Optimize #to_s for String, Symbol, Integer

compile.c

@@ -2438,6 +2438,7 @@ iseq_specialized_instruction(rb_iseq_t *iseq, INSN *iobj)
 		  case idEmptyP: SP_INSN(empty_p);return COMPILE_OK;
 		  case idSucc:	 SP_INSN(succ);	  return COMPILE_OK;
 		  case idNot:	 SP_INSN(not);	  return COMPILE_OK;
+		  case idTo_s:	 SP_INSN(tos);	  return COMPILE_OK;
 		}
 		break;
 	      case 1:

insns.def

@@ -1531,6 +1531,25 @@ opt_not
     }
 }
 
+/**
+  @c optimize
+  @e optimized to_s
+  @j 最適化された recv.to_s。
+ */
+DEFINE_INSN
+opt_tos
+(CALL_INFO ci, CALL_CACHE cc)
+(VALUE recv)
+(VALUE val)
+{
+    val = vm_opt_tos(ci, cc, recv);
+
+    if (val == Qundef) {
+	/* other */
+	PUSH(recv);
+	CALL_SIMPLE_METHOD(recv);
+    }
+}
 
 /**
   @c optimize

vm.c

@@ -1577,6 +1577,7 @@ vm_init_redefined_flag(void)
     OP(UMinus, UMINUS), (C(String));
     OP(Max, MAX), (C(Array));
     OP(Min, MIN), (C(Array));
+    OP(To_s, TOS), (C(String), C(Symbol), C(Integer));
 #undef C
 #undef OP
 }

vm_core.h

@@ -456,6 +456,7 @@ enum ruby_basic_operators {
     BOP_UMINUS,
     BOP_MAX,
     BOP_MIN,
+    BOP_TOS,
 
     BOP_LAST_
 };

vm_insnhelper.c

@@ -3661,6 +3661,29 @@ vm_opt_not(CALL_INFO ci, CALL_CACHE cc, VALUE recv)
     }
 }
 
+static VALUE
+vm_opt_tos(CALL_INFO ci, CALL_CACHE cc, VALUE recv)
+{
+    if (SPECIAL_CONST_P(recv)) {
+	return Qundef;
+    }
+    else if (RBASIC_CLASS(recv) == rb_cString &&
+	     BASIC_OP_UNREDEFINED_P(BOP_TOS, STRING_REDEFINED_OP_FLAG)) {
+	return recv;
+    }
+    else if (RBASIC_CLASS(recv) == rb_cSymbol &&
+	     BASIC_OP_UNREDEFINED_P(BOP_TOS, SYMBOL_REDEFINED_OP_FLAG)) {
+	return rb_sym_to_s(recv);
+    }
+    else if (RBASIC_CLASS(recv) == rb_cInteger &&
+	     BASIC_OP_UNREDEFINED_P(BOP_TOS, INTEGER_REDEFINED_OP_FLAG)) {
+	return rb_int2str(recv, 10);
+    }
+    else {
+	return Qundef;
+    }
+}
+
 static VALUE
 vm_opt_regexpmatch1(VALUE recv, VALUE obj)
 {