ENH: Improve link line generation for static library cycles.

  - Move Tarjan algorithm from cmComputeTargetDepends
    into its own class cmComputeComponentGraph
  - Use cmComputeComponentGraph to identify the component DAG
    of link dependencies in cmComputeLinkDepends
  - Emit non-trivial component members more than once but always
    in a contiguous group on the link line

8 files changed, 512 insertions, 255 deletions

diff --git a/Source/CMakeLists.txt b/Source/CMakeLists.txt
index 55dc3a1..bef596e 100644
--- a/Source/CMakeLists.txt
+++ b/Source/CMakeLists.txt
@@ -87,6 +87,8 @@ SET(SRCS
   cmCommandArgumentLexer.cxx
   cmCommandArgumentParser.cxx
   cmCommandArgumentParserHelper.cxx
+  cmComputeComponentGraph.cxx
+  cmComputeComponentGraph.h
   cmComputeLinkDepends.cxx
   cmComputeLinkDepends.h
   cmComputeLinkInformation.cxx
@@ -138,6 +140,7 @@ SET(SRCS
   cmGlobalGenerator.h
   cmGlobalUnixMakefileGenerator3.cxx
   cmGlobalUnixMakefileGenerator3.h
+  cmGraphAdjacencyList.h
   cmInstallGenerator.h
   cmInstallGenerator.cxx
   cmInstallExportGenerator.cxx
diff --git a/Source/cmComputeComponentGraph.cxx b/Source/cmComputeComponentGraph.cxx
new file mode 100644
index 0000000..b76635f
--- /dev/null
+++ b/Source/cmComputeComponentGraph.cxx
@@ -0,0 +1,161 @@
+/*=========================================================================
+
+  Program:   CMake - Cross-Platform Makefile Generator
+  Module:    $RCSfile$
+  Language:  C++
+  Date:      $Date$
+  Version:   $Revision$
+
+  Copyright (c) 2002 Kitware, Inc., Insight Consortium.  All rights reserved.
+  See Copyright.txt or http://www.cmake.org/HTML/Copyright.html for details.
+
+     This software is distributed WITHOUT ANY WARRANTY; without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+     PURPOSE.  See the above copyright notices for more information.
+
+=========================================================================*/
+#include "cmComputeComponentGraph.h"
+
+#include <algorithm>
+
+#include <assert.h>
+
+//----------------------------------------------------------------------------
+cmComputeComponentGraph::cmComputeComponentGraph(Graph const& input):
+  InputGraph(input)
+{
+  // Identify components.
+  this->Tarjan();
+
+  // Compute the component graph.
+  this->ComponentGraph.resize(0);
+  this->ComponentGraph.resize(this->Components.size());
+  this->TransferEdges();
+}
+
+//----------------------------------------------------------------------------
+cmComputeComponentGraph::~cmComputeComponentGraph()
+{
+}
+
+//----------------------------------------------------------------------------
+void cmComputeComponentGraph::Tarjan()
+{
+  int n = static_cast<int>(this->InputGraph.size());
+  TarjanEntry entry = {0,0};
+  this->TarjanEntries.resize(0);
+  this->TarjanEntries.resize(n, entry);
+  this->TarjanComponents.resize(0);
+  this->TarjanComponents.resize(n, -1);
+  this->TarjanWalkId = 0;
+  this->TarjanVisited.resize(0);
+  this->TarjanVisited.resize(n, 0);
+  for(int i = 0; i < n; ++i)
+    {
+    // Start a new DFS from this node if it has never been visited.
+    if(!this->TarjanVisited[i])
+      {
+      assert(this->TarjanStack.empty());
+      ++this->TarjanWalkId;
+      this->TarjanIndex = 0;
+      this->TarjanVisit(i);
+      }
+    }
+}
+
+//----------------------------------------------------------------------------
+void cmComputeComponentGraph::TarjanVisit(int i)
+{
+  // We are now visiting this node.
+  this->TarjanVisited[i] = this->TarjanWalkId;
+
+  // Initialize the entry.
+  this->TarjanEntries[i].Root = i;
+  this->TarjanComponents[i] = -1;
+  this->TarjanEntries[i].VisitIndex = ++this->TarjanIndex;
+  this->TarjanStack.push(i);
+
+  // Follow outgoing edges.
+  NodeList const& nl = this->InputGraph[i];
+  for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
+    {
+    int j = *ni;
+
+    // Ignore edges to nodes that have been reached by a previous DFS
+    // walk.  Since we did not reach the current node from that walk
+    // it must not belong to the same component and it has already
+    // been assigned to a component.
+    if(this->TarjanVisited[j] > 0 &&
+       this->TarjanVisited[j] < this->TarjanWalkId)
+      {
+      continue;
+      }
+
+    // Visit the destination if it has not yet been visited.
+    if(!this->TarjanVisited[j])
+      {
+      this->TarjanVisit(j);
+      }
+
+    // If the destination has not yet been assigned to a component,
+    // check if it has a better root for the current object.
+    if(this->TarjanComponents[j] < 0)
+      {
+      if(this->TarjanEntries[this->TarjanEntries[j].Root].VisitIndex <
+         this->TarjanEntries[this->TarjanEntries[i].Root].VisitIndex)
+        {
+        this->TarjanEntries[i].Root = this->TarjanEntries[j].Root;
+        }
+      }
+    }
+
+  // Check if we have found a component.
+  if(this->TarjanEntries[i].Root == i)
+    {
+    // Yes.  Create it.
+    int c = static_cast<int>(this->Components.size());
+    this->Components.push_back(NodeList());
+    NodeList& component = this->Components[c];
+
+    // Populate the component list.
+    int j;
+    do
+      {
+      // Get the next member of the component.
+      j = this->TarjanStack.top();
+      this->TarjanStack.pop();
+
+      // Assign the member to the component.
+      this->TarjanComponents[j] = c;
+      this->TarjanEntries[j].Root = i;
+
+      // Store the node in its component.
+      component.push_back(j);
+      } while(j != i);
+
+    // Sort the component members for clarity.
+    std::sort(component.begin(), component.end());
+    }
+}
+
+//----------------------------------------------------------------------------
+void cmComputeComponentGraph::TransferEdges()
+{
+  // Map inter-component edges in the original graph to edges in the
+  // component graph.
+  int n = static_cast<int>(this->InputGraph.size());
+  for(int i=0; i < n; ++i)
+    {
+    int i_component = this->TarjanComponents[i];
+    NodeList const& nl = this->InputGraph[i];
+    for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
+      {
+      int j = *ni;
+      int j_component = this->TarjanComponents[j];
+      if(i_component != j_component)
+        {
+        this->ComponentGraph[i_component].push_back(j_component);
+        }
+      }
+    }
+}
diff --git a/Source/cmComputeComponentGraph.h b/Source/cmComputeComponentGraph.h
new file mode 100644
index 0000000..a75afcf
--- /dev/null
+++ b/Source/cmComputeComponentGraph.h
@@ -0,0 +1,87 @@
+/*=========================================================================
+
+  Program:   CMake - Cross-Platform Makefile Generator
+  Module:    $RCSfile$
+  Language:  C++
+  Date:      $Date$
+  Version:   $Revision$
+
+  Copyright (c) 2002 Kitware, Inc., Insight Consortium.  All rights reserved.
+  See Copyright.txt or http://www.cmake.org/HTML/Copyright.html for details.
+
+     This software is distributed WITHOUT ANY WARRANTY; without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+     PURPOSE.  See the above copyright notices for more information.
+
+=========================================================================*/
+#ifndef cmComputeComponentGraph_h
+#define cmComputeComponentGraph_h
+
+#include "cmStandardIncludes.h"
+
+#include "cmGraphAdjacencyList.h"
+
+#include <stack>
+
+/** \class cmComputeComponentGraph
+ * \brief Analyze a graph to determine strongly connected components.
+ *
+ * Convert a directed graph into a directed acyclic graph whose nodes
+ * correspond to strongly connected components of the original graph.
+ *
+ * We use Tarjan's algorithm to enumerate the components efficiently.
+ * An advantage of this approach is that the components are identified
+ * in a topologically sorted order.
+ */
+class cmComputeComponentGraph
+{
+public:
+  // Represent the graph with an adjacency list.
+  typedef cmGraphNodeList NodeList;
+  typedef cmGraphAdjacencyList Graph;
+
+  cmComputeComponentGraph(Graph const& input);
+  ~cmComputeComponentGraph();
+
+  /** Get the adjacency list of the component graph.  */
+  Graph const& GetComponentGraph() const
+    { return this->ComponentGraph; }
+  NodeList const& GetComponentGraphEdges(int c) const
+    { return this->ComponentGraph[c]; }
+
+  /** Get map from component index to original node indices.  */
+  std::vector<NodeList> const& GetComponents() const
+    { return this->Components; }
+  NodeList const& GetComponent(int c) const
+    { return this->Components[c]; }
+
+  /** Get map from original node index to component index.  */
+  std::vector<int> const& GetComponentMap() const
+    { return this->TarjanComponents; }
+
+private:
+  void TransferEdges();
+
+  Graph const& InputGraph;
+  Graph ComponentGraph;
+
+  // Tarjan's algorithm.
+  struct TarjanEntry
+  {
+    int Root;
+    int VisitIndex;
+  };
+  int TarjanWalkId;
+  std::vector<int> TarjanVisited;
+  std::vector<int> TarjanComponents;
+  std::vector<TarjanEntry> TarjanEntries;
+  std::stack<int> TarjanStack;
+  int TarjanIndex;
+  void Tarjan();
+  void TarjanVisit(int i);
+
+  // Connected components.
+  std::vector<NodeList> Components;
+};
+
+#endif
diff --git a/Source/cmComputeLinkDepends.cxx b/Source/cmComputeLinkDepends.cxx
index cfcfe24..30f43f8 100644
--- a/Source/cmComputeLinkDepends.cxx
+++ b/Source/cmComputeLinkDepends.cxx
@@ -16,6 +16,7 @@
 =========================================================================*/
 #include "cmComputeLinkDepends.h"
 
+#include "cmComputeComponentGraph.h"
 #include "cmGlobalGenerator.h"
 #include "cmLocalGenerator.h"
 #include "cmMakefile.h"
@@ -96,31 +97,47 @@ For the unknown items, we infer dependencies by looking at the
   B: intersect( {Y,C}   , {}    ) = {}    ; infer no edges
   C: intersect( {}      , {B}   ) = {}    ; infer no edges
 
+------------------------------------------------------------------------------
+
 Once the complete graph is formed from all known and inferred
-dependencies, we walk the graph with a series of depth-first-searches
-in order to emit link items.  When visiting a node all edges are
-followed first because the neighbors must precede the item.  Once
-neighbors across all edges have been emitted it is safe to emit the
-current node.
+dependencies we must use it to produce a valid link line.  If the
+dependency graph were known to be acyclic a simple depth-first-search
+would produce a correct link line.  Unfortunately we cannot make this
+assumption so the following technique is used.
+
+The original graph is converted to a directed acyclic graph in which
+each node corresponds to a strongly connected component of the
+original graph.  For example, the dependency graph
+
+  X <- A <- B <- C <- A <- Y
 
-If a single DFS returns to a node it previously reached then a cycle
-is present.  Cyclic link dependencies are resolved simply by repeating
-one of the cycle entries at the beginning and end of the cycle
-members.  For example, the graph
+contains strongly connected components {X}, {A,B,C}, and {Y}.  The
+implied directed acyclic graph (DAG) is
 
-  A <- B  ,  B <- C  ,  C <- A
+  {X} <- {A,B,C} <- {Y}
 
-can be satisfied with the link item list
+The final list of link items is constructed by a series of
+depth-first-searches through this DAG of components.  When visiting a
+component all outgoing edges are followed first because the neighbors
+must precede it.  Once neighbors across all edges have been emitted it
+is safe to emit the current component.
 
-  A B C A
+Trivial components (those with one item) are handled simply by
+emitting the item.  Non-trivial components (those with more than one
+item) are assumed to consist only of static libraries that may be
+safely repeated on the link line.  We emit members of the component
+multiple times (see code below for details).  The final link line for
+the example graph might be
 
-When a node is reached a second time during the same DFS we make sure
-its item has been emitted and then skip following its outgoing edges
-again.
+  X A B C A B C Y
+
+------------------------------------------------------------------------------
 
 The initial exploration of dependencies using a BFS associates an
 integer index with each link item.  When the graph is built outgoing
-edges are sorted by this index.  This preserves the original link
+edges are sorted by this index.
+
+This preserves the original link
 order as much as possible subject to the dependencies.
 
 After the initial exploration of the link interface tree, any
@@ -190,6 +207,9 @@ cmComputeLinkDepends::Compute()
   // Infer dependencies of targets for which they were not known.
   this->InferDependencies();
 
+  // Cleanup the constraint graph.
+  this->CleanConstraintGraph();
+
   // Display the constraint graph.
   if(this->DebugMode)
     {
@@ -223,7 +243,7 @@ cmComputeLinkDepends::AllocateLinkEntry(std::string const& item)
     lei = this->LinkEntryIndex.insert(index_entry).first;
   this->EntryList.push_back(LinkEntry());
   this->InferredDependSets.push_back(0);
-  this->EntryConstraintGraph.push_back(EntryConstraintSet());
+  this->EntryConstraintGraph.push_back(NodeList());
   return lei;
 }
 
@@ -354,7 +374,7 @@ void cmComputeLinkDepends::HandleSharedDependency(SharedDepEntry const& dep)
 
   // This shared library dependency must be preceded by the item that
   // listed it.
-  this->EntryConstraintGraph[index].insert(dep.DependerIndex);
+  this->EntryConstraintGraph[index].push_back(dep.DependerIndex);
 
   // Target items may have their own dependencies.
   if(entry.Target)
@@ -469,7 +489,7 @@ cmComputeLinkDepends::AddLinkEntries(int depender_index,
     // The depender must come before the dependee.
     if(depender_index >= 0)
       {
-      this->EntryConstraintGraph[dependee_index].insert(depender_index);
+      this->EntryConstraintGraph[dependee_index].push_back(depender_index);
       }
 
     // Update the inferred dependencies for earlier items.
@@ -531,22 +551,37 @@ void cmComputeLinkDepends::InferDependencies()
     for(DependSet::const_iterator j = common.begin(); j != common.end(); ++j)
       {
       int dependee_index = *j;
-      this->EntryConstraintGraph[dependee_index].insert(depender_index);
+      this->EntryConstraintGraph[dependee_index].push_back(depender_index);
       }
     }
 }
 
 //----------------------------------------------------------------------------
+void cmComputeLinkDepends::CleanConstraintGraph()
+{
+  for(Graph::iterator i = this->EntryConstraintGraph.begin();
+      i != this->EntryConstraintGraph.end(); ++i)
+    {
+    // Sort the outgoing edges for each graph node so that the
+    // original order will be preserved as much as possible.
+    cmsys_stl::sort(i->begin(), i->end());
+
+    // Make the edge list unique.
+    NodeList::iterator last = cmsys_stl::unique(i->begin(), i->end());
+    i->erase(last, i->end());
+    }
+}
+
+//----------------------------------------------------------------------------
 void cmComputeLinkDepends::DisplayConstraintGraph()
 {
-  // Display the conflict graph.
+  // Display the graph nodes and their edges.
   cmOStringStream e;
   for(unsigned int i=0; i < this->EntryConstraintGraph.size(); ++i)
     {
-    EntryConstraintSet const& cset = this->EntryConstraintGraph[i];
+    NodeList const& nl = this->EntryConstraintGraph[i];
     e << "item " << i << " is [" << this->EntryList[i].Item << "]\n";
-    for(EntryConstraintSet::const_iterator j = cset.begin();
-        j != cset.end(); ++j)
+    for(NodeList::const_iterator j = nl.begin(); j != nl.end(); ++j)
       {
       e << "  item " << *j << " must precede it\n";
       }
@@ -557,56 +592,107 @@ void cmComputeLinkDepends::DisplayConstraintGraph()
 //----------------------------------------------------------------------------
 void cmComputeLinkDepends::OrderLinkEntires()
 {
+  // Compute the DAG of strongly connected components.  The algorithm
+  // used by cmComputeComponentGraph should identify the components in
+  // the same order in which the items were originally discovered in
+  // the BFS.  This should preserve the original order when no
+  // constraints disallow it.
+  cmComputeComponentGraph ccg(this->EntryConstraintGraph);
+  Graph const& cgraph = ccg.GetComponentGraph();
+  if(this->DebugMode)
+    {
+    this->DisplayComponents(ccg);
+    }
+
   // Setup visit tracking.
-  this->EntryVisited.resize(this->EntryList.size(), 0);
-  this->WalkId = 0;
+  this->ComponentVisited.resize(cgraph.size(), 0);
 
-  // Start a DFS from every entry.
-  for(unsigned int i=0; i < this->EntryList.size(); ++i)
+  // The component graph is guaranteed to be acyclic.  Start a DFS
+  // from every entry.
+  for(unsigned int c=0; c < cgraph.size(); ++c)
     {
-    ++this->WalkId;
-    this->VisitLinkEntry(i);
+    this->VisitComponent(ccg, c);
     }
 }
 
 //----------------------------------------------------------------------------
-void cmComputeLinkDepends::VisitLinkEntry(unsigned int i)
+void
+cmComputeLinkDepends::DisplayComponents(cmComputeComponentGraph const& ccg)
 {
-  // Check if the node has already been visited.
-  if(this->EntryVisited[i])
+  fprintf(stderr, "The strongly connected components are:\n");
+  std::vector<NodeList> const& components = ccg.GetComponents();
+  for(unsigned int c=0; c < components.size(); ++c)
     {
-    if(this->EntryVisited[i] == this->WalkId)
+    fprintf(stderr, "Component (%u):\n", c);
+    NodeList const& nl = components[c];
+    for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
       {
-      // We have reached a node previously visited on this DFS.  There
-      // is a cycle.  In order to allow linking with cyclic
-      // dependencies we make sure the item is emitted but do not
-      // follow its outgoing edges again.
-      if(this->EntryEmitted.insert(i).second)
-        {
-        // The item has not been previously emitted so we emit it now.
-        // It will be emitted again when the stack unwinds back up to
-        // the beginning of the cycle.
-        this->FinalLinkEntries.push_back(this->EntryList[i]);
-        }
+      int i = *ni;
+      fprintf(stderr, "  item %d [%s]\n", i,
+              this->EntryList[i].Item.c_str());
       }
+    }
+  fprintf(stderr, "\n");
+}
+
+//----------------------------------------------------------------------------
+void
+cmComputeLinkDepends::VisitComponent(cmComputeComponentGraph const& ccg,
+                                     unsigned int c)
+{
+  // Check if the node has already been visited.
+  if(this->ComponentVisited[c])
+    {
     return;
     }
 
-  // We are now visiting this node so mark it.
-  this->EntryVisited[i] = this->WalkId;
+  // We are now visiting this component so mark it.
+  this->ComponentVisited[c] = 1;
 
-  // Visit the neighbors of the node first.
-  EntryConstraintSet const& cset = this->EntryConstraintGraph[i];
-  for(EntryConstraintSet::const_iterator j = cset.begin();
-      j != cset.end(); ++j)
+  // Visit the neighbors of the component first.
+  NodeList const& nl = ccg.GetComponentGraphEdges(c);
+  for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
     {
-    this->VisitLinkEntry(*j);
+    this->VisitComponent(ccg, *ni);
     }
 
   // Now that all items required to come before this one have been
-  // emmitted, emit this item.
-  this->EntryEmitted.insert(i);
-  this->FinalLinkEntries.push_back(this->EntryList[i]);
+  // emmitted, emit this component's items.
+  this->EmitComponent(ccg.GetComponent(c));
+}
+
+//----------------------------------------------------------------------------
+void cmComputeLinkDepends::EmitComponent(NodeList const& nl)
+{
+  assert(!nl.empty());
+
+  // Handle trivial components.
+  if(nl.size() == 1)
+    {
+    this->FinalLinkEntries.push_back(this->EntryList[nl[0]]);
+    return;
+    }
+
+  // This is a non-trivial strongly connected component of the
+  // original graph.  It consists of two or more libraries (archives)
+  // that mutually require objects from one another.  In the worst
+  // case we may have to repeat the list of libraries as many times as
+  // there are object files in the biggest archive.  For now we just
+  // list them twice.
+  //
+  // The list of items in the component has been sorted by the order
+  // of discovery in the original BFS of dependencies.  This has the
+  // advantage that the item directly linked by a target requiring
+  // this component will come first which minimizes the number of
+  // repeats needed.
+  for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
+    {
+    this->FinalLinkEntries.push_back(this->EntryList[*ni]);
+    }
+  for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
+    {
+    this->FinalLinkEntries.push_back(this->EntryList[*ni]);
+    }
 }
 
 //----------------------------------------------------------------------------
diff --git a/Source/cmComputeLinkDepends.h b/Source/cmComputeLinkDepends.h
index 1e422a6..b81f8bc 100644
--- a/Source/cmComputeLinkDepends.h
+++ b/Source/cmComputeLinkDepends.h
@@ -20,8 +20,11 @@
 #include "cmStandardIncludes.h"
 #include "cmTarget.h"
 
+#include "cmGraphAdjacencyList.h"
+
 #include <queue>
 
+class cmComputeComponentGraph;
 class cmGlobalGenerator;
 class cmLocalGenerator;
 class cmMakefile;
@@ -109,16 +112,18 @@ private:
   void InferDependencies();
 
   // Ordering constraint graph adjacency list.
-  struct EntryConstraintSet: public std::set<int> {};
-  std::vector<EntryConstraintSet> EntryConstraintGraph;
+  typedef cmGraphNodeList NodeList;
+  typedef cmGraphAdjacencyList Graph;
+  Graph EntryConstraintGraph;
+  void CleanConstraintGraph();
   void DisplayConstraintGraph();
 
   // Ordering algorithm.
-  std::vector<int> EntryVisited;
-  std::set<int> EntryEmitted;
-  int WalkId;
   void OrderLinkEntires();
-  void VisitLinkEntry(unsigned int i);
+  std::vector<char> ComponentVisited;
+  void DisplayComponents(cmComputeComponentGraph const& ccg);
+  void VisitComponent(cmComputeComponentGraph const& ccg, unsigned int i);
+  void EmitComponent(NodeList const& nl);
   void DisplayFinalEntries();
 };
 
diff --git a/Source/cmComputeTargetDepends.cxx b/Source/cmComputeTargetDepends.cxx
index 3062c4d..d13a6db 100644
--- a/Source/cmComputeTargetDepends.cxx
+++ b/Source/cmComputeTargetDepends.cxx
@@ -16,6 +16,7 @@
 =========================================================================*/
 #include "cmComputeTargetDepends.h"
 
+#include "cmComputeComponentGraph.h"
 #include "cmGlobalGenerator.h"
 #include "cmLocalGenerator.h"
 #include "cmMakefile.h"
@@ -117,25 +118,25 @@ bool cmComputeTargetDepends::Compute()
   this->CollectDepends();
   if(this->DebugMode)
     {
-    this->DisplayGraph(this->TargetDependGraph, "initial");
+    this->DisplayGraph(this->InitialGraph, "initial");
     }
 
   // Identify components.
-  this->Tarjan();
+  cmComputeComponentGraph ccg(this->InitialGraph);
   if(this->DebugMode)
     {
-    this->DisplayComponents();
+    this->DisplayComponents(ccg);
     }
-  if(!this->CheckComponents())
+  if(!this->CheckComponents(ccg))
     {
     return false;
     }
 
   // Compute the final dependency graph.
-  this->ComputeFinalDepends();
+  this->ComputeFinalDepends(ccg);
   if(this->DebugMode)
     {
-    this->DisplayGraph(this->FinalDependGraph, "final");
+    this->DisplayGraph(this->FinalGraph, "final");
     }
 
   return true;
@@ -153,11 +154,10 @@ cmComputeTargetDepends::GetTargetDirectDepends(cmTarget* t,
   int i = tii->second;
 
   // Get its final dependencies.
-  TargetDependList const& tdl = this->FinalDependGraph[i];
-  for(TargetDependList::const_iterator di = tdl.begin();
-      di != tdl.end(); ++di)
+  NodeList const& nl = this->FinalGraph[i];
+  for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
     {
-    deps.insert(this->Targets[*di]);
+    deps.insert(this->Targets[*ni]);
     }
 }
 
@@ -184,7 +184,7 @@ void cmComputeTargetDepends::CollectTargets()
 void cmComputeTargetDepends::CollectDepends()
 {
   // Allocate the dependency graph adjacency lists.
-  this->TargetDependGraph.resize(this->Targets.size());
+  this->InitialGraph.resize(this->Targets.size());
 
   // Compute each dependency list.
   for(unsigned int i=0; i < this->Targets.size(); ++i)
@@ -265,27 +265,24 @@ void cmComputeTargetDepends::AddTargetDepend(int depender_index,
   int dependee_index = tii->second;
 
   // Add this entry to the dependency graph.
-  this->TargetDependGraph[depender_index].push_back(dependee_index);
+  this->InitialGraph[depender_index].push_back(dependee_index);
 }
 
 //----------------------------------------------------------------------------
 void
-cmComputeTargetDepends
-::DisplayGraph(std::vector<TargetDependList> const& graph,
-               const char* name)
+cmComputeTargetDepends::DisplayGraph(Graph const& graph, const char* name)
 {
   fprintf(stderr, "The %s target dependency graph is:\n", name);
   int n = static_cast<int>(graph.size());
   for(int depender_index = 0; depender_index < n; ++depender_index)
     {
-    TargetDependList const& tdl = graph[depender_index];
+    NodeList const& nl = graph[depender_index];
     cmTarget* depender = this->Targets[depender_index];
     fprintf(stderr, "target %d is [%s]\n",
             depender_index, depender->GetName());
-    for(TargetDependList::const_iterator di = tdl.begin();
-        di != tdl.end(); ++di)
+    for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
       {
-      int dependee_index = *di;
+      int dependee_index = *ni;
       cmTarget* dependee = this->Targets[dependee_index];
       fprintf(stderr, "  depends on target %d [%s]\n", dependee_index,
               dependee->GetName());
@@ -295,115 +292,20 @@ cmComputeTargetDepends
 }
 
 //----------------------------------------------------------------------------
-void cmComputeTargetDepends::Tarjan()
-{
-  int n = static_cast<int>(this->TargetDependGraph.size());
-  TarjanEntry entry = {0,-1,0};
-  this->TarjanEntries.resize(n, entry);
-  this->TarjanWalkId = 0;
-  this->TarjanVisited.resize(n, 0);
-  for(int i = 0; i < n; ++i)
-    {
-    // Start a new DFS from this node if it has never been visited.
-    if(!this->TarjanVisited[i])
-      {
-      assert(this->TarjanStack.empty());
-      ++this->TarjanWalkId;
-      this->TarjanIndex = 0;
-      this->TarjanVisit(i);
-      }
-    }
-}
-
-//----------------------------------------------------------------------------
-void cmComputeTargetDepends::TarjanVisit(int i)
-{
-  // We are now visiting this node.
-  this->TarjanVisited[i] = this->TarjanWalkId;
-
-  // Initialize the entry.
-  this->TarjanEntries[i].Root = i;
-  this->TarjanEntries[i].Component = -1;
-  this->TarjanEntries[i].VisitIndex = ++this->TarjanIndex;
-  this->TarjanStack.push(i);
-
-  // Follow outgoing edges.
-  TargetDependList const& tdl = this->TargetDependGraph[i];
-  for(TargetDependList::const_iterator di = tdl.begin();
-      di != tdl.end(); ++di)
-    {
-    int j = *di;
-
-    // Ignore edges to nodes that have been reached by a previous DFS
-    // walk.  Since we did not reach the current node from that walk
-    // it must not belong to the same component and it has already
-    // been assigned to a component.
-    if(this->TarjanVisited[j] > 0 &&
-       this->TarjanVisited[j] < this->TarjanWalkId)
-      {
-      continue;
-      }
-
-    // Visit the destination if it has not yet been visited.
-    if(!this->TarjanVisited[j])
-      {
-      this->TarjanVisit(j);
-      }
-
-    // If the destination has not yet been assigned to a component,
-    // check if it is a better potential root for the current object.
-    if(this->TarjanEntries[j].Component < 0)
-      {
-      if(this->TarjanEntries[this->TarjanEntries[j].Root].VisitIndex <
-         this->TarjanEntries[this->TarjanEntries[i].Root].VisitIndex)
-        {
-        this->TarjanEntries[i].Root = this->TarjanEntries[j].Root;
-        }
-      }
-    }
-
-  // Check if we have found a component.
-  if(this->TarjanEntries[i].Root == i)
-    {
-    // Yes.  Create it.
-    int c = static_cast<int>(this->Components.size());
-    this->Components.push_back(ComponentList());
-    ComponentList& component = this->Components[c];
-
-    // Populate the component list.
-    int j;
-    do
-      {
-      // Get the next member of the component.
-      j = this->TarjanStack.top();
-      this->TarjanStack.pop();
-
-      // Assign the member to the component.
-      this->TarjanEntries[j].Component = c;
-      this->TarjanEntries[j].Root = i;
-
-      // Store the node in its component.
-      component.push_back(j);
-      } while(j != i);
-
-    // Sort the component members for clarity.
-    std::sort(component.begin(), component.end());
-    }
-}
-
-//----------------------------------------------------------------------------
-void cmComputeTargetDepends::DisplayComponents()
+void
+cmComputeTargetDepends
+::DisplayComponents(cmComputeComponentGraph const& ccg)
 {
   fprintf(stderr, "The strongly connected components are:\n");
-  int n = static_cast<int>(this->Components.size());
+  std::vector<NodeList> const& components = ccg.GetComponents();
+  int n = static_cast<int>(components.size());
   for(int c = 0; c < n; ++c)
     {
-    ComponentList const& cl = this->Components[c];
+    NodeList const& nl = components[c];
     fprintf(stderr, "Component (%d):\n", c);
-    for(ComponentList::const_iterator ci = cl.begin();
-        ci != cl.end(); ++ci)
+    for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
       {
-      int i = *ci;
+      int i = *ni;
       fprintf(stderr, "  contains target %d [%s]\n",
               i, this->Targets[i]->GetName());
       }
@@ -412,28 +314,31 @@ void cmComputeTargetDepends::DisplayComponents()
 }
 
 //----------------------------------------------------------------------------
-bool cmComputeTargetDepends::CheckComponents()
+bool
+cmComputeTargetDepends
+::CheckComponents(cmComputeComponentGraph const& ccg)
 {
   // All non-trivial components should consist only of static
   // libraries.
-  int nc = static_cast<int>(this->Components.size());
+  std::vector<NodeList> const& components = ccg.GetComponents();
+  int nc = static_cast<int>(components.size());
   for(int c=0; c < nc; ++c)
     {
     // Get the current component.
-    ComponentList const& cl = this->Components[c];
+    NodeList const& nl = components[c];
 
     // Skip trivial components.
-    if(cl.size() < 2)
+    if(nl.size() < 2)
       {
       continue;
       }
 
     // Make sure the component is all STATIC_LIBRARY targets.
-    for(ComponentList::const_iterator ci = cl.begin(); ci != cl.end(); ++ci)
+    for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
       {
-      if(this->Targets[*ci]->GetType() != cmTarget::STATIC_LIBRARY)
+      if(this->Targets[*ni]->GetType() != cmTarget::STATIC_LIBRARY)
         {
-        this->ComplainAboutBadComponent(c);
+        this->ComplainAboutBadComponent(ccg, c);
         return false;
         }
       }
@@ -443,16 +348,17 @@ bool cmComputeTargetDepends::CheckComponents()
 
 //----------------------------------------------------------------------------
 void
-cmComputeTargetDepends::ComplainAboutBadComponent(int c)
+cmComputeTargetDepends
+::ComplainAboutBadComponent(cmComputeComponentGraph const& ccg, int c)
 {
-  // Get the bad component.
-  ComponentList const& cl = this->Components[c];
-
   // Construct the error message.
   cmOStringStream e;
   e << "The inter-target dependency graph contains the following "
     << "strongly connected component (cycle):\n";
-  for(ComponentList::const_iterator ci = cl.begin(); ci != cl.end(); ++ci)
+  std::vector<NodeList> const& components = ccg.GetComponents();
+  std::vector<int> const& cmap = ccg.GetComponentMap();
+  NodeList const& cl = components[c];
+  for(NodeList::const_iterator ci = cl.begin(); ci != cl.end(); ++ci)
     {
     // Get the depender.
     int i = *ci;
@@ -463,12 +369,11 @@ cmComputeTargetDepends::ComplainAboutBadComponent(int c)
       << cmTarget::TargetTypeNames[depender->GetType()] << "\n";
 
     // List its dependencies that are inside the component.
-    TargetDependList const& tdl = this->TargetDependGraph[i];
-    for(TargetDependList::const_iterator di = tdl.begin();
-        di != tdl.end(); ++di)
+    NodeList const& nl = this->InitialGraph[i];
+    for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
       {
-      int j = *di;
-      if(this->TarjanEntries[j].Component == c)
+      int j = *ni;
+      if(cmap[j] == c)
         {
         cmTarget* dependee = this->Targets[j];
         e << "    depends on " << dependee->GetName() << "\n";
@@ -481,46 +386,45 @@ cmComputeTargetDepends::ComplainAboutBadComponent(int c)
 }
 
 //----------------------------------------------------------------------------
-void cmComputeTargetDepends::ComputeFinalDepends()
+void
+cmComputeTargetDepends
+::ComputeFinalDepends(cmComputeComponentGraph const& ccg)
 {
-  int n = static_cast<int>(this->TargetDependGraph.size());
-  this->FinalDependGraph.resize(n);
+  // Get the component graph information.
+  std::vector<NodeList> const& components = ccg.GetComponents();
+  Graph const& cgraph = ccg.GetComponentGraph();
+
+  // Allocate the final graph.
+  this->FinalGraph.resize(0);
+  this->FinalGraph.resize(this->InitialGraph.size());
 
   // Convert inter-component edges to connect component tails to heads.
-  for(int i=0; i < n; ++i)
+  int n = static_cast<int>(cgraph.size());
+  for(int depender_component=0; depender_component < n; ++depender_component)
     {
-    int depender_component = this->TarjanEntries[i].Component;
-    int depender_component_tail =
-      this->Components[depender_component].back();
-
-    TargetDependList const& tdl = this->TargetDependGraph[i];
-    for(TargetDependList::const_iterator di = tdl.begin();
-        di != tdl.end(); ++di)
+    int depender_component_tail = components[depender_component].back();
+    NodeList const& nl = cgraph[depender_component];
+    for(NodeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni)
       {
-      int j = *di;
-      int dependee_component = this->TarjanEntries[j].Component;
-      int dependee_component_head =
-        this->Components[dependee_component].front();
-      if(depender_component != dependee_component)
-        {
-        this->FinalDependGraph[depender_component_tail]
-          .push_back(dependee_component_head);
-        }
+      int dependee_component = *ni;
+      int dependee_component_head = components[dependee_component].front();
+      this->FinalGraph[depender_component_tail]
+        .push_back(dependee_component_head);
       }
     }
 
   // Compute intra-component edges.
-  int nc = static_cast<int>(this->Components.size());
+  int nc = static_cast<int>(components.size());
   for(int c=0; c < nc; ++c)
     {
     // Within the component each target depends on that following it.
-    ComponentList const& cl = this->Components[c];
-    ComponentList::const_iterator ci = cl.begin();
-    int last_i = *ci;
-    for(++ci; ci != cl.end(); ++ci)
+    NodeList const& nl = components[c];
+    NodeList::const_iterator ni = nl.begin();
+    int last_i = *ni;
+    for(++ni; ni != nl.end(); ++ni)
       {
-      int i = *ci;
-      this->FinalDependGraph[last_i].push_back(i);
+      int i = *ni;
+      this->FinalGraph[last_i].push_back(i);
       last_i = i;
       }
     }
diff --git a/Source/cmComputeTargetDepends.h b/Source/cmComputeTargetDepends.h
index 9c17731..707256e 100644
--- a/Source/cmComputeTargetDepends.h
+++ b/Source/cmComputeTargetDepends.h
@@ -19,8 +19,11 @@
 
 #include "cmStandardIncludes.h"
 
+#include "cmGraphAdjacencyList.h"
+
 #include <stack>
 
+class cmComputeComponentGraph;
 class cmGlobalGenerator;
 class cmTarget;
 
@@ -46,7 +49,7 @@ private:
   void CollectDepends();
   void CollectTargetDepends(int depender_index);
   void AddTargetDepend(int depender_index, const char* dependee_name);
-  void ComputeFinalDepends();
+  void ComputeFinalDepends(cmComputeComponentGraph const& ccg);
 
   cmGlobalGenerator* GlobalGenerator;
   bool DebugMode;
@@ -58,33 +61,16 @@ private:
   // Represent the target dependency graph.  The entry at each
   // top-level index corresponds to a depender whose dependencies are
   // listed.
-  struct TargetDependList: public std::vector<int> {};
-  std::vector<TargetDependList> TargetDependGraph;
-  std::vector<TargetDependList> FinalDependGraph;
-  void DisplayGraph(std::vector<TargetDependList> const& graph,
-                    const char* name);
-
-  // Tarjan's algorithm.
-  struct TarjanEntry
-  {
-    int Root;
-    int Component;
-    int VisitIndex;
-  };
-  int TarjanWalkId;
-  std::vector<int> TarjanVisited;
-  std::vector<TarjanEntry> TarjanEntries;
-  std::stack<int> TarjanStack;
-  int TarjanIndex;
-  void Tarjan();
-  void TarjanVisit(int i);
-
-  // Connected components.
-  struct ComponentList: public std::vector<int> {};
-  std::vector<ComponentList> Components;
-  void DisplayComponents();
-  bool CheckComponents();
-  void ComplainAboutBadComponent(int c);
+  typedef cmGraphNodeList NodeList;
+  typedef cmGraphAdjacencyList Graph;
+  Graph InitialGraph;
+  Graph FinalGraph;
+  void DisplayGraph(Graph const& graph, const char* name);
+
+  // Deal with connected components.
+  void DisplayComponents(cmComputeComponentGraph const& ccg);
+  bool CheckComponents(cmComputeComponentGraph const& ccg);
+  void ComplainAboutBadComponent(cmComputeComponentGraph const& ccg, int c);
 };
 
 #endif
diff --git a/Source/cmGraphAdjacencyList.h b/Source/cmGraphAdjacencyList.h
new file mode 100644
index 0000000..ef0aa09
--- /dev/null
+++ b/Source/cmGraphAdjacencyList.h
@@ -0,0 +1,25 @@
+/*=========================================================================
+
+  Program:   CMake - Cross-Platform Makefile Generator
+  Module:    $RCSfile$
+  Language:  C++
+  Date:      $Date$
+  Version:   $Revision$
+
+  Copyright (c) 2002 Kitware, Inc., Insight Consortium.  All rights reserved.
+  See Copyright.txt or http://www.cmake.org/HTML/Copyright.html for details.
+
+     This software is distributed WITHOUT ANY WARRANTY; without even
+     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+     PURPOSE.  See the above copyright notices for more information.
+
+=========================================================================*/
+#ifndef cmGraphAdjacencyList_h
+#define cmGraphAdjacencyList_h
+
+#include "cmStandardIncludes.h"
+
+struct cmGraphNodeList: public std::vector<int> {};
+struct cmGraphAdjacencyList: public std::vector<cmGraphNodeList> {};
+
+#endif