aboutsummaryrefslogblamecommitdiffstats
path: root/lib/hipe/rtl/hipe_rtl_ssa_const_prop.erl
blob: 71583830100a6434ec6a63f1f6a319c1e348d83f (plain) (tree)
1
2
3
4
5
6
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
                                 


                   
                                                        
   










                                                                           














































































                                                                               
































































































                                                                               
                                                               














































































































































































































                                                                                
                                                                               







































                                                                               

                                                                        



                                                                         

                                                     














































































































































































































































































































































































































































































































                                                                                         

                                                  























                                                                             






                                                                              







                                                 





                                                                         



























































                                                                               
                                                                          




























                                                                               
%% -*- erlang-indent-level: 2 -*-
%%
%% %CopyrightBegin%
%% 
%% Copyright Ericsson AB 2004-2016. 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%
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% ============================================================================
%%  Filename :  hipe_rtl_ssa_const_prop.erl
%%  Authors  :  Bjorn Bergman, Bjarni Juliusson
%%  Purpose  :  Perform sparse conditional constant propagation on RTL.
%%  Notes    :  Works on an SSA-converted control-flow graph.
%%
%%  History  :  * 2004-03-14: Blatantly stolen from Icode (code by
%%                  Daniel Luna and Erik Andersson) and query-replaced for RTL.
%%              * 2004-04-30: Added in the repository.
%% ============================================================================
%%
%% Exports: propagate/1.
%%
%% ============================================================================
%%
%% Some things to note:
%%
%% 1. All precoloured registers are assumed to contain bottom. We can not
%%    do anything with them since they are not in SSA-form. This might be
%%    possible to resolve in some way, but we decided to not go there.
%%
%% 2. const_labels are assumed to be bottom, we can not find the address
%%    in any nice way (that I know of, maybe someone can help ?). I
%%    suppose they don't get a value until linking (or some step that
%%    resembles it). They are only affecting bignums and floats (at least
%%    as far as I can tell), which are both stored in memory and hence
%%    not handled very well by us anyway.
%%
%% 3. can v <- Constant be removed ? I think so. all uses of v will be
%%    replaced with an immediate. So why not ?
%%
%% ============================================================================
%%
%% TODO: 
%%
%% Take care of failures in call and replace operation with apropriate
%% failure.
%%
%% Handle ifs with non-binary operators
%%
%% We want multisets for easier (and faster) creation of env->ssa_edges
%% 
%% Propagation of constant arguments when some of the arguments are bottom
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


-module(hipe_rtl_ssa_const_prop).
-export([propagate/1]).

-include("../main/hipe.hrl").
-include("hipe_rtl.hrl").
-include("../flow/cfg.hrl").

%-define(DEBUG, true).

-ifdef(DEBUG).
-define(SCCPDBG(W), W).
-define(DEBUG_TST, true).  % make sure that we can use ?DEBUG in if-cases...
-else.
-define(DEBUG_TST, false).  % make sure that we can use ?DEBUG in if-cases...
-define(SCCPDBG(W), ok).
-endif.

%%-----------------------------------------------------------------------------
%% Include stuff shared between SCCP on Icode and RTL.
%% NOTE: Needs to appear after DEBUG is possibly defined.
%%-----------------------------------------------------------------------------

-define(CODE, hipe_rtl).
-define(CFG,  hipe_rtl_cfg).
-include("../ssa/hipe_ssa_const_prop.inc").

-type bool_lattice() :: 'true' | 'false' | 'top' | 'bottom'.

%%-----------------------------------------------------------------------------
%% Procedure : visit_expression/2
%% Purpose   : do a symbolic execution of the given instruction.  This is just
%%	       a wrapper that chooses the right function to handle a particular
%%	       instruction.
%% Arguments : Instructions - the instruction
%%             Environment  - have a guess.
%% Returns   : {FlowWorkList, SSAWorkList, Environment}
%%-----------------------------------------------------------------------------
visit_expression(Instruction, Environment) ->
  case Instruction of
    #alu{} ->
      visit_alu(Instruction, Environment);
    #alub{} ->
      visit_alub(Instruction, Environment);
    #branch{} ->
      visit_branch(Instruction, Environment);
    #call{} ->
      visit_call(Instruction, Environment);
%%    #comment{} ->
%%      visit_comment(Instruction, Environment);
%%    #enter{} ->
%%      visit_enter(Instruction, Environment);
    #fconv{} ->
      visit_fconv(Instruction, Environment);
    #fixnumop{} ->
      visit_fixnumop(Instruction, Environment);
    #fload{} ->
      visit_fload(Instruction, Environment);
    #fmove{} ->
      visit_fmove(Instruction, Environment);
    #fp{} ->
      visit_fp(Instruction, Environment);
    #fp_unop{} ->
      visit_fp_unop(Instruction, Environment);
%%    #fstore{} ->
%%      visit_fstore(Instruction, Environment);
%%    #gctest{} ->
%%      visit_gctest(Instruction, Environment);
    #goto{} ->
      visit_goto(Instruction, Environment);
    #goto_index{} ->
      visit_goto_index(Instruction, Environment);
%%    #label{} ->
%%      visit_label(Instruction, Environment);
    #load{} ->
      visit_load(Instruction, Environment);
    #load_address{} ->
      visit_load_address(Instruction, Environment);
    #load_atom{} ->
      visit_load_atom(Instruction, Environment);
    #load_word_index{} ->
      visit_load_word_index(Instruction, Environment);
    #move{} ->
      visit_move(Instruction, Environment);
    #multimove{} ->
      visit_multimove(Instruction, Environment);
%% phi-nodes are handled in scc
%%    #phi{} ->
%%      visit_phi(Instruction, Environment);
%%    #return{} ->
%%      visit_return(Instruction, Environment);
%%    #store{} ->
%%      visit_store(Instruction, Environment);
    #switch{} ->
      visit_switch(Instruction, Environment);
    _ ->
      %% label, end_try, comment, return, fail, et al
      {[], [], Environment}
  end.


%%-----------------------------------------------------------------------------
%% Procedure : set_to/3
%% Purpose   : many of the visit_<inst> functions ends in a update of the 
%%             environment (and resulting SSA-edges) this function does the 
%%             update in a nice way and formats the result so that it can be
%%             imediatly returned to visit_expression
%% Arguments : Dst - the destination may be a list of destinations.
%%             Val - the new value (bottom, or some constant).
%%             Env - the environment in which the update should be done.
%% Returns   : { FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

set_to(Dst, Val, Env) ->
  {Env1, SSAWork} = update_lattice_value({Dst, Val}, Env),
  {[], SSAWork, Env1}.

%%-----------------------------------------------------------------------------
%% Procedure : visit_branch/2
%% Purpose   : do symbolic exection of branch instructions.
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : { FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_branch(Inst, Env) -> %% Titta också på exekverbarflagga
  Val1 = lookup_lattice_value(hipe_rtl:branch_src1(Inst), Env),
  Val2 = lookup_lattice_value(hipe_rtl:branch_src2(Inst), Env),
  CFGWL = case evaluate_relop(Val1, hipe_rtl:branch_cond(Inst), Val2) of
            true   -> [hipe_rtl:branch_true_label(Inst)];
            false  -> [hipe_rtl:branch_false_label(Inst)];
            bottom -> [hipe_rtl:branch_true_label(Inst), 
	               hipe_rtl:branch_false_label(Inst)];
            top    -> []
          end,
  {CFGWL, [], Env}.

%%-----------------------------------------------------------------------------
%% Procedure : evaluate_relop/3
%% Purpose   : evaluate the given relop. While taking care to handle top & 
%%             bottom in some sane way.
%% Arguments : Val1, Val2 - The operands Integers or top or bottom
%%             RelOp  - some relop atom from rtl. 
%% Returns   : bottom, top, true or false
%%-----------------------------------------------------------------------------

evaluate_relop(Val1, RelOp, Val2) ->
  if 
    (Val1==bottom) or (Val2==bottom) -> bottom ;
    (Val1==top) or (Val2==top)       ->  top;
    true ->  hipe_rtl_arch:eval_cond(RelOp, Val1, Val2)
  end.

%%-----------------------------------------------------------------------------
%% Procedure : evaluate_fixnumop/2 
%% Purpose   : try to evaluate a fixnumop.
%% Arguments : Val1 - operand (an integer, 'top' or 'bottom')
%%             Op - the operation.
%% Returns   : Result
%%              where result is an integer, 'top' or 'bottom'
%%-----------------------------------------------------------------------------

evaluate_fixnumop(Val1, Op) ->
  if Val1 =:= top ->
      top;
     Val1 =:= bottom ->
      bottom;
     is_integer(Val1) ->
      case Op of
	tag ->
	  hipe_tagscheme:mk_fixnum(Val1);
	untag ->
	  hipe_tagscheme:fixnum_val(Val1)
      end
  end.	

%%-----------------------------------------------------------------------------
%% Procedure : visit_alu/2
%% Purpose   : do symbolic exection of a alu
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : { FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_alu(Inst, Env) ->
  Val1 = lookup_lattice_value(hipe_rtl:alu_src1(Inst), Env),
  Val2 = lookup_lattice_value(hipe_rtl:alu_src2(Inst), Env),
  {NewVal, _, _, _, _} = evaluate_alu(Val1, hipe_rtl:alu_op(Inst), Val2),
  set_to(hipe_rtl:alu_dst(Inst), NewVal, Env).

%% Here follows the alu-evaluation stuff. This is the most involved part I
%% guess. The function that you may want to use is evaluate_alu/3. The 
%% evaluation functions returns 
%%  { Result, SignFlag, ZeroFlag, Overflow flag, CarryBit}
%% it uses some helpers which are explained breifly:
%% lattice_meet/2 - handles the general case of most alu-operations, called 
%%                  when at least one of the operands is nonconstant, and the
%%                  operation-specifics have been taken care of.
%% all_ones/0     - returns the value of a rtl-word set to all 1 bits.
%% partial_eval_alu - tries to catch some operation specific special cases 
%%                    when one (or both) of the operands is nonconstant.

lattice_meet(Val1, Val2) ->
  M = if (Val1 =:= top) or (Val2 =:= top) -> top;
         (Val1 =:= bottom) or (Val2 =:= bottom) -> bottom
	 % the check is realy just sanity
      end,
  {M, M, M, M, M}.

all_ones() ->
  (1 bsl ?bytes_to_bits(hipe_rtl_arch:word_size())) - 1.

%% when calling partial_eval*() we know that at least one of the Values 
%% are bottom or top. They return { Value, Sign, Zero, Overflow, Carry }. 
%% (just like hipe_rtl_arch:eval_alu)

%% logic shifts are very similar each other. Limit is the number of
%% bits in the words.
partial_eval_shift(Limit, Val1, Val2) ->
  if 
    Val2 =:= 0 -> {Val1, Val1, Val1, Val1, Val1};
    Val1 =:= 0 -> {0, false, true, false, false};
    is_integer(Val2), Val2 >= Limit -> % (Val2 =/= top) and (Val2 =/= bottom)
      {0, false, true, Val1, Val1}; % OVerflow & carry we dont know about.
    true -> lattice_meet(Val1, Val2)
  end.

%%-----------------------------------------------------------------------------
%% Procedure : partial_eval_alu/3
%% Purpose   : try to evaluate as much as possible an alu operation where at 
%%             least one of the operands is not constant.
%% Arguments : Val1, Val2 - operands (integer, top or bottom)
%%             Op  - the operation.
%% Returns   : {Result, Sign, Zero, Overflow, Carry}
%%              where Result is an integer, 'top' or 'bottom'
%%              and the others are bool, 'top' or 'bottom'.
%%-----------------------------------------------------------------------------

partial_eval_alu(Val1, add, Val2) ->
  if 
    (Val1 == 0) -> {Val2,  Val2, Val2, false, false};
    (Val2 == 0) -> {Val1,  Val1, Val1, false, false};
    true -> lattice_meet(Val1, Val2)
  end;
partial_eval_alu(Val1, sub, Val2) ->
  if 
    (Val2 == 0) -> {Val1,  Val1, Val1, false, false};
    true -> lattice_meet(Val1, Val2)
  end;
partial_eval_alu(Val1, 'or', Val2) ->
  All_ones = all_ones(),
  if 
    (Val1 == 0) -> {Val2,  Val2, Val2, false, false};
    (Val2 == 0) -> {Val1,  Val1, Val1, false, false};
    (Val1 == All_ones) or (Val2 == All_ones) -> 
      {All_ones,  true, false, false, false};
    true -> lattice_meet(Val1, Val2)
  end;
partial_eval_alu(Val1, 'and', Val2) ->
  All_ones = all_ones(),
  if 
    Val1 == All_ones -> {Val2,  Val2, Val2, false, false};
    Val2 == All_ones -> {Val1,  Val1, Val1, false, false};
    (Val1 == 0) or (Val2 == 0) -> {0,  false, true, false, false};
    true -> lattice_meet(Val1, Val2)
  end;
partial_eval_alu(Val1, 'xor', Val2) ->
  if
    (Val1 == 0) -> {Val2,  Val2, Val2, false, false};
    (Val2 == 0) -> {Val1,  Val1, Val1, false, false};
    true -> lattice_meet(Val1, Val2)
  end;
partial_eval_alu(Val1, 'xornot', Val2) ->
  All_ones = all_ones(),
  if
    Val1 == All_ones -> {Val2,  Val2, Val2, false, false};
    Val2 == All_ones -> {Val1,  Val1, Val1, false, false};
    true -> lattice_meet(Val1, Val2)
  end;
partial_eval_alu(Val1, andnot, Val2) ->
  All_ones = all_ones(),
  if 
    (Val2 == 0) -> {Val1,  Val1, Val1, false, false};
    (Val1 == 0) or (Val2 == All_ones) -> {0,  false, true, false, false};
    true -> lattice_meet(Val1, Val2)
  end;
partial_eval_alu(Val1, Op, Val2) when (Op =:= 'sll') or (Op =:= 'srl') ->
  BitSize = ?bytes_to_bits(hipe_rtl_arch:word_size()),
  partial_eval_shift(BitSize, Val1, Val2);
partial_eval_alu(Val1, Op, Val2) when (Op =:= 'sllx') or (Op =:= 'srlx') ->
  partial_eval_shift(64, Val1, Val2);
partial_eval_alu(Val1, mul, Val2) -> lattice_meet(Val1, Val2); % XXX: suboptimal

% arithmetic shifts are more tricky, shifting something unknown can
% generate all_ones() and 0 depenging on the sign of Val1.
partial_eval_alu(Val1, Op, Val2) when (Op =:= 'sra') or (Op =:= 'srax') ->
  if 
    (Val2 == 0) -> {Val1,  Val1, Val1, false, false};
    (Val1 == 0) -> {0, false, true, false, false};
    true -> lattice_meet(Val1, Val2)
  end.

%%-----------------------------------------------------------------------------
%% Procedure : evaluate_alu/3 
%% Purpose   : try to evaluate as much as possible of a alu operation.
%% Arguments : Val1, Val2 - operands (an integer, 'top' or 'bottom')
%%             Op - the operation.
%% Returns   : {Result, Sign, Zero, Overflow, Carry}
%%              where result is an integer, 'top' or 'bottom'
%%              and the others are Bool, 'top' or 'bottom'.
%%-----------------------------------------------------------------------------

evaluate_alu(Val1, Op, Val2) ->
  if 
    (Val1 =:= top) or (Val2 =:= top) or 
    (Val1 =:= bottom) or (Val2 =:= bottom) -> partial_eval_alu(Val1, Op, Val2);
    true ->
      case Op of
        sllx -> hipe_rtl_arith_64:eval_alu('sll', Val1, Val2);
        srlx -> hipe_rtl_arith_64:eval_alu('srl', Val1, Val2); 
        srax -> hipe_rtl_arith_64:eval_alu('sra', Val1, Val2);
        _    -> hipe_rtl_arch:eval_alu(Op, Val1, Val2)
      end
  end.

maybe_top_or_bottom(List) ->
  maybe_top_or_bottom(List, false).

maybe_top_or_bottom([],          TB) -> TB;
maybe_top_or_bottom([top | Rest], _) -> maybe_top_or_bottom(Rest, top);
maybe_top_or_bottom([bottom | _], _) -> bottom;
maybe_top_or_bottom([_ | Rest],  TB) -> maybe_top_or_bottom(Rest, TB).

-spec partial_eval_branch(hipe_rtl:alub_cond(), bool_lattice(), bool_lattice(),
			  bool_lattice() | 0, bool_lattice() | 0) ->
	 bool_lattice().
partial_eval_branch(Cond, N0, Z0, V0, C0) ->
  {N, Z, V, C} =
    if Cond =:= 'eq';
       Cond =:= 'ne'           -> {true, Z0,   true, true};
       Cond =:= 'gt';
       Cond =:= 'le'           -> {N0,   Z0,   V0,   true};
       Cond =:= 'gtu'          -> {true, Z0,   true, C0  };
       Cond =:= 'lt';
       Cond =:= 'ge'           -> {N0,   true, V0,   true};
       Cond =:= 'geu';
       Cond =:= 'ltu'          -> {true, true, true, C0  };
       Cond =:= 'overflow';
       Cond =:= 'not_overflow' -> {true, true, V0,   true}
    end,
  case maybe_top_or_bottom([N, Z, V, C]) of
    false  -> hipe_rtl_arch:eval_cond_bits(Cond, N, Z, V, C);
    top    -> top;
    bottom -> bottom
  end.

%%-----------------------------------------------------------------------------
%% Procedure : visit_alub/2
%% Purpose   : do symbolic exection of a alub instruction
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : { FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_alub(Inst, Env) ->
  Val1 = lookup_lattice_value(hipe_rtl:alub_src1(Inst), Env),
  Val2 = lookup_lattice_value(hipe_rtl:alub_src2(Inst), Env),
  {NewVal, N, Z, C, V} = evaluate_alu(Val1, hipe_rtl:alub_op(Inst), Val2),
  Labels = 
    case NewVal of
      bottom -> [hipe_rtl:alub_true_label(Inst), 
                 hipe_rtl:alub_false_label(Inst)];
      top    -> [];
      _      ->
        %% if the partial branch cannot be evaluated we must execute the
        %% instruction at runtime.
        case partial_eval_branch(hipe_rtl:alub_cond(Inst), N, Z, C, V) of
          bottom -> [hipe_rtl:alub_true_label(Inst), 
                     hipe_rtl:alub_false_label(Inst)];
          top    -> [];
          true   -> [hipe_rtl:alub_true_label(Inst)];
          false  -> [hipe_rtl:alub_false_label(Inst)]
        end
     end,
  {[], NewSSA, NewEnv} = set_to(hipe_rtl:alub_dst(Inst), NewVal,  Env),
  {Labels, NewSSA, NewEnv}.
      
%%-----------------------------------------------------------------------------
%% Procedure : visit_fixnumop/2
%% Purpose   : do symbolic exection of a fixnumop instruction.
%%             fixnumop is like a specialized alu.
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : { FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_fixnumop(Inst, Env) ->
  Val = lookup_lattice_value(hipe_rtl:fixnumop_src(Inst), Env),
  Res = evaluate_fixnumop(Val, hipe_rtl:fixnumop_type(Inst)),
  set_to(hipe_rtl:fixnumop_dst(Inst), Res, Env).

%%-----------------------------------------------------------------------------
%% Procedure : visit_f*
%% Purpose   : Do symbolic execution of floating point instructions.
%%             All floating-point hitngs are mapped to bottom. In order to 
%%             implement them we would have to add hipe_rtl_arch:eval_f* 
%%             instructions since floating point is no exact science.
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_fconv(Inst, Env) ->
  set_to(hipe_rtl:fconv_dst(Inst), bottom, Env).

visit_fp(Inst, Env) ->
  set_to(hipe_rtl:fp_dst(Inst), bottom, Env).

visit_fp_unop(Inst, Env) ->
  set_to(hipe_rtl:fp_unop_dst(Inst), bottom, Env).

visit_fload(Inst, Env) ->
  set_to(hipe_rtl:fload_dst(Inst), bottom, Env).

visit_fmove(Inst, Env) ->
  set_to(hipe_rtl:fmove_dst(Inst), bottom, Env).

%%-----------------------------------------------------------------------------
%% Procedure : visit_move/2
%% Purpose   : execute a register-copy
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_move(Inst, Env) ->
  Src = hipe_rtl:move_src(Inst),
  Dst = hipe_rtl:move_dst(Inst),
  set_to(Dst, lookup_lattice_value(Src, Env), Env).

%%-----------------------------------------------------------------------------
%% Procedure : visit_goto/2
%% Purpose   : execute a goto
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_goto(Instruction, Environment) ->
  GotoLabel = hipe_rtl:goto_label(Instruction),
  {[GotoLabel], [], Environment}.

%%-----------------------------------------------------------------------------
%% Procedure : visit_goto_index/2
%% Purpose   : execute a goto_index
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_goto_index(Inst, Env) ->
  Index = hipe_rtl:goto_index_index(Inst),
  case lookup_lattice_value(Index, Env) of 
    top    ->   { [], [], Env };
    bottom -> %% everything is reachable
      { hipe_rtl:goto_index_labels(Inst), [], Env };
    I   -> %% only the ith label will be taken.
      io:format("hipe_rtl_ssa_const_prop foud goto-index with constant index ~w in ~w\n",
                [I, Inst]),      
      { [ lists:nth(hipe_rtl:goto_index_labels(Inst), I) ], [], Env }
  end.

%%-----------------------------------------------------------------------------
%% Procedure : visit_load/2
%% Purpose   : do a visit_load. Its hard to track whats in memory, and it's 
%%             not in ssa form, so let's assume bottom-values !
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_load(Inst, Env) ->
  set_to(hipe_rtl:load_dst(Inst), bottom, Env).

%%-----------------------------------------------------------------------------
%% Procedure : visit_load_address/2
%% Purpose   : execute a load_address instruction, while there might be things 
%%             here that are runtime-constant they are not compile-time
%%             constant since code loading interferes with addresses.
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_load_address(Inst, Env) ->
  Dst = hipe_rtl:load_address_dst(Inst),
  Val = bottom, %% all these are probably run-time, but not
                %% compile-time constants
  set_to(Dst, Val, Env).

%%-----------------------------------------------------------------------------
%% Procedure : visit_load_atom/2
%% Purpose   : Like loadadress this one gets something that is not 
%%             compiletime-constant
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_load_atom(Inst, Env) ->
  set_to(hipe_rtl:load_atom_dst(Inst), bottom, Env).
  
%%-----------------------------------------------------------------------------
%% Procedure : visit_load_word_index/2
%% Purpose   : execute a load_word_index. Here is probably room for 
%%             improvement, we should be able to find some constants here, 
%%             since we can get the labeled values from the environment, and 
%%             then find the value with the given index.
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_load_word_index(Inst, Env) ->
  io:format(" this is load word index: ~w\n", [Inst]),
  set_to(hipe_rtl:load_word_index_dst(Inst), bottom, Env).

%%-----------------------------------------------------------------------------
%% Procedure : visit_multimove/2 & visit_multimove/4
%% Purpose   : execute a multimove instruction. 
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_multimove([Dst | Dsts], [Val | Vals], MyEnv, MySSA) ->
  {NewEnv, NewSSA} = update_lattice_value({Dst, Val}, MyEnv),
  visit_multimove(Dsts, Vals, NewEnv, MySSA ++ NewSSA);
visit_multimove([], [], MyEnv, MySSA) ->
  {MyEnv, MySSA}.

visit_multimove(Inst, Env) ->
  Srcs = [lookup_lattice_value(S, Env) || 
	   S <- hipe_rtl:multimove_srclist(Inst)],
  {NewEnv, NewSSA} = visit_multimove(hipe_rtl:multimove_dstlist(Inst),
				     Srcs, Env, []),
  {[], NewSSA, NewEnv}.
  
%%-----------------------------------------------------------------------------
%% Procedure : visit_call/2
%% Purpose   : execute a call-instruction. All calls return bottom. We make 
%%             this assumption since the icode-leel have taken care of BIF's
%%             and we belive that we are left with the things that can not be
%%             done att compile time.
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

visit_call(Inst, Env) ->
  {Env1, SSAWork} =
    update_lattice_value({hipe_rtl:call_dstlist(Inst), bottom}, Env),
    % remeber to add both continuation & failto things to the cfgwl
  Cont = case hipe_rtl:call_continuation(Inst) of
	   [] -> [];
	   C  -> [C]
         end,
  Succ = case hipe_rtl:call_fail(Inst) of
	   [] -> Cont;
	   Fail -> [Fail | Cont]
         end,
  {Succ, SSAWork, Env1}.

%%-----------------------------------------------------------------------------
%% Procedure : visit_switch/2
%% Purpose   : execute a switch-statement. 
%% Arguments : Inst - The instruction
%%             Env  - The environment
%% Returns   : {FlowWorkList, SSAWorkList, NewEnvironment}
%%-----------------------------------------------------------------------------

%% first two helpers that are used to handle the mapping from value to label.
%% why isn't there a function that does this ?

find_switch_label(Inst, Val) ->
  Labels = hipe_rtl:switch_labels(Inst),
  ?SCCPDBG(io:format("finding switch_label, ~w in ~w\n", [Val,Inst])),
  %% it seems like the index is zero based. nth uses 1-based indexing.
  lists:nth(Val + 1, Labels).

%% Switches seem tricky. the sort-order is a list of key-values to be
%% tested in order. (if elem i matches then we should jump to elem i of
%% the labels-list)
visit_switch(Inst, Env) ->
  case lookup_lattice_value(hipe_rtl:switch_src(Inst), Env) of
    top ->
      {[], [], Env};
    bottom ->
      {hipe_rtl:switch_labels(Inst), [], Env};
    Val ->
      {[find_switch_label(Inst, Val) ], [], Env}
  end.

%%-----------------------------------------------------------------------------
%% Procedure : update_instruction/2
%% Purpose   : update the given instruction using any information found in 
%%             the environment.
%% Arguments : Inst - the instruction
%%             Environment - in which everything happens.
%% Returns   : list of new instructions.
%%-----------------------------------------------------------------------------

%% idea: what to do with vi <- Constant. wouldn't it be possible to
%% remove those ? (and similarily for alu-instructions. and alub
%% instructions also ! (of course this will be done in some later step dead
%%  code elimination ? but it's a simple check.)
update_instruction(Inst, Env) ->
  case Inst of 
    #alu{} ->
      update_alu(Inst, Env);
    #alub{} ->
      update_alub(Inst, Env);
    #branch{} ->
      update_branch(Inst, Env);
    #call{} ->
      subst_all_uses(Inst, Env);
%%    #comment{} ->
%%      [Inst];
    #enter{} ->
      subst_all_uses(Inst, Env);
    #fconv{} ->
      subst_all_uses(Inst, Env);
    #fload{} ->
      subst_all_uses(Inst, Env);
    #fmove{} ->
      subst_all_uses(Inst, Env);
    #fp{} ->
      subst_all_uses(Inst, Env);
    #fp_unop{} ->
      subst_all_uses(Inst, Env);
    #fstore{} ->
      subst_all_uses(Inst, Env);
    #gctest{} ->
      subst_all_uses(Inst, Env);
%%    #goto{} ->
%%       [ Inst ];
    #goto_index{} ->
      update_goto_index(Inst, Env);
%%    #label{} ->
%%      [ Inst ];
    #load{} ->
      subst_all_uses(Inst, Env);
    #load_address{} ->
      subst_all_uses(Inst, Env);
    #load_atom{} ->
      subst_all_uses(Inst, Env);
    #load_word_index{} ->
      subst_all_uses(Inst, Env);
    #move{} ->
      subst_all_uses(Inst, Env);
    #multimove{} ->
      subst_all_uses(Inst, Env);
    #return{} ->
      subst_all_uses(Inst, Env);
    #store{} ->
      subst_all_uses(Inst, Env);
    #switch{} ->
      update_switch(Inst, Env);
    #phi{} ->
      update_phi(Inst, Env);
    _ ->  % for the others it's sufficient to just update any thing they use.
      [ Inst ]
  end.

%%-----------------------------------------------------------------------------
%% Procedure : subst_uses/2
%% Purpose   : looks up all things that an instruction uses and replaces
%%             anything that is determined to be constant.
%% Arguments : Inst - the instruction
%%             Env - in which everything happen.
%% Returns   : list of instructions to replace Inst with.
%%-----------------------------------------------------------------------------

subst_all_uses(Inst, Env) ->
  Uses = hipe_rtl_ssa:uses_to_rename(Inst),
  [ hipe_rtl:subst_uses(update_srcs(Uses, Env), Inst) ].

%%-----------------------------------------------------------------------------
%% Procedure : update_srcs/2
%% Purpose   : given the things that a instruction use return a list 
%%             {Src, NewValue} pairs that can be sent to subs_uses.
%% Arguments : Srcs - list of uses
%%             Env - in which everything happens.
%% Returns   : list of {Src, NewValue} pairs.
%%-----------------------------------------------------------------------------

update_srcs(Srcs, Env) ->
  Update = 
    fun(Src, Os) ->
      case lookup_lattice_value(Src, Env) of 
        bottom -> Os;
        top -> % this would be realy strange.
          ?EXIT({"update_src, top", Src });
        Constant ->
          [ {Src, hipe_rtl:mk_imm(Constant)} | Os]
      end
    end,
  lists:foldl(Update, [], Srcs ).
  
%%-----------------------------------------------------------------------------
%% functions for performing partial evaluation of alu-operations. They can 
%% return either an integer (the actual result), move_src1 or move_src2 in 
%% which case the alu-operation can be replace with a move, or keep_it in 
%% which case the instruction must be kept.

%%-----------------------------------------------------------------------------
%% Procedure : partial_update_shift/3
%% Purpose   : perform a shift
%% Arguments : Limit - the number of bits in the word to shift.
%%             Val1 - the shiftee
%%             Val2 - number of bits to shift
%% Returns   : Integer, move_src1, keep_it
%%-----------------------------------------------------------------------------

partial_update_shift(Limit, Val1, Val2) ->
  if
    (Val1 =:= bottom) and (Val2 =:= 0) -> move_src1;
    (Val1 =:= 0) or ((Val2 =/= bottom) and (Val2 >= Limit)) -> 0;
    true -> keep_it
  end.

%%-----------------------------------------------------------------------------
%% Procedure : partial_update_alu/3
%% Purpose   : perform as much of alu-operations where exatcly one of the
%%             operands is bottom.
%% Arguments : Val1, Val2 - operands
%%             Op - the operation.
%% Returns   : Integer, move_src1, move_src2, keep_it
%%-----------------------------------------------------------------------------

%% we know that exactly one of the operands are bottom this one
%% returns what to do with the instruction (it's either replace with
%% src1, replace src2 replace with constant or keep it.

partial_update_alu(Val1, 'add', Val2) ->
  if
    (Val1 == 0) -> move_src2;
    (Val2 == 0) -> move_src1;
    true -> keep_it
  end;
partial_update_alu(_Val1, 'sub', Val2) ->
  if
    (Val2 == 0) -> move_src1;
    true -> keep_it
  end;
partial_update_alu(Val1, 'or', Val2) ->
  All_ones = all_ones(),
  if 
    (Val1 == 0) -> move_src2;
    (Val2 == 0) -> move_src1;
    (Val1 == All_ones) or (Val2 == All_ones) -> All_ones;
    true -> keep_it
  end;
partial_update_alu(Val1, 'and', Val2) ->
  All_ones = all_ones(),
  if 
    Val1 == All_ones -> move_src2;
    Val2 == All_ones -> move_src1;
    (Val1 == 0) or (Val2 == 0) -> 0;
    true -> keep_it
  end;
partial_update_alu(Val1, 'xor', Val2) ->
  if 
    (Val1 == 0) -> move_src2;
    (Val2 == 0) -> move_src1;
    true -> keep_it
  end;
partial_update_alu(Val1, 'xornot', Val2) ->
  All_ones = all_ones(),
  if 
    (Val1 == All_ones) -> move_src2;
    (Val2 == All_ones) -> move_src1;
    true -> keep_it
  end;
partial_update_alu(Val1, andnot, Val2) ->
  All_ones = all_ones(),
  if 
    Val2 == 0 -> move_src1;
    (Val1 == 0) or (Val2 == All_ones) -> 0;
    true -> keep_it
  end;
partial_update_alu(Val1, Op, Val2) when (Op =:= 'sll') or (Op =:= 'srl') ->
  BitSize = ?bytes_to_bits(hipe_rtl_arch:word_size()),
  partial_update_shift(BitSize, Val1, Val2);
partial_update_alu(Val1, Op, Val2) when (Op =:= 'sllx') or (Op =:= 'srlx') ->
  partial_update_shift(64, Val1, Val2);
partial_update_alu(Val1, Op, Val2) when (Op =:= 'sra') or (Op =:= 'srax') ->
  if 
    Val2 == 0 -> move_src1;
    Val1 == 0 -> 0;
    true -> keep_it
  end.

%%-----------------------------------------------------------------------------
%% Procedure : update_alu/2
%% Purpose   : update an alu-instruction.
%% Arguments : Inst - the instruction.
%%             Env - in which everything happens.
%% Returns   : list of new instruction
%%-----------------------------------------------------------------------------

update_alu(Inst, Env) ->
  Val1 = lookup_lattice_value(hipe_rtl:alu_src1(Inst), Env),
  Val2 = lookup_lattice_value(hipe_rtl:alu_src2(Inst), Env),
  if 
    (Val1 =:= bottom) and (Val2 =:= bottom) ->
      [Inst];
    (Val1 =:= bottom) or (Val2 =:= bottom) ->
      NewInst =
	case partial_update_alu(Val1, hipe_rtl:alu_op(Inst), Val2) of
          move_src1 -> 
            hipe_rtl:mk_move(hipe_rtl:alu_dst(Inst), hipe_rtl:alu_src1(Inst));
          move_src2 ->
            hipe_rtl:mk_move(hipe_rtl:alu_dst(Inst), hipe_rtl:alu_src2(Inst));
          keep_it ->
            S1 = make_alub_subst_list(Val1, hipe_rtl:alu_src1(Inst), []),
            S2 = make_alub_subst_list(Val2, hipe_rtl:alu_src2(Inst), S1),
            hipe_rtl:subst_uses(S2, Inst);
          Constant ->
            hipe_rtl:mk_move(hipe_rtl:alu_dst(Inst), hipe_rtl:mk_imm(Constant))
        end,
      [NewInst];
    true ->
      {Val,_,_,_,_} = evaluate_alu(Val1, hipe_rtl:alu_op(Inst), Val2),
      [hipe_rtl:mk_move(hipe_rtl:alu_dst(Inst), hipe_rtl:mk_imm(Val))]
  end.
 
%%-----------------------------------------------------------------------------
%% Procedure : update_branch/2
%% Purpose   : update an branch-instruction
%% Arguments : Inst - the instruction.
%%             Env - in which everything happens.
%% Returns   : list of new instruction
%%-----------------------------------------------------------------------------

update_branch(Inst, Env) ->
  Src1 = hipe_rtl:branch_src1(Inst),
  Src2 = hipe_rtl:branch_src2(Inst),
  Val1 = lookup_lattice_value(Src1, Env),
  Val2 = lookup_lattice_value(Src2, Env),
  if
    (Val1 =:= bottom) and (Val2 =:= bottom) ->
      [Inst];
    Val1 =:= bottom ->
      [hipe_rtl:subst_uses([{Src2, hipe_rtl:mk_imm(Val2)}], Inst)];
    Val2 =:= bottom -> 
      [hipe_rtl:subst_uses([{Src1, hipe_rtl:mk_imm(Val1)}], Inst)];
    true ->
      case hipe_rtl_arch:eval_cond(hipe_rtl:branch_cond(Inst), Val1, Val2) of
        true  -> [hipe_rtl:mk_goto(hipe_rtl:branch_true_label(Inst))];
        false -> [hipe_rtl:mk_goto(hipe_rtl:branch_false_label(Inst))]
      end
  end.

%%-----------------------------------------------------------------------------
%% Procedure : update_alub/2
%% Purpose   : update an alub-instruction. Here are some finer points, we might
%%             be able to do the math (think b = a+0), but it's hard to replace
%%             the branch, since the mapping b/w AluOp,RelOp to BranchInstr is
%%             boring to do. (lazyness is a bliss).
%% Arguments : Inst - the instruction.
%%             Env - in which everything happens.
%% Returns   : list of new instructions
%%-----------------------------------------------------------------------------

%% some small helpers.
alub_to_move(Inst, Res, Lab) ->
  [hipe_rtl:mk_move(hipe_rtl:alub_dst(Inst), Res),
   hipe_rtl:mk_goto(Lab)].

make_alub_subst_list(bottom, _, Tail) ->  Tail;
make_alub_subst_list(top, Src, _) ->
  ?EXIT({"~w is top during update",Src });
make_alub_subst_list(Val, Src, Tail)  -> 
  case hipe_rtl:is_imm(Src) of
    true -> Tail;
    false -> [{Src, hipe_rtl:mk_imm(Val)} | Tail]
  end.

update_alub(Inst, Env) ->
  Src1 = hipe_rtl:alub_src1(Inst),
  Src2 = hipe_rtl:alub_src2(Inst),
  Val1 = lookup_lattice_value(Src1, Env),
  Val2 = lookup_lattice_value(Src2, Env),
  {ResVal, N, Z, C, V}  = evaluate_alu(Val1, hipe_rtl:alub_op(Inst), Val2),  
  CondRes = partial_eval_branch(hipe_rtl:alub_cond(Inst), N, Z, C, V),
  case CondRes of
    bottom -> 
      %% if we can't evaluate the branch, we have to keep it as a alub isnt
      %% since other optimizations might insert other instructions b/w the 
      %% move and the branch. We can however replace variable with constants:
      S1 = make_alub_subst_list(Val1, Src1, []),
      S2 = make_alub_subst_list(Val2, Src2, S1),
      [hipe_rtl:subst_uses(S2, Inst)];
    _ -> %% we know where we will be going, let's find out what Dst should be.
         %% knowing where we are going means that at most one of the values is
         %% bottom, hence we can replace the alu-instr with a move.
         %% remember, a = b + 0 can give us enough info to know what jump to
         %% do without knowing the value of a. (I wonder if this will ever
         %% actualy happen ;)
      Res = case ResVal of 
              bottom ->  % something nonconstant.
                if (Val1 =:= bottom) -> Src1;
	           (Val2 =:= bottom) -> Src2 
                end;
              _ -> hipe_rtl:mk_imm(ResVal)
            end,
      case CondRes of 
        top ->
	  io:format("oops. something VERY bad: ~w ~w V1 & 2 ~w ~w\n",
		    [Inst, {ResVal, N, Z, C, V} , Val1, Val2]),
	  [Inst];
        true  -> alub_to_move(Inst, Res, hipe_rtl:alub_true_label(Inst));
        false -> alub_to_move(Inst, Res, hipe_rtl:alub_false_label(Inst))
      end
  end.

%%-----------------------------------------------------------------------------
%% Procedure : update_goto_index/2
%% Purpose   : update a goto_index instruction.
%% Arguments : Inst - the instruction.
%%             Env  - in which everything happens.
%% Returns   : list of new instructions.
%%-----------------------------------------------------------------------------

update_goto_index(Inst, Env) ->
  Index = hipe_rtl:goto_index_index(Inst),
  case lookup_lattice_value(Index, Env) of 
    bottom -> %% everything is reachable
      [Inst];
    I -> %% only the ith label will be taken.
      [hipe_rtl:mk_goto(lists:nth(hipe_rtl:goto_index_labels(Inst), I))]
  end.

%%-----------------------------------------------------------------------------
%% Procedure : update_switch/2
%% Purpose   : update a switch instruction.
%% Arguments : Inst - the instruction.
%%             Env - in which everything happens.
%% Returns   : list of new instructions.
%%-----------------------------------------------------------------------------

update_switch(Inst, Env) ->
  case lookup_lattice_value(hipe_rtl:switch_src(Inst), Env) of
    bottom ->
      [Inst];
    Const ->
      Lab = find_switch_label(Inst, Const),
      [hipe_rtl:mk_goto(Lab)]
  end.

%%-----------------------------------------------------------------------------
%% Procedure : update_phi/3
%% Purpose   : Update a phi-function w.r.t. constants. do nothing for now.
%% Arguments : Instruction - The instruction
%%             Environment - The environment
%% Returns   : [NewInstruction]
%%-----------------------------------------------------------------------------

update_phi(Instruction, Environment) ->
  Destination = hipe_rtl:phi_dst(Instruction),
  case lookup_lattice_value(Destination, Environment) of
    bottom -> 
      [Instruction];
    top -> 
      ?WARNING_MSG("The dst of ~w is top after SCCP. Strange\n",[Instruction]),
      ?EXIT({"bang !", Instruction}),
      [Instruction];
    Value ->
      [hipe_rtl:mk_move(Destination, hipe_rtl:mk_imm(Value))]
  end.

%%-----------------------------------------------------------------------------

%% make sure that all precoloured registers are taken out of the equation.
lookup_lattice_value(X, Environment) ->
  case hipe_rtl_arch:is_precoloured(X) or hipe_rtl:is_const_label(X) of 
    true ->
      bottom;
    false ->
      lookup_lattice_value2(X, Environment)
  end.

lookup_lattice_value2(X, Environment) ->
  LatticeValues = env__lattice_values(Environment),
  case hipe_rtl:is_imm(X) of
    true ->
      hipe_rtl:imm_value(X);
    false ->
      case gb_trees:lookup(X, LatticeValues) of
        none ->
	  io:format("~w~n",[LatticeValues]),
          ?WARNING_MSG("Earlier compiler steps generated erroneous " 
                       "code for X = ~w. We are ignoring this.\n",[X]),
          bottom;
        {value, top} ->
          ?EXIT({"lookup_lattice_value, top", X}),
          top;
        {value, Y} ->
          Y
      end
  end.

%%----------------------------- End of file -----------------------------------