[InstCombine] Remove the (not (sext)) case from foldBoolSextMaskToSelect and inline...

[InstCombine] Remove the (not (sext)) case from foldBoolSextMaskToSelect and inline the remaining code to match visitOr

Summary:
The (not (sext)) case is really (xor (sext), -1) which should have been simplified to (sext (xor, 1)) before we got here. So we shouldn't need to handle it.

With that taken care of we only need to two cases so don't need the swap anymore. This makes us in sync with the equivalent code in visitOr so inline this to match.

Reviewers: spatel, eli.friedman, majnemer

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D36240

llvm-svn: 310063