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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - attribute instantiation for class template specializations can lead to deserialization cycles"
href="https://bugs.llvm.org/show_bug.cgi?id=48434">48434</a>
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<th>Summary</th>
<td>attribute instantiation for class template specializations can lead to deserialization cycles
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Modules
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>richard-llvm@metafoo.co.uk
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<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<p>
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<pre>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.</pre>
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