Merging r243519:

Merging r243519:
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r243519 | wschmidt | 2015-07-29 07:31:57 -0700 (Wed, 29 Jul 2015) | 14 lines

[PPC] Fix PR24216: Don't generate splat for misaligned shuffle mask

Given certain shuffle-vector masks, LLVM emits splat instructions
which splat the wrong bytes from the source register.  The issue is
that the function PPC::isSplatShuffleMask() in PPCISelLowering.cpp
does not ensure that the splat pattern found is requesting bytes that
are aligned on an EltSize boundary.  This patch detects this situation
as not a valid splat mask, resulting in a permute being generated
instead of a splat.

Patch and test case by Tyler Kenney, cleaned up a bit by me.

This is a simple bug fix that would be good to incorporate into 3.7.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_37@243528 91177308-0d34-0410-b5e6-96231b3b80d8