[LLVMbugs] [Bug 18026] New: [-cxx-abi microsoft] clang overaligns packed struct

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18026

            Bug ID: 18026
           Summary: [-cxx-abi microsoft] clang overaligns packed struct
           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; }
#pragma pack(push, 4)
struct ClassName0 {
    int ClassName0FieldName0;
    ClassName0() {
        printf("ClassName0FieldName0 : %llu\n", (unsigned long
long)((size_t)&ClassName0FieldName0 - (size_t)buffer));
    }
};
#pragma pack(pop)
struct ClassName1: public virtual ClassName0 {
    __declspec(align(2)) bool ClassName1FieldName0;
    ClassName1() {
        printf("ClassName1FieldName0 : %llu\n", (unsigned long
long)((size_t)&ClassName1FieldName0 - (size_t)buffer));
    }
};
#pragma pack(push, 1)
struct ClassName2: public virtual ClassName1, public ClassName0 {
    ClassName0 ClassName2FieldName0;
    ClassName2() {
        printf("ClassName2FieldName0 : %llu\n", (unsigned long
long)((size_t)&ClassName2FieldName0 - (size_t)buffer));
    }
};
#pragma pack(pop)
#pragma pack(push, 16)
struct ClassName3: public ClassName2 {
    char ClassName3FieldName0;
    ClassName3() {
        printf("ClassName3FieldName0 : %llu\n", (unsigned long
long)((size_t)&ClassName3FieldName0 - (size_t)buffer));
    }
};
#pragma pack(pop)
int main() {
    memset(buffer, 0, sizeof(buffer));
    new (buffer) ClassName0;
    printf("   sizeof(ClassName0): %Iu\n",    sizeof(ClassName0));
    printf("__alignof(ClassName0): %Iu\n", __alignof(ClassName0));
    memset(buffer, 0, sizeof(buffer));
    new (buffer) ClassName1;
    printf("   sizeof(ClassName1): %Iu\n",    sizeof(ClassName1));
    printf("__alignof(ClassName1): %Iu\n", __alignof(ClassName1));
    memset(buffer, 0, sizeof(buffer));
    new (buffer) ClassName2;
    printf("   sizeof(ClassName2): %Iu\n",    sizeof(ClassName2));
    printf("__alignof(ClassName2): %Iu\n", __alignof(ClassName2));
    memset(buffer, 0, sizeof(buffer));
    new (buffer) ClassName3;
    printf("   sizeof(ClassName3): %Iu\n",    sizeof(ClassName3));
    printf("__alignof(ClassName3): %Iu\n", __alignof(ClassName3));
}

vs:
ClassName0FieldName0 : 0
   sizeof(ClassName0): 4
__alignof(ClassName0): 4
ClassName0FieldName0 : 8
ClassName1FieldName0 : 4
   sizeof(ClassName1): 12
__alignof(ClassName1): 4
ClassName0FieldName0 : 12
ClassName1FieldName0 : 20
ClassName0FieldName0 : 0
ClassName0FieldName0 : 8
ClassName2FieldName0 : 8
   sizeof(ClassName2): 24
__alignof(ClassName2): 2
ClassName0FieldName0 : 16
ClassName1FieldName0 : 24
ClassName0FieldName0 : 0
ClassName0FieldName0 : 8
ClassName2FieldName0 : 8
ClassName3FieldName0 : 12
   sizeof(ClassName3): 28
__alignof(ClassName3): 4

clang:
ClassName0FieldName0 : 0
   sizeof(ClassName0): 4
__alignof(ClassName0): 4
ClassName0FieldName0 : 8
ClassName1FieldName0 : 4
   sizeof(ClassName1): 12
__alignof(ClassName1): 4
ClassName0FieldName0 : 12
ClassName1FieldName0 : 20
ClassName0FieldName0 : 0
ClassName0FieldName0 : 8
ClassName2FieldName0 : 8
   sizeof(ClassName2): 24
__alignof(ClassName2): 4
ClassName0FieldName0 : 16
ClassName1FieldName0 : 24
ClassName0FieldName0 : 0
ClassName0FieldName0 : 8
ClassName2FieldName0 : 8
ClassName3FieldName0 : 12
   sizeof(ClassName3): 28
__alignof(ClassName3): 4

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