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.

4 files changed, 21 insertions, 4 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().
diff --git a/lib/compiler/test/compile_SUITE.erl b/lib/compiler/test/compile_SUITE.erl
index 4e2753ba5f..f647a4030d 100644
--- a/lib/compiler/test/compile_SUITE.erl
+++ b/lib/compiler/test/compile_SUITE.erl
@@ -371,6 +371,7 @@ do_file_listings(DataDir, PrivDir, [File|Files]) ->
     do_listing(Simple, TargetDir, dinline, ".inline"),
     do_listing(Simple, TargetDir, dcore, ".core"),
     do_listing(Simple, TargetDir, dcopt, ".copt"),
+    do_listing(Simple, TargetDir, dcbsm, ".core_bsm"),
     do_listing(Simple, TargetDir, dsetel, ".dsetel"),
     do_listing(Simple, TargetDir, dkern, ".kernel"),
     do_listing(Simple, TargetDir, dlife, ".life"),
diff --git a/lib/compiler/test/misc_SUITE.erl b/lib/compiler/test/misc_SUITE.erl
index 01b064cc10..4bd884d86b 100644
--- a/lib/compiler/test/misc_SUITE.erl
+++ b/lib/compiler/test/misc_SUITE.erl
@@ -161,11 +161,12 @@ md5_1(Beam) ->
 %% Cover some code that handles internal errors.
 
 silly_coverage(Config) when is_list(Config) ->
-    %% sys_core_fold, sys_core_setel, v3_kernel
+    %% sys_core_fold, sys_core_bsm, sys_core_setel, v3_kernel
     BadCoreErlang = {c_module,[],
 		     name,[],[],
 		     [{{c_var,[],{foo,2}},seriously_bad_body}]},
     expect_error(fun() -> sys_core_fold:module(BadCoreErlang, []) end),
+    expect_error(fun() -> sys_core_bsm:module(BadCoreErlang, []) end),
     expect_error(fun() -> sys_core_dsetel:module(BadCoreErlang, []) end),
     expect_error(fun() -> v3_kernel:module(BadCoreErlang, []) end),
 
diff --git a/lib/compiler/test/warnings_SUITE.erl b/lib/compiler/test/warnings_SUITE.erl
index 7c27750556..77e4234c70 100644
--- a/lib/compiler/test/warnings_SUITE.erl
+++ b/lib/compiler/test/warnings_SUITE.erl
@@ -529,7 +529,7 @@ bin_opt_info(Config) when is_list(Config) ->
 	    Code,
 	    [bin_opt_info],
 	    {warnings,
-	     [{4,sys_core_fold,orig_bin_var_used_in_guard},
+	     [{4,sys_core_bsm,orig_bin_var_used_in_guard},
 	      {5,beam_bsm,{no_bin_opt,{{t1,1},no_suitable_bs_start_match}}},
 	      {9,beam_bsm,{no_bin_opt,
 			   {binary_used_in,{extfunc,erlang,split_binary,2}}}} ]}}],