[LLVMbugs] [Bug 21046] New: MS ABI: Extra vtordisp inserted

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21046

            Bug ID: 21046
           Summary: MS ABI: Extra vtordisp inserted
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: david.majnemer at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

consider:
struct __declspec(dllexport) A {
 virtual void f();
};
struct __declspec(dllexport) B : virtual A {
 virtual void f() = 0;
 B() {}
};
struct __declspec(dllexport) C : virtual B { };

we get the following:
--- different.cpp_clang.obj.dump        2014-09-23 15:09:04.840112200 -0700
+++ different.cpp_vs.obj.dump   2014-09-23 15:09:04.900112200 -0700
@@ -2,9 +2,9 @@
 const B::`vftable'[0]: __purecall
 const C::`vftable'[0]: __purecall
 const B::`vbtable'[0]: 0
-const B::`vbtable'[4]: 8
+const B::`vbtable'[4]: 4
 const C::`vbtable'{for `C'}[0]: 0
-const C::`vbtable'{for `C'}[4]: 8
-const C::`vbtable'{for `C'}[8]: 12
+const C::`vbtable'{for `C'}[4]: 4
+const C::`vbtable'{for `C'}[8]: 8
 const C::`vbtable'{for `B'}[0]: 0
 const C::`vbtable'{for `B'}[4]: -4


It appears that we thinkg B needs a vtordisp even though it overrides a method
in A with a pure virtual function.

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