QmlCompiler: Implement ConvertThisToObject and basic DTZ

We know that 'this' is a QObject* since the metatypes stack frame
mandates it. Whenever you pass 'this' to anything it's loaded from the
special 'This' stack slot which then triggers a DTZ check. A DTZ check
is a noop if we can prove that the type is statically known, though.

In QmlCompiler, if we have a valid register content, then the register
has been set in all code paths that lead to the instruction in question.

Fixes: QTBUG-111439
Change-Id: I81d1cd140eea63f85628c3bef3a8f6db0a12096d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
index 14cdee5501..6131224ef0 100644
--- a/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
+++ b/tests/auto/qml/qmlcppcodegen/tst_qmlcppcodegen.cpp
@@ -179,6 +179,7 @@ private slots:
     void boolPointerMerge();
     void mergedObjectReadWrite();
     void listConversion();
+    void thisObject();
 };
 
 void tst_QmlCppCodegen::initTestCase()
@@ -3611,7 +3612,16 @@ void tst_QmlCppCodegen::listConversion()
         QVariant::fromValue<qsizetype>(3),
         QVariant::fromValue<Person *>(nullptr)
     }));
+}
 
+void tst_QmlCppCodegen::thisObject()
+{
+    QQmlEngine e;
+    QQmlComponent c(&e, QUrl(u"qrc:/qt/qml/TestTypes/thisObject.qml"_s));
+    QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+    QScopedPointer<QObject> o(c.create());
+    QVERIFY(!o.isNull());
+    QCOMPARE(o->property("warned").value<QObject *>(), o.data());
 }
 
 QTEST_MAIN(tst_QmlCppCodegen)