From c5e36feada9d0362108890f42c40dd2398b1b531 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 13 Aug 2019 06:38:24 +0200
Subject: Fix compiler crash when compiling some receive statements

The compiler would crash when compiling the following code:

    do(Acc) ->
        receive
            {Pid, abc} ->
                ok;
            {Pid, []} ->
                ok;
            {Pid, _Res} ->
                exit(_Res)
        end,
        do([Pid | Acc]).

The last clause that always raises an exception would confuse the
compiler so that it would think that the `receive` statement was at the
end of the function and it would generate incorrect code for the `do/1`
call following the `receive`.

https://bugs.erlang.org/browse/ERL-1022
---
 lib/compiler/test/receive_SUITE.erl | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

(limited to 'lib/compiler/test/receive_SUITE.erl')

diff --git a/lib/compiler/test/receive_SUITE.erl b/lib/compiler/test/receive_SUITE.erl
index 752491f0f8..8cd864c59e 100644
--- a/lib/compiler/test/receive_SUITE.erl
+++ b/lib/compiler/test/receive_SUITE.erl
@@ -431,6 +431,20 @@ elusive_common_exit(_Config) ->
     self() ! {1, a},
     self() ! {2, b},
     {[z], [{2,b},{1,a}]} = elusive_loop([x,y,z], 2, []),
+
+    CodeServer = whereis(code_server),
+    Self = self(),
+    Self ! {Self, abc},
+    Self ! {CodeServer, []},
+    Self ! {Self, other},
+    try elusive2([]) of
+        Unexpected ->
+            ct:fail("Expected an exception; got ~p\n", [Unexpected])
+    catch
+        throw:[other, CodeServer, Self] ->
+            ok
+    end,
+
     ok.
 
 elusive_loop(List, 0, Results) ->
@@ -449,4 +463,25 @@ elusive_loop(List, ToReceive, Results) ->
     %% that it would not insert all necessary copy instructions.
     elusive_loop(RemList, ToReceive-1, [Result | Results]).
 
+
+elusive2(Acc) ->
+    receive
+        {Pid, abc} ->
+            ok;
+        {Pid, []} ->
+            ok;
+        {Pid, Res} ->
+            %% beam_ssa_pre_codegen:find_loop_exit/2 attempts to find
+            %% the first block of the common code after the receive
+            %% statement. It used to only look at the two last clauses
+            %% of the receive. In this function, the last two clauses
+            %% don't have any common block, so it would be assumed
+            %% that there was no common block for any of the
+            %% clauses. That would mean that copy instructions would
+            %% not be inserted as needed.
+            throw([Res | Acc])
+    end,
+    %% Common code.
+    elusive2([Pid | Acc]).
+
 id(I) -> I.
-- 
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