https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88173
Bug ID: 88173
Summary: `std::numeric_limits<double>::quiet_NaN()` is not
constexpr
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: g...@christoph-conrads.name
Target Milestone: ---
Consider the following C++11 code:
$ cat nan.cpp
#include <limits>
constexpr bool foo(double x)
{
return !(x <= 0);
}
int main()
{
static_assert(std::numeric_limits<double>::has_quiet_NaN, "");
static_assert(!(0 <= std::numeric_limits<double>::quiet_NaN()), "");
static_assert(foo(std::numeric_limits<double>::quiet_NaN()), "");
}
I expect this code to compile because `foo()` is a constexpr function and
because `std::numeric_limits<double>::quiet_NaN()` must be a constexpr function
according to §18.3.2.4 of the C++ standard draft N3337 (and because there are
quiet NaNs on my computer). Nevertheless, the code fails to compile with GCC:
$ g++ -Wextra -Wall -std=c++11 -pedantic nan.cpp
nan.cpp: In function ‘int main()’:
nan.cpp:12:2: error: non-constant condition for static assertion
static_assert(foo(std::numeric_limits<double>::quiet_NaN()), "");
^~~~~~~~~~~~~
nan.cpp:12:19: in constexpr expansion of
‘foo(std::numeric_limits<double>::quiet_NaN())’
nan.cpp:5:13: error: ‘(+QNaN <= 0.0)’ is not a constant expression
return !(x <= 0);
~~~^~~~~
The errors is the same with GCC 7.3.0 on Ubuntu 18.04 LTS (Bionic Beaver), GCC
7.3.0 on Gentoo (no output posted), and GCC 6.3.0 on Raspbian (output below).
$ lsb_release --all
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic
$ g++ -Wextra -Wall -std=c++11 -pedantic -v nan.cpp
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
7.3.0-27ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-7
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 7.3.0 (Ubuntu 7.3.0-27ubuntu1~18.04)
COLLECT_GCC_OPTIONS='-Wextra' '-Wall' '-std=c++11' '-Wpedantic' '-v'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-linux-gnu/7/cc1plus -quiet -v -imultiarch x86_64-linux-gnu
-D_GNU_SOURCE nan.cpp -quiet -dumpbase nan.cpp -mtune=generic -march=x86-64
-auxbase nan -Wextra -Wall -Wpedantic -std=c++11 -version
-fstack-protector-strong -Wformat-security -o /tmp/ccSEEcsH.s
GNU C++11 (Ubuntu 7.3.0-27ubuntu1~18.04) version 7.3.0 (x86_64-linux-gnu)
compiled by GNU C version 7.3.0, GMP version 6.1.2, MPFR version 4.0.1,
MPC version 1.1.0, isl version isl-0.19-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring duplicate directory "/usr/include/x86_64-linux-gnu/c++/7"
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/7/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/7
/usr/include/x86_64-linux-gnu/c++/7
/usr/include/c++/7/backward
/usr/lib/gcc/x86_64-linux-gnu/7/include
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/7/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
GNU C++11 (Ubuntu 7.3.0-27ubuntu1~18.04) version 7.3.0 (x86_64-linux-gnu)
compiled by GNU C version 7.3.0, GMP version 6.1.2, MPFR version 4.0.1,
MPC version 1.1.0, isl version isl-0.19-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 1bfae38ae5df64de6196cbd8c3b07d86
nan.cpp: In function ‘int main()’:
nan.cpp:12:2: error: non-constant condition for static assertion
static_assert(foo(std::numeric_limits<double>::quiet_NaN()), "");
^~~~~~~~~~~~~
nan.cpp:12:19: in constexpr expansion of
‘foo(std::numeric_limits<double>::quiet_NaN())’
nan.cpp:5:13: error: ‘(+QNaN <= 0.0)’ is not a constant expression
return !(x <= 0);
~~~^~~~~
$ lsb_release --all
No LSB modules are available.
Distributor ID: Raspbian
Description: Raspbian GNU/Linux 9.4 (stretch)
Release: 9.4
Codename: stretch
$ g++ -Wextra -Wall -std=c++11 -pedantic -v nan.cpp
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/arm-linux-gnueabihf/6/lto-wrapper
Target: arm-linux-gnueabihf
Configured with: ../src/configure -v --with-pkgversion='Raspbian
6.3.0-18+rpi1+deb9u1' --with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-6 --program-prefix=arm-linux-gnueabihf- --enable-shared
--enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/
--enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm
--disable-libquadmath --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-6-armhf/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-armhf
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-armhf
--with-arch-directory=arm --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--with-target-system-zlib --enable-objc-gc=auto --enable-multiarch
--disable-sjlj-exceptions --with-arch=armv6 --with-fpu=vfp --with-float=hard
--enable-checking=release --build=arm-linux-gnueabihf
--host=arm-linux-gnueabihf --target=arm-linux-gnueabihf
Thread model: posix
gcc version 6.3.0 20170516 (Raspbian 6.3.0-18+rpi1+deb9u1)
COLLECT_GCC_OPTIONS='-Wextra' '-Wall' '-std=c++11' '-Wpedantic' '-v'
'-shared-libgcc' '-march=armv6' '-mfloat-abi=hard' '-mfpu=vfp'
'-mtls-dialect=gnu'
/usr/lib/gcc/arm-linux-gnueabihf/6/cc1plus -quiet -v -imultilib . -imultiarch
arm-linux-gnueabihf -D_GNU_SOURCE nan.cpp -quiet -dumpbase nan.cpp -march=armv6
-mfloat-abi=hard -mfpu=vfp -mtls-dialect=gnu -auxbase nan -Wextra -Wall
-Wpedantic -std=c++11 -version -o /tmp/ccfELtIA.s
GNU C++11 (Raspbian 6.3.0-18+rpi1+deb9u1) version 6.3.0 20170516
(arm-linux-gnueabihf)
compiled by GNU C version 6.3.0 20170516, GMP version 6.1.2, MPFR
version 3.1.5, MPC version 1.0.3, isl version 0.15
GGC heuristics: --param ggc-min-expand=93 --param ggc-min-heapsize=118681
ignoring duplicate directory "/usr/include/arm-linux-gnueabihf/c++/6"
ignoring nonexistent directory "/usr/local/include/arm-linux-gnueabihf"
ignoring nonexistent directory
"/usr/lib/gcc/arm-linux-gnueabihf/6/../../../../arm-linux-gnueabihf/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/6
/usr/include/arm-linux-gnueabihf/c++/6
/usr/include/c++/6/backward
/usr/lib/gcc/arm-linux-gnueabihf/6/include
/usr/local/include
/usr/lib/gcc/arm-linux-gnueabihf/6/include-fixed
/usr/include/arm-linux-gnueabihf
/usr/include
End of search list.
GNU C++11 (Raspbian 6.3.0-18+rpi1+deb9u1) version 6.3.0 20170516
(arm-linux-gnueabihf)
compiled by GNU C version 6.3.0 20170516, GMP version 6.1.2, MPFR
version 3.1.5, MPC version 1.0.3, isl version 0.15
GGC heuristics: --param ggc-min-expand=93 --param ggc-min-heapsize=118681
Compiler executable checksum: 79dca666fccaa96025c9107a8b3f60f3
nan.cpp: In function ‘int main()’:
nan.cpp:12:2: error: non-constant condition for static assertion
static_assert(foo(std::numeric_limits<double>::quiet_NaN()), "");
^~~~~~~~~~~~~
nan.cpp:12:19: in constexpr expansion of
‘foo(std::numeric_limits<double>::quiet_NaN())’
nan.cpp:5:13: error: ‘(+QNaN <= 0.0)’ is not a constant expression
return !(x <= 0);
~~~^~~~~
