From a8d5f3853741b6027658ad2c8a8d2b72a58de852 Mon Sep 17 00:00:00 2001
From: Lars Knoll <lars.knoll@qt.io>
Date: Thu, 21 Nov 2019 11:59:45 +0100
Subject: Avoid allocating a d-pointer for empty strings

Those can simply be handled as compile time constant strings
pointing to the empty (Q)Char.

Change-Id: I1f6f6ab923a30c68a720003ca68c34c572aa29da
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/text/qbytearray.cpp | 16 ++++++----------
 src/corelib/text/qstring.cpp    | 21 ++++++++-------------
 src/corelib/text/qstring.h      |  2 +-
 3 files changed, 15 insertions(+), 24 deletions(-)

(limited to 'src/corelib/text')

diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index 26e3b64c9d..350fa3be25 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -1149,12 +1149,10 @@ QByteArray &QByteArray::operator=(const QByteArray & other) noexcept
 
 QByteArray &QByteArray::operator=(const char *str)
 {
-    if (!str || !*str) {
-        if (!str) {
-            d.clear();
-        } else {
-            d = QByteArrayData(Data::allocate(0), 0);
-        }
+    if (!str) {
+        d.clear();
+    } else if (!*str) {
+        d = DataPointer::fromRawData(&_empty, 0);
     } else {
         const int len = int(strlen(str));
         const uint fullLen = uint(len) + 1;
@@ -1612,7 +1610,7 @@ QByteArray::QByteArray(const char *data, int size)
 QByteArray::QByteArray(int size, char ch)
 {
     if (size <= 0) {
-        d = DataPointer(Data::allocate(0), 0);
+        d = DataPointer::fromRawData(&_empty, 0);
     } else {
         d = DataPointer(Data::allocate(uint(size) + 1u), size);
         memset(d.data(), ch, size);
@@ -2885,9 +2883,7 @@ QByteArray QByteArray::mid(int pos, int len) const
         return QByteArray();
     case QContainerImplHelper::Empty:
     {
-        auto alloc = Data::allocate(0);
-        QByteArray::DataPointer empty = { alloc.first, alloc.second, 0 };
-        return QByteArray(empty);
+        return QByteArray(DataPointer::fromRawData(&_empty, 0));
     }
     case QContainerImplHelper::Full:
         return *this;
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index 985c00ae6b..8e572691c6 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -2130,7 +2130,7 @@ QString::QString(const QChar *unicode, int size)
                 ++size;
         }
         if (!size) {
-            d = DataPointer(Data::allocate(0), 0);
+            d = DataPointer::fromRawData(&_empty, 0);
         } else {
             d = DataPointer(Data::allocate(size + 1), size);
             memcpy(d.data(), unicode, size * sizeof(QChar));
@@ -2148,7 +2148,7 @@ QString::QString(const QChar *unicode, int size)
 QString::QString(int size, QChar ch)
 {
     if (size <= 0) {
-        d = DataPointer(Data::allocate(0), 0);
+        d = DataPointer::fromRawData(&_empty, 0);
     } else {
         d = DataPointer(Data::allocate(size + 1), size);
         d.data()[size] = '\0';
@@ -4548,11 +4548,7 @@ QString QString::mid(int position, int n) const
     case QContainerImplHelper::Null:
         return QString();
     case QContainerImplHelper::Empty:
-    {
-        QPair<Data *, char16_t *> pair = Data::allocate(0);
-        DataPointer empty = { pair.first, pair.second, 0 };
-        return QString(std::move(empty));
-    }
+        return QString(DataPointer::fromRawData(&_empty, 0));
     case QContainerImplHelper::Full:
         return *this;
     case QContainerImplHelper::Subset:
@@ -5010,7 +5006,7 @@ QString::DataPointer QString::fromLatin1_helper(const char *str, int size)
     if (!str) {
         // nothing to do
     } else if (size == 0 || (!*str && size < 0)) {
-        d = DataPointer(Data::allocate(0), 0);
+        d = DataPointer::fromRawData(&_empty, 0);
     } else {
         if (size < 0)
             size = qstrlen(str);
@@ -5065,11 +5061,10 @@ QString QString::fromLocal8Bit_helper(const char *str, int size)
 {
     if (!str)
         return QString();
-    if (size == 0 || (!*str && size < 0)) {
-        QPair<Data *, char16_t *> pair = Data::allocate(0);
-        QString::DataPointer empty = { pair.first, pair.second, 0 };
-        return QString(std::move(empty));
-    }
+    if (size < 0)
+        size = qstrlen(str);
+    if (size == 0)
+        return QString(DataPointer::fromRawData(&_empty, 0));
     QStringDecoder toUtf16(QStringDecoder::System, QStringDecoder::Flag::Stateless);
     return toUtf16(str, size);
 }
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index da553ddde4..2db2e8cb85 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -1469,7 +1469,7 @@ public:
     inline const QChar *unicode() const
     {
         if (!m_string)
-            return reinterpret_cast<const QChar *>(QString::Data::sharedNullData());
+            return reinterpret_cast<const QChar *>(&QString::_empty);
         return m_string->unicode() + m_position;
     }
     inline const QChar *data() const { return unicode(); }
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