http://llvm.org/bugs/show_bug.cgi?id=16993
Bug ID: 16993
Summary: Assign rvalue to self
Product: libc++
Version: unspecified
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
I've found out that some libc++ STL containers works incorrect while
assigning rvalue to self. For example std::vector:
#include <iostream> // std::cout
#include <vector>
int main() {
std::vector<int> a(1000);
std::cout << a.capacity() << std::endl; // 1000
a = std::move(a);
std::cout << a.capacity() << std::endl; // 0
a[100] = 0x0; // Segmentation fault
return EXIT_SUCCESS;
}
And, I think, is right.
>From standard 17.6.4.9 Function arguments [res.on.arguments]:
— If a function argument binds to an rvalue reference parameter, the
implementation may assume that this parameter is a unique reference to this
argument. [ Note: If the parameter is a generic parameter of the form T&& and
an lvalue of type A is bound, the argument binds to an lvalue reference
(14.8.2.1) and thus is not covered by the previous sentence. —end note ] [
Note: If a program casts an lvalue to an xvalue while passing that lvalue to a
library function (e.g. by calling the function with the argument move(x)), the
program is effectively asking that function to treat that lvalue as a
temporary. The implementation is free to optimize away aliasing checks which
might be needed if the argument was an lvalue. —end note ]
1. Am I quoting standard correctly?
2. Is it refer to STL containers only ("evil" optimization) or general C++11
rule (good practice?)
3. Can you provide an assert(_LIBCPP_ASSERT?) in debug mode to check violation
of this rule?
PS MSVC check (this != &ref) and works correcty, libstdc++ not check and
segfaulting too.
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