${jprt.my.solaris.x64.jdk7}
+jprt.my.solaris.x64.jdk7u6=${jprt.my.solaris.x64.jdk7}
 jprt.my.solaris.x64=${jprt.my.solaris.x64.${jprt.tools.default.release}}
 
 jprt.my.linux.i586.jdk8=linux_i586_2.6
 jprt.my.linux.i586.jdk7=linux_i586_2.6
-jprt.my.linux.i586.jdk7u4=${jprt.my.linux.i586.jdk7}
+jprt.my.linux.i586.jdk7u6=${jprt.my.linux.i586.jdk7}
 jprt.my.linux.i586=${jprt.my.linux.i586.${jprt.tools.default.release}}
 
 jprt.my.linux.x64.jdk8=linux_x64_2.6
 jprt.my.linux.x64.jdk7=linux_x64_2.6
-jprt.my.linux.x64.jdk7u4=${jprt.my.linux.x64.jdk7}
+jprt.my.linux.x64.jdk7u6=${jprt.my.linux.x64.jdk7}
 jprt.my.linux.x64=${jprt.my.linux.x64.${jprt.tools.default.release}}
 
 jprt.my.linux.ppc.jdk8=linux_ppc_2.6
 jprt.my.linux.ppc.jdk7=linux_ppc_2.6
-jprt.my.linux.ppc.jdk7u4=${jprt.my.linux.ppc.jdk7}
+jprt.my.linux.ppc.jdk7u6=${jprt.my.linux.ppc.jdk7}
 jprt.my.linux.ppc=${jprt.my.linux.ppc.${jprt.tools.default.release}}
 
 jprt.my.linux.ppcv2.jdk8=linux_ppcv2_2.6
 jprt.my.linux.ppcv2.jdk7=linux_ppcv2_2.6
-jprt.my.linux.ppcv2.jdk7u4=${jprt.my.linux.ppcv2.jdk7}
+jprt.my.linux.ppcv2.jdk7u6=${jprt.my.linux.ppcv2.jdk7}
 jprt.my.linux.ppcv2=${jprt.my.linux.ppcv2.${jprt.tools.default.release}}
 
 jprt.my.linux.ppcsflt.jdk8=linux_ppcsflt_2.6
 jprt.my.linux.ppcsflt.jdk7=linux_ppcsflt_2.6
-jprt.my.linux.ppcsflt.jdk7u4=${jprt.my.linux.ppcsflt.jdk7}
+jprt.my.linux.ppcsflt.jdk7u6=${jprt.my.linux.ppcsflt.jdk7}
 jprt.my.linux.ppcsflt=${jprt.my.linux.ppcsflt.${jprt.tools.default.release}}
 
 jprt.my.linux.armvfp.jdk8=linux_armvfp_2.6
 jprt.my.linux.armvfp.jdk7=linux_armvfp_2.6
-jprt.my.linux.armvfp.jdk7u4=${jprt.my.linux.armvfp.jdk7}
+jprt.my.linux.armvfp.jdk7u6=${jprt.my.linux.armvfp.jdk7}
 jprt.my.linux.armvfp=${jprt.my.linux.armvfp.${jprt.tools.default.release}}
 
 jprt.my.linux.armsflt.jdk8=linux_armsflt_2.6
 jprt.my.linux.armsflt.jdk7=linux_armsflt_2.6
-jprt.my.linux.armsflt.jdk7u4=${jprt.my.linux.armsflt.jdk7}
+jprt.my.linux.armsflt.jdk7u6=${jprt.my.linux.armsflt.jdk7}
 jprt.my.linux.armsflt=${jprt.my.linux.armsflt.${jprt.tools.default.release}}
 
 jprt.my.macosx.x64.jdk8=macosx_x64_10.7
 jprt.my.macosx.x64.jdk7=macosx_x64_10.7
-jprt.my.macosx.x64.jdk7u4=${jprt.my.macosx.x64.jdk7}
+jprt.my.macosx.x64.jdk7u6=${jprt.my.macosx.x64.jdk7}
 jprt.my.macosx.x64=${jprt.my.macosx.x64.${jprt.tools.default.release}}
 
 jprt.my.windows.i586.jdk8=windows_i586_5.1
 jprt.my.windows.i586.jdk7=windows_i586_5.1
-jprt.my.windows.i586.jdk7u4=${jprt.my.windows.i586.jdk7}
+jprt.my.windows.i586.jdk7u6=${jprt.my.windows.i586.jdk7}
 jprt.my.windows.i586=${jprt.my.windows.i586.${jprt.tools.default.release}}
 
 jprt.my.windows.x64.jdk8=windows_x64_5.2
 jprt.my.windows.x64.jdk7=windows_x64_5.2
-jprt.my.windows.x64.jdk7u4=${jprt.my.windows.x64.jdk7}
+jprt.my.windows.x64.jdk7u6=${jprt.my.windows.x64.jdk7}
 jprt.my.windows.x64=${jprt.my.windows.x64.${jprt.tools.default.release}}
 
 # Standard list of jprt build targets for this source tree
@@ -154,7 +154,7 @@ jprt.build.targets.all=${jprt.build.targets.standard}, \
 
 jprt.build.targets.jdk8=${jprt.build.targets.all}
 jprt.build.targets.jdk7=${jprt.build.targets.all}
-jprt.build.targets.jdk7u4=${jprt.build.targets.all}
+jprt.build.targets.jdk7u6=${jprt.build.targets.all}
 jprt.build.targets=${jprt.build.targets.${jprt.tools.default.release}}
 
 # Subset lists of test targets for this source tree
@@ -447,7 +447,7 @@ jprt.test.targets.embedded= 		\
 
 jprt.test.targets.jdk8=${jprt.test.targets.standard}
 jprt.test.targets.jdk7=${jprt.test.targets.standard}
-jprt.test.targets.jdk7u4=${jprt.test.targets.jdk7}
+jprt.test.targets.jdk7u6=${jprt.test.targets.jdk7}
 jprt.test.targets=${jprt.test.targets.${jprt.tools.default.release}}
 
 # The default test/Makefile targets that should be run
@@ -507,7 +507,7 @@ jprt.make.rule.test.targets.embedded = \
 
 jprt.make.rule.test.targets.jdk8=${jprt.make.rule.test.targets.standard}
 jprt.make.rule.test.targets.jdk7=${jprt.make.rule.test.targets.standard}
-jprt.make.rule.test.targets.jdk7u4=${jprt.make.rule.test.targets.jdk7}
+jprt.make.rule.test.targets.jdk7u6=${jprt.make.rule.test.targets.jdk7}
 jprt.make.rule.test.targets=${jprt.make.rule.test.targets.${jprt.tools.default.release}}
 
 # 7155453: Work-around to prevent popups on OSX from blocking test completion

src/share/vm/c1/c1_Canonicalizer.cpp

@@ -42,6 +42,11 @@ void Canonicalizer::set_canonical(Value x) {
   // the instruction stream (because the instruction list is embedded
   // in the instructions).
   if (canonical() != x) {
+#ifndef PRODUCT
+    if (!x->has_printable_bci()) {
+      x->set_printable_bci(bci());
+    }
+#endif
     if (PrintCanonicalization) {
       PrintValueVisitor do_print_value;
       canonical()->input_values_do(&do_print_value);
@@ -451,6 +456,28 @@ void Canonicalizer::do_Intrinsic      (Intrinsic*       x) {
     }
     break;
   }
+  case vmIntrinsics::_isInstance          : {
+    assert(x->number_of_arguments() == 2, "wrong type");
+
+    InstanceConstant* c = x->argument_at(0)->type()->as_InstanceConstant();
+    if (c != NULL && !c->value()->is_null_object()) {
+      // ciInstance::java_mirror_type() returns non-NULL only for Java mirrors
+      ciType* t = c->value()->as_instance()->java_mirror_type();
+      if (t->is_klass()) {
+        // substitute cls.isInstance(obj) of a constant Class into
+        // an InstantOf instruction
+        InstanceOf* i = new InstanceOf(t->as_klass(), x->argument_at(1), x->state_before());
+        set_canonical(i);
+        // and try to canonicalize even further
+        do_InstanceOf(i);
+      } else {
+        assert(t->is_primitive_type(), "should be a primitive type");
+        // cls.isInstance(obj) always returns false for primitive classes
+        set_constant(0);
+      }
+    }
+    break;
+  }
   }
 }
 
@@ -677,8 +704,8 @@ void Canonicalizer::do_If(If* x) {
                 return;
             }
           }
-          set_canonical(canon);
           set_bci(cmp->state_before()->bci());
+          set_canonical(canon);
         }
       }
     } else if (l->as_InstanceOf() != NULL) {

src/share/vm/c1/c1_GraphBuilder.cpp

@@ -3170,6 +3170,7 @@ bool GraphBuilder::try_inline_intrinsics(ciMethod* callee) {
       break;
 
     case vmIntrinsics::_getClass      :
+    case vmIntrinsics::_isInstance    :
       if (!InlineClassNatives) return false;
       preserves_state = true;
       break;

src/share/vm/c1/c1_Instruction.hpp

@@ -302,8 +302,6 @@ class Instruction: public CompilationResourceObj {
 
   void update_exception_state(ValueStack* state);
 
-  bool has_printable_bci() const                 { return NOT_PRODUCT(_printable_bci != -99) PRODUCT_ONLY(false); }
-
  protected:
   void set_type(ValueType* type) {
     assert(type != NULL, "type must exist");
@@ -392,8 +390,9 @@ class Instruction: public CompilationResourceObj {
   // accessors
   int id() const                                 { return _id; }
 #ifndef PRODUCT
+  bool has_printable_bci() const                 { return _printable_bci != -99; }
   int printable_bci() const                      { assert(has_printable_bci(), "_printable_bci should have been set"); return _printable_bci; }
-  void set_printable_bci(int bci)                { NOT_PRODUCT(_printable_bci = bci;) }
+  void set_printable_bci(int bci)                { _printable_bci = bci; }
 #endif
   int use_count() const                          { return _use_count; }
   int pin_state() const                          { return _pin_state; }
@@ -576,6 +575,7 @@ LEAF(Phi, Instruction)
   , _block(b)
   , _index(index)
   {
+    NOT_PRODUCT(set_printable_bci(Value(b)->printable_bci()));
     if (type->is_illegal()) {
       make_illegal();
     }
@@ -631,7 +631,9 @@ LEAF(Local, Instruction)
     : Instruction(type)
     , _java_index(index)
     , _declared_type(declared)
-  {}
+  {
+    NOT_PRODUCT(set_printable_bci(-1));
+  }
 
   // accessors
   int java_index() const                         { return _java_index; }

src/share/vm/c1/c1_LIRGenerator.cpp

@@ -1242,6 +1242,36 @@ void LIRGenerator::do_Reference_get(Intrinsic* x) {
               NULL   /* info */);
 }
 
+// Example: clazz.isInstance(object)
+void LIRGenerator::do_isInstance(Intrinsic* x) {
+  assert(x->number_of_arguments() == 2, "wrong type");
+
+  // TODO could try to substitute this node with an equivalent InstanceOf
+  // if clazz is known to be a constant Class. This will pick up newly found
+  // constants after HIR construction. I'll leave this to a future change.
+
+  // as a first cut, make a simple leaf call to runtime to stay platform independent.
+  // could follow the aastore example in a future change.
+
+  LIRItem clazz(x->argument_at(0), this);
+  LIRItem object(x->argument_at(1), this);
+  clazz.load_item();
+  object.load_item();
+  LIR_Opr result = rlock_result(x);
+
+  // need to perform null check on clazz
+  if (x->needs_null_check()) {
+    CodeEmitInfo* info = state_for(x);
+    __ null_check(clazz.result(), info);
+  }
+
+  LIR_Opr call_result = call_runtime(clazz.value(), object.value(),
+                                     CAST_FROM_FN_PTR(address, Runtime1::is_instance_of),
+                                     x->type(),
+                                     NULL); // NULL CodeEmitInfo results in a leaf call
+  __ move(call_result, result);
+}
+
 // Example: object.getClass ()
 void LIRGenerator::do_getClass(Intrinsic* x) {
   assert(x->number_of_arguments() == 1, "wrong type");
@@ -2951,6 +2981,7 @@ void LIRGenerator::do_Intrinsic(Intrinsic* x) {
     break;
 
   case vmIntrinsics::_Object_init:    do_RegisterFinalizer(x); break;
+  case vmIntrinsics::_isInstance:     do_isInstance(x);    break;
   case vmIntrinsics::_getClass:       do_getClass(x);      break;
   case vmIntrinsics::_currentThread:  do_currentThread(x); break;
 

src/share/vm/c1/c1_LIRGenerator.hpp

@@ -238,6 +238,7 @@ class LIRGenerator: public InstructionVisitor, public BlockClosure {
   LIR_Opr getThreadPointer();
 
   void do_RegisterFinalizer(Intrinsic* x);
+  void do_isInstance(Intrinsic* x);
   void do_getClass(Intrinsic* x);
   void do_currentThread(Intrinsic* x);
   void do_MathIntrinsic(Intrinsic* x);

src/share/vm/c1/c1_Runtime1.cpp

@@ -294,6 +294,7 @@ const char* Runtime1::name_for_address(address entry) {
   FUNCTION_CASE(entry, SharedRuntime::lrem);
   FUNCTION_CASE(entry, SharedRuntime::dtrace_method_entry);
   FUNCTION_CASE(entry, SharedRuntime::dtrace_method_exit);
+  FUNCTION_CASE(entry, is_instance_of);
   FUNCTION_CASE(entry, trace_block_entry);
 #ifdef TRACE_HAVE_INTRINSICS
   FUNCTION_CASE(entry, TRACE_TIME_METHOD);
@@ -1270,6 +1271,19 @@ JRT_LEAF(void, Runtime1::oop_arraycopy(HeapWord* src, HeapWord* dst, int num))
 JRT_END
 
 
+JRT_LEAF(int, Runtime1::is_instance_of(oopDesc* mirror, oopDesc* obj))
+  // had to return int instead of bool, otherwise there may be a mismatch
+  // between the C calling convention and the Java one.
+  // e.g., on x86, GCC may clear only %al when returning a bool false, but
+  // JVM takes the whole %eax as the return value, which may misinterpret
+  // the return value as a boolean true.
+
+  assert(mirror != NULL, "should null-check on mirror before calling");
+  klassOop k = java_lang_Class::as_klassOop(mirror);
+  return (k != NULL && obj != NULL && obj->is_a(k)) ? 1 : 0;
+JRT_END
+
+
 #ifndef PRODUCT
 void Runtime1::print_statistics() {
   tty->print_cr("C1 Runtime statistics:");

src/share/vm/c1/c1_Runtime1.hpp

@@ -186,6 +186,7 @@ class Runtime1: public AllStatic {
   static int  arraycopy(oopDesc* src, int src_pos, oopDesc* dst, int dst_pos, int length);
   static void primitive_arraycopy(HeapWord* src, HeapWord* dst, int length);
   static void oop_arraycopy(HeapWord* src, HeapWord* dst, int length);
+  static int  is_instance_of(oopDesc* mirror, oopDesc* obj);
 
   static void print_statistics()                 PRODUCT_RETURN;
 };

src/share/vm/c1/c1_ValueMap.hpp

@@ -141,8 +141,11 @@ class ValueNumberingVisitor: public InstructionVisitor {
 
   // visitor functions
   void do_StoreField     (StoreField*      x) {
-    if (x->is_init_point()) {
-      // putstatic is an initialization point so treat it as a wide kill
+    if (x->is_init_point() ||  // putstatic is an initialization point so treat it as a wide kill
+        // This is actually too strict and the JMM doesn't require
+        // this in all cases (e.g. load a; volatile store b; load a)
+        // but possible future optimizations might require this.
+        x->field()->is_volatile()) {
       kill_memory();
     } else {
       kill_field(x->field());
@@ -160,8 +163,8 @@ class ValueNumberingVisitor: public InstructionVisitor {
   void do_Local          (Local*           x) { /* nothing to do */ }
   void do_Constant       (Constant*        x) { /* nothing to do */ }
   void do_LoadField      (LoadField*       x) {
-    if (x->is_init_point()) {
-      // getstatic is an initialization point so treat it as a wide kill
+    if (x->is_init_point() ||         // getstatic is an initialization point so treat it as a wide kill
+        x->field()->is_volatile()) {  // the JMM requires this
       kill_memory();
     }
   }

src/share/vm/opto/parse.hpp

@@ -527,6 +527,9 @@ class Parse : public GraphKit {
   int     repush_if_args();
   void    adjust_map_after_if(BoolTest::mask btest, Node* c, float prob,
                               Block* path, Block* other_path);
+  void    sharpen_type_after_if(BoolTest::mask btest,
+                                Node* con, const Type* tcon,
+                                Node* val, const Type* tval);
   IfNode* jump_if_fork_int(Node* a, Node* b, BoolTest::mask mask);
   Node*   jump_if_join(Node* iffalse, Node* iftrue);
   void    jump_if_true_fork(IfNode *ifNode, int dest_bci_if_true, int prof_table_index);

src/share/vm/opto/parse2.cpp

@@ -1233,6 +1233,71 @@ void Parse::adjust_map_after_if(BoolTest::mask btest, Node* c, float prob,
   if (!have_con)                        // remaining adjustments need a con
     return;
 
+  sharpen_type_after_if(btest, con, tcon, val, tval);
+}
+
+
+static Node* extract_obj_from_klass_load(PhaseGVN* gvn, Node* n) {
+  Node* ldk;
+  if (n->is_DecodeN()) {
+    if (n->in(1)->Opcode() != Op_LoadNKlass) {
+      return NULL;
+    } else {
+      ldk = n->in(1);
+    }
+  } else if (n->Opcode() != Op_LoadKlass) {
+    return NULL;
+  } else {
+    ldk = n;
+  }
+  assert(ldk != NULL && ldk->is_Load(), "should have found a LoadKlass or LoadNKlass node");
+
+  Node* adr = ldk->in(MemNode::Address);
+  intptr_t off = 0;
+  Node* obj = AddPNode::Ideal_base_and_offset(adr, gvn, off);
+  if (obj == NULL || off != oopDesc::klass_offset_in_bytes()) // loading oopDesc::_klass?
+    return NULL;
+  const TypePtr* tp = gvn->type(obj)->is_ptr();
+  if (tp == NULL || !(tp->isa_instptr() || tp->isa_aryptr())) // is obj a Java object ptr?
+    return NULL;
+
+  return obj;
+}
+
+void Parse::sharpen_type_after_if(BoolTest::mask btest,
+                                  Node* con, const Type* tcon,
+                                  Node* val, const Type* tval) {
+  // Look for opportunities to sharpen the type of a node
+  // whose klass is compared with a constant klass.
+  if (btest == BoolTest::eq && tcon->isa_klassptr()) {
+    Node* obj = extract_obj_from_klass_load(&_gvn, val);
+    const TypeOopPtr* con_type = tcon->isa_klassptr()->as_instance_type();
+    if (obj != NULL && (con_type->isa_instptr() || con_type->isa_aryptr())) {
+       // Found:
+       //   Bool(CmpP(LoadKlass(obj._klass), ConP(Foo.klass)), [eq])
+       // or the narrowOop equivalent.
+       const Type* obj_type = _gvn.type(obj);
+       const TypeOopPtr* tboth = obj_type->join(con_type)->isa_oopptr();
+       if (tboth != NULL && tboth != obj_type && tboth->higher_equal(obj_type)) {
+          // obj has to be of the exact type Foo if the CmpP succeeds.
+          assert(tboth->klass_is_exact(), "klass should be exact");
+          int obj_in_map = map()->find_edge(obj);
+          JVMState* jvms = this->jvms();
+          if (obj_in_map >= 0 &&
+              (jvms->is_loc(obj_in_map) || jvms->is_stk(obj_in_map))) {
+            TypeNode* ccast = new (C, 2) CheckCastPPNode(control(), obj, tboth);
+            const Type* tcc = ccast->as_Type()->type();
+            assert(tcc != obj_type && tcc->higher_equal(obj_type), "must improve");
+            // Delay transform() call to allow recovery of pre-cast value
+            // at the control merge.
+            _gvn.set_type_bottom(ccast);
+            record_for_igvn(ccast);
+            // Here's the payoff.
+            replace_in_map(obj, ccast);
+          }
+       }
+    }
+  }
 
   int val_in_map = map()->find_edge(val);
   if (val_in_map < 0)  return;          // replace_in_map would be useless
@@ -1265,6 +1330,7 @@ void Parse::adjust_map_after_if(BoolTest::mask btest, Node* c, float prob,
         // Exclude tests vs float/double 0 as these could be
         // either +0 or -0.  Just because you are equal to +0
         // doesn't mean you ARE +0!
+        // Note, following code also replaces Long and Oop values.
         if ((!tf || tf->_f != 0.0) &&
             (!td || td->_d != 0.0))
           cast = con;                   // Replace non-constant val by con.

src/share/vm/opto/subnode.cpp

@@ -702,12 +702,84 @@ const Type *CmpPNode::sub( const Type *t1, const Type *t2 ) const {
     return TypeInt::CC;
 }
 
+static inline Node* isa_java_mirror_load(PhaseGVN* phase, Node* n) {
+  // Return the klass node for
+  //   LoadP(AddP(foo:Klass, #java_mirror))
+  //   or NULL if not matching.
+  if (n->Opcode() != Op_LoadP) return NULL;
+
+  const TypeInstPtr* tp = phase->type(n)->isa_instptr();
+  if (!tp || tp->klass() != phase->C->env()->Class_klass()) return NULL;
+
+  Node* adr = n->in(MemNode::Address);
+  intptr_t off = 0;
+  Node* k = AddPNode::Ideal_base_and_offset(adr, phase, off);
+  if (k == NULL)  return NULL;
+  const TypeKlassPtr* tkp = phase->type(k)->isa_klassptr();
+  if (!tkp || off != in_bytes(Klass::java_mirror_offset())) return NULL;
+
+  // We've found the klass node of a Java mirror load.
+  return k;
+}
+
+static inline Node* isa_const_java_mirror(PhaseGVN* phase, Node* n) {
+  // for ConP(Foo.class) return ConP(Foo.klass)
+  // otherwise return NULL
+  if (!n->is_Con()) return NULL;
+
+  const TypeInstPtr* tp = phase->type(n)->isa_instptr();
+  if (!tp) return NULL;
+
+  ciType* mirror_type = tp->java_mirror_type();
+  // TypeInstPtr::java_mirror_type() returns non-NULL for compile-
+  // time Class constants only.
+  if (!mirror_type) return NULL;
+
+  // x.getClass() == int.class can never be true (for all primitive types)
+  // Return a ConP(NULL) node for this case.
+  if (mirror_type->is_classless()) {
+    return phase->makecon(TypePtr::NULL_PTR);
+  }
+
+  // return the ConP(Foo.klass)
+  assert(mirror_type->is_klass(), "mirror_type should represent a klassOop");
+  return phase->makecon(TypeKlassPtr::make(mirror_type->as_klass()));
+}
+
 //------------------------------Ideal------------------------------------------
-// Check for the case of comparing an unknown klass loaded from the primary
+// Normalize comparisons between Java mirror loads to compare the klass instead.
+//
+// Also check for the case of comparing an unknown klass loaded from the primary
 // super-type array vs a known klass with no subtypes.  This amounts to
 // checking to see an unknown klass subtypes a known klass with no subtypes;
 // this only happens on an exact match.  We can shorten this test by 1 load.
 Node *CmpPNode::Ideal( PhaseGVN *phase, bool can_reshape ) {
+  // Normalize comparisons between Java mirrors into comparisons of the low-
+  // level klass, where a dependent load could be shortened.
+  //
+  // The new pattern has a nice effect of matching the same pattern used in the
+  // fast path of instanceof/checkcast/Class.isInstance(), which allows
+  // redundant exact type check be optimized away by GVN.
+  // For example, in
+  //   if (x.getClass() == Foo.class) {
+  //     Foo foo = (Foo) x;
+  //     // ... use a ...
+  //   }
+  // a CmpPNode could be shared between if_acmpne and checkcast
+  {
+    Node* k1 = isa_java_mirror_load(phase, in(1));
+    Node* k2 = isa_java_mirror_load(phase, in(2));
+    Node* conk2 = isa_const_java_mirror(phase, in(2));
+
+    if (k1 && (k2 || conk2)) {
+      Node* lhs = k1;
+      Node* rhs = (k2 != NULL) ? k2 : conk2;
+      this->set_req(1, lhs);
+      this->set_req(2, rhs);
+      return this;
+    }
+  }
+
   // Constant pointer on right?
   const TypeKlassPtr* t2 = phase->type(in(2))->isa_klassptr();
   if (t2 == NULL || !t2->klass_is_exact())