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

[Andreas Schwab <schwab at suse dot de>]

Zack Weinberg <zack@codesourcery.com> writes:

>>  10 (see patch)
>>
>>   The target for which this was a problem isn't mentioned, so it is
>>   not even clear what the problem is.  There is no way to check if
>>   the problem still exists.
> ...
>> -  <li value="10">
>> -  <pre>
>> -        movl a3@,a0
>> -        movl a3@(16),a1
>> -        clrb a0@(a1:l)
>> -  </pre>
>> -  <p>is generated and may be worse than</p>
>> -  <pre>
>> -        movl a3@,a0
>> -        addl a3@(16),a0
>> -        clrb a0@
>> -  </pre>
>
> 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

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux AG, Maxfeldstraße 5, 90409 Nürnberg, Germany
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