[llvm] [IR][Attribute] Add support for intersecting AttributeLists; NFC (PR #109719)

[Nikita Popov via llvm-commits]

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@@ -775,6 +793,12 @@ class AttributeList {
   addAllocSizeParamAttr(LLVMContext &C, unsigned ArgNo, unsigned ElemSizeArg,
                         const std::optional<unsigned> &NumElemsArg);
 
+  /// Try to intersect this AttributeList with Other. Returns std::nullopt if
+  /// the two lists are inherently incompatible (imply different behavior, not
+  /// just analysis).
+  [[nodiscard]] std::optional<AttributeList>
+  intersectAttributes(LLVMContext &C, AttributeList Other) const;
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nikic wrote:

```suggestion
  intersectWith(LLVMContext &C, AttributeList Other) const;
```
For consistency with the AttributeSet method? Or is there a reason they have different names?

https://github.com/llvm/llvm-project/pull/109719