Merging r232142:

Merging r232142:

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r232142 | Hao.Liu | 2015-03-13 01:15:23 -0400 (Fri, 13 Mar 2015) | 9 lines

[MachineCopyPropagation] Fix a bug causing incorrect removal for the instruction sequences as follows
   %Q5_Q6<def> = COPY %Q2_Q3
   %D5<def> =
   %D3<def> =
   %D3<def> = COPY %D6     // Incorrectly removed in MachineCopyPropagation
   Using of %D3 results in incorrect result ...

   Reviewed in http://reviews.llvm.org/D8242

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_36@236065 91177308-0d34-0410-b5e6-96231b3b80d8