beam_ssa_type: Fix type subtraction in #b_switch{}

A switch is equivalent to a series of '=:=', so we have to subtract
each value individually from the type. Subtracting a join risks
removing too much type information, and managed to narrow "number"
into "float" in the attached test case.

2 files changed, 24 insertions, 6 deletions

diff --git a/lib/compiler/src/beam_ssa_type.erl b/lib/compiler/src/beam_ssa_type.erl
index 7ef49fee64..fcfb7b86f6 100644
--- a/lib/compiler/src/beam_ssa_type.erl
+++ b/lib/compiler/src/beam_ssa_type.erl
@@ -478,7 +478,9 @@ update_successors(#b_switch{arg=#b_var{}=V,fail=Fail,list=List}, Ts0, D0) ->
                 end,
             foldl(F, D, List);
         false ->
-            FailTs = subtract_types([{V,join_sw_list(List, Ts0, none)}], Ts0),
+            %% V can not be equal to any of the values in List at the fail
+            %% block.
+            FailTs = subtract_sw_list(V, List, Ts0),
             D = update_successor(Fail, FailTs, D0),
             F = fun({Val,S}, A) ->
                         T = get_type(Val, Ts0),
@@ -488,9 +490,14 @@ update_successors(#b_switch{arg=#b_var{}=V,fail=Fail,list=List}, Ts0, D0) ->
         end;
 update_successors(#b_ret{}, _Ts, D) -> D.
 
-join_sw_list([{Val,_}|T], Ts, Type) ->
-    join_sw_list(T, Ts, join(Type, get_type(Val, Ts)));
-join_sw_list([], _, Type) -> Type.
+subtract_sw_list(V, List, Ts) ->
+    Ts#{ V := sub_sw_list_1(get_type(V, Ts), List, Ts) }.
+
+sub_sw_list_1(Type, [{Val,_}|T], Ts) ->
+    ValType = get_type(Val, Ts),
+    sub_sw_list_1(subtract(Type, ValType), T, Ts);
+sub_sw_list_1(Type, [], _Ts) ->
+    Type.
 
 update_successor_bool(#b_var{}=Var, BoolValue, S, Ts, D) ->
     case t_is_boolean(get_type(Var, Ts)) of
diff --git a/lib/compiler/test/float_SUITE.erl b/lib/compiler/test/float_SUITE.erl
index 012810aba2..831e8279aa 100644
--- a/lib/compiler/test/float_SUITE.erl
+++ b/lib/compiler/test/float_SUITE.erl
@@ -20,7 +20,8 @@
 -module(float_SUITE).
 -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1, 
 	 init_per_group/2,end_per_group/2,
-	 pending/1,bif_calls/1,math_functions/1,mixed_float_and_int/1]).
+	 pending/1,bif_calls/1,math_functions/1,mixed_float_and_int/1,
+         subtract_number_type/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
@@ -28,7 +29,7 @@ suite() -> [{ct_hooks,[ts_install_cth]}].
 
 all() -> 
     [pending, bif_calls, math_functions,
-     mixed_float_and_int].
+     mixed_float_and_int, subtract_number_type].
 
 groups() -> 
     [].
@@ -176,5 +177,15 @@ mixed_float_and_int(Config) when is_list(Config) ->
 pc(Cov, NotCov, X) ->
     round(Cov/(Cov+NotCov)*100) + 42 + 2.0*X.
 
+subtract_number_type(Config) when is_list(Config) ->
+    120 = fact(5).
+
+fact(N) ->
+    fact(N, 1).
+
+fact(0, P) -> P;
+fact(1, P) -> P;
+fact(N, P) -> fact(N-1, P*N).
+
 id(I) -> I.