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, 2 insertions, 1 deletions

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),