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Avoid linear AST expansion for local array initializers #603

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97 changes: 82 additions & 15 deletions cparser/Unblock.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -22,9 +22,11 @@
open C
open Cutil

(* Convert an initializer to a list of assignment expressions. *)
(* Convert an initializer to a list of assignment expressions.
Used for compound literals, where initialization is embedded in an
expression at the appropriate sequence point. *)

let rec local_initializer env path init k =
let rec local_initializer_expr env path init k =
match init with
| Init_single e ->
{ edesc = EBinop(Oassign, path, e, path.etyp); etyp = path.etyp } :: k
Expand All @@ -42,7 +44,7 @@ let rec local_initializer env path init k =
match il with
| [] -> (default_init env ty_elt, [])
| i1 :: il' -> (i1, il') in
local_initializer env
local_initializer_expr env
{ edesc = EBinop(Oindex, path, intconst pos IInt, TPtr(ty_elt, []));
etyp = ty_elt }
i1
Expand All @@ -51,27 +53,92 @@ let rec local_initializer env path init k =
array_init 0L il
| Init_struct(id, fil) ->
let field_init (fld, i) k =
local_initializer env
local_initializer_expr env
{ edesc = EUnop(Odot fld.fld_name, path); etyp = fld.fld_typ }
i k in
List.fold_right field_init fil k
| Init_union(id, fld, i) ->
local_initializer env
local_initializer_expr env
{ edesc = EUnop(Odot fld.fld_name, path); etyp = fld.fld_typ }
i k

(* Prepend assignments to the given statement. *)

let add_inits_stmt loc inits s =
List.fold_right
(fun e s -> sseq loc {sdesc = Sdo e; sloc = loc} s)
inits s

(* Record new variables to be locally or globally defined *)

let local_variables = ref ([]: decl list)
let global_variables = ref ([]: decl list)

let new_local name ty =
let id = Env.fresh_ident name in
local_variables :=
(Storage_default, id, ty, None) :: !local_variables;
{ edesc = EVar id; etyp = ty }

(* Convert a declaration initializer to assignment statements. The explicitly
supplied outer array prefix is traversed directly. A nonempty implicit
array tail is initialized by a typed counted loop, so the generated AST
does not grow with the number of omitted elements. *)

let rec local_initializer_stmt env loc path init k =
match init with
| Init_single e ->
sseq loc (sassign loc path e) k
| Init_array il ->
let (ty_elt, sz) =
match unroll env path.etyp with
| TArray(ty_elt, Some sz, _) -> (ty_elt, sz)
(* We accept empty array initializer for flexible array members, which
has size zero *)
| TArray(ty_elt, None, _) when il = [] -> (ty_elt, 0L)
| _ ->
Diagnostics.fatal_error Diagnostics.no_loc
"wrong type for array initializer" in
let array_elt index =
{ edesc = EBinop(Oindex, path, index, TPtr(ty_elt, []));
etyp = ty_elt } in
let array_default_init pos =
let index_kind = size_t_ikind () in
let index_type = TInt(index_kind, []) in
let index = new_local "__init_index" index_type in
let init_index = sassign loc index (intconst pos index_kind) in
let test_index =
{ edesc = EBinop(Olt, index, intconst sz index_kind, index_type);
etyp = TInt(IInt, []) } in
let incr_index =
{ sdesc = Sdo { edesc = EUnop(Opreincr, index);
etyp = index_type };
sloc = loc } in
let body =
local_initializer_stmt env loc
(array_elt index)
(default_init env ty_elt)
sskip in
let loop =
{ sdesc = Sfor(init_index, test_index, incr_index, body);
sloc = loc } in
sseq loc loop k in
let rec array_init pos il =
if pos >= sz then k else begin
match il with
| i1 :: il' ->
local_initializer_stmt env loc
(array_elt (intconst pos IInt))
i1
(array_init (Int64.succ pos) il')
| [] ->
array_default_init pos
end in
array_init 0L il
| Init_struct(id, fil) ->
let field_init (fld, i) k =
local_initializer_stmt env loc
{ edesc = EUnop(Odot fld.fld_name, path); etyp = fld.fld_typ }
i k in
List.fold_right field_init fil k
| Init_union(id, fld, i) ->
local_initializer_stmt env loc
{ edesc = EUnop(Odot fld.fld_name, path); etyp = fld.fld_typ }
i k

(* Note: "const int x = y - 1;" is legal, but we turn it into
"const int x; x = y - 1;", which is not. Therefore, remove
top-level 'const' attribute. Also remove it on element type of
Expand All @@ -94,7 +161,7 @@ let process_compound_literal islocal env ty init =
let e = {edesc = EVar id; etyp = ty'} in
local_variables :=
(Storage_default, id, ty', None) :: !local_variables;
(local_initializer env e init [], e)
(local_initializer_expr env e init [], e)
end else begin
global_variables :=
(Storage_static, id, ty, Some init) :: !global_variables;
Expand Down Expand Up @@ -253,8 +320,8 @@ let process_decl loc env ctx (sto, id, ty, optinit) k =
k
| Some init ->
let init' = expand_init true env init in
let l = local_initializer env { edesc = EVar id; etyp = ty' } init' [] in
add_inits_stmt loc l k
local_initializer_stmt env loc
{ edesc = EVar id; etyp = ty' } init' k

(* Simplification of blocks within a statement *)

Expand Down