[Bug c++/61856] New: Ternary operator in an NSDMI causes double evaluation
ville.voutilainen at gmail dot com
gcc-bugzilla@gcc.gnu.org
Sun Jul 20 12:18:00 GMT 2014
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61856
Bug ID: 61856
Summary: Ternary operator in an NSDMI causes double evaluation
Product: gcc
Version: 4.10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ville.voutilainen at gmail dot com
First test:
#include <iostream>
#ifdef OK
struct ostream { } cout;
bool operator<<(ostream&, const char* s)
{ __builtin_printf("%s", s); return true; }
#else
using std::cout;
#endif
struct X { int a = (cout<<"hmm\n") ? 1 : 2;};
int main()
{
X x;
}
With -DOK, this prints "hmm" once, otherwise it prints "hmm" twice. This
suggested
that perhaps the problem is specific to iostream, but wrapping the NSDMI into
a lambda fixes the double evaluation:
#include <iostream>
#ifdef OK
struct ostream { } cout;
bool operator<<(ostream&, const char* s)
{ __builtin_printf("%s", s); return true; }
#else
using std::cout;
#endif
struct X { int a = ([]{return bool(cout<<"hmm\n");}()) ? 1 : 2;};
int main()
{
X x;
}
Simpler cases like just incrementing a global variable in the ternary
operator seem to work fine:
#include <iostream>
int global_x = 0;
struct X { int a = (global_x++) ? 1 : 2;};
int main()
{
X x;
std::cout << global_x << std::endl;
}
Perhaps this is some weird gimplification bug.
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