vm: add OP_SEND0 and OP_SSEND0 for zero-argument method calls

These opcodes use BB format instead of BBB, saving 1 byte per call.
In the standard library, this saves ~790 bytes (568 SEND0 + 222 SSEND0).

Co-authored-by: Claude <noreply@anthropic.com>

Author: matz

include/mruby/ops.h

@@ -60,8 +60,10 @@ OPCODE(RESCUE,     BB)       /* R[b] = R[a].isa?(R[b]) */
 OPCODE(RAISEIF,    B)        /* raise(R[a]) if R[a] */
 OPCODE(MATCHERR,   B)        /* raise NoMatchingPatternError unless R[a] */
 OPCODE(SSEND,      BBB)      /* R[a] = self.send(Syms[b],R[a+1]..,R[a+n+1]:R[a+n+2]..) (c=n|k<<4) */
+OPCODE(SSEND0,     BB)       /* R[a] = self.send(Syms[b]) (no args) */
 OPCODE(SSENDB,     BBB)      /* R[a] = self.send(Syms[b],R[a+1]..,R[a+n+1]:R[a+n+2]..,&R[a+n+2k+1]) */
 OPCODE(SEND,       BBB)      /* R[a] = R[a].send(Syms[b],R[a+1]..,R[a+n+1]:R[a+n+2]..) (c=n|k<<4) */
+OPCODE(SEND0,      BB)       /* R[a] = R[a].send(Syms[b]) (no args) */
 OPCODE(SENDB,      BBB)      /* R[a] = R[a].send(Syms[b],R[a+1]..,R[a+n+1]:R[a+n+2]..,&R[a+n+2k+1]) */
 OPCODE(CALL,       Z)        /* self.call(*, **, &) (But overlay the current call frame; tailcall) */
 OPCODE(BLKCALL,    BB)       /* R[a] = R[a].call(R[a+1],... ,R[a+b]); direct block call */

mrbgems/mruby-compiler/core/codegen.c

@@ -3643,7 +3643,15 @@ codegen_call(codegen_scope *s, node *varnode, int val)
     /* constant folding succeeded */
   }
   else if (noself) {
-    genop_3(s, blk ? OP_SSENDB : OP_SSEND, cursp(), sym_idx(s, sym), n|(nk<<4));
+    if (!blk && n == 0 && nk == 0) {
+      genop_2(s, OP_SSEND0, cursp(), sym_idx(s, sym));
+    }
+    else {
+      genop_3(s, blk ? OP_SSENDB : OP_SSEND, cursp(), sym_idx(s, sym), n|(nk<<4));
+    }
+  }
+  else if (!blk && n == 0 && nk == 0) {
+    genop_2(s, OP_SEND0, cursp(), sym_idx(s, sym));
   }
   else {
     genop_3(s, blk ? OP_SENDB : OP_SEND, cursp(), sym_idx(s, sym), n|(nk<<4));

src/codedump.c

@@ -336,6 +336,9 @@ codedump(mrb_state *mrb, const mrb_irep *irep, FILE *out)
       fprintf(out, "SSEND\t\tR%d\t:%s\t", a, mrb_sym_dump(mrb, irep->syms[b]));
       print_args(c, out);
       break;
+    CASE(OP_SSEND0, BB):
+      fprintf(out, "SSEND0\tR%d\t:%s\n", a, mrb_sym_dump(mrb, irep->syms[b]));
+      break;
     CASE(OP_SSENDB, BBB):
       fprintf(out, "SSENDB\tR%d\t:%s\t", a, mrb_sym_dump(mrb, irep->syms[b]));
       print_args(c, out);
@@ -344,6 +347,9 @@ codedump(mrb_state *mrb, const mrb_irep *irep, FILE *out)
       fprintf(out, "SEND\t\tR%d\t:%s\t", a, mrb_sym_dump(mrb, irep->syms[b]));
       print_args(c, out);
       break;
+    CASE(OP_SEND0, BB):
+      fprintf(out, "SEND0\t\tR%d\t:%s\n", a, mrb_sym_dump(mrb, irep->syms[b]));
+      break;
     CASE(OP_SENDB, BBB):
       fprintf(out, "SENDB\t\tR%d\t:%s\t", a, mrb_sym_dump(mrb, irep->syms[b]));
       print_args(c, out);

src/vm.c

@@ -2211,6 +2211,12 @@ mrb_vm_exec(mrb_state *mrb, const struct RProc *begin_proc, const mrb_code *iseq
     }
     goto L_SENDB;
 
+    CASE(OP_SSEND0, BB) {
+      regs[a] = regs[0];
+      c = 0;
+    }
+    goto L_SENDB;
+
     CASE(OP_SSENDB, BBB) {
       regs[a] = regs[0];
     }
@@ -2219,6 +2225,11 @@ mrb_vm_exec(mrb_state *mrb, const struct RProc *begin_proc, const mrb_code *iseq
     CASE(OP_SEND, BBB)
     goto L_SENDB;
 
+    CASE(OP_SEND0, BB) {
+      c = 0;
+    }
+    goto L_SENDB;
+
     L_SEND_SYM:
     c = 1;
     /* push nil after arguments */
@@ -2259,7 +2270,7 @@ mrb_vm_exec(mrb_state *mrb, const struct RProc *begin_proc, const mrb_code *iseq
       }
 
       mrb_assert(bidx < irep->nregs);
-      if (insn == OP_SEND || insn == OP_SSEND) {
+      if (insn == OP_SEND || insn == OP_SEND0 || insn == OP_SSEND || insn == OP_SSEND0) {
         /* clear block argument */
         SET_NIL_VALUE(regs[new_bidx]);
         SET_NIL_VALUE(blk);
@@ -2280,7 +2291,7 @@ mrb_vm_exec(mrb_state *mrb, const struct RProc *begin_proc, const mrb_code *iseq
       else {
         ci->mid = mid;
       }
-      if (insn == OP_SEND || insn == OP_SENDB) {
+      if (insn == OP_SEND || insn == OP_SEND0 || insn == OP_SENDB) {
         mrb_bool priv = TRUE;
         if (m.flags & MRB_METHOD_PRIVATE_FL) {
         vis_err:;