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.

2 files changed, 4 insertions, 2 deletions

diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
index e796908..a850950 100644
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -221,8 +221,10 @@
 #endif
 
 #if __GNUC_PREREQ__(2, 96)
+#define	__malloc_like	__attribute__((__malloc__))
 #define	__pure		__attribute__((__pure__))
 #else
+#define	__malloc_like
 #define	__pure
 #endif
 
diff --git a/sys/sys/malloc.h b/sys/sys/malloc.h
index 33b287f..24a044c 100644
--- a/sys/sys/malloc.h
+++ b/sys/sys/malloc.h
@@ -190,9 +190,9 @@ typedef void malloc_type_list_func_t(struct malloc_type *, void *);
 void	contigfree(void *addr, unsigned long size, struct malloc_type *type);
 void	*contigmalloc(unsigned long size, struct malloc_type *type, int flags,
 	    vm_paddr_t low, vm_paddr_t high, unsigned long alignment,
-	    unsigned long boundary);
+	    unsigned long boundary) __malloc_like;
 void	free(void *addr, struct malloc_type *type);
-void	*malloc(unsigned long size, struct malloc_type *type, int flags);
+void	*malloc(unsigned long size, struct malloc_type *type, int flags) __malloc_like;
 void	malloc_init(void *);
 int	malloc_last_fail(void);
 void	malloc_type_allocated(struct malloc_type *type, unsigned long size);