Merging r229731:

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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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_36@229757 91177308-0d34-0410-b5e6-96231b3b80d8