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

[Jan Voung via llvm-commits]

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@@ -267,6 +281,9 @@ class Attribute {
   /// Returns the value of the range attribute.
   ConstantRange getRange() const;
 
+  /// Returns the value of the initializes attribute.
+  ConstantRangeList getInitializes() const;
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jvoung wrote:

nit: Perhaps return ArrayRef<ConstantRange> to be consistent with getValueAsConstantRangeList(), then the caller can decide to make it a ConstantRangeList or not?

Also ArrayRef allows the caller to avoid a copy if it isn't needed.

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