LR_SIZE_BITS
#define LR_SIZE_MASK ((1ull << LR_SIZE_BITS) - 1)
static_assert(LINKED_REGS_MAX < (1 << LR_SIZE_BITS));
static_assert(LINKED_REGS_MAX * LR_ENTRY_BITS + LR_SIZE_BITS <= 64);
val <<= LR_SIZE_BITS;
val >>= LR_SIZE_BITS;