Merge branch 'bjorn/compiler/fix-receive-patch/ERL-950/OTP-15832' into maint

* bjorn/compiler/fix-receive-patch/ERL-950/OTP-15832:
  Eliminate compiler crash when compiling complex receive statements

2 files changed, 31 insertions, 6 deletions

diff --git a/lib/compiler/src/beam_ssa_pre_codegen.erl b/lib/compiler/src/beam_ssa_pre_codegen.erl
index bf99e8fc26..9af72afca7 100644
--- a/lib/compiler/src/beam_ssa_pre_codegen.erl
+++ b/lib/compiler/src/beam_ssa_pre_codegen.erl
@@ -1415,12 +1415,15 @@ fix_receive([], _Defs, Blocks, Count) ->
 find_loop_exit([L1,L2|_Ls], Blocks) ->
     Path1 = beam_ssa:rpo([L1], Blocks),
     Path2 = beam_ssa:rpo([L2], Blocks),
-    find_loop_exit_1(reverse(Path1), reverse(Path2), none);
+    find_loop_exit_1(Path1, cerl_sets:from_list(Path2));
 find_loop_exit(_, _) -> none.
 
-find_loop_exit_1([H|T1], [H|T2], _) ->
-    find_loop_exit_1(T1, T2, H);
-find_loop_exit_1(_, _, Exit) -> Exit.
+find_loop_exit_1([H|T], OtherPath) ->
+    case cerl_sets:is_element(H, OtherPath) of
+        true -> H;
+        false ->  find_loop_exit_1(T, OtherPath)
+    end;
+find_loop_exit_1([], _) -> none.
 
 %% find_rm_blocks(StartLabel, Blocks) -> [Label].
 %%  Find all blocks that start with remove_message within the receive
diff --git a/lib/compiler/test/receive_SUITE.erl b/lib/compiler/test/receive_SUITE.erl
index 0038eb1a4b..752491f0f8 100644
--- a/lib/compiler/test/receive_SUITE.erl
+++ b/lib/compiler/test/receive_SUITE.erl
@@ -26,7 +26,7 @@
 	 init_per_testcase/2,end_per_testcase/2,
 	 export/1,recv/1,coverage/1,otp_7980/1,ref_opt/1,
 	 wait/1,recv_in_try/1,double_recv/1,receive_var_zero/1,
-         match_built_terms/1]).
+         match_built_terms/1,elusive_common_exit/1]).
 
 -include_lib("common_test/include/ct.hrl").
 
@@ -47,7 +47,7 @@ groups() ->
     [{p,test_lib:parallel(),
       [recv,coverage,otp_7980,ref_opt,export,wait,
        recv_in_try,double_recv,receive_var_zero,
-       match_built_terms]}].
+       match_built_terms,elusive_common_exit]}].
 
 
 init_per_suite(Config) ->
@@ -427,4 +427,26 @@ match_built_terms(Config) when is_list(Config) ->
     ?MATCH_BUILT_TERM(Ref, <<A, B>>),
     ?MATCH_BUILT_TERM(Ref, #{ 1 => A, 2 => B}).
 
+elusive_common_exit(_Config) ->
+    self() ! {1, a},
+    self() ! {2, b},
+    {[z], [{2,b},{1,a}]} = elusive_loop([x,y,z], 2, []),
+    ok.
+
+elusive_loop(List, 0, Results) ->
+    {List, Results};
+elusive_loop(List, ToReceive, Results) ->
+    {Result, RemList} =
+        receive
+            {_Pos, _R} = Res when List =/= [] ->
+                [_H|T] = List,
+                {Res, T};
+            {_Pos, _R} = Res when List =:= [] ->
+                {Res, []}
+        end,
+    %% beam_ssa_pre_codegen:fix_receives() would fail to find
+    %% the common exit block for this receive. That would mean
+    %% that it would not insert all necessary copy instructions.
+    elusive_loop(RemList, ToReceive-1, [Result | Results]).
+
 id(I) -> I.