https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90706
Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|target |rtl-optimization
Summary|Useless code generated for |[9 Regression] Useless code
|stack / register operations |generated for stack /
|on AVR |register operations on AVR
--- Comment #1 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
(In reply to Berni from comment #0)
> pushing r0 does not make sense at all since it is by definition a temporary
> register that can freely be modified. Maybe it's just pushed to make room
> for the stack operations?
Yes.
The code from v8 is already suboptimal: It's nonsense to load R28 with 0x1 just
to survive a function call. Better use a call-used register and load it after
the function call to where the return value is computed. Then there would be no
need to push/pop R28.
Does -fno-caller-saves improve v9 code?
This is definitely not a target issue. It's likely a register-allocation
problem. And the v8 problem is because some (tree) passes move setters away
from their consumers.
