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Make mkdeps.com go faster

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This program usually runs once at the begininng of each GNU Make
invocation. It generates an o//depend file with 170,000 lines of
Makefile code to define source -> headers relationships.

This change makes that take 650 milliseconds rather than 1,100ms
by improving the performance of strstr(), using longsort(), plus
migrating to the new append library.
This commit is contained in:
Justine Tunney 2021-10-04 06:24:56 -07:00
parent 725f4d79f6
commit 28997f3acb
5 changed files with 120 additions and 94 deletions
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43
libc/str/strstr.c
View file

@ -16,34 +16,55 @@
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/dce.h"
#include "libc/intrin/asan.internal.h"
#include "libc/str/str.h"
typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(16)));
/**
* Searches for substring.
*
* @param haystack is the search area, as a NUL-terminated string
* @param needle is the desired substring, also NUL-terminated
* @return pointer to first substring within haystack, or NULL
* @note this implementation goes fast in practice but isn't hardened
* against pathological cases, and therefore shouldn't be used on
* untrustworthy data
* @asyncsignalsafe
* @see memmem()
*/
char *strstr(const char *haystack, const char *needle) {
noasan char *strstr(const char *haystack, const char *needle) {
xmm_t *p;
size_t i;
const char *p;
if (!needle[0]) return haystack;
if (haystack == needle) return haystack;
p = strchr(haystack, needle[0]);
if (!needle[1]) return p;
if (p) haystack = p;
/* TODO: make not quadratic */
unsigned k, m;
xmm_t v, n, z = {0};
if (IsAsan()) __asan_verify(needle, 1);
if (IsAsan()) __asan_verify(haystack, 1);
if (haystack == needle || !*needle) return haystack;
n = (xmm_t){*needle, *needle, *needle, *needle, *needle, *needle,
*needle, *needle, *needle, *needle, *needle, *needle,
*needle, *needle, *needle, *needle};
for (;;) {
for (i = 0;;) {
k = (uintptr_t)haystack & 15;
p = (const xmm_t *)((uintptr_t)haystack & -16);
v = *p;
m = __builtin_ia32_pmovmskb128(__builtin_ia32_pcmpeqb128(v, z) |
__builtin_ia32_pcmpeqb128(v, n));
m >>= k;
m <<= k;
while (!m) {
v = *++p;
m = __builtin_ia32_pmovmskb128(__builtin_ia32_pcmpeqb128(v, z) |
__builtin_ia32_pcmpeqb128(v, n));
}
haystack = (const char *)p + __builtin_ctzl(m);
for (i = 0;; ++i) {
if (!needle[i]) return (/*unconst*/ char *)haystack;
if (!haystack[i]) break;
if (needle[i] != haystack[i]) break;
++i;
}
if (!*haystack++) break;
}
return NULL;
return 0;
}