Don't run unsafe compiler passes

As a preparation for replacing v3_codegen with a new code generator,
remove unsafe optimization passes. Especially the older compiler
passes have implicit assumptions about how the code is generated.

Remove the optimizations in beam_block (keep the code that creates
blocks) because they are unsafe. beam_block also calls
beam_utils:live_opt/1, which is unsafe.

Remove beam_type because it calls beam_utils:live_opt/1, and also
because it recalculates the number of heaps words and number of live
registers in allocation instructions, thus potentially hiding bugs in
other passes.

Remove beam_receive because it is unsafe.

Remove beam_record because it is the only remaining user
of beam_utils:anno_defs/1.

Remove beam_reorder because it makes much more sense to run it
as an early SSA-based optimization pass.

Remove the now unused functions in beam_utils:

    anno_def/1
    delete_annos/1
    is_killed_block/2
    live_opt/1
    usage/3

Note that the following test cases will fail because of the
removed optimizations:

    compile_SUITE:optimized_guards/1
    compile_SUITE:bc_options/1
    receive_SUITE:ref_opt/1

1 files changed, 6 insertions, 568 deletions

diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl
index fe43163455..3e28ff2c01 100644
--- a/lib/compiler/src/beam_block.erl
+++ b/lib/compiler/src/beam_block.erl
@@ -23,31 +23,20 @@
 -module(beam_block).
 
 -export([module/2]).
--import(lists, [reverse/1,reverse/2,member/2]).
+-import(lists, [reverse/1]).
 
 -spec module(beam_utils:module_code(), [compile:option()]) ->
                     {'ok',beam_utils:module_code()}.
 
-module({Mod,Exp,Attr,Fs0,Lc}, Opts) ->
-    Blockify = not member(no_blockify, Opts),
-    Fs = [function(F, Blockify) || F <- Fs0],
+module({Mod,Exp,Attr,Fs0,Lc}, _Opts) ->
+    Fs = [function(F) || F <- Fs0],
     {ok,{Mod,Exp,Attr,Fs,Lc}}.
 
-function({function,Name,Arity,CLabel,Is0}, Blockify) ->
+function({function,Name,Arity,CLabel,Is0}) ->
     try
 	%% Collect basic blocks and optimize them.
-        Is1 = case Blockify of
-                  false -> Is0;
-                  true -> blockify(Is0)
-              end,
-        Is2 = embed_lines(Is1),
-        Is3 = local_cse(Is2),
-        Is4 = beam_utils:anno_defs(Is3),
-        Is5 = move_allocates(Is4),
-        Is6 = beam_utils:live_opt(Is5),
-        Is7 = opt_blocks(Is6),
-        Is8 = beam_utils:delete_annos(Is7),
-        Is = opt_allocs(Is8),
+        Is1 = blockify(Is0),
+        Is = embed_lines(Is1),
 
         %% Done.
         {function,Name,Arity,CLabel,Is}
@@ -137,557 +126,6 @@ embed_lines([{block,B2},{line,_}=Line,{block,B1}|T], Acc) ->
 embed_lines([{block,B1},{line,_}=Line|T], Acc) ->
     B = {block,[{set,[],[],Line}|B1]},
     embed_lines([B|T], Acc);
-embed_lines([{block,B2},{block,B1}|T], Acc) ->
-    %% This can only happen when beam_block is run for
-    %% the second time.
-    B = {block,B1++B2},
-    embed_lines([B|T], Acc);
 embed_lines([I|Is], Acc) ->
     embed_lines(Is, [I|Acc]);
 embed_lines([], Acc) -> Acc.
-
-opt_blocks([{block,Bl0}|Is]) ->
-    %% The live annotation at the beginning is not useful.
-    [{'%anno',_}|Bl] = Bl0,
-    [{block,opt_block(Bl)}|opt_blocks(Is)];
-opt_blocks([I|Is]) ->
-    [I|opt_blocks(Is)];
-opt_blocks([]) -> [].
-
-opt_block(Is0) ->
-    find_fixpoint(fun(Is) ->
-                          opt_tuple_element(opt(Is))
-                  end, Is0).
-
-find_fixpoint(OptFun, Is0) ->
-    case OptFun(Is0) of
-	Is0 -> Is0;
-	Is1 -> find_fixpoint(OptFun, Is1)
-    end.
-
-%% move_allocates(Is0) -> Is
-%%  Move allocate instructions upwards in the instruction stream
-%%  (within the same block), in the hope of getting more possibilities
-%%  for optimizing away moves later.
-%%
-%%  For example, we can transform the following instructions:
-%%
-%%     get_tuple_element x(1) Element => x(2)
-%%     allocate_zero StackSize 3    %% x(0), x(1), x(2) are live
-%%
-%%  to the following instructions:
-%%
-%%     allocate_zero StackSize 2    %% x(0) and x(1) are live
-%%     get_tuple_element x(1) Element => x(2)
-%%
-%%  NOTE: Since the beam_reorder pass has been run, it is no longer
-%%  safe to assume that if x(N) is initialized, then all lower-numbered
-%%  x registers are also initialized.
-%%
-%%  For example, we must be careful when transforming the following
-%%  instructions:
-%%
-%%     get_tuple_element x(0) Element => x(1)
-%%     allocate_zero StackSize 3    %x(0), x(1), x(2) are live
-%%
-%%  to the following instructions:
-%%
-%%     allocate_zero StackSize 3
-%%     get_tuple_element x(0) Element => x(1)
-%%
-%%  The transformation is safe if and only if x(1) has been
-%%  initialized previously.  We will use the annotations added by
-%%  beam_utils:anno_defs/1 to determine whether x(a) has been
-%%  initialized.
-
-move_allocates([{block,Bl0}|Is]) ->
-    Bl = move_allocates_1(reverse(Bl0), []),
-    [{block,Bl}|move_allocates(Is)];
-move_allocates([I|Is]) ->
-    [I|move_allocates(Is)];
-move_allocates([]) -> [].
-
-move_allocates_1([{'%anno',_}|Is], Acc) ->
-    move_allocates_1(Is, Acc);
-move_allocates_1([I|Is], [{set,[],[],{alloc,Live0,Info0}}|Acc]=Acc0) ->
-    case alloc_may_pass(I) of
-        false ->
-            move_allocates_1(Is, [I|Acc0]);
-        true ->
-            case alloc_live_regs(I, Is, Live0) of
-                not_possible ->
-                    move_allocates_1(Is, [I|Acc0]);
-                Live when is_integer(Live) ->
-                    Info = safe_info(Info0),
-                    A = {set,[],[],{alloc,Live,Info}},
-                    move_allocates_1(Is, [A,I|Acc])
-            end
-    end;
-move_allocates_1([I|Is], Acc) ->
-    move_allocates_1(Is, [I|Acc]);
-move_allocates_1([], Acc) -> Acc.
-
-alloc_may_pass({set,_,[{fr,_}],fmove}) -> false;
-alloc_may_pass({set,_,_,{alloc,_,_}}) -> false;
-alloc_may_pass({set,_,_,{set_tuple_element,_}}) -> false;
-alloc_may_pass({set,_,_,put_list}) -> false;
-alloc_may_pass({set,_,_,put}) -> false;
-alloc_may_pass({set,_,_,_}) -> true.
-
-safe_info({nozero,Stack,Heap,_}) ->
-    %% nozero is not safe if the allocation instruction is moved
-    %% upwards past an instruction that may throw an exception
-    %% (such as element/2).
-    {zero,Stack,Heap,[]};
-safe_info(Info) -> Info.
-
-%% opt([Instruction]) -> [Instruction]
-%%  Optimize the instruction stream inside a basic block.
-
-opt([{set,[X],[X],move}|Is]) -> opt(Is);
-opt([{set,[Dst],_,move},{set,[Dst],[Src],move}=I|Is]) when Dst =/= Src ->
-    opt([I|Is]);
-opt([{set,[{x,0}],[S1],move}=I1,{set,[D2],[{x,0}],move}|Is]) ->
-    opt([I1,{set,[D2],[S1],move}|Is]);
-opt([{set,[{x,0}],[S1],move}=I1,{set,[D2],[S2],move}|Is0]) when S1 =/= D2 ->
-    %% Place move S x0 at the end of move sequences so that
-    %% loader can merge with the following instruction
-    {Ds,Is} = opt_moves([D2], Is0),
-    [{set,Ds,[S2],move}|opt([I1|Is])];
-opt([{set,_,_,{line,_}}=Line1,
-     {set,[D1],[{integer,Idx1},Reg],{bif,element,{f,0}}}=I1,
-     {set,_,_,{line,_}}=Line2,
-     {set,[D2],[{integer,Idx2},Reg],{bif,element,{f,0}}}=I2|Is])
-  when Idx1 < Idx2, D1 =/= D2, D1 =/= Reg, D2 =/= Reg ->
-    opt([Line2,I2,Line1,I1|Is]);
-opt([{set,[D1],[{integer,Idx1},Reg],{bif,element,{f,L}}}=I1,
-     {set,[D2],[{integer,Idx2},Reg],{bif,element,{f,L}}}=I2|Is])
-  when Idx1 < Idx2, D1 =/= D2, D1 =/= Reg, D2 =/= Reg ->
-    opt([I2,I1|Is]);
-opt([{set,Hd0,Cons,get_hd}=GetHd,
-     {set,Tl0,Cons,get_tl}=GetTl|Is0]) ->
-    case {opt_moves(Hd0, [GetTl|Is0]),opt_moves(Tl0, [GetHd|Is0])} of
-        {{Hd0,Is},{Tl0,_}} ->
-            [GetHd|opt(Is)];
-        {{Hd,Is},{Tl0,_}} ->
-            [{set,Hd,Cons,get_hd}|opt(Is)];
-        {{_,_},{Tl,Is}} ->
-            [{set,Tl,Cons,get_tl}|opt(Is)]
-    end;
-opt([{set,Ds0,Ss,Op}|Is0]) ->
-    {Ds,Is} = opt_moves(Ds0, Is0),
-    [{set,Ds,Ss,Op}|opt(Is)];
-opt([{'%anno',_}=I|Is]) ->
-    [I|opt(Is)];
-opt([]) -> [].
-
-%% opt_moves([Dest], [Instruction]) -> {[Dest],[Instruction]}
-%%  For each Dest, does the optimization described in opt_move/2.
-
-opt_moves([], Is0) -> {[],Is0};
-opt_moves([D0]=Ds, Is0) ->
-    case opt_move(D0, Is0) of
-	not_possible -> {Ds,Is0};
-	{D1,Is} -> {[D1],Is}
-    end.
-
-%% opt_move(Dest, [Instruction]) -> {UpdatedDest,[Instruction]} | not_possible
-%%  If there is a {move,Dest,FinalDest} instruction
-%%  in the instruction stream, remove the move instruction
-%%  and let FinalDest be the destination.
-
-opt_move(Dest, Is) ->
-    opt_move_1(Dest, Is, []).
-
-opt_move_1(R, [{set,[D],[R],move}|Is0], Acc) ->
-    %% Provided that the source register is killed by instructions
-    %% that follow, the optimization is safe.
-    case eliminate_use_of_from_reg(Is0, R, D) of
-	{yes,Is} -> opt_move_rev(D, Acc, Is);
-	no -> not_possible
-    end;
-opt_move_1(_R, [{set,_,_,{alloc,_,_}}|_], _) ->
-    %% The optimization is either not possible or not safe.
-    %%
-    %% If R is an X register killed by allocation, the optimization is
-    %% not safe. On the other hand, if the X register is killed, there
-    %% will not follow a 'move' instruction with this X register as
-    %% the source.
-    %%
-    %% If R is a Y register, the optimization is still not safe
-    %% because the new target register is an X register that cannot
-    %% safely pass the alloc instruction.
-    not_possible;
-opt_move_1(R, [{set,_,_,_}=I|Is], Acc) ->
-    %% If the source register is either killed or used by this
-    %% instruction, the optimimization is not possible.
-    case is_killed_or_used(R, I) of
-	true -> not_possible;
-	false -> opt_move_1(R, Is, [I|Acc])
-    end;
-opt_move_1(_, _, _) ->
-    not_possible.
-
-%% opt_tuple_element([Instruction]) -> [Instruction]
-%%  If possible, move get_tuple_element instructions forward
-%%  in the instruction stream to a move instruction, eliminating
-%%  the move instruction. Example:
-%%
-%%    get_tuple_element Tuple Pos Dst1
-%%    ...
-%%    move Dst1 Dst2
-%%
-%%  This code may be possible to rewrite to:
-%%
-%%    %%(Moved get_tuple_element instruction)
-%%    ...
-%%    get_tuple_element Tuple Pos Dst2
-%%
-
-opt_tuple_element([{set,[D],[S],{get_tuple_element,_}}=I|Is0]) ->
-    case opt_tuple_element_1(Is0, I, {S,D}, []) of
-	no ->
-	    [I|opt_tuple_element(Is0)];
-	{yes,Is} ->
-	    opt_tuple_element(Is)
-    end;
-opt_tuple_element([I|Is]) ->
-    [I|opt_tuple_element(Is)];
-opt_tuple_element([]) -> [].
-
-opt_tuple_element_1([{set,_,_,{alloc,_,_}}|_], _, _, _) ->
-    no;
-opt_tuple_element_1([{set,_,_,{try_catch,_,_}}|_], _, _, _) ->
-    no;
-opt_tuple_element_1([{set,[D],[S],move}|Is0], I0, {_,S}, Acc) ->
-    case eliminate_use_of_from_reg(Is0, S, D) of
-	no ->
-	    no;
-	{yes,Is1} ->
-	    {set,[S],Ss,Op} = I0,
-	    I = {set,[D],Ss,Op},
-            case opt_move_rev(S, Acc, [I|Is1]) of
-                not_possible ->
-                    %% Not safe because the move of the
-                    %% get_tuple_element instruction would cause the
-                    %% result of a previous instruction to be ignored.
-                    no;
-                {_,Is} ->
-                    {yes,Is}
-            end
-    end;
-opt_tuple_element_1([{set,Ds,Ss,_}=I|Is], MovedI, {S,D}=Regs, Acc) ->
-    case member(S, Ds) orelse member(D, Ss) of
-	true ->
-	    no;
-	false ->
-	    opt_tuple_element_1(Is, MovedI, Regs, [I|Acc])
-    end;
-opt_tuple_element_1(_, _, _, _) -> no.
-
-%% Reverse the instructions, while checking that there are no
-%% instructions that would interfere with using the new destination
-%% register (D).
-
-opt_move_rev(D, [I|Is], Acc) ->
-    case is_killed_or_used(D, I) of
-	true -> not_possible;
-	false -> opt_move_rev(D, Is, [I|Acc])
-    end;
-opt_move_rev(D, [], Acc) -> {D,Acc}.
-
-%% is_killed_or_used(Register, {set,_,_,_}) -> bool()
-%%  Test whether the register is used by the instruction.
-
-is_killed_or_used(R, {set,Ss,Ds,_}) ->
-    member(R, Ds) orelse member(R, Ss).
-
-%% eliminate_use_of_from_reg([Instruction], FromRegister, ToRegister, Acc) ->
-%%       {yes,Is} | no
-%%  Eliminate any use of FromRegister in the instruction sequence
-%%  by replacing uses of FromRegister with ToRegister. If FromRegister
-%%  is referenced by an allocation instruction, return 'no' to indicate
-%%  that FromRegister is still used and that the optimization is not
-%%  possible.
-
-eliminate_use_of_from_reg(Is, From, To) ->
-    try
-        eliminate_use_of_from_reg(Is, From, To, [])
-    catch
-        throw:not_possible ->
-            no
-    end.
-
-eliminate_use_of_from_reg([{set,_,_,{alloc,Live,_}}|_]=Is0, {x,X}, _, Acc) ->
-    if
-	X < Live ->
-	    no;
-	true ->
-	    {yes,reverse(Acc, Is0)}
-    end;
-eliminate_use_of_from_reg([{set,Ds,Ss0,Op}=I0|Is], From, To, Acc) ->
-    ensure_safe_tuple(I0, To),
-    I = case member(From, Ss0) of
-            true ->
-                Ss = [case S of
-                          From -> To;
-                          _ -> S
-                      end || S <- Ss0],
-                {set,Ds,Ss,Op};
-            false ->
-                I0
-        end,
-    case member(From, Ds) of
-        true ->
-            {yes,reverse(Acc, [I|Is])};
-        false ->
-            case member(To, Ds) of
-                true ->
-                    case beam_utils:is_killed_block(From, Is) of
-                        true ->
-                            {yes,reverse(Acc, [I|Is])};
-                        false ->
-                            no
-                    end;
-                false ->
-                    eliminate_use_of_from_reg(Is, From, To, [I|Acc])
-            end
-    end;
-eliminate_use_of_from_reg([I]=Is, From, _To, Acc) ->
-    case beam_utils:is_killed_block(From, [I]) of
-	true ->
-	    {yes,reverse(Acc, Is)};
-	false ->
-	    no
-    end.
-
-ensure_safe_tuple({set,[To],[],{put_tuple,_}}, To) ->
-    throw(not_possible);
-ensure_safe_tuple(_, _) -> ok.
-
-%% opt_allocs(Instructions) -> Instructions.  Optimize allocate
-%%  instructions inside blocks. If safe, replace an allocate_zero
-%%  instruction with the slightly cheaper allocate instruction.
-
-opt_allocs(Is) ->
-    D = beam_utils:index_labels(Is),
-    opt_allocs_1(Is, D).
-
-opt_allocs_1([{block,Bl0}|Is], D) ->
-    Bl = opt_alloc(Bl0, {D,Is}),
-    [{block,Bl}|opt_allocs_1(Is, D)];
-opt_allocs_1([I|Is], D) ->
-    [I|opt_allocs_1(Is, D)];
-opt_allocs_1([], _) -> [].
-
-%% opt_alloc(Instructions) -> Instructions'
-%%  Optimises all allocate instructions.
-
-opt_alloc([{set,[],[],{alloc,Live0,Info0}},
-           {set,[],[],{alloc,Live,Info}}|Is], D) ->
-    Live = Live0,				%Assertion.
-    Alloc = combine_alloc(Info0, Info),
-    I = {set,[],[],{alloc,Live,Alloc}},
-    opt_alloc([I|Is], D);
-opt_alloc([{set,[],[],{alloc,R,{_,Ns,Nh,[]}}}|Is], D) ->
-    [{set,[],[],opt_alloc(Is, D, Ns, Nh, R)}|Is];
-opt_alloc([I|Is], D) -> [I|opt_alloc(Is, D)];
-opt_alloc([], _) -> [].
-
-combine_alloc({_,Ns,Nh1,Init}, {_,nostack,Nh2,[]})  ->
-    {zero,Ns,beam_utils:combine_heap_needs(Nh1, Nh2),Init}.
-
-%% opt_alloc(Instructions, FrameSize, HeapNeed, LivingRegs) -> [Instr]
-%%  Generates the optimal sequence of instructions for
-%%  allocating and initalizing the stack frame and needed heap.
-
-opt_alloc(_Is, _D, nostack, Nh, LivingRegs) ->
-    {alloc,LivingRegs,{nozero,nostack,Nh,[]}};
-opt_alloc(Bl, {D,OuterIs}, Ns, Nh, LivingRegs) ->
-    Is = [{block,Bl}|OuterIs],
-    InitRegs = init_yregs(Ns, Is, D),
-    case count_ones(InitRegs) of
-	N when N*2 > Ns ->
-	    {alloc,LivingRegs,{nozero,Ns,Nh,gen_init(Ns, InitRegs)}};
-	_ ->
-	    {alloc,LivingRegs,{zero,Ns,Nh,[]}}
-    end.
-
-gen_init(Fs, Regs) -> gen_init(Fs, Regs, 0, []).
-
-gen_init(SameFs, _Regs, SameFs, Acc) -> reverse(Acc);
-gen_init(Fs, Regs, Y, Acc) when Regs band 1 =:= 0 ->
-    gen_init(Fs, Regs bsr 1, Y+1, [{init,{y,Y}}|Acc]);
-gen_init(Fs, Regs, Y, Acc) ->
-    gen_init(Fs, Regs bsr 1, Y+1, Acc).
-
-init_yregs(Y, Is, D) when Y >= 0 ->
-    case beam_utils:is_killed({y,Y}, Is, D) of
-        true ->
-            (1 bsl Y) bor init_yregs(Y-1, Is, D);
-        false ->
-            init_yregs(Y-1, Is, D)
-    end;
-init_yregs(_, _, _) -> 0.
-
-count_ones(Bits) -> count_ones(Bits, 0).
-count_ones(0, Acc) -> Acc;
-count_ones(Bits, Acc) ->
-    count_ones(Bits bsr 1, Acc + (Bits band 1)).
-
-%% Calculate the new number of live registers when we move an allocate
-%% instruction upwards, passing a 'set' instruction.
-
-alloc_live_regs({set,Ds,Ss,_}, Is, Regs0) ->
-    Rset = x_live(Ss, x_dead(Ds, (1 bsl Regs0)-1)),
-    Live = live_regs(0, Rset),
-    case ensure_contiguous(Rset, Live) of
-        not_possible ->
-            %% Liveness information (looking forward in the
-            %% instruction stream) can't prove that moving this
-            %% allocation instruction is safe. Now use the annotation
-            %% of defined registers at the beginning of the current
-            %% block to see whether moving would be safe.
-            Def0 = defined_regs(Is, 0),
-            Def = Def0 band ((1 bsl Live) - 1),
-            ensure_contiguous(Rset bor Def, Live);
-        Live ->
-            %% Safe based on liveness information.
-            Live
-    end.
-
-live_regs(N, 0) ->
-    N;
-live_regs(N, Regs) ->
-    live_regs(N+1, Regs bsr 1).
-
-ensure_contiguous(Regs, Live) ->
-    case (1 bsl Live) - 1 of
-        Regs -> Live;
-        _ -> not_possible
-    end.
-
-x_dead([{x,N}|Rs], Regs) -> x_dead(Rs, Regs band (bnot (1 bsl N)));
-x_dead([_|Rs], Regs) -> x_dead(Rs, Regs);
-x_dead([], Regs) -> Regs.
-
-x_live([{x,N}|Rs], Regs) -> x_live(Rs, Regs bor (1 bsl N));
-x_live([_|Rs], Regs) -> x_live(Rs, Regs);
-x_live([], Regs) -> Regs.
-
-%% defined_regs(ReversedInstructions) -> RegBitmap.
-%%  Given a reversed instruction stream, determine the
-%%  the registers that are defined.
-
-defined_regs([{'%anno',{def,Def}}|_], Regs) ->
-    Def bor Regs;
-defined_regs([{set,Ds,_,{alloc,Live,_}}|_], Regs) ->
-    x_live(Ds, Regs bor ((1 bsl Live) - 1));
-defined_regs([{set,Ds,_,_}|Is], Regs) ->
-    defined_regs(Is, x_live(Ds, Regs)).
-
-%%%
-%%% Do local common sub expression elimination (CSE) in each block.
-%%%
-
-local_cse([{block,Bl0}|Is]) ->
-    Bl = cse_block(Bl0, orddict:new(), []),
-    [{block,Bl}|local_cse(Is)];
-local_cse([I|Is]) ->
-    [I|local_cse(Is)];
-local_cse([]) -> [].
-
-cse_block([I|Is], Es0, Acc0) ->
-    Es1 = cse_clear(I, Es0),
-    case cse_expr(I) of
-        none ->
-            %% Instruction is not suitable for CSE.
-            cse_block(Is, Es1, [I|Acc0]);
-        {ok,D,Expr} ->
-            %% Suitable instruction. First update the dictionary of
-            %% suitable expressions for the next iteration.
-            Es = cse_add(D, Expr, Es1),
-
-            %% Search for a previous identical expression.
-            case cse_find(Expr, Es0) of
-                error ->
-                    %% Nothing found
-                    cse_block(Is, Es, [I|Acc0]);
-                Src ->
-                    %% Use the previously calculated result.
-                    %% Also eliminate any line instruction.
-                    Move = {set,[D],[Src],move},
-                    case Acc0 of
-                        [{set,_,_,{line,_}}|Acc] ->
-                            cse_block(Is, Es, [Move|Acc]);
-                        [_|_] ->
-                            cse_block(Is, Es, [Move|Acc0])
-                    end
-            end
-    end;
-cse_block([], _, Acc) ->
-    reverse(Acc).
-
-%% cse_find(Expr, Expressions) -> error | Register.
-%%  Find a previously evaluated expression whose result can be reused,
-%%  or return 'error' if no such expression is found.
-
-cse_find(Expr, Es) ->
-    case orddict:find(Expr, Es) of
-        {ok,{Src,_}} -> Src;
-        error -> error
-    end.
-
-cse_expr({set,[D],Ss,{bif,N,_}}) ->
-    case D of
-        {fr,_} ->
-            %% There are too many things that can go wrong.
-            none;
-        _ ->
-            {ok,D,{{bif,N},Ss}}
-    end;
-cse_expr({set,[D],Ss,{alloc,_,{gc_bif,N,_}}}) ->
-    {ok,D,{{gc_bif,N},Ss}};
-cse_expr({set,[D],Ss,put_list}) ->
-    {ok,D,{put_list,Ss}};
-cse_expr(_) -> none.
-
-%% cse_clear(Instr, Expressions0) -> Expressions.
-%%  Remove all previous expressions that will become
-%%  invalid when this instruction is executed. Basically,
-%%  an expression is no longer safe to reuse when the
-%%  register it has been stored to has been modified, killed,
-%%  or if any of the source operands have changed.
-
-cse_clear({set,Ds,_,{alloc,Live,_}}, Es) ->
-    cse_clear_1(Es, Live, Ds);
-cse_clear({set,Ds,_,_}, Es) ->
-    cse_clear_1(Es, all, Ds).
-
-cse_clear_1(Es, Live, Ds0) ->
-    Ds = ordsets:from_list(Ds0),
-    [E || E <- Es, cse_is_safe(E, Live, Ds)].
-
-cse_is_safe({_,{Dst,Interfering}}, Live, Ds) ->
-    ordsets:is_disjoint(Interfering, Ds) andalso
-        case Dst of
-            {x,X} ->
-                X < Live;
-            _ ->
-                true
-        end.
-
-%% cse_add(Dest, Expr, Expressions0) -> Expressions.
-%%  Provided that it is safe, add a new expression to the dictionary
-%%  of already evaluated expressions.
-
-cse_add(D, {_,Ss}=Expr, Es) ->
-    case member(D, Ss) of
-        false ->
-            Interfering = ordsets:from_list([D|Ss]),
-            orddict:store(Expr, {D,Interfering}, Es);
-        true ->
-            %% Unsafe because the instruction overwrites one of
-            %% source operands.
-            Es
-    end.