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

[Nikita Popov via llvm-commits]

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@@ -22,6 +22,37 @@ def ParamAttr : AttrProperty;
 /// Can be used as return attribute.
 def RetAttr : AttrProperty;
 
+
+
+/// Intersection rules. Used for example in sinking/hoisting two
+/// callbases to find a set of attributes that apply to both.
+/// If no rule is specified, the assumed rule is that the attrs
+/// must be equal, otherwise the intersection will fail. Having
+/// any rule implies that it is legal to drop the attribute.
+/// Note, there are some attributes we can (probably) legally drop
+/// but are intentionally excluded as of now. Those include:
+///     - initializes
+///     - allockind
+///     - allocsize
+///     - minsize
+///     - optsize
+///     - optnone
+///     - optdebug
+///     - optforfuzzing    
+///
+/// When intersecting take the AND of the two attrs.
+/// Invalid for Int/ConstantRange/ConstantRangeList attrs.
+def IntersectAnd : AttrProperty;
+
+/// When intersecting take the min value of the two attrs.
+/// Only valid for Int attrs.
+def IntersectMin : AttrProperty;
+
+/// When intersecting rely on some user defined code.
+def IntersectCustom : AttrProperty;
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nikic wrote:

Yes, exactly.

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