Strange asm generated by GCC...

Why in the world would GCC use an XCHG instruction for the following code. The damn XCHG has an implied LOCK prefix! Yikes!
https://godbolt.org/z/Thxchdcr8
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#include <atomic>
int main()
{
     std::atomic<unsigned long> m_state = 0;
     m_state.store(std::memory_order_relaxed);
     return 0;
}
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Here is the generated ASM:
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main:
         mov     QWORD PTR [rsp-8], 0
         xor     eax, eax
         xchg    rax, QWORD PTR [rsp-8]
         xor     eax, eax
         ret
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WTF!!!!!!!!