Skip to content

optimize beam_trim #10272

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 3 commits into from
Closed

optimize beam_trim #10272

Changes from 2 commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
d03275e
optimize beam_trim
Schultzer Oct 9, 2025
dbbb219
revert unnecessary changes and leverage gb_sets
Schultzer Oct 10, 2025
e66847c
revert changes and leverage is_equal for assertion
Schultzer Oct 18, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
132 changes: 69 additions & 63 deletions lib/compiler/src/beam_trim.erl
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -24,12 +24,12 @@
-moduledoc false.
-export([module/2]).

-import(lists, [any/2,reverse/1,reverse/2,seq/2,sort/1]).
-import(lists, [any/2,merge/1,reverse/2,seq/2,sort/1]).

-include("beam_asm.hrl").

-record(st,
{safe :: sets:set(beam_asm:label()), %Safe labels.
{safe :: gb_sets:set(beam_asm:label()), %Safe labels.
Copy link
Contributor

@bjorng bjorng Oct 20, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Changing from sets to gb_sets is unnecessary since the only operation performed on this set is checking for membership (in is_safe_branch/2). Generally, checking for membership is faster for sets than for gb_sets.

fsz :: non_neg_integer()
}).

Expand All @@ -48,8 +48,8 @@ function({function,Name,Arity,CLabel,Is0}) ->
{function,Name,Arity,CLabel,Is}
catch
Class:Error:Stack ->
io:fwrite("Function: ~w/~w\n", [Name,Arity]),
erlang:raise(Class, Error, Stack)
io:fwrite("Function: ~w/~w\n", [Name,Arity]),
erlang:raise(Class, Error, Stack)
end.

trim([{init_yregs,_}=I|Is], none, St0) ->
Expand Down Expand Up @@ -116,7 +116,7 @@ is_not_recursive(_) -> false.
%% Y registers. Return the recipe that trims the most.

trim_recipe(Layout, IsNotRecursive, {Us,Ns}) ->
UsedRegs = ordsets:union(Us, Ns),
UsedRegs = gb_sets:union(Us, Ns),
Recipes = construct_recipes(Layout, 0, [], []),
NumOrigKills = length([I || {kill,_}=I <- Layout]),
IsTooExpensive = is_too_expensive_fun(IsNotRecursive),
Expand Down Expand Up @@ -151,15 +151,18 @@ construct_recipes(_, _, _, Acc) ->
Acc.

take_last_dead(L) ->
take_last_dead_1(reverse(L)).

take_last_dead_1([{live,_}|Is]) ->
take_last_dead_1(Is);
take_last_dead_1([{kill,Reg}|Is]) ->
{Reg,reverse(Is)};
take_last_dead_1([{dead,Reg}|Is]) ->
{Reg,reverse(Is)};
take_last_dead_1(_) -> none.
take_last_dead_1(L, []).

take_last_dead_1([{live,_}|T], Acc) ->
take_last_dead_1(T, Acc);
take_last_dead_1([{kill,Reg}|T], Acc) ->
{Reg,reverse(T, Acc)};
take_last_dead_1([{dead,Reg}|T], Acc) ->
{Reg,reverse(T, Acc)};
take_last_dead_1([], _) ->
none;
take_last_dead_1([H|T], Acc) ->
take_last_dead_1(T, [H|Acc]).
Copy link
Contributor

@jhogberg jhogberg Oct 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The semantics of this function has changed; you're not taking the last kill/dead anymore, but the first, resulting in a much weaker optimization.

Try running scripts/diffable 0 just before the changes in this branch, and then scripts/diffable 1 afterwards (don't forget to make compiler in between). This will create two folders with assembly listings for all of OTP before and after the change. Ideally, when optimizing a compiler pass a comparison of these (diff -u 0 1 | grep ^diff) should only show a change in the assembly listing of the pass you've optimized.


%% Is trimming too expensive?
is_too_expensive({Ks,_,Moves}, NumOrigKills, IsTooExpensive) ->
Expand Down Expand Up @@ -199,13 +202,12 @@ is_too_expensive_fun(false) ->
end.

is_recipe_viable({_,Trim,Moves}, UsedRegs) ->
Moved = ordsets:from_list([Src || {move,Src,_} <- Moves]),
Illegal = ordsets:from_list([Dst || {move,_,Dst} <- Moves]),
Moved = gb_sets:from_list([Src || {move,Src,_} <- Moves]),
Illegal = gb_sets:from_list([Dst || {move,_,Dst} <- Moves]),
Eliminated = [{y,N} || N <- seq(0, Trim - 1)],
%% All eliminated registers that are also in the used set must be moved.
UsedEliminated = ordsets:intersection(Eliminated, UsedRegs),
case ordsets:is_subset(UsedEliminated, Moved) andalso
ordsets:is_disjoint(Illegal, UsedRegs) of
UsedEliminated = gb_sets:intersection(gb_sets:from_list(Eliminated), UsedRegs),
case gb_sets:is_subset(UsedEliminated, Moved) andalso gb_sets:is_disjoint(Illegal, UsedRegs) of
true ->
UsedEliminated = Moved, %Assertion.
Copy link
Contributor

@jhogberg jhogberg Oct 17, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

gb_sets can have multiple representations for the same set, so the is_equal/2 function must be used here.

Suggested change
UsedEliminated = Moved, %Assertion.
true = gb_sets:is_equal(UsedEliminated, Moved), %Assertion.

true;
Expand Down Expand Up @@ -365,7 +367,7 @@ safe_labels([{label,L}|Is], Acc) ->
end;
safe_labels([_|Is], Acc) ->
safe_labels(Is, Acc);
safe_labels([], Acc) -> sets:from_list(Acc).
safe_labels([], Acc) -> gb_sets:from_list(Acc).

is_safe_label([{'%',_}|Is]) ->
is_safe_label(Is);
Expand Down Expand Up @@ -405,12 +407,15 @@ is_safe_label_block([]) -> true.
%% Figure out the layout of the stack frame.

frame_layout(N, Killed, {U,_}) ->
Dead0 = [{y,R} || R <- seq(0, N - 1)],
Dead = ordsets:subtract(Dead0, ordsets:union(U, Killed)),
Is = [[{R,{live,R}} || R <- U],
AllRegisters = [{y,R} || R <- seq(0, N - 1)],
LiveOrKilledSet = gb_sets:union(U, gb_sets:from_list(Killed)),
DeadSet = gb_sets:subtract(gb_sets:from_list(AllRegisters), LiveOrKilledSet),
UsedRegs = gb_sets:to_list(U),
Dead = gb_sets:to_list(DeadSet),
Is = [[{R,{live,R}} || R <- UsedRegs],
[{R,{dead,R}} || R <- Dead],
[{R,{kill,R}} || R <- Killed]],
[I || {_,I} <:- lists:merge(Is)].
[I || {_,I} <:- merge(Is)].

%% usage([Instruction], SafeLabels) -> {FrameSize,[UsedYRegs]}
%% Find out the frame size and usage information by looking at the
Expand All @@ -435,8 +440,9 @@ usage_1([], Acc) ->
do_usage(Is0, #st{safe=Safe}) ->
case Is0 of
[return,{deallocate,N}|Is] ->
Regs = [],
case do_usage(Is, Safe, Regs, [], []) of
Regs = gb_sets:new(),
Ns = gb_sets:new(),
case do_usage(Is, Safe, Regs, Ns, []) of
none ->
none;
Us ->
Expand All @@ -458,30 +464,30 @@ do_usage([{block,Blk}|Is], Safe, Regs0, Ns0, Acc) ->
do_usage([{bs_create_bin,Fail,_,_,_,Dst,{list,Args}}|Is], Safe, Regs0, Ns0, Acc) ->
case is_safe_branch(Fail, Safe) of
true ->
Regs1 = ordsets:del_element(Dst, Regs0),
Regs = ordsets:union(Regs1, yregs(Args)),
Ns = ordsets:union(yregs([Dst]), Ns0),
Regs1 = gb_sets:del_element(Dst, Regs0),
Regs = gb_sets:union(Regs1, yregs(Args)),
Ns = gb_sets:union(yregs([Dst]), Ns0),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
false ->
none
end;
do_usage([{bs_get_tail,Src,Dst,_}|Is], Safe, Regs0, Ns0, Acc) ->
Regs1 = ordsets:del_element(Dst, Regs0),
Regs = ordsets:union(Regs1, yregs([Src])),
Ns = ordsets:union(yregs([Dst]), Ns0),
Regs1 = gb_sets:del_element(Dst, Regs0),
Regs = gb_sets:union(Regs1, yregs([Src])),
Ns = gb_sets:union(yregs([Dst]), Ns0),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{bs_set_position,Src1,Src2}|Is], Safe, Regs0, Ns, Acc) ->
Regs = ordsets:union(Regs0, yregs([Src1,Src2])),
Regs = gb_sets:union(Regs0, yregs([Src1,Src2])),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{bs_start_match4,Fail,_Live,Src,Dst}|Is], Safe, Regs0, Ns, Acc) ->
case (Fail =:= {atom,no_fail} orelse
Fail =:= {atom,resume} orelse
is_safe_branch(Fail, Safe)) of
true ->
Regs = ordsets:union(Regs0, yregs([Src,Dst])),
Regs = gb_sets:union(Regs0, yregs([Src,Dst])),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
false ->
Expand All @@ -497,15 +503,15 @@ do_usage([{call_fun,_}|Is], Safe, Regs, Ns, Acc) ->
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{call_fun2,_,_,Ss}|Is], Safe, Regs0, Ns, Acc) ->
Regs = ordsets:union(Regs0, yregs([Ss])),
Regs = gb_sets:union(Regs0, yregs([Ss])),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{bif,_,Fail,Ss,Dst}|Is], Safe, Regs0, Ns0, Acc) ->
case is_safe_branch(Fail, Safe) of
true ->
Regs1 = ordsets:del_element(Dst, Regs0),
Regs = ordsets:union(Regs1, yregs(Ss)),
Ns = ordsets:union(yregs([Dst]), Ns0),
Regs1 = gb_sets:del_element(Dst, Regs0),
Regs = gb_sets:union(Regs1, yregs(Ss)),
Ns = gb_sets:union(yregs([Dst]), Ns0),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
false ->
Expand All @@ -514,9 +520,9 @@ do_usage([{bif,_,Fail,Ss,Dst}|Is], Safe, Regs0, Ns0, Acc) ->
do_usage([{gc_bif,_,Fail,_,Ss,Dst}|Is], Safe, Regs0, Ns0, Acc) ->
case is_safe_branch(Fail, Safe) of
true ->
Regs1 = ordsets:del_element(Dst, Regs0),
Regs = ordsets:union(Regs1, yregs(Ss)),
Ns = ordsets:union(yregs([Dst]), Ns0),
Regs1 = gb_sets:del_element(Dst, Regs0),
Regs = gb_sets:union(Regs1, yregs(Ss)),
Ns = gb_sets:union(yregs([Dst]), Ns0),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
false ->
Expand All @@ -527,46 +533,46 @@ do_usage([{get_map_elements,Fail,S,{list,List}}|Is], Safe, Regs0, Ns0, Acc) ->
true ->
{Ss,Ds1} = beam_utils:split_even(List),
Ds = yregs(Ds1),
Regs1 = ordsets:subtract(Regs0, Ds),
Regs = ordsets:union(Regs1, yregs([S|Ss])),
Ns = ordsets:union(Ns0, Ds),
Regs1 = gb_sets:subtract(Regs0, Ds),
Regs = gb_sets:union(Regs1, yregs([S|Ss])),
Ns = gb_sets:union(Ns0, Ds),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
false ->
none
end;
do_usage([{init_yregs,{list,Ds}}|Is], Safe, Regs0, Ns0, Acc) ->
Regs = ordsets:subtract(Regs0, Ds),
Ns = ordsets:union(Ns0, Ds),
Regs = gb_sets:subtract(Regs0, yregs(Ds)),
Ns = gb_sets:union(Ns0, gb_sets:from_list(Ds)),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{make_fun3,_,_,_,Dst,{list,Ss}}|Is], Safe, Regs0, Ns0, Acc) ->
Regs1 = ordsets:del_element(Dst, Regs0),
Regs = ordsets:union(Regs1, yregs(Ss)),
Ns = ordsets:union(yregs([Dst]), Ns0),
Regs1 = gb_sets:del_element(Dst, Regs0),
Regs = gb_sets:union(Regs1, yregs(Ss)),
Ns = gb_sets:union(yregs([Dst]), Ns0),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{update_record,_,_,Src,Dst,{list,Ss}}|Is], Safe, Regs0, Ns0, Acc) ->
Regs1 = ordsets:del_element(Dst, Regs0),
Regs = ordsets:union(Regs1, yregs([Src|Ss])),
Ns = ordsets:union(yregs([Dst]), Ns0),
Regs1 = gb_sets:del_element(Dst, Regs0),
Regs = gb_sets:union(Regs1, yregs([Src|Ss])),
Ns = gb_sets:union(yregs([Dst]), Ns0),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{line,_}|Is], Safe, Regs, Ns, Acc) ->
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{recv_marker_clear,Src}|Is], Safe, Regs0, Ns, Acc) ->
Regs = ordsets:union(Regs0, yregs([Src])),
Regs = gb_sets:union(Regs0, yregs([Src])),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{recv_marker_reserve,Src}|Is], Safe, Regs0, Ns, Acc) ->
Regs = ordsets:union(Regs0, yregs([Src])),
Regs = gb_sets:union(Regs0, yregs([Src])),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
do_usage([{test,_,Fail,Ss}|Is], Safe, Regs0, Ns, Acc) ->
case is_safe_branch(Fail, Safe) of
true ->
Regs = ordsets:union(Regs0, yregs(Ss)),
Regs = gb_sets:union(Regs0, yregs(Ss)),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
false ->
Expand All @@ -575,9 +581,9 @@ do_usage([{test,_,Fail,Ss}|Is], Safe, Regs0, Ns, Acc) ->
do_usage([{test,_,Fail,_,Ss,Dst}|Is], Safe, Regs0, Ns0, Acc) ->
case is_safe_branch(Fail, Safe) of
true ->
Regs1 = ordsets:del_element(Dst, Regs0),
Regs = ordsets:union(Regs1, yregs(Ss)),
Ns = ordsets:union(yregs([Dst]), Ns0),
Regs1 = gb_sets:del_element(Dst, Regs0),
Regs = gb_sets:union(Regs1, yregs(Ss)),
Ns = gb_sets:union(yregs([Dst]), Ns0),
U = {Regs,Ns},
do_usage(Is, Safe, Regs, Ns, [U|Acc]);
false ->
Expand All @@ -590,19 +596,19 @@ do_usage([], _Safe, _Regs, _Ns, Acc) -> Acc.
do_usage_blk([{set,Ds0,Ss,_}|Is], Regs0, Ns0) ->
Ds = yregs(Ds0),
{Regs1,Ns1} = do_usage_blk(Is, Regs0, Ns0),
Regs2 = ordsets:subtract(Regs1, Ds),
Regs = ordsets:union(Regs2, yregs(Ss)),
Ns = ordsets:union(Ns1, Ds),
Regs2 = gb_sets:subtract(Regs1, Ds),
Regs = gb_sets:union(Regs2, yregs(Ss)),
Ns = gb_sets:union(Ns1, Ds),
{Regs,Ns};
do_usage_blk([], Regs, Ns) -> {Regs,Ns}.

is_safe_branch({f,0}, _Safe) ->
true;
is_safe_branch({f,L}, Safe) ->
sets:is_element(L, Safe).
gb_sets:is_element(L, Safe).

yregs(Rs) ->
ordsets:from_list(yregs_1(Rs)).
gb_sets:from_list(yregs_1(Rs)).

yregs_1([{y,_}=Y|Rs]) ->
[Y|yregs_1(Rs)];
Expand Down