[PATCH] Fix PR21694 - Revert improper use of divide in SCEV HowFarToZero computation

[Andrew Trick]

Sorry I didn't respond. I wasn't able to easily convince myself that this fixes the problem. Since this reverts to the previous implementation, I think it's a good change. But the code is written in a way that is extremely hard to reason about.

For example:

- StepV could be negative but still be a power of two, is this expected?

- Why are we checking GetMinTrailingZeros(getNegativeSCEV(Start)) instead of GetMinTrailingZeros(Distance)?

If we can only handle counting up here, lets be more clear about that.


http://reviews.llvm.org/D6546

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