Merging r259381:

Merging r259381:
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r259381 | uweigand | 2016-02-01 10:31:19 -0800 (Mon, 01 Feb 2016) | 21 lines

[SystemZ] Fix wrong-code generation for certain always-false conditions

We've found another bug in the code generation logic conditions for a
certain class of always-false conditions, those of the form
   if ((a & 1) < 0)

These only reach the back end when compiling without optimization.

The bug was introduced by the choice of using TEST UNDER MASK
to implement a check for
   if ((a & MASK) < VAL)
as
   if ((a & MASK) == 0)

where VAL is less than the the lowest bit of MASK.  This is correct
in all cases except for VAL == 0, in which case the original
condition is always false, but the replacement isn't.

Fixed by excluding that particular case.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_38@259940 91177308-0d34-0410-b5e6-96231b3b80d8