Don't touch gvars when compiling for an external back-end.

[maleadt]

I noticed in JuliaGPU/CUDA.jl#552 that exported global variables in an llvmcall got internalized along the way:

function main()
    Base.llvmcall(
        ("""@constant_memory = addrspace(4) externally_initialized global [1 x i32] [i32 42]
            define void @entry() {
                ret void
            }
         """, "entry"), Nothing, Tuple{})
end

main()  # make sure it works


## compile the code using the aot compiler interface

using LLVM

# get the method instance
world = Base.get_world_counter()
meth = which(main, Tuple{})
sig = Base.signature_type(main, Tuple{})::Type
(ti, env) = ccall(:jl_type_intersection_with_env, Any,
                    (Any, Any), sig, meth.sig)::Core.SimpleVector
meth = Base.func_for_method_checked(meth, ti, env)
method_instance = ccall(:jl_specializations_get_linfo, Ref{Core.MethodInstance},
                (Any, Any, Any, UInt), meth, ti, env, world)

# set-up the compiler interface
params = Base.CodegenParams()

# generate IR
native_code = ccall(:jl_create_native, Ptr{Cvoid},
                    (Vector{Core.MethodInstance}, Base.CodegenParams, Cint),
                    [method_instance], params, #=extern policy=# 1)
@assert native_code != C_NULL
llvm_mod_ref = ccall(:jl_get_llvm_module, LLVM.API.LLVMModuleRef,
                        (Ptr{Cvoid},), native_code)
@assert llvm_mod_ref != C_NULL
llvm_mod = LLVM.Module(llvm_mod_ref)

@constant_memory = internal addrspace(4) externally_initialized global [1 x i32] [i32 42]

It seems like this functionality should not trigger when compiling for an external compiler back-end.

---

FWIW, regular @code_llvm does not trigger this conversion, so just doing @code_llvm dump_module=true main() still results in:

@constant_memory = addrspace(4) externally_initialized global [1 x i32] [i32 42]

[vchuravy]

Means backends will have to initialize the personality functions themselves, but I suspect that's okay.

[maleadt]

CI failures unrelated (Profile, timeout).

[KristofferC]

Might have been good to squash.

[maleadt]

Ah, of course... 🤦‍♂️