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Mon, 20 Sep 2021 09:10:51 -0700 (PDT) Received: from [192.168.1.11] ([71.212.134.125]) by smtp.gmail.com with ESMTPSA id 126sm17542415pgi.86.2021.09.20.09.10.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Sep 2021 09:10:50 -0700 (PDT) Subject: Re: [PATCH 15/30] tcg/loongarch: Implement clz/ctz ops To: WANG Xuerui , qemu-devel@nongnu.org References: <20210920080451.408655-1-git@xen0n.name> <20210920080451.408655-16-git@xen0n.name> From: Richard Henderson Message-ID: <82af9bf5-d809-9201-d142-c94688137239@linaro.org> Date: Mon, 20 Sep 2021 09:10:49 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20210920080451.408655-16-git@xen0n.name> 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::102b; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x102b.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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 9/20/21 1:04 AM, WANG Xuerui wrote: > +static void tcg_out_clzctz(TCGContext *s, LoongArchInsn opc, > + TCGReg a0, TCGReg a1, TCGReg a2) > +{ > + /* all clz/ctz insns belong to DJ-format */ > + tcg_out32(s, encode_dj_insn(opc, TCG_REG_TMP0, a1)); > + /* a0 = a1 ? REG_TMP0 : a2 */ > + tcg_out_opc_maskeqz(s, TCG_REG_TMP0, TCG_REG_TMP0, a1); > + tcg_out_opc_masknez(s, a0, a2, a1); > + tcg_out_opc_or(s, a0, TCG_REG_TMP0, a0); > +} From Song Gao's translation, I believe that ctz(0) == 32 or 64, depending on the operation width. This is in fact the most common result, so it's worth specializing. See tcg/i386/tcg-target.c.inc, tcg_out_clz, have_lzcnt. But what's here looks ok. Reviewed-by: Richard Henderson r~