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Re: [PATCH] configure: disable -Wxor-used-as-pow
From: |
Paolo Bonzini |
Subject: |
Re: [PATCH] configure: disable -Wxor-used-as-pow |
Date: |
Tue, 23 Jun 2020 21:53:30 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 |
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