'malloc' attribute?

[Chris Lattner <sabre at nondot dot org>]

Apparently C99 doesn't allow declaring a function to return a 'restrict'
pointer (GCC rejects it at least), but GCC does allow you to attach the
malloc attribute to a function.  It seems to me that this is the exact
same information, ie, the following two function prototypes should be
equivalent:

restrict int* foo();            // Currently rejected with -std=c99
int *foo() __attribute__((malloc));

According to the C rationale, a restrict pointer is known to not point to
anything else in the scope: a returned restrict pointer is similar,
indicating that the returned value from the function is a new logical
object.  Is use of the 'malloc' attribute on a function return value
conceptually any different than declaring the returned pointer 'restrict'?

If not, then:
  1. It would seem like a useful extension for the next C standard to
     incorporate, allowing portable code to express the semantics of
     functions like xmalloc.
  2. It would seem like a useful extension to include in the gnu C dialect
     until it is official.
  3. It seems that code for handling A_MALLOC could be merged with the
     code to handle RID_RESTRICT, possibly reducing some code
     duplication.

Comments?  Am I totally confused here?  :)

-Chris

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