From 33159f5e0f18a6d9f4ca015bfb9a2a53089d1dfa Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Sat, 10 Feb 2024 12:49:43 -0800
Subject: [PATCH] QDataStream: make the public-ish private members smaller in
 Qt 7

pahole says:
  class QScopedPointer<QDataStreamPrivate> d;      /*     0     8 */
  class QIODevice *          dev;                  /*     8     8 */
  bool                       owndev;               /*    16     1 */
  bool                       noswap;               /*    17     1 */
  quint8                     fpPrecision;          /*    18     1 */
  quint8                     q_status;             /*    19     1 */
  enum ByteOrder             byteorder;            /*    20     4 */
  int                        ver;                  /*    24     4 */
  quint16                    transactionDepth;     /*    28     2 */
  /* size: 32, cachelines: 1, members: 10 */

Which is unnecessary overhead. The previous commit took care of
byteorder for Qt 7; this one reduces the size a bit more, to 16 bytes on
32-bit systems and 24 on 64-bit ones.

After this, pahole says for the bootstrap library:
  class QScopedPointer<QDataStreamPrivate> d;      /*     0     8 */
  class QIODevice *          dev;                  /*     8     8 */
  bool                       owndev;               /*    16     1 */
  bool                       noswap;               /*    17     1 */
  quint8                     fpPrecision;          /*    18     1 */
  quint8                     q_status;             /*    19     1 */
  enum Version               ver;                  /*    20     1 */
  /* XXX 1 byte hole, try to pack */
  quint16                    transactionDepth;     /*    22     2 */
  /* size: 24, cachelines: 1, members: 9 */

Further packing isn't possible, because of the alignment at 64-bit for
this class.

Change-Id: I50e2158aeade4256ad1dfffd17b29b80237a8c5b
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
---
 src/corelib/serialization/qdatastream.h | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/corelib/serialization/qdatastream.h b/src/corelib/serialization/qdatastream.h
index 36d8a618ff..d3932372fa 100644
--- a/src/corelib/serialization/qdatastream.h
+++ b/src/corelib/serialization/qdatastream.h
@@ -45,7 +45,7 @@ QDataStream &writeAssociativeMultiContainer(QDataStream &s, const Container &c);
 class Q_CORE_EXPORT QDataStream : public QIODeviceBase
 {
 public:
-    enum Version {
+    enum Version QT7_ONLY(: quint8) {
         Qt_1_0 = 1,
         Qt_2_0 = 2,
         Qt_2_1 = 3,
@@ -98,7 +98,7 @@ public:
         LittleEndian = QSysInfo::LittleEndian
     };
 
-    enum Status {
+    enum Status QT7_ONLY(: quint8) {
         Ok,
         ReadPastEnd,
         ReadCorruptData,
@@ -106,7 +106,7 @@ public:
         SizeLimitExceeded,
     };
 
-    enum FloatingPointPrecision {
+    enum FloatingPointPrecision QT7_ONLY(: quint8) {
         SinglePrecision,
         DoublePrecision
     };
@@ -223,8 +223,10 @@ private:
     quint8 q_status = Ok;
 #if QT_VERSION < QT_VERSION_CHECK(7, 0, 0) && !defined(QT_BOOTSTRAPPED)
     ByteOrder byteorder = BigEndian;
-#endif
     int ver = Qt_DefaultCompiledVersion;
+#else
+    Version ver = Qt_DefaultCompiledVersion;
+#endif
     quint16 transactionDepth = 0;
 
 #if QT_CORE_REMOVED_SINCE(6, 7)
@@ -450,7 +452,7 @@ inline int QDataStream::version() const
 { return ver; }
 
 inline void QDataStream::setVersion(int v)
-{ ver = v; }
+{ ver = Version(v); }
 
 qint64 QDataStream::readQSizeType(QDataStream &s)
 {