Merging r196508:
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r196508 | arnolds | 2013-12-05 07:14:40 -0800 (Thu, 05 Dec 2013) | 12 lines

SLPVectorizer: An in-tree vectorized entry cannot also be a scalar external use

We were creating external uses for scalar values in MustGather entries that also
had a ScalarToTreeEntry (they also are present in a vectorized tuple). This
meant we would keep a value 'alive' as a scalar and vectorized causing havoc.
This is not necessary because when we create a MustGather vector we explicitly
create external uses entries for the insertelement instructions of the
MustGather vector elements.

Fixes PR18129.

radar://15582184
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@196571 91177308-0d34-0410-b5e6-96231b3b80d8