[PATCH] Handle some cases of mismatched types in IRCE

[hfinkel at anl.gov]

In http://reviews.llvm.org/D7082#112586, @sanjoy wrote:

> > This sounds like a bug in indvars. Is it obvious how to fix it there?
>
>
> I think this is intentional -- `IndVarSimplify` has code to deal with this when verifying that the loop-backedge counts have not changed:
>
> https://github.com/llvm-mirror/llvm/blob/master/lib/Transforms/Scalar/IndVarSimplify.cpp#L2026


Intentional or not, I think this is a bad idea. The results of an analysis should not depend on what transformations were run previously, but only on the current state of the IR. Do you agree?

If nothing else, there should at least be a loud warning about it on the interface to getBackedgeTakenCount in ScalarEvolution.h. I'd rather fix this so that we can get the backedge count of the proper size (maybe we need a better updating interface in SE? -- IndVars seems to *have* the correct updated BETC).


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