[regexp] Turn last match info into a simple FixedArray

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index aa8c9693442877c18b848d54e8e1e2ab3148ecc8..6aa0cbe7f9c4fc86e40b7aeab0d04d2bd879c89a 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1004,6 +1004,7 @@ template <class C> inline bool Is(Object* obj);
   V(FixedDoubleArray)            \
   V(WeakFixedArray)              \
   V(ArrayList)                   \
+  V(RegExpMatchInfo)             \
   V(Context)                     \
   V(ScriptContextTable)          \
   V(NativeContext)               \
@@ -2964,6 +2965,57 @@ class ArrayList : public FixedArray {
   DISALLOW_IMPLICIT_CONSTRUCTORS(ArrayList);
 };
 
+// The property RegExpMatchInfo includes the matchIndices
+// array of the last successful regexp match (an array of start/end index
+// pairs for the match and all the captured substrings), the invariant is
+// that there are at least two capture indices.  The array also contains
+// the subject string for the last successful match.
+// After creation the result must be treated as a FixedArray in all regards.
+class RegExpMatchInfo : public FixedArray {
+ public:
+  // Returns the number of captures, which is defined as the length of the
+  // matchIndices objects of the last match. matchIndices contains two indices
+  // for each capture (including the match itself), i.e. 2 * #captures + 2.
+  inline int NumberOfCaptureRegisters();
+  inline void SetNumberOfCaptureRegisters(int value);
+
+  // Returns the subject string of the last match.
+  inline String* LastSubject();
+  inline void SetLastSubject(String* value);
+
+  // Like LastSubject, but modifiable by the user.
+  inline Object* LastInput();
+  inline void SetLastInput(Object* value);
+
+  // Returns the i'th capture index, 0 <= i < NumberOfCaptures(). Capture(0) and
+  // Capture(1) determine the start- and endpoint of the match itself.
+  inline int Capture(int i);
+  inline void SetCapture(int i, int value);
+
+  // Reserves space for captures.
+  static Handle<RegExpMatchInfo> ReserveCaptures(
+      Handle<RegExpMatchInfo> match_info, int capture_count);
+
+  DECLARE_CAST(RegExpMatchInfo)
+
+  static const int kNumberOfCapturesIndex = 0;
+  static const int kLastSubjectIndex = 1;
+  static const int kLastInputIndex = 2;
+  static const int kFirstCaptureIndex = 3;
+  static const int kLastMatchOverhead = kFirstCaptureIndex;
+
+  static const int kNumberOfCapturesOffset = FixedArray::kHeaderSize;
+  static const int kLastSubjectOffset = kNumberOfCapturesOffset + kPointerSize;
+  static const int kLastInputOffset = kLastSubjectOffset + kPointerSize;
+  static const int kFirstCaptureOffset = kLastInputOffset + kPointerSize;
+
+  // Every match info is guaranteed to have enough space to store two captures.
+  static const int kInitialCaptureIndices = 2;
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(RegExpMatchInfo);
+};
+
 #define FRAME_ARRAY_FIELD_LIST(V) \
   V(WasmObject, Object)           \
   V(WasmFunctionIndex, Smi)       \