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/stdlib.h b/include/stdlib.h
index 0a8327066bd7..91be536668b7 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -88,14 +88,14 @@ int	 atoi(const char *);
 long	 atol(const char *);
 void	*bsearch(const void *, const void *, size_t,
 	    size_t, int (*)(const void *, const void *));
-void	*calloc(size_t, size_t);
+void	*calloc(size_t, size_t) __malloc_like;
 div_t	 div(int, int) __pure2;
 void	 exit(int) __dead2;
 void	 free(void *);
 char	*getenv(const char *);
 long	 labs(long) __pure2;
 ldiv_t	 ldiv(long, long) __pure2;
-void	*malloc(size_t);
+void	*malloc(size_t) __malloc_like;
 int	 mblen(const char *, size_t);
 size_t	 mbstowcs(wchar_t * __restrict , const char * __restrict, size_t);
 int	 mbtowc(wchar_t * __restrict, const char * __restrict, size_t);