[avr-gcc-list] GCC loop optimization and volatile data question

[Larry Barello]

When using variable to communicate between interrupt handlers and C code,
one needs to use the 'volatile' keyword so GCC doesn't optimize reading the
variable outside of any loops.

If the variable is "extern", does one still need to declare it volatile?

If the usage is thus:

extern int some_external_variable;
...
while (...)
{
    ...
    if (some_external_variable == 0)
        break;
}

do I need to declare 'some_external_variable' as volatile?

Thanks!