aboutsummaryrefslogtreecommitdiffstats
path: root/lib/compiler/src/beam_dead.erl
diff options
context:
space:
mode:
Diffstat (limited to 'lib/compiler/src/beam_dead.erl')
-rw-r--r--lib/compiler/src/beam_dead.erl129
1 files changed, 118 insertions, 11 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl
index ead88b57e9..d379fdc4eb 100644
--- a/lib/compiler/src/beam_dead.erl
+++ b/lib/compiler/src/beam_dead.erl
@@ -1,7 +1,7 @@
%%
%% %CopyrightBegin%
%%
-%% Copyright Ericsson AB 2002-2013. All Rights Reserved.
+%% Copyright Ericsson AB 2002-2016. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
@@ -29,6 +29,10 @@
-import(lists, [mapfoldl/3,reverse/1]).
+
+-spec module(beam_utils:module_code(), [compile:option()]) ->
+ {'ok',beam_utils:module_code()}.
+
module({Mod,Exp,Attr,Fs0,_}, _Opts) ->
{Fs1,Lc1} = beam_clean:clean_labels(Fs0),
{Fs,Lc} = mapfoldl(fun function/2, Lc1, Fs1),
@@ -239,32 +243,69 @@ backward([{test,is_eq_exact,Fail,[Dst,{integer,Arity}]}=I|
backward([{label,Lbl}=L|Is], D, Acc) ->
backward(Is, beam_utils:index_label(Lbl, Acc, D), [L|Acc]);
backward([{select,select_val,Reg,{f,Fail0},List0}|Is], D, Acc) ->
- List = shortcut_select_list(List0, Reg, D, []),
+ List1 = shortcut_select_list(List0, Reg, D, []),
Fail1 = shortcut_label(Fail0, D),
Fail = shortcut_bs_test(Fail1, Is, D),
- Sel = {select,select_val,Reg,{f,Fail},List},
- backward(Is, D, [Sel|Acc]);
+ List = prune_redundant(List1, Fail),
+ case List of
+ [] ->
+ Jump = {jump,{f,Fail}},
+ backward([Jump|Is], D, Acc);
+ [V,F] ->
+ Test = {test,is_eq_exact,{f,Fail},[Reg,V]},
+ Jump = {jump,F},
+ backward([Jump,Test|Is], D, Acc);
+ [{atom,B1},F,{atom,B2},F] when B1 =:= not B2 ->
+ Test = {test,is_boolean,{f,Fail},[Reg]},
+ Jump = {jump,F},
+ backward([Jump,Test|Is], D, Acc);
+ [_|_] ->
+ Sel = {select,select_val,Reg,{f,Fail},List},
+ backward(Is, D, [Sel|Acc])
+ end;
backward([{jump,{f,To0}},{move,Src,Reg}=Move|Is], D, Acc) ->
To = shortcut_select_label(To0, Reg, Src, D),
Jump = {jump,{f,To}},
- case beam_utils:is_killed_at(Reg, To, D) of
+ case is_killed_at(Reg, To, D) of
false -> backward([Move|Is], D, [Jump|Acc]);
true -> backward([Jump|Is], D, Acc)
end;
-backward([{jump,{f,To}}=J|[{bif,Op,_,Ops,Reg}|Is]=Is0], D, Acc) ->
+backward([{jump,{f,To}}=J|[{bif,Op,{f,BifFail},Ops,Reg}|Is]=Is0], D, Acc) ->
try replace_comp_op(To, Reg, Op, Ops, D) of
I -> backward(Is, D, I++Acc)
catch
- throw:not_possible -> backward(Is0, D, [J|Acc])
+ throw:not_possible ->
+ case To =:= BifFail of
+ true ->
+ %% The bif instruction is redundant. See the comment
+ %% in the next clause for why there is no need to
+ %% test for liveness of Reg at label To.
+ backward([J|Is], D, Acc);
+ false ->
+ backward(Is0, D, [J|Acc])
+ end
end;
-backward([{test,bs_start_match2,F,_,[R,_],Ctxt}=I|Is], D,
+backward([{jump,{f,To}}=J|[{gc_bif,_,{f,To},_,_,_Dst}|Is]], D, Acc) ->
+ %% The gc_bif instruction is redundant, since either the gc_bif
+ %% instruction itself or the jump instruction will transfer control
+ %% to label To. Note that a gc_bif instruction does not assign its
+ %% destination register if the failure branch is taken; therefore,
+ %% the code at label To is not allowed to assume that the destination
+ %% register is initialized, and it is therefore no need to test
+ %% for liveness of the destination register at label To.
+ backward([J|Is], D, Acc);
+backward([{test,bs_start_match2,F,Live,[R,_]=Args,Ctxt}|Is], D,
[{test,bs_match_string,F,[Ctxt,Bs]},
{test,bs_test_tail2,F,[Ctxt,0]}|Acc0]=Acc) ->
+ {f,To0} = F,
case beam_utils:is_killed(Ctxt, Acc0, D) of
true ->
- Eq = {test,is_eq_exact,F,[R,{literal,Bs}]},
+ To = shortcut_bs_context_to_binary(To0, R, D),
+ Eq = {test,is_eq_exact,{f,To},[R,{literal,Bs}]},
backward(Is, D, [Eq|Acc0]);
false ->
+ To = shortcut_bs_start_match(To0, R, D),
+ I = {test,bs_start_match2,{f,To},Live,Args,Ctxt},
backward(Is, D, [I|Acc])
end;
backward([{test,bs_start_match2,{f,To0},Live,[Src|_]=Info,Dst}|Is], D, Acc) ->
@@ -295,7 +336,28 @@ backward([{test,Op,{f,To0},Ops0}|Is], D, Acc) ->
is_eq_exact -> combine_eqs(To, Ops0, D, Acc);
_ -> {test,Op,{f,To},Ops0}
end,
- backward(Is, D, [I|Acc]);
+ case {I,Acc} of
+ {{test,is_atom,Fail,Ops0},[{test,is_boolean,Fail,Ops0}|_]} ->
+ %% An is_atom test before an is_boolean test (with the
+ %% same failure label) is redundant.
+ backward(Is, D, Acc);
+ {{test,is_atom,Fail,[R]},
+ [{test,is_eq_exact,Fail,[R,{atom,_}]}|_]} ->
+ %% An is_atom test before a comparison with an atom (with
+ %% the same failure label) is redundant.
+ backward(Is, D, Acc);
+ {{test,is_integer,Fail,[R]},
+ [{test,is_eq_exact,Fail,[R,{integer,_}]}|_]} ->
+ %% An is_integer test before a comparison with an integer
+ %% (with the same failure label) is redundant.
+ backward(Is, D, Acc);
+ {{test,_,_,_},_} ->
+ %% Still a test instruction. Done.
+ backward(Is, D, [I|Acc]);
+ {_,_} ->
+ %% Rewritten to a select_val. Rescan.
+ backward([I|Is], D, Acc)
+ end;
backward([{test,Op,{f,To0},Live,Ops0,Dst}|Is], D, Acc) ->
To1 = shortcut_bs_test(To0, Is, D),
To2 = shortcut_label(To1, D),
@@ -321,6 +383,14 @@ backward([{kill,_}=I|Is], D, [{line,_},Exit|_]=Acc) ->
false -> backward(Is, D, [I|Acc]);
true -> backward(Is, D, Acc)
end;
+backward([{bif,'or',{f,To0},[Dst,{atom,false}],Dst}=I|Is], D,
+ [{test,is_eq_exact,{f,To},[Dst,{atom,true}]}|_]=Acc) ->
+ case shortcut_label(To0, D) of
+ To ->
+ backward(Is, D, Acc);
+ _ ->
+ backward(Is, D, [I|Acc])
+ end;
backward([I|Is], D, Acc) ->
backward(Is, D, [I|Acc]);
backward([], _D, Acc) -> Acc.
@@ -339,6 +409,8 @@ shortcut_select_list([Lit,{f,To0}|T], Reg, D, Acc) ->
shortcut_select_list(T, Reg, D, [{f,To},Lit|Acc]);
shortcut_select_list([], _, _, Acc) -> reverse(Acc).
+shortcut_label(0, _) ->
+ 0;
shortcut_label(To0, D) ->
case beam_utils:code_at(To0, D) of
[{jump,{f,To}}|_] -> shortcut_label(To, D);
@@ -348,6 +420,12 @@ shortcut_label(To0, D) ->
shortcut_select_label(To, Reg, Lit, D) ->
shortcut_rel_op(To, is_ne_exact, [Reg,Lit], D).
+prune_redundant([_,{f,Fail}|T], Fail) ->
+ prune_redundant(T, Fail);
+prune_redundant([V,F|T], Fail) ->
+ [V,F|prune_redundant(T, Fail)];
+prune_redundant([], _) -> [].
+
%% Replace a comparison operator with a test instruction and a jump.
%% For example, if we have this code:
%%
@@ -375,7 +453,7 @@ comp_op_find_shortcut(To0, Reg, Val, D) ->
To0 ->
not_possible();
To ->
- case beam_utils:is_killed_at(Reg, To, D) of
+ case is_killed_at(Reg, To, D) of
false -> not_possible();
true -> To
end
@@ -509,6 +587,21 @@ shortcut_bs_start_match_1([{test,bs_start_match2,{f,To},_,[Reg|_],_}|_],
shortcut_bs_start_match_1(_, _, To, _) ->
To.
+%% shortcut_bs_context_to_binary(TargetLabel, Reg) -> TargetLabel
+%% If a bs_start_match2 instruction has been eliminated, the
+%% bs_context_to_binary instruction can be eliminated too.
+
+shortcut_bs_context_to_binary(To, Reg, D) ->
+ shortcut_bs_ctb_1(beam_utils:code_at(To, D), Reg, To, D).
+
+shortcut_bs_ctb_1([{bs_context_to_binary,Reg}|Is], Reg, To, D) ->
+ shortcut_bs_ctb_1(Is, Reg, To, D);
+shortcut_bs_ctb_1([{jump,{f,To}}|_], Reg, _, D) ->
+ Code = beam_utils:code_at(To, D),
+ shortcut_bs_ctb_1(Code, Reg, To, D);
+shortcut_bs_ctb_1(_, _, To, _) ->
+ To.
+
%% shortcut_rel_op(FailLabel, Operator, [Operand], D) -> FailLabel'
%% Try to shortcut the given test instruction. Example:
%%
@@ -818,3 +911,17 @@ get_literal(nil) ->
get_literal({literal,_}=Lit) ->
Lit;
get_literal({_,_}) -> error.
+
+
+%%%
+%%% Removing stores to Y registers is not always safe
+%%% if there is an instruction that causes an exception
+%%% within a catch. In practice, there are few or no
+%%% opportunities for removing stores to Y registers anyway
+%%% if sys_core_fold has been run.
+%%%
+
+is_killed_at({x,_}=Reg, Lbl, D) ->
+ beam_utils:is_killed_at(Reg, Lbl, D);
+is_killed_at({y,_}, _, _) ->
+ false.
generated by cgit v1.2.3 (git 2.25.1) at 2025-04-26 16:48:39 +0000