[Bug c++/101906] Constant evaluation failure in concepts
cvs-commit at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Mon Sep 12 21:06:31 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101906
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:c3ba0eaaa223f7b8208d279e3f39ff134912f9e9
commit r13-2633-gc3ba0eaaa223f7b8208d279e3f39ff134912f9e9
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Jun 7 14:19:53 2022 -0400
c++: template-id arguments are evaluated [PR101906]
Here we're neglecting to clear cp_unevaluated_operand when substituting
into the arguments of the alias template-id 'skip<(T(), 0), T>' with T=A,
which means cp_unevaluated_operand remains set during mark_used for
A::A() and so we don't synthesize it. Later constant evaluation for
the substituted template argument '(A(), 0)' (from coerce_template_parms)
fails with "'constexpr A::A()' used before its definition" since it was
never synthesized.
This doesn't happen with a class template because tsubst_aggr_type
clears cp_unevaluated_operand during substitution thereof. But since
template arguments are generally manifestly constant-evaluated, which in
turn are evaluated even in an unevaluated operand, we should be clearing
cp_unevaluated_operand more broadly whenever substituting into any set
of template arguments. To that end this patch makes us clear it during
tsubst_template_args.
PR c++/101906
gcc/cp/ChangeLog:
* pt.cc (tsubst_template_args): Set cp_evaluated here.
(tsubst_aggr_type): Not here.
gcc/testsuite/ChangeLog:
* g++.dg/template/evaluated1.C: New test.
* g++.dg/template/evaluated1a.C: New test.
* g++.dg/template/evaluated1b.C: New test.
* g++.dg/template/evaluated1c.C: New test.
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