Merging r195787:

Merging r195787:
------------------------------------------------------------------------
r195787 | arnolds | 2013-11-26 14:11:23 -0800 (Tue, 26 Nov 2013) | 8 lines

LoopVectorizer: Truncate i64 trip counts of i32 phis if necessary

In signed arithmetic we could end up with an i64 trip count for an i32 phi.
Because it is signed arithmetic we know that this is only defined if the i32
does not wrap. It is therefore safe to truncate the i64 trip count to a i32
value.

Fixes PR18049.
------------------------------------------------------------------------

git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@195991 91177308-0d34-0410-b5e6-96231b3b80d8