From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-x535.google.com (mail-pg1-x535.google.com [IPv6:2607:f8b0:4864:20::535]) by sourceware.org (Postfix) with ESMTPS id 2346F382D470 for ; Tue, 7 Jun 2022 04:11:46 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 2346F382D470 Received: by mail-pg1-x535.google.com with SMTP id y187so14704891pgd.3 for ; Mon, 06 Jun 2022 21:11:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=3Byb9AcnYuw5ZiR1YFre9WoHXGkvs8TUUJqyY/kdUj0=; b=zW2wAUE/kcir6Djgk3kLvbAbpqW6qzLTSj9ZaEU5ICH7JjcXNjTNdifPjxxfCR155h 3LgG9ik1+jWCdkOQsxhrxXwnw+nBEoLA2wunSIL0+No682wOGV1gfNND6Mg3JMquqILk 2mbI9sCelcXLsmbU4tNTTJHC1mtmsYtglIitagtCacKI6GVE1EDnr+jfo0Aye01KzWtp TpxZ1XgefdECKD+q3QeNvf2RiHjmwqwCdwBD71ki4vFNOsu8285qqw080iqd7N4dgWZB pfarFuXvn/mDcybt1s/msUxYsRhWMxiTMUJALJBmJa5JT9ebqKLKfj9mvlZSZ1WEqIcj EbEA== X-Gm-Message-State: AOAM530wAcvOOOAds+M0kbHH66EzWe7iqeN0H9smzDp3QVuabohclHj1 FpXvtM6pTz6tE08pQjQB+HqN/6vLv+M= X-Google-Smtp-Source: ABdhPJwwkx7uRpoXdieuQEeTlciwIwC1bzMXi/NGOpP4SSQPFpj1/bgNk5pI5U9euRqc5PYqiUxsPw== X-Received: by 2002:a63:788:0:b0:3fc:6922:704 with SMTP id 130-20020a630788000000b003fc69220704mr23914953pgh.6.1654575105272; Mon, 06 Jun 2022 21:11:45 -0700 (PDT) Received: from noah-tgl.. ([2600:1010:b04a:6ef:921e:3108:9361:2ef8]) by smtp.gmail.com with ESMTPSA id fv9-20020a17090b0e8900b001e30a16c609sm10689205pjb.21.2022.06.06.21.11.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Jun 2022 21:11:44 -0700 (PDT) From: Noah Goldstein To: libc-alpha@sourceware.org Subject: [PATCH v6 5/8] x86: Optimize memrchr-evex.S Date: Mon, 6 Jun 2022 21:11:31 -0700 Message-Id: <20220607041134.2369903-5-goldstein.w.n@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220607041134.2369903-1-goldstein.w.n@gmail.com> References: <20220603044229.2180216-2-goldstein.w.n@gmail.com> <20220607041134.2369903-1-goldstein.w.n@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.0 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 07 Jun 2022 04:11:48 -0000 The new code: 1. prioritizes smaller user-arg lengths more. 2. optimizes target placement more carefully 3. reuses logic more 4. fixes up various inefficiencies in the logic. The biggest case here is the `lzcnt` logic for checking returns which saves either a branch or multiple instructions. The total code size saving is: 263 bytes Geometric Mean of all benchmarks New / Old: 0.755 Regressions: There are some regressions. Particularly where the length (user arg length) is large but the position of the match char is near the beginning of the string (in first VEC). This case has roughly a 20% regression. This is because the new logic gives the hot path for immediate matches to shorter lengths (the more common input). This case has roughly a 35% speedup. Full xcheck passes on x86_64. --- sysdeps/x86_64/multiarch/memrchr-evex.S | 539 ++++++++++++------------ 1 file changed, 268 insertions(+), 271 deletions(-) diff --git a/sysdeps/x86_64/multiarch/memrchr-evex.S b/sysdeps/x86_64/multiarch/memrchr-evex.S index 0b99709c6b..2d7da06dfc 100644 --- a/sysdeps/x86_64/multiarch/memrchr-evex.S +++ b/sysdeps/x86_64/multiarch/memrchr-evex.S @@ -19,319 +19,316 @@ #if IS_IN (libc) # include +# include "evex256-vecs.h" +# if VEC_SIZE != 32 +# error "VEC_SIZE != 32 unimplemented" +# endif + +# ifndef MEMRCHR +# define MEMRCHR __memrchr_evex +# endif + +# define PAGE_SIZE 4096 +# define VECMATCH VEC(0) + + .section SECTION(.text), "ax", @progbits +ENTRY_P2ALIGN(MEMRCHR, 6) +# ifdef __ILP32__ + /* Clear upper bits. */ + and %RDX_LP, %RDX_LP +# else + test %RDX_LP, %RDX_LP +# endif + jz L(zero_0) + + /* Get end pointer. Minus one for two reasons. 1) It is necessary for a + correct page cross check and 2) it correctly sets up end ptr to be + subtract by lzcnt aligned. */ + leaq -1(%rdi, %rdx), %rax + vpbroadcastb %esi, %VECMATCH + + /* Check if we can load 1x VEC without cross a page. */ + testl $(PAGE_SIZE - VEC_SIZE), %eax + jz L(page_cross) + + /* Don't use rax for pointer here because EVEX has better encoding with + offset % VEC_SIZE == 0. */ + vpcmpb $0, -(VEC_SIZE)(%rdi, %rdx), %VECMATCH, %k0 + kmovd %k0, %ecx + + /* Fall through for rdx (len) <= VEC_SIZE (expect small sizes). */ + cmpq $VEC_SIZE, %rdx + ja L(more_1x_vec) +L(ret_vec_x0_test): + + /* If ecx is zero (no matches) lzcnt will set it 32 (VEC_SIZE) which + will guarantee edx (len) is less than it. */ + lzcntl %ecx, %ecx + cmpl %ecx, %edx + jle L(zero_0) + subq %rcx, %rax + ret -# define VMOVA vmovdqa64 - -# define YMMMATCH ymm16 - -# define VEC_SIZE 32 - - .section .text.evex,"ax",@progbits -ENTRY (__memrchr_evex) - /* Broadcast CHAR to YMMMATCH. */ - vpbroadcastb %esi, %YMMMATCH - - sub $VEC_SIZE, %RDX_LP - jbe L(last_vec_or_less) - - add %RDX_LP, %RDI_LP - - /* Check the last VEC_SIZE bytes. */ - vpcmpb $0, (%rdi), %YMMMATCH, %k1 - kmovd %k1, %eax - testl %eax, %eax - jnz L(last_vec_x0) - - subq $(VEC_SIZE * 4), %rdi - movl %edi, %ecx - andl $(VEC_SIZE - 1), %ecx - jz L(aligned_more) - - /* Align data for aligned loads in the loop. */ - addq $VEC_SIZE, %rdi - addq $VEC_SIZE, %rdx - andq $-VEC_SIZE, %rdi - subq %rcx, %rdx - - .p2align 4 -L(aligned_more): - subq $(VEC_SIZE * 4), %rdx - jbe L(last_4x_vec_or_less) - - /* Check the last 4 * VEC_SIZE. Only one VEC_SIZE at a time - since data is only aligned to VEC_SIZE. */ - vpcmpb $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k1 - kmovd %k1, %eax - testl %eax, %eax - jnz L(last_vec_x3) - - vpcmpb $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k2 - kmovd %k2, %eax - testl %eax, %eax - jnz L(last_vec_x2) - - vpcmpb $0, VEC_SIZE(%rdi), %YMMMATCH, %k3 - kmovd %k3, %eax - testl %eax, %eax - jnz L(last_vec_x1) - - vpcmpb $0, (%rdi), %YMMMATCH, %k4 - kmovd %k4, %eax - testl %eax, %eax - jnz L(last_vec_x0) - - /* Align data to 4 * VEC_SIZE for loop with fewer branches. - There are some overlaps with above if data isn't aligned - to 4 * VEC_SIZE. */ - movl %edi, %ecx - andl $(VEC_SIZE * 4 - 1), %ecx - jz L(loop_4x_vec) - - addq $(VEC_SIZE * 4), %rdi - addq $(VEC_SIZE * 4), %rdx - andq $-(VEC_SIZE * 4), %rdi - subq %rcx, %rdx + /* Fits in aligning bytes of first cache line. */ +L(zero_0): + xorl %eax, %eax + ret - .p2align 4 -L(loop_4x_vec): - /* Compare 4 * VEC at a time forward. */ - subq $(VEC_SIZE * 4), %rdi - subq $(VEC_SIZE * 4), %rdx - jbe L(last_4x_vec_or_less) - - vpcmpb $0, (%rdi), %YMMMATCH, %k1 - vpcmpb $0, VEC_SIZE(%rdi), %YMMMATCH, %k2 - kord %k1, %k2, %k5 - vpcmpb $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k3 - vpcmpb $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k4 - - kord %k3, %k4, %k6 - kortestd %k5, %k6 - jz L(loop_4x_vec) - - /* There is a match. */ - kmovd %k4, %eax - testl %eax, %eax - jnz L(last_vec_x3) - - kmovd %k3, %eax - testl %eax, %eax - jnz L(last_vec_x2) - - kmovd %k2, %eax - testl %eax, %eax - jnz L(last_vec_x1) - - kmovd %k1, %eax - bsrl %eax, %eax - addq %rdi, %rax + .p2align 4,, 9 +L(ret_vec_x0_dec): + decq %rax +L(ret_vec_x0): + lzcntl %ecx, %ecx + subq %rcx, %rax ret - .p2align 4 -L(last_4x_vec_or_less): - addl $(VEC_SIZE * 4), %edx - cmpl $(VEC_SIZE * 2), %edx - jbe L(last_2x_vec) + .p2align 4,, 10 +L(more_1x_vec): + testl %ecx, %ecx + jnz L(ret_vec_x0) - vpcmpb $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k1 - kmovd %k1, %eax - testl %eax, %eax - jnz L(last_vec_x3) + /* Align rax (pointer to string). */ + andq $-VEC_SIZE, %rax - vpcmpb $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k2 - kmovd %k2, %eax - testl %eax, %eax - jnz L(last_vec_x2) + /* Recompute length after aligning. */ + movq %rax, %rdx - vpcmpb $0, VEC_SIZE(%rdi), %YMMMATCH, %k3 - kmovd %k3, %eax - testl %eax, %eax - jnz L(last_vec_x1_check) - cmpl $(VEC_SIZE * 3), %edx - jbe L(zero) + /* Need no matter what. */ + vpcmpb $0, -(VEC_SIZE)(%rax), %VECMATCH, %k0 + kmovd %k0, %ecx - vpcmpb $0, (%rdi), %YMMMATCH, %k4 - kmovd %k4, %eax - testl %eax, %eax - jz L(zero) - bsrl %eax, %eax - subq $(VEC_SIZE * 4), %rdx - addq %rax, %rdx - jl L(zero) - addq %rdi, %rax - ret + subq %rdi, %rdx - .p2align 4 + cmpq $(VEC_SIZE * 2), %rdx + ja L(more_2x_vec) L(last_2x_vec): - vpcmpb $0, (VEC_SIZE * 3)(%rdi), %YMMMATCH, %k1 - kmovd %k1, %eax - testl %eax, %eax - jnz L(last_vec_x3_check) + + /* Must dec rax because L(ret_vec_x0_test) expects it. */ + decq %rax cmpl $VEC_SIZE, %edx - jbe L(zero) - - vpcmpb $0, (VEC_SIZE * 2)(%rdi), %YMMMATCH, %k1 - kmovd %k1, %eax - testl %eax, %eax - jz L(zero) - bsrl %eax, %eax - subq $(VEC_SIZE * 2), %rdx - addq %rax, %rdx - jl L(zero) - addl $(VEC_SIZE * 2), %eax - addq %rdi, %rax + jbe L(ret_vec_x0_test) + + testl %ecx, %ecx + jnz L(ret_vec_x0) + + /* Don't use rax for pointer here because EVEX has better encoding with + offset % VEC_SIZE == 0. */ + vpcmpb $0, -(VEC_SIZE * 2)(%rdi, %rdx), %VECMATCH, %k0 + kmovd %k0, %ecx + /* NB: 64-bit lzcnt. This will naturally add 32 to position. */ + lzcntq %rcx, %rcx + cmpl %ecx, %edx + jle L(zero_0) + subq %rcx, %rax ret - .p2align 4 -L(last_vec_x0): - bsrl %eax, %eax - addq %rdi, %rax + /* Inexpensive place to put this regarding code size / target alignments + / ICache NLP. Necessary for 2-byte encoding of jump to page cross + case which in turn in necessary for hot path (len <= VEC_SIZE) to fit + in first cache line. */ +L(page_cross): + movq %rax, %rsi + andq $-VEC_SIZE, %rsi + vpcmpb $0, (%rsi), %VECMATCH, %k0 + kmovd %k0, %r8d + /* Shift out negative alignment (because we are starting from endptr and + working backwards). */ + movl %eax, %ecx + /* notl because eax already has endptr - 1. (-x = ~(x - 1)). */ + notl %ecx + shlxl %ecx, %r8d, %ecx + cmpq %rdi, %rsi + ja L(more_1x_vec) + lzcntl %ecx, %ecx + cmpl %ecx, %edx + jle L(zero_1) + subq %rcx, %rax ret - .p2align 4 -L(last_vec_x1): - bsrl %eax, %eax - addl $VEC_SIZE, %eax - addq %rdi, %rax + /* Continue creating zero labels that fit in aligning bytes and get + 2-byte encoding / are in the same cache line as condition. */ +L(zero_1): + xorl %eax, %eax ret - .p2align 4 -L(last_vec_x2): - bsrl %eax, %eax - addl $(VEC_SIZE * 2), %eax - addq %rdi, %rax + .p2align 4,, 8 +L(ret_vec_x1): + /* This will naturally add 32 to position. */ + bsrl %ecx, %ecx + leaq -(VEC_SIZE * 2)(%rcx, %rax), %rax ret - .p2align 4 -L(last_vec_x3): - bsrl %eax, %eax - addl $(VEC_SIZE * 3), %eax - addq %rdi, %rax - ret + .p2align 4,, 8 +L(more_2x_vec): + testl %ecx, %ecx + jnz L(ret_vec_x0_dec) - .p2align 4 -L(last_vec_x1_check): - bsrl %eax, %eax - subq $(VEC_SIZE * 3), %rdx - addq %rax, %rdx - jl L(zero) - addl $VEC_SIZE, %eax - addq %rdi, %rax - ret + vpcmpb $0, -(VEC_SIZE * 2)(%rax), %VECMATCH, %k0 + kmovd %k0, %ecx + testl %ecx, %ecx + jnz L(ret_vec_x1) - .p2align 4 -L(last_vec_x3_check): - bsrl %eax, %eax - subq $VEC_SIZE, %rdx - addq %rax, %rdx - jl L(zero) - addl $(VEC_SIZE * 3), %eax - addq %rdi, %rax - ret + /* Need no matter what. */ + vpcmpb $0, -(VEC_SIZE * 3)(%rax), %VECMATCH, %k0 + kmovd %k0, %ecx - .p2align 4 -L(zero): - xorl %eax, %eax + subq $(VEC_SIZE * 4), %rdx + ja L(more_4x_vec) + + cmpl $(VEC_SIZE * -1), %edx + jle L(ret_vec_x2_test) +L(last_vec): + testl %ecx, %ecx + jnz L(ret_vec_x2) + + + /* Need no matter what. */ + vpcmpb $0, -(VEC_SIZE * 4)(%rax), %VECMATCH, %k0 + kmovd %k0, %ecx + lzcntl %ecx, %ecx + subq $(VEC_SIZE * 3 + 1), %rax + subq %rcx, %rax + cmpq %rax, %rdi + ja L(zero_1) ret - .p2align 4 -L(last_vec_or_less_aligned): - movl %edx, %ecx - - vpcmpb $0, (%rdi), %YMMMATCH, %k1 - - movl $1, %edx - /* Support rdx << 32. */ - salq %cl, %rdx - subq $1, %rdx - - kmovd %k1, %eax - - /* Remove the trailing bytes. */ - andl %edx, %eax - testl %eax, %eax - jz L(zero) - - bsrl %eax, %eax - addq %rdi, %rax + .p2align 4,, 8 +L(ret_vec_x2_test): + lzcntl %ecx, %ecx + subq $(VEC_SIZE * 2 + 1), %rax + subq %rcx, %rax + cmpq %rax, %rdi + ja L(zero_1) ret - .p2align 4 -L(last_vec_or_less): - addl $VEC_SIZE, %edx - - /* Check for zero length. */ - testl %edx, %edx - jz L(zero) - - movl %edi, %ecx - andl $(VEC_SIZE - 1), %ecx - jz L(last_vec_or_less_aligned) - - movl %ecx, %esi - movl %ecx, %r8d - addl %edx, %esi - andq $-VEC_SIZE, %rdi + .p2align 4,, 8 +L(ret_vec_x2): + bsrl %ecx, %ecx + leaq -(VEC_SIZE * 3)(%rcx, %rax), %rax + ret - subl $VEC_SIZE, %esi - ja L(last_vec_2x_aligned) + .p2align 4,, 8 +L(ret_vec_x3): + bsrl %ecx, %ecx + leaq -(VEC_SIZE * 4)(%rcx, %rax), %rax + ret - /* Check the last VEC. */ - vpcmpb $0, (%rdi), %YMMMATCH, %k1 - kmovd %k1, %eax + .p2align 4,, 8 +L(more_4x_vec): + testl %ecx, %ecx + jnz L(ret_vec_x2) - /* Remove the leading and trailing bytes. */ - sarl %cl, %eax - movl %edx, %ecx + vpcmpb $0, -(VEC_SIZE * 4)(%rax), %VECMATCH, %k0 + kmovd %k0, %ecx - movl $1, %edx - sall %cl, %edx - subl $1, %edx + testl %ecx, %ecx + jnz L(ret_vec_x3) - andl %edx, %eax - testl %eax, %eax - jz L(zero) + /* Check if near end before re-aligning (otherwise might do an + unnecessary loop iteration). */ + addq $-(VEC_SIZE * 4), %rax + cmpq $(VEC_SIZE * 4), %rdx + jbe L(last_4x_vec) - bsrl %eax, %eax - addq %rdi, %rax - addq %r8, %rax - ret + decq %rax + andq $-(VEC_SIZE * 4), %rax + movq %rdi, %rdx + /* Get endptr for loop in rdx. NB: Can't just do while rax > rdi because + lengths that overflow can be valid and break the comparison. */ + andq $-(VEC_SIZE * 4), %rdx .p2align 4 -L(last_vec_2x_aligned): - movl %esi, %ecx - - /* Check the last VEC. */ - vpcmpb $0, VEC_SIZE(%rdi), %YMMMATCH, %k1 +L(loop_4x_vec): + /* Store 1 were not-equals and 0 where equals in k1 (used to mask later + on). */ + vpcmpb $4, (VEC_SIZE * 3)(%rax), %VECMATCH, %k1 + + /* VEC(2/3) will have zero-byte where we found a CHAR. */ + vpxorq (VEC_SIZE * 2)(%rax), %VECMATCH, %VEC(2) + vpxorq (VEC_SIZE * 1)(%rax), %VECMATCH, %VEC(3) + vpcmpb $0, (VEC_SIZE * 0)(%rax), %VECMATCH, %k4 + + /* Combine VEC(2/3) with min and maskz with k1 (k1 has zero bit where + CHAR is found and VEC(2/3) have zero-byte where CHAR is found. */ + vpminub %VEC(2), %VEC(3), %VEC(3){%k1}{z} + vptestnmb %VEC(3), %VEC(3), %k2 + + /* Any 1s and we found CHAR. */ + kortestd %k2, %k4 + jnz L(loop_end) + + addq $-(VEC_SIZE * 4), %rax + cmpq %rdx, %rax + jne L(loop_4x_vec) + + /* Need to re-adjust rdx / rax for L(last_4x_vec). */ + subq $-(VEC_SIZE * 4), %rdx + movq %rdx, %rax + subl %edi, %edx +L(last_4x_vec): + + /* Used no matter what. */ + vpcmpb $0, (VEC_SIZE * -1)(%rax), %VECMATCH, %k0 + kmovd %k0, %ecx - movl $1, %edx - sall %cl, %edx - subl $1, %edx + cmpl $(VEC_SIZE * 2), %edx + jbe L(last_2x_vec) - kmovd %k1, %eax + testl %ecx, %ecx + jnz L(ret_vec_x0_dec) - /* Remove the trailing bytes. */ - andl %edx, %eax - testl %eax, %eax - jnz L(last_vec_x1) + vpcmpb $0, (VEC_SIZE * -2)(%rax), %VECMATCH, %k0 + kmovd %k0, %ecx - /* Check the second last VEC. */ - vpcmpb $0, (%rdi), %YMMMATCH, %k1 + testl %ecx, %ecx + jnz L(ret_vec_x1) - movl %r8d, %ecx + /* Used no matter what. */ + vpcmpb $0, (VEC_SIZE * -3)(%rax), %VECMATCH, %k0 + kmovd %k0, %ecx - kmovd %k1, %eax + cmpl $(VEC_SIZE * 3), %edx + ja L(last_vec) - /* Remove the leading bytes. Must use unsigned right shift for - bsrl below. */ - shrl %cl, %eax - testl %eax, %eax - jz L(zero) + lzcntl %ecx, %ecx + subq $(VEC_SIZE * 2 + 1), %rax + subq %rcx, %rax + cmpq %rax, %rdi + jbe L(ret_1) + xorl %eax, %eax +L(ret_1): + ret - bsrl %eax, %eax - addq %rdi, %rax - addq %r8, %rax + .p2align 4,, 6 +L(loop_end): + kmovd %k1, %ecx + notl %ecx + testl %ecx, %ecx + jnz L(ret_vec_x0_end) + + vptestnmb %VEC(2), %VEC(2), %k0 + kmovd %k0, %ecx + testl %ecx, %ecx + jnz L(ret_vec_x1_end) + + kmovd %k2, %ecx + kmovd %k4, %esi + /* Combine last 2 VEC matches. If ecx (VEC3) is zero (no CHAR in VEC3) + then it won't affect the result in esi (VEC4). If ecx is non-zero + then CHAR in VEC3 and bsrq will use that position. */ + salq $32, %rcx + orq %rsi, %rcx + bsrq %rcx, %rcx + addq %rcx, %rax + ret + .p2align 4,, 4 +L(ret_vec_x0_end): + addq $(VEC_SIZE), %rax +L(ret_vec_x1_end): + bsrl %ecx, %ecx + leaq (VEC_SIZE * 2)(%rax, %rcx), %rax ret -END (__memrchr_evex) + +END(MEMRCHR) #endif -- 2.34.1