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Wed, 23 Sep 2026 03:38:57 -0700 (PDT) Received: from linaro.org ([2a10:d582:31e:0:805c:5b2c:d225:9d51]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6aab386e596sm1402745a12.7.2026.09.23.03.38.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2026 03:38:56 -0700 (PDT) Date: Wed, 23 Sep 2026 11:38:52 +0100 From: Jim MacArthur To: qemu-devel@nongnu.org Cc: richard.henderson@linaro.org Subject: Re: [PATCH 1/2] tcg/optimize: Fix fold_multiply2 vs 1 Message-ID: References: <20260915014115.1809286-1-richard.henderson@linaro.org> <20260915014115.1809286-2-richard.henderson@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260915014115.1809286-2-richard.henderson@linaro.org> Received-SPF: pass client-ip=2a00:1450:4864:20::535; envelope-from=jim.macarthur@linaro.org; helo=mail-ed1-x535.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, 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: qemu development 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 Mon, Sep 14, 2026 at 03:41:14PM -1000, Richard Henderson wrote: > For muls2, we returned from fold_multiply2 without finish_folding > or any other mechanism to update value tracking for the rh output. > We might as well do this via fold_shift, which will also mark rh > as having all copies of the sign bit. > > For the movi paths of multiply vs 0 or mulu2, we're better off tail > calling to tcg_opt_gen_movi rather than explicitly returning true. > > Cc: qemu-stable@nongnu.org > Fixes: c9349965ce4 ("tcg: Optimize INDEX_op_mul[us]2 for 0 and 1") > Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4448 > Signed-off-by: Richard Henderson > --- > tcg/optimize.c | 17 +++++++---------- > 1 file changed, 7 insertions(+), 10 deletions(-) > Reviewed-by: Jim MacArthur