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324 lines
8.4 KiB
324 lines
8.4 KiB
commit a910d7e164f1d9b8e77bbea35a2d2ab89a5e26cc
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Author: Noah Goldstein <goldstein.w.n@gmail.com>
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Date: Mon Jun 6 21:11:33 2022 -0700
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x86: Shrink code size of memchr-avx2.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: 59 bytes
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There are no major changes in the benchmarks.
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Geometric Mean of all benchmarks New / Old: 0.967
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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 6dcbb7d95dded20153b12d76d2f4e0ef0cda4f35)
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x86: Fix page cross case in rawmemchr-avx2 [BZ #29234]
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commit 6dcbb7d95dded20153b12d76d2f4e0ef0cda4f35
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Author: Noah Goldstein <goldstein.w.n@gmail.com>
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Date: Mon Jun 6 21:11:33 2022 -0700
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x86: Shrink code size of memchr-avx2.S
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Changed how the page cross case aligned string (rdi) in
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rawmemchr. This was incompatible with how
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`L(cross_page_continue)` expected the pointer to be aligned and
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would cause rawmemchr to read data start started before the
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beginning of the string. What it would read was in valid memory
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but could count CHAR matches resulting in an incorrect return
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value.
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This commit fixes that issue by essentially reverting the changes to
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the L(page_cross) case as they didn't really matter.
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Test cases added and all pass with the new code (and where confirmed
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to fail with the old code).
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Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
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(cherry picked from commit 2c9af8421d2b4a7fcce163e7bc81a118d22fd346)
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diff --git a/string/test-rawmemchr.c b/string/test-rawmemchr.c
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index 085098aba8fdbc13..327c0654e69e7669 100644
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--- a/string/test-rawmemchr.c
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+++ b/string/test-rawmemchr.c
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@@ -18,6 +18,7 @@
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<https://www.gnu.org/licenses/>. */
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#include <assert.h>
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+#include <support/xunistd.h>
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#define TEST_MAIN
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#define TEST_NAME "rawmemchr"
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@@ -51,13 +52,45 @@ do_one_test (impl_t *impl, const char *s, int c, char *exp_res)
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}
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}
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+static void
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+do_test_bz29234 (void)
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+{
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+ size_t i, j;
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+ char *ptr_start;
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+ char *buf = xmmap (0, 8192, PROT_READ | PROT_WRITE,
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+ MAP_PRIVATE | MAP_ANONYMOUS, -1);
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+
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+ memset (buf, -1, 8192);
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+
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+ ptr_start = buf + 4096 - 8;
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+
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+ /* Out of range matches before the start of a page. */
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+ memset (ptr_start - 8, 0x1, 8);
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+
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+ for (j = 0; j < 8; ++j)
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+ {
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+ for (i = 0; i < 128; ++i)
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+ {
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+ ptr_start[i + j] = 0x1;
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+
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+ FOR_EACH_IMPL (impl, 0)
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+ do_one_test (impl, (char *) (ptr_start + j), 0x1,
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+ ptr_start + i + j);
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+
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+ ptr_start[i + j] = 0xff;
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+ }
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+ }
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+
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+ xmunmap (buf, 8192);
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+}
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+
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static void
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do_test (size_t align, size_t pos, size_t len, int seek_char)
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{
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size_t i;
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char *result;
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- align &= 7;
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+ align &= getpagesize () - 1;
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if (align + len >= page_size)
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return;
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@@ -115,6 +148,13 @@ do_random_tests (void)
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}
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}
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+ if (align)
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+ {
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+ p[align - 1] = seek_char;
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+ if (align > 4)
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+ p[align - 4] = seek_char;
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+ }
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+
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assert (pos < len);
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size_t r = random ();
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if ((r & 31) == 0)
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@@ -130,6 +170,13 @@ do_random_tests (void)
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result, p);
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ret = 1;
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}
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+
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+ if (align)
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+ {
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+ p[align - 1] = seek_char;
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+ if (align > 4)
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+ p[align - 4] = seek_char;
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+ }
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}
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}
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@@ -151,14 +198,22 @@ test_main (void)
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do_test (i, 64, 256, 23);
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do_test (0, 16 << i, 2048, 0);
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do_test (i, 64, 256, 0);
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+
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+ do_test (getpagesize () - i, 64, 256, 23);
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+ do_test (getpagesize () - i, 64, 256, 0);
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}
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for (i = 1; i < 32; ++i)
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{
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do_test (0, i, i + 1, 23);
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do_test (0, i, i + 1, 0);
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+
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+ do_test (getpagesize () - 7, i, i + 1, 23);
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+ do_test (getpagesize () - i / 2, i, i + 1, 23);
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+ do_test (getpagesize () - i, i, i + 1, 23);
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}
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do_random_tests ();
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+ do_test_bz29234 ();
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return ret;
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}
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diff --git a/sysdeps/x86_64/multiarch/memchr-avx2-rtm.S b/sysdeps/x86_64/multiarch/memchr-avx2-rtm.S
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index 87b076c7c403ba85..c4d71938c5a3ed24 100644
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--- a/sysdeps/x86_64/multiarch/memchr-avx2-rtm.S
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+++ b/sysdeps/x86_64/multiarch/memchr-avx2-rtm.S
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@@ -2,6 +2,7 @@
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# define MEMCHR __memchr_avx2_rtm
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#endif
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+#define COND_VZEROUPPER COND_VZEROUPPER_XTEST
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#define ZERO_UPPER_VEC_REGISTERS_RETURN \
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ZERO_UPPER_VEC_REGISTERS_RETURN_XTEST
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diff --git a/sysdeps/x86_64/multiarch/memchr-avx2.S b/sysdeps/x86_64/multiarch/memchr-avx2.S
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index afdb95650232fdac..9e0b7dd1f4fe9909 100644
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--- a/sysdeps/x86_64/multiarch/memchr-avx2.S
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+++ b/sysdeps/x86_64/multiarch/memchr-avx2.S
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@@ -57,7 +57,7 @@
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# define CHAR_PER_VEC (VEC_SIZE / CHAR_SIZE)
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.section SECTION(.text),"ax",@progbits
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-ENTRY (MEMCHR)
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+ENTRY_P2ALIGN (MEMCHR, 5)
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# ifndef USE_AS_RAWMEMCHR
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/* Check for zero length. */
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# ifdef __ILP32__
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@@ -87,12 +87,14 @@ ENTRY (MEMCHR)
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# endif
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testl %eax, %eax
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jz L(aligned_more)
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- tzcntl %eax, %eax
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+ bsfl %eax, %eax
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addq %rdi, %rax
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- VZEROUPPER_RETURN
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+L(return_vzeroupper):
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+ ZERO_UPPER_VEC_REGISTERS_RETURN
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+
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# ifndef USE_AS_RAWMEMCHR
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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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@@ -100,58 +102,31 @@ L(first_vec_x0):
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/* NB: Multiply length by 4 to get byte count. */
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sall $2, %edx
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# endif
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- xorl %ecx, %ecx
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+ COND_VZEROUPPER
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+ /* Use branch instead of cmovcc so L(first_vec_x0) fits in one fetch
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+ block. branch here as opposed to cmovcc is not that costly. Common
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+ usage of memchr is to check if the return was NULL (if string was
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+ known to contain CHAR user would use rawmemchr). This branch will be
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+ highly correlated with the user branch and can be used by most
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+ modern branch predictors to predict the user branch. */
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cmpl %eax, %edx
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- leaq (%rdi, %rax), %rax
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- cmovle %rcx, %rax
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- VZEROUPPER_RETURN
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-
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-L(null):
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- xorl %eax, %eax
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- ret
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-# endif
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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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- adjusting length if it is not and this is memchr. */
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- movq %rdi, %rcx
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- /* Align data to VEC_SIZE - 1. ALGN_PTR_REG is rcx for memchr
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- and rdi for rawmemchr. */
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- orq $(VEC_SIZE - 1), %ALGN_PTR_REG
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- VPCMPEQ -(VEC_SIZE - 1)(%ALGN_PTR_REG), %ymm0, %ymm1
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- vpmovmskb %ymm1, %eax
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-# ifndef USE_AS_RAWMEMCHR
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- /* Calculate length until end of page (length checked for a
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- match). */
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- leaq 1(%ALGN_PTR_REG), %rsi
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- subq %RRAW_PTR_REG, %rsi
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-# ifdef USE_AS_WMEMCHR
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- /* NB: Divide bytes by 4 to get wchar_t count. */
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- shrl $2, %esi
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-# endif
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-# endif
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- /* Remove the leading bytes. */
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- sarxl %ERAW_PTR_REG, %eax, %eax
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-# ifndef USE_AS_RAWMEMCHR
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- /* Check the end of data. */
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- cmpq %rsi, %rdx
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- jbe L(first_vec_x0)
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+ jle L(null)
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+ addq %rdi, %rax
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+ ret
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# endif
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- testl %eax, %eax
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- jz L(cross_page_continue)
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- tzcntl %eax, %eax
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- addq %RRAW_PTR_REG, %rax
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-L(return_vzeroupper):
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- ZERO_UPPER_VEC_REGISTERS_RETURN
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- .p2align 4
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+ .p2align 4,, 10
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L(first_vec_x1):
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- tzcntl %eax, %eax
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+ bsfl %eax, %eax
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incq %rdi
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addq %rdi, %rax
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VZEROUPPER_RETURN
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-
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+# ifndef USE_AS_RAWMEMCHR
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+ /* First in aligning bytes here. */
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+L(null):
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+ xorl %eax, %eax
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+ ret
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+# endif
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.p2align 4
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L(first_vec_x2):
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tzcntl %eax, %eax
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@@ -340,7 +315,7 @@ L(first_vec_x1_check):
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incq %rdi
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addq %rdi, %rax
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VZEROUPPER_RETURN
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- .p2align 4
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+ .p2align 4,, 6
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L(set_zero_end):
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xorl %eax, %eax
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VZEROUPPER_RETURN
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@@ -428,5 +403,39 @@ L(last_vec_x3):
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VZEROUPPER_RETURN
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# endif
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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 necessary for
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+ computer return address if byte is found or adjusting length if it
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+ is not and this is memchr. */
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+ movq %rdi, %rcx
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+ /* Align data to VEC_SIZE - 1. ALGN_PTR_REG is rcx for memchr
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+ and rdi for rawmemchr. */
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+ orq $(VEC_SIZE - 1), %ALGN_PTR_REG
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+ VPCMPEQ -(VEC_SIZE - 1)(%ALGN_PTR_REG), %ymm0, %ymm1
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+ vpmovmskb %ymm1, %eax
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+# ifndef USE_AS_RAWMEMCHR
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+ /* Calculate length until end of page (length checked for a match). */
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+ leaq 1(%ALGN_PTR_REG), %rsi
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+ subq %RRAW_PTR_REG, %rsi
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+# ifdef USE_AS_WMEMCHR
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+ /* NB: Divide bytes by 4 to get wchar_t count. */
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+ shrl $2, %esi
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+# endif
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+# endif
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+ /* Remove the leading bytes. */
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+ sarxl %ERAW_PTR_REG, %eax, %eax
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+# ifndef USE_AS_RAWMEMCHR
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+ /* Check the end of data. */
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+ cmpq %rsi, %rdx
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+ jbe L(first_vec_x0)
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+# endif
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+ testl %eax, %eax
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+ jz L(cross_page_continue)
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+ bsfl %eax, %eax
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+ addq %RRAW_PTR_REG, %rax
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+ VZEROUPPER_RETURN
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+
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+
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END (MEMCHR)
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#endif
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