Fix unsafe bit syntax matching optimization

As part of sys_core_fold, variables involved in bit syntax
matching would be annotated when it would be safe for a later
pass to do the delayed sub-binary creation optimization.

An implicit assumption regarding the annotation was that the
code must not be further optimized. That assumption was broken
in 05130e48555891, which introduced a fixpoint iteration
(applying the optimizations until there were no more changes).
That means that a variable could be annotated as safe for
reusing the match context in one iteration, but a later iteration
could rewrite the code in a way that would make the optimization
unsafe.

One way to fix this would be to clear all reuse_for_context
annotations before each iteration. But that would be wasteful.

Instead I chose to fix the problem by moving out the annotation
code to a separate pass (sys_core_bsm) that is run later after
all major optimizations of Core Erlang has been done.

1 files changed, 17 insertions, 2 deletions

diff --git a/lib/compiler/test/bs_match_SUITE.erl b/lib/compiler/test/bs_match_SUITE.erl
index 89f851ac3b..106d8eb45a 100644
--- a/lib/compiler/test/bs_match_SUITE.erl
+++ b/lib/compiler/test/bs_match_SUITE.erl
@@ -39,7 +39,7 @@
 	 match_string_opt/1,select_on_integer/1,
 	 map_and_binary/1,unsafe_branch_caching/1,
 	 bad_literals/1,good_literals/1,constant_propagation/1,
-	 parse_xml/1]).
+	 parse_xml/1,get_payload/1]).
 
 -export([coverage_id/1,coverage_external_ignore/2]).
 
@@ -70,7 +70,8 @@ groups() ->
        no_partition,calling_a_binary,binary_in_map,
        match_string_opt,select_on_integer,
        map_and_binary,unsafe_branch_caching,
-       bad_literals,good_literals,constant_propagation,parse_xml]}].
+       bad_literals,good_literals,constant_propagation,parse_xml,
+       get_payload]}].
 
 
 init_per_suite(Config) ->
@@ -1508,6 +1509,20 @@ do_parse_xml(<<"<?xml"/utf8,Rest/binary>> = Bytes) ->
 is_next_char_whitespace(<<C/utf8,_/binary>>) ->
     C =:= $\s.
 
+-record(ext_header,
+        {this_hdr = 17,
+         ext_hdr_opts}).
+
+get_payload(Config) ->
+    <<3445:48>> = do_get_payload(#ext_header{ext_hdr_opts = <<3445:48>>}),
+    {'EXIT',_} = (catch do_get_payload(#ext_header{})),
+    ok.
+
+do_get_payload(ExtHdr) ->
+    _ = ExtHdr#ext_header.this_hdr,
+    ExtHdrOptions = ExtHdr#ext_header.ext_hdr_opts,
+    <<_:13,_:35>> = ExtHdr#ext_header.ext_hdr_opts,
+    ExtHdrOptions.
 
 check(F, R) ->
     R = F().