Just calculate pretenuring ratio when needed.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index a0256fb416429940c41002429ae7731c6024e984..320bdf3e5f99477a196ff6bc71d5cf98ca114631 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1551,10 +1551,11 @@ inline bool AllocationSite::DigestPretenuringFeedback() {
   bool decision_changed = false;
   int create_count = memento_create_count();
   int found_count = memento_found_count();
-  double ratio = static_cast<double>(found_count) / create_count;
+  double ratio = 0.0;
   PretenureFlag current_mode = GetPretenureMode();
 
   if (create_count >= kPretenureMinimumCreated) {
+    ratio = static_cast<double>(found_count) / create_count;

[mvstanton, 2014/02/06 11:23:33]

Per our chat, something like:

bool minimum_met = create_count >= kPretenureMinimumCreated;
double ratio = (minimum_met | FLAG_trace_pretenuring_statistics)
  ? static_cast<double>(found_count) / create_count
  : 0;

and later...
if (minimum_met) { ...decision code.

[Hannes Payer (out of office), 2014/02/06 11:26:53]

Done.

     PretenureDecision result = ratio >= kPretenureRatio
         ? kTenure
         : kDontTenure;
@@ -1568,6 +1569,7 @@ inline bool AllocationSite::DigestPretenuringFeedback() {
   }
 
   if (FLAG_trace_pretenuring_statistics) {
+    ratio = static_cast<double>(found_count) / create_count;
     PrintF(
         "AllocationSite(%p): (created, found, ratio) (%d, %d, %f) %s => %s\n",
          static_cast<void*>(this), create_count, found_count, ratio,