Avoid overflowing the atom table

Use integer variable names instead of atoms in v3_core, sys_core_fold,
and v3_kernel to avoid overflowing the atom table.

It is a deliberate design decision to calculate the first free integer
variable name (in sys_core_fold and v3_kernel) instead of somehow
passing it from one pass to another. I don't want that kind of
dependency between compiler passes. Also note that the next free
variable name is not easily available after running the inliner.

3 files changed, 18 insertions, 9 deletions

diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index 0354981562..395b6bd677 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -108,16 +108,20 @@
 
 module(#c_module{defs=Ds0}=Mod, Opts) ->
     put(no_inline_list_funcs, not member(inline_list_funcs, Opts)),
-    case get(new_var_num) of
-	undefined -> put(new_var_num, 0);
-	_ -> ok
-    end,
     init_warnings(),
     Ds1 = [function_1(D) || D <- Ds0],
+    erase(new_var_num),
     erase(no_inline_list_funcs),
     {ok,Mod#c_module{defs=Ds1},get_warnings()}.
 
 function_1({#c_var{name={F,Arity}}=Name,B0}) ->
+    %% Find a suitable starting value for the variable counter. Note
+    %% that this pass assumes that new_var_name/1 returns a variable
+    %% name distinct from any variable used in the entire body of
+    %% the function. We use integers as variable names to avoid
+    %% filling up the atom table when compiling huge functions.
+    Count = cerl_trees:next_free_variable_name(B0),
+    put(new_var_num, Count),
     try
         %% Find a suitable starting value for the variable
         %% counter. Note that this pass assumes that new_var_name/1
@@ -2162,7 +2166,7 @@ make_var(A) ->
 make_var_name() ->
     N = get(new_var_num),
     put(new_var_num, N+1),
-    list_to_atom("@f"++integer_to_list(N)).
+    N.
 
 letify(Bs, Body) ->
     Ann = cerl:get_ann(Body),
diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index 6029b91cdc..df0cc3684f 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -2005,7 +2005,7 @@ new_fun_name(Type, #core{fcount=C}=St) ->
 %% new_var_name(State) -> {VarName,State}.
 
 new_var_name(#core{vcount=C}=St) ->
-    {list_to_atom("@c" ++ integer_to_list(C)),St#core{vcount=C + 1}}.
+    {C,St#core{vcount=C + 1}}.
 
 %% new_var(State) -> {{var,Name},State}.
 %% new_var(LineAnno, State) -> {{var,Name},State}.
diff --git a/lib/compiler/src/v3_kernel.erl b/lib/compiler/src/v3_kernel.erl
index dfe8d26afb..4e3ceedbc0 100644
--- a/lib/compiler/src/v3_kernel.erl
+++ b/lib/compiler/src/v3_kernel.erl
@@ -157,7 +157,13 @@ include_attribute(_) -> true.
 function({#c_var{name={F,Arity}=FA},Body}, St0) ->
     %%io:format("~w/~w~n", [F,Arity]),
     try
-	St1 = St0#kern{func=FA,ff=undefined,vcount=0,fcount=0,ds=cerl_sets:new()},
+        %% Find a suitable starting value for the variable counter. Note
+        %% that this pass assumes that new_var_name/1 returns a variable
+        %% name distinct from any variable used in the entire body of
+        %% the function. We use integers as variable names to avoid
+        %% filling up the atom table when compiling huge functions.
+        Count = cerl_trees:next_free_variable_name(Body),
+	St1 = St0#kern{func=FA,ff=undefined,vcount=Count,fcount=0,ds=cerl_sets:new()},
 	{#ifun{anno=Ab,vars=Kvs,body=B0},[],St2} = expr(Body, new_sub(), St1),
 	{B1,_,St3} = ubody(B0, return, St2),
 	%%B1 = B0, St3 = St2,				%Null second pass
@@ -168,7 +174,6 @@ function({#c_var{name={F,Arity}=FA},Body}, St0) ->
 	    erlang:raise(Class, Error, Stack)
     end.
 
-
 %% body(Cexpr, Sub, State) -> {Kexpr,[PreKepxr],State}.
 %%  Do the main sequence of a body.  A body ends in an atomic value or
 %%  values.  Must check if vector first so do expr.
@@ -1356,7 +1361,7 @@ new_fun_name(Type, #kern{func={F,Arity},fcount=C}=St) ->
 %% new_var_name(State) -> {VarName,State}.
 
 new_var_name(#kern{vcount=C}=St) ->
-    {list_to_atom("@k" ++ integer_to_list(C)),St#kern{vcount=C+1}}.
+    {C,St#kern{vcount=C+1}}.
 
 %% new_var(State) -> {#k_var{},State}.