--- a/hotspot/src/share/vm/opto/compile.cpp	Mon Mar 04 13:15:01 2013 -0800
+++ b/hotspot/src/share/vm/opto/compile.cpp	Tue Mar 05 04:24:50 2013 -0800
@@ -3669,3 +3669,38 @@
     n->set_req(0, NULL);
   }
 }
+
+// Auxiliary method to support randomized stressing/fuzzing.
+//
+// This method can be called the arbitrary number of times, with current count
+// as the argument. The logic allows selecting a single candidate from the
+// running list of candidates as follows:
+//    int count = 0;
+//    Cand* selected = null;
+//    while(cand = cand->next()) {
+//      if (randomized_select(++count)) {
+//        selected = cand;
+//      }
+//    }
+//
+// Including count equalizes the chances any candidate is "selected".
+// This is useful when we don't have the complete list of candidates to choose
+// from uniformly. In this case, we need to adjust the randomicity of the
+// selection, or else we will end up biasing the selection towards the latter
+// candidates.
+//
+// Quick back-envelope calculation shows that for the list of n candidates
+// the equal probability for the candidate to persist as "best" can be
+// achieved by replacing it with "next" k-th candidate with the probability
+// of 1/k. It can be easily shown that by the end of the run, the
+// probability for any candidate is converged to 1/n, thus giving the
+// uniform distribution among all the candidates.
+//
+// We don't care about the domain size as long as (RANDOMIZED_DOMAIN / count) is large.
+#define RANDOMIZED_DOMAIN_POW 29
+#define RANDOMIZED_DOMAIN (1 << RANDOMIZED_DOMAIN_POW)
+#define RANDOMIZED_DOMAIN_MASK ((1 << (RANDOMIZED_DOMAIN_POW + 1)) - 1)
+bool Compile::randomized_select(int count) {
+  assert(count > 0, "only positive");
+  return (os::random() & RANDOMIZED_DOMAIN_MASK) < (RANDOMIZED_DOMAIN / count);
+}