From 6c91e303fe844ec9a795216bb9e4d39e760cecb8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Mon, 5 Dec 2011 09:05:21 +0100
Subject: Teach the compiler the 'no_dead' option

To facilitate debugging of compiler bugs, teach the compiler the
'no_dead' option. Since the beam_dead pass used to do the necessary
splitting of basic blocks to expose all labels, we must move that
splitting into a separate pass that is always run.
---
 lib/compiler/src/beam_split.erl | 85 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 lib/compiler/src/beam_split.erl

(limited to 'lib/compiler/src/beam_split.erl')

diff --git a/lib/compiler/src/beam_split.erl b/lib/compiler/src/beam_split.erl
new file mode 100644
index 0000000000..cacaaebffe
--- /dev/null
+++ b/lib/compiler/src/beam_split.erl
@@ -0,0 +1,85 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2011. All Rights Reserved.
+%%
+%% The contents of this file are subject to the Erlang Public License,
+%% Version 1.1, (the "License"); you may not use this file except in
+%% compliance with the License. You should have received a copy of the
+%% Erlang Public License along with this software. If not, it can be
+%% retrieved online at http://www.erlang.org/.
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and limitations
+%% under the License.
+%%
+%% %CopyrightEnd%
+%%
+
+-module(beam_split).
+-export([module/2]).
+
+-import(lists, [reverse/1]).
+
+module({Mod,Exp,Attr,Fs0,Lc}, _Opts) ->
+    Fs = [split_blocks(F) || F <- Fs0],
+    {ok,{Mod,Exp,Attr,Fs,Lc}}.
+
+%% We must split the basic block when we encounter instructions with labels,
+%% such as catches and BIFs. All labels must be visible outside the blocks.
+
+split_blocks({function,Name,Arity,CLabel,Is0}) ->
+    Is = split_blocks(Is0, []),
+    {function,Name,Arity,CLabel,Is}.
+
+split_blocks([{block,Bl}|Is], Acc0) ->
+    Acc = split_block(Bl, [], Acc0),
+    split_blocks(Is, Acc);
+split_blocks([I|Is], Acc) ->
+    split_blocks(Is, [I|Acc]);
+split_blocks([], Acc) -> reverse(Acc).
+
+split_block([{set,[R],[_,_,_]=As,{bif,is_record,{f,Lbl}}}|Is], Bl, Acc) ->
+    %% is_record/3 must be translated by beam_clean; therefore,
+    %% it must be outside of any block.
+    split_block(Is, [], [{bif,is_record,{f,Lbl},As,R}|make_block(Bl, Acc)]);
+split_block([{set,[R],As,{bif,N,{f,Lbl}=Fail}}|Is], Bl, Acc) when Lbl =/= 0 ->
+    split_block(Is, [], [{bif,N,Fail,As,R}|make_block(Bl, Acc)]);
+split_block([{set,[R],As,{alloc,Live,{gc_bif,N,{f,Lbl}=Fail}}}|Is], Bl, Acc)
+  when Lbl =/= 0 ->
+    split_block(Is, [], [{gc_bif,N,Fail,Live,As,R}|make_block(Bl, Acc)]);
+split_block([{set,[R],[],{'catch',L}}|Is], Bl, Acc) ->
+    split_block(Is, [], [{'catch',R,L}|make_block(Bl, Acc)]);
+split_block([{set,[],[],{line,_}=Line}|Is], Bl, Acc) ->
+    split_block(Is, [], [Line|make_block(Bl, Acc)]);
+split_block([I|Is], Bl, Acc) ->
+    split_block(Is, [I|Bl], Acc);
+split_block([], Bl, Acc) -> make_block(Bl, Acc).
+
+make_block([], Acc) -> Acc;
+make_block([{set,[D],Ss,{bif,Op,Fail}}|Bl]=Bl0, Acc) ->
+    %% If the last instruction in the block is a comparison or boolean operator
+    %% (such as '=:='), move it out of the block to facilitate further
+    %% optimizations.
+    Arity = length(Ss),
+    case erl_internal:comp_op(Op, Arity) orelse
+	erl_internal:new_type_test(Op, Arity) orelse
+	erl_internal:bool_op(Op, Arity) of
+	false ->
+	    [{block,reverse(Bl0)}|Acc];
+	true ->
+	    I = {bif,Op,Fail,Ss,D},
+	    case Bl =:= [] of
+		true -> [I|Acc];
+		false -> [I,{block,reverse(Bl)}|Acc]
+	    end
+    end;
+make_block([{set,[Dst],[Src],move}|Bl], Acc) ->
+    %% Make optimization of {move,Src,Dst}, {jump,...} possible.
+    I = {move,Src,Dst},
+    case Bl =:= [] of
+	true -> [I|Acc];
+	false -> [I,{block,reverse(Bl)}|Acc]
+    end;
+make_block(Bl, Acc) -> [{block,reverse(Bl)}|Acc].
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