VM(CoreLib): Work around JIT optimization issue revealed by cec963f028198ec5871840491ba78b096ad0b819

runtime/lib/growable_array.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.
 
 class _GrowableList<T> extends ListBase<T> {
   void insert(int index, T element) {
     if ((index < 0) || (index > length)) {
       throw new RangeError.range(index, 0, length);
     }
     if (index == this.length) {
@@ skipping 216 matching lines @@
     // Round up size to the next odd number, since this is free
     // because of alignment requirements of the GC.
     return new _List(capacity | 1);
   }
 
   // Grow from 0 to 3, and then double + 1.
   int _nextCapacity(int old_capacity) => (old_capacity * 2) | 3;
 
   void _grow(int new_capacity) {
     var newData = _allocateData(new_capacity);
-    for (int i = 0; i < length; i++) {
-      newData[i] = this[i];
+    // This is a work-around for dartbug.com/30090: array-bound-check
+    // generalization causes excessive deoptimizations because it
+    // hoists CheckArrayBound(i, ...) out of the loop below and turns it
+    // into CheckArrayBound(length - 1, ...). Which deoptimizes
+    // if length == 0. However the loop itself does not execute
+    // if length == 0.
+    if (length > 0) {
+      for (int i = 0; i < length; i++) {
+        newData[i] = this[i];
+      }
     }
     _setData(newData);
   }
 
   void _shrink(int new_capacity, int new_length) {
     var newData = _allocateData(new_capacity);
-    for (int i = 0; i < new_length; i++) {
-      newData[i] = this[i];
+    // This is a work-around for dartbug.com/30090. See the comment in _grow.
+    if (new_length > 0) {
+      for (int i = 0; i < new_length; i++) {
+        newData[i] = this[i];
+      }
     }
     _setData(newData);
   }
 
   // Iterable interface.
 
   void forEach(f(T element)) {
     int initialLength = length;
     for (int i = 0; i < length; i++) {
       f(this[i]);
@@ skipping 101 matching lines @@
       result._setLength(length);
       return result;
     }
     return growable ? <T>[] : new List<T>(0);
   }
 
   Set<T> toSet() {
     return new Set<T>.from(this);
   }
 }