[LLVMdev] C Backend Ressurected

[Isaac Dupree]

Is the C backend at all suitable to be adapted to emit OpenCL code?  Or
do the target-dependence, and/or things that C can do but OpenCL can't,
make that hopeless?
-Isaac

On 08/19/2014 03:08 PM, Carback, Richard T., III wrote:
> It provides a useful starting point, but I agree with Jim that it is not
> a complete solution and requires rework of the results in a lot cases. I
> think we could improve it further to address these issues but that work
> is nontrivial.
> 
>  
> 
> If you are deciding between a quick and dirty implementation of a custom
> backend vs. the C backend, then the C backend is sometimes preferable in
> my experience although it depends on the complexity of the code you are
> trying to run and how often you need to change it.
> 
>  
> 
> *From:*llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
> *On Behalf Of *Jim Grosbach
> *Sent:* Tuesday, August 19, 2014 2:12 PM
> *To:* Bruce Hoult
> *Cc:* llvmdev at cs.uiuc.edu
> *Subject:* Re: [LLVMdev] C Backend Ressurected
> 
>  
> 
> This is part of the problem with the C backend. This is very much not
> what it’s useful for, yet it very much looks like it is. The LLVM IR is
> target dependent, including things like structure layout, pointer size,
> and other ABI issues. Even with a resurrected C backend, you can’t use
> it as a substitute for real target support.
> 
>  
> 
> -Jim
> 
>  
> 
>     On Aug 18, 2014, at 7:02 PM, Bruce Hoult <bruce at hoult.org
>     <mailto:bruce at hoult.org>> wrote:
> 
>      
> 
>     I don't know how good it is, but the applications seem obvious. e.g.
>     compiling programs in any of a number of original formats to run
>     natively on CPUs that have a working simple C compiler (maybe only
>     K&R or C89) but don't have an LLVM back end.
> 
>      
> 
>     The source program could be in modern C, C++, or any other high
>     level language or assembly language with a translator to LLVM.
> 
>      
> 
>     On Tue, Aug 19, 2014 at 1:40 PM, Jun Koi <junkoi2004 at gmail.com
>     <mailto:junkoi2004 at gmail.com>> wrote:
> 
>      
> 
>      
> 
>     On Mon, Aug 18, 2014 at 9:18 PM, Carback, Richard T., III
>     <rcarback at draper.com <mailto:rcarback at draper.com>> wrote:
> 
>         Hi All,
> 
>          
> 
>         2 of my summer interns (Aimee Dipietro and Greg Simpson) used
>         their time over the summer to resurrect the LLVM C Backend:
> 
>          
> 
>         https://github.com/draperlaboratory/llvm-cbe
> 
>          
> 
>         Improvements include recovery of simple for/while loops (instead
>         of goto), better variable naming, inline asm support, and making
>         it work on a more recent version of llvm. I believe they used
>         the repository here as a starting point:
> 
>          
> 
>         https://github.com/glycerine/llvm/tree/cbe_revival
> 
>          
> 
>         Feedback is welcomed. I would like to see this feature put back
>         into LLVM, and any help on how to make that happen would be
>         appreciated.
> 
>      
> 
>     would you mind explaining what this backend is for, and its
>     applications?
> 
>     i guess it is to get the C code at the output of the backend, but
>     dont get why we need it.
> 
>     thanks,
> 
>     Jun
> 
> 
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