Python: Test demonstrating the need for phi-read-nodes

[yoff]

Or for a data flow node filling that role, at least.

[hvitved]

You could also add a test for normal phi nodes, i.e. something like

    if(cond > 3):
      if(cond > 2):
        if(cond > 1):
           pass
        else:
          x = 1
      else:
        x = 2
    else:
      x = 3

    if(cond > 3):
      if(cond > 2):
        if(cond > 1):
           pass
        else:
          use(x)
      else:
        use(x)
    else:
      use(x)

[yoff]

I put that in #14861. (Looks like I came to the exact same example :-))