[JIT] Avoid generating fast property assign path for readonly properties (php#15260)

readonly properties will usually be IS_UNDEF on assignment, dodging the fast
path anyway. The fast path does not handle the readonly scope check. The
alternative would be handling scope there, but since there are some many
variants that might be more trouble than it's worth.

Author: iluuu1994

ext/opcache/jit/zend_jit_ir.c

@@ -14435,7 +14435,13 @@ static int zend_jit_assign_obj(zend_jit_ctx         *jit,
 	} else {
 		prop_ref = ir_ADD_OFFSET(obj_ref, prop_info->offset);
 		prop_addr = ZEND_ADDR_REF_ZVAL(prop_ref);
-		if (!ce || ce_is_instanceof || !(ce->ce_flags & ZEND_ACC_IMMUTABLE) || ce->__get || ce->__set || (prop_info->flags & ZEND_ACC_READONLY)) {
+		/* With the exception of __clone(), readonly assignment always happens on IS_UNDEF, doding
+		 * the fast path. Thus, the fast path is not useful. */
+		if (prop_info->flags & ZEND_ACC_READONLY) {
+			ZEND_ASSERT(slow_inputs == IR_UNUSED);
+			goto slow_path;
+		}
+		if (!ce || ce_is_instanceof || !(ce->ce_flags & ZEND_ACC_IMMUTABLE) || ce->__get || ce->__set) {
 			// Undefined property with magic __get()/__set()
 			if (JIT_G(trigger) == ZEND_JIT_ON_HOT_TRACE) {
 				int32_t exit_point = zend_jit_trace_get_exit_point(opline, ZEND_JIT_EXIT_TO_VM);
@@ -14527,6 +14533,8 @@ static int zend_jit_assign_obj(zend_jit_ctx         *jit,
 		ir_ref arg3, arg5;
 
 		ir_MERGE_list(slow_inputs);
+
+slow_path:
 		jit_SET_EX_OPLINE(jit, opline);
 
 		if (Z_MODE(val_addr) == IS_REG) {