Merging r370036:

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r370036 | tnorthover | 2019-08-27 12:21:11 +0200 (Tue, 27 Aug 2019) | 8 lines

AArch64: avoid creating cycle in DAG for post-increment NEON ops.

Inserting a value into Visited has the effect of terminating a search for
predecessors if that node is seen. This is legitimate for the base address, and
acts as a slight performance optimization, but the vector-building node can be
paert of a legitimate cycle so we shouldn't stop searching there.

PR43056.
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llvm-svn: 370063