[CIR] Add runAtStartOfConvertCIRToMLIRPass() to ConvertCIRToMLIRPass

This allows injecting some dialects and patterns to the
cir::ConvertCIRToMLIRPass lowering pass.

Author: keryell

clang/include/clang/CIR/LowerToMLIR.h

@@ -12,11 +12,15 @@
 #ifndef CLANG_CIR_LOWERTOMLIR_H
 #define CLANG_CIR_LOWERTOMLIR_H
 
+#include "mlir/Transforms/DialectConversion.h"
+#include <functional>
+
 namespace cir {
 
 void populateCIRLoopToSCFConversionPatterns(mlir::RewritePatternSet &patterns,
                                             mlir::TypeConverter &converter);
 mlir::TypeConverter prepareTypeConverter();
+void runAtStartOfConvertCIRToMLIRPass(std::function<void(mlir::ConversionTarget)>);
 } // namespace cir
 
 #endif // CLANG_CIR_LOWERTOMLIR_H_

clang/lib/CIR/Lowering/ThroughMLIR/LowerCIRToMLIR.cpp

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include <functional>
+
 #include "LowerToMLIRHelpers.h"
 #include "mlir/Conversion/AffineToStandard/AffineToStandard.h"
 #include "mlir/Conversion/ArithToLLVM/ArithToLLVM.h"
@@ -91,6 +93,8 @@ struct ConvertCIRToMLIRPass
   }
 
   StringRef getArgument() const override { return "cir-to-mlir"; }
+
+  inline static std::function<void(mlir::ConversionTarget)> runAtStartHook;
 };
 
 class CIRCallOpLowering : public mlir::OpConversionPattern<cir::CallOp> {
@@ -1454,10 +1458,20 @@ void ConvertCIRToMLIRPass::runOnOperation() {
                        mlir::math::MathDialect, mlir::vector::VectorDialect>();
   target.addIllegalDialect<cir::CIRDialect>();
 
+  if (runAtStartHook)
+    runAtStartHook(target);
+
   if (failed(applyPartialConversion(module, target, std::move(patterns))))
     signalPassFailure();
 }
 
+/// Set a hook to be called just before applying the dialect conversion so other
+/// dialects or patterns can be added
+void runAtStartOfConvertCIRToMLIRPass(
+    std::function<void(mlir::ConversionTarget)> hook) {
+  ConvertCIRToMLIRPass::runAtStartHook = std::move(hook);
+}
+
 std::unique_ptr<llvm::Module>
 lowerFromCIRToMLIRToLLVMIR(mlir::ModuleOp theModule,
                            std::unique_ptr<mlir::MLIRContext> mlirCtx,