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[83.52.55.163]) by smtp.gmail.com with ESMTPSA id m64sm11481793wmm.41.2021.08.06.14.09.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Aug 2021 14:09:26 -0700 (PDT) Subject: Re: [PATCH] target/mips: Remove JR opcode unused arguments To: qemu-devel@nongnu.org References: <20210730225507.2642827-1-f4bug@amsat.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <97f3de74-212e-72bd-ec07-3ae9e8312a8c@amsat.org> Date: Fri, 6 Aug 2021 23:09:25 +0200 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: <20210730225507.2642827-1-f4bug@amsat.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::42a; envelope-from=philippe.mathieu.daude@gmail.com; helo=mail-wr1-x42a.google.com X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FORGED_FROMDOMAIN=0.249, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.249, NICE_REPLY_A=-2.619, 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: Aleksandar Rikalo , Richard Henderson , Aurelien Jarno Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/31/21 12:55 AM, Philippe Mathieu-Daudé wrote: > JR opcode (Jump Register) only takes 1 argument, $rs. > JALR (Jump And Link Register) takes 3: $rs, $rd and $hint. > > Commit 6af0bf9c7c3 added their processing into decode_opc() as: > > case 0x08 ... 0x09: /* Jumps */ > gen_compute_branch(ctx, op1 | EXT_SPECIAL, rs, rd, sa); > > having both opcodes handled in the same function: gen_compute_branch. > > Per JR encoding, both $rd and $hint ('sa') are decoded as zero. > > Later this code got extracted to decode_opc_special(), > commit 7a387fffce5 used definitions instead of magic values: > > case OPC_JR ... OPC_JALR: > gen_compute_branch(ctx, op1, rs, rd, sa); > > Finally commit 0aefa33318b moved OPC_JR out of decode_opc_special, > to a new 'decode_opc_special_legacy' function: > > @@ -15851,6 +15851,9 @@ static void decode_opc_special_legacy(CPUMIPSState *env, DisasContext *ctx) > + case OPC_JR: > + gen_compute_branch(ctx, op1, 4, rs, rd, sa); > + break; > > @@ -15933,7 +15936,7 @@ static void decode_opc_special(CPUMIPSState *env, DisasContext *ctx) > - case OPC_JR ... OPC_JALR: > + case OPC_JALR: > gen_compute_branch(ctx, op1, 4, rs, rd, sa); > break; > > Since JR is now handled individually, it is pointless to decode > and pass it unused arguments. Replace them by simple zero value > to avoid confusion with this opcode. > > Signed-off-by: Philippe Mathieu-Daudé > --- > target/mips/tcg/translate.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Thanks, applied to mips-next.