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-rw-r--r--lib/compiler/src/beam_ssa_pre_codegen.erl120
1 files changed, 102 insertions, 18 deletions
diff --git a/lib/compiler/src/beam_ssa_pre_codegen.erl b/lib/compiler/src/beam_ssa_pre_codegen.erl
index 9af72afca7..7f816b9802 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
@@ -1409,21 +1463,51 @@ fix_receive([], _Defs, Blocks, Count) ->
{Blocks,Count}.
%% find_loop_exit([Label], Blocks) -> Label | none.
-%% Find the block to which control is transferred when the
-%% the receive loop is exited.
-
-find_loop_exit([L1,L2|_Ls], Blocks) ->
- Path1 = beam_ssa:rpo([L1], Blocks),
- Path2 = beam_ssa:rpo([L2], Blocks),
- find_loop_exit_1(Path1, cerl_sets:from_list(Path2));
-find_loop_exit(_, _) -> none.
-
-find_loop_exit_1([H|T], OtherPath) ->
- case cerl_sets:is_element(H, OtherPath) of
- true -> H;
- false -> find_loop_exit_1(T, OtherPath)
+%% Given the list of all blocks with the remove_message instructions
+%% for this receive, find the block to which control is transferred
+%% when the receive loop is exited (if any).
+
+find_loop_exit([_,_|_]=RmBlocks, Blocks) ->
+ %% We used to only analyze the path from two of the remove_message
+ %% blocks. That would fail to find a common block if one or both
+ %% of the blocks happened to raise an exception. To be sure that
+ %% we always find a common block if there is one (shared by at
+ %% least two clauses), we must analyze the path from all
+ %% remove_message blocks.
+ {Dominators,_} = beam_ssa:dominators(Blocks),
+ RmSet = cerl_sets:from_list(RmBlocks),
+ Rpo = beam_ssa:rpo(RmBlocks, Blocks),
+ find_loop_exit_1(Rpo, RmSet, Dominators);
+find_loop_exit(_, _) ->
+ %% There is (at most) a single clause. There is no common
+ %% loop exit block.
+ none.
+
+find_loop_exit_1([?BADARG_BLOCK|Ls], RmSet, Dominators) ->
+ %% ?BADARG_BLOCK is a marker and not an actual block, so it is not
+ %% the block we are looking for.
+ find_loop_exit_1(Ls, RmSet, Dominators);
+find_loop_exit_1([L|Ls], RmSet, Dominators) ->
+ DomBy = map_get(L, Dominators),
+ case any(fun(E) -> cerl_sets:is_element(E, RmSet) end, DomBy) of
+ true ->
+ %% This block is dominated by one of the remove_message blocks,
+ %% which means that the block is part of only one clause.
+ %% It is not the block we are looking for.
+ find_loop_exit_1(Ls, RmSet, Dominators);
+ false ->
+ %% This block is the first block that is not dominated by
+ %% any of the blocks with remove_message instructions,
+ %% which means that at least two of the receive clauses
+ %% will ultimately transfer control to it. It is the block
+ %% we are looking for.
+ L
end;
-find_loop_exit_1([], _) -> none.
+find_loop_exit_1([], _, _) ->
+ %% None of clauses transfers control to a common block after the receive
+ %% statement. That means that the receive statement is a the end of a
+ %% function (or that all clauses raise exceptions).
+ none.
%% find_rm_blocks(StartLabel, Blocks) -> [Label].
%% Find all blocks that start with remove_message within the receive