How to produce a "Intrinsic Function" call instruction?

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#1

Hi, all.
I have noticed that LLVM supports some Intrinsic Functions such as "__llvm.sadd.with.overflow" described in http://llvm.org/docs/LangRef.html#int_sadd_overflow. We can use these functions and needn’t define the function bodies.

For example, I can manually insert codes:

%res = call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)
%sum = extractvalue {i32, i1} %res, 0
%obit = extractvalue {i32, i1} %res, 1
br i1 %obit, label %overflow, label %normal

into an assembly file, and it works OK.

And now, my question is “How to produce such a call instruction using the LLVM classes?”

I have also noticed that LLVM provides some classes like "MemCpyInst" to wrap the "llvm.memcpy" Intrinsic. But other intrinsic functions such as "__llvm.sadd.with.overflow" I’ve mentioned above don’t have the corresponding classes. How to deal with it?

Anyone could help me? Thank you!

#2

You can use your module to get the function or if not available create the function and use it like any other functions you may have. This how I do :

Function fun = 0;
if ((fun=module->getFunction(“llvm.sadd.with.overflow”))==0) {
vector<Type*> fun_arguments;
fun_arguments.push_back(…); //depends on your type
fun_arguments.push_back(…); //depends on your type
FunctionType *fun_type = FunctionType::get(Type::VoidTy, fun_arguments, false);
fun = llvm::Function::Create(fun_type, GlobalValue::ExternalLinkage, “llvm.sadd.with.overflow”, module);
}
// insert your call to fun here

Olivier.

#3

Hey,

?? wrote:

I have also noticed that LLVM provides some classes like
"/*MemCpyInst"*/ to wrap the "/*llvm.memcpy"*/ Intrinsic. But other
intrinsic functions such as /*"*//*llvm.sadd.with.overflow"*/ I've
mentioned above don't have the corresponding classes. How to deal with it?

For special instruction set intrinsics like SSE, you can use
Intrinsic::getDeclaration() which returns an llvm::Function* :
Intrinsic::getDeclaration(module, Intrinsic::sadd_with_overflow);

Have a look at include/llvm/Intrinsics.gen for the exact names.

Cheers,
Ralf