Fix rare bug in binary matching (again)

2e40d8d1c51a attempted fix a bug in binary matching, but it only
fixed the bug for the minimized test case.

This commit removes the previous fix and fixes the bug in a more
effective way. See the comments in the new code in `sys_core_bsm`
for an explanation.

This commit restores the optimizations in string.erl and dets_v9.erl
that the previous fix disabled.

I have not found any code where this commit will disable optimizations
when they are actually safe. There are some changes to the code
in ssl_cipher.erl in that some bs_start_match2 instruction did not
reuse the binary register for the match context, but the delayed
sub binary optimizations was never applied to the code in the first
place.

https://bugs.erlang.org/browse/ERL-689

1 files changed, 35 insertions, 3 deletions

diff --git a/lib/compiler/test/bs_match_SUITE.erl b/lib/compiler/test/bs_match_SUITE.erl
index 7814738449..e97dbac8a6 100644
--- a/lib/compiler/test/bs_match_SUITE.erl
+++ b/lib/compiler/test/bs_match_SUITE.erl
@@ -1690,30 +1690,62 @@ non_opt_eq([], <<>>) ->
 
 %% ERL-689
 
-erl_689(Config) ->
+erl_689(_Config) ->
     {{0, 0, 0}, <<>>} = do_erl_689_1(<<0>>, ?MODULE),
     {{2018, 8, 7}, <<>>} = do_erl_689_1(<<4,2018:16/little,8,7>>, ?MODULE),
     {{0, 0, 0}, <<>>} = do_erl_689_2(?MODULE, <<0>>),
     {{2018, 8, 7}, <<>>} = do_erl_689_2(?MODULE, <<4,2018:16/little,8,7>>),
     ok.
 
-do_erl_689_1(<<Length, Data/binary>>, _) ->
+do_erl_689_1(Arg1, Arg2) ->
+    Res = do_erl_689_1a(Arg1, Arg2),
+    Res = do_erl_689_1b(Arg1, Arg2).
+
+do_erl_689_2(Arg1, Arg2) ->
+    Res = do_erl_689_2a(Arg1, Arg2),
+    Res = do_erl_689_2b(Arg1, Arg2).
+
+do_erl_689_1a(<<Length, Data/binary>>, _) ->
+    case {Data, Length} of
+        {_, 0} ->
+            %% bs_context_to_binary would incorrectly set Data to the original
+            %% binary (before matching in the function head).
+            {{0, 0, 0}, Data};
+        {<<Y:16/little, M, D, Rest/binary>>, 4} ->
+            {{Y, M, D}, Rest}
+    end.
+
+do_erl_689_1b(<<Length, Data/binary>>, _) ->
     case {Data, Length} of
         {_, 0} ->
             %% bs_context_to_binary would incorrectly set Data to the original
             %% binary (before matching in the function head).
+            id(0),
             {{0, 0, 0}, Data};
         {<<Y:16/little, M, D, Rest/binary>>, 4} ->
+            id(1),
+            {{Y, M, D}, Rest}
+    end.
+
+do_erl_689_2a(_, <<Length, Data/binary>>) ->
+    case {Length, Data} of
+        {0, _} ->
+            %% bs_context_to_binary would incorrectly set Data to the original
+            %% binary (before matching in the function head).
+            {{0, 0, 0}, Data};
+        {4, <<Y:16/little, M, D, Rest/binary>>} ->
             {{Y, M, D}, Rest}
     end.
 
-do_erl_689_2(_, <<Length, Data/binary>>) ->
+do_erl_689_2b(_, <<Length, Data/binary>>) ->
     case {Length, Data} of
         {0, _} ->
             %% bs_context_to_binary would incorrectly set Data to the original
             %% binary (before matching in the function head).
+            id(0),
             {{0, 0, 0}, Data};
         {4, <<Y:16/little, M, D, Rest/binary>>} ->
+            id(1),
             {{Y, M, D}, Rest}
     end.