%% -*- Erlang -*-
%% -*- erlang-indent-level: 2 -*-
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2001-2016. 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.
%% 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%
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% CONTROL FLOW GRAPHS
%%
%% Construct and manipulate the control flow graph of a function (program?).
%%
%% Exports:
%% ~~~~~~~~
%% init(Code) - makes a CFG out of code.
%% bb(CFG, Label) - returns the basic block named 'Label' from the CFG.
%% bb_add(CFG, Label, NewBB) - makes NewBB the basic block associated
%% with Label.
%% succ(Map, Label) - returns a list of successors of basic block 'Label'.
%% pred(Map, Label) - returns the predecessors of basic block 'Label'.
%% fallthrough(CFG, Label) - returns fall-through successor of basic
%% block 'Label' (or 'none').
%% conditional(CFG, Label) - returns conditional successor (or 'none')
%% start_label(CFG) - returns the label of the entry basic block.
%% params(CFG) - returns the list of parameters to the CFG.
%% labels(CFG) - returns a list of labels of all basic blocks in the CFG.
%% postorder(CFG) - returns a list of labels in postorder.
%% reverse_postorder(CFG) - returns a list of labels in reverse postorder.
%% cfg_to_linear(CFG) - converts CFG to linearized code.
%% remove_trivial_bbs(CFG) - removes empty BBs or BBs with only a goto.
%% remove_unreachable_code(CFG) - removes unreachable BBs.
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% TODO:
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%=====================================================================
%% The following are ugly as hell, but what else can I do???
%%=====================================================================
-ifdef(GEN_CFG).
-define(PRED_NEEDED,true).
-endif.
-ifdef(ICODE_CFG).
-define(CLOSURE_ARITY_NEEDED,true).
-define(INFO_NEEDED,true).
-define(PARAMS_NEEDED,true).
-define(PARAMS_UPDATE_NEEDED,true).
-define(PRED_NEEDED,true).
-define(REMOVE_TRIVIAL_BBS_NEEDED,true).
-define(REMOVE_UNREACHABLE_CODE,true).
-define(START_LABEL_UPDATE_NEEDED,true).
-define(CFG_CAN_HAVE_PHI_NODES,true).
-endif.
-ifdef(RTL_CFG).
-define(PREORDER,true).
-define(FIND_NEW_LABEL_NEEDED,true).
-define(INFO_NEEDED,true).
-define(PARAMS_NEEDED,true).
-define(PARAMS_UPDATE_NEEDED,true).
-define(PRED_NEEDED,true).
-define(REMOVE_TRIVIAL_BBS_NEEDED,true).
-define(REMOVE_UNREACHABLE_CODE,true).
-define(START_LABEL_UPDATE_NEEDED,true).
-define(CFG_CAN_HAVE_PHI_NODES,true).
-endif.
-ifdef(SPARC_CFG).
-define(BREADTH_ORDER,true). % for linear scan
-define(PARAMS_NEEDED,true).
-define(START_LABEL_UPDATE_NEEDED,true).
-endif.
%%=====================================================================
-ifdef(START_LABEL_UPDATE_NEEDED).
-export([start_label_update/2]).
-endif.
-ifdef(BREADTH_ORDER).
-export([breadthorder/1]).
-endif.
-compile(inline).
%%=====================================================================
%%
%% Interface functions that MUST be implemented in the including file:
%%
%% linear_to_cfg(LinearCode) -> CFG, constructs the cfg.
%% is_label(Instr) -> boolean(), true if instruction is a label.
%% label_name(Instr) -> term(), the name of a label.
%% branch_successors(Instr) -> [term()], the successors of a branch.
%% fails_to(Instr) -> [term()], the fail-successors of an instruction.
%% is_branch(Instr) -> boolean(), true if instruction is a branch.
%% is_comment(Instr) -> boolean(),
%% true if instruction is a comment, used by remove dead code.
%% is_goto(Instr) -> boolean(),
%% true if instruction is a pure goto, used by remove dead code.
%% redirect_jmp(Jmp, ToOld, ToNew) -> NewJmp,
%% redirect_ops(Labels, CFG, Map) -> CFG.
%% Rewrite instructions with labels in operands to use
%% the new label as given by map.
%% Use find_new_label(OldLab,Map) to get the new label.
%% (See hipe_sparc_cfg for example)
%% pp(CFG) -> ok, do some nifty output.
%% cfg_to_linear(CFG) -> LinearCode, linearizes the code of CFG
%% mk_goto(Label) -> instruction
%% is_phi(Instr) -> boolean(), true if the instruction is a phi-instruction.
%% phi_remove_pred(PhiInstr, Pred) -> NewPhi,
%% Removes the predecessor Pred from the phi instruction.
%% highest_var(Code) -> term(),
%% Returns the highest variable used or defined in the code.
%%
%%=====================================================================
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% Primitives (not all of these are exported)
%%
-spec start_label(cfg()) -> cfg_lbl().
start_label(CFG) -> (CFG#cfg.info)#cfg_info.start_label.
-ifndef(GEN_CFG).
-spec start_label_update(cfg(), cfg_lbl()) -> cfg().
start_label_update(CFG, NewStartLabel) ->
Info = CFG#cfg.info,
CFG#cfg{info = Info#cfg_info{start_label = NewStartLabel}}.
-spec function(cfg()) -> mfa().
function(CFG) -> (CFG#cfg.info)#cfg_info.'fun'.
-spec is_closure(cfg()) -> boolean().
is_closure(CFG) -> (CFG#cfg.info)#cfg_info.is_closure.
-spec is_leaf(cfg()) -> boolean().
is_leaf(CFG) -> (CFG#cfg.info)#cfg_info.is_leaf.
mk_empty_cfg(Fun, StartLbl, Data, Closure, Leaf, Params) ->
Info = #cfg_info{'fun' = Fun,
start_label = StartLbl,
is_closure = Closure,
is_leaf = Leaf,
params = Params},
#cfg{table = gb_trees:empty(), data = Data, info = Info}.
data(CFG) -> CFG#cfg.data.
-endif. % GEN_CFG
-ifdef(REMOVE_TRIVIAL_BBS_NEEDED).
-spec update_data(cfg(), cfg_data()) -> cfg().
update_data(CFG, D) ->
CFG#cfg{data = D}.
-endif.
-ifdef(PARAMS_NEEDED).
params(CFG) -> (CFG#cfg.info)#cfg_info.params.
-endif.
-ifdef(PARAMS_UPDATE_NEEDED).
params_update(CFG, NewParams) ->
Info = CFG#cfg.info,
CFG#cfg{info = Info#cfg_info{params = NewParams}}.
-endif.
-ifdef(CLOSURE_ARITY_NEEDED).
-spec closure_arity(cfg()) -> arity().
closure_arity(CFG) ->
Info = CFG#cfg.info,
Info#cfg_info.closure_arity.
-spec closure_arity_update(cfg(), arity()) -> cfg().
closure_arity_update(CFG, Arity) ->
Info = CFG#cfg.info,
CFG#cfg{info = Info#cfg_info{closure_arity = Arity}}.
-endif.
%% %% Don't forget to do a start_label_update if necessary.
%% update_code(CFG, NewCode) ->
%% take_bbs(NewCode, CFG).
-ifdef(INFO_NEEDED).
info(CFG) -> (CFG#cfg.info)#cfg_info.info.
%% info_add(CFG, A) ->
%% As = info(CFG),
%% Info = CFG#cfg.info,
%% CFG#cfg{info = Info#cfg_info{info = [A|As]}}.
info_update(CFG, I) ->
Info = CFG#cfg.info,
CFG#cfg{info = Info#cfg_info{info = I}}.
-endif.
%%=====================================================================
-ifndef(GEN_CFG).
-spec other_entrypoints(cfg()) -> [cfg_lbl()].
%% @doc Returns a list of labels that are refered to from the data section.
other_entrypoints(CFG) ->
hipe_consttab:referred_labels(data(CFG)).
%% is_entry(Lbl, CFG) ->
%% Lbl =:= start_label(CFG) orelse
%% lists:member(Lbl, other_entrypoints(CFG)).
%% @spec bb(CFG::cfg(), Label::cfg_lbl()) -> basic_block()
%% @doc Returns the basic block of the CFG which begins at the Label.
bb(CFG, Label) ->
HT = CFG#cfg.table,
case gb_trees:lookup(Label, HT) of
{value, {Block,_Succ,_Pred}} ->
Block;
none ->
not_found
end.
%% Remove duplicates from a list. The first instance (in left-to-right
%% order) of an element is kept, remaining instances are removed.
-spec remove_duplicates([cfg_lbl()]) -> [cfg_lbl()].
remove_duplicates(List) ->
remove_duplicates(List, []).
-spec remove_duplicates([cfg_lbl()], [cfg_lbl()]) -> [cfg_lbl()].
remove_duplicates([H|T], Acc) ->
NewAcc =
case lists:member(H, Acc) of
false -> [H|Acc];
true -> Acc
end,
remove_duplicates(T, NewAcc);
remove_duplicates([], Acc) ->
lists:reverse(Acc).
-ifdef(RTL_CFG). %% this could be CFG_CAN_HAVE_PHI_NODES
%% if Icode also starts using this function
%% @spec bb_insert_between(CFG::cfg(),
%% Label::cfg_lbl(), NewBB::basic_block(),
%% Pred::cfg_lbl(), Succ::cfg_lbl()) -> cfg()
%%
%% @doc Insert the new basic block with label Label in the edge from
%% Pred to Succ
bb_insert_between(CFG, Label, NewBB, Pred, Succ) ->
Last = hipe_bb:last(NewBB),
%% Asserts that NewBB ends in a label
true = is_branch(Last),
%% Asserts that the only Successor of NewBB is Succ
[Succ] = remove_duplicates(branch_successors(Last)),
HT = CFG#cfg.table,
%% Asserts that Label does not exist in the CFG
none = gb_trees:lookup(Label, HT),
%% Updates the predecessor of NewBB
{value, {PBB, PSucc, PPred}} = gb_trees:lookup(Pred, HT),
NewPSucc = [Label|lists:delete(Succ, PSucc)],
PLast = hipe_bb:last(PBB),
PButLast = hipe_bb:butlast(PBB),
NewPBB = hipe_bb:code_update(PBB, PButLast++[redirect_jmp(PLast, Succ, Label)]),
HT1 = gb_trees:update(Pred, {NewPBB,NewPSucc,PPred}, HT),
%% Updates the successor of NewBB
{value, {SBB, SSucc, SPred}} = gb_trees:lookup(Succ, HT1),
NewSPred = [Label|lists:delete(Pred, SPred)],
SCode = hipe_bb:code(SBB),
NewSCode = redirect_phis(SCode, Pred, Label, []),
NewSBB = hipe_bb:code_update(SBB, NewSCode),
HT2 = gb_trees:update(Succ, {NewSBB,SSucc,NewSPred}, HT1),
%% Enters NewBB into the CFG
HT3 = gb_trees:insert(Label, {NewBB,[Succ],[Pred]}, HT2),
CFG#cfg{table = HT3}.
redirect_phis([], _OldPred, _NewPred, Acc) ->
lists:reverse(Acc);
redirect_phis([I|Rest], OldPred, NewPred, Acc) ->
case is_phi(I) of
true ->
Phi = phi_redirect_pred(I, OldPred, NewPred),
redirect_phis(Rest, OldPred, NewPred, [Phi|Acc]);
false ->
redirect_phis(Rest, OldPred, NewPred, [I|Acc])
end.
-endif.
%% @spec bb_add(CFG::cfg(), Label::cfg_lbl(), NewBB::basic_block()) -> cfg()
%% @doc Adds a new basic block to a CFG (or updates an existing block).
bb_add(CFG, Label, NewBB) ->
%% Asserting that the NewBB is a legal basic block
Last = hipe_bb:last(NewBB),
case is_branch(Last) of
true -> ok;
false -> throw({?MODULE, {"Basic block ends without branch", Last}})
end,
%% The order of the elements from branch_successors/1 is
%% significant. It determines the basic block order when the CFG is
%% converted to linear form. That order may have been tuned for
%% branch prediction purposes.
Succ = remove_duplicates(branch_successors(Last)),
HT = CFG#cfg.table,
{OldSucc, OldPred} = case gb_trees:lookup(Label, HT) of
{value, {_Block, OSucc, OPred}} ->
{OSucc, OPred};
none ->
{[], []}
end,
%% Change this block to contain new BB and new successors, but keep
%% the old predecessors which will be updated in the following steps
HT1 = gb_trees:enter(Label, {NewBB, Succ, OldPred}, HT),
%% Add this block as predecessor to its new successors
HT2 = lists:foldl(fun (P, HTAcc) ->
add_pred(HTAcc, P, Label)
end,
HT1, Succ -- OldSucc),
%% Remove this block as predecessor of its former successors
HT3 = lists:foldl(fun (S, HTAcc) ->
remove_pred(HTAcc, S, Label)
end,
HT2, OldSucc -- Succ),
CFG#cfg{table = HT3}.
remove_pred(HT, FromL, PredL) ->
case gb_trees:lookup(FromL, HT) of
{value, {Block, Succ, Preds}} ->
Code = hipe_bb:code(Block),
NewCode = remove_pred_from_phis(Code, PredL, []),
NewBlock = hipe_bb:code_update(Block, NewCode),
gb_trees:update(FromL, {NewBlock,Succ,lists:delete(PredL,Preds)}, HT);
none ->
HT
end.
add_pred(HT, ToL, PredL) ->
case gb_trees:lookup(ToL, HT) of
{value,{Block,Succ,Preds}} ->
gb_trees:update(ToL, {Block,Succ,[PredL|lists:delete(PredL,Preds)]}, HT);
none ->
gb_trees:insert(ToL, {[],[],[PredL]}, HT)
end.
%% find_highest_label(CFG) ->
%% Labels = labels(CFG),
%% lists:foldl(fun(X, Acc) -> erlang:max(X, Acc) end, 0, Labels).
%%
%% find_highest_var(CFG) ->
%% Labels = labels(CFG),
%% Fun = fun(X, Max) ->
%% Code = hipe_bb:code(bb(CFG, X)),
%% NewMax = highest_var(Code),
%% erlang:max(Max, NewMax)
%% end,
%% lists:foldl(Fun, 0, Labels).
-ifdef(CFG_CAN_HAVE_PHI_NODES).
%% phi-instructions in a removed block's successors must be aware of
%% the change.
remove_pred_from_phis(List = [I|Left], Label, Acc) ->
case is_phi(I) of
true ->
NewAcc = [phi_remove_pred(I, Label)|Acc],
remove_pred_from_phis(Left, Label, NewAcc);
false ->
lists:reverse(Acc) ++ List
end;
remove_pred_from_phis([], _Label, Acc) ->
lists:reverse(Acc).
-else.
%% this is used for code representations like those of back-ends which
%% do not have phi-nodes.
remove_pred_from_phis(Code, _Label, _Acc) ->
Code.
-endif.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% Constructs a CFG from a list of instructions.
%%
take_bbs([], CFG) ->
CFG;
take_bbs(Xs, CFG) ->
Lbl = hd(Xs),
case is_label(Lbl) of
true ->
case take_bb(tl(Xs), []) of
{Code, Rest} ->
NewCFG = bb_add(CFG, label_name(Lbl), hipe_bb:mk_bb(Code)),
take_bbs(Rest, NewCFG)
end;
false ->
erlang:error({?MODULE,"basic block doesn't start with a label",Xs})
end.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% Take_bb returns:
%% - {Code, Rest}.
%% * Code is a list of all the instructions.
%% * Rest is the remainder of the instructions
take_bb([], Code) ->
{lists:reverse(Code), []};
take_bb([X, Y|Xs], Code) ->
case is_label(X) of
true -> %% Empty block fallthrough
{[mk_goto(label_name(X))], [X,Y|Xs]};
false ->
case is_branch(X) of
true ->
case is_label(Y) of
true ->
{lists:reverse([X|Code]), [Y|Xs]};
false ->
%% This should not happen...
%% move the problem to the next BB.
{lists:reverse([X|Code]), [Y|Xs]}
end;
false -> %% X not branch
case is_label(Y) of
true ->
{lists:reverse([mk_goto(label_name(Y)),X|Code]), [Y|Xs]};
false ->
take_bb([Y|Xs], [X|Code])
end
end
end;
take_bb([X], []) ->
case is_label(X) of
true ->
%% We don't want the CFG to just end with a label...
%% We loop forever instead...
{[X,mk_goto(label_name(X))],[]};
false ->
{[X],[]}
end;
take_bb([X], Code) ->
case is_label(X) of
true ->
%% We don't want the CFG to just end with a label...
%% We loop for ever instead...
{lists:reverse(Code),[X,mk_goto(label_name(X))]};
false ->
{lists:reverse([X|Code]),[]}
end.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% Functions for extracting the names of the basic blocks in various
%% orders.
%%
labels(CFG) ->
HT = CFG#cfg.table,
gb_trees:keys(HT).
postorder(CFG) ->
lists:reverse(reverse_postorder(CFG)).
reverse_postorder(CFG) ->
Start = start_label(CFG),
{Ordering, _Visited} =
depth_search([Start|other_entrypoints(CFG)], none_visited(), CFG, []),
Ordering.
depth_search([N|Ns], Visited, CFG, Acc) ->
case is_visited(N, Visited) of
true ->
depth_search(Ns, Visited, CFG, Acc);
false ->
{Order, Vis} = depth_search(succ(CFG, N), visit(N, Visited), CFG, Acc),
depth_search(Ns, Vis, CFG, [N|Order])
end;
depth_search([], Visited, _, Ordering) ->
{Ordering, Visited}.
-ifdef(PREORDER).
preorder(CFG) ->
Start = start_label(CFG),
{Ordering, _Visited} =
preorder_search([Start|other_entrypoints(CFG)], none_visited(), CFG, []),
lists:reverse(Ordering).
preorder_search([N|Ns], Visited, CFG, Acc) ->
case is_visited(N, Visited) of
true ->
preorder_search(Ns, Visited, CFG, Acc);
false ->
{Order, Vis} =
preorder_search(succ(CFG, N), visit(N, Visited), CFG, [N|Acc]),
preorder_search(Ns, Vis, CFG, Order)
end;
preorder_search([], Visited, _, Ordering) ->
{Ordering,Visited}.
-endif. % PREORDER
-ifdef(BREADTH_ORDER).
breadthorder(CFG) ->
lists:reverse(reverse_breadthorder(CFG)).
reverse_breadthorder(CFG) ->
Start = start_label(CFG),
{Vis, RBO1} = breadth_list([Start], none_visited(), CFG, []),
{_Vis1, RBO2} = breadth_list(other_entrypoints(CFG), Vis, CFG, RBO1),
RBO2.
breadth_list([X|Xs], Vis, CFG, BO) ->
case is_visited(X, Vis) of
true ->
breadth_list(Xs, Vis, CFG, BO);
false ->
breadth_list(Xs ++ succ(CFG, X), visit(X, Vis), CFG, [X|BO])
end;
breadth_list([], Vis, _CFG, BO) ->
{Vis, BO}.
-endif.
-spec none_visited() -> gb_sets:set().
none_visited() ->
gb_sets:empty().
visit(X, Vis) ->
gb_sets:add(X, Vis).
is_visited(X, Vis) ->
gb_sets:is_member(X, Vis).
-endif. % GEN_CFG
%%---------------------------------------------------------------------
succ(SuccMap, Label) ->
HT = SuccMap#cfg.table,
case gb_trees:lookup(Label, HT) of
{value, {_Block,Succ,_Pred}} ->
Succ;
none ->
erlang:error({"successor not found", Label, SuccMap})
end.
-ifdef(PRED_NEEDED).
pred(Map, Label) ->
HT = Map#cfg.table,
case gb_trees:lookup(Label, HT) of
{value, {_Block,_Succ,Pred}} ->
Pred;
none ->
erlang:error({"predecessor not found", Label, Map})
end.
-endif. % PRED_NEEDED
-ifndef(GEN_CFG).
fallthrough(CFG, Label) ->
HT = CFG#cfg.table,
case gb_trees:lookup(Label, HT) of
{value, {_Block, Succ, _}} ->
case Succ of
[X|_] -> X;
_ -> none
end;
none ->
erlang:error({"fallthrough label not found", Label})
end.
conditional(CFG, Label) ->
HT = CFG#cfg.table,
{value,{_Block,Succ,_}} = gb_trees:lookup(Label, HT),
case Succ of
[] -> none;
[_] -> none;
[_|Labels] -> Labels
end.
-endif. % GEN_CFG
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% Linearize the code in a CFG. Returns a list of instructions.
%%
-ifdef(GEN_CFG).
-else.
linearize_cfg(CFG) ->
Start = start_label(CFG),
Vis = none_visited(),
{Vis0, NestedCode} = lin_succ(Start, CFG, Vis),
BlocksInData = hipe_consttab:referred_labels(data(CFG)),
AllCode = lin_other_entries(NestedCode, CFG, BlocksInData, Vis0),
lists:flatten(AllCode).
lin_succ(none, _CFG, Vis) ->
{Vis, []};
lin_succ([Label|Labels], CFG, Vis) ->
{Vis1, Code1} = lin_succ(Label, CFG, Vis),
{Vis2, Code2} = lin_succ(Labels, CFG, Vis1),
{Vis2, [Code1,Code2]};
lin_succ([], _CFG, Vis) ->
{Vis, []};
lin_succ(Label, CFG, Vis) ->
case is_visited(Label, Vis) of
true ->
{Vis, []}; % already visited
false ->
Vis0 = visit(Label, Vis),
case bb(CFG, Label) of
not_found ->
erlang:error({?MODULE, "No basic block with label", Label});
BB ->
Fallthrough = fallthrough(CFG, Label),
Cond = conditional(CFG, Label),
LblInstr = mk_label(Label),
{Vis1, Code1} = lin_succ(Fallthrough, CFG, Vis0),
{Vis2, Code2} = lin_succ(Cond, CFG, Vis1),
{Vis2, [[LblInstr|hipe_bb:code(BB)], Code1, Code2]}
end
end.
lin_other_entries(Code, _CFG, [], _Vis) ->
Code;
lin_other_entries(Code, CFG, [E|Es], Vis) ->
{Vis0, MoreCode} = lin_succ(E, CFG, Vis),
lin_other_entries([Code, MoreCode], CFG, Es, Vis0).
-endif.
-ifdef(FIND_NEW_LABEL_NEEDED).
find_new_label(Old, Map) ->
forward(Old, Map).
-endif.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% Remove empty BBs.
%%
%% Removes basic blocks containing only a goto to another BB.
%% Branches to removed blocks are updated to the successor of the
%% removed block.
%% Loads (or other operations) on the label of the BB are also
%% updated. So are any references from the data section.
%%
-ifdef(REMOVE_TRIVIAL_BBS_NEEDED).
-spec remove_trivial_bbs(cfg()) -> cfg().
remove_trivial_bbs(CFG) ->
?opt_start_timer("Merge BBs"),
CFG0 = merge_bbs(rewrite_trivial_branches(CFG)),
?opt_stop_timer("Merge BBs"),
%% pp(CFG0),
?opt_start_timer("FindDead"),
{NewMap, CFG1} = remap(labels(CFG0), rd_map_new(), CFG0),
?opt_stop_timer("FindDead"),
?opt_start_timer("Labels"),
Labels = labels(CFG1),
?opt_stop_timer("Labels"),
?opt_start_timer("RedirectBranches"),
CFG2 = redirect_branches(NewMap, CFG1),
?opt_stop_timer("RedirectBranches"),
?opt_start_timer("RedirectOps"),
CFG3 = redirect_ops(Labels, CFG2, NewMap),
?opt_stop_timer("RedirectOps"),
?opt_start_timer("RedirectData"),
CFG4 = redirect_data(CFG3, NewMap),
?opt_stop_timer("RedirectData"),
?opt_start_timer("RedirectStart"),
CFG5 = redirect_start(CFG4, NewMap),
?opt_stop_timer("RedirectStart"),
%% pp(CFG5),
CFG5.
redirect_start(CFG, Map) ->
Start = start_label(CFG),
case forward(Start, Map) of
Start -> CFG;
NewStart ->
start_label_update(CFG, NewStart)
end.
redirect_data(CFG, Map) ->
Data = data(CFG),
NewData = hipe_consttab:update_referred_labels(Data, rd_succs(Map)),
update_data(CFG, NewData).
redirect_branches(Map, CFG) ->
lists:foldl(fun ({From,{newsuccs,Redirects}}, CFGAcc) ->
lists:foldl(
fun({ToOld,ToNew}, CFG1) ->
case bb(CFG1, From) of
not_found ->
CFG1;
_ ->
To = forward(ToNew, Map),
redirect(CFG1, From, ToOld, To)
end
end,
CFGAcc,
Redirects);
(_, CFGAcc) -> CFGAcc
end,
CFG,
gb_trees:to_list(Map)).
redirect(CFG, From, ToOld, ToNew) ->
BB = bb(CFG, From),
LastInstr = hipe_bb:last(BB),
NewLastInstr = redirect_jmp(LastInstr, ToOld, ToNew),
NewBB = hipe_bb:mk_bb(hipe_bb:butlast(BB) ++ [NewLastInstr]),
bb_add(CFG, From, NewBB).
bb_remove(CFG, Label) ->
HT = CFG#cfg.table,
case gb_trees:lookup(Label, HT) of
{value, {_Block, Succ, _Preds}} ->
%% Remove this block as a pred from all successors.
HT1 = lists:foldl(fun (S,HTAcc) ->
remove_pred(HTAcc, S, Label)
end,
HT, Succ),
CFG#cfg{table = gb_trees:delete(Label, HT1)};
none ->
CFG
end.
remap([L|Rest], Map, CFG) ->
case is_empty(bb(CFG, L)) of
true ->
case succ(CFG, L) of
[L] -> %% This is an empty (infinite) self loop. Leave it.
remap(Rest, Map, CFG);
[SuccL] ->
CFG1 = bb_remove(CFG, L),
NewMap = remap_to_succ(L, SuccL, Map, CFG),
remap(Rest, NewMap, CFG1)
end;
false ->
remap(Rest, Map, CFG)
end;
remap([], Map, CFG) ->
{Map, CFG}.
remap_to_succ(L, SuccL, Map, PredMap) ->
insert_remap(L, forward(SuccL,Map), pred(PredMap,L), Map).
%% Find the proxy for a BB
forward(L, Map) ->
case gb_trees:lookup(L, Map) of
{value, {dead, To}} ->
forward(To, Map); %% Hope this terminates.
_ -> L
end.
%% A redirection map contains mappings from labels to
%% none -> this BB is not affected by the remapping.
%% {dead,To} -> this BB is dead, To is the new proxy.
%% {newsuccs,[{X,Y}|...]} -> The successor X is redirected to Y.
rd_map_new() -> gb_trees:empty().
rd_succs(M) ->
lists:foldl(fun ({From,{dead,To}}, Acc) -> [{From,forward(To,M)}|Acc];
(_, Acc) -> Acc
end,
[],
gb_trees:to_list(M)).
add_redirectedto(L, From, To, Map) ->
case gb_trees:lookup(L, Map) of
{value, {newsuccs, NS}} ->
gb_trees:update(L,{newsuccs,[{From,To}|lists:keydelete(From,1,NS)]},Map);
{value, {dead, _}} -> Map;
none ->
gb_trees:insert(L, {newsuccs, [{From, To}]}, Map)
end.
insert_remap(L, ToL, Preds, Map) ->
Map2 = gb_trees:enter(L, {dead, ToL}, Map),
lists:foldl(fun (Pred, AccMap) ->
add_redirectedto(Pred, L, ToL, AccMap)
end,
Map2,
Preds).
is_empty(BB) ->
is_empty_bb(hipe_bb:code(BB)).
is_empty_bb([I]) ->
is_goto(I); %% A BB with just a 'goto' is empty.
is_empty_bb([I|Is]) ->
case is_comment(I) of
true ->
is_empty_bb(Is);
false ->
false
end;
is_empty_bb([]) ->
true.
%% Rewrite all pure branches with one successor to goto:s
-spec rewrite_trivial_branches(cfg()) -> cfg().
rewrite_trivial_branches(CFG) ->
rewrite_trivial_branches(postorder(CFG), CFG).
rewrite_trivial_branches([L|Left], CFG) ->
BB = bb(CFG, L),
Last = hipe_bb:last(BB),
case is_goto(Last) of
true ->
rewrite_trivial_branches(Left, CFG);
false ->
case is_pure_branch(Last) of
false ->
rewrite_trivial_branches(Left, CFG);
true ->
case succ(CFG, L) of
[Successor] ->
Head = hipe_bb:butlast(BB),
NewBB = hipe_bb:mk_bb(Head ++ [mk_goto(Successor)]),
NewCFG = bb_add(CFG, L, NewBB),
rewrite_trivial_branches(Left, NewCFG);
_ ->
rewrite_trivial_branches(Left, CFG)
end
end
end;
rewrite_trivial_branches([], CFG) ->
CFG.
%% Go through the CFG and find pairs of BBs that can be merged to one BB.
%% They are of the form:
%%
%% L
%% |
%% Successor
%%
%% That is, the block L has only one successor (Successor) and that
%% successor has no other predecessors than L.
%%
%% Note: calls might end a basic block
merge_bbs(CFG) ->
lists:foldl(fun merge_successor/2, CFG, postorder(CFG)).
%% If L fulfills the requirements, merge it with its successor.
merge_successor(L, CFG) ->
%% Get the BB L (If it still exists).
case bb(CFG, L) of
not_found -> CFG;
BB ->
StartLabel = start_label(CFG),
Last = hipe_bb:last(BB),
%% Note: Cannot use succ/2 since the instruction can have more than
%% one successor that are the same label.
case {branch_successors(Last), fails_to(Last)} of
{[Successor],[Successor]} ->
%% The single successor is the fail-label; don't merge.
CFG;
{[Successor],_} when Successor =/= StartLabel ->
%% Make sure the succesor only have this block as predecessor.
case [L] =:= pred(CFG, Successor) of
true ->
%% Remove the goto or remap fall-through in BB and merge the BBs
NewCode = merge(BB, bb(CFG, Successor), Successor),
NewBB = hipe_bb:mk_bb(NewCode),
bb_add(bb_remove(CFG, Successor), L, NewBB);
false ->
CFG
end;
_ ->
%% Not exactly one successor or tried to merge with the
%% entry point
CFG
end
end.
%% Merge BB and BB2
merge(BB, BB2, BB2_Label) ->
Head = hipe_bb:butlast(BB),
Last = hipe_bb:last(BB),
Tail = hipe_bb:code(BB2),
case is_goto(Last) of
true ->
%% Just ignore the goto.
Head ++ Tail;
false ->
%% The last instr is not a goto,
%% e.g. a call with only fall-through
%% Remove the fall-through with the []-label.
Head ++ [redirect_jmp(Last, BB2_Label, [])|Tail]
end.
-endif. % REMOVE_TRIVIAL_BBS_NEEDED
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% Remove unreachable BBs.
%%
%% A BB is unreachable if it cannot be reached by any path from the
%% start label of the function.
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-ifdef(REMOVE_UNREACHABLE_CODE).
-spec remove_unreachable_code(cfg()) -> cfg().
remove_unreachable_code(CFG) ->
Start = start_label(CFG),
Reachable = find_reachable([Start], CFG, gb_sets:from_list([Start])),
%% Reachable is an ordset: it comes from gb_sets:to_list/1.
%% So use ordset:subtract instead of '--' below.
Labels = ordsets:from_list(labels(CFG)),
case ordsets:subtract(Labels, Reachable) of
[] ->
CFG;
Remove ->
NewCFG = lists:foldl(fun(X, Acc) -> bb_remove(Acc, X) end, CFG, Remove),
remove_unreachable_code(NewCFG)
end.
find_reachable([Label|Left], CFG, Acc) ->
NewAcc = gb_sets:add(Label, Acc),
Succ = succ(CFG, Label),
find_reachable([X || X <- Succ, not gb_sets:is_member(X, Acc)] ++ Left,
CFG, NewAcc);
find_reachable([], _CFG, Acc) ->
gb_sets:to_list(Acc).
-endif.
