Merge branch 'john/compiler/validator-container-type-subtraction-pt2/GH-4774/OTP-17437' into maint

* john/compiler/validator-container-type-subtraction-pt2/GH-4774/OTP-17437:
  beam_validator: Update containers in infer_types/4

1 files changed, 25 insertions, 0 deletions

diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index 54a91d037c..171b3f0ddd 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -1997,6 +1997,31 @@ infer_types_1(#value{op={bif,tuple_size}, args=[Tuple]},
         eq_exact -> update_type(fun meet/2, Type, Tuple, Vst);
         ne_exact -> update_type(fun subtract/2, Type, Tuple, Vst)
     end;
+infer_types_1(#value{op={bif,element},args=[{integer,Index}, Tuple]},
+              Val, eq_exact, Vst) ->
+    ValType = get_term_type(Val, Vst),
+    Es = beam_types:set_tuple_element(Index, ValType, #{}),
+    TupleType = #t_tuple{size=Index,elements=Es},
+    update_type(fun meet/2, TupleType, Tuple, Vst);
+infer_types_1(#value{op={bif,element},args=[{integer,Index}, Tuple]},
+              Val, ne_exact, Vst) ->
+    %% Subtraction is only safe with singletons, see update_ne_types/3 for
+    %% details.
+    ValType = get_term_type(Val, Vst),
+    case beam_types:is_singleton_type(ValType) of
+        true ->
+            case beam_types:set_tuple_element(Index, ValType, #{}) of
+                #{ Index := _ }=Es ->
+                    TupleType = #t_tuple{size=Index,elements=Es},
+                    update_type(fun subtract/2, TupleType, Tuple, Vst);
+                #{} ->
+                    %% Index was above the element limit; subtraction is not
+                    %% safe.
+                    Vst
+            end;
+        false ->
+            Vst
+    end;
 infer_types_1(_, _, _, Vst) ->
     Vst.