Merging r215818:

Merging r215818:
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r215818 | majnemer | 2014-08-16 02:23:42 -0700 (Sat, 16 Aug 2014) | 12 lines

InstCombine: Fix a potential bug in 0 - (X sdiv C)  -> (X sdiv -C)

While *most* (X sdiv 1) operations will get caught by InstSimplify, it
is still possible for a sdiv to appear in the worklist which hasn't been
simplified yet.

This means that it is possible for 0 - (X sdiv 1) to get transformed
into (X sdiv -1); dividing by -1 can make the transform produce undef
values instead of the proper result.

Sorry for the lack of testcase, it's a bit problematic because it relies
on the exact order of operations in the worklist.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_35@223645 91177308-0d34-0410-b5e6-96231b3b80d8