dart2js cps: Add helpers for common IR manipulation.

pkg/compiler/lib/src/cps_ir/scalar_replacement.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.scalar_replacement;
 
 import 'optimizers.dart';
 
 import 'dart:collection' show Queue;
 
 import '../closure.dart' show
@@ skipping 123 matching lines @@
     for (FieldElement field in writes) {
       MutableVariable variable = new MutableVariable(field);
       variable.type = new TypeMask.nonNullEmpty();
       cells[field] = variable;
       Primitive initialValue = fieldInitialValues[field];
       if (initialValue == null) {
         assert(allocation is CreateBox);
         initialValue = new Constant(new NullConstantValue());
         LetPrim let = new LetPrim(initialValue);
         let.primitive.parent = let;
-        insertionPoint = insertAtBody(insertionPoint, let);
+        insertionPoint = let..insertBelow(insertionPoint);
       }
       LetMutable let = new LetMutable(variable, initialValue);
       let.value.parent = let;
-      insertionPoint = insertAtBody(insertionPoint, let);
+      insertionPoint = let..insertBelow(insertionPoint);
     }
 
     // Replace references with MutableVariable operations or references to the
     // field's value.
     for (Reference ref = allocation.firstRef; ref != null; ref = ref.next) {
       Node use = ref.parent;
       if (use is GetField) {
         GetField getField = use;
         MutableVariable variable = cells[getField.field];
         if (variable != null) {
@@ skipping 22 matching lines @@
       } else {
         assert(false);
       }
     }
 
     // Delete [allocation] since that might 'free' another scalar replacement
     // candidate by deleting the last non-field-access.
     deleteLetPrimOf(allocation);
   }
 
-  InteriorNode insertAtBody(
-      InteriorNode insertionPoint, InteriorExpression let) {
-    let.parent = insertionPoint;
-    let.body = insertionPoint.body;
-    let.body.parent = let;
-    insertionPoint.body = let;
-    return let;
-  }
-
   /// Replaces [old] with [primitive] in [old]'s parent [LetPrim].
   void replacePrimitive(Primitive old, Primitive primitive) {
     LetPrim letPrim = old.parent;
     letPrim.primitive = primitive;
   }
 
   void deleteLetPrimOf(Primitive primitive) {
     assert(primitive.hasNoUses);
     LetPrim letPrim = primitive.parent;
-    Node child = letPrim.body;
-    InteriorNode parent = letPrim.parent;
-    child.parent = parent;
-    parent.body  = child;
-
+    letPrim.remove();
     deletePrimitive(primitive);
   }
 
   void deletePrimitive(Primitive primitive) {
     assert(primitive.hasNoUses);
     removalVisitor.visit(primitive);
   }
 
   void reconsider(Definition node) {
     if (node is CreateInstance || node is CreateBox) {
@@ skipping 25 matching lines @@
 class ScalarReplacementRemovalVisitor extends RecursiveVisitor {
   ScalarReplacementVisitor process;
 
   ScalarReplacementRemovalVisitor(this.process);
 
   processReference(Reference reference) {
     process.reconsider(reference.definition);
     reference.unlink();
   }
 }