https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71449
Bug ID: 71449
Summary: builtins accepted in default template arguments but
rejected when explicitly specified
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
In C++ 98 mode, all versions of G++ reject the instantiation of template B
below with an error but accepts the equivalent instantion of A. Either they
both should be rejected, or they both should be accepted as they are in C++ 11
mode and later.
Clang accepts the code in all C++ modes.
$ cat cst.C && /home/msebor/build/gcc-6-branch/gcc/xgcc
-B/home/msebor/build/gcc-6-branch/gcc -S -Wall -Wextra -Wpedantic -std=c++98
cst.C
template <int = __builtin_parity (0)> struct A { };
A<> a;
template <int> struct B { };
B<__builtin_parity (0)> b;
cst.C:5:3: error: ‘int __builtin_parity(unsigned int)’ cannot appear in a
constant-expression
B<__builtin_parity (0)> b;
^~~~~~~~~~~~~~~~
cst.C:5:22: error: a function call cannot appear in a constant-expression
B<__builtin_parity (0)> b;
^
cst.C:5:23: error: template argument 1 is invalid
B<__builtin_parity (0)> b;
^
