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From: "gjl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/110217] [avr] SREG: use BSET and BCLR instead of
 load/modify/write
Date: Fri, 30 Jun 2023 16:53:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110217

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

--- Comment #1 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
The only case where this might make sense is for bit 7 (the I-flag), however
the established coding style is to use cli() and sei() from AVR-LibC, cf.
documentation of #include <avr/interrupt.h>:

https://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html

For more sophitsticated use cases there is even ATOMIC_BLOCK and friends
provided by #include <util/atomic.h>, cf:

https://www.nongnu.org/avr-libc/user-manual/group__util__atomic.html

This has the additional benefit of being more readable than bit manipulatio=
ns.=20=20

Apart from that, the proposed patch won't work for indirect addressing, or =
when
the compiler is turning direct addresses to indirect addresses (using CSE e=
tc,
common subexpression elimination and similar strategies).

Also the patch relies on insn combine which only runs when optimization is =
on,
thus any application which relies on that optimization will glitch at -O0.

So I am inclined to "won't fix" this PR.

Maybe you just missed avr/interrupt.h and / or util/atomic.h ?

If you must not use AVR-LibC for some reason, then the next best approach i=
s to
use __builtin_avr_sei(), cf. AVR built-in functions:

https://gcc.gnu.org/onlinedocs/gcc-13.1.0/gcc/AVR-Built-in-Functions.html

Or implement it as static inline function that does __asm volatile ("sei" :=
::
"memory") if you are not allowed to use built-ins.=