dart2js cps: Streamline expressions and primitives.

pkg/compiler/lib/src/cps_ir/mutable_ssa.dart

 // Copyright (c) 2015, 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 dart2js.cps_ir.mutable_ssa;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
 
 /// Determines which mutable variables should be rewritten to phi assignments
@@ skipping 137 matching lines @@
         // Put the initial value into the environment.
         Primitive value = node.value.definition;
         environment[node.variable] = value;
 
         // Preserve variable names.
         mergeHints(node.variable, value);
 
         // Remove the mutable variable binding.
         node.value.unlink();
         removeNode(node);
-      } else if (node is SetMutableVariable &&
-                 shouldRewrite(node.variable.definition)) {
-        // As above, update the environment, preserve variables and remove
-        // the mutable variable assignment.
-        MutableVariable variable = node.variable.definition;
-        environment[variable] = node.value.definition;
-        mergeHints(variable, node.value.definition);
-        node.value.unlink();
-        removeNode(node);
+      } else if (node is LetPrim && node.primitive is SetMutableVariable) {
+        SetMutableVariable setter = node.primitive;
+        MutableVariable variable = setter.variable.definition;
+        if (shouldRewrite(variable)) {
+          // As above, update the environment, preserve variables and remove
+          // the mutable variable assignment.
+          environment[variable] = setter.value.definition;
+          mergeHints(variable, setter.value.definition);
+          setter.value.unlink();
+          removeNode(node);
+        }
       } else if (node is LetPrim && node.primitive is GetMutableVariable) {
         GetMutableVariable getter = node.primitive;
         MutableVariable variable = getter.variable.definition;
         if (shouldRewrite(variable)) {
           // Replace with the reaching definition from the environment.
           Primitive value = environment[variable];
           value.substituteFor(getter);
           mergeHints(variable, value);
           removeNode(node);
         }
@@ skipping 66 matching lines @@
 class VariableItem extends StackItem {}
 
 /// Represents a yet unprocessed continuation together with the
 /// environment in which to process it.
 class ContinuationItem extends StackItem {
   final Continuation continuation;
   final Map<MutableVariable, Primitive> environment;
 
   ContinuationItem(this.continuation, this.environment);
 }