From: Segher Boessenkool <segher@kernel.crashing.org>
To: Richard Biener <richard.guenther@gmail.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] bb-reorder: Improve the simple algorithm for -Os (PR67864)
Date: Fri, 09 Oct 2015 16:08:00 -0000 [thread overview]
Message-ID: <20151009160820.GA32545@gate.crashing.org> (raw)
In-Reply-To: <CAFiYyc3pioW-Xe0A1JXW2JPkcVbVecV784fHy7OP2yVRR0T5OQ@mail.gmail.com>
On Fri, Oct 09, 2015 at 11:29:16AM +0200, Richard Biener wrote:
> I think the patch makes sense but it also raises a question for me - how
> did we decide what edge gets EDGE_FALLTHRU when going out-of-cfglayout?
Good question. I think it just tries to make "natural" control flow; I'll
investigate.
> And isn't _that_ mechanism then not part of basic-block reordering that
> needs to be tweaked for choosing the EDGE_FALLTHRU as better?
Yes.
This patch uses the existing fallthrough for conditional branches, which
seems to work best; but it still can significantly improve on unconditional
branches. I'm sure there are better heuristics possible but I don't know
them (and actually *solving* the problem isn't even polynomial of course).
Segher
next prev parent reply other threads:[~2015-10-09 16:08 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-08 16:57 Segher Boessenkool
2015-10-09 9:29 ` Richard Biener
2015-10-09 16:08 ` Segher Boessenkool [this message]
2015-10-09 10:35 ` Bernd Schmidt
2015-10-09 16:27 ` Segher Boessenkool
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