Generalise optimisation of nested matches

compiler/shared_ast/optimizations.ml

@@ -19,43 +19,6 @@ open Definitions
 
 type ('a, 'b, 'm) optimizations_ctx = { decl_ctx : decl_ctx }
 
-let all_match_cases_are_id_fun cases n =
-  EnumConstructor.Map.for_all
-    (fun i case ->
-      match Mark.remove case with
-      | EAbs { binder; _ } -> (
-        let var, body = Bindlib.unmbind binder in
-        (* because of invariant [invariant_match], the arity is always one. *)
-        let[@warning "-8"] [| var |] = var in
-        match Mark.remove body with
-        | EInj { cons = i'; name = n'; e = EVar x, _ } ->
-          EnumConstructor.equal i i'
-          && EnumName.equal n n'
-          && Bindlib.eq_vars x var
-        | EInj { cons = i'; name = n'; e = ELit LUnit, _ } ->
-          (* since unit is the only value of type unit. We don't need to check
-             the equality. *)
-          EnumConstructor.equal i i' && EnumName.equal n n'
-        | _ -> false)
-      | _ ->
-        (* because of invariant [invariant_match], there is always some EAbs in
-           each cases. *)
-        assert false)
-    cases
-
-let all_match_cases_map_to_same_constructor cases n =
-  EnumConstructor.Map.for_all
-    (fun i case ->
-      match Mark.remove case with
-      | EAbs { binder; _ } -> (
-        let _, body = Bindlib.unmbind binder in
-        match Mark.remove body with
-        | EInj { cons = i'; name = n'; _ } ->
-          EnumConstructor.equal i i' && EnumName.equal n n'
-        | _ -> false)
-      | _ -> assert false)
-    cases
-
 let binder_vars_used_at_most_once
     (binder :
       ( ('a dcalc_lcalc, 'a dcalc_lcalc, 'm) base_gexpr,
@@ -79,6 +42,113 @@ let binder_vars_used_at_most_once
   in
   not (Array.exists (fun c -> c > 1) (vars_count body))
 
+(* beta reduction when variables not used, and for variable aliases and
+   literal *)
+let simplified_apply f args tys =
+  match f with
+  | EAbs { binder; _ }, _
+    when binder_vars_used_at_most_once binder
+         || List.for_all
+              (function (EVar _ | ELit _), _ -> true | _ -> false)
+              args ->
+    Mark.remove (Bindlib.msubst binder (List.map fst args |> Array.of_list))
+  | _ -> EApp { f; args; tys }
+
+let literal_bool = function
+  | ELit (LBool b), _
+  | EAppOp { op = Log _, _; args = [(ELit (LBool b), _)]; _ }, _ ->
+    Some b
+  | _ -> None
+
+let simplified_ifthenelse cond etrue efalse m =
+  if Expr.equal etrue efalse then Mark.remove etrue
+  else
+    match literal_bool etrue, literal_bool efalse with
+    | Some true, Some false -> Mark.remove cond
+    | Some false, Some true ->
+      EAppOp
+        {
+          op = Not, Expr.mark_pos m;
+          tys = [TLit TBool, Expr.mark_pos m];
+          args = [cond];
+        }
+    | Some true, Some true | Some false, Some false -> Mark.remove etrue
+    | _ -> (
+      match literal_bool cond with
+      | Some true -> Mark.remove etrue
+      | Some false -> Mark.remove efalse
+      | None -> EIfThenElse { cond; etrue; efalse })
+
+(* builds a [EMatch] term, flattening nested matches/if-then-else: the matching
+   arg branching are explored, and if they all lead to enum constructor
+   literals, the surrounding match cases are inlined. Code duplication is
+   detected and aborts the inlining. *)
+let simplified_match enum_name match_arg cases mark =
+  let max_duplicate_inlining_size = 3 in
+  let allow_duplicate_inlining_cases =
+    EnumConstructor.Map.fold
+      (fun cons f acc ->
+        if Expr.size f <= max_duplicate_inlining_size then
+          EnumConstructor.Set.add cons acc
+        else acc)
+      cases EnumConstructor.Set.empty
+  in
+  let app_cases cons e =
+    simplified_apply
+      (EnumConstructor.Map.find cons cases)
+      [e]
+      [Expr.maybe_ty (Mark.get e)]
+  in
+  let ret_ty = Expr.maybe_ty mark in
+  let rec aux seen_constrs = function
+    | EInj { cons; e; _ }, m ->
+      if EnumConstructor.Set.mem cons seen_constrs then raise Exit;
+      (* Abort inlining to avoid code duplication *)
+      let seen_constrs =
+        if EnumConstructor.Set.mem cons allow_duplicate_inlining_cases then
+          seen_constrs
+        else EnumConstructor.Set.add cons seen_constrs
+      in
+      seen_constrs, (app_cases cons e, Expr.with_ty m ret_ty)
+    | EMatch ({ cases; _ } as ematch), m ->
+      let seen_constrs, cases =
+        EnumConstructor.Map.fold
+          (fun cons case (seen_constrs, acc) ->
+            match case with
+            | EAbs ({ binder; _ } as eabs), m ->
+              let vars, body = Bindlib.unmbind binder in
+              let seen_constrs, body = aux seen_constrs body in
+              let binder = Bindlib.unbox (Expr.bind vars (Expr.rebox body)) in
+              let m =
+                Expr.map_ty
+                  (function
+                    | TArrow (args, _), pos -> TArrow (args, ret_ty), pos
+                    | (TAny, _) as t -> t
+                    | _ -> assert false)
+                  m
+              in
+              ( seen_constrs,
+                EnumConstructor.Map.add cons (EAbs { eabs with binder }, m) acc
+              )
+            | _ -> assert false)
+          cases
+          (seen_constrs, EnumConstructor.Map.empty)
+      in
+      seen_constrs, (EMatch { ematch with cases }, Expr.with_ty m ret_ty)
+    | EIfThenElse { cond; etrue; efalse }, m ->
+      let seen_constrs, etrue = aux seen_constrs etrue in
+      let seen_constrs, efalse = aux seen_constrs efalse in
+      let mark = Expr.with_ty m ret_ty in
+      seen_constrs, (simplified_ifthenelse cond etrue efalse mark, mark)
+    | _ -> raise Exit
+  in
+  try
+    let _seen_contrs, e = aux EnumConstructor.Set.empty match_arg in
+    Mark.remove e
+  with Exit ->
+    (* Optimisation was aborted due a non-terminal or code duplication *)
+    EMatch { e = match_arg; cases; name = enum_name }
+
 let rec optimize_expr :
     type a b.
     (a, b, 'm) optimizations_ctx ->
@@ -108,59 +178,8 @@ let rec optimize_expr :
     | EAppOp { op = And, _; args = [(e, _); (ELit (LBool b), _)]; _ } ->
       (* reduction of logical and *)
       if b then e else ELit (LBool false)
-    | EMatch { e = EInj { e = e'; cons; name = n' }, _; cases; name = n }
-    (* iota-reduction *)
-      when EnumName.equal n n' -> (
-      (* match E x with | E y -> e1 = e1[y |-> x]*)
-      match Mark.remove @@ EnumConstructor.Map.find cons cases with
-      (* holds because of invariant_match_inversion *)
-      | EAbs { binder; _ } ->
-        Mark.remove
-          (Bindlib.msubst binder ([e'] |> List.map fst |> Array.of_list))
-      | _ -> assert false)
-    | EMatch { e = e'; cases; name = n } when all_match_cases_are_id_fun cases n
-      ->
-      (* iota-reduction when the match is equivalent to an identity function *)
-      Mark.remove e'
-    | EMatch
-        {
-          e = EMatch { e = arg; cases = cases1; name = n1 }, _;
-          cases = cases2;
-          name = n2;
-        }
-      when EnumName.equal n1 n2
-           && all_match_cases_map_to_same_constructor cases1 n1 ->
-      (* iota-reduction when the matched expression is itself a match of the
-         same enum mapping all constructors to themselves *)
-      let cases =
-        EnumConstructor.Map.merge
-          (fun _i o1 o2 ->
-            match o1, o2 with
-            | Some b1, Some e2 -> (
-              match Mark.remove b1, Mark.remove e2 with
-              | EAbs { binder = b1; _ }, EAbs { binder = b2; tys } -> (
-                let v1, e1 = Bindlib.unmbind b1 in
-                match Mark.remove e1 with
-                | EInj { e = e1, _; _ } ->
-                  Some
-                    (Expr.unbox
-                       (Expr.make_abs v1
-                          (Expr.rebox (Bindlib.msubst b2 [| e1 |]))
-                          tys (Expr.pos e2)))
-                | _ -> assert false)
-              | _ -> assert false)
-            | _ -> assert false)
-          cases1 cases2
-      in
-      EMatch { e = arg; cases; name = n1 }
-    | EApp { f = EAbs { binder; _ }, _; args; _ }
-      when binder_vars_used_at_most_once binder
-           || List.for_all
-                (function (EVar _ | ELit _), _ -> true | _ -> false)
-                args ->
-      (* beta reduction when variables not used, and for variable aliases and
-         literal *)
-      Mark.remove (Bindlib.msubst binder (List.map fst args |> Array.of_list))
+    | EMatch { name; e; cases } -> simplified_match name e cases mark
+    | EApp { f; args; tys } -> simplified_apply f args tys
     | EStructAccess { name; field; e = EStruct { name = name1; fields }, _ }
       when StructName.equal name name1 ->
       Mark.remove (StructField.Map.find field fields)
@@ -193,12 +212,7 @@ let rec optimize_expr :
           ->
           (* No exceptions with condition [true] *)
           Mark.remove cons
-        | ( [],
-            ( ( ELit (LBool false)
-              | EAppOp { op = Log _, _; args = [(ELit (LBool false), _)]; _ } ),
-              _ ) ) ->
-          (* No exceptions and condition false *)
-          EEmpty
+        | [], cond -> simplified_ifthenelse cond cons (EEmpty, mark) mark
         | ( [except],
             ( ( ELit (LBool false)
               | EAppOp { op = Log _, _; args = [(ELit (LBool false), _)]; _ } ),
@@ -206,49 +220,8 @@ let rec optimize_expr :
           (* Single exception and condition false *)
           Mark.remove except
         | excepts, just -> EDefault { excepts; just; cons })
-    | EIfThenElse
-        {
-          cond =
-            ( ELit (LBool true), _
-            | EAppOp { op = Log _, _; args = [(ELit (LBool true), _)]; _ }, _ );
-          etrue;
-          _;
-        } ->
-      Mark.remove etrue
-    | EIfThenElse
-        {
-          cond =
-            ( ( ELit (LBool false)
-              | EAppOp { op = Log _, _; args = [(ELit (LBool false), _)]; _ } ),
-              _ );
-          efalse;
-          _;
-        } ->
-      Mark.remove efalse
-    | EIfThenElse
-        {
-          cond;
-          etrue =
-            ( ( ELit (LBool btrue)
-              | EAppOp { op = Log _, _; args = [(ELit (LBool btrue), _)]; _ } ),
-              _ );
-          efalse =
-            ( ( ELit (LBool bfalse)
-              | EAppOp { op = Log _, _; args = [(ELit (LBool bfalse), _)]; _ }
-                ),
-              _ );
-        } ->
-      if btrue && not bfalse then Mark.remove cond
-      else if (not btrue) && bfalse then
-        EAppOp
-          {
-            op = Not, Expr.mark_pos mark;
-            tys = [TLit TBool, Expr.mark_pos mark];
-            args = [cond];
-          }
-        (* note: this last call eliminates the condition & might skip log calls
-           as well *)
-      else (* btrue = bfalse *) ELit (LBool btrue)
+    | EIfThenElse { cond; etrue; efalse } ->
+      simplified_ifthenelse cond etrue efalse mark
     | EAppOp { op = Op.Fold, _; args = [_f; init; (EArray [], _)]; _ } ->
       (*reduces a fold with an empty list *)
       Mark.remove init

tests/func/good/scope_call_func_struct_closure.catala_en

@@ -131,13 +131,9 @@ let scope Foo
     Foo_in.b_in
   in
   let set b : bool =
-    match
-      (match (handle_exceptions [b.0 b.1 ()]) with
-       | ENone → ESome true
-       | ESome x → ESome x)
-    with
-    | ENone → error NoValue
-    | ESome arg → arg
+    match (handle_exceptions [b.0 b.1 ()]) with
+    | ENone → true
+    | ESome x → x
   in
   let set r :
       Result {