Merging r277371:

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r277371 | mkuper | 2016-08-01 12:39:49 -0700 (Mon, 01 Aug 2016) | 9 lines

[DAGCombine] Make sext(setcc) combine respect getBooleanContents

We used to combine "sext(setcc x, y, cc) -> (select (setcc x, y, cc), -1, 0)"
Instead, we should combine to (select (setcc x, y, cc), T, 0) where the value
of T is 1 or -1, depending on the type of the setcc, and getBooleanContents()
for the type if it is not i1.

This fixes PR28504.

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llvm-svn: 277509