How can I create CallInst with a pointer to function

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1

Hi

I mean when I have in my program pointer to a function how should I
build IR to call the function by the pointer?
Or how can I create llvm::Function with a pointer to a function?
I want to have something like this:

int factorial (int n) { return n==0 ? 1 : n*factorial(n-1); }

typedef int (*intFunc) (int);
intFunc fptr = factorial;

Value * N = ConstantInt::get(Type::Int32Ty,10);
irb.CreateCall(fptr,N);

OR

Function *F = Function::Create(intFuncTy,Function::ExternalLinkage,fptr,myModule);
irb.CreateCall(F,N);

Thanks

2

If you're just asking how to construct an indirect call, then calling a LoadInst* or Argument* or any other Value* is no different than calling a Function*.

If your goal is to take an arbitrary function pointer (possibly precompiled) from the compiler's context and statically embed a call to it in the program you're building, then you can do this in a couple of ways. Both only work in a JIT context, for reasons that should be obvious.

The first is to use something like this:

   Value *value = ConstantExpr::getIntToPtr(
       ConstantInt::get(reinterpret_cast<intptr_t>(fptr)),
       FunctionType::get(.......));

Secondly, you can create a Function* with no body (a declaration) and then use ExecutionEngine::addGlobalMapping.

— Gordon