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Re: [Qemu-devel] possible qemu miscompilation by latest gcc


From: Richard Henderson
Subject: Re: [Qemu-devel] possible qemu miscompilation by latest gcc
Date: Thu, 21 Jan 2010 08:57:32 -0800
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.5) Gecko/20091209 Fedora/3.0-4.fc12 Thunderbird/3.0

On 01/20/2010 10:15 PM, John Regehr wrote:
Hi folks-

Just wanted to let you know that perhaps the function
helper_neon_rshl_s8() is being miscompiled by the latest gcc.

I'm using qemu 0.12.2 and gcc rev 156103, which is a pre-version of gcc
4.5. This is on an x86 machine running Ubuntu 9.10.

At -O2 or higher this is the resulting object code:

00002060 <helper_neon_rshl_s8>:
2060: 31 c0 xor %eax,%eax
2062: c3 ret

If this is not the intended result, then either the function has a
latent bug or else the compiler is doing something bad.

Confirmed.  The compiler is at fault.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42833


r~




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