How to get a pointer to a constant struct?


I'm trying to create a constant (named) struct and store a pointer to it in another struct using the C Api (and the llvm-fs bindings). As a contrived example, this is what I want to do:

%A = type { %VTable* }
%VTable = type { void (%A*)*, void (%A*)* }

define void @main(%A* %a) {
   %0 = getelementptr inbounds %A* %a, i32 0, i32 0 ; [type=%VTable**]
   %2 = somehow make a pointer to: { void(%A*)* null, void (%A*)* @main }
   store %VTable* %2, %VTable** %1
   ret void

How would I do the "somehow make a pointer to" part? I currently make the constant named struct by using LLVMConstNamedStruct(passing in %VTable, [null, @main]) and have tried using LLVMConstGEP with [0] as the indices on this but both times I get an assertion error saying:

"Assertion failed: getOperand(0)->getType() == cast<PointerType>(getOperand(1)->getType())->getElementType() && "Ptr must be a pointer to Val type!", file I
nstructions.cpp, line 1056"

Callum Rogers

(I am using LLVM 3.1 btw)

Hi Callum, if you want to take the address of a constant, then you need to
allocate some memory to hold the constant. This can be done as follows:
create a global variable (with the type T of your constant), use your constant
as the initial value, and mark the global as being constant (read-only). You
may want to give it private linkage so it isn't visible from outside of your
compile unit. The resulting GlobalVariable API object then has type T* and
is the pointer you are looking for.

Ciao, Duncan.