By the way, the explicit initialization to zero can make a difference in some cases. From gcc docs:

-fno-zero-initialized-in-bss

If the target supports a BSS section, GCC by default puts variables that are initialized to zero into BSS. This can save space in the resulting code.

This option turns off this behavior because some programs explicitly rely on variables going to the data section—e.g., so that the resulting executable can find the beginning of that section and/or make assumptions based on that.

This could be useful, for example if you want your "hot" global variables to go together in .data section for improved data locality. But there are better ways to achieve the same.