Add a function attribute called `__malloc_like', which informs gcc

that the annotated function returns a pointer that doesn't alias any
extant pointer. This results in a 50%+ speedup in microbenchmarks such
as the following:

    char *cp = malloc(1), *buf = malloc(BUF);
    for (i = 0; i < BUF; i++) buf[i] = *cp;

In real programs, your mileage will vary. Note that gcc already
performs this optimization automatically for any function called
`malloc', `calloc', `strdup', or `strndup' unless -fno-builtins is
used.

1 files changed, 2 insertions, 2 deletions

diff --git a/include/string.h b/include/string.h
index 32a9ad3e5608..4770d101a139 100644
--- a/include/string.h
+++ b/include/string.h
@@ -78,7 +78,7 @@ int	 strcoll(const char *, const char *);
 char	*strcpy(char * __restrict, const char * __restrict);
 size_t	 strcspn(const char *, const char *) __pure;
 #if __POSIX_VISIBLE >= 200112 || __XSI_VISIBLE
-char	*strdup(const char *);
+char	*strdup(const char *) __malloc_like;
 #endif
 char	*strerror(int);
 #if __POSIX_VISIBLE >= 200112
@@ -96,7 +96,7 @@ char	*strncat(char * __restrict, const char * __restrict, size_t);
 int	 strncmp(const char *, const char *, size_t) __pure;
 char	*strncpy(char * __restrict, const char * __restrict, size_t);
 #if __BSD_VISIBLE
-char	*strndup(const char *, size_t);
+char	*strndup(const char *, size_t) __malloc_like;
 char	*strnstr(const char *, const char *, size_t) __pure;
 #endif
 char	*strpbrk(const char *, const char *) __pure;