[Bug libstdc++/37718] New: Demangling of variadic functions

["jakub at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

int f()
{
  return 0;
}

template <typename T, typename... U>
int f(T t, U... u)
{
  return (t ? 1 : 0) * sizeof...(U) + f(u...);
}

int
main()
{
  return f(1, 1.0, 2);
}

has 3 mangled names, but 2 of them demangle weirdly (I'd say we should demangle
U10__variadic to something containing ..., not __variadic) and one doesn't
demangle at all:

#include <cxxabi.h>
#include <iostream>

int
main ()
{
  char buf[128];
  size_t len;
  int status;
  len = sizeof (buf);
  status = 0;
  abi::__cxa_demangle ("_Z1fIdiEiT_U10__variadicT0_", buf, &len, &status);
  std::cout << buf << " " << len << " " << status << std::endl;
  abi::__cxa_demangle ("_Z1fIiEiT_U10__variadicT0_", buf, &len, &status);
  std::cout << buf << " " << len << " " << status << std::endl;
  abi::__cxa_demangle ("_Z1fIidiEiT_U10__variadicT0_", buf, &len, &status);
  std::cout << buf << " " << len << " " << status << std::endl;
}

G++ in all cases mangles the variadic arg as U10__variadicT0_, as the variadic
template parameter is 2nd, but that parameter is never mangled among the I
parameters and so the demangler considers it out of range and refuses to
demangle it.  Not mentioning the parameter packs in the I list IMHO has a
bigger
effect than just having out of range U10__variadic template parameter types.
As for functions the parameter packs don't need to be at the end of template
argument list, we get out of range mangling even for say:
template <typename T, typename... U, typename W, typename ... V>
int foo (T a, W b)
{
  return a + b;
}

int
bar (void)
{
  return foo (1, 2);
}

_Z3fooIiiEiT_T1_


-- 
           Summary: Demangling of variadic functions
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: ABI
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37718