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Date: Thu, 08 Mar 2012 19:07:31 +0100
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Subject: Re: [Qemu-devel] [PATCH] vnc: Fix packed boolean struct members
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: QEMU Trivial <qemu-trivial@nongnu.org>, Stefan Hajnoczi <stefanha@gmail.com>, Anthony Liguori <aliguori@us.ibm.com>, qemu-devel@nongnu.org, Stefan Weil <sw@weilnetz.de>

Il 08/03/2012 17:25, Anthony Liguori ha scritto:
>>
>> Looks like a GCC bug where
>>
>>     x = y = 0;
>>
>> is converted to
>>
>>     x = (y = 0) != 0;
> 
> Curious, why convert like this?  What does this optimization do?

Nothing, it's just that if "y = 0" is an int (for some reason, I didn't
check if it's implicit promotion or just that y is already an int), then
it has to be converted back to a truth value before assigning to bool.
If you do

  bool x;
  int y;

  x = y = 2;

x is actually set to 1.

Paolo