[v1,3/3] x86: Optimize memset-vec-unaligned-erms.S
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Build for i686
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Commit Message
No bug.
Optimization are
1. change control flow for L(more_2x_vec) to fall through to loop and
jump for L(less_4x_vec) and L(less_8x_vec). This uses less code
size and saves jumps for length > 4x VEC_SIZE.
2. For EVEX/AVX512 move L(less_vec) closer to entry.
3. Avoid complex address mode for length > 2x VEC_SIZE
4. Slightly better aligning code for the loop from the perspective of
code size and uops.
5. Align targets so they make full use of their fetch block and if
possible cache line.
6. Try and reduce total number of icache lines that will need to be
pulled in for a given length.
7. Include "local" version of stosb target. For AVX2/EVEX/AVX512
jumping to the stosb target in the sse2 code section will almost
certainly be to a new page. The new version does increase code size
marginally by duplicating the target but should get better iTLB
behavior as a result.
test-memset, test-wmemset, and test-bzero are all passing.
Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
---
Performance numbers attached in reply.
Notes on testing.
I page aligned the start and end of MEMSET so that the bench-memset.c
code would not be affected by code size changes.
I replaced `_x86_rep_stosb_threshold` with `$2048`. Note this takes
the exact same code size. I did this because the load of
`_x86_rep_stosb_threshold` can stall due to 4k aliasing from stores
during the benchmark. I don't think this is what we are intending to
benchmark and I believe it adds more confusion/noise to the
results. (Not to say there is no reason to benchmark that case, just I
don't think it should be accidental).
Notes on numbers:
There are degregations in the (2x, 4x] VEC_SIZE range. This is
expected and because the current version gives a fallthrough patch to
that size range whereas the new version has a jump. Generally this is
also conditional on the previous ENTRY_ALIGNMENT % 64, with
ENTRY_ALIGNMENT % 64 == 16 being the best for that size range in the
current implementation. The new implementation hopefully makes up for
this with the higher magnitude gains in the (4x, stosb_threshold)
VEC_SIZE range. Is this a blocker?
For Skylake there are two other degregations.
One where length = 416 with alignment = 416. I have not been able to
find this root cause of this. All other size/alignment pairs in the
medium sized range seem to perform better. Does anyone have an
explination for this or think its a blocker?
The other is conditionally on length in [1x, 2x] VEC_SIZE. I believe
this is related to reordering the two overlapping stores. The previous
version had complex address mode first. Its possible that the simple
address mode is taking p23 AGU stalling the complex address
calculation for the second store. Having the complex address mode
first prevents this. This only appears to be n issue for the first set
of tests (c=-65) and only appears to sometimes matter. My general
feeling is that if possible ordering for sequantial strided memory
access makes the most sense hence the reordering. Does anyone think it
should keep the original order?
Other than those 1/3 cases the new version wins out in all other cases
against all prior alignments.
sysdeps/x86_64/memset.S | 10 +-
.../multiarch/memset-avx2-unaligned-erms.S | 10 +-
.../multiarch/memset-avx512-unaligned-erms.S | 11 +-
.../multiarch/memset-evex-unaligned-erms.S | 11 +-
.../multiarch/memset-vec-unaligned-erms.S | 285 ++++++++++++------
5 files changed, 232 insertions(+), 95 deletions(-)
Comments
On Sun, Sep 26, 2021 at 3:54 PM Noah Goldstein <goldstein.w.n@gmail.com>
wrote:
> No bug.
>
> Optimization are
>
> 1. change control flow for L(more_2x_vec) to fall through to loop and
> jump for L(less_4x_vec) and L(less_8x_vec). This uses less code
> size and saves jumps for length > 4x VEC_SIZE.
>
> 2. For EVEX/AVX512 move L(less_vec) closer to entry.
>
> 3. Avoid complex address mode for length > 2x VEC_SIZE
>
> 4. Slightly better aligning code for the loop from the perspective of
> code size and uops.
>
> 5. Align targets so they make full use of their fetch block and if
> possible cache line.
>
> 6. Try and reduce total number of icache lines that will need to be
> pulled in for a given length.
>
> 7. Include "local" version of stosb target. For AVX2/EVEX/AVX512
> jumping to the stosb target in the sse2 code section will almost
> certainly be to a new page. The new version does increase code size
> marginally by duplicating the target but should get better iTLB
> behavior as a result.
>
> test-memset, test-wmemset, and test-bzero are all passing.
>
> Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> ---
> Performance numbers attached in reply.
>
Numbers attached here.
>
> Notes on testing.
>
> I page aligned the start and end of MEMSET so that the bench-memset.c
> code would not be affected by code size changes.
>
> I replaced `_x86_rep_stosb_threshold` with `$2048`. Note this takes
> the exact same code size. I did this because the load of
> `_x86_rep_stosb_threshold` can stall due to 4k aliasing from stores
> during the benchmark. I don't think this is what we are intending to
> benchmark and I believe it adds more confusion/noise to the
> results. (Not to say there is no reason to benchmark that case, just I
> don't think it should be accidental).
>
> Notes on numbers:
>
> There are degregations in the (2x, 4x] VEC_SIZE range. This is
> expected and because the current version gives a fallthrough patch to
> that size range whereas the new version has a jump. Generally this is
> also conditional on the previous ENTRY_ALIGNMENT % 64, with
> ENTRY_ALIGNMENT % 64 == 16 being the best for that size range in the
> current implementation. The new implementation hopefully makes up for
> this with the higher magnitude gains in the (4x, stosb_threshold)
> VEC_SIZE range. Is this a blocker?
>
> For Skylake there are two other degregations.
>
> One where length = 416 with alignment = 416. I have not been able to
> find this root cause of this. All other size/alignment pairs in the
> medium sized range seem to perform better. Does anyone have an
> explination for this or think its a blocker?
>
> The other is conditionally on length in [1x, 2x] VEC_SIZE. I believe
> this is related to reordering the two overlapping stores. The previous
> version had complex address mode first. Its possible that the simple
> address mode is taking p23 AGU stalling the complex address
> calculation for the second store. Having the complex address mode
> first prevents this. This only appears to be n issue for the first set
> of tests (c=-65) and only appears to sometimes matter. My general
> feeling is that if possible ordering for sequantial strided memory
> access makes the most sense hence the reordering. Does anyone think it
> should keep the original order?
>
> Other than those 1/3 cases the new version wins out in all other cases
> against all prior alignments.
>
> sysdeps/x86_64/memset.S | 10 +-
> .../multiarch/memset-avx2-unaligned-erms.S | 10 +-
> .../multiarch/memset-avx512-unaligned-erms.S | 11 +-
> .../multiarch/memset-evex-unaligned-erms.S | 11 +-
> .../multiarch/memset-vec-unaligned-erms.S | 285 ++++++++++++------
> 5 files changed, 232 insertions(+), 95 deletions(-)
>
> diff --git a/sysdeps/x86_64/memset.S b/sysdeps/x86_64/memset.S
> index 7d4a327eba..0137eba4cd 100644
> --- a/sysdeps/x86_64/memset.S
> +++ b/sysdeps/x86_64/memset.S
> @@ -18,13 +18,15 @@
> <https://www.gnu.org/licenses/>. */
>
> #include <sysdep.h>
> +#define USE_WITH_SSE2 1
>
> #define VEC_SIZE 16
> +#define MOV_SIZE 3
> +#define RET_SIZE 1
> +
> #define VEC(i) xmm##i
> -/* Don't use movups and movaps since it will get larger nop paddings for
> - alignment. */
> -#define VMOVU movdqu
> -#define VMOVA movdqa
> +#define VMOVU movups
> +#define VMOVA movaps
>
> #define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> movd d, %xmm0; \
> diff --git a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> index ae0860f36a..1af668af0a 100644
> --- a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> @@ -1,8 +1,14 @@
> #if IS_IN (libc)
> +# define USE_WITH_AVX2 1
> +
> # define VEC_SIZE 32
> +# define MOV_SIZE 4
> +# define RET_SIZE 4
> +
> # define VEC(i) ymm##i
> -# define VMOVU vmovdqu
> -# define VMOVA vmovdqa
> +
> +# define VMOVU vmovdqu
> +# define VMOVA vmovdqa
>
> # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> vmovd d, %xmm0; \
> diff --git a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> index 8ad842fc2f..5937a974bf 100644
> --- a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> @@ -1,11 +1,18 @@
> #if IS_IN (libc)
> +# define USE_WITH_AVX512 1
> +
> # define VEC_SIZE 64
> +# define MOV_SIZE 6
> +# define RET_SIZE 1
> +
> # define XMM0 xmm16
> # define YMM0 ymm16
> # define VEC0 zmm16
> # define VEC(i) VEC##i
> -# define VMOVU vmovdqu64
> -# define VMOVA vmovdqa64
> +
> +# define VMOVU vmovdqu64
> +# define VMOVA vmovdqa64
> +
> # define VZEROUPPER
>
> # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> diff --git a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> index 640f092903..64b09e77cc 100644
> --- a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> @@ -1,11 +1,18 @@
> #if IS_IN (libc)
> +# define USE_WITH_EVEX 1
> +
> # define VEC_SIZE 32
> +# define MOV_SIZE 6
> +# define RET_SIZE 1
> +
> # define XMM0 xmm16
> # define YMM0 ymm16
> # define VEC0 ymm16
> # define VEC(i) VEC##i
> -# define VMOVU vmovdqu64
> -# define VMOVA vmovdqa64
> +
> +# define VMOVU vmovdqu64
> +# define VMOVA vmovdqa64
> +
> # define VZEROUPPER
>
> # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> index ff196844a0..e723413a66 100644
> --- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> @@ -63,8 +63,27 @@
> # endif
> #endif
>
> +#if VEC_SIZE == 64
> +# define LOOP_4X_OFFSET (VEC_SIZE * 4)
> +#else
> +# define LOOP_4X_OFFSET (0)
> +#endif
> +
> +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> +# define END_REG rcx
> +# define LOOP_REG rdi
> +#else
> +# define END_REG rdi
> +# define LOOP_REG rdx
> +#endif
> +
> #define PAGE_SIZE 4096
>
> +/* Macro to calculate size of small memset block for aligning
> + purposes. */
> +#define SMALL_MEMSET_ALIGN(mov_sz, ret_sz) (2 * (mov_sz) + (ret_sz) +
> 1)
> +
> +
> #ifndef SECTION
> # error SECTION is not defined!
> #endif
> @@ -74,6 +93,7 @@
> ENTRY (__bzero)
> mov %RDI_LP, %RAX_LP /* Set return value. */
> mov %RSI_LP, %RDX_LP /* Set n. */
> + xorl %esi, %esi
> pxor %XMM0, %XMM0
> jmp L(entry_from_bzero)
> END (__bzero)
> @@ -158,7 +178,7 @@ ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk,
> unaligned_erms))
> END_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
> # endif
>
> -ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
> +ENTRY_P2ALIGN (MEMSET_SYMBOL (__memset, unaligned_erms), 6)
> MEMSET_VDUP_TO_VEC0_AND_SET_RETURN (%esi, %rdi)
> # ifdef __ILP32__
> /* Clear the upper 32 bits. */
> @@ -168,75 +188,43 @@ ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
> jb L(less_vec)
> cmp $(VEC_SIZE * 2), %RDX_LP
> ja L(stosb_more_2x_vec)
> - /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE. */
> - VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
> - VMOVU %VEC(0), (%rdi)
> + /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE.
> + */
> + VMOVU %VEC(0), (%rax)
> + VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
> VZEROUPPER_RETURN
> -
> - .p2align 4
> -L(stosb_more_2x_vec):
> - cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
> - ja L(stosb)
> -#else
> - .p2align 4
> #endif
> -L(more_2x_vec):
> - /* Stores to first 2x VEC before cmp as any path forward will
> - require it. */
> - VMOVU %VEC(0), (%rdi)
> - VMOVU %VEC(0), VEC_SIZE(%rdi)
> - cmpq $(VEC_SIZE * 4), %rdx
> - ja L(loop_start)
> - VMOVU %VEC(0), -(VEC_SIZE * 2)(%rdi,%rdx)
> - VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
> -L(return):
> -#if VEC_SIZE > 16
> - ZERO_UPPER_VEC_REGISTERS_RETURN
> +
> + .p2align 4,, 10
> +L(last_2x_vec):
> +#ifdef USE_LESS_VEC_MASK_STORE
> + VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%rcx)
> + VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%rcx)
> #else
> - ret
> + VMOVU %VEC(0), (VEC_SIZE * -2)(%rdi)
> + VMOVU %VEC(0), (VEC_SIZE * -1)(%rdi)
> #endif
> + VZEROUPPER_RETURN
>
> -L(loop_start):
> - VMOVU %VEC(0), (VEC_SIZE * 2)(%rdi)
> - VMOVU %VEC(0), (VEC_SIZE * 3)(%rdi)
> - cmpq $(VEC_SIZE * 8), %rdx
> - jbe L(loop_end)
> - andq $-(VEC_SIZE * 2), %rdi
> - subq $-(VEC_SIZE * 4), %rdi
> - leaq -(VEC_SIZE * 4)(%rax, %rdx), %rcx
> - .p2align 4
> -L(loop):
> - VMOVA %VEC(0), (%rdi)
> - VMOVA %VEC(0), VEC_SIZE(%rdi)
> - VMOVA %VEC(0), (VEC_SIZE * 2)(%rdi)
> - VMOVA %VEC(0), (VEC_SIZE * 3)(%rdi)
> - subq $-(VEC_SIZE * 4), %rdi
> - cmpq %rcx, %rdi
> - jb L(loop)
> -L(loop_end):
> - /* NB: rax is set as ptr in MEMSET_VDUP_TO_VEC0_AND_SET_RETURN.
> - rdx as length is also unchanged. */
> - VMOVU %VEC(0), -(VEC_SIZE * 4)(%rax, %rdx)
> - VMOVU %VEC(0), -(VEC_SIZE * 3)(%rax, %rdx)
> - VMOVU %VEC(0), -(VEC_SIZE * 2)(%rax, %rdx)
> - VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
> - VZEROUPPER_SHORT_RETURN
> -
> - .p2align 4
> + /* If have AVX512 mask instructions put L(less_vec) close to
> + entry as it doesn't take much space and is likely a hot target.
> + */
> +#ifdef USE_LESS_VEC_MASK_STORE
> + .p2align 4,, 10
> L(less_vec):
> /* Less than 1 VEC. */
> # if VEC_SIZE != 16 && VEC_SIZE != 32 && VEC_SIZE != 64
> # error Unsupported VEC_SIZE!
> # endif
> -# ifdef USE_LESS_VEC_MASK_STORE
> /* Clear high bits from edi. Only keeping bits relevant to page
> cross check. Note that we are using rax which is set in
> - MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out.
> - */
> + MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out. */
> andl $(PAGE_SIZE - 1), %edi
> - /* Check if VEC_SIZE store cross page. Mask stores suffer serious
> - performance degradation when it has to fault supress. */
> + /* Check if VEC_SIZE store cross page. Mask stores suffer
> + serious performance degradation when it has to fault supress.
> + */
> cmpl $(PAGE_SIZE - VEC_SIZE), %edi
> + /* This is generally considered a cold target. */
> ja L(cross_page)
> # if VEC_SIZE > 32
> movq $-1, %rcx
> @@ -247,58 +235,185 @@ L(less_vec):
> bzhil %edx, %ecx, %ecx
> kmovd %ecx, %k1
> # endif
> - vmovdqu8 %VEC(0), (%rax) {%k1}
> + vmovdqu8 %VEC(0), (%rax){%k1}
> VZEROUPPER_RETURN
>
> +# if defined USE_MULTIARCH && IS_IN (libc)
> + /* Include L(stosb_local) here if including L(less_vec) between
> + L(stosb_more_2x_vec) and ENTRY. This is to cache align the
> + L(stosb_more_2x_vec) target. */
> + .p2align 4,, 10
> +L(stosb_local):
> + movzbl %sil, %eax
> + mov %RDX_LP, %RCX_LP
> + mov %RDI_LP, %RDX_LP
> + rep stosb
> + mov %RDX_LP, %RAX_LP
> + VZEROUPPER_RETURN
> +# endif
> +#endif
> +
> +#if defined USE_MULTIARCH && IS_IN (libc)
> .p2align 4
> -L(cross_page):
> +L(stosb_more_2x_vec):
> + cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
> + ja L(stosb_local)
> +#endif
> + /* Fallthrough goes to L(loop_4x_vec). Tests for memset (2x, 4x]
> + and (4x, 8x] jump to target. */
> +L(more_2x_vec):
> +
> + /* Two different methods of setting up pointers / compare. The
> + two methods are based on the fact that EVEX/AVX512 mov
> + instructions take more bytes then AVX2/SSE2 mov instructions. As
> + well that EVEX/AVX512 machines also have fast LEA_BID. Both
> + setup and END_REG to avoid complex address mode. For EVEX/AVX512
> + this saves code size and keeps a few targets in one fetch block.
> + For AVX2/SSE2 this helps prevent AGU bottlenecks. */
> +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> + /* If EVEX/AVX512 compute END_REG - (VEC_SIZE * 4 +
> + LOOP_4X_OFFSET) with LEA_BID. */
> +
> + /* END_REG is rcx for EVEX/AVX512. */
> + leaq -(VEC_SIZE * 4 + LOOP_4X_OFFSET)(%rdi, %rdx), %END_REG
> +#endif
> +
> + /* Stores to first 2x VEC before cmp as any path forward will
> + require it. */
> + VMOVU %VEC(0), (%rax)
> + VMOVU %VEC(0), VEC_SIZE(%rax)
> +
> +
> +#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
> + /* If AVX2/SSE2 compute END_REG (rdi) with ALU. */
> + addq %rdx, %END_REG
> +#endif
> +
> + cmpq $(VEC_SIZE * 4), %rdx
> + jbe L(last_2x_vec)
> +
> + /* Store next 2x vec regardless. */
> + VMOVU %VEC(0), (VEC_SIZE * 2)(%rax)
> + VMOVU %VEC(0), (VEC_SIZE * 3)(%rax)
> +
> +
> +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> + /* If LOOP_4X_OFFSET don't readjust LOOP_REG (rdi), just add
> + extra offset to addresses in loop. Used for AVX512 to save space
> + as no way to get (VEC_SIZE * 4) in imm8. */
> +# if LOOP_4X_OFFSET == 0
> + subq $-(VEC_SIZE * 4), %LOOP_REG
> # endif
> -# if VEC_SIZE > 32
> - cmpb $32, %dl
> - jae L(between_32_63)
> + /* Avoid imm32 compare here to save code size. */
> + cmpq %rdi, %rcx
> +#else
> + addq $-(VEC_SIZE * 4), %END_REG
> + cmpq $(VEC_SIZE * 8), %rdx
> +#endif
> + jbe L(last_4x_vec)
> +#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
> + /* Set LOOP_REG (rdx). */
> + leaq (VEC_SIZE * 4)(%rax), %LOOP_REG
> +#endif
> + /* Align dst for loop. */
> + andq $(VEC_SIZE * -2), %LOOP_REG
> + .p2align 4
> +L(loop):
> + VMOVA %VEC(0), LOOP_4X_OFFSET(%LOOP_REG)
> + VMOVA %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%LOOP_REG)
> + VMOVA %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%LOOP_REG)
> + VMOVA %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%LOOP_REG)
> + subq $-(VEC_SIZE * 4), %LOOP_REG
> + cmpq %END_REG, %LOOP_REG
> + jb L(loop)
> + .p2align 4,, MOV_SIZE
> +L(last_4x_vec):
> + VMOVU %VEC(0), LOOP_4X_OFFSET(%END_REG)
> + VMOVU %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%END_REG)
> + VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%END_REG)
> + VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%END_REG)
> +L(return):
> +#if VEC_SIZE > 16
> + ZERO_UPPER_VEC_REGISTERS_RETURN
> +#else
> + ret
> +#endif
> +
> + .p2align 4,, 10
> +#ifndef USE_LESS_VEC_MASK_STORE
> +# if defined USE_MULTIARCH && IS_IN (libc)
> + /* If no USE_LESS_VEC_MASK put L(stosb_local) here. Will be in
> + range for 2-byte jump encoding. */
> +L(stosb_local):
> + movzbl %sil, %eax
> + mov %RDX_LP, %RCX_LP
> + mov %RDI_LP, %RDX_LP
> + rep stosb
> + mov %RDX_LP, %RAX_LP
> + VZEROUPPER_RETURN
> # endif
> -# if VEC_SIZE > 16
> - cmpb $16, %dl
> + /* Define L(less_vec) only if not otherwise defined. */
> + .p2align 4
> +L(less_vec):
> +#endif
> +L(cross_page):
> +#if VEC_SIZE > 32
> + cmpl $32, %edx
> + jae L(between_32_63)
> +#endif
> +#if VEC_SIZE > 16
> + cmpl $16, %edx
> jae L(between_16_31)
> -# endif
> - MOVQ %XMM0, %rcx
> - cmpb $8, %dl
> +#endif
> + MOVQ %XMM0, %rdi
> + cmpl $8, %edx
> jae L(between_8_15)
> - cmpb $4, %dl
> + cmpl $4, %edx
> jae L(between_4_7)
> - cmpb $1, %dl
> + cmpl $1, %edx
> ja L(between_2_3)
> - jb 1f
> - movb %cl, (%rax)
> -1:
> + jb L(return)
> + movb %sil, (%rax)
> VZEROUPPER_RETURN
> -# if VEC_SIZE > 32
> +
> + /* Align small targets only if not doing so would cross a fetch
> + line. */
> +#if VEC_SIZE > 32
> + .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
> /* From 32 to 63. No branch when size == 32. */
> L(between_32_63):
> - VMOVU %YMM0, -32(%rax,%rdx)
> VMOVU %YMM0, (%rax)
> + VMOVU %YMM0, -32(%rax, %rdx)
> VZEROUPPER_RETURN
> -# endif
> -# if VEC_SIZE > 16
> - /* From 16 to 31. No branch when size == 16. */
> +#endif
> +
> +#if VEC_SIZE >= 32
> + .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
> L(between_16_31):
> - VMOVU %XMM0, -16(%rax,%rdx)
> + /* From 16 to 31. No branch when size == 16. */
> VMOVU %XMM0, (%rax)
> + VMOVU %XMM0, -16(%rax, %rdx)
> VZEROUPPER_RETURN
> -# endif
> - /* From 8 to 15. No branch when size == 8. */
> +#endif
> +
> + .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
> L(between_8_15):
> - movq %rcx, -8(%rax,%rdx)
> - movq %rcx, (%rax)
> + /* From 8 to 15. No branch when size == 8. */
> + movq %rdi, (%rax)
> + movq %rdi, -8(%rax, %rdx)
> VZEROUPPER_RETURN
> +
> + .p2align 4,, SMALL_MEMSET_ALIGN(2, RET_SIZE)
> L(between_4_7):
> /* From 4 to 7. No branch when size == 4. */
> - movl %ecx, -4(%rax,%rdx)
> - movl %ecx, (%rax)
> + movl %edi, (%rax)
> + movl %edi, -4(%rax, %rdx)
> VZEROUPPER_RETURN
> +
> + .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
> L(between_2_3):
> /* From 2 to 3. No branch when size == 2. */
> - movw %cx, -2(%rax,%rdx)
> - movw %cx, (%rax)
> + movw %di, (%rax)
> + movb %dil, -1(%rax, %rdx)
> VZEROUPPER_RETURN
> END (MEMSET_SYMBOL (__memset, unaligned_erms))
> --
> 2.25.1
>
>
On Sun, Sep 26, 2021 at 1:54 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> No bug.
>
> Optimization are
>
> 1. change control flow for L(more_2x_vec) to fall through to loop and
> jump for L(less_4x_vec) and L(less_8x_vec). This uses less code
> size and saves jumps for length > 4x VEC_SIZE.
>
> 2. For EVEX/AVX512 move L(less_vec) closer to entry.
>
> 3. Avoid complex address mode for length > 2x VEC_SIZE
>
> 4. Slightly better aligning code for the loop from the perspective of
> code size and uops.
>
> 5. Align targets so they make full use of their fetch block and if
> possible cache line.
>
> 6. Try and reduce total number of icache lines that will need to be
> pulled in for a given length.
>
> 7. Include "local" version of stosb target. For AVX2/EVEX/AVX512
> jumping to the stosb target in the sse2 code section will almost
> certainly be to a new page. The new version does increase code size
> marginally by duplicating the target but should get better iTLB
> behavior as a result.
>
> test-memset, test-wmemset, and test-bzero are all passing.
>
> Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> ---
> Performance numbers attached in reply.
>
> Notes on testing.
>
> I page aligned the start and end of MEMSET so that the bench-memset.c
> code would not be affected by code size changes.
>
> I replaced `_x86_rep_stosb_threshold` with `$2048`. Note this takes
> the exact same code size. I did this because the load of
> `_x86_rep_stosb_threshold` can stall due to 4k aliasing from stores
> during the benchmark. I don't think this is what we are intending to
> benchmark and I believe it adds more confusion/noise to the
> results. (Not to say there is no reason to benchmark that case, just I
> don't think it should be accidental).
>
> Notes on numbers:
>
> There are degregations in the (2x, 4x] VEC_SIZE range. This is
> expected and because the current version gives a fallthrough patch to
> that size range whereas the new version has a jump. Generally this is
> also conditional on the previous ENTRY_ALIGNMENT % 64, with
> ENTRY_ALIGNMENT % 64 == 16 being the best for that size range in the
> current implementation. The new implementation hopefully makes up for
> this with the higher magnitude gains in the (4x, stosb_threshold)
> VEC_SIZE range. Is this a blocker?
>
> For Skylake there are two other degregations.
>
> One where length = 416 with alignment = 416. I have not been able to
> find this root cause of this. All other size/alignment pairs in the
> medium sized range seem to perform better. Does anyone have an
> explination for this or think its a blocker?
>
> The other is conditionally on length in [1x, 2x] VEC_SIZE. I believe
> this is related to reordering the two overlapping stores. The previous
> version had complex address mode first. Its possible that the simple
> address mode is taking p23 AGU stalling the complex address
> calculation for the second store. Having the complex address mode
> first prevents this. This only appears to be n issue for the first set
> of tests (c=-65) and only appears to sometimes matter. My general
> feeling is that if possible ordering for sequantial strided memory
> access makes the most sense hence the reordering. Does anyone think it
> should keep the original order?
>
> Other than those 1/3 cases the new version wins out in all other cases
> against all prior alignments.
>
> sysdeps/x86_64/memset.S | 10 +-
> .../multiarch/memset-avx2-unaligned-erms.S | 10 +-
> .../multiarch/memset-avx512-unaligned-erms.S | 11 +-
> .../multiarch/memset-evex-unaligned-erms.S | 11 +-
> .../multiarch/memset-vec-unaligned-erms.S | 285 ++++++++++++------
> 5 files changed, 232 insertions(+), 95 deletions(-)
>
> diff --git a/sysdeps/x86_64/memset.S b/sysdeps/x86_64/memset.S
> index 7d4a327eba..0137eba4cd 100644
> --- a/sysdeps/x86_64/memset.S
> +++ b/sysdeps/x86_64/memset.S
> @@ -18,13 +18,15 @@
> <https://www.gnu.org/licenses/>. */
>
> #include <sysdep.h>
> +#define USE_WITH_SSE2 1
>
> #define VEC_SIZE 16
> +#define MOV_SIZE 3
> +#define RET_SIZE 1
> +
> #define VEC(i) xmm##i
> -/* Don't use movups and movaps since it will get larger nop paddings for
> - alignment. */
> -#define VMOVU movdqu
> -#define VMOVA movdqa
> +#define VMOVU movups
> +#define VMOVA movaps
>
> #define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> movd d, %xmm0; \
> diff --git a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> index ae0860f36a..1af668af0a 100644
> --- a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> @@ -1,8 +1,14 @@
> #if IS_IN (libc)
> +# define USE_WITH_AVX2 1
> +
> # define VEC_SIZE 32
> +# define MOV_SIZE 4
> +# define RET_SIZE 4
> +
> # define VEC(i) ymm##i
> -# define VMOVU vmovdqu
> -# define VMOVA vmovdqa
> +
> +# define VMOVU vmovdqu
> +# define VMOVA vmovdqa
>
> # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> vmovd d, %xmm0; \
> diff --git a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> index 8ad842fc2f..5937a974bf 100644
> --- a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> @@ -1,11 +1,18 @@
> #if IS_IN (libc)
> +# define USE_WITH_AVX512 1
> +
> # define VEC_SIZE 64
> +# define MOV_SIZE 6
> +# define RET_SIZE 1
> +
> # define XMM0 xmm16
> # define YMM0 ymm16
> # define VEC0 zmm16
> # define VEC(i) VEC##i
> -# define VMOVU vmovdqu64
> -# define VMOVA vmovdqa64
> +
> +# define VMOVU vmovdqu64
> +# define VMOVA vmovdqa64
> +
> # define VZEROUPPER
>
> # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> diff --git a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> index 640f092903..64b09e77cc 100644
> --- a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> @@ -1,11 +1,18 @@
> #if IS_IN (libc)
> +# define USE_WITH_EVEX 1
> +
> # define VEC_SIZE 32
> +# define MOV_SIZE 6
> +# define RET_SIZE 1
> +
> # define XMM0 xmm16
> # define YMM0 ymm16
> # define VEC0 ymm16
> # define VEC(i) VEC##i
> -# define VMOVU vmovdqu64
> -# define VMOVA vmovdqa64
> +
> +# define VMOVU vmovdqu64
> +# define VMOVA vmovdqa64
> +
> # define VZEROUPPER
>
> # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> index ff196844a0..e723413a66 100644
> --- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> +++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> @@ -63,8 +63,27 @@
> # endif
> #endif
>
> +#if VEC_SIZE == 64
> +# define LOOP_4X_OFFSET (VEC_SIZE * 4)
> +#else
> +# define LOOP_4X_OFFSET (0)
> +#endif
> +
> +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> +# define END_REG rcx
> +# define LOOP_REG rdi
> +#else
> +# define END_REG rdi
> +# define LOOP_REG rdx
> +#endif
> +
> #define PAGE_SIZE 4096
>
> +/* Macro to calculate size of small memset block for aligning
> + purposes. */
> +#define SMALL_MEMSET_ALIGN(mov_sz, ret_sz) (2 * (mov_sz) + (ret_sz) + 1)
> +
> +
> #ifndef SECTION
> # error SECTION is not defined!
> #endif
> @@ -74,6 +93,7 @@
> ENTRY (__bzero)
> mov %RDI_LP, %RAX_LP /* Set return value. */
> mov %RSI_LP, %RDX_LP /* Set n. */
> + xorl %esi, %esi
> pxor %XMM0, %XMM0
> jmp L(entry_from_bzero)
> END (__bzero)
> @@ -158,7 +178,7 @@ ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
> END_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
> # endif
>
> -ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
> +ENTRY_P2ALIGN (MEMSET_SYMBOL (__memset, unaligned_erms), 6)
> MEMSET_VDUP_TO_VEC0_AND_SET_RETURN (%esi, %rdi)
> # ifdef __ILP32__
> /* Clear the upper 32 bits. */
> @@ -168,75 +188,43 @@ ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
> jb L(less_vec)
> cmp $(VEC_SIZE * 2), %RDX_LP
> ja L(stosb_more_2x_vec)
> - /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE. */
> - VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
> - VMOVU %VEC(0), (%rdi)
> + /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE.
> + */
> + VMOVU %VEC(0), (%rax)
> + VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
> VZEROUPPER_RETURN
> -
> - .p2align 4
> -L(stosb_more_2x_vec):
> - cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
> - ja L(stosb)
> -#else
> - .p2align 4
> #endif
> -L(more_2x_vec):
> - /* Stores to first 2x VEC before cmp as any path forward will
> - require it. */
> - VMOVU %VEC(0), (%rdi)
> - VMOVU %VEC(0), VEC_SIZE(%rdi)
> - cmpq $(VEC_SIZE * 4), %rdx
> - ja L(loop_start)
> - VMOVU %VEC(0), -(VEC_SIZE * 2)(%rdi,%rdx)
> - VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
> -L(return):
> -#if VEC_SIZE > 16
> - ZERO_UPPER_VEC_REGISTERS_RETURN
> +
> + .p2align 4,, 10
> +L(last_2x_vec):
> +#ifdef USE_LESS_VEC_MASK_STORE
> + VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%rcx)
> + VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%rcx)
> #else
> - ret
> + VMOVU %VEC(0), (VEC_SIZE * -2)(%rdi)
> + VMOVU %VEC(0), (VEC_SIZE * -1)(%rdi)
> #endif
> + VZEROUPPER_RETURN
>
> -L(loop_start):
> - VMOVU %VEC(0), (VEC_SIZE * 2)(%rdi)
> - VMOVU %VEC(0), (VEC_SIZE * 3)(%rdi)
> - cmpq $(VEC_SIZE * 8), %rdx
> - jbe L(loop_end)
> - andq $-(VEC_SIZE * 2), %rdi
> - subq $-(VEC_SIZE * 4), %rdi
> - leaq -(VEC_SIZE * 4)(%rax, %rdx), %rcx
> - .p2align 4
> -L(loop):
> - VMOVA %VEC(0), (%rdi)
> - VMOVA %VEC(0), VEC_SIZE(%rdi)
> - VMOVA %VEC(0), (VEC_SIZE * 2)(%rdi)
> - VMOVA %VEC(0), (VEC_SIZE * 3)(%rdi)
> - subq $-(VEC_SIZE * 4), %rdi
> - cmpq %rcx, %rdi
> - jb L(loop)
> -L(loop_end):
> - /* NB: rax is set as ptr in MEMSET_VDUP_TO_VEC0_AND_SET_RETURN.
> - rdx as length is also unchanged. */
> - VMOVU %VEC(0), -(VEC_SIZE * 4)(%rax, %rdx)
> - VMOVU %VEC(0), -(VEC_SIZE * 3)(%rax, %rdx)
> - VMOVU %VEC(0), -(VEC_SIZE * 2)(%rax, %rdx)
> - VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
> - VZEROUPPER_SHORT_RETURN
> -
> - .p2align 4
> + /* If have AVX512 mask instructions put L(less_vec) close to
> + entry as it doesn't take much space and is likely a hot target.
> + */
> +#ifdef USE_LESS_VEC_MASK_STORE
> + .p2align 4,, 10
> L(less_vec):
> /* Less than 1 VEC. */
> # if VEC_SIZE != 16 && VEC_SIZE != 32 && VEC_SIZE != 64
> # error Unsupported VEC_SIZE!
> # endif
> -# ifdef USE_LESS_VEC_MASK_STORE
> /* Clear high bits from edi. Only keeping bits relevant to page
> cross check. Note that we are using rax which is set in
> - MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out.
> - */
> + MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out. */
> andl $(PAGE_SIZE - 1), %edi
> - /* Check if VEC_SIZE store cross page. Mask stores suffer serious
> - performance degradation when it has to fault supress. */
> + /* Check if VEC_SIZE store cross page. Mask stores suffer
> + serious performance degradation when it has to fault supress.
> + */
> cmpl $(PAGE_SIZE - VEC_SIZE), %edi
> + /* This is generally considered a cold target. */
> ja L(cross_page)
> # if VEC_SIZE > 32
> movq $-1, %rcx
> @@ -247,58 +235,185 @@ L(less_vec):
> bzhil %edx, %ecx, %ecx
> kmovd %ecx, %k1
> # endif
> - vmovdqu8 %VEC(0), (%rax) {%k1}
> + vmovdqu8 %VEC(0), (%rax){%k1}
> VZEROUPPER_RETURN
>
> +# if defined USE_MULTIARCH && IS_IN (libc)
> + /* Include L(stosb_local) here if including L(less_vec) between
> + L(stosb_more_2x_vec) and ENTRY. This is to cache align the
> + L(stosb_more_2x_vec) target. */
> + .p2align 4,, 10
> +L(stosb_local):
> + movzbl %sil, %eax
> + mov %RDX_LP, %RCX_LP
> + mov %RDI_LP, %RDX_LP
> + rep stosb
> + mov %RDX_LP, %RAX_LP
> + VZEROUPPER_RETURN
> +# endif
> +#endif
> +
> +#if defined USE_MULTIARCH && IS_IN (libc)
> .p2align 4
> -L(cross_page):
> +L(stosb_more_2x_vec):
> + cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
> + ja L(stosb_local)
> +#endif
> + /* Fallthrough goes to L(loop_4x_vec). Tests for memset (2x, 4x]
> + and (4x, 8x] jump to target. */
> +L(more_2x_vec):
> +
> + /* Two different methods of setting up pointers / compare. The
> + two methods are based on the fact that EVEX/AVX512 mov
> + instructions take more bytes then AVX2/SSE2 mov instructions. As
> + well that EVEX/AVX512 machines also have fast LEA_BID. Both
> + setup and END_REG to avoid complex address mode. For EVEX/AVX512
> + this saves code size and keeps a few targets in one fetch block.
> + For AVX2/SSE2 this helps prevent AGU bottlenecks. */
> +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> + /* If EVEX/AVX512 compute END_REG - (VEC_SIZE * 4 +
> + LOOP_4X_OFFSET) with LEA_BID. */
> +
> + /* END_REG is rcx for EVEX/AVX512. */
> + leaq -(VEC_SIZE * 4 + LOOP_4X_OFFSET)(%rdi, %rdx), %END_REG
> +#endif
> +
> + /* Stores to first 2x VEC before cmp as any path forward will
> + require it. */
> + VMOVU %VEC(0), (%rax)
> + VMOVU %VEC(0), VEC_SIZE(%rax)
> +
> +
> +#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
> + /* If AVX2/SSE2 compute END_REG (rdi) with ALU. */
> + addq %rdx, %END_REG
> +#endif
> +
> + cmpq $(VEC_SIZE * 4), %rdx
> + jbe L(last_2x_vec)
> +
> + /* Store next 2x vec regardless. */
> + VMOVU %VEC(0), (VEC_SIZE * 2)(%rax)
> + VMOVU %VEC(0), (VEC_SIZE * 3)(%rax)
> +
> +
> +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> + /* If LOOP_4X_OFFSET don't readjust LOOP_REG (rdi), just add
> + extra offset to addresses in loop. Used for AVX512 to save space
> + as no way to get (VEC_SIZE * 4) in imm8. */
> +# if LOOP_4X_OFFSET == 0
> + subq $-(VEC_SIZE * 4), %LOOP_REG
> # endif
> -# if VEC_SIZE > 32
> - cmpb $32, %dl
> - jae L(between_32_63)
> + /* Avoid imm32 compare here to save code size. */
> + cmpq %rdi, %rcx
> +#else
> + addq $-(VEC_SIZE * 4), %END_REG
> + cmpq $(VEC_SIZE * 8), %rdx
> +#endif
> + jbe L(last_4x_vec)
> +#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
> + /* Set LOOP_REG (rdx). */
> + leaq (VEC_SIZE * 4)(%rax), %LOOP_REG
> +#endif
> + /* Align dst for loop. */
> + andq $(VEC_SIZE * -2), %LOOP_REG
> + .p2align 4
> +L(loop):
> + VMOVA %VEC(0), LOOP_4X_OFFSET(%LOOP_REG)
> + VMOVA %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%LOOP_REG)
> + VMOVA %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%LOOP_REG)
> + VMOVA %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%LOOP_REG)
> + subq $-(VEC_SIZE * 4), %LOOP_REG
> + cmpq %END_REG, %LOOP_REG
> + jb L(loop)
> + .p2align 4,, MOV_SIZE
> +L(last_4x_vec):
> + VMOVU %VEC(0), LOOP_4X_OFFSET(%END_REG)
> + VMOVU %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%END_REG)
> + VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%END_REG)
> + VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%END_REG)
> +L(return):
> +#if VEC_SIZE > 16
> + ZERO_UPPER_VEC_REGISTERS_RETURN
> +#else
> + ret
> +#endif
> +
> + .p2align 4,, 10
> +#ifndef USE_LESS_VEC_MASK_STORE
> +# if defined USE_MULTIARCH && IS_IN (libc)
> + /* If no USE_LESS_VEC_MASK put L(stosb_local) here. Will be in
> + range for 2-byte jump encoding. */
> +L(stosb_local):
> + movzbl %sil, %eax
> + mov %RDX_LP, %RCX_LP
> + mov %RDI_LP, %RDX_LP
> + rep stosb
> + mov %RDX_LP, %RAX_LP
> + VZEROUPPER_RETURN
> # endif
> -# if VEC_SIZE > 16
> - cmpb $16, %dl
> + /* Define L(less_vec) only if not otherwise defined. */
> + .p2align 4
> +L(less_vec):
> +#endif
> +L(cross_page):
> +#if VEC_SIZE > 32
> + cmpl $32, %edx
> + jae L(between_32_63)
> +#endif
> +#if VEC_SIZE > 16
> + cmpl $16, %edx
> jae L(between_16_31)
> -# endif
> - MOVQ %XMM0, %rcx
> - cmpb $8, %dl
> +#endif
> + MOVQ %XMM0, %rdi
> + cmpl $8, %edx
> jae L(between_8_15)
> - cmpb $4, %dl
> + cmpl $4, %edx
> jae L(between_4_7)
> - cmpb $1, %dl
> + cmpl $1, %edx
> ja L(between_2_3)
> - jb 1f
> - movb %cl, (%rax)
> -1:
> + jb L(return)
> + movb %sil, (%rax)
> VZEROUPPER_RETURN
> -# if VEC_SIZE > 32
> +
> + /* Align small targets only if not doing so would cross a fetch
> + line. */
> +#if VEC_SIZE > 32
> + .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
> /* From 32 to 63. No branch when size == 32. */
> L(between_32_63):
> - VMOVU %YMM0, -32(%rax,%rdx)
> VMOVU %YMM0, (%rax)
> + VMOVU %YMM0, -32(%rax, %rdx)
> VZEROUPPER_RETURN
> -# endif
> -# if VEC_SIZE > 16
> - /* From 16 to 31. No branch when size == 16. */
> +#endif
> +
> +#if VEC_SIZE >= 32
> + .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
> L(between_16_31):
> - VMOVU %XMM0, -16(%rax,%rdx)
> + /* From 16 to 31. No branch when size == 16. */
> VMOVU %XMM0, (%rax)
> + VMOVU %XMM0, -16(%rax, %rdx)
> VZEROUPPER_RETURN
> -# endif
> - /* From 8 to 15. No branch when size == 8. */
> +#endif
> +
> + .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
> L(between_8_15):
> - movq %rcx, -8(%rax,%rdx)
> - movq %rcx, (%rax)
> + /* From 8 to 15. No branch when size == 8. */
> + movq %rdi, (%rax)
> + movq %rdi, -8(%rax, %rdx)
> VZEROUPPER_RETURN
> +
> + .p2align 4,, SMALL_MEMSET_ALIGN(2, RET_SIZE)
> L(between_4_7):
> /* From 4 to 7. No branch when size == 4. */
> - movl %ecx, -4(%rax,%rdx)
> - movl %ecx, (%rax)
> + movl %edi, (%rax)
> + movl %edi, -4(%rax, %rdx)
> VZEROUPPER_RETURN
> +
> + .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
> L(between_2_3):
> /* From 2 to 3. No branch when size == 2. */
> - movw %cx, -2(%rax,%rdx)
> - movw %cx, (%rax)
> + movw %di, (%rax)
> + movb %dil, -1(%rax, %rdx)
> VZEROUPPER_RETURN
> END (MEMSET_SYMBOL (__memset, unaligned_erms))
> --
> 2.25.1
>
LGTM.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Thanks.
On Tue, Oct 12, 2021 at 10:24 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Sun, Sep 26, 2021 at 1:54 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > No bug.
> >
> > Optimization are
> >
> > 1. change control flow for L(more_2x_vec) to fall through to loop and
> > jump for L(less_4x_vec) and L(less_8x_vec). This uses less code
> > size and saves jumps for length > 4x VEC_SIZE.
> >
> > 2. For EVEX/AVX512 move L(less_vec) closer to entry.
> >
> > 3. Avoid complex address mode for length > 2x VEC_SIZE
> >
> > 4. Slightly better aligning code for the loop from the perspective of
> > code size and uops.
> >
> > 5. Align targets so they make full use of their fetch block and if
> > possible cache line.
> >
> > 6. Try and reduce total number of icache lines that will need to be
> > pulled in for a given length.
> >
> > 7. Include "local" version of stosb target. For AVX2/EVEX/AVX512
> > jumping to the stosb target in the sse2 code section will almost
> > certainly be to a new page. The new version does increase code size
> > marginally by duplicating the target but should get better iTLB
> > behavior as a result.
> >
> > test-memset, test-wmemset, and test-bzero are all passing.
> >
> > Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> > ---
> > Performance numbers attached in reply.
> >
> > Notes on testing.
> >
> > I page aligned the start and end of MEMSET so that the bench-memset.c
> > code would not be affected by code size changes.
> >
> > I replaced `_x86_rep_stosb_threshold` with `$2048`. Note this takes
> > the exact same code size. I did this because the load of
> > `_x86_rep_stosb_threshold` can stall due to 4k aliasing from stores
> > during the benchmark. I don't think this is what we are intending to
> > benchmark and I believe it adds more confusion/noise to the
> > results. (Not to say there is no reason to benchmark that case, just I
> > don't think it should be accidental).
> >
> > Notes on numbers:
> >
> > There are degregations in the (2x, 4x] VEC_SIZE range. This is
> > expected and because the current version gives a fallthrough patch to
> > that size range whereas the new version has a jump. Generally this is
> > also conditional on the previous ENTRY_ALIGNMENT % 64, with
> > ENTRY_ALIGNMENT % 64 == 16 being the best for that size range in the
> > current implementation. The new implementation hopefully makes up for
> > this with the higher magnitude gains in the (4x, stosb_threshold)
> > VEC_SIZE range. Is this a blocker?
> >
> > For Skylake there are two other degregations.
> >
> > One where length = 416 with alignment = 416. I have not been able to
> > find this root cause of this. All other size/alignment pairs in the
> > medium sized range seem to perform better. Does anyone have an
> > explination for this or think its a blocker?
> >
> > The other is conditionally on length in [1x, 2x] VEC_SIZE. I believe
> > this is related to reordering the two overlapping stores. The previous
> > version had complex address mode first. Its possible that the simple
> > address mode is taking p23 AGU stalling the complex address
> > calculation for the second store. Having the complex address mode
> > first prevents this. This only appears to be n issue for the first set
> > of tests (c=-65) and only appears to sometimes matter. My general
> > feeling is that if possible ordering for sequantial strided memory
> > access makes the most sense hence the reordering. Does anyone think it
> > should keep the original order?
> >
> > Other than those 1/3 cases the new version wins out in all other cases
> > against all prior alignments.
> >
> > sysdeps/x86_64/memset.S | 10 +-
> > .../multiarch/memset-avx2-unaligned-erms.S | 10 +-
> > .../multiarch/memset-avx512-unaligned-erms.S | 11 +-
> > .../multiarch/memset-evex-unaligned-erms.S | 11 +-
> > .../multiarch/memset-vec-unaligned-erms.S | 285 ++++++++++++------
> > 5 files changed, 232 insertions(+), 95 deletions(-)
> >
> > diff --git a/sysdeps/x86_64/memset.S b/sysdeps/x86_64/memset.S
> > index 7d4a327eba..0137eba4cd 100644
> > --- a/sysdeps/x86_64/memset.S
> > +++ b/sysdeps/x86_64/memset.S
> > @@ -18,13 +18,15 @@
> > <https://www.gnu.org/licenses/>. */
> >
> > #include <sysdep.h>
> > +#define USE_WITH_SSE2 1
> >
> > #define VEC_SIZE 16
> > +#define MOV_SIZE 3
> > +#define RET_SIZE 1
> > +
> > #define VEC(i) xmm##i
> > -/* Don't use movups and movaps since it will get larger nop paddings for
> > - alignment. */
> > -#define VMOVU movdqu
> > -#define VMOVA movdqa
> > +#define VMOVU movups
> > +#define VMOVA movaps
> >
> > #define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> > movd d, %xmm0; \
> > diff --git a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> > index ae0860f36a..1af668af0a 100644
> > --- a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> > +++ b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> > @@ -1,8 +1,14 @@
> > #if IS_IN (libc)
> > +# define USE_WITH_AVX2 1
> > +
> > # define VEC_SIZE 32
> > +# define MOV_SIZE 4
> > +# define RET_SIZE 4
> > +
> > # define VEC(i) ymm##i
> > -# define VMOVU vmovdqu
> > -# define VMOVA vmovdqa
> > +
> > +# define VMOVU vmovdqu
> > +# define VMOVA vmovdqa
> >
> > # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> > vmovd d, %xmm0; \
> > diff --git a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> > index 8ad842fc2f..5937a974bf 100644
> > --- a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> > +++ b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> > @@ -1,11 +1,18 @@
> > #if IS_IN (libc)
> > +# define USE_WITH_AVX512 1
> > +
> > # define VEC_SIZE 64
> > +# define MOV_SIZE 6
> > +# define RET_SIZE 1
> > +
> > # define XMM0 xmm16
> > # define YMM0 ymm16
> > # define VEC0 zmm16
> > # define VEC(i) VEC##i
> > -# define VMOVU vmovdqu64
> > -# define VMOVA vmovdqa64
> > +
> > +# define VMOVU vmovdqu64
> > +# define VMOVA vmovdqa64
> > +
> > # define VZEROUPPER
> >
> > # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> > diff --git a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> > index 640f092903..64b09e77cc 100644
> > --- a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> > +++ b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> > @@ -1,11 +1,18 @@
> > #if IS_IN (libc)
> > +# define USE_WITH_EVEX 1
> > +
> > # define VEC_SIZE 32
> > +# define MOV_SIZE 6
> > +# define RET_SIZE 1
> > +
> > # define XMM0 xmm16
> > # define YMM0 ymm16
> > # define VEC0 ymm16
> > # define VEC(i) VEC##i
> > -# define VMOVU vmovdqu64
> > -# define VMOVA vmovdqa64
> > +
> > +# define VMOVU vmovdqu64
> > +# define VMOVA vmovdqa64
> > +
> > # define VZEROUPPER
> >
> > # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> > diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > index ff196844a0..e723413a66 100644
> > --- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > +++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > @@ -63,8 +63,27 @@
> > # endif
> > #endif
> >
> > +#if VEC_SIZE == 64
> > +# define LOOP_4X_OFFSET (VEC_SIZE * 4)
> > +#else
> > +# define LOOP_4X_OFFSET (0)
> > +#endif
> > +
> > +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> > +# define END_REG rcx
> > +# define LOOP_REG rdi
> > +#else
> > +# define END_REG rdi
> > +# define LOOP_REG rdx
> > +#endif
> > +
> > #define PAGE_SIZE 4096
> >
> > +/* Macro to calculate size of small memset block for aligning
> > + purposes. */
> > +#define SMALL_MEMSET_ALIGN(mov_sz, ret_sz) (2 * (mov_sz) + (ret_sz) + 1)
> > +
> > +
> > #ifndef SECTION
> > # error SECTION is not defined!
> > #endif
> > @@ -74,6 +93,7 @@
> > ENTRY (__bzero)
> > mov %RDI_LP, %RAX_LP /* Set return value. */
> > mov %RSI_LP, %RDX_LP /* Set n. */
> > + xorl %esi, %esi
> > pxor %XMM0, %XMM0
> > jmp L(entry_from_bzero)
> > END (__bzero)
> > @@ -158,7 +178,7 @@ ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
> > END_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
> > # endif
> >
> > -ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
> > +ENTRY_P2ALIGN (MEMSET_SYMBOL (__memset, unaligned_erms), 6)
> > MEMSET_VDUP_TO_VEC0_AND_SET_RETURN (%esi, %rdi)
> > # ifdef __ILP32__
> > /* Clear the upper 32 bits. */
> > @@ -168,75 +188,43 @@ ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
> > jb L(less_vec)
> > cmp $(VEC_SIZE * 2), %RDX_LP
> > ja L(stosb_more_2x_vec)
> > - /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE. */
> > - VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
> > - VMOVU %VEC(0), (%rdi)
> > + /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE.
> > + */
> > + VMOVU %VEC(0), (%rax)
> > + VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
> > VZEROUPPER_RETURN
> > -
> > - .p2align 4
> > -L(stosb_more_2x_vec):
> > - cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
> > - ja L(stosb)
> > -#else
> > - .p2align 4
> > #endif
> > -L(more_2x_vec):
> > - /* Stores to first 2x VEC before cmp as any path forward will
> > - require it. */
> > - VMOVU %VEC(0), (%rdi)
> > - VMOVU %VEC(0), VEC_SIZE(%rdi)
> > - cmpq $(VEC_SIZE * 4), %rdx
> > - ja L(loop_start)
> > - VMOVU %VEC(0), -(VEC_SIZE * 2)(%rdi,%rdx)
> > - VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
> > -L(return):
> > -#if VEC_SIZE > 16
> > - ZERO_UPPER_VEC_REGISTERS_RETURN
> > +
> > + .p2align 4,, 10
> > +L(last_2x_vec):
> > +#ifdef USE_LESS_VEC_MASK_STORE
> > + VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%rcx)
> > + VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%rcx)
> > #else
> > - ret
> > + VMOVU %VEC(0), (VEC_SIZE * -2)(%rdi)
> > + VMOVU %VEC(0), (VEC_SIZE * -1)(%rdi)
> > #endif
> > + VZEROUPPER_RETURN
> >
> > -L(loop_start):
> > - VMOVU %VEC(0), (VEC_SIZE * 2)(%rdi)
> > - VMOVU %VEC(0), (VEC_SIZE * 3)(%rdi)
> > - cmpq $(VEC_SIZE * 8), %rdx
> > - jbe L(loop_end)
> > - andq $-(VEC_SIZE * 2), %rdi
> > - subq $-(VEC_SIZE * 4), %rdi
> > - leaq -(VEC_SIZE * 4)(%rax, %rdx), %rcx
> > - .p2align 4
> > -L(loop):
> > - VMOVA %VEC(0), (%rdi)
> > - VMOVA %VEC(0), VEC_SIZE(%rdi)
> > - VMOVA %VEC(0), (VEC_SIZE * 2)(%rdi)
> > - VMOVA %VEC(0), (VEC_SIZE * 3)(%rdi)
> > - subq $-(VEC_SIZE * 4), %rdi
> > - cmpq %rcx, %rdi
> > - jb L(loop)
> > -L(loop_end):
> > - /* NB: rax is set as ptr in MEMSET_VDUP_TO_VEC0_AND_SET_RETURN.
> > - rdx as length is also unchanged. */
> > - VMOVU %VEC(0), -(VEC_SIZE * 4)(%rax, %rdx)
> > - VMOVU %VEC(0), -(VEC_SIZE * 3)(%rax, %rdx)
> > - VMOVU %VEC(0), -(VEC_SIZE * 2)(%rax, %rdx)
> > - VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
> > - VZEROUPPER_SHORT_RETURN
> > -
> > - .p2align 4
> > + /* If have AVX512 mask instructions put L(less_vec) close to
> > + entry as it doesn't take much space and is likely a hot target.
> > + */
> > +#ifdef USE_LESS_VEC_MASK_STORE
> > + .p2align 4,, 10
> > L(less_vec):
> > /* Less than 1 VEC. */
> > # if VEC_SIZE != 16 && VEC_SIZE != 32 && VEC_SIZE != 64
> > # error Unsupported VEC_SIZE!
> > # endif
> > -# ifdef USE_LESS_VEC_MASK_STORE
> > /* Clear high bits from edi. Only keeping bits relevant to page
> > cross check. Note that we are using rax which is set in
> > - MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out.
> > - */
> > + MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out. */
> > andl $(PAGE_SIZE - 1), %edi
> > - /* Check if VEC_SIZE store cross page. Mask stores suffer serious
> > - performance degradation when it has to fault supress. */
> > + /* Check if VEC_SIZE store cross page. Mask stores suffer
> > + serious performance degradation when it has to fault supress.
> > + */
> > cmpl $(PAGE_SIZE - VEC_SIZE), %edi
> > + /* This is generally considered a cold target. */
> > ja L(cross_page)
> > # if VEC_SIZE > 32
> > movq $-1, %rcx
> > @@ -247,58 +235,185 @@ L(less_vec):
> > bzhil %edx, %ecx, %ecx
> > kmovd %ecx, %k1
> > # endif
> > - vmovdqu8 %VEC(0), (%rax) {%k1}
> > + vmovdqu8 %VEC(0), (%rax){%k1}
> > VZEROUPPER_RETURN
> >
> > +# if defined USE_MULTIARCH && IS_IN (libc)
> > + /* Include L(stosb_local) here if including L(less_vec) between
> > + L(stosb_more_2x_vec) and ENTRY. This is to cache align the
> > + L(stosb_more_2x_vec) target. */
> > + .p2align 4,, 10
> > +L(stosb_local):
> > + movzbl %sil, %eax
> > + mov %RDX_LP, %RCX_LP
> > + mov %RDI_LP, %RDX_LP
> > + rep stosb
> > + mov %RDX_LP, %RAX_LP
> > + VZEROUPPER_RETURN
> > +# endif
> > +#endif
> > +
> > +#if defined USE_MULTIARCH && IS_IN (libc)
> > .p2align 4
> > -L(cross_page):
> > +L(stosb_more_2x_vec):
> > + cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
> > + ja L(stosb_local)
> > +#endif
> > + /* Fallthrough goes to L(loop_4x_vec). Tests for memset (2x, 4x]
> > + and (4x, 8x] jump to target. */
> > +L(more_2x_vec):
> > +
> > + /* Two different methods of setting up pointers / compare. The
> > + two methods are based on the fact that EVEX/AVX512 mov
> > + instructions take more bytes then AVX2/SSE2 mov instructions. As
> > + well that EVEX/AVX512 machines also have fast LEA_BID. Both
> > + setup and END_REG to avoid complex address mode. For EVEX/AVX512
> > + this saves code size and keeps a few targets in one fetch block.
> > + For AVX2/SSE2 this helps prevent AGU bottlenecks. */
> > +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> > + /* If EVEX/AVX512 compute END_REG - (VEC_SIZE * 4 +
> > + LOOP_4X_OFFSET) with LEA_BID. */
> > +
> > + /* END_REG is rcx for EVEX/AVX512. */
> > + leaq -(VEC_SIZE * 4 + LOOP_4X_OFFSET)(%rdi, %rdx), %END_REG
> > +#endif
> > +
> > + /* Stores to first 2x VEC before cmp as any path forward will
> > + require it. */
> > + VMOVU %VEC(0), (%rax)
> > + VMOVU %VEC(0), VEC_SIZE(%rax)
> > +
> > +
> > +#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
> > + /* If AVX2/SSE2 compute END_REG (rdi) with ALU. */
> > + addq %rdx, %END_REG
> > +#endif
> > +
> > + cmpq $(VEC_SIZE * 4), %rdx
> > + jbe L(last_2x_vec)
> > +
> > + /* Store next 2x vec regardless. */
> > + VMOVU %VEC(0), (VEC_SIZE * 2)(%rax)
> > + VMOVU %VEC(0), (VEC_SIZE * 3)(%rax)
> > +
> > +
> > +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> > + /* If LOOP_4X_OFFSET don't readjust LOOP_REG (rdi), just add
> > + extra offset to addresses in loop. Used for AVX512 to save space
> > + as no way to get (VEC_SIZE * 4) in imm8. */
> > +# if LOOP_4X_OFFSET == 0
> > + subq $-(VEC_SIZE * 4), %LOOP_REG
> > # endif
> > -# if VEC_SIZE > 32
> > - cmpb $32, %dl
> > - jae L(between_32_63)
> > + /* Avoid imm32 compare here to save code size. */
> > + cmpq %rdi, %rcx
> > +#else
> > + addq $-(VEC_SIZE * 4), %END_REG
> > + cmpq $(VEC_SIZE * 8), %rdx
> > +#endif
> > + jbe L(last_4x_vec)
> > +#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
> > + /* Set LOOP_REG (rdx). */
> > + leaq (VEC_SIZE * 4)(%rax), %LOOP_REG
> > +#endif
> > + /* Align dst for loop. */
> > + andq $(VEC_SIZE * -2), %LOOP_REG
> > + .p2align 4
> > +L(loop):
> > + VMOVA %VEC(0), LOOP_4X_OFFSET(%LOOP_REG)
> > + VMOVA %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%LOOP_REG)
> > + VMOVA %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%LOOP_REG)
> > + VMOVA %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%LOOP_REG)
> > + subq $-(VEC_SIZE * 4), %LOOP_REG
> > + cmpq %END_REG, %LOOP_REG
> > + jb L(loop)
> > + .p2align 4,, MOV_SIZE
> > +L(last_4x_vec):
> > + VMOVU %VEC(0), LOOP_4X_OFFSET(%END_REG)
> > + VMOVU %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%END_REG)
> > + VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%END_REG)
> > + VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%END_REG)
> > +L(return):
> > +#if VEC_SIZE > 16
> > + ZERO_UPPER_VEC_REGISTERS_RETURN
> > +#else
> > + ret
> > +#endif
> > +
> > + .p2align 4,, 10
> > +#ifndef USE_LESS_VEC_MASK_STORE
> > +# if defined USE_MULTIARCH && IS_IN (libc)
> > + /* If no USE_LESS_VEC_MASK put L(stosb_local) here. Will be in
> > + range for 2-byte jump encoding. */
> > +L(stosb_local):
> > + movzbl %sil, %eax
> > + mov %RDX_LP, %RCX_LP
> > + mov %RDI_LP, %RDX_LP
> > + rep stosb
> > + mov %RDX_LP, %RAX_LP
> > + VZEROUPPER_RETURN
> > # endif
> > -# if VEC_SIZE > 16
> > - cmpb $16, %dl
> > + /* Define L(less_vec) only if not otherwise defined. */
> > + .p2align 4
> > +L(less_vec):
> > +#endif
> > +L(cross_page):
> > +#if VEC_SIZE > 32
> > + cmpl $32, %edx
> > + jae L(between_32_63)
> > +#endif
> > +#if VEC_SIZE > 16
> > + cmpl $16, %edx
> > jae L(between_16_31)
> > -# endif
> > - MOVQ %XMM0, %rcx
> > - cmpb $8, %dl
> > +#endif
> > + MOVQ %XMM0, %rdi
> > + cmpl $8, %edx
> > jae L(between_8_15)
> > - cmpb $4, %dl
> > + cmpl $4, %edx
> > jae L(between_4_7)
> > - cmpb $1, %dl
> > + cmpl $1, %edx
> > ja L(between_2_3)
> > - jb 1f
> > - movb %cl, (%rax)
> > -1:
> > + jb L(return)
> > + movb %sil, (%rax)
> > VZEROUPPER_RETURN
> > -# if VEC_SIZE > 32
> > +
> > + /* Align small targets only if not doing so would cross a fetch
> > + line. */
> > +#if VEC_SIZE > 32
> > + .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
> > /* From 32 to 63. No branch when size == 32. */
> > L(between_32_63):
> > - VMOVU %YMM0, -32(%rax,%rdx)
> > VMOVU %YMM0, (%rax)
> > + VMOVU %YMM0, -32(%rax, %rdx)
> > VZEROUPPER_RETURN
> > -# endif
> > -# if VEC_SIZE > 16
> > - /* From 16 to 31. No branch when size == 16. */
> > +#endif
> > +
> > +#if VEC_SIZE >= 32
> > + .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
> > L(between_16_31):
> > - VMOVU %XMM0, -16(%rax,%rdx)
> > + /* From 16 to 31. No branch when size == 16. */
> > VMOVU %XMM0, (%rax)
> > + VMOVU %XMM0, -16(%rax, %rdx)
> > VZEROUPPER_RETURN
> > -# endif
> > - /* From 8 to 15. No branch when size == 8. */
> > +#endif
> > +
> > + .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
> > L(between_8_15):
> > - movq %rcx, -8(%rax,%rdx)
> > - movq %rcx, (%rax)
> > + /* From 8 to 15. No branch when size == 8. */
> > + movq %rdi, (%rax)
> > + movq %rdi, -8(%rax, %rdx)
> > VZEROUPPER_RETURN
> > +
> > + .p2align 4,, SMALL_MEMSET_ALIGN(2, RET_SIZE)
> > L(between_4_7):
> > /* From 4 to 7. No branch when size == 4. */
> > - movl %ecx, -4(%rax,%rdx)
> > - movl %ecx, (%rax)
> > + movl %edi, (%rax)
> > + movl %edi, -4(%rax, %rdx)
> > VZEROUPPER_RETURN
> > +
> > + .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
> > L(between_2_3):
> > /* From 2 to 3. No branch when size == 2. */
> > - movw %cx, -2(%rax,%rdx)
> > - movw %cx, (%rax)
> > + movw %di, (%rax)
> > + movb %dil, -1(%rax, %rdx)
> > VZEROUPPER_RETURN
> > END (MEMSET_SYMBOL (__memset, unaligned_erms))
> > --
> > 2.25.1
> >
>
> LGTM.
>
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
>
> Thanks.
>
> --
> H.J.
Thanks! Pushed.
On Tue, Oct 12, 2021 at 12:02 PM Noah Goldstein via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Tue, Oct 12, 2021 at 10:24 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Sun, Sep 26, 2021 at 1:54 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> > >
> > > No bug.
> > >
> > > Optimization are
> > >
> > > 1. change control flow for L(more_2x_vec) to fall through to loop and
> > > jump for L(less_4x_vec) and L(less_8x_vec). This uses less code
> > > size and saves jumps for length > 4x VEC_SIZE.
> > >
> > > 2. For EVEX/AVX512 move L(less_vec) closer to entry.
> > >
> > > 3. Avoid complex address mode for length > 2x VEC_SIZE
> > >
> > > 4. Slightly better aligning code for the loop from the perspective of
> > > code size and uops.
> > >
> > > 5. Align targets so they make full use of their fetch block and if
> > > possible cache line.
> > >
> > > 6. Try and reduce total number of icache lines that will need to be
> > > pulled in for a given length.
> > >
> > > 7. Include "local" version of stosb target. For AVX2/EVEX/AVX512
> > > jumping to the stosb target in the sse2 code section will almost
> > > certainly be to a new page. The new version does increase code size
> > > marginally by duplicating the target but should get better iTLB
> > > behavior as a result.
> > >
> > > test-memset, test-wmemset, and test-bzero are all passing.
> > >
> > > Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> > > ---
> > > Performance numbers attached in reply.
> > >
> > > Notes on testing.
> > >
> > > I page aligned the start and end of MEMSET so that the bench-memset.c
> > > code would not be affected by code size changes.
> > >
> > > I replaced `_x86_rep_stosb_threshold` with `$2048`. Note this takes
> > > the exact same code size. I did this because the load of
> > > `_x86_rep_stosb_threshold` can stall due to 4k aliasing from stores
> > > during the benchmark. I don't think this is what we are intending to
> > > benchmark and I believe it adds more confusion/noise to the
> > > results. (Not to say there is no reason to benchmark that case, just I
> > > don't think it should be accidental).
> > >
> > > Notes on numbers:
> > >
> > > There are degregations in the (2x, 4x] VEC_SIZE range. This is
> > > expected and because the current version gives a fallthrough patch to
> > > that size range whereas the new version has a jump. Generally this is
> > > also conditional on the previous ENTRY_ALIGNMENT % 64, with
> > > ENTRY_ALIGNMENT % 64 == 16 being the best for that size range in the
> > > current implementation. The new implementation hopefully makes up for
> > > this with the higher magnitude gains in the (4x, stosb_threshold)
> > > VEC_SIZE range. Is this a blocker?
> > >
> > > For Skylake there are two other degregations.
> > >
> > > One where length = 416 with alignment = 416. I have not been able to
> > > find this root cause of this. All other size/alignment pairs in the
> > > medium sized range seem to perform better. Does anyone have an
> > > explination for this or think its a blocker?
> > >
> > > The other is conditionally on length in [1x, 2x] VEC_SIZE. I believe
> > > this is related to reordering the two overlapping stores. The previous
> > > version had complex address mode first. Its possible that the simple
> > > address mode is taking p23 AGU stalling the complex address
> > > calculation for the second store. Having the complex address mode
> > > first prevents this. This only appears to be n issue for the first set
> > > of tests (c=-65) and only appears to sometimes matter. My general
> > > feeling is that if possible ordering for sequantial strided memory
> > > access makes the most sense hence the reordering. Does anyone think it
> > > should keep the original order?
> > >
> > > Other than those 1/3 cases the new version wins out in all other cases
> > > against all prior alignments.
> > >
> > > sysdeps/x86_64/memset.S | 10 +-
> > > .../multiarch/memset-avx2-unaligned-erms.S | 10 +-
> > > .../multiarch/memset-avx512-unaligned-erms.S | 11 +-
> > > .../multiarch/memset-evex-unaligned-erms.S | 11 +-
> > > .../multiarch/memset-vec-unaligned-erms.S | 285 ++++++++++++------
> > > 5 files changed, 232 insertions(+), 95 deletions(-)
> > >
> > > diff --git a/sysdeps/x86_64/memset.S b/sysdeps/x86_64/memset.S
> > > index 7d4a327eba..0137eba4cd 100644
> > > --- a/sysdeps/x86_64/memset.S
> > > +++ b/sysdeps/x86_64/memset.S
> > > @@ -18,13 +18,15 @@
> > > <https://www.gnu.org/licenses/>. */
> > >
> > > #include <sysdep.h>
> > > +#define USE_WITH_SSE2 1
> > >
> > > #define VEC_SIZE 16
> > > +#define MOV_SIZE 3
> > > +#define RET_SIZE 1
> > > +
> > > #define VEC(i) xmm##i
> > > -/* Don't use movups and movaps since it will get larger nop paddings for
> > > - alignment. */
> > > -#define VMOVU movdqu
> > > -#define VMOVA movdqa
> > > +#define VMOVU movups
> > > +#define VMOVA movaps
> > >
> > > #define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> > > movd d, %xmm0; \
> > > diff --git a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> > > index ae0860f36a..1af668af0a 100644
> > > --- a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> > > +++ b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
> > > @@ -1,8 +1,14 @@
> > > #if IS_IN (libc)
> > > +# define USE_WITH_AVX2 1
> > > +
> > > # define VEC_SIZE 32
> > > +# define MOV_SIZE 4
> > > +# define RET_SIZE 4
> > > +
> > > # define VEC(i) ymm##i
> > > -# define VMOVU vmovdqu
> > > -# define VMOVA vmovdqa
> > > +
> > > +# define VMOVU vmovdqu
> > > +# define VMOVA vmovdqa
> > >
> > > # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> > > vmovd d, %xmm0; \
> > > diff --git a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> > > index 8ad842fc2f..5937a974bf 100644
> > > --- a/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> > > +++ b/sysdeps/x86_64/multiarch/memset-avx512-unaligned-erms.S
> > > @@ -1,11 +1,18 @@
> > > #if IS_IN (libc)
> > > +# define USE_WITH_AVX512 1
> > > +
> > > # define VEC_SIZE 64
> > > +# define MOV_SIZE 6
> > > +# define RET_SIZE 1
> > > +
> > > # define XMM0 xmm16
> > > # define YMM0 ymm16
> > > # define VEC0 zmm16
> > > # define VEC(i) VEC##i
> > > -# define VMOVU vmovdqu64
> > > -# define VMOVA vmovdqa64
> > > +
> > > +# define VMOVU vmovdqu64
> > > +# define VMOVA vmovdqa64
> > > +
> > > # define VZEROUPPER
> > >
> > > # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> > > diff --git a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> > > index 640f092903..64b09e77cc 100644
> > > --- a/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> > > +++ b/sysdeps/x86_64/multiarch/memset-evex-unaligned-erms.S
> > > @@ -1,11 +1,18 @@
> > > #if IS_IN (libc)
> > > +# define USE_WITH_EVEX 1
> > > +
> > > # define VEC_SIZE 32
> > > +# define MOV_SIZE 6
> > > +# define RET_SIZE 1
> > > +
> > > # define XMM0 xmm16
> > > # define YMM0 ymm16
> > > # define VEC0 ymm16
> > > # define VEC(i) VEC##i
> > > -# define VMOVU vmovdqu64
> > > -# define VMOVA vmovdqa64
> > > +
> > > +# define VMOVU vmovdqu64
> > > +# define VMOVA vmovdqa64
> > > +
> > > # define VZEROUPPER
> > >
> > > # define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
> > > diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > > index ff196844a0..e723413a66 100644
> > > --- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > > +++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
> > > @@ -63,8 +63,27 @@
> > > # endif
> > > #endif
> > >
> > > +#if VEC_SIZE == 64
> > > +# define LOOP_4X_OFFSET (VEC_SIZE * 4)
> > > +#else
> > > +# define LOOP_4X_OFFSET (0)
> > > +#endif
> > > +
> > > +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> > > +# define END_REG rcx
> > > +# define LOOP_REG rdi
> > > +#else
> > > +# define END_REG rdi
> > > +# define LOOP_REG rdx
> > > +#endif
> > > +
> > > #define PAGE_SIZE 4096
> > >
> > > +/* Macro to calculate size of small memset block for aligning
> > > + purposes. */
> > > +#define SMALL_MEMSET_ALIGN(mov_sz, ret_sz) (2 * (mov_sz) + (ret_sz) + 1)
> > > +
> > > +
> > > #ifndef SECTION
> > > # error SECTION is not defined!
> > > #endif
> > > @@ -74,6 +93,7 @@
> > > ENTRY (__bzero)
> > > mov %RDI_LP, %RAX_LP /* Set return value. */
> > > mov %RSI_LP, %RDX_LP /* Set n. */
> > > + xorl %esi, %esi
> > > pxor %XMM0, %XMM0
> > > jmp L(entry_from_bzero)
> > > END (__bzero)
> > > @@ -158,7 +178,7 @@ ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
> > > END_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
> > > # endif
> > >
> > > -ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
> > > +ENTRY_P2ALIGN (MEMSET_SYMBOL (__memset, unaligned_erms), 6)
> > > MEMSET_VDUP_TO_VEC0_AND_SET_RETURN (%esi, %rdi)
> > > # ifdef __ILP32__
> > > /* Clear the upper 32 bits. */
> > > @@ -168,75 +188,43 @@ ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
> > > jb L(less_vec)
> > > cmp $(VEC_SIZE * 2), %RDX_LP
> > > ja L(stosb_more_2x_vec)
> > > - /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE. */
> > > - VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
> > > - VMOVU %VEC(0), (%rdi)
> > > + /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE.
> > > + */
> > > + VMOVU %VEC(0), (%rax)
> > > + VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
> > > VZEROUPPER_RETURN
> > > -
> > > - .p2align 4
> > > -L(stosb_more_2x_vec):
> > > - cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
> > > - ja L(stosb)
> > > -#else
> > > - .p2align 4
> > > #endif
> > > -L(more_2x_vec):
> > > - /* Stores to first 2x VEC before cmp as any path forward will
> > > - require it. */
> > > - VMOVU %VEC(0), (%rdi)
> > > - VMOVU %VEC(0), VEC_SIZE(%rdi)
> > > - cmpq $(VEC_SIZE * 4), %rdx
> > > - ja L(loop_start)
> > > - VMOVU %VEC(0), -(VEC_SIZE * 2)(%rdi,%rdx)
> > > - VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
> > > -L(return):
> > > -#if VEC_SIZE > 16
> > > - ZERO_UPPER_VEC_REGISTERS_RETURN
> > > +
> > > + .p2align 4,, 10
> > > +L(last_2x_vec):
> > > +#ifdef USE_LESS_VEC_MASK_STORE
> > > + VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%rcx)
> > > + VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%rcx)
> > > #else
> > > - ret
> > > + VMOVU %VEC(0), (VEC_SIZE * -2)(%rdi)
> > > + VMOVU %VEC(0), (VEC_SIZE * -1)(%rdi)
> > > #endif
> > > + VZEROUPPER_RETURN
> > >
> > > -L(loop_start):
> > > - VMOVU %VEC(0), (VEC_SIZE * 2)(%rdi)
> > > - VMOVU %VEC(0), (VEC_SIZE * 3)(%rdi)
> > > - cmpq $(VEC_SIZE * 8), %rdx
> > > - jbe L(loop_end)
> > > - andq $-(VEC_SIZE * 2), %rdi
> > > - subq $-(VEC_SIZE * 4), %rdi
> > > - leaq -(VEC_SIZE * 4)(%rax, %rdx), %rcx
> > > - .p2align 4
> > > -L(loop):
> > > - VMOVA %VEC(0), (%rdi)
> > > - VMOVA %VEC(0), VEC_SIZE(%rdi)
> > > - VMOVA %VEC(0), (VEC_SIZE * 2)(%rdi)
> > > - VMOVA %VEC(0), (VEC_SIZE * 3)(%rdi)
> > > - subq $-(VEC_SIZE * 4), %rdi
> > > - cmpq %rcx, %rdi
> > > - jb L(loop)
> > > -L(loop_end):
> > > - /* NB: rax is set as ptr in MEMSET_VDUP_TO_VEC0_AND_SET_RETURN.
> > > - rdx as length is also unchanged. */
> > > - VMOVU %VEC(0), -(VEC_SIZE * 4)(%rax, %rdx)
> > > - VMOVU %VEC(0), -(VEC_SIZE * 3)(%rax, %rdx)
> > > - VMOVU %VEC(0), -(VEC_SIZE * 2)(%rax, %rdx)
> > > - VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
> > > - VZEROUPPER_SHORT_RETURN
> > > -
> > > - .p2align 4
> > > + /* If have AVX512 mask instructions put L(less_vec) close to
> > > + entry as it doesn't take much space and is likely a hot target.
> > > + */
> > > +#ifdef USE_LESS_VEC_MASK_STORE
> > > + .p2align 4,, 10
> > > L(less_vec):
> > > /* Less than 1 VEC. */
> > > # if VEC_SIZE != 16 && VEC_SIZE != 32 && VEC_SIZE != 64
> > > # error Unsupported VEC_SIZE!
> > > # endif
> > > -# ifdef USE_LESS_VEC_MASK_STORE
> > > /* Clear high bits from edi. Only keeping bits relevant to page
> > > cross check. Note that we are using rax which is set in
> > > - MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out.
> > > - */
> > > + MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out. */
> > > andl $(PAGE_SIZE - 1), %edi
> > > - /* Check if VEC_SIZE store cross page. Mask stores suffer serious
> > > - performance degradation when it has to fault supress. */
> > > + /* Check if VEC_SIZE store cross page. Mask stores suffer
> > > + serious performance degradation when it has to fault supress.
> > > + */
> > > cmpl $(PAGE_SIZE - VEC_SIZE), %edi
> > > + /* This is generally considered a cold target. */
> > > ja L(cross_page)
> > > # if VEC_SIZE > 32
> > > movq $-1, %rcx
> > > @@ -247,58 +235,185 @@ L(less_vec):
> > > bzhil %edx, %ecx, %ecx
> > > kmovd %ecx, %k1
> > > # endif
> > > - vmovdqu8 %VEC(0), (%rax) {%k1}
> > > + vmovdqu8 %VEC(0), (%rax){%k1}
> > > VZEROUPPER_RETURN
> > >
> > > +# if defined USE_MULTIARCH && IS_IN (libc)
> > > + /* Include L(stosb_local) here if including L(less_vec) between
> > > + L(stosb_more_2x_vec) and ENTRY. This is to cache align the
> > > + L(stosb_more_2x_vec) target. */
> > > + .p2align 4,, 10
> > > +L(stosb_local):
> > > + movzbl %sil, %eax
> > > + mov %RDX_LP, %RCX_LP
> > > + mov %RDI_LP, %RDX_LP
> > > + rep stosb
> > > + mov %RDX_LP, %RAX_LP
> > > + VZEROUPPER_RETURN
> > > +# endif
> > > +#endif
> > > +
> > > +#if defined USE_MULTIARCH && IS_IN (libc)
> > > .p2align 4
> > > -L(cross_page):
> > > +L(stosb_more_2x_vec):
> > > + cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
> > > + ja L(stosb_local)
> > > +#endif
> > > + /* Fallthrough goes to L(loop_4x_vec). Tests for memset (2x, 4x]
> > > + and (4x, 8x] jump to target. */
> > > +L(more_2x_vec):
> > > +
> > > + /* Two different methods of setting up pointers / compare. The
> > > + two methods are based on the fact that EVEX/AVX512 mov
> > > + instructions take more bytes then AVX2/SSE2 mov instructions. As
> > > + well that EVEX/AVX512 machines also have fast LEA_BID. Both
> > > + setup and END_REG to avoid complex address mode. For EVEX/AVX512
> > > + this saves code size and keeps a few targets in one fetch block.
> > > + For AVX2/SSE2 this helps prevent AGU bottlenecks. */
> > > +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> > > + /* If EVEX/AVX512 compute END_REG - (VEC_SIZE * 4 +
> > > + LOOP_4X_OFFSET) with LEA_BID. */
> > > +
> > > + /* END_REG is rcx for EVEX/AVX512. */
> > > + leaq -(VEC_SIZE * 4 + LOOP_4X_OFFSET)(%rdi, %rdx), %END_REG
> > > +#endif
> > > +
> > > + /* Stores to first 2x VEC before cmp as any path forward will
> > > + require it. */
> > > + VMOVU %VEC(0), (%rax)
> > > + VMOVU %VEC(0), VEC_SIZE(%rax)
> > > +
> > > +
> > > +#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
> > > + /* If AVX2/SSE2 compute END_REG (rdi) with ALU. */
> > > + addq %rdx, %END_REG
> > > +#endif
> > > +
> > > + cmpq $(VEC_SIZE * 4), %rdx
> > > + jbe L(last_2x_vec)
> > > +
> > > + /* Store next 2x vec regardless. */
> > > + VMOVU %VEC(0), (VEC_SIZE * 2)(%rax)
> > > + VMOVU %VEC(0), (VEC_SIZE * 3)(%rax)
> > > +
> > > +
> > > +#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
> > > + /* If LOOP_4X_OFFSET don't readjust LOOP_REG (rdi), just add
> > > + extra offset to addresses in loop. Used for AVX512 to save space
> > > + as no way to get (VEC_SIZE * 4) in imm8. */
> > > +# if LOOP_4X_OFFSET == 0
> > > + subq $-(VEC_SIZE * 4), %LOOP_REG
> > > # endif
> > > -# if VEC_SIZE > 32
> > > - cmpb $32, %dl
> > > - jae L(between_32_63)
> > > + /* Avoid imm32 compare here to save code size. */
> > > + cmpq %rdi, %rcx
> > > +#else
> > > + addq $-(VEC_SIZE * 4), %END_REG
> > > + cmpq $(VEC_SIZE * 8), %rdx
> > > +#endif
> > > + jbe L(last_4x_vec)
> > > +#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
> > > + /* Set LOOP_REG (rdx). */
> > > + leaq (VEC_SIZE * 4)(%rax), %LOOP_REG
> > > +#endif
> > > + /* Align dst for loop. */
> > > + andq $(VEC_SIZE * -2), %LOOP_REG
> > > + .p2align 4
> > > +L(loop):
> > > + VMOVA %VEC(0), LOOP_4X_OFFSET(%LOOP_REG)
> > > + VMOVA %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%LOOP_REG)
> > > + VMOVA %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%LOOP_REG)
> > > + VMOVA %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%LOOP_REG)
> > > + subq $-(VEC_SIZE * 4), %LOOP_REG
> > > + cmpq %END_REG, %LOOP_REG
> > > + jb L(loop)
> > > + .p2align 4,, MOV_SIZE
> > > +L(last_4x_vec):
> > > + VMOVU %VEC(0), LOOP_4X_OFFSET(%END_REG)
> > > + VMOVU %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%END_REG)
> > > + VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%END_REG)
> > > + VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%END_REG)
> > > +L(return):
> > > +#if VEC_SIZE > 16
> > > + ZERO_UPPER_VEC_REGISTERS_RETURN
> > > +#else
> > > + ret
> > > +#endif
> > > +
> > > + .p2align 4,, 10
> > > +#ifndef USE_LESS_VEC_MASK_STORE
> > > +# if defined USE_MULTIARCH && IS_IN (libc)
> > > + /* If no USE_LESS_VEC_MASK put L(stosb_local) here. Will be in
> > > + range for 2-byte jump encoding. */
> > > +L(stosb_local):
> > > + movzbl %sil, %eax
> > > + mov %RDX_LP, %RCX_LP
> > > + mov %RDI_LP, %RDX_LP
> > > + rep stosb
> > > + mov %RDX_LP, %RAX_LP
> > > + VZEROUPPER_RETURN
> > > # endif
> > > -# if VEC_SIZE > 16
> > > - cmpb $16, %dl
> > > + /* Define L(less_vec) only if not otherwise defined. */
> > > + .p2align 4
> > > +L(less_vec):
> > > +#endif
> > > +L(cross_page):
> > > +#if VEC_SIZE > 32
> > > + cmpl $32, %edx
> > > + jae L(between_32_63)
> > > +#endif
> > > +#if VEC_SIZE > 16
> > > + cmpl $16, %edx
> > > jae L(between_16_31)
> > > -# endif
> > > - MOVQ %XMM0, %rcx
> > > - cmpb $8, %dl
> > > +#endif
> > > + MOVQ %XMM0, %rdi
> > > + cmpl $8, %edx
> > > jae L(between_8_15)
> > > - cmpb $4, %dl
> > > + cmpl $4, %edx
> > > jae L(between_4_7)
> > > - cmpb $1, %dl
> > > + cmpl $1, %edx
> > > ja L(between_2_3)
> > > - jb 1f
> > > - movb %cl, (%rax)
> > > -1:
> > > + jb L(return)
> > > + movb %sil, (%rax)
> > > VZEROUPPER_RETURN
> > > -# if VEC_SIZE > 32
> > > +
> > > + /* Align small targets only if not doing so would cross a fetch
> > > + line. */
> > > +#if VEC_SIZE > 32
> > > + .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
> > > /* From 32 to 63. No branch when size == 32. */
> > > L(between_32_63):
> > > - VMOVU %YMM0, -32(%rax,%rdx)
> > > VMOVU %YMM0, (%rax)
> > > + VMOVU %YMM0, -32(%rax, %rdx)
> > > VZEROUPPER_RETURN
> > > -# endif
> > > -# if VEC_SIZE > 16
> > > - /* From 16 to 31. No branch when size == 16. */
> > > +#endif
> > > +
> > > +#if VEC_SIZE >= 32
> > > + .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
> > > L(between_16_31):
> > > - VMOVU %XMM0, -16(%rax,%rdx)
> > > + /* From 16 to 31. No branch when size == 16. */
> > > VMOVU %XMM0, (%rax)
> > > + VMOVU %XMM0, -16(%rax, %rdx)
> > > VZEROUPPER_RETURN
> > > -# endif
> > > - /* From 8 to 15. No branch when size == 8. */
> > > +#endif
> > > +
> > > + .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
> > > L(between_8_15):
> > > - movq %rcx, -8(%rax,%rdx)
> > > - movq %rcx, (%rax)
> > > + /* From 8 to 15. No branch when size == 8. */
> > > + movq %rdi, (%rax)
> > > + movq %rdi, -8(%rax, %rdx)
> > > VZEROUPPER_RETURN
> > > +
> > > + .p2align 4,, SMALL_MEMSET_ALIGN(2, RET_SIZE)
> > > L(between_4_7):
> > > /* From 4 to 7. No branch when size == 4. */
> > > - movl %ecx, -4(%rax,%rdx)
> > > - movl %ecx, (%rax)
> > > + movl %edi, (%rax)
> > > + movl %edi, -4(%rax, %rdx)
> > > VZEROUPPER_RETURN
> > > +
> > > + .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
> > > L(between_2_3):
> > > /* From 2 to 3. No branch when size == 2. */
> > > - movw %cx, -2(%rax,%rdx)
> > > - movw %cx, (%rax)
> > > + movw %di, (%rax)
> > > + movb %dil, -1(%rax, %rdx)
> > > VZEROUPPER_RETURN
> > > END (MEMSET_SYMBOL (__memset, unaligned_erms))
> > > --
> > > 2.25.1
> > >
> >
> > LGTM.
> >
> > Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
> >
> > Thanks.
> >
> > --
> > H.J.
>
> Thanks! Pushed.
I would like to backport this patch to release branches.
Any comments or objections?
--Sunil
@@ -18,13 +18,15 @@
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
+#define USE_WITH_SSE2 1
#define VEC_SIZE 16
+#define MOV_SIZE 3
+#define RET_SIZE 1
+
#define VEC(i) xmm##i
-/* Don't use movups and movaps since it will get larger nop paddings for
- alignment. */
-#define VMOVU movdqu
-#define VMOVA movdqa
+#define VMOVU movups
+#define VMOVA movaps
#define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
movd d, %xmm0; \
@@ -1,8 +1,14 @@
#if IS_IN (libc)
+# define USE_WITH_AVX2 1
+
# define VEC_SIZE 32
+# define MOV_SIZE 4
+# define RET_SIZE 4
+
# define VEC(i) ymm##i
-# define VMOVU vmovdqu
-# define VMOVA vmovdqa
+
+# define VMOVU vmovdqu
+# define VMOVA vmovdqa
# define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
vmovd d, %xmm0; \
@@ -1,11 +1,18 @@
#if IS_IN (libc)
+# define USE_WITH_AVX512 1
+
# define VEC_SIZE 64
+# define MOV_SIZE 6
+# define RET_SIZE 1
+
# define XMM0 xmm16
# define YMM0 ymm16
# define VEC0 zmm16
# define VEC(i) VEC##i
-# define VMOVU vmovdqu64
-# define VMOVA vmovdqa64
+
+# define VMOVU vmovdqu64
+# define VMOVA vmovdqa64
+
# define VZEROUPPER
# define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
@@ -1,11 +1,18 @@
#if IS_IN (libc)
+# define USE_WITH_EVEX 1
+
# define VEC_SIZE 32
+# define MOV_SIZE 6
+# define RET_SIZE 1
+
# define XMM0 xmm16
# define YMM0 ymm16
# define VEC0 ymm16
# define VEC(i) VEC##i
-# define VMOVU vmovdqu64
-# define VMOVA vmovdqa64
+
+# define VMOVU vmovdqu64
+# define VMOVA vmovdqa64
+
# define VZEROUPPER
# define MEMSET_VDUP_TO_VEC0_AND_SET_RETURN(d, r) \
@@ -63,8 +63,27 @@
# endif
#endif
+#if VEC_SIZE == 64
+# define LOOP_4X_OFFSET (VEC_SIZE * 4)
+#else
+# define LOOP_4X_OFFSET (0)
+#endif
+
+#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
+# define END_REG rcx
+# define LOOP_REG rdi
+#else
+# define END_REG rdi
+# define LOOP_REG rdx
+#endif
+
#define PAGE_SIZE 4096
+/* Macro to calculate size of small memset block for aligning
+ purposes. */
+#define SMALL_MEMSET_ALIGN(mov_sz, ret_sz) (2 * (mov_sz) + (ret_sz) + 1)
+
+
#ifndef SECTION
# error SECTION is not defined!
#endif
@@ -74,6 +93,7 @@
ENTRY (__bzero)
mov %RDI_LP, %RAX_LP /* Set return value. */
mov %RSI_LP, %RDX_LP /* Set n. */
+ xorl %esi, %esi
pxor %XMM0, %XMM0
jmp L(entry_from_bzero)
END (__bzero)
@@ -158,7 +178,7 @@ ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
END_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
# endif
-ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
+ENTRY_P2ALIGN (MEMSET_SYMBOL (__memset, unaligned_erms), 6)
MEMSET_VDUP_TO_VEC0_AND_SET_RETURN (%esi, %rdi)
# ifdef __ILP32__
/* Clear the upper 32 bits. */
@@ -168,75 +188,43 @@ ENTRY (MEMSET_SYMBOL (__memset, unaligned_erms))
jb L(less_vec)
cmp $(VEC_SIZE * 2), %RDX_LP
ja L(stosb_more_2x_vec)
- /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE. */
- VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
- VMOVU %VEC(0), (%rdi)
+ /* From VEC and to 2 * VEC. No branch when size == VEC_SIZE.
+ */
+ VMOVU %VEC(0), (%rax)
+ VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
VZEROUPPER_RETURN
-
- .p2align 4
-L(stosb_more_2x_vec):
- cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
- ja L(stosb)
-#else
- .p2align 4
#endif
-L(more_2x_vec):
- /* Stores to first 2x VEC before cmp as any path forward will
- require it. */
- VMOVU %VEC(0), (%rdi)
- VMOVU %VEC(0), VEC_SIZE(%rdi)
- cmpq $(VEC_SIZE * 4), %rdx
- ja L(loop_start)
- VMOVU %VEC(0), -(VEC_SIZE * 2)(%rdi,%rdx)
- VMOVU %VEC(0), -VEC_SIZE(%rdi,%rdx)
-L(return):
-#if VEC_SIZE > 16
- ZERO_UPPER_VEC_REGISTERS_RETURN
+
+ .p2align 4,, 10
+L(last_2x_vec):
+#ifdef USE_LESS_VEC_MASK_STORE
+ VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%rcx)
+ VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%rcx)
#else
- ret
+ VMOVU %VEC(0), (VEC_SIZE * -2)(%rdi)
+ VMOVU %VEC(0), (VEC_SIZE * -1)(%rdi)
#endif
+ VZEROUPPER_RETURN
-L(loop_start):
- VMOVU %VEC(0), (VEC_SIZE * 2)(%rdi)
- VMOVU %VEC(0), (VEC_SIZE * 3)(%rdi)
- cmpq $(VEC_SIZE * 8), %rdx
- jbe L(loop_end)
- andq $-(VEC_SIZE * 2), %rdi
- subq $-(VEC_SIZE * 4), %rdi
- leaq -(VEC_SIZE * 4)(%rax, %rdx), %rcx
- .p2align 4
-L(loop):
- VMOVA %VEC(0), (%rdi)
- VMOVA %VEC(0), VEC_SIZE(%rdi)
- VMOVA %VEC(0), (VEC_SIZE * 2)(%rdi)
- VMOVA %VEC(0), (VEC_SIZE * 3)(%rdi)
- subq $-(VEC_SIZE * 4), %rdi
- cmpq %rcx, %rdi
- jb L(loop)
-L(loop_end):
- /* NB: rax is set as ptr in MEMSET_VDUP_TO_VEC0_AND_SET_RETURN.
- rdx as length is also unchanged. */
- VMOVU %VEC(0), -(VEC_SIZE * 4)(%rax, %rdx)
- VMOVU %VEC(0), -(VEC_SIZE * 3)(%rax, %rdx)
- VMOVU %VEC(0), -(VEC_SIZE * 2)(%rax, %rdx)
- VMOVU %VEC(0), -VEC_SIZE(%rax, %rdx)
- VZEROUPPER_SHORT_RETURN
-
- .p2align 4
+ /* If have AVX512 mask instructions put L(less_vec) close to
+ entry as it doesn't take much space and is likely a hot target.
+ */
+#ifdef USE_LESS_VEC_MASK_STORE
+ .p2align 4,, 10
L(less_vec):
/* Less than 1 VEC. */
# if VEC_SIZE != 16 && VEC_SIZE != 32 && VEC_SIZE != 64
# error Unsupported VEC_SIZE!
# endif
-# ifdef USE_LESS_VEC_MASK_STORE
/* Clear high bits from edi. Only keeping bits relevant to page
cross check. Note that we are using rax which is set in
- MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out.
- */
+ MEMSET_VDUP_TO_VEC0_AND_SET_RETURN as ptr from here on out. */
andl $(PAGE_SIZE - 1), %edi
- /* Check if VEC_SIZE store cross page. Mask stores suffer serious
- performance degradation when it has to fault supress. */
+ /* Check if VEC_SIZE store cross page. Mask stores suffer
+ serious performance degradation when it has to fault supress.
+ */
cmpl $(PAGE_SIZE - VEC_SIZE), %edi
+ /* This is generally considered a cold target. */
ja L(cross_page)
# if VEC_SIZE > 32
movq $-1, %rcx
@@ -247,58 +235,185 @@ L(less_vec):
bzhil %edx, %ecx, %ecx
kmovd %ecx, %k1
# endif
- vmovdqu8 %VEC(0), (%rax) {%k1}
+ vmovdqu8 %VEC(0), (%rax){%k1}
VZEROUPPER_RETURN
+# if defined USE_MULTIARCH && IS_IN (libc)
+ /* Include L(stosb_local) here if including L(less_vec) between
+ L(stosb_more_2x_vec) and ENTRY. This is to cache align the
+ L(stosb_more_2x_vec) target. */
+ .p2align 4,, 10
+L(stosb_local):
+ movzbl %sil, %eax
+ mov %RDX_LP, %RCX_LP
+ mov %RDI_LP, %RDX_LP
+ rep stosb
+ mov %RDX_LP, %RAX_LP
+ VZEROUPPER_RETURN
+# endif
+#endif
+
+#if defined USE_MULTIARCH && IS_IN (libc)
.p2align 4
-L(cross_page):
+L(stosb_more_2x_vec):
+ cmp __x86_rep_stosb_threshold(%rip), %RDX_LP
+ ja L(stosb_local)
+#endif
+ /* Fallthrough goes to L(loop_4x_vec). Tests for memset (2x, 4x]
+ and (4x, 8x] jump to target. */
+L(more_2x_vec):
+
+ /* Two different methods of setting up pointers / compare. The
+ two methods are based on the fact that EVEX/AVX512 mov
+ instructions take more bytes then AVX2/SSE2 mov instructions. As
+ well that EVEX/AVX512 machines also have fast LEA_BID. Both
+ setup and END_REG to avoid complex address mode. For EVEX/AVX512
+ this saves code size and keeps a few targets in one fetch block.
+ For AVX2/SSE2 this helps prevent AGU bottlenecks. */
+#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
+ /* If EVEX/AVX512 compute END_REG - (VEC_SIZE * 4 +
+ LOOP_4X_OFFSET) with LEA_BID. */
+
+ /* END_REG is rcx for EVEX/AVX512. */
+ leaq -(VEC_SIZE * 4 + LOOP_4X_OFFSET)(%rdi, %rdx), %END_REG
+#endif
+
+ /* Stores to first 2x VEC before cmp as any path forward will
+ require it. */
+ VMOVU %VEC(0), (%rax)
+ VMOVU %VEC(0), VEC_SIZE(%rax)
+
+
+#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
+ /* If AVX2/SSE2 compute END_REG (rdi) with ALU. */
+ addq %rdx, %END_REG
+#endif
+
+ cmpq $(VEC_SIZE * 4), %rdx
+ jbe L(last_2x_vec)
+
+ /* Store next 2x vec regardless. */
+ VMOVU %VEC(0), (VEC_SIZE * 2)(%rax)
+ VMOVU %VEC(0), (VEC_SIZE * 3)(%rax)
+
+
+#if defined USE_WITH_EVEX || defined USE_WITH_AVX512
+ /* If LOOP_4X_OFFSET don't readjust LOOP_REG (rdi), just add
+ extra offset to addresses in loop. Used for AVX512 to save space
+ as no way to get (VEC_SIZE * 4) in imm8. */
+# if LOOP_4X_OFFSET == 0
+ subq $-(VEC_SIZE * 4), %LOOP_REG
# endif
-# if VEC_SIZE > 32
- cmpb $32, %dl
- jae L(between_32_63)
+ /* Avoid imm32 compare here to save code size. */
+ cmpq %rdi, %rcx
+#else
+ addq $-(VEC_SIZE * 4), %END_REG
+ cmpq $(VEC_SIZE * 8), %rdx
+#endif
+ jbe L(last_4x_vec)
+#if !(defined USE_WITH_EVEX || defined USE_WITH_AVX512)
+ /* Set LOOP_REG (rdx). */
+ leaq (VEC_SIZE * 4)(%rax), %LOOP_REG
+#endif
+ /* Align dst for loop. */
+ andq $(VEC_SIZE * -2), %LOOP_REG
+ .p2align 4
+L(loop):
+ VMOVA %VEC(0), LOOP_4X_OFFSET(%LOOP_REG)
+ VMOVA %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%LOOP_REG)
+ VMOVA %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%LOOP_REG)
+ VMOVA %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%LOOP_REG)
+ subq $-(VEC_SIZE * 4), %LOOP_REG
+ cmpq %END_REG, %LOOP_REG
+ jb L(loop)
+ .p2align 4,, MOV_SIZE
+L(last_4x_vec):
+ VMOVU %VEC(0), LOOP_4X_OFFSET(%END_REG)
+ VMOVU %VEC(0), (VEC_SIZE + LOOP_4X_OFFSET)(%END_REG)
+ VMOVU %VEC(0), (VEC_SIZE * 2 + LOOP_4X_OFFSET)(%END_REG)
+ VMOVU %VEC(0), (VEC_SIZE * 3 + LOOP_4X_OFFSET)(%END_REG)
+L(return):
+#if VEC_SIZE > 16
+ ZERO_UPPER_VEC_REGISTERS_RETURN
+#else
+ ret
+#endif
+
+ .p2align 4,, 10
+#ifndef USE_LESS_VEC_MASK_STORE
+# if defined USE_MULTIARCH && IS_IN (libc)
+ /* If no USE_LESS_VEC_MASK put L(stosb_local) here. Will be in
+ range for 2-byte jump encoding. */
+L(stosb_local):
+ movzbl %sil, %eax
+ mov %RDX_LP, %RCX_LP
+ mov %RDI_LP, %RDX_LP
+ rep stosb
+ mov %RDX_LP, %RAX_LP
+ VZEROUPPER_RETURN
# endif
-# if VEC_SIZE > 16
- cmpb $16, %dl
+ /* Define L(less_vec) only if not otherwise defined. */
+ .p2align 4
+L(less_vec):
+#endif
+L(cross_page):
+#if VEC_SIZE > 32
+ cmpl $32, %edx
+ jae L(between_32_63)
+#endif
+#if VEC_SIZE > 16
+ cmpl $16, %edx
jae L(between_16_31)
-# endif
- MOVQ %XMM0, %rcx
- cmpb $8, %dl
+#endif
+ MOVQ %XMM0, %rdi
+ cmpl $8, %edx
jae L(between_8_15)
- cmpb $4, %dl
+ cmpl $4, %edx
jae L(between_4_7)
- cmpb $1, %dl
+ cmpl $1, %edx
ja L(between_2_3)
- jb 1f
- movb %cl, (%rax)
-1:
+ jb L(return)
+ movb %sil, (%rax)
VZEROUPPER_RETURN
-# if VEC_SIZE > 32
+
+ /* Align small targets only if not doing so would cross a fetch
+ line. */
+#if VEC_SIZE > 32
+ .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
/* From 32 to 63. No branch when size == 32. */
L(between_32_63):
- VMOVU %YMM0, -32(%rax,%rdx)
VMOVU %YMM0, (%rax)
+ VMOVU %YMM0, -32(%rax, %rdx)
VZEROUPPER_RETURN
-# endif
-# if VEC_SIZE > 16
- /* From 16 to 31. No branch when size == 16. */
+#endif
+
+#if VEC_SIZE >= 32
+ .p2align 4,, SMALL_MEMSET_ALIGN(MOV_SIZE, RET_SIZE)
L(between_16_31):
- VMOVU %XMM0, -16(%rax,%rdx)
+ /* From 16 to 31. No branch when size == 16. */
VMOVU %XMM0, (%rax)
+ VMOVU %XMM0, -16(%rax, %rdx)
VZEROUPPER_RETURN
-# endif
- /* From 8 to 15. No branch when size == 8. */
+#endif
+
+ .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
L(between_8_15):
- movq %rcx, -8(%rax,%rdx)
- movq %rcx, (%rax)
+ /* From 8 to 15. No branch when size == 8. */
+ movq %rdi, (%rax)
+ movq %rdi, -8(%rax, %rdx)
VZEROUPPER_RETURN
+
+ .p2align 4,, SMALL_MEMSET_ALIGN(2, RET_SIZE)
L(between_4_7):
/* From 4 to 7. No branch when size == 4. */
- movl %ecx, -4(%rax,%rdx)
- movl %ecx, (%rax)
+ movl %edi, (%rax)
+ movl %edi, -4(%rax, %rdx)
VZEROUPPER_RETURN
+
+ .p2align 4,, SMALL_MEMSET_ALIGN(3, RET_SIZE)
L(between_2_3):
/* From 2 to 3. No branch when size == 2. */
- movw %cx, -2(%rax,%rdx)
- movw %cx, (%rax)
+ movw %di, (%rax)
+ movb %dil, -1(%rax, %rdx)
VZEROUPPER_RETURN
END (MEMSET_SYMBOL (__memset, unaligned_erms))