The existing conversion no longer worked and was not save to undo. Furthermore, the pattern for mhlo.return had been removed.
Also adds some tests to ensure this does not degrade again.
PiperOrigin-RevId: 321542071
Following on the plan of isolating the compiler/mlir/hlo directory.
Another xla_lhlo dialect will be created under compiler/mlir/xla/ later.
PiperOrigin-RevId: 320210326
Also add a localized `mlir-hlo-opt` binary for the testing of
tensorflow/compiler/mlir/hlo/... ; this directory is intended to be self-contained
and depend only on MLIR.
PiperOrigin-RevId: 319878984