https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90313
Bug ID: 90313
Summary: Is an assignment elided with gcc7.3 -O2?
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nina.korshunova at tum dot de
Target Milestone: ---
#include <array>
#include <iostream>
using Coordinates = std::array<double, 3>;
Coordinates map( const Coordinates& c, size_t level )
{
Coordinates result{ c[1], c[2], c[0] };
if( level != 0 )
{
result = map( result, level - 1 );
}
return result;
}
int main( )
{
Coordinates vecOfCoordinates = { 1.0, 2.0, 3.0 };
size_t level = 1;
auto result = map( vecOfCoordinates, level );
std::cout << "result = (" << result[0] << ", " << result[1] << ", " <<
result[2] << "), should be (3, 1, 2)" << std::endl;
return 0;
}
This minimal example delivers the following results with different
optimizations:
g++-6 -O2 : result = (3, 1, 2), should be (3, 1, 2)
g++-7: result = (3, 1, 2), should be (3, 1, 2)
g++-7 -O2: result = (3, 1, 3), should be (3, 1, 2)
g++-7 -O2 -fno-elide-constructors: result = (3, 1, 2), should be (3, 1, 2)
g++-8 -O2: result = (3, 1, 2), should be (3, 1, 2)
Gcc7.3.0 and -O2 deliver the wrong result. -fno-elide-constructors fixes the
result. -Wall -Wextra -fno-strict-aliasing -fwrap did not make a difference. Is
this a possible bug, or is there a problem in the code?
Everything is run on Ubuntu 18.04.
