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130 lines
3.4 KiB
130 lines
3.4 KiB
commit 3c87383a20daff9a230439e31b778716bfed4d8b |
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Author: Noah Goldstein <goldstein.w.n@gmail.com> |
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Date: Mon Jun 6 21:11:34 2022 -0700 |
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x86: Shrink code size of memchr-evex.S |
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This is not meant as a performance optimization. The previous code was |
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far to liberal in aligning targets and wasted code size unnecissarily. |
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The total code size saving is: 64 bytes |
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There are no non-negligible changes in the benchmarks. |
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Geometric Mean of all benchmarks New / Old: 1.000 |
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Full xcheck passes on x86_64. |
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Reviewed-by: H.J. Lu <hjl.tools@gmail.com> |
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(cherry picked from commit 56da3fe1dd075285fa8186d44b3c28e68c687e62) |
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diff --git a/sysdeps/x86_64/multiarch/memchr-evex.S b/sysdeps/x86_64/multiarch/memchr-evex.S |
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index 4d0ed6d136f099e1..68381c99a4948134 100644 |
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--- a/sysdeps/x86_64/multiarch/memchr-evex.S |
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+++ b/sysdeps/x86_64/multiarch/memchr-evex.S |
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@@ -88,7 +88,7 @@ |
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# define PAGE_SIZE 4096 |
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.section SECTION(.text),"ax",@progbits |
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-ENTRY (MEMCHR) |
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+ENTRY_P2ALIGN (MEMCHR, 6) |
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# ifndef USE_AS_RAWMEMCHR |
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/* Check for zero length. */ |
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test %RDX_LP, %RDX_LP |
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@@ -131,22 +131,24 @@ L(zero): |
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xorl %eax, %eax |
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ret |
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- .p2align 5 |
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+ .p2align 4 |
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L(first_vec_x0): |
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- /* Check if first match was before length. */ |
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- tzcntl %eax, %eax |
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- xorl %ecx, %ecx |
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- cmpl %eax, %edx |
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- leaq (%rdi, %rax, CHAR_SIZE), %rax |
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- cmovle %rcx, %rax |
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+ /* Check if first match was before length. NB: tzcnt has false data- |
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+ dependency on destination. eax already had a data-dependency on esi |
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+ so this should have no affect here. */ |
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+ tzcntl %eax, %esi |
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+# ifdef USE_AS_WMEMCHR |
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+ leaq (%rdi, %rsi, CHAR_SIZE), %rdi |
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+# else |
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+ addq %rsi, %rdi |
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+# endif |
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+ xorl %eax, %eax |
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+ cmpl %esi, %edx |
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+ cmovg %rdi, %rax |
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ret |
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-# else |
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- /* NB: first_vec_x0 is 17 bytes which will leave |
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- cross_page_boundary (which is relatively cold) close enough |
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- to ideal alignment. So only realign L(cross_page_boundary) if |
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- rawmemchr. */ |
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- .p2align 4 |
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# endif |
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+ |
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+ .p2align 4 |
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L(cross_page_boundary): |
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/* Save pointer before aligning as its original value is |
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necessary for computer return address if byte is found or |
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@@ -400,10 +402,14 @@ L(last_2x_vec): |
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L(zero_end): |
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ret |
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+L(set_zero_end): |
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+ xorl %eax, %eax |
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+ ret |
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.p2align 4 |
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L(first_vec_x1_check): |
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- tzcntl %eax, %eax |
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+ /* eax must be non-zero. Use bsfl to save code size. */ |
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+ bsfl %eax, %eax |
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/* Adjust length. */ |
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subl $-(CHAR_PER_VEC * 4), %edx |
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/* Check if match within remaining length. */ |
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@@ -412,9 +418,6 @@ L(first_vec_x1_check): |
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/* NB: Multiply bytes by CHAR_SIZE to get the wchar_t count. */ |
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leaq VEC_SIZE(%rdi, %rax, CHAR_SIZE), %rax |
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ret |
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-L(set_zero_end): |
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- xorl %eax, %eax |
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- ret |
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.p2align 4 |
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L(loop_4x_vec_end): |
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@@ -464,7 +467,7 @@ L(loop_4x_vec_end): |
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# endif |
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ret |
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- .p2align 4 |
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+ .p2align 4,, 10 |
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L(last_vec_x1_return): |
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tzcntl %eax, %eax |
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# if defined USE_AS_WMEMCHR || RET_OFFSET != 0 |
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@@ -496,6 +499,7 @@ L(last_vec_x3_return): |
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# endif |
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# ifndef USE_AS_RAWMEMCHR |
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+ .p2align 4,, 5 |
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L(last_4x_vec_or_less_cmpeq): |
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VPCMP $0, (VEC_SIZE * 5)(%rdi), %YMMMATCH, %k0 |
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kmovd %k0, %eax |
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@@ -546,7 +550,7 @@ L(last_4x_vec): |
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# endif |
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andl %ecx, %eax |
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jz L(zero_end2) |
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- tzcntl %eax, %eax |
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+ bsfl %eax, %eax |
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leaq (VEC_SIZE * 4)(%rdi, %rax, CHAR_SIZE), %rax |
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L(zero_end2): |
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ret |
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@@ -562,6 +566,6 @@ L(last_vec_x3): |
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leaq (VEC_SIZE * 3)(%rdi, %rax, CHAR_SIZE), %rax |
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ret |
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# endif |
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- |
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+ /* 7 bytes from next cache line. */ |
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END (MEMCHR) |
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#endif
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