[llvm] [ADT] Add `[[clang::lifetimebound]]` annotations to Twine.h (PR #210474)

[Balázs Benics via llvm-commits]

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@@ -470,8 +479,8 @@ class Twine {
   /// given SmallVector and a StringRef to the SmallVector's data is returned.
   ///
   /// The returned StringRef's size does not include the null terminator.
-  LLVM_ABI StringRef
-  toNullTerminatedStringRef(SmallVectorImpl<char> &Out) const;
+  LLVM_ABI StringRef toNullTerminatedStringRef(
+      SmallVectorImpl<char> &Out LLVM_LIFETIME_BOUND) const;
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steakhal wrote:

Thinking about this a bit, I think `this` should be annotated for `toNullTerminatedStringRef` , right? That's the whole point of this function that if it's a stringref, it just returns that instead.

https://github.com/llvm/llvm-project/pull/210474