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

[Arthur Eubanks via llvm-commits]

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@@ -1993,6 +1993,14 @@ void Verifier::verifyParameterAttrs(AttributeSet Attrs, Type *Ty,
           Attrs.hasAttribute(Attribute::ReadOnly)),
         "Attributes writable and readonly are incompatible!", V);
 
+  Check(!(Attrs.hasAttribute(Attribute::Initialized) &&
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aeubanks wrote:

I don't think this is true. A function that immediately unwinds can be marked as initializing all arguments according to our semantics, but is also readnone

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