From: Ian Lance Taylor <iant@google.com>
To: "PRC" <panruochen@gmail.com>
Cc: "gcc-help" <gcc-help@gcc.gnu.org>
Subject: Re: Why does gcc produce an unnecessary `nop' instruction?
Date: Sat, 26 Jan 2008 04:48:00 -0000 [thread overview]
Message-ID: <m3ve5i53vx.fsf@localhost.localdomain> (raw)
In-Reply-To: <200801251719424202892@gmail.com>
"PRC" <panruochen@gmail.com> writes:
> >It's probably caused by requested alignment of the next function.
> >Note that nop is just the value 0.
> >
> >To see whether gcc is actually generating the nop, use the
> >--save-temps option when you compile, and look at the .s file. If you
> >don't see the nop there, it's coming from something other than gcc.
>
> I look at the `objdump'ed assembly file again and I find that all functions
> start at the address which is 8-byte aligned.
> Is there a particular good reason for 8-byte alignment, even if the target ARCH
> is 32-bit rather than 64-bit and aligment is quite a little waste of storage and
> runtime memory?
Assuming you haven't used the -falign-functions option, then they are
probably being aligned so that they start on cache line boundaries. I
don't see any code in the ARC backend to do this, so I'm not sure
where it is coming from.
Ian
next prev parent reply other threads:[~2008-01-25 15:20 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-25 19:41 PRC
2008-01-25 22:55 ` Ian Lance Taylor
2008-01-25 22:55 ` PRC
2008-01-26 2:33 ` John Love-Jensen
2008-01-26 4:48 ` Ian Lance Taylor [this message]
2008-01-28 3:12 ` Darryl Miles
2008-01-28 12:12 ` Ian Lance Taylor
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