From: Segher Boessenkool <segher@kernel.crashing.org>
To: "Richard Earnshaw (lists)" <Richard.Earnshaw@arm.com>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [rtlanal] Do a better job of costing parallel sets containing flag-setting operations.
Date: Tue, 20 Jun 2017 12:55:00 -0000 [thread overview]
Message-ID: <20170620125458.GR16550@gate.crashing.org> (raw)
In-Reply-To: <20170619174052.GN16550@gate.crashing.org>
On Mon, Jun 19, 2017 at 12:40:53PM -0500, Segher Boessenkool wrote:
> On Mon, Jun 19, 2017 at 05:01:10PM +0100, Richard Earnshaw (lists) wrote:
> > Yeah, and I'm not suggesting we change the logic there (sorry if the
> > description was misleading). Instead I'm proposing that we handle more
> > cases for parallels to not return zero.
>
> Right. My test run is half way through, will have results later --
> your change looks good to me, but it is always surprising whether
> better costs help or not, or even *hurt* good code generation (things
> are just too tightly tuned to the current behaviour, so some things
> may need retuning).
Everything built successfully (31 targets); --enable-checking=yes,rtl,tree
so it took a while, sorry.
The targets with any differences (table shows code size):
old patched
arm 11545709 11545797
powerpc 8442762 8442746
x86_64 10627428 10627363
Arm has very many differences, the others do not. For powerpc (which
is 32-bit, 64-bit showed no differences) most of the difference is
scheduling deciding to do things a bit differently, and most of it
in places where we have not-so-good costs anyway. For arm the effects
often cascade to bb-reorder making different decisions.
Anyway, all differences are small, it is not likely to hurt anything.
I support the patch, if that helps -- but I cannot approve it.
Segher
next prev parent reply other threads:[~2017-06-20 12:55 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-19 13:47 Richard Earnshaw (lists)
2017-06-19 14:08 ` Segher Boessenkool
2017-06-19 14:28 ` Richard Earnshaw (lists)
2017-06-19 15:06 ` Segher Boessenkool
2017-06-19 14:45 ` Richard Earnshaw (lists)
2017-06-19 15:09 ` Segher Boessenkool
2017-06-19 16:01 ` Richard Earnshaw (lists)
2017-06-19 17:41 ` Segher Boessenkool
2017-06-20 12:55 ` Segher Boessenkool [this message]
2017-06-30 9:03 ` Richard Earnshaw (lists)
2017-06-30 15:20 ` Jeff Law
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