diff --git a/filter/Makefile b/filter/Makefile
index 4f515864..65602ea8 100644
--- a/filter/Makefile
+++ b/filter/Makefile
@@ -10,16 +10,13 @@ M4FLAGS_FILTERS=$(filter-out -s,$(M4FLAGS))
 $(o)f-inst-interpret.c: $(s)interpret.m4 $(s)f-inst.c $(objdir)/.dir-stamp
 	$(M4) $(M4FLAGS_FILTERS) -P $^ >$@
 
-$(o)f-inst-same.c: $(s)same.m4 $(s)f-inst.c $(objdir)/.dir-stamp
-	$(M4) $(M4FLAGS_FILTERS) -P $^ >$@
-
 $(o)inst-gen.h: $(s)decl.m4 $(s)f-inst.c $(objdir)/.dir-stamp
 	$(M4) $(M4FLAGS_FILTERS) -DTARGET=H -P $^ >$@
 
 $(o)inst-gen.c: $(s)decl.m4 $(s)f-inst.c $(objdir)/.dir-stamp
 	$(M4) $(M4FLAGS_FILTERS) -DTARGET=C -P $^ >$@
 
-$(o)filter.o: $(o)f-inst-interpret.c $(o)f-inst-same.c $(o)inst-gen.h
+$(o)filter.o: $(o)f-inst-interpret.c $(o)inst-gen.h
 
 tests_src := tree_test.c filter_test.c trie_test.c
 tests_targets := $(tests_targets) $(tests-target-files)
diff --git a/filter/config.Y b/filter/config.Y
index 42624f44..488b9ced 100644
--- a/filter/config.Y
+++ b/filter/config.Y
@@ -441,7 +441,7 @@ CF_KEYWORDS(FUNCTION, PRINT, PRINTN, UNSET, RETURN,
 	PREPEND, FIRST, LAST, LAST_NONAGGREGATED, MATCH,
 	EMPTY,
 	FILTER, WHERE, EVAL, ATTRIBUTE,
-	BT_ASSERT, BT_TEST_SUITE, BT_CHECK_ASSIGN, FORMAT)
+	BT_ASSERT, BT_TEST_SUITE, BT_CHECK_ASSIGN, BT_TEST_SAME, FORMAT)
 
 %nonassoc THEN
 %nonassoc ELSE
@@ -489,7 +489,7 @@ custom_attr: ATTRIBUTE type CF_SYM_VOID ';' {
 conf: bt_test_suite ;
 bt_test_suite:
  BT_TEST_SUITE '(' CF_SYM_FUNCTION ',' text ')' {
-  struct f_bt_test_suite *t = cfg_alloc(sizeof(struct f_bt_test_suite));
+  struct f_bt_test_suite *t = cfg_allocz(sizeof(struct f_bt_test_suite));
   t->fn = $3->def;
   t->fn_name = $3->name;
   t->dsc = $5;
@@ -498,6 +498,19 @@ bt_test_suite:
  }
  ;
 
+conf: bt_test_same ;
+bt_test_same:
+ BT_TEST_SAME '(' CF_SYM_FUNCTION ',' CF_SYM_FUNCTION ',' NUM ')' {
+  struct f_bt_test_suite *t = cfg_allocz(sizeof(struct f_bt_test_suite));
+  t->fn = $3->def;
+  t->cmp = $5->def;
+  t->result = $7;
+  t->fn_name = $3->name;
+  t->dsc = $5->name;
+  add_tail(&new_config->tests, &t->n);
+ }
+ ;
+
 type:
    INT { $$ = T_INT; }
  | BOOL { $$ = T_BOOL; }
diff --git a/filter/data.c b/filter/data.c
index b389b8e8..912e2b00 100644
--- a/filter/data.c
+++ b/filter/data.c
@@ -146,34 +146,41 @@ val_compare(const struct f_val *v1, const struct f_val *v2)
   }
 }
 
+static inline int
+pmi_same(const struct f_path_mask_item *mi1, const struct f_path_mask_item *mi2)
+{
+  if (mi1->kind != mi2->kind)
+    return 0;
+
+  switch (mi1->kind) {
+    case PM_ASN:
+      if (mi1->asn != mi2->asn)
+	return 0;
+      break;
+    case PM_ASN_EXPR:
+      if (!f_same(mi1->expr, mi2->expr))
+	return 0;
+      break;
+    case PM_ASN_RANGE:
+      if (mi1->from != mi2->from)
+	return 0;
+      if (mi1->to != mi2->to)
+	return 0;
+      break;
+  }
+
+  return 1;
+}
+
 static int
 pm_same(const struct f_path_mask *m1, const struct f_path_mask *m2)
 {
   if (m1->len != m2->len)
 
   for (uint i=0; i<m1->len; i++)
-  {
-    if (m1->item[i].kind != m2->item[i].kind)
+    if (!pmi_same(&(m1->item[i]), &(m2->item[i])))
       return 0;
 
-    switch (m1->item[i].kind) {
-      case PM_ASN:
-	if (m1->item[i].asn != m2->item[i].asn)
-	  return 0;
-	break;
-      case PM_ASN_EXPR:
-	if (!f_same(m1->item[i].expr, m2->item[i].expr))
-	  return 0;
-	break;
-      case PM_ASN_RANGE:
-	if (m1->item[i].from != m2->item[i].from)
-	  return 0;
-	if (m1->item[i].to != m2->item[i].to)
-	  return 0;
-	break;
-    }
-  }
-
   return 1;
 }
 
@@ -200,6 +207,8 @@ val_same(const struct f_val *v1, const struct f_val *v2)
   switch (v1->type) {
   case T_PATH_MASK:
     return pm_same(v1->val.path_mask, v2->val.path_mask);
+  case T_PATH_MASK_ITEM:
+    return pmi_same(&(v1->val.pmi), &(v2->val.pmi));
   case T_PATH:
   case T_CLIST:
   case T_ECLIST:
diff --git a/filter/decl.m4 b/filter/decl.m4
index 4670de33..5ac62cbd 100644
--- a/filter/decl.m4
+++ b/filter/decl.m4
@@ -13,6 +13,7 @@ m4_divert(-1)m4_dnl
 #	6	dump line item
 #	7	dump line item callers
 #	8	postfixify
+#	9	same (filter comparator)
 #	1	struct f_inst_FI_...
 #	2	union in struct f_inst
 #	3	constructors
@@ -23,6 +24,7 @@ m4_divert(-1)m4_dnl
 #	103	constructor body
 #	104	dump line item content
 #	105	postfixify body
+#	106	comparator body
 #
 #	Diversions for TARGET=C: 8xx
 #	Diversions for TARGET=H: 9xx
@@ -41,12 +43,14 @@ m4_define(FID_ENUM_STR, `FID_ZONE(5, Code enum to string)')
 m4_define(FID_DUMP, `FID_ZONE(6, Dump line)')
 m4_define(FID_DUMP_CALLER, `FID_ZONE(7, Dump line caller)')
 m4_define(FID_POSTFIXIFY, `FID_ZONE(8, Postfixify)')
+m4_define(FID_SAME, `FID_ZONE(9, Comparison)')
 
 m4_define(FID_STRUCT_IN, `m4_divert(101)')
 m4_define(FID_NEW_ARGS, `m4_divert(102)')
 m4_define(FID_NEW_BODY, `m4_divert(103)')
 m4_define(FID_DUMP_BODY, `m4_divert(104)m4_define([[FID_DUMP_BODY_EXISTS]])')
 m4_define(FID_POSTFIXIFY_BODY, `m4_divert(105)m4_define([[FID_POSTFIXIFY_BODY_EXISTS]])')
+m4_define(FID_SAME_BODY, `m4_divert(106)')
 
 m4_define(FID_ALL, `m4_ifdef([[FID_CURDIV]], [[m4_divert(FID_CURDIV)m4_undefine([[FID_CURDIV]])]])')
 m4_define(FID_C, `m4_ifelse(TARGET, [[C]], FID_ALL, [[m4_define(FID_CURDIV, m4_divnum)m4_divert(-1)]])')
@@ -105,6 +109,11 @@ m4_ifdef([[FID_POSTFIXIFY_BODY_EXISTS]], [[const struct f_inst_]]INST_NAME()[[ *
 }
 m4_undefine([[FID_POSTFIXIFY_BODY_EXISTS]])
 
+FID_SAME
+case INST_NAME():
+m4_undivert(106)
+break;
+
 FID_END
 ]])')
 
@@ -114,6 +123,7 @@ m4_dnl FID_MEMBER call:
 m4_dnl type
 m4_dnl name in f_inst
 m4_dnl name in f_line_item
+m4_dnl comparator for same
 m4_dnl dump format string
 m4_dnl dump format args
 m4_define(FID_MEMBER, `m4_dnl
@@ -128,24 +138,28 @@ FID_POSTFIXIFY_BODY
 dest->items[pos].$3 = what->$2;
 ]])
 m4_ifelse($4,,,[[
+FID_SAME_BODY
+if ($4) return 0;
+]])
+m4_ifelse($5,,,[[
 FID_DUMP_BODY
-debug("%s$4\n", INDENT, $5);
+debug("%s$5\n", INDENT, $6);
 ]])
 FID_END')
 
-m4_define(ARG, `FID_MEMBER(const struct f_inst *, f$1,,,)
+m4_define(ARG, `FID_MEMBER(const struct f_inst *, f$1,,,,)
 FID_NEW_BODY
 for (const struct f_inst *child = f$1; child; child = child->next) what_->size += child->size;
 FID_POSTFIXIFY_BODY
 pos = postfixify(dest, what->f$1, pos);
 FID_END')
-m4_define(ARG_ANY, `FID_MEMBER(const struct f_inst *, f$1,,,)
+m4_define(ARG_ANY, `FID_MEMBER(const struct f_inst *, f$1,,,,)
 FID_NEW_BODY
 for (const struct f_inst *child = f$1; child; child = child->next) what_->size += child->size;
 FID_POSTFIXIFY_BODY
 pos = postfixify(dest, what->f$1, pos);
 FID_END')
-m4_define(LINE, `FID_MEMBER(const struct f_inst *, f$1,,,)
+m4_define(LINE, `FID_MEMBER(const struct f_inst *, f$1,,[[!f_same(f1->lines[$2], f2->lines[$2])]],,)
 FID_DUMP_BODY
 f_dump_line(item->lines[$2], indent + 1);
 FID_POSTFIXIFY_BODY
@@ -157,10 +171,13 @@ FID_DUMP_BODY
 f_dump_line(item->lines[$2], indent + 1)
 FID_POSTFIXIFY_BODY
 dest->items[pos].lines[$2] = what->fl$1;
+FID_SAME_BODY
+if (!f_same(f1->lines[$2], f2->lines[$2])) return 0;
 FID_END')
-m4_define(SYMBOL, `FID_MEMBER(const struct symbol *, sym, sym, symbol %s, item->sym->name)')
-m4_define(VALI, `FID_MEMBER(struct f_val, vali, val, value %s, val_dump(&item->val))')
-m4_define(VALP, `FID_MEMBER(const struct f_val *, valp,, value %s, val_dump(&item->val))
+m4_define(SYMBOL, `FID_MEMBER(const struct symbol *, sym, sym,
+[[strcmp(f1->sym->name, f2->sym->name) || (f1->sym->class != f2->sym->class)]], symbol %s, item->sym->name)')
+m4_define(VALI, `FID_MEMBER(struct f_val, vali, val, [[!val_same(&f1->val, &f2->val)]], value %s, val_dump(&item->val))')
+m4_define(VALP, `FID_MEMBER(const struct f_val *, valp,, [[!val_same(&f1->val, &f2->val)]], value %s, val_dump(&item->val))
 FID_POSTFIXIFY_BODY
 dest->items[pos].val = *(what->valp);
 FID_END')
@@ -174,17 +191,19 @@ FID_NEW_BODY
 what->valp = (what->sym = sym)->def;
 FID_POSTFIXIFY_BODY
 dest->items[pos].vp = (dest->items[pos].sym = what->sym)->def;
+FID_SAME_BODY
+if (strcmp(f1->sym->name, f2->sym->name) || (f1->sym->class != f2->sym->class)) return 0;
 FID_DUMP_BODY
 debug("%svariable %s with value %s\n", INDENT, item->sym->name, val_dump(item->vp));
 FID_END')
-m4_define(FRET, `FID_MEMBER(enum filter_return, fret, fret, %s, filter_return_str(item->fret))')
-m4_define(ECS, `FID_MEMBER(enum ec_subtype, ecs, ecs, ec subtype %s, ec_subtype_str(item->ecs))')
-m4_define(RTC, `FID_MEMBER(const struct rtable_config *, rtc, rtc, route table %s, item->rtc->name)')
-m4_define(STATIC_ATTR, `FID_MEMBER(struct f_static_attr, sa, sa)')
-m4_define(DYNAMIC_ATTR, `FID_MEMBER(struct f_dynamic_attr, da, da)')
-m4_define(COUNT, `FID_MEMBER(uint, count, count, number %u, item->count)')
-m4_define(TREE, `FID_MEMBER(const struct f_tree *, tree, tree, tree %p, item->tree)')
-m4_define(STRING, `FID_MEMBER(const char *, s, s, string \"%s\", item->s)')
+m4_define(FRET, `FID_MEMBER(enum filter_return, fret, fret, f1->fret != f2->fret, %s, filter_return_str(item->fret))')
+m4_define(ECS, `FID_MEMBER(enum ec_subtype, ecs, ecs, f1->ecs != f2->ecs, ec subtype %s, ec_subtype_str(item->ecs))')
+m4_define(RTC, `FID_MEMBER(const struct rtable_config *, rtc, rtc, [[strcmp(f1->rtc->name, f2->rtc->name)]], route table %s, item->rtc->name)')
+m4_define(STATIC_ATTR, `FID_MEMBER(struct f_static_attr, sa, sa, f1->sa.sa_code != f2->sa.sa_code)')
+m4_define(DYNAMIC_ATTR, `FID_MEMBER(struct f_dynamic_attr, da, da, f1->da.ea_code != f2->da.ea_code)')
+m4_define(COUNT, `FID_MEMBER(uint, count, count, f1->count != f2->count, number %u, item->count)')
+m4_define(TREE, `FID_MEMBER(const struct f_tree *, tree, tree, [[!same_tree(f1->tree, f2->tree)]], tree %p, item->tree)')
+m4_define(STRING, `FID_MEMBER(const char *, s, s, [[strcmp(f1->s, f2->s)]], string \"%s\", item->s)')
 
 m4_define(FID_WR_PUT_LIST)
 m4_define(FID_WR_DROP_LIST)
@@ -275,6 +294,32 @@ f_postfixify_concat(const struct f_inst * const inst[], uint count)
   return out;
 }
 
+/* Filter line comparison */
+int
+f_same(const struct f_line *fl1, const struct f_line *fl2)
+{
+  if ((!fl1) && (!fl2))
+    return 1;
+  if ((!fl1) || (!fl2))
+    return 0;
+  if (fl1->len != fl2->len)
+    return 0;
+  for (uint i=0; i<fl1->len; i++) {
+#define f1 (&(fl1->items[i]))
+#define f2 (&(fl2->items[i]))
+    if (f1->fi_code != f2->fi_code)
+      return 0;
+    if (f1->flags != f2->flags)
+      return 0;
+
+    switch(f1->fi_code) {
+FID_WR_PUT(9)
+    }
+  }
+  return 1;
+}
+
+
 FID_WR_DIRECT(900,H)
 /* Filter instruction codes */
 enum f_instruction_code {
diff --git a/filter/f-inst.c b/filter/f-inst.c
index 7d2641c2..4ab46529 100644
--- a/filter/f-inst.c
+++ b/filter/f-inst.c
@@ -730,6 +730,8 @@
       if (count != sym->aux2)
 	cf_error("Function %s takes %u arguments, got %u.", sym->name, sym->aux2, count);
     FID_END
+
+    /* FIXME: Optimization of function comparison. */
   }
 
   INST(FI_DROP_RESULT, 1, 0) {
diff --git a/filter/f-inst.h b/filter/f-inst.h
index ad994857..e1d0b675 100644
--- a/filter/f-inst.h
+++ b/filter/f-inst.h
@@ -82,8 +82,10 @@ extern void (*bt_assert_hook)(int result, const struct f_line_item *assert);
 struct f_bt_test_suite {
   node n;			/* Node in config->tests */
   struct f_line *fn;		/* Root of function */
+  struct f_line *cmp;		/* Compare to this function */
   const char *fn_name;		/* Name of test */
   const char *dsc;		/* Description */
+  int result;			/* Desired result */
 };
 
 #endif
diff --git a/filter/filter.c b/filter/filter.c
index d80309b8..29e78204 100644
--- a/filter/filter.c
+++ b/filter/filter.c
@@ -220,33 +220,6 @@ interpret(struct filter_state *fs, const struct f_line *line, struct f_val *val)
 }
 
 
-/*
- * f_same - function that does real comparing of instruction trees, you should call filter_same from outside
- */
-int
-f_same(const struct f_line *fl1, const struct f_line *fl2)
-{
-  if ((!fl1) && (!fl2))
-    return 1;
-  if ((!fl1) || (!fl2))
-    return 0;
-  if (fl1->len != fl2->len)
-    return 0;
-  for (uint i=0; i<fl1->len; i++) {
-#define f1 (&(fl1->items[i]))
-#define f2 (&(fl2->items[i]))
-    if (f1->fi_code != f2->fi_code)
-      return 0;
-    if (f1->flags != f2->flags)
-      return 0;
-
-    switch(f1->fi_code) {
-#include "filter/f-inst-same.c"
-    }
-  }
-  return 1;
-}
-
 /**
  * f_run - run a filter for a route
  * @filter: filter to run
diff --git a/filter/filter_test.c b/filter/filter_test.c
index edd73ac8..d83e8a8b 100644
--- a/filter/filter_test.c
+++ b/filter/filter_test.c
@@ -42,13 +42,22 @@ parse_config_file(const void *argv)
 }
 
 static int
-run_function(const void *parsed_fn_def)
+run_function(const void *arg)
 {
-  const struct f_line *f = (const struct f_line *) parsed_fn_def;
+  const struct f_bt_test_suite *t = arg;
+
+  if (t->cmp)
+    return t->result == f_same(t->fn, t->cmp);
+
+  if (!f_same(t->fn, t->fn)) {
+    bt_result = bt_suite_result = 0;
+    bt_log_suite_case_result(0, "The function doesn't compare to itself as the same");
+    return 0;
+  }
 
   linpool *tmp = lp_new_default(&root_pool);
   struct f_val res;
-  enum filter_return fret = f_eval(f, tmp, &res);
+  enum filter_return fret = f_eval(t->fn, tmp, &res);
   rfree(tmp);
 
   return (fret < F_REJECT);
@@ -79,6 +88,7 @@ main(int argc, char *argv[])
   struct config *c = NULL;
   struct parse_config_file_arg pcfa = { .cp = &c, .filename = BT_CONFIG_FILE };
   bt_test_suite_base(parse_config_file, "conf", (const void *) &pcfa, 0, 0, "parse config file");
+  bt_test_suite_base(parse_config_file, "reconf", (const void *) &pcfa, 0, 0, "reconfigure with the same file");
 
   bt_bird_cleanup();
 
@@ -86,7 +96,7 @@ main(int argc, char *argv[])
   {
     struct f_bt_test_suite *t;
     WALK_LIST(t, c->tests)
-      bt_test_suite_base(run_function, t->fn_name, t->fn, BT_FORKING, BT_TIMEOUT, "%s", t->dsc);
+      bt_test_suite_base(run_function, t->fn_name, t, BT_FORKING, BT_TIMEOUT, "%s", t->dsc);
   }
 
   return bt_exit_value();
diff --git a/filter/same.m4 b/filter/same.m4
deleted file mode 100644
index cf739af4..00000000
--- a/filter/same.m4
+++ /dev/null
@@ -1,63 +0,0 @@
-m4_divert(-1)m4_dnl
-#
-#	BIRD -- Filter Comparator Generator
-#
-#	(c) 2018 Maria Matejka <mq@jmq.cz>
-#
-#	Can be freely distributed and used under the terms of the GNU GPL.
-#
-
-# Common aliases
-m4_define(DNL, `m4_dnl')
-
-m4_define(INST_FLUSH, `m4_ifdef([[INST_NAME]], [[
-m4_divert(1)
-case INST_NAME():
-m4_undivert(2)
-break;
-m4_divert(-1)
-]])')
-m4_define(INST, `INST_FLUSH()m4_define([[INST_NAME]], [[$1]])')
-
-m4_define(ARG, `')
-m4_define(ARG_ANY, `')
-
-m4_define(LINE, `m4_divert(2)if (!f_same(f1->lines[$2], f2->lines[$2])) return 0;
-m4_divert(-1)')
-m4_define(LINEP, LINE)
-
-m4_define(SYMBOL, `m4_divert(2){
-  const struct symbol *s1 = f1->sym, *s2 = f2->sym;
-  if (strcmp(s1->name, s2->name)) return 0;
-  if (s1->class != s2->class) return 0;
-}
-m4_divert(-1)')
-
-m4_define(VALI, `m4_divert(2)if (!val_same(f1->vp, f2->vp)) return 0;
-m4_divert(-1)')
-m4_define(VALP, `m4_divert(2)if (!val_same(f1->vp, f2->vp)) return 0;
-m4_divert(-1)')
-m4_define(VAR, `SYMBOL()VALP()')
-
-m4_define(FRET, `m4_divert(2)if (f1->fret != f2->fret) return 0;
-m4_divert(-1)')
-m4_define(ECS, `m4_divert(2)if (f1->ecs != f2->ecs) return 0;
-m4_divert(-1)')
-m4_define(RTC, `m4_divert(2)if (strcmp(f1->rtc->name, f2->rtc->name)) return 0;
-m4_divert(-1)')
-m4_define(STATIC_ATTR, `m4_divert(2)if (f1->sa.sa_code != f2->sa.sa_code) return 0;
-m4_divert(-1)')
-m4_define(DYNAMIC_ATTR, `m4_divert(2)if (f1->da.ea_code != f2->da.ea_code) return 0;
-m4_divert(-1)')
-
-m4_define(SAME, `m4_divert(2)$1m4_divert(-1)')
-
-m4_m4wrap(`
-INST_FLUSH()
-m4_divert(0)DNL
-m4_undivert(1)
-default: bug( "Unknown instruction %d (%c)", f1->fi_code, f1->fi_code & 0xff);
-')
-
-m4_changequote([[,]])
-
diff --git a/filter/test.conf b/filter/test.conf
index e6b6ca4e..89215d1c 100644
--- a/filter/test.conf
+++ b/filter/test.conf
@@ -25,8 +25,19 @@ function onef(int a)
 	return 1;
 }
 
+function twof(int a)
+{
+	return 2;
+}
 
+function oneg(int a)
+{
+	return 1;
+}
 
+bt_test_same(onef, onef, 1);
+bt_test_same(onef, oneg, 1);
+bt_test_same(onef, twof, 0);
 
 /*
  * 	Testing boolean expressions
@@ -62,7 +73,6 @@ bt_test_suite(t_bool, "Testing boolean expressions");
 
 
 
-
 /*
  *	Testing integers
  *	----------------
@@ -1347,8 +1357,6 @@ filter vpn_filter
 	  NET_IP6: print "IPV6";
 	}
 
-# aoiufahkejtrhaweifdsbhydkfj,ysdnm
-
 	bt_check_assign(from, 10.20.30.40);
 	bt_check_assign(gw, 55.55.55.44);