Merging r197178:

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r197178 | hfinkel | 2013-12-12 12:45:24 -0800 (Thu, 12 Dec 2013) | 9 lines

Fix a use-after-free error in GlobalOpt CleanupConstantGlobalUsers

GlobalOpt's CleanupConstantGlobalUsers function uses a worklist array to manage
constant users to be visited. The pointers in this array need to be weak
handles because when we delete a constant array, we may also be holding a
pointer to one of its elements (or an element of one of its elements if we're
dealing with an array of arrays) in the worklist.

Fixes PR17347.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@197322 91177308-0d34-0410-b5e6-96231b3b80d8