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* [Bug c++/114138] New: [c++2b] ICE on valid code using `auto(expr)` DECAY-COPY
@ 2024-02-27 17:59 eric.niebler at gmail dot com
2024-02-27 19:46 ` [Bug c++/114138] " ppalka at gcc dot gnu.org
2024-03-01 17:51 ` cvs-commit at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: eric.niebler at gmail dot com @ 2024-02-27 17:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114138
Bug ID: 114138
Summary: [c++2b] ICE on valid code using `auto(expr)`
DECAY-COPY
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: eric.niebler at gmail dot com
Target Milestone: ---
Compile the following with -c++=2b:
```
namespace std {
template <class T>
T&& declval() noexcept requires true;
template <class>
void declval() noexcept;
namespace detail {
struct none_such;
template <class>
using none_such_t = none_such;
template <class T>
extern const none_such_t<T> _getter_for;
template <class T>
using _decay_t = decltype(auto(declval<T>()));
static_assert(__is_same_as(_decay_t<void>, void));
}
template <const auto& Fn, class... Args>
using _result_of_t = decltype(Fn(declval<Args>()...));
template <unsigned I, class Tuple>
using tuple_element_t =
_result_of_t<detail::_getter_for<detail::_decay_t<Tuple>>, char(*)[I+1],
Tuple>;
template <class First, class Second>
struct pair {
First first;
Second second;
};
template <class>
inline constexpr bool _is_pair = false;
template <class First, class Second>
inline constexpr bool _is_pair<pair<First, Second>> = true;
template <class T>
concept Pair = _is_pair<decltype(auto(std::declval<T>()))>;
template <unsigned I, Pair P>
requires (I <= 1)
decltype(auto) get(P&& p) noexcept {
if constexpr (I == 0) {
return (static_cast<P&&>(p).first);
} else {
return (static_cast<P&&>(p).second);
}
}
namespace detail {
inline constexpr auto _pair_getter =
[]<unsigned J, class Pair>(char(*)[J], Pair&& p) noexcept ->
decltype(auto) {
return std::get<J-1>(static_cast<Pair&&>(p));
};
template <class First, class Second>
inline constexpr auto _getter_for<pair<First, Second>> = _pair_getter;
}
}
int main() {
static_assert(__is_same_as(int&, std::tuple_element_t<0, std::pair<int,
float>&>));
static_assert(__is_same_as(float&&, std::tuple_element_t<1, std::pair<int,
float>&&>));
}
```
Result:
```
<source>: In substitution of 'template<unsigned int I, class Tuple> using
std::tuple_element_t = std::_result_of_t<_getter_for<decltype
((auto)(declval<Tuple>()))>, char (*)[(I + 1)], Tuple> [with unsigned int I =
0; Tuple = std::pair<int, float>&]':
<source>:71:82: required from here
71 | static_assert(__is_same_as(int&, std::tuple_element_t<0,
std::pair<int, float>&>));
|
^
<source>:21:31: internal compiler error: in tsubst, at cp/pt.cc:16367
21 | using _decay_t = decltype(auto(declval<T>()));
| ^~~~~~~~~~~~~~~~~~
0x265412c internal_error(char const*, ...)
???:0
0xa548c3 fancy_abort(char const*, int, char const*)
???:0
0xc99307 tsubst(tree_node*, tree_node*, int, tree_node*)
???:0
0xc9f3c9 tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
???:0
0xc9f3c9 tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
???:0
0xc98a19 tsubst(tree_node*, tree_node*, int, tree_node*)
???:0
0xc80873 instantiate_template(tree_node*, tree_node*, int)
???:0
0xc9a0fc tsubst(tree_node*, tree_node*, int, tree_node*)
???:0
0xc973cc lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*,
int, int)
???:0
0xcd370f finish_template_type(tree_node*, tree_node*, int)
???:0
0xc577da c_parse_file()
???:0
0xdaba19 c_common_parse_file()
???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1
```
See https://godbolt.org/z/r13Yff5bM
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/114138] [c++2b] ICE on valid code using `auto(expr)` DECAY-COPY
2024-02-27 17:59 [Bug c++/114138] New: [c++2b] ICE on valid code using `auto(expr)` DECAY-COPY eric.niebler at gmail dot com
@ 2024-02-27 19:46 ` ppalka at gcc dot gnu.org
2024-03-01 17:51 ` cvs-commit at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: ppalka at gcc dot gnu.org @ 2024-02-27 19:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114138
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2024-02-27
Keywords| |rejects-valid
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug c++/114138] [c++2b] ICE on valid code using `auto(expr)` DECAY-COPY
2024-02-27 17:59 [Bug c++/114138] New: [c++2b] ICE on valid code using `auto(expr)` DECAY-COPY eric.niebler at gmail dot com
2024-02-27 19:46 ` [Bug c++/114138] " ppalka at gcc dot gnu.org
@ 2024-03-01 17:51 ` cvs-commit at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2024-03-01 17:51 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114138
--- 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:a6a1920b592b58c38137c5c891b3bbb02b084f38
commit r14-9260-ga6a1920b592b58c38137c5c891b3bbb02b084f38
Author: Patrick Palka <ppalka@redhat.com>
Date: Fri Mar 1 12:50:18 2024 -0500
c++: auto(x) partial substitution [PR110025, PR114138]
In r12-6773-g09845ad7569bac we gave CTAD placeholders a level of 0 and
ensured we never replaced them via tsubst. It turns out that autos
representing an explicit cast need the same treatment and for the same
reason: such autos appear in an expression context and so their level
gets easily messed up after partial substitution, leading to premature
replacement via an incidental tsubst instead of via do_auto_deduction.
This patch fixes this by extending the r12-6773 approach to auto(x).
PR c++/110025
PR c++/114138
gcc/cp/ChangeLog:
* cp-tree.h (make_cast_auto): Declare.
* parser.cc (cp_parser_functional_cast): If the type is an auto,
replace it with a level-less one via make_cast_auto.
* pt.cc (find_parameter_packs_r): Don't treat level-less auto
as a type parameter pack.
(tsubst) <case TEMPLATE_TYPE_PARM>: Generalize CTAD placeholder
auto handling to all level-less autos.
(make_cast_auto): Define.
(do_auto_deduction): Handle replacement of a level-less auto.
gcc/testsuite/ChangeLog:
* g++.dg/cpp23/auto-fncast16.C: New test.
* g++.dg/cpp23/auto-fncast17.C: New test.
* g++.dg/cpp23/auto-fncast18.C: New test.
Reviewed-by: Jason Merrill <jason@redhat.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2024-02-27 17:59 [Bug c++/114138] New: [c++2b] ICE on valid code using `auto(expr)` DECAY-COPY eric.niebler at gmail dot com
2024-02-27 19:46 ` [Bug c++/114138] " ppalka at gcc dot gnu.org
2024-03-01 17:51 ` cvs-commit at gcc dot gnu.org
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