Comment 2 for bug 1473674

I looked into this and the issue is the following:

There is a Cdrom wrapper:
"""
class Cdrom : public pkgCdrom {
   public:
      bool FindPackages(std::string const &CD,
     std::vector<std::string> &List,
     std::vector<std::string> &SList,
     std::vector<std::string> &SigList,
     std::vector<std::string> &TransList,
     std::string &InfoDir) {
  std::string const startdir = SafeGetCWD();
  EXPECT_FALSE(startdir.empty());
  bool const result = pkgCdrom::FindPackages(CD, List, SList, SigList, TransList, InfoDir, NULL, 0);
...
}
"""

and a unittest that calls it:
"""
TEST(CDROMTest,FindPackages)
{
   Cdrom cd;
  std::string InfoDir;
  EXPECT_TRUE(cd.FindPackages(path, Packages, Sources, Signatur, Translation, InfoDir));
...
  EXPECT_EQ(path + "/.disk/", InfoDir);
}
"""

The actual code for this is apt-pkg/cdrom.cc:
"""
bool pkgCdrom::FindPackages(string CD,
       vector<string> &List,
       vector<string> &SList,
       vector<string> &SigList,
       vector<string> &TransList,
       string &InfoDir, pkgCdromStatus *log,
       unsigned int Depth)
{
...
   if (DirectoryExists(".disk") == true)
   {
      if (InfoDir.empty() == true)
  InfoDir = CD + ".disk/";
   }
...
"""

So I suspect that the optimizer gets confused that InfoDir is a reference or it gets confused because InfoDir is not used in FindPackages anymore and it assumes its dead code.

I tried to create a simplified testcase but failed so far. Whats interessting is that if I add a std::cerr << "debug" line into cdrom.cc lines (or even a "CD = CD"):
"""
   if (DirectoryExists(".disk") == true)
   {
      if (InfoDir.empty() == true) {
std::cerr << "debug" << std::endl;
  InfoDir = CD + ".disk/";
}
   }
"""
it works (which indicates dead-code elimination to me).