Re: malloc attributes and realloc

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

Jonathan Lennox <lennox@cs.columbia.edu> writes:

| Joseph S. Myers writes:
| > 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}.
| 
| This isn't directly relevant to the current thread, but another aspect of
| malloc-like functions came up recently: the memory they return is writable.
| I.e., if char *p was returned by an attribute(malloc) function, then
|   if (*p != 'a')
|     *p = 'a';
| 
| can be safely optimized into
|   *p = 'a';

That transformation caanot be applied for pointers returned by
realloc, in general.

-- Gaby