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Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH v5 16/36] tcg: Add tcg_gen_{non}atomic_cmpxchg_i128 Content-Language: en-US To: Richard Henderson , qemu-devel@nongnu.org Cc: alex.bennee@linaro.org References: <20230126043824.54819-1-richard.henderson@linaro.org> <20230126043824.54819-17-richard.henderson@linaro.org> <8b021470-b335-4b85-d516-906308ddea69@linaro.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::332; envelope-from=philmd@linaro.org; helo=mail-wm1-x332.google.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 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=-1.148, 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: 2.1.29 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 27/1/23 07:39, Richard Henderson wrote: > On 1/26/23 14:45, Philippe Mathieu-Daudé wrote: >>> +        /* Compare i128 */ >>> +        tcg_gen_xor_i64(t0, TCGV128_LOW(oldv), TCGV128_LOW(cmpv)); >>> +        tcg_gen_xor_i64(t1, TCGV128_HIGH(oldv), TCGV128_HIGH(cmpv)); >>> +        tcg_gen_or_i64(t0, t0, t1); >> >> Can we skip the OR ... >> >>> +        /* tmpv = equal ? newv : oldv */ >>> +        tcg_gen_movcond_i64(TCG_COND_EQ, TCGV128_LOW(tmpv), t0, z, >>> +                            TCGV128_LOW(newv), TCGV128_LOW(oldv)); >>> +        tcg_gen_movcond_i64(TCG_COND_EQ, TCGV128_HIGH(tmpv), t0, z, >> >> ... and test t1 here to partially update LO/HI? (we could remove t1 and >> just use t0 as twice 'xor + movcond' but the code is less readable). > > No. > > We want equality on the entire 128-bit comparison to control the > conditional moves. Reviewed-by: Philippe Mathieu-Daudé