[RFC] propagate malloc attribute in ipa-pure-const pass

[Martin Sebor]

> The patch passes bootstrap+test on x86_64 and found a few functions in
> the source tree (attached func_names.txt) that could be annotated with
> malloc (I gave a brief look at some of the functions and didn't appear
> to be false positives but I will recheck thoroughly)

virtual char* libcp1::compiler::find(std::__cxx11::string&) const

The virtual on the list of your candidates gave me pause.  Consider
this completely contrived example:

   struct B {
     virtual void* f (unsigned n) {
       return new char [n];
     }
   };

   void* foo (B &b, unsigned n)
   {
     return b.f (n);
   }

Based on these definitions alone both functions are candidates
for attribute malloc.

But suppose foo is called with an object of a type derived from
B that overrides f() to do something wacky (but strictly not
invalid) like:

   struct D: B {
     char buf[32];
     virtual void* f (unsigned n) {
       if (n < 32)
       return n <= 32 ? buf : B::f (n);
     }

Breaking foo's attribute malloc constraint.

In other words, I think virtual functions need to be excluded
from the list (unless they're defined in a class marked final,
or unless we know they're not overridden to break the constraint
like above).

Martin