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* [Bug c++/90679] Template specialization with const: “ambiguous template instantiation” error
[not found] <bug-90679-4@http.gcc.gnu.org/bugzilla/>
@ 2023-12-19 16:40 ` cvs-commit at gcc dot gnu.org
2023-12-19 16:40 ` cvs-commit at gcc dot gnu.org
2023-12-19 16:43 ` ppalka at gcc dot gnu.org
2 siblings, 0 replies; 3+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-12-19 16:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90679
--- Comment #1 from GCC 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:6d27ee7fcc3e31c2142124027dc87e5a0288c9ab
commit r14-6714-g6d27ee7fcc3e31c2142124027dc87e5a0288c9ab
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Dec 19 11:26:34 2023 -0500
c++: refine dependent_alias_template_spec_p [PR90679]
For a (complex) alias template-id, dependent_alias_template_spec_p
returns true if any template argument of the template-id is dependent.
This predicate indicates that substitution into the template-id may
behave differently with respect to SFINAE than substitution into the
expanded alias, and so the alias is in a way non-transparent.
For example, 'first_t<T, T&>' in
template<class T, class...> using first_t = T;
template<class T> first_t<T, T&> f();
is such an alias template-id since first_t doesn't use its second
template parameter and so the substitution into the expanded alias would
discard the SFINAE effects of the corresponding (dependent) argument 'T&'.
But this predicate is overly conservative since what really matters for
sake of SFINAE equivalence is whether a template argument corresponding
to an _unused_ template parameter is dependent. So the predicate should
return false for e.g. 'first_t<T&, int>'.
This patch refines the predicate appropriately. We need to be able to
efficiently determine which template parameters of a complex alias
template are unused, so to that end we add a new out parameter to
complex_alias_template_p and cache its result in an on-the-side hash_map
that replaces the existing TEMPLATE_DECL_COMPLEX_ALIAS_P flag.
PR c++/90679
gcc/cp/ChangeLog:
* cp-tree.h (TEMPLATE_DECL_COMPLEX_ALIAS_P): Remove.
(most_general_template): Constify parameter.
* pt.cc (push_template_decl): Adjust after removing
TEMPLATE_DECL_COMPLEX_ALIAS_P.
(complex_alias_tmpl_info): New hash_map.
(uses_all_template_parms_data::seen): Change type to
tree* from bool*.
(complex_alias_template_r): Adjust accordingly.
(complex_alias_template_p): Add 'seen_out' out parameter.
Call most_general_template and check PRIMARY_TEMPLATE_P.
Use complex_alias_tmpl_info to cache the result and set
'*seen_out' accordigly.
(dependent_alias_template_spec_p): Add !processing_template_decl
early exit test. Consider dependence of only template arguments
corresponding to seen template parameters as per
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/alias-decl-76.C: New test.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/90679] Template specialization with const: “ambiguous template instantiation” error
[not found] <bug-90679-4@http.gcc.gnu.org/bugzilla/>
2023-12-19 16:40 ` [Bug c++/90679] Template specialization with const: “ambiguous template instantiation” error cvs-commit at gcc dot gnu.org
@ 2023-12-19 16:40 ` cvs-commit at gcc dot gnu.org
2023-12-19 16:43 ` ppalka at gcc dot gnu.org
2 siblings, 0 replies; 3+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-12-19 16:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90679
--- Comment #2 from GCC 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:0a37463758dabc9647fa3d675dffdf43a737035d
commit r14-6715-g0a37463758dabc9647fa3d675dffdf43a737035d
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Dec 19 11:40:15 2023 -0500
c++: partial ordering and dep alias tmpl specs [PR90679]
During partial ordering, we want to look through dependent alias
template specializations within template arguments and otherwise
treat them as opaque in other contexts (see e.g. r7-7116-g0c942f3edab108
and r11-7011-g6e0a231a4aa240). To that end template_args_equal was
given a partial_order flag that controls this behavior. This flag
does the right thing when a dependent alias template specialization
appears as template argument of the partial specialization, e.g. in
template<class T, class...> using first_t = T;
template<class T> struct traits;
template<class T> struct traits<first_t<T, T&>> { }; // #1
template<class T> struct traits<first_t<const T, T&>> { }; // #2
we correctly consider #2 to be more specialized than #1. But if the
alias specialization appears as a nested template argument of another
class template specialization, e.g. in
template<class T> struct traits<A<first_t<T, T&>>> { }; // #1
template<class T> struct traits<A<first_t<const T, T&>>> { }; // #2
then we incorrectly consider #1 and #2 to be unordered. This is because
1. we don't propagate the flag to recursive template_args_equal calls
2. we don't use structural equality for class template specializations
written in terms of dependent alias template specializations
This patch fixes the first issue by turning the partial_order flag into
a global. This patch fixes the second issue by making us propagate
structural equality appropriately when building a class template
specialization. In passing this patch also improves hashing of
specializations that use structural equality.
PR c++/90679
gcc/cp/ChangeLog:
* cp-tree.h (comp_template_args): Remove partial_order parameter.
(template_args_equal): Likewise.
* pt.cc (comparing_for_partial_ordering): New global flag.
(iterative_hash_template_arg) <case tcc_type>: Hash the template
and arguments for specializations that use structural equality.
(template_args_equal): Remove partial order parameter and
use comparing_for_partial_ordering instead.
(comp_template_args): Likewise.
(comp_template_args_porder): Set comparing_for_partial_ordering
instead. Make static.
(any_template_arguments_need_structural_equality_p): Return true
for an argument that's a dependent alias template specialization
or a class template specialization that itself needs structural
equality.
* tree.cc (cp_tree_equal) <case TREE_VEC>: Adjust call to
comp_template_args.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/alias-decl-75a.C: New test.
* g++.dg/cpp0x/alias-decl-75b.C: New test.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/90679] Template specialization with const: “ambiguous template instantiation” error
[not found] <bug-90679-4@http.gcc.gnu.org/bugzilla/>
2023-12-19 16:40 ` [Bug c++/90679] Template specialization with const: “ambiguous template instantiation” error cvs-commit at gcc dot gnu.org
2023-12-19 16:40 ` cvs-commit at gcc dot gnu.org
@ 2023-12-19 16:43 ` ppalka at gcc dot gnu.org
2 siblings, 0 replies; 3+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-12-19 16:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90679
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org
Resolution|--- |FIXED
Target Milestone|--- |14.0
CC| |ppalka at gcc dot gnu.org
Status|UNCONFIRMED |RESOLVED
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 14, thanks for the bug report.
^ permalink raw reply [flat|nested] 3+ messages in thread
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