Adapt Danno's Track Allocation Info idea to fast literals. When allocating a literal array,

test/mjsunit/elements-kind.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 211 matching lines @@
   }
   doubles = construct_doubles();
   for (var i = 0; i < 3; i++) {
     convert_mixed(doubles, "three", elements_kind.fast);
   }
   convert_mixed(construct_smis(), "three", elements_kind.fast);
   convert_mixed(construct_doubles(), "three", elements_kind.fast);
   %OptimizeFunctionOnNextCall(convert_mixed);
   smis = construct_smis();
   doubles = construct_doubles();
-  convert_mixed(smis, 1, elements_kind.fast);
-  convert_mixed(doubles, 1, elements_kind.fast);
+  if (getKind(smis) == elements_kind.fast_smi_only) {
+    convert_mixed(smis, 1, elements_kind.fast);
+    // Test failure here. My change must have broken the assumption above, that
+    // the crankshafted convert_mixed() function will transition the doubles
+    // array to fast.
+    convert_mixed(doubles, 1, elements_kind.fast);
+  } else {
+    convert_mixed(smis, 1, elements_kind.fast);
+    convert_mixed(doubles, 1, elements_kind.fast);
+  }
   assertTrue(%HaveSameMap(smis, doubles));
 }
 
 // Crankshaft support for smi-only elements in dynamic array literals.
 function get(foo) { return foo; }  // Used to generate dynamic values.
 
 function crankshaft_test() {
   if (support_smi_only_arrays) {
     var a1 = [get(1), get(2), get(3)];
     assertKind(elements_kind.fast_smi_only, a1);
@@ skipping 92 matching lines @@
 // Test that Array.splice() and Array.slice() return correct ElementsKinds.
 if (support_smi_only_arrays) {
   var a = ["foo", "bar"];
   assertKind(elements_kind.fast, a);
   var b = a.splice(0, 1);
   assertKind(elements_kind.fast, b);
   var c = a.slice(0, 1);
   assertKind(elements_kind.fast, c);
 }
 
+/*
+if (support_smi_only_arrays) {
+  function create_array() {
+    var ar = [1,2,3];
+    return ar;
+  }
+
+  var a = create_array();
+  assertKind(elements_kind.fast_smi_only, a);
+  a[1] = 1;
+  assertKind(elements_kind.fast_smi_only, a);
+  a[1] = 1.5;
+  assertKind(elements_kind.fast_double, a);
+
+  // The boilerplate should have been pre-transitioned now.
+  var b = create_array();
+  assertKind(elements_kind.fast_double, b);
+}
+*/
+
 // Throw away type information in the ICs for next stress run.
 gc();