https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102573
Bug ID: 102573
Summary: optimized code removes the underlying elements of the
std::initializer_list being copied
Product: gcc
Version: 4.8.5
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: 13508417 at qq dot com
Target Milestone: ---
Using clang++ compiler with libstdc++, the output of below program differs
whether use -O option.
----
code:
#include<iostream>
#include<initializer_list>
using namespace std;
int main()
{
initializer_list<int> il;
il = {111, 222};
cout << "initializer_list size: " << il.size() << endl;
cout << "initializer_list underlying elements: " << endl;
for (auto i : il)
cout << i << endl;
return 0;
}
----
command:
➜ clang++ test_2.cpp -std=c++11 -O1 -v
clang version 10.0.0
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
Found candidate GCC installation: /usr/lib/gcc/i686-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/i686-redhat-linux/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
...
----
output without -O:
initializer_list size: 2
initializer_list underlying elements:
111
222
----
output with -O1:
initializer_list size: 2
initializer_list underlying elements:
1402476368
32767
----
Question:
>From https://timsong-cpp.github.io/cppwp/n4659/dcl.init.list, I know that the
reason is because the lifetime of the underlying array should be same as the
temporary initializer_list constructed directly from the "{111, 222}", and the
variable "il" only copy the address and length of the underlying array using
the default copy member, but cannot affect the lifetime of the underlying
array.
But my question is, since the copied initializer_list can't affect the lifetime
of the underlying array bound to the original initializer_list, can we just
prohibit the copy member in the library implementation of
std::initializer_list? It seems to me that the copy member makes not much
sense, but probably lures the user to make mistakes.
