Passing through cir.func attributes to func.func operation in CIRtoMLIR lowering

[felixdaas]

In the CIRtoMLIR lowering, when lowering a cir.func operation with

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

Lines 524 to 559 in 5df5009

	class CIRFuncOpLowering : public mlir::OpConversionPattern<cir::FuncOp> {
	public:
	using OpConversionPattern<cir::FuncOp>::OpConversionPattern;
	mlir::LogicalResult
	matchAndRewrite(cir::FuncOp op, OpAdaptor adaptor,
	mlir::ConversionPatternRewriter &rewriter) const override {
	auto fnType = op.getFunctionType();
	mlir::TypeConverter::SignatureConversion signatureConversion(
	fnType.getNumInputs());
	for (const auto &argType : enumerate(fnType.getInputs())) {
	auto convertedType = typeConverter->convertType(argType.value());
	if (!convertedType)
	return mlir::failure();
	signatureConversion.addInputs(argType.index(), convertedType);
	}
	mlir::Type resultType =
	getTypeConverter()->convertType(fnType.getReturnType());
	auto fn = rewriter.create<mlir::func::FuncOp>(
	op.getLoc(), op.getName(),
	rewriter.getFunctionType(signatureConversion.getConvertedTypes(),
	resultType ? mlir::TypeRange(resultType)
	: mlir::TypeRange()));
	if (failed(rewriter.convertRegionTypes(&op.getBody(), *typeConverter,
	&signatureConversion)))
	return mlir::failure();
	rewriter.inlineRegionBefore(op.getBody(), fn.getBody(), fn.end());
	rewriter.eraseOp(op);
	return mlir::LogicalResult::success();
	}
	};

no attributes are passed/set to the created func.func operation. Because of this the lowering fails with the following error if the the c-code includes function declarations:

error: 'func.func' op symbol declaration cannot have public visibility

I would suggest fixing this by passing the sym_visibility and maybe also the arg_attrs, res_attrs attributes of the cir.func to the created func.func (arg_attrs, res_attrs don't fix this particular issue and I'm not sure if they are currently used for anything, maybe someone else can explain what the purpose of the attributes is)

Here's a minimal example that triggers the issue:

test.c

#include "example.h"

int main(int argc, char *argv[]) {
    // Variables
    int number = 15;

    number = add10(number);

    return 0;
} 

example.h

#ifndef ADD10_H
#define ADD10_H

int add10(int x);

#endif

example.c

#include "example.h"

int add10(int x) {
    return x + 10;
}

trying to lower throughmlir here leads to the describe error:

clang -fclangir -S -Xclang -emit-mlir=core -fno-clangir-direct-lowering test.c
loc(fused["./example.h":4:1, "./example.h":4:16]): error: 'func.func' op symbol declaration cannot have public visibility
fatal error: error in backend: The pass manager failed to lower CIR to MLIR standard dialects!

[bcardosolopes]

Thanks for creating a PR for this!