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+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2018. 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.
+%% You may obtain a copy of the License at
+%%
+%% http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% %CopyrightEnd%
+%%
+
+%%
+%% Share code for semantically equivalent blocks referred to
+%% to by `br` and `switch` instructions.
+%%
+%% A similar optimization is done in beam_jump, but doing it here as
+%% well is beneficial as it may enable other optimizations. If there
+%% are many semantically equivalent clauses, this optimization can
+%% substanstially decrease compilation times.
+%%
+%% block/2 is called from the liveness optimization pass in
+%% beam_ssa_opt, as code sharing helps the liveness pass and vice
+%% versa.
+%%
+
+-module(beam_ssa_share).
+-export([module/2,block/2]).
+
+-include("beam_ssa.hrl").
+
+-import(lists, [keyfind/3,reverse/1,sort/1]).
+
+-spec module(beam_ssa:b_module(), [compile:option()]) ->
+ {'ok',beam_ssa:b_module()}.
+
+module(#b_module{body=Fs0}=Module, _Opts) ->
+ Fs = [function(F) || F <- Fs0],
+ {ok,Module#b_module{body=Fs}}.
+
+-spec block(Blk0, Blocks0) -> Blk when
+ Blk0 :: beam_ssa:b_blk(),
+ Blocks0 :: beam_ssa:block_map(),
+ Blk :: beam_ssa:b_blk().
+
+block(#b_blk{last=Last0}=Blk, Blocks) ->
+ case share_terminator(Last0, Blocks) of
+ none -> Blk;
+ Last -> Blk#b_blk{last=beam_ssa:normalize(Last)}
+ end.
+
+%%%
+%%% Local functions.
+%%%
+
+function(#b_function{anno=Anno,bs=Blocks0}=F) ->
+ try
+ PO = reverse(beam_ssa:rpo(Blocks0)),
+ {Blocks1,Changed} = blocks(PO, Blocks0, false),
+ Blocks = case Changed of
+ true ->
+ beam_ssa:trim_unreachable(Blocks1);
+ false ->
+ Blocks0
+ end,
+ F#b_function{bs=Blocks}
+ catch
+ Class:Error:Stack ->
+ #{func_info:={_,Name,Arity}} = Anno,
+ io:fwrite("Function: ~w/~w\n", [Name,Arity]),
+ erlang:raise(Class, Error, Stack)
+ end.
+
+blocks([L|Ls], Blocks, Changed) ->
+ #b_blk{last=Last0} = Blk0 = map_get(L, Blocks),
+ case block(Blk0, Blocks) of
+ #b_blk{last=Last0} ->
+ blocks(Ls, Blocks, Changed);
+ #b_blk{}=Blk ->
+ blocks(Ls, Blocks#{L:=Blk}, true)
+ end;
+blocks([], Blocks, Changed) ->
+ {Blocks,Changed}.
+
+share_terminator(#b_br{bool=#b_var{},succ=Succ0,fail=Fail0}=Br, Blocks) ->
+ {Succ,SuccBlk} = shortcut_nonempty_block(Succ0, Blocks),
+ {Fail,FailBlk} = shortcut_nonempty_block(Fail0, Blocks),
+ case are_equivalent(Succ, SuccBlk, Fail, FailBlk, Blocks) of
+ true ->
+ %% The blocks are semantically equivalent.
+ Br#b_br{succ=Succ,fail=Succ};
+ false ->
+ if
+ Succ =:= Succ0, Fail =:= Fail0 ->
+ %% None of blocks were cut short.
+ none;
+ true ->
+ %% One or both labels were cut short
+ %% to avoid jumping to an empty block.
+ Br#b_br{succ=Succ,fail=Fail}
+ end
+ end;
+share_terminator(#b_switch{}=Sw, Blocks) ->
+ share_switch(Sw, Blocks);
+share_terminator(_Last, _Blocks) -> none.
+
+%% Test whether the two blocks are semantically equivalent. This
+%% function is specially optimized to return `false` as fast as
+%% possible if the blocks are not equivalent, as that is the common
+%% case.
+
+are_equivalent(_Succ, _, ?BADARG_BLOCK, _, _Blocks) ->
+ %% ?BADARG_BLOCK is special. Sharing could be incorrect.
+ false;
+are_equivalent(_Succ, #b_blk{is=Is1,last=#b_ret{arg=RetVal1}=Ret1},
+ _Fail, #b_blk{is=Is2,last=#b_ret{arg=RetVal2}=Ret2}, _Blocks) ->
+ case {RetVal1,RetVal2} of
+ {#b_literal{},#b_literal{}} ->
+ case RetVal1 =:= RetVal2 of
+ true ->
+ %% The return values are identical literals. We
+ %% only need to compare the canonicalized bodies.
+ Can1 = canonical_is(Is1),
+ Can2 = canonical_is(Is2),
+ Can1 =:= Can2;
+ false ->
+ %% Non-equal literals.
+ false
+ end;
+ {#b_var{},#b_var{}} ->
+ %% The return values are varibles. We must canonicalize
+ %% the blocks (including returns) and compare them.
+ Can1 = canonical_is(Is1 ++ [Ret1]),
+ Can2 = canonical_is(Is2 ++ [Ret2]),
+ Can1 =:= Can2;
+ {_,_} ->
+ %% One literal and one variable.
+ false
+ end;
+are_equivalent(Succ,
+ #b_blk{is=Is1,
+ last=#b_br{bool=#b_literal{val=true},
+ succ=Target}},
+ Fail,
+ #b_blk{is=Is2,
+ last=#b_br{bool=#b_literal{val=true},
+ succ=Target}},
+ Blocks) ->
+ %% Both blocks end with an unconditional branch to the
+ %% same target block. If the target block has phi nodes,
+ %% we must pick up the values from the phi nodes and
+ %% compare them.
+ #b_blk{is=Is} = map_get(Target, Blocks),
+ Phis1 = canonical_terminator_phis(Is, Succ),
+ Phis2 = canonical_terminator_phis(Is, Fail),
+ case {Phis1,Phis2} of
+ {[#b_set{args=[#b_literal{}]}|_],_} when Phis1 =/= Phis2 ->
+ %% Different values are used in the phi nodes.
+ false;
+ {_,[#b_set{args=[#b_literal{}]}|_]} when Phis1 =/= Phis2 ->
+ %% Different values are used in the phi nodes.
+ false;
+ {_,_} ->
+ %% The values in the phi nodes are variables or identical
+ %% literals. We must canonicalize the blocks and compare
+ %% them.
+ Can1 = canonical_is(Is1 ++ Phis1),
+ Can2 = canonical_is(Is2 ++ Phis2),
+ Can1 =:= Can2
+ end;
+are_equivalent(Succ0, #b_blk{is=Is1,last=#b_br{bool=#b_var{},fail=Same}},
+ Fail0, #b_blk{is=Is2,last=#b_br{bool=#b_var{},fail=Same}},
+ Blocks) ->
+ %% Two-way branches with identical failure labels. First compare the
+ %% canonicalized bodies of the blocks.
+ case canonical_is(Is1) =:= canonical_is(Is2) of
+ false ->
+ %% Different bodies.
+ false;
+ true ->
+ %% Bodies were equal. That is fairly uncommon, so to keep
+ %% the code simple we will rewrite the `br` to a `switch`
+ %% and let share_switch/2 do the work of following the
+ %% branches.
+ Sw = #b_switch{arg=#b_var{name=not_used},fail=Fail0,
+ list=[{#b_literal{},Succ0}]},
+ #b_switch{fail=Fail,list=[{_,Succ}]} = share_switch(Sw, Blocks),
+ Fail =:= Succ
+ end;
+are_equivalent(_, _, _, _, _) -> false.
+
+share_switch(#b_switch{fail=Fail0,list=List0}=Sw, Blocks) ->
+ Prep = share_prepare_sw([{value,Fail0}|List0], Blocks, 0, []),
+ Res = do_share_switch(Prep, Blocks, []),
+ [{_,Fail}|List] = [VL || {_,VL} <- sort(Res)],
+ Sw#b_switch{fail=Fail,list=List}.
+
+share_prepare_sw([{V,L0}|T], Blocks, N, Acc) ->
+ {L,_Blk} = shortcut_nonempty_block(L0, Blocks),
+ share_prepare_sw(T, Blocks, N+1, [{{L,#{}},{N,{V,L}}}|Acc]);
+share_prepare_sw([], _, _, Acc) -> Acc.
+
+do_share_switch(Prep, Blocks, Acc) ->
+ Map = share_switch_1(Prep, Blocks, #{}),
+ share_switch_2(maps:values(Map), Blocks, Acc).
+
+share_switch_1([{Next0,Res}|T], Blocks, Map) ->
+ {Can,Next} = canonical_block(Next0, Blocks),
+ case Map of
+ #{Can:=Ls} ->
+ share_switch_1(T, Blocks, Map#{Can:=[{Next,Res}|Ls]});
+ #{} ->
+ share_switch_1(T, Blocks, Map#{Can=>[{Next,Res}]})
+ end;
+share_switch_1([], _Blocks, Map) -> Map.
+
+share_switch_2([[{_,{N,Res}}]|T], Blocks, Acc) ->
+ %% This block is not equivalent to any other block.
+ share_switch_2(T, Blocks, [{N,Res}|Acc]);
+share_switch_2([[{done,{_,{_,Common}}}|_]=Eqs|T], Blocks, Acc0) ->
+ %% Two or more blocks are semantically equivalent, and all blocks
+ %% are either terminated with a `ret` or a `br` to the same target
+ %% block. Replace the labels in the `switch` for all of those
+ %% blocks with the label for the first of the blocks.
+ Acc = [{N,{V,Common}} || {done,{N,{V,_}}} <- Eqs] ++ Acc0,
+ share_switch_2(T, Blocks, Acc);
+share_switch_2([[{_,_}|_]=Prep|T], Blocks, Acc0) ->
+ %% Two or more blocks are semantically equivalent, but they have
+ %% different successful successor blocks. Now we must check
+ %% recursively whether the successor blocks are equivalent too.
+ Acc = do_share_switch(Prep, Blocks, Acc0),
+ share_switch_2(T, Blocks, Acc);
+share_switch_2([], _, Acc) -> Acc.
+
+canonical_block({L,VarMap0}, Blocks) ->
+ #b_blk{is=Is,last=Last0} = map_get(L, Blocks),
+ case canonical_terminator(L, Last0, Blocks) of
+ none ->
+ %% The block has a terminator that we don't handle.
+ {{none,L},done};
+ {Last,done} ->
+ %% The block ends with a `ret` or an unconditional `br` to
+ %% another block.
+ {Can,_VarMap} = canonical_is(Is ++ Last, VarMap0, []),
+ {Can,done};
+ {Last,Next} ->
+ %% The block ends with a conditional branch.
+ {Can,VarMap} = canonical_is(Is ++ Last, VarMap0, []),
+ {Can,{Next,VarMap}}
+ end.
+
+%% Translate a sequence of instructions to a canonical representation. If the
+%% canonical representation of two blocks compare equal, the blocks are
+%% semantically equivalent. The following translations are done:
+%%
+%% * Variables defined in the instruction sequence are replaced with
+%% {var,0}, {var,1}, and so on. Free variables are not changed.
+%%
+%% * `location` annotations that would produce a `line` instruction are
+%% kept. All other annotations are cleared.
+%%
+%% * Instructions are repackaged into tuples instead of into the
+%% usual records. The main reason is to avoid violating the types for
+%% the SSA records. We can simplify things a little by linking the
+%% instructions directly instead of putting them into a list.
+
+canonical_is(Is) ->
+ {Can,_} = canonical_is(Is, #{}, []),
+ Can.
+
+canonical_is([#b_set{op=Op,dst=Dst,args=Args0}=I|Is], VarMap0, Acc) ->
+ Args = [canonical_arg(Arg, VarMap0) || Arg <-Args0],
+ Var = {var,map_size(VarMap0)},
+ VarMap = VarMap0#{Dst=>Var},
+ LineAnno = case Op of
+ bs_match ->
+ %% The location annotation for a bs_match instruction
+ %% is only used in warnings, never to emit a `line`
+ %% instruction. Therefore, it should not be included.
+ [];
+ _ ->
+ %% The location annotation will be used in a `line`
+ %% instruction. It must be included.
+ beam_ssa:get_anno(location, I, none)
+ end,
+ canonical_is(Is, VarMap, {Op,LineAnno,Var,Args,Acc});
+canonical_is([#b_ret{arg=Arg}], VarMap, Acc0) ->
+ Acc1 = case Acc0 of
+ {call,_Anno,Var,[#b_local{}|_]=Args,PrevAcc} ->
+ %% This is a tail-recursive call to a local function.
+ %% There will be no line instruction generated;
+ %% thus, the annotation is not significant.
+ {call,[],Var,Args,PrevAcc};
+ _ ->
+ Acc0
+ end,
+ {{ret,canonical_arg(Arg, VarMap),Acc1},VarMap};
+canonical_is([#b_br{bool=#b_var{},fail=Fail}], VarMap, Acc) ->
+ {{br,succ,Fail,Acc},VarMap};
+canonical_is([#b_br{succ=Succ}], VarMap, Acc) ->
+ {{br,Succ,Acc},VarMap};
+canonical_is([], VarMap, Acc) ->
+ {Acc,VarMap}.
+
+canonical_terminator(_L, #b_ret{}=Ret, _Blocks) ->
+ {[Ret],done};
+canonical_terminator(L, #b_br{bool=#b_literal{val=true},succ=Succ}=Br, Blocks) ->
+ #b_blk{is=Is} = map_get(Succ, Blocks),
+ case canonical_terminator_phis(Is, L) of
+ [] ->
+ {[],Succ};
+ [_|_]=Phis ->
+ {Phis ++ [Br],done}
+ end;
+canonical_terminator(_L, #b_br{bool=#b_var{},succ=Succ}=Br, _Blocks) ->
+ {[Br],Succ};
+canonical_terminator(_, _, _) -> none.
+
+canonical_terminator_phis([#b_set{op=phi,args=PhiArgs}=Phi|Is], L) ->
+ {Value,L} = keyfind(L, 2, PhiArgs),
+ [Phi#b_set{op=copy,args=[Value]}|canonical_terminator_phis(Is, L)];
+canonical_terminator_phis([#b_set{op=peek_message}=I|_], L) ->
+ %% We could get stuck into an infinite loop if we allowed the
+ %% comparisons to continue into this block. Force an unequal
+ %% compare with all other predecessors of this block.
+ [I#b_set{op=copy,args=[#b_literal{val=L}]}];
+canonical_terminator_phis(_, _) -> [].
+
+canonical_arg(#b_var{}=Var, VarMap) ->
+ case VarMap of
+ #{Var:=CanonicalVar} ->
+ CanonicalVar;
+ #{} ->
+ Var
+ end;
+canonical_arg(#b_remote{mod=Mod,name=Name}, VarMap) ->
+ {remote,canonical_arg(Mod, VarMap),
+ canonical_arg(Name, VarMap)};
+canonical_arg(Other, _VarMap) -> Other.
+
+%% Shortcut branches to empty blocks if safe.
+
+shortcut_nonempty_block(L, Blocks) ->
+ case map_get(L, Blocks) of
+ #b_blk{is=[],last=#b_br{bool=#b_literal{val=true},succ=Succ}}=Blk ->
+ %% This block is empty.
+ case is_forbidden(Succ, Blocks) of
+ false ->
+ shortcut_nonempty_block(Succ, Blocks);
+ true ->
+ {L,Blk}
+ end;
+ #b_blk{}=Blk ->
+ {L,Blk}
+ end.
+
+is_forbidden(L, Blocks) ->
+ case map_get(L, Blocks) of
+ #b_blk{is=[#b_set{op=phi}|_]} -> true;
+ #b_blk{is=[#b_set{op=peek_message}|_]} -> true;
+ #b_blk{} -> false
+ end.