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Thu, 15 Apr 2021 09:59:11 -0700 (PDT) Received: from [192.168.1.11] ([71.212.131.83]) by smtp.gmail.com with ESMTPSA id w3sm2869772pjg.7.2021.04.15.09.59.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 15 Apr 2021 09:59:10 -0700 (PDT) Subject: Re: [PATCH 5/5] target/ppc: Implement paddi and replace addi insns From: Richard Henderson To: Luis Pires , qemu-devel@nongnu.org, qemu-ppc@nongnu.org References: <20210413211129.457272-1-luis.pires@eldorado.org.br> <20210413211129.457272-6-luis.pires@eldorado.org.br> <35a37fdc-0580-7c0b-5748-1f194386007c@linaro.org> Message-ID: Date: Thu, 15 Apr 2021 09:59:08 -0700 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: <35a37fdc-0580-7c0b-5748-1f194386007c@linaro.org> 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::42f; envelope-from=richard.henderson@linaro.org; helo=mail-pf1-x42f.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: lagarcia@br.ibm.com, bruno.larsen@eldorado.org.br, matheus.ferst@eldorado.org.br, f4bug@amsat.org, david@gibson.dropbear.id.au Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/14/21 12:11 PM, Richard Henderson wrote: > This approach seems like it will work fine for MLS and MMIR prefixes.  For 8LS, > 8RR, and MRR prefixes, we'll need some extra help within ppc_tr_translate_insn. >  E.g. > >     insn = translator_ldl_swap(env, ctx->base.pc_next, >                                need_byteswap(ctx)); >     switch (ctx->prefix_type) { >     case PREFIX_NONE: >         ok = decode_opcode_space_0(ctx, insn) || >              decode_legacy(ctx, insn); >         break; >     case PREFIX_MLS: >     case PREFIX_MMIRR: >         ok = decode_opcode_space_0(ctx, insn); >         break; I played about with this last night, and there's an interesting trade-off: (1) The thousands of 32-bit insns which do not allow prefixes now each require 3 lines to assert that no prefix is present, (2) There are only 12 MLS and 29 MMIRR prefixed insns. I think it may well be that eliminating boiler-plate from thousands of insns it a good trade-off to special-casing 41 insns. At which point, considering the multiple variations on 8RR and MMIRR prefixes, seems to indicate that we should decode all 64 bits all at once. r~