https://llvm.org/bugs/show_bug.cgi?id=26504
Bug ID: 26504
Summary: Overload resolution is strange with constexpr
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: C++11
Assignee: unassignedclangb...@nondot.org
Reporter: nicolaswe...@gmx.de
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org
Classification: Unclassified
Consider this:
Nicos-MBP:llvm-build thakis$ cat test.cc
template<class T> const T& min(const T& a, const T& b) {
return a < b ? a : b;
}
struct A {
A();
operator int() const;
operator unsigned() const;
A foo() const {
return min(*this, A());
}
};
inline bool operator<(const A &a, const A &b) { return true; }
Nicos-MBP:llvm-build thakis$ bin/clang -c test.cc -std=c++11
This builds fine. Now make max() constexpr:
Nicos-MBP:llvm-build thakis$ bin/clang -c test.cc -std=c++11
test.cc:2:12: error: use of overloaded operator '<' is ambiguous (with operand
types 'const A' and 'const A')
return a < b ? a : b;
~ ^ ~
test.cc:10:12: note: in instantiation of function template specialization
'min<A>' requested here
return min(*this, A());
^
test.cc:2:12: note: because of ambiguity in conversion of 'const A' to 'float'
return a < b ? a : b;
^
test.cc:6:3: note: candidate function
operator int() const;
^
test.cc:7:3: note: candidate function
operator unsigned() const;
^
test.cc:2:12: note: because of ambiguity in conversion of 'const A' to 'float'
return a < b ? a : b;
^
test.cc:6:3: note: candidate function
operator int() const;
^
test.cc:7:3: note: candidate function
operator unsigned() const;
^
test.cc:2:12: note: built-in candidate operator<(float, float)
return a < b ? a : b;
^
test.cc:2:12: note: built-in candidate operator<(float, double)
test.cc:2:12: note: built-in candidate operator<(float, long double)
test.cc:2:12: note: built-in candidate operator<(float, int)
test.cc:2:12: note: built-in candidate operator<(float, long)
test.cc:2:12: note: built-in candidate operator<(float, long long)
test.cc:2:12: note: built-in candidate operator<(float, __int128)
test.cc:2:12: note: built-in candidate operator<(float, unsigned int)
test.cc:2:12: note: built-in candidate operator<(float, unsigned long)
test.cc:2:12: note: built-in candidate operator<(float, unsigned long long)
test.cc:2:12: note: built-in candidate operator<(float, unsigned __int128)
test.cc:2:12: note: built-in candidate operator<(double, float)
test.cc:2:12: note: built-in candidate operator<(double, double)
test.cc:2:12: note: built-in candidate operator<(double, long double)
test.cc:2:12: note: built-in candidate operator<(double, int)
test.cc:2:12: note: built-in candidate operator<(double, long)
test.cc:2:12: note: built-in candidate operator<(double, long long)
test.cc:2:12: note: built-in candidate operator<(double, __int128)
test.cc:2:12: note: built-in candidate operator<(double, unsigned int)
test.cc:2:12: note: built-in candidate operator<(double, unsigned long)
test.cc:2:12: note: built-in candidate operator<(double, unsigned long long)
test.cc:2:12: note: built-in candidate operator<(double, unsigned __int128)
test.cc:2:12: note: built-in candidate operator<(long double, float)
test.cc:2:12: note: built-in candidate operator<(long double, double)
test.cc:2:12: note: built-in candidate operator<(long double, long double)
test.cc:2:12: note: built-in candidate operator<(long double, int)
test.cc:2:12: note: built-in candidate operator<(long double, long)
test.cc:2:12: note: built-in candidate operator<(long double, long long)
test.cc:2:12: note: built-in candidate operator<(long double, __int128)
test.cc:2:12: note: built-in candidate operator<(long double, unsigned int)
test.cc:2:12: note: built-in candidate operator<(long double, unsigned long)
test.cc:2:12: note: built-in candidate operator<(long double, unsigned long
long)
test.cc:2:12: note: built-in candidate operator<(long double, unsigned
__int128)
test.cc:2:12: note: built-in candidate operator<(int, float)
test.cc:2:12: note: built-in candidate operator<(int, double)
test.cc:2:12: note: built-in candidate operator<(int, long double)
test.cc:2:12: note: built-in candidate operator<(int, int)
test.cc:2:12: note: built-in candidate operator<(int, long)
test.cc:2:12: note: built-in candidate operator<(int, long long)
test.cc:2:12: note: built-in candidate operator<(int, __int128)
test.cc:2:12: note: built-in candidate operator<(int, unsigned int)
test.cc:2:12: note: built-in candidate operator<(int, unsigned long)
test.cc:2:12: note: built-in candidate operator<(int, unsigned long long)
test.cc:2:12: note: built-in candidate operator<(int, unsigned __int128)
test.cc:2:12: note: built-in candidate operator<(long, float)
test.cc:2:12: note: built-in candidate operator<(long, double)
test.cc:2:12: note: built-in candidate operator<(long, long double)
test.cc:2:12: note: built-in candidate operator<(long, int)
test.cc:2:12: note: built-in candidate operator<(long, long)
test.cc:2:12: note: built-in candidate operator<(long, long long)
test.cc:2:12: note: built-in candidate operator<(long, __int128)
test.cc:2:12: note: built-in candidate operator<(long, unsigned int)
test.cc:2:12: note: built-in candidate operator<(long, unsigned long)
test.cc:2:12: note: built-in candidate operator<(long, unsigned long long)
test.cc:2:12: note: built-in candidate operator<(long, unsigned __int128)
test.cc:2:12: note: built-in candidate operator<(long long, float)
test.cc:2:12: note: built-in candidate operator<(long long, double)
test.cc:2:12: note: built-in candidate operator<(long long, long double)
test.cc:2:12: note: built-in candidate operator<(long long, int)
test.cc:2:12: note: built-in candidate operator<(long long, long)
test.cc:2:12: note: built-in candidate operator<(long long, long long)
test.cc:2:12: note: built-in candidate operator<(long long, __int128)
test.cc:2:12: note: built-in candidate operator<(long long, unsigned int)
test.cc:2:12: note: built-in candidate operator<(long long, unsigned long)
test.cc:2:12: note: built-in candidate operator<(long long, unsigned long long)
test.cc:2:12: note: built-in candidate operator<(long long, unsigned __int128)
test.cc:2:12: note: built-in candidate operator<(__int128, float)
test.cc:2:12: note: built-in candidate operator<(__int128, double)
test.cc:2:12: note: built-in candidate operator<(__int128, long double)
test.cc:2:12: note: built-in candidate operator<(__int128, int)
test.cc:2:12: note: built-in candidate operator<(__int128, long)
test.cc:2:12: note: built-in candidate operator<(__int128, long long)
test.cc:2:12: note: built-in candidate operator<(__int128, __int128)
test.cc:2:12: note: built-in candidate operator<(__int128, unsigned int)
test.cc:2:12: note: built-in candidate operator<(__int128, unsigned long)
test.cc:2:12: note: built-in candidate operator<(__int128, unsigned long long)
test.cc:2:12: note: built-in candidate operator<(__int128, unsigned __int128)
test.cc:2:12: note: built-in candidate operator<(unsigned int, float)
test.cc:2:12: note: built-in candidate operator<(unsigned int, double)
test.cc:2:12: note: built-in candidate operator<(unsigned int, long double)
test.cc:2:12: note: built-in candidate operator<(unsigned int, int)
test.cc:2:12: note: built-in candidate operator<(unsigned int, long)
test.cc:2:12: note: built-in candidate operator<(unsigned int, long long)
test.cc:2:12: note: built-in candidate operator<(unsigned int, __int128)
test.cc:2:12: note: built-in candidate operator<(unsigned int, unsigned int)
test.cc:2:12: note: built-in candidate operator<(unsigned int, unsigned long)
test.cc:2:12: note: built-in candidate operator<(unsigned int, unsigned long
long)
test.cc:2:12: note: built-in candidate operator<(unsigned int, unsigned
__int128)
test.cc:2:12: note: built-in candidate operator<(unsigned long, float)
test.cc:2:12: note: built-in candidate operator<(unsigned long, double)
test.cc:2:12: note: built-in candidate operator<(unsigned long, long double)
test.cc:2:12: note: built-in candidate operator<(unsigned long, int)
test.cc:2:12: note: built-in candidate operator<(unsigned long, long)
test.cc:2:12: note: built-in candidate operator<(unsigned long, long long)
test.cc:2:12: note: built-in candidate operator<(unsigned long, __int128)
test.cc:2:12: note: built-in candidate operator<(unsigned long, unsigned int)
test.cc:2:12: note: built-in candidate operator<(unsigned long, unsigned long)
test.cc:2:12: note: built-in candidate operator<(unsigned long, unsigned long
long)
test.cc:2:12: note: built-in candidate operator<(unsigned long, unsigned
__int128)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, float)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, double)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, long
double)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, int)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, long)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, long long)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, __int128)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, unsigned
int)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, unsigned
long)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, unsigned
long long)
test.cc:2:12: note: built-in candidate operator<(unsigned long long, unsigned
__int128)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, float)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, double)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, long
double)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, int)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, long)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, long long)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, __int128)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, unsigned
int)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, unsigned
long)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, unsigned
long long)
test.cc:2:12: note: built-in candidate operator<(unsigned __int128, unsigned
__int128)
1 error generated.
cl.exe builds this fine, and that's how it implements std::min().
a) Who is right?
b) If it's clang, we need to figure out what cl.exe does and accept that as an
extension.
(Also, the diagnostic is not very good.)
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