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-rw-r--r--lib/compiler/src/beam_reorder.erl150
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diff --git a/lib/compiler/src/beam_reorder.erl b/lib/compiler/src/beam_reorder.erl
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-%%
-%% %CopyrightBegin%
-%%
-%% Copyright Ericsson AB 1999-2018. 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%
-%%
-
--module(beam_reorder).
-
--export([module/2]).
--import(lists, [member/2,reverse/1]).
-
--spec module(beam_utils:module_code(), [compile:option()]) ->
- {'ok',beam_utils:module_code()}.
-
-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 ->
- 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.