From 81c5e15544679baeeb8c18b72156b79aa4badebb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 13 Sep 2016 12:35:24 +0200
Subject: beam_validator: Handle unreachable instructions

ab03678e introduced an optimization in the beam_z pass that could
introduce unreachable code in BEAM files (a 'jump' instruction is
removed after a 'raise' instruction, but the code following the
target of the 'jump' is not removed).

Since this situation happens very rarely, there is no point in adding
another pass that can remove unreachable code after beam_z. Instead we
will make sure that beam_validator can skip the unreachable code.
Skipping unreachable code is already done in valfun_1/2 (for
historical reasons), but we will also need to do it in val_dsetel/2.
---
 lib/compiler/src/beam_validator.erl        |  4 +++-
 lib/compiler/test/beam_validator_SUITE.erl | 25 +++++++++++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index 4c0cb6780a..16dba35adc 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -808,9 +808,11 @@ validate_bs_skip_utf(Fail, Ctx, Live, Vst0) ->
 %% A possibility for garbage collection must not occur between setelement/3 and
 %% set_tuple_element/3.
 %%
+%% Note that #vst.current will be 'none' if the instruction is unreachable.
+%%
 val_dsetel({move,_,_}, Vst) ->
     Vst;
-val_dsetel({call_ext,3,{extfunc,erlang,setelement,3}}, #vst{current=St}=Vst) ->
+val_dsetel({call_ext,3,{extfunc,erlang,setelement,3}}, #vst{current=#st{}=St}=Vst) ->
     Vst#vst{current=St#st{setelem=true}};
 val_dsetel({set_tuple_element,_,_,_}, #vst{current=#st{setelem=false}}) ->
     error(illegal_context_for_set_tuple_element);
diff --git a/lib/compiler/test/beam_validator_SUITE.erl b/lib/compiler/test/beam_validator_SUITE.erl
index 263fd2ca7e..ca85eef688 100644
--- a/lib/compiler/test/beam_validator_SUITE.erl
+++ b/lib/compiler/test/beam_validator_SUITE.erl
@@ -32,7 +32,8 @@
 	 bad_bin_match/1,bad_dsetel/1,
 	 state_after_fault_in_catch/1,no_exception_in_catch/1,
 	 undef_label/1,illegal_instruction/1,failing_gc_guard_bif/1,
-	 map_field_lists/1,cover_bin_opt/1]).
+	 map_field_lists/1,cover_bin_opt/1,
+	 val_dsetel/1]).
 	 
 -include_lib("common_test/include/ct.hrl").
 
@@ -60,7 +61,7 @@ groups() ->
        freg_state,bad_bin_match,bad_dsetel,
        state_after_fault_in_catch,no_exception_in_catch,
        undef_label,illegal_instruction,failing_gc_guard_bif,
-       map_field_lists,cover_bin_opt]}].
+       map_field_lists,cover_bin_opt,val_dsetel]}].
 
 init_per_suite(Config) ->
     Config.
@@ -546,3 +547,23 @@ beam_val(M) ->
     _ = [io:put_chars(beam_validator:format_error(E)) ||
 	    E <- Errors],
     Errors.
+
+%%%-------------------------------------------------------------------------
+
+val_dsetel(_Config) ->
+    self() ! 13,
+    {'EXIT',{{try_clause,participating},_}} = (catch night(0)),
+    ok.
+
+night(Turned) ->
+    receive
+	13 ->
+	    try participating of engine -> 16 after false end
+    end,
+    %% The setelement/3 call is unreachable.
+    Turned(setelement(#{true => Turned},
+		      participating(Turned, "suit", 40, []),
+		      Turned < Turned)),
+    ok.
+
+participating(_, _, _, _) -> ok.
-- 
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