Merge branch 'bjorn/compiler/beam_validator/ERL-832'

* bjorn/compiler/beam_validator/ERL-832:
  Make the beam_validator smarter (again)

2 files changed, 37 insertions, 9 deletions

diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index 46c689e034..3d53054f69 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -828,13 +828,14 @@ valfun_4({test,is_map,{f,Lbl},[Src]}, Vst0) ->
 	_ ->
 	    kill_state(Vst0)
     end;
-valfun_4({test,is_nil,{f,Lbl},[Src]}, Vst) ->
-    case get_term_type(Src, Vst) of
-        list ->
-            branch_state(Lbl, set_type_reg(cons, Src, Vst));
-        _ ->
-            branch_state(Lbl, Vst)
-    end;
+valfun_4({test,is_nil,{f,Lbl},[Src]}, Vst0) ->
+    Vst = case get_term_type(Src, Vst0) of
+               list ->
+                   branch_state(Lbl, set_type_reg(cons, Src, Vst0));
+               _ ->
+                   branch_state(Lbl, Vst0)
+           end,
+    set_aliased_type(nil, Src, Vst);
 valfun_4({test,is_eq_exact,{f,Lbl},[Src,Val]=Ss}, Vst0) ->
     validate_src(Ss, Vst0),
     Infer = infer_types(Src, Vst0),
@@ -1903,6 +1904,10 @@ merge_types({atom,A}, bool) ->
     merge_bool(A);
 merge_types(cons, {literal,[_|_]}) ->
     cons;
+merge_types(cons, nil) ->
+    list;
+merge_types(nil, cons) ->
+    list;
 merge_types({literal,[_|_]}, cons) ->
     cons;
 merge_types({literal,[_|_]}, {literal,[_|_]}) ->
diff --git a/lib/compiler/test/beam_validator_SUITE.erl b/lib/compiler/test/beam_validator_SUITE.erl
index 661b48a080..c9df066958 100644
--- a/lib/compiler/test/beam_validator_SUITE.erl
+++ b/lib/compiler/test/beam_validator_SUITE.erl
@@ -579,14 +579,23 @@ receive_stacked(Config) ->
 
     ok.
 
+aliased_types(Config) ->
+    Seq = lists:seq(1, 5),
+    1 = aliased_types_1(Seq, Config),
+
+    {1,1} = aliased_types_2(Seq),
+    {42,none} = aliased_types_2([]),
+
+    ok.
+
 %% ERL-735: validator failed to track types on aliased registers, rejecting
 %% legitimate optimizations.
 %%
 %%    move x0 y0
 %%    bif hd L1 x0
 %%    get_hd y0     %% The validator failed to see that y0 was a list
-aliased_types(Config) when is_list(Config) ->
-    Bug = lists:seq(1, 5),
+%%
+aliased_types_1(Bug, Config) ->
     if
         Config =/= [gurka, gaffel] -> %% Pointless branch.
             _ = hd(Bug),
@@ -594,6 +603,17 @@ aliased_types(Config) when is_list(Config) ->
             hd(Bug)
     end.
 
+%% ERL-832: validator failed to realize that a Y register was a cons.
+aliased_types_2(Bug) ->
+    Res = case Bug of
+              [] -> id(42);
+              _ -> hd(Bug)
+          end,
+    {Res,case Bug of
+             [] -> none;
+             _ -> hd(Bug)
+         end}.
+
 %%%-------------------------------------------------------------------------
 
 transform_remove(Remove, Module) ->
@@ -652,3 +672,6 @@ night(Turned) ->
     ok.
 
 participating(_, _, _, _) -> ok.
+
+id(I) ->
+    I.