LLVM Insert function call into another function

Question

I am trying to insert function call inside a main function, so then when i run generated binary file, function will be executed automatically. Since language i am trying to "compile" looks like a "scripted" language :

function foo () begin 3 end;
function boo () begin 4 end;

writeln (foo()+boo()) ;
writeln (8) ;
writeln (9) ;

where writeln is a function available by default, and after executing binary i expect to see 7 8 9. Is there a way to insert last function call right before return statement of a main function ? Right now I have

define i32 @main() {
entry:
  ret i32 0
}

and i want to have something like

define i32 @main() {
entry:
  %calltmp = call double @writeln(double 7.000000e+00)
  %calltmp = call double @writeln(double 8.000000e+00)
  %calltmp = call double @writeln(double 9.000000e+00)
  ret i32 0
}

editing IR file manually and compile it afterwards works, but i want to do it in codegen part of my code.

edit

what i generate right now is

define double @__anon_expr() {
entry:
  %main = call double @writeln(double 3.000000e+00)
  ret double %main
}

define i32 @main() {
entry:
  ret i32 0
}

so when i execute binary - nothing happens

It's not quite clear what you're trying to do. If it is the IR you're generating anyway, you can do whatever you like. If you want to modify some existing IR - that's probably not what you should be doing. If you still insist, then just write a function pass and run it with opt. — SK-logic
– SK-logic, Commented May 12, 2019 at 12:11
@SK-logic I am generating IR, but i don't know how to add function calls inside a main function. Right now the look like this ``` define double @__anon_expr() { entry: %main = call double @writeln(double 3.000000e+00) ret double %main } define i32 @main() { entry: ret i32 0 } ``` so nothing is executed — John Galt
– John Galt, Commented May 12, 2019 at 12:13

Atyoum Ustainof · Accepted Answer · 2019-05-12 15:54:43Z

6

feel free to source your inspiration from here

Type * returnType = Type::getInt32Ty(TheContext);
std::vector<Type *> argTypes;
FunctionType * functionType = FunctionType::get(returnType, argTypes, false);
Function * function = Function::Create(functionType, Function::ExternalLinkage, "main", TheModule.get());

    BasicBlock * BB = BasicBlock::Create(TheContext, "entry", function);
    Builder.SetInsertPoint(BB);
    vector<Value *> args;
    args.push_back(ConstantFP::get(TheContext, APFloat(4.0)));
    Builder.CreateCall(getFunction("writeln"), args, "call");
    Value * returnValue = Builder.getInt32(0);
    Builder.CreateRet(returnValue);

edited May 12, 2019 at 15:54

answered May 12, 2019 at 12:50

Atyoum Ustainof

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