From ab03678e87732407625150c202e177a85a025beb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Thu, 7 Apr 2016 12:43:06 +0200
Subject: Remove unreachable code after 'raise' instructions

Remove the unreachable instructions after a 'raise' instruction
(e.g. a 'jump' or 'deallocate', 'return') to decrease code size.
---
 lib/compiler/src/beam_block.erl            |  4 +++-
 lib/compiler/src/beam_split.erl            |  2 ++
 lib/compiler/src/beam_validator.erl        |  3 +++
 lib/compiler/src/beam_z.erl                | 12 ++++++++++++
 lib/compiler/test/beam_validator_SUITE.erl |  2 +-
 5 files changed, 21 insertions(+), 2 deletions(-)

(limited to 'lib/compiler')

diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl
index d1052303e0..429b1aa010 100644
--- a/lib/compiler/src/beam_block.erl
+++ b/lib/compiler/src/beam_block.erl
@@ -88,7 +88,9 @@ collect_block([I|Is]=Is0, Acc) ->
     case collect(I) of
 	error -> {reverse(Acc),Is0};
 	Instr -> collect_block(Is, [Instr|Acc])
-    end.
+    end;
+collect_block([], Acc) ->
+    {reverse(Acc),[]}.
 
 collect({allocate,N,R})      -> {set,[],[],{alloc,R,{nozero,N,0,[]}}};
 collect({allocate_zero,N,R}) -> {set,[],[],{alloc,R,{zero,N,0,[]}}};
diff --git a/lib/compiler/src/beam_split.erl b/lib/compiler/src/beam_split.erl
index bb1c0e23a9..7b7f0a0f80 100644
--- a/lib/compiler/src/beam_split.erl
+++ b/lib/compiler/src/beam_split.erl
@@ -47,6 +47,8 @@ split_block([{set,[R],[_,_,_]=As,{bif,is_record,{f,Lbl}}}|Is], Bl, Acc) ->
     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,{bif,raise,{f,_}=Fail}}|Is], Bl, Acc) ->
+    split_block(Is, [], [{bif,raise,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)]);
diff --git a/lib/compiler/src/beam_validator.erl b/lib/compiler/src/beam_validator.erl
index fd38fc0095..1c052789fd 100644
--- a/lib/compiler/src/beam_validator.erl
+++ b/lib/compiler/src/beam_validator.erl
@@ -509,6 +509,9 @@ valfun_4({bif,element,{f,Fail},[Pos,Tuple],Dst}, Vst0) ->
     TupleType = upgrade_tuple_type({tuple,[get_tuple_size(PosType)]}, TupleType0),
     Vst = set_type(TupleType, Tuple, Vst1),
     set_type_reg(term, Dst, Vst);
+valfun_4({bif,raise,{f,0},Src,_Dst}, Vst) ->
+    validate_src(Src, Vst),
+    kill_state(Vst);
 valfun_4({bif,Op,{f,Fail},Src,Dst}, Vst0) ->
     validate_src(Src, Vst0),
     Vst = branch_state(Fail, Vst0),
diff --git a/lib/compiler/src/beam_z.erl b/lib/compiler/src/beam_z.erl
index 8381578b68..e44423d257 100644
--- a/lib/compiler/src/beam_z.erl
+++ b/lib/compiler/src/beam_z.erl
@@ -24,6 +24,8 @@
 
 -export([module/2]).
 
+-import(lists, [dropwhile/2]).
+
 module({Mod,Exp,Attr,Fs0,Lc}, _Opt) ->
     Fs = [function(F) || F <- Fs0],
     {ok,{Mod,Exp,Attr,Fs,Lc}}.
@@ -51,6 +53,16 @@ undo_renames([{call,A,F},return|Is]) ->
     [{call_only,A,F}|undo_renames(Is)];
 undo_renames([{call_ext,A,F},return|Is]) ->
     [{call_ext_only,A,F}|undo_renames(Is)];
+undo_renames([{bif,raise,_,_,_}=I|Is0]) ->
+    %% A minor optimization. Done here because:
+    %%  (1) beam_jump may move or share 'raise' instructions, and that
+    %%      may confuse beam_validator.
+    %%  (2) beam_trim cannot do its optimization if the 'deallocate'
+    %%      instruction after 'raise' has been removed.
+    Is = dropwhile(fun({label,_}) -> false;
+		      (_) -> true
+		   end, Is0),
+    [I|undo_renames(Is)];
 undo_renames([I|Is]) ->
     [undo_rename(I)|undo_renames(Is)];
 undo_renames([]) -> [].
diff --git a/lib/compiler/test/beam_validator_SUITE.erl b/lib/compiler/test/beam_validator_SUITE.erl
index d27512b6eb..b3fb091f46 100644
--- a/lib/compiler/test/beam_validator_SUITE.erl
+++ b/lib/compiler/test/beam_validator_SUITE.erl
@@ -312,7 +312,7 @@ state_after_fault_in_catch(Config) when is_list(Config) ->
 no_exception_in_catch(Config) when is_list(Config) ->
     Errors = do_val(no_exception_in_catch, Config),
     [{{no_exception_in_catch,nested_of_1,4},
-      {{move,{x,3},{x,0}},88,{uninitialized_reg,{x,3}}}}] = Errors,
+      {{move,{x,3},{x,0}},87,{uninitialized_reg,{x,3}}}}] = Errors,
     ok.
 
 undef_label(Config) when is_list(Config) ->
-- 
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