module T = Types module PV = PrimitiveValues module V = Values module E = Expressions module C = Contexts module Subst = Substitute module A = LlbcAst module L = Logging open ValuesUtils module Inv = Invariants module S = SynthesizeSymbolic open Cps open InterpreterUtils open InterpreterLoopsCore open InterpreterLoopsMatchCtxs open InterpreterLoopsFixedPoint (** The local logger *) let log = L.loops_log (** Evaluate a loop in concrete mode *) let eval_loop_concrete (eval_loop_body : st_cm_fun) : st_cm_fun = fun cf ctx -> (* We need a loop id for the [LoopReturn]. In practice it won't be used (it is useful only for the symbolic execution *) let loop_id = C.fresh_loop_id () in (* Continuation for after we evaluate the loop body: depending the result of doing one loop iteration: - redoes a loop iteration - exits the loop - other... We need a specific function because of the {!Continue} case: in case we continue, we might have to reevaluate the current loop body with the new context (and repeat this an indefinite number of times). *) let rec reeval_loop_body (res : statement_eval_res) : m_fun = match res with | Return -> cf (LoopReturn loop_id) | Panic -> cf Panic | Break i -> (* Break out of the loop by calling the continuation *) let res = if i = 0 then Unit else Break (i - 1) in cf res | Continue 0 -> (* Re-evaluate the loop body *) eval_loop_body reeval_loop_body | Continue i -> (* Continue to an outer loop *) cf (Continue (i - 1)) | Unit -> (* We can't get there. * Note that if we decide not to fail here but rather do * the same thing as for [Continue 0], we could make the * code slightly simpler: calling {!reeval_loop_body} with * {!Unit} would account for the first iteration of the loop. * We prefer to write it this way for consistency and sanity, * though. *) raise (Failure "Unreachable") | LoopReturn _ | EndEnterLoop _ | EndContinue _ -> (* We can't get there: this is only used in symbolic mode *) raise (Failure "Unreachable") in (* Apply *) eval_loop_body reeval_loop_body ctx (** Evaluate a loop in symbolic mode *) let eval_loop_symbolic (config : C.config) (eval_loop_body : st_cm_fun) : st_cm_fun = fun cf ctx -> (* Debug *) log#ldebug (lazy ("eval_loop_symbolic:\nContext:\n" ^ eval_ctx_to_string ctx ^ "\n\n")); (* Generate a fresh loop id *) let loop_id = C.fresh_loop_id () in (* Compute the fixed point at the loop entrance *) let fp_ctx, fixed_ids, rg_to_abs = compute_loop_entry_fixed_point config loop_id eval_loop_body ctx in (* Debug *) log#ldebug (lazy ("eval_loop_symbolic:\nInitial context:\n" ^ eval_ctx_to_string ctx ^ "\n\nFixed point:\n" ^ eval_ctx_to_string fp_ctx)); (* Compute the loop input parameters *) let fresh_sids, input_svalues = compute_fp_ctx_symbolic_values ctx fp_ctx in let fp_input_svalues = List.map (fun sv -> sv.V.sv_id) input_svalues in (* Synthesize the end of the function - we simply match the context at the loop entry with the fixed point: in the synthesized code, the function will end with a call to the loop translation *) let fp_bl_corresp = compute_fixed_point_id_correspondance fixed_ids ctx fp_ctx in let end_expr = match_ctx_with_target config loop_id true fp_bl_corresp fp_input_svalues fixed_ids fp_ctx cf ctx in (* Synthesize the loop body by evaluating it, with the continuation for after the loop starting at the *fixed point*, but with a special treatment for the [Break] and [Continue] cases *) let cf_loop : st_m_fun = fun res ctx -> match res with | Return -> (* We replace the [Return] with a [LoopReturn] *) cf (LoopReturn loop_id) ctx | Panic -> cf res ctx | Break i -> (* Break out of the loop by calling the continuation *) let res = if i = 0 then Unit else Break (i - 1) in cf res ctx | Continue i -> (* We don't support nested loops for now *) assert (i = 0); let cc = match_ctx_with_target config loop_id false fp_bl_corresp fp_input_svalues fixed_ids fp_ctx in cc cf ctx | Unit | LoopReturn _ | EndEnterLoop _ | EndContinue _ -> (* For why we can't get [Unit], see the comments inside {!eval_loop_concrete}. For [EndEnterLoop] and [EndContinue]: we don't support nested loops for now. *) raise (Failure "Unreachable") in let loop_expr = eval_loop_body cf_loop fp_ctx in log#ldebug (lazy ("eval_loop_symbolic: result:" ^ "\n- src context:\n" ^ eval_ctx_to_string_no_filter ctx ^ "\n- fixed point:\n" ^ eval_ctx_to_string_no_filter fp_ctx ^ "\n- fixed_sids: " ^ V.SymbolicValueId.Set.show fixed_ids.sids ^ "\n- fresh_sids: " ^ V.SymbolicValueId.Set.show fresh_sids ^ "\n- input_svalues: " ^ Print.list_to_string (symbolic_value_to_string ctx) input_svalues ^ "\n\n")); (* For every abstraction introduced by the fixed-point, compute the types of the given back values. We need to explore the abstractions, looking for the mutable borrows. Moreover, we list the borrows in the same order as the loans (this is important in {!SymbolicToPure}, where we expect the given back values to have a specific order. *) let compute_abs_given_back_tys (abs : V.abs) : T.RegionId.Set.t * T.rty list = let is_borrow (av : V.typed_avalue) : bool = match av.V.value with | ABorrow _ -> true | ALoan _ -> false | _ -> raise (Failure "Unreachable") in let borrows, loans = List.partition is_borrow abs.avalues in let borrows = List.filter_map (fun av -> match av.V.value with | V.ABorrow (V.AMutBorrow (bid, child_av)) -> assert (is_aignored child_av.V.value); Some (bid, child_av.V.ty) | V.ABorrow (V.ASharedBorrow _) -> None | _ -> raise (Failure "Unreachable")) borrows in let borrows = ref (V.BorrowId.Map.of_list borrows) in let loan_ids = List.filter_map (fun av -> match av.V.value with | V.ALoan (V.AMutLoan (bid, child_av)) -> assert (is_aignored child_av.V.value); Some bid | V.ALoan (V.ASharedLoan _) -> None | _ -> raise (Failure "Unreachable")) loans in (* List the given back types, in the order given by the loans *) let given_back_tys = List.map (fun lid -> let bid = V.BorrowId.InjSubst.find lid fp_bl_corresp.loan_to_borrow_id_map in let ty = V.BorrowId.Map.find bid !borrows in borrows := V.BorrowId.Map.remove bid !borrows; ty) loan_ids in assert (V.BorrowId.Map.is_empty !borrows); (abs.regions, given_back_tys) in let rg_to_given_back = T.RegionGroupId.Map.map compute_abs_given_back_tys rg_to_abs in (* Put together *) S.synthesize_loop loop_id input_svalues fresh_sids rg_to_given_back end_expr loop_expr let eval_loop (config : C.config) (eval_loop_body : st_cm_fun) : st_cm_fun = fun cf ctx -> match config.C.mode with | ConcreteMode -> eval_loop_concrete eval_loop_body cf ctx | SymbolicMode -> (* We want to make sure the loop will *not* manipulate shared avalues containing themselves shared loans (i.e., nested shared loans in the abstractions), because it complexifies the matches between values (when joining environments, or checking that two environments are equivalent). We thus call {!prepare_ashared_loans} once *before* diving into the loop, to make sure the shared values are deconstructed. Note that we will call this function again inside {!eval_loop_symbolic}, to introduce fresh, non-fixed abstractions containing the shared values which can be manipulated (and thus borrowed, expanded, etc.) so that the fixed abstractions are never modified. This is important to understand: we call this function once here to introduce *fixed* abstractions, and again later to introduce *non-fixed* abstractions. *) let cc = prepare_ashared_loans None in comp cc (eval_loop_symbolic config eval_loop_body) cf ctx