From 5deda2b73383bf16788cc83c8ea6262d89608263 Mon Sep 17 00:00:00 2001

From: Noah Goldstein <goldstein.w.n@gmail.com>

Date: Mon, 20 Sep 2021 16:20:15 -0500

Subject: [PATCH] x86: Optimize memset-vec-unaligned-erms.S

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>

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

(cherry picked from commit e59ced238482fd71f3e493717f14f6507346741e)

---

 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 b3426795..8672b030 100644

--- a/sysdeps/x86_64/memset.S

+++ b/sysdeps/x86_64/memset.S

@@ -18,13 +18,15 @@

    <http://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 ae0860f3..1af668af 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 8ad842fc..f14d6f84 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 640f0929..64b09e77 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 909c33f6..f08b7323 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))

-- 

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