Does `noalias` still apply if a pointer is never dereferenced?

Beginners
1

I would like to know if the noalias/readonly annotation sticks to a pointer if it travels through another function. Eg:

define void @main(){
%x = alloca i16
store i16 0, ptr %x
%1 = call void @subfunc(%x,%0)
ret %1

define void @subfunc(i16 *readonly dereference{2} noalias data,i8* dereference{2} modify){
%0 = call Ptr @lauder(%data)
%1 = getelementptr i8 i16* i8 1
%2 = load i8 ptr %1
store i8 %data ptr %1
}
define Ptr @launder(Ptr target){
ret %target
}

Would this cause Undefined Behavior? It might because I am writing through a pointer marked readonly, but the the data written to is never accessed in the function and the pointer is passed through a different function first. If it is Undefined Behavior, is there a way to change @launder so it does work?

2

Could you please fix your IR so it is valid? It is currently broken to the point that it’s not clear what you’re asking.

Noalias applies if the memory location is written while the noalias pointer is live. It is not possible to “launder” a noalias pointer in anyway.