[avr-gcc-list] Can functions modify register 'r0' or not?

[林楠]

Hi all,

In my code, I found that the global interrupts is disabled after one
function is called. By reading the assembly code I found that this
function uses register 'r0' to save the global interrupts in the
prologue and restore it in the end.  One of the functions been called
in this function modified the register 'r0' and caused this problem.

I wonder whether or 'r0' can be clobbered in functions. If so, why
register 'r0' is used to save the global interrupts in that function.

THX