[clang] [OpenACC] Improve C++20 compatibility of private/firstprivate test (PR #152233)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Douglas (dgg5503)

<details>
<summary>Changes</summary>

Under C++17, `DeletedCopy` and `DefaultedCopy` in the test `clang/test/SemaOpenACC/private_firstprivate_reduction_required_ops.cpp` are eligible for aggregate initialization. Under C++20 and up, that is no longer the case. Therefore, an explicit constructor must be declared to avoid additional diagnostics which the test does not expect.

This test was failing in our downstream testing where our toolchain uses C++20 as the default dialect.

See this reduced example for more details: https://godbolt.org/z/46oErYT43

---
Full diff: https://github.com/llvm/llvm-project/pull/152233.diff


1 Files Affected:

- (modified) clang/test/SemaOpenACC/private_firstprivate_reduction_required_ops.cpp (+16) 


``````````diff
diff --git a/clang/test/SemaOpenACC/private_firstprivate_reduction_required_ops.cpp b/clang/test/SemaOpenACC/private_firstprivate_reduction_required_ops.cpp
index 4644bdeeacc0e..ae7ac33fb391f 100644
--- a/clang/test/SemaOpenACC/private_firstprivate_reduction_required_ops.cpp
+++ b/clang/test/SemaOpenACC/private_firstprivate_reduction_required_ops.cpp
@@ -37,10 +37,26 @@ struct ImplicitDelDtor {
 };
 
 struct DeletedCopy {
+#if __cplusplus >= 202002L
+  // C++20 performs value-initialization while previous language versions
+  // performed aggregate-initialization. This class is also not eligible for
+  // an implicit default constructor. Therefore, the constructor must be
+  // explicitly declared for value-initialization to avoid additional
+  // diagnostics.
+  DeletedCopy();
+#endif
   DeletedCopy(const DeletedCopy&) = delete;
 };
 
 struct DefaultedCopy {
+#if __cplusplus >= 202002L
+  // C++20 performs value-initialization while previous language versions
+  // performed aggregate-initialization. This class is also not eligible for
+  // an implicit default constructor. Therefore, the constructor must be
+  // explicitly declared for value-initialization to avoid additional
+  // diagnostics.
+  DefaultedCopy();
+#endif
   DefaultedCopy(const DefaultedCopy&) = default;
 };
 struct UserCopy {

``````````

</details>


https://github.com/llvm/llvm-project/pull/152233