[UniQP]

> So it's not impossible, but libfirm avoids it or performs the necessary phi insertion in various places to avoid creating invalid SSA for the representation it has.

It's impossible to have one edge pointing to multiple reaching definitions.

[DannyBee]

Of course, but I think you missed the point of what i said. Which was: It's possible to get into situations where that that node could have multiple possible reaching definitions, even if it only points to one at a given time. That is still not SSA. In that case, the edge is just wrong, even if it only points to one arbitrarily selected possible reaching definition.

In short: Your argument is "it's SSA because the data structures only allow for a single reaching definition". This is not right. If i don't insert phi nodes, and just have the IR point at random reaching definitions, it's not magically SSA, because there is not actually a unique reaching definition for each point, it just happens you've pointed the edges at arbitrarily selected reaching definitions (IE made the graph wrong :P)