Question about a few properties of ideal graph

[Roland Westrelin]

> Region/Phi are special cases because they merge multiple control
> flows. So if one of their inputs become top but all other inputs are
> not, the Region/Phi is still reachable.

Actually to be accurate, it also depends whether the Region is a loop
head or node. A back edge becoming top doesn't make the Region
unreachable.

Roland.