Support Ruby3.0 keyword arguments.

The Difference

Since Ruby1.9, the keyword arguments were emulated by Ruby using the hash
object at the bottom of the arguments. But we have gradually moved toward
keyword arguments separated from normal (positinal) arguments.

At the same time, we value compatibility, so that Ruby3.0 keyword
arguments are somewhat compromise. Basically, keyword arguments are
separated from positional arguments, except when the method does not
take any formal keyword arguments, given keyword arguments (packed
in the hash object) are considered as the last argument.

And we also allow non symbol keys in the keyword arguments. In that
case, those keys are just passed in the `**` hash (or raise
`ArgumentError` for unknown keys).

The Instruction Changes

We have changed `OP_SEND` instruction. `OP_SEND` instruction used to
take 3 operands, the register, the symbol, the number of (positional)
arguments. The meaning of the third operand has been changed. It is now
considered as `n|(nk<<4)`, where `n` is the number of positional
arguments, and `nk` is the number of keyword arguments, both occupies
4 bits in the operand.

The number `15` in both `n` and `nk` means variable sized arguments are
packed in the object. Positional arguments will be packed in the array,
and keyword arguments will be packed in the hash object. That means
arguments more than 14 values are always packed in the object.

Arguments information for other instructions (`OP_SENDB` and `OP_SUPER`)
are also changed. It works as the third operand of `OP_SEND`. the
difference between `OP_SEND` and `OP_SENDB` is just trivial. It assigns
`nil` to the block hidden arguments (right after arguments).

The instruction `OP_SENDV` and `OP_SENDVB` are removed. Those
instructions are replaced by `OP_SEND` and `OP_SENDB` respectively with
the `15` (variable sized) argument information.

Calling Convention

When calling a method, the stack elements shall be in the order of the
receiver of the method, positional arguments, keyword arguments and the
block argument. If the number of positional or keyword arugument (`n` or
`nk`) is zero, corresponding arguments will be empty. So when `n=0` and
`nk=0` the stack layout (from bottom to top) will be:

+-----------------------+
| recv | block (or nil) |
+-----------------------+

The last elements `block` should be explicitly filled before `OP_SEND`
or assigned to `nil` by `OP_SENDB` internally. In other words, the
following have exactly same behavior:

OP_SENDB clears `block` implicitly:

```
OP_SENDB reg sym 0
```

OP_SEND clears `block` implicitly:

```
OP_LOADNIL  R2
OP_SEND     R2 sym 0
```

When calling a method with only positional arguments (n=0..14) without
keyword arguments, the stack layout will be like following:

+--------------------------------------------+
| recv | arg1 | ... | arg_n | block (or nil) |
+--------------------------------------------+

When calling a method with arguments packed in the array (n=15) which
means argument splat (*) is used in the actual arguments, or more than
14 arguments are passed the stack layout will be like following:

+-------------------------------+
| recv | array | block (or nil) |
+-------------------------------+

The number of the actual arguments is determined by the length of the
argument array.

When keyword arguments are given (nk>0), keyword arguments are passed
between positional arguments and the block argument. For example, when
we pass one positional argument `1` and one keyword argument `a: 2`,
the stack layout will be like:

+------------------------------------+
| recv | 1 | :a | 2 | block (or nil) |
+------------------------------------+

Note that keyword arguments consume `2*nk` elements in the stack when
`nk=0..14` (unpacked).

When calling a method with keyword arguments packed in the hash object
(nk=15) which means keyword argument splat (**) is used or more than
14 keyword arguments in the actual arguments, the stack layout will
be like:

+------------------------------+
| recv | hash | block (or nil) |
+------------------------------+

Note for mruby/c

When mruby/c authors try to support new keyword arguments, they need
to handle the new meaning of the argument information operand. If they
choose not to support keyword arguments in mruby/c, it just raise
error when `nk` (taken by `(c>>4)&0xf`) is not zero. And combine
`OP_SENDV` behavior with `OP_SEND` when `n` is `15`.

If they want to support keyword arguments seriously, contact me at
<[email protected]> or `@yukihiro_matz`. I can help you.

7 files changed, 407 insertions, 366 deletions

diff --git a/src/class.c b/src/class.c
index fdf63794b..1403ed48e 100644
--- a/src/class.c
+++ b/src/class.c
@@ -812,9 +812,9 @@ ensure_class_type(mrb_state *mrb, mrb_value val)
 MRB_API mrb_int
 mrb_get_argc(mrb_state *mrb)
 {
-  mrb_int argc = mrb->c->ci->argc;
+  mrb_int argc = mrb->c->ci->n;
 
-  if (argc < 0) {
+  if (argc == 15) {
     struct RArray *a = mrb_ary_ptr(mrb->c->ci->stack[1]);
 
     argc = ARY_LEN(a);
@@ -825,9 +825,9 @@ mrb_get_argc(mrb_state *mrb)
 MRB_API const mrb_value*
 mrb_get_argv(mrb_state *mrb)
 {
-  mrb_int argc = mrb->c->ci->argc;
+  mrb_int argc = mrb->c->ci->n;
   mrb_value *array_argv = mrb->c->ci->stack + 1;
-  if (argc < 0) {
+  if (argc == 15) {
     struct RArray *a = mrb_ary_ptr(*array_argv);
 
     array_argv = ARY_PTR(a);
@@ -838,33 +838,37 @@ mrb_get_argv(mrb_state *mrb)
 MRB_API mrb_value
 mrb_get_arg1(mrb_state *mrb)
 {
-  mrb_int argc = mrb->c->ci->argc;
-  mrb_value *array_argv = mrb->c->ci->stack + 1;
-  if (argc < 0) {
+  mrb_callinfo *ci = mrb->c->ci;
+  mrb_int argc = ci->n;
+  mrb_value *array_argv = ci->stack + 1;
+  if (argc == 15) {
     struct RArray *a = mrb_ary_ptr(*array_argv);
 
     argc = ARY_LEN(a);
     array_argv = ARY_PTR(a);
   }
+  if (argc == 0 && ci->nk == 15) {
+    mrb_int n = ci->n;
+    if (n == 15) n = 1;
+    return ci->stack[n+1];      /* kwhash next to positional arguments */
+  }
   if (argc != 1) {
     mrb_argnum_error(mrb, argc, 1, 1);
   }
   return array_argv[0];
 }
 
+mrb_int mrb_ci_bidx(mrb_callinfo *ci);
+
 MRB_API mrb_bool
 mrb_block_given_p(mrb_state *mrb)
 {
-  const mrb_callinfo *ci = mrb->c->ci;
-  int argc = ci->argc;
-  int idx = (argc < 0) ? 2 : argc + 1;
-  mrb_value b = ci->stack[idx];
+  mrb_callinfo *ci = mrb->c->ci;
+  mrb_value b = ci->stack[mrb_ci_bidx(ci)];
 
   return !mrb_nil_p(b);
 }
 
-void mrb_hash_check_kdict(mrb_state *mrb, mrb_value self);
-
 /*
   retrieve arguments from mrb_state.
 
@@ -911,21 +915,17 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
   char c;
   int i = 0;
   va_list ap;
-  int argc = mrb->c->ci->argc;
-  const mrb_value *argv = mrb->c->ci->stack+1;
-  mrb_bool argv_on_stack = argc >= 0;
+  mrb_callinfo *ci = mrb->c->ci;
+  int argc = ci->n;
+  const mrb_value *argv = ci->stack+1;
+  mrb_bool argv_on_stack;
   mrb_bool opt = FALSE;
   mrb_bool opt_skip = TRUE;
   const mrb_value *pickarg = NULL; /* arguments currently being processed */
-  mrb_value kdict;
+  mrb_value kdict = mrb_nil_value();
   mrb_bool reqkarg = FALSE;
   int argc_min = 0, argc_max = 0;
 
-  if (!argv_on_stack) {
-    struct RArray *a = mrb_ary_ptr(*argv);
-    argv = ARY_PTR(a);
-    argc = ARY_LEN(a);
-  }
   va_start(ap, format);
 
   while ((c = *fmt++)) {
@@ -955,12 +955,41 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
   }
 
  check_exit:
-  if (reqkarg && argc > argc_min && mrb_hash_p(kdict = argv[argc - 1])) {
-    mrb_hash_check_kdict(mrb, kdict);
-    argc--;
+  if (!reqkarg && ci->nk > 0) {
+    mrb_assert(ci->nk == 15);
+    kdict = ci->stack[mrb_ci_bidx(ci)-1];
+    if (mrb_hash_p(kdict) && mrb_hash_size(mrb, kdict) > 0) {
+      if (argc < 14) {
+        ci->n++;
+        argc++;    /* include kdict in normal arguments */
+      }
+      else {
+        /* 14+1 == 15 so pack first */
+        if (argc == 14) {
+          /* pack arguments and kdict */
+          ci->stack[1] = mrb_ary_new_from_values(mrb, argc+1, &ci->stack[1]);
+          argc = ci->n = 15;
+        }
+        else {
+          /* push kdict to packed arguments */
+          mrb_ary_push(mrb, ci->stack[1], kdict);
+        }
+        ci->stack[2] = ci->stack[mrb_ci_bidx(ci)];
+      }
+      ci->nk = 0;
+    }
   }
-  else {
-    kdict = mrb_nil_value();
+  if (reqkarg && ci->nk > 0) {
+    kdict = ci->stack[mrb_ci_bidx(ci)-1];
+    mrb_assert(ci->nk == 15);
+    mrb_assert(mrb_hash_p(kdict));
+  }
+
+  argv_on_stack = argc < 15;
+  if (!argv_on_stack) {
+    struct RArray *a = mrb_ary_ptr(*argv);
+    argv = ARY_PTR(a);
+    argc = ARY_LEN(a);
   }
 
   opt = FALSE;
@@ -989,7 +1018,7 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
     case '|': case '*': case '&': case '?': case ':':
       if (needmodify) {
       bad_needmodify:
-        mrb_raisef(mrb, E_ARGUMENT_ERROR, "wrong `%c+` modified specifer`", c);
+        mrb_raisef(mrb, E_ARGUMENT_ERROR, "wrong `%c+` modified specifier`", c);
       }
       break;
     default:
@@ -1200,12 +1229,7 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
         mrb_value *p, *bp;
 
         p = va_arg(ap, mrb_value*);
-        if (mrb->c->ci->argc < 0) {
-          bp = mrb->c->ci->stack + 2;
-        }
-        else {
-          bp = mrb->c->ci->stack + mrb->c->ci->argc + 1;
-        }
+        bp = ci->stack + mrb_ci_bidx(ci);
         if (altmode && mrb_nil_p(*bp)) {
           mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
         }
@@ -2812,14 +2836,15 @@ inspect_main(mrb_state *mrb, mrb_value mod)
 }
 
 static const mrb_code new_iseq[] = {
-  OP_ENTER, 0x0, 0x10, 0x1,  /* OP_ENTER     0:0:1:0:0:0:1 */
-  OP_LOADSELF, 0x3,          /* OP_LOADSELF  R3 */
-  OP_SEND, 0x3, 0x0, 0x0,    /* OP_SEND      R3  :allocate  0 */
-  OP_MOVE, 0x0, 0x3,         /* OP_MOVE      R0  R3 */
-  OP_MOVE, 0x4, 0x1,         /* OP_MOVE      R4  R1 */
-  OP_MOVE, 0x5, 0x2,         /* OP_MOVE      R5  R2 */
-  OP_SENDVB, 0x3, 0x1,       /* OP_SENDVB    R3  :initialize */
-  OP_RETURN, 0x0             /* OP_RETURN    R0 */
+  OP_ENTER, 0x0, 0x10, 0x3,  // OP_ENTER     0:0:1:0:0:1:1
+  OP_LOADSELF, 4,            // OP_LOADSELF  R4
+  OP_SEND, 4, 0, 0,          // OP_SEND      R4  :allocate  n=0
+  OP_MOVE, 0, 4,             // OP_MOVE      R0  R4
+  OP_MOVE, 5, 1,             // OP_MOVE      R5  R1 (*)
+  OP_MOVE, 6, 2,             // OP_MOVE      R6  R2 (**)
+  OP_MOVE, 7, 3,             // OP_MOVE      R7  R3
+  OP_SENDB, 4, 1, 255,       // OP_SENDB     R4  :initialize n=*|nk=*
+  OP_RETURN, 0               // OP_RETURN    R0
 };
 
 MRB_PRESYM_DEFINE_VAR_AND_INITER(new_syms, 2, MRB_SYM(allocate), MRB_SYM(initialize))
diff --git a/src/codedump.c b/src/codedump.c
index 64f6314cf..6a9fcfb6a 100644
--- a/src/codedump.c
+++ b/src/codedump.c
@@ -57,6 +57,30 @@ print_header(mrb_state *mrb, const mrb_irep *irep, uint32_t i)
   printf("%03d ", (int)i);
 }
 
+static void
+print_args(uint8_t i)
+{
+  uint8_t n = i&0xf;
+  uint8_t nk = (i>>4)&0xf;
+
+  if (n == 15) {
+    printf("n=*");
+  }
+  else {
+    printf("n=%d", n);
+  }
+  if (nk > 0) {
+    printf("|");
+    if (nk == 15) {
+      printf("nk=*");
+    }
+    else {
+      printf("nk=%d", nk);
+    }
+  }
+  printf(" (0x%02x)\n", i);
+}
+
 #define CASE(insn,ops) case insn: FETCH_ ## ops (); L_ ## insn
 
 static void
@@ -294,26 +318,20 @@ codedump(mrb_state *mrb, const mrb_irep *irep)
       printf("OP_JMPNIL\tR%d\t%03d\t", a, (int)i+(int16_t)b);
       print_lv_a(mrb, irep, a);
       break;
-    CASE(OP_SENDV, BB):
-      printf("OP_SENDV\tR%d\t:%s\n", a, mrb_sym_dump(mrb, irep->syms[b]));
-      break;
-    CASE(OP_SENDVB, BB):
-      printf("OP_SENDVB\tR%d\t:%s\n", a, mrb_sym_dump(mrb, irep->syms[b]));
-      break;
     CASE(OP_SEND, BBB):
-      printf("OP_SEND\tR%d\t:%s\t%d\n", a, mrb_sym_dump(mrb, irep->syms[b]), c);
+      printf("OP_SEND\tR%d\t:%s\t", a, mrb_sym_dump(mrb, irep->syms[b]));
+      print_args(c);
       break;
     CASE(OP_SENDB, BBB):
-      printf("OP_SENDB\tR%d\t:%s\t%d\n", a, mrb_sym_dump(mrb, irep->syms[b]), c);
-      break;
-    CASE(OP_SENDVK, BB):
-      printf("OP_SENDVK\tR%d\t:%s\n", a, mrb_sym_dump(mrb, irep->syms[b]));
+      printf("OP_SENDB\tR%d\t:%s\t", a, mrb_sym_dump(mrb, irep->syms[b]));
+      print_args(c);
       break;
     CASE(OP_CALL, Z):
       printf("OP_CALL\n");
       break;
     CASE(OP_SUPER, BB):
-      printf("OP_SUPER\tR%d\t%d\n", a, b);
+      printf("OP_SUPER\tR%d\t", a);
+      print_args(b);
       break;
     CASE(OP_ARGARY, BS):
       printf("OP_ARGARY\tR%d\t%d:%d:%d:%d (%d)\t", a,
diff --git a/src/gc.c b/src/gc.c
index 2a7d7f6e1..8e8941cd7 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -599,27 +599,7 @@ add_gray_list(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
   gc->gray_list = obj;
 }
 
-static mrb_int
-ci_nregs(mrb_callinfo *ci)
-{
-  const struct RProc *p = ci->proc;
-  mrb_int n = 0;
-
-  if (!p) {
-    if (ci->argc < 0) return 3;
-    return ci->argc+2;
-  }
-  if (!MRB_PROC_CFUNC_P(p) && p->body.irep) {
-    n = p->body.irep->nregs;
-  }
-  if (ci->argc < 0) {
-    if (n < 3) n = 3; /* self + args + blk */
-  }
-  if (ci->argc > n) {
-    n = ci->argc + 2; /* self + blk */
-  }
-  return n;
-}
+mrb_int mrb_ci_nregs(mrb_callinfo *ci);
 
 static void
 mark_context_stack(mrb_state *mrb, struct mrb_context *c)
@@ -631,7 +611,7 @@ mark_context_stack(mrb_state *mrb, struct mrb_context *c)
   if (c->stbase == NULL) return;
   if (c->ci) {
     e = (c->ci->stack ? c->ci->stack - c->stbase : 0);
-    e += ci_nregs(c->ci);
+    e += mrb_ci_nregs(c->ci);
   }
   else {
     e = 0;
@@ -1029,7 +1009,7 @@ gc_gray_counts(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
       i = c->ci->stack - c->stbase;
 
       if (c->ci) {
-        i += ci_nregs(c->ci);
+        i += mrb_ci_nregs(c->ci);
       }
       if (c->stbase + i > c->stend) i = c->stend - c->stbase;
       children += i;
diff --git a/src/hash.c b/src/hash.c
index 918722a2b..a12e45bd7 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -1189,15 +1189,6 @@ mrb_hash_init_copy(mrb_state *mrb, mrb_value self)
   return self;
 }
 
-void
-mrb_hash_check_kdict(mrb_state *mrb, mrb_value self)
-{
-  h_each(mrb_hash_ptr(self), entry, {
-    if (mrb_symbol_p(entry->key)) continue;
-    mrb_raise(mrb, E_ARGUMENT_ERROR, "keyword argument hash with non symbol keys");
-  });
-}
-
 MRB_API mrb_value
 mrb_hash_dup(mrb_state *mrb, mrb_value self)
 {
diff --git a/src/kernel.c b/src/kernel.c
index f8ef1bfe1..ae9709f3c 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -186,13 +186,10 @@ mrb_f_block_given_p_m(mrb_state *mrb, mrb_value self)
     bp = &e->stack[bidx];
   }
   else {
-    bp = ci->stack+1;
-    if (ci->argc >= 0) {
-      bp += ci->argc;
-    }
-    else {
-      bp++;
-    }
+    uint8_t n = ci->n == 15 ? 1 : ci->n;
+    uint8_t k = ci->nk == 15 ? 1 : ci->nk*2;
+    bidx = n + k + 1;      /* self + args + kargs => bidx */
+    bp = &ci->stack[bidx];
   }
  block_given:
   if (mrb_nil_p(*bp))
diff --git a/src/proc.c b/src/proc.c
index d48145f13..c79a53399 100644
--- a/src/proc.c
+++ b/src/proc.c
@@ -79,14 +79,15 @@ struct REnv*
 mrb_env_new(mrb_state *mrb, struct mrb_context *c, mrb_callinfo *ci, int nstacks, mrb_value *stack, struct RClass *tc)
 {
   struct REnv *e;
-  mrb_int bidx;
+  mrb_int bidx = 1;
+  int n = ci->n;
+  int nk = ci->nk;
 
   e = MRB_OBJ_ALLOC(mrb, MRB_TT_ENV, NULL);
   e->c = tc;
   MRB_ENV_SET_LEN(e, nstacks);
-  bidx = ci->argc;
-  if (bidx < 0) bidx = 2;
-  else bidx += 1;
+  bidx += (n == 15) ? 1 : n;
+  bidx += (nk == 15) ? 1 : (2*nk);
   MRB_ENV_SET_BIDX(e, bidx);
   e->mid = ci->mid;
   e->stack = stack;
diff --git a/src/vm.c b/src/vm.c
index 7c69b9c3b..1c59d4406 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -80,7 +80,8 @@ mrb_gc_arena_shrink(mrb_state *mrb, int idx)
 #define mrb_gc_arena_shrink(mrb,idx) mrb_gc_arena_restore(mrb,idx)
 #endif
 
-#define CALL_MAXARGS 127
+#define CALL_MAXARGS 15
+#define CALL_VARARGS (CALL_MAXARGS<<4 | CALL_MAXARGS)
 
 void mrb_method_missing(mrb_state *mrb, mrb_sym name, mrb_value self, mrb_value args);
 
@@ -244,7 +245,7 @@ top_proc(mrb_state *mrb, const struct RProc *proc)
 
 static inline mrb_callinfo*
 cipush(mrb_state *mrb, mrb_int push_stacks, uint8_t cci,
-       struct RClass *target_class, const struct RProc *proc, mrb_sym mid, mrb_int argc)
+       struct RClass *target_class, const struct RProc *proc, mrb_sym mid, uint8_t argc)
 {
   struct mrb_context *c = mrb->c;
   mrb_callinfo *ci = c->ci;
@@ -263,7 +264,8 @@ cipush(mrb_state *mrb, mrb_int push_stacks, uint8_t cci,
   ci->mid = mid;
   mrb_vm_ci_proc_set(ci, proc);
   ci->stack = ci[-1].stack + push_stacks;
-  ci->argc = (int16_t)argc;
+  ci->n = argc & 0xf;
+  ci->nk = (argc>>4) & 0xf;
   ci->cci = cci;
   ci->u.target_class = target_class;
 
@@ -392,27 +394,41 @@ mrb_funcall_id(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc, ...)
 }
 
 static mrb_int
-ci_nregs(mrb_callinfo *ci)
+mrb_ci_kidx(mrb_callinfo *ci)
+{
+  if (ci->nk == 0) return -1;
+  return (ci->n % 14) + 1;
+}
+
+static mrb_int
+mrb_bidx(uint16_t c)
+{
+  uint8_t n = c & 0xf;
+  uint8_t k = (c>>4) & 0xf;
+  if (n == 15) n = 1;
+  if (k == 15) n += 1;
+  else n += k*2;
+  return n + 1;                 /* self + args + kargs */
+}
+
+mrb_int
+mrb_ci_bidx(mrb_callinfo *ci)
+{
+  return mrb_bidx(ci->n|(ci->nk<<4));
+}
+
+mrb_int
+mrb_ci_nregs(mrb_callinfo *ci)
 {
   const struct RProc *p;
-  mrb_int n = 0;
 
-  if (!ci) return 3;
+  if (!ci) return 4;
+  uint8_t nregs = mrb_ci_bidx(ci) + 1; /* self + args + kargs + blk */
   p = ci->proc;
-  if (!p) {
-    if (ci->argc < 0) return 3;
-    return ci->argc+2;
+  if (p && !MRB_PROC_CFUNC_P(p) && p->body.irep && p->body.irep->nregs > nregs) {
+    return p->body.irep->nregs;
   }
-  if (!MRB_PROC_CFUNC_P(p) && p->body.irep) {
-    n = p->body.irep->nregs;
-  }
-  if (ci->argc < 0) {
-    if (n < 3) n = 3; /* self + args + blk */
-  }
-  if (ci->argc > n) {
-    n = ci->argc + 2; /* self + blk */
-  }
-  return n;
+  return nregs;
 }
 
 MRB_API mrb_value
@@ -444,43 +460,45 @@ mrb_funcall_with_block(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc
   else {
     mrb_method_t m;
     struct RClass *c;
-    mrb_callinfo *ci;
-    mrb_int n = ci_nregs(mrb->c->ci);
+    mrb_callinfo *ci = mrb->c->ci;
+    mrb_int n = mrb_ci_nregs(ci);
     ptrdiff_t voff = -1;
 
     if (!mrb->c->stbase) {
       stack_init(mrb);
     }
+    if (ci - mrb->c->cibase > MRB_CALL_LEVEL_MAX) {
+      mrb_exc_raise(mrb, mrb_obj_value(mrb->stack_err));
+    }
+    if (mrb->c->stbase <= argv && argv < mrb->c->stend) {
+      voff = argv - mrb->c->stbase;
+    }
     if (argc < 0) {
       mrb_raisef(mrb, E_ARGUMENT_ERROR, "negative argc for funcall (%i)", argc);
     }
     c = mrb_class(mrb, self);
     m = mrb_method_search_vm(mrb, &c, mid);
+    mrb_stack_extend(mrb, argc + 3);
+    if (MRB_METHOD_UNDEF_P(m) || argc >= 15) {
+      mrb_value args = mrb_ary_new_from_values(mrb, argc, argv);
+
+      ci->stack[n+1] = args;
+      argc = 15;
+    }
     if (MRB_METHOD_UNDEF_P(m)) {
       mrb_sym missing = MRB_SYM(method_missing);
-      mrb_value args = mrb_ary_new_from_values(mrb, argc, argv);
+      mrb_value args = ci->stack[n+1];
+
       m = mrb_method_search_vm(mrb, &c, missing);
       if (MRB_METHOD_UNDEF_P(m)) {
         mrb_method_missing(mrb, mid, self, args);
       }
       mrb_ary_unshift(mrb, args, mrb_symbol_value(mid));
       mrb_stack_extend(mrb, n+2);
-      mrb->c->ci->stack[n+1] = args;
-      argc = -1;
+      ci->stack[n+1] = args;
+      argc = 15;
     }
     ci = cipush(mrb, n, 0, c, NULL, mid, argc);
-    if (argc < 0) argc = 1;
-    if (mrb->c->stbase <= argv && argv < mrb->c->stend) {
-      voff = argv - mrb->c->stbase;
-    }
-    if (argc >= CALL_MAXARGS) {
-      mrb_value args = mrb_ary_new_from_values(mrb, argc, argv);
-
-      mrb->c->ci->stack[1] = args;
-      ci->argc = -1;
-      argc = 1;
-    }
-    mrb_stack_extend(mrb, argc + 2);
     if (MRB_METHOD_PROC_P(m)) {
       struct RProc *p = MRB_METHOD_PROC(m);
 
@@ -492,11 +510,15 @@ mrb_funcall_with_block(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc
     if (voff >= 0) {
       argv = mrb->c->stbase + voff;
     }
-    mrb->c->ci->stack[0] = self;
-    if (ci->argc > 0) {
-      stack_copy(mrb->c->ci->stack+1, argv, argc);
+    ci->stack[0] = self;
+    if (argc < 15) {
+      if (argc > 0)
+        stack_copy(ci->stack+1, argv, argc);
+      ci->stack[argc+1] = blk;
+    }
+    else {
+      ci->stack[2] = blk;
     }
-    mrb->c->ci->stack[argc+1] = blk;
 
     if (MRB_METHOD_CFUNC_P(m)) {
       ci->cci = CINFO_DIRECT;
@@ -531,8 +553,7 @@ exec_irep(mrb_state *mrb, mrb_value self, struct RProc *p)
     return MRB_PROC_CFUNC(p)(mrb, self);
   }
   nregs = p->body.irep->nregs;
-  if (ci->argc < 0) keep = 3;
-  else keep = ci->argc + 2;
+  keep = mrb_ci_bidx(ci)+1;
   if (nregs < keep) {
     mrb_stack_extend(mrb, keep);
   }
@@ -556,12 +577,12 @@ mrb_exec_irep(mrb_state *mrb, mrb_value self, struct RProc *p)
   else {
     mrb_value ret;
     if (MRB_PROC_CFUNC_P(p)) {
-      cipush(mrb, 0, CINFO_DIRECT, mrb_vm_ci_target_class(ci), p, ci->mid, ci->argc);
+      cipush(mrb, 0, CINFO_DIRECT, mrb_vm_ci_target_class(ci), p, ci->mid, ci->n|(ci->nk<<4));
       ret = MRB_PROC_CFUNC(p)(mrb, self);
       cipop(mrb);
     }
     else {
-      int keep = (ci->argc < 0 ? 1 : ci->argc) + 2 /* receiver + block */;
+      int keep = mrb_ci_bidx(ci) + 1; /* receiver + block */
       ret = mrb_top_run(mrb, p, self, keep);
     }
     if (mrb->exc && mrb->jmp) {
@@ -595,19 +616,31 @@ mrb_f_send(mrb_state *mrb, mrb_value self)
 {
   mrb_sym name;
   mrb_value block, *regs;
-  const mrb_value *argv;
-  mrb_int argc, i, len;
   mrb_method_t m;
   struct RClass *c;
-  mrb_callinfo *ci;
+  mrb_callinfo *ci = mrb->c->ci;
+  int n = ci->n;
 
-  mrb_get_args(mrb, "n*&", &name, &argv, &argc, &block);
-  ci = mrb->c->ci;
   if (ci->cci > CINFO_NONE) {
-  funcall:
+  funcall:;
+    const mrb_value *argv;
+    mrb_int argc;
+    mrb_get_args(mrb, "n*&", &name, &argv, &argc, &block);
     return mrb_funcall_with_block(mrb, self, name, argc, argv, block);
   }
 
+  regs = mrb->c->ci->stack+1;
+
+  if (n == 0) {
+    mrb_argnum_error(mrb, 0, 1, -1);
+  }
+  else if (n == 15) {
+    name = mrb_obj_to_sym(mrb, RARRAY_PTR(regs[0])[0]);
+  }
+  else {
+    name = mrb_obj_to_sym(mrb, regs[0]);
+  }
+
   c = mrb_class(mrb, self);
   m = mrb_method_search_vm(mrb, &c, name);
   if (MRB_METHOD_UNDEF_P(m)) {            /* call method_mising */
@@ -616,16 +649,19 @@ mrb_f_send(mrb_state *mrb, mrb_value self)
 
   ci->mid = name;
   ci->u.target_class = c;
-  regs = mrb->c->ci->stack+1;
   /* remove first symbol from arguments */
-  if (ci->argc >= 0) {
-    for (i=0,len=ci->argc; i<len; i++) {
+  if (n == 15) {     /* variable length arguments */
+    regs[0] = mrb_ary_subseq(mrb, regs[0], 1, RARRAY_LEN(regs[0]) - 1);
+  }
+  else { /* n > 0 */
+    for (int i=0; i<n; i++) {
       regs[i] = regs[i+1];
     }
-    ci->argc--;
-  }
-  else {                     /* variable length arguments */
-    regs[0] = mrb_ary_subseq(mrb, regs[0], 1, RARRAY_LEN(regs[0]) - 1);
+    regs[n] = regs[n+1];        /* copy kdict or block */
+    if (ci->nk > 0) {
+      regs[n+1] = regs[n+2];    /* copy block */
+    }
+    ci->n--;
   }
 
   if (MRB_METHOD_CFUNC_P(m)) {
@@ -654,17 +690,18 @@ eval_under(mrb_state *mrb, mrb_value self, mrb_value blk, struct RClass *c)
   ci->u.target_class = c;
   p = mrb_proc_ptr(blk);
   mrb_vm_ci_proc_set(ci, p);
-  ci->argc = 1;
+  ci->n = 1;
+  ci->nk = 0;
   ci->mid = ci[-1].mid;
   if (MRB_PROC_CFUNC_P(p)) {
-    mrb_stack_extend(mrb, 3);
+    mrb_stack_extend(mrb, 4);
     mrb->c->ci->stack[0] = self;
     mrb->c->ci->stack[1] = self;
     mrb->c->ci->stack[2] = mrb_nil_value();
     return MRB_PROC_CFUNC(p)(mrb, self);
   }
   nregs = p->body.irep->nregs;
-  if (nregs < 3) nregs = 3;
+  if (nregs < 4) nregs = 4;
   mrb_stack_extend(mrb, nregs);
   mrb->c->ci->stack[0] = self;
   mrb->c->ci->stack[1] = self;
@@ -740,27 +777,28 @@ mrb_yield_with_class(mrb_state *mrb, mrb_value b, mrb_int argc, const mrb_value
     mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
   }
   ci = mrb->c->ci;
-  n = ci_nregs(ci);
+  n = mrb_ci_nregs(ci);
   p = mrb_proc_ptr(b);
   ci = cipush(mrb, n, CINFO_SKIP, c, p, mid, 0 /* dummy */);
+  ci->nk = 0;
   if (argc >= CALL_MAXARGS) {
-    ci->argc = -1;
+    ci->n = 15;
     n = 3;
   }
   else {
-    ci->argc = (int)argc;
+    ci->n = argc;
     n = argc + 2;
   }
   mrb_stack_extend(mrb, n);
   mrb->c->ci->stack[0] = self;
-  if (ci->argc < 0) {
+  if (ci->n == 15) {
     mrb->c->ci->stack[1] = mrb_ary_new_from_values(mrb, argc, argv);
     argc = 1;
   }
   else if (argc > 0) {
     stack_copy(mrb->c->ci->stack+1, argv, argc);
   }
-  mrb->c->ci->stack[argc+1] = mrb_nil_value();
+  mrb->c->ci->stack[argc+1] = mrb_nil_value(); /* clear blk */
 
   if (MRB_PROC_CFUNC_P(p)) {
     ci->cci = CINFO_DIRECT;
@@ -805,10 +843,12 @@ mrb_yield_cont(mrb_state *mrb, mrb_value b, mrb_value self, mrb_int argc, const
   p = mrb_proc_ptr(b);
   ci = mrb->c->ci;
 
-  mrb_stack_extend(mrb, 3);
+  mrb_stack_extend(mrb, 4);
   mrb->c->ci->stack[1] = mrb_ary_new_from_values(mrb, argc, argv);
   mrb->c->ci->stack[2] = mrb_nil_value();
-  ci->argc = -1;
+  mrb->c->ci->stack[3] = mrb_nil_value();
+  ci->n = 15;
+  ci->nk = 0;
   return exec_irep(mrb, self, p);
 }
 
@@ -890,9 +930,9 @@ argnum_error(mrb_state *mrb, mrb_int num)
 {
   mrb_value exc;
   mrb_value str;
-  mrb_int argc = mrb->c->ci->argc;
+  mrb_int argc = mrb->c->ci->n;
 
-  if (argc < 0) {
+  if (argc == 15) {
     mrb_value args = mrb->c->ci->stack[1];
     if (mrb_array_p(args)) {
       argc = RARRAY_LEN(args);
@@ -1051,15 +1091,63 @@ check_target_class(mrb_state *mrb)
   return target;
 }
 
-mrb_value
-get_send_args(mrb_state *mrb, mrb_int argc, mrb_value *regs)
+static mrb_value
+hash_new_from_values(mrb_state *mrb, mrb_int argc, mrb_value *regs)
 {
-  if (argc < 0) return regs[0];
-  return mrb_ary_new_from_values(mrb, argc, regs);
+  mrb_value hash = mrb_hash_new_capa(mrb, argc);
+  while (argc--) {
+    mrb_hash_set(mrb, hash, regs[0], regs[1]);
+    regs += 2;
+  }
+  return hash;
 }
 
 mrb_value mrb_obj_missing(mrb_state *mrb, mrb_value mod);
-void mrb_hash_check_kdict(mrb_state *mrb, mrb_value self);
+
+static mrb_method_t
+prepare_missing(mrb_state *mrb, mrb_value recv, mrb_sym mid, struct RClass **clsp, uint32_t a, uint16_t *c, mrb_value blk, int super)
+{
+  mrb_sym missing = MRB_SYM(method_missing);
+  mrb_callinfo *ci = mrb->c->ci;
+  uint16_t b = *c;
+  mrb_int n = b & 0xf;
+  mrb_int nk = (b>>4) & 0xf;
+  mrb_value *argv = &ci->stack[a+1];
+  mrb_value args;
+  mrb_method_t m;
+
+  /* pack positional arguments */
+  if (n == 15) args = argv[0];
+  else args = mrb_ary_new_from_values(mrb, n, argv);
+
+  if (mrb_func_basic_p(mrb, recv, missing, mrb_obj_missing)) {
+  method_missing:
+    if (super) mrb_no_method_error(mrb, mid, args, "no superclass method '%n'", mid);
+    else mrb_method_missing(mrb, mid, recv, args);
+    /* not reached */
+  }
+  if (mid != missing) {
+    *clsp = mrb_class(mrb, recv);
+  }
+  m = mrb_method_search_vm(mrb, clsp, missing);
+  if (MRB_METHOD_UNDEF_P(m)) goto method_missing; /* just in case */
+  mrb_stack_extend(mrb, a+4);
+
+  argv = &ci->stack[a+1];       /* maybe reallocated */
+  argv[0] = args;
+  if (nk == 0) {
+    argv[1] = blk;
+  }
+  else {
+    mrb_assert(nk == 15);
+    argv[1] = argv[n];
+    argv[2] = blk;
+  }
+  *c = 15 | (nk<<4);
+  mrb_ary_unshift(mrb, args, mrb_symbol_value(mid));
+  return m;
+}
+
 void mrb_method_added(mrb_state *mrb, struct RClass *c, mrb_sym mid);
 mrb_value mrb_str_aref(mrb_state *mrb, mrb_value str, mrb_value idx, mrb_value len);
 
@@ -1451,84 +1539,63 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_SENDV, BB) {
-      c = CALL_MAXARGS;
-      goto L_SEND;
-    };
-
-    CASE(OP_SENDVB, BB) {
-      c = CALL_MAXARGS;
-      goto L_SENDB;
-    };
-
     CASE(OP_SEND, BBB)
-    L_SEND:
-    {
-      /* push nil after arguments */
-      int bidx = (c == CALL_MAXARGS) ? a+2 : a+c+1;
-      SET_NIL_VALUE(regs[bidx]);
-      goto L_SENDB;
-    };
+    goto L_SENDB;
+
     L_SEND_SYM:
-    {
-      /* push nil after arguments */
-      int bidx = (c == CALL_MAXARGS) ? a+2 : a+c+1;
-      SET_NIL_VALUE(regs[bidx]);
-      goto L_SENDB_SYM;
-    };
+    c = 1;
+    /* push nil after arguments */
+    SET_NIL_VALUE(regs[a+2]);
+    goto L_SENDB_SYM;
 
     CASE(OP_SENDB, BBB)
     L_SENDB:
     mid = syms[b];
     L_SENDB_SYM:
     {
-      mrb_int argc = (c == CALL_MAXARGS) ? -1 : c;
-      mrb_int bidx = (argc < 0) ? a+2 : a+c+1;
+      int n = c&0xf;
+      int nk = (c>>4)&0xf;
+      mrb_callinfo *ci = mrb->c->ci;
+      mrb_int bidx = a + ((n == 15) ? 1 : n) + ((nk == 15) ? 1 : 2*nk) + 1;
       mrb_method_t m;
       struct RClass *cls;
-      mrb_callinfo *ci = mrb->c->ci;
-      mrb_value recv, blk;
+      mrb_value recv;
 
-      mrb_assert(bidx < irep->nregs);
+      if (0 < nk && nk < 15) {  /* pack keyword arguments */
+        mrb_int kidx = a+n+1;
+        mrb_value kdict = hash_new_from_values(mrb, nk, regs+kidx);
+        regs[kidx] = kdict;
+        nk = 15;
+        c = n | (nk<<4);
+      }
 
-      recv = regs[a];
-      blk = regs[bidx];
-      if (!mrb_nil_p(blk) && !mrb_proc_p(blk)) {
-        blk = mrb_type_convert(mrb, blk, MRB_TT_PROC, MRB_SYM(to_proc));
-        /* The stack might have been reallocated during mrb_type_convert(),
-           see #3622 */
-        regs[bidx] = blk;
+      mrb_assert(bidx < irep->nregs+a);
+      mrb_value blk = mrb_nil_value();
+      mrb_int new_bidx = a+((n==15)?1:n)+1+(nk==15);
+      if (insn == OP_SEND) {
+        /* clear block argument */
+        SET_NIL_VALUE(regs[new_bidx]);
+      }
+      else {
+        blk = regs[bidx];
+        if (!mrb_nil_p(blk) && !mrb_proc_p(blk)) {
+          blk = mrb_type_convert(mrb, blk, MRB_TT_PROC, MRB_SYM(to_proc));
+          /* The stack might have been reallocated during mrb_type_convert(),
+             see #3622 */
+        }
+        regs[new_bidx] = blk;
       }
+
+      recv = regs[a];
       cls = mrb_class(mrb, recv);
       m = mrb_method_search_vm(mrb, &cls, mid);
       if (MRB_METHOD_UNDEF_P(m)) {
-        mrb_sym missing = MRB_SYM(method_missing);
-        mrb_value args;
-
-        if (mrb_func_basic_p(mrb, recv, missing, mrb_obj_missing)) {
-        method_missing:
-          args = get_send_args(mrb, argc, regs+a+1);
-          mrb_method_missing(mrb, mid, recv, args);
-        }
-        if (mid != missing) {
-          cls = mrb_class(mrb, recv);
-        }
-        m = mrb_method_search_vm(mrb, &cls, missing);
-        if (MRB_METHOD_UNDEF_P(m)) goto method_missing; /* just in case */
-        if (argc >= 0) {
-          if (a+2 >= irep->nregs) {
-            mrb_stack_extend(mrb, a+3);
-          }
-          regs[a+1] = mrb_ary_new_from_values(mrb, c, regs+a+1);
-          regs[a+2] = blk;
-          argc = -1;
-        }
-        mrb_ary_unshift(mrb, regs[a+1], mrb_symbol_value(mid));
-        mid = missing;
+        m = prepare_missing(mrb, recv, mid, &cls, a, &c, blk, 0);
+        mid = MRB_SYM(method_missing);
       }
 
       /* push callinfo */
-      ci = cipush(mrb, a, 0, cls, NULL, mid, argc);
+      ci = cipush(mrb, a, 0, cls, NULL, mid, c);
 
       if (MRB_METHOD_CFUNC_P(m)) {
         if (MRB_METHOD_PROC_P(m)) {
@@ -1538,7 +1605,7 @@ RETRY_TRY_BLOCK:
           recv = p->body.func(mrb, recv);
         }
         else if (MRB_METHOD_NOARG_P(m) &&
-                 (argc > 0 || (argc == -1 && RARRAY_LEN(regs[1]) != 0))) {
+                 !(n == 0 || (n == CALL_MAXARGS && RARRAY_LEN(regs[1]) == 0))) {
           argnum_error(mrb, 0);
           goto L_RAISE;
         }
@@ -1567,7 +1634,7 @@ RETRY_TRY_BLOCK:
             syms = irep->syms;
           }
         }
-        mrb->c->ci->stack[0] = recv;
+        ci->stack[0] = recv;
         /* pop stackpos */
         ci = cipop(mrb);
         pc = ci->pc;
@@ -1578,19 +1645,18 @@ RETRY_TRY_BLOCK:
         irep = proc->body.irep;
         pool = irep->pool;
         syms = irep->syms;
-        mrb_stack_extend(mrb, (argc < 0 && irep->nregs < 3) ? 3 : irep->nregs);
+        mrb_stack_extend(mrb, (irep->nregs < 4) ? 4 : irep->nregs);
         pc = irep->iseq;
       }
     }
     JUMP;
 
     CASE(OP_CALL, Z) {
-      mrb_callinfo *ci;
-      mrb_value recv = mrb->c->ci->stack[0];
+      mrb_callinfo *ci = mrb->c->ci;
+      mrb_value recv = ci->stack[0];
       struct RProc *m = mrb_proc_ptr(recv);
 
       /* replace callinfo */
-      ci = mrb->c->ci;
       ci->u.target_class = MRB_PROC_TARGET_CLASS(m);
       mrb_vm_ci_proc_set(ci, m);
       if (MRB_PROC_ENV_P(m)) {
@@ -1623,14 +1689,10 @@ RETRY_TRY_BLOCK:
         }
         pool = irep->pool;
         syms = irep->syms;
-        mrb_stack_extend(mrb, irep->nregs);
-        if (ci->argc < 0) {
-          if (irep->nregs > 3) {
-            stack_clear(regs+3, irep->nregs-3);
-          }
-        }
-        else if (ci->argc+2 < irep->nregs) {
-          stack_clear(regs+ci->argc+2, irep->nregs-ci->argc-2);
+        mrb_int nargs = mrb_ci_bidx(ci)+1;
+        if (nargs < irep->nregs) {
+          mrb_stack_extend(mrb, irep->nregs);
+          stack_clear(regs+nargs, irep->nregs-nargs);
         }
         if (MRB_PROC_ENV_P(m)) {
           regs[0] = MRB_PROC_ENV(m)->stack[0];
@@ -1641,11 +1703,10 @@ RETRY_TRY_BLOCK:
     }
 
     CASE(OP_SUPER, BB) {
-      mrb_int argc = (b == CALL_MAXARGS) ? -1 : b;
-      int bidx = (argc < 0) ? a+2 : a+b+1;
       mrb_method_t m;
       struct RClass *cls;
       mrb_callinfo *ci = mrb->c->ci;
+      mrb_int bidx = mrb_bidx(b)+a;
       mrb_value recv, blk;
       const struct RProc *p = ci->proc;
       mrb_sym mid = ci->mid;
@@ -1689,36 +1750,15 @@ RETRY_TRY_BLOCK:
       cls = target_class->super;
       m = mrb_method_search_vm(mrb, &cls, mid);
       if (MRB_METHOD_UNDEF_P(m)) {
-        mrb_sym missing = MRB_SYM(method_missing);
-        mrb_value args;
-
-        if (mrb_func_basic_p(mrb, recv, missing, mrb_obj_missing)) {
-        super_missing:
-          args = get_send_args(mrb, argc, regs+a+1);
-          mrb_no_method_error(mrb, mid, args, "no superclass method '%n'", mid);
-        }
-        if (mid != missing) {
-          cls = mrb_class(mrb, recv);
-        }
-        m = mrb_method_search_vm(mrb, &cls, missing);
-        if (MRB_METHOD_UNDEF_P(m)) goto super_missing; /* just in case */
-        if (argc >= 0) {
-          if (a+2 >= irep->nregs) {
-            mrb_stack_extend(mrb, a+3);
-          }
-          regs[a+1] = mrb_ary_new_from_values(mrb, b, regs+a+1);
-          regs[a+2] = blk;
-          argc = -1;
-        }
-        mrb_ary_unshift(mrb, regs[a+1], mrb_symbol_value(mid));
-        mid = missing;
+        m = prepare_missing(mrb, recv, mid, &cls, a, &b, blk, 1);
+        mid = MRB_SYM(method_missing);
       }
 
       /* push callinfo */
-      ci = cipush(mrb, a, 0, cls, NULL, mid, argc);
+      ci = cipush(mrb, a, 0, cls, NULL, mid, b);
 
       /* prepare stack */
-      mrb->c->ci->stack[0] = recv;
+      ci->stack[0] = recv;
 
       if (MRB_METHOD_CFUNC_P(m)) {
         mrb_value v;
@@ -1755,7 +1795,7 @@ RETRY_TRY_BLOCK:
         irep = proc->body.irep;
         pool = irep->pool;
         syms = irep->syms;
-        mrb_stack_extend(mrb, (argc < 0 && irep->nregs < 3) ? 3 : irep->nregs);
+        mrb_stack_extend(mrb, (irep->nregs < 4) ? 4 : irep->nregs);
         pc = irep->iseq;
         JUMP;
       }
@@ -1781,12 +1821,12 @@ RETRY_TRY_BLOCK:
       else {
         struct REnv *e = uvenv(mrb, lv-1);
         if (!e) goto L_NOSUPER;
-        if (MRB_ENV_LEN(e) <= m1+r+m2+kd+1)
+        if (MRB_ENV_LEN(e) <= m1+r+m2+1)
           goto L_NOSUPER;
         stack = e->stack + 1;
       }
       if (r == 0) {
-        regs[a] = mrb_ary_new_from_values(mrb, m1+m2+kd, stack);
+        regs[a] = mrb_ary_new_from_values(mrb, m1+m2, stack);
       }
       else {
         mrb_value *pp = NULL;
@@ -1799,7 +1839,7 @@ RETRY_TRY_BLOCK:
           pp = ARY_PTR(ary);
           len = ARY_LEN(ary);
         }
-        regs[a] = mrb_ary_new_capa(mrb, m1+len+m2+kd);
+        regs[a] = mrb_ary_new_capa(mrb, m1+len+m2);
         rest = mrb_ary_ptr(regs[a]);
         if (m1 > 0) {
           stack_copy(ARY_PTR(rest), stack, m1);
@@ -1810,12 +1850,15 @@ RETRY_TRY_BLOCK:
         if (m2 > 0) {
           stack_copy(ARY_PTR(rest)+m1+len, stack+m1+1, m2);
         }
-        if (kd) {
-          stack_copy(ARY_PTR(rest)+m1+len+m2, stack+m1+m2+1, kd);
-        }
-        ARY_SET_LEN(rest, m1+len+m2+kd);
+        ARY_SET_LEN(rest, m1+len+m2);
+      }
+      if (kd) {
+        regs[a+1] = stack[m1+r+m2];
+        regs[a+2] = stack[m1+r+m2+1];
+      }
+      else {
+        regs[a+1] = stack[m1+r+m2];
       }
-      regs[a+1] = stack[m1+r+m2];
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
@@ -1829,17 +1872,48 @@ RETRY_TRY_BLOCK:
       /* unused
       int b  = MRB_ASPEC_BLOCK(a);
       */
-      mrb_int argc = mrb->c->ci->argc;
+      mrb_int const len = m1 + o + r + m2;
+
+      mrb_callinfo *ci = mrb->c->ci;
+      mrb_int argc = ci->n;
       mrb_value *argv = regs+1;
       mrb_value * const argv0 = argv;
-      mrb_int const len = m1 + o + r + m2;
-      mrb_int const blk_pos = len + kd + 1;
-      mrb_value *blk = &argv[argc < 0 ? 1 : argc];
+      mrb_int const kw_pos = len + kd;    /* where kwhash should be */
+      mrb_int const blk_pos = kw_pos + 1; /* where block should be */
+      mrb_value blk = regs[mrb_ci_bidx(ci)];
       mrb_value kdict = mrb_nil_value();
-      mrb_int kargs = kd;
+
+      /* keyword arguments */
+      if (ci->nk > 0) {
+        mrb_int kidx = mrb_ci_kidx(ci);
+        kdict = regs[kidx];
+        if (!mrb_hash_p(kdict) || mrb_hash_size(mrb, kdict) == 0) {
+          kdict = mrb_nil_value();
+          ci->nk = 0;
+        }
+      }
+      if (!kd && !mrb_nil_p(kdict)) {
+        if (argc < 14) {
+          ci->n++;
+          argc++;    /* include kdict in normal arguments */
+        }
+        else if (argc == 14) {
+          /* pack arguments and kdict */
+          regs[1] = mrb_ary_new_from_values(mrb, argc+1, &regs[1]);
+          argc = ci->n = 15;
+        }
+        else {/* argc == 15 */
+          /* push kdict to packed arguments */
+          mrb_ary_push(mrb, regs[1], regs[2]);
+        }
+        ci->nk = 0;
+      }
+      if (kd && MRB_ASPEC_KEY(a) > 0 && mrb_hash_p(kdict)) {
+        kdict = mrb_hash_dup(mrb, kdict);
+      }
 
       /* arguments is passed with Array */
-      if (argc < 0) {
+      if (argc == 15) {
         struct RArray *ary = mrb_ary_ptr(regs[1]);
         argv = ARY_PTR(ary);
         argc = (int)ARY_LEN(ary);
@@ -1847,8 +1921,8 @@ RETRY_TRY_BLOCK:
       }
 
       /* strict argument check */
-      if (mrb->c->ci->proc && MRB_PROC_STRICT_P(mrb->c->ci->proc)) {
-        if (argc < m1 + m2 || (r == 0 && argc > len + kd)) {
+      if (ci->proc && MRB_PROC_STRICT_P(ci->proc)) {
+        if (argc < m1 + m2 || (r == 0 && argc > len)) {
           argnum_error(mrb, m1+m2);
           goto L_RAISE;
         }
@@ -1860,40 +1934,13 @@ RETRY_TRY_BLOCK:
         argv = RARRAY_PTR(argv[0]);
       }
 
-      if (kd) {
-        /* check last arguments is hash if method takes keyword arguments */
-        if (argc == m1+m2) {
-          kdict = mrb_hash_new(mrb);
-          kargs = 0;
-        }
-        else {
-          if (argv && argc > 0 && mrb_hash_p(argv[argc-1])) {
-            kdict = argv[argc-1];
-            mrb_hash_check_kdict(mrb, kdict);
-          }
-          else if (r || argc <= m1+m2+o
-                   || !(mrb->c->ci->proc && MRB_PROC_STRICT_P(mrb->c->ci->proc))) {
-            kdict = mrb_hash_new(mrb);
-            kargs = 0;
-          }
-          else {
-            argnum_error(mrb, m1+m2);
-            goto L_RAISE;
-          }
-          if (MRB_ASPEC_KEY(a) > 0) {
-            kdict = mrb_hash_dup(mrb, kdict);
-          }
-        }
-      }
-
-      /* no rest arguments */
-      if (argc-kargs < len) {
+      /* rest arguments */
+      mrb_value rest = mrb_nil_value();
+      if (argc < len) {
         mrb_int mlen = m2;
         if (argc < m1+m2) {
           mlen = m1 < argc ? argc - m1 : 0;
         }
-        regs[blk_pos] = *blk; /* move block */
-        if (kd) regs[len + 1] = kdict;
 
         /* copy mandatory and optional arguments */
         if (argv0 != argv && argv) {
@@ -1911,40 +1958,39 @@ RETRY_TRY_BLOCK:
         }
         /* initialize rest arguments with empty Array */
         if (r) {
-          regs[m1+o+1] = mrb_ary_new_capa(mrb, 0);
+          rest = mrb_ary_new_capa(mrb, 0);
+          regs[m1+o+1] = rest;
         }
         /* skip initializer of passed arguments */
-        if (o > 0 && argc-kargs > m1+m2)
-          pc += (argc - kargs - m1 - m2)*3;
+        if (o > 0 && argc > m1+m2)
+          pc += (argc - m1 - m2)*3;
       }
       else {
         mrb_int rnum = 0;
         if (argv0 != argv) {
-          regs[blk_pos] = *blk; /* move block */
-          if (kd) regs[len + 1] = kdict;
           value_move(&regs[1], argv, m1+o);
         }
         if (r) {
-          mrb_value ary;
-
-          rnum = argc-m1-o-m2-kargs;
-          ary = mrb_ary_new_from_values(mrb, rnum, argv+m1+o);
-          regs[m1+o+1] = ary;
-        }
-        if (m2) {
-          if (argc-m2 > m1) {
-            value_move(&regs[m1+o+r+1], &argv[m1+o+rnum], m2);
-          }
+          rnum = argc-m1-o-m2;
+          rest = mrb_ary_new_from_values(mrb, rnum, argv+m1+o);
+          regs[m1+o+1] = rest;
         }
-        if (argv0 == argv) {
-          regs[blk_pos] = *blk; /* move block */
-          if (kd) regs[len + 1] = kdict;
+        if (m2 > 0 && argc-m2 > m1) {
+          value_move(&regs[m1+o+r+1], &argv[m1+o+rnum], m2);
         }
         pc += o*3;
       }
 
+      /* need to be update blk first to protect blk from GC */
+      regs[blk_pos] = blk;              /* move block */
+      if (kd) {
+        if (mrb_nil_p(kdict))
+          kdict = mrb_hash_new_capa(mrb, 0);
+        regs[kw_pos] = kdict;           /* set kwhash */
+      }
+
       /* format arguments for generated code */
-      mrb->c->ci->argc = (int16_t)(len + kd);
+      mrb->c->ci->n = len;
 
       /* clear local (but non-argument) variables */
       if (irep->nlocals-blk_pos-1 > 0) {
@@ -1955,9 +2001,10 @@ RETRY_TRY_BLOCK:
 
     CASE(OP_KARG, BB) {
       mrb_value k = mrb_symbol_value(syms[b]);
-      mrb_value kdict = regs[mrb->c->ci->argc];
+      mrb_int kidx = mrb_ci_kidx(mrb->c->ci);
+      mrb_value kdict;
 
-      if (!mrb_hash_p(kdict) || !mrb_hash_key_p(mrb, kdict, k)) {
+      if (kidx < 0 || !mrb_hash_p(kdict=regs[kidx]) || !mrb_hash_key_p(mrb, kdict, k)) {
         mrb_value str = mrb_format(mrb, "missing keyword: %v", k);
         mrb_exc_set(mrb, mrb_exc_new_str(mrb, E_ARGUMENT_ERROR, str));
         goto L_RAISE;
@@ -1969,10 +2016,11 @@ RETRY_TRY_BLOCK:
 
     CASE(OP_KEY_P, BB) {
       mrb_value k = mrb_symbol_value(syms[b]);
-      mrb_value kdict = regs[mrb->c->ci->argc];
+      mrb_int kidx = mrb_ci_kidx(mrb->c->ci);
+      mrb_value kdict;
       mrb_bool key_p = FALSE;
 
-      if (mrb_hash_p(kdict)) {
+      if (kidx >= 0 && mrb_hash_p(kdict=regs[kidx])) {
         key_p = mrb_hash_key_p(mrb, kdict, k);
       }
       regs[a] = mrb_bool_value(key_p);
@@ -1980,9 +2028,10 @@ RETRY_TRY_BLOCK:
     }
 
     CASE(OP_KEYEND, Z) {
-      mrb_value kdict = regs[mrb->c->ci->argc];
+      mrb_int kidx = mrb_ci_kidx(mrb->c->ci);
+      mrb_value kdict;
 
-      if (mrb_hash_p(kdict) && !mrb_hash_empty_p(mrb, kdict)) {
+      if (kidx >= 0 && mrb_hash_p(kdict=regs[kidx]) && !mrb_hash_empty_p(mrb, kdict)) {
         mrb_value keys = mrb_hash_keys(mrb, kdict);
         mrb_value key1 = RARRAY_PTR(keys)[0];
         mrb_value str = mrb_format(mrb, "unknown keyword: %v", key1);
@@ -2008,14 +2057,8 @@ RETRY_TRY_BLOCK:
 
       ci = mrb->c->ci;
       if (ci->mid) {
-        mrb_value blk;
+        mrb_value blk = regs[mrb_ci_bidx(ci)];
 
-        if (ci->argc < 0) {
-          blk = regs[2];
-        }
-        else {
-          blk = regs[ci->argc+1];
-        }
         if (mrb_proc_p(blk)) {
           struct RProc *p = mrb_proc_ptr(blk);
 
@@ -2310,7 +2353,7 @@ RETRY_TRY_BLOCK:
         }
         stack = e->stack + 1;
       }
-      if (mrb_nil_p(stack[m1+r+m2])) {
+      if (mrb_nil_p(stack[m1+r+m2+kd])) {
         localjump_error(mrb, LOCALJUMP_ERROR_YIELD);
         goto L_RAISE;
       }
@@ -2335,7 +2378,6 @@ RETRY_TRY_BLOCK:
     OP_MATH_CASE_FLOAT(op_name, float,  float);                             \
     OP_MATH_CASE_STRING_##op_name();                                        \
     default:                                                                \
-      c = 1;                                                                \
       mid = MRB_OPSYM(op_name);                                             \
       goto L_SEND_SYM;                                                      \
   }                                                                         \
@@ -2417,7 +2459,6 @@ RETRY_TRY_BLOCK:
         break;
 #endif
       default:
-        c = 1;
         mid = MRB_OPSYM(div);
         goto L_SEND_SYM;
       }
@@ -2436,7 +2477,6 @@ RETRY_TRY_BLOCK:
     OP_MATHI_CASE_FLOAT(op_name);                                           \
     default:                                                                \
       SET_INT_VALUE(mrb,regs[a+1], b);                                      \
-      c = 1;                                                                \
       mid = MRB_OPSYM(op_name);                                             \
       goto L_SEND_SYM;                                                      \
   }                                                                         \
@@ -2482,7 +2522,6 @@ RETRY_TRY_BLOCK:
     result = OP_CMP_BODY(op,mrb_fixnum,mrb_fixnum);\
     break;\
   default:\
-    c = 1;\
     mid = MRB_OPSYM(sym);\
     goto L_SEND_SYM;\
   }\
@@ -2511,7 +2550,6 @@ RETRY_TRY_BLOCK:
     result = OP_CMP_BODY(op,mrb_float,mrb_float);\
     break;\
   default:\
-    c = 1;\
     mid = MRB_OPSYM(sym);\
     goto L_SEND_SYM;\
   }\
@@ -2910,10 +2948,6 @@ RETRY_TRY_BLOCK:
       goto L_RAISE;
     }
 
-    CASE(OP_SENDVK, BB) {       /* not yet implemented */
-      NEXT;
-    }
-
     CASE(OP_EXT1, Z) {
       insn = READ_B();
       switch (insn) {
@@ -2981,12 +3015,7 @@ RETRY_TRY_BLOCK:
 static mrb_value
 mrb_run(mrb_state *mrb, const struct RProc *proc, mrb_value self)
 {
-  if (mrb->c->ci->argc < 0) {
-    return mrb_vm_run(mrb, proc, self, 3); /* receiver, args and block) */
-  }
-  else {
-    return mrb_vm_run(mrb, proc, self, mrb->c->ci->argc + 2); /* argc + 2 (receiver and block) */
-  }
+  return mrb_vm_run(mrb, proc, self, mrb_ci_bidx(mrb->c->ci) + 1);
 }
 
 MRB_API mrb_value