There is the following code size regression, filed as
https://gcc.gnu.org/PR90706
Simple test cases are, for example
#define PORT (*((unsigned char volatile*) 0x24))
unsigned short var16;
void func (void)
{
if (2048000ul * var16 > 1200000ul)
PORT |= 1;
}
When I compile it with
$ avr-gcc -Os bloat1.c -c && avr-size bloat1.o
the code size increases from 36 bytes (v8) to 88 bytes (v13).
Apart from that, register pressure is much higher because a frame
pointer is set up for no reason, and the values go through stack slots
for no reason.
Even test cases which don't require any code like
long func2 (void)
{
long var32;
__asm ("; some code %0" : "=r" (var32));
return var32;
}
increase in register pressure (x2), stack usage (from 0 to 6 bytes) and
code size from 2 bytes (v8) to 34 bytes (v13).
Some projects like QMK "solved" the problem by declaring GCC > v8 to be
"incompatible" with their project, see
https://github.com/qmk/qmk_firmware/issues/6719
In own projects I observed the problem, too, and the only solution is to
use v8 or older. Options like -fcaller-saves or -fira-algorithm= have
no effect.
To configure, I used --target=avr --disable-nls --with-dwarf2
--enable-languages=c,c++ --with-gnu-as --with-gnu-ld --disable-shared,
so nothing special.
The problem is present in v9, v10, v11, v12 and master (future v13), so
sitting around for quite a while, so maybe it's not fixed because RA
maintainers are not aware of the problem.
Thanks for any help,
Johann
