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From 7f3e7c262cab4e2401e4331a6ef29c428de02044 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Fri, 23 Apr 2021 15:56:25 -0400
Subject: [PATCH] x86: Optimize strchr-evex.S
Content-type: text/plain; charset=UTF-8
No bug. This commit optimizes strchr-evex.S. The optimizations are
mostly small things such as save an ALU in the alignment process,
saving a few instructions in the loop return. The one significant
change is saving 2 instructions in the 4x loop. test-strchr,
test-strchrnul, test-wcschr, and test-wcschrnul are all passing.
Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
---
sysdeps/x86_64/multiarch/strchr-evex.S | 392 ++++++++++++++-----------
1 file changed, 218 insertions(+), 174 deletions(-)
diff --git a/sysdeps/x86_64/multiarch/strchr-evex.S b/sysdeps/x86_64/multiarch/strchr-evex.S
index ddc86a70..7f9d4ee4 100644
--- a/sysdeps/x86_64/multiarch/strchr-evex.S
+++ b/sysdeps/x86_64/multiarch/strchr-evex.S
@@ -32,13 +32,15 @@
# define VPCMP vpcmpd
# define VPMINU vpminud
# define CHAR_REG esi
-# define SHIFT_REG r8d
+# define SHIFT_REG ecx
+# define CHAR_SIZE 4
# else
# define VPBROADCAST vpbroadcastb
# define VPCMP vpcmpb
# define VPMINU vpminub
# define CHAR_REG sil
-# define SHIFT_REG ecx
+# define SHIFT_REG edx
+# define CHAR_SIZE 1
# endif
# define XMMZERO xmm16
@@ -56,23 +58,20 @@
# define VEC_SIZE 32
# define PAGE_SIZE 4096
+# define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
.section .text.evex,"ax",@progbits
ENTRY (STRCHR)
- movl %edi, %ecx
-# ifndef USE_AS_STRCHRNUL
- xorl %edx, %edx
-# endif
-
/* Broadcast CHAR to YMM0. */
- VPBROADCAST %esi, %YMM0
-
+ VPBROADCAST %esi, %YMM0
+ movl %edi, %eax
+ andl $(PAGE_SIZE - 1), %eax
vpxorq %XMMZERO, %XMMZERO, %XMMZERO
- /* Check if we cross page boundary with one vector load. */
- andl $(PAGE_SIZE - 1), %ecx
- cmpl $(PAGE_SIZE - VEC_SIZE), %ecx
- ja L(cross_page_boundary)
+ /* Check if we cross page boundary with one vector load.
+ Otherwise it is safe to use an unaligned load. */
+ cmpl $(PAGE_SIZE - VEC_SIZE), %eax
+ ja L(cross_page_boundary)
/* Check the first VEC_SIZE bytes. Search for both CHAR and the
null bytes. */
@@ -83,251 +82,296 @@ ENTRY (STRCHR)
VPMINU %YMM2, %YMM1, %YMM2
/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
VPCMP $0, %YMMZERO, %YMM2, %k0
- ktestd %k0, %k0
- jz L(more_vecs)
kmovd %k0, %eax
+ testl %eax, %eax
+ jz L(aligned_more)
tzcntl %eax, %eax
- /* Found CHAR or the null byte. */
# ifdef USE_AS_WCSCHR
- /* NB: Multiply wchar_t count by 4 to get the number of bytes. */
- leaq (%rdi, %rax, 4), %rax
+ /* NB: Multiply wchar_t count by 4 to get the number of bytes.
+ */
+ leaq (%rdi, %rax, CHAR_SIZE), %rax
# else
addq %rdi, %rax
# endif
# ifndef USE_AS_STRCHRNUL
- cmp (%rax), %CHAR_REG
- cmovne %rdx, %rax
+ /* Found CHAR or the null byte. */
+ cmp (%rax), %CHAR_REG
+ jne L(zero)
# endif
ret
- .p2align 4
-L(more_vecs):
- /* Align data for aligned loads in the loop. */
- andq $-VEC_SIZE, %rdi
-L(aligned_more):
-
- /* Check the next 4 * VEC_SIZE. Only one VEC_SIZE at a time
- since data is only aligned to VEC_SIZE. */
- VMOVA VEC_SIZE(%rdi), %YMM1
- addq $VEC_SIZE, %rdi
-
- /* Leaves only CHARS matching esi as 0. */
- vpxorq %YMM1, %YMM0, %YMM2
- VPMINU %YMM2, %YMM1, %YMM2
- /* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM2, %k0
- kmovd %k0, %eax
- testl %eax, %eax
- jnz L(first_vec_x0)
-
- VMOVA VEC_SIZE(%rdi), %YMM1
- /* Leaves only CHARS matching esi as 0. */
- vpxorq %YMM1, %YMM0, %YMM2
- VPMINU %YMM2, %YMM1, %YMM2
- /* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM2, %k0
- kmovd %k0, %eax
- testl %eax, %eax
- jnz L(first_vec_x1)
-
- VMOVA (VEC_SIZE * 2)(%rdi), %YMM1
- /* Leaves only CHARS matching esi as 0. */
- vpxorq %YMM1, %YMM0, %YMM2
- VPMINU %YMM2, %YMM1, %YMM2
- /* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM2, %k0
- kmovd %k0, %eax
- testl %eax, %eax
- jnz L(first_vec_x2)
-
- VMOVA (VEC_SIZE * 3)(%rdi), %YMM1
- /* Leaves only CHARS matching esi as 0. */
- vpxorq %YMM1, %YMM0, %YMM2
- VPMINU %YMM2, %YMM1, %YMM2
- /* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM2, %k0
- ktestd %k0, %k0
- jz L(prep_loop_4x)
-
- kmovd %k0, %eax
+ /* .p2align 5 helps keep performance more consistent if ENTRY()
+ alignment % 32 was either 16 or 0. As well this makes the
+ alignment % 32 of the loop_4x_vec fixed which makes tuning it
+ easier. */
+ .p2align 5
+L(first_vec_x3):
tzcntl %eax, %eax
+# ifndef USE_AS_STRCHRNUL
/* Found CHAR or the null byte. */
-# ifdef USE_AS_WCSCHR
- /* NB: Multiply wchar_t count by 4 to get the number of bytes. */
- leaq (VEC_SIZE * 3)(%rdi, %rax, 4), %rax
-# else
- leaq (VEC_SIZE * 3)(%rdi, %rax), %rax
+ cmp (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
+ jne L(zero)
# endif
+ /* NB: Multiply sizeof char type (1 or 4) to get the number of
+ bytes. */
+ leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax
+ ret
+
# ifndef USE_AS_STRCHRNUL
- cmp (%rax), %CHAR_REG
- cmovne %rdx, %rax
-# endif
+L(zero):
+ xorl %eax, %eax
ret
+# endif
.p2align 4
-L(first_vec_x0):
+L(first_vec_x4):
+# ifndef USE_AS_STRCHRNUL
+ /* Check to see if first match was CHAR (k0) or null (k1). */
+ kmovd %k0, %eax
tzcntl %eax, %eax
- /* Found CHAR or the null byte. */
-# ifdef USE_AS_WCSCHR
- /* NB: Multiply wchar_t count by 4 to get the number of bytes. */
- leaq (%rdi, %rax, 4), %rax
+ kmovd %k1, %ecx
+ /* bzhil will not be 0 if first match was null. */
+ bzhil %eax, %ecx, %ecx
+ jne L(zero)
# else
- addq %rdi, %rax
-# endif
-# ifndef USE_AS_STRCHRNUL
- cmp (%rax), %CHAR_REG
- cmovne %rdx, %rax
+ /* Combine CHAR and null matches. */
+ kord %k0, %k1, %k0
+ kmovd %k0, %eax
+ tzcntl %eax, %eax
# endif
+ /* NB: Multiply sizeof char type (1 or 4) to get the number of
+ bytes. */
+ leaq (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax
ret
.p2align 4
L(first_vec_x1):
tzcntl %eax, %eax
- /* Found CHAR or the null byte. */
-# ifdef USE_AS_WCSCHR
- /* NB: Multiply wchar_t count by 4 to get the number of bytes. */
- leaq VEC_SIZE(%rdi, %rax, 4), %rax
-# else
- leaq VEC_SIZE(%rdi, %rax), %rax
-# endif
# ifndef USE_AS_STRCHRNUL
- cmp (%rax), %CHAR_REG
- cmovne %rdx, %rax
+ /* Found CHAR or the null byte. */
+ cmp (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
+ jne L(zero)
+
# endif
+ /* NB: Multiply sizeof char type (1 or 4) to get the number of
+ bytes. */
+ leaq (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %rax
ret
.p2align 4
L(first_vec_x2):
+# ifndef USE_AS_STRCHRNUL
+ /* Check to see if first match was CHAR (k0) or null (k1). */
+ kmovd %k0, %eax
tzcntl %eax, %eax
- /* Found CHAR or the null byte. */
-# ifdef USE_AS_WCSCHR
- /* NB: Multiply wchar_t count by 4 to get the number of bytes. */
- leaq (VEC_SIZE * 2)(%rdi, %rax, 4), %rax
+ kmovd %k1, %ecx
+ /* bzhil will not be 0 if first match was null. */
+ bzhil %eax, %ecx, %ecx
+ jne L(zero)
# else
- leaq (VEC_SIZE * 2)(%rdi, %rax), %rax
-# endif
-# ifndef USE_AS_STRCHRNUL
- cmp (%rax), %CHAR_REG
- cmovne %rdx, %rax
+ /* Combine CHAR and null matches. */
+ kord %k0, %k1, %k0
+ kmovd %k0, %eax
+ tzcntl %eax, %eax
# endif
+ /* NB: Multiply sizeof char type (1 or 4) to get the number of
+ bytes. */
+ leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
ret
-L(prep_loop_4x):
- /* Align data to 4 * VEC_SIZE. */
+ .p2align 4
+L(aligned_more):
+ /* Align data to VEC_SIZE. */
+ andq $-VEC_SIZE, %rdi
+L(cross_page_continue):
+ /* Check the next 4 * VEC_SIZE. Only one VEC_SIZE at a time since
+ data is only aligned to VEC_SIZE. Use two alternating methods
+ for checking VEC to balance latency and port contention. */
+
+ /* This method has higher latency but has better port
+ distribution. */
+ VMOVA (VEC_SIZE)(%rdi), %YMM1
+ /* Leaves only CHARS matching esi as 0. */
+ vpxorq %YMM1, %YMM0, %YMM2
+ VPMINU %YMM2, %YMM1, %YMM2
+ /* Each bit in K0 represents a CHAR or a null byte in YMM1. */
+ VPCMP $0, %YMMZERO, %YMM2, %k0
+ kmovd %k0, %eax
+ testl %eax, %eax
+ jnz L(first_vec_x1)
+
+ /* This method has higher latency but has better port
+ distribution. */
+ VMOVA (VEC_SIZE * 2)(%rdi), %YMM1
+ /* Each bit in K0 represents a CHAR in YMM1. */
+ VPCMP $0, %YMM1, %YMM0, %k0
+ /* Each bit in K1 represents a CHAR in YMM1. */
+ VPCMP $0, %YMM1, %YMMZERO, %k1
+ kortestd %k0, %k1
+ jnz L(first_vec_x2)
+
+ VMOVA (VEC_SIZE * 3)(%rdi), %YMM1
+ /* Leaves only CHARS matching esi as 0. */
+ vpxorq %YMM1, %YMM0, %YMM2
+ VPMINU %YMM2, %YMM1, %YMM2
+ /* Each bit in K0 represents a CHAR or a null byte in YMM1. */
+ VPCMP $0, %YMMZERO, %YMM2, %k0
+ kmovd %k0, %eax
+ testl %eax, %eax
+ jnz L(first_vec_x3)
+
+ VMOVA (VEC_SIZE * 4)(%rdi), %YMM1
+ /* Each bit in K0 represents a CHAR in YMM1. */
+ VPCMP $0, %YMM1, %YMM0, %k0
+ /* Each bit in K1 represents a CHAR in YMM1. */
+ VPCMP $0, %YMM1, %YMMZERO, %k1
+ kortestd %k0, %k1
+ jnz L(first_vec_x4)
+
+ /* Align data to VEC_SIZE * 4 for the loop. */
+ addq $VEC_SIZE, %rdi
andq $-(VEC_SIZE * 4), %rdi
.p2align 4
L(loop_4x_vec):
- /* Compare 4 * VEC at a time forward. */
+ /* Check 4x VEC at a time. No penalty to imm32 offset with evex
+ encoding. */
VMOVA (VEC_SIZE * 4)(%rdi), %YMM1
VMOVA (VEC_SIZE * 5)(%rdi), %YMM2
VMOVA (VEC_SIZE * 6)(%rdi), %YMM3
VMOVA (VEC_SIZE * 7)(%rdi), %YMM4
- /* Leaves only CHARS matching esi as 0. */
+ /* For YMM1 and YMM3 use xor to set the CHARs matching esi to
+ zero. */
vpxorq %YMM1, %YMM0, %YMM5
- vpxorq %YMM2, %YMM0, %YMM6
+ /* For YMM2 and YMM4 cmp not equals to CHAR and store result in
+ k register. Its possible to save either 1 or 2 instructions
+ using cmp no equals method for either YMM1 or YMM1 and YMM3
+ respectively but bottleneck on p5 makes it not worth it. */
+ VPCMP $4, %YMM0, %YMM2, %k2
vpxorq %YMM3, %YMM0, %YMM7
- vpxorq %YMM4, %YMM0, %YMM8
-
- VPMINU %YMM5, %YMM1, %YMM5
- VPMINU %YMM6, %YMM2, %YMM6
- VPMINU %YMM7, %YMM3, %YMM7
- VPMINU %YMM8, %YMM4, %YMM8
-
- VPMINU %YMM5, %YMM6, %YMM1
- VPMINU %YMM7, %YMM8, %YMM2
-
- VPMINU %YMM1, %YMM2, %YMM1
-
- /* Each bit in K0 represents a CHAR or a null byte. */
- VPCMP $0, %YMMZERO, %YMM1, %k0
-
- addq $(VEC_SIZE * 4), %rdi
-
- ktestd %k0, %k0
+ VPCMP $4, %YMM0, %YMM4, %k4
+
+ /* Use min to select all zeros from either xor or end of string).
+ */
+ VPMINU %YMM1, %YMM5, %YMM1
+ VPMINU %YMM3, %YMM7, %YMM3
+
+ /* Use min + zeromask to select for zeros. Since k2 and k4 will
+ have 0 as positions that matched with CHAR which will set
+ zero in the corresponding destination bytes in YMM2 / YMM4.
+ */
+ VPMINU %YMM1, %YMM2, %YMM2{%k2}{z}
+ VPMINU %YMM3, %YMM4, %YMM4
+ VPMINU %YMM2, %YMM4, %YMM4{%k4}{z}
+
+ VPCMP $0, %YMMZERO, %YMM4, %k1
+ kmovd %k1, %ecx
+ subq $-(VEC_SIZE * 4), %rdi
+ testl %ecx, %ecx
jz L(loop_4x_vec)
- /* Each bit in K0 represents a CHAR or a null byte in YMM1. */
- VPCMP $0, %YMMZERO, %YMM5, %k0
+ VPCMP $0, %YMMZERO, %YMM1, %k0
kmovd %k0, %eax
testl %eax, %eax
- jnz L(first_vec_x0)
+ jnz L(last_vec_x1)
- /* Each bit in K1 represents a CHAR or a null byte in YMM2. */
- VPCMP $0, %YMMZERO, %YMM6, %k1
- kmovd %k1, %eax
+ VPCMP $0, %YMMZERO, %YMM2, %k0
+ kmovd %k0, %eax
testl %eax, %eax
- jnz L(first_vec_x1)
-
- /* Each bit in K2 represents a CHAR or a null byte in YMM3. */
- VPCMP $0, %YMMZERO, %YMM7, %k2
- /* Each bit in K3 represents a CHAR or a null byte in YMM4. */
- VPCMP $0, %YMMZERO, %YMM8, %k3
+ jnz L(last_vec_x2)
+ VPCMP $0, %YMMZERO, %YMM3, %k0
+ kmovd %k0, %eax
+ /* Combine YMM3 matches (eax) with YMM4 matches (ecx). */
# ifdef USE_AS_WCSCHR
- /* NB: Each bit in K2/K3 represents 4-byte element. */
- kshiftlw $8, %k3, %k1
+ sall $8, %ecx
+ orl %ecx, %eax
+ tzcntl %eax, %eax
# else
- kshiftlq $32, %k3, %k1
+ salq $32, %rcx
+ orq %rcx, %rax
+ tzcntq %rax, %rax
# endif
+# ifndef USE_AS_STRCHRNUL
+ /* Check if match was CHAR or null. */
+ cmp (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
+ jne L(zero_end)
+# endif
+ /* NB: Multiply sizeof char type (1 or 4) to get the number of
+ bytes. */
+ leaq (VEC_SIZE * 2)(%rdi, %rax, CHAR_SIZE), %rax
+ ret
- /* Each bit in K1 represents a NULL or a mismatch. */
- korq %k1, %k2, %k1
- kmovq %k1, %rax
+# ifndef USE_AS_STRCHRNUL
+L(zero_end):
+ xorl %eax, %eax
+ ret
+# endif
- tzcntq %rax, %rax
-# ifdef USE_AS_WCSCHR
- /* NB: Multiply wchar_t count by 4 to get the number of bytes. */
- leaq (VEC_SIZE * 2)(%rdi, %rax, 4), %rax
-# else
- leaq (VEC_SIZE * 2)(%rdi, %rax), %rax
+ .p2align 4
+L(last_vec_x1):
+ tzcntl %eax, %eax
+# ifndef USE_AS_STRCHRNUL
+ /* Check if match was null. */
+ cmp (%rdi, %rax, CHAR_SIZE), %CHAR_REG
+ jne L(zero_end)
# endif
+ /* NB: Multiply sizeof char type (1 or 4) to get the number of
+ bytes. */
+ leaq (%rdi, %rax, CHAR_SIZE), %rax
+ ret
+
+ .p2align 4
+L(last_vec_x2):
+ tzcntl %eax, %eax
# ifndef USE_AS_STRCHRNUL
- cmp (%rax), %CHAR_REG
- cmovne %rdx, %rax
+ /* Check if match was null. */
+ cmp (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %CHAR_REG
+ jne L(zero_end)
# endif
+ /* NB: Multiply sizeof char type (1 or 4) to get the number of
+ bytes. */
+ leaq (VEC_SIZE)(%rdi, %rax, CHAR_SIZE), %rax
ret
/* Cold case for crossing page with first load. */
.p2align 4
L(cross_page_boundary):
+ movq %rdi, %rdx
+ /* Align rdi. */
andq $-VEC_SIZE, %rdi
- andl $(VEC_SIZE - 1), %ecx
-
VMOVA (%rdi), %YMM1
-
/* Leaves only CHARS matching esi as 0. */
vpxorq %YMM1, %YMM0, %YMM2
VPMINU %YMM2, %YMM1, %YMM2
/* Each bit in K0 represents a CHAR or a null byte in YMM1. */
VPCMP $0, %YMMZERO, %YMM2, %k0
kmovd %k0, %eax
- testl %eax, %eax
-
+ /* Remove the leading bits. */
# ifdef USE_AS_WCSCHR
+ movl %edx, %SHIFT_REG
/* NB: Divide shift count by 4 since each bit in K1 represent 4
bytes. */
- movl %ecx, %SHIFT_REG
- sarl $2, %SHIFT_REG
+ sarl $2, %SHIFT_REG
+ andl $(CHAR_PER_VEC - 1), %SHIFT_REG
# endif
-
- /* Remove the leading bits. */
sarxl %SHIFT_REG, %eax, %eax
+ /* If eax is zero continue. */
testl %eax, %eax
-
- jz L(aligned_more)
+ jz L(cross_page_continue)
tzcntl %eax, %eax
- addq %rcx, %rdi
+# ifndef USE_AS_STRCHRNUL
+ /* Check to see if match was CHAR or null. */
+ cmp (%rdx, %rax, CHAR_SIZE), %CHAR_REG
+ jne L(zero_end)
+# endif
# ifdef USE_AS_WCSCHR
- /* NB: Multiply wchar_t count by 4 to get the number of bytes. */
- leaq (%rdi, %rax, 4), %rax
+ /* NB: Multiply wchar_t count by 4 to get the number of
+ bytes. */
+ leaq (%rdx, %rax, CHAR_SIZE), %rax
# else
- addq %rdi, %rax
-# endif
-# ifndef USE_AS_STRCHRNUL
- cmp (%rax), %CHAR_REG
- cmovne %rdx, %rax
+ addq %rdx, %rax
# endif
ret
--
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