The code below, when compiled with out optimization, produces the expected
result:
% g++ bug.cc -o bug
% ./bug
{1, 2, 3, 4}
{5, 6, 7, 8}
{9, 0, 1, 2}
{3, 4, 5, 6}
When compiled with optimization, it produces garbage for all rows of the matrix
except the first row:
% g++ -O2 bug.cc -o bug
% ./bug
{1, 2, 3, 4}
{3.11042e-317, 2.07381e-317, 4.94066e-323, 2.07372e-317}
{0, 2.07321e-317, 6.92543e-310, 2.07375e-317}
{6.92543e-310, 2.07372e-317, 0, 2.0733e-317}
bug.cc:
#include <iostream>
template <unsigned R, unsigned C>
class M {
public:
M( const double* arr ) {
for (unsigned r = 0; r < R; ++r)
for (unsigned c = 0; c < C; ++c)
m[r*C+c] = arr[r*C+c];
}
double operator()(unsigned r, unsigned c) const
{ return m[r*C+c]; }
private:
double m[R*C];
};
template <unsigned R, unsigned C>
std::ostream& operator<<( std::ostream& str, const M<R,C>& m )
{
for (unsigned r = 0; r < R; ++r) {
str << "{" << m(r,0);
for (unsigned c = 1; c < C; ++c)
str << ", " << m(r,c);
str << "}" << std::endl;
}
return str;
}
int main()
{
double vals[4][4] = { { 1, 2, 3, 4 },
{ 5, 6, 7, 8 },
{ 9, 0, 1, 2 },
{ 3, 4, 5, 6 } };
M<4,4> m( &(vals[0][0]) );
std::cout << m << std::endl;
return 0;
}
--
Summary: optimization bug initializing from cast array
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: kraftche at cae dot wisc dot edu
GCC build triplet: x86_64-unknown-linux-gnu
GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44069
