[clang] [CIR] Add support for indirect calls (PR #139748)

[Sirui Mu via cfe-commits]

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@@ -1500,6 +1507,14 @@ static void prepareTypeConverter(mlir::LLVMTypeConverter &converter,
   converter.addConversion([&](cir::BF16Type type) -> mlir::Type {
     return mlir::BFloat16Type::get(type.getContext());
   });
+  converter.addConversion([&](cir::FuncType type) -> mlir::Type {
+    auto result = converter.convertType(type.getReturnType());
+    llvm::SmallVector<mlir::Type> arguments;
+    if (converter.convertTypes(type.getInputs(), arguments).failed())
+      llvm_unreachable("Failed to convert function type parameters");
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Lancern wrote:

I just realized that we could indicate failure by returning an empty `std::optional` from the converter function, see https://github.com/llvm/llvm-project/blob/252ba8e3fb361772003c38566c99233c07adc4bd/mlir/include/mlir/Transforms/DialectConversion.h#L144-L148 . Maybe we could return an `std::nullopt` here instead?

https://github.com/llvm/llvm-project/pull/139748