Re: [avr-gcc-list] Long prologue/epilogue sequences

[Bernard Fouché]

Simon Han wrote:

>     One thing I don't understand is why all these register pushes.  
> Wouldn't it be more efficient to only push the ones that SIGNAL uses?  
> It seems to me that when there is function call in SIGNAL handler, 
> there will be at least 12 register pushes/pops.  When there is no 
> function in SIGNAL handler, the register pushes are like normal 
> function calls with "reti".
>
>     Could someone point me the documentation that talks about the 
> reason and/or possible solution to this?

If the function called in the SIGNAL handler is in the same source file 
and declared as 'static' (if possible), the code size will be reduced 
since the compiler has all the information to know where a register is 
really used

Also if the function to call can be defined as 'inline', you will 
reduce the code size for the signal handler (but grow the global code 
size of the project if this function is used somewhere else)

I suppose that things are done the way you describe since when a 
function is called in a signal handler, and unless this function is 
defined as static and/or inline, the compiler can not know what register 
will be used: a function can call a function that calls another 
function, etc.

May be all this is more efficient with gcc-4.0 since the optimizer has 
been deeply changed...