[clang] [clang] Implement a bitwise_copyable builtin type trait. (PR #86512)

[Haojian Wu via cfe-commits]

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@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+
+// Scalar types are bitwise copyable.
+static_assert(__is_bitwise_copyable(int));
+static_assert(__is_bitwise_copyable(int*));
+// array
+static_assert(__is_bitwise_copyable(int[10]));
+
+
+struct Forward; // expected-note 2{{forward declaration of 'Forward'}}
+static_assert(!__is_bitwise_copyable(Forward)); // expected-error {{incomplete type 'Forward' used in type trait expression}}
+
+struct Foo { int a; };
+static_assert(__is_bitwise_copyable(Foo));
+
+struct DynamicClass { virtual int Foo(); };
+static_assert(__is_bitwise_copyable(DynamicClass));
+
+template <typename T>
+void TemplateFunction() {
+  static_assert(__is_bitwise_copyable(T)); // expected-error {{incomplete type 'Forward' used in type trait expression}}
+}
+void CallTemplateFunc() {
+  TemplateFunction<Forward>(); // expected-note {{in instantiation of function template specialization}}
+  TemplateFunction<Foo>();
+}
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hokein wrote:

Added some negative test cases (`int&`). Note that `struct Foo { int &x; };` is considered bitwise cloneable (as it is trivially copyable).

https://github.com/llvm/llvm-project/pull/86512