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[216.228.167.147]) by smtp.gmail.com with ESMTPSA id l1sm1231220pfc.164.2020.08.25.07.02.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Aug 2020 07:02:49 -0700 (PDT) Subject: Re: [PATCH 15/20] target/arm: Fix sve_uzp_p vs odd vector lengths To: Peter Maydell References: <20200815013145.539409-1-richard.henderson@linaro.org> <20200815013145.539409-16-richard.henderson@linaro.org> From: Richard Henderson Message-ID: Date: Tue, 25 Aug 2020 07:02:47 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::443; envelope-from=richard.henderson@linaro.org; helo=mail-pf1-x443.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -46 X-Spam_score: -4.7 X-Spam_bar: ---- X-Spam_report: (-4.7 / 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=-2.602, 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: Laurent Desnogues , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/25/20 6:43 AM, Peter Maydell wrote: > On Sat, 15 Aug 2020 at 02:32, Richard Henderson > wrote: >> >> Missed out on compressing the second half of a predicate >> with length vl % 512 > 256. >> >> Adjust all of the x + (y << s) to x | (y << s) as a >> general style fix. >> >> Reported-by: Laurent Desnogues >> Signed-off-by: Richard Henderson >> --- >> target/arm/sve_helper.c | 30 +++++++++++++++++++++--------- >> 1 file changed, 21 insertions(+), 9 deletions(-) >> >> diff --git a/target/arm/sve_helper.c b/target/arm/sve_helper.c >> index 4758d46f34..fcb46f150f 100644 >> --- a/target/arm/sve_helper.c >> +++ b/target/arm/sve_helper.c >> @@ -1938,7 +1938,7 @@ void HELPER(sve_uzp_p)(void *vd, void *vn, void *vm, uint32_t pred_desc) >> if (oprsz <= 8) { >> l = compress_bits(n[0] >> odd, esz); >> h = compress_bits(m[0] >> odd, esz); >> - d[0] = extract64(l + (h << (4 * oprsz)), 0, 8 * oprsz); >> + d[0] = l | (h << (4 * oprsz)); > > Why did we drop the extract64() here ? This doesn't seem > to correspond to either of the things the commit message > says we're doing. Indeed, the commit message could use expansion. > Also, if oprsz is < 8, don't we need to mask out the high > bits in l that would otherwise overlap with h << (4 * oprsz) ? > Are they guaranteed zeroes somehow? They are guaranteed zeros. See aarch64_sve_narrow_vq. >> for (i = 0; i < oprsz_16; i++) { >> l = m[2 * i + 0]; >> h = m[2 * i + 1]; >> l = compress_bits(l >> odd, esz); >> h = compress_bits(h >> odd, esz); >> - tmp_m.p[i] = l + (h << 32); >> + tmp_m.p[i] = l | (h << 32); >> } >> - tmp_m.p[i] = compress_bits(m[2 * i] >> odd, esz); >> + l = m[2 * i + 0]; >> + h = m[2 * i + 1]; >> + l = compress_bits(l >> odd, esz); >> + h = compress_bits(h >> odd, esz); >> + tmp_m.p[i] = l | (h << final_shift); >> >> swap_memmove(vd + oprsz / 2, &tmp_m, oprsz / 2); > > Aren't there cases where the 'n' part of the result doesn't > end up a whole number of bytes and we have to do a shift as > well as a byte copy? No, oprsz will always be a multiple of 2 for predicates. Just like oprsz will always be a multiple of 16 for sve vectors. r~