[PATCH] [Jump-Threading] Fixed jump threading hang issues (PR15386, PR15851)

[Rafael Ávila de Espíndola]

It is not clear why this check is the correct one.One issue is

* If in the first pass we update 3 BBs, and in the second pass we update 2, this will stop, right? How do you know that there is no further changes to be done?

The more important one is that it doesn't address the root of the problem. From the description it looks like two parts of the pass disagree as to what the canonical form is. Shouldn't we change one of them avoid the transformation?

What are the two forms that cause us to bounce back and forth?

The testcase should also use FileCheck to see that the output is in the canonical form (whatever we decide that to be).

http://reviews.llvm.org/D3991