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Fri, 20 Aug 2021 11:47:11 -0700 (PDT) Received: from [192.168.3.43] ([173.197.107.15]) by smtp.gmail.com with ESMTPSA id n41sm7946086pfv.43.2021.08.20.11.47.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Aug 2021 11:47:11 -0700 (PDT) Subject: Re: [PATCH v3 13/14] tcg/arm: Reserve a register for guest_base To: Peter Maydell References: <20210818212912.396794-1-richard.henderson@linaro.org> <20210818212912.396794-14-richard.henderson@linaro.org> From: Richard Henderson Message-ID: <47d219b3-72fb-f9bf-d420-cd08bc781119@linaro.org> Date: Fri, 20 Aug 2021 08:47:08 -1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: 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::534; envelope-from=richard.henderson@linaro.org; helo=mail-pg1-x534.google.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 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=-1.49, 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: QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/20/21 2:03 AM, Peter Maydell wrote: >> - } else if (datalo != addend) { >> + } else if (scratch_addend) { >> tcg_out_ld32_rwb(s, COND_AL, datalo, addend, addrlo); >> tcg_out_ld32_12(s, COND_AL, datahi, addend, 4); >> } else { > > I don't understand this change. Yes, we can trash the addend > register, but if it's the same as 'datalo' then the second load > is not going to DTRT... Shouldn't this be > if (scratch_addend && datalo != addend) > ? Previously, addend was *always* a scratch register, TCG_REG_TMP or such. Afterward, addend may be TCG_REG_GUEST_BASE, which should not be modified. At no point is there overlap between addend and data{hi,lo}. r~