2011/9/26 Georg-Johann Lay <a...@gjlay.de>:
> This is a minor tweak to do eq/ne comparisons one instruction shorter in the
> case where the compare target is unused after the comparison:
>
> For 1:
> DEC R0
> OR R0,R1
> OR R0,R2
> OR R0,R3
>
> For -1:
> AND R0,R3
> AND R0,R2
> AND R0,R1
> COM R0
>
> The text peephole casesi+2 used 0xffff where -1 is the right canonical
> representation, e.g. the following source
>
> char c;
>
> unsigned int cmp_p (unsigned int x)
> {
> if (--x == 65535)
> c = 0;
> return x;
> }
>
> compiles with -S -Os -dP -fno-peephole to
>
> ; (insn 7 6 8 (parallel [
> ; (set (cc0)
> ; (compare (reg/v:HI 24 r24 [orig:42 x ] [42])
> ; (const_int -1 [0xffffffff])))
> ; (clobber (reg:QI 18 r18))
> ; ]) cmp.c:6 184 {*cmphi}
> ; (expr_list:REG_UNUSED (reg:QI 18 r18)
> ; (nil)))
>
>
> Fixed that, too. Test suite passes fine.
>
> Ok?
>
> Johann
>
> * config/avr/avr.md (peephole casesi+2): Use -1
> instead of 65535.
> * config/avr/avr.c (avr_out_compare): Print shorter sequence for
> EQ/NE comparisons against +/-1 in the case of unused-after,
> non-ld-regs target.
>
Please commit.
Denis.
