聊一聊关于php源码中refcount的疑问

<?php
class ReturnInfo {
    const REFCOUNT_0 = "0";
    const REFCOUNT_1 = "1";
    const REFCOUNT_N = "N";

    const REFCOUNTS = [
        self::REFCOUNT_0,
        self::REFCOUNT_1,
        self::REFCOUNT_N,
    ];

    //...
    
    private function setRefcount(?string $refcount): void
    {
        $type = $this->phpDocType ?? $this->type;
        $isScalarType = $type !== null && $type->isScalar();

        if ($refcount === null) {
            $this->refcount = $isScalarType ? self::REFCOUNT_0 : self::REFCOUNT_N;
            return;
        }

        if (!in_array($refcount, ReturnInfo::REFCOUNTS, true)) {
            throw new Exception("@refcount must have one of the following values: \"0\", \"1\", \"N\", $refcount given");
        }

        if ($isScalarType && $refcount !== self::REFCOUNT_0) {
            throw new Exception('A scalar return type of "' . $type->__toString() . '" must have a refcount of "' . self::REFCOUNT_0 . '"');
        }

        if (!$isScalarType && $refcount === self::REFCOUNT_0) {
            throw new Exception('A non-scalar return type of "' . $type->__toString() . '" cannot have a refcount of "' . self::REFCOUNT_0 . '"');
        }

        $this->refcount = $refcount;
    }

/**
 * @return array<int, string>
 * @refcount 1
 */
function ob_list_handlers(): array {}

public function getOptimizerInfo(): ?string {
        if ($this->isMethod()) {
            return null;
        }

        if ($this->alias !== null) {
            return null;
        }

        if ($this->return->refcount !== ReturnInfo::REFCOUNT_1 && $this->return->phpDocType === null) {
            return null;
        }

        $type = $this->return->phpDocType ?? $this->return->type;
        if ($type === null) {
            return null;
        }

        return "\tF" . $this->return->refcount . '("' . $this->name->__toString() . '", ' . $type->toOptimizerTypeMask() . "),\n";
    }

static const func_info_t func_infos[] = {
    F1("zend_version", MAY_BE_STRING),
    FN("func_get_args", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_ANY),
    F1("get_class_vars", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_ANY|MAY_BE_ARRAY_OF_REF),
    F1("get_class_methods", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING),
    F1("get_included_files", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING),
    FN("set_error_handler", MAY_BE_STRING|MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING|MAY_BE_ARRAY_OF_OBJECT|MAY_BE_OBJECT|MAY_BE_NULL),
    FN("set_exception_handler", MAY_BE_STRING|MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING|MAY_BE_ARRAY_OF_OBJECT|MAY_BE_OBJECT|MAY_BE_NULL),
    F1("get_declared_classes", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING),
    F1("get_declared_traits", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING),
    F1("get_declared_interfaces", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING),
    F1("get_defined_functions", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_ARRAY),
    F1("get_defined_vars", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_ANY|MAY_BE_ARRAY_OF_REF),
    F1("get_resource_type", MAY_BE_STRING),
    F1("get_loaded_extensions", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING),
    F1("get_defined_constants", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_ANY),
    F1("debug_backtrace", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_ARRAY),
    F1("get_extension_funcs", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_OF_STRING|MAY_BE_FALSE),
    F1("gc_status", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_LONG|MAY_BE_ARRAY_OF_FALSE|MAY_BE_ARRAY_OF_TRUE),
    F1("bcadd", MAY_BE_STRING),
    F1("bcsub", MAY_BE_STRING),
    F1("bcmul", MAY_BE_STRING),
    F1("bcdiv", MAY_BE_STRING),
    F1("bcmod", MAY_BE_STRING),
    F1("bcpowmod", MAY_BE_STRING),
    F1("bcpow", MAY_BE_STRING),
    F1("bcsqrt", MAY_BE_STRING),
    FN("bzopen", MAY_BE_RESOURCE|MAY_BE_FALSE),
    F1("bzerror", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_LONG|MAY_BE_ARRAY_OF_STRING),
    F1("cal_from_jd", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_LONG|MAY_BE_ARRAY_OF_STRING|MAY_BE_ARRAY_OF_NULL),
    F1("cal_info", MAY_BE_ARRAY|MAY_BE_ARRAY_KEY_LONG|MAY_BE_ARRAY_KEY_STRING|MAY_BE_ARRAY_OF_LONG|MAY_BE_ARRAY_OF_STRING|MAY_BE_ARRAY_OF_ARRAY),
    F1("curl_copy_handle", MAY_BE_OBJECT|MAY_BE_FALSE),
    //...
};

typedef struct _func_info_t {
    const char *name;
    unsigned    name_len;
    uint32_t    info;
    info_func_t info_func;
} func_info_t;

#define F0(name, info) \
    {name, sizeof(name)-1, (info), NULL}
#define F1(name, info) \
    {name, sizeof(name)-1, (MAY_BE_RC1 | (info)), NULL}
#define FN(name, info) \
    {name, sizeof(name)-1, (MAY_BE_RC1 | MAY_BE_RCN | (info)), NULL}
#define FC(name, callback) \
    {name, sizeof(name)-1, 0, callback}

#ifdef ZEND_JIT_USE_RC_INFERENCE
    /* Refcount may be increased by RETURN opcode */
    if ((info & MAY_BE_RC1) && !(info & MAY_BE_RCN)) {
        for (j = 0; j < ssa->cfg.blocks_count; j++) {
            if ((ssa->cfg.blocks[j].flags & ZEND_BB_REACHABLE) &&
                ssa->cfg.blocks[j].len > 0) {
                const zend_op *opline = op_array->opcodes + ssa->cfg.blocks[j].start + ssa->cfg.blocks[j].len - 1;

                if (opline->opcode == ZEND_RETURN) {
                    if (opline->op1_type == IS_CV && opline->op1.var == EX_NUM_TO_VAR(var)) {
                        info |= MAY_BE_RCN;
                        break;
                    }
                }
            }
        }
    }
#endif