[LLVMbugs] [Bug 13883] New: clang doesn't compute "nearly empty" correctly in edge cases

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=13883

             Bug #: 13883
           Summary: clang doesn't compute "nearly empty" correctly in edge
                    cases
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: sharparrow1 at yahoo.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Testcase (from gcc testsuite):
struct E1 {};
struct E2 : public E1 {};
struct E : public E1, public E2 {};
struct N : public E { virtual void f () {} };

struct X : virtual public N {
};

int main () {
  X x;
  /* N should not be the primary base of X; it is not nearly empty.  */
  if ((void*)&x == (void*)(N*)&x)
    return 1;
}

clang's implementation of ItaniumCXXABI::isNearlyEmpty in particular doesn't
check the rule that a nearly empty class "has no proper base class that is
empty, not morally virtual, and at an offset other than zero".

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