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diff --git a/include/llvm/TableGen/SetTheory.h b/include/llvm/TableGen/SetTheory.h
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+//===- SetTheory.h - Generate ordered sets from DAG expressions -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the SetTheory class that computes ordered sets of
+// Records from DAG expressions.  Operators for standard set operations are
+// predefined, and it is possible to add special purpose set operators as well.
+//
+// The user may define named sets as Records of predefined classes. Set
+// expanders can be added to a SetTheory instance to teach it how to find the
+// elements of such a named set.
+//
+// These are the predefined operators. The argument lists can be individual
+// elements (defs), other sets (defs of expandable classes), lists, or DAG
+// expressions that are evaluated recursively.
+//
+// - (add S1, S2 ...) Union sets. This is also how sets are created from element
+//   lists.
+//
+// - (sub S1, S2, ...) Set difference. Every element in S1 except for the
+//   elements in S2, ...
+//
+// - (and S1, S2) Set intersection. Every element in S1 that is also in S2.
+//
+// - (shl S, N) Shift left. Remove the first N elements from S.
+//
+// - (trunc S, N) Truncate. The first N elements of S.
+//
+// - (rotl S, N) Rotate left. Same as (add (shl S, N), (trunc S, N)).
+//
+// - (rotr S, N) Rotate right.
+//
+// - (decimate S, N) Decimate S by picking every N'th element, starting with
+//   the first one. For instance, (decimate S, 2) returns the even elements of
+//   S.
+//
+// - (sequence "Format", From, To) Generate a sequence of defs with printf.
+//   For instance, (sequence "R%u", 0, 3) -> [ R0, R1, R2, R3 ]
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SETTHEORY_H
+#define SETTHEORY_H
+
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/Support/SourceMgr.h"
+#include <map>
+#include <vector>
+
+namespace llvm {
+
+class DagInit;
+class Init;
+class Record;
+class RecordKeeper;
+
+class SetTheory {
+public:
+  typedef std::vector<Record*> RecVec;
+  typedef SmallSetVector<Record*, 16> RecSet;
+
+  /// Operator - A callback representing a DAG operator.
+  class Operator {
+    virtual void anchor();
+  public:
+    virtual ~Operator() {}
+
+    /// apply - Apply this operator to Expr's arguments and insert the result
+    /// in Elts.
+    virtual void apply(SetTheory&, DagInit *Expr, RecSet &Elts,
+                       ArrayRef<SMLoc> Loc) =0;
+  };
+
+  /// Expander - A callback function that can transform a Record representing a
+  /// set into a fully expanded list of elements. Expanders provide a way for
+  /// users to define named sets that can be used in DAG expressions.
+  class Expander {
+    virtual void anchor();
+  public:
+    virtual ~Expander() {}
+
+    virtual void expand(SetTheory&, Record*, RecSet &Elts) =0;
+  };
+
+private:
+  // Map set defs to their fully expanded contents. This serves as a memoization
+  // cache and it makes it possible to return const references on queries.
+  typedef std::map<Record*, RecVec> ExpandMap;
+  ExpandMap Expansions;
+
+  // Known DAG operators by name.
+  StringMap<Operator*> Operators;
+
+  // Typed expanders by class name.
+  StringMap<Expander*> Expanders;
+
+public:
+  /// Create a SetTheory instance with only the standard operators.
+  SetTheory();
+
+  /// addExpander - Add an expander for Records with the named super class.
+  void addExpander(StringRef ClassName, Expander*);
+
+  /// addFieldExpander - Add an expander for ClassName that simply evaluates
+  /// FieldName in the Record to get the set elements.  That is all that is
+  /// needed for a class like:
+  ///
+  ///   class Set<dag d> {
+  ///     dag Elts = d;
+  ///   }
+  ///
+  void addFieldExpander(StringRef ClassName, StringRef FieldName);
+
+  /// addOperator - Add a DAG operator.
+  void addOperator(StringRef Name, Operator*);
+
+  /// evaluate - Evaluate Expr and append the resulting set to Elts.
+  void evaluate(Init *Expr, RecSet &Elts, ArrayRef<SMLoc> Loc);
+
+  /// evaluate - Evaluate a sequence of Inits and append to Elts.
+  template<typename Iter>
+  void evaluate(Iter begin, Iter end, RecSet &Elts, ArrayRef<SMLoc> Loc) {
+    while (begin != end)
+      evaluate(*begin++, Elts, Loc);
+  }
+
+  /// expand - Expand a record into a set of elements if possible.  Return a
+  /// pointer to the expanded elements, or NULL if Set cannot be expanded
+  /// further.
+  const RecVec *expand(Record *Set);
+};
+
+} // end namespace llvm
+
+#endif
+