1. Open src/gui/kernel/qkeysequence.cpp.
2. Put a breakpoint on line 1458.
3. Debug this app:

#include <QtGui>

#if (QT_VERSION >= QT_VERSION_CHECK(5, 0, 0))
#include <QtWidgets>
#endif

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    qDebug() << QKeySequence(Qt::Key_Cancel).toString();

    return 0;
}

4. Add the expression "keyname" to the Locals and Expressions window.
5. Click on the expand icon of the expression. It will take roughly 20 seconds to display the elements. Expanding any of the elements themselves takes the same amount of time.