core_lib: Teach is_var_used/2 to handle keys in map patterns

is_var_used/2 did not notice that variable keys in map patterns
were used, which could cause sys_core_fold to do unsafe
optimizations.

2 files changed, 25 insertions, 6 deletions

diff --git a/lib/compiler/src/core_lib.erl b/lib/compiler/src/core_lib.erl
index 0d95971f91..730e3a5317 100644
--- a/lib/compiler/src/core_lib.erl
+++ b/lib/compiler/src/core_lib.erl
@@ -236,10 +236,15 @@ vu_pat_seg_list(V, Ss, St) ->
 			end
 		end, St, Ss).
 
-vu_map_pairs(V, [#c_map_pair{val=Pat}|T], St0) ->
-    case vu_pattern(V, Pat, St0) of
-	{true,_}=St -> St;
-	St -> vu_map_pairs(V, T, St)
+vu_map_pairs(V, [#c_map_pair{key=Key,val=Pat}|T], St0) ->
+    case vu_expr(V, Key) of
+	true ->
+	    {true,false};
+	false ->
+	    case vu_pattern(V, Pat, St0) of
+		{true,_}=St -> St;
+		St -> vu_map_pairs(V, T, St)
+	    end
     end;
 vu_map_pairs(_, [], St) -> St.
 
diff --git a/lib/compiler/test/match_SUITE.erl b/lib/compiler/test/match_SUITE.erl
index e5aaf49d6f..1234197cd7 100644
--- a/lib/compiler/test/match_SUITE.erl
+++ b/lib/compiler/test/match_SUITE.erl
@@ -22,7 +22,8 @@
 	 init_per_group/2,end_per_group/2,
 	 pmatch/1,mixed/1,aliases/1,match_in_call/1,
 	 untuplify/1,shortcut_boolean/1,letify_guard/1,
-	 selectify/1,underscore/1,match_map/1,coverage/1]).
+	 selectify/1,underscore/1,match_map/1,map_vars_used/1,
+      coverage/1]).
 	 
 -include_lib("test_server/include/test_server.hrl").
 
@@ -36,7 +37,7 @@ groups() ->
     [{p,test_lib:parallel(),
       [pmatch,mixed,aliases,match_in_call,untuplify,
        shortcut_boolean,letify_guard,selectify,
-       underscore,match_map,coverage]}].
+       underscore,match_map,map_vars_used,coverage]}].
 
 
 init_per_suite(Config) ->
@@ -412,6 +413,19 @@ do_match_map(#s{map=#{key:=Val}}=S) ->
     %% Would crash with a 'badarg' exception.
     S#s{t=Val}.
 
+map_vars_used(Config) when is_list(Config) ->
+    {some,value} = do_map_vars_used(a, b, #{{a,b}=>42,v=>{some,value}}),
+    ok.
+
+do_map_vars_used(X, Y, Map) ->
+    case {X,Y} of
+	T ->
+	    %% core_lib:is_var_used/2 would not consider T used.
+	    #{T:=42,v:=Val} = Map,
+	    Val
+    end.
+
+
 coverage(Config) when is_list(Config) ->
     %% Cover beam_dead.
     ok = coverage_1(x, a),