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glibc/SOURCES/glibc-upstream-2.34-283.patch

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commit 4901009dad8b3ab141ac6e0caebe99e03a67f5eb
Author: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Mon Jun 6 21:11:30 2022 -0700
x86: Optimize memrchr-sse2.S
The new code:
1. prioritizes smaller lengths more.
2. optimizes target placement more carefully.
3. reuses logic more.
4. fixes up various inefficiencies in the logic.
The total code size saving is: 394 bytes
Geometric Mean of all benchmarks New / Old: 0.874
Regressions:
1. The page cross case is now colder, especially re-entry from the
page cross case if a match is not found in the first VEC
(roughly 50%). My general opinion with this patch is this is
acceptable given the "coldness" of this case (less than 4%) and
generally performance improvement in the other far more common
cases.
2. There are some regressions 5-15% for medium/large user-arg
lengths that have a match in the first VEC. This is because the
logic was rewritten to optimize finds in the first VEC if the
user-arg length is shorter (where we see roughly 20-50%
performance improvements). It is not always the case this is a
regression. My intuition is some frontend quirk is partially
explaining the data although I haven't been able to find the
root cause.
Full xcheck passes on x86_64.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit 731feee3869550e93177e604604c1765d81de571)
diff --git a/sysdeps/x86_64/memrchr.S b/sysdeps/x86_64/memrchr.S
index cc2001167d77c83c..c2a5902bf9385c67 100644
--- a/sysdeps/x86_64/memrchr.S
+++ b/sysdeps/x86_64/memrchr.S
@@ -19,362 +19,333 @@
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
+#define VEC_SIZE 16
+#define PAGE_SIZE 4096
.text
-ENTRY (__memrchr)
- movd %esi, %xmm1
-
- sub $16, %RDX_LP
- jbe L(length_less16)
-
- punpcklbw %xmm1, %xmm1
- punpcklbw %xmm1, %xmm1
-
- add %RDX_LP, %RDI_LP
- pshufd $0, %xmm1, %xmm1
-
- movdqu (%rdi), %xmm0
- pcmpeqb %xmm1, %xmm0
-
-/* Check if there is a match. */
- pmovmskb %xmm0, %eax
- test %eax, %eax
- jnz L(matches0)
-
- sub $64, %rdi
- mov %edi, %ecx
- and $15, %ecx
- jz L(loop_prolog)
-
- add $16, %rdi
- add $16, %rdx
- and $-16, %rdi
- sub %rcx, %rdx
-
- .p2align 4
-L(loop_prolog):
- sub $64, %rdx
- jbe L(exit_loop)
-
- movdqa 48(%rdi), %xmm0
- pcmpeqb %xmm1, %xmm0
- pmovmskb %xmm0, %eax
- test %eax, %eax
- jnz L(matches48)
-
- movdqa 32(%rdi), %xmm2
- pcmpeqb %xmm1, %xmm2
- pmovmskb %xmm2, %eax
- test %eax, %eax
- jnz L(matches32)
-
- movdqa 16(%rdi), %xmm3
- pcmpeqb %xmm1, %xmm3
- pmovmskb %xmm3, %eax
- test %eax, %eax
- jnz L(matches16)
-
- movdqa (%rdi), %xmm4
- pcmpeqb %xmm1, %xmm4
- pmovmskb %xmm4, %eax
- test %eax, %eax
- jnz L(matches0)
-
- sub $64, %rdi
- sub $64, %rdx
- jbe L(exit_loop)
-
- movdqa 48(%rdi), %xmm0
- pcmpeqb %xmm1, %xmm0
- pmovmskb %xmm0, %eax
- test %eax, %eax
- jnz L(matches48)
-
- movdqa 32(%rdi), %xmm2
- pcmpeqb %xmm1, %xmm2
- pmovmskb %xmm2, %eax
- test %eax, %eax
- jnz L(matches32)
-
- movdqa 16(%rdi), %xmm3
- pcmpeqb %xmm1, %xmm3
- pmovmskb %xmm3, %eax
- test %eax, %eax
- jnz L(matches16)
-
- movdqa (%rdi), %xmm3
- pcmpeqb %xmm1, %xmm3
- pmovmskb %xmm3, %eax
- test %eax, %eax
- jnz L(matches0)
-
- mov %edi, %ecx
- and $63, %ecx
- jz L(align64_loop)
-
- add $64, %rdi
- add $64, %rdx
- and $-64, %rdi
- sub %rcx, %rdx
-
- .p2align 4
-L(align64_loop):
- sub $64, %rdi
- sub $64, %rdx
- jbe L(exit_loop)
-
- movdqa (%rdi), %xmm0
- movdqa 16(%rdi), %xmm2
- movdqa 32(%rdi), %xmm3
- movdqa 48(%rdi), %xmm4
-
- pcmpeqb %xmm1, %xmm0
- pcmpeqb %xmm1, %xmm2
- pcmpeqb %xmm1, %xmm3
- pcmpeqb %xmm1, %xmm4
-
- pmaxub %xmm3, %xmm0
- pmaxub %xmm4, %xmm2
- pmaxub %xmm0, %xmm2
- pmovmskb %xmm2, %eax
-
- test %eax, %eax
- jz L(align64_loop)
-
- pmovmskb %xmm4, %eax
- test %eax, %eax
- jnz L(matches48)
-
- pmovmskb %xmm3, %eax
- test %eax, %eax
- jnz L(matches32)
-
- movdqa 16(%rdi), %xmm2
-
- pcmpeqb %xmm1, %xmm2
- pcmpeqb (%rdi), %xmm1
-
- pmovmskb %xmm2, %eax
- test %eax, %eax
- jnz L(matches16)
-
- pmovmskb %xmm1, %eax
- bsr %eax, %eax
-
- add %rdi, %rax
+ENTRY_P2ALIGN(__memrchr, 6)
+#ifdef __ILP32__
+ /* Clear upper bits. */
+ mov %RDX_LP, %RDX_LP
+#endif
+ movd %esi, %xmm0
+
+ /* Get end pointer. */
+ leaq (%rdx, %rdi), %rcx
+
+ punpcklbw %xmm0, %xmm0
+ punpcklwd %xmm0, %xmm0
+ pshufd $0, %xmm0, %xmm0
+
+ /* Check if we can load 1x VEC without cross a page. */
+ testl $(PAGE_SIZE - VEC_SIZE), %ecx
+ jz L(page_cross)
+
+ /* NB: This load happens regardless of whether rdx (len) is zero. Since
+ it doesn't cross a page and the standard gurantees any pointer have
+ at least one-valid byte this load must be safe. For the entire
+ history of the x86 memrchr implementation this has been possible so
+ no code "should" be relying on a zero-length check before this load.
+ The zero-length check is moved to the page cross case because it is
+ 1) pretty cold and including it pushes the hot case len <= VEC_SIZE
+ into 2-cache lines. */
+ movups -(VEC_SIZE)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
+
+ subq $VEC_SIZE, %rdx
+ ja L(more_1x_vec)
+L(ret_vec_x0_test):
+ /* Zero-flag set if eax (src) is zero. Destination unchanged if src is
+ zero. */
+ bsrl %eax, %eax
+ jz L(ret_0)
+ /* Check if the CHAR match is in bounds. Need to truly zero `eax` here
+ if out of bounds. */
+ addl %edx, %eax
+ jl L(zero_0)
+ /* Since we subtracted VEC_SIZE from rdx earlier we can just add to base
+ ptr. */
+ addq %rdi, %rax
+L(ret_0):
ret
- .p2align 4
-L(exit_loop):
- add $64, %edx
- cmp $32, %edx
- jbe L(exit_loop_32)
-
- movdqa 48(%rdi), %xmm0
- pcmpeqb %xmm1, %xmm0
- pmovmskb %xmm0, %eax
- test %eax, %eax
- jnz L(matches48)
-
- movdqa 32(%rdi), %xmm2
- pcmpeqb %xmm1, %xmm2
- pmovmskb %xmm2, %eax
- test %eax, %eax
- jnz L(matches32)
-
- movdqa 16(%rdi), %xmm3
- pcmpeqb %xmm1, %xmm3
- pmovmskb %xmm3, %eax
- test %eax, %eax
- jnz L(matches16_1)
- cmp $48, %edx
- jbe L(return_null)
-
- pcmpeqb (%rdi), %xmm1
- pmovmskb %xmm1, %eax
- test %eax, %eax
- jnz L(matches0_1)
- xor %eax, %eax
+ .p2align 4,, 5
+L(ret_vec_x0):
+ bsrl %eax, %eax
+ leaq -(VEC_SIZE)(%rcx, %rax), %rax
ret
- .p2align 4
-L(exit_loop_32):
- movdqa 48(%rdi), %xmm0
- pcmpeqb %xmm1, %xmm0
- pmovmskb %xmm0, %eax
- test %eax, %eax
- jnz L(matches48_1)
- cmp $16, %edx
- jbe L(return_null)
-
- pcmpeqb 32(%rdi), %xmm1
- pmovmskb %xmm1, %eax
- test %eax, %eax
- jnz L(matches32_1)
- xor %eax, %eax
+ .p2align 4,, 2
+L(zero_0):
+ xorl %eax, %eax
ret
- .p2align 4
-L(matches0):
- bsr %eax, %eax
- add %rdi, %rax
- ret
-
- .p2align 4
-L(matches16):
- bsr %eax, %eax
- lea 16(%rax, %rdi), %rax
- ret
- .p2align 4
-L(matches32):
- bsr %eax, %eax
- lea 32(%rax, %rdi), %rax
+ .p2align 4,, 8
+L(more_1x_vec):
+ testl %eax, %eax
+ jnz L(ret_vec_x0)
+
+ /* Align rcx (pointer to string). */
+ decq %rcx
+ andq $-VEC_SIZE, %rcx
+
+ movq %rcx, %rdx
+ /* NB: We could consistenyl save 1-byte in this pattern with `movaps
+ %xmm0, %xmm1; pcmpeq IMM8(r), %xmm1; ...`. The reason against it is
+ it adds more frontend uops (even if the moves can be eliminated) and
+ some percentage of the time actual backend uops. */
+ movaps -(VEC_SIZE)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ subq %rdi, %rdx
+ pmovmskb %xmm1, %eax
+
+ cmpq $(VEC_SIZE * 2), %rdx
+ ja L(more_2x_vec)
+L(last_2x_vec):
+ subl $VEC_SIZE, %edx
+ jbe L(ret_vec_x0_test)
+
+ testl %eax, %eax
+ jnz L(ret_vec_x0)
+
+ movaps -(VEC_SIZE * 2)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
+
+ subl $VEC_SIZE, %edx
+ bsrl %eax, %eax
+ jz L(ret_1)
+ addl %edx, %eax
+ jl L(zero_0)
+ addq %rdi, %rax
+L(ret_1):
ret
- .p2align 4
-L(matches48):
- bsr %eax, %eax
- lea 48(%rax, %rdi), %rax
+ /* Don't align. Otherwise lose 2-byte encoding in jump to L(page_cross)
+ causes the hot pause (length <= VEC_SIZE) to span multiple cache
+ lines. Naturally aligned % 16 to 8-bytes. */
+L(page_cross):
+ /* Zero length check. */
+ testq %rdx, %rdx
+ jz L(zero_0)
+
+ leaq -1(%rcx), %r8
+ andq $-(VEC_SIZE), %r8
+
+ movaps (%r8), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %esi
+ /* Shift out negative alignment (because we are starting from endptr and
+ working backwards). */
+ negl %ecx
+ /* 32-bit shift but VEC_SIZE=16 so need to mask the shift count
+ explicitly. */
+ andl $(VEC_SIZE - 1), %ecx
+ shl %cl, %esi
+ movzwl %si, %eax
+ leaq (%rdi, %rdx), %rcx
+ cmpq %rdi, %r8
+ ja L(more_1x_vec)
+ subl $VEC_SIZE, %edx
+ bsrl %eax, %eax
+ jz L(ret_2)
+ addl %edx, %eax
+ jl L(zero_1)
+ addq %rdi, %rax
+L(ret_2):
ret
- .p2align 4
-L(matches0_1):
- bsr %eax, %eax
- sub $64, %rdx
- add %rax, %rdx
- jl L(return_null)
- add %rdi, %rax
+ /* Fits in aliging bytes. */
+L(zero_1):
+ xorl %eax, %eax
ret
- .p2align 4
-L(matches16_1):
- bsr %eax, %eax
- sub $48, %rdx
- add %rax, %rdx
- jl L(return_null)
- lea 16(%rdi, %rax), %rax
+ .p2align 4,, 5
+L(ret_vec_x1):
+ bsrl %eax, %eax
+ leaq -(VEC_SIZE * 2)(%rcx, %rax), %rax
ret
- .p2align 4
-L(matches32_1):
- bsr %eax, %eax
- sub $32, %rdx
- add %rax, %rdx
- jl L(return_null)
- lea 32(%rdi, %rax), %rax
- ret
+ .p2align 4,, 8
+L(more_2x_vec):
+ testl %eax, %eax
+ jnz L(ret_vec_x0)
- .p2align 4
-L(matches48_1):
- bsr %eax, %eax
- sub $16, %rdx
- add %rax, %rdx
- jl L(return_null)
- lea 48(%rdi, %rax), %rax
- ret
+ movaps -(VEC_SIZE * 2)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
+ testl %eax, %eax
+ jnz L(ret_vec_x1)
- .p2align 4
-L(return_null):
- xor %eax, %eax
- ret
- .p2align 4
-L(length_less16_offset0):
- test %edx, %edx
- jz L(return_null)
+ movaps -(VEC_SIZE * 3)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
- mov %dl, %cl
- pcmpeqb (%rdi), %xmm1
+ subq $(VEC_SIZE * 4), %rdx
+ ja L(more_4x_vec)
- mov $1, %edx
- sal %cl, %edx
- sub $1, %edx
+ addl $(VEC_SIZE), %edx
+ jle L(ret_vec_x2_test)
- pmovmskb %xmm1, %eax
+L(last_vec):
+ testl %eax, %eax
+ jnz L(ret_vec_x2)
- and %edx, %eax
- test %eax, %eax
- jz L(return_null)
+ movaps -(VEC_SIZE * 4)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
- bsr %eax, %eax
- add %rdi, %rax
+ subl $(VEC_SIZE), %edx
+ bsrl %eax, %eax
+ jz L(ret_3)
+ addl %edx, %eax
+ jl L(zero_2)
+ addq %rdi, %rax
+L(ret_3):
ret
- .p2align 4
-L(length_less16):
- punpcklbw %xmm1, %xmm1
- punpcklbw %xmm1, %xmm1
-
- add $16, %edx
-
- pshufd $0, %xmm1, %xmm1
-
- mov %edi, %ecx
- and $15, %ecx
- jz L(length_less16_offset0)
-
- mov %cl, %dh
- mov %ecx, %esi
- add %dl, %dh
- and $-16, %rdi
-
- sub $16, %dh
- ja L(length_less16_part2)
-
- pcmpeqb (%rdi), %xmm1
- pmovmskb %xmm1, %eax
-
- sar %cl, %eax
- mov %dl, %cl
-
- mov $1, %edx
- sal %cl, %edx
- sub $1, %edx
-
- and %edx, %eax
- test %eax, %eax
- jz L(return_null)
-
- bsr %eax, %eax
- add %rdi, %rax
- add %rsi, %rax
+ .p2align 4,, 6
+L(ret_vec_x2_test):
+ bsrl %eax, %eax
+ jz L(zero_2)
+ addl %edx, %eax
+ jl L(zero_2)
+ addq %rdi, %rax
ret
- .p2align 4
-L(length_less16_part2):
- movdqa 16(%rdi), %xmm2
- pcmpeqb %xmm1, %xmm2
- pmovmskb %xmm2, %eax
-
- mov %dh, %cl
- mov $1, %edx
- sal %cl, %edx
- sub $1, %edx
-
- and %edx, %eax
+L(zero_2):
+ xorl %eax, %eax
+ ret
- test %eax, %eax
- jnz L(length_less16_part2_return)
- pcmpeqb (%rdi), %xmm1
- pmovmskb %xmm1, %eax
+ .p2align 4,, 5
+L(ret_vec_x2):
+ bsrl %eax, %eax
+ leaq -(VEC_SIZE * 3)(%rcx, %rax), %rax
+ ret
- mov %esi, %ecx
- sar %cl, %eax
- test %eax, %eax
- jz L(return_null)
+ .p2align 4,, 5
+L(ret_vec_x3):
+ bsrl %eax, %eax
+ leaq -(VEC_SIZE * 4)(%rcx, %rax), %rax
+ ret
- bsr %eax, %eax
- add %rdi, %rax
- add %rsi, %rax
+ .p2align 4,, 8
+L(more_4x_vec):
+ testl %eax, %eax
+ jnz L(ret_vec_x2)
+
+ movaps -(VEC_SIZE * 4)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
+
+ testl %eax, %eax
+ jnz L(ret_vec_x3)
+
+ addq $-(VEC_SIZE * 4), %rcx
+ cmpq $(VEC_SIZE * 4), %rdx
+ jbe L(last_4x_vec)
+
+ /* Offset everything by 4x VEC_SIZE here to save a few bytes at the end
+ keeping the code from spilling to the next cache line. */
+ addq $(VEC_SIZE * 4 - 1), %rcx
+ andq $-(VEC_SIZE * 4), %rcx
+ leaq (VEC_SIZE * 4)(%rdi), %rdx
+ andq $-(VEC_SIZE * 4), %rdx
+
+ .p2align 4,, 11
+L(loop_4x_vec):
+ movaps (VEC_SIZE * -1)(%rcx), %xmm1
+ movaps (VEC_SIZE * -2)(%rcx), %xmm2
+ movaps (VEC_SIZE * -3)(%rcx), %xmm3
+ movaps (VEC_SIZE * -4)(%rcx), %xmm4
+ pcmpeqb %xmm0, %xmm1
+ pcmpeqb %xmm0, %xmm2
+ pcmpeqb %xmm0, %xmm3
+ pcmpeqb %xmm0, %xmm4
+
+ por %xmm1, %xmm2
+ por %xmm3, %xmm4
+ por %xmm2, %xmm4
+
+ pmovmskb %xmm4, %esi
+ testl %esi, %esi
+ jnz L(loop_end)
+
+ addq $-(VEC_SIZE * 4), %rcx
+ cmpq %rdx, %rcx
+ jne L(loop_4x_vec)
+
+ subl %edi, %edx
+
+ /* Ends up being 1-byte nop. */
+ .p2align 4,, 2
+L(last_4x_vec):
+ movaps -(VEC_SIZE)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
+
+ cmpl $(VEC_SIZE * 2), %edx
+ jbe L(last_2x_vec)
+
+ testl %eax, %eax
+ jnz L(ret_vec_x0)
+
+
+ movaps -(VEC_SIZE * 2)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
+
+ testl %eax, %eax
+ jnz L(ret_vec_end)
+
+ movaps -(VEC_SIZE * 3)(%rcx), %xmm1
+ pcmpeqb %xmm0, %xmm1
+ pmovmskb %xmm1, %eax
+
+ subl $(VEC_SIZE * 3), %edx
+ ja L(last_vec)
+ bsrl %eax, %eax
+ jz L(ret_4)
+ addl %edx, %eax
+ jl L(zero_3)
+ addq %rdi, %rax
+L(ret_4):
ret
- .p2align 4
-L(length_less16_part2_return):
- bsr %eax, %eax
- lea 16(%rax, %rdi), %rax
+ /* Ends up being 1-byte nop. */
+ .p2align 4,, 3
+L(loop_end):
+ pmovmskb %xmm1, %eax
+ sall $16, %eax
+ jnz L(ret_vec_end)
+
+ pmovmskb %xmm2, %eax
+ testl %eax, %eax
+ jnz L(ret_vec_end)
+
+ pmovmskb %xmm3, %eax
+ /* Combine last 2 VEC matches. If ecx (VEC3) is zero (no CHAR in VEC3)
+ then it won't affect the result in esi (VEC4). If ecx is non-zero
+ then CHAR in VEC3 and bsrq will use that position. */
+ sall $16, %eax
+ orl %esi, %eax
+ bsrl %eax, %eax
+ leaq -(VEC_SIZE * 4)(%rcx, %rax), %rax
ret
-END (__memrchr)
+L(ret_vec_end):
+ bsrl %eax, %eax
+ leaq (VEC_SIZE * -2)(%rax, %rcx), %rax
+ ret
+ /* Use in L(last_4x_vec). In the same cache line. This is just a spare
+ aligning bytes. */
+L(zero_3):
+ xorl %eax, %eax
+ ret
+ /* 2-bytes from next cache line. */
+END(__memrchr)
weak_alias (__memrchr, memrchr)