Re: [cxx-abi-dev] Scope encoding of string literals in default arguments questions

[scott douglass <sdouglass@xxxxxxx>]

Mark Mitchell wrote:
> --On Friday, November 01, 2002 11:47:59 AM +0000 scott douglass 
> <sdouglass@xxxxxxx> wrote:
> > Hi,
> >
> > I have some questions about the scope encoding of string literals in
> > inline functions.  Consider,
> >
> >   bool g(const char*);
> >
> >   inline const char* f1(const char* p = "world");  // _ZZ2f1Es ?
> >
> >   inline const char* f1(const char* p) {
> >     g(p);
> >     g("hello");  // _ZZ2f1Es_0 ?
> >     g("world");  // _ZZ2f1Es ?
> >   }
>
> I think that the only consistent thing to do is to move the default
> argument into the callers; that is where it will be emitted.
But, doesn't the expression 'f1()' have to supply the same pointer for 'p' even in different translation units?  As far as I can tell the standard doesn't address this directly.

> > I'll also suggest some minor clarifications to the wording in 5.1.6:
> >   "Note that this assumes that the same string literal occurring twice in
> > a given function in fact represents a single entity, i.e. has a unique
> > address."
> >
> > would be better as
> >   "Note that this means that the same string literal occurring twice in a
> > given inline function in fact represents a single entity, i.e. has a
> > unique address.  It also means that string literals in inline functions
> > do not "tail-share", i.e. the string literals "abc" and "bc" are
> > completely distinct in inline functions."
>
> Why?
I think I see what you mean.  As long as the compiler counts the orignial string literals:

 void h(const char *);

 inline void k() {
   h("bc"); // _ZZ1kEs
   h("abc"); // _ZZ1kEs_0
 }

A compiler could make the references to '_ZZ1kEs_0 + 1' and '_ZZ1kEs_0'.  It doesn't even need to emit '_ZZ1kEs' because anyone referring to '_ZZ1kEs' will also emit it.