Merging r292651:

Merging r292651:
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r292651 | jvesely | 2017-01-20 13:24:26 -0800 (Fri, 20 Jan 2017) | 8 lines

AMDGPU/R600: Serialize vector trunc stores to private AS

Add DUMMY_CHAIN SDNode to denote stores of interest

Bugzilla: https://llvm.org/bugs/show_bug.cgi?id=28915
Bugzilla: https://llvm.org/bugs/show_bug.cgi?id=30411

Differential Revision: https://reviews.llvm.org/D27964
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_40@293118 91177308-0d34-0410-b5e6-96231b3b80d8