[clang] [CIR] Add cir-opt tool to exercise CIR dialect parsing (PR #128254)

[Henrich Lauko via cfe-commits]

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@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Similar to MLIR/LLVM's "opt" tools but also deals with analysis and custom
+// arguments. TODO: this is basically a copy from MlirOptMain.cpp, but capable
+// of module emission as specified by the user.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Conversion/ReconcileUnrealizedCasts/ReconcileUnrealizedCasts.h"
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
+#include "mlir/Dialect/MemRef/IR/MemRef.h"
+#include "mlir/InitAllPasses.h"
+#include "mlir/Pass/PassManager.h"
+#include "mlir/Pass/PassOptions.h"
+#include "mlir/Pass/PassRegistry.h"
+#include "mlir/Tools/mlir-opt/MlirOptMain.h"
+#include "clang/CIR/Dialect/IR/CIRDialect.h"
+#include "clang/CIR/Passes.h"
+
+struct CIRToLLVMPipelineOptions
+    : public mlir::PassPipelineOptions<CIRToLLVMPipelineOptions> {};
+
+int main(int argc, char **argv) {
+  // TODO: register needed MLIR passes for CIR?
+  mlir::DialectRegistry registry;
+  registry.insert<mlir::BuiltinDialect, cir::CIRDialect,
+                  mlir::memref::MemRefDialect, mlir::LLVM::LLVMDialect>();
+
+  mlir::PassPipelineRegistration<CIRToLLVMPipelineOptions> pipeline(
+      "cir-to-llvm", "",
+      [](mlir::OpPassManager &pm, const CIRToLLVMPipelineOptions &options) {
+        cir::direct::populateCIRToLLVMPasses(pm);
+      });
+
+  mlir::registerTransformsPasses();
+
+  return failed(MlirOptMain(
----------------
xlauko wrote:

```suggestion
  return mlir::asMainReturnCode(MlirOptMain(
```

https://github.com/llvm/llvm-project/pull/128254