Teaching SimplifyCFG to recognize the Or-Mask trick that InstCombine uses to

reduce the number of comparisons.

Specifically, InstCombine can turn:
  (i == 5334 || i == 5335)
into:
  ((i | 1) == 5335)

SimplifyCFG was already able to detect the pattern:
  (i == 5334 || i == 5335)
to:
  ((i & -2) == 5334)

This patch supersedes D21315 and resolves PR27555
(https://llvm.org/bugs/show_bug.cgi?id=27555).

Thanks to David and Chandler for the suggestions!

Author: Thomas Jablin (tjablin)
Reviewers: majnemer chandlerc halfdan cycheng

http://reviews.llvm.org/D21397

llvm-svn: 273639