Support double allocations when folding allocation.

test/mjsunit/allocation-folding.js

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-// Flags: --allow-natives-syntax --nouse-osr
+// Flags: --allow-natives-syntax --nouse-osr --expose-gc
+
+// Test loop barrier when folding allocations.
+
 function f() {
   var elem1 = [1,2,3];
   for (var i=0; i < 100000; i++) {
     var bar = [1];
   }
   var elem2 = [1,2,3];
   return elem2;
 }
 
 f(); f(); f();
 %OptimizeFunctionOnNextCall(f);
 var result = f();
 
-for (var i=0; i < 100000; i++) {
-  var bar = [1];
+gc();
+
+assertEquals(result[2], 3);
+
+// Test allocation folding of doubles.
+
+function doubles() {
+  var elem1 = [1.1, 1.2];
+  var elem2 = [2.1, 2.2];
+  return elem2;
 }
 
-assertEquals(result[2], 3);
+doubles(); doubles(); doubles();
+%OptimizeFunctionOnNextCall(doubles);
+var result = doubles();
+
+gc();
+
+assertEquals(result[1], 2.2);