[PATCH] D89649: Fix __has_unique_object_representations with no_unique_address

[Gabor Bencze via Phabricator via cfe-commits]

gbencze added inline comments.


================
Comment at: clang/lib/AST/ASTContext.cpp:2580-2581
       if (!isStructEmpty(Base.getType())) {
         llvm::Optional<int64_t> Size = structHasUniqueObjectRepresentations(
             Context, Base.getType()->castAs<RecordType>()->getDecl());
         if (!Size)
----------------
rsmith wrote:
> We need to do this for non-empty `[[no_unique_address]]` members of class type too, to handle tail padding reuse in cases such as:
> 
> ```
> struct A {
>     ~A();
>     int a;
>     char b;
> };
> struct B {
>     [[no_unique_address]] A a;
>     char c[3];
> };
> static_assert(sizeof(B) == 8, "");
> static_assert(__has_unique_object_representations(B), "");
> ```
You're right, I missed the case of reusing tail padding. I'll try to update this review to include this soon. 

But I don't think that this exact example is incorrect now as `A` is not trivially copyable due to the user defined destructor. 
It should return true when the class type member is trivially copyable but non-standard-layout though: 

```
struct A {
private:
    int a;
public:
    char b;
};
struct B {
    [[no_unique_address]] A a;
    char c[3];
};
static_assert(sizeof(B) == 8, "");
static_assert(__has_unique_object_representations(B), "");
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D89649/new/

https://reviews.llvm.org/D89649