[LLVMdev] Handling of built-in functions

[Javier Martinez]

The issue is that there is no runtime function. I'm not sure we're in the
same page but just in case we aren't I'm trying to provide support for
built-in functions at compilation time. Some functions can be expressed in
LLVM and others only in the target language. For the first group I'm trying
to inline the implementation in a module pass added in addPassesToEmitFile.
For the second I'm thinking of using an asm node to insert the
implementation.

My first question was if the approach is correct; the second was how to add
the module pass if addPassesToEmitFile gets a FunctionPAssManager from otp.

Thanks,
Javier

On Mon, 20 Jul 2009 08:33:44 -0500, Kenneth Uildriks <kennethuil at gmail.com>
wrote:
> 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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