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* [Bug libstdc++/105440] New: c++20: std::string's destructor not a constant expression when it should
@ 2022-04-30 13:28 janpmoeller at gmx dot de
2022-05-04 16:16 ` [Bug libstdc++/105440] " redi at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: janpmoeller at gmx dot de @ 2022-04-30 13:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105440
Bug ID: 105440
Summary: c++20: std::string's destructor not a constant
expression when it should
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: janpmoeller at gmx dot de
Target Milestone: ---
The following valid c++20 program fails to compile on both gcc and clang when
compiled with libstdc++:
/************************************************************/
#include <string>
#include <array>
constexpr auto foo(char c){
std::array a{std::string{"foo"} + c};
return true;
}
static_assert(foo('a'));
/************************************************************/
The emitted error is:
/************************************************************/
<source>:9:18: error: non-constant condition for static assertion
9 | static_assert(foo('a'));
| ~~~^~~~~
In file included from
/opt/compiler-explorer/gcc-trunk-20220430/include/c++/13.0.0/string:53,
from <source>:1:
<source>:9:18: in 'constexpr' expansion of 'foo(97)'
<source>:7:1: in 'constexpr' expansion of '(&
a)->std::array<std::__cxx11::basic_string<char>, 1>::~array()'
/opt/compiler-explorer/gcc-trunk-20220430/include/c++/13.0.0/array:99:12: in
'constexpr' expansion of
'<anonymous>->std::__cxx11::basic_string<char>::~basic_string()'
/opt/compiler-explorer/gcc-trunk-20220430/include/c++/13.0.0/bits/basic_string.h:795:19:
in 'constexpr' expansion of
'((std::__cxx11::basic_string<char>*)this)->std::__cxx11::basic_string<char>::_M_dispose()'
/opt/compiler-explorer/gcc-trunk-20220430/include/c++/13.0.0/bits/basic_string.h:275:26:
error: '((& a) == <anonymous>)' is not a constant expression
275 | { return _M_data() == _M_local_data(); }
| ~~~~~~~~~~^~~~~~~~~~~~~~~~~~
Compiler returned: 1
/************************************************************/
The same program compiles with libc++, and on msvc. Also see the following
godbolt link for comparison:
https://godbolt.org/z/zfn1Pr7P1
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/105440] c++20: std::string's destructor not a constant expression when it should
2022-04-30 13:28 [Bug libstdc++/105440] New: c++20: std::string's destructor not a constant expression when it should janpmoeller at gmx dot de
@ 2022-05-04 16:16 ` redi at gcc dot gnu.org
2023-04-17 14:27 ` ppalka at gcc dot gnu.org
2023-05-08 12:24 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: redi at gcc dot gnu.org @ 2022-05-04 16:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105440
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Ever confirmed|0 |1
Keywords| |rejects-valid
Last reconfirmed| |2022-05-04
Assignee|unassigned at gcc dot gnu.org |redi at gcc dot gnu.org
Target Milestone|--- |12.2
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/105440] c++20: std::string's destructor not a constant expression when it should
2022-04-30 13:28 [Bug libstdc++/105440] New: c++20: std::string's destructor not a constant expression when it should janpmoeller at gmx dot de
2022-05-04 16:16 ` [Bug libstdc++/105440] " redi at gcc dot gnu.org
@ 2023-04-17 14:27 ` ppalka at gcc dot gnu.org
2023-05-08 12:24 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-04-17 14:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105440
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ppalka at gcc dot gnu.org
--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Seems this is ultimately an FE bug which is fixed by:
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index d1097764b10..9dbbf6eec03 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -3213,7 +3213,12 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree
t,
&& CLASS_TYPE_P (TREE_TYPE (res))
&& !is_empty_class (TREE_TYPE (res)))
if (replace_decl (&result, res, ctx->object))
- cacheable = false;
+ {
+ cacheable = false;
+ result = cxx_eval_constant_expression (ctx, result, lval,
+ non_constant_p,
+ overflow_p);
+ }
}
else
/* Couldn't get a function copy to evaluate. */
In some cases we can simplify a call result further after replacing RESULT_DECL
with the current object under construction throughout the call result, which
allows fold_binary_loc etc to later successfully fold comparisons involving the
call result such as _M_data() == _M_local_data() in this case.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug libstdc++/105440] c++20: std::string's destructor not a constant expression when it should
2022-04-30 13:28 [Bug libstdc++/105440] New: c++20: std::string's destructor not a constant expression when it should janpmoeller at gmx dot de
2022-05-04 16:16 ` [Bug libstdc++/105440] " redi at gcc dot gnu.org
2023-04-17 14:27 ` ppalka at gcc dot gnu.org
@ 2023-05-08 12:24 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-05-08 12:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105440
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|12.3 |12.4
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 12.3 is being released, retargeting bugs to GCC 12.4.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-05-08 12:24 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2022-04-30 13:28 [Bug libstdc++/105440] New: c++20: std::string's destructor not a constant expression when it should janpmoeller at gmx dot de
2022-05-04 16:16 ` [Bug libstdc++/105440] " redi at gcc dot gnu.org
2023-04-17 14:27 ` ppalka at gcc dot gnu.org
2023-05-08 12:24 ` rguenth at gcc dot gnu.org
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