1 files changed, 152 insertions, 85 deletions

diff --git a/lib/compiler/src/v3_codegen.erl b/lib/compiler/src/v3_codegen.erl
index 34c67b16ca..47c1567f10 100644
--- a/lib/compiler/src/v3_codegen.erl
+++ b/lib/compiler/src/v3_codegen.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 1999-2012. All Rights Reserved.
+%% 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.
@@ -69,6 +69,10 @@
 	     stk=[],				%Stack table
 	     res=[]}).				%Reserved regs: [{reserved,I,V}]
 
+-type life_module() :: {module(),_,_,[_]}.
+
+-spec module(life_module(), [compile:option()]) -> {'ok',beam_asm:module_code()}.
+
 module({Mod,Exp,Attr,Forms}, _Options) ->
     {Fs,St} = functions(Forms, {atom,Mod}),
     {ok,{Mod,Exp,Attr,Fs,St#cg.lcount}}.
@@ -151,6 +155,8 @@ cg({bif,Bif,As,Rs}, Le, Vdb, Bef, St) ->
     bif_cg(Bif, As, Rs, Le, Vdb, Bef, St);
 cg({gc_bif,Bif,As,Rs}, Le, Vdb, Bef, St) ->
     gc_bif_cg(Bif, As, Rs, Le, Vdb, Bef, St);
+cg({internal,Bif,As,Rs}, Le, Vdb, Bef, St) ->
+    internal_cg(Bif, As, Rs, Le, Vdb, Bef, St);
 cg({receive_loop,Te,Rvar,Rm,Tes,Rs}, Le, Vdb, Bef, St) ->
     recv_loop_cg(Te, Rvar, Rm, Tes, Rs, Le, Vdb, Bef, St);
 cg(receive_next, Le, Vdb, Bef, St) ->
@@ -208,15 +214,10 @@ need_heap_1(#l{ke={set,_,Val}}, H) ->
 		{tuple,Es} -> 1 + length(Es);
 		_Other -> 0
 	    end};
-need_heap_1(#l{ke={bif,dsetelement,_As,_Rs},i=I}, H) ->
-    {need_heap_need(I, H),0};
-need_heap_1(#l{ke={bif,{make_fun,_,_,_,_},_As,_Rs},i=I}, H) ->
-    {need_heap_need(I, H),0};
-need_heap_1(#l{ke={bif,bs_init_writable,_As,_Rs},i=I}, H) ->
-    {need_heap_need(I, H),0};
 need_heap_1(#l{ke={bif,_Bif,_As,_Rs}}, H) ->
     {[],H};
 need_heap_1(#l{i=I}, H) ->
+    %% Call or call-like instruction such as set_tuple_element/3.
     {need_heap_need(I, H),0}.
 
 need_heap_need(_I, 0) -> [];
@@ -366,7 +367,7 @@ bsm_rename_ctx(#l{ke={match,Ms0,Rs}}=L, Old, New, InProt) ->
 bsm_rename_ctx(#l{ke={guard_match,Ms0,Rs}}=L, Old, New, InProt) ->
     Ms = bsm_rename_ctx(Ms0, Old, New, InProt),
     L#l{ke={guard_match,Ms,Rs}};
-bsm_rename_ctx(#l{ke={test,_,_}}=L, _, _, _) -> L;
+bsm_rename_ctx(#l{ke={test,_,_,_}}=L, _, _, _) -> L;
 bsm_rename_ctx(#l{ke={bif,_,_,_}}=L, _, _, _) -> L;
 bsm_rename_ctx(#l{ke={gc_bif,_,_,_}}=L, _, _, _) -> L;
 bsm_rename_ctx(#l{ke={set,_,_}}=L, _, _, _) -> L;
@@ -827,21 +828,24 @@ select_extract_bin([{var,Hd},{var,Tl}], Size0, Unit, Type, Flags, Vf,
 		  {bs_save2,CtxReg,{Ctx,Tl}}],Int1}
 	end,
     {Es,clear_dead(Aft, I, Vdb),St};
-select_extract_bin([{var,Hd}], Size0, Unit, binary, Flags, Vf,
+select_extract_bin([{var,Hd}], Size, Unit, binary, Flags, Vf,
 		   I, Vdb, Bef, Ctx, Body, St) ->
-    SizeReg = get_bin_size_reg(Size0, Bef),
+    %% Match the last segment of a binary. We KNOW that the size
+    %% must be 'all'.
+    Size = {atom,all},				%Assertion.
     {Es,Aft} =
 	case vdb_find(Hd, Vdb) of
 	    {_,_,Lhd} when Lhd =< I ->
+		%% The result will not be used. Furthermore, since we
+		%% we are at the end of the binary, the position will
+		%% not be used again; thus, it is safe to do a cheaper
+		%% test of the unit.
 		CtxReg = fetch_var(Ctx, Bef),
-		{case SizeReg =:= {atom,all} andalso is_context_unused(Body) of
-		     true when Unit =:= 1 ->
+		{case Unit of
+		     1 ->
 			 [];
-		     true ->
-			 [{test,bs_test_unit,{f,Vf},[CtxReg,Unit]}];
-		     false ->
-			 [{test,bs_skip_bits2,{f,Vf},
-			   [CtxReg,SizeReg,Unit,{field_flags,Flags}]}]
+		     _ ->
+			 [{test,bs_test_unit,{f,Vf},[CtxReg,Unit]}]
 		 end,Bef};
 	    {_,_,_} ->
 		case is_context_unused(Body) of
@@ -853,7 +857,7 @@ select_extract_bin([{var,Hd}], Size0, Unit, binary, Flags, Vf,
 			Name = bs_get_binary2,
 			Live = max_reg(Bef#sr.reg),
 			{[{test,Name,{f,Vf},Live,
-			   [CtxReg,SizeReg,Unit,{field_flags,Flags}],Rhd}],
+			   [CtxReg,Size,Unit,{field_flags,Flags}],Rhd}],
 			 Int1};
 		    true ->
 			%% Since the matching context will not be used again,
@@ -868,7 +872,7 @@ select_extract_bin([{var,Hd}], Size0, Unit, binary, Flags, Vf,
 			Name = bs_get_binary2,
 			Live = max_reg(Int1#sr.reg),
 			{[{test,Name,{f,Vf},Live,
-			   [CtxReg,SizeReg,Unit,{field_flags,Flags}],CtxReg}],
+			   [CtxReg,Size,Unit,{field_flags,Flags}],CtxReg}],
 			 Int1}
 		end
 	end,
@@ -1051,8 +1055,15 @@ guard_cg(#l{ke={protected,Ts,Rs},i=I,vdb=Pdb}, Fail, _Vdb, Bef, St) ->
     protected_cg(Ts, Rs, Fail, I, Pdb, Bef, St);
 guard_cg(#l{ke={block,Ts},i=I,vdb=Bdb}, Fail, _Vdb, Bef, St) ->
     guard_cg_list(Ts, Fail, I, Bdb, Bef, St);
-guard_cg(#l{ke={test,Test,As},i=I,vdb=_Tdb}, Fail, Vdb, Bef, St) ->
-    test_cg(Test, As, Fail, I, Vdb, Bef, St);
+guard_cg(#l{ke={test,Test,As,Inverted},i=I,vdb=_Tdb}, Fail, Vdb, Bef, St0) ->
+    case Inverted of
+	false ->
+	    test_cg(Test, As, Fail, I, Vdb, Bef, St0);
+	true ->
+	    {Psucc,St1} = new_label(St0),
+	    {Is,Aft,St2} = test_cg(Test, As, Psucc, I, Vdb, Bef, St1),
+	    {Is++[{jump,{f,Fail}},{label,Psucc}],Aft,St2}
+    end;
 guard_cg(G, _Fail, Vdb, Bef, St) ->
     %%ok = io:fwrite("cg ~w: ~p~n", [?LINE,{G,Fail,Vdb,Bef}]),
     {Gis,Aft,St1} = cg(G, Vdb, Bef, St),
@@ -1086,6 +1097,30 @@ protected_cg(Ts, Rs, _Fail, I, Vdb, Bef, St0) ->
 %% test_cg(TestName, Args, Fail, I, Vdb, Bef, St) -> {[Ainstr],Aft,St}.
 %%  Generate test instruction.  Use explicit fail label here.
 
+test_cg(is_map, [A], Fail, I, Vdb, Bef, St) ->
+    %% We must avoid creating code like this:
+    %%
+    %%   move x(0) y(0)
+    %%   is_map Fail [x(0)]
+    %%   make_fun => x(0)  %% Overwrite x(0)
+    %%   put_map_assoc y(0) ...
+    %%
+    %% The code is safe, but beam_validator does not understand that.
+    %% Extending beam_validator to handle such (rare) code as the
+    %% above would make it slower for all programs. Instead, change
+    %% the code generator to always prefer the Y register for is_map()
+    %% and put_map_assoc() instructions, ensuring that they use the
+    %% same register.
+    Arg = cg_reg_arg_prefer_y(A, Bef),
+    Aft = clear_dead(Bef, I, Vdb),
+    {[{test,is_map,{f,Fail},[Arg]}],Aft,St};
+test_cg(is_boolean, [{atom,Val}], Fail, I, Vdb, Bef, St) ->
+    Aft = clear_dead(Bef, I, Vdb),
+    Is = case is_boolean(Val) of
+	     true -> [];
+	     false -> [{jump,{f,Fail}}]
+	 end,
+    {Is,Aft,St};
 test_cg(Test, As, Fail, I, Vdb, Bef, St) ->
     Args = cg_reg_args(As, Bef),
     Aft = clear_dead(Bef, I, Vdb),
@@ -1152,19 +1187,15 @@ call_cg(Func, As, Rs, Le, Vdb, Bef, St0) ->
 	    %% Inside a guard. The only allowed function call is to
 	    %% erlang:error/1,2. We will generate the following code:
 	    %%
-	    %%     jump FailureLabel
 	    %%     move {atom,ok} DestReg
-	    %%
-	    %% The 'move' instruction will never be executed, but we
-	    %% generate it anyway in case the beam_validator is run
-	    %% on unoptimized code.
+	    %%     jump FailureLabel
 	    {remote,{atom,erlang},{atom,error}} = Func,	%Assertion.
 	    [{var,DestVar}] = Rs,
 	    Int0 = clear_dead(Bef, Le#l.i, Vdb),
 	    Reg = put_reg(DestVar, Int0#sr.reg),
 	    Int = Int0#sr{reg=Reg},
 	    Dst = fetch_reg(DestVar, Reg),
-	    {[{jump,{f,Fail}},{move,{atom,ok},Dst}],
+	    {[{move,{atom,ok},Dst},{jump,{f,Fail}}],
 	     clear_dead(Int, Le#l.i, Vdb),St0};
 	#cg{} ->
 	    %% Ordinary function call in a function body.
@@ -1285,10 +1316,10 @@ trap_bif(erlang, group_leader, 2) -> true;
 trap_bif(erlang, exit, 2) -> true;
 trap_bif(_, _, _) -> false.
 
-%% bif_cg(Bif, [Arg], [Ret], Le, Vdb, StackReg, State) ->
+%% internal_cg(Bif, [Arg], [Ret], Le, Vdb, StackReg, State) ->
 %%      {[Ainstr],StackReg,State}.
 
-bif_cg(bs_context_to_binary=Instr, [Src0], [], Le, Vdb, Bef, St0) ->
+internal_cg(bs_context_to_binary=Instr, [Src0], [], Le, Vdb, Bef, St0) ->
     [Src] = cg_reg_args([Src0], Bef),
     case is_register(Src) of
 	false ->
@@ -1296,25 +1327,34 @@ bif_cg(bs_context_to_binary=Instr, [Src0], [], Le, Vdb, Bef, St0) ->
 	true ->
 	    {[{Instr,Src}],clear_dead(Bef, Le#l.i, Vdb), St0}
     end;
-bif_cg(dsetelement, [Index0,Tuple0,New0], _Rs, Le, Vdb, Bef, St0) ->
+internal_cg(dsetelement, [Index0,Tuple0,New0], _Rs, Le, Vdb, Bef, St0) ->
     [New,Tuple,{integer,Index1}] = cg_reg_args([New0,Tuple0,Index0], Bef),
     Index = Index1-1,
     {[{set_tuple_element,New,Tuple,Index}],
      clear_dead(Bef, Le#l.i, Vdb), St0};
-bif_cg({make_fun,Func,Arity,Index,Uniq}, As, Rs, Le, Vdb, Bef, St0) ->
+internal_cg(make_fun, [Func0,Arity0|As], Rs, Le, Vdb, Bef, St0) ->
     %% This behaves more like a function call.
+    {atom,Func} = Func0,
+    {integer,Arity} = Arity0,
     {Sis,Int} = cg_setup_call(As, Bef, Le#l.i, Vdb),
     Reg = load_vars(Rs, clear_regs(Int#sr.reg)),
     {FuncLbl,St1} = local_func_label(Func, Arity, St0),
-    MakeFun = {make_fun2,{f,FuncLbl},Index,Uniq,length(As)},
+    MakeFun = {make_fun2,{f,FuncLbl},0,0,length(As)},
     {Sis ++ [MakeFun],
      clear_dead(Int#sr{reg=Reg}, Le#l.i, Vdb),
      St1};
-bif_cg(bs_init_writable=I, As, Rs, Le, Vdb, Bef, St) ->
+internal_cg(bs_init_writable=I, As, Rs, Le, Vdb, Bef, St) ->
     %% This behaves like a function call.
     {Sis,Int} = cg_setup_call(As, Bef, Le#l.i, Vdb),
     Reg = load_vars(Rs, clear_regs(Int#sr.reg)),
     {Sis++[I],clear_dead(Int#sr{reg=Reg}, Le#l.i, Vdb),St};
+internal_cg(raise, As, Rs, Le, Vdb, Bef, St) ->
+    %% raise can be treated like a guard BIF.
+    bif_cg(raise, As, Rs, Le, Vdb, Bef, St).
+
+%% bif_cg(Bif, [Arg], [Ret], Le, Vdb, StackReg, State) ->
+%%      {[Ainstr],StackReg,State}.
+
 bif_cg(Bif, As, [{var,V}], Le, Vdb, Bef, St0) ->
     Ars = cg_reg_args(As, Bef),
 
@@ -1327,12 +1367,13 @@ bif_cg(Bif, As, [{var,V}], Le, Vdb, Bef, St0) ->
     %% that we save any variable that will be live after this BIF call.
 
     MayFail = not erl_bifs:is_safe(erlang, Bif, length(As)),
-    {Sis,Int0} = case St0#cg.in_catch andalso
-		     St0#cg.bfail =:= 0 andalso
-		     MayFail of
-		     true -> adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb);
-		     false -> {[],Bef}
-		 end,
+    {Sis,Int0} =
+	case MayFail of
+	    true ->
+		maybe_adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb, St0);
+	    false ->
+		{[],Bef}
+	end,
     Int1 = clear_dead(Int0, Le#l.i, Vdb),
     Reg = put_reg(V, Int1#sr.reg),
     Int = Int1#sr{reg=Reg},
@@ -1363,11 +1404,7 @@ gc_bif_cg(Bif, As, [{var,V}], Le, Vdb, Bef, St0) ->
     %%   Currently, we are somewhat pessimistic in
     %% that we save any variable that will be live after this BIF call.
 
-    {Sis,Int0} =
-	case St0#cg.in_catch andalso St0#cg.bfail =:= 0 of
-	    true -> adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb);
-	    false -> {[],Bef}
-	end,
+    {Sis,Int0} = maybe_adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb, St0),
 
     Int1 = clear_dead(Int0, Le#l.i, Vdb),
     Reg = put_reg(V, Int1#sr.reg),
@@ -1512,8 +1549,7 @@ set_cg([{var,R}], {cons,Es}, Le, Vdb, Bef, St) ->
     Int1 = Int0#sr{reg=put_reg(R, Int0#sr.reg)},
     Ret = fetch_reg(R, Int1#sr.reg),
     {[{put_list,S1,S2,Ret}], Int1, St};
-set_cg([{var,R}], {binary,Segs}, Le, Vdb, Bef,
-       #cg{in_catch=InCatch, bfail=Bfail}=St) ->
+set_cg([{var,R}], {binary,Segs}, Le, Vdb, Bef, #cg{bfail=Bfail}=St) ->
     %% At run-time, binaries are constructed in three stages:
     %% 1) First the size of the binary is calculated.
     %% 2) Then the binary is allocated.
@@ -1532,28 +1568,19 @@ set_cg([{var,R}], {binary,Segs}, Le, Vdb, Bef,
     %% First generate the code that constructs each field.
     Fail = {f,Bfail},
     PutCode = cg_bin_put(Segs, Fail, Bef),
-    {Sis,Int1} =
-	case InCatch of
-	    true -> adjust_stack(Int0, Le#l.i, Le#l.i+1, Vdb);
-	    false -> {[],Int0}
-	end,
+    {Sis,Int1} = maybe_adjust_stack(Int0, Le#l.i, Le#l.i+1, Vdb, St),
     MaxRegs = max_reg(Bef#sr.reg),
     Aft = clear_dead(Int1, Le#l.i, Vdb),
 
     %% Now generate the complete code for constructing the binary.
     Code = cg_binary(PutCode, Target, Temp, Fail, MaxRegs, Le#l.a),
     {Sis++Code,Aft,St};
-% Map single variable key
-set_cg([{var,R}], {map,Op,Map,[{map_pair,{var,_}=K,V}]}, Le, Vdb, Bef,
-       #cg{in_catch=InCatch,bfail=Bfail}=St) ->
 
-    Fail = {f,Bfail},
-    {Sis,Int0} =
-	case InCatch of
-	    true -> adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb);
-	    false -> {[],Bef}
-	end,
-    SrcReg = cg_reg_arg(Map,Int0),
+%% Map: single variable key.
+set_cg([{var,R}], {map,Op,Map,[{map_pair,{var,_}=K,V}]}, Le, Vdb, Bef, St0) ->
+    {Sis,Int0} = maybe_adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb, St0),
+
+    SrcReg = cg_reg_arg_prefer_y(Map, Int0),
     Line = line(Le#l.a),
 
     List = [cg_reg_arg(K,Int0),cg_reg_arg(V,Int0)],
@@ -1565,26 +1592,17 @@ set_cg([{var,R}], {map,Op,Map,[{map_pair,{var,_}=K,V}]}, Le, Vdb, Bef,
     Aft = Aft0#sr{reg=put_reg(R, Aft0#sr.reg)},
     Target = fetch_reg(R, Aft#sr.reg),
 
-    I = case Op of
-	assoc -> put_map_assoc;
-	exact -> put_map_exact
-    end,
-    {Sis++[Line]++[{I,Fail,SrcReg,Target,Live,{list,List}}],Aft,St};
+    {Is,St1} = set_cg_map(Line, Op, SrcReg, Target, Live, List, St0),
+    {Sis++Is,Aft,St1};
 
-% Map (possibly) multiple literal keys
-set_cg([{var,R}], {map,Op,Map,Es}, Le, Vdb, Bef,
-       #cg{in_catch=InCatch,bfail=Bfail}=St) ->
+%% Map: (possibly) multiple literal keys.
+set_cg([{var,R}], {map,Op,Map,Es}, Le, Vdb, Bef, St0) ->
 
     %% assert key literals
     [] = [Var||{map_pair,{var,_}=Var,_} <- Es],
 
-    Fail = {f,Bfail},
-    {Sis,Int0} =
-	case InCatch of
-	    true -> adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb);
-	    false -> {[],Bef}
-	end,
-    SrcReg = cg_reg_arg(Map,Int0),
+    {Sis,Int0} = maybe_adjust_stack(Bef, Le#l.i, Le#l.i+1, Vdb, St0),
+    SrcReg = cg_reg_arg_prefer_y(Map, Int0),
     Line = line(Le#l.a),
 
     %% fetch registers for values to be put into the map
@@ -1598,11 +1616,10 @@ set_cg([{var,R}], {map,Op,Map,Es}, Le, Vdb, Bef,
     Aft = Aft0#sr{reg=put_reg(R, Aft0#sr.reg)},
     Target = fetch_reg(R, Aft#sr.reg),
 
-    I = case Op of
-	assoc -> put_map_assoc;
-	exact -> put_map_exact
-    end,
-    {Sis++[Line]++[{I,Fail,SrcReg,Target,Live,{list,List}}],Aft,St};
+    {Is,St1} = set_cg_map(Line, Op, SrcReg, Target, Live, List, St0),
+    {Sis++Is,Aft,St1};
+
+%% Everything else.
 set_cg([{var,R}], Con, Le, Vdb, Bef, St) ->
     %% Find a place for the return register first.
     Int = Bef#sr{reg=put_reg(R, Bef#sr.reg)},
@@ -1615,6 +1632,34 @@ set_cg([{var,R}], Con, Le, Vdb, Bef, St) ->
 	  end,
     {Ais,clear_dead(Int, Le#l.i, Vdb),St}.
 
+
+set_cg_map(Line, Op0, SrcReg, Target, Live, List, St0) ->
+    Bfail = St0#cg.bfail,
+    Fail = {f,St0#cg.bfail},
+    Op = case Op0 of
+	     assoc -> put_map_assoc;
+	     exact -> put_map_exact
+	 end,
+    {OkLbl,St1} = new_label(St0),
+    {BadLbl,St2} = new_label(St1),
+    Is = if
+	     Bfail =:= 0 orelse Op =:= put_map_assoc ->
+		 [Line,{Op,{f,0},SrcReg,Target,Live,{list,List}}];
+	     true ->
+		 %% Ensure that Target is always set, even if
+		 %% the map update operation fails. That is necessary
+		 %% because Target may be included in a test_heap
+		 %% instruction.
+		 [Line,
+		  {Op,{f,BadLbl},SrcReg,Target,Live,{list,List}},
+		  {jump,{f,OkLbl}},
+		  {label,BadLbl},
+		  {move,{atom,ok},Target},
+		  {jump,Fail},
+		  {label,OkLbl}]
+	 end,
+    {Is,St2}.
+
 %%%
 %%% Code generation for constructing binaries.
 %%%
@@ -1857,6 +1902,9 @@ cg_reg_args(As, Bef) -> [cg_reg_arg(A, Bef) || A <- As].
 cg_reg_arg({var,V}, Bef) -> fetch_var(V, Bef);
 cg_reg_arg(Literal, _) -> Literal.
 
+cg_reg_arg_prefer_y({var,V}, Bef) -> fetch_var_prefer_y(V, Bef);
+cg_reg_arg_prefer_y(Literal, _) -> Literal.
+
 %% cg_setup_call([Arg], Bef, Cur, Vdb) -> {[Instr],Aft}.
 %%  Do the complete setup for a call/enter.
 
@@ -2038,6 +2086,19 @@ trim_free([R|Rs0]) ->
     end;
 trim_free([]) -> [].
 
+%% maybe_adjust_stack(Bef, FirstBefore, LastFrom, Vdb, St) -> {[Ainstr],Aft}.
+%%  Adjust the stack, but only if the code is inside a catch and not
+%%  inside a guard.  Use this funtion before instructions that may
+%%  cause an exception.
+
+maybe_adjust_stack(Bef, Fb, Lf, Vdb, St) ->
+    case St of
+	#cg{in_catch=true,bfail=0} ->
+	    adjust_stack(Bef, Fb, Lf, Vdb);
+	#cg{} ->
+	    {[],Bef}
+    end.
+
 %% adjust_stack(Bef, FirstBefore, LastFrom, Vdb) -> {[Ainstr],Aft}.
 %%  Do complete stack adjustment by compressing stack and adding
 %%  variables to be saved.  Try to optimise ordering on stack by
@@ -2085,6 +2146,12 @@ fetch_var(V, Sr) ->
 	error -> fetch_stack(V, Sr#sr.stk)
     end.
 
+fetch_var_prefer_y(V, #sr{reg=Reg,stk=Stk}) ->
+    case find_stack(V, Stk) of
+	{ok,R} -> R;
+	error -> fetch_reg(V, Reg)
+    end.
+
 load_vars(Vs, Regs) ->
     foldl(fun ({var,V}, Rs) -> put_reg(V, Rs) end, Regs, Vs).
 
@@ -2158,11 +2225,11 @@ fetch_stack(Var, Stk) -> fetch_stack(Var, Stk, 0).
 fetch_stack(V, [{V}|_], I) -> {yy,I};
 fetch_stack(V, [_|Stk], I) -> fetch_stack(V, Stk, I+1).
 
-% find_stack(Var, Stk) -> find_stack(Var, Stk, 0).
+find_stack(Var, Stk) -> find_stack(Var, Stk, 0).
 
-% find_stack(V, [{V}|Stk], I) -> {ok,{yy,I}};
-% find_stack(V, [O|Stk], I) -> find_stack(V, Stk, I+1);
-% find_stack(V, [], I) -> error.
+find_stack(V, [{V}|_], I) -> {ok,{yy,I}};
+find_stack(V, [_|Stk], I) -> find_stack(V, Stk, I+1);
+find_stack(_, [], _) -> error.
 
 on_stack(V, Stk) -> keymember(V, 1, Stk).