linux-kernel - RE: [patch 2.6.19-rc6] Stop gcc 4.1.0 optimizing wait_hpet

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Message-ID: <MDEHLPKNGKAHNMBLJOLKCEINADAC.davids@webmaster.com>
Date:	Thu, 7 Dec 2006 20:22:17 -0800
From:	"David Schwartz" <davids@...master.com>
To:	<mrmacman_g4@....com>
Cc:	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	<schwab@...e.de>
Subject: RE: [patch 2.6.19-rc6] Stop gcc 4.1.0 optimizing wait_hpet_tick away


> In that case it specifies that any evaluation of "*foo" in an rvalue
> context specifies a read (with a few exceptions for G++ where the C++
> language generally confuses things).  Specifically it mentions the
> statement "*src;" and discusses the statement as providing "a void
> context".  In other words, a statement such as "(void)(expr);" is
> redundant because the statement already implies void context and the
> extra cast-to-void is just extra text.  As such "(void)(*src);" on a
> "volatile int *src;" is documented to force a read of "*src".  Now,
> if you actually _use_ the result over just casting it to void and
> discarding it, then GCC can provide no _less_ guarantee with regards
> to the read-and-store than it provides to the read-and-discard.

I read over this section and didn't realize the implications of the void
context. I now agree with you.

DS


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