From: Jakub Jelinek <jakub@redhat.com>
To: Jan Beulich <JBeulich@suse.com>, hjl.tools@gmail.com
Cc: gcc-patches@gcc.gnu.org
Subject: Re: avoid alignment of static variables affecting stack's
Date: Thu, 23 Oct 2014 06:54:00 -0000 [thread overview]
Message-ID: <20141023065015.GX10376@tucnak.redhat.com> (raw)
In-Reply-To: <5448BCA30200007800041508@mail.emea.novell.com>
On Thu, Oct 23, 2014 at 07:30:27AM +0100, Jan Beulich wrote:
> Function (or more narrow) scope static variables (as well as others not
> placed on the stack) should also not have any effect on the stack
> alignment. I noticed the issue first with Linux'es dynamic_pr_debug()
> construct using an 8-byte aligned sub-file-scope local variable.
>
> According to my checking bad behavior started with 4.6.x (4.5.3 was
> still okay), but generated code got quite a bit worse as of 4.9.0.
If the static/external var has BLKmode, then perhaps it is safe, but I
wonder about other vars, say vectors etc. Such vars are most likely
loaded from their memory location, and if for some reason that needs to be
spilled again, stack realignment would not be able to do that.
Or do we inspect the IL and for any pseudos with modes needing larger
alignment we adjust the dynamic stack realignment fields?
Jakub
next prev parent reply other threads:[~2014-10-23 6:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-23 6:50 Jan Beulich
2014-10-23 6:54 ` Jakub Jelinek [this message]
2014-10-23 7:11 ` Jan Beulich
2014-10-23 18:14 ` Jeff Law
2014-10-24 9:11 ` Jan Beulich
2014-10-24 9:12 ` Richard Biener
2014-10-24 9:18 ` Jan Beulich
2014-10-24 9:19 ` Jakub Jelinek
2014-10-24 9:54 ` Richard Biener
2014-10-24 10:16 ` Jan Beulich
2014-10-24 10:42 ` Richard Biener
2014-10-24 16:42 ` Jeff Law
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