Question about pre_edge_insert () in gcse.c

[Daniel Berlin]

> If what I'm saying here is correct, some redundant expression might
> be inserted.

We have testcases (search bugzilla for GCSE) with redundant expressions
being inserted by GCSE (repeatedly, such that if you run GCSE 5 times,
it inserts the same expression 5 times in the same place).  If you are
correct, some of these should be fixed by changing that.

--Dan