QString/QByteArray: further inline the most common indexOf operations

In the case of QString, the vast majority of searches are case-
sensitive, so by inlining we make the user code call qustrchr() directly
instead of QtPrivate::findString(). In the case of QByteArray, the call
is to memchr(), which being a compiler intrinsic, may itself be inlined
or even just resolved at compile time.

In both cases, a great deal of searches use from=0.

Benchmark for QByteArray; before:
     8.83207052 nsecs per iteration
     22.01568546 CPU cycles per iteration, 2.49 GHz
     60.00000331 instructions per iteration, 2.725 instr/cycle
     21.00000281 branch instructions per iteration, 2.38 G/sec

After:
     6.42561493 nsecs per iteration
     16.01623130 CPU cycles per iteration, 2.49 GHz
     49.00000261 instructions per iteration, 3.059 instr/cycle
     18.00000211 branch instructions per iteration, 2.8 G/sec

This shaves 6 cycles in the execution and 11 instructions (3 of which
were branches), slightly improving the IPC raito, for the QByteArray
case. For QByteArrayView, there are 2 fewer instructions (1 a branch),
but the number of cycles is the same at 16.

Task-number: QTBUG-119750
Change-Id: Ica7a43f6147b49c187ccfffd179e2204ebb6a348
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/corelib/text/qstringview.h b/src/corelib/text/qstringview.h
index a598d7a445..76acbd92aa 100644
--- a/src/corelib/text/qstringview.h
+++ b/src/corelib/text/qstringview.h
@@ -456,6 +456,27 @@ inline QStringView qToStringViewIgnoringNull(const QStringLike &s) noexcept
                                    R{{char16_t(c), u'\0'}} ;
 }
 
+qsizetype QtPrivate::findString(QStringView str, qsizetype from, QChar ch, Qt::CaseSensitivity cs) noexcept
+{
+    if (from < -str.size()) // from < 0 && abs(from) > str.size(), avoiding overflow
+        return -1;
+    if (from < 0)
+        from = qMax(from + str.size(), qsizetype(0));
+    if (from < str.size()) {
+        const char16_t *s = str.utf16();
+        char16_t c = ch.unicode();
+        const char16_t *n = s + from;
+        const char16_t *e = s + str.size();
+        if (cs == Qt::CaseSensitive)
+            n = qustrchr(QStringView(n, e), c);
+        else
+            n = qustrcasechr(QStringView(n, e), c);
+        if (n != e)
+            return n - s;
+    }
+    return -1;
+}
+
 QT_END_NAMESPACE
 
 #endif /* QSTRINGVIEW_H */