Re: [PATCH] configure: disable -Wxor-used-as-pow

[Paolo Bonzini <pbonzini@redhat.com>]

On 23/06/20 20:41, Eric Blake wrote:
> On 6/23/20 12:37 PM, Paolo Bonzini wrote:
>> Clang being clang and adding more pointless warnings.  In a hardware
>> emulator there are going to be plenty of bitwise operations, and the
>> chance of someone writing ^ for pow and not being caught is basically
>> zero.
> 
> Did this warning actually fire?
> 
> My understanding (from a quick glance of
> https://reviews.llvm.org/D63423) is that it is supposed to catch
> instances of '2 ^ 16' where someone meant '1 << 16' instead of 18.  I
> don't know if it is supposed to flag 'a ^ 16' (if it does, then it is
> indeed useless), or only when both lhs and rhs are constants and where
> lhs is 2 or 10, so my initial reaction is that without seeing an actual
> false positive, we are premature in disabling it.

There is an instance of 2 ^ 20.

But it's actually a bug.  Objection (and faith in humanity) retracted.

Paolo