Use the property load IC for accessing the array length.

test/mjsunit/array-length.js

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+// Flags: --allow-natives-syntax
+
 var a = [0,1,2,3];
 assertEquals(0, a.length = 0);
 
 assertEquals('undefined', typeof a[0]);
 assertEquals('undefined', typeof a[1]);
 assertEquals('undefined', typeof a[2]);
 assertEquals('undefined', typeof a[3]);
 
 
 var a = [0,1,2,3];
@@ skipping 74 matching lines @@
 
 // Check case of compiled stubs.
 var a = [];
 for (var i = 0; i < 7; i++) {
   assertEquals(3, a.length = 3);
 
   var t = 239;
   t = a.length = 7;
   assertEquals(7, t);
 }
+
+function TestLengthAccess() {
+  var TestGetLength = function(a, l, getLength, getKeyedLength) {
+    assertEquals(l, getLength(a));
+    assertEquals(l, getKeyedLength(a));
+  }
+
+  var Test = function(a, l) {
+    var getLength = function(a) { return a.length; }

[Jakob Kummerow, 2012/11/16 12:57:10]

What's the point of doing this? Are you trying to get a fresh copy of the
function with uninitialized ICs? That won't work, because closures created from
the same literal will share the same code (it's why we have SharedFunctionInfo).

Otherwise, you could just declare these functions globally and avoid passing
them around all the time.

[Massi, 2012/11/19 12:26:15]

Yes, now I am creating new functions every time.

+    var getKeyedLength = function(a) { return a['length']; }
+    // Make the ICs reach the state we want.
+    TestGetLength(a, l, getLength, getKeyedLength);
+    TestGetLength(a, l, getLength, getKeyedLength);
+    TestGetLength(a, l, getLength, getKeyedLength);
+    // Also test crankshaft.
+    %OptimizeFunctionOnNextCall(getLength);
+    %OptimizeFunctionOnNextCall(getKeyedLength);
+    TestGetLength(a, l, getLength, getKeyedLength);
+  }
+
+  Test(new Array(4), 4);
+  Test([1, 2, 3, 4], 4);
+  Test(Object.create(new Array(4)), 4);
+  length = 4;

[Jakob Kummerow, 2012/11/16 12:57:10]

unused variable?

[Massi, 2012/11/19 12:26:15]

No, I am setting the 'length property' of the global object.
Now I added a comment to state it :-)

+  var globalObject = (1,eval)("this");
+  Test(globalObject, 4);
+}
+TestLengthAccess();
+