[cfe-dev] [llvm-dev] Query about JIT

[Mehdi AMINI via cfe-dev]

Hi Rajesh,

Adding the cfe-dev (Clang FrontEnd) mailing list as your question seems to
be more targeted towards clang (your input is C code if I understood
correctly).

At the LLVM level, there is a (limited but "stable") C API here:
https://github.com/llvm/llvm-project/tree/master/llvm/include/llvm-c
For the JIT, this file seems relevant:
https://github.com/llvm/llvm-project/blob/master/llvm/include/llvm-c/OrcBindings.h
But this assumes you get LLVM IR in the first place, and I don't know of a
C API for clang for this.

Best,

-- 
Mehdi


On Tue, Mar 12, 2019 at 7:05 AM Rajesh Jayaprakash via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi Alexey,
>
> Thank you very much for your detailed reply, will look into the resources
> indicated. I'd like to avoid C++ if possible, let me see how it goes.
>
> Regards,
> Rajesh Jayaprakash
>
> On Tue 12 Mar, 2019, 6:35 PM Sachkov, Alexey, <alexey.sachkov at intel.com>
> wrote:
>
>> Hi Rajesh,
>>
>> If I understand correctly, libclang is a C interface to Clang features,
>> not LLVM. That means that you cannot get LLVM IR via libclang: The C
>> Interface to Clang provides a relatively small API that exposes facilities
>> for parsing source code into an abstract syntax tree (AST), loading
>> already-parsed ASTs, traversing the AST, associating physical source
>> locations with elements within the AST, and other facilities that support
>> Clang-based development tools.
>>
>> To get LLVM IR and perform JIT compilation you need to use C++ API of
>> Clang and LLVM.
>>
>>
>>
>> Here is some links which might be helpful:
>>
>> * [cfe-dev] How to use clang and llvm for JIT, preferably via the C API
>> http://lists.llvm.org/pipermail/cfe-dev/2015-August/044869.html
>>
>> * [cfe-dev] Help on Generating LLVM Module from C++ file using libClang
>> http://lists.llvm.org/pipermail/cfe-dev/2017-November/056033.html
>>
>> * [LLVMdev] libclang JIT frontend
>> http://lists.llvm.org/pipermail/llvm-dev/2013-October/066088.html
>>
>> * Generate assembly from C code in memory using libclang
>> https://stackoverflow.com/questions/34828480/generate-assembly-from-c-code-in-memory-using-libclang
>>
>>
>>
>> BTW, there is a library for translating OpenCL C source code into a LLVM
>> IR which features in-memory translation:
>>
>> * https://github.com/intel/opencl-clang
>> It is not suitable for performing the whole JIT compilation, but it is
>> used by https://github.com/intel/intel-graphics-compiler as a front-end.
>> Also I’m not sure that you will be able to use it as-is for your purposes,
>> but at least it can be used as an example
>>
>>
>>
>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of *Rajesh
>> Jayaprakash via llvm-dev
>> *Sent:* Friday, March 8, 2019 2:14 PM
>> *To:* llvm-dev at lists.llvm.org
>> *Subject:* [llvm-dev] Query about JIT
>>
>>
>>
>> Dear llvm-dev list,
>>
>>
>>
>> Apologies if this list is not the right venue for this query - suitable
>> redirection would be appreciated in that case.
>>
>>
>>
>> I have a JIT use case that I'd like to know the best way to implement
>> using LLVM.
>>
>>
>>
>> I am looking to migrate from the existing native compilation option (Tiny
>> C Compiler - TCC) for pLisp, a Lisp dialect and IDE.
>>
>>
>>
>> At present, the native compilation is done by converting the Lisp code to
>> C, storing the C code in a char buffer, and passing it to TCC
>> programmatically via the API provided. I get a function pointer in return,
>> which I store and invoke as needed.
>>
>>
>>
>> Delving into the LLVM documentation, I found that one possible way to
>> achieve the same functionality in LLVM is to use clag/libclang to convert
>> the C source to LLVM IR, load this IR into the the JIT context and
>> (skipping some steps I'm yet to figure out) get the desired function
>> pointer.
>>
>>
>>
>> Is this approach the right one? One issue I foresee is that libclang's
>> clang_parseTranslateUnit() function expects the C code to be from a file
>> (although the file can be in-memory), whereas in my case the C code needs
>> to be picked up from a char buffer - necessitating fmemopen(), etc.
>>
>>
>>
>> Thanks for your assistance.
>>
>>
>>
>> Regards,
>> Rajesh Jayaprakash
>>
>> (https://github.com/shikantaza/plisp)
>>
>>
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