[LLVMdev] Handling of built-in functions

[Javier Martinez]

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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>>      
>
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