Remove signature classes from the VM.

runtime/vm/flow_graph_compiler_x64.cc

Index: runtime/vm/flow_graph_compiler_x64.cc
diff --git a/runtime/vm/flow_graph_compiler_x64.cc b/runtime/vm/flow_graph_compiler_x64.cc
index 30382e6e81dd26cbca8c9ba3aab6572bbee1f2fa..5e176e5df1936242a55d5dc8ed85611f5a27c45c 100644
--- a/runtime/vm/flow_graph_compiler_x64.cc
+++ b/runtime/vm/flow_graph_compiler_x64.cc
@@ -274,7 +274,7 @@ FlowGraphCompiler::GenerateInstantiatedTypeWithArgumentsTest(
   __ Comment("InstantiatedTypeWithArgumentsTest");
   ASSERT(type.IsInstantiated());
   const Class& type_class = Class::ZoneHandle(zone(), type.type_class());
-  ASSERT((type_class.NumTypeArguments() > 0) || type_class.IsSignatureClass());
+  ASSERT(type.IsFunctionType() || (type_class.NumTypeArguments() > 0));
   const Register kInstanceReg = RAX;
   Error& bound_error = Error::Handle(zone());
   const Type& int_type = Type::Handle(zone(), Type::IntType());
@@ -287,15 +287,15 @@ FlowGraphCompiler::GenerateInstantiatedTypeWithArgumentsTest(
   } else {
     __ j(ZERO, is_not_instance_lbl);
   }
-  const intptr_t num_type_args = type_class.NumTypeArguments();
-  const intptr_t num_type_params = type_class.NumTypeParameters();
-  const intptr_t from_index = num_type_args - num_type_params;
-  const TypeArguments& type_arguments =
-      TypeArguments::ZoneHandle(zone(), type.arguments());
-  const bool is_raw_type = type_arguments.IsNull() ||
-      type_arguments.IsRaw(from_index, num_type_params);
-  // Signature class is an instantiated parameterized type.
-  if (!type_class.IsSignatureClass()) {
+  // A function type test requires checking the function signature.
+  if (!type.IsFunctionType()) {
+    const intptr_t num_type_args = type_class.NumTypeArguments();
+    const intptr_t num_type_params = type_class.NumTypeParameters();
+    const intptr_t from_index = num_type_args - num_type_params;
+    const TypeArguments& type_arguments =
+        TypeArguments::ZoneHandle(zone(), type.arguments());
+    const bool is_raw_type = type_arguments.IsNull() ||
+        type_arguments.IsRaw(from_index, num_type_params);
     if (is_raw_type) {
       const Register kClassIdReg = R10;
       // dynamic type argument, check only classes.
@@ -362,6 +362,10 @@ bool FlowGraphCompiler::GenerateInstantiatedTypeNoArgumentsTest(
     Label* is_not_instance_lbl) {
   __ Comment("InstantiatedTypeNoArgumentsTest");
   ASSERT(type.IsInstantiated());
+  if (type.IsFunctionType()) {
+    // Fallthrough.
+    return true;
+  }
   const Class& type_class = Class::Handle(zone(), type.type_class());
   ASSERT(type_class.NumTypeArguments() == 0);
 
@@ -392,12 +396,10 @@ bool FlowGraphCompiler::GenerateInstantiatedTypeNoArgumentsTest(
     __ jmp(is_not_instance_lbl);
     return false;
   }
-  if (type.IsFunctionType()) {
+  if (type.IsDartFunctionType()) {
     // Check if instance is a closure.
-    __ LoadClassById(R13, kClassIdReg);
-    __ movq(R13, FieldAddress(R13, Class::signature_function_offset()));
-    __ CompareObject(R13, Object::null_object());
-    __ j(NOT_EQUAL, is_instance_lbl);
+    __ cmpq(kClassIdReg, Immediate(kClosureCid));
+    __ j(EQUAL, is_instance_lbl);
   }
   // Custom checking for numbers (Smi, Mint, Bigint and Double).
   // Note that instance is not Smi (checked above).
@@ -549,10 +551,10 @@ RawSubtypeTestCache* FlowGraphCompiler::GenerateInlineInstanceof(
   }
   if (type.IsInstantiated()) {
     const Class& type_class = Class::ZoneHandle(zone(), type.type_class());
-    // A class equality check is only applicable with a dst type of a
-    // non-parameterized class, non-signature class, or with a raw dst type of
+    // A class equality check is only applicable with a dst type (not a
+    // function type) of a non-parameterized class or with a raw dst type of
     // a parameterized class.
-    if (type_class.IsSignatureClass() || (type_class.NumTypeArguments() > 0)) {
+    if (type.IsFunctionType() || (type_class.NumTypeArguments() > 0)) {
       return GenerateInstantiatedTypeWithArgumentsTest(token_pos,
                                                        type,
                                                        is_instance_lbl,