From 479eaa7cf2eb0701af7aeb4a94da5cd13ec7de67 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 15 Aug 2019 06:38:38 +0200
Subject: Fix an internal consistency check failure caused by beam_except

https://bugs.erlang.org/browse/ERL-1026
---
 lib/compiler/src/beam_except.erl        | 32 ++++++++++++++++++++------------
 lib/compiler/test/beam_except_SUITE.erl | 14 ++++++++++++++
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/lib/compiler/src/beam_except.erl b/lib/compiler/src/beam_except.erl
index 2305502800..2b9c1b0cf5 100644
--- a/lib/compiler/src/beam_except.erl
+++ b/lib/compiler/src/beam_except.erl
@@ -152,7 +152,7 @@ dig_out_fc(Arity, Is0) ->
                              ({test,_,_,_}) -> false;
                              (_) -> true
                           end, Is0),
-    {Regs,Acc} = dig_out_fc_1(reverse(Is), Regs0, Acc0),
+    {Regs,Acc} = dig_out_fc_1(reverse(Is), Arity, Regs0, Acc0),
     case Regs of
         #{{x,0}:={atom,function_clause},{x,1}:=Args} ->
             case moves_from_stack(Args, 0, []) of
@@ -165,19 +165,27 @@ dig_out_fc(Arity, Is0) ->
             no
     end.
 
-dig_out_fc_1([{block,Bl}|Is], Regs0, Acc) ->
+dig_out_fc_1([{block,Bl}|Is], Arity, Regs0, Acc) ->
     Regs = dig_out_fc_block(Bl, Regs0),
-    dig_out_fc_1(Is, Regs, Acc);
-dig_out_fc_1([{bs_set_position,_,_}=I|Is], Regs, Acc) ->
-    dig_out_fc_1(Is, Regs, [I|Acc]);
-dig_out_fc_1([{bs_get_tail,Src,Dst,Live0}|Is], Regs0, Acc) ->
-    Regs = prune_xregs(Live0, Regs0),
-    Live = dig_out_stack_live(Regs, Live0),
-    I = {bs_get_tail,Src,Dst,Live},
-    dig_out_fc_1(Is, Regs, [I|Acc]);
-dig_out_fc_1([_|_], _Regs, _Acc) ->
+    dig_out_fc_1(Is, Arity, Regs, Acc);
+dig_out_fc_1([{bs_set_position,_,_}=I|Is], Arity, Regs, Acc) ->
+    dig_out_fc_1(Is, Arity, Regs, [I|Acc]);
+dig_out_fc_1([{bs_get_tail,Src,Dst,Live0}|Is], Arity, Regs0, Acc) ->
+    case Src of
+        {x,X} when X < Arity ->
+            %% The heuristic for determining the number of live
+            %% registers is likely to give an incorrect result.
+            %% Give up.
+            {#{},[]};
+        _ ->
+            Regs = prune_xregs(Live0, Regs0),
+            Live = dig_out_stack_live(Regs, Live0),
+            I = {bs_get_tail,Src,Dst,Live},
+            dig_out_fc_1(Is, Arity, Regs, [I|Acc])
+    end;
+dig_out_fc_1([_|_], _Arity, _Regs, _Acc) ->
     {#{},[]};
-dig_out_fc_1([], Regs, Acc) ->
+dig_out_fc_1([], _Arity, Regs, Acc) ->
     {Regs,Acc}.
 
 dig_out_fc_block([{set,[],[],{alloc,Live,_}}|Is], Regs0) ->
diff --git a/lib/compiler/test/beam_except_SUITE.erl b/lib/compiler/test/beam_except_SUITE.erl
index 67947dc292..f52239f2a8 100644
--- a/lib/compiler/test/beam_except_SUITE.erl
+++ b/lib/compiler/test/beam_except_SUITE.erl
@@ -72,11 +72,25 @@ bs_get_tail(Config) ->
      {function_clause,
       [{?MODULE,bs_get_tail_1,[<<>>,0,0,Config],_}|_]}} =
         (catch bs_get_tail_1(id(<<>>), 0, 0, Config)),
+
+    ok = bs_get_tail_2(<<"W">>, <<"X">>, <<"Z">>),
+    ok = bs_get_tail_2(<<"M">>, <<"X">>, <<"Z">>),
+    {'EXIT',
+     {function_clause,
+      [{?MODULE,do_get_bs_tail_2,[<<"A">>,<<"B">>,[],<<"C">>],_}|_]}} =
+        (catch bs_get_tail_2(<<"A">>, <<"B">>, <<"C">>)),
+
     ok.
 
 bs_get_tail_1(<<_:32, Rest/binary>>, Z1, Z2, F1) ->
     {Rest,Z1,Z2,F1}.
 
+bs_get_tail_2(A, B, C) ->
+    do_get_bs_tail_2(A, B, [], C).
+
+do_get_bs_tail_2(<<"W">>, <<"X">>, _, <<"Z">>) -> ok;
+do_get_bs_tail_2(<<"M">>, <<"X">>, _, <<"Z">>) -> ok.
+
 coverage(_) ->
     File = {file,"fake.erl"},
     ok = fc(a),
-- 
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