Consider updates of locals in type promotion.

pkg/compiler/lib/src/inferrer/inferrer_visitor.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.
 
 library inferrer_visitor;
 
 import '../dart2jslib.dart' hide Selector, TypedSelector;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../tree/tree.dart';
@@ skipping 132 matching lines @@
 
   VariableScope.deepCopyOf(VariableScope<T> other)
       : variables = other.variables == null
             ? null
             : new Map<Local, T>.from(other.variables),
         block = other.block,
         parent = other.parent == null
             ? null
             : new VariableScope<T>.deepCopyOf(other.parent);
 
+  VariableScope.shallowCopyOf(VariableScope<T> other)
+      : variables = other.variables == null
+            ? null
+            : new Map<Local, T>.from(other.variables),
+        block = other.block,
+        parent = other.parent;
+
   T operator [](Local variable) {
     T result;
     if (variables == null || (result = variables[variable]) == null) {
       return parent == null ? null : parent[variable];
     }
     return result;
   }
 
   void operator []=(Local variable, T mask) {
     assert(mask != null);
@@ skipping 231 matching lines @@
   LocalsHandler.deepCopyOf(LocalsHandler<T> other)
       : locals = new VariableScope<T>.deepCopyOf(other.locals),
         fieldScope = new FieldInitializationScope<T>.from(other.fieldScope),
         captured = other.captured,
         capturedAndBoxed = other.capturedAndBoxed,
         tryBlock = other.tryBlock,
         types = other.types,
         inferrer = other.inferrer,
         compiler = other.compiler;
 
+  LocalsHandler.shallowCopyOf(LocalsHandler<T> other)
+      : locals = new VariableScope<T>.shallowCopyOf(other.locals),
+        fieldScope = new FieldInitializationScope<T>.from(other.fieldScope),
+        captured = other.captured,
+        capturedAndBoxed = other.capturedAndBoxed,
+        tryBlock = other.tryBlock,
+        types = other.types,
+        inferrer = other.inferrer,
+        compiler = other.compiler;
+
   T use(Local local) {
     if (capturedAndBoxed.containsKey(local)) {
       return inferrer.typeOfElement(capturedAndBoxed[local]);
     } else {
       if (captured.containsKey(local)) {
         inferrer.recordCapturedLocalRead(local);
       }
       return locals[local];
     }
   }
@@ skipping 485 matching lines @@
       bool oldAccumulateIsChecks = accumulateIsChecks;
       List<Send> oldIsChecks = isChecks;
       if (!accumulateIsChecks) {
         accumulateIsChecks = true;
         isChecks = <Send>[];
       }
       visit(node.receiver);
       LocalsHandler<T> saved = locals;
       locals = new LocalsHandler<T>.from(locals, node);
       updateIsChecks(isChecks, usePositive: true);
-      if (!oldAccumulateIsChecks) {
+      LocalsHandler<T> narrowed;
+      if (oldAccumulateIsChecks) {
+        narrowed = new LocalsHandler<T>.shallowCopyOf(locals);

[floitsch, 2015/01/21 14:34:02]

Would it be better to just copy out the locals?

It reaches more into the privates of the LocalsHandler, but on the other hand it
is not completely clear now, what "shallow" involves.

[herhut, 2015/01/21 14:45:19]

It only copies the top level, so I have renamed it to topLevelCopyOf to make
that clear. Even if I only do the locals, I need a way to copy one level deep
there, so I prefer to just do it with the whole thing. 

+      } else {
         accumulateIsChecks = false;
         isChecks = oldIsChecks;
       }
       visit(node.arguments.head);
+      if (oldAccumulateIsChecks) {
+        invalidatedInRightHandSide (Send test) {

[floitsch, 2015/01/21 14:34:02]

bool invalidate ...
new line before and after.

[herhut, 2015/01/21 14:45:19]

Done.

+          Element receiver = elements[test.receiver];
+          if (receiver is LocalElement) {
+            return narrowed.locals[receiver] != locals.locals[receiver];
+          }
+          return false;
+        }
+        isChecks.removeWhere(invalidatedInRightHandSide);
+      }
       saved.mergeDiamondFlow(locals, null);
       locals = saved;
       return types.boolType;
     } else if ("||" == op.source) {
       conditionIsSimple = false;
       List<Send> tests = <Send>[];
       bool isSimple = handleCondition(node.receiver, tests);
       LocalsHandler<T> saved = locals;
       locals = new LocalsHandler<T>.from(locals, node);
       if (isSimple) updateIsChecks(tests, usePositive: false);
@@ skipping 345 matching lines @@
     return type;
   }
 
   T visitCascade(Cascade node) {
     // Ignore the result of the cascade send and return the type of the cascade
     // receiver.
     visit(node.expression);
     return cascadeReceiverStack.removeLast();
   }
 }