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

[Arthur Eubanks via llvm-commits]

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@@ -616,6 +652,23 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
     return Result;
   }
 
+  if (hasAttribute(Attribute::Initialized)) {
+    auto Ranges = getValueAsRanges();
+    if (Ranges.empty())
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aeubanks wrote:

is this allowed? I think we should forbid an empty list

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