https://gcc.gnu.org/r238850
Applied this obvious change to __muldi3 which cleared zero_reg at the end of the function. This is not needed because there was a call to __umulsidi3 which already cleared zero_reg.
Johann libgcc/ * config/avr/lib1funcs.S (__muldi3) [have MUL]: No need to clear zero_reg as previous call to __umulhisi3 already cleared it. Index: config/avr/lib1funcs.S =================================================================== --- config/avr/lib1funcs.S (revision 238849) +++ config/avr/lib1funcs.S (working copy) @@ -958,7 +958,6 @@ DEFUN __muldi3 wmov A4, C4 wmov A6, C6 - clr __zero_reg__ pop r16 pop r17 pop r28