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Diffstat (limited to 'lib/compiler/src/beam_reorder.erl')
| -rw-r--r-- | lib/compiler/src/beam_reorder.erl | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/lib/compiler/src/beam_reorder.erl b/lib/compiler/src/beam_reorder.erl new file mode 100644 index 0000000000..41586a7bf2 --- /dev/null +++ b/lib/compiler/src/beam_reorder.erl @@ -0,0 +1,139 @@ +%% +%% %CopyrightBegin% +%% +%% Copyright Ericsson AB 1999-2013. 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,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. |