QLogging: use return-by-value in qt_message

This also enables NRVO in almost all callers (a macro
prevents it in one case), saving one default construction
and one (move) assignment per call.

Effects on Linux GCC 4.9 stripped release builds:
 text   -896B
 data    +-0B
 relocs  +-0

Change-Id: Id3cde01057baaa408c4cbf95d8d15eaeeeec1604
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 16 insertions, 40 deletions

diff --git a/src/corelib/global/qlogging.cpp b/src/corelib/global/qlogging.cpp
index ca27ba26ca..d8f5b59c63 100644
--- a/src/corelib/global/qlogging.cpp
+++ b/src/corelib/global/qlogging.cpp
@@ -249,11 +249,11 @@ static inline void convert_to_wchar_t_elided(wchar_t *d, size_t space, const cha
     \internal
 */
 Q_NEVER_INLINE
-static void qt_message(QtMsgType msgType, const QMessageLogContext &context, const char *msg,
-                       va_list ap, QString &buf)
+static QString qt_message(QtMsgType msgType, const QMessageLogContext &context, const char *msg, va_list ap)
 {
-    buf = QString::vasprintf(msg, ap);
+    QString buf = QString::vasprintf(msg, ap);
     qt_message_print(msgType, context, buf);
+    return buf;
 }
 
 #undef qDebug
@@ -265,11 +265,9 @@ static void qt_message(QtMsgType msgType, const QMessageLogContext &context, con
 */
 void QMessageLogger::debug(const char *msg, ...) const
 {
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtDebugMsg, context, msg, ap, message);
+    const QString message = qt_message(QtDebugMsg, context, msg, ap);
     va_end(ap);
 
     if (isFatal(QtDebugMsg))
@@ -287,11 +285,9 @@ void QMessageLogger::debug(const char *msg, ...) const
 */
 void QMessageLogger::info(const char *msg, ...) const
 {
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtInfoMsg, context, msg, ap, message);
+    const QString message = qt_message(QtInfoMsg, context, msg, ap);
     va_end(ap);
 
     if (isFatal(QtInfoMsg))
@@ -328,11 +324,9 @@ void QMessageLogger::debug(const QLoggingCategory &cat, const char *msg, ...) co
     ctxt.copy(context);
     ctxt.category = cat.categoryName();
 
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtDebugMsg, ctxt, msg, ap, message);
+    const QString message = qt_message(QtDebugMsg, ctxt, msg, ap);
     va_end(ap);
 
     if (isFatal(QtDebugMsg))
@@ -357,11 +351,9 @@ void QMessageLogger::debug(QMessageLogger::CategoryFunction catFunc,
     ctxt.copy(context);
     ctxt.category = cat.categoryName();
 
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtDebugMsg, ctxt, msg, ap, message);
+    const QString message = qt_message(QtDebugMsg, ctxt, msg, ap);
     va_end(ap);
 
     if (isFatal(QtDebugMsg))
@@ -443,11 +435,9 @@ void QMessageLogger::info(const QLoggingCategory &cat, const char *msg, ...) con
     ctxt.copy(context);
     ctxt.category = cat.categoryName();
 
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtInfoMsg, ctxt, msg, ap, message);
+    const QString message = qt_message(QtInfoMsg, ctxt, msg, ap);
     va_end(ap);
 
     if (isFatal(QtInfoMsg))
@@ -472,11 +462,9 @@ void QMessageLogger::info(QMessageLogger::CategoryFunction catFunc,
     ctxt.copy(context);
     ctxt.category = cat.categoryName();
 
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtInfoMsg, ctxt, msg, ap, message);
+    const QString message = qt_message(QtInfoMsg, ctxt, msg, ap);
     va_end(ap);
 
     if (isFatal(QtInfoMsg))
@@ -540,11 +528,9 @@ QDebug QMessageLogger::info(QMessageLogger::CategoryFunction catFunc) const
 */
 void QMessageLogger::warning(const char *msg, ...) const
 {
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtWarningMsg, context, msg, ap, message);
+    const QString message = qt_message(QtWarningMsg, context, msg, ap);
     va_end(ap);
 
     if (isFatal(QtWarningMsg))
@@ -567,11 +553,9 @@ void QMessageLogger::warning(const QLoggingCategory &cat, const char *msg, ...)
     ctxt.copy(context);
     ctxt.category = cat.categoryName();
 
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtWarningMsg, ctxt, msg, ap, message);
+    const QString message = qt_message(QtWarningMsg, ctxt, msg, ap);
     va_end(ap);
 
     if (isFatal(QtWarningMsg))
@@ -596,11 +580,9 @@ void QMessageLogger::warning(QMessageLogger::CategoryFunction catFunc,
     ctxt.copy(context);
     ctxt.category = cat.categoryName();
 
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtWarningMsg, ctxt, msg, ap, message);
+    const QString message = qt_message(QtWarningMsg, ctxt, msg, ap);
     va_end(ap);
 
     if (isFatal(QtWarningMsg))
@@ -662,11 +644,9 @@ QDebug QMessageLogger::warning(QMessageLogger::CategoryFunction catFunc) const
 */
 void QMessageLogger::critical(const char *msg, ...) const
 {
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtCriticalMsg, context, msg, ap, message);
+    const QString message = qt_message(QtCriticalMsg, context, msg, ap);
     va_end(ap);
 
     if (isFatal(QtCriticalMsg))
@@ -689,11 +669,9 @@ void QMessageLogger::critical(const QLoggingCategory &cat, const char *msg, ...)
     ctxt.copy(context);
     ctxt.category = cat.categoryName();
 
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtCriticalMsg, ctxt, msg, ap, message);
+    const QString message = qt_message(QtCriticalMsg, ctxt, msg, ap);
     va_end(ap);
 
     if (isFatal(QtCriticalMsg))
@@ -718,11 +696,9 @@ void QMessageLogger::critical(QMessageLogger::CategoryFunction catFunc,
     ctxt.copy(context);
     ctxt.category = cat.categoryName();
 
-    QString message;
-
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    qt_message(QtCriticalMsg, ctxt, msg, ap, message);
+    const QString message = qt_message(QtCriticalMsg, ctxt, msg, ap);
     va_end(ap);
 
     if (isFatal(QtCriticalMsg))
@@ -788,7 +764,7 @@ void QMessageLogger::fatal(const char *msg, ...) const Q_DECL_NOTHROW
 
     va_list ap;
     va_start(ap, msg); // use variable arg list
-    QT_TERMINATE_ON_EXCEPTION(qt_message(QtFatalMsg, context, msg, ap, message));
+    QT_TERMINATE_ON_EXCEPTION(message = qt_message(QtFatalMsg, context, msg, ap));
     va_end(ap);
 
     qt_message_fatal(QtFatalMsg, context, message);