[LLVMdev] LLVM as a DLL

[Owen Anderson]

On May 10, 2008, at 4:42 AM, kr512 wrote:

>
> Hi there
>
> LLVM is a great idea, congratulations.  Do you mind if I
> give you a little bit of constructive criticism from the
> point of view of a developer who would like to use LLVM as a
> back-end?
>
> I will write this email from the point of view of MS
> Windows, but the same applies to MacOS and Linux.
>
> LLVM is difficult/awkward to use in a real-world
> environment/situation.  To solve this problem, take a hint
> from the developer of the popular SQLite:
> http://www.sqlite.org/download.html
>
> On that page, you can see that sqlite.org provides a
> precompiled sqlite DLL for MS Windows.  That is great,
> because it means that a developer can simply grab the
> compiled DLL, and start using it, incorporating it into
> their project, without having to go through all of the
> difficulty of compiling SQLite (or LLVM) themselves, and
> without having to make their program awkwardly invoke the
> LLVM command-line tools.

Question:  have you actually downloaded and built a copy of LLVM?  I'm  
going to guess that the answer is no, because otherwise you would have  
realized that LLVM is, in fact, already built as a set of libraries.   
The tools (llc, lli, opt, etc.) are just thin wrappers around these  
libraries.  They're only meant for use by LLVM developers.  Client  
applications are expected to use the LLVM APIs.

For examples of using it programmatically, see http://llvm.org/docs/tutorial/

>
>
> Furthermore, an LLVM DLL should go "all the way".   Your
> "llc" tool is supposed to be a back-end tool, but it is more
> like an almost-back-end tool, because it generates assembly
> language to a text file, rather than a native code
> executable program file.
>
> So we need a precompiled LLVM DLL that can be invoked,
> passing in LLVM bytecode, and it should generate a native
> code ready-to-execute MS Windows .EXE or .DLL file.   This
> would make it more practical to use in a real-world
> situation.
>
> GCC needs to be cut out of the back-end picture.  Currently,
> it is impossible to use LLVM as a back-end without GCC
> because GCC is still required to convert the assembly
> language .S text file into a native machine code .EXE or
> .DLL file.
>

Not true.  Two things are required: an assembler and a linker.  GCC  
uses both behind the scenes (gas and ld).  The invocation of GCC in  
the example docs you cited is purely for convenience.  It could  
equally well be replaced with invocations of gas and ld.

As a side note, there IS an assembler included with the MS toolset:  
MASM.  It's called ml.exe in recent versions, or ml64.exe for the 64- 
bit variant.  I have no idea if we currently generate MASM-syntax  
assembly.

--Owen
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