From f9ea85611faca82c7494449ddb8bcb1ef1d194cb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 17 Jan 2019 10:42:41 +0100
Subject: Make the beam_validator smarter (again)

Needed because of the optimizations in 48f20bd589fa69.

https://bugs.erlang.org/browse/ERL-832
---
 lib/compiler/src/beam_validator.erl | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

(limited to 'lib/compiler/src')

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,[_|_]}) ->
-- 
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