Denis Chertykov writes:
> 2016-08-01 15:17 GMT+03:00 Georg-Johann Lay <a...@gjlay.de>:
>> Problem with -fcaller-saves is that there are situations where it triggers
>> an expensive frame just to store a variable around a function call even
>> though there are plenty of call-saved registers.
>>
>> Example:
>>
>> typedef __UINT8_TYPE__ uint8_t;
>>
>> extern uint8_t uart0_getc (void);
>>
>> void foo (uint8_t *buffer, uint8_t cnt)
>> {
>> while (--cnt)
>> {
>> *buffer++ = uart0_getc();
>> }
>> }
>>
>> $ avr-gcc -Os -S -dp -mmcu=atmega8 loop-buf.c
>>
>> $ avr-gcc gcc -B$TV -Os -c -save-temps -dp -mmcu=atmega8 loop-buf.c &&
>> avr-size loop-buf.o
>> text data bss dec hex filename
>> 50 0 0 50 32 loop-buf.o
>>
>> $ avr-gcc -Os -c -save-temps -dp -mmcu=atmega8 loop-buf.c -fno-caller-saves
>> && avr-size loop-buf.o
>> text data bss dec hex filename
>> 32 0 0 32 20 loop-buf.o
>>
>> I actually came never across a situation where -fcaller-saves improved the
>> code performance, hence this patch proposes to switch off -fcaller-saved per
>> default.
Like you mentioned in the bug report, would fixing the costs be a better
way to fix this rather than a blanket disabling of the option?
Regards
Senthil
