[PATCH] Bugfix: SCEV incorrectly marks certain add recurrences as nsw

[Andrew Trick]

> On Feb 9, 2015, at 12:13 AM, Sanjoy Das <sanjoy at playingwithpointers.com> wrote:
> 
> In practice it seems the two places that actually do something with `<nw>` work only with a constant non-zero step size, so it is probably okay to remove the check.  But I think the comments in the header file should be changed to state that `<nw>` means that `step` is either `0` or `abs(step) * max-iteration(loop) <= unsigned-max(bitwidth)`.

It seems more natural to me that violating <nw> requires a non-zero step. If you agree, can you add those comments?

Andy

> 
> 
> http://reviews.llvm.org/D7495
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