QMimeDatabase benchmark: port away from Q_FOREACH

The original code duplicated contained elements of a QStringList by
repeated appending it to itself, preventing the container from being
marked const.

Instead, keep a list of unique mime-types, and iterate over the list
eight times.

As a drive-by, port from QList to a C array ("never use a
dynamically-sized container for statically-sized data"), use u""_s
UDLs (since we're touching almost all lines of the function, anyway,
also in the unrelated mimeTypeForName() call).

This allows porting the Q_FOREACH loop (which anyway cannot deal with
C arrays) to a ranged for one (which can).

Pick-to: 6.6 6.5
Task-number: QTBUG-115839
Change-Id: I844ae38104bb2980ea194b85f9017a3e95791ea2
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 17 insertions, 12 deletions

diff --git a/tests/benchmarks/corelib/mimetypes/qmimedatabase/tst_bench_qmimedatabase.cpp b/tests/benchmarks/corelib/mimetypes/qmimedatabase/tst_bench_qmimedatabase.cpp
index bd30c5b812..3f6a5cc969 100644
--- a/tests/benchmarks/corelib/mimetypes/qmimedatabase/tst_bench_qmimedatabase.cpp
+++ b/tests/benchmarks/corelib/mimetypes/qmimedatabase/tst_bench_qmimedatabase.cpp
@@ -53,22 +53,27 @@ void tst_QMimeDatabase::inheritsPerformance()
 {
     // Check performance of inherits().
     // This benchmark (which started in 2009 in kmimetypetest.cpp) uses 40 mimetypes.
-    QStringList mimeTypes;
-    mimeTypes << QLatin1String("image/jpeg") << QLatin1String("image/png") << QLatin1String("image/tiff") << QLatin1String("text/plain") << QLatin1String("text/html");
-    mimeTypes += mimeTypes;
-    mimeTypes += mimeTypes;
-    mimeTypes += mimeTypes;
-    QCOMPARE(mimeTypes.size(), 40);
+    // (eight groups of five unique ones)
+    const QString uniqueMimeTypes[] = {
+        u"image/jpeg"_s,
+        u"image/png"_s,
+        u"image/tiff"_s,
+        u"text/plain"_s,
+        u"text/html"_s,
+    };
+    constexpr size_t NumOuterLoops = 40 / std::size(uniqueMimeTypes);
     QMimeDatabase db;
-    QMimeType mime = db.mimeTypeForName(QString::fromLatin1("text/x-chdr"));
+    const QMimeType mime = db.mimeTypeForName(u"text/x-chdr"_s);
     QVERIFY(mime.isValid());
     QString match;
     QBENCHMARK {
-        for (const QString &mt : std::as_const(mimeTypes)) {
-            if (mime.inherits(mt)) {
-                match = mt;
-                // of course there would normally be a "break" here, but we're testing worse-case
-                // performance here
+        for (size_t i = 0; i < NumOuterLoops; ++i) {
+            for (const QString &mt : uniqueMimeTypes) {
+                if (mime.inherits(mt)) {
+                    match = mt;
+                    // of course there would normally be a "break" here, but
+                    // we're testing worse-case performance here
+                }
             }
         }
     }