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

[Andy Kaylor via cfe-commits]

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@@ -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>,
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andykaylor wrote:

If we add `emit_mlir_EQ` will that peacefully coexist with the `def emit_mlir : Flag<["-"], "emit-mlir">, Alias<emit_fir>;` definition until we can update flang to align the behavior of the option with no argument?

@clementval Does flang have the ability to lower to MLIR core dialects? I think that's what we're saying we'd like `-emit-mlir` with no argument to do in clang. Or should we have both clang and flang emit their default dialects if no argument is used?

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