https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97276
--- Comment #4 from Georg-Johann Lay <gjl at gcc dot gnu.org> --- Created attachment 54518 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54518&action=edit pwn-i.c pre-compiled test case Ok, I found it and attached a cleaned-up version. IIUC correctly, the relevant options you are using to compile are: -O1 -mmcu=atxmega32a4 -g -ggdb -std=gnu99 With these options (and with -fverbose-asm to easier navigate in asm) I could not reproduce the problem with avr-gcc v8.5. The respective part of .s reads (I dropped -g for legibility, but with -g it's same): ; pwm-i.c:287: if (last_brightness < 181 && j >= 181) ldi r30,lo8(-76) ; , ; 320 [c=4 l=1] movqi_insn/1 cp r30,r11 ; , last_brightness ; 193 [c=4 l=1] cmpqi3/1 brsh .+2 ; ; 194 [c=16 l=2] branch rjmp .L16 ; ; pwm-i.c:287: if (last_brightness < 181 && j >= 181) cpi r22,lo8(-75) ; iftmp.3_5, ; 196 [c=4 l=1] cmpqi3/2 brsh .+2 ; ; 197 [c=16 l=2] branch rjmp .L16 ; ; pwm-i.c:289: slot->top = 0xfe00; st X+,r8 ; tmp226 ; 200 [c=4 l=3] *movhi/3 st X,r9 ; tmp226 sbiw r26,1 ; pwm-i.c:290: slot->mask = ~mask; movw r30,r24 ; tmp200, mask ; 321 [c=4 l=1] *movhi/0 com r30 ; tmp200 ; 201 [c=8 l=2] one_cmplhi2 com r31 ; tmp200 ; pwm-i.c:290: slot->mask = ~mask; adiw r26,2 ; slot_172->mask ; 202 [c=4 l=4] *movhi/3 st X+,r30 ; tmp200 st X,r31 ; tmp200 sbiw r26,2+1 ; slot_172->mask ; pwm-i.c:291: ++slot; adiw r26,4 ; slot, ; 203 [c=4 l=1] addhi3_clobber/0
