From: Paolo Bonzini <bonzini@gnu.org>
To: gcc@gcc.gnu.org, richard.sandiford@linaro.org
Subject: Re: Just what are rtx costs?
Date: Wed, 17 Aug 2011 18:56:00 -0000 [thread overview]
Message-ID: <4E4C0ECE.8060503@gnu.org> (raw)
In-Reply-To: <m3aab8rsya.fsf@richards-thinkpad.stglab.manchester.uk.ibm.com>
On 08/17/2011 07:52 AM, Richard Sandiford wrote:
> cost = rtx_cost (SET_SRC (set), SET, speed);
> return cost> 0 ? cost : COSTS_N_INSNS (1);
>
> This ignores SET_DEST (the problem I'm trying to fix). It also means
> that constants that are slightly more expensive than a register --
> somewhere in the range [0, COSTS_N_INSNS (1)] -- end up seeming
> cheaper than registers.
This can be fixed by doing
return cost >= COSTS_N_INSNS (1) ? cost : COSTS_N_INSNS (1);
> One approach I'm trying is to make sure that every target that doesn't
> explicitly handle SET does nothing with it. (Targets that do handle
> SET remain unchanged.) Then, if we see a SET whose SET_SRC is a
> register, constant, memory or subreg, we give it cost:
>
> COSTS_N_INSNS (1)
> + rtx_cost (SET_DEST (x), SET, speed)
> + rtx_cost (SET_SRC (x), SET, speed)
>
> as now. In other cases we give it a cost of:
>
> rtx_cost (SET_DEST (x), SET, speed)
> + rtx_cost (SET_SRC (x), SET, speed)
>
> But that hardly seems clean either. Perhaps we should instead make
> the SET_SRC always include the cost of the SET, even for registers,
> constants and the like. Thoughts?
Similarly, this becomes
dest_cost = rtx_cost (SET_DEST (x), SET, speed);
src_cost = MAX (rtx_cost (SET_SRC (x), SET, speed),
COSTS_N_INSNS (1));
return dest_cost + src_cost;
How does this look?
Paolo
next prev parent reply other threads:[~2011-08-17 18:56 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-17 14:52 Richard Sandiford
2011-08-17 17:29 ` Georg-Johann Lay
2011-08-19 12:25 ` Richard Sandiford
2011-08-21 17:03 ` Georg-Johann Lay
2011-08-22 8:20 ` Richard Sandiford
2011-08-22 9:59 ` Richard Guenther
2011-08-22 13:08 ` Joern Rennecke
2011-08-22 15:53 ` David Edelsohn
2011-08-22 12:12 ` Georg-Johann Lay
2011-08-22 23:23 ` Peter Bigot
2011-08-26 14:41 ` Georg-Johann Lay
2011-08-17 18:56 ` Paolo Bonzini [this message]
2011-08-18 7:58 ` Richard Sandiford
2011-08-18 0:55 ` Hans-Peter Nilsson
2011-08-18 8:14 ` Richard Sandiford
2011-08-19 14:17 ` Richard Sandiford
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