From e20015186fa2372793650a98005faf88e6f6e0fa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20H=C3=B6gberg?= <john@erlang.org>
Date: Mon, 8 Jul 2019 14:37:50 +0200
Subject: compiler: Fix broken 'receive' in try/catch blocks

This fix is rather ugly and tacked-on, but I'm not comfortable
refactoring the pass in an emergency patch.
---
 lib/compiler/src/beam_ssa_pre_codegen.erl | 62 +++++++++++++++++++++++++++++--
 lib/compiler/test/beam_ssa_SUITE.erl      | 26 +++++++++++++
 2 files changed, 84 insertions(+), 4 deletions(-)

diff --git a/lib/compiler/src/beam_ssa_pre_codegen.erl b/lib/compiler/src/beam_ssa_pre_codegen.erl
index 9af72afca7..a2e687930b 100644
--- a/lib/compiler/src/beam_ssa_pre_codegen.erl
+++ b/lib/compiler/src/beam_ssa_pre_codegen.erl
@@ -156,7 +156,9 @@ passes(Opts) ->
           %% Allocate registers.
           ?PASS(linear_scan),
           ?PASS(frame_size),
-          ?PASS(turn_yregs)],
+          ?PASS(turn_yregs),
+
+          ?PASS(assert_no_critical_edges)],
     [P || P <- Ps, P =/= ignore].
 
 function(#b_function{anno=Anno,args=Args,bs=Blocks0,cnt=Count0}=F0,
@@ -1321,10 +1323,11 @@ fix_receives_1([{L,Blk}|Ls], Blocks0, Count0) ->
             LoopExit = find_loop_exit(Rm, Blocks0),
             Defs0 = beam_ssa:def([L], Blocks0),
             CommonUsed = recv_common(Defs0, LoopExit, Blocks0),
-            {Blocks1,Count1} = recv_fix_common(CommonUsed, LoopExit, Rm,
-                                               Blocks0, Count0),
+            {Blocks1,Count1} = recv_crit_edges(Rm, LoopExit, Blocks0, Count0),
+            {Blocks2,Count2} = recv_fix_common(CommonUsed, LoopExit, Rm,
+                                               Blocks1, Count1),
             Defs = ordsets:subtract(Defs0, CommonUsed),
-            {Blocks,Count} = fix_receive(Rm, Defs, Blocks1, Count1),
+            {Blocks,Count} = fix_receive(Rm, Defs, Blocks2, Count2),
             fix_receives_1(Ls, Blocks, Count);
         #b_blk{} ->
             fix_receives_1(Ls, Blocks0, Count0)
@@ -1341,6 +1344,57 @@ recv_common(Defs, Exit, Blocks) ->
     Def = ordsets:subtract(Defs, ExitDefs),
     ordsets:intersection(Def, ExitUsed).
 
+%% recv_crit_edges([RemoveMessageLabel], LoopExit,
+%%                 Blocks0, Count0) -> {Blocks,Count}.
+%%
+%%  Adds dummy blocks on all conditional jumps to the exit block so that
+%%  recv_fix_common/5 can insert phi nodes without having to worry about
+%%  critical edges.
+
+recv_crit_edges(_Rms, none, Blocks0, Count0) ->
+    {Blocks0, Count0};
+recv_crit_edges(Rms, Exit, Blocks0, Count0) ->
+    Ls = beam_ssa:rpo(Rms, Blocks0),
+    rce_insert_edges(Ls, Exit, Count0, Blocks0).
+
+rce_insert_edges([L | Ls], Exit, Count0, Blocks0) ->
+    Successors = beam_ssa:successors(map_get(L, Blocks0)),
+    case member(Exit, Successors) of
+        true when Successors =/= [Exit] ->
+            {Blocks, Count} = rce_insert_edge(L, Exit, Count0, Blocks0),
+            rce_insert_edges(Ls, Exit, Count, Blocks);
+        _ ->
+            rce_insert_edges(Ls, Exit, Count0, Blocks0)
+    end;
+rce_insert_edges([], _Exit, Count, Blocks) ->
+    {Blocks, Count}.
+
+rce_insert_edge(L, Exit, Count, Blocks0) ->
+    #b_blk{last=Last0} = FromBlk0 = map_get(L, Blocks0),
+
+    ToExit = #b_br{bool=#b_literal{val=true},succ=Exit,fail=Exit},
+
+    FromBlk = FromBlk0#b_blk{last=rce_reroute_terminator(Last0, Exit, Count)},
+    EdgeBlk = #b_blk{anno=#{},is=[],last=ToExit},
+
+    Blocks = Blocks0#{ Count => EdgeBlk, L => FromBlk },
+    {Blocks, Count + 1}.
+
+rce_reroute_terminator(#b_br{succ=Exit}=Last, Exit, New) ->
+    rce_reroute_terminator(Last#b_br{succ=New}, Exit, New);
+rce_reroute_terminator(#b_br{fail=Exit}=Last, Exit, New) ->
+    rce_reroute_terminator(Last#b_br{fail=New}, Exit, New);
+rce_reroute_terminator(#b_br{}=Last, _Exit, _New) ->
+    Last;
+rce_reroute_terminator(#b_switch{fail=Exit}=Last, Exit, New) ->
+    rce_reroute_terminator(Last#b_switch{fail=New}, Exit, New);
+rce_reroute_terminator(#b_switch{list=List0}=Last, Exit, New) ->
+    List = [if
+                Lbl =:= Exit -> {Arg, New};
+                Lbl =/= Exit -> {Arg, Lbl}
+            end || {Arg, Lbl} <- List0],
+    Last#b_switch{list=List}.
+
 %% recv_fix_common([CommonVar], LoopExit, [RemoveMessageLabel],
 %%                 Blocks0, Count0) -> {Blocks,Count}.
 %%  Handle variables alwys defined in a receive and used
diff --git a/lib/compiler/test/beam_ssa_SUITE.erl b/lib/compiler/test/beam_ssa_SUITE.erl
index a741ebbdf9..256bb95559 100644
--- a/lib/compiler/test/beam_ssa_SUITE.erl
+++ b/lib/compiler/test/beam_ssa_SUITE.erl
@@ -190,6 +190,12 @@ recv(_Config) ->
     self() ! {[self(),r1],{2,99,<<"data">>}},
     {Parent,r1,<<1:32,2:8,99:8,"data">>} = tricky_recv_4(),
 
+    %% Test tricky_recv_5/0.
+    self() ! 1,
+    a = tricky_recv_5(),
+    self() ! 2,
+    b = tricky_recv_5(),
+
     ok.
 
 sync_wait_mon({Pid, Ref}, Timeout) ->
@@ -295,6 +301,26 @@ tricky_recv_4() ->
 	end,
     id({Pid,R,Request}).
 
+%% beam_ssa_pre_codegen would accidentally create phi nodes on critical edges
+%% when fixing up receives; the call to id/2 can either succeed or land in the
+%% catch block, and we added a phi node to its immediate successor.
+tricky_recv_5() ->
+    try
+        receive
+            X=1 ->
+                id(42),
+                a;
+            X=2 ->
+                b
+        end,
+        case X of
+            1 -> a;
+            2 -> b
+        end
+    catch
+        _:_ -> c
+    end.
+
 maps(_Config) ->
     {'EXIT',{{badmatch,#{}},_}} = (catch maps_1(any)),
     ok.
-- 
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