[LLVMdev] JIT compiled intrinsics calls is call to null pointer

[Nicholas Chapman]

Hi Taco,
I think I know what is happening here, I ran into it not too long ago.
if you are calling pow with a base of 2, e.g. pow(2.0f, x), then LLVM 
will try and optimise it to exp2f(x).
However exp2f doesn't exist on windows.
LLVM *should* know this, but it requires that you tell the target triple 
to the optimisation passes, something like:

fpm.add(new llvm::TargetLibraryInfo(llvm::Triple(this->triple)));

This requirement is undocumented.

Even doing this, the issue will still occur in LLVM 3.3, but is fixed in 
trunk.
For this reason powf() is the only intrinsic I don't use yet, I just use 
a call to the library function.

Cheers,
     Nick

Nicholas Chapman

Managing Director,
Glare Technologies Limited

On 18/09/2013 7:32 a.m., Taco H. in den Bosch wrote:
>
> Hi everyone,
>
> I am trying to call an LLVM intrinsic (llvm.pow.f32), inserted with 
> the following call:
>
> std::vector<llvm::Type *> arg_types;
> arg_types.push_back(llvm::Type::getFloatTy(context));
> auto function=llvm::Intrinsic::getDeclaration(module, 
> llvm::Intrinsic::pow, arg_types);
> auto result=ir_builder->CreateCall(function, args);
>
> When I try to execute the code generated by the JIT compiler, I see 
> that the intrinsic is not compiled into a math coprocessor 
> instruction, but in a call to a null address:
>
> 002300B8  sub esp,8
> 002300BB  movss       xmm0,dword ptr ds:[2300B0h]
> 002300C3  movss       dword ptr [esp+4],xmm0
> 002300C9  movss       xmm0,dword ptr ds:[2300B4h]
> 002300D1  movss       dword ptr [esp],xmm0
> 002300D6 call        00000000
> 002300DB  add         esp,8
> 002300DE  ret
>
> Is there anything special that I need to do in order to be able to 
> call intrinsics, either in general or when JITting? I am either doing 
> something wrong, or forgetting to do something, but I don't know what.
>
> I am working with a Visual Studio compiled version on Windows (x86).
>
> All hints will be appreciated, with kind regards,
>
> Taco H. in den Bosch.
>
>
>
>
>
>
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