[llvm] Add the 'initialized' attribute langref and support (PR #84803)

[Jan Voung via llvm-commits]

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@@ -318,6 +321,9 @@ def Writable : EnumAttr<"writable", [ParamAttr]>;
 /// Function only writes to memory.
 def WriteOnly : EnumAttr<"writeonly", [ParamAttr]>;
 
+/// Pointer argument memory [%p+LoN, %p+HiN) is initialized.
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jvoung wrote:

The list looks almost sorted, so may be better to put it near InAlloca or ?

https://github.com/llvm/llvm-project/pull/84803