You can test this on godbolt. Using gcc 12.2 on x86-64 linux

There appears to be an unnecessary instruction. I commented the assembly below

	struct T2 { bool a, b; };
	static T2 test();
	int myfunc() {
		auto [a, b] = test();
		return ((int)a<<1) + b;
	}

Result

	myfunc():
		sub     rsp, 8
		call    test()  <-- Result is b<<8 | a
		add     rsp, 8
		movzx   edx, al <--- moves a
		movzx   eax, ah <--- extends b into itself
		movzx   eax, al <--- Huh?
		lea     eax, [rax+rdx*2]
		ret