Create a LLVM function with a reference argument (e.g. double &x) - llvm

Question

I want to create, from scratch, a new function in LLVM IR. The LLVM code should correspond to a C++ function with a reference argument, say
void foo(double &x){
x=0;
}
The tutorial such as http://llvm.org/releases/2.6/docs/tutorial/JITTutorial1.html is too old (llvm 2.6) and does not consider pass-by-reference function.
Any hint on how to do this? Thanks.

Answer 1

In LLVM, Reference types are typically implemented with pointer types. For the following C++ source code,
int foo(int & i) {
return i;
}
int bar(int *i) {
return *i;
}
void baz(int i) {
foo(i);
bar(&i);
}
The corresponding IR is:
; Function Attrs: nounwind
define i32 #_Z3fooRi(i32* dereferenceable(4) %i) #0 {
entry:
%i.addr = alloca i32*, align 8
store i32* %i, i32** %i.addr, align 8
%0 = load i32*, i32** %i.addr, align 8
%1 = load i32, i32* %0, align 4
ret i32 %1
}
; Function Attrs: nounwind
define i32 #_Z3barPi(i32* %i) #0 {
entry:
%i.addr = alloca i32*, align 8
store i32* %i, i32** %i.addr, align 8
%0 = load i32*, i32** %i.addr, align 8
%1 = load i32, i32* %0, align 4
ret i32 %1
}
; Function Attrs: nounwind
define void #_Z3bazi(i32 %i) #0 {
entry:
%i.addr = alloca i32, align 4
store i32 %i, i32* %i.addr, align 4
%call = call i32 #_Z3fooRi(i32* dereferenceable(4) %i.addr)
%call1 = call i32 #_Z3barPi(i32* %i.addr)
ret void
}
You can find that there is no essential difference for i between functions foo and bar: dereferenceable is just a parameter attribute that you can add yourself during the code generation from the frontend.