diff options
Diffstat (limited to 'lib/compiler/src/beam_ssa_pre_codegen.erl')
| -rw-r--r-- | lib/compiler/src/beam_ssa_pre_codegen.erl | 265 |
1 files changed, 159 insertions, 106 deletions
diff --git a/lib/compiler/src/beam_ssa_pre_codegen.erl b/lib/compiler/src/beam_ssa_pre_codegen.erl index a5fcb91cc0..61c42fdb6d 100644 --- a/lib/compiler/src/beam_ssa_pre_codegen.erl +++ b/lib/compiler/src/beam_ssa_pre_codegen.erl @@ -120,6 +120,7 @@ passes(Opts) -> %% Preliminaries. ?PASS(fix_bs), + ?PASS(exception_trampolines), ?PASS(sanitize), ?PASS(match_fail_instructions), case FixTuples of @@ -158,7 +159,9 @@ passes(Opts) -> %% Allocate registers. ?PASS(linear_scan), ?PASS(frame_size), - ?PASS(turn_yregs)], + ?PASS(turn_yregs), + + ?PASS(assert_no_critical_edges)], [P || P <- Ps, P =/= ignore]. function(#b_function{anno=Anno,args=Args,bs=Blocks0,cnt=Count0}=F0, @@ -600,6 +603,10 @@ bs_instrs([{L,#b_blk{is=Is0}=Blk}|Bs], CtxChain, Acc0) -> bs_instrs([], _, Acc) -> reverse(Acc). +bs_instrs_is([#b_set{op=succeeded}=I|Is], CtxChain, Acc) -> + %% This instruction refers to a specific operation, so we must not + %% substitute the context argument. + bs_instrs_is(Is, CtxChain, [I | Acc]); bs_instrs_is([#b_set{op=Op,args=Args0}=I0|Is], CtxChain, Acc) -> Args = [bs_subst_ctx(A, CtxChain) || A <- Args0], I1 = I0#b_set{args=Args}, @@ -693,6 +700,44 @@ legacy_bs_is([I|Is], Last, IsYreg, Count, Copies, Acc) -> legacy_bs_is([], _Last, _IsYreg, Count, Copies, Acc) -> {reverse(Acc),Count,Copies}. +%% exception_trampolines(St0) -> St. +%% +%% Removes the "exception trampolines" that were added to prevent exceptions +%% from being optimized away. + +exception_trampolines(#st{ssa=Blocks0}=St) -> + RPO = reverse(beam_ssa:rpo(Blocks0)), + Blocks = et_1(RPO, #{}, Blocks0), + St#st{ssa=Blocks}. + +et_1([L | Ls], Trampolines, Blocks) -> + #{ L := #b_blk{is=Is,last=Last0}=Block0 } = Blocks, + case {Is, Last0} of + {[#b_set{op=exception_trampoline}], #b_br{succ=Succ}} -> + et_1(Ls, Trampolines#{ L => Succ }, maps:remove(L, Blocks)); + {_, #b_br{succ=Same,fail=Same}} when Same =:= ?EXCEPTION_BLOCK -> + %% The exception block is just a marker saying that we should raise + %% an exception (= {f,0}) instead of jumping to a particular fail + %% block. Since it's not a reachable block we can't allow + %% unconditional jumps to it except through a trampoline. + error({illegal_jump_to_exception_block, L}); + {_, #b_br{succ=Succ0,fail=Fail0}} -> + Succ = maps:get(Succ0, Trampolines, Succ0), + Fail = maps:get(Fail0, Trampolines, Fail0), + if + Succ =/= Succ0; Fail =/= Fail0 -> + Last = Last0#b_br{succ=Succ,fail=Fail}, + Block = Block0#b_blk{last=Last}, + et_1(Ls, Trampolines, Blocks#{ L := Block }); + Succ =:= Succ0, Fail =:= Fail0 -> + et_1(Ls, Trampolines, Blocks) + end; + {_, _} -> + et_1(Ls, Trampolines, Blocks) + end; +et_1([], _Trampolines, Blocks) -> + Blocks. + %% sanitize(St0) -> St. %% Remove constructs that can cause problems later: %% @@ -1021,9 +1066,8 @@ use_set_tuple_element(#st{ssa=Blocks0}=St) -> Blocks = use_ste_1(RPO, Uses, Blocks0), St#st{ssa=Blocks}. -use_ste_1([L|Ls], Uses, Blocks0) -> - {Blk0,Blocks} = use_ste_across(L, Uses, Blocks0), - #b_blk{is=Is0} = Blk0, +use_ste_1([L|Ls], Uses, Blocks) -> + #b_blk{is=Is0} = Blk0 = map_get(L, Blocks), case use_ste_is(Is0, Uses) of Is0 -> use_ste_1(Ls, Uses, Blocks); @@ -1086,69 +1130,6 @@ extract_ste(#b_set{op=call,dst=Dst, end; extract_ste(#b_set{}) -> none. -%%% Optimize accross blocks within a try/catch block. - -use_ste_across(L, Uses, Blocks) -> - case map_get(L, Blocks) of - #b_blk{last=#b_br{bool=#b_var{}}}=Blk -> - try - use_ste_across_1(L, Blk, Uses, Blocks) - catch - throw:not_possible -> - {Blk,Blocks} - end; - #b_blk{}=Blk -> - {Blk,Blocks} - end. - -use_ste_across_1(L, Blk0, Uses, Blocks0) -> - #b_blk{is=IsThis,last=#b_br{bool=Bool,succ=Next}} = Blk0, - case reverse(IsThis) of - [#b_set{op=succeeded,dst=Bool,args=[Result]}=Succ0, - #b_set{op=call,args=[#b_remote{}|_],dst=Result}=Call1|Prefix] -> - case is_single_use(Bool, Uses) andalso - is_n_uses(2, Result, Uses) of - true -> ok; - false -> throw(not_possible) - end, - Call2 = use_ste_across_next(Next, Uses, Blocks0), - Is = [Call1,Call2], - case use_ste_is(Is, decrement_uses(Result, Uses)) of - [#b_set{}=Call,#b_set{op=set_tuple_element}=Ste] -> - Blocks1 = use_ste_fix_next(Ste, Next, Blocks0), - Succ = Succ0#b_set{args=[Call#b_set.dst]}, - Blk = Blk0#b_blk{is=reverse(Prefix, [Call,Succ])}, - Blocks = Blocks1#{L:=Blk}, - {Blk,Blocks}; - _ -> - throw(not_possible) - end; - _ -> - throw(not_possible) - end. - -use_ste_across_next(Next, Uses, Blocks) -> - case map_get(Next, Blocks) of - #b_blk{is=[#b_set{op=call,dst=Result,args=[#b_remote{}|_]}=Call, - #b_set{op=succeeded,dst=Bool,args=[Result]}], - last=#b_br{bool=Bool}} -> - case is_single_use(Bool, Uses) andalso - is_n_uses(2, Result, Uses) of - true -> ok; - false -> throw(not_possible) - end, - Call; - #b_blk{} -> - throw(not_possible) - end. - -use_ste_fix_next(Ste, Next, Blocks) -> - Blk0 = map_get(Next, Blocks), - #b_blk{is=[#b_set{op=call},#b_set{op=succeeded}],last=Br0} = Blk0, - Br = beam_ssa:normalize(Br0#b_br{bool=#b_literal{val=true}}), - Blk = Blk0#b_blk{is=[Ste],last=Br}, - Blocks#{Next:=Blk}. - %% Count how many times each variable is used. count_uses(Blocks) -> @@ -1158,7 +1139,7 @@ count_uses_blk([#b_blk{is=Is,last=Last}|Bs], CountMap0) -> F = fun(I, CountMap) -> foldl(fun(Var, Acc) -> case Acc of - #{Var:=3} -> Acc; + #{Var:=2} -> Acc; #{Var:=C} -> Acc#{Var:=C+1}; #{} -> Acc#{Var=>1} end @@ -1168,16 +1149,6 @@ count_uses_blk([#b_blk{is=Is,last=Last}|Bs], CountMap0) -> count_uses_blk(Bs, CountMap); count_uses_blk([], CountMap) -> CountMap. -decrement_uses(V, Uses) -> - #{V:=C} = Uses, - Uses#{V:=C-1}. - -is_n_uses(N, V, Uses) -> - case Uses of - #{V:=N} -> true; - #{} -> false - end. - is_single_use(V, Uses) -> case Uses of #{V:=1} -> true; @@ -1299,10 +1270,10 @@ place_frame_here(L, Blocks, Doms, Frames) -> Descendants = beam_ssa:rpo([L], Blocks), PhiPredecessors = phi_predecessors(L, Blocks), MustDominate = ordsets:from_list(PhiPredecessors ++ Descendants), - Dominates = all(fun(?BADARG_BLOCK) -> + Dominates = all(fun(?EXCEPTION_BLOCK) -> %% This block defines no variables and calls %% erlang:error(badarg). It does not matter - %% whether L dominates ?BADARG_BLOCK or not; + %% whether L dominates ?EXCEPTION_BLOCK or not; %% it is still safe to put the frame in L. true; (Bl) -> @@ -1433,10 +1404,11 @@ fix_receives_1([{L,Blk}|Ls], Blocks0, Count0) -> LoopExit = find_loop_exit(Rm, Blocks0), Defs0 = beam_ssa:def([L], Blocks0), CommonUsed = recv_common(Defs0, LoopExit, Blocks0), - {Blocks1,Count1} = recv_fix_common(CommonUsed, LoopExit, Rm, - Blocks0, Count0), + {Blocks1,Count1} = recv_crit_edges(Rm, LoopExit, Blocks0, Count0), + {Blocks2,Count2} = recv_fix_common(CommonUsed, LoopExit, Rm, + Blocks1, Count1), Defs = ordsets:subtract(Defs0, CommonUsed), - {Blocks,Count} = fix_receive(Rm, Defs, Blocks1, Count1), + {Blocks,Count} = fix_receive(Rm, Defs, Blocks2, Count2), fix_receives_1(Ls, Blocks, Count); #b_blk{} -> fix_receives_1(Ls, Blocks0, Count0) @@ -1449,9 +1421,60 @@ recv_common(_Defs, none, _Blocks) -> %% in the tail position of a function. []; recv_common(Defs, Exit, Blocks) -> - {ExitDefs,ExitUsed} = beam_ssa:def_used([Exit], Blocks), + {ExitDefs,ExitUnused} = beam_ssa:def_unused([Exit], Defs, Blocks), Def = ordsets:subtract(Defs, ExitDefs), - ordsets:intersection(Def, ExitUsed). + ordsets:subtract(Def, ExitUnused). + +%% recv_crit_edges([RemoveMessageLabel], LoopExit, +%% Blocks0, Count0) -> {Blocks,Count}. +%% +%% Adds dummy blocks on all conditional jumps to the exit block so that +%% recv_fix_common/5 can insert phi nodes without having to worry about +%% critical edges. + +recv_crit_edges(_Rms, none, Blocks0, Count0) -> + {Blocks0, Count0}; +recv_crit_edges(Rms, Exit, Blocks0, Count0) -> + Ls = beam_ssa:rpo(Rms, Blocks0), + rce_insert_edges(Ls, Exit, Count0, Blocks0). + +rce_insert_edges([L | Ls], Exit, Count0, Blocks0) -> + Successors = beam_ssa:successors(map_get(L, Blocks0)), + case member(Exit, Successors) of + true when Successors =/= [Exit] -> + {Blocks, Count} = rce_insert_edge(L, Exit, Count0, Blocks0), + rce_insert_edges(Ls, Exit, Count, Blocks); + _ -> + rce_insert_edges(Ls, Exit, Count0, Blocks0) + end; +rce_insert_edges([], _Exit, Count, Blocks) -> + {Blocks, Count}. + +rce_insert_edge(L, Exit, Count, Blocks0) -> + #b_blk{last=Last0} = FromBlk0 = map_get(L, Blocks0), + + ToExit = #b_br{bool=#b_literal{val=true},succ=Exit,fail=Exit}, + + FromBlk = FromBlk0#b_blk{last=rce_reroute_terminator(Last0, Exit, Count)}, + EdgeBlk = #b_blk{anno=#{},is=[],last=ToExit}, + + Blocks = Blocks0#{ Count => EdgeBlk, L => FromBlk }, + {Blocks, Count + 1}. + +rce_reroute_terminator(#b_br{succ=Exit}=Last, Exit, New) -> + rce_reroute_terminator(Last#b_br{succ=New}, Exit, New); +rce_reroute_terminator(#b_br{fail=Exit}=Last, Exit, New) -> + rce_reroute_terminator(Last#b_br{fail=New}, Exit, New); +rce_reroute_terminator(#b_br{}=Last, _Exit, _New) -> + Last; +rce_reroute_terminator(#b_switch{fail=Exit}=Last, Exit, New) -> + rce_reroute_terminator(Last#b_switch{fail=New}, Exit, New); +rce_reroute_terminator(#b_switch{list=List0}=Last, Exit, New) -> + List = [if + Lbl =:= Exit -> {Arg, New}; + Lbl =/= Exit -> {Arg, Lbl} + end || {Arg, Lbl} <- List0], + Last#b_switch{list=List}. %% recv_fix_common([CommonVar], LoopExit, [RemoveMessageLabel], %% Blocks0, Count0) -> {Blocks,Count}. @@ -1505,9 +1528,9 @@ exit_predecessors([], _Exit, _Blocks) -> []. %% later used within a clause of the receive. fix_receive([L|Ls], Defs, Blocks0, Count0) -> - {RmDefs,Used0} = beam_ssa:def_used([L], Blocks0), + {RmDefs,Unused} = beam_ssa:def_unused([L], Defs, Blocks0), Def = ordsets:subtract(Defs, RmDefs), - Used = ordsets:intersection(Def, Used0), + Used = ordsets:subtract(Def, Unused), {NewVars,Count} = new_vars([Base || #b_var{name=Base} <- Used], Count0), Ren = zip(Used, NewVars), Blocks1 = beam_ssa:rename_vars(Ren, [L], Blocks0), @@ -1521,21 +1544,51 @@ fix_receive([], _Defs, Blocks, Count) -> {Blocks,Count}. %% find_loop_exit([Label], Blocks) -> Label | none. -%% Find the block to which control is transferred when the -%% the receive loop is exited. - -find_loop_exit([L1,L2|_Ls], Blocks) -> - Path1 = beam_ssa:rpo([L1], Blocks), - Path2 = beam_ssa:rpo([L2], Blocks), - find_loop_exit_1(Path1, cerl_sets:from_list(Path2)); -find_loop_exit(_, _) -> none. - -find_loop_exit_1([H|T], OtherPath) -> - case cerl_sets:is_element(H, OtherPath) of - true -> H; - false -> find_loop_exit_1(T, OtherPath) +%% Given the list of all blocks with the remove_message instructions +%% for this receive, find the block to which control is transferred +%% when the receive loop is exited (if any). + +find_loop_exit([_,_|_]=RmBlocks, Blocks) -> + %% We used to only analyze the path from two of the remove_message + %% blocks. That would fail to find a common block if one or both + %% of the blocks happened to raise an exception. To be sure that + %% we always find a common block if there is one (shared by at + %% least two clauses), we must analyze the path from all + %% remove_message blocks. + {Dominators,_} = beam_ssa:dominators(Blocks), + RmSet = cerl_sets:from_list(RmBlocks), + Rpo = beam_ssa:rpo(RmBlocks, Blocks), + find_loop_exit_1(Rpo, RmSet, Dominators); +find_loop_exit(_, _) -> + %% There is (at most) a single clause. There is no common + %% loop exit block. + none. + +find_loop_exit_1([?EXCEPTION_BLOCK|Ls], RmSet, Dominators) -> + %% ?EXCEPTION_BLOCK is a marker and not an actual block, so it is not + %% the block we are looking for. + find_loop_exit_1(Ls, RmSet, Dominators); +find_loop_exit_1([L|Ls], RmSet, Dominators) -> + DomBy = map_get(L, Dominators), + case any(fun(E) -> cerl_sets:is_element(E, RmSet) end, DomBy) of + true -> + %% This block is dominated by one of the remove_message blocks, + %% which means that the block is part of only one clause. + %% It is not the block we are looking for. + find_loop_exit_1(Ls, RmSet, Dominators); + false -> + %% This block is the first block that is not dominated by + %% any of the blocks with remove_message instructions, + %% which means that at least two of the receive clauses + %% will ultimately transfer control to it. It is the block + %% we are looking for. + L end; -find_loop_exit_1([], _) -> none. +find_loop_exit_1([], _, _) -> + %% None of clauses transfers control to a common block after the receive + %% statement. That means that the receive statement is a the end of a + %% function (or that all clauses raise exceptions). + none. %% find_rm_blocks(StartLabel, Blocks) -> [Label]. %% Find all blocks that start with remove_message within the receive @@ -1784,7 +1837,7 @@ collect_yregs([], Yregs) -> Yregs. copy_retval_2([L|Ls], Yregs, Copy0, Blocks0, Count0) -> #b_blk{is=Is0,last=Last} = Blk = map_get(L, Blocks0), RC = case {Last,Ls} of - {#b_br{succ=Succ,fail=?BADARG_BLOCK},[Succ|_]} -> + {#b_br{succ=Succ,fail=?EXCEPTION_BLOCK},[Succ|_]} -> true; {_,_} -> false @@ -2133,8 +2186,8 @@ reserve_yregs(#st{frames=Frames}=St0) -> reserve_yregs_1(L, #st{ssa=Blocks0,cnt=Count0,res=Res0}=St) -> Blk = map_get(L, Blocks0), Yregs = beam_ssa:get_anno(yregs, Blk), - {Def,Used} = beam_ssa:def_used([L], Blocks0), - UsedYregs = ordsets:intersection(Yregs, Used), + {Def,Unused} = beam_ssa:def_unused([L], Yregs, Blocks0), + UsedYregs = ordsets:subtract(Yregs, Unused), DefBefore = ordsets:subtract(UsedYregs, Def), {BeforeVars,Blocks,Count} = rename_vars(DefBefore, L, Blocks0, Count0), InsideVars = ordsets:subtract(UsedYregs, DefBefore), @@ -2523,9 +2576,9 @@ reserve_xregs_is([], Res, Xs, _Used) -> {Res,Xs}. %% Pick up register hints from the successors of this blocks. -reserve_terminator(_L, _Is, #b_br{bool=#b_var{},succ=Succ,fail=?BADARG_BLOCK}, +reserve_terminator(_L, _Is, #b_br{bool=#b_var{},succ=Succ,fail=?EXCEPTION_BLOCK}, _Blocks, XsMap, _Res) -> - %% We know that no variables are used at ?BADARG_BLOCK, so + %% We know that no variables are used at ?EXCEPTION_BLOCK, so %% any register hints from the success blocks are safe to use. map_get(Succ, XsMap); reserve_terminator(L, Is, #b_br{bool=#b_var{},succ=Succ,fail=Fail}, |