[Bug c++/50776] New: unused object optimized out, despite having constructor

[Bug c++/50776] New: unused object optimized out, despite having constructor

[nyh at math dot technion.ac.il]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50776

             Bug #: 50776
           Summary: unused object optimized out, despite having
                    constructor
    Classification: Unclassified
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: nyh@math.technion.ac.il


Consider the following simple program:

        #include <cstdio>
        class Ident {
        public:
                Ident(const char *ident){
                        // This constructor prints a message!
                        printf("yo\n");
                }
        };

        static Ident id("$Id: hello $");

        main(){
                printf("hello\n");
        }

When you compile it with g++ without additional parameters, its output rightly
looks like:

        yo
        hello

I.e., the object "id" gets instantiated, and its constructor prints the message
"yo".
However, if you compile it with optimization enabled - g++ -O2 - the output is
DIFFERENT: the "id" object is optimized out (because it is static, but nobody
uses it in this source file), and therefore its constructor no longer runs.

I think it is a bug for optimization to change the behavior (not just the
performance) of a program. I think that if an object has a non-trivial
constructor with any side effects beside setting class fields, then we cannot
optimize its construction out because this would change the program behavior.

[Bug c++/50776] unused object optimized out, despite having constructor

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50776

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-10-18 14:18:49 UTC ---
I can't reproduce this with any version.

What platform are you using? (You failed to provide that, as requested by the
http://gcc.gnu.org/bugs/ page)

[Bug c++/50776] unused object optimized out, despite having constructor

[nyh at math dot technion.ac.il]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50776

Nadav Har'El <nyh at math dot technion.ac.il> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |WORKSFORME

--- Comment #2 from Nadav Har'El <nyh at math dot technion.ac.il> 2011-10-18 15:46:37 UTC ---
I'm really sorry, I don't know what happened - now I don't see this bug myself!
I must have done something wrong earlier (!?). Closing, and If I ever can
replicate this again, I'll reopen. Sorry :(