[clang] [llvm] [Clang] Add __builtin_assume_dereferenceable to encode deref assumption. (PR #121789)

[Nikolas Klauser via llvm-commits]

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@@ -839,6 +839,12 @@ def BuiltinAssumeAligned : Builtin {
   let Prototype = "void*(void const*, size_t, ...)";
 }
 
+def BuiltinAssumeDereferenceable : Builtin {
+  let Spellings = ["__builtin_assume_dereferenceable"];
+  let Attributes = [NoThrow, Const, Constexpr];
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philnik777 wrote:

I think it would be really nice to make this `constexpr`, since we'd have to jump through hoops otherwise to use this in e.g. `string` (yes, I already have ideas).

https://github.com/llvm/llvm-project/pull/121789