We need to call instantiate_non_dependent_expr before cxx_constant_value in a template.
Tested x86_64-pc-linux-gnu, applying to trunk and 7.
commit 1645e51aeab6cea4e7206cb6a3520eaf383e47f6 Author: Jason Merrill <ja...@redhat.com> Date: Mon Jun 19 15:47:47 2017 -0400 PR c++/80562 - ICE with constexpr if. * semantics.c (finish_if_stmt_cond): Call instantiate_non_dependent_expr. diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c index 5b5ec54..5fe772a 100644 --- a/gcc/cp/semantics.c +++ b/gcc/cp/semantics.c @@ -733,7 +733,10 @@ finish_if_stmt_cond (tree cond, tree if_stmt) if (IF_STMT_CONSTEXPR_P (if_stmt) && require_potential_rvalue_constant_expression (cond) && !value_dependent_expression_p (cond)) - cond = cxx_constant_value (cond, NULL_TREE); + { + cond = instantiate_non_dependent_expr (cond); + cond = cxx_constant_value (cond, NULL_TREE); + } finish_cond (&IF_COND (if_stmt), cond); add_stmt (if_stmt); THEN_CLAUSE (if_stmt) = push_stmt_list (); diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if12.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if12.C new file mode 100644 index 0000000..1ed2c30 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if12.C @@ -0,0 +1,14 @@ +// PR c++/80562 +// { dg-options -std=c++1z } + +struct T { + constexpr auto foo() { return false; } +}; + +template <class MustBeTemplate> +constexpr auto bf(T t) { + if constexpr(t.foo()) { + return false; + } + return true; +}