[{"id":3680178,"web_url":"http://patchwork.ozlabs.org/comment/3680178/","msgid":"<544be217-d0b9-4ba3-ac52-06056782e637@linaro.org>","list_archive_url":null,"date":"2026-04-22T01:44:09","subject":"Re: [PATCH v2 02/13] target/mips: fix Octeon arithmetic destination\n handling","submitter":{"id":72104,"url":"http://patchwork.ozlabs.org/api/people/72104/","name":"Richard Henderson","email":"richard.henderson@linaro.org"},"content":"On 4/22/26 03:27, James Hilliard wrote:\n> BADDU and DMUL write their results to rd, not rt. Avoid treating rt ==\n> $zero as a nop, and route writes through gen_store_gpr() so rd == $zero\n> is handled consistently.\n\nIf you do the second, you can completely remove the initial IF.\n\nThat has been my preferred solution for other targets: minimize the number of checks for \nthese unlikely cases for all instruction implementations. You know for a fact that no \ncompiler is going to generate such instructions. The only place they'll appear are within \narchitectural compliance testsuites. Let code be generated and then the store_gpr helper \nwill discard the results.\n\nThe only place a special write-to-zero-register check is useful are for the architected \nNOP instructions, because we do expect a fair few of those. Even then, when using \ndecodetree, consider specialization within the decode, not within the helpers. See the \nnop/copy/or example at the end of docs/devel/decodetree.rst.\n\n\nr~","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=YFPIPLuT;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists1p.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g0hr72FqGz1y2d\n\tfor ; Wed, 22 Apr 2026 11:45:25 +1000 (AEST)","from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists1p.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from )\n\tid 1wFMda-00055g-5j; 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