[clang] [CIR] Initial implementation of lowering CIR to MLIR (PR #127835)

[Andy Kaylor via cfe-commits]

================
@@ -2958,6 +2958,8 @@ defm clangir : BoolFOption<"clangir",
   BothFlags<[], [ClangOption, CC1Option], "">>;
 def emit_cir : Flag<["-"], "emit-cir">, Visibility<[ClangOption, CC1Option]>,
   Group<Action_Group>, HelpText<"Build ASTs and then lower to ClangIR">;
+def emit_cir_mlir : Flag<["-"], "emit-cir-mlir">, Visibility<[CC1Option]>, Group<Action_Group>,
----------------
andykaylor wrote:

Agreed. One problem with aligning the two is that in flang, currently, -emit-mlir means to emit the fir dialect, whereas here we wanted it to mean, emit MLIR but **not** the cir dialect. This highlights the problem that "emit MLIR" isn't very specific. Even the interpretation used in the ClangIR incubator is emitting a handful of different dialects (affine, scf, arith, memref, vector, etc.).

https://github.com/llvm/llvm-project/pull/127835