flambda_invariants.ml

(**************************************************************************)
(*                                                                        *)
(*                                 OCaml                                  *)
(*                                                                        *)
(*                       Pierre Chambart, OCamlPro                        *)
(*           Mark Shinwell and Leo White, Jane Street Europe              *)
(*                                                                        *)
(*   Copyright 2013--2016 OCamlPro SAS                                    *)
(*   Copyright 2014--2016 Jane Street Group LLC                           *)
(*                                                                        *)
(*   All rights reserved.  This file is distributed under the terms of    *)
(*   the GNU Lesser General Public License version 2.1, with the          *)
(*   special exception on linking described in the file LICENSE.          *)
(*                                                                        *)
(**************************************************************************)

[@@@ocaml.warning "+a-4-30-40-41-42"]

type flambda_kind =
  | Normal
  | Lifted

(* Explicit "ignore" functions.  We name every pattern variable, avoiding
   underscores, to try to avoid accidentally failing to handle (for example)
   a particular variable.
   We also avoid explicit record field access during the checking functions,
   preferring instead to use exhaustive record matches.
*)
(* CR-someday pchambart: for sum types, we should probably add an exhaustive
   pattern in ignores functions to be reminded if a type change *)
let already_added_bound_variable_to_env (_ : Variable.t) = ()
let will_traverse_named_expression_later (_ : Flambda.named) = ()
let ignore_variable (_ : Variable.t) = ()
let ignore_call_kind (_ : Flambda.call_kind) = ()
let ignore_debuginfo (_ : Debuginfo.t) = ()
let ignore_meth_kind (_ : Lambda.meth_kind) = ()
let ignore_int (_ : int) = ()
let ignore_int_set (_ : Numbers.Int.Set.t) = ()
let ignore_bool (_ : bool) = ()
let ignore_string (_ : string) = ()
let ignore_static_exception (_ : Static_exception.t) = ()
let ignore_direction_flag (_ : Asttypes.direction_flag) = ()
let ignore_primitive ( _ : Lambda.primitive) = ()
let ignore_const (_ : Flambda.const) = ()
let ignore_allocated_const (_ : Allocated_const.t) = ()
let ignore_set_of_closures_id (_ : Set_of_closures_id.t) = ()
let ignore_set_of_closures_origin (_ : Set_of_closures_origin.t) = ()
let ignore_closure_id (_ : Closure_id.t) = ()
let ignore_var_within_closure (_ : Var_within_closure.t) = ()
let ignore_tag (_ : Tag.t) = ()
let ignore_inline_attribute (_ : Lambda.inline_attribute) = ()
let ignore_specialise_attribute (_ : Lambda.specialise_attribute) = ()
let ignore_value_kind (_ : Lambda.value_kind) = ()

exception Binding_occurrence_not_from_current_compilation_unit of Variable.t
exception Mutable_binding_occurrence_not_from_current_compilation_unit of
  Mutable_variable.t
exception Binding_occurrence_of_variable_already_bound of Variable.t
exception Binding_occurrence_of_mutable_variable_already_bound of
  Mutable_variable.t
exception Binding_occurrence_of_symbol_already_bound of Symbol.t
exception Unbound_variable of Variable.t
exception Unbound_mutable_variable of Mutable_variable.t
exception Unbound_symbol of Symbol.t
exception Vars_in_function_body_not_bound_by_closure_or_params of
  Variable.Set.t * Flambda.set_of_closures * Variable.t
exception Function_decls_have_overlapping_parameters of Variable.Set.t
exception Specialised_arg_that_is_not_a_parameter of Variable.t
exception Projection_must_be_a_free_var of Projection.t
exception Projection_must_be_a_specialised_arg of Projection.t
exception Free_variables_set_is_lying of
  Variable.t * Variable.Set.t * Variable.Set.t * Flambda.function_declaration
exception Set_of_closures_free_vars_map_has_wrong_range of Variable.Set.t
exception Static_exception_not_caught of Static_exception.t
exception Static_exception_caught_in_multiple_places of Static_exception.t
exception Access_to_global_module_identifier of Lambda.primitive
exception Pidentity_should_not_occur
exception Pdirapply_should_be_expanded
exception Prevapply_should_be_expanded
exception Sequential_logical_operator_primitives_must_be_expanded of
  Lambda.primitive
exception Var_within_closure_bound_multiple_times of Var_within_closure.t
exception Declared_closure_from_another_unit of Compilation_unit.t
exception Closure_id_is_bound_multiple_times of Closure_id.t
exception Set_of_closures_id_is_bound_multiple_times of Set_of_closures_id.t
exception Unbound_closure_ids of Closure_id.Set.t
exception Unbound_vars_within_closures of Var_within_closure.Set.t
exception Move_to_a_closure_not_in_the_free_variables
  of Variable.t * Variable.Set.t

exception Flambda_invariants_failed

(* CR-someday mshinwell: We should make "direct applications should not have
   overapplication" be an invariant throughout.  At the moment I think this is
   only true after [Inline_and_simplify] has split overapplications. *)

(* CR-someday mshinwell: What about checks for shadowed variables and
   symbols? *)

let variable_and_symbol_invariants (program : Flambda.program) =
  let all_declared_variables = ref Variable.Set.empty in
  let declare_variable var =
    if Variable.Set.mem var !all_declared_variables then
      raise (Binding_occurrence_of_variable_already_bound var);
    all_declared_variables := Variable.Set.add var !all_declared_variables
  in
  let declare_variables vars =
    Variable.Set.iter declare_variable vars
  in
  let all_declared_mutable_variables = ref Mutable_variable.Set.empty in
  let declare_mutable_variable mut_var =
    if Mutable_variable.Set.mem mut_var !all_declared_mutable_variables then
      raise (Binding_occurrence_of_mutable_variable_already_bound mut_var);
    all_declared_mutable_variables :=
      Mutable_variable.Set.add mut_var !all_declared_mutable_variables
  in
  let add_binding_occurrence (var_env, mut_var_env, sym_env) var =
    let compilation_unit = Compilation_unit.get_current_exn () in
    if not (Variable.in_compilation_unit var compilation_unit) then
      raise (Binding_occurrence_not_from_current_compilation_unit var);
    declare_variable var;
    Variable.Set.add var var_env, mut_var_env, sym_env
  in
  let add_mutable_binding_occurrence (var_env, mut_var_env, sym_env) mut_var =
    let compilation_unit = Compilation_unit.get_current_exn () in
    if not (Mutable_variable.in_compilation_unit mut_var compilation_unit) then
      raise (Mutable_binding_occurrence_not_from_current_compilation_unit
        mut_var);
    declare_mutable_variable mut_var;
    var_env, Mutable_variable.Set.add mut_var mut_var_env, sym_env
  in
  let add_binding_occurrence_of_symbol (var_env, mut_var_env, sym_env) sym =
    if Symbol.Set.mem sym sym_env then
      raise (Binding_occurrence_of_symbol_already_bound sym)
    else
      var_env, mut_var_env, Symbol.Set.add sym sym_env
  in
  let add_binding_occurrences env vars =
    List.fold_left (fun env var -> add_binding_occurrence env var) env vars
  in
  let check_variable_is_bound (var_env, _, _) var =
    if not (Variable.Set.mem var var_env) then raise (Unbound_variable var)
  in
  let check_symbol_is_bound (_, _, sym_env) sym =
    if not (Symbol.Set.mem sym sym_env) then raise (Unbound_symbol sym)
  in
  let check_variables_are_bound env vars =
    List.iter (check_variable_is_bound env) vars
  in
  let check_mutable_variable_is_bound (_, mut_var_env, _) mut_var =
    if not (Mutable_variable.Set.mem mut_var mut_var_env) then begin
      raise (Unbound_mutable_variable mut_var)
    end
  in
  let rec loop env (flam : Flambda.t) =
    match flam with
    (* Expressions that can bind [Variable.t]s: *)
    | Let { var; defining_expr; body; _ } ->
      loop_named env defining_expr;
      loop (add_binding_occurrence env var) body
    | Let_mutable { var = mut_var; initial_value = var;
                    body; contents_kind } ->
      ignore_value_kind contents_kind;
      check_variable_is_bound env var;
      loop (add_mutable_binding_occurrence env mut_var) body
    | Let_rec (defs, body) ->
      let env =
        List.fold_left (fun env (var, def) ->
            will_traverse_named_expression_later def;
            add_binding_occurrence env var)
          env defs
      in
      List.iter (fun (var, def) ->
        already_added_bound_variable_to_env var;
        loop_named env def) defs;
      loop env body
    | For { bound_var; from_value; to_value; direction; body; } ->
      ignore_direction_flag direction;
      check_variable_is_bound env from_value;
      check_variable_is_bound env to_value;
      loop (add_binding_occurrence env bound_var) body
    | Static_catch (static_exn, vars, body, handler) ->
      ignore_static_exception static_exn;
      loop env body;
      loop (add_binding_occurrences env vars) handler
    | Try_with (body, var, handler) ->
      loop env body;
      loop (add_binding_occurrence env var) handler
    (* Everything else: *)
    | Var var -> check_variable_is_bound env var
    | Apply { func; args; kind; dbg; inline; specialise; } ->
      check_variable_is_bound env func;
      check_variables_are_bound env args;
      ignore_call_kind kind;
      ignore_debuginfo dbg;
      ignore_inline_attribute inline;
      ignore_specialise_attribute specialise
    | Assign { being_assigned; new_value; } ->
      check_mutable_variable_is_bound env being_assigned;
      check_variable_is_bound env new_value
    | Send { kind; meth; obj; args; dbg; } ->
      ignore_meth_kind kind;
      check_variable_is_bound env meth;
      check_variable_is_bound env obj;
      check_variables_are_bound env args;
      ignore_debuginfo dbg
    | If_then_else (cond, ifso, ifnot) ->
      check_variable_is_bound env cond;
      loop env ifso;
      loop env ifnot
    | Switch (arg, { numconsts; consts; numblocks; blocks; failaction; }) ->
      check_variable_is_bound env arg;
      ignore_int_set numconsts;
      ignore_int_set numblocks;
      List.iter (fun (n, e) ->
          ignore_int n;
          loop env e)
        (consts @ blocks);
      Misc.may (loop env) failaction
    | String_switch (arg, cases, e_opt) ->
      check_variable_is_bound env arg;
      List.iter (fun (label, case) ->
          ignore_string label;
          loop env case)
        cases;
      Misc.may (loop env) e_opt
    | Static_raise (static_exn, es) ->
      ignore_static_exception static_exn;
      List.iter (check_variable_is_bound env) es
    | While (e1, e2) ->
      loop env e1;
      loop env e2
    | Proved_unreachable -> ()
  and loop_named env (named : Flambda.named) =
    match named with
    | Symbol symbol -> check_symbol_is_bound env symbol
    | Const const -> ignore_const const
    | Allocated_const const -> ignore_allocated_const const
    | Read_mutable mut_var ->
      check_mutable_variable_is_bound env mut_var
    | Read_symbol_field (symbol, index) ->
      check_symbol_is_bound env symbol;
      assert (index >= 0)  (* CR-someday mshinwell: add proper error *)
    | Set_of_closures set_of_closures ->
      loop_set_of_closures env set_of_closures
    | Project_closure { set_of_closures; closure_id; } ->
      check_variable_is_bound env set_of_closures;
      ignore_closure_id closure_id
    | Move_within_set_of_closures { closure; start_from; move_to; } ->
      check_variable_is_bound env closure;
      ignore_closure_id start_from;
      ignore_closure_id move_to;
    | Project_var { closure; closure_id; var; } ->
      check_variable_is_bound env closure;
      ignore_closure_id closure_id;
      ignore_var_within_closure var
    | Prim (prim, args, dbg) ->
      ignore_primitive prim;
      check_variables_are_bound env args;
      ignore_debuginfo dbg
    | Expr expr ->
      loop env expr
  and loop_set_of_closures env
      ({ Flambda.function_decls; free_vars; specialised_args;
          direct_call_surrogates = _; } as set_of_closures) =
      (* CR-soon mshinwell: check [direct_call_surrogates] *)
    let { Flambda. is_classic_mode;
          set_of_closures_id; set_of_closures_origin; funs; } =
        function_decls
      in
      ignore (is_classic_mode : bool);
      ignore_set_of_closures_id set_of_closures_id;
      ignore_set_of_closures_origin set_of_closures_origin;
      let functions_in_closure = Variable.Map.keys funs in
      let variables_in_closure =
        Variable.Map.fold (fun var (var_in_closure : Flambda.specialised_to)
                  variables_in_closure ->
            (* [var] may occur in the body, but will effectively be renamed
               to [var_in_closure], so the latter is what we check to make
               sure it's bound. *)
            ignore_variable var;
            check_variable_is_bound env var_in_closure.var;
            Variable.Set.add var variables_in_closure)
          free_vars Variable.Set.empty
      in
      let all_params, all_free_vars =
        Variable.Map.fold (fun fun_var function_decl acc ->
            let all_params, all_free_vars = acc in
            (* CR-soon mshinwell: check function_decl.all_symbols *)
            let { Flambda.params; body; free_variables; stub; dbg; _ } =
              function_decl
            in
            assert (Variable.Set.mem fun_var functions_in_closure);
            ignore_bool stub;
            ignore_debuginfo dbg;
            (* Check that [free_variables], which is only present as an
               optimization, is not lying. *)
            let free_variables' = Flambda.free_variables body in
            if not (Variable.Set.subset free_variables' free_variables) then
              raise (Free_variables_set_is_lying (fun_var,
                free_variables, free_variables', function_decl));
            (* Check that every variable free in the body of the function is
               bound by either the set of closures or the parameter list. *)
            let acceptable_free_variables =
              Variable.Set.union
                (Variable.Set.union variables_in_closure functions_in_closure)
                (Parameter.Set.vars params)
            in
            let bad =
              Variable.Set.diff free_variables acceptable_free_variables
            in
            if not (Variable.Set.is_empty bad) then begin
              raise (Vars_in_function_body_not_bound_by_closure_or_params
                (bad, set_of_closures, fun_var))
            end;
            (* Check that parameters are unique across all functions in the
               declaration. *)
            let old_all_params_size = Variable.Set.cardinal all_params in
            let params = Parameter.Set.vars params in
            let params_size = Variable.Set.cardinal params in
            let all_params = Variable.Set.union all_params params in
            let all_params_size = Variable.Set.cardinal all_params in
            if all_params_size <> old_all_params_size + params_size then begin
              raise (Function_decls_have_overlapping_parameters all_params)
            end;
            (* Check that parameters and function variables are not
               bound somewhere else in the program *)
            declare_variables params;
            declare_variable fun_var;
            (* Check that the body of the functions is correctly structured *)
            let body_env =
              let (var_env, _, sym_env) = env in
              let var_env =
                Variable.Set.fold (fun var -> Variable.Set.add var)
                  free_variables var_env
              in
              (* Mutable variables cannot be captured by closures *)
              let mut_env = Mutable_variable.Set.empty in
              (var_env, mut_env, sym_env)
            in
            loop body_env body;
            all_params, Variable.Set.union free_variables all_free_vars)
          funs (Variable.Set.empty, Variable.Set.empty)
      in
      (* CR-soon pchambart: This is not a property that we can certainly
         ensure.
         If the function get inlined, it is possible for the inlined version
         to still use that variable. To be able to ensure that, we need to
         also ensure that the inlined version will certainly be transformed
         in a same way that can drop the dependency.
         mshinwell: This should get some thought after the first release to
         decide for sure what to do. *)
      (* Check that the free variables rewriting map in the set of closures
         does not contain variables in its domain that are not actually free
         variables of any of the function bodies. *)
      let bad_free_vars =
        Variable.Set.diff (Variable.Map.keys free_vars) all_free_vars
      in
(*
      if not (Variable.Set.is_empty bad_free_vars) then begin
        raise (Set_of_closures_free_vars_map_has_wrong_range bad_free_vars)
      end;
*)
      (* CR-someday pchambart: Ignore it to avoid the warning: get rid of that
         when the case is settled *)
      ignore (Set_of_closures_free_vars_map_has_wrong_range bad_free_vars);
      (* Check that free variables are not bound somewhere
         else in the program *)
      declare_variables (Variable.Map.keys free_vars);
      (* Check that every "specialised arg" is a parameter of one of the
         functions being declared, and that the variable to which the
         parameter is being specialised is bound. *)
      Variable.Map.iter (fun _inner_var
                (specialised_to : Flambda.specialised_to) ->
          check_variable_is_bound env specialised_to.var;
          match specialised_to.projection with
          | None -> ()
          | Some projection ->
            let projecting_from = Projection.projecting_from projection in
            if not (Variable.Map.mem projecting_from free_vars)
            then begin
              raise (Projection_must_be_a_free_var projection)
            end)
        free_vars;
      Variable.Map.iter (fun being_specialised
                (specialised_to : Flambda.specialised_to) ->
          if not (Variable.Set.mem being_specialised all_params) then begin
            raise (Specialised_arg_that_is_not_a_parameter being_specialised)
          end;
          check_variable_is_bound env specialised_to.var;
          match specialised_to.projection with
          | None -> ()
          | Some projection ->
            let projecting_from = Projection.projecting_from projection in
            if not (Variable.Map.mem projecting_from specialised_args)
            then begin
              raise (Projection_must_be_a_specialised_arg projection)
            end)
        specialised_args
  in
  let loop_constant_defining_value env
        (const : Flambda.constant_defining_value) =
    match const with
    | Flambda.Allocated_const c ->
      ignore_allocated_const c
    | Flambda.Block (tag,fields) ->
      ignore_tag tag;
      List.iter (fun (fields : Flambda.constant_defining_value_block_field) ->
          match fields with
          | Const c -> ignore_const c
          | Symbol s -> check_symbol_is_bound env s)
        fields
    | Flambda.Set_of_closures set_of_closures ->
      loop_set_of_closures env set_of_closures;
      (* Constant set of closures must not have free variables *)
      if not (Variable.Map.is_empty set_of_closures.free_vars) then
        assert false; (* TODO: correct error *)
      if not (Variable.Map.is_empty set_of_closures.specialised_args) then
        assert false; (* TODO: correct error *)
    | Flambda.Project_closure (symbol,closure_id) ->
      ignore_closure_id closure_id;
      check_symbol_is_bound env symbol
  in
  let rec loop_program_body env (program : Flambda.program_body) =
    match program with
    | Let_rec_symbol (defs, program) ->
      let env =
        List.fold_left (fun env (symbol, _) ->
            add_binding_occurrence_of_symbol env symbol)
          env defs
      in
      List.iter (fun (_, def) ->
          loop_constant_defining_value env def)
        defs;
      loop_program_body env program
    | Let_symbol (symbol, def, program) ->
      loop_constant_defining_value env def;
      let env = add_binding_occurrence_of_symbol env symbol in
      loop_program_body env program
    | Initialize_symbol (symbol, _tag, fields, program) ->
      List.iter (loop env) fields;
      let env = add_binding_occurrence_of_symbol env symbol in
      loop_program_body env program
    | Effect (expr, program) ->
      loop env expr;
      loop_program_body env program
    | End root ->
      check_symbol_is_bound env root
  in
  let env =
    Symbol.Set.fold (fun symbol env ->
        add_binding_occurrence_of_symbol env symbol)
      program.imported_symbols
      (Variable.Set.empty, Mutable_variable.Set.empty, Symbol.Set.empty)
  in
  loop_program_body env program.program_body

let primitive_invariants flam ~no_access_to_global_module_identifiers =
  Flambda_iterators.iter_named (function
      | Prim (prim, _, _) ->
        begin match prim with
        | Psequand | Psequor ->
          raise (Sequential_logical_operator_primitives_must_be_expanded prim)
        | Pgetglobal id ->
          if no_access_to_global_module_identifiers
            && not (Ident.is_predef_exn id) then
          begin
            raise (Access_to_global_module_identifier prim)
          end
        | Pidentity -> raise Pidentity_should_not_occur
        | Pdirapply -> raise Pdirapply_should_be_expanded
        | Prevapply -> raise Prevapply_should_be_expanded
        | _ -> ()
        end
      | _ -> ())
    flam

let declared_var_within_closure (flam:Flambda.program) =
  let bound = ref Var_within_closure.Set.empty in
  let bound_multiple_times = ref None in
  let add_and_check var =
    if Var_within_closure.Set.mem var !bound then begin
      bound_multiple_times := Some var
    end;
    bound := Var_within_closure.Set.add var !bound
  in
  Flambda_iterators.iter_on_set_of_closures_of_program
    ~f:(fun ~constant:_ { Flambda. free_vars; _ } ->
      Variable.Map.iter (fun id _ ->
          let var = Var_within_closure.wrap id in
          add_and_check var)
        free_vars)
    flam;
  !bound, !bound_multiple_times

let no_var_within_closure_is_bound_multiple_times (flam:Flambda.program) =
  match declared_var_within_closure flam with
  | _, Some var -> raise (Var_within_closure_bound_multiple_times var)
  | _, None -> ()

let every_declared_closure_is_from_current_compilation_unit flam =
  let current_compilation_unit = Compilation_unit.get_current_exn () in
  Flambda_iterators.iter_on_sets_of_closures (fun
        { Flambda. function_decls; _ } ->
      let compilation_unit =
        Set_of_closures_id.get_compilation_unit
          function_decls.set_of_closures_id
      in
      if not (Compilation_unit.equal compilation_unit current_compilation_unit)
      then raise (Declared_closure_from_another_unit compilation_unit))
    flam

let declared_closure_ids program =
  let bound = ref Closure_id.Set.empty in
  let bound_multiple_times = ref None in
  let add_and_check var =
    if Closure_id.Set.mem var !bound
    then bound_multiple_times := Some var;
    bound := Closure_id.Set.add var !bound
  in
  Flambda_iterators.iter_on_set_of_closures_of_program program
    ~f:(fun ~constant:_ { Flambda. function_decls; _; } ->
        Variable.Map.iter (fun id _ ->
            let var = Closure_id.wrap id in
            add_and_check var)
          function_decls.funs);
  !bound, !bound_multiple_times

let no_closure_id_is_bound_multiple_times program =
  match declared_closure_ids program with
  | _, Some closure_id ->
    raise (Closure_id_is_bound_multiple_times closure_id)
  | _, None -> ()

let declared_set_of_closures_ids program =
  let bound = ref Set_of_closures_id.Set.empty in
  let bound_multiple_times = ref None in
  let add_and_check var =
    if Set_of_closures_id.Set.mem var !bound
    then bound_multiple_times := Some var;
    bound := Set_of_closures_id.Set.add var !bound
  in
  Flambda_iterators.iter_on_set_of_closures_of_program program
    ~f:(fun ~constant:_ { Flambda. function_decls; _; } ->
        add_and_check function_decls.set_of_closures_id);
  !bound, !bound_multiple_times

let no_set_of_closures_id_is_bound_multiple_times program =
  match declared_set_of_closures_ids program with
  | _, Some set_of_closures_id ->
    raise (Set_of_closures_id_is_bound_multiple_times set_of_closures_id)
  | _, None -> ()

let used_closure_ids (program:Flambda.program) =
  let used = ref Closure_id.Set.empty in
  let f (flam : Flambda.named) =
    match flam with
    | Project_closure { closure_id; _} ->
      used := Closure_id.Set.add closure_id !used;
    | Move_within_set_of_closures { closure = _; start_from; move_to; } ->
      used := Closure_id.Set.add start_from !used;
      used := Closure_id.Set.add move_to !used
    | Project_var { closure = _; closure_id; var = _ } ->
      used := Closure_id.Set.add closure_id !used
    | Set_of_closures _ | Symbol _ | Const _ | Allocated_const _
    | Prim _ | Expr _ | Read_mutable _ | Read_symbol_field _ -> ()
  in
  (* CR-someday pchambart: check closure_ids of constant_defining_values'
     project_closures *)
  Flambda_iterators.iter_named_of_program ~f program;
  !used

let used_vars_within_closures (flam:Flambda.program) =
  let used = ref Var_within_closure.Set.empty in
  let f (flam : Flambda.named) =
    match flam with
    | Project_var { closure = _; closure_id = _; var; } ->
      used := Var_within_closure.Set.add var !used
    | _ -> ()
  in
  Flambda_iterators.iter_named_of_program ~f flam;
  !used

let every_used_function_from_current_compilation_unit_is_declared
      (program:Flambda.program) =
  let current_compilation_unit = Compilation_unit.get_current_exn () in
  let declared, _ = declared_closure_ids program in
  let used = used_closure_ids program in
  let used_from_current_unit =
    Closure_id.Set.filter (fun cu ->
        Closure_id.in_compilation_unit cu current_compilation_unit)
      used
  in
  let counter_examples =
    Closure_id.Set.diff used_from_current_unit declared
  in
  if Closure_id.Set.is_empty counter_examples
  then ()
  else raise (Unbound_closure_ids counter_examples)

let every_used_var_within_closure_from_current_compilation_unit_is_declared
      (flam:Flambda.program) =
  let current_compilation_unit = Compilation_unit.get_current_exn () in
  let declared, _ = declared_var_within_closure flam in
  let used = used_vars_within_closures flam in
  let used_from_current_unit =
    Var_within_closure.Set.filter (fun cu ->
        Var_within_closure.in_compilation_unit cu current_compilation_unit)
      used
  in
  let counter_examples =
    Var_within_closure.Set.diff used_from_current_unit declared in
  if Var_within_closure.Set.is_empty counter_examples
  then ()
  else raise (Unbound_vars_within_closures counter_examples)

let every_static_exception_is_caught flam =
  let check env (flam : Flambda.t) =
    match flam with
    | Static_raise (exn, _) ->
      if not (Static_exception.Set.mem exn env)
      then raise (Static_exception_not_caught exn)
    | _ -> ()
  in
  let rec loop env (flam : Flambda.t) =
    match flam with
    | Static_catch (i, _, body, handler) ->
      let env = Static_exception.Set.add i env in
      loop env handler;
      loop env body
    | exp ->
      check env exp;
      Flambda_iterators.apply_on_subexpressions (loop env)
        (fun (_ : Flambda.named) -> ()) exp
  in
  loop Static_exception.Set.empty flam

let every_static_exception_is_caught_at_a_single_position flam =
  let caught = ref Static_exception.Set.empty in
  let f (flam : Flambda.t) =
    match flam with
    | Static_catch (i, _, _body, _handler) ->
      if Static_exception.Set.mem i !caught then
        raise (Static_exception_caught_in_multiple_places i);
      caught := Static_exception.Set.add i !caught
    | _ -> ()
  in
  Flambda_iterators.iter f (fun (_ : Flambda.named) -> ()) flam

let _every_move_within_set_of_closures_is_to_a_function_in_the_free_vars
      program =
  let moves = ref Closure_id.Map.empty in
  Flambda_iterators.iter_named_of_program program
    ~f:(function
        | Move_within_set_of_closures { start_from; move_to; _ } ->
          let moved_to =
            try Closure_id.Map.find start_from !moves with
            | Not_found -> Closure_id.Set.empty
          in
          moves :=
            Closure_id.Map.add start_from
              (Closure_id.Set.add move_to moved_to)
              !moves
        | _ -> ());
  Flambda_iterators.iter_on_set_of_closures_of_program program
    ~f:(fun ~constant:_ { Flambda.function_decls = { funs; _ }; _ } ->
        Variable.Map.iter (fun fun_var { Flambda.free_variables; _ } ->
            match Closure_id.Map.find (Closure_id.wrap fun_var) !moves with
            | exception Not_found -> ()
            | moved_to ->
              let missing_dependencies =
                Variable.Set.diff (Closure_id.unwrap_set moved_to)
                  free_variables
              in
              if not (Variable.Set.is_empty missing_dependencies) then
                raise (Move_to_a_closure_not_in_the_free_variables
                         (fun_var, missing_dependencies)))
          funs)

let check_exn ?(kind=Normal) ?(cmxfile=false) (flam:Flambda.program) =
  ignore kind;
  try
    variable_and_symbol_invariants flam;
    no_closure_id_is_bound_multiple_times flam;
    no_set_of_closures_id_is_bound_multiple_times flam;
    every_used_function_from_current_compilation_unit_is_declared flam;
    no_var_within_closure_is_bound_multiple_times flam;
    every_used_var_within_closure_from_current_compilation_unit_is_declared
      flam;
    (* CR-soon pchambart: This invariant is not maintained. It should be
       either relaxed or reformulated. Currently, it is safe to disable it as
       the potential related errors would result in fatal errors, not in
       miscompilations *)
    (* every_move_within_set_of_closures_is_to_a_function_in_the_free_vars
        flam; *)
    Flambda_iterators.iter_exprs_at_toplevel_of_program flam ~f:(fun flam ->
      primitive_invariants flam ~no_access_to_global_module_identifiers:cmxfile;
      every_static_exception_is_caught flam;
      every_static_exception_is_caught_at_a_single_position flam;
      every_declared_closure_is_from_current_compilation_unit flam)
  with exn -> begin
  (* CR-someday split printing code into its own function *)
    begin match exn with
    | Binding_occurrence_not_from_current_compilation_unit var ->
      Format.eprintf ">> Binding occurrence of variable marked as not being \
          from the current compilation unit: %a"
        Variable.print var
    | Mutable_binding_occurrence_not_from_current_compilation_unit mut_var ->
      Format.eprintf ">> Binding occurrence of mutable variable marked as not \
          being from the current compilation unit: %a"
        Mutable_variable.print mut_var
    | Binding_occurrence_of_variable_already_bound var ->
      Format.eprintf ">> Binding occurrence of variable that was already \
            bound: %a"
        Variable.print var
    | Binding_occurrence_of_mutable_variable_already_bound mut_var ->
      Format.eprintf ">> Binding occurrence of mutable variable that was \
            already bound: %a"
        Mutable_variable.print mut_var
    | Binding_occurrence_of_symbol_already_bound sym ->
      Format.eprintf ">> Binding occurrence of symbol that was already \
            bound: %a"
        Symbol.print sym
    | Unbound_variable var ->
      Format.eprintf ">> Unbound variable: %a" Variable.print var
    | Unbound_mutable_variable mut_var ->
      Format.eprintf ">> Unbound mutable variable: %a"
        Mutable_variable.print mut_var
    | Unbound_symbol sym ->
      Format.eprintf ">> Unbound symbol: %a %s"
        Symbol.print sym
        (Printexc.raw_backtrace_to_string (Printexc.get_callstack 100))
    | Vars_in_function_body_not_bound_by_closure_or_params
        (vars, set_of_closures, fun_var) ->
      Format.eprintf ">> Variable(s) (%a) in the body of a function \
          declaration (fun_var = %a) that is not bound by either the closure \
          or the function's parameter list.  Set of closures: %a"
        Variable.Set.print vars
        Variable.print fun_var
        Flambda.print_set_of_closures set_of_closures
    | Function_decls_have_overlapping_parameters vars ->
      Format.eprintf ">> Function declarations whose parameters overlap: \
          %a"
        Variable.Set.print vars
    | Specialised_arg_that_is_not_a_parameter var ->
      Format.eprintf ">> Variable in [specialised_args] that is not a \
          parameter of any of the function(s) in the corresponding \
          declaration(s): %a"
        Variable.print var
    | Projection_must_be_a_free_var var ->
      Format.eprintf ">> Projection %a in [free_vars] from a variable that is \
          not a (inner) free variable of the set of closures"
        Projection.print var
    | Projection_must_be_a_specialised_arg var ->
      Format.eprintf ">> Projection %a in [specialised_args] from a variable \
          that is not a (inner) specialised argument variable of the set of \
          closures"
        Projection.print var
    | Free_variables_set_is_lying (var, claimed, calculated, function_decl) ->
      Format.eprintf ">> Function declaration whose [free_variables] set (%a) \
          is not a superset of the result of [Flambda.free_variables] \
          applied to the body of the function (%a).  Declaration: %a"
        Variable.Set.print claimed
        Variable.Set.print calculated
        Flambda.print_function_declaration (var, function_decl)
    | Set_of_closures_free_vars_map_has_wrong_range vars ->
      Format.eprintf ">> [free_vars] map in set of closures has in its range \
          variables that are not free variables of the corresponding \
          functions: %a"
        Variable.Set.print vars
    | Sequential_logical_operator_primitives_must_be_expanded prim ->
      Format.eprintf ">> Sequential logical operator primitives must be \
          expanded (see closure_conversion.ml): %a"
        Printlambda.primitive prim
    | Var_within_closure_bound_multiple_times var ->
      Format.eprintf ">> Variable within a closure is bound multiple times: \
          %a"
        Var_within_closure.print var
    | Closure_id_is_bound_multiple_times closure_id ->
      Format.eprintf ">> Closure ID is bound multiple times: %a"
        Closure_id.print closure_id
    | Set_of_closures_id_is_bound_multiple_times set_of_closures_id ->
      Format.eprintf ">> Set of closures ID is bound multiple times: %a"
        Set_of_closures_id.print set_of_closures_id
    | Declared_closure_from_another_unit compilation_unit ->
      Format.eprintf ">> Closure declared as being from another compilation \
          unit: %a"
        Compilation_unit.print compilation_unit
    | Unbound_closure_ids closure_ids ->
      Format.eprintf ">> Unbound closure ID(s) from the current compilation \
          unit: %a"
        Closure_id.Set.print closure_ids
    | Unbound_vars_within_closures vars_within_closures ->
      Format.eprintf ">> Unbound variable(s) within closure(s) from the \
          current compilation_unit: %a"
        Var_within_closure.Set.print vars_within_closures
    | Static_exception_not_caught static_exn ->
      Format.eprintf ">> Uncaught static exception: %a"
        Static_exception.print static_exn
    | Static_exception_caught_in_multiple_places static_exn ->
      Format.eprintf ">> Static exception caught in multiple places: %a"
        Static_exception.print static_exn
    | Access_to_global_module_identifier prim ->
      (* CR-someday mshinwell: backend-specific checks should move to another
         module, in the asmcomp/ directory. *)
      Format.eprintf ">> Forbidden access to a global module identifier (not \
          allowed in Flambda that will be exported to a .cmx file): %a"
        Printlambda.primitive prim
    | Pidentity_should_not_occur ->
      Format.eprintf ">> The Pidentity primitive should never occur in an \
        Flambda expression (see closure_conversion.ml)"
    | Pdirapply_should_be_expanded ->
      Format.eprintf ">> The Pdirapply primitive should never occur in an \
        Flambda expression (see simplif.ml); use Apply instead"
    | Prevapply_should_be_expanded ->
      Format.eprintf ">> The Prevapply primitive should never occur in an \
        Flambda expression (see simplif.ml); use Apply instead"
    | Move_to_a_closure_not_in_the_free_variables (start_from, move_to) ->
      Format.eprintf ">> A Move_within_set_of_closures from the closure %a \
        to closures that are not parts of its free variables: %a"
          Variable.print start_from
          Variable.Set.print move_to
    | exn -> raise exn
    end;
    Format.eprintf "\n@?";
    raise Flambda_invariants_failed
  end