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[187.189.51.144]) by smtp.gmail.com with ESMTPSA id b14sm2113698ooj.26.2021.03.20.15.33.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 20 Mar 2021 15:33:59 -0700 (PDT) Subject: Re: [PATCH] configure: Improve alias attribute check To: Paolo Bonzini , Gavin Shan , qemu-devel@nongnu.org References: <20210320042753.69297-1-gshan@redhat.com> <5a6e5d96-7b23-7a56-3096-fb80155cac26@redhat.com> From: Richard Henderson Message-ID: <107a73a0-aafe-bfce-7c28-8ed5fe6c022f@linaro.org> Date: Sat, 20 Mar 2021 16:33:55 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <5a6e5d96-7b23-7a56-3096-fb80155cac26@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::334; envelope-from=richard.henderson@linaro.org; helo=mail-ot1-x334.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no 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: , Cc: thuth@redhat.com, qemu-arm@nongnu.org, philmd@redhat.com, laurent@vivier.eu, shan.gavin@gmail.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/20/21 11:52 AM, Paolo Bonzini wrote: >> +int main(void) >> +{ >> +    return read_y(); >> +} > > I think this should be "read_y() == 1 ? 0 : 1". As a testcase returning 0 on success, yes. > I can reproduce it with -flto -O2 but not without -flto, do you agree? Agreed. Replicated with a random recent gcc 11 snapshot. This is really annoying of lto. It's clear something needs to change though. > Perhaps we can obtain the same optimization by wrapping reads of the page size > in an inline __attribute__((const)) function.  Richard, what do you think? I'll give it a shot and see what happens. r~