From 7dce10bc84e0e8f88233cf5d8e659d5e2f58496c Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Thu, 28 Feb 2019 16:25:14 +0100 Subject: Keep the set of unset variables as small as possible Refactor the code to avoid putting any variable from a skippable block into the set of unset variables. Keeping the set of unset variables as small as possible will make beam_ssa_dead almost twice as fast when compiling lib/unicode/tokenizer.ex in elixir. --- lib/compiler/src/beam_ssa_dead.erl | 243 ++++++++++++++++++++----------------- 1 file changed, 129 insertions(+), 114 deletions(-) (limited to 'lib/compiler') diff --git a/lib/compiler/src/beam_ssa_dead.erl b/lib/compiler/src/beam_ssa_dead.erl index 2cca9ebadf..dc0381f105 100644 --- a/lib/compiler/src/beam_ssa_dead.erl +++ b/lib/compiler/src/beam_ssa_dead.erl @@ -27,7 +27,8 @@ -export([opt/1]). -include("beam_ssa.hrl"). --import(lists, [append/1,last/1,member/2,takewhile/2,reverse/1]). +-import(lists, [append/1,keymember/3,last/1,member/2, + takewhile/2,reverse/1]). -type used_vars() :: #{beam_ssa:label():=ordsets:ordset(beam_ssa:var_name())}. @@ -181,139 +182,148 @@ shortcut_2(L, Bs0, UnsetVars0, St) -> %% We have a potentially suitable br. %% Now update the set of variables that will never %% be set if this block will be skipped. - SetInThisBlock = [V || #b_set{dst=V} <- Is], - UnsetVars = update_unset_vars(L, Br, SetInThisBlock, - UnsetVars0, St), - - %% Continue checking whether this br is suitable. - shortcut_3(Br, Bs#{from:=L}, UnsetVars, St) + case update_unset_vars(L, Is, Br, UnsetVars0, St) of + unsafe -> + %% It is unsafe to use this br, + %% because it refers to a variable defined + %% in this block. + shortcut_unsafe_br(Br, Bs, UnsetVars0, St); + UnsetVars -> + %% Continue checking whether this br is + %% suitable. + shortcut_test_br(Br, Bs#{from:=L}, + UnsetVars, St) + end end end. -shortcut_3(Br, Bs, UnsetVars, #st{target=Target}=St) -> +shortcut_test_br(Br, Bs, UnsetVars, St) -> case is_br_safe(UnsetVars, Br, St) of false -> - %% Branching using this `br` is unsafe, either because it - %% is an unconditional branch to a phi node, or because - %% one or more of the variables that are not set will be - %% used. Try to follow branches of this `br`, to find a - %% safe `br`. - case Br of - #b_br{bool=#b_literal{val=true},succ=L} -> - case Target of - L -> - %% We have reached the forced target, and it - %% is unsafe. Give up. - none; - _ -> - %% Try following this branch to see whether it - %% leads to a safe `br`. - shortcut_2(L, Bs, UnsetVars, St) - end; - #b_br{bool=#b_var{},succ=Succ,fail=Fail} -> - case {Succ,Fail} of - {L,Target} -> - %% The failure label is the forced target. - %% Try following the success label to see - %% whether it also ultimately ends up at the - %% forced target. - shortcut_2(L, Bs, UnsetVars, St); - {Target,L} -> - %% The success label is the forced target. - %% Try following the failure label to see - %% whether it also ultimately ends up at the - %% forced target. - shortcut_2(L, Bs, UnsetVars, St); - {_,_} -> - case Target of - any -> - %% This two-way branch is unsafe. Try reducing - %% it to a one-way branch. - shortcut_two_way(Br, Bs, UnsetVars, St); - one_way -> - %% This two-way branch is unsafe. Try reducing - %% it to a one-way branch. - shortcut_two_way(Br, Bs, UnsetVars, St); - _ when is_integer(Target) -> - %% This two-way branch is unsafe, and - %% there already is a forced target. - %% Give up. - none - end - end - end; + shortcut_unsafe_br(Br, Bs, UnsetVars, St); true -> - %% This `br` instruction is safe. It does not - %% branch to a phi node, and all variables that - %% will be used are guaranteed to be defined. - case Br of - #b_br{bool=#b_literal{val=true},succ=L} -> - %% This is a one-way branch. + shortcut_safe_br(Br, Bs, UnsetVars, St) + end. + +shortcut_unsafe_br(Br, Bs, UnsetVars, #st{target=Target}=St) -> + %% Branching using this `br` is unsafe, either because it + %% is an unconditional branch to a phi node, or because + %% one or more of the variables that are not set will be + %% used. Try to follow branches of this `br`, to find a + %% safe `br`. + case Br of + #b_br{bool=#b_literal{val=true},succ=L} -> + case Target of + L -> + %% We have reached the forced target, and it + %% is unsafe. Give up. + none; + _ -> + %% Try following this branch to see whether it + %% leads to a safe `br`. + shortcut_2(L, Bs, UnsetVars, St) + end; + #b_br{bool=#b_var{},succ=Succ,fail=Fail} -> + case {Succ,Fail} of + {L,Target} -> + %% The failure label is the forced target. + %% Try following the success label to see + %% whether it also ultimately ends up at the + %% forced target. + shortcut_2(L, Bs, UnsetVars, St); + {Target,L} -> + %% The success label is the forced target. + %% Try following the failure label to see + %% whether it also ultimately ends up at the + %% forced target. + shortcut_2(L, Bs, UnsetVars, St); + {_,_} -> case Target of any -> - %% No forced target. Success! - {Br,Bs,UnsetVars}; + %% This two-way branch is unsafe. Try + %% reducing it to a one-way branch. + shortcut_two_way(Br, Bs, UnsetVars, St); one_way -> - %% The target must be a one-way branch, which this - %% `br` is. Success! - {Br,Bs,UnsetVars}; - L when is_integer(Target) -> - %% The forced target is L. Success! - {Br,Bs,UnsetVars}; + %% This two-way branch is unsafe. Try + %% reducing it to a one-way branch. + shortcut_two_way(Br, Bs, UnsetVars, St); _ when is_integer(Target) -> - %% Wrong forced target. Try following this branch - %% to see if it ultimately ends up at the forced - %% target. - shortcut_2(L, Bs, UnsetVars, St) - end; - #b_br{bool=#b_var{}} -> - %% This is a two-way branch. - if - Target =:= any; Target =:= one_way -> - %% No specific forced target. Try to reduce the - %% two-way branch to an one-way branch. - case shortcut_two_way(Br, Bs, UnsetVars, St) of - none when Target =:= any -> - %% This `br` can't be reduced to a one-way - %% branch. Return the `br` as-is. - {Br,Bs,UnsetVars}; - none when Target =:= one_way -> - %% This `br` can't be reduced to a one-way - %% branch. The caller wants a one-way branch. - %% Give up. - none; - {_,_,_}=Res -> - %% This `br` was successfully reduced to a - %% one-way branch. - Res - end; - is_integer(Target) -> - %% There is a forced target, which can't - %% be reached because this `br` is a two-way - %% branch. Give up. + %% This two-way branch is unsafe, and + %% there already is a forced target. + %% Give up. none end end end. -update_unset_vars(L, Br, SetInThisBlock, UnsetVars, #st{skippable=Skippable}) -> +shortcut_safe_br(Br, Bs, UnsetVars, #st{target=Target}=St) -> + %% This `br` instruction is safe. It does not branch to a phi + %% node, and all variables that will be used are guaranteed to be + %% defined. + case Br of + #b_br{bool=#b_literal{val=true},succ=L} -> + %% This is a one-way branch. + case Target of + any -> + %% No forced target. Success! + {Br,Bs,UnsetVars}; + one_way -> + %% The target must be a one-way branch, which this + %% `br` is. Success! + {Br,Bs,UnsetVars}; + L when is_integer(Target) -> + %% The forced target is L. Success! + {Br,Bs,UnsetVars}; + _ when is_integer(Target) -> + %% Wrong forced target. Try following this branch + %% to see if it ultimately ends up at the forced + %% target. + shortcut_2(L, Bs, UnsetVars, St) + end; + #b_br{bool=#b_var{}} -> + %% This is a two-way branch. + if + Target =:= any; Target =:= one_way -> + %% No specific forced target. Try to reduce the + %% two-way branch to an one-way branch. + case shortcut_two_way(Br, Bs, UnsetVars, St) of + none when Target =:= any -> + %% This `br` can't be reduced to a one-way + %% branch. Return the `br` as-is. + {Br,Bs,UnsetVars}; + none when Target =:= one_way -> + %% This `br` can't be reduced to a one-way + %% branch. The caller wants a one-way + %% branch. Give up. + none; + {_,_,_}=Res -> + %% This `br` was successfully reduced to a + %% one-way branch. + Res + end; + is_integer(Target) -> + %% There is a forced target, which can't + %% be reached because this `br` is a two-way + %% branch. Give up. + none + end + end. + +update_unset_vars(L, Is, Br, UnsetVars, #st{skippable=Skippable}) -> case is_map_key(L, Skippable) of true -> %% None of the variables used in this block are used in - %% the successors. We can speed up compilation by avoiding - %% adding variables to the UnsetVars if the presence of - %% those variable would not change the outcome of the - %% tests in is_br_safe/2. + %% the successors. Thus, there is no need to add the + %% variables to the set of unset variables. case Br of - #b_br{bool=Bool} -> - case member(Bool, SetInThisBlock) of + #b_br{bool=#b_var{}=Bool} -> + case keymember(Bool, #b_set.dst, Is) of true -> %% Bool is a variable defined in this - %% block. It will change the outcome of - %% the `not member(V, UnsetVars)` check in - %% is_br_safe/2. The other variables - %% defined in this block will not. - ordsets:add_element(Bool, UnsetVars); + %% block. Using the br instruction from + %% this block (and skipping the body of + %% the block) is unsafe. + unsafe; false -> %% Bool is either a variable not defined %% in this block or a literal. Adding it @@ -321,9 +331,14 @@ update_unset_vars(L, Br, SetInThisBlock, UnsetVars, #st{skippable=Skippable}) -> %% the outcome of the tests in %% is_br_safe/2. UnsetVars - end + end; + #b_br{} -> + UnsetVars end; false -> + %% Some variables defined in this block are used by + %% successors. We must update the set of unset variables. + SetInThisBlock = [V || #b_set{dst=V} <- Is], ordsets:union(UnsetVars, ordsets:from_list(SetInThisBlock)) end. -- cgit v1.2.3