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* [Bug c++/99700] New: gcc takes an uninitialized variable as a constant expression
@ 2021-03-21 18:22 hewillk at gmail dot com
2021-04-15 0:14 ` [Bug c++/99700] uninitialized variable accepted as a constant expression in C++ 20 msebor at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: hewillk at gmail dot com @ 2021-03-21 18:22 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99700
Bug ID: 99700
Summary: gcc takes an uninitialized variable as a constant
expression
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
https://godbolt.org/z/93qM1b
====
struct A {
constexpr A() { c[0] = 0; }
char c[2];
};
constexpr A a;
====
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/99700] uninitialized variable accepted as a constant expression in C++ 20
2021-03-21 18:22 [Bug c++/99700] New: gcc takes an uninitialized variable as a constant expression hewillk at gmail dot com
@ 2021-04-15 0:14 ` msebor at gcc dot gnu.org
2021-04-15 0:15 ` [Bug c++/99700] [10/11 Regression] " msebor at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-04-15 0:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99700
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |msebor at gcc dot gnu.org
Summary|gcc takes an uninitialized |uninitialized variable
|variable as a constant |accepted as a constant
|expression |expression in C++ 20
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-04-15
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
Confirmed with -std=c++20. In earlier modes GCC rejects the test case as
expected.
$ (set -x && gcc -O2 -S -Wall -std=c++20 pr99700.C && gcc -O2 -S -Wall
-std=c++17 pr99700.C)
+ gcc -O2 -S -Wall -std=c++20 pr99700.C
+ gcc -O2 -S -Wall -std=c++17 pr99700.C
pr99700.C: In constructor ‘constexpr A::A()’:
pr99700.C:2:29: error: member ‘A::c’ must be initialized by mem-initializer in
‘constexpr’ constructor
2 | constexpr A() { c[0] = 0; }
| ^
pr99700.C:3:8: note: declared here
3 | char c[2];
| ^
pr99700.C: At global scope:
pr99700.C:6:13: error: ‘constexpr A::A()’ called in a constant expression
6 | constexpr A a;
| ^
pr99700.C:2:13: note: ‘constexpr A::A()’ declared here
2 | constexpr A() { c[0] = 0; }
| ^
When reporting bugs please include all the information we ask for here:
https://gcc.gnu.org/bugs/#need. Links to other sites are not a substitute.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/99700] [10/11 Regression] uninitialized variable accepted as a constant expression in C++ 20
2021-03-21 18:22 [Bug c++/99700] New: gcc takes an uninitialized variable as a constant expression hewillk at gmail dot com
2021-04-15 0:14 ` [Bug c++/99700] uninitialized variable accepted as a constant expression in C++ 20 msebor at gcc dot gnu.org
@ 2021-04-15 0:15 ` msebor at gcc dot gnu.org
2021-04-15 16:55 ` ppalka at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: msebor at gcc dot gnu.org @ 2021-04-15 0:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99700
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|uninitialized variable |[10/11 Regression]
|accepted as a constant |uninitialized variable
|expression in C++ 20 |accepted as a constant
| |expression in C++ 20
Known to fail| |10.2.0, 11.0
--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Bisection points to r279019 AKA the fix for PR c++/91353 as the first revision
when the code started to be accepted.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/99700] [10/11 Regression] uninitialized variable accepted as a constant expression in C++ 20
2021-03-21 18:22 [Bug c++/99700] New: gcc takes an uninitialized variable as a constant expression hewillk at gmail dot com
2021-04-15 0:14 ` [Bug c++/99700] uninitialized variable accepted as a constant expression in C++ 20 msebor at gcc dot gnu.org
2021-04-15 0:15 ` [Bug c++/99700] [10/11 Regression] " msebor at gcc dot gnu.org
@ 2021-04-15 16:55 ` ppalka at gcc dot gnu.org
2021-04-16 13:25 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-04-15 16:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99700
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ppalka at gcc dot gnu.org
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org
Status|NEW |ASSIGNED
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
It seems reduced_constant_expression_p needs to check that a
CONSTRUCTOR_NO_CLEARING array ctor initializes all elements.
I'm testing:
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index c8d9dae36fb..6e530f9c88d 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -46,6 +46,7 @@ do {
\
static HOST_WIDE_INT find_array_ctor_elt (tree ary, tree dindex,
bool insert = false);
+static int array_index_cmp (tree key, tree index);
/* Returns true iff FUN is an instantiation of a constexpr function
template or a defaulted constexpr function. */
@@ -2912,7 +2913,25 @@ reduced_constant_expression_p (tree t)
else if (cxx_dialect >= cxx20
/* An ARRAY_TYPE doesn't have any TYPE_FIELDS. */
&& TREE_CODE (TREE_TYPE (t)) == ARRAY_TYPE)
- field = NULL_TREE;
+ {
+ tree min = TYPE_MIN_VALUE (TYPE_DOMAIN (TREE_TYPE (t)));
+ tree max = TYPE_MAX_VALUE (TYPE_DOMAIN (TREE_TYPE (t)));
+ if (find_array_ctor_elt (t, min) == -1
+ || find_array_ctor_elt (t, max) == -1)
+ return false;
+ tree cursor = size_zero_node;
+ FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (t), i, idx, val)
+ {
+ if (!reduced_constant_expression_p (val))
+ return false;
+ if (array_index_cmp (cursor, idx) != 0)
+ return false;
+ if (TREE_CODE (idx) == RANGE_EXPR)
+ cursor = TREE_OPERAND (idx, 1);
+ cursor = int_const_binop (PLUS_EXPR, cursor, size_one_node);
+ }
+ return true;
+ }
else if (cxx_dialect >= cxx20
&& TREE_CODE (TREE_TYPE (t)) == UNION_TYPE)
{
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/99700] [10/11 Regression] uninitialized variable accepted as a constant expression in C++ 20
2021-03-21 18:22 [Bug c++/99700] New: gcc takes an uninitialized variable as a constant expression hewillk at gmail dot com
` (2 preceding siblings ...)
2021-04-15 16:55 ` ppalka at gcc dot gnu.org
@ 2021-04-16 13:25 ` cvs-commit at gcc dot gnu.org
2021-04-16 13:27 ` [Bug c++/99700] [10 " ppalka at gcc dot gnu.org
2022-05-11 17:07 ` ppalka at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-04-16 13:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99700
--- Comment #4 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:baf05d54dc919c968d12de9d049e36e5bac10dec
commit r11-8216-gbaf05d54dc919c968d12de9d049e36e5bac10dec
Author: Patrick Palka <ppalka@redhat.com>
Date: Fri Apr 16 09:24:46 2021 -0400
c++: partially initialized constexpr array [PR99700]
Here, reduced_constant_expression_p is incorrectly returning true for a
partially initialized array CONSTRUCTOR (in C++20 mode) because when the
CONSTRUCTOR_NO_CLEARING flag is set, the predicate doesn't check that
the CONSTRUCTOR spans the entire array like it does for class CONSTRUCTORS.
This patch adds a dedicated loop for the array case that simultaneously
verifies the CONSTRUCTOR spans the entire array and is made up of valid
constant expressions.
gcc/cp/ChangeLog:
PR c++/99700
* constexpr.c (reduced_constant_expression_p): For array
CONSTRUCTORs, use a dedicated loop that additionally verifies
the CONSTRUCTOR spans the entire array.
gcc/testsuite/ChangeLog:
PR c++/99700
* g++.dg/cpp2a/constexpr-init21.C: New test.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/99700] [10 Regression] uninitialized variable accepted as a constant expression in C++ 20
2021-03-21 18:22 [Bug c++/99700] New: gcc takes an uninitialized variable as a constant expression hewillk at gmail dot com
` (3 preceding siblings ...)
2021-04-16 13:25 ` cvs-commit at gcc dot gnu.org
@ 2021-04-16 13:27 ` ppalka at gcc dot gnu.org
2022-05-11 17:07 ` ppalka at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-04-16 13:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99700
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|[10/11 Regression] |[10 Regression]
|uninitialized variable |uninitialized variable
|accepted as a constant |accepted as a constant
|expression in C++ 20 |expression in C++ 20
Target Milestone|--- |10.4
--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 11 so far.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c++/99700] [10 Regression] uninitialized variable accepted as a constant expression in C++ 20
2021-03-21 18:22 [Bug c++/99700] New: gcc takes an uninitialized variable as a constant expression hewillk at gmail dot com
` (4 preceding siblings ...)
2021-04-16 13:27 ` [Bug c++/99700] [10 " ppalka at gcc dot gnu.org
@ 2022-05-11 17:07 ` ppalka at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: ppalka at gcc dot gnu.org @ 2022-05-11 17:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99700
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.4 |11.0
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
The patch doesn't apply cleanly to the 10 branch, and since this is only a
C++20 regression, it doesn't seem worth backporting.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2022-05-11 17:07 UTC | newest]
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2021-03-21 18:22 [Bug c++/99700] New: gcc takes an uninitialized variable as a constant expression hewillk at gmail dot com
2021-04-15 0:14 ` [Bug c++/99700] uninitialized variable accepted as a constant expression in C++ 20 msebor at gcc dot gnu.org
2021-04-15 0:15 ` [Bug c++/99700] [10/11 Regression] " msebor at gcc dot gnu.org
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2021-04-16 13:25 ` cvs-commit at gcc dot gnu.org
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