Object function fails to compile when starting with endless loop

[ursgraf]

check with https://gitlab.ost.ch/tech/inf/teaching/sysp/fachausbildung/mikrocontroller/musterloesungen/-/blob/main/src/sysp/fachausb/wifi/WifiReceiverLED.java

[ursgraf]

while (true) {
IntPacket.Type type = wifi.intPacket.readInt();           
if (null == null) break;           
if (type == IntPacket.Type.None) break;
produces an internal error during: "Launching MusterLsg.deep". Cannot invoke "Object.equals(Object)" because "this.idom" is null
when if(null == null) comes before readInt() it works fine

[ursgraf]

What happens? Let's look at another example:
int c;
Object o;
public void m3() {
while (true) {
if (null == null) {c = 100;}
else if (o == null) {c = 200; break;}
}
}

the cfg is determined to be:
CFGNode nr:0 [0:6], is loop header, bckwd branches=1, idom=null, ref=1, visited:false
predecessor: [0:6]
successor: [0:6]

CFGNode nr:1 [16:23], idom=null, ref=0, visited:false
predecessor:
successor:

That looks reasonable: the first node is an endless loop with no connection to the second node. When calculating the SSA these nodes get sorted which fails in that particular case