[LLVMbugs] [Bug 17768] New: [-cxx-abi microsoft] clang doesn't layout derived class on top of empty virtual base class

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17768

            Bug ID: 17768
           Summary: [-cxx-abi microsoft] clang doesn't layout derived
                    class on top of empty virtual base class
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            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

#include <stddef.h>
#include <stdio.h>
#include <string.h>
char buffer[419430400];
inline void *operator new(size_t, void *pv) { return pv; }
struct TypeName0 {
        TypeName0() {
                printf("TypeName0 (this): %llu\n", (unsigned long
long)((size_t)this - (size_t)buffer));
        }
};
struct TypeName1: public TypeName0 {
        char TypeName1FieldName5;
        TypeName1() {
                printf("TypeName1 (this): %llu\n", (unsigned long
long)((size_t)this - (size_t)buffer));
                printf("TypeName1 (fiel): %llu\n", (unsigned long
long)((size_t)&TypeName1FieldName5 - (size_t)buffer));
        }
};
struct TypeName2: public virtual TypeName0 {
        int TypeName2FieldName0;
        TypeName2() {
                printf("TypeName2 (this): %llu\n", (unsigned long
long)((size_t)this - (size_t)buffer));
        }
};
struct TypeName3: public virtual TypeName1, public virtual TypeName2 {
        int TypeName3FieldName0;
        TypeName3() {
                printf("TypeName3 (this): %llu\n", (unsigned long
long)((size_t)this - (size_t)buffer));
                printf("TypeName3 (fiel): %llu\n", (unsigned long
long)((size_t)&TypeName3FieldName0 - (size_t)buffer));
        }
};
int main() {
        memset(buffer, 0, sizeof(buffer));
        new (buffer) TypeName3;
}

clang:
TypeName0 (this): 8
TypeName1 (this): 8
TypeName1 (fiel): 8
TypeName0 (this): 9
TypeName2 (this): 12
TypeName3 (this): 0
TypeName3 (fiel): 4

vs:
TypeName0 (this): 8
TypeName1 (this): 8
TypeName1 (fiel): 8
TypeName0 (this): 16
TypeName2 (this): 16
TypeName3 (this): 0
TypeName3 (fiel): 4

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