Split up String type into a regular and a ComplexString

Saves some memory for many cases, and will allow re-using the
String itself as an identifier

Change-Id: I462d63bc6f113dff1dce0de28ee4eea3949a4b95
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 43 insertions, 30 deletions

diff --git a/src/qml/jsruntime/qv4string_p.h b/src/qml/jsruntime/qv4string_p.h
index 1acdbf3e4b..d1b38f4336 100644
--- a/src/qml/jsruntime/qv4string_p.h
+++ b/src/qml/jsruntime/qv4string_p.h
@@ -67,35 +67,31 @@ namespace Heap {
 struct Q_QML_PRIVATE_EXPORT String : Base {
     static void markObjects(Heap::Base *that, MarkStack *markStack);
     enum StringType {
-        StringType_Unknown,
         StringType_Regular,
-        StringType_ArrayIndex
+        StringType_ArrayIndex,
+        StringType_Unknown,
+        StringType_AddedString,
+        StringType_Complex = StringType_AddedString
     };
 
 #ifndef V4_BOOTSTRAP
     void init(const QString &text);
-    void init(String *l, String *n);
     void destroy();
     void simplifyString() const;
-    int length() const {
-        Q_ASSERT((largestSubLength &&
-                  (len == left->len + right->len)) ||
-                 len == (uint)text->size);
-        return len;
-    }
+    int length() const;
     std::size_t retainedTextSize() const {
-        return largestSubLength ? 0 : (std::size_t(text->size) * sizeof(QChar));
+        return subtype >= StringType_Complex ? 0 : (std::size_t(text->size) * sizeof(QChar));
     }
     void createHashValue() const;
     inline unsigned hashValue() const {
-        if (subtype == StringType_Unknown)
+        if (subtype >= StringType_Unknown)
             createHashValue();
-        Q_ASSERT(!largestSubLength);
+        Q_ASSERT(subtype < StringType_Complex);
 
         return stringHash;
     }
     inline QString toQString() const {
-        if (largestSubLength)
+        if (subtype >= StringType_Complex)
             simplifyString();
         QStringDataPtr ptr = { text };
         text->ref.ref();
@@ -106,7 +102,7 @@ struct Q_QML_PRIVATE_EXPORT String : Base {
             return true;
         if (hashValue() != other->hashValue())
             return false;
-        Q_ASSERT(!largestSubLength);
+        Q_ASSERT(subtype < StringType_Complex);
         if (identifier && identifier == other->identifier)
             return true;
         if (subtype == Heap::String::StringType_ArrayIndex && other->subtype == Heap::String::StringType_ArrayIndex)
@@ -115,24 +111,33 @@ struct Q_QML_PRIVATE_EXPORT String : Base {
         return toQString() == other->toQString();
     }
 
-    union {
-        mutable QStringData *text;
-        mutable String *left;
-    };
-    union {
-        mutable Identifier *identifier;
-        mutable String *right;
-    };
+    mutable QStringData *text;
+    mutable Identifier *identifier;
     mutable uint subtype;
     mutable uint stringHash;
-    mutable uint largestSubLength;
-    uint len;
 private:
     static void append(const String *data, QChar *ch);
 #endif
 };
 Q_STATIC_ASSERT(std::is_trivial< String >::value);
 
+#ifndef V4_BOOTSTRAP
+struct ComplexString : String {
+    void init(String *l, String *n);
+    mutable uint nestingLevel;
+    mutable String *left;
+    mutable String *right;
+    mutable int largestSubLength;
+    int len;
+};
+Q_STATIC_ASSERT(std::is_trivial< ComplexString >::value);
+
+inline
+int String::length() const {
+    return text ? text->size : static_cast<const ComplexString *>(this)->len;
+}
+#endif
+
 }
 
 struct Q_QML_PRIVATE_EXPORT String : public Managed {
@@ -169,7 +174,7 @@ struct Q_QML_PRIVATE_EXPORT String : public Managed {
     uint asArrayIndex() const {
         if (subtype() == Heap::String::StringType_Unknown)
             d()->createHashValue();
-        Q_ASSERT(!d()->largestSubLength);
+        Q_ASSERT(d()->subtype < Heap::String::StringType_Complex);
         if (subtype() == Heap::String::StringType_ArrayIndex)
             return d()->stringHash;
         return UINT_MAX;
@@ -198,10 +203,8 @@ struct Q_QML_PRIVATE_EXPORT String : public Managed {
     }
 
     bool startsWithUpper() const {
-        const String::Data *l = d();
-        while (l->largestSubLength)
-            l = l->left;
-        return l->text->size && QChar::isUpper(l->text->data()[0]);
+        Q_ASSERT(d()->subtype < Heap::String::StringType_Complex);
+        return d()->text->size && QChar::isUpper(d()->text->data()[0]);
     }
 
     Identifier *identifier() const { return d()->identifier; }
@@ -263,12 +266,22 @@ public:
     }
 };
 
+#ifndef V4_BOOTSTRAP
+struct ComplexString : String {
+    typedef QV4::Heap::ComplexString Data;
+    QV4::Heap::ComplexString *d_unchecked() const { return static_cast<QV4::Heap::ComplexString *>(m()); }
+    QV4::Heap::ComplexString *d() const {
+        QV4::Heap::ComplexString *dptr = d_unchecked();
+        dptr->_checkIsInitialized();
+        return dptr;
+    }
+};
+
 template<>
 inline const String *Value::as() const {
     return isManaged() && m()->vtable()->isString ? static_cast<const String *>(this) : 0;
 }
 
-#ifndef V4_BOOTSTRAP
 template<>
 inline ReturnedValue value_convert<String>(ExecutionEngine *e, const Value &v)
 {