[Bug target/81268] New: [avr] Support __gcc_isr pseudo-instruction for more efficient ISR prologues

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81268

            Bug ID: 81268
           Summary: [avr] Support __gcc_isr pseudo-instruction for more
                    efficient ISR prologues
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

GNU assembler supports the __gcc_isr pseudo-instruction, cf.

https://sourceware.org/bugzilla/show_bug.cgi?id=21683

This can be used up reduce overhead in ISR prologues and epilogues due to GCC's
modeling of TMP_REG and ZERO_REG as fixed regs und using cc0 to model SREG.