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

[Andrzej Warzyński 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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banach-space wrote:

No objections. In fact, `-emit-mlir` is a misnomer and `emit_mlir_EQ` would make more sense to me. 

>  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.

The semantics in Flang and Clang can differ. Whenever that's the case, please use `HelpTextForVariant` in Options.td to document that.

That said,`-emit-mlir` is very ambiguous - there's no single MLIR representation.

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