Enhance type inference for non-literal ranges

Author: bjorng

lib/compiler/src/beam_ssa_type.erl

@@ -2721,6 +2721,15 @@ make_number({'-inf','+inf'}) ->
 make_number({_,_}=R) ->
     #t_number{elements=R}.
 
+make_integer({'-inf','+inf'}) ->
+    #t_integer{};
+make_integer({'-inf',_}=R) ->
+    #t_integer{elements=R};
+make_integer({Min,Max}=R) when is_integer(Min), Min =< Max ->
+    #t_integer{elements=R};
+make_integer(_) ->
+    #t_integer{}.
+
 inv_relop({bif,Op}) -> inv_relop_1(Op);
 inv_relop(_) -> none.
 
@@ -2736,6 +2745,16 @@ infer_get_range(#t_integer{elements=R}) -> R;
 infer_get_range(#t_number{elements=R}) -> R;
 infer_get_range(_) -> unknown.
 
+infer_integer_get_range(Arg, Ts) ->
+    case concrete_type(Arg, Ts) of
+        #t_integer{elements={_,_}=R} ->
+            R;
+        #t_number{elements={Min,Max}=R}
+          when is_integer(Min), is_integer(Max) -> R;
+        _ ->
+            {'-inf','+inf'}
+    end.
+
 infer_br_value(_V, _Bool, none) ->
     none;
 infer_br_value(V, Bool, NewTs) ->
@@ -2819,18 +2838,12 @@ infer_type({bif,is_integer}, [#b_var{}=Arg,
                               #b_literal{val=Max}], _Ts, _Ds) when Min =< Max ->
     T = {Arg, beam_types:make_integer(Min, Max)},
     {[T], [T]};
-infer_type({bif,is_integer}, [#b_var{}=Arg,
-                              #b_literal{val=Min},_], _Ts, _Ds) ->
-    T = {Arg, make_number({Min,'+inf'})},
-    {[T], [T]};
-infer_type({bif,is_integer}, [#b_var{}=Arg,_,
-                              #b_literal{val=Max}], _Ts, _Ds) ->
-    T = {Arg, make_number({'-inf',Max})},
-    {[T], [T]};
-infer_type({bif,is_integer}, [#b_var{}=Arg, _, _], _Ts, _Ds) ->
-    %% We cannot subtract the type when the bounds are unknown: `Arg` may still
-    %% be an integer if it is not in the tested range.
-    T = {Arg, #t_integer{}},
+infer_type({bif,is_integer}, [#b_var{}=Arg,Min0,Max0], Ts, _Ds) ->
+    {Min,_} = infer_integer_get_range(Min0, Ts),
+    {_,Max} = infer_integer_get_range(Max0, Ts),
+    T = {Arg, make_integer({Min,Max})},
+    %% Conservatively never attempt to subtract the type; subtraction
+    %% will most likely be incorrect or useless.
     {[T], []};
 infer_type({bif,is_list}, [#b_var{}=Arg], _Ts, _Ds) ->
     T = {Arg, #t_list{}},