Parmatch.matrix_stable_vars: optimize the all-negative case

ocaml · Jan 3, 2018 · a10bff1 · a10bff1
1 parent 801a2d5
commit a10bff1
Showing 1 changed file with 5 additions and 0 deletions.
diff --git a/typing/parmatch.ml b/typing/parmatch.ml
@@ -2366,6 +2366,11 @@ let rec matrix_stable_vars m = match m with
           (* The stable variables are those stable at any position *)
           Vars (List.fold_left IdSet.union IdSet.empty stables_in_varsets)
       end
+  | m when List.for_all (function Negative _ -> true | Positive _ -> false) m ->
+      (* optimization: if m has many negative cases and few positive cases
+         (a small guarded clause after a long list of clauses), many sub-matrices
+         may have no positives at all; quit early in this case *)
+      All
   | m ->
       let m = simplify_first_amb_col m in
       if not (all_coherent (first_column m))