Strange build dependencies from Tofino backend

[asl]

Building e.g. a frontend target actually builds Tofino backend, which does not look correct to me.

[fruffy]

If I'd wager a guess it might be because of the Tofino IR sources: https://github.com/p4lang/p4c/blob/main/backends/tofino/CMakeLists.txt#L219 which need to be compile with the ir-generated blob.

[asl]

https://github.com/p4lang/p4c/blob/main/backends/tofino/CMakeLists.txt#L219 which need to be compile with the ir-generated blob.

But looks like these are not entirely frontend...

[fruffy]

But looks like these are not entirely frontend...

Yeah I also think they could be cleaned up. There includes are quite messy and there are some circular dependencies.

[ChrisDodd]

The way the code is set up, it builds IR Visitor infrastructure as part of the frontend, supporting all IR types that are declared in any backend that is enabled in the build as part of the frontend. That ends up pulling a few backend files (those related to the IR types) into the frontend, and is required due C++ ODR requirements (otherwise you would get undefined behavior by linking code that doesn't agree on the vtable layout for classes like IR::Node).

To not include this backend code, you need to use -DENABLE_TOFINO=OFF to cmake and rebuild everything.

[asl]

The way the code is set up, it builds IR Visitor infrastructure as part of the frontend, supporting all IR types that are declared in any backend that is enabled in the build as part of the frontend. That ends up pulling a few backend files (those related to the IR types) into the frontend, and is required due C++ ODR requirements (otherwise you would get undefined behavior by linking code that doesn't agree on the vtable layout for classes like IR::Node).

To not include this backend code, you need to use -DENABLE_TOFINO=OFF to cmake and rebuild everything.

But are files like bf-p4c/midend/path_linearizer.cpp or bf-utils/src/dynamic_hash/dynamic_hash.c bf-utils/src/dynamic_hash/bfn_hash_algorithm.c constitute IR Visitor infrastructure?

[ChrisDodd]

But are files like bf-p4c/midend/path_linearizer.cpp or bf-utils/src/dynamic_hash/dynamic_hash.c bf-utils/src/dynamic_hash/bfn_hash_algorithm.c constitute IR Visitor infrastructure?

No, but disentangling them is likely to require splitting some source files to only include the minimum to get things to build while not including other things that pull in more dependencies.