[LLVMdev] Preferring to use GCC instead of LLVM

[Emílio Wuerges]

Is this thread suposed to be a bad joke?

2008/5/10 kr512 <kr512 at optusnet.com.au>:
>
> Chris Lattner wrote:
>> If you'd prefer to use GCC, go for it.  No one is forcing
>> you to use LLVM.
>
> No, we would prefer to use LLVM, but a missing part in LLVM
> makes it difficult.  It would be wonderful if this missing
> part could be supplied.
>
>> You are seriously ignorant of what LLVM is all about.
>> Please go inform yourself.
>
> Alright, I read some more on llvm.org and it confirmed what
> I was saying:
> http://www.llvm.org/docs/GettingStarted.html#tutorial
>
> See at the end where it says:
> -----------
> 6.Compile the program to native assembly using the LLC code
> generator:
>  % llc hello.bc -o hello.s
> 7.Assemble the native assembly language file into a program:
>  % gcc hello.s -o hello.native
> 8.Execute the native code program:
>  % ./hello.native
> -----------
>
> See how gcc is invoked to generate the final executable
> file.  This means LLVM is an incomplete backend,
> unfortunately.
>
> Here are the instructions for MS Win, where the situation is
> even worse:
> http://www.llvm.org/docs/GettingStartedVS.html#tutorial
>
> -----------
> 5. Compile the program to C using the LLC code generator:
>   % llc -march=c hello.bc
> 6. Compile to binary using Microsoft C:
>   % cl hello.cbe.c
> 7. Execute the native code program:
>   % hello.cbe.exe
> -----------
>
> See how nasty that is?  Compiling to C source code, and then
> invoking the Microsoft C compiler!  If you are going to do
> that, then you may as well just use the Microsoft C compiler
> by itself, and not bother with LLVM.  This is a major
> problem that needs to be resolved.
>
> Terence Parr wrote:
>> GCC is not the only assembler / linker on windoze.  I
>> believe M$ provides assemblers / linkers so people can
>> develop on windoze.
>
> Yes, but if you install the Microsoft development tools,
> then you may as well just use them to do everything, and not
> bother with LLVM.   But I would prefer to use LLVM.  But I
> can't because LLVM is missing the final stages.  LLVM is an
> incomplete backend.
>
> Bill Wendling wrote:
>> I don't know about your computer, by mine comes with an
>> assembler.
>
> MS Windows does not come with an assembler, AFAIK.  So your
> computer is superior in that area, yes, but we have
> customers using MS Win, and we have customers using Linux,
> and we need to support them both.
>
> John Criswell wrote:
>> As other have stated, most systems come with an assembler
>> (even GCC relies on an assembler to generate native code).
>
> Correct me if I am wrong, but MS Windows does not come with
> an assembler.  The Microsoft development tools can be
> obtained separately and installed, but that is too difficult
> for an average end-user to do -- we cannot reasonably tell
> them to first install the Microsoft dev tools before they
> can use our product.   And if installing the Microsoft dev
> tools is a requirement, then as I said, may as well just use
> them to do everything and not bother with LLVM, which is a
> real shame because I would prefer to use LLVM and get the
> other advantages of LLVM.
>
> jlh wrote:
>> GCC merely generates assembler files which then run
>> through the assembler to generate object files.  Then the
>> linker is called to generate the final executable.  GCC
>> just can call these steps for your convenience, but it
>> doesn't do it itself.  And there's nothing wrong with
>> separating those steps.  LLVM does exactly the same.
>
> Yes there is nothing wrong with separating those steps, but
> the point is that LLVM does not provide the necessary final
> steps to make a ready-to-execute .EXE or .DLL, and for this
> reason unfortunately LLVM fails to appeal over using the
> normal GCC or MS compiler.  But this issue could be solved,
> and then LLVM would be the better choice.
>
>> LLVM only uses GCC as a front-end for languages such as C
>> and C++.
>
> Additionally, LLVM appears to require use of the GCC package
> or MS compiler (or an assembler provided with the system) as
> part of the backend as well -- to generate the final
> ready-to-execute .EXE or .DLL file.  LLVM fails to provide a
> complete backend solution.
>
>> However, an own front-end (clang) is in the works, which
>> will remove this dependency.
>
> That doesn't help us.  We have a front-end.  We need a
> back-end.   But LLVM is an incomplete backend because LLVM
> by itself cannot generate ready-to-execute .EXE or .DLL
> file.
>
>> You also failed to see all the things that LLVM can do,
>> but stable GCCs can't.  For example
>> link-time-optimization, but there are many more
>> advantages.
>
> Yes LLVM is an excellent idea and a very worthy project, but
> this problem of it being an incomplete back-end is a major
> problem that should be rectified.
>
> Mark
>
>
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-- 
Emilio Wuerges
LAPS - Laboratorio de Automacao de Projeto de Sistemas
UFSC - Universidade Federal de Santa Catarina
Brasil