[LLVMdev] C Backend Ressurected

[Matt Arsenault]

On Sep 3, 2014, at 7:10 PM, Isaac Dupree <ml at isaac.cedarswampstudios.org> wrote:

> I would like to ship an application that can compute on multiple brands
> of modern GPU.  I would like to write my GPU code in a slightly higher
> level language than OpenCL's C variant -- for example, C++ templates
> would be useful to have.  One way might be compiling some higher level
> language to OpenCL that I ship.  Can you suggest better ways to do this?
> 
> Best,
> -Isaac

This was the intended use case for SPIR

> 
> On 09/03/2014 04:10 PM, Eric Christopher wrote:
>> I can't see why you'd want to do this, no.
>> 
>> -eric
>> 
>> 
>> On Tue, Aug 19, 2014 at 8:02 PM, Isaac Dupree
>> <ml at isaac.cedarswampstudios.org <mailto:ml at isaac.cedarswampstudios.org>>
>> wrote:
>> 
>>    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>
>>    [mailto: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 <mailto: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>
>>>    <mailto: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>
>>>    <mailto: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>
>>    <mailto: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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