[llvm-dev] Query about JIT

[Rajesh Jayaprakash via llvm-dev]

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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