[Mesa-dev] [PATCH 5/8] i965: Prepare the uip/jip setting for compacted instructions in the program.

[Eric Anholt]

Paul Berry <stereotype441 at gmail.com> writes:

> On 31 August 2012 11:32, Eric Anholt <eric at anholt.net> wrote:
>
>> The first cut at instruction compaction won't compact things that
>> would change control flow jump distances, but we do need to still be
>> able to walk the instruction stream, which involves jumping by 8 or 16
>> bytes between instructions.
>>
>
> I'm not thrilled by the fact that after instruction compaction, p->store
> still has type struct brw_instruction *, but the data it points to doesn't
> always make sense as an array of struct brw_instruction.  It seems like
> there's a risk that we will later come along and add a p->store[...]
> reference somewhere it doesn't belong, and get ourselves into trouble.  But
> I don't really have a better suggestion to offer.

Yeah, I didn't come up with something better either.

>>        switch (insn->header.opcode) {
>>        case BRW_OPCODE_BREAK:
>> -        insn->bits3.break_cont.jip = br * (brw_find_next_block_end(p, ip)
>> - ip);
>> +        insn->bits3.break_cont.jip =
>> +            (brw_find_next_block_end(p, ip) - ip) / scale;
>>          /* Gen7 UIP points to WHILE; Gen6 points just after it */
>>          insn->bits3.break_cont.uip =
>> -           br * (brw_find_loop_end(p, ip) - ip + (intel->gen == 6 ? 1 :
>> 0));
>> +           (brw_find_loop_end(p, ip) - ip +
>> +             (intel->gen == 6 ? 16 : 0)) / scale;
>>
>
> It looks from patch 7/8 like the WHILE instruction is never compacted, so I
> believe this is correct.  However, if we ever decide to compact the WHILE
> instruction this will be wrong for gen6.  Would it be possible to add an
> assertion here (or at the very least a comment) to alert us to the fact
> that this will need to be fixed when we get around to compacting WHILE?

The out-of-diff-context comment describing this function says that it's
just for adjusting break/cont (and HALT as well when we had that
around).  I clarified that in the commit message.
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