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[50.78.183.178]) by smtp.gmail.com with ESMTPSA id y24sm6900740pfn.81.2021.05.29.08.21.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 29 May 2021 08:21:22 -0700 (PDT) Subject: Re: [PATCH 03/11] softfloat: Introduce float_flag_inorm_denormal To: Michael Morrell , "qemu-devel@nongnu.org" References: <20210527041405.391567-1-richard.henderson@linaro.org> <20210527041405.391567-4-richard.henderson@linaro.org> <44a76e8c6504461cbd4dc5752f0d443b@tachyum.com> From: Richard Henderson Message-ID: Date: Sat, 29 May 2021 08:21:19 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <44a76e8c6504461cbd4dc5752f0d443b@tachyum.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::52e; envelope-from=richard.henderson@linaro.org; helo=mail-pg1-x52e.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=ham 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: "alex.bennee@linaro.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/28/21 10:41 AM, Michael Morrell wrote: > I'm probably missing something, but why do we need both "float_flag_inorm_denormal" and "float_flag_iflush_denormal"? > > Couldn't the code that sets these flags set just a single flag for all denormal inputs and the code that checks these flags check that single flag > combined with the "flush_inputs_to_zero" flag to accomplish what the two separate "input denormal" flags do? The thing that you're missing is that many guests leave the accumulated softfloat exceptions in the float_status structure until the guest FPSCR register is read. Unless the guest needs to raise an exception immediately, there's no reason to do otherwise. With this setup, you have no temporal connection between "any denormal" and "flush-to-zero is set", thus two flags. r~