QXmlStream: optimize PrivateTagStack::addToStringStorage()

De-duplicate the QString/Ref code paths by using QStringView instead.
Keep the old overloads so we can centrally apply the qToStringView-
IgnoringNull() optimization.

Replace insert(p, ..) where p = size() with append(..). The code
ensures in the lines before that the insertion position is the end of
the string.

Port the few QLatin1String arguments to addToStringStorage() to
QStringViewLiteral. I also considered adding a QLatin1String()
overload, but the test size increased, so the function wasn't pulling
its own weight.

This version saves 360B in text size on optimized GCC 6.1 Linux AMD64
builds.

Change-Id: I4b759fddc38b1f97a7218954e756cc19400922e9
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

3 files changed, 14 insertions, 18 deletions

diff --git a/src/corelib/xml/qxmlstream.cpp b/src/corelib/xml/qxmlstream.cpp
index 3d600c2380..195466e803 100644
--- a/src/corelib/xml/qxmlstream.cpp
+++ b/src/corelib/xml/qxmlstream.cpp
@@ -775,8 +775,8 @@ QXmlStreamPrivateTagStack::QXmlStreamPrivateTagStack()
     tagStackStringStorage.reserve(32);
     tagStackStringStorageSize = 0;
     NamespaceDeclaration &namespaceDeclaration = namespaceDeclarations.push();
-    namespaceDeclaration.prefix = addToStringStorage(QLatin1String("xml"));
-    namespaceDeclaration.namespaceUri = addToStringStorage(QLatin1String("http://www.w3.org/XML/1998/namespace"));
+    namespaceDeclaration.prefix = addToStringStorage(QStringViewLiteral("xml"));
+    namespaceDeclaration.namespaceUri = addToStringStorage(QStringViewLiteral("http://www.w3.org/XML/1998/namespace"));
     initialTagStackStringStorageSize = tagStackStringStorageSize;
 }
 
diff --git a/src/corelib/xml/qxmlstream.g b/src/corelib/xml/qxmlstream.g
index d4dd7b2622..73085bda8a 100644
--- a/src/corelib/xml/qxmlstream.g
+++ b/src/corelib/xml/qxmlstream.g
@@ -205,20 +205,18 @@ public:
     bool tagsDone;
 
     inline QStringRef addToStringStorage(const QStringRef &s) {
-        int pos = tagStackStringStorageSize;
-        int sz = s.size();
-        if (pos != tagStackStringStorage.size())
-            tagStackStringStorage.resize(pos);
-        tagStackStringStorage.insert(pos, s.unicode(), sz);
-        tagStackStringStorageSize += sz;
-        return QStringRef(&tagStackStringStorage, pos, sz);
+        return addToStringStorage(qToStringViewIgnoringNull(s));
     }
     inline QStringRef addToStringStorage(const QString &s) {
+        return addToStringStorage(qToStringViewIgnoringNull(s));
+    }
+    QStringRef addToStringStorage(QStringView s)
+    {
         int pos = tagStackStringStorageSize;
         int sz = s.size();
         if (pos != tagStackStringStorage.size())
             tagStackStringStorage.resize(pos);
-        tagStackStringStorage.insert(pos, s.unicode(), sz);
+        tagStackStringStorage.append(s.data(), sz);
         tagStackStringStorageSize += sz;
         return QStringRef(&tagStackStringStorage, pos, sz);
     }
diff --git a/src/corelib/xml/qxmlstream_p.h b/src/corelib/xml/qxmlstream_p.h
index ab422ec48a..8ef6e4b8fe 100644
--- a/src/corelib/xml/qxmlstream_p.h
+++ b/src/corelib/xml/qxmlstream_p.h
@@ -701,20 +701,18 @@ public:
     bool tagsDone;
 
     inline QStringRef addToStringStorage(const QStringRef &s) {
-        int pos = tagStackStringStorageSize;
-        int sz = s.size();
-        if (pos != tagStackStringStorage.size())
-            tagStackStringStorage.resize(pos);
-        tagStackStringStorage.insert(pos, s.unicode(), sz);
-        tagStackStringStorageSize += sz;
-        return QStringRef(&tagStackStringStorage, pos, sz);
+        return addToStringStorage(qToStringViewIgnoringNull(s));
     }
     inline QStringRef addToStringStorage(const QString &s) {
+        return addToStringStorage(qToStringViewIgnoringNull(s));
+    }
+    QStringRef addToStringStorage(QStringView s)
+    {
         int pos = tagStackStringStorageSize;
         int sz = s.size();
         if (pos != tagStackStringStorage.size())
             tagStackStringStorage.resize(pos);
-        tagStackStringStorage.insert(pos, s.unicode(), sz);
+        tagStackStringStorage.append(s.data(), sz);
         tagStackStringStorageSize += sz;
         return QStringRef(&tagStackStringStorage, pos, sz);
     }