[PATCH] Added InstCombine for ((1 << X) & C) pattern

[Dinesh Dwivedi]

I have written smt-lib program to verify these transformations.

  http://rise4fun.com/Z3/Skhom (verifies ((1 << x) & c)? c : 0, if c is power of 2)
  http://rise4fun.com/Z3/p4BF (verifies ((1 << x) & c)? (1 << x) : 0, if c+1 is power of 2)

This verification assumes:
1) c > 0, this case is ensured by existing code, => x & 0 = 0
2) (1 << x) does not overflow, assumed handled in existing code, (http://reviews.llvm.org/D3371)

Update patch to use c in place of (1 << x) in ICmp in new SelectInst.
Updated test case for (1 << x) & 8, to non 'if' version as there are similar test case in icmp.ll (test17, test19)

http://reviews.llvm.org/D3678

Files:
  lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  test/Transforms/InstCombine/icmp.ll
  test/Transforms/InstCombine/shift.ll
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