tests: fix some -Wvolatile

C++20 deprecated compound volatile statements such as pre- and
post-increments, to stress that they're not atomic. So instead of

    volatile i;
    ~~~~;
    ++i;

you're now supposed to write

    volatile i;
    ~~~~;
    int j = i; // volatile load
    ++j;
    i = j; // volatile store

which matches more closely what hardware does.

Instead of fixing every use of volatile pre- or post-increment in this
fashion individually, and realising that probably a few more Qt
modules will have the same kind of code patterns in them, write
QtPrivate functions to do the job centrally.

Change-Id: I838097bd484ef2118c071726963f103c080d2ba5
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 5 insertions, 3 deletions

diff --git a/tests/benchmarks/corelib/thread/qmutex/CMakeLists.txt b/tests/benchmarks/corelib/thread/qmutex/CMakeLists.txt
index 8872a50227..923bfba117 100644
--- a/tests/benchmarks/corelib/thread/qmutex/CMakeLists.txt
+++ b/tests/benchmarks/corelib/thread/qmutex/CMakeLists.txt
@@ -8,6 +8,7 @@ qt_internal_add_benchmark(tst_bench_qmutex
     SOURCES
         tst_qmutex.cpp
     PUBLIC_LIBRARIES
+        Qt::CorePrivate
         Qt::Test
 )
 
diff --git a/tests/benchmarks/corelib/thread/qmutex/tst_qmutex.cpp b/tests/benchmarks/corelib/thread/qmutex/tst_qmutex.cpp
index 9cea995433..9b14cbca5d 100644
--- a/tests/benchmarks/corelib/thread/qmutex/tst_qmutex.cpp
+++ b/tests/benchmarks/corelib/thread/qmutex/tst_qmutex.cpp
@@ -28,6 +28,7 @@
 
 #include <QtCore/QtCore>
 #include <QTest>
+#include <QtCore/private/qvolatile_p.h>
 
 #include <math.h>
 
@@ -158,7 +159,7 @@ void tst_QMutex::noThread()
             QBENCHMARK {
                 count = 0;
                 for (int i = 0; i < N; i++) {
-                    count++;
+                    QtPrivate::volatilePreIncrement(count);
                 }
             }
             break;
@@ -167,7 +168,7 @@ void tst_QMutex::noThread()
                 count = 0;
                 for (int i = 0; i < N; i++) {
                     mtx.lock();
-                    count++;
+                    QtPrivate::volatilePreIncrement(count);
                     mtx.unlock();
                 }
             }
@@ -177,7 +178,7 @@ void tst_QMutex::noThread()
                 count = 0;
                 for (int i = 0; i < N; i++) {
                     QMutexLocker locker(&mtx);
-                    count++;
+                    QtPrivate::volatilePreIncrement(count);
                 }
             }
             break;