Re: [avr-gcc-list] code selection: ijmp and icall

[Joerg Wunsch]

Markus Oertel <address@hidden> wrote:

> So my question is: does the compiler create jumptargets for IJMP and
> ICALL that are not labeled.

A simple test (large case statement with many labels) compiles
into something like this:

..global foo
        .type   foo, @function
foo:
/* prologue: frame size=0 */
/* prologue end (size=0) */
        mov r31,r25
        mov r30,r24
        cpi r24,255
        cpc r25,__zero_reg__
        breq .+4
        brlo .+2
        rjmp .L2
        subi r30,lo8(-(gs(.L259)))
        sbci r31,hi8(-(gs(.L259)))
        ijmp
        .data
        .section .progmem.gcc_sw_table, "ax", @progbits
        .p2align 1
..L259:
        .data
        .section .progmem.gcc_sw_table, "ax", @progbits
        .p2align 1
        rjmp .L3
        rjmp .L4
        rjmp .L5
        rjmp .L6
        rjmp .L7
        rjmp .L8
        rjmp .L9
        rjmp .L10
        rjmp .L11
....
        .text
..L3:
        ldi r24,lo8(1024)
        ldi r25,hi8(1024)
        ret
..L4:
        ldi r24,lo8(1023)
        ldi r25,hi8(1023)
        ret
..L5:
        ldi r24,lo8(1022)
        ldi r25,hi8(1022)
        ret
..L6:
        ldi r24,lo8(1021)
        ldi r25,hi8(1021)
        ret
..L7:
        ldi r24,lo8(1020)
        ldi r25,hi8(1020)
        ret
....

But of course, as Eric wrote, if you want to be really sure, you'd
have to lookup all instances of "ijmp" in the AVR-specific part of the
GCC source code, and see whether all of them are used that way.

-- 
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)