From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-x730.google.com (mail-qk1-x730.google.com [IPv6:2607:f8b0:4864:20::730]) by sourceware.org (Postfix) with ESMTPS id 263363858C2C; Sat, 23 Apr 2022 01:17:43 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 263363858C2C Received: by mail-qk1-x730.google.com with SMTP id y129so7033590qkb.2; Fri, 22 Apr 2022 18:17:43 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=k7k7XvYtnh2NzjxYdou/+1Nb+tYOhGTZZIJlQktCmW4=; b=tMn+5ccehUZF/yHMXkHCEPcX3SpQ7livLcLJcTUWAe22+JcMTuwysl1+TPT7o/q/GF mFeTd7FjP+Cl+97Nd7+PHVVx+katcQdxhvRIdE7hCq/72mV8RLf2xmDL85+KPdLu5ulY wxuOOuIEZLdBIwMTH5JSEt0jtfBmVBoUdPNjvxkbo9iS+ByDWZxK/CcCFw6Th6IqbAGO jYHB+yk3nuFc2TZJq0IXmx6Kpl1j8XZ4CWMfI9IcynCIq/4cIgTNTH+iKcs/WnUs4e2w nUBzKG3Pdy2JNSjHyL3wySCvHQjiwLRYj/A3fPTr3RE76h6Gm8AglqEoWzfR6JRl7pFT 7Mhg== X-Gm-Message-State: AOAM531HqAPmLG2VEiIqy3u460PvkI3INSKV2IowJGONp03tvPSlFtDL 7YIl4/NnN+K70ql6HazYVOjOo4wtLRFE+KUk9dY= X-Google-Smtp-Source: ABdhPJzVaIjvzu9LJs0d0mgsVxeDEd0KbEPjJ4eurZMUvbZEdo/HUj5DvFttEoG+T5z8dStKFkKiO5tttzYSKwSspnc= X-Received: by 2002:a05:620a:414f:b0:69f:feb:eb61 with SMTP id k15-20020a05620a414f00b0069f0febeb61mr4380771qko.540.1650676662006; Fri, 22 Apr 2022 18:17:42 -0700 (PDT) MIME-Version: 1.0 References: <20210922005018.1542107-1-goldstein.w.n@gmail.com> <20210922005018.1542107-2-goldstein.w.n@gmail.com> In-Reply-To: From: Sunil Pandey Date: Fri, 22 Apr 2022 18:17:06 -0700 Message-ID: Subject: Re: [PATCH v1 2/2] x86: Optimize memcmp-evex-movbe.S for frontend behavior and size To: Noah Goldstein , libc-stable@sourceware.org Cc: "H.J. Lu" , GNU C Library Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-5.8 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_ENVFROM_END_DIGIT, FREEMAIL_FROM, GIT_PATCH_0, HK_RANDOM_ENVFROM, HK_RANDOM_FROM, KAM_STORAGE_GOOGLE, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, URIBL_SBL_A autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-stable@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-stable mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 23 Apr 2022 01:17:46 -0000 On Tue, Oct 12, 2021 at 10:44 AM Noah Goldstein via Libc-alpha wrote: > > On Tue, Oct 12, 2021 at 10:25 AM H.J. Lu wrote: > > > > On Tue, Sep 21, 2021 at 5:51 PM Noah Goldstein wrote: > > > > > > No bug. > > > > > > The frontend optimizations are to: > > > 1. Reorganize logically connected basic blocks so they are either in > > > the same cache line or adjacent cache lines. > > > 2. Avoid cases when basic blocks unnecissarily cross cache lines. > > > 3. Try and 32 byte align any basic blocks possible without sacrificing > > > code size. Smaller / Less hot basic blocks are used for this. > > > > > > Overall code size shrunk by 168 bytes. This should make up for any > > > extra costs due to aligning to 64 bytes. > > > > > > In general performance before deviated a great deal dependending on > > > whether entry alignment % 64 was 0, 16, 32, or 48. These changes > > > essentially make it so that the current implementation is at least > > > equal to the best alignment of the original for any arguments. > > > > > > The only additional optimization is in the page cross case. Branch on > > > equals case was removed from the size == [4, 7] case. As well the [4, > > > 7] and [2, 3] case where swapped as [4, 7] is likely a more hot > > > argument size. > > > > > > test-memcmp and test-wmemcmp are both passing. > > > --- > > > Performance results attached in reply. > > > > > > Benchmark CPU: https://ark.intel.com/content/www/us/en/ark/products/208921/intel-core-i7-1165g7-processor-12m-cache-up-to-4-70-ghz-with-ipu.html > > > > > > Results are from geometric mean of N = 20 runs. > > > > > > Time for new implemention shown. > > > > > > Score(N) is the New Time / Old Time with entry alignment == N > > > > > > In general there is one performance degregation for size range [2, 3] > > > in the page cross case. This is expected as the new code intentionally > > > gives the fallthrough path to the hotter size range [4, 7]. > > > > > > > > > For the micro benchmarks there is no outright performance improvement > > > in the sense that for each benchmark configuration there is at least > > > one entry alignment where the old version had roughly the same > > > performance. But this should provide a great deal more performance > > > stability. > > > > > > The hope, however, is that with the code size shrink and > > > reorganization of basic blocks for better icache behavior. Concerns > > > such as those brought up in this paper: > > > > > > https://storage.googleapis.com/pub-tools-public-publication-data/pdf/e52f61fd2c51e8962305120548581efacbc06ffc.pdf > > > > > > should be better addressed. > > > > > > sysdeps/x86_64/multiarch/memcmp-evex-movbe.S | 434 +++++++++++-------- > > > 1 file changed, 242 insertions(+), 192 deletions(-) > > > > > > diff --git a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > > > index 654dc7ac8c..2761b54f2e 100644 > > > --- a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > > > +++ b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > > > @@ -34,7 +34,24 @@ > > > area. > > > 7. Use 2 vector compares when size is 2 * CHAR_PER_VEC or less. > > > 8. Use 4 vector compares when size is 4 * CHAR_PER_VEC or less. > > > - 9. Use 8 vector compares when size is 8 * CHAR_PER_VEC or less. */ > > > + 9. Use 8 vector compares when size is 8 * CHAR_PER_VEC or less. > > > + > > > +When possible the implementation tries to optimize for frontend in the > > > +following ways: > > > +Throughput: > > > + 1. All code sections that fit are able to run optimally out of the > > > + LSD. > > > + 2. All code sections that fit are able to run optimally out of the > > > + DSB > > > + 3. Basic blocks are contained in minimum number of fetch blocks > > > + necessary. > > > + > > > +Latency: > > > + 1. Logically connected basic blocks are put in the same > > > + cache-line. > > > + 2. Logically connected basic blocks that do not fit in the same > > > + cache-line are put in adjacent lines. This can get beneficial > > > + L2 spatial prefetching and L1 next-line prefetching. */ > > > > > > # include > > > > > > @@ -47,9 +64,11 @@ > > > # ifdef USE_AS_WMEMCMP > > > # define CHAR_SIZE 4 > > > # define VPCMP vpcmpd > > > +# define VPTEST vptestmd > > > # else > > > # define CHAR_SIZE 1 > > > # define VPCMP vpcmpub > > > +# define VPTEST vptestmb > > > # endif > > > > > > # define VEC_SIZE 32 > > > @@ -75,7 +94,9 @@ > > > */ > > > > > > .section .text.evex,"ax",@progbits > > > -ENTRY (MEMCMP) > > > +/* Cache align memcmp entry. This allows for much more thorough > > > + frontend optimization. */ > > > +ENTRY_P2ALIGN (MEMCMP, 6) > > > # ifdef __ILP32__ > > > /* Clear the upper 32 bits. */ > > > movl %edx, %edx > > > @@ -89,7 +110,7 @@ ENTRY (MEMCMP) > > > VPCMP $4, (%rdi), %YMM1, %k1 > > > kmovd %k1, %eax > > > /* NB: eax must be destination register if going to > > > - L(return_vec_[0,2]). For L(return_vec_3 destination register > > > + L(return_vec_[0,2]). For L(return_vec_3) destination register > > > must be ecx. */ > > > testl %eax, %eax > > > jnz L(return_vec_0) > > > @@ -121,10 +142,6 @@ ENTRY (MEMCMP) > > > testl %ecx, %ecx > > > jnz L(return_vec_3) > > > > > > - /* Zero YMM0. 4x VEC reduction is done with vpxor + vtern so > > > - compare with zero to get a mask is needed. */ > > > - vpxorq %XMM0, %XMM0, %XMM0 > > > - > > > /* Go to 4x VEC loop. */ > > > cmpq $(CHAR_PER_VEC * 8), %rdx > > > ja L(more_8x_vec) > > > @@ -148,47 +165,61 @@ ENTRY (MEMCMP) > > > > > > VMOVU (VEC_SIZE * 2)(%rsi), %YMM3 > > > vpxorq (VEC_SIZE * 2)(%rdi), %YMM3, %YMM3 > > > - /* Or together YMM1, YMM2, and YMM3 into YMM3. */ > > > - vpternlogd $0xfe, %YMM1, %YMM2, %YMM3 > > > > > > VMOVU (VEC_SIZE * 3)(%rsi), %YMM4 > > > /* Ternary logic to xor (VEC_SIZE * 3)(%rdi) with YMM4 while > > > - oring with YMM3. Result is stored in YMM4. */ > > > - vpternlogd $0xde, (VEC_SIZE * 3)(%rdi), %YMM3, %YMM4 > > > - /* Compare YMM4 with 0. If any 1s s1 and s2 don't match. */ > > > - VPCMP $4, %YMM4, %YMM0, %k1 > > > + oring with YMM1. Result is stored in YMM4. */ > > > + vpternlogd $0xde, (VEC_SIZE * 3)(%rdi), %YMM1, %YMM4 > > > + > > > + /* Or together YMM2, YMM3, and YMM4 into YMM4. */ > > > + vpternlogd $0xfe, %YMM2, %YMM3, %YMM4 > > > + > > > + /* Test YMM4 against itself. Store any CHAR mismatches in k1. > > > + */ > > > + VPTEST %YMM4, %YMM4, %k1 > > > + /* k1 must go to ecx for L(return_vec_0_1_2_3). */ > > > kmovd %k1, %ecx > > > testl %ecx, %ecx > > > jnz L(return_vec_0_1_2_3) > > > /* NB: eax must be zero to reach here. */ > > > ret > > > > > > - /* NB: aligning 32 here allows for the rest of the jump targets > > > - to be tuned for 32 byte alignment. Most important this ensures > > > - the L(more_8x_vec) loop is 32 byte aligned. */ > > > - .p2align 5 > > > -L(less_vec): > > > - /* Check if one or less CHAR. This is necessary for size = 0 but > > > - is also faster for size = CHAR_SIZE. */ > > > - cmpl $1, %edx > > > - jbe L(one_or_less) > > > + .p2align 4 > > > +L(8x_end_return_vec_0_1_2_3): > > > + movq %rdx, %rdi > > > +L(8x_return_vec_0_1_2_3): > > > + addq %rdi, %rsi > > > +L(return_vec_0_1_2_3): > > > + VPTEST %YMM1, %YMM1, %k0 > > > + kmovd %k0, %eax > > > + testl %eax, %eax > > > + jnz L(return_vec_0) > > > > > > - /* Check if loading one VEC from either s1 or s2 could cause a > > > - page cross. This can have false positives but is by far the > > > - fastest method. */ > > > - movl %edi, %eax > > > - orl %esi, %eax > > > - andl $(PAGE_SIZE - 1), %eax > > > - cmpl $(PAGE_SIZE - VEC_SIZE), %eax > > > - jg L(page_cross_less_vec) > > > + VPTEST %YMM2, %YMM2, %k0 > > > + kmovd %k0, %eax > > > + testl %eax, %eax > > > + jnz L(return_vec_1) > > > > > > - /* No page cross possible. */ > > > - VMOVU (%rsi), %YMM2 > > > - VPCMP $4, (%rdi), %YMM2, %k1 > > > - kmovd %k1, %eax > > > - /* Create mask in ecx for potentially in bound matches. */ > > > - bzhil %edx, %eax, %eax > > > - jnz L(return_vec_0) > > > + VPTEST %YMM3, %YMM3, %k0 > > > + kmovd %k0, %eax > > > + testl %eax, %eax > > > + jnz L(return_vec_2) > > > +L(return_vec_3): > > > + /* bsf saves 1 byte from tzcnt. This keep L(return_vec_3) in one > > > + fetch block and the entire L(*return_vec_0_1_2_3) in 1 cache > > > + line. */ > > > + bsfl %ecx, %ecx > > > +# ifdef USE_AS_WMEMCMP > > > + movl (VEC_SIZE * 3)(%rdi, %rcx, CHAR_SIZE), %eax > > > + xorl %edx, %edx > > > + cmpl (VEC_SIZE * 3)(%rsi, %rcx, CHAR_SIZE), %eax > > > + setg %dl > > > + leal -1(%rdx, %rdx), %eax > > > +# else > > > + movzbl (VEC_SIZE * 3)(%rdi, %rcx), %eax > > > + movzbl (VEC_SIZE * 3)(%rsi, %rcx), %ecx > > > + subl %ecx, %eax > > > +# endif > > > ret > > > > > > .p2align 4 > > > @@ -209,10 +240,11 @@ L(return_vec_0): > > > # endif > > > ret > > > > > > - /* NB: No p2align necessary. Alignment % 16 is naturally 1 > > > - which is good enough for a target not in a loop. */ > > > + .p2align 4 > > > L(return_vec_1): > > > - tzcntl %eax, %eax > > > + /* bsf saves 1 byte over tzcnt and keeps L(return_vec_1) in one > > > + fetch block. */ > > > + bsfl %eax, %eax > > > # ifdef USE_AS_WMEMCMP > > > movl VEC_SIZE(%rdi, %rax, CHAR_SIZE), %ecx > > > xorl %edx, %edx > > > @@ -226,10 +258,11 @@ L(return_vec_1): > > > # endif > > > ret > > > > > > - /* NB: No p2align necessary. Alignment % 16 is naturally 2 > > > - which is good enough for a target not in a loop. */ > > > + .p2align 4,, 10 > > > L(return_vec_2): > > > - tzcntl %eax, %eax > > > + /* bsf saves 1 byte over tzcnt and keeps L(return_vec_2) in one > > > + fetch block. */ > > > + bsfl %eax, %eax > > > # ifdef USE_AS_WMEMCMP > > > movl (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %ecx > > > xorl %edx, %edx > > > @@ -243,40 +276,6 @@ L(return_vec_2): > > > # endif > > > ret > > > > > > - .p2align 4 > > > -L(8x_return_vec_0_1_2_3): > > > - /* Returning from L(more_8x_vec) requires restoring rsi. */ > > > - addq %rdi, %rsi > > > -L(return_vec_0_1_2_3): > > > - VPCMP $4, %YMM1, %YMM0, %k0 > > > - kmovd %k0, %eax > > > - testl %eax, %eax > > > - jnz L(return_vec_0) > > > - > > > - VPCMP $4, %YMM2, %YMM0, %k0 > > > - kmovd %k0, %eax > > > - testl %eax, %eax > > > - jnz L(return_vec_1) > > > - > > > - VPCMP $4, %YMM3, %YMM0, %k0 > > > - kmovd %k0, %eax > > > - testl %eax, %eax > > > - jnz L(return_vec_2) > > > -L(return_vec_3): > > > - tzcntl %ecx, %ecx > > > -# ifdef USE_AS_WMEMCMP > > > - movl (VEC_SIZE * 3)(%rdi, %rcx, CHAR_SIZE), %eax > > > - xorl %edx, %edx > > > - cmpl (VEC_SIZE * 3)(%rsi, %rcx, CHAR_SIZE), %eax > > > - setg %dl > > > - leal -1(%rdx, %rdx), %eax > > > -# else > > > - movzbl (VEC_SIZE * 3)(%rdi, %rcx), %eax > > > - movzbl (VEC_SIZE * 3)(%rsi, %rcx), %ecx > > > - subl %ecx, %eax > > > -# endif > > > - ret > > > - > > > .p2align 4 > > > L(more_8x_vec): > > > /* Set end of s1 in rdx. */ > > > @@ -288,21 +287,19 @@ L(more_8x_vec): > > > andq $-VEC_SIZE, %rdi > > > /* Adjust because first 4x vec where check already. */ > > > subq $-(VEC_SIZE * 4), %rdi > > > + > > > .p2align 4 > > > L(loop_4x_vec): > > > VMOVU (%rsi, %rdi), %YMM1 > > > vpxorq (%rdi), %YMM1, %YMM1 > > > - > > > VMOVU VEC_SIZE(%rsi, %rdi), %YMM2 > > > vpxorq VEC_SIZE(%rdi), %YMM2, %YMM2 > > > - > > > VMOVU (VEC_SIZE * 2)(%rsi, %rdi), %YMM3 > > > vpxorq (VEC_SIZE * 2)(%rdi), %YMM3, %YMM3 > > > - vpternlogd $0xfe, %YMM1, %YMM2, %YMM3 > > > - > > > VMOVU (VEC_SIZE * 3)(%rsi, %rdi), %YMM4 > > > - vpternlogd $0xde, (VEC_SIZE * 3)(%rdi), %YMM3, %YMM4 > > > - VPCMP $4, %YMM4, %YMM0, %k1 > > > + vpternlogd $0xde, (VEC_SIZE * 3)(%rdi), %YMM1, %YMM4 > > > + vpternlogd $0xfe, %YMM2, %YMM3, %YMM4 > > > + VPTEST %YMM4, %YMM4, %k1 > > > kmovd %k1, %ecx > > > testl %ecx, %ecx > > > jnz L(8x_return_vec_0_1_2_3) > > > @@ -319,28 +316,25 @@ L(loop_4x_vec): > > > cmpl $(VEC_SIZE * 2), %edi > > > jae L(8x_last_2x_vec) > > > > > > + vpxorq (VEC_SIZE * 2)(%rdx), %YMM3, %YMM3 > > > + > > > VMOVU (%rsi, %rdx), %YMM1 > > > vpxorq (%rdx), %YMM1, %YMM1 > > > > > > VMOVU VEC_SIZE(%rsi, %rdx), %YMM2 > > > vpxorq VEC_SIZE(%rdx), %YMM2, %YMM2 > > > - > > > - vpxorq (VEC_SIZE * 2)(%rdx), %YMM3, %YMM3 > > > - vpternlogd $0xfe, %YMM1, %YMM2, %YMM3 > > > - > > > VMOVU (VEC_SIZE * 3)(%rsi, %rdx), %YMM4 > > > - vpternlogd $0xde, (VEC_SIZE * 3)(%rdx), %YMM3, %YMM4 > > > - VPCMP $4, %YMM4, %YMM0, %k1 > > > + vpternlogd $0xde, (VEC_SIZE * 3)(%rdx), %YMM1, %YMM4 > > > + vpternlogd $0xfe, %YMM2, %YMM3, %YMM4 > > > + VPTEST %YMM4, %YMM4, %k1 > > > kmovd %k1, %ecx > > > - /* Restore s1 pointer to rdi. */ > > > - movq %rdx, %rdi > > > testl %ecx, %ecx > > > - jnz L(8x_return_vec_0_1_2_3) > > > + jnz L(8x_end_return_vec_0_1_2_3) > > > /* NB: eax must be zero to reach here. */ > > > ret > > > > > > /* Only entry is from L(more_8x_vec). */ > > > - .p2align 4 > > > + .p2align 4,, 10 > > > L(8x_last_2x_vec): > > > VPCMP $4, (VEC_SIZE * 2)(%rdx), %YMM3, %k1 > > > kmovd %k1, %eax > > > @@ -355,7 +349,31 @@ L(8x_last_1x_vec): > > > jnz L(8x_return_vec_3) > > > ret > > > > > > - .p2align 4 > > > + /* Not ideally aligned (at offset +9 bytes in fetch block) but > > > + not aligning keeps it in the same cache line as > > > + L(8x_last_1x/2x_vec) so likely worth it. As well, saves code > > > + size. */ > > > + .p2align 4,, 4 > > > +L(8x_return_vec_2): > > > + subq $VEC_SIZE, %rdx > > > +L(8x_return_vec_3): > > > + bsfl %eax, %eax > > > +# ifdef USE_AS_WMEMCMP > > > + leaq (%rdx, %rax, CHAR_SIZE), %rax > > > + movl (VEC_SIZE * 3)(%rax), %ecx > > > + xorl %edx, %edx > > > + cmpl (VEC_SIZE * 3)(%rsi, %rax), %ecx > > > + setg %dl > > > + leal -1(%rdx, %rdx), %eax > > > +# else > > > + addq %rdx, %rax > > > + movzbl (VEC_SIZE * 3)(%rsi, %rax), %ecx > > > + movzbl (VEC_SIZE * 3)(%rax), %eax > > > + subl %ecx, %eax > > > +# endif > > > + ret > > > + > > > + .p2align 4,, 10 > > > L(last_2x_vec): > > > /* Check second to last VEC. */ > > > VMOVU -(VEC_SIZE * 2)(%rsi, %rdx, CHAR_SIZE), %YMM1 > > > @@ -374,26 +392,49 @@ L(last_1x_vec): > > > jnz L(return_vec_0_end) > > > ret > > > > > > - .p2align 4 > > > -L(8x_return_vec_2): > > > - subq $VEC_SIZE, %rdx > > > -L(8x_return_vec_3): > > > - tzcntl %eax, %eax > > > + .p2align 4,, 10 > > > +L(return_vec_1_end): > > > + /* Use bsf to save code size. This is necessary to have > > > + L(one_or_less) fit in aligning bytes between. */ > > > + bsfl %eax, %eax > > > + addl %edx, %eax > > > # ifdef USE_AS_WMEMCMP > > > - leaq (%rdx, %rax, CHAR_SIZE), %rax > > > - movl (VEC_SIZE * 3)(%rax), %ecx > > > + movl -(VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %ecx > > > xorl %edx, %edx > > > - cmpl (VEC_SIZE * 3)(%rsi, %rax), %ecx > > > + cmpl -(VEC_SIZE * 2)(%rsi, %rax, CHAR_SIZE), %ecx > > > setg %dl > > > leal -1(%rdx, %rdx), %eax > > > # else > > > - addq %rdx, %rax > > > - movzbl (VEC_SIZE * 3)(%rsi, %rax), %ecx > > > - movzbl (VEC_SIZE * 3)(%rax), %eax > > > + movzbl -(VEC_SIZE * 2)(%rsi, %rax), %ecx > > > + movzbl -(VEC_SIZE * 2)(%rdi, %rax), %eax > > > subl %ecx, %eax > > > # endif > > > ret > > > > > > + /* NB: L(one_or_less) fits in alignment padding between > > > + L(return_vec_1_end) and L(return_vec_0_end). */ > > > +# ifdef USE_AS_WMEMCMP > > > +L(one_or_less): > > > + jb L(zero) > > > + movl (%rdi), %ecx > > > + xorl %edx, %edx > > > + cmpl (%rsi), %ecx > > > + je L(zero) > > > + setg %dl > > > + leal -1(%rdx, %rdx), %eax > > > + ret > > > +# else > > > +L(one_or_less): > > > + jb L(zero) > > > + movzbl (%rsi), %ecx > > > + movzbl (%rdi), %eax > > > + subl %ecx, %eax > > > + ret > > > +# endif > > > +L(zero): > > > + xorl %eax, %eax > > > + ret > > > + > > > .p2align 4 > > > L(return_vec_0_end): > > > tzcntl %eax, %eax > > > @@ -412,23 +453,56 @@ L(return_vec_0_end): > > > ret > > > > > > .p2align 4 > > > -L(return_vec_1_end): > > > +L(less_vec): > > > + /* Check if one or less CHAR. This is necessary for size == 0 > > > + but is also faster for size == CHAR_SIZE. */ > > > + cmpl $1, %edx > > > + jbe L(one_or_less) > > > + > > > + /* Check if loading one VEC from either s1 or s2 could cause a > > > + page cross. This can have false positives but is by far the > > > + fastest method. */ > > > + movl %edi, %eax > > > + orl %esi, %eax > > > + andl $(PAGE_SIZE - 1), %eax > > > + cmpl $(PAGE_SIZE - VEC_SIZE), %eax > > > + jg L(page_cross_less_vec) > > > + > > > + /* No page cross possible. */ > > > + VMOVU (%rsi), %YMM2 > > > + VPCMP $4, (%rdi), %YMM2, %k1 > > > + kmovd %k1, %eax > > > + /* Check if any matches where in bounds. Intentionally not > > > + storing result in eax to limit dependency chain if it goes to > > > + L(return_vec_0_lv). */ > > > + bzhil %edx, %eax, %edx > > > + jnz L(return_vec_0_lv) > > > + xorl %eax, %eax > > > + ret > > > + > > > + /* Essentially duplicate of L(return_vec_0). Ends up not costing > > > + any code as shrinks L(less_vec) by allowing 2-byte encoding of > > > + the jump and ends up fitting in aligning bytes. As well fits on > > > + same cache line as L(less_vec) so also saves a line from having > > > + to be fetched on cold calls to memcmp. */ > > > + .p2align 4,, 4 > > > +L(return_vec_0_lv): > > > tzcntl %eax, %eax > > > - addl %edx, %eax > > > # ifdef USE_AS_WMEMCMP > > > - movl -(VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %ecx > > > + movl (%rdi, %rax, CHAR_SIZE), %ecx > > > xorl %edx, %edx > > > - cmpl -(VEC_SIZE * 2)(%rsi, %rax, CHAR_SIZE), %ecx > > > + cmpl (%rsi, %rax, CHAR_SIZE), %ecx > > > + /* NB: no partial register stall here because xorl zero idiom > > > + above. */ > > > setg %dl > > > leal -1(%rdx, %rdx), %eax > > > # else > > > - movzbl -(VEC_SIZE * 2)(%rsi, %rax), %ecx > > > - movzbl -(VEC_SIZE * 2)(%rdi, %rax), %eax > > > + movzbl (%rsi, %rax), %ecx > > > + movzbl (%rdi, %rax), %eax > > > subl %ecx, %eax > > > # endif > > > ret > > > > > > - > > > .p2align 4 > > > L(page_cross_less_vec): > > > /* if USE_AS_WMEMCMP it can only be 0, 4, 8, 12, 16, 20, 24, 28 > > > @@ -439,108 +513,84 @@ L(page_cross_less_vec): > > > cmpl $8, %edx > > > jae L(between_8_15) > > > cmpl $4, %edx > > > - jae L(between_4_7) > > > -L(between_2_3): > > > - /* Load as big endian to avoid branches. */ > > > - movzwl (%rdi), %eax > > > - movzwl (%rsi), %ecx > > > - shll $8, %eax > > > - shll $8, %ecx > > > - bswap %eax > > > - bswap %ecx > > > - movzbl -1(%rdi, %rdx), %edi > > > - movzbl -1(%rsi, %rdx), %esi > > > - orl %edi, %eax > > > - orl %esi, %ecx > > > - /* Subtraction is okay because the upper 8 bits are zero. */ > > > - subl %ecx, %eax > > > - ret > > > - .p2align 4 > > > -L(one_or_less): > > > - jb L(zero) > > > - movzbl (%rsi), %ecx > > > - movzbl (%rdi), %eax > > > - subl %ecx, %eax > > > + jb L(between_2_3) > > > + > > > + /* Load as big endian with overlapping movbe to avoid branches. > > > + */ > > > + movbe (%rdi), %eax > > > + movbe (%rsi), %ecx > > > + shlq $32, %rax > > > + shlq $32, %rcx > > > + movbe -4(%rdi, %rdx), %edi > > > + movbe -4(%rsi, %rdx), %esi > > > + orq %rdi, %rax > > > + orq %rsi, %rcx > > > + subq %rcx, %rax > > > + /* edx is guranteed to be positive int32 in range [4, 7]. */ > > > + cmovne %edx, %eax > > > + /* ecx is -1 if rcx > rax. Otherwise 0. */ > > > + sbbl %ecx, %ecx > > > + /* If rcx > rax, then ecx is 0 and eax is positive. If rcx == > > > + rax then eax and ecx are zero. If rax < rax then ecx is -1 so > > > + eax doesn't matter. */ > > > + orl %ecx, %eax > > > ret > > > > > > - .p2align 4 > > > + .p2align 4,, 8 > > > L(between_8_15): > > > # endif > > > /* If USE_AS_WMEMCMP fall through into 8-15 byte case. */ > > > - vmovq (%rdi), %XMM1 > > > - vmovq (%rsi), %XMM2 > > > - VPCMP $4, %XMM1, %XMM2, %k1 > > > + vmovq (%rdi), %xmm1 > > > + vmovq (%rsi), %xmm2 > > > + VPCMP $4, %xmm1, %xmm2, %k1 > > > kmovd %k1, %eax > > > testl %eax, %eax > > > - jnz L(return_vec_0) > > > + jnz L(return_vec_0_lv) > > > /* Use overlapping loads to avoid branches. */ > > > - leaq -8(%rdi, %rdx, CHAR_SIZE), %rdi > > > - leaq -8(%rsi, %rdx, CHAR_SIZE), %rsi > > > - vmovq (%rdi), %XMM1 > > > - vmovq (%rsi), %XMM2 > > > - VPCMP $4, %XMM1, %XMM2, %k1 > > > + vmovq -8(%rdi, %rdx, CHAR_SIZE), %xmm1 > > > + vmovq -8(%rsi, %rdx, CHAR_SIZE), %xmm2 > > > + VPCMP $4, %xmm1, %xmm2, %k1 > > > + addl $(CHAR_PER_VEC - (8 / CHAR_SIZE)), %edx > > > kmovd %k1, %eax > > > testl %eax, %eax > > > - jnz L(return_vec_0) > > > - ret > > > - > > > - .p2align 4 > > > -L(zero): > > > - xorl %eax, %eax > > > + jnz L(return_vec_0_end) > > > ret > > > > > > - .p2align 4 > > > + .p2align 4,, 8 > > > L(between_16_31): > > > /* From 16 to 31 bytes. No branch when size == 16. */ > > > - VMOVU (%rsi), %XMM2 > > > - VPCMP $4, (%rdi), %XMM2, %k1 > > > + > > > + /* Use movups to save code size. */ > > > + movups (%rsi), %xmm2 > > > + VPCMP $4, (%rdi), %xmm2, %k1 > > > kmovd %k1, %eax > > > testl %eax, %eax > > > - jnz L(return_vec_0) > > > - > > > + jnz L(return_vec_0_lv) > > > /* Use overlapping loads to avoid branches. */ > > > - > > > - VMOVU -16(%rsi, %rdx, CHAR_SIZE), %XMM2 > > > - leaq -16(%rdi, %rdx, CHAR_SIZE), %rdi > > > - leaq -16(%rsi, %rdx, CHAR_SIZE), %rsi > > > - VPCMP $4, (%rdi), %XMM2, %k1 > > > + movups -16(%rsi, %rdx, CHAR_SIZE), %xmm2 > > > + VPCMP $4, -16(%rdi, %rdx, CHAR_SIZE), %xmm2, %k1 > > > + addl $(CHAR_PER_VEC - (16 / CHAR_SIZE)), %edx > > > kmovd %k1, %eax > > > testl %eax, %eax > > > - jnz L(return_vec_0) > > > - ret > > > - > > > -# ifdef USE_AS_WMEMCMP > > > - .p2align 4 > > > -L(one_or_less): > > > - jb L(zero) > > > - movl (%rdi), %ecx > > > - xorl %edx, %edx > > > - cmpl (%rsi), %ecx > > > - je L(zero) > > > - setg %dl > > > - leal -1(%rdx, %rdx), %eax > > > + jnz L(return_vec_0_end) > > > ret > > > -# else > > > > > > - .p2align 4 > > > -L(between_4_7): > > > - /* Load as big endian with overlapping movbe to avoid branches. > > > - */ > > > - movbe (%rdi), %eax > > > - movbe (%rsi), %ecx > > > - shlq $32, %rax > > > - shlq $32, %rcx > > > - movbe -4(%rdi, %rdx), %edi > > > - movbe -4(%rsi, %rdx), %esi > > > - orq %rdi, %rax > > > - orq %rsi, %rcx > > > - subq %rcx, %rax > > > - jz L(zero_4_7) > > > - sbbl %eax, %eax > > > - orl $1, %eax > > > -L(zero_4_7): > > > +# ifndef USE_AS_WMEMCMP > > > +L(between_2_3): > > > + /* Load as big endian to avoid branches. */ > > > + movzwl (%rdi), %eax > > > + movzwl (%rsi), %ecx > > > + shll $8, %eax > > > + shll $8, %ecx > > > + bswap %eax > > > + bswap %ecx > > > + movzbl -1(%rdi, %rdx), %edi > > > + movzbl -1(%rsi, %rdx), %esi > > > + orl %edi, %eax > > > + orl %esi, %ecx > > > + /* Subtraction is okay because the upper 8 bits are zero. */ > > > + subl %ecx, %eax > > > ret > > > # endif > > > - > > > END (MEMCMP) > > > #endif > > > -- > > > 2.25.1 > > > > > > > LGTM. > > > > Reviewed-by: H.J. Lu > > > > Thanks. > > > > -- > > H.J. > > Thanks! Pushed. I would like to backport this patch to release branches. Any comments or objections? --Sunil