[LLVMdev] Handling of built-in functions

[Javier Martinez]

The last sentence should have llc instead of opt.

On Tue, 21 Jul 2009 09:52:17 -0700, Javier Martinez <javier at jmartinez.org>
wrote:
> 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
llc.
> 
> 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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>> 
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