Merging r277691, r277693, and r277773:

------------------------------------------------------------------------
r277691 | majnemer | 2016-08-03 21:24:02 -0700 (Wed, 03 Aug 2016) | 4 lines

Reinstate "[CloneFunction] Don't remove side effecting calls"

This reinstates r277611 + r277614 and reverts r277642.  A cast_or_null
should have been a dyn_cast_or_null.
------------------------------------------------------------------------

------------------------------------------------------------------------
r277693 | majnemer | 2016-08-03 21:47:18 -0700 (Wed, 03 Aug 2016) | 1 line

Forgot the dyn_cast_or_null intended for r277691.
------------------------------------------------------------------------

------------------------------------------------------------------------
r277773 | majnemer | 2016-08-04 14:28:59 -0700 (Thu, 04 Aug 2016) | 6 lines

[CloneFunction] Add a testcase for r277691/r277693

PR28848 had a very nice reduction of the underlying cause of the bug.
Our ValueMap had, in an entry for an Instruction, a ConstantInt.

This is not at all unexpected but should be handled properly.
------------------------------------------------------------------------

llvm-svn: 277781