ahatanak added inline comments.
================
Comment at: clang/lib/Sema/SemaDeclCXX.cpp:6502
+ // except that it has a non-trivial member *with* the trivial_abi attribute.
+ for (auto Base : D->bases()) {
+ if (auto CxxRecord = Base.getType()->getAsCXXRecordDecl())
----------------
zoecarver wrote:
> ahatanak wrote:
> > It looks like this patch changes the way `D` is passed in the following
> > code:
> >
> > ```
> > struct B {
> > int i[4];
> > B();
> > B(const B &) = default;
> > B(B &&);
> > };
> >
> > struct D : B {
> > D();
> > D(const D &) = default;
> > D(D &&) = delete;
> > };
> >
> > void testB(B a);
> > void testD(D a);
> >
> > void testCallB() {
> > B b;
> > testB(b);
> > }
> >
> > void testCallD() {
> > D d;
> > testD(d);
> > }
> > ```
> >
> > `B` cannot be passed in registers because it has a non-trivial move
> > constructor, whereas `D` can be passed in registers because the move
> > constructor is deleted and the copy constructor is trivial.
> >
> > I'm not sure what the best way to handle this is, but I just wanted to
> > point this out.
> Hmm. Good catch. One way to fix this would be to simply create a
> `HasPassableSubobject` variable and add that to the conditions below (instead
> of returning false here). But, it seems that `D` isn't passed by registers
> (even though, maybe it should be) on ToT: https://godbolt.org/z/4xevW5
>
> Given that, do you think it's OK to return false here, or should I update
> this patch to use the logic I just described (even though that would be a
> nfc)?
The argument is byval, so `D` is passed directly. If you remove `-O3` and add
`-target aarch64`, you'll see that `[2 x i64]` is being passed
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D92361/new/
https://reviews.llvm.org/D92361
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