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

[Arthur Eubanks via llvm-commits]

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@@ -943,11 +947,20 @@ void ModuleBitcodeWriter::writeAttributeGroupTable() {
         Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
         if (Ty)
           Record.push_back(VE.getTypeID(Attr.getValueAsType()));
-      } else {
-        assert(Attr.isConstantRangeAttribute());
+      } else if (Attr.isConstantRangeAttribute()) {
         Record.push_back(7);
         Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
-        emitConstantRange(Record, Attr.getValueAsConstantRange());
+        emitConstantRange(Record, Attr.getValueAsConstantRange(),
+                          /*EmitBitWidth=*/true);
+      } else {
+        assert(Attr.isConstantRangeListAttribute());
+        Record.push_back(8);
+        Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
+        ArrayRef<ConstantRange> Val = Attr.getValueAsConstantRangeList();
+        Record.push_back(Val.size());
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aeubanks wrote:

this needs to emit the bit width once so we don't hardcode 64-bit ranges in ConstantRangeList, then read that back in in the bitcode reader and use that as the ConstantRange/APInt bit width

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