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From: Blue Swirl <blauwirbel@gmail.com>
Date: Fri, 27 May 2011 20:07:01 +0300
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Subject: Re: [Qemu-devel] [PATCH 5/6] Do constant folding for shift
	operations.
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To: Richard Henderson <rth@twiddle.net>
Cc: mj.mccormack@samsung.com, qemu-devel@nongnu.org, zhur@ispras.ru, Kirill Batuzov <batuzovk@ispras.ru>

On Fri, May 27, 2011 at 12:14 AM, Richard Henderson <rth@twiddle.net> wrote=
:
> On 05/26/2011 01:25 PM, Blue Swirl wrote:
>>> I don't see the point. =C2=A0The C99 implementation defined escape hatc=
h
>>> exists for weird cpus. =C2=A0Which we won't be supporting as a QEMU hos=
t.
>>
>> Maybe not, but a compiler with this property could arrive. For
>> example, GCC developers could decide that since this weirdness is
>> allowed by the standard, it may be implemented as well.
>
> If you like, you can write a configure test for it. =C2=A0But, honestly,
> essentially every place in qemu that uses shifts on signed types
> would have to be audited. =C2=A0Really.

OK.

> The C99 hook exists to efficiently support targets that don't have
> arithmetic shift operations. =C2=A0Honestly.

So it would be impossible for a compiler developer to change the logic
for shifts for some supported two's-complement logic CPUs (like x86)
just because it's legal?