bad optimisation for js Array in do while loop

On the example, there are 2 rectangles with same code except a print in the first rectangle.
If you click on the first rectangle, the result is good.
If you click on the second, there is the error:
qrc:/main.qml:48: TypeError: Cannot read property '0' of undefined

If we don't print all the values for the first rectangle, it also have the error and we can see the values:
for variable pieces:
[4,21,6,22,8,23,12,24,10,25,8,26,6,27,4,28,2,31,2,32,2,33,2,35,2,36,2,37,2,38,2,54]
qml: 2
for variable p:
qml: [2,54]
qml: undefined

To compile: qmake && make && ./jsoptim

The code was working fine with Qt5.7 and before.
The issue is with do-while loop, it works fine with a while loop.