Merging r296163:

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r296163 | yaxunl | 2017-02-24 15:27:25 -0500 (Fri, 24 Feb 2017) | 9 lines

[InstCombine] Fix bug in pointer replacement

This optimisation was crashing when there was a chain of more than one bitcast
instruction to replace, as a result of the changes in D27283.

Patch by James Price.

Differential Revision: https://reviews.llvm.org/D30347

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llvm-svn: 303166