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Re: negative latencies


On 05/19/2014 02:13 AM, shmeel gutl wrote:
> Are there hooks in gcc to deal with negative latencies? In other
> words, an architecture that permits an instruction to use a result
> from an instruction that will be issued later.
>

Could you explain more on *an example* what are you trying to achieve
with the negative latency.

Scheduler is based on a critical path algorithm.  Generally speaking
latency time can be negative for this algorithm.  But I guess that is
not what you are asking.

> At first glance it seems that it will will break a few things.
> 1) The definition of dependencies cannot come from the simple ordering
> of rtl.
> 2) The scheduling problem starts to look like "get off the train 3
> stops before me".
> 3) The definition of live ranges needs to use actual instruction
> timing information, not just instruction sequencing.
>
> The hooks in the scheduler seem to be enough to stop damage but not
> enough to take advantage of this "feature".
>


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