http://bugs.llvm.org/show_bug.cgi?id=32427
Bug ID: 32427
Summary: Clang should warn for not initializing field in a move
constructor
Product: clang
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: C++
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
The C++ standard states that a move constructor is called when returning a
value from a method unless the compiler is able to elide the move,
For example, the following code invokes undefined behaviour:
#include <iostream>
class CallEmission {
public:
bool assumedPlusZeroSelf;
CallEmission(bool assumedPlusZeroSelf) :
assumedPlusZeroSelf(assumedPlusZeroSelf) {}
CallEmission(CallEmission &&e) {
std::cout << "Called move constructor" << "\n";
}
};
CallEmission method() {
CallEmission x(false);
return x;
}
int main() {
CallEmission x = method();
std::cout << x.assumedPlusZeroSelf;
}
MSVC:
> Called move constructor
> 140
Clang:
> 0
This is because with MSVC the move constructor is called, which fails to
initialize the memory of `assumedPlusZeroSelf`.
This caused a crash in Swift on Windows with MSVC
(https://github.com/apple/swift/pull/8337)
Michael Gottesman, an engineer on the Swift team said "@hughbe Nice find! I
wonder if there is a warning for this.". Seemingly there is not, so it would be
nice to issue a warning here to prevent different behaviour on different
compilers.
Maybe something like "field assumedPlusZeroSelf is not initialized in
constructor CallEmission(CallEmission&&)"
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