http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55663
--- Comment #5 from Dodji Seketeli <dodji at gcc dot gnu.org> 2013-01-15 09:12:42 UTC --- Author: dodji Date: Tue Jan 15 09:12:30 2013 New Revision: 195189 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195189 Log: PR c++/55663 - constexpr function templ instantiation Consider the example of the problem report 1 template <typename> 2 constexpr bool the_truth () { return true; } 3 4 template <bool> 5 struct Takes_bool { }; 6 7 template<bool B> 8 using Alias = Takes_bool<B>; 9 10 template<typename T> 11 struct test { using type = Alias<the_truth<T>()>; }; 12 13 int main () { 14 test<int> a; 15 16 return 0; 17 } that yields the error: test.cc: In substitution of ‘template<bool B> using Alias = Takes_bool<B> [with bool B = the_truth<int>()]’: test.cc:11:51: required from ‘struct test<int>’ test.cc:14:13: required from here test.cc:11:51: error: integral expression ‘the_truth<int>()’ is not constant struct test { using type = Alias<the_truth<T>()>; }; I think the issue happens in the course of instantiating test<int> at line 14, when we look into instantiating Alias<the_truth<T>()> (at line 11) (using instantiate_alias_template) with T = int. There, when we check the argument 'the_truth<int>()' to see if it actually is a constant expression, in check_instantiated_arg, we fail to recognize it constexpr-ness b/c we just look at its TREE_CONSTANT. At that point, the_truth<int> should have been folded, and it's not, because instantiate_alias_template forgets to call coerce_template_parms on its arguments. Fixed thus, bootstapped and tested on x86_64-unknown-linux-gnu against trunk. gcc/cp/ PR c++/55663 * pt.c (coerce_innermost_template_parms): New static function. (instantiate_alias_template): Use it here. gcc/testsuite/ PR c++/55663 * g++.dg/cpp0x/alias-decl-31.C: New test. Added: trunk/gcc/testsuite/g++.dg/cpp0x/alias-decl-31.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/pt.c trunk/gcc/testsuite/ChangeLog
