Clarify SCEV code which handle powers of 2

[Mark Heffernan]

r224274.

On Mon, Dec 15, 2014 at 1:12 PM, Andrew Trick <atrick at apple.com> wrote:

>
> > On Dec 15, 2014, at 1:02 PM, Mark Heffernan <meheff at google.com> wrote:
> >
> > Hi Andy,
> >
> > As discussed in the patch for fixing PR21694, here's a little patch
> which clarifies the HowFarToZero computation when the step is a positive
> power of two.  Functionally this should be identical to the existing code
> except for the case where Step is maximally negative (eg, INT_MIN).  We now
> punt in that one corner case to make reasoning about the code easier.
> >
> > Mark
> > <scev_clearup.patch>
>
> Perfect. Thanks Mark.
> -Andy
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