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Date: Sat, 21 Jul 2001 15:10:55 -0700
From: Richard Henderson <rth@twiddle.net>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Why Plan 9 C compilers don't have asm("")
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In-Reply-To: <9hvjd4$1ok$1@penguin.transmeta.com>; from torvalds@transmeta.com on Wed, Jul 04, 2001 at 05:22:44PM +0000
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On Wed, Jul 04, 2001 at 05:22:44PM +0000, Linus Torvalds wrote:
> [ And yes, I know there are optimizing linkers for the alpha around that
>   improve this and notice when they don't need to change GP and can do a
>   straight branch etc.  I don't think GNU ld _still_ does that, but who
>   knows.

GNU ld does it with the "-relax" flag.

>   Even the "good" Digital compilers tended to nop out unnecessary
>   instructions rather than remove them, causing more icache pressure on
>   a CPU that was already famous for needing tons of icache ]

But you're absolutely right about the nopping -- removing the nops would
require debug info and EH info to be re-coded.  The later being a matter
of correctness.  This is a bit nastier than I ever cared to deal with.


r~
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