Revert "Void is not required to be `null` anymore."

runtime/vm/flow_graph_compiler_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
@@ skipping 515 matching lines @@
 //   optional function type arguments in RCX.
 // Note that this inlined code must be followed by the runtime_call code, as it
 // may fall through to it. Otherwise, this inline code will jump to the label
 // is_instance or to the label is_not_instance.
 RawSubtypeTestCache* FlowGraphCompiler::GenerateInlineInstanceof(
     TokenPosition token_pos,
     const AbstractType& type,
     Label* is_instance_lbl,
     Label* is_not_instance_lbl) {
   __ Comment("InlineInstanceof");
+  if (type.IsVoidType()) {
+    // A non-null value is returned from a void function, which will result in a
+    // type error. A null value is handled prior to executing this inline code.
+    return SubtypeTestCache::null();
+  }
   if (type.IsInstantiated()) {
     const Class& type_class = Class::ZoneHandle(zone(), type.type_class());
     // 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.IsFunctionType() || (type_class.NumTypeArguments() > 0)) {
       return GenerateInstantiatedTypeWithArgumentsTest(
           token_pos, type, is_instance_lbl, is_not_instance_lbl);
       // Fall through to runtime call.
     }
@@ skipping 22 matching lines @@
 // - RAX: object.
 // - RDX: instantiator type arguments or raw_null.
 // - RCX: function type arguments or raw_null.
 // Returns:
 // - true or false in RAX.
 void FlowGraphCompiler::GenerateInstanceOf(TokenPosition token_pos,
                                            intptr_t deopt_id,
                                            const AbstractType& type,
                                            LocationSummary* locs) {
   ASSERT(type.IsFinalized() && !type.IsMalformedOrMalbounded());
-  ASSERT(!type.IsObjectType() && !type.IsDynamicType() && !type.IsVoidType());
+  ASSERT(!type.IsObjectType() && !type.IsDynamicType());
 
   __ pushq(RDX);  // Store instantiator type arguments.
   __ pushq(RCX);  // Store function type arguments.
 
   Label is_instance, is_not_instance;
   // If type is instantiated and non-parameterized, we can inline code
   // checking whether the tested instance is a Smi.
   if (type.IsInstantiated()) {
-    // A null object is only an instance of Null, Object, void and dynamic.
-    // Object void and dynamic have already been checked above (if the type is
+    // A null object is only an instance of Null, Object, and dynamic.
+    // Object and dynamic have already been checked above (if the type is
     // instantiated). So we can return false here if the instance is null,
     // unless the type is Null (and if the type is instantiated).
     // We can only inline this null check if the type is instantiated at compile
     // time, since an uninstantiated type at compile time could be Null, Object,
     // or dynamic at run time.
     __ CompareObject(RAX, Object::null_object());
     __ j(EQUAL, type.IsNullType() ? &is_instance : &is_not_instance);
   }
 
   // Generate inline instanceof test.
@@ skipping 48 matching lines @@
 void FlowGraphCompiler::GenerateAssertAssignable(TokenPosition token_pos,
                                                  intptr_t deopt_id,
                                                  const AbstractType& dst_type,
                                                  const String& dst_name,
                                                  LocationSummary* locs) {
   ASSERT(!token_pos.IsClassifying());
   ASSERT(!dst_type.IsNull());
   ASSERT(dst_type.IsFinalized());
   // Assignable check is skipped in FlowGraphBuilder, not here.
   ASSERT(dst_type.IsMalformedOrMalbounded() ||
-         (!dst_type.IsDynamicType() && !dst_type.IsObjectType() &&
-          !dst_type.IsVoidType()));
+         (!dst_type.IsDynamicType() && !dst_type.IsObjectType()));
   __ pushq(RDX);  // Store instantiator type arguments.
   __ pushq(RCX);  // Store function type arguments.
   // A null object is always assignable and is returned as result.
   Label is_assignable, runtime_call;
   __ CompareObject(RAX, Object::null_object());
   __ j(EQUAL, &is_assignable);
 
   // Generate throw new TypeError() if the type is malformed or malbounded.
   if (dst_type.IsMalformedOrMalbounded()) {
     __ PushObject(Object::null_object());  // Make room for the result.
@@ skipping 1051 matching lines @@
   __ movups(reg, Address(RSP, 0));
   __ AddImmediate(RSP, Immediate(kFpuRegisterSize));
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64