[PATCH v3 3/4] x86: Optimize {str|wcs}rchr-avx2
Sunil Pandey
skpgkp2@gmail.com
Thu May 12 20:14:54 GMT 2022
On Fri, Apr 22, 2022 at 12:08 PM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Thu, Apr 21, 2022 at 6:52 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > The new code unrolls the main loop slightly without adding too much
> > overhead and minimizes the comparisons for the search CHAR.
> >
> > Geometric Mean of all benchmarks New / Old: 0.832
> > See email for all results.
> >
> > Full xcheck passes on x86_64 with and without multiarch enabled.
> > ---
> > sysdeps/x86_64/multiarch/strrchr-avx2.S | 426 +++++++++++++++---------
> > 1 file changed, 269 insertions(+), 157 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/multiarch/strrchr-avx2.S b/sysdeps/x86_64/multiarch/strrchr-avx2.S
> > index 1df2adfad0..bd26ba80d5 100644
> > --- a/sysdeps/x86_64/multiarch/strrchr-avx2.S
> > +++ b/sysdeps/x86_64/multiarch/strrchr-avx2.S
> > @@ -27,9 +27,13 @@
> > # ifdef USE_AS_WCSRCHR
> > # define VPBROADCAST vpbroadcastd
> > # define VPCMPEQ vpcmpeqd
> > +# define VPMIN vpminud
> > +# define CHAR_SIZE 4
> > # else
> > # define VPBROADCAST vpbroadcastb
> > # define VPCMPEQ vpcmpeqb
> > +# define VPMIN vpminub
> > +# define CHAR_SIZE 1
> > # endif
> >
> > # ifndef VZEROUPPER
> > @@ -41,196 +45,304 @@
> > # endif
> >
> > # define VEC_SIZE 32
> > +# define PAGE_SIZE 4096
> >
> > - .section SECTION(.text),"ax",@progbits
> > -ENTRY (STRRCHR)
> > - movd %esi, %xmm4
> > - movl %edi, %ecx
> > + .section SECTION(.text), "ax", @progbits
> > +ENTRY(STRRCHR)
> > + movd %esi, %xmm7
> > + movl %edi, %eax
> > /* Broadcast CHAR to YMM4. */
> > - VPBROADCAST %xmm4, %ymm4
> > + VPBROADCAST %xmm7, %ymm7
> > vpxor %xmm0, %xmm0, %xmm0
> >
> > - /* Check if we may cross page boundary with one vector load. */
> > - andl $(2 * VEC_SIZE - 1), %ecx
> > - cmpl $VEC_SIZE, %ecx
> > - ja L(cros_page_boundary)
> > + /* Shift here instead of `andl` to save code size (saves a fetch
> > + block). */
> > + sall $20, %eax
> > + cmpl $((PAGE_SIZE - VEC_SIZE) << 20), %eax
> > + ja L(cross_page)
> >
> > +L(page_cross_continue):
> > vmovdqu (%rdi), %ymm1
> > - VPCMPEQ %ymm1, %ymm0, %ymm2
> > - VPCMPEQ %ymm1, %ymm4, %ymm3
> > - vpmovmskb %ymm2, %ecx
> > - vpmovmskb %ymm3, %eax
> > - addq $VEC_SIZE, %rdi
> > + /* Check end of string match. */
> > + VPCMPEQ %ymm1, %ymm0, %ymm6
> > + vpmovmskb %ymm6, %ecx
> > + testl %ecx, %ecx
> > + jz L(aligned_more)
> > +
> > + /* Only check match with search CHAR if needed. */
> > + VPCMPEQ %ymm1, %ymm7, %ymm1
> > + vpmovmskb %ymm1, %eax
> > + /* Check if match before first zero. */
> > + blsmskl %ecx, %ecx
> > + andl %ecx, %eax
> > + jz L(ret0)
> > + bsrl %eax, %eax
> > + addq %rdi, %rax
> > + /* We are off by 3 for wcsrchr if search CHAR is non-zero. If
> > + search CHAR is zero we are correct. Either way `andq
> > + -CHAR_SIZE, %rax` gets the correct result. */
> > +# ifdef USE_AS_WCSRCHR
> > + andq $-CHAR_SIZE, %rax
> > +# endif
> > +L(ret0):
> > +L(return_vzeroupper):
> > + ZERO_UPPER_VEC_REGISTERS_RETURN
> > +
> > + /* Returns for first vec x1/x2 have hard coded backward search
> > + path for earlier matches. */
> > + .p2align 4,, 10
> > +L(first_vec_x1):
> > + VPCMPEQ %ymm2, %ymm7, %ymm6
> > + vpmovmskb %ymm6, %eax
> > + blsmskl %ecx, %ecx
> > + andl %ecx, %eax
> > + jnz L(first_vec_x1_return)
> > +
> > + .p2align 4,, 4
> > +L(first_vec_x0_test):
> > + VPCMPEQ %ymm1, %ymm7, %ymm6
> > + vpmovmskb %ymm6, %eax
> > + testl %eax, %eax
> > + jz L(ret1)
> > + bsrl %eax, %eax
> > + addq %r8, %rax
> > +# ifdef USE_AS_WCSRCHR
> > + andq $-CHAR_SIZE, %rax
> > +# endif
> > +L(ret1):
> > + VZEROUPPER_RETURN
> >
> > + .p2align 4,, 10
> > +L(first_vec_x0_x1_test):
> > + VPCMPEQ %ymm2, %ymm7, %ymm6
> > + vpmovmskb %ymm6, %eax
> > + /* Check ymm2 for search CHAR match. If no match then check ymm1
> > + before returning. */
> > testl %eax, %eax
> > - jnz L(first_vec)
> > + jz L(first_vec_x0_test)
> > + .p2align 4,, 4
> > +L(first_vec_x1_return):
> > + bsrl %eax, %eax
> > + leaq 1(%rdi, %rax), %rax
> > +# ifdef USE_AS_WCSRCHR
> > + andq $-CHAR_SIZE, %rax
> > +# endif
> > + VZEROUPPER_RETURN
> >
> > - testl %ecx, %ecx
> > - jnz L(return_null)
> >
> > - andq $-VEC_SIZE, %rdi
> > - xorl %edx, %edx
> > - jmp L(aligned_loop)
> > + .p2align 4,, 10
> > +L(first_vec_x2):
> > + VPCMPEQ %ymm3, %ymm7, %ymm6
> > + vpmovmskb %ymm6, %eax
> > + blsmskl %ecx, %ecx
> > + /* If no in-range search CHAR match in ymm3 then need to check
> > + ymm1/ymm2 for an earlier match (we delay checking search
> > + CHAR matches until needed). */
> > + andl %ecx, %eax
> > + jz L(first_vec_x0_x1_test)
> > + bsrl %eax, %eax
> > + leaq (VEC_SIZE + 1)(%rdi, %rax), %rax
> > +# ifdef USE_AS_WCSRCHR
> > + andq $-CHAR_SIZE, %rax
> > +# endif
> > + VZEROUPPER_RETURN
> > +
> >
> > .p2align 4
> > -L(first_vec):
> > - /* Check if there is a nul CHAR. */
> > +L(aligned_more):
> > + /* Save original pointer if match was in VEC 0. */
> > + movq %rdi, %r8
> > +
> > + /* Align src. */
> > + orq $(VEC_SIZE - 1), %rdi
> > + vmovdqu 1(%rdi), %ymm2
> > + VPCMPEQ %ymm2, %ymm0, %ymm6
> > + vpmovmskb %ymm6, %ecx
> > testl %ecx, %ecx
> > - jnz L(char_and_nul_in_first_vec)
> > + jnz L(first_vec_x1)
> >
> > - /* Remember the match and keep searching. */
> > - movl %eax, %edx
> > - movq %rdi, %rsi
> > - andq $-VEC_SIZE, %rdi
> > - jmp L(aligned_loop)
> > + vmovdqu (VEC_SIZE + 1)(%rdi), %ymm3
> > + VPCMPEQ %ymm3, %ymm0, %ymm6
> > + vpmovmskb %ymm6, %ecx
> > + testl %ecx, %ecx
> > + jnz L(first_vec_x2)
> >
> > + /* Save pointer again before realigning. */
> > + movq %rdi, %rsi
> > + addq $(VEC_SIZE + 1), %rdi
> > + andq $-(VEC_SIZE * 2), %rdi
> > .p2align 4
> > -L(cros_page_boundary):
> > - andl $(VEC_SIZE - 1), %ecx
> > - andq $-VEC_SIZE, %rdi
> > - vmovdqa (%rdi), %ymm1
> > - VPCMPEQ %ymm1, %ymm0, %ymm2
> > - VPCMPEQ %ymm1, %ymm4, %ymm3
> > - vpmovmskb %ymm2, %edx
> > - vpmovmskb %ymm3, %eax
> > - shrl %cl, %edx
> > - shrl %cl, %eax
> > - addq $VEC_SIZE, %rdi
> > -
> > - /* Check if there is a CHAR. */
> > +L(first_aligned_loop):
> > + /* Do 2x VEC at a time. Any more and the cost of finding the
> > + match outweights loop benefit. */
> > + vmovdqa (VEC_SIZE * 0)(%rdi), %ymm4
> > + vmovdqa (VEC_SIZE * 1)(%rdi), %ymm5
> > +
> > + VPCMPEQ %ymm4, %ymm7, %ymm6
> > + VPMIN %ymm4, %ymm5, %ymm8
> > + VPCMPEQ %ymm5, %ymm7, %ymm10
> > + vpor %ymm6, %ymm10, %ymm5
> > + VPCMPEQ %ymm8, %ymm0, %ymm8
> > + vpor %ymm5, %ymm8, %ymm9
> > +
> > + vpmovmskb %ymm9, %eax
> > + addq $(VEC_SIZE * 2), %rdi
> > + /* No zero or search CHAR. */
> > testl %eax, %eax
> > - jnz L(found_char)
> > -
> > - testl %edx, %edx
> > - jnz L(return_null)
> > + jz L(first_aligned_loop)
> >
> > - jmp L(aligned_loop)
> > -
> > - .p2align 4
> > -L(found_char):
> > - testl %edx, %edx
> > - jnz L(char_and_nul)
> > + /* If no zero CHAR then go to second loop (this allows us to
> > + throw away all prior work). */
> > + vpmovmskb %ymm8, %ecx
> > + testl %ecx, %ecx
> > + jz L(second_aligned_loop_prep)
> >
> > - /* Remember the match and keep searching. */
> > - movl %eax, %edx
> > - leaq (%rdi, %rcx), %rsi
> > + /* Search char could be zero so we need to get the true match.
> > + */
> > + vpmovmskb %ymm5, %eax
> > + testl %eax, %eax
> > + jnz L(first_aligned_loop_return)
> >
> > - .p2align 4
> > -L(aligned_loop):
> > - vmovdqa (%rdi), %ymm1
> > - VPCMPEQ %ymm1, %ymm0, %ymm2
> > - addq $VEC_SIZE, %rdi
> > - VPCMPEQ %ymm1, %ymm4, %ymm3
> > - vpmovmskb %ymm2, %ecx
> > - vpmovmskb %ymm3, %eax
> > - orl %eax, %ecx
> > - jnz L(char_nor_null)
> > -
> > - vmovdqa (%rdi), %ymm1
> > - VPCMPEQ %ymm1, %ymm0, %ymm2
> > - add $VEC_SIZE, %rdi
> > - VPCMPEQ %ymm1, %ymm4, %ymm3
> > - vpmovmskb %ymm2, %ecx
> > + .p2align 4,, 4
> > +L(first_vec_x1_or_x2):
> > + VPCMPEQ %ymm3, %ymm7, %ymm3
> > + VPCMPEQ %ymm2, %ymm7, %ymm2
> > vpmovmskb %ymm3, %eax
> > - orl %eax, %ecx
> > - jnz L(char_nor_null)
> > -
> > - vmovdqa (%rdi), %ymm1
> > - VPCMPEQ %ymm1, %ymm0, %ymm2
> > - addq $VEC_SIZE, %rdi
> > - VPCMPEQ %ymm1, %ymm4, %ymm3
> > - vpmovmskb %ymm2, %ecx
> > - vpmovmskb %ymm3, %eax
> > - orl %eax, %ecx
> > - jnz L(char_nor_null)
> > -
> > - vmovdqa (%rdi), %ymm1
> > - VPCMPEQ %ymm1, %ymm0, %ymm2
> > - addq $VEC_SIZE, %rdi
> > - VPCMPEQ %ymm1, %ymm4, %ymm3
> > - vpmovmskb %ymm2, %ecx
> > - vpmovmskb %ymm3, %eax
> > - orl %eax, %ecx
> > - jz L(aligned_loop)
> > -
> > - .p2align 4
> > -L(char_nor_null):
> > - /* Find a CHAR or a nul CHAR in a loop. */
> > - testl %eax, %eax
> > - jnz L(match)
> > -L(return_value):
> > - testl %edx, %edx
> > - jz L(return_null)
> > - movl %edx, %eax
> > - movq %rsi, %rdi
> > + vpmovmskb %ymm2, %edx
> > + /* Use add for macro-fusion. */
> > + addq %rax, %rdx
> > + jz L(first_vec_x0_test)
> > + /* NB: We could move this shift to before the branch and save a
> > + bit of code size / performance on the fall through. The
> > + branch leads to the null case which generally seems hotter
> > + than char in first 3x VEC. */
> > + salq $32, %rax
> > + addq %rdx, %rax
> > + bsrq %rax, %rax
> > + leaq 1(%rsi, %rax), %rax
> > +# ifdef USE_AS_WCSRCHR
> > + andq $-CHAR_SIZE, %rax
> > +# endif
> > + VZEROUPPER_RETURN
> >
> > + .p2align 4,, 8
> > +L(first_aligned_loop_return):
> > + VPCMPEQ %ymm4, %ymm0, %ymm4
> > + vpmovmskb %ymm4, %edx
> > + salq $32, %rcx
> > + orq %rdx, %rcx
> > +
> > + vpmovmskb %ymm10, %eax
> > + vpmovmskb %ymm6, %edx
> > + salq $32, %rax
> > + orq %rdx, %rax
> > + blsmskq %rcx, %rcx
> > + andq %rcx, %rax
> > + jz L(first_vec_x1_or_x2)
> > +
> > + bsrq %rax, %rax
> > + leaq -(VEC_SIZE * 2)(%rdi, %rax), %rax
> > # ifdef USE_AS_WCSRCHR
> > - /* Keep the first bit for each matching CHAR for bsr. */
> > - andl $0x11111111, %eax
> > + andq $-CHAR_SIZE, %rax
> > # endif
> > - bsrl %eax, %eax
> > - leaq -VEC_SIZE(%rdi, %rax), %rax
> > -L(return_vzeroupper):
> > - ZERO_UPPER_VEC_REGISTERS_RETURN
> > + VZEROUPPER_RETURN
> >
> > + /* Search char cannot be zero. */
> > .p2align 4
> > -L(match):
> > - /* Find a CHAR. Check if there is a nul CHAR. */
> > - vpmovmskb %ymm2, %ecx
> > - testl %ecx, %ecx
> > - jnz L(find_nul)
> > -
> > - /* Remember the match and keep searching. */
> > - movl %eax, %edx
> > +L(second_aligned_loop_set_furthest_match):
> > + /* Save VEC and pointer from most recent match. */
> > +L(second_aligned_loop_prep):
> > movq %rdi, %rsi
> > - jmp L(aligned_loop)
> > + vmovdqu %ymm6, %ymm2
> > + vmovdqu %ymm10, %ymm3
> >
> > .p2align 4
> > -L(find_nul):
> > -# ifdef USE_AS_WCSRCHR
> > - /* Keep the first bit for each matching CHAR for bsr. */
> > - andl $0x11111111, %ecx
> > - andl $0x11111111, %eax
> > -# endif
> > - /* Mask out any matching bits after the nul CHAR. */
> > - movl %ecx, %r8d
> > - subl $1, %r8d
> > - xorl %ecx, %r8d
> > - andl %r8d, %eax
> > +L(second_aligned_loop):
> > + /* Search 2x at at time. */
> > + vmovdqa (VEC_SIZE * 0)(%rdi), %ymm4
> > + vmovdqa (VEC_SIZE * 1)(%rdi), %ymm5
> > +
> > + VPCMPEQ %ymm4, %ymm7, %ymm6
> > + VPMIN %ymm4, %ymm5, %ymm1
> > + VPCMPEQ %ymm5, %ymm7, %ymm10
> > + vpor %ymm6, %ymm10, %ymm5
> > + VPCMPEQ %ymm1, %ymm0, %ymm1
> > + vpor %ymm5, %ymm1, %ymm9
> > +
> > + vpmovmskb %ymm9, %eax
> > + addq $(VEC_SIZE * 2), %rdi
> > testl %eax, %eax
> > - /* If there is no CHAR here, return the remembered one. */
> > - jz L(return_value)
> > - bsrl %eax, %eax
> > - leaq -VEC_SIZE(%rdi, %rax), %rax
> > - VZEROUPPER_RETURN
> > -
> > - .p2align 4
> > -L(char_and_nul):
> > - /* Find both a CHAR and a nul CHAR. */
> > - addq %rcx, %rdi
> > - movl %edx, %ecx
> > -L(char_and_nul_in_first_vec):
> > -# ifdef USE_AS_WCSRCHR
> > - /* Keep the first bit for each matching CHAR for bsr. */
> > - andl $0x11111111, %ecx
> > - andl $0x11111111, %eax
> > -# endif
> > - /* Mask out any matching bits after the nul CHAR. */
> > - movl %ecx, %r8d
> > - subl $1, %r8d
> > - xorl %ecx, %r8d
> > - andl %r8d, %eax
> > + jz L(second_aligned_loop)
> > + vpmovmskb %ymm1, %ecx
> > + testl %ecx, %ecx
> > + jz L(second_aligned_loop_set_furthest_match)
> > + vpmovmskb %ymm5, %eax
> > testl %eax, %eax
> > - /* Return null pointer if the nul CHAR comes first. */
> > - jz L(return_null)
> > - bsrl %eax, %eax
> > - leaq -VEC_SIZE(%rdi, %rax), %rax
> > + jnz L(return_new_match)
> > +
> > + /* This is the hot patch. We know CHAR is inbounds and that
> > + ymm3/ymm2 have latest match. */
> > + .p2align 4,, 4
> > +L(return_old_match):
> > + vpmovmskb %ymm3, %eax
> > + vpmovmskb %ymm2, %edx
> > + salq $32, %rax
> > + orq %rdx, %rax
> > + bsrq %rax, %rax
> > + /* Search char cannot be zero so safe to just use lea for
> > + wcsrchr. */
> > + leaq (VEC_SIZE * -2 -(CHAR_SIZE - 1))(%rsi, %rax), %rax
> > VZEROUPPER_RETURN
> >
> > - .p2align 4
> > -L(return_null):
> > - xorl %eax, %eax
> > + /* Last iteration also potentially has a match. */
> > + .p2align 4,, 8
> > +L(return_new_match):
> > + VPCMPEQ %ymm4, %ymm0, %ymm4
> > + vpmovmskb %ymm4, %edx
> > + salq $32, %rcx
> > + orq %rdx, %rcx
> > +
> > + vpmovmskb %ymm10, %eax
> > + vpmovmskb %ymm6, %edx
> > + salq $32, %rax
> > + orq %rdx, %rax
> > + blsmskq %rcx, %rcx
> > + andq %rcx, %rax
> > + jz L(return_old_match)
> > + bsrq %rax, %rax
> > + /* Search char cannot be zero so safe to just use lea for
> > + wcsrchr. */
> > + leaq (VEC_SIZE * -2 -(CHAR_SIZE - 1))(%rdi, %rax), %rax
> > VZEROUPPER_RETURN
> >
> > -END (STRRCHR)
> > + .p2align 4,, 4
> > +L(cross_page):
> > + movq %rdi, %rsi
> > + andq $-VEC_SIZE, %rsi
> > + vmovdqu (%rsi), %ymm1
> > + VPCMPEQ %ymm1, %ymm0, %ymm6
> > + vpmovmskb %ymm6, %ecx
> > + /* Shift out zero CHAR matches that are before the begining of
> > + src (rdi). */
> > + shrxl %edi, %ecx, %ecx
> > + testl %ecx, %ecx
> > + jz L(page_cross_continue)
> > + VPCMPEQ %ymm1, %ymm7, %ymm1
> > + vpmovmskb %ymm1, %eax
> > +
> > + /* Shift out search CHAR matches that are before the begining of
> > + src (rdi). */
> > + shrxl %edi, %eax, %eax
> > + blsmskl %ecx, %ecx
> > + /* Check if any search CHAR match in range. */
> > + andl %ecx, %eax
> > + jz L(ret2)
> > + bsrl %eax, %eax
> > + addq %rdi, %rax
> > +# ifdef USE_AS_WCSRCHR
> > + andq $-CHAR_SIZE, %rax
> > +# endif
> > +L(ret2):
> > + VZEROUPPER_RETURN
> > +END(STRRCHR)
> > #endif
> > --
> > 2.25.1
> >
>
> LGTM.
>
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
>
> Thanks.
>
> --
> H.J.
I would like to backport this patch to release branches.
Any comments or objections?
--Sunil
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