seen at least on x86_64. bug submitter writes:
g++ appears to be (incorrectly) using a signed int comparison when -O3
optimization is enabled. Compiling with -O2 or lower produces the correct
output.
#include <numeric>
#include <iostream>
template <typename T>
struct maximum
{
T operator()(T& a, T& b)
{
return (a < b) ? b : a;
}
};
int main(void)
{
typedef unsigned int T;
T data[13] = {2411691434, 187758716, 2874577865, 1532192406,
850395381, 3670100461, 1052104929, 352534891,
1000719294, 2219234747, 4264598888, 4166615811,
1898580612};
T init = 0;
T result = std::accumulate(data, data + 13, init, maximum<T>());
std::cout << result << std::endl;
return 0;
}
$ g++ -O2 -Wall bug.cpp && ./a.out
4264598888
g++ -O3 -Wall bug.cpp && ./a.out
1898580612
--
Summary: g++ -O3 produces incorrect results for less-than
operator
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: debian-gcc at lists dot debian dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42542
