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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH 27/37] target/i386: Use tcg gvec ops for pmovmskb Content-Language: en-US To: Paolo Bonzini Cc: qemu-devel@nongnu.org References: <20220911230418.340941-1-pbonzini@redhat.com> <20220911230418.340941-28-pbonzini@redhat.com> <58a3c681-a46a-d433-38b5-37c03515a3c9@linaro.org> From: Richard Henderson In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2a00:1450:4864:20::330; envelope-from=richard.henderson@linaro.org; helo=mail-wm1-x330.google.com X-Spam_score_int: -36 X-Spam_score: -3.7 X-Spam_bar: --- X-Spam_report: (-3.7 / 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=-1.583, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: 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" On 9/14/22 23:59, Paolo Bonzini wrote: > On Tue, Sep 13, 2022 at 10:17 AM Richard Henderson > wrote: >> >> On 9/12/22 00:04, Paolo Bonzini wrote: >>> + while (vec_len > 8) { >>> + vec_len -= 8; >>> + tcg_gen_shli_tl(s->T0, s->T0, 8); >>> + tcg_gen_ld8u_tl(t, cpu_env, offsetof(CPUX86State, xmm_t0.ZMM_B(vec_len - 1))); >>> + tcg_gen_or_tl(s->T0, s->T0, t); >>> } >> >> The shl + or is deposit, for those hosts that have it, >> and will be re-expanded to shl + or for those that don't: >> >> tcg_gen_ld8u_tl(t, ...); >> tcg_gen_deposit_tl(s->T0, t, s->T0, 8, TARGET_LONG_BITS - 8); > > What you get from that is an shl(t, 56) followed by extract2 (i.e. > SHRD). Yeah there are targets with a native deposit (x86 itself could > add PDEP/PEXT support I guess) but I find it hard to believe that it > outperforms a simple shl + or. Perhaps the shl+shrd (or shrd+rol if the deposit is slightly different) is over-cleverness on my part in the expansion, and pdep requires a constant mask. But for other hosts, deposit is the same cost as shift. r~