Merging r155984:
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    r155984 | void | 2012-05-02 02:59:45 -0700 (Wed, 02 May 2012) | 4 lines
    
    The value held in the vector may be RAUW'ed by some of the canonicalization
    methods. Use a weak value handle to keep up with this.
    PR12245
    
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    llvm-svn: 155985