Re: GCC + libJIT instead of LLVM

[Kirill Kononenko <kirill dot kononenko at gmail dot com>]

2009/4/1 Dave Korn <dave.korn.cygwin@googlemail.com>:
> Kirill Kononenko wrote:
>>>> 2009/4/1 Andrew Haley:
>>>>> Kirill Kononenko wrote:
>>>>>
>>>>>> I would like to ask your opinion about possibility for integration of
>>>>>> the libJIT Just-In-Time compilation library and GCC. For example, the
>>>>>> same way as libffi is integrated within gcc source tree. It seems to
>>>>>> me that LLVM solves many goals that are already complete and solved in
>>>>>> GCC. So I think libJIT potentially is more useful for GCC and software
>>>>>> developers.
>>>>> Useful for what?  I think you have to tell us how this will improve the
>>>>> experience of gcc users .
>>> Kirill Kononenko wrote:
>>>> More useful in implementation of Just-In-Time compilation in Virtual
>>>> Machine runtimes. For example, for Microsoft Common Intermediate
>>>> Language (.NET).
>>> We already know what a JIT does, thank you.  I think you have to tell us how
>>
>> Please could you specify more precisely the 'we' here?
>
>  I think he means "Every single reader of the GCC mailing list, or as close
> as makes no difference".
>
>> I really don't understand what you exactly mean here.
>>
>>> having libjit integrated in gcc will improve the experience of gcc users.
>>> As opposed to them, say, using libjit as a library separate from gcc.
>>>
>>
>> Just read my first post.
>
>  Hi, I also read your first post.  It says
>
>> It seems to
>> me that LLVM solves many goals that are already complete and solved in
>> GCC. So I think libJIT potentially is more useful for GCC and software
>> developers.
>
> but you don't say what libjit would be more useful than, or how this overlap
> between "solved goals" between gcc and llvm implies that.  Do you simply mean
> that, because llvm and gcc both cover similar areas, and because libjit is
> useful for llvm, it must also be useful for gcc?  Could you list some of these
> goals and explain how they relate to JIT?
>
>  You also wrote
>
>> I think GCC could benefit a lot if an
>> integration of both libJIT and GCC could be considered
>
> but you don't explicitly describe any of the benefits you think will arise.
> Can you enlarge on exactly what effect it would have if libjit was integrated
> into GCC (presumably in the runtime support libraries somewhere) rather than
> just existing as a separate installation?  I can't see how it would perform
> any differently.

LLVM is an overkill for JIT compilation. I think the tasks which LLVM
solves are already solved within GCC transformations, or can be
integrated very easily with libJIT. LibJIT is also much easier in
usage, for ordinary developers. So what I see here, LLVM is rather a
competitor to GCC, considering which tasks it solves. And complexity
of code rises inproportionally to the task it is used for. While both
could be potentionaly useful for their area of expertise. I think an
GCC+libJIT solves 99% of areas of LLVM usage.


Thanks,
Kirill