Merge 81821 from mainline.

Don't pull a load through a callseq_start if the load's chain
has multiple uses, as one of the other uses may be on a path
to a different node above the callseq_start, because that
leads to a cyclic graph. This problem is exposed when
-combiner-global-alias-analysis is used. This fixes PR4880.

llvm-svn: 81978