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x86: Shrink code size of memchr-avx2.S
This is not meant as a performance optimization. The previous code was far to liberal in aligning targets and wasted code size unnecissarily. The total code size saving is: 59 bytes There are no major changes in the benchmarks. Geometric Mean of all benchmarks New / Old: 0.967 Full xcheck passes on x86_64. Reviewed-by: H.J. Lu <hjl.tools@gmail.com> (cherry picked from commit6dcbb7d95d
) x86: Fix page cross case in rawmemchr-avx2 [BZ #29234] commit6dcbb7d95d
Author: Noah Goldstein <goldstein.w.n@gmail.com> Date: Mon Jun 6 21:11:33 2022 -0700 x86: Shrink code size of memchr-avx2.S Changed how the page cross case aligned string (rdi) in rawmemchr. This was incompatible with how `L(cross_page_continue)` expected the pointer to be aligned and would cause rawmemchr to read data start started before the beginning of the string. What it would read was in valid memory but could count CHAR matches resulting in an incorrect return value. This commit fixes that issue by essentially reverting the changes to the L(page_cross) case as they didn't really matter. Test cases added and all pass with the new code (and where confirmed to fail with the old code). Reviewed-by: H.J. Lu <hjl.tools@gmail.com> (cherry picked from commit2c9af8421d
)
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@ -17,6 +17,7 @@
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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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@ -50,13 +51,45 @@ 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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memset (buf, -1, 8192);
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ptr_start = buf + 4096 - 8;
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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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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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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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ptr_start[i + j] = 0xff;
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}
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}
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xmunmap (buf, 8192);
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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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@ -114,6 +147,13 @@ 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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assert (pos < len);
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size_t r = random ();
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if ((r & 31) == 0)
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@ -129,6 +169,13 @@ do_random_tests (void)
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result, p);
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ret = 1;
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}
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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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@ -150,14 +197,22 @@ 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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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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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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@ -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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@ -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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# 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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jle L(null)
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addq %rdi, %rax
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ret
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# endif
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.p2align 4,, 10
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L(first_vec_x1):
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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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# 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(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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# 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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L(first_vec_x1):
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tzcntl %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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.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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END (MEMCHR)
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#endif
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