Merging r181397:
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r181397 | nicholas | 2013-05-08 02:00:10 -0700 (Wed, 08 May 2013) | 3 lines

Fix a bug in codegenprep where it was losing track of values OptimizeMemoryInst
by switching to a ValueMap. Patch by Andrea DiBiagio!

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_33@181619 91177308-0d34-0410-b5e6-96231b3b80d8