[LLVMdev] Handling of built-in functions

[Kenneth Uildriks]

I don't see why.  Your compiler would just do a declare and then a
call, and your runtime function gets called.

On Mon, Jul 20, 2009 at 4:13 AM, Javier Martinez<javier at jmartinez.org> wrote:
> Hi Daniel,
>
> Thanks for the reply. If I understand correctly, your suggestion is to have
> the backend call a library that handles the built-in functions. Would the
> calls need to be lowered and redirected (e.g. by a big switch statement or a
> jump table) to the corresponding function in the library?
>
> Thanks,
> Javier
>
> On 7/20/2009 12:11 AM, Daniel Dunbar wrote:
>
> Hi Javier,
>
> I'm not the right person to answer your question, but since no one
> else took it: I believe this is a situation where the backend would
> typically emit a call the the compiler's runtime library (e.g.,
> libgcc).
>
> While it isn't currently completely wired up, we do have our own
> compiler runtime library available under the compiler-rt project in
> the LLVM repo.
>
>  - Daniel
>
> On Thu, Jul 16, 2009 at 2:07 AM, Javier Martinez<javier at jmartinez.org>
> wrote:
>
>
> Hi,
>
> I'm trying to add support in my back end for certain functions that are
> seen as built-in by the target. Some of these functions can be
> implemented in a) LLVM, and some in b) the native target language.
>
> My approach to case a) is to write the built-in function implementation
> in C, compile it to LLVM using Clang, link it to the module that uses it
> and finally add a pass to inline it. The last two steps can be made
> inside a ModulePass. The definition of TargetMachine allows for any pass
> manager deriving form BasicPass to be passed to AddPassesToEmitFile.
> However, I see that llc uses a FunctionPassManager for all the passes. A
> (module)PassManager is used only if the target implements
> AddPassesToEmitWholeFile but the comments on the base class discourage
> this path. Am I approaching the problem the wrong way?
>
> I haven't worked much on case b) but my idea was to use a similar
> approach but instead of writing the built-in function implementation in
> straight C an asm block would be used to insert the code. Does this make
> sense?
>
> Thanks,
> Javier
>
>
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