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Make memcmp() and memchr() go fast again

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Readahead within the specified size is legal, even if it overlaps a page
boundary; it's the fault of the caller if that causes a segfault.
This commit is contained in:
Justine Tunney 2023-11-29 05:17:21 -08:00
parent 70155df7a9
commit ff955aaa01
No known key found for this signature in database
GPG key ID: BE714B4575D6E328
4 changed files with 137 additions and 49 deletions
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14
libc/intrin/memchr.c
View file

@ -17,11 +17,12 @@
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/dce.h"
#include "libc/intrin/asan.internal.h"
#include "libc/nexgen32e/x86feature.h"
#include "libc/str/str.h"
#ifndef __aarch64__
typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(16)));
typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(1)));
static inline const unsigned char *memchr_pure(const unsigned char *s,
unsigned char c, size_t n) {
@ -69,15 +70,8 @@ static inline const unsigned char *memchr_sse(const unsigned char *s,
void *memchr(const void *s, int c, size_t n) {
#if defined(__x86_64__) && !defined(__chibicc__)
const void *r;
const unsigned char *p = (const unsigned char *)s;
while (n && ((intptr_t)p & 15)) {
if (*p == (unsigned char)c) {
return (void *)p;
}
++p;
--n;
}
r = memchr_sse(p, c, n);
if (IsAsan()) __asan_verify(s, n);
r = memchr_sse(s, c, n);
return (void *)r;
#else
return (void *)memchr_pure(s, c, n);

143
libc/intrin/memcmp.c
View file

@ -21,8 +21,88 @@
#include "libc/nexgen32e/x86feature.h"
#include "libc/str/str.h"
#define PMOVMSKB(x) __builtin_ia32_pmovmskb128(x)
typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(1)));
#if defined(__x86_64__) && !defined(__chibicc__)
static dontinline antiquity int memcmp_sse(const unsigned char *p,
const unsigned char *q, size_t n) {
unsigned u;
if (n > 32) {
while (n > 16 + 16) {
if (!(u = PMOVMSKB(*(xmm_t *)p == *(xmm_t *)q) ^ 0xffff)) {
n -= 16;
p += 16;
q += 16;
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
}
}
}
if (!(u = PMOVMSKB(*(xmm_t *)p == *(xmm_t *)q) ^ 0xffff)) {
if (!(u = PMOVMSKB(*(xmm_t *)(p + n - 16) == *(xmm_t *)(q + n - 16)) ^
0xffff)) {
return 0;
} else {
u = __builtin_ctzl(u);
return p[n - 16 + u] - q[n - 16 + u];
}
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
}
}
_Microarchitecture("avx") static int memcmp_avx(const unsigned char *p,
const unsigned char *q,
size_t n) {
uint64_t w;
unsigned u;
if (n > 32) {
while (n >= 16 + 64) {
w = (uint64_t)PMOVMSKB(((xmm_t *)p)[0] == ((xmm_t *)q)[0]) << 000 |
(uint64_t)PMOVMSKB(((xmm_t *)p)[1] == ((xmm_t *)q)[1]) << 020 |
(uint64_t)PMOVMSKB(((xmm_t *)p)[2] == ((xmm_t *)q)[2]) << 040 |
(uint64_t)PMOVMSKB(((xmm_t *)p)[3] == ((xmm_t *)q)[3]) << 060;
if (w == -1) {
n -= 64;
p += 64;
q += 64;
} else {
w = __builtin_ctzll(w ^ -1);
return p[w] - q[w];
}
}
while (n > 16 + 16) {
if (!(u = PMOVMSKB(*(xmm_t *)p == *(xmm_t *)q) ^ 0xffff)) {
n -= 16;
p += 16;
q += 16;
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
}
}
}
if (!(u = PMOVMSKB(*(xmm_t *)p == *(xmm_t *)q) ^ 0xffff)) {
if (!(u = PMOVMSKB(*(xmm_t *)(p + n - 16) == *(xmm_t *)(q + n - 16)) ^
0xffff)) {
return 0;
} else {
u = __builtin_ctzl(u);
return p[n - 16 + u] - q[n - 16 + u];
}
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
}
}
#endif /* __x86_64__ */
/**
* Compares memory byte by byte.
*
@ -57,21 +137,64 @@ typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(1)));
*/
int memcmp(const void *a, const void *b, size_t n) {
int c;
#if defined(__x86_64__) && !defined(__chibicc__)
unsigned u;
uint32_t k, i, j;
uint64_t w, x, y;
#endif
const unsigned char *p, *q;
if ((p = a) == (q = b) || !n) return 0;
if ((c = *p - *q)) return c;
#if defined(__x86_64__) && !defined(__chibicc__)
unsigned u;
while (n >= 16 && (((uintptr_t)p & 0xfff) <= 0x1000 - 16 &&
((uintptr_t)q & 0xfff) <= 0x1000 - 16)) {
if (!(u = __builtin_ia32_pmovmskb128(*(xmm_t *)p == *(xmm_t *)q) ^
0xffff)) {
n -= 16;
p += 16;
q += 16;
if (!IsTiny()) {
if (n <= 16) {
if (n >= 8) {
if (!(w = (x = ((uint64_t)p[0] << 000 | (uint64_t)p[1] << 010 |
(uint64_t)p[2] << 020 | (uint64_t)p[3] << 030 |
(uint64_t)p[4] << 040 | (uint64_t)p[5] << 050 |
(uint64_t)p[6] << 060 | (uint64_t)p[7] << 070)) ^
(y = ((uint64_t)q[0] << 000 | (uint64_t)q[1] << 010 |
(uint64_t)q[2] << 020 | (uint64_t)q[3] << 030 |
(uint64_t)q[4] << 040 | (uint64_t)q[5] << 050 |
(uint64_t)q[6] << 060 | (uint64_t)q[7] << 070)))) {
p += n - 8;
q += n - 8;
if (!(w = (x = ((uint64_t)p[0] << 000 | (uint64_t)p[1] << 010 |
(uint64_t)p[2] << 020 | (uint64_t)p[3] << 030 |
(uint64_t)p[4] << 040 | (uint64_t)p[5] << 050 |
(uint64_t)p[6] << 060 | (uint64_t)p[7] << 070)) ^
(y = ((uint64_t)q[0] << 000 | (uint64_t)q[1] << 010 |
(uint64_t)q[2] << 020 | (uint64_t)q[3] << 030 |
(uint64_t)q[4] << 040 | (uint64_t)q[5] << 050 |
(uint64_t)q[6] << 060 | (uint64_t)q[7] << 070)))) {
return 0;
}
}
u = __builtin_ctzll(w);
u = u & -8;
return ((x >> u) & 255) - ((y >> u) & 255);
} else if (n >= 4) {
if (!(k = (i = ((uint32_t)p[0] << 000 | (uint32_t)p[1] << 010 |
(uint32_t)p[2] << 020 | (uint32_t)p[3] << 030)) ^
(j = ((uint32_t)q[0] << 000 | (uint32_t)q[1] << 010 |
(uint32_t)q[2] << 020 | (uint32_t)q[3] << 030)))) {
p += n - 4;
q += n - 4;
if (!(k = (i = ((uint32_t)p[0] << 000 | (uint32_t)p[1] << 010 |
(uint32_t)p[2] << 020 | (uint32_t)p[3] << 030)) ^
(j = ((uint32_t)q[0] << 000 | (uint32_t)q[1] << 010 |
(uint32_t)q[2] << 020 | (uint32_t)q[3] << 030)))) {
return 0;
}
}
u = __builtin_ctzl(k);
u = u & -8;
return ((i >> u) & 255) - ((j >> u) & 255);
}
} else if (LIKELY(X86_HAVE(AVX))) {
return memcmp_avx(p, q, n);
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
return memcmp_sse(p, q, n);
}
}
#endif /* __x86_64__ */

14
test/libc/intrin/memchr_test.c
View file

@ -16,24 +16,10 @@
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/runtime/runtime.h"
#include "libc/runtime/sysconf.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/map.h"
#include "libc/sysv/consts/prot.h"
#include "libc/testlib/testlib.h"
TEST(memchr, test) {
const char *s = "hello";
ASSERT_EQ(s + 1, memchr(s, 'e', 5));
}
TEST(memchr, pageOverlapTorture) {
long pagesz = sysconf(_SC_PAGESIZE);
char *map = mmap(0, pagesz * 2, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
ASSERT_SYS(0, 0, mprotect(map + pagesz, pagesz, PROT_NONE));
strcpy(map + pagesz - 9, "12345678");
EXPECT_EQ(map + pagesz - 1, memchr(map + pagesz - 9, 0, 79));
EXPECT_SYS(0, 0, munmap(map, pagesz * 2));
}

15
test/libc/intrin/memcmp_test.c
View file

@ -113,21 +113,6 @@ TEST(memcmp, fuzz) {
}
}
TEST(memcmp, pageOverlapTorture) {
long pagesz = sysconf(_SC_PAGESIZE);
char *map = mmap(0, pagesz * 2, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
char *map2 = mmap(0, pagesz * 2, PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
ASSERT_SYS(0, 0, mprotect(map + pagesz, pagesz, PROT_NONE));
ASSERT_SYS(0, 0, mprotect(map2 + pagesz, pagesz, PROT_NONE));
strcpy(map + pagesz - 9, "12345678");
strcpy(map2 + pagesz - 9, "12345679");
EXPECT_LT(memcmp(map + pagesz - 9, map2 + pagesz - 9, 79), 0);
EXPECT_SYS(0, 0, munmap(map2, pagesz * 2));
EXPECT_SYS(0, 0, munmap(map, pagesz * 2));
}
int buncmp(const void *, const void *, size_t) asm("bcmp");
int funcmp(const void *, const void *, size_t) asm("memcmp");