lib/Support/IntEqClasses.cpp

   1 //===-- llvm/ADT/IntEqClasses.cpp - Equivalence Classes of Integers -------===//
   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 #include "llvm/ADT/IntEqClasses.h"
  22
  23 using namespace llvm;
  24
  25 void IntEqClasses::grow(unsigned N) {
  26   assert(NumClasses == 0 && "grow() called after compress().");
  27   EC.reserve(N);
  28   while (EC.size() < N)
  29     EC.push_back(EC.size());
  30 }
  31
  32 void IntEqClasses::join(unsigned a, unsigned b) {
  33   assert(NumClasses == 0 && "join() called after compress().");
  34   unsigned eca = EC[a];
  35   unsigned ecb = EC[b];
  36   // Update pointers while searching for the leaders, compressing the paths
  37   // incrementally. The larger leader will eventually be updated, joining the
  38   // classes.
  39   while (eca != ecb)
  40     if (eca < ecb)
  41       EC[b] = eca, b = ecb, ecb = EC[b];
  42     else
  43       EC[a] = ecb, a = eca, eca = EC[a];
  44 }
  45
  46 unsigned IntEqClasses::findLeader(unsigned a) const {
  47   assert(NumClasses == 0 && "findLeader() called after compress().");
  48   while (a != EC[a])
  49     a = EC[a];
  50   return a;
  51 }
  52
  53 void IntEqClasses::compress() {
  54   if (NumClasses)
  55     return;
  56   for (unsigned i = 0, e = EC.size(); i != e; ++i)
  57     EC[i] = (EC[i] == i) ? NumClasses++ : EC[EC[i]];
  58 }
  59
  60 void IntEqClasses::uncompress() {
  61   if (!NumClasses)
  62     return;
  63   SmallVector<unsigned, 8> Leader;
  64   for (unsigned i = 0, e = EC.size(); i != e; ++i)
  65     if (EC[i] < Leader.size())
  66       EC[i] = Leader[EC[i]];
  67     else
  68       Leader.push_back(EC[i] = i);
  69   NumClasses = 0;
  70 }