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

[Henrich Lauko 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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xlauko wrote:

This is being reworked in incubator: https://github.com/llvm/clangir/pull/1316

I agree that `-emit-mlir` is ambiguous, though @bcardosolopes wanted to keep original semantics there for now.
TLDR we are working towards `-emit-mlir=<name-of-target-dialect-set>`, e.g., `-emit-mlir=std` (can be renamed to core), `-emit-mlir=cir`, `-emit-mlir=llvm`.

Where these need to cooperate with `-f[no]-clangir-direct-lowering` to translate through `core` dialects or directly from `cir` to `llvm dialect`.


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