Re: [Qemu-devel] [PATCH for 2.5] QEMU does not care about left shifts of signed negative values

[Peter Maydell]

On 17 November 2015 at 10:37, Paolo Bonzini <address@hidden> 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