Re: [PATCH v4 4/5] x86: Optimize memmove-vec-unaligned-erms.S

["H.J. Lu" <hjl.tools@gmail.com>]

On Sat, Nov 6, 2021 at 11:33 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> No bug.
>
> The optimizations are as follows:
>
> 1) Always align entry to 64 bytes. This makes behavior more
>    predictable and makes other frontend optimizations easier.
>
> 2) Make the L(more_8x_vec) cases 4k aliasing aware. This can have
>    significant benefits in the case that:
>         0 < (dst - src) < [256, 512]
>
> 3) Align before `rep movsb`. For ERMS this is roughly a [0, 30%]
>    improvement and for FSRM [-10%, 25%].
>
> In addition to these primary changes there is general cleanup
> throughout to optimize the aligning routines and control flow logic.
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
> ---
>  sysdeps/x86_64/memmove.S                      |   2 +-
>  .../memmove-avx-unaligned-erms-rtm.S          |   2 +-
>  .../multiarch/memmove-avx-unaligned-erms.S    |   2 +-
>  .../multiarch/memmove-avx512-unaligned-erms.S |   2 +-
>  .../multiarch/memmove-evex-unaligned-erms.S   |   2 +-
>  .../multiarch/memmove-vec-unaligned-erms.S    | 595 +++++++++++-------
>  6 files changed, 381 insertions(+), 224 deletions(-)
>
> diff --git a/sysdeps/x86_64/memmove.S b/sysdeps/x86_64/memmove.S
> index db106a7a1f..b2b3180848 100644
> --- a/sysdeps/x86_64/memmove.S
> +++ b/sysdeps/x86_64/memmove.S
> @@ -25,7 +25,7 @@
>  /* Use movups and movaps for smaller code sizes.  */
>  #define VMOVU          movups
>  #define VMOVA          movaps
> -
> +#define MOV_SIZE       3
>  #define SECTION(p)             p
>
>  #ifdef USE_MULTIARCH
> diff --git a/sysdeps/x86_64/multiarch/memmove-avx-unaligned-erms-rtm.S b/sysdeps/x86_64/multiarch/memmove-avx-unaligned-erms-rtm.S
> index 1ec1962e86..67a55f0c85 100644
> --- a/sysdeps/x86_64/multiarch/memmove-avx-unaligned-erms-rtm.S
> +++ b/sysdeps/x86_64/multiarch/memmove-avx-unaligned-erms-rtm.S
> @@ -4,7 +4,7 @@
>  # define VMOVNT                vmovntdq
>  # define VMOVU         vmovdqu
>  # define VMOVA         vmovdqa
> -
> +# define MOV_SIZE      4
>  # define ZERO_UPPER_VEC_REGISTERS_RETURN \
>    ZERO_UPPER_VEC_REGISTERS_RETURN_XTEST
>
> diff --git a/sysdeps/x86_64/multiarch/memmove-avx-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-avx-unaligned-erms.S
> index e195e93f15..975ae6c051 100644
> --- a/sysdeps/x86_64/multiarch/memmove-avx-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memmove-avx-unaligned-erms.S
> @@ -4,7 +4,7 @@
>  # define VMOVNT                vmovntdq
>  # define VMOVU         vmovdqu
>  # define VMOVA         vmovdqa
> -
> +# define MOV_SIZE      4
>  # define SECTION(p)            p##.avx
>  # define MEMMOVE_SYMBOL(p,s)   p##_avx_##s
>
> diff --git a/sysdeps/x86_64/multiarch/memmove-avx512-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-avx512-unaligned-erms.S
> index 848848ab39..0fa7126830 100644
> --- a/sysdeps/x86_64/multiarch/memmove-avx512-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memmove-avx512-unaligned-erms.S
> @@ -25,7 +25,7 @@
>  # define VMOVU         vmovdqu64
>  # define VMOVA         vmovdqa64
>  # define VZEROUPPER
> -
> +# define MOV_SIZE      6
>  # define SECTION(p)            p##.evex512
>  # define MEMMOVE_SYMBOL(p,s)   p##_avx512_##s
>
> diff --git a/sysdeps/x86_64/multiarch/memmove-evex-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-evex-unaligned-erms.S
> index 0cbce8f944..88715441fe 100644
> --- a/sysdeps/x86_64/multiarch/memmove-evex-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memmove-evex-unaligned-erms.S
> @@ -25,7 +25,7 @@
>  # define VMOVU         vmovdqu64
>  # define VMOVA         vmovdqa64
>  # define VZEROUPPER
> -
> +# define MOV_SIZE      6
>  # define SECTION(p)            p##.evex
>  # define MEMMOVE_SYMBOL(p,s)   p##_evex_##s
>
> diff --git a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> index abde8438d4..7b27cbdda5 100644
> --- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
> @@ -76,6 +76,25 @@
>  # endif
>  #endif
>
> +/* Whether to align before movsb. Ultimately we want 64 byte
> +   align and not worth it to load 4x VEC for VEC_SIZE == 16.  */
> +#define ALIGN_MOVSB    (VEC_SIZE > 16)
> +/* Number of bytes to align movsb to.  */
> +#define MOVSB_ALIGN_TO 64
> +
> +#define SMALL_MOV_SIZE (MOV_SIZE <= 4)
> +#define LARGE_MOV_SIZE (MOV_SIZE > 4)
> +
> +#if SMALL_MOV_SIZE + LARGE_MOV_SIZE != 1
> +# error MOV_SIZE Unknown
> +#endif
> +
> +#if LARGE_MOV_SIZE
> +# define SMALL_SIZE_OFFSET     (4)
> +#else
> +# define SMALL_SIZE_OFFSET     (0)
> +#endif
> +
>  #ifndef PAGE_SIZE
>  # define PAGE_SIZE 4096
>  #endif
> @@ -199,25 +218,21 @@ L(start):
>  # endif
>         cmp     $VEC_SIZE, %RDX_LP
>         jb      L(less_vec)
> +       /* Load regardless.  */
> +       VMOVU   (%rsi), %VEC(0)
>         cmp     $(VEC_SIZE * 2), %RDX_LP
>         ja      L(more_2x_vec)
> -#if !defined USE_MULTIARCH || !IS_IN (libc)
> -L(last_2x_vec):
> -#endif
>         /* From VEC and to 2 * VEC.  No branch when size == VEC_SIZE.  */
> -       VMOVU   (%rsi), %VEC(0)
>         VMOVU   -VEC_SIZE(%rsi,%rdx), %VEC(1)
>         VMOVU   %VEC(0), (%rdi)
>         VMOVU   %VEC(1), -VEC_SIZE(%rdi,%rdx)
> -#if !defined USE_MULTIARCH || !IS_IN (libc)
> -L(nop):
> -       ret
> +#if !(defined USE_MULTIARCH && IS_IN (libc))
> +       ZERO_UPPER_VEC_REGISTERS_RETURN
>  #else
>         VZEROUPPER_RETURN
>  #endif
>  #if defined USE_MULTIARCH && IS_IN (libc)
>  END (MEMMOVE_SYMBOL (__memmove, unaligned))
> -
>  # if VEC_SIZE == 16
>  ENTRY (__mempcpy_chk_erms)
>         cmp     %RDX_LP, %RCX_LP
> @@ -289,7 +304,7 @@ ENTRY (MEMMOVE_CHK_SYMBOL (__memmove_chk, unaligned_erms))
>  END (MEMMOVE_CHK_SYMBOL (__memmove_chk, unaligned_erms))
>  # endif
>
> -ENTRY (MEMMOVE_SYMBOL (__memmove, unaligned_erms))
> +ENTRY_P2ALIGN (MEMMOVE_SYMBOL (__memmove, unaligned_erms), 6)
>         movq    %rdi, %rax
>  L(start_erms):
>  # ifdef __ILP32__
> @@ -298,310 +313,448 @@ L(start_erms):
>  # endif
>         cmp     $VEC_SIZE, %RDX_LP
>         jb      L(less_vec)
> +       /* Load regardless.  */
> +       VMOVU   (%rsi), %VEC(0)
>         cmp     $(VEC_SIZE * 2), %RDX_LP
>         ja      L(movsb_more_2x_vec)
> -L(last_2x_vec):
> -       /* From VEC and to 2 * VEC.  No branch when size == VEC_SIZE. */
> -       VMOVU   (%rsi), %VEC(0)
> -       VMOVU   -VEC_SIZE(%rsi,%rdx), %VEC(1)
> +       /* From VEC and to 2 * VEC.  No branch when size == VEC_SIZE.
> +        */
> +       VMOVU   -VEC_SIZE(%rsi, %rdx), %VEC(1)
>         VMOVU   %VEC(0), (%rdi)
> -       VMOVU   %VEC(1), -VEC_SIZE(%rdi,%rdx)
> +       VMOVU   %VEC(1), -VEC_SIZE(%rdi, %rdx)
>  L(return):
> -#if VEC_SIZE > 16
> +# if VEC_SIZE > 16
>         ZERO_UPPER_VEC_REGISTERS_RETURN
> -#else
> +# else
>         ret
> +# endif
>  #endif
>
> -L(movsb):
> -       cmp     __x86_rep_movsb_stop_threshold(%rip), %RDX_LP
> -       jae     L(more_8x_vec)
> -       cmpq    %rsi, %rdi
> -       jb      1f
> -       /* Source == destination is less common.  */
> -       je      L(nop)
> -       leaq    (%rsi,%rdx), %r9
> -       cmpq    %r9, %rdi
> -       /* Avoid slow backward REP MOVSB.  */
> -       jb      L(more_8x_vec_backward)
> -# if AVOID_SHORT_DISTANCE_REP_MOVSB
> -       testl   $X86_STRING_CONTROL_AVOID_SHORT_DISTANCE_REP_MOVSB, __x86_string_control(%rip)
> -       jz      3f
> -       movq    %rdi, %rcx
> -       subq    %rsi, %rcx
> -       jmp     2f
> -# endif
> -1:
> -# if AVOID_SHORT_DISTANCE_REP_MOVSB
> -       testl   $X86_STRING_CONTROL_AVOID_SHORT_DISTANCE_REP_MOVSB, __x86_string_control(%rip)
> -       jz      3f
> -       movq    %rsi, %rcx
> -       subq    %rdi, %rcx
> -2:
> -/* Avoid "rep movsb" if RCX, the distance between source and destination,
> -   is N*4GB + [1..63] with N >= 0.  */
> -       cmpl    $63, %ecx
> -       jbe     L(more_2x_vec)  /* Avoid "rep movsb" if ECX <= 63.  */
> -3:
> -# endif
> -       mov     %RDX_LP, %RCX_LP
> -       rep movsb
> -L(nop):
> +#if LARGE_MOV_SIZE
> +       /* If LARGE_MOV_SIZE this fits in the aligning bytes between the
> +          ENTRY block and L(less_vec).  */
> +       .p2align 4,, 8
> +L(between_4_7):
> +       /* From 4 to 7.  No branch when size == 4.  */
> +       movl    (%rsi), %ecx
> +       movl    (%rsi, %rdx), %esi
> +       movl    %ecx, (%rdi)
> +       movl    %esi, (%rdi, %rdx)
>         ret
>  #endif
>
> +       .p2align 4
>  L(less_vec):
>         /* Less than 1 VEC.  */
>  #if VEC_SIZE != 16 && VEC_SIZE != 32 && VEC_SIZE != 64
>  # error Unsupported VEC_SIZE!
>  #endif
>  #if VEC_SIZE > 32
> -       cmpb    $32, %dl
> +       cmpl    $32, %edx
>         jae     L(between_32_63)
>  #endif
>  #if VEC_SIZE > 16
> -       cmpb    $16, %dl
> +       cmpl    $16, %edx
>         jae     L(between_16_31)
>  #endif
> -       cmpb    $8, %dl
> +       cmpl    $8, %edx
>         jae     L(between_8_15)
> -       cmpb    $4, %dl
> +#if SMALL_MOV_SIZE
> +       cmpl    $4, %edx
> +#else
> +       subq    $4, %rdx
> +#endif
>         jae     L(between_4_7)
> -       cmpb    $1, %dl
> -       ja      L(between_2_3)
> -       jb      1f
> -       movzbl  (%rsi), %ecx
> +       cmpl    $(1 - SMALL_SIZE_OFFSET), %edx
> +       jl      L(copy_0)
> +       movb    (%rsi), %cl
> +       je      L(copy_1)
> +       movzwl  (-2 + SMALL_SIZE_OFFSET)(%rsi, %rdx), %esi
> +       movw    %si, (-2 + SMALL_SIZE_OFFSET)(%rdi, %rdx)
> +L(copy_1):
>         movb    %cl, (%rdi)
> -1:
> +L(copy_0):
>         ret
> +
> +#if SMALL_MOV_SIZE
> +       .p2align 4,, 8
> +L(between_4_7):
> +       /* From 4 to 7.  No branch when size == 4.  */
> +       movl    -4(%rsi, %rdx), %ecx
> +       movl    (%rsi), %esi
> +       movl    %ecx, -4(%rdi, %rdx)
> +       movl    %esi, (%rdi)
> +       ret
> +#endif
> +
> +#if VEC_SIZE > 16
> +       /* From 16 to 31.  No branch when size == 16.  */
> +       .p2align 4,, 8
> +L(between_16_31):
> +       vmovdqu (%rsi), %xmm0
> +       vmovdqu -16(%rsi, %rdx), %xmm1
> +       vmovdqu %xmm0, (%rdi)
> +       vmovdqu %xmm1, -16(%rdi, %rdx)
> +       /* No ymm registers have been touched.  */
> +       ret
> +#endif
> +
>  #if VEC_SIZE > 32
> +       .p2align 4,, 10
>  L(between_32_63):
>         /* From 32 to 63.  No branch when size == 32.  */
>         VMOVU   (%rsi), %YMM0
> -       VMOVU   -32(%rsi,%rdx), %YMM1
> +       VMOVU   -32(%rsi, %rdx), %YMM1
>         VMOVU   %YMM0, (%rdi)
> -       VMOVU   %YMM1, -32(%rdi,%rdx)
> -       VZEROUPPER_RETURN
> -#endif
> -#if VEC_SIZE > 16
> -       /* From 16 to 31.  No branch when size == 16.  */
> -L(between_16_31):
> -       VMOVU   (%rsi), %XMM0
> -       VMOVU   -16(%rsi,%rdx), %XMM1
> -       VMOVU   %XMM0, (%rdi)
> -       VMOVU   %XMM1, -16(%rdi,%rdx)
> +       VMOVU   %YMM1, -32(%rdi, %rdx)
>         VZEROUPPER_RETURN
>  #endif
> +
> +       .p2align 4,, 10
>  L(between_8_15):
>         /* From 8 to 15.  No branch when size == 8.  */
> -       movq    -8(%rsi,%rdx), %rcx
> +       movq    -8(%rsi, %rdx), %rcx
>         movq    (%rsi), %rsi
> -       movq    %rcx, -8(%rdi,%rdx)
>         movq    %rsi, (%rdi)
> +       movq    %rcx, -8(%rdi, %rdx)
>         ret
> -L(between_4_7):
> -       /* From 4 to 7.  No branch when size == 4.  */
> -       movl    -4(%rsi,%rdx), %ecx
> -       movl    (%rsi), %esi
> -       movl    %ecx, -4(%rdi,%rdx)
> -       movl    %esi, (%rdi)
> -       ret
> -L(between_2_3):
> -       /* From 2 to 3.  No branch when size == 2.  */
> -       movzwl  -2(%rsi,%rdx), %ecx
> -       movzwl  (%rsi), %esi
> -       movw    %cx, -2(%rdi,%rdx)
> -       movw    %si, (%rdi)
> -       ret
>
> +       .p2align 4,, 10
> +L(last_4x_vec):
> +       /* Copy from 2 * VEC + 1 to 4 * VEC, inclusively.  */
> +
> +       /* VEC(0) and VEC(1) have already been loaded.  */
> +       VMOVU   -VEC_SIZE(%rsi, %rdx), %VEC(2)
> +       VMOVU   -(VEC_SIZE * 2)(%rsi, %rdx), %VEC(3)
> +       VMOVU   %VEC(0), (%rdi)
> +       VMOVU   %VEC(1), VEC_SIZE(%rdi)
> +       VMOVU   %VEC(2), -VEC_SIZE(%rdi, %rdx)
> +       VMOVU   %VEC(3), -(VEC_SIZE * 2)(%rdi, %rdx)
> +       VZEROUPPER_RETURN
> +
> +       .p2align 4
>  #if defined USE_MULTIARCH && IS_IN (libc)
>  L(movsb_more_2x_vec):
>         cmp     __x86_rep_movsb_threshold(%rip), %RDX_LP
>         ja      L(movsb)
>  #endif
>  L(more_2x_vec):
> -       /* More than 2 * VEC and there may be overlap between destination
> -          and source.  */
> +       /* More than 2 * VEC and there may be overlap between
> +          destination and source.  */
>         cmpq    $(VEC_SIZE * 8), %rdx
>         ja      L(more_8x_vec)
> +       /* Load VEC(1) regardless. VEC(0) has already been loaded.  */
> +       VMOVU   VEC_SIZE(%rsi), %VEC(1)
>         cmpq    $(VEC_SIZE * 4), %rdx
>         jbe     L(last_4x_vec)
> -       /* Copy from 4 * VEC + 1 to 8 * VEC, inclusively. */
> -       VMOVU   (%rsi), %VEC(0)
> -       VMOVU   VEC_SIZE(%rsi), %VEC(1)
> +       /* Copy from 4 * VEC + 1 to 8 * VEC, inclusively.  */
>         VMOVU   (VEC_SIZE * 2)(%rsi), %VEC(2)
>         VMOVU   (VEC_SIZE * 3)(%rsi), %VEC(3)
> -       VMOVU   -VEC_SIZE(%rsi,%rdx), %VEC(4)
> -       VMOVU   -(VEC_SIZE * 2)(%rsi,%rdx), %VEC(5)
> -       VMOVU   -(VEC_SIZE * 3)(%rsi,%rdx), %VEC(6)
> -       VMOVU   -(VEC_SIZE * 4)(%rsi,%rdx), %VEC(7)
> +       VMOVU   -VEC_SIZE(%rsi, %rdx), %VEC(4)
> +       VMOVU   -(VEC_SIZE * 2)(%rsi, %rdx), %VEC(5)
> +       VMOVU   -(VEC_SIZE * 3)(%rsi, %rdx), %VEC(6)
> +       VMOVU   -(VEC_SIZE * 4)(%rsi, %rdx), %VEC(7)
>         VMOVU   %VEC(0), (%rdi)
>         VMOVU   %VEC(1), VEC_SIZE(%rdi)
>         VMOVU   %VEC(2), (VEC_SIZE * 2)(%rdi)
>         VMOVU   %VEC(3), (VEC_SIZE * 3)(%rdi)
> -       VMOVU   %VEC(4), -VEC_SIZE(%rdi,%rdx)
> -       VMOVU   %VEC(5), -(VEC_SIZE * 2)(%rdi,%rdx)
> -       VMOVU   %VEC(6), -(VEC_SIZE * 3)(%rdi,%rdx)
> -       VMOVU   %VEC(7), -(VEC_SIZE * 4)(%rdi,%rdx)
> -       VZEROUPPER_RETURN
> -L(last_4x_vec):
> -       /* Copy from 2 * VEC + 1 to 4 * VEC, inclusively. */
> -       VMOVU   (%rsi), %VEC(0)
> -       VMOVU   VEC_SIZE(%rsi), %VEC(1)
> -       VMOVU   -VEC_SIZE(%rsi,%rdx), %VEC(2)
> -       VMOVU   -(VEC_SIZE * 2)(%rsi,%rdx), %VEC(3)
> -       VMOVU   %VEC(0), (%rdi)
> -       VMOVU   %VEC(1), VEC_SIZE(%rdi)
> -       VMOVU   %VEC(2), -VEC_SIZE(%rdi,%rdx)
> -       VMOVU   %VEC(3), -(VEC_SIZE * 2)(%rdi,%rdx)
> +       VMOVU   %VEC(4), -VEC_SIZE(%rdi, %rdx)
> +       VMOVU   %VEC(5), -(VEC_SIZE * 2)(%rdi, %rdx)
> +       VMOVU   %VEC(6), -(VEC_SIZE * 3)(%rdi, %rdx)
> +       VMOVU   %VEC(7), -(VEC_SIZE * 4)(%rdi, %rdx)
>         VZEROUPPER_RETURN
>
> +       .p2align 4,, 4
>  L(more_8x_vec):
> +       movq    %rdi, %rcx
> +       subq    %rsi, %rcx
> +       /* Go to backwards temporal copy if overlap no matter what as
> +          backward REP MOVSB is slow and we don't want to use NT stores if
> +          there is overlap.  */
> +       cmpq    %rdx, %rcx
> +       /* L(more_8x_vec_backward_check_nop) checks for src == dst.  */
> +       jb      L(more_8x_vec_backward_check_nop)
>         /* Check if non-temporal move candidate.  */
>  #if (defined USE_MULTIARCH || VEC_SIZE == 16) && IS_IN (libc)
>         /* Check non-temporal store threshold.  */
> -       cmp __x86_shared_non_temporal_threshold(%rip), %RDX_LP
> +       cmp     __x86_shared_non_temporal_threshold(%rip), %RDX_LP
>         ja      L(large_memcpy_2x)
>  #endif
> -       /* Entry if rdx is greater than non-temporal threshold but there
> -       is overlap.  */
> +       /* To reach this point there cannot be overlap and dst > src. So
> +          check for overlap and src > dst in which case correctness
> +          requires forward copy. Otherwise decide between backward/forward
> +          copy depending on address aliasing.  */
> +
> +       /* Entry if rdx is greater than __x86_rep_movsb_stop_threshold
> +          but less than __x86_shared_non_temporal_threshold.  */
>  L(more_8x_vec_check):
> -       cmpq    %rsi, %rdi
> -       ja      L(more_8x_vec_backward)
> -       /* Source == destination is less common.  */
> -       je      L(nop)
> -       /* Load the first VEC and last 4 * VEC to support overlapping
> -          addresses.  */
> -       VMOVU   (%rsi), %VEC(4)
> +       /* rcx contains dst - src. Add back length (rdx).  */
> +       leaq    (%rcx, %rdx), %r8
> +       /* If r8 has different sign than rcx then there is overlap so we
> +          must do forward copy.  */
> +       xorq    %rcx, %r8
> +       /* Isolate just sign bit of r8.  */
> +       shrq    $63, %r8
> +       /* Get 4k difference dst - src.  */
> +       andl    $(PAGE_SIZE - 256), %ecx
> +       /* If r8 is non-zero must do foward for correctness. Otherwise
> +          if ecx is non-zero there is 4k False Alaising so do backward
> +          copy.  */
> +       addl    %r8d, %ecx
> +       jz      L(more_8x_vec_backward)
> +
> +       /* if rdx is greater than __x86_shared_non_temporal_threshold
> +          but there is overlap, or from short distance movsb.  */
> +L(more_8x_vec_forward):
> +       /* Load first and last 4 * VEC to support overlapping addresses.
> +        */
> +
> +       /* First vec was already loaded into VEC(0).  */
>         VMOVU   -VEC_SIZE(%rsi, %rdx), %VEC(5)
>         VMOVU   -(VEC_SIZE * 2)(%rsi, %rdx), %VEC(6)
> +       /* Save begining of dst.  */
> +       movq    %rdi, %rcx
> +       /* Align dst to VEC_SIZE - 1.  */
> +       orq     $(VEC_SIZE - 1), %rdi
>         VMOVU   -(VEC_SIZE * 3)(%rsi, %rdx), %VEC(7)
>         VMOVU   -(VEC_SIZE * 4)(%rsi, %rdx), %VEC(8)
> -       /* Save start and stop of the destination buffer.  */
> -       movq    %rdi, %r11
> -       leaq    -VEC_SIZE(%rdi, %rdx), %rcx
> -       /* Align destination for aligned stores in the loop.  Compute
> -          how much destination is misaligned.  */
> -       movq    %rdi, %r8
> -       andq    $(VEC_SIZE - 1), %r8
> -       /* Get the negative of offset for alignment.  */
> -       subq    $VEC_SIZE, %r8
> -       /* Adjust source.  */
> -       subq    %r8, %rsi
> -       /* Adjust destination which should be aligned now.  */
> -       subq    %r8, %rdi
> -       /* Adjust length.  */
> -       addq    %r8, %rdx
>
> -       .p2align 4
> +       /* Subtract dst from src. Add back after dst aligned.  */
> +       subq    %rcx, %rsi
> +       /* Finish aligning dst.  */
> +       incq    %rdi
> +       /* Restore src adjusted with new value for aligned dst.  */
> +       addq    %rdi, %rsi
> +       /* Store end of buffer minus tail in rdx.  */
> +       leaq    (VEC_SIZE * -4)(%rcx, %rdx), %rdx
> +
> +       /* Dont use multi-byte nop to align.  */
> +       .p2align 4,, 11
>  L(loop_4x_vec_forward):
>         /* Copy 4 * VEC a time forward.  */
> -       VMOVU   (%rsi), %VEC(0)
> -       VMOVU   VEC_SIZE(%rsi), %VEC(1)
> -       VMOVU   (VEC_SIZE * 2)(%rsi), %VEC(2)
> -       VMOVU   (VEC_SIZE * 3)(%rsi), %VEC(3)
> +       VMOVU   (%rsi), %VEC(1)
> +       VMOVU   VEC_SIZE(%rsi), %VEC(2)
> +       VMOVU   (VEC_SIZE * 2)(%rsi), %VEC(3)
> +       VMOVU   (VEC_SIZE * 3)(%rsi), %VEC(4)
>         subq    $-(VEC_SIZE * 4), %rsi
> -       addq    $-(VEC_SIZE * 4), %rdx
> -       VMOVA   %VEC(0), (%rdi)
> -       VMOVA   %VEC(1), VEC_SIZE(%rdi)
> -       VMOVA   %VEC(2), (VEC_SIZE * 2)(%rdi)
> -       VMOVA   %VEC(3), (VEC_SIZE * 3)(%rdi)
> +       VMOVA   %VEC(1), (%rdi)
> +       VMOVA   %VEC(2), VEC_SIZE(%rdi)
> +       VMOVA   %VEC(3), (VEC_SIZE * 2)(%rdi)
> +       VMOVA   %VEC(4), (VEC_SIZE * 3)(%rdi)
>         subq    $-(VEC_SIZE * 4), %rdi
> -       cmpq    $(VEC_SIZE * 4), %rdx
> +       cmpq    %rdi, %rdx
>         ja      L(loop_4x_vec_forward)
>         /* Store the last 4 * VEC.  */
> -       VMOVU   %VEC(5), (%rcx)
> -       VMOVU   %VEC(6), -VEC_SIZE(%rcx)
> -       VMOVU   %VEC(7), -(VEC_SIZE * 2)(%rcx)
> -       VMOVU   %VEC(8), -(VEC_SIZE * 3)(%rcx)
> +       VMOVU   %VEC(5), (VEC_SIZE * 3)(%rdx)
> +       VMOVU   %VEC(6), (VEC_SIZE * 2)(%rdx)
> +       VMOVU   %VEC(7), VEC_SIZE(%rdx)
> +       VMOVU   %VEC(8), (%rdx)
>         /* Store the first VEC.  */
> -       VMOVU   %VEC(4), (%r11)
> +       VMOVU   %VEC(0), (%rcx)
> +       /* Keep L(nop_backward) target close to jmp for 2-byte encoding.
> +        */
> +L(nop_backward):
>         VZEROUPPER_RETURN
>
> +       .p2align 4,, 8
> +L(more_8x_vec_backward_check_nop):
> +       /* rcx contains dst - src. Test for dst == src to skip all of
> +          memmove.  */
> +       testq   %rcx, %rcx
> +       jz      L(nop_backward)
>  L(more_8x_vec_backward):
>         /* Load the first 4 * VEC and last VEC to support overlapping
>            addresses.  */
> -       VMOVU   (%rsi), %VEC(4)
> +
> +       /* First vec was also loaded into VEC(0).  */
>         VMOVU   VEC_SIZE(%rsi), %VEC(5)
>         VMOVU   (VEC_SIZE * 2)(%rsi), %VEC(6)
> +       /* Begining of region for 4x backward copy stored in rcx.  */
> +       leaq    (VEC_SIZE * -4 + -1)(%rdi, %rdx), %rcx
>         VMOVU   (VEC_SIZE * 3)(%rsi), %VEC(7)
> -       VMOVU   -VEC_SIZE(%rsi,%rdx), %VEC(8)
> -       /* Save stop of the destination buffer.  */
> -       leaq    -VEC_SIZE(%rdi, %rdx), %r11
> -       /* Align destination end for aligned stores in the loop.  Compute
> -          how much destination end is misaligned.  */
> -       leaq    -VEC_SIZE(%rsi, %rdx), %rcx
> -       movq    %r11, %r9
> -       movq    %r11, %r8
> -       andq    $(VEC_SIZE - 1), %r8
> -       /* Adjust source.  */
> -       subq    %r8, %rcx
> -       /* Adjust the end of destination which should be aligned now.  */
> -       subq    %r8, %r9
> -       /* Adjust length.  */
> -       subq    %r8, %rdx
> -
> -       .p2align 4
> +       VMOVU   -VEC_SIZE(%rsi, %rdx), %VEC(8)
> +       /* Subtract dst from src. Add back after dst aligned.  */
> +       subq    %rdi, %rsi
> +       /* Align dst.  */
> +       andq    $-(VEC_SIZE), %rcx
> +       /* Restore src.  */
> +       addq    %rcx, %rsi
> +
> +       /* Don't use multi-byte nop to align.  */
> +       .p2align 4,, 11
>  L(loop_4x_vec_backward):
>         /* Copy 4 * VEC a time backward.  */
> -       VMOVU   (%rcx), %VEC(0)
> -       VMOVU   -VEC_SIZE(%rcx), %VEC(1)
> -       VMOVU   -(VEC_SIZE * 2)(%rcx), %VEC(2)
> -       VMOVU   -(VEC_SIZE * 3)(%rcx), %VEC(3)
> -       addq    $-(VEC_SIZE * 4), %rcx
> -       addq    $-(VEC_SIZE * 4), %rdx
> -       VMOVA   %VEC(0), (%r9)
> -       VMOVA   %VEC(1), -VEC_SIZE(%r9)
> -       VMOVA   %VEC(2), -(VEC_SIZE * 2)(%r9)
> -       VMOVA   %VEC(3), -(VEC_SIZE * 3)(%r9)
> -       addq    $-(VEC_SIZE * 4), %r9
> -       cmpq    $(VEC_SIZE * 4), %rdx
> -       ja      L(loop_4x_vec_backward)
> +       VMOVU   (VEC_SIZE * 3)(%rsi), %VEC(1)
> +       VMOVU   (VEC_SIZE * 2)(%rsi), %VEC(2)
> +       VMOVU   (VEC_SIZE * 1)(%rsi), %VEC(3)
> +       VMOVU   (VEC_SIZE * 0)(%rsi), %VEC(4)
> +       addq    $(VEC_SIZE * -4), %rsi
> +       VMOVA   %VEC(1), (VEC_SIZE * 3)(%rcx)
> +       VMOVA   %VEC(2), (VEC_SIZE * 2)(%rcx)
> +       VMOVA   %VEC(3), (VEC_SIZE * 1)(%rcx)
> +       VMOVA   %VEC(4), (VEC_SIZE * 0)(%rcx)
> +       addq    $(VEC_SIZE * -4), %rcx
> +       cmpq    %rcx, %rdi
> +       jb      L(loop_4x_vec_backward)
>         /* Store the first 4 * VEC.  */
> -       VMOVU   %VEC(4), (%rdi)
> +       VMOVU   %VEC(0), (%rdi)
>         VMOVU   %VEC(5), VEC_SIZE(%rdi)
>         VMOVU   %VEC(6), (VEC_SIZE * 2)(%rdi)
>         VMOVU   %VEC(7), (VEC_SIZE * 3)(%rdi)
>         /* Store the last VEC.  */
> -       VMOVU   %VEC(8), (%r11)
> +       VMOVU   %VEC(8), -VEC_SIZE(%rdx, %rdi)
> +       VZEROUPPER_RETURN
> +
> +#if defined USE_MULTIARCH && IS_IN (libc)
> +       /* L(skip_short_movsb_check) is only used with ERMS. Not for
> +          FSRM.  */
> +       .p2align 5,, 16
> +# if ALIGN_MOVSB
> +L(skip_short_movsb_check):
> +#  if MOVSB_ALIGN_TO > VEC_SIZE
> +       VMOVU   VEC_SIZE(%rsi), %VEC(1)
> +#  endif
> +#  if MOVSB_ALIGN_TO > (VEC_SIZE * 2)
> +#   error Unsupported MOVSB_ALIGN_TO
> +#  endif
> +       /* If CPU does not have FSRM two options for aligning. Align src
> +          if dst and src 4k alias. Otherwise align dst.  */
> +       testl   $(PAGE_SIZE - 512), %ecx
> +       jnz     L(movsb_align_dst)
> +       /* Fall through. dst and src 4k alias. It's better to align src
> +          here because the bottleneck will be loads dues to the false
> +          dependency on dst.  */
> +
> +       /* rcx already has dst - src.  */
> +       movq    %rcx, %r9
> +       /* Add src to len. Subtract back after src aligned. -1 because
> +          src is initially aligned to MOVSB_ALIGN_TO - 1.  */
> +       leaq    -1(%rsi, %rdx), %rcx
> +       /* Inclusively align src to MOVSB_ALIGN_TO - 1.  */
> +       orq     $(MOVSB_ALIGN_TO - 1), %rsi
> +       /* Restore dst and len adjusted with new values for aligned dst.
> +        */
> +       leaq    1(%rsi, %r9), %rdi
> +       subq    %rsi, %rcx
> +       /* Finish aligning src.  */
> +       incq    %rsi
> +
> +       rep     movsb
> +
> +       VMOVU   %VEC(0), (%r8)
> +#  if MOVSB_ALIGN_TO > VEC_SIZE
> +       VMOVU   %VEC(1), VEC_SIZE(%r8)
> +#  endif
>         VZEROUPPER_RETURN
> +# endif
> +
> +       .p2align 4,, 12
> +L(movsb):
> +       movq    %rdi, %rcx
> +       subq    %rsi, %rcx
> +       /* Go to backwards temporal copy if overlap no matter what as
> +          backward REP MOVSB is slow and we don't want to use NT stores if
> +          there is overlap.  */
> +       cmpq    %rdx, %rcx
> +       /* L(more_8x_vec_backward_check_nop) checks for src == dst.  */
> +       jb      L(more_8x_vec_backward_check_nop)
> +# if ALIGN_MOVSB
> +       /* Save dest for storing aligning VECs later.  */
> +       movq    %rdi, %r8
> +# endif
> +       /* If above __x86_rep_movsb_stop_threshold most likely is
> +          candidate for NT moves aswell.  */
> +       cmp     __x86_rep_movsb_stop_threshold(%rip), %RDX_LP
> +       jae     L(large_memcpy_2x_check)
> +# if AVOID_SHORT_DISTANCE_REP_MOVSB || ALIGN_MOVSB
> +       /* Only avoid short movsb if CPU has FSRM.  */
> +       testl   $X86_STRING_CONTROL_AVOID_SHORT_DISTANCE_REP_MOVSB, __x86_string_control(%rip)
> +       jz      L(skip_short_movsb_check)
> +#  if AVOID_SHORT_DISTANCE_REP_MOVSB
> +       /* Avoid "rep movsb" if RCX, the distance between source and
> +          destination, is N*4GB + [1..63] with N >= 0.  */
> +
> +       /* ecx contains dst - src. Early check for backward copy
> +          conditions means only case of slow movsb with src = dst + [0,
> +          63] is ecx in [-63, 0]. Use unsigned comparison with -64 check
> +          for that case.  */
> +       cmpl    $-64, %ecx
> +       ja      L(more_8x_vec_forward)
> +#  endif
> +# endif
> +# if ALIGN_MOVSB
> +#  if MOVSB_ALIGN_TO > VEC_SIZE
> +       VMOVU   VEC_SIZE(%rsi), %VEC(1)
> +#  endif
> +#  if MOVSB_ALIGN_TO > (VEC_SIZE * 2)
> +#   error Unsupported MOVSB_ALIGN_TO
> +#  endif
> +       /* Fall through means cpu has FSRM. In that case exclusively
> +          align destination.  */
> +L(movsb_align_dst):
> +       /* Subtract dst from src. Add back after dst aligned.  */
> +       subq    %rdi, %rsi
> +       /* Exclusively align dst to MOVSB_ALIGN_TO (64).  */
> +       addq    $(MOVSB_ALIGN_TO - 1), %rdi
> +       /* Add dst to len. Subtract back after dst aligned.  */
> +       leaq    (%r8, %rdx), %rcx
> +       /* Finish aligning dst.  */
> +       andq    $-(MOVSB_ALIGN_TO), %rdi
> +       /* Restore src and len adjusted with new values for aligned dst.
> +        */
> +       addq    %rdi, %rsi
> +       subq    %rdi, %rcx
> +
> +       rep     movsb
> +
> +       /* Store VECs loaded for aligning.  */
> +       VMOVU   %VEC(0), (%r8)
> +#  if MOVSB_ALIGN_TO > VEC_SIZE
> +       VMOVU   %VEC(1), VEC_SIZE(%r8)
> +#  endif
> +       VZEROUPPER_RETURN
> +# else /* !ALIGN_MOVSB.  */
> +L(skip_short_movsb_check):
> +       mov     %RDX_LP, %RCX_LP
> +       rep     movsb
> +       ret
> +# endif
> +#endif
>
> +       .p2align 4,, 10
>  #if (defined USE_MULTIARCH || VEC_SIZE == 16) && IS_IN (libc)
> -       .p2align 4
> +L(large_memcpy_2x_check):
> +       cmp     __x86_rep_movsb_threshold(%rip), %RDX_LP
> +       jb      L(more_8x_vec_check)
>  L(large_memcpy_2x):
> -       /* Compute absolute value of difference between source and
> -          destination.  */
> -       movq    %rdi, %r9
> -       subq    %rsi, %r9
> -       movq    %r9, %r8
> -       leaq    -1(%r9), %rcx
> -       sarq    $63, %r8
> -       xorq    %r8, %r9
> -       subq    %r8, %r9
> -       /* Don't use non-temporal store if there is overlap between
> -          destination and source since destination may be in cache when
> -          source is loaded.  */
> -       cmpq    %r9, %rdx
> -       ja      L(more_8x_vec_check)
> +       /* To reach this point it is impossible for dst > src and
> +          overlap. Remaining to check is src > dst and overlap. rcx
> +          already contains dst - src. Negate rcx to get src - dst. If
> +          length > rcx then there is overlap and forward copy is best.  */
> +       negq    %rcx
> +       cmpq    %rcx, %rdx
> +       ja      L(more_8x_vec_forward)
>
>         /* Cache align destination. First store the first 64 bytes then
>            adjust alignments.  */
> -       VMOVU   (%rsi), %VEC(8)
> -#if VEC_SIZE < 64
> -       VMOVU   VEC_SIZE(%rsi), %VEC(9)
> -#if VEC_SIZE < 32
> -       VMOVU   (VEC_SIZE * 2)(%rsi), %VEC(10)
> -       VMOVU   (VEC_SIZE * 3)(%rsi), %VEC(11)
> -#endif
> -#endif
> -       VMOVU   %VEC(8), (%rdi)
> -#if VEC_SIZE < 64
> -       VMOVU   %VEC(9), VEC_SIZE(%rdi)
> -#if VEC_SIZE < 32
> -       VMOVU   %VEC(10), (VEC_SIZE * 2)(%rdi)
> -       VMOVU   %VEC(11), (VEC_SIZE * 3)(%rdi)
> -#endif
> -#endif
> +
> +       /* First vec was also loaded into VEC(0).  */
> +# if VEC_SIZE < 64
> +       VMOVU   VEC_SIZE(%rsi), %VEC(1)
> +#  if VEC_SIZE < 32
> +       VMOVU   (VEC_SIZE * 2)(%rsi), %VEC(2)
> +       VMOVU   (VEC_SIZE * 3)(%rsi), %VEC(3)
> +#  endif
> +# endif
> +       VMOVU   %VEC(0), (%rdi)
> +# if VEC_SIZE < 64
> +       VMOVU   %VEC(1), VEC_SIZE(%rdi)
> +#  if VEC_SIZE < 32
> +       VMOVU   %VEC(2), (VEC_SIZE * 2)(%rdi)
> +       VMOVU   %VEC(3), (VEC_SIZE * 3)(%rdi)
> +#  endif
> +# endif
> +
>         /* Adjust source, destination, and size.  */
>         movq    %rdi, %r8
>         andq    $63, %r8
> @@ -614,9 +767,13 @@ L(large_memcpy_2x):
>         /* Adjust length.  */
>         addq    %r8, %rdx
>
> -       /* Test if source and destination addresses will alias. If they do
> -          the larger pipeline in large_memcpy_4x alleviated the
> +       /* Test if source and destination addresses will alias. If they
> +          do the larger pipeline in large_memcpy_4x alleviated the
>            performance drop.  */
> +
> +       /* ecx contains -(dst - src). not ecx will return dst - src - 1
> +          which works for testing aliasing.  */
> +       notl    %ecx
>         testl   $(PAGE_SIZE - VEC_SIZE * 8), %ecx
>         jz      L(large_memcpy_4x)
>
> @@ -704,8 +861,8 @@ L(loop_large_memcpy_4x_outer):
>         /* ecx stores inner loop counter.  */
>         movl    $(PAGE_SIZE / LARGE_LOAD_SIZE), %ecx
>  L(loop_large_memcpy_4x_inner):
> -       /* Only one prefetch set per page as doing 4 pages give more time
> -          for prefetcher to keep up.  */
> +       /* Only one prefetch set per page as doing 4 pages give more
> +          time for prefetcher to keep up.  */
>         PREFETCH_ONE_SET(1, (%rsi), PREFETCHED_LOAD_SIZE)
>         PREFETCH_ONE_SET(1, (%rsi), PAGE_SIZE + PREFETCHED_LOAD_SIZE)
>         PREFETCH_ONE_SET(1, (%rsi), PAGE_SIZE * 2 + PREFETCHED_LOAD_SIZE)
> --
> 2.25.1
>

LGTM.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

Thanks.

-- 
H.J.