[cfe-dev] Flag for generating LLVM IR from forward declarations

[Gianluca Stivan via cfe-dev]

True,

I was toying with the idea of having a separate step in the pipeline that
plugs in after AST is turned into a Module[*] which generates frontend code.
But to do so, I would have to have forward declarations be actually
emitted, hence my proposal. Otherwise I'd just be iterating over an empty
set of instructions :)
My theory is that LLVM IR at that point is going to be way more
straightforward (just basic types, structs and `declare @..`s) to deal with.
Could this approach make sense?

Cheers,

-yawnt

[*] a Clang plugin? Can they be run over Modules, that is LLVM IR, instead
of AST?


2016-11-30 10:59 GMT+00:00 Alex L <arphaman at gmail.com>:

>
>
> On 30 November 2016 at 09:12, Gianluca Stivan via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> Hi everyone,
>>
>> I was playing around with the LLVM toolchain and it occurred to me that,
>> should I decide to target LLVM IR, it would be neat to have Clang generate
>> declarations from C header files for easier FFI. Someone seems to have had
>> my same idea [1] [2]. This is kind of the opposite of what other projects
>> have gone for, where they use libclang to parse header files to achieve the
>> same result [3].
>>
>
> Sounds like an interesting idea. I how one question though, if you're
> generating only the C function declarations in LLVM IR, how will your
> frontend that targets LLVM IR call these declarations? Maybe I'm
> misunderstanding something, but I don't see how can you generate the calls
> to these functions without getting clang involved.
>
> Cheers,
> Alex
>
>
>>
>> Now, forward declaration generation is doable by patching
>> CodeGenModule.cpp (I kinda have a PoC working locally, except it generates
>> *all* the forward declarations, instead of just the ones from the header
>> files I care about)
>>
>> Is this something that you guys would be interested in merging into Clang
>> through a flag? Or what would the proper way to do this be?
>> I saw there's a `-femit-all-decls`, but it doesn't really emit all
>> declarations.
>>
>> Apologies if this is a dumb idea, kinda new to the whole Clang thing :)!
>>
>> Cheers,
>>
>> -yawnt
>>
>> [1] http://stackoverflow.com/questions/24728901/clang-compiling-
>> a-c-header-to-llvm-ir-bitcode
>> [2] http://stackoverflow.com/questions/14032496/how-can-i-co
>> de-generate-unused-declarations-with-clang?noredirect=1&lq=1
>> [3] https://github.com/tjfontaine/node-ffi-generate
>>
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>>
>>
>
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