From b79cde3bb7ddf34b4c1f6411393feec9ef85340a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20H=C3=B6gberg?= <john@erlang.org>
Date: Mon, 18 Mar 2019 09:41:02 +0100
Subject: beam_validator: Infer types on both sides of '=:='

---
 lib/compiler/src/beam_validator.erl | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

(limited to 'lib/compiler/src')

diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index ab8caa1a0d..4fba3fa1c6 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -1595,8 +1595,11 @@ infer_types(_, #vst{}) ->
 
 infer_types_1(#value{op={bif,'=:='},args=[LHS,RHS]}) ->
     fun({atom,true}, S) ->
-            Infer = infer_types(RHS, S),
-            Infer(LHS, S);
+            %% Either side might contain something worth inferring, so we need
+            %% to check them both.
+            Infer_L = infer_types(RHS, S),
+            Infer_R = infer_types(LHS, S),
+            Infer_R(RHS, Infer_L(LHS, S));
        (_, S) -> S
     end;
 infer_types_1(#value{op={bif,element},args=[{integer,Index}=Key,Tuple]}) ->
@@ -1772,8 +1775,11 @@ update_ne_types(LHS, RHS, Vst) ->
     end.
 
 update_eq_types(LHS, RHS, Vst0) ->
-    Infer = infer_types(LHS, Vst0),
-    Vst1 = Infer(RHS, Vst0),
+    %% Either side might contain something worth inferring, so we need
+    %% to check them both.
+    Infer_L = infer_types(RHS, Vst0),
+    Infer_R = infer_types(LHS, Vst0),
+    Vst1 = Infer_R(RHS, Infer_L(LHS, Vst0)),
 
     T1 = get_term_type(LHS, Vst1),
     T2 = get_term_type(RHS, Vst1),
-- 
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