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

[Nikita Popov via llvm-commits]

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@@ -2332,6 +2335,23 @@ Error BitcodeReader::parseAttributeGroupBlock() {
           i--;
 
           B.addConstantRangeAttr(Kind, MaybeCR.get());
+        } else if (Record[i] == 8) {
+          Attribute::AttrKind Kind;
+          if (Error Err = parseAttrKind(Record[++i], &Kind))
+            return Err;
+          if (!Attribute::isConstantRangeListAttrKind(Kind))
+            return error("Not a constant range list attribute");
+
+          SmallVector<ConstantRange, 2> Val;
+          int RangeSize = Record[++i];
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nikic wrote:

```suggestion
          unsigned RangeSize = Record[++i];
```

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