This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: malloc attributes and realloc
On Fri, 2 Jan 2004, Daniel Berlin wrote:
> 1. heap allocation functions return pointers that don't point to
> anything.
> 2. pointer destroying operations destroy pointers irreversibly.
>
> If #1 does not hold for realloc, it should not be attribute malloc.
> The fact that it has worked okay so far doesn't mean it will continue
> to work in the future. If you change the definition of attribute
> malloc so that #1 doesn't hold for them, it makes it useless for
> points-to analysis use in determining heap allocation functions. Which
> may or may not be okay by everyone, i don't know.
My current draft documentation change for attribute malloc (for this issue
and PR 3414) is
The @code{malloc} attribute is used to tell the compiler that a function
-may be treated as if it were the malloc function. The compiler assumes
-that calls to malloc result in pointers that cannot alias anything.
+may be treated as if any non-@code{NULL} pointer it returns cannot
+alias any other pointer valid when the function returns.
This will often improve optimization.
+Standard functions with this property include @code{malloc},
+@code{calloc} and @code{realloc}.
Does this description (non-NULL pointers don't alias anything valid when
the allocation function returns) accurately describe what is appropriate
for the points-to analysis, or not? (And quite what does the malloc
attribute do at present, given the lack of points-to analysis in GCC?)
--
Joseph S. Myers
jsm@polyomino.org.uk