Merging r229731:
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    r229731 | sanjoy | 2015-02-18 11:32:25 -0800 (Wed, 18 Feb 2015) | 10 lines
    
    Partial fix for bug 22589
    
    Don't spend the entire iteration space in the scalar loop prologue if
    computing the trip count overflows.  This change also gets rid of the
    backedge check in the prologue loop and the extra check for
    overflowing trip-count.
    
    Differential Revision: http://reviews.llvm.org/D7715
    
    
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    llvm-svn: 229757