https://bugs.llvm.org/show_bug.cgi?id=48434
Bug ID: 48434
Summary: attribute instantiation for class template
specializations can lead to deserialization cycles
Product: clang
Version: unspecified
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Modules
Assignee: unassignedclangb...@nondot.org
Reporter: richard-l...@metafoo.co.uk
CC: dgre...@apple.com, llvm-bugs@lists.llvm.org,
richard-l...@metafoo.co.uk
Consider:
```
template<typename T> struct A;
using X = A<int>;
template<typename T> struct [[attr(X)]] A {};
X x;
```
Now, deserializing `x` crashes, because it hits a cycle:
* Deserializing `x` reads the TypedefNameDecl `X`
* Deserializing `X` reads its RecordType `A<int>`
* Deserializing `A<int>` reads its attributes
* Deserializing `attr(X)` finds we already have an `X`, so tries to use it
* Using the `X` to form a `TypedefType` crashes, because `X` is not
sufficiently initialized
This is broken because we violated the deserialization invariant by emitting
bitcode for `X` that (indirectly) refers to a lexically-later part of the
program, specifically the attributes for `A<int>`.
To fix this, I think we need to lazily load attributes, at least for template
specializations.
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