[Pipeliner] Drop memrefs instead of creating ones with size UINT64_MAX

Absence of memory operands is treated as "aliasing everything", so
dropping them is sufficient.

Recommit r326256 with a fixed testcase.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@326262 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed