Merging r326521:

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r326521 | indutny | 2018-03-01 16:59:27 -0800 (Thu, 01 Mar 2018) | 13 lines

[ArgumentPromotion] don't break musttail invariant PR36543

Summary:
Do not break musttail invariant by promoting arguments of musttail
callee or caller.

Reviewers: sanjoy, dberlin, hfinkel, george.burgess.iv, fhahn, rnk

Reviewed By: rnk

Subscribers: rnk, llvm-commits

Differential Revision: https://reviews.llvm.org/D43926
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llvm-svn: 329858