[llvm] r185954 - ValueTracking: Fix bugs in isKnownToBeAPowerOfTwo

[Jay Foad]

On 9 July 2013 19:11, David Majnemer <david.majnemer at gmail.com> wrote:
> Author: majnemer
> Date: Tue Jul  9 13:11:10 2013
> New Revision: 185954
>
> URL: http://llvm.org/viewvc/llvm-project?rev=185954&view=rev
> Log:
> ValueTracking: Fix bugs in isKnownToBeAPowerOfTwo
>
> (add nsw x, (and x, y)) isn't a power of two if x is zero, it's zero
> (add nsw x, (xor x, y)) isn't a power of two if y has bits set that aren't set in x

Thanks! Please be very very careful not to introduce subtle
mis-optimizations like this. If in doubt, get someone else to stare at
the code before committing.

Thanks,
Jay.