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Re: negative latencies
- From: Andrew Pinski <pinskia at gmail dot com>
- To: shmeel gutl <shmeelgutl at shmuelhome dot mine dot nu>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Vladimir Makarov <vmakarov at redhat dot com>
- Date: Sun, 18 May 2014 23:39:13 -0700
- Subject: Re: negative latencies
- Authentication-results: sourceware.org; auth=none
- References: <5379A125 dot 5090405 at shmuelhome dot mine dot nu>
On Sun, May 18, 2014 at 11:13 PM, shmeel gutl
> 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.
Do you mean bypasses? If so there is a bypass feature which you can use:
> 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
> 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".