Reland of [interpreter] Add string type feedback to add

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index f2631ff4cc14fe0874d56bf38d1cb861182bee1f..9b7f7ca7f45bb13cd61c42698ad58b95f89ef293 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1213,9 +1213,16 @@ inline uint32_t ObjectHash(Address address) {
 // at different points by performing an 'OR' operation. Type feedback moves
 // to a more generic type when we combine feedback.
 // kSignedSmall -> kNumber  -> kAny
+//                 kString  -> kAny
 class BinaryOperationFeedback {
  public:
-  enum { kNone = 0x00, kSignedSmall = 0x01, kNumber = 0x3, kAny = 0x7 };
+  enum {
+    kNone = 0x0,
+    kSignedSmall = 0x1,
+    kNumber = 0x3,
+    kString = 0x4,

[rmcilroy, 2016/10/04 08:05:32]

This needs to keep the or-combining from kNumber->kString->kAny, so kString
should be 0x7 and kAny should be 0xF (update comment above too).

[Leszek Swirski, 2016/10/04 08:30:40]

Should it? or-combining kNumber and kString shouldn't output kString, I wouldn't
have thought?

[Leszek Swirski, 2016/10/04 08:49:59]

Never mind, Mythri explained f2f that number is a subtype of string, which
doesn't make sense in my heart but at least now makes sense in my brain.

+    kAny = 0xF
+  };
 };
 
 // TODO(epertoso): consider unifying this with BinaryOperationFeedback.