[clang] [clang][Sema] Move the initializer lifetime checking code from SemaInit.cpp to a new place, NFC (PR #96758)

[Ilya Biryukov via cfe-commits]

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@@ -0,0 +1,1258 @@
+//===--- CheckExprLifetime.cpp --------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "CheckExprLifetime.h"
+#include "clang/AST/Expr.h"
+#include "clang/Sema/Sema.h"
+#include "llvm/ADT/PointerIntPair.h"
+
+namespace clang::sema {
+namespace {
+enum LifetimeKind {
+  /// The lifetime of a temporary bound to this entity ends at the end of the
+  /// full-expression, and that's (probably) fine.
+  LK_FullExpression,
+
+  /// The lifetime of a temporary bound to this entity is extended to the
+  /// lifeitme of the entity itself.
+  LK_Extended,
+
+  /// The lifetime of a temporary bound to this entity probably ends too soon,
+  /// because the entity is allocated in a new-expression.
+  LK_New,
+
+  /// The lifetime of a temporary bound to this entity ends too soon, because
+  /// the entity is a return object.
+  LK_Return,
+
+  /// The lifetime of a temporary bound to this entity ends too soon, because
+  /// the entity is the result of a statement expression.
+  LK_StmtExprResult,
+
+  /// This is a mem-initializer: if it would extend a temporary (other than via
+  /// a default member initializer), the program is ill-formed.
+  LK_MemInitializer,
+};
+using LifetimeResult =
+    llvm::PointerIntPair<const InitializedEntity *, 3, LifetimeKind>;
+}
----------------
ilya-biryukov wrote:

LLVM Style Guide actually has a position on this that encourages to use `static` and have small anonymous namespace, see https://llvm.org/docs/CodingStandards.html#anonymous-namespaces

> we have a simple guideline: make anonymous namespaces as small as possible, and only use them for class declarations.

The rationale is to make it easier to find which functions are local to the file when reading the code. If you have `static`, it's local information, with anonymous namespace you need to know in which namespace the function's in.

https://github.com/llvm/llvm-project/pull/96758