the readnone. Since MallocInst is scheduled for deletion
it doesn't seem worth doing anything more subtle, such as
having mayWriteToMemory return true for MallocInst.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@71077 91177308-0d34-0410-b5e6-96231b3b80d8