Add ADT/IntEqClasses.h as a light-weight implementation of EquivalenceClasses.h.

This implementation already exists as ConnectedVNInfoEqClasses in
LiveInterval.cpp, and it seems to be generally useful to have a light-weight way
of forming equivalence classes of small integers.

IntEqClasses doesn't allow enumeration of the elements in a class.

llvm-svn: 122293

llvm/include/llvm/ADT/IntEqClasses.h

@@ -0,0 +1,81 @@
+//===-- llvm/ADT/IntEqClasses.h - Equiv. Classes of Integers ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Equivalence classes for small integers. This is a mapping of the integers
+// 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
+//
+// Initially each integer has its own equivalence class. Classes are joined by
+// passing a representative member of each class to join().
+//
+// Once the classes are built, compress() will number them 0 .. M-1 and prevent
+// further changes.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_INTEQCLASSES_H
+#define LLVM_ADT_INTEQCLASSES_H
+
+#include "llvm/ADT/SmallVector.h"
+
+namespace llvm {
+
+class IntEqClasses {
+  /// EC - When uncompressed, map each integer to a smaller member of its
+  /// equivalence class. The class leader is the smallest member and maps to
+  /// itself.
+  ///
+  /// When compressed, EC[i] is the equivalence class of i.
+  SmallVector<unsigned, 8> EC;
+
+  /// NumClasses - The number of equivalence classes when compressed, or 0 when
+  /// uncompressed.
+  unsigned NumClasses;
+
+public:
+  /// IntEqClasses - Create an equivalence class mapping for 0 .. N-1.
+  IntEqClasses(unsigned N) : NumClasses(0) { grow(N); }
+
+  /// grow - Increase capacity to hold 0 .. N-1, putting new integers in unique
+  /// equivalence classes.
+  /// This requires an uncompressed map.
+  void grow(unsigned N);
+
+  /// join - Join the equivalence classes of a and b. After joining classes,
+  /// findLeader(a) == findLeader(b).
+  /// This requires an uncompressed map.
+  void join(unsigned a, unsigned b);
+
+  /// findLeader - Compute the leader of a's equivalence class. This is the
+  /// smallest member of the class.
+  /// This requires an uncompressed map.
+  unsigned findLeader(unsigned a) const;
+
+  /// compress - Compress equivalence classes by numbering them 0 .. M.
+  /// This makes the equivalence class map immutable.
+  void compress();
+
+  /// getNumClasses - Return the number of equivalence classes after compress()
+  /// was called.
+  unsigned getNumClasses() const { return NumClasses; }
+
+  /// operator[] - Return a's equivalence class number, 0 .. getNumClasses()-1.
+  /// This requires a compressed map.
+  unsigned operator[](unsigned a) const {
+    assert(NumClasses && "operator[] called before compress()");
+    return EC[a];
+  }
+
+  /// uncompress - Change back to the uncompressed representation that allows
+  /// editing.
+  void uncompress();
+};
+
+} // End llvm namespace
+
+#endif

llvm/lib/Support/CMakeLists.txt

@@ -22,6 +22,7 @@ add_llvm_library(LLVMSupport
   FoldingSet.cpp
   FormattedStream.cpp
   GraphWriter.cpp
+  IntEqClasses.cpp
   IntervalMap.cpp
   IsInf.cpp
   IsNAN.cpp

llvm/lib/Support/IntEqClasses.cpp

@@ -0,0 +1,69 @@
+//===-- llvm/ADT/IntEqClasses.cpp - Equivalence Classes of Integers -------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Equivalence classes for small integers. This is a mapping of the integers
+// 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
+//
+// Initially each integer has its own equivalence class. Classes are joined by
+// passing a representative member of each class to join().
+//
+// Once the classes are built, compress() will number them 0 .. M-1 and prevent
+// further changes.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/IntEqClasses.h"
+
+using namespace llvm;
+
+void IntEqClasses::grow(unsigned N) {
+  assert(NumClasses == 0 && "grow() called after compress().");
+  while (EC.size() < N)
+    EC.push_back(EC.size());
+}
+
+void IntEqClasses::join(unsigned a, unsigned b) {
+  assert(NumClasses == 0 && "join() called after compress().");
+  unsigned eca = EC[a];
+  unsigned ecb = EC[b];
+  // Update pointers while searching for the leaders, compressing the paths
+  // incrementally. The larger leader will eventually be updated, joining the
+  // classes.
+  while (eca != ecb)
+    if (eca < ecb)
+      EC[b] = eca, b = ecb, ecb = EC[b];
+    else
+      EC[a] = ecb, a = eca, eca = EC[a];
+}
+
+unsigned IntEqClasses::findLeader(unsigned a) const {
+  assert(NumClasses == 0 && "findLeader() called after compress().");
+  while (a != EC[a])
+    a = EC[a];
+  return a;
+}
+
+void IntEqClasses::compress() {
+  if (NumClasses)
+    return;
+  for (unsigned i = 0, e = EC.size(); i != e; ++i)
+    EC[i] = (EC[i] == i) ? NumClasses++ : EC[EC[i]];
+}
+
+void IntEqClasses::uncompress() {
+  if (!NumClasses)
+    return;
+  SmallVector<unsigned, 8> Leader;
+  for (unsigned i = 0, e = EC.size(); i != e; ++i)
+    if (EC[i] < Leader.size())
+      EC[i] = Leader[EC[i]];
+    else
+      Leader.push_back(EC[i] = i);
+  NumClasses = 0;
+}

llvm/unittests/ADT/IntEqClassesTest.cpp

@@ -0,0 +1,107 @@
+//===---- ADT/IntEqClassesTest.cpp - IntEqClasses unit tests ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/IntEqClasses.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(IntEqClasses, Simple) {
+  IntEqClasses ec(10);
+
+  ec.join(0, 1);
+  ec.join(3, 2);
+  ec.join(4, 5);
+  ec.join(7, 6);
+
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(2u, ec.findLeader(2));
+  EXPECT_EQ(2u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(8u, ec.findLeader(8));
+  EXPECT_EQ(9u, ec.findLeader(9));
+
+  // join two non-leaders.
+  ec.join(1, 3);
+
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(0u, ec.findLeader(2));
+  EXPECT_EQ(0u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(8u, ec.findLeader(8));
+  EXPECT_EQ(9u, ec.findLeader(9));
+
+  // join two leaders.
+  ec.join(4, 8);
+
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(0u, ec.findLeader(2));
+  EXPECT_EQ(0u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(4u, ec.findLeader(8));
+  EXPECT_EQ(9u, ec.findLeader(9));
+
+  // join mixed.
+  ec.join(9, 1);
+
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(0u, ec.findLeader(2));
+  EXPECT_EQ(0u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(4u, ec.findLeader(8));
+  EXPECT_EQ(0u, ec.findLeader(9));
+
+  // compressed map.
+  ec.compress();
+  EXPECT_EQ(3u, ec.getNumClasses());
+
+  EXPECT_EQ(0u, ec[0]);
+  EXPECT_EQ(0u, ec[1]);
+  EXPECT_EQ(0u, ec[2]);
+  EXPECT_EQ(0u, ec[3]);
+  EXPECT_EQ(1u, ec[4]);
+  EXPECT_EQ(1u, ec[5]);
+  EXPECT_EQ(2u, ec[6]);
+  EXPECT_EQ(2u, ec[7]);
+  EXPECT_EQ(1u, ec[8]);
+  EXPECT_EQ(0u, ec[9]);
+
+  // uncompressed map.
+  ec.uncompress();
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(0u, ec.findLeader(2));
+  EXPECT_EQ(0u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(4u, ec.findLeader(8));
+  EXPECT_EQ(0u, ec.findLeader(9));
+}
+
+} // end anonymous namespace

llvm/unittests/CMakeLists.txt

@@ -54,6 +54,7 @@ add_llvm_unittest(ADT
   ADT/FoldingSet.cpp
   ADT/ilistTest.cpp
   ADT/ImmutableSetTest.cpp
+  ADT/IntEqClassesTest.cpp
   ADT/IntervalMapTest.cpp
   ADT/SmallBitVectorTest.cpp
   ADT/SmallStringTest.cpp