Optimize QString::insert()

When the insertion position is not beyond end(), call
resize() instead of expand(), which fills the new size
with spaces, which, however would just be overwritten
by the following memmove().

Add some Q_UNLIKELY to indicate that we strongly
expect the resize() case to be the more common.

Change-Id: Iaf3215dd53c2cbd18f2fd8a5f80af8f6844944da
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Anton Kudryavtsev <a.kudryavtsev@netris.ru>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 12 insertions, 3 deletions

diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp
index 629a0bc744..9dc7136d2a 100644
--- a/src/corelib/tools/qstring.cpp
+++ b/src/corelib/tools/qstring.cpp
@@ -1985,7 +1985,10 @@ QString &QString::insert(int i, QLatin1String str)
         return *this;
 
     int len = str.size();
-    expand(qMax(d->size, i) + len - 1);
+    if (Q_UNLIKELY(i > d->size))
+        expand(i + len - 1);
+    else
+        resize(d->size + len);
 
     ::memmove(d->data() + i + len, d->data() + i, (d->size - i - len) * sizeof(QChar));
     qt_from_latin1(d->data() + i, s, uint(len));
@@ -2015,7 +2018,10 @@ QString& QString::insert(int i, const QChar *unicode, int size)
         return *this;
     }
 
-    expand(qMax(d->size, i) + size - 1);
+    if (Q_UNLIKELY(i > d->size))
+        expand(i + size - 1);
+    else
+        resize(d->size + size);
 
     ::memmove(d->data() + i + size, d->data() + i, (d->size - i - size) * sizeof(QChar));
     memcpy(d->data() + i, s, size * sizeof(QChar));
@@ -2035,7 +2041,10 @@ QString& QString::insert(int i, QChar ch)
         i += d->size;
     if (i < 0)
         return *this;
-    expand(qMax(i, d->size));
+    if (Q_UNLIKELY(i > d->size))
+        expand(i);
+    else
+        resize(d->size + 1);
     ::memmove(d->data() + i + 1, d->data() + i, (d->size - i - 1) * sizeof(QChar));
     d->data()[i] = ch.unicode();
     return *this;