Bug 1362338: Take a bit from the atom's length to store a tristate. r=froydnj

MozReview-Commit-ID: Elu9EioSDXk

parser/html/nsHtml5Atom.cpp

@@ -9,7 +9,7 @@
 nsHtml5Atom::nsHtml5Atom(const nsAString& aString)
 {
   mLength = aString.Length();
-  mIsStatic = false;
+  SetKind(AtomKind::HTML5Atom);
   RefPtr<nsStringBuffer> buf = nsStringBuffer::FromString(aString);
   if (buf) {
     mString = static_cast<char16_t*>(buf->Data());

xpcom/ds/nsAtomTable.cpp

@@ -93,7 +93,7 @@ private:
     : mRefCnt(1)
   {
     mLength = aString.Length();
-    mIsStatic = false;
+    SetKind(AtomKind::DynamicAtom);
     RefPtr<nsStringBuffer> buf = nsStringBuffer::FromString(aString);
     if (buf) {
       mString = static_cast<char16_t*>(buf->Data());
@@ -171,7 +171,7 @@ public:
   StaticAtom(nsStringBuffer* aStringBuffer, uint32_t aLength, uint32_t aHash)
   {
     mLength = aLength;
-    mIsStatic = true;
+    SetKind(AtomKind::StaticAtom);
     mString = static_cast<char16_t*>(aStringBuffer->Data());
 
 #if defined(NS_BUILD_REFCNT_LOGGING)

xpcom/ds/nsIAtom.idl

@@ -37,6 +37,14 @@ interface nsIAtom : nsISupports
   size_t SizeOfIncludingThis(in MallocSizeOf aMallocSizeOf);
 
 %{C++
+  // The kind of atom we have, in order to be able to devirtualize hot stuff
+  // looking at mKind.
+  enum class AtomKind : uint8_t {
+    DynamicAtom = 0,
+    StaticAtom = 1,
+    HTML5Atom = 2,
+  };
+
   // note these are NOT virtual so they won't muck with the vtable!
   inline bool Equals(char16ptr_t aString, uint32_t aLength) const
   {
@@ -48,8 +56,25 @@ interface nsIAtom : nsISupports
     return Equals(aString.BeginReading(), aString.Length());
   }
 
+  inline void SetKind(AtomKind aKind) {
+    mKind = static_cast<uint32_t>(aKind);
+    MOZ_ASSERT(Kind() == aKind);
+  }
+
+  inline AtomKind Kind() const {
+    return static_cast<AtomKind>(mKind);
+  }
+
+  inline bool IsDynamicAtom() const {
+    return Kind() == AtomKind::DynamicAtom;
+  }
+
+  inline bool IsHTML5Atom() const {
+    return Kind() == AtomKind::HTML5Atom;
+  }
+
   inline bool IsStaticAtom() const {
-    return mIsStatic;
+    return Kind() == AtomKind::StaticAtom;
   }
 
   inline char16ptr_t GetUTF16String() const {
@@ -80,8 +105,8 @@ interface nsIAtom : nsISupports
   }
 
 protected:
-  uint32_t mLength:31;
-  uint32_t mIsStatic:1;
+  uint32_t mLength: 30;
+  uint32_t mKind: 2; // nsIAtom::AtomKind
   uint32_t mHash;
   /**
    * WARNING! There is an invisible constraint on |mString|: the chars it