Handle switch with default case, and do/while loop better in the inferrer.

tests/compiler/dart2js/simple_inferrer_test.dart

 // 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.
 
 import 'package:expect/expect.dart';
 import
     '../../../sdk/lib/_internal/compiler/implementation/types/types.dart'
     show TypeMask;
 
 import 'compiler_helper.dart';
@@ skipping 278 matching lines @@
   var a = 42;
   var b;
   switch (topLevelGetter) {
     L1: case 1: b = a + 42; break;
     case 2: a = 'foo'; continue L1;
   }
   return b;
 }
 
 testSwitch4() {
-  switch(topLevelGetter) {
+  switch (topLevelGetter) {
     case 1: break;
     default: break;
   }
   return 42;
 }
 
+testSwitch5() {
+  switch (topLevelGetter) {
+    case 1: return 1;
+    default: return 2;
+  }
+}
+
 testContinue1() {
   var a = 42;
   var b;
   while (true) {
     b = a + 54;
     if (b == 42) continue;
     a = 'foo';
   }
   return b;
 }
@@ skipping 41 matching lines @@
 
 testReturnElementOfConstList2() {
   return topLevelConstList[0];
 }
 
 testReturnItselfOrInt(a) {
   if (a) return 42;
   return testReturnItselfOrInt(a);
 }
 
+testDoWhile1() {
+  var a = 42;
+  do {
+    a = 'foo';
+  } while (true);
+  return a;
+}
+
+testDoWhile2() {
+  var a = 42;
+  do {
+    a = 'foo';
+    return;
+  } while (true);
+  return a;
+}
+
+testDoWhile3() {
+  var a = 42;
+  do {
+    a = 'foo';
+    if (true) continue;
+    return 42;
+  } while (true);
+  return a;
+}
+
+testDoWhile4() {
+  var a = 'foo';
+  do {
+    a = 54;
+    if (true) break;
+    return 3.5;
+  } while (true);
+  return a;
+}
+
 testReturnInvokeDynamicGetter() => new A().myFactory();
 
 var topLevelConstList = const [42];
 
 get topLevelGetter => 42;
 returnDynamic() => topLevelGetter(42);
 returnTopLevelGetter() => topLevelGetter;
 
 class A {
   factory A() = A.generative;
@@ skipping 69 matching lines @@
   returnAsString();
   returnIntAsNum();
   returnAsTypedef();
   returnTopLevelGetter();
   testDeadCode();
   testLabeledIf();
   testSwitch1();
   testSwitch2();
   testSwitch3();
   testSwitch4();
+  testSwitch5();
   testContinue1();
   testBreak1();
   testContinue2();
   testBreak2();
+  testDoWhile1();
+  testDoWhile2();
+  testDoWhile3();
+  testDoWhile4();
   new A() == null;
   new A()..returnInt1()
          ..returnInt2()
          ..returnInt3()
          ..returnInt4()
          ..returnInt5()
          ..returnInt6();
 
   new B()..returnInt1()
          ..returnInt2()
@@ skipping 67 matching lines @@
   checkReturn('testIsCheck20', typesTask.dynamicType.nonNullable());
   checkReturn('returnAsString',
       new TypeMask.subtype(compiler.stringClass.computeType(compiler)));
   checkReturn('returnIntAsNum', typesTask.intType);
   checkReturn('returnAsTypedef', typesTask.functionType.nullable());
   checkReturn('returnTopLevelGetter', typesTask.intType);
   checkReturn('testDeadCode', typesTask.intType);
   checkReturn('testLabeledIf', typesTask.intType.nullable());
   checkReturn('testSwitch1', typesTask.intType
       .union(typesTask.doubleType, compiler).nullable().simplify(compiler));
-  // TODO(12320): testSwitch2 should be non-nullable.  The quick fix for 12320
-  // models control flow through as though there is an additional empty default
-  // case.
-  checkReturn('testSwitch2', typesTask.intType.nullable());
+  checkReturn('testSwitch2', typesTask.intType);
   checkReturn('testSwitch3', interceptorType.nullable());
   checkReturn('testSwitch4', typesTask.intType);
+  checkReturn('testSwitch5', typesTask.intType);
   checkReturn('testContinue1', interceptorType.nullable());
   checkReturn('testBreak1', interceptorType.nullable());
   checkReturn('testContinue2', interceptorType.nullable());
   checkReturn('testBreak2', typesTask.intType.nullable());
   checkReturn('testReturnElementOfConstList1', typesTask.intType);
   checkReturn('testReturnElementOfConstList2', typesTask.intType);
   checkReturn('testReturnItselfOrInt', typesTask.intType);
   checkReturn('testReturnInvokeDynamicGetter', typesTask.dynamicType);
 
+  checkReturn('testDoWhile1', typesTask.stringType);
+  checkReturn('testDoWhile2', typesTask.nullType);
+  checkReturn('testDoWhile3', interceptorType);
+  checkReturn('testDoWhile4', typesTask.numType);
+
   checkReturnInClass(String className, String methodName, type) {
     var cls = findElement(compiler, className);
     var element = cls.lookupLocalMember(buildSourceString(methodName));
     Expect.equals(type,
         typesInferrer.getReturnTypeOfElement(element).simplify(compiler));
   }
 
   checkReturnInClass('A', 'returnInt1', typesTask.intType);
   checkReturnInClass('A', 'returnInt2', typesTask.intType);
   checkReturnInClass('A', 'returnInt3', typesTask.intType);
@@ skipping 13 matching lines @@
   checkReturnInClass('B', 'returnInt9', typesTask.intType);
 
   checkFactoryConstructor(String className, String factoryName) {
     var cls = findElement(compiler, className);
     var element = cls.localLookup(buildSourceString(factoryName));
     Expect.equals(new TypeMask.nonNullExact(cls.rawType),
                   typesInferrer.getReturnTypeOfElement(element));
   }
   checkFactoryConstructor('A', '');
 }