hazohelet added a comment.
@aaron.ballman
Thanks for the review! I'll add a release note.
================
Comment at: clang/lib/AST/ExprConstant.cpp:2357-2361
+ if (SubobjectDecl) {
+ Info.FFDiag(DiagLoc, diag::note_constexpr_uninitialized) <<
SubobjectDecl;
+ Info.Note(SubobjectDecl->getLocation(),
+ diag::note_constexpr_subobject_declared_here);
+ }
----------------
aaron.ballman wrote:
> Hmm, this breaks one of the contracts of our constexpr evaluation engine,
> doesn't it? My understanding is that if constexpr evaluation fails, we will
> have emitted a note diagnostic for why it failed. But if the caller doesn't
> pass a nonnull `SubobjectDecl`, we'll return `false` but we won't issue a
> diagnostic.
>
> I'm surprised no tests lost notes as a result of this change, that suggests
> we're missing test coverage for the cases where nullptr is passed in
> explicitly to this function.
Yeah, I was looking into when `SubobjectDecl` can be null here. I `assert`ed
the non-nullness of `SubobjectDecl` before and found that there exists two
lines of code
(https://github.com/llvm/llvm-project/blob/22a3f974d35da89247c0396594f2e4cd592742eb/clang/test/SemaCXX/attr-weak.cpp#L49
and
https://github.com/llvm/llvm-project/blob/abf4a8cb15d4faf04ee0da14e37d7349d3bde9a1/clang/test/CodeGenCXX/weak-external.cpp#L97)
in the test codes that nulls here.
It seems they are doing the same thing, doing comparison against a pointer to a
`[[gnu::weak]]` member. A simple reproducing code is here:
https://godbolt.org/z/qn997n85n
As you can see from the compiler explorer, there's no note emitted here before
the patch.
I inserted some `printf` into the code before this patch and confirmed
`Info.FFDiag(DiagLoc, diag::note_constexpr_uninitialized) << true << Type` was
actually called when compiling the reproducing code and that somehow it is
ignored. FWIW, `SubobjectLoc.isValid()` was `false` here.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D146358/new/
https://reviews.llvm.org/D146358
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