Revert r288115 for PR31847.

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r288115 | abataev | 2016-11-29 09:21:14 +0100 (Tue, 29 Nov 2016) | 8 lines

[SLPVectorizer] Improved support of partial tree vectorization.

Currently SLP vectorizer tries to vectorize a binary operation and dies
immediately after unsuccessful the first unsuccessfull attempt. Patch
tries to improve the situation, trying to vectorize all binary
operations of all children nodes in the binop tree.

Differential Revision: https://reviews.llvm.org/D25517
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llvm-svn: 296185