[NewGVN] Check that call has an access.

Check that a call has an attached MemoryAccess before calling
getClobbering on the instruction.
If no access is attached, the instruction does not access memory.

Resolves PR43441.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@374920 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed