Merging r294003:

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r294003 | abataev | 2017-02-03 04:28:40 -0800 (Fri, 03 Feb 2017) | 8 lines

[SelectionDAG] Fix for PR30775: Assertion `NodeToMatch->getOpcode() !=
ISD::DELETED_NODE && "NodeToMatch was removed partway through
selection"' failed.

NodeToMatch can be modified during matching, but code does not handle
this situation.

Differential Revision: https://reviews.llvm.org/D29292
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llvm-svn: 295249