Implementation of Equivalence Classes

llvm-svn: 6422

include/Support/EquivalenceClasses.h

@@ -0,0 +1,93 @@
+//===-- Support/EquivalenceClasses.h -------------------------*- C++ -*--=//
+// 
+// Generic implementation of equivalence classes and implementation of 
+// union-find algorithms
+// A not-so-fancy implementation: 2 level tree i.e root and one more level
+// Overhead of a union = size of the equivalence class being attached
+// Overhead of a find = 1.
+// 
+//===------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_EQUIVALENCE_CLASSES_H
+#define LLVM_SUPPORT_EQUIVALENCE_CLASSES_H
+
+#include <map>
+#include <set>
+#include <vector>
+using std::map;
+using std::set;
+using std::vector;
+
+template <class ElemTy>
+class EquivalenceClasses {
+  // Maps each element to the element that is the leader of its 
+  // equivalence class.
+  map<ElemTy, ElemTy> Elem2ECLeaderMap;
+  
+  // Make Element2 the leader of the union of classes Element1 and Element2
+  // Element1 and Element2 are presumed to be leaders of their respective
+  // equivalence classes.
+  void attach(ElemTy Element1, ElemTy Element2) {
+    for (typename map<ElemTy, ElemTy>::iterator ElemI = 
+	   Elem2ECLeaderMap.begin(), ElemE = Elem2ECLeaderMap.end(); 
+	 ElemI != ElemE; ++ElemI) {
+      if (ElemI->second == Element1)
+	Elem2ECLeaderMap[ElemI->first] = Element2;
+    }
+  }
+
+public:
+  
+  void addElement (ElemTy NewElement) {
+    if (Elem2ECLeaderMap.find(NewElement) == Elem2ECLeaderMap.end())
+      Elem2ECLeaderMap[NewElement] = NewElement;
+  }
+  
+  ElemTy findClass(ElemTy Element) {
+    if (Elem2ECLeaderMap.find(Element) == Elem2ECLeaderMap.end())
+      return 0;
+    else 
+      return Elem2ECLeaderMap[Element];
+  }
+
+  /// Attach the set with Element1 to the set with Element2 adding Element1 and
+  /// Element2 to the set of equivalence classes if they are not there already.
+  /// Implication: Make Element1 the element in the smaller set.
+  void unionElements(ElemTy Element1, ElemTy Element2) {
+    // If either Element1 or Element2 does not already exist, include it
+    if (Elem2ECLeaderMap.find(Element1) == Elem2ECLeaderMap.end())
+      Elem2ECLeaderMap[Element1] = Element1;
+    if (Elem2ECLeaderMap.find(Element2) == Elem2ECLeaderMap.end())
+      Elem2ECLeaderMap[Element2] = Element2;
+
+    attach(Elem2ECLeaderMap[Element1], Elem2ECLeaderMap[Element2]);
+  }
+  
+  // Returns a vector containing all the elements in the equivalent class
+  // including Element1
+  vector<ElemTy> getEqClass(ElemTy Element1) {
+    vector<ElemTy> EqClass;
+    
+    if (Elem2ECLeaderMap.find(EqClass) == Elem2ECLeaderMap.end())
+      return EqClass;
+    
+    ElemTy classLeader = Elem2ECLeaderMap[Element1];
+
+    for (typename map<ElemTy, ElemTy>::iterator ElemI = 
+	   Elem2ECLeaderMap.begin(), ElemE = Elem2ECLeaderMap.end(); 
+	 ElemI != ElemE; ++ElemI) {
+      if (ElemI->second == classLeader)
+	EqClass.push_back(ElemI->first);
+    }
+    
+    return EqClass;
+    
+  }
+
+  map<ElemTy, ElemTy> getLeaderMap() {
+    return Elem2ECLeaderMap ;
+  }
+  
+};
+
+#endif