(***********************************************************************) (* *) (* Caml Special Light *) (* *) (* Xavier Leroy, projet Cristal, INRIA Rocquencourt *) (* *) (* Copyright 1995 Institut National de Recherche en Informatique et *) (* Automatique. Distributed only by permission. *) (* *) (***********************************************************************) (* $Id$ *) (* Compilation of pattern matching *) open Misc open Location open Asttypes open Primitive open Typedtree open Lambda (* See Peyton-Jones, "The Implementation of functional programming languages", chapter 5. *) type pattern_matching = { mutable cases : (pattern list * lambda) list; args : (lambda * let_kind) list } (* To group lines of patterns with identical keys *) let add_line patl_action pm = pm.cases <- patl_action :: pm.cases; pm let add make_matching_fun division key patl_action args = try let pm = List.assoc key division in pm.cases <- patl_action :: pm.cases; division with Not_found -> let pm = make_matching_fun args in pm.cases <- patl_action :: pm.cases; (key, pm) :: division (* To find reasonable names for let-bound and lambda-bound idents *) let rec name_pattern default = function (pat :: patl, action) :: rem -> begin match pat.pat_desc with Tpat_var id -> id | Tpat_alias(p, id) -> id | _ -> name_pattern default rem end | _ -> Ident.create default (* To remove aliases and bind named components *) let any_pat = {pat_desc = Tpat_any; pat_loc = Location.none; pat_type = Ctype.none} let simplify_matching m = match m.args with [] -> m | (arg, mut) :: argl -> let rec simplify = function (pat :: patl, action as patl_action) :: rem -> begin match pat.pat_desc with Tpat_var id -> (any_pat :: patl, Llet(Alias, id, arg, action)) :: simplify rem | Tpat_alias(p, id) -> simplify ((p :: patl, Llet(Alias, id, arg, action)) :: rem) | _ -> patl_action :: simplify rem end | cases -> cases in { args = m.args; cases = simplify m.cases } (* Matching against a constant *) let make_constant_matching = function [] -> fatal_error "Matching.make_constant_matching" | (arg :: argl) -> {cases = []; args = argl} let divide_constant {cases = cl; args = al} = let rec divide = function ({pat_desc = Tpat_constant cst} :: patl, action) :: rem -> let (constants, others) = divide rem in (add make_constant_matching constants cst (patl, action) al, others) | cl -> ([], {cases = cl; args = al}) in divide cl (* Matching against a constructor *) let make_constr_matching cstr = function [] -> fatal_error "Matching.make_constr_matching" | ((arg, mut) :: argl) -> let (first_pos, last_pos) = match cstr.cstr_tag with Cstr_constant _ | Cstr_block _ -> (0, cstr.cstr_arity - 1) | Cstr_exception _ -> (1, cstr.cstr_arity) in let rec make_args pos = if pos > last_pos then argl else (Lprim(Pfield pos, [arg]), Alias) :: make_args (pos + 1) in {cases = []; args = make_args first_pos} let divide_constructor {cases = cl; args = al} = let rec divide = function ({pat_desc = Tpat_construct(cstr, args)} :: patl, action) :: rem -> let (constructs, others) = divide rem in (add (make_constr_matching cstr) constructs cstr.cstr_tag (args @ patl, action) al, others) | cl -> ([], {cases = cl; args = al}) in divide cl (* Matching against a variable *) let divide_var {cases = cl; args = al} = let rec divide = function ({pat_desc = Tpat_any} :: patl, action) :: rem -> let (vars, others) = divide rem in (add_line (patl, action) vars, others) | cl -> (make_constant_matching al, {cases = cl; args = al}) in divide cl (* Matching against a tuple pattern *) let make_tuple_matching num_comps = function [] -> fatal_error "Matching.make_tuple_matching" | (arg, mut) :: argl -> let rec make_args pos = if pos >= num_comps then argl else (Lprim(Pfield pos, [arg]), Alias) :: make_args (pos + 1) in {cases = []; args = make_args 0} let divide_tuple arity {cases = cl; args = al} = let rec divide = function ({pat_desc = Tpat_tuple args} :: patl, action) :: rem -> let (tuples, others) = divide rem in (add_line (args @ patl, action) tuples, others) | ({pat_desc = Tpat_any} :: patl, action) :: rem -> let (tuples, others) = divide rem in (add_line (replicate_list any_pat arity @ patl, action) tuples, others) | cl -> (make_tuple_matching arity al, {cases = cl; args = al}) in divide cl (* Matching against a record pattern *) let make_record_matching all_labels = function [] -> fatal_error "Matching.make_tuple_matching" | ((arg, mut) :: argl) -> let rec make_args pos = if pos >= Array.length all_labels then argl else begin let lbl = all_labels.(pos) in let access = match lbl.lbl_repres with Record_regular -> Pfield lbl.lbl_pos | Record_float -> Pfloatfield lbl.lbl_pos in let str = match lbl.lbl_mut with Immutable -> Alias | Mutable -> StrictOpt in (Lprim(access, [arg]), str) :: make_args(pos + 1) end in {cases = []; args = make_args 0} let divide_record all_labels {cases = cl; args = al} = let num_fields = Array.length all_labels in let record_matching_line lbl_pat_list = let patv = Array.create num_fields any_pat in List.iter (fun (lbl, pat) -> patv.(lbl.lbl_pos) <- pat) lbl_pat_list; Array.to_list patv in let rec divide = function ({pat_desc = Tpat_record lbl_pat_list} :: patl, action) :: rem -> let (records, others) = divide rem in (add_line (record_matching_line lbl_pat_list @ patl, action) records, others) | ({pat_desc = Tpat_any} :: patl, action) :: rem -> let (records, others) = divide rem in (add_line (record_matching_line [] @ patl, action) records, others) | cl -> (make_record_matching all_labels al, {cases = cl; args = al}) in divide cl (* Matching against an or pattern. *) let rec flatten_orpat_match pat = match pat.pat_desc with Tpat_or(p1, p2) -> flatten_orpat_match p1 @ flatten_orpat_match p2 | _ -> [[pat], lambda_unit] let divide_orpat = function {cases = (orpat :: patl, act) :: casel; args = arg1 :: argl as args} -> ({cases = flatten_orpat_match orpat; args = [arg1]}, {cases = [patl, act]; args = argl}, {cases = casel; args = args}) | _ -> fatal_error "Matching.divide_orpat" (* To combine sub-matchings together *) let combine_var (lambda1, total1) (lambda2, total2) = if total1 then (lambda1, true) else if lambda2 = Lstaticfail then (lambda1, total1) else (Lcatch(lambda1, lambda2), total2) let make_test_sequence tst arg const_lambda_list = List.fold_right (fun (c, act) rem -> Lifthenelse(Lprim(tst, [arg; Lconst(Const_base c)]), act, rem)) const_lambda_list Lstaticfail let make_switch_or_test_sequence arg const_lambda_list int_lambda_list = let min_key = List.fold_right (fun (k, l) m -> min k m) int_lambda_list max_int in let max_key = List.fold_right (fun (k, l) m -> max k m) int_lambda_list min_int in if 4 * List.length int_lambda_list <= 4 + max_key - min_key then (* Sparse matching -- use a sequence of tests (4 bytecode instructions per test) *) make_test_sequence (Pintcomp Ceq) arg const_lambda_list else begin (* Dense matching -- use a jump table (2 bytecode instructions + 1 word per entry in the table) *) let numcases = max_key - min_key + 1 in let cases = List.map (fun (key, l) -> (key - min_key, l)) int_lambda_list in let offsetarg = if min_key = 0 then arg else Lprim(Poffsetint(-min_key), [arg]) in Lswitch(offsetarg, {sw_numconsts = numcases; sw_consts = cases; sw_numblocks = 0; sw_blocks = []; sw_checked = true}) end let make_bitvect_check arg int_lambda_list = let bv = String.make 32 '\000' in List.iter (fun (n, l) -> bv.[n lsr 3] <- Char.chr(Char.code bv.[n lsr 3] lor (1 lsl (n land 7)))) int_lambda_list; Lifthenelse(Lprim(Pbittest, [Lconst(Const_base(Const_string bv)); arg]), lambda_unit, Lstaticfail) let prim_string_equal = Pccall{prim_name = "string_equal"; prim_arity = 2; prim_alloc = false; prim_native_name = ""; prim_native_float = false} let combine_constant arg cst (const_lambda_list, total1) (lambda2, total2) = let lambda1 = match cst with Const_int _ -> let int_lambda_list = List.map (fun (Const_int n, l) -> (n, l)) const_lambda_list in make_switch_or_test_sequence arg const_lambda_list int_lambda_list | Const_char _ -> let int_lambda_list = List.map (fun (Const_char c, l) -> (Char.code c, l)) const_lambda_list in if List.for_all (fun (c, l) -> l = lambda_unit) const_lambda_list then make_bitvect_check arg int_lambda_list else make_switch_or_test_sequence arg const_lambda_list int_lambda_list | Const_string _ -> make_test_sequence prim_string_equal arg const_lambda_list | Const_float _ -> make_test_sequence (Pfloatcomp Ceq) arg const_lambda_list in (Lcatch(lambda1, lambda2), total2) let combine_constructor arg cstr (tag_lambda_list, total1) (lambda2, total2) = if cstr.cstr_consts < 0 then begin (* Special cases for exceptions *) let lambda1 = List.fold_right (fun (Cstr_exception path, act) rem -> Lifthenelse(Lprim(Pintcomp Ceq, [Lprim(Pfield 0, [arg]); transl_path path]), act, rem)) tag_lambda_list Lstaticfail in (Lcatch(lambda1, lambda2), total2) end else begin (* Regular concrete type *) let rec split_cases = function [] -> ([], []) | (cstr, act) :: rem -> let (consts, nonconsts) = split_cases rem in match cstr with Cstr_constant n -> ((n, act) :: consts, nonconsts) | Cstr_block n -> (consts, (n, act) :: nonconsts) in let (consts, nonconsts) = split_cases tag_lambda_list in let lambda1 = match (cstr.cstr_consts, cstr.cstr_nonconsts, consts, nonconsts) with (1, 0, [0, act], []) -> act | (0, 1, [], [0, act]) -> act | (1, 1, [0, act1], [0, act2]) -> Lifthenelse(arg, act2, act1) | (1, 1, [0, act1], []) -> Lifthenelse(arg, Lstaticfail, act1) | (1, 1, [], [0, act2]) -> Lifthenelse(arg, act2, Lstaticfail) | (_, _, _, _) -> Lswitch(arg, {sw_numconsts = cstr.cstr_consts; sw_consts = consts; sw_numblocks = cstr.cstr_nonconsts; sw_blocks = nonconsts; sw_checked = false}) in if total1 & List.length tag_lambda_list = cstr.cstr_consts + cstr.cstr_nonconsts then (lambda1, true) else (Lcatch(lambda1, lambda2), total2) end let combine_orpat (lambda1, total1) (lambda2, total2) (lambda3, total3) = (Lcatch(Lsequence(lambda1, lambda2), lambda3), total3) (* The main compilation function. Input: a pattern matching. Output: a lambda term, a "total" flag (true if we're sure that the matching covers all cases; this is an approximation). *) let rec compile_match m = let rec compile_list = function [] -> ([], true) | (key, pm) :: rem -> let (lambda1, total1) = compile_match pm in let (list2, total2) = compile_list rem in ((key, lambda1) :: list2, total1 & total2) in match m with { cases = [] } -> (Lstaticfail, false) | { cases = ([], action) :: rem; args = argl } -> if is_guarded action then begin let (lambda, total) = compile_match { cases = rem; args = argl } in (Lcatch(action, lambda), total) end else (action, true) | { args = (arg, str) :: argl } -> let v = name_pattern "match" m.cases in let newarg = Lvar v in let pm = simplify_matching { cases = m.cases; args = (newarg, Alias) :: argl } in let (lam, total) = match pm.cases with (pat :: patl, action) :: _ -> begin match pat.pat_desc with Tpat_any -> let (vars, others) = divide_var pm in combine_var (compile_match vars) (compile_match others) | Tpat_constant cst -> let (constants, others) = divide_constant pm in combine_constant newarg cst (compile_list constants) (compile_match others) | Tpat_tuple patl -> let (tuples, others) = divide_tuple (List.length patl) pm in combine_var (compile_match tuples) (compile_match others) | Tpat_construct(cstr, patl) -> let (constrs, others) = divide_constructor pm in combine_constructor newarg cstr (compile_list constrs) (compile_match others) | Tpat_record((lbl, _) :: _) -> let (records, others) = divide_record lbl.lbl_all pm in combine_var (compile_match records) (compile_match others) | Tpat_or(pat1, pat2) -> (* Avoid duplicating the code of the action *) let (or_match, remainder_line, others) = divide_orpat pm in combine_orpat (compile_match or_match) (compile_match remainder_line) (compile_match others) | _ -> fatal_error "Matching.compile_match1" end | _ -> fatal_error "Matching.compile_match2" in (Llet(str, v, arg, lam), total) (* The entry points *) let compile_matching handler_fun arg pat_act_list = let pm = { cases = List.map (fun (pat, act) -> ([pat], act)) pat_act_list; args = [arg, Strict] } in let (lambda, total) = compile_match pm in if total then lambda else Lcatch(lambda, handler_fun()) let partial_function loc () = Lprim(Praise, [Lprim(Pmakeblock(0, Immutable), [transl_path Predef.path_match_failure; Lconst(Const_block(0, [Const_base(Const_string !Location.input_name); Const_base(Const_int loc.loc_start); Const_base(Const_int loc.loc_end)]))])]) let for_function loc param pat_act_list = compile_matching (partial_function loc) param pat_act_list let for_trywith param pat_act_list = compile_matching (fun () -> Lprim(Praise, [param])) param pat_act_list let for_let loc param pat body = compile_matching (partial_function loc) param [pat, body] let for_multiple_match loc paraml pat_act_list = let pm1 = { cases = List.map (fun (pat, act) -> ([pat], act)) pat_act_list; args = [Lprim(Pmakeblock(0, Immutable), paraml), Strict] } in let pm2 = simplify_matching pm1 in let rec flatten_patterns = function ({pat_desc = Tpat_tuple args} :: _, action) :: rem -> (args, action) :: flatten_patterns rem | ({pat_desc = Tpat_any} :: patl, action) :: rem -> (replicate_list any_pat (List.length paraml), action) :: flatten_patterns rem | _ -> [] in let pm3 = { cases = flatten_patterns pm2.cases; args = List.map (fun lam -> (lam, Strict)) paraml } in let (lambda, total) = compile_match pm3 in if total then lambda else Lcatch(lambda, partial_function loc ())