Merge branch 'maint'

* maint:
  beam_bsm: Eliminate unsafe optimization

1 files changed, 23 insertions, 0 deletions

diff --git a/lib/compiler/test/bs_match_SUITE.erl b/lib/compiler/test/bs_match_SUITE.erl
index f8af070c44..6742571b86 100644
--- a/lib/compiler/test/bs_match_SUITE.erl
+++ b/lib/compiler/test/bs_match_SUITE.erl
@@ -769,6 +769,11 @@ multiple_uses(Config) when is_list(Config) ->
     {344,62879,345,<<245,159,1,89>>} = multiple_uses_1(<<1,88,245,159,1,89>>),
     true = multiple_uses_2(<<0,0,197,18>>),
     <<42,43>> = multiple_uses_3(<<0,0,42,43>>, fun id/1),
+
+    ok = first_after(<<>>, 42),
+    <<1>> = first_after(<<1,2,3>>, 0),
+    <<2>> = first_after(<<1,2,3>>, 1),
+
     ok.
 
 multiple_uses_1(<<X:16,Tail/binary>>) ->
@@ -790,6 +795,24 @@ multiple_uses_match(<<Y:16,Z:16>>) ->
 multiple_uses_cmp(<<Y:16>>, <<Y:16>>) -> true;
 multiple_uses_cmp(<<_:16>>, <<_:16>>) -> false.
 
+first_after(Data, Offset) ->
+    case byte_size(Data) > Offset of
+	false ->
+	    {First, Rest} = {ok, ok},
+	    ok;
+	true ->
+	    <<_:Offset/binary, Rest/binary>> = Data,
+	    %% 'Rest' saved in y(0) before the call.
+            {First, _} = match_first(Data, Rest),
+            %% When beam_bsm sees the code, the following line
+            %% which uses y(0) has been optimized away.
+	    {First, Rest} = {First, Rest},
+	    First
+    end.
+
+match_first(_, <<First:1/binary, Rest/binary>>) ->
+    {First, Rest}.
+
 zero_label(Config) when is_list(Config) ->
     <<"nosemouth">> = read_pols(<<"FACE","nose","mouth">>),
     <<"CE">> = read_pols(<<"noFACE">>),