http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54399
Bug #: 54399
Summary: Invalid partial change from dynamic to static
initialization
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: rafael.espind...@gmail.com
I initially thought that this was a missed optimization in llvm
(http://llvm.org/pr13677), but Richard Smith convinced me this actually a bug
in gcc.
$ cat test1.cpp
struct foo {
int a;
int b;
int c;
int d;
int e;
};
int zed();
int x = zed();
foo bar = {x, 1, 2, 3, 4};
$ cat test2.cpp
#include <stdio.h>
struct foo {
int a;
int b;
int c;
int d;
int e;
};
extern foo bar;
int zed() { return bar.d; }
int main(void) {
printf("%d\n", bar.a);
return 0;
}
With gcc:
$ ~/gcc/build/gcc/xgcc -std=c++11 -B ~/gcc/build/gcc -c test1.cpp
$ ~/gcc/build/gcc/xgcc -std=c++11 -B ~/gcc/build/gcc -c test2.cpp
$ g++ test1.o test2.o -o t
$ ./t
3
and with clang:
$ clang test1.cpp test2.cpp -o t
[espindola@desktop llvm]$ ./t
0
If I understand Richard's argument correctly, the program must print 0 because
* from [basic.start.init] p2 both x and bar get dynamic initializations. In
that case x is initialized first and zed will see bar zero initialized.
* from p3, we can convert a variable to static initialization, but not part of
it. The possibilities are:
1) Only x is converted to static initialization. x should be static
initialized to 0. When bar is dynamic initialized it will be initialized to {0,
1, 2, 3, 4}.
2) Only bar is converted to static initialization. It should still be
initialized to {0, 1, 2, 3, 4}. In this case x is dynamically initialized to 3.
3) Both x and bar are converted to static initialization. In this case x is 0
and bar is {0, 1, 2, 3, 4}.
The output produced by gcc doesn't match any of the possibilities provided by
the standard.
