diff --git a/complex.c b/complex.c
index 3e9d63117a..a83c63e3d8 100644
--- a/complex.c
+++ b/complex.c
@@ -18,10 +18,10 @@
 
 VALUE rb_cComplex;
 
-static ID id_abs, id_abs2, id_arg, id_cmp, id_conj, id_convert,
-    id_denominator, id_divmod, id_eqeq_p, id_expt, id_fdiv,  id_floor,
-    id_idiv, id_imag, id_inspect, id_negate, id_numerator, id_quo,
-    id_real, id_real_p, id_to_f, id_to_i, id_to_r, id_to_s,
+static ID id_abs, id_arg, id_convert,
+    id_denominator, id_eqeq_p, id_expt, id_fdiv,
+    id_inspect, id_negate, id_numerator, id_quo,
+    id_real_p, id_to_f, id_to_i, id_to_r, id_to_s,
     id_i_real, id_i_imag;
 
 #define f_boolcast(x) ((x) ? Qtrue : Qfalse)
@@ -75,20 +75,6 @@ f_add(VALUE x, VALUE y)
     return rb_funcall(x, '+', 1, y);
 }
 
-inline static VALUE
-f_cmp(VALUE x, VALUE y)
-{
-    if (FIXNUM_P(x) && FIXNUM_P(y)) {
-	long c = FIX2LONG(x) - FIX2LONG(y);
-	if (c > 0)
-	    c = 1;
-	else if (c < 0)
-	    c = -1;
-	return INT2FIX(c);
-    }
-    return rb_funcall(x, id_cmp, 1, y);
-}
-
 inline static VALUE
 f_div(VALUE x, VALUE y)
 {
@@ -105,16 +91,6 @@ f_gt_p(VALUE x, VALUE y)
     return rb_funcall(x, '>', 1, y);
 }
 
-inline static VALUE
-f_lt_p(VALUE x, VALUE y)
-{
-    if (FIXNUM_P(x) && FIXNUM_P(y))
-	return f_boolcast(FIX2LONG(x) < FIX2LONG(y));
-    return rb_funcall(x, '<', 1, y);
-}
-
-binop(mod, '%')
-
 inline static VALUE
 f_mul(VALUE x, VALUE y)
 {
@@ -152,16 +128,11 @@ f_sub(VALUE x, VALUE y)
 }
 
 fun1(abs)
-fun1(abs2)
 fun1(arg)
-fun1(conj)
 fun1(denominator)
-fun1(floor)
-fun1(imag)
 fun1(inspect)
 fun1(negate)
 fun1(numerator)
-fun1(real)
 fun1(real_p)
 
 inline static VALUE
@@ -182,8 +153,6 @@ f_to_f(VALUE x)
 fun1(to_r)
 fun1(to_s)
 
-fun2(divmod)
-
 inline static VALUE
 f_eqeq_p(VALUE x, VALUE y)
 {
@@ -194,7 +163,6 @@ f_eqeq_p(VALUE x, VALUE y)
 
 fun2(expt)
 fun2(fdiv)
-fun2(idiv)
 fun2(quo)
 
 inline static VALUE
@@ -257,12 +225,6 @@ k_numeric_p(VALUE x)
     return f_kind_of_p(x, rb_cNumeric);
 }
 
-inline static VALUE
-k_integer_p(VALUE x)
-{
-    return f_kind_of_p(x, rb_cInteger);
-}
-
 inline static VALUE
 k_fixnum_p(VALUE x)
 {
@@ -456,13 +418,6 @@ nucomp_s_new(int argc, VALUE *argv, VALUE klass)
     return nucomp_s_canonicalize_internal(klass, real, imag);
 }
 
-inline static VALUE
-f_complex_new1(VALUE klass, VALUE x)
-{
-    assert(!k_complex_p(x));
-    return nucomp_s_canonicalize_internal(klass, x, ZERO);
-}
-
 inline static VALUE
 f_complex_new2(VALUE klass, VALUE x, VALUE y)
 {
@@ -537,7 +492,6 @@ m_log_bang(VALUE x)
 
 imp1(sin)
 imp1(sinh)
-imp1(sqrt)
 
 static VALUE
 m_cos(VALUE x)
@@ -570,6 +524,8 @@ m_sin(VALUE x)
 }
 
 #if 0
+imp1(sqrt)
+
 static VALUE
 m_sqrt(VALUE x)
 {
@@ -2091,24 +2047,16 @@ Init_Complex(void)
     assert(fprintf(stderr, "assert() is now active\n"));
 
     id_abs = rb_intern("abs");
-    id_abs2 = rb_intern("abs2");
     id_arg = rb_intern("arg");
-    id_cmp = rb_intern("<=>");
-    id_conj = rb_intern("conj");
     id_convert = rb_intern("convert");
     id_denominator = rb_intern("denominator");
-    id_divmod = rb_intern("divmod");
     id_eqeq_p = rb_intern("==");
     id_expt = rb_intern("**");
     id_fdiv = rb_intern("fdiv");
-    id_floor = rb_intern("floor");
-    id_idiv = rb_intern("div");
-    id_imag = rb_intern("imag");
     id_inspect = rb_intern("inspect");
     id_negate = rb_intern("-@");
     id_numerator = rb_intern("numerator");
     id_quo = rb_intern("quo");
-    id_real = rb_intern("real");
     id_real_p = rb_intern("real?");
     id_to_f = rb_intern("to_f");
     id_to_i = rb_intern("to_i");
diff --git a/enc/utf_16be.c b/enc/utf_16be.c
index 8b25d473a7..3af8359caf 100644
--- a/enc/utf_16be.c
+++ b/enc/utf_16be.c
@@ -33,6 +33,7 @@
 #define UTF16_IS_SURROGATE_SECOND(c)   (((c) & 0xfc) == 0xdc)
 #define UTF16_IS_SURROGATE(c)          (((c) & 0xf8) == 0xd8)
 
+#if 0
 static const int EncLen_UTF16[] = {
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
@@ -51,6 +52,7 @@ static const int EncLen_UTF16[] = {
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
 };
+#endif
 
 static int
 utf16be_mbc_enc_len(const UChar* p, const OnigUChar* e ARG_UNUSED,
diff --git a/enc/utf_16le.c b/enc/utf_16le.c
index 8feb7ad769..453c771cc5 100644
--- a/enc/utf_16le.c
+++ b/enc/utf_16le.c
@@ -33,6 +33,7 @@
 #define UTF16_IS_SURROGATE_SECOND(c)   (((c) & 0xfc) == 0xdc)
 #define UTF16_IS_SURROGATE(c)          (((c) & 0xf8) == 0xd8)
 
+#if 0
 static const int EncLen_UTF16[] = {
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
@@ -51,6 +52,7 @@ static const int EncLen_UTF16[] = {
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
 };
+#endif
 
 static int
 utf16le_mbc_enc_len(const UChar* p, const OnigUChar* e,
diff --git a/ext/date/date_core.c b/ext/date/date_core.c
index 176c76ef0c..372f7bfd36 100644
--- a/ext/date/date_core.c
+++ b/ext/date/date_core.c
@@ -1723,23 +1723,6 @@ m_real_year(union DateData *x)
     return ry;
 }
 
-
-#ifdef USE_PACK
-inline static int
-m_pc(union DateData *x)
-{
-    if (simple_dat_p(x)) {
-	get_s_civil(x);
-	return x->s.pc;
-    }
-    else {
-	get_c_civil(x);
-	get_c_time(x);
-	return x->c.pc;
-    }
-}
-#endif
-
 inline static int
 m_mon(union DateData *x)
 {
@@ -1979,12 +1962,6 @@ k_date_p(VALUE x)
     return f_kind_of_p(x, cDate);
 }
 
-inline static VALUE
-k_datetime_p(VALUE x)
-{
-    return f_kind_of_p(x, cDateTime);
-}
-
 inline static VALUE
 k_numeric_p(VALUE x)
 {
diff --git a/rational.c b/rational.c
index fe2d11e692..c035a1a89f 100644
--- a/rational.c
+++ b/rational.c
@@ -31,7 +31,7 @@
 VALUE rb_cRational;
 
 static ID id_abs, id_cmp, id_convert, id_eqeq_p, id_expt, id_fdiv,
-    id_floor, id_idiv, id_integer_p, id_negate, id_to_f,
+    id_idiv, id_integer_p, id_negate, id_to_f,
     id_to_i, id_truncate, id_i_num, id_i_den;
 
 #define f_boolcast(x) ((x) ? Qtrue : Qfalse)
@@ -91,14 +91,6 @@ f_div(VALUE x, VALUE y)
     return rb_funcall(x, '/', 1, y);
 }
 
-inline static VALUE
-f_gt_p(VALUE x, VALUE y)
-{
-    if (FIXNUM_P(x) && FIXNUM_P(y))
-	return f_boolcast(FIX2LONG(x) > FIX2LONG(y));
-    return rb_funcall(x, '>', 1, y);
-}
-
 inline static VALUE
 f_lt_p(VALUE x, VALUE y)
 {
@@ -142,7 +134,6 @@ f_sub(VALUE x, VALUE y)
 }
 
 fun1(abs)
-fun1(floor)
 fun1(integer_p)
 fun1(negate)
 
@@ -161,8 +152,6 @@ f_to_f(VALUE x)
     return rb_funcall(x, id_to_f, 0);
 }
 
-fun1(truncate)
-
 inline static VALUE
 f_eqeq_p(VALUE x, VALUE y)
 {
@@ -474,14 +463,6 @@ f_rational_new_bang1(VALUE klass, VALUE x)
     return nurat_s_new_internal(klass, x, ONE);
 }
 
-inline static VALUE
-f_rational_new_bang2(VALUE klass, VALUE x, VALUE y)
-{
-    assert(f_positive_p(y));
-    assert(f_nonzero_p(y));
-    return nurat_s_new_internal(klass, x, y);
-}
-
 #ifdef CANONICALIZATION_FOR_MATHN
 #define CANON
 #endif
@@ -579,13 +560,6 @@ nurat_s_new(int argc, VALUE *argv, VALUE klass)
     return nurat_s_canonicalize_internal(klass, num, den);
 }
 
-inline static VALUE
-f_rational_new1(VALUE klass, VALUE x)
-{
-    assert(!k_rational_p(x));
-    return nurat_s_canonicalize_internal(klass, x, ONE);
-}
-
 inline static VALUE
 f_rational_new2(VALUE klass, VALUE x, VALUE y)
 {
@@ -594,13 +568,6 @@ f_rational_new2(VALUE klass, VALUE x, VALUE y)
     return nurat_s_canonicalize_internal(klass, x, y);
 }
 
-inline static VALUE
-f_rational_new_no_reduce1(VALUE klass, VALUE x)
-{
-    assert(!k_rational_p(x));
-    return nurat_s_canonicalize_internal_no_reduce(klass, x, ONE);
-}
-
 inline static VALUE
 f_rational_new_no_reduce2(VALUE klass, VALUE x, VALUE y)
 {
@@ -2530,7 +2497,6 @@ Init_Rational(void)
     id_eqeq_p = rb_intern("==");
     id_expt = rb_intern("**");
     id_fdiv = rb_intern("fdiv");
-    id_floor = rb_intern("floor");
     id_idiv = rb_intern("div");
     id_integer_p = rb_intern("integer?");
     id_negate = rb_intern("-@");