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([2001:b07:6468:f312:24f5:23b:4085:b879]) by smtp.gmail.com with ESMTPSA id w17sm25115229wra.42.2020.06.23.12.53.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Jun 2020 12:53:31 -0700 (PDT) Subject: Re: [PATCH] configure: disable -Wxor-used-as-pow To: Eric Blake , qemu-devel@nongnu.org References: <20200623173726.20909-1-pbonzini@redhat.com> From: Paolo Bonzini Message-ID: 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 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/23 01:55:08 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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