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Message-ID: <4CD843DC.10106@gmail.com>
Date: Mon, 08 Nov 2010 18:39:24 +0000
From: Dave Korn <dave.korn.cygwin@gmail.com>
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To: Andi Kleen <andi@firstfloor.org>
CC: Richard Guenther <richard.guenther@gmail.com>,
        Andreas Schwab <schwab@linux-m68k.org>, Jim <jim876@xs4all.nl>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        gcc@gcc.gnu.org
Subject: Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?
References: <4CD538CA.8010901@xs4all.nl> <87wroostw3.fsf@basil.nowhere.org>	<m2hbfsu57i.fsf@igel.home> <87k4kospnd.fsf@basil.nowhere.org>	<AANLkTikG6kBxSrO7EZ5_nZqTKqo8Rjm2stoEGVJWxanz@mail.gmail.com> <877hgorrj1.fsf@basil.nowhere.org>
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On 08/11/2010 11:20, Andi Kleen wrote:

> An asm with live inputs and outputs should never be optimized
> way. If 4.5.1 started doing that it's seriously broken.

  I don't see that.  Consider:

void foo (void)
{
  int x, y, z;
  x = 23;
  y = x + 1;
  z = y + 1;
}

  So far, you'd agree the compiler may optimise the entire function away?  So
why not this:

void foo (void)
{
  int x, y, z;
  x = 23;
  asm ("do something" : "=r" (y) : "r" (x) );
  z = y + 1;
}

  ?

    cheers,
      DaveK
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