From 8fc37349e32629c8cf84eae97e2e9d80b194de21 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Wed, 7 Feb 2024 11:56:38 +0100
Subject: [PATCH] QLibraryStore: cut out the QMap middle-man

In Qt 6, QMap is just a shared pointer to a std::map.

QLibraryStore::libraryMap is never copied, though, so the implicit
sharing that QMap adds on top of std::map is useless.

Use the underlying std::map directly.

Yes, the std::map API is a bit raw around the edges (std::pair
value_type), but we're professionals here.

This one saves more than 3.7KiB in TEXT size on optimized AMD64 GCC 11
C++20 Linux builds.

As a drive-by, port iterator- to range-based loops, and take advantage
of loop variables being real references now.

Change-Id: I1a8970b21e34a69d88a122f31699a51fd982feb9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
---
 src/corelib/plugin/qlibrary.cpp | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/src/corelib/plugin/qlibrary.cpp b/src/corelib/plugin/qlibrary.cpp
index 622b244d19..a3ef8e3c52 100644
--- a/src/corelib/plugin/qlibrary.cpp
+++ b/src/corelib/plugin/qlibrary.cpp
@@ -11,7 +11,6 @@
 #include <qfile.h>
 #include <qfileinfo.h>
 #include <qjsondocument.h>
-#include <qmap.h>
 #include <qmutex.h>
 #include <qoperatingsystemversion.h>
 #include <qstringlist.h>
@@ -30,6 +29,8 @@
 
 #include <qtcore_tracepoints_p.h>
 
+#include <QtCore/q20map.h>
+
 QT_BEGIN_NAMESPACE
 
 using namespace Qt::StringLiterals;
@@ -321,7 +322,7 @@ private:
     static inline QLibraryStore *instance();
 
     // all members and instance() are protected by qt_library_mutex
-    typedef QMap<QString, QLibraryPrivate *> LibraryMap;
+    typedef std::map<QString, QLibraryPrivate *> LibraryMap;
     LibraryMap libraryMap;
 };
 
@@ -341,9 +342,7 @@ inline void QLibraryStore::cleanup()
         return;
 
     // find any libraries that are still loaded but have a no one attached to them
-    LibraryMap::Iterator it = data->libraryMap.begin();
-    for (; it != data->libraryMap.end(); ++it) {
-        QLibraryPrivate *lib = it.value();
+    for (auto &[_, lib] : data->libraryMap) {
         if (lib->libraryRefCount.loadRelaxed() == 1) {
             if (lib->libraryUnloadCount.loadRelaxed() > 0) {
                 Q_ASSERT(lib->pHnd.loadRelaxed());
@@ -357,14 +356,13 @@ inline void QLibraryStore::cleanup()
                 lib->unload();
 #endif
             }
-            delete lib;
-            it.value() = nullptr;
+            delete std::exchange(lib, nullptr);
         }
     }
 
     // dump all objects that remain
     if (lcDebugLibrary().isDebugEnabled()) {
-        for (QLibraryPrivate *lib : std::as_const(data->libraryMap)) {
+        for (auto &[_, lib] : data->libraryMap) {
             if (lib)
                 qDebug(lcDebugLibrary)
                         << "On QtCore unload," << lib->fileName << "was leaked, with"
@@ -440,8 +438,9 @@ inline void QLibraryStore::releaseLibrary(QLibraryPrivate *lib)
     Q_ASSERT(lib->libraryUnloadCount.loadRelaxed() == 0);
 
     if (Q_LIKELY(data) && !lib->fileName.isEmpty()) {
-        qsizetype n = erase_if(data->libraryMap, [lib](LibraryMap::iterator it) {
-            return it.value() == lib;
+        using q20::erase_if;
+        const auto n = erase_if(data->libraryMap, [lib](const auto &e) {
+            return e.second == lib;
         });
         Q_ASSERT_X(n, "~QLibrary", "Did not find this library in the library map");
         Q_UNUSED(n);