[llvm] Add clang::lifetimebound annotation to ArrayRef constructors. (PR #113547)

[Haojian Wu via llvm-commits]

https://github.com/hokein created https://github.com/llvm/llvm-project/pull/113547

This enables clang to detect more dangling issues.

```
ArrayRef<int> func() {
   constexpr int array[] = {...}; // oops, missing the static
   return array; // return a dangling reference, bomb.
}
```

See #113533.

>From 57ed7711c3c09e8c99b37d88e4002a696cba1338 Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Thu, 24 Oct 2024 12:12:37 +0200
Subject: [PATCH] Add clang::lifetimebound annotation to ArrayRef constructors.

---
 llvm/include/llvm/ADT/ArrayRef.h     | 5 +++--
 llvm/include/llvm/Support/Compiler.h | 6 ++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/llvm/include/llvm/ADT/ArrayRef.h b/llvm/include/llvm/ADT/ArrayRef.h
index d9897320ce091a..1a2a8a307a2995 100644
--- a/llvm/include/llvm/ADT/ArrayRef.h
+++ b/llvm/include/llvm/ADT/ArrayRef.h
@@ -70,7 +70,7 @@ namespace llvm {
     /*implicit*/ ArrayRef(std::nullopt_t) {}
 
     /// Construct an ArrayRef from a single element.
-    /*implicit*/ ArrayRef(const T &OneElt)
+    /*implicit*/ ArrayRef(const T &OneElt LLVM_LIFETIME_BOUND)
       : Data(&OneElt), Length(1) {}
 
     /// Construct an ArrayRef from a pointer and length.
@@ -103,7 +103,8 @@ namespace llvm {
 
     /// Construct an ArrayRef from a C array.
     template <size_t N>
-    /*implicit*/ constexpr ArrayRef(const T (&Arr)[N]) : Data(Arr), Length(N) {}
+    /*implicit*/ constexpr ArrayRef(const T (&Arr LLVM_LIFETIME_BOUND)[N])
+        : Data(Arr), Length(N) {}
 
     /// Construct an ArrayRef from a std::initializer_list.
 #if LLVM_GNUC_PREREQ(9, 0, 0)
diff --git a/llvm/include/llvm/Support/Compiler.h b/llvm/include/llvm/Support/Compiler.h
index 591e7647795bb2..3b03c2851a4214 100644
--- a/llvm/include/llvm/Support/Compiler.h
+++ b/llvm/include/llvm/Support/Compiler.h
@@ -413,6 +413,12 @@
 #define LLVM_GSL_POINTER
 #endif
 
+#if LLVM_HAS_CPP_ATTRIBUTE(clang::lifetimebound)
+#define LLVM_LIFETIME_BOUND [[clang::lifetimebound]]
+#else
+#define LLVM_LLVM_LIFETIME_BOUND
+#endif
+
 #if LLVM_HAS_CPP_ATTRIBUTE(nodiscard) >= 201907L
 #define LLVM_CTOR_NODISCARD [[nodiscard]]
 #else