[PATCH] D125802: Fix std::has_unique_object_representations for _BitInt types with padding bits

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a comment.

In D125802#3552047 <https://reviews.llvm.org/D125802#3552047>, @browneee wrote:

> It looks like the leak is rooted at the allocation here:
> https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp#L3857
>
> The VarTemplateSpecializationDecl is allocated using placement new which uses the AST structure for ownership: https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/lib/AST/DeclBase.cpp#L99
>
> The problem is the TemplateArgumentListInfo inside https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/include/clang/AST/DeclTemplate.h#L2721
> This object contains a vector which does not use placement new: https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/include/clang/AST/TemplateBase.h#L564
>
> Apparently ASTTemplateArgumentListInfo <https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/include/clang/AST/TemplateBase.h#L612> should be used instead https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/include/clang/AST/TemplateBase.h#L575

Wow, thank you for the fantastic sleuthing! It seems that declaration is nine years old, so I'm surprised the leak is only being discovered now and as part of this particular test case.

I don't have a particularly easy way to test this locally at the moment -- do you know if switching `VarTemplateSpecializationDecl::TemplateArgsInfo` to be a `ASTTemplateArgumentListInfo` solves the issue for you?


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https://reviews.llvm.org/D125802