Merging r266152:

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r266152 | thomas.stellard | 2016-04-12 16:57:30 -0700 (Tue, 12 Apr 2016) | 13 lines

AMDGPU/SI: Fix spilling of 96-bit registers

Summary:
It seems like this was broken in r252327.  I thought we had test cases
for this, but it's really hard to tirgger spills of this exact register
size since they aren't used very much.

Reviewers: arsenm, nhaehnle

Subscribers: nhaehnle, arsenm, llvm-commits

Differential Revision: http://reviews.llvm.org/D19021

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llvm-svn: 271735