https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113578
Bug ID: 113578
Summary: Incorrect signbit for -nan on RISC-V
Product: gcc
Version: 11.4.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
CC: doko at gcc dot gnu.org
Target Milestone: ---
Target: riscv64-linux-gnu
int main()
{
float f = std::bit_cast<float>(0xfff80000);
__builtin_printf("%f %d\n", f, __builtin_signbit(f));
}
With no optimization this prints:
nan 1
With optimization it prints:
-nan 1
i.e. signbit is always set, but sometimes the nan is printed as positive.
g++ -v:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/riscv64-linux-gnu/11/lto-wrapper
Target: riscv64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
11.4.0-1ubuntu1~22.04' --with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=riscv64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-libitm --disable-libquadmath
--disable-libquadmath-support --enable-plugin --enable-default-pie
--with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --disable-multilib --with-arch=rv64gc --with-abi=lp64d
--enable-checking=release --build=riscv64-linux-gnu --host=riscv64-linux-gnu
--target=riscv64-linux-gnu --with-build-config=bootstrap-lto-lean
--enable-link-serialization=4
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.4.0 (Ubuntu 11.4.0-1ubuntu1~22.04)
Originally reported to
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1059340
I've only tested this with Ubuntu's gcc, I haven't tried a build of upstream
GCC, nor a newer version. Sorry if it's Debian specific.
