https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105696
Bug ID: 105696
Summary: invalid use of constexpr static class member accepted
as constant expression
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: yiz152 at ucsd dot edu
Target Milestone: ---
Created attachment 53017
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53017&action=edit
Test case
G++ 12.1.0 accepts constexpr static class members referenced using class member
access syntax (see below/attached). The working draft states
(https://eel.is/c++draft/class.static#general-1) that in such cases, the object
expression (this->val) is evaluated, thereby breaking constexpr-ness (cf.
https://eel.is/c++draft/expr.const#5.1).
Compiled/tested with gcc 12.1.0, clang 13.0.1, -pedantic -Wall -Wextra
-std=c++1z. Also tested with -std=c++11,-std=c++14. Code/error (same as the
attached file):
#include <type_traits>
struct A {
constexpr static int a = 17;
};
struct B {
A val;
int foo() {
// gcc compiles without warning; clang rejects
return std::integral_constant<int, val.a>::value;
}
int good_foo() {
// gcc compiles without warning, correct
return std::integral_constant<int, decltype(val)::a>::value;
}
void bar() {
char a[val.a]; // gcc compiles without warning, clang warns -Wvla
(void) a;
}
void var_bar(int len) {
char a[len]; // gcc compiles with -Wvla, clang does as well
(void) a;
}
};
int main() {}
gcc -v:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-bootstrap
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit
--enable-cet=auto --enable-checking=release --enable-clocale=gnu
--enable-default-pie --enable-default-ssp --enable-gnu-indirect-function
--enable-gnu-unique-object --enable-linker-build-id --enable-lto
--enable-multilib --enable-plugin --enable-shared --enable-threads=posix
--disable-libssp --disable-libstdcxx-pch --disable-werror
--with-build-config=bootstrap-lto --enable-link-serialization=1
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.1.0 (GCC)
