Needs testing. Would save 3-400 bytes.
Current:
text data bss dec hex filename
3972 0 1740 5712 1650 npk_SH7051
4088 0 2104 6192 1830 npk_SH7055_35
3548 0 2100 5648 1610 npk_SH7055_18
3548 0 2100 5648 1610 npk_SH7058
3516 0 2100 5616 15f0 ssmk_SH7058
With -flto :
text data bss dec hex filename
3660 0 1736 5396 1514 npk_SH7051
3716 0 2100 5816 16b8 npk_SH7055_35
3216 0 2096 5312 14c0 npk_SH7055_18
3216 0 2096 5312 14c0 npk_SH7058
3176 0 2096 5272 1498 ssmk_SH7058
Needs testing. Would save 3-400 bytes.