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      1 //===-- llvm/ADT/IntEqClasses.h - Equiv. Classes of Integers ----*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // Equivalence classes for small integers. This is a mapping of the integers
     11 // 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
     12 //
     13 // Initially each integer has its own equivalence class. Classes are joined by
     14 // passing a representative member of each class to join().
     15 //
     16 // Once the classes are built, compress() will number them 0 .. M-1 and prevent
     17 // further changes.
     18 //
     19 //===----------------------------------------------------------------------===//
     20 
     21 #ifndef LLVM_ADT_INTEQCLASSES_H
     22 #define LLVM_ADT_INTEQCLASSES_H
     23 
     24 #include "llvm/ADT/SmallVector.h"
     25 
     26 namespace llvm {
     27 
     28 class IntEqClasses {
     29   /// EC - When uncompressed, map each integer to a smaller member of its
     30   /// equivalence class. The class leader is the smallest member and maps to
     31   /// itself.
     32   ///
     33   /// When compressed, EC[i] is the equivalence class of i.
     34   SmallVector<unsigned, 8> EC;
     35 
     36   /// NumClasses - The number of equivalence classes when compressed, or 0 when
     37   /// uncompressed.
     38   unsigned NumClasses;
     39 
     40 public:
     41   /// IntEqClasses - Create an equivalence class mapping for 0 .. N-1.
     42   IntEqClasses(unsigned N = 0) : NumClasses(0) { grow(N); }
     43 
     44   /// grow - Increase capacity to hold 0 .. N-1, putting new integers in unique
     45   /// equivalence classes.
     46   /// This requires an uncompressed map.
     47   void grow(unsigned N);
     48 
     49   /// clear - Clear all classes so that grow() will assign a unique class to
     50   /// every integer.
     51   void clear() {
     52     EC.clear();
     53     NumClasses = 0;
     54   }
     55 
     56   /// join - Join the equivalence classes of a and b. After joining classes,
     57   /// findLeader(a) == findLeader(b).
     58   /// This requires an uncompressed map.
     59   void join(unsigned a, unsigned b);
     60 
     61   /// findLeader - Compute the leader of a's equivalence class. This is the
     62   /// smallest member of the class.
     63   /// This requires an uncompressed map.
     64   unsigned findLeader(unsigned a) const;
     65 
     66   /// compress - Compress equivalence classes by numbering them 0 .. M.
     67   /// This makes the equivalence class map immutable.
     68   void compress();
     69 
     70   /// getNumClasses - Return the number of equivalence classes after compress()
     71   /// was called.
     72   unsigned getNumClasses() const { return NumClasses; }
     73 
     74   /// operator[] - Return a's equivalence class number, 0 .. getNumClasses()-1.
     75   /// This requires a compressed map.
     76   unsigned operator[](unsigned a) const {
     77     assert(NumClasses && "operator[] called before compress()");
     78     return EC[a];
     79   }
     80 
     81   /// uncompress - Change back to the uncompressed representation that allows
     82   /// editing.
     83   void uncompress();
     84 };
     85 
     86 } // End llvm namespace
     87 
     88 #endif
     89