sys_core_fold: Run optimizations to a fixpoint

Run the optimizations until a fixpoint is reached, or until
the maximum iteration count is reached.

The hope is that in the future we can many small optimizations
instead of optimizations that try to do everything in one pass.

This change allows us to remove the ad-hoc calls to expr/2
to run more optimizations on a piece of code.

1 files changed, 41 insertions, 36 deletions

diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index b8df4e04f8..303ce52ee3 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -121,7 +121,10 @@ module(#c_module{defs=Ds0}=Mod, Opts) ->
 
 function_1({#c_var{name={F,Arity}}=Name,B0}) ->
     try
-	B = expr(B0, value, sub_new()),			%This must be a fun!
+	B = find_fixpoint(fun(Core) ->
+				  %% This must be a fun!
+				  expr(Core, value, sub_new())
+			  end, B0, 20),
 	{Name,B}
     catch
 	Class:Error ->
@@ -130,6 +133,14 @@ function_1({#c_var{name={F,Arity}}=Name,B0}) ->
 	    erlang:raise(Class, Error, Stack)
     end.
 
+find_fixpoint(_OptFun, Core, 0) ->
+    Core;
+find_fixpoint(OptFun, Core0, Max) ->
+    case OptFun(Core0) of
+	Core0 -> Core0;
+	Core -> find_fixpoint(OptFun, Core, Max-1)
+    end.
+
 %% body(Expr, Sub) -> Expr.
 %% body(Expr, Context, Sub) -> Expr.
 %%  No special handling of anything except values.
@@ -240,7 +251,7 @@ expr(#c_cons{anno=Anno,hd=H0,tl=T0}=Cons, Ctxt, Sub) ->
     case Ctxt of
 	effect ->
 	    add_warning(Cons, useless_building),
-	    expr(make_effect_seq([H1,T1], Sub), Ctxt, Sub);
+	    make_effect_seq([H1,T1], Sub);
 	value ->
 	    ann_c_cons(Anno, H1, T1)
     end;
@@ -249,7 +260,7 @@ expr(#c_tuple{anno=Anno,es=Es0}=Tuple, Ctxt, Sub) ->
     case Ctxt of
 	effect ->
 	    add_warning(Tuple, useless_building),
-	    expr(make_effect_seq(Es, Sub), Ctxt, Sub);
+	    make_effect_seq(Es, Sub);
 	value ->
 	    ann_c_tuple(Anno, Es)
     end;
@@ -258,7 +269,7 @@ expr(#c_map{anno=Anno,arg=V0,es=Es0}=Map, Ctxt, Sub) ->
     case Ctxt of
 	effect ->
 	    add_warning(Map, useless_building),
-	    expr(make_effect_seq(Es, Sub), Ctxt, Sub);
+	    make_effect_seq(Es, Sub);
 	value ->
 	    V = expr(V0, Ctxt, Sub),
 	    ann_c_map(Anno,V,Es)
@@ -311,7 +322,7 @@ expr(#c_let{}=Let0, Ctxt, Sub) ->
 	Expr ->
 	    %% The let body was successfully moved into the let argument.
 	    %% Now recursively re-process the new expression.
-	    expr(Expr, Ctxt, sub_new_preserve_types(Sub))
+	    Expr
     end;
 expr(#c_letrec{body=#c_var{}}=Letrec, effect, _Sub) ->
     %% This is named fun in an 'effect' context. Warn and ignore.
@@ -365,7 +376,7 @@ expr(#c_case{}=Case0, Ctxt, Sub) ->
                 impossible ->
                     bsm_an(Expr);
                 Other ->
-                    expr(Other, Ctxt, sub_new_preserve_types(Sub))
+		    Other
             end;
 	Other ->
 	    expr(Other, Ctxt, Sub)
@@ -1398,9 +1409,6 @@ sub_new() -> #sub{v=orddict:new(),s=cerl_sets:new(),t=#{}}.
 sub_new(#sub{}=Sub) ->
     Sub#sub{v=orddict:new(),t=#{}}.
 
-sub_new_preserve_types(#sub{}=Sub) ->
-    Sub#sub{v=orddict:new()}.
-
 sub_get_var(#c_var{name=V}=Var, #sub{v=S}) ->
     case orddict:find(V, S) of
 	{ok,Val} -> Val;
@@ -2220,24 +2228,24 @@ inverse_rel_op('=<') -> '>';
 inverse_rel_op(_) -> no.
 
 
-%% opt_bool_case_in_let(LetExpr, Sub) -> Core
+%% opt_bool_case_in_let(LetExpr) -> Core
 
-opt_bool_case_in_let(#c_let{vars=Vs,arg=Arg,body=B}=Let, Sub) ->
-    opt_case_in_let_1(Vs, Arg, B, Let, Sub).
+opt_bool_case_in_let(#c_let{vars=Vs,arg=Arg,body=B}=Let) ->
+    opt_bool_case_in_let_1(Vs, Arg, B, Let).
 
-opt_case_in_let_1([#c_var{name=V}], Arg,
-		  #c_case{arg=#c_var{name=V}}=Case0, Let, Sub) ->
+opt_bool_case_in_let_1([#c_var{name=V}], Arg,
+		  #c_case{arg=#c_var{name=V}}=Case0, Let) ->
     case is_simple_case_arg(Arg) of
 	true ->
 	    Case = opt_bool_case(Case0#c_case{arg=Arg}),
 	    case core_lib:is_var_used(V, Case) of
-		false -> expr(Case, sub_new(Sub));
+		false -> Case;
 		true -> Let
 	    end;
 	false ->
 	    Let
     end;
-opt_case_in_let_1(_, _, _, Let, _) -> Let.
+opt_bool_case_in_let_1(_, _, _, Let) -> Let.
 
 %% is_simple_case_arg(Expr) -> true|false
 %%  Determine whether the Expr is simple enough to be worth
@@ -2645,25 +2653,23 @@ opt_simple_let_2(Let0, Vs0, Arg0, Body, PrevBody, Ctxt, Sub) ->
 		false ->
 		    %% let <Var> = Arg in <OtherVar>  ==>  seq Arg OtherVar
 		    Arg = maybe_suppress_warnings(Arg1, Vs0, PrevBody),
-		    expr(#c_seq{arg=Arg,body=Body}, Ctxt,
-			 sub_new_preserve_types(Sub))
+		    #c_seq{arg=Arg,body=Body}
 	    end;
 	{[],#c_values{es=[]},_} ->
 	    %% No variables left.
 	    Body;
 	{Vs,Arg1,#c_literal{}} ->
 	    Arg = maybe_suppress_warnings(Arg1, Vs, PrevBody),
-	    E = case Ctxt of
-		    effect ->
-			%% Throw away the literal body.
-			Arg;
-		    value ->
-			%% Since the variable is not used in the body, we
-			%% can rewrite the let to a sequence.
-			%%  let <Var> = Arg in Literal ==> seq Arg Literal
-			#c_seq{arg=Arg,body=Body}
-		end,
-	    expr(E, Ctxt, sub_new_preserve_types(Sub));
+	    case Ctxt of
+		effect ->
+		    %% Throw away the literal body.
+		    Arg;
+		value ->
+		    %% Since the variable is not used in the body, we
+		    %% can rewrite the let to a sequence.
+		    %%  let <Var> = Arg in Literal ==> seq Arg Literal
+		    #c_seq{arg=Arg,body=Body}
+	    end;
 	{Vs,Arg1,Body} ->
 	    %% If none of the variables are used in the body, we can
 	    %% rewrite the let to a sequence:
@@ -2672,11 +2678,10 @@ opt_simple_let_2(Let0, Vs0, Arg0, Body, PrevBody, Ctxt, Sub) ->
 	    case is_any_var_used(Vs, Body) of
 		false ->
 		    Arg = maybe_suppress_warnings(Arg1, Vs, PrevBody),
-		    expr(#c_seq{arg=Arg,body=Body}, Ctxt,
-			 sub_new_preserve_types(Sub));
+		    #c_seq{arg=Arg,body=Body};
 		true ->
 		    Let1 = Let0#c_let{vars=Vs,arg=Arg1,body=Body},
-		    Let2 = opt_bool_case_in_let(Let1, Sub),
+		    Let2 = opt_bool_case_in_let(Let1),
 		    opt_case_in_let_arg(Let2, Ctxt, Sub)
 	    end
     end.
@@ -2834,16 +2839,16 @@ opt_case_in_let_arg(#c_let{arg=#c_case{}=Case}=Let, Ctxt,
 opt_case_in_let_arg(Let, _, _) -> Let.
 
 opt_case_in_let_arg_1(Let0, #c_case{arg=#c_values{es=[]},
-				   clauses=Cs}=Case0, Ctxt, Sub) ->
+				    clauses=Cs}=Case0, _Ctxt, _Sub) ->
     Let = mark_compiler_generated(Let0),
     case Cs of
 	[#c_clause{body=#c_literal{}=BodyA}=Ca0,
 	 #c_clause{body=#c_literal{}=BodyB}=Cb0] ->
 	    Ca = Ca0#c_clause{body=Let#c_let{arg=BodyA}},
 	    Cb = Cb0#c_clause{body=Let#c_let{arg=BodyB}},
-	    Case = Case0#c_case{clauses=[Ca,Cb]},
-	    expr(Case, Ctxt, sub_new_preserve_types(Sub));
-	_ -> Let
+	    Case0#c_case{clauses=[Ca,Cb]};
+	_ ->
+	    Let
     end;
 opt_case_in_let_arg_1(Let, _, _, _) -> Let.