https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67798
Bug ID: 67798
Summary: Constant shift operation to the openmp unsigned loop
variable gives a wrong result .
Product: gcc
Version: 5.2.0
Status: UNCONFIRMED
Severity: critical
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: min.25.hy at gmail dot com
Target Milestone: ---
Constant shift operations to the openmp-unsigned loop variable gave a wrong
result.
---[here is a source code]---
#include <cstdio>
#include <omp.h>
int main() {
// output 4294967296 4294967296 instead of 0 4294967296
#pragma omp parallel for
for (unsigned i = 1; i <= 1; ++i) {
__uint128_t a = __uint128_t(i) << 32;
printf("%llu %llu\n",
(unsigned long long) (a >> 64),
(unsigned long long) (a & 0xFFFFFFFFFFFFFFFFull));
}
// output 0 4294967296
#pragma omp parallel for
for (int i = 1; i <= 1; ++i) {
__uint128_t a = __uint128_t(i) << 32;
printf("%llu %llu\n",
(unsigned long long) (a >> 64),
(unsigned long long) (a & 0xFFFFFFFFFFFFFFFFull));
}
return 0;
}
$ g++-5 -v
Using built-in specs.
COLLECT_GCC=g++-5
COLLECT_LTO_WRAPPER=/usr/local/Cellar/gcc/5.2.0/libexec/gcc/x86_64-apple-darwin11.4.2/5.2.0/lto-wrapper
Target: x86_64-apple-darwin11.4.2
Configured with: ../configure --build=x86_64-apple-darwin11.4.2
--prefix=/usr/local/Cellar/gcc/5.2.0
--libdir=/usr/local/Cellar/gcc/5.2.0/lib/gcc/5
--enable-languages=c,c++,objc,obj-c++,fortran --program-suffix=-5
--with-gmp=/usr/local/opt/gmp --with-mpfr=/usr/local/opt/mpfr
--with-mpc=/usr/local/opt/libmpc --with-isl=/usr/local/opt/isl
--with-system-zlib --enable-libstdcxx-time=yes --enable-stage1-checking
--enable-checking=release --enable-lto --with-build-config=bootstrap-debug
--disable-werror --with-pkgversion='Homebrew gcc 5.2.0'
--with-bugurl=https://github.com/Homebrew/homebrew/issues --enable-plugin
--disable-nls --enable-multilib
Thread model: posix
gcc version 5.2.0 (Homebrew gcc 5.2.0)
$ g++-5 -O3 -fopenmp shift.cpp
$ ./a.out
4294967296 4294967296
0 4294967296
