From: Peter Maydell <peter.maydell@linaro.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values
Date: Tue, 17 Nov 2015 10:42:26 +0000 [thread overview]
Message-ID: <CAFEAcA_PO=pVD4krX+igpVV4ungEcrnLcP-tTw-Hpq4zQ5P2dA@mail.gmail.com> (raw)
In-Reply-To: <564B0386.4030701@redhat.com>
On 17 November 2015 at 10:37, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>
> On 17/11/2015 11:36, Peter Maydell wrote:
>> > If and when this happens we will add "-fno-strict-overflow" for clang,
>> > just like we are using "-fno-strict-aliasing" already.
>>
>> -fno-strict-overflow in clang is AFAICT just an alias for -fwrapv.
>> These options control handling of signed overflow of addition,
>> subtraction and multiplication; there is nothing I can find in the
>> gcc or clang docs that suggests they have any effect on shift operations.
>
> In the case of GCC, that's a corollary of the compiler not treating that
> overflow as undefined.
>
> Probably the same is true for clang.
Again, can you get both sets of compiler devs to agree and
document this? If not, we can't rely on it.
thanks
-- PMM
next prev parent reply other threads:[~2015-11-17 10:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-17 9:59 [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values Paolo Bonzini
2015-11-17 10:19 ` Peter Maydell
2015-11-17 10:28 ` Paolo Bonzini
2015-11-17 10:36 ` Peter Maydell
2015-11-17 10:37 ` Paolo Bonzini
2015-11-17 10:42 ` Peter Maydell [this message]
2015-11-17 10:55 ` Peter Maydell
2015-11-17 10:57 ` Paolo Bonzini
2015-11-17 11:22 ` Peter Maydell
2015-11-17 12:10 ` Paolo Bonzini
2015-11-17 12:22 ` Peter Maydell
2015-11-17 10:41 ` Laszlo Ersek
2015-11-17 10:43 ` Paolo Bonzini
2015-11-17 10:52 ` Laszlo Ersek
2015-11-17 11:59 ` Markus Armbruster
2015-11-17 12:04 ` Peter Maydell
2015-11-17 12:17 ` Laszlo Ersek
2015-11-17 13:48 ` Paolo Bonzini
2015-11-17 12:18 ` Laszlo Ersek
2015-11-17 10:26 ` Markus Armbruster
2015-11-17 10:36 ` Laszlo Ersek
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