beam_ssa_type: Infer the type for a tuple used as a lookup table

Find the type of a call to `erlang/2` where a literal tuple is
used as a lookup table. Here is a truncated example from the
`base64` module:

    element(X+1, {$A, $B, $C, $D, $E, $F, ...})

The type will be the join of the types of the elements.

1 files changed, 22 insertions, 1 deletions

diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index adbddc7059..63b2dc9e07 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -3055,7 +3055,28 @@ assert_not_fragile(Lit, #vst{}) ->
 
 bif_types(Op, Ss, Vst) ->
     Args = [normalize(get_term_type(Arg, Vst)) || Arg <- Ss],
-    beam_call_types:types(erlang, Op, Args).
+    case {Op,Ss} of
+        {element,[_,{literal,Tuple}]} when tuple_size(Tuple) > 0 ->
+            case beam_call_types:types(erlang, Op, Args) of
+                {any,ArgTypes,Safe} ->
+                    RetType = join_tuple_elements(Tuple),
+                    {RetType,ArgTypes,Safe};
+                Other ->
+                    Other
+            end;
+        {_,_} ->
+            beam_call_types:types(erlang, Op, Args)
+    end.
+
+join_tuple_elements(Tuple) ->
+    join_tuple_elements(tuple_size(Tuple), Tuple, none).
+
+join_tuple_elements(0, _Tuple, Type) ->
+    Type;
+join_tuple_elements(I, Tuple, Type0) ->
+    Type1 = beam_types:make_type_from_value(element(I, Tuple)),
+    Type = beam_types:join(Type0, Type1),
+    join_tuple_elements(I - 1, Tuple, Type).
 
 call_types({extfunc,M,F,A}, A, Vst) ->
     Args = get_call_args(A, Vst),