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glibc/SOURCES/glibc-RHEL-15696-70.patch

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From abddd61de090ae84e380aff68a98bd94ef704667 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Fri, 24 Dec 2021 18:54:41 -0600
Subject: [PATCH] x86: Optimize L(less_vec) case in memcmp-evex-movbe.S
Content-type: text/plain; charset=UTF-8
No bug.
Optimizations are twofold.
1) Replace page cross and 0/1 checks with masked load instructions in
L(less_vec). In applications this reduces branch-misses in the
hot [0, 32] case.
2) Change controlflow so that L(less_vec) case gets the fall through.
Change 2) helps copies in the [0, 32] size range but comes at the cost
of copies in the [33, 64] size range. From profiles of GCC and
Python3, 94%+ and 99%+ of calls are in the [0, 32] range so this
appears to the the right tradeoff.
Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---
sysdeps/x86_64/multiarch/memcmp-evex-movbe.S | 249 +++++--------------
1 file changed, 56 insertions(+), 193 deletions(-)
diff --git a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S
index 640f6757..d2899e7c 100644
--- a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S
+++ b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S
@@ -62,15 +62,18 @@ Latency:
# 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)
@@ -102,12 +105,48 @@ ENTRY_P2ALIGN (MEMCMP, 6)
movl %edx, %edx
# endif
cmp $CHAR_PER_VEC, %RDX_LP
- jb L(less_vec)
+ /* 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
+ 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
@@ -131,13 +170,13 @@ ENTRY_P2ALIGN (MEMCMP, 6)
/* Check third and fourth VEC no matter what. */
VMOVU (VEC_SIZE * 2)(%rsi), %YMM3
- VPCMP $4, (VEC_SIZE * 2)(%rdi), %YMM3, %k1
+ 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
+ VPCMP $4,(VEC_SIZE * 3)(%rdi), %YMM4, %k1
kmovd %k1, %ecx
testl %ecx, %ecx
jnz L(return_vec_3)
@@ -169,7 +208,7 @@ ENTRY_P2ALIGN (MEMCMP, 6)
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
+ vpternlogd $0xde,(VEC_SIZE * 3)(%rdi), %YMM1, %YMM4
/* Or together YMM2, YMM3, and YMM4 into YMM4. */
vpternlogd $0xfe, %YMM2, %YMM3, %YMM4
@@ -184,7 +223,8 @@ ENTRY_P2ALIGN (MEMCMP, 6)
/* NB: eax must be zero to reach here. */
ret
- .p2align 4
+
+ .p2align 4,, 8
L(8x_end_return_vec_0_1_2_3):
movq %rdx, %rdi
L(8x_return_vec_0_1_2_3):
@@ -222,23 +262,6 @@ L(return_vec_3):
# endif
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(return_vec_1):
@@ -297,7 +320,7 @@ L(loop_4x_vec):
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 $0xde,(VEC_SIZE * 3)(%rdi), %YMM1, %YMM4
vpternlogd $0xfe, %YMM2, %YMM3, %YMM4
VPTEST %YMM4, %YMM4, %k1
kmovd %k1, %ecx
@@ -324,7 +347,7 @@ L(loop_4x_vec):
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 $0xde,(VEC_SIZE * 3)(%rdx), %YMM1, %YMM4
vpternlogd $0xfe, %YMM2, %YMM3, %YMM4
VPTEST %YMM4, %YMM4, %k1
kmovd %k1, %ecx
@@ -336,14 +359,14 @@ L(loop_4x_vec):
/* Only entry is from L(more_8x_vec). */
.p2align 4,, 10
L(8x_last_2x_vec):
- VPCMP $4, (VEC_SIZE * 2)(%rdx), %YMM3, %k1
+ 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
+ VPCMP $4,(VEC_SIZE * 3)(%rdx), %YMM1, %k1
kmovd %k1, %eax
testl %eax, %eax
jnz L(8x_return_vec_3)
@@ -392,7 +415,9 @@ L(last_1x_vec):
jnz L(return_vec_0_end)
ret
- .p2align 4,, 10
+
+ /* 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. */
@@ -411,31 +436,8 @@ L(return_vec_1_end):
# endif
ret
- /* NB: L(one_or_less) fits in alignment padding between
- L(return_vec_1_end) and L(return_vec_0_end). */
-# ifdef USE_AS_WMEMCMP
-L(one_or_less):
- jb L(zero)
- movl (%rdi), %ecx
- xorl %edx, %edx
- cmpl (%rsi), %ecx
- je L(zero)
- setg %dl
- leal -1(%rdx, %rdx), %eax
- ret
-# else
-L(one_or_less):
- jb L(zero)
- movzbl (%rsi), %ecx
- movzbl (%rdi), %eax
- subl %ecx, %eax
- ret
-# endif
-L(zero):
- xorl %eax, %eax
- ret
-
- .p2align 4
+ /* 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
@@ -451,146 +453,7 @@ L(return_vec_0_end):
subl %ecx, %eax
# endif
ret
+ /* 1-byte until next cache line. */
- .p2align 4
-L(less_vec):
- /* Check if one or less CHAR. This is necessary for size == 0
- but is also faster for size == CHAR_SIZE. */
- cmpl $1, %edx
- jbe L(one_or_less)
-
- /* Check if loading one VEC from either s1 or s2 could cause a
- page cross. This can have false positives but is by far the
- fastest method. */
- movl %edi, %eax
- orl %esi, %eax
- andl $(PAGE_SIZE - 1), %eax
- cmpl $(PAGE_SIZE - VEC_SIZE), %eax
- jg L(page_cross_less_vec)
-
- /* No page cross possible. */
- VMOVU (%rsi), %YMM2
- VPCMP $4, (%rdi), %YMM2, %k1
- kmovd %k1, %eax
- /* Check if any matches where in bounds. Intentionally not
- storing result in eax to limit dependency chain if it goes to
- L(return_vec_0_lv). */
- bzhil %edx, %eax, %edx
- jnz L(return_vec_0_lv)
- xorl %eax, %eax
- ret
-
- /* Essentially duplicate of L(return_vec_0). Ends up not costing
- any code as shrinks L(less_vec) by allowing 2-byte encoding of
- the jump and ends up fitting in aligning bytes. As well fits on
- same cache line as L(less_vec) so also saves a line from having
- to be fetched on cold calls to memcmp. */
- .p2align 4,, 4
-L(return_vec_0_lv):
- 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(page_cross_less_vec):
- /* if USE_AS_WMEMCMP it can only be 0, 4, 8, 12, 16, 20, 24, 28
- bytes. */
- cmpl $(16 / CHAR_SIZE), %edx
- jae L(between_16_31)
-# ifndef USE_AS_WMEMCMP
- cmpl $8, %edx
- jae L(between_8_15)
- cmpl $4, %edx
- jb L(between_2_3)
-
- /* Load as big endian with overlapping movbe to avoid branches.
- */
- movbe (%rdi), %eax
- movbe (%rsi), %ecx
- shlq $32, %rax
- shlq $32, %rcx
- movbe -4(%rdi, %rdx), %edi
- movbe -4(%rsi, %rdx), %esi
- orq %rdi, %rax
- orq %rsi, %rcx
- subq %rcx, %rax
- /* edx is guranteed to be positive int32 in range [4, 7]. */
- cmovne %edx, %eax
- /* ecx is -1 if rcx > rax. Otherwise 0. */
- sbbl %ecx, %ecx
- /* If rcx > rax, then ecx is 0 and eax is positive. If rcx ==
- rax then eax and ecx are zero. If rax < rax then ecx is -1 so
- eax doesn't matter. */
- orl %ecx, %eax
- ret
-
- .p2align 4,, 8
-L(between_8_15):
-# endif
- /* If USE_AS_WMEMCMP fall through into 8-15 byte case. */
- vmovq (%rdi), %xmm1
- vmovq (%rsi), %xmm2
- VPCMP $4, %xmm1, %xmm2, %k1
- kmovd %k1, %eax
- testl %eax, %eax
- jnz L(return_vec_0_lv)
- /* Use overlapping loads to avoid branches. */
- vmovq -8(%rdi, %rdx, CHAR_SIZE), %xmm1
- vmovq -8(%rsi, %rdx, CHAR_SIZE), %xmm2
- VPCMP $4, %xmm1, %xmm2, %k1
- addl $(CHAR_PER_VEC - (8 / CHAR_SIZE)), %edx
- kmovd %k1, %eax
- testl %eax, %eax
- jnz L(return_vec_0_end)
- ret
-
- .p2align 4,, 8
-L(between_16_31):
- /* From 16 to 31 bytes. No branch when size == 16. */
-
- /* Use movups to save code size. */
- vmovdqu (%rsi), %xmm2
- VPCMP $4, (%rdi), %xmm2, %k1
- kmovd %k1, %eax
- testl %eax, %eax
- jnz L(return_vec_0_lv)
- /* Use overlapping loads to avoid branches. */
- vmovdqu -16(%rsi, %rdx, CHAR_SIZE), %xmm2
- VPCMP $4, -16(%rdi, %rdx, CHAR_SIZE), %xmm2, %k1
- addl $(CHAR_PER_VEC - (16 / CHAR_SIZE)), %edx
- kmovd %k1, %eax
- testl %eax, %eax
- jnz L(return_vec_0_end)
- ret
-
-# ifndef USE_AS_WMEMCMP
-L(between_2_3):
- /* Load as big endian to avoid branches. */
- movzwl (%rdi), %eax
- movzwl (%rsi), %ecx
- shll $8, %eax
- shll $8, %ecx
- bswap %eax
- bswap %ecx
- movzbl -1(%rdi, %rdx), %edi
- movzbl -1(%rsi, %rdx), %esi
- orl %edi, %eax
- orl %esi, %ecx
- /* Subtraction is okay because the upper 8 bits are zero. */
- subl %ecx, %eax
- ret
-# endif
END (MEMCMP)
#endif
--
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