[Bug c++/55446] New: array new with size zero vanishes from object code

[jens.maurer at gmx dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55446



             Bug #: 55446

           Summary: array new with size zero vanishes from object code

    Classification: Unclassified

           Product: gcc

           Version: 4.7.2

            Status: UNCONFIRMED

          Severity: major

          Priority: P3

         Component: c++

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: jens.mau...@gmx.net

              Host: x86_64-unknown-linux-gnu

            Target: x86_64-unknown-linux-gnu





The following program compiles successfully and outputs nothing at all.  In

fact, the generated assembly has an empty "main".  This happens even when

compiling with -O0.



#include <iostream>



struct S {

  S() { }

};



int main()

{

  std::cout << new S[0] << " bla" << std::endl;

}



$  g++ new-opt.cc -Wall -Wextra 

$ ./a.out 

(no output)



The issue goes away when removing the default constructor of "S".  It seems gcc

believes array-new with zero size is undefined behavior and thus removes the

rest of the expression.  I can't follow the "undefined behavior" part;

array-new with zero size should yield a non-zero pointer (see 3.7.3.1p2

[basic.stc.dynamic.allocation] and 5.3.4p7 [expr.new]).