[tree-ssa]: out-of-ssa breaks if something adds a pred

[Chris Lattner]

Daniel Berlin said:

> When something ends up adding a predecessor block to a block with phi's
> in it, out-of-ssa breaks. This is because it expects all the phi's to
> have the same number of args/edges as preds, but phi's created *before*
> the pred was added have one less argument/edge.

...

> Unless i'm having a stupid moment, this really shouldn't be an abort
> case. If a phi doesn't have an argument for a given edge, it means
> nothing needs to be done for that edge, no?

IMO, this is a failure of the edge insertion routines or the caller of the
routine.  An invariant in SSA is that the number of entries in a PHI node
must be equal to the number of predecessors.  The out-of-ssa pass is
correct to break if this is not true...

-Chris

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