glibc/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S

/* memcmp/wmemcmp optimized with 256-bit EVEX instructions.
   Copyright (C) 2021 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#if IS_IN (libc)

/* memcmp/wmemcmp is implemented as:
   1. Use ymm vector compares when possible. The only case where
      vector compares is not possible for when size < CHAR_PER_VEC
      and loading from either s1 or s2 would cause a page cross.
   2. For size from 2 to 7 bytes on page cross, load as big endian
      with movbe and bswap to avoid branches.
   3. Use xmm vector compare when size >= 4 bytes for memcmp or
      size >= 8 bytes for wmemcmp.
   4. Optimistically compare up to first 4 * CHAR_PER_VEC one at a
      to check for early mismatches. Only do this if its guranteed the
      work is not wasted.
   5. If size is 8 * VEC_SIZE or less, unroll the loop.
   6. Compare 4 * VEC_SIZE at a time with the aligned first memory
      area.
   7. Use 2 vector compares when size is 2 * CHAR_PER_VEC or less.
   8. Use 4 vector compares when size is 4 * CHAR_PER_VEC or less.
   9. Use 8 vector compares when size is 8 * CHAR_PER_VEC or less.

When possible the implementation tries to optimize for frontend in the
following ways:
Throughput:
    1. All code sections that fit are able to run optimally out of the
       LSD.
    2. All code sections that fit are able to run optimally out of the
       DSB
    3. Basic blocks are contained in minimum number of fetch blocks
       necessary.

Latency:
    1. Logically connected basic blocks are put in the same
       cache-line.
    2. Logically connected basic blocks that do not fit in the same
       cache-line are put in adjacent lines. This can get beneficial
       L2 spatial prefetching and L1 next-line prefetching.  */

# include <sysdep.h>

# ifndef MEMCMP
#  define MEMCMP	__memcmp_evex_movbe
# endif

# define VMOVU		vmovdqu64

# ifdef USE_AS_WMEMCMP
#  define VMOVU_MASK	vmovdqu32
#  define CHAR_SIZE	4
#  define VPCMP	vpcmpd
#  define VPTEST	vptestmd
# else
#  define VMOVU_MASK	vmovdqu8
#  define CHAR_SIZE	1
#  define VPCMP	vpcmpub
#  define VPTEST	vptestmb
# endif


# define VEC_SIZE	32
# define PAGE_SIZE	4096
# define CHAR_PER_VEC	(VEC_SIZE / CHAR_SIZE)

# define XMM0		xmm16
# define XMM1		xmm17
# define XMM2		xmm18
# define YMM0		ymm16
# define XMM1		xmm17
# define XMM2		xmm18
# define YMM1		ymm17
# define YMM2		ymm18
# define YMM3		ymm19
# define YMM4		ymm20
# define YMM5		ymm21
# define YMM6		ymm22

/* Warning!
           wmemcmp has to use SIGNED comparison for elements.
           memcmp has to use UNSIGNED comparison for elemnts.
*/

	.section .text.evex,"ax",@progbits
/* Cache align memcmp entry. This allows for much more thorough
   frontend optimization.  */
ENTRY_P2ALIGN (MEMCMP, 6)
# ifdef __ILP32__
	/* Clear the upper 32 bits.  */
	movl	%edx, %edx
# endif
	cmp	$CHAR_PER_VEC, %RDX_LP
	/* Fall through for [0, VEC_SIZE] as its the hottest.  */
	ja	L(more_1x_vec)

	/* Create mask for CHAR's we want to compare. This allows us to
	   avoid having to include page cross logic.  */
	movl	$-1, %ecx
	bzhil	%edx, %ecx, %ecx
	kmovd	%ecx, %k2

	/* Safe to load full ymm with mask.  */
	VMOVU_MASK (%rsi), %YMM2{%k2}
	VPCMP	$4,(%rdi), %YMM2, %k1{%k2}
	kmovd	%k1, %eax
	testl	%eax, %eax
	jnz	L(return_vec_0)
	ret

	.p2align 4
L(return_vec_0):
	tzcntl	%eax, %eax
# ifdef USE_AS_WMEMCMP
	movl	(%rdi, %rax, CHAR_SIZE), %ecx
	xorl	%edx, %edx
	cmpl	(%rsi, %rax, CHAR_SIZE), %ecx
	/* NB: no partial register stall here because xorl zero idiom
	   above.  */
	setg	%dl
	leal	-1(%rdx, %rdx), %eax
# else
	movzbl	(%rsi, %rax), %ecx
	movzbl	(%rdi, %rax), %eax
	subl	%ecx, %eax
# endif
	ret


	.p2align 4
L(more_1x_vec):
	/* From VEC to 2 * VEC.  No branch when size == VEC_SIZE.  */
	VMOVU	(%rsi), %YMM1
	/* Use compare not equals to directly check for mismatch.  */
	VPCMP	$4,(%rdi), %YMM1, %k1
	kmovd	%k1, %eax
	/* NB: eax must be destination register if going to
	   L(return_vec_[0,2]). For L(return_vec_3) destination register
	   must be ecx.  */
	testl	%eax, %eax
	jnz	L(return_vec_0)

	cmpq	$(CHAR_PER_VEC * 2), %rdx
	jbe	L(last_1x_vec)

	/* Check second VEC no matter what.  */
	VMOVU	VEC_SIZE(%rsi), %YMM2
	VPCMP	$4, VEC_SIZE(%rdi), %YMM2, %k1
	kmovd	%k1, %eax
	testl	%eax, %eax
	jnz	L(return_vec_1)

	/* Less than 4 * VEC.  */
	cmpq	$(CHAR_PER_VEC * 4), %rdx
	jbe	L(last_2x_vec)

	/* Check third and fourth VEC no matter what.  */
	VMOVU	(VEC_SIZE * 2)(%rsi), %YMM3
	VPCMP	$4,(VEC_SIZE * 2)(%rdi), %YMM3, %k1
	kmovd	%k1, %eax
	testl	%eax, %eax
	jnz	L(return_vec_2)

	VMOVU	(VEC_SIZE * 3)(%rsi), %YMM4
	VPCMP	$4,(VEC_SIZE * 3)(%rdi), %YMM4, %k1
	kmovd	%k1, %ecx
	testl	%ecx, %ecx
	jnz	L(return_vec_3)

	/* Go to 4x VEC loop.  */
	cmpq	$(CHAR_PER_VEC * 8), %rdx
	ja	L(more_8x_vec)

	/* Handle remainder of size = 4 * VEC + 1 to 8 * VEC without any
	   branches.  */

	/* Load first two VEC from s2 before adjusting addresses.  */
	VMOVU	-(VEC_SIZE * 4)(%rsi, %rdx, CHAR_SIZE), %YMM1
	VMOVU	-(VEC_SIZE * 3)(%rsi, %rdx, CHAR_SIZE), %YMM2
	leaq	-(4 * VEC_SIZE)(%rdi, %rdx, CHAR_SIZE), %rdi
	leaq	-(4 * VEC_SIZE)(%rsi, %rdx, CHAR_SIZE), %rsi

	/* Wait to load from s1 until addressed adjust due to
	   unlamination of microfusion with complex address mode.  */

	/* vpxor will be all 0s if s1 and s2 are equal. Otherwise it
	   will have some 1s.  */
	vpxorq	(%rdi), %YMM1, %YMM1
	vpxorq	(VEC_SIZE)(%rdi), %YMM2, %YMM2

	VMOVU	(VEC_SIZE * 2)(%rsi), %YMM3
	vpxorq	(VEC_SIZE * 2)(%rdi), %YMM3, %YMM3

	VMOVU	(VEC_SIZE * 3)(%rsi), %YMM4
	/* Ternary logic to xor (VEC_SIZE * 3)(%rdi) with YMM4 while
	   oring with YMM1. Result is stored in YMM4.  */
	vpternlogd $0xde,(VEC_SIZE * 3)(%rdi), %YMM1, %YMM4

	/* Or together YMM2, YMM3, and YMM4 into YMM4.  */
	vpternlogd $0xfe, %YMM2, %YMM3, %YMM4

	/* Test YMM4 against itself. Store any CHAR mismatches in k1.
	 */
	VPTEST	%YMM4, %YMM4, %k1
	/* k1 must go to ecx for L(return_vec_0_1_2_3).  */
	kmovd	%k1, %ecx
	testl	%ecx, %ecx
	jnz	L(return_vec_0_1_2_3)
	/* NB: eax must be zero to reach here.  */
	ret


	.p2align 4,, 8
L(8x_end_return_vec_0_1_2_3):
	movq	%rdx, %rdi
L(8x_return_vec_0_1_2_3):
	addq	%rdi, %rsi
L(return_vec_0_1_2_3):
	VPTEST	%YMM1, %YMM1, %k0
	kmovd	%k0, %eax
	testl	%eax, %eax
	jnz	L(return_vec_0)

	VPTEST	%YMM2, %YMM2, %k0
	kmovd	%k0, %eax
	testl	%eax, %eax
	jnz	L(return_vec_1)

	VPTEST	%YMM3, %YMM3, %k0
	kmovd	%k0, %eax
	testl	%eax, %eax
	jnz	L(return_vec_2)
L(return_vec_3):
	/* bsf saves 1 byte from tzcnt. This keep L(return_vec_3) in one
	   fetch block and the entire L(*return_vec_0_1_2_3) in 1 cache
	   line.  */
	bsfl	%ecx, %ecx
# ifdef USE_AS_WMEMCMP
	movl	(VEC_SIZE * 3)(%rdi, %rcx, CHAR_SIZE), %eax
	xorl	%edx, %edx
	cmpl	(VEC_SIZE * 3)(%rsi, %rcx, CHAR_SIZE), %eax
	setg	%dl
	leal	-1(%rdx, %rdx), %eax
# else
	movzbl	(VEC_SIZE * 3)(%rdi, %rcx), %eax
	movzbl	(VEC_SIZE * 3)(%rsi, %rcx), %ecx
	subl	%ecx, %eax
# endif
	ret


	.p2align 4
L(return_vec_1):
	/* bsf saves 1 byte over tzcnt and keeps L(return_vec_1) in one
	   fetch block.  */
	bsfl	%eax, %eax
# ifdef USE_AS_WMEMCMP
	movl	VEC_SIZE(%rdi, %rax, CHAR_SIZE), %ecx
	xorl	%edx, %edx
	cmpl	VEC_SIZE(%rsi, %rax, CHAR_SIZE), %ecx
	setg	%dl
	leal	-1(%rdx, %rdx), %eax
# else
	movzbl	VEC_SIZE(%rsi, %rax), %ecx
	movzbl	VEC_SIZE(%rdi, %rax), %eax
	subl	%ecx, %eax
# endif
	ret

	.p2align 4,, 10
L(return_vec_2):
	/* bsf saves 1 byte over tzcnt and keeps L(return_vec_2) in one
	   fetch block.  */
	bsfl	%eax, %eax
# ifdef USE_AS_WMEMCMP
	movl	(VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %ecx
	xorl	%edx, %edx
	cmpl	(VEC_SIZE * 2)(%rsi, %rax, CHAR_SIZE), %ecx
	setg	%dl
	leal	-1(%rdx, %rdx), %eax
# else
	movzbl	(VEC_SIZE * 2)(%rsi, %rax), %ecx
	movzbl	(VEC_SIZE * 2)(%rdi, %rax), %eax
	subl	%ecx, %eax
# endif
	ret

	.p2align 4
L(more_8x_vec):
	/* Set end of s1 in rdx.  */
	leaq	-(VEC_SIZE * 4)(%rdi, %rdx, CHAR_SIZE), %rdx
	/* rsi stores s2 - s1. This allows loop to only update one
	   pointer.  */
	subq	%rdi, %rsi
	/* Align s1 pointer.  */
	andq	$-VEC_SIZE, %rdi
	/* Adjust because first 4x vec where check already.  */
	subq	$-(VEC_SIZE * 4), %rdi

	.p2align 4
L(loop_4x_vec):
	VMOVU	(%rsi, %rdi), %YMM1
	vpxorq	(%rdi), %YMM1, %YMM1
	VMOVU	VEC_SIZE(%rsi, %rdi), %YMM2
	vpxorq	VEC_SIZE(%rdi), %YMM2, %YMM2
	VMOVU	(VEC_SIZE * 2)(%rsi, %rdi), %YMM3
	vpxorq	(VEC_SIZE * 2)(%rdi), %YMM3, %YMM3
	VMOVU	(VEC_SIZE * 3)(%rsi, %rdi), %YMM4
	vpternlogd $0xde,(VEC_SIZE * 3)(%rdi), %YMM1, %YMM4
	vpternlogd $0xfe, %YMM2, %YMM3, %YMM4
	VPTEST	%YMM4, %YMM4, %k1
	kmovd	%k1, %ecx
	testl	%ecx, %ecx
	jnz	L(8x_return_vec_0_1_2_3)
	subq	$-(VEC_SIZE * 4), %rdi
	cmpq	%rdx, %rdi
	jb	L(loop_4x_vec)

	subq	%rdx, %rdi
	/* rdi has 4 * VEC_SIZE - remaining length.  */
	cmpl	$(VEC_SIZE * 3), %edi
	jae	L(8x_last_1x_vec)
	/* Load regardless of branch.  */
	VMOVU	(VEC_SIZE * 2)(%rsi, %rdx), %YMM3
	cmpl	$(VEC_SIZE * 2), %edi
	jae	L(8x_last_2x_vec)

	vpxorq	(VEC_SIZE * 2)(%rdx), %YMM3, %YMM3

	VMOVU	(%rsi, %rdx), %YMM1
	vpxorq	(%rdx), %YMM1, %YMM1

	VMOVU	VEC_SIZE(%rsi, %rdx), %YMM2
	vpxorq	VEC_SIZE(%rdx), %YMM2, %YMM2
	VMOVU	(VEC_SIZE * 3)(%rsi, %rdx), %YMM4
	vpternlogd $0xde,(VEC_SIZE * 3)(%rdx), %YMM1, %YMM4
	vpternlogd $0xfe, %YMM2, %YMM3, %YMM4
	VPTEST	%YMM4, %YMM4, %k1
	kmovd	%k1, %ecx
	testl	%ecx, %ecx
	jnz	L(8x_end_return_vec_0_1_2_3)
	/* NB: eax must be zero to reach here.  */
	ret

	/* Only entry is from L(more_8x_vec).  */
	.p2align 4,, 10
L(8x_last_2x_vec):
	VPCMP	$4,(VEC_SIZE * 2)(%rdx), %YMM3, %k1
	kmovd	%k1, %eax
	testl	%eax, %eax
	jnz	L(8x_return_vec_2)
	/* Naturally aligned to 16 bytes.  */
L(8x_last_1x_vec):
	VMOVU	(VEC_SIZE * 3)(%rsi, %rdx), %YMM1
	VPCMP	$4,(VEC_SIZE * 3)(%rdx), %YMM1, %k1
	kmovd	%k1, %eax
	testl	%eax, %eax
	jnz	L(8x_return_vec_3)
	ret

	/* Not ideally aligned (at offset +9 bytes in fetch block) but
	   not aligning keeps it in the same cache line as
	   L(8x_last_1x/2x_vec) so likely worth it. As well, saves code
	   size.  */
	.p2align 4,, 4
L(8x_return_vec_2):
	subq	$VEC_SIZE, %rdx
L(8x_return_vec_3):
	bsfl	%eax, %eax
# ifdef USE_AS_WMEMCMP
	leaq	(%rdx, %rax, CHAR_SIZE), %rax
	movl	(VEC_SIZE * 3)(%rax), %ecx
	xorl	%edx, %edx
	cmpl	(VEC_SIZE * 3)(%rsi, %rax), %ecx
	setg	%dl
	leal	-1(%rdx, %rdx), %eax
# else
	addq	%rdx, %rax
	movzbl	(VEC_SIZE * 3)(%rsi, %rax), %ecx
	movzbl	(VEC_SIZE * 3)(%rax), %eax
	subl	%ecx, %eax
# endif
	ret

	.p2align 4,, 10
L(last_2x_vec):
	/* Check second to last VEC.  */
	VMOVU	-(VEC_SIZE * 2)(%rsi, %rdx, CHAR_SIZE), %YMM1
	VPCMP	$4, -(VEC_SIZE * 2)(%rdi, %rdx, CHAR_SIZE), %YMM1, %k1
	kmovd	%k1, %eax
	testl	%eax, %eax
	jnz	L(return_vec_1_end)

	/* Check last VEC.  */
	.p2align 4
L(last_1x_vec):
	VMOVU	-(VEC_SIZE * 1)(%rsi, %rdx, CHAR_SIZE), %YMM1
	VPCMP	$4, -(VEC_SIZE * 1)(%rdi, %rdx, CHAR_SIZE), %YMM1, %k1
	kmovd	%k1, %eax
	testl	%eax, %eax
	jnz	L(return_vec_0_end)
	ret


	/* Don't align. Takes 2-fetch blocks either way and aligning
	   will cause code to spill into another cacheline.  */
L(return_vec_1_end):
	/* Use bsf to save code size. This is necessary to have
	   L(one_or_less) fit in aligning bytes between.  */
	bsfl	%eax, %eax
	addl	%edx, %eax
# ifdef USE_AS_WMEMCMP
	movl	-(VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %ecx
	xorl	%edx, %edx
	cmpl	-(VEC_SIZE * 2)(%rsi, %rax, CHAR_SIZE), %ecx
	setg	%dl
	leal	-1(%rdx, %rdx), %eax
# else
	movzbl	-(VEC_SIZE * 2)(%rsi, %rax), %ecx
	movzbl	-(VEC_SIZE * 2)(%rdi, %rax), %eax
	subl	%ecx, %eax
# endif
	ret

	/* Don't align. Takes 2-fetch blocks either way and aligning
	   will cause code to spill into another cacheline.  */
L(return_vec_0_end):
	tzcntl	%eax, %eax
	addl	%edx, %eax
# ifdef USE_AS_WMEMCMP
	movl	-VEC_SIZE(%rdi, %rax, CHAR_SIZE), %ecx
	xorl	%edx, %edx
	cmpl	-VEC_SIZE(%rsi, %rax, CHAR_SIZE), %ecx
	setg	%dl
	leal	-1(%rdx, %rdx), %eax
# else
	movzbl	-VEC_SIZE(%rsi, %rax), %ecx
	movzbl	-VEC_SIZE(%rdi, %rax), %eax
	subl	%ecx, %eax
# endif
	ret
	/* 1-byte until next cache line.  */

END (MEMCMP)
#endif