Reapply: [LIR] Add support for creating memsets from loops with a negative stride.

The simple fix is to prevent forming memcpy from loops with a negative stride.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251518 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed