Merging r195162:

Merging r195162:
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r195162 | arnolds | 2013-11-19 14:20:20 -0800 (Tue, 19 Nov 2013) | 12 lines

SLPVectorizer: Fix stale for Value pointer array

We are slicing an array of Value pointers and process those slices in a loop.
The problem is that we might invalidate a later slice by vectorizing a former
slice.

Use a WeakVH to track the pointer. If the pointer is deleted or RAUW'ed we can
tell.

The test case will only fail when running with libgmalloc.

radar://15498655
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@195222 91177308-0d34-0410-b5e6-96231b3b80d8