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Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values |
Date: |
Tue, 17 Nov 2015 11:28:32 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 17/11/2015 11:19, Peter Maydell wrote:
> I think we should only take this patch if you can get a cast-iron
> guarantee from both clang and gcc that they will never use this
> UB to drive optimizations. As you say gcc already say this more or
> less, but clang doesn't, and if they're warning about it that to
> me suggests that they will feel freer to rely on the UB in future.
If and when this happens we will add "-fno-strict-overflow" for clang,
just like we are using "-fno-strict-aliasing" already.
> GCC is not our only supported compiler; UB is a real thing that
> compilers in general take advantage of; we should be trying to
> reduce our reliance on UB, not carving out extra areas where we
> feel free to use it.
We are already feeling free to use it.
Paolo
- [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Laszlo Ersek, 2015/11/17
- Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17