benchmarks: fix some (future) -Wunused-result warnings

Clang 10 warns about unused results of relational operators, which is
where this is coming from.

Fix by adding the usual prefix

  [[maybe_unused]] auto r = ~~~;

to silence the warning. Do this elsewhere, too, since [[nodiscard]] is
slowly being rolled out across all our APIs. This is not a complete
sweep, though.

Not picking to 5.15, because this pattern doesn't work there and I
don't want to introduce a new one.

Pick-to: 6.3 6.2
Change-Id: I40dd8ad07496b686979dce533e044cbb486e30f3
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

tests/benchmarks/corelib/io/qurl/tst_bench_qurl.cpp

@@ -188,7 +188,7 @@ void tst_QUrl::equality()
         QUrl url("pics/avatar.png");
         QUrl url2("pics/avatar2.png");
         QBENCHMARK {
-            url == url2;
+            [[maybe_unused]] auto r = url == url2;
         }
     }
 }

tests/benchmarks/corelib/plugin/quuid/tst_bench_quuid.cpp

@@ -55,7 +55,7 @@ private slots:
 void tst_QUuid::createUuid()
 {
     QBENCHMARK {
-        QUuid::createUuid();
+        [[maybe_unused]] auto r = QUuid::createUuid();
     }
 }
 
@@ -70,7 +70,7 @@ void tst_QUuid::toString()
 {
     QUuid uuid = QUuid::createUuid();
     QBENCHMARK {
-        uuid.toString();
+        [[maybe_unused]] auto r = uuid.toString();
     }
 }
 
@@ -86,7 +86,7 @@ void tst_QUuid::toByteArray()
 {
     QUuid uuid = QUuid::createUuid();
     QBENCHMARK {
-        uuid.toByteArray();
+        [[maybe_unused]] auto r = uuid.toByteArray();
     }
 }
 
@@ -102,7 +102,7 @@ void tst_QUuid::toRfc4122()
 {
     QUuid uuid = QUuid::createUuid();
     QBENCHMARK {
-        uuid.toRfc4122();
+        [[maybe_unused]] auto r = uuid.toRfc4122();
     }
 }
 
@@ -168,7 +168,7 @@ void tst_QUuid::isNull()
 {
     QUuid uuid = QUuid();
     QBENCHMARK {
-        uuid.isNull();
+        [[maybe_unused]] auto r = uuid.isNull();
     }
 }
 
@@ -178,7 +178,7 @@ void tst_QUuid::operatorLess()
     uuid1 = QUuid::createUuid();
     uuid2 = QUuid::createUuid();
     QBENCHMARK {
-        uuid1 < uuid2;
+        [[maybe_unused]] auto r = uuid1 < uuid2;
     }
 }
 
@@ -188,7 +188,7 @@ void tst_QUuid::operatorMore()
     uuid1 = QUuid::createUuid();
     uuid2 = QUuid::createUuid();
     QBENCHMARK {
-        uuid1 > uuid2;
+        [[maybe_unused]] auto r = uuid1 > uuid2;
     }
 }
 

tests/benchmarks/gui/painting/qtransform/tst_qtransform.cpp

@@ -266,7 +266,7 @@ void tst_QTransform::operatorEqual()
     QFETCH(QTransform, x2);
     QTransform x = x1;
     QBENCHMARK {
-        x == x2;
+        [[maybe_unused]] auto r = x == x2;
     }
 }
 
@@ -278,7 +278,7 @@ void tst_QTransform::operatorNotEqual()
     QFETCH(QTransform, x2);
     QTransform x = x1;
     QBENCHMARK {
-        x != x2;
+        [[maybe_unused]] auto r = x != x2;
     }
 }
 
@@ -290,7 +290,7 @@ void tst_QTransform::operatorMultiply()
     QFETCH(QTransform, x2);
     QTransform x = x1;
     QBENCHMARK {
-        x * x2;
+        [[maybe_unused]] auto r = x * x2;
     }
 }
 
@@ -357,7 +357,7 @@ void tst_QTransform::mapQPoint()
     QFETCH(QTransform, transform);
     QTransform x = transform;
     QBENCHMARK {
-        x.map(QPoint(3, 3));
+        [[maybe_unused]] auto r = x.map(QPoint(3, 3));
     }
 }
 
@@ -368,7 +368,7 @@ void tst_QTransform::mapQPointF()
     QFETCH(QTransform, transform);
     QTransform x = transform;
     QBENCHMARK {
-        x.map(QPointF(3, 3));
+        [[maybe_unused]] auto r = x.map(QPointF(3, 3));
     }
 }
 
@@ -379,7 +379,7 @@ void tst_QTransform::mapRect()
     QFETCH(QTransform, transform);
     QTransform x = transform;
     QBENCHMARK {
-        x.mapRect(QRect(0, 0, 100, 100));
+        [[maybe_unused]] auto r = x.mapRect(QRect(0, 0, 100, 100));
     }
 }
 
@@ -390,7 +390,7 @@ void tst_QTransform::mapRectF()
     QFETCH(QTransform, transform);
     QTransform x = transform;
     QBENCHMARK {
-        x.mapRect(QRectF(0, 0, 100, 100));
+        [[maybe_unused]] auto r = x.mapRect(QRectF(0, 0, 100, 100));
     }
 }
 
@@ -402,7 +402,7 @@ void tst_QTransform::mapQPolygon()
     QTransform x = transform;
     QPolygon poly = QPolygon(QRect(0, 0, 100, 100));
     QBENCHMARK {
-        x.map(poly);
+        [[maybe_unused]] auto r = x.map(poly);
     }
 }
 
@@ -414,7 +414,7 @@ void tst_QTransform::mapQPolygonF()
     QTransform x = transform;
     QPolygonF poly = QPolygonF(QRectF(0, 0, 100, 100));
     QBENCHMARK {
-        x.map(poly);
+        [[maybe_unused]] auto r = x.map(poly);
     }
 }
 
@@ -428,7 +428,7 @@ void tst_QTransform::mapQRegion()
     for (int i = 0; i < 10; ++i)
         region += QRect(i * 10, i * 10, 100, 100);
     QBENCHMARK {
-        x.map(region);
+        [[maybe_unused]] auto r = x.map(region);
     }
 }
 
@@ -439,7 +439,7 @@ void tst_QTransform::mapToPolygon()
     QFETCH(QTransform, transform);
     QTransform x = transform;
     QBENCHMARK {
-        x.mapToPolygon(QRect(0, 0, 100, 100));
+        [[maybe_unused]] auto r = x.mapToPolygon(QRect(0, 0, 100, 100));
     }
 }
 
@@ -454,7 +454,7 @@ void tst_QTransform::mapQPainterPath()
     for (int i = 0; i < 10; ++i)
         path.addEllipse(i * 10, i * 10, 100, 100);
     QBENCHMARK {
-        x.map(path);
+        [[maybe_unused]] auto r = x.map(path);
     }
 }
 
@@ -464,7 +464,7 @@ void tst_QTransform::isIdentity()
 {
     QFETCH(QTransform, transform);
     QBENCHMARK {
-        transform.isIdentity();
+        [[maybe_unused]] auto r = transform.isIdentity();
     }
 }
 
@@ -474,7 +474,7 @@ void tst_QTransform::isAffine()
 {
     QFETCH(QTransform, transform);
     QBENCHMARK {
-        transform.isAffine();
+        [[maybe_unused]] auto r = transform.isAffine();
     }
 }
 
@@ -484,7 +484,7 @@ void tst_QTransform::isInvertible()
 {
     QFETCH(QTransform, transform);
     QBENCHMARK {
-        transform.isInvertible();
+        [[maybe_unused]] auto r = transform.isInvertible();
     }
 }
 
@@ -494,7 +494,7 @@ void tst_QTransform::isRotating()
 {
     QFETCH(QTransform, transform);
     QBENCHMARK {
-        transform.isRotating();
+        [[maybe_unused]] auto r = transform.isRotating();
     }
 }
 
@@ -504,7 +504,7 @@ void tst_QTransform::isScaling()
 {
     QFETCH(QTransform, transform);
     QBENCHMARK {
-        transform.isScaling();
+        [[maybe_unused]] auto r = transform.isScaling();
     }
 }
 
@@ -514,7 +514,7 @@ void tst_QTransform::isTranslating()
 {
     QFETCH(QTransform, transform);
     QBENCHMARK {
-        transform.isTranslating();
+        [[maybe_unused]] auto r = transform.isTranslating();
     }
 }
 
@@ -524,7 +524,7 @@ void tst_QTransform::type()
 {
     QFETCH(QTransform, transform);
     QBENCHMARK {
-        transform.type();
+        [[maybe_unused]] auto r = transform.type();
     }
 }
 
@@ -534,7 +534,7 @@ void tst_QTransform::determinant()
 {
     QFETCH(QTransform, transform);
     QBENCHMARK {
-        transform.determinant();
+        [[maybe_unused]] auto r = transform.determinant();
     }
 }