C2 should recognize "obj.getClass() == A.class" code pattern. Diff against jdk8/jdk8/hotspot tip. New version: https://gist.github.com/2499019

class_eq.patch

diff -r dce0525b7ee5 src/share/vm/opto/subnode.cpp
--- a/src/share/vm/opto/subnode.cpp     Thu Apr 19 12:18:46 2012 -0700
+++ b/src/share/vm/opto/subnode.cpp     Wed Apr 25 00:03:52 2012 +0800
@@ -703,11 +703,69 @@
 }
 
 //------------------------------Ideal------------------------------------------
-// Check for the case of comparing an unknown klass loaded from the primary
+// Check for the case of comparing a Java mirror returned from getClass() vs
+// a constant Java mirror. Simplify the pattern 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.
+static inline bool is_java_mirror_ptr(const TypeOopPtr* ptr, PhaseGVN* phase) {
+  return ptr && ptr->klass_is_exact() && ptr->klass() == phase->C->env()->Class_klass();
+}
+
 Node *CmpPNode::Ideal( PhaseGVN *phase, bool can_reshape ) {
+  // Simplify the code pattern
+  //   x.getClass() == A.class
+  // into
+  //   x._klass == klassof(A)
+  // 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() == A.class) {
+  //     A a = (A) a;
+  //     // ... use a ...
+  //   }
+  // a CmpPNode could be shared between if_acmpne and checkcast
+  if (in(1)->Opcode() == Op_LoadP &&
+      in(2)->Opcode() == Op_ConP) {
+    Node* ldp1 = in(1);
+    const TypeOopPtr* t1 = phase->type(ldp1)->isa_oopptr();
+    const TypeOopPtr* t2 = phase->type(in(2))->isa_oopptr();
+
+    bool match = is_java_mirror_ptr(t1, phase) && is_java_mirror_ptr(t2, phase);
+    if (match) {
+      Node* adr1 = ldp1->in(MemNode::Address);
+      intptr_t off = 0;
+      Node* ldk2 = AddPNode::Ideal_base_and_offset(adr1, phase, off);
+
+      ciType* mirror_type = ((ciInstance*) t2->const_oop())->java_mirror_type();
+      match = ldk2 && mirror_type->is_klass();
+      if (match) {
+        match = false; // set to false here so we only match on the exact cases below
+        if (ldk2->is_DecodeN()) {
+          if (ldk2->in(1)->Opcode() == Op_LoadNKlass) {
+            match = true;
+          }
+        } else if (ldk2->Opcode() == Op_LoadKlass) {
+          match = true;
+        }
+      }
+
+      assert(!match || off == in_bytes(Klass::java_mirror_offset()),
+             "should be loading mirror from java_mirror_offset");
+
+      if (match) {
+        Node* lhs = ldk2;
+        Node* rhs = phase->makecon(TypeKlassPtr::make((ciKlass*) mirror_type));
+        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())

class_eq_ver_2.patch

diff -r dce0525b7ee5 src/share/vm/opto/parse2.cpp
--- a/src/share/vm/opto/parse2.cpp      Thu Apr 19 12:18:46 2012 -0700
+++ b/src/share/vm/opto/parse2.cpp      Wed Apr 25 22:06:18 2012 +0800
@@ -1171,6 +1171,34 @@
 // branch, seeing how it constrains a tested value, and then
 // deciding if it's worth our while to encode this constraint
 // as graph nodes in the current abstract interpretation map.
+static Node* extract_obj_from_load_klass(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, "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) return NULL;
+  assert(off == oopDesc::klass_offset_in_bytes(),
+         "should be loading klass from obj");
+
+  // obj may be a CastPP, introduced when parsing invokevirtual on getClass()
+  //   Parse::do_call() -> GraphKit::cast_not_null()
+  // TODO should we preserve the cast, or should we uncast here?
+  return obj; // preserve the cast (if any) for now
+}
+
 void Parse::adjust_map_after_if(BoolTest::mask btest, Node* c, float prob,
                                 Block* path, Block* other_path) {
   if (stopped() || !c->is_Cmp() || btest == BoolTest::illegal)
@@ -1234,6 +1262,25 @@
     return;
 
 
+  Node* obj = extract_obj_from_load_klass(&_gvn, val);
+  const TypeKlassPtr* tkp = tcon->isa_klassptr();
+  if (obj && tkp && btest == BoolTest::eq) {
+    // Found:
+    //   Bool(CmpP(LoadKlass(obj._klass), ConP(Foo.klass)), [eq])
+    // or the narrowOop equivalent.
+    // obj has to be of the exact type Foo if the CmpP succeeds.
+    const TypeOopPtr* obj_xtype = tkp->as_instance_type();
+    assert(obj_xtype->higher_equal(_gvn.type(obj)), "must improve");
+
+    CheckCastPPNode* ccast = new (C, 2) CheckCastPPNode(control(), obj, obj_xtype);
+    // Delay transform() call to allow recovery of pre-cast value
+    // at the control merge.
+    _gvn.set_type_bottom(ccast);
+    record_for_igvn(ccast);
+    replace_in_map(obj, ccast);
+    return;
+  }
+
   int val_in_map = map()->find_edge(val);
   if (val_in_map < 0)  return;          // replace_in_map would be useless
   {
diff -r dce0525b7ee5 src/share/vm/opto/subnode.cpp
--- a/src/share/vm/opto/subnode.cpp     Thu Apr 19 12:18:46 2012 -0700
+++ b/src/share/vm/opto/subnode.cpp     Wed Apr 25 22:06:18 2012 +0800
@@ -703,11 +703,89 @@
 }
 
 //------------------------------Ideal------------------------------------------
-// Check for the case of comparing an unknown klass loaded from the primary
+// Normalize comparisons between two Java mirror returned from getClass(), or
+// comparisons between a Java mirror returned from getClass() vs a Java mirror
+// constant. Simplify the pattern 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.
+static inline bool is_java_mirror_ptr(PhaseGVN* phase, const TypeOopPtr* ptr) {
+  return ptr && ptr->klass_is_exact() &&
+         ptr->klass() == phase->C->env()->Class_klass();
+}
+
+static inline Node* isa_java_getClass(PhaseGVN* phase, Node* n) {
+  // return the klass node for
+  //   LoadP(LoadKlass(obj._klass).java_mirror)
+  // or
+  //   LoadP(DecodeN(LoadNKlass(obj._compressed_klass)).java_mirror)
+  // , or NULL if not matching
+  if (n->Opcode() != Op_LoadP) return NULL;
+
+  const TypeOopPtr* tp = phase->type(n)->isa_oopptr();
+  if (!is_java_mirror_ptr(phase, tp)) return NULL;
+
+  Node* adr = n->in(MemNode::Address);
+  intptr_t off = 0;
+  Node* ldk = AddPNode::Ideal_base_and_offset(adr, phase, off);
+
+  if (ldk->is_DecodeN()) {
+    if (ldk->in(1)->Opcode() != Op_LoadNKlass) {
+      return NULL;
+    }
+  } else if (ldk->Opcode() != Op_LoadKlass) {
+    return NULL;
+  }
+
+  assert(off == in_bytes(Klass::java_mirror_offset()),
+         "should be loading mirror from java_mirror_offset");
+  return ldk;
+}
+
+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 TypeOopPtr* tp = phase->type(n)->isa_oopptr();
+  if (!is_java_mirror_ptr(phase, tp)) return NULL;
+
+  ciType* mirror_type = ((ciInstance*) tp->const_oop())->java_mirror_type();
+  if (!mirror_type->is_klass()) return NULL;
+
+  return phase->makecon(TypeKlassPtr::make((ciKlass*) mirror_type));
+}
+
 Node *CmpPNode::Ideal( PhaseGVN *phase, bool can_reshape ) {
+  // Normalize the code pattern
+  //   x.getClass() == Foo.class into x._klass == Foo.klass
+  // or
+  //   x.getClass() == y.getClass() into x._klass == y._klass
+  // 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* ldk1 = isa_java_getClass(phase, in(1));
+    Node* ldk2 = isa_java_getClass(phase, in(2));
+    Node* conk2 = isa_const_java_mirror(phase, in(2));
+
+    if (ldk1 && (ldk2 || conk2)) {
+      Node* lhs = ldk1;
+      Node* rhs = ldk2 != NULL ? ldk2 : 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())