Reland of [interpreter] Add string type feedback to add

src/globals.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_GLOBALS_H_
 #define V8_GLOBALS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 1195 matching lines @@
   // All objects are at least pointer aligned, so we can remove the trailing
   // zeros.
   return static_cast<uint32_t>(bit_cast<uintptr_t>(address) >>
                                kPointerSizeLog2);
 }
 
 // Type feedback is encoded in such a way that, we can combine the feedback
 // 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.
 class CompareOperationFeedback {
  public:
   enum { kNone = 0x00, kSignedSmall = 0x01, kNumber = 0x3, kAny = 0x7 };
 };
 
 // Describes how exactly a frame has been dropped from stack.
 enum LiveEditFrameDropMode {
   // No frame has been dropped.
   LIVE_EDIT_FRAMES_UNTOUCHED,
   // The top JS frame had been calling debug break slot stub. Patch the
   // address this stub jumps to in the end.
   LIVE_EDIT_FRAME_DROPPED_IN_DEBUG_SLOT_CALL,
   // The top JS frame had been calling some C++ function. The return address
   // gets patched automatically.
   LIVE_EDIT_FRAME_DROPPED_IN_DIRECT_CALL,
   LIVE_EDIT_FRAME_DROPPED_IN_RETURN_CALL,
   LIVE_EDIT_CURRENTLY_SET_MODE
 };
 
 }  // namespace internal
 }  // namespace v8
 
 namespace i = v8::internal;
 
 #endif  // V8_GLOBALS_H_