Change how we deal with manual inlining of argument error and NSM when propagating types. This chan…

sdk/lib/_internal/compiler/implementation/ssa/codegen.dart

 // Copyright (c) 2012, 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.
 
 part of ssa;
 
 class SsaCodeGeneratorTask extends CompilerTask {
 
   final JavaScriptBackend backend;
 
@@ skipping 2403 matching lines @@
         push(new js.Binary('&&', pop(), pop()), node);
       } else {
         checkNull(input);
         push(new js.Binary('||', pop(), pop()), node);
       }
     }
   }
 
   js.Expression generateTest(HCheck node) {
     HInstruction input = node.checkedInput;
+    TypeMask receiver = input.instructionType.computeMask(compiler);
+    TypeMask mask = node.instructionType.computeMask(compiler);
+    bool turnIntoNullCheck = mask.nullable() == receiver;
     js.Expression test;
-    if (node.isInteger()) {
+    if (turnIntoNullCheck) {
+      use(input);
+      test = new js.Binary("==", pop(), new js.LiteralNull());
+    } else if (node.isInteger()) {
       // input is !int
       checkInt(input, '!==');
       test = pop();
     } else if (node.isNumber()) {
       // input is !num
       checkNum(input, '!==');
       test = pop();
     } else if (node.isBoolean()) {
       // input is !bool
       checkBool(input, '!==');
@@ skipping 43 matching lines @@
       checkObject(input, '!==');
       js.Expression objectTest = pop();
       checkArray(input, '!==');
       js.Expression arrayTest = pop();
       checkIndexingBehavior(input, negative: true);
       js.Binary notIndexingTest = new js.Binary('&&', arrayTest, pop());
       js.Binary notObjectOrIndexingTest =
           new js.Binary('||', objectTest, notIndexingTest);
       test = new js.Binary('&&', stringTest, notObjectOrIndexingTest);
     } else {
-      compiler.internalError('Unexpected type guard', instruction: input);
+      compiler.internalError('Unexpected check', instruction: input);
     }
     return test;
   }
 
   void visitTypeConversion(HTypeConversion node) {
     if (!node.isChecked) {
       use(node.checkedInput);
       return;
     }
     if (node.isArgumentTypeCheck || node.isReceiverTypeCheck) {
@@ skipping 515 matching lines @@
   if (leftType.canBeNull() && rightType.canBeNull()) {
     if (left.isConstantNull() || right.isConstantNull() ||
         (leftType.isPrimitive(compiler) && leftType == rightType)) {
       return '==';
     }
     return null;
   } else {
     return '===';
   }
 }