llvm dev - Sep 2013 - [LLVMdev] JIT compiled intrinsics calls is call to null pointer

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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Hi Taco,

We had a similar issue where a math intrinsic was being converted to a call
to null and it turned out to be because the system didn't support the CPU
instructions for the operation so the intrinsic used a call to the library
function (pow in your case). However because we weren't expecting this math
function to be looked up by MCJIT in our
JITMemoryManager::getPointerToNamedFunction() we weren't making it
available and it was returning null.

Not sure if this is relevant to your case but maybe it'll help point you in
the right direction.

Cheers,
Andrew


On Wed, Sep 18, 2013 at 8:32 AM, Taco H. in den Bosch <taco at
heddesit.nl>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.
>
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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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.
>
>
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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