[llvm] [PowerPC][AIX] Using milicode for memcmp instead of libcall (PR #147093)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

The compiler should not directly emit string calls. This needs an entry in RuntimeLibcalls.td to emit the call. Further, this should not be based on a triple call in the DAG builder 

https://github.com/llvm/llvm-project/pull/147093