QmlCompiler: Really fix writing into argument values

Arguments are now treated as registers "written" at the beginning of
the first basic block. By modeling them this way, we can avoid all the
complicated logic on whether to use a local or the arguments array when
accessing any particular one of them. Furthermore, we can detect whether
they are overwritten or not. If they are not overwritten, we can
initialize them as a const reference into the arguments array. This way
we save a copy.

Treating the arguments as generic registers causes the basic blocks pass
to aggressively adjust their types, pushing some conversions back into
the QML engine. This is good. Unused arguments become void, for example,
and don't have to be passed at all. However, we also need a special case
for QJSPrimitiveValue arguments now.

Pick-to: 6.4
Fixes: QTBUG-104462
Change-Id: I994bea0929bd508aa41db58dee4a7f12cd20f053
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Sami Shalayel <sami.shalayel@qt.io>

1 files changed, 23 insertions, 0 deletions

diff --git a/src/qml/jsapi/qjsprimitivevalue.cpp b/src/qml/jsapi/qjsprimitivevalue.cpp
index 7039d6387b..e094972c3a 100644
--- a/src/qml/jsapi/qjsprimitivevalue.cpp
+++ b/src/qml/jsapi/qjsprimitivevalue.cpp
@@ -131,6 +131,29 @@ QT_BEGIN_NAMESPACE
  */
 
 /*!
+  \fn QJSPrimitiveValue::QJSPrimitiveValue(QMetaType type, const void *value)
+  \since 6.4
+
+  Creates a QJSPrimitiveValue of type \a type, and initializes with
+  \a value if \a type can be stored in QJSPrimtiveValue. \a value must not
+  be nullptr in that case. If \a type cannot be stored this results in a
+  QJSPrimitiveValue of type Undefined.
+
+  Note that you have to pass the address of the variable you want stored.
+
+  Usually, you never have to use this constructor, use the one taking QVariant
+  instead.
+ */
+
+/*!
+  \fn QJSPrimitiveValue::QJSPrimitiveValue(const QVariant &value)
+
+  Creates a QJSPrimitiveValue from the contents of \a value if those contents
+  can be stored in QJSPrimtiveValue. Otherwise this results in a
+  QJSPrimitiveValue of type Undefined.
+ */
+
+/*!
   \fn bool QJSPrimitiveValue::toBoolean() const
 
   Returns the value coerced a boolean by JavaScript rules.