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+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 1999-2016. 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%
+%%
+
+-module(beam_reorder).
+
+-export([module/2]).
+-import(lists, [member/2,reverse/1]).
+
+module({Mod,Exp,Attr,Fs0,Lc}, _Opt) ->
+ Fs = [function(F) || F <- Fs0],
+ {ok,{Mod,Exp,Attr,Fs,Lc}}.
+
+function({function,Name,Arity,CLabel,Is0}) ->
+ try
+ Is = reorder(Is0),
+ {function,Name,Arity,CLabel,Is}
+ catch
+ Class:Error ->
+ Stack = erlang:get_stacktrace(),
+ io:fwrite("Function: ~w/~w\n", [Name,Arity]),
+ erlang:raise(Class, Error, Stack)
+ end.
+
+%% reorder(Instructions0) -> Instructions
+%% Reorder instructions before the beam_block pass, because reordering
+%% will be more cumbersome when the blocks are in place.
+%%
+%% Execution of get_tuple_element instructions can be delayed until
+%% they are actually needed. Consider the sequence:
+%%
+%% get_tuple_element Tuple Pos Dst
+%% test Test Fail Operands
+%%
+%% If Dst is killed at label Fail (and not referenced in Operands),
+%% we can can swap the instructions:
+%%
+%% test Test Fail Operands
+%% get_tuple_element Tuple Pos Dst
+%%
+%% That can be beneficial in two ways: Firstly, if the branch is taken
+%% we have avoided execution of the get_tuple_element instruction.
+%% Secondly, even if the branch is not taken, subsequent optimization
+%% (opt_blocks/1) may be able to change Dst to the final destination
+%% register and eliminate a 'move' instruction.
+
+reorder(Is) ->
+ D = beam_utils:index_labels(Is),
+ reorder_1(Is, D, []).
+
+reorder_1([{Op,_,_}=TryCatch|[I|Is]=Is0], D, Acc)
+ when Op =:= 'catch'; Op =:= 'try' ->
+ %% Don't allow 'try' or 'catch' instructions to split blocks if
+ %% it can be avoided.
+ case is_safe(I) of
+ false ->
+ reorder_1(Is0, D, [TryCatch|Acc]);
+ true ->
+ reorder_1([TryCatch|Is], D, [I|Acc])
+ end;
+reorder_1([{label,L}=I|_], D, Acc) ->
+ Is = beam_utils:code_at(L, D),
+ reorder_1(Is, D, [I|Acc]);
+reorder_1([{test,is_nonempty_list,_,_}=I|Is], D, Acc) ->
+ %% The run-time system may combine the is_nonempty_list test with
+ %% the following get_list instruction.
+ reorder_1(Is, D, [I|Acc]);
+reorder_1([{test,_,_,_}=I,
+ {select,_,_,_,_}=S|Is], D, Acc) ->
+ %% There is nothing to gain by inserting a get_tuple_element
+ %% instruction between the test instruction and the select
+ %% instruction.
+ reorder_1(Is, D, [S,I|Acc]);
+reorder_1([{test,_,{f,_},[Src|_]}=I|Is], D,
+ [{get_tuple_element,Src,_,_}|_]=Acc) ->
+ %% We want to avoid code that can confuse beam_validator such as:
+ %% is_tuple Fail Src
+ %% test_arity Fail Src Arity
+ %% is_map Fail Src
+ %% get_tuple_element Src Pos Dst
+ %% Therefore, don't reorder the instructions in such cases.
+ reorder_1(Is, D, [I|Acc]);
+reorder_1([{test,_,{f,L},Ss}=I|Is0], D0,
+ [{get_tuple_element,_,_,El}=G|Acc0]=Acc) ->
+ case member(El, Ss) of
+ true ->
+ reorder_1(Is0, D0, [I|Acc]);
+ false ->
+ case beam_utils:is_killed_at(El, L, D0) of
+ true ->
+ Is = [I,G|Is0],
+ reorder_1(Is, D0, Acc0);
+ false ->
+ case beam_utils:is_killed(El, Is0, D0) of
+ true ->
+ Code0 = beam_utils:code_at(L, D0),
+ Code = [G|Code0],
+ D = beam_utils:index_label(L, Code, D0),
+ Is = [I|Is0],
+ reorder_1(Is, D, Acc0);
+ false ->
+ reorder_1(Is0, D0, [I|Acc])
+ end
+ end
+ end;
+reorder_1([{allocate_zero,N,Live}=I0|Is], D,
+ [{get_tuple_element,{x,Tup},_,{x,Dst}}=G|Acc]=Acc0) ->
+ case Tup < Dst andalso Dst+1 =:= Live of
+ true ->
+ %% Move allocation instruction upwards past
+ %% get_tuple_element instructions to create more
+ %% opportunities for moving get_tuple_element
+ %% instructions.
+ I = {allocate_zero,N,Dst},
+ reorder_1([I,G|Is], D, Acc);
+ false ->
+ reorder_1(Is, D, [I0|Acc0])
+ end;
+reorder_1([I|Is], D, Acc) ->
+ reorder_1(Is, D, [I|Acc]);
+reorder_1([], _, Acc) -> reverse(Acc).
+
+%% is_safe(Instruction) -> true|false
+%% Test whether an instruction is safe (cannot cause an exception).
+
+is_safe({kill,_}) -> true;
+is_safe({move,_,_}) -> true;
+is_safe({put,_}) -> true;
+is_safe({put_list,_,_,_}) -> true;
+is_safe({put_tuple,_,_}) -> true;
+is_safe({test_heap,_,_}) -> true;
+is_safe(_) -> false.