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

[Haojian Wu via cfe-commits]

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@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
+
+// Scalar types are bitwise clonable.
+static_assert(__is_bitwise_cloneable(int));
+static_assert(__is_bitwise_cloneable(int*));
+// array
+static_assert(__is_bitwise_cloneable(int[10]));
+
+// non-scalar types.
+static_assert(!__is_bitwise_cloneable(int&));
+
+
+struct Forward; // expected-note 2{{forward declaration of 'Forward'}}
+static_assert(!__is_bitwise_cloneable(Forward)); // expected-error {{incomplete type 'Forward' used in type trait expression}}
+
+struct Foo { int a; };
+static_assert(__is_bitwise_cloneable(Foo));
+
+struct DynamicClass { virtual int Foo(); };
+static_assert(__is_bitwise_cloneable(DynamicClass));
+
+struct Bar { int& b; }; // trivially copyable
+static_assert(__is_trivially_copyable(Bar));
+static_assert(__is_bitwise_cloneable(Bar));
----------------
hokein wrote:

This is a tricky bit.

The question arises: should we consider all trivially copyable types to be bitwise cloneable? My inclination is to say yes. Since memcpy is `safe` on all trivially copyable types, it's probably a good idea to ensure that bitwise_clonable covers as many types as possible.

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