https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65133
Bug ID: 65133
Summary: [C++11] Result type deduction proceeds even though
argument deduction fails
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: mbianco at cscs dot ch
GCC 4.8.0 to 4.9.0 fails in employing SFINAE to find the proper implementation
when infinite template recursion is hit. ICPC (15) and CLANG++ (3.7) compile
and run the code correctly.
#STANDALONE SOURCE
#include <iostream>
#include <type_traits>
template <int I>
struct count
{
using type = typename count<I-1>::type;
};
template <>
struct count<0>
{
using type = void;
};
template <int I>
auto foo(typename std::enable_if<(I>=0)>::type * = nullptr) -> typename
count<I>::type
/* Substituting count<I>::type with void would make the code to compile.*/
{
std::cout << "I>=0" << std::endl;
}
// Specialization #2
template <int I>
void foo(typename std::enable_if<(I<0)>::type * = nullptr)
{
std::cout << "I<0" << std::endl;
}
int main() {
foo<2>(); // This Works fine
foo<-1>(); // This should go the specialization #2 but GCC fails since it
goes into counting down 900 times without resolution
return 0;
}
### COMPILER INVOCATION:
g++ -std=c++11 -c main.cpp
### EXPECTED OUTPUT:
Successful compile.
### ACTUAL OUTPUT:
main.cpp:7:43: error: template instantiation depth exceeds maximum of 900 (use
-ftemplate-depth= to increase the maximum) instantiating ‘struct count<-900>’
using type = typename count<I-1>::type;
^
main.cpp:7:43: recursively required from ‘struct count<-2>’
main.cpp:7:43: required from ‘struct count<-1>’
main.cpp:18:6: required by substitution of ‘template<int I> typename
count<I>::type foo(typename std::enable_if<(I >= 0)>::type*) [with int I = -1]’
main.cpp:35:13: required from here
main.cpp:7:43: error: invalid use of incomplete type ‘struct count<-900>’
main.cpp:5:8: error: declaration of ‘struct count<-900>’
struct count
^
### g++ -v OUTPUT:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/apps/dom/gcc/4.9.0/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ./configure --prefix=/apps/dom/gcc/4.9.0
--enable-languages=c,c++,fortran --with-mpfr=/apps/dom/gnu/mpfr/3.1.2
--with-mpc=/apps/dom/gnu/mpc/1.0.2 --with-gmp=/apps/dom/gnu/gmp/5.1.3
--with-isl=/apps/dom/gnu/isl/0.12.2 --with-cloog=/apps/dom/gnu/cloog/0.18.1
Thread model: posix
gcc version 4.9.0 (GCC)
