From: Michael Matz <matz@suse.de>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Peter Bergner <bergner@linux.ibm.com>,
Alan Modra <amodra@gmail.com>, GCC <gcc@gcc.gnu.org>
Subject: Re: Question regarding constraint usage within inline asm
Date: Thu, 28 Feb 2019 13:01:00 -0000 [thread overview]
Message-ID: <alpine.LSU.2.21.1902281257410.5354@wotan.suse.de> (raw)
In-Reply-To: <20190225231054.GH14180@gate.crashing.org>
Hi,
On Mon, 25 Feb 2019, Segher Boessenkool wrote:
> Yup. All good points, I didn't think this through enough obviously.
>
> The _1+_1 isn't great if that single pseudo then ends up in mem (it will
> need a reload again on most archs, probably causing another spill), btw.
But at least it'll get only a single reload, not two ...
> You get worse code that way. Reload is much too late to make optimised
> code, and that isn't its task anyway: its task is to make something that
> works where the passes before it couldn't manage.
... but yes, if we're entering the optimization- (in difference to
correctness-) territory, then sure, expand (or any other pass between it
and reload) might want to handle some sitations in a special way to ensure
good code with the least amount of work.
> Yes, reload should be able to fix up anything (well, within some
> limits). That is not an excuse to generate code that we know will need
> such fixups though.
(Within some limits :) ), I agree.
Ciao,
Michael.
next prev parent reply other threads:[~2019-02-28 13:01 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-18 19:14 Peter Bergner
2019-02-20 3:10 ` Alan Modra
2019-02-20 16:08 ` Peter Bergner
2019-02-20 19:24 ` Segher Boessenkool
2019-02-20 22:04 ` Alan Modra
2019-02-20 22:19 ` Alan Modra
2019-02-21 2:57 ` Peter Bergner
2019-02-21 3:40 ` Alan Modra
2019-02-21 23:16 ` Peter Bergner
2019-02-22 1:08 ` Segher Boessenkool
2019-02-25 18:32 ` Michael Matz
2019-02-28 4:16 ` Segher Boessenkool
2019-02-28 13:01 ` Michael Matz [this message]
2019-02-21 3:03 ` Peter Bergner
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