[OCaml] Handle nullptr in Llvm.global_initializer

[kren1]

Summary

LLVMGetInitializer returns nullptr in case there is no
initializer. There is not much that can be done with nullptr in OCaml,
not even test if it is null. Also, there does not seem to be a C or
OCaml API to test if there is an initializer. So this diff changes
Llvm.global_initializer to return an option.

[whitequark]

LGTM

[kren1]

Thanks @whitequark . @modocache could you commit this for me?

[gribozavr]

This change broke tests: http://lab.llvm.org:8011/builders/clang-x86_64-debian-fast/builds/18485. I reverted it in r373311.

Committers: please always run ninja check-all before committing.

[kren1]

Apologies my bad, forgot to run the tests for this one...

I fixed the LLVM (ocaml) tests. I don't believe the clang failure was my fault and check-all passes in my setup.

[vaivaswatha]

llvm/bindings/ocaml/llvm/llvm_ocaml.c

1341 ↗

(On Diff #331257)

ptr_to_option was recently introduced and is defined in this same file above. So you could just do something like this: https://github.com/llvm/llvm-project/blob/main/llvm/bindings/ocaml/debuginfo/debuginfo_ocaml.c#L839

[jberdine]

llvm/bindings/ocaml/llvm/llvm_ocaml.c

1341 ↗

(On Diff #331257)

Good call, I will send such a simplification.

bindings/ocaml/llvm/llvm.ml

 external define_global : string -> llvalue -> llmodule -> llvalue
                        = "llvm_define_global"
 external define_qualified_global : string -> llvalue -> int -> llmodule ->
                                    llvalue
                                  = "llvm_define_qualified_global"
 external lookup_global : string -> llmodule -> llvalue option
                        = "llvm_lookup_global"
 external delete_global : llvalue -> unit = "llvm_delete_global"
-external global_initializer : llvalue -> llvalue = "LLVMGetInitializer"
+external global_initializer : llvalue -> llvalue option = "llvm_global_initializer"
 external set_initializer : llvalue -> llvalue -> unit = "llvm_set_initializer"
 external remove_initializer : llvalue -> unit = "llvm_remove_initializer"
 external is_thread_local : llvalue -> bool = "llvm_is_thread_local"
 external set_thread_local : bool -> llvalue -> unit = "llvm_set_thread_local"
 external thread_local_mode : llvalue -> ThreadLocalMode.t
                            = "llvm_thread_local_mode"
 external set_thread_local_mode : ThreadLocalMode.t -> llvalue -> unit
                                = "llvm_set_thread_local_mode"

bindings/ocaml/llvm/llvm.mli

(** [is_global_constant gv] returns [true] if the global variabile [gv] is a
     See the method [llvm::GlobalVariable::isConstant]. *)
 val is_global_constant : llvalue -> bool
 
 (** [set_global_constant c gv] sets the global variable [gv] to be a constant if
     [c] is [true] and not if [c] is [false].
     See the method [llvm::GlobalVariable::setConstant]. *)
 val set_global_constant : bool -> llvalue -> unit
 
-(** [global_initializer gv] returns the initializer for the global variable
-    [gv]. See the method [llvm::GlobalVariable::getInitializer]. *)
-val global_initializer : llvalue -> llvalue
+(** [global_initializer gv] If global variable [gv] has an initializer it is returned,
+    otherwise returns [None]. See the method [llvm::GlobalVariable::getInitializer]. *)
+val global_initializer : llvalue -> llvalue option
 
 (** [set_initializer c gv] sets the initializer for the global variable
     [gv] to the constant [c].
     See the method [llvm::GlobalVariable::setInitializer]. *)
 val set_initializer : llvalue -> llvalue -> unit
 
 (** [remove_initializer gv] unsets the initializer for the global variable
     [gv].

bindings/ocaml/llvm/llvm_ocaml.c

 }
 
 /* llvalue -> unit */
 CAMLprim value llvm_delete_global(LLVMValueRef GlobalVar) {
   LLVMDeleteGlobal(GlobalVar);
   return Val_unit;
 }
 
+/* llvalue -> llvalue option */
+CAMLprim value llvm_global_initializer(LLVMValueRef GlobalVar) {
+  CAMLparam0();
+  LLVMValueRef Init;
+  if ((Init = LLVMGetInitializer(GlobalVar))) {
+    value Option = alloc(1, 0);
+    Field(Option, 0) = (value) Init;
+    CAMLreturn(Option);
+  }
+  CAMLreturn(Val_int(0));
+}
+
 /* llvalue -> llvalue -> unit */
 CAMLprim value llvm_set_initializer(LLVMValueRef ConstantVal,
                                     LLVMValueRef GlobalVar) {
   LLVMSetInitializer(GlobalVar, ConstantVal);
   return Val_unit;
 }
 
 /* llvalue -> unit */