Recognise x.==(null) and generate HIdentical

pkg/compiler/lib/src/ssa/builder_kernel.dart

 // Copyright (c) 2016, 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.
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/names.dart';
 import '../common/tasks.dart' show CompilerTask;
@@ skipping 1515 matching lines @@
       push(new HInvokeDynamicSetter(selector, mask, null, inputs, type));
     } else {
       push(new HInvokeDynamicMethod(
           selector, mask, inputs, type, isIntercepted));
     }
   }
 
   // TODO(het): Decide when to inline
   @override
   void visitMethodInvocation(ir.MethodInvocation invocation) {
+    // Handle `x == null` specially. When these come from null-aware operators,
+    // there is no mapping in the astAdapter.
+    if (_handleEqualsNull(invocation)) return;
     invocation.receiver.accept(this);
     HInstruction receiver = pop();
 
     _pushDynamicInvocation(
         invocation,
         astAdapter.typeOfInvocation(invocation),
         <HInstruction>[receiver]
           ..addAll(_visitArguments(invocation.arguments)));
   }
 
+  bool _handleEqualsNull(ir.MethodInvocation invocation) {
+    if (invocation.name.name == '==') {
+      ir.Arguments arguments = invocation.arguments;
+      if (arguments.types.isEmpty &&
+          arguments.positional.length == 1 &&
+          arguments.named.isEmpty) {
+        bool finish(ir.Expression comparand) {
+          comparand.accept(this);
+          pushCheckNull(pop());
+          return true;
+        }
+
+        ir.Expression receiver = invocation.receiver;
+        ir.Expression argument = arguments.positional.first;
+        if (argument is ir.NullLiteral) return finish(receiver);
+        if (receiver is ir.NullLiteral) return finish(argument);
+      }
+    }
+    return false;
+  }
+
   HInterceptor _interceptorFor(HInstruction intercepted) {
     HInterceptor interceptor =
         new HInterceptor(intercepted, backend.nonNullType);
     add(interceptor);
     return interceptor;
   }
 
   static ir.Class _containingClass(ir.TreeNode node) {
     while (node != null) {
       if (node is ir.Class) return node;
@@ skipping 77 matching lines @@
     push(new HNot(popBoolified(), backend.boolType));
   }
 
   @override
   void visitStringConcatenation(ir.StringConcatenation stringConcat) {
     KernelStringBuilder stringBuilder = new KernelStringBuilder(this);
     stringConcat.accept(stringBuilder);
     stack.add(stringBuilder.result);
   }
 }