Re: [wwwdocs] Round 1 of cleaning up "old PROBLEMS"

[Zack Weinberg <zack at codesourcery dot com>]

Andreas Schwab <schwab@suse.de> writes:

>> That appears to be m68k assembly language.  I don't think it's worth
>> trying very hard to reconstruct a test case, though.
>
> That's pretty straightforward.  Compiling this:
>
>     struct X {
>       char *a;
>       /* other members */
>       int b;
>     };
>
>     void f (struct X *x)
>     {
>       x->a[x->b] = 0;
>     }
>
> with current mainline on m68k at -O2 yields the following, which looks
> exactly like what this entry is about:
>
> f:
>         link.w %fp,#0
>         move.l 8(%fp),%a0
>         move.l (%a0),%a1
>         move.l 4(%a0),%a0
>         clr.b (%a0,%a1.l)
>         unlk %fp
>         rts

Can you express an opinion on whether the suggested variant code (in
this notation,

f:
        link.w %fp,#0
        move.l 8(%fp),%a0
        add.l 4(%a0),%a0
        clr.b (%a0)
        unlk %fp
        rts

) is indeed more efficient than what GCC does generate?

zw