QTranslator: Extract Method is_readable_file from find_translation()

The old code re-used a QFileInfo object, repeatedly
setting new file names with QFileInfo::setFile(QString).

But QFileInfo::setFile() simply assigns itself a
new QFileInfo object:
    *this = QFileInfo(...)
so it's just as efficient to re-create a new QFIleInfo
object for every file name under test.

To avoid extra {} for object lifetime scoping, factor
the repeated evaluation of isReadable() && isFile()
into a small helper function, which also creates and
destroys the QFileInfo object.

The deeper significance of this change is that it
avoids implicit sharing of 'realname', which is
permanently modified. A later patch will make
changes that make 'realname' re-use its capacity
through the lifetime of the find_translation()
function, and sharing the variable implicitly will
nip any auch attempts in the bud.

Force the compiler to not inline the new function.
There's really no point in spending ~0.5KiB in text
size on inlining the code; the miniscule speed
improvement is dwarfed by the memory allocation of
the QFileInfo ctor, anyway.

As a consequence, this change even saves 96b in text
size on optimized GCC 4.9 Linux AMD64 builds, even
though that wasn't even the goal.

Change-Id: I08c5cbb7b6f1ba59440a1597e28d962ce63a7c65
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 14 insertions, 15 deletions

diff --git a/src/corelib/kernel/qtranslator.cpp b/src/corelib/kernel/qtranslator.cpp
index 794a4aaa0c..b5a941c205 100644
--- a/src/corelib/kernel/qtranslator.cpp
+++ b/src/corelib/kernel/qtranslator.cpp
@@ -613,6 +613,13 @@ bool QTranslatorPrivate::do_load(const QString &realname, const QString &directo
     return false;
 }
 
+Q_NEVER_INLINE
+static bool is_readable_file(const QString &name)
+{
+    const QFileInfo fi(name);
+    return fi.isReadable() && fi.isFile();
+}
+
 static QString find_translation(const QLocale & locale,
                                 const QString & filename,
                                 const QString & prefix,
@@ -626,7 +633,6 @@ static QString find_translation(const QLocale & locale,
             path += QLatin1Char('/');
     }
 
-    QFileInfo fi;
     QString realname;
     QStringList fuzzyLocales;
 
@@ -647,13 +653,11 @@ static QString find_translation(const QLocale & locale,
         localeName.replace(QLatin1Char('-'), QLatin1Char('_'));
 
         realname = path + filename + prefix + localeName + (suffix.isNull() ? QLatin1String(".qm") : suffix);
-        fi.setFile(realname);
-        if (fi.isReadable() && fi.isFile())
+        if (is_readable_file(realname))
             return realname;
 
         realname = path + filename + prefix + localeName;
-        fi.setFile(realname);
-        if (fi.isReadable() && fi.isFile())
+        if (is_readable_file(realname))
             return realname;
 
         fuzzyLocales.append(localeName);
@@ -669,32 +673,27 @@ static QString find_translation(const QLocale & locale,
             localeName.truncate(rightmost);
 
             realname = path + filename + prefix + localeName + (suffix.isNull() ? QLatin1String(".qm") : suffix);
-            fi.setFile(realname);
-            if (fi.isReadable() && fi.isFile())
+            if (is_readable_file(realname))
                 return realname;
 
             realname = path + filename + prefix + localeName;
-            fi.setFile(realname);
-            if (fi.isReadable() && fi.isFile())
+            if (is_readable_file(realname))
                 return realname;
         }
     }
 
     if (!suffix.isNull()) {
         realname = path + filename + suffix;
-        fi.setFile(realname);
-        if (fi.isReadable() && fi.isFile())
+        if (is_readable_file(realname))
             return realname;
     }
 
     realname = path + filename + prefix;
-    fi.setFile(realname);
-    if (fi.isReadable() && fi.isFile())
+    if (is_readable_file(realname))
         return realname;
 
     realname = path + filename;
-    fi.setFile(realname);
-    if (fi.isReadable() && fi.isFile())
+    if (is_readable_file(realname))
         return realname;
 
     return QString();