diff --git a/lib/CompilerDriver/CompilationGraph.cpp b/lib/CompilerDriver/CompilationGraph.cpp
new file mode 100644
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--- /dev/null
+++ b/lib/CompilerDriver/CompilationGraph.cpp
@@ -0,0 +1,534 @@
+//===--- CompilationGraph.cpp - The LLVM Compiler Driver --------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open
+// Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  Compilation graph - implementation.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CompilerDriver/CompilationGraph.h"
+#include "llvm/CompilerDriver/Error.h"
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/DOTGraphTraits.h"
+#include "llvm/Support/GraphWriter.h"
+
+#include <algorithm>
+#include <cstring>
+#include <iostream>
+#include <iterator>
+#include <limits>
+#include <queue>
+#include <stdexcept>
+
+using namespace llvm;
+using namespace llvmc;
+
+extern cl::list<std::string> InputFilenames;
+extern cl::list<std::string> Languages;
+
+namespace llvmc {
+
+  const std::string& LanguageMap::GetLanguage(const sys::Path& File) const {
+    LanguageMap::const_iterator Lang = this->find(File.getSuffix());
+    if (Lang == this->end())
+      throw std::runtime_error("Unknown suffix: " + File.getSuffix());
+    return Lang->second;
+  }
+}
+
+namespace {
+
+  /// ChooseEdge - Return the edge with the maximum weight.
+  template <class C>
+  const Edge* ChooseEdge(const C& EdgesContainer,
+                         const InputLanguagesSet& InLangs,
+                         const std::string& NodeName = "root") {
+    const Edge* MaxEdge = 0;
+    unsigned MaxWeight = 0;
+    bool SingleMax = true;
+
+    for (typename C::const_iterator B = EdgesContainer.begin(),
+           E = EdgesContainer.end(); B != E; ++B) {
+      const Edge* e = B->getPtr();
+      unsigned EW = e->Weight(InLangs);
+      if (EW > MaxWeight) {
+        MaxEdge = e;
+        MaxWeight = EW;
+        SingleMax = true;
+      } else if (EW == MaxWeight) {
+        SingleMax = false;
+      }
+    }
+
+    if (!SingleMax)
+      throw std::runtime_error("Node " + NodeName +
+                               ": multiple maximal outward edges found!"
+                               " Most probably a specification error.");
+    if (!MaxEdge)
+      throw std::runtime_error("Node " + NodeName +
+                               ": no maximal outward edge found!"
+                               " Most probably a specification error.");
+    return MaxEdge;
+  }
+
+}
+
+void Node::AddEdge(Edge* Edg) {
+  // If there already was an edge between two nodes, modify it instead
+  // of adding a new edge.
+  const std::string& ToolName = Edg->ToolName();
+  for (container_type::iterator B = OutEdges.begin(), E = OutEdges.end();
+       B != E; ++B) {
+    if ((*B)->ToolName() == ToolName) {
+      llvm::IntrusiveRefCntPtr<Edge>(Edg).swap(*B);
+      return;
+    }
+  }
+  OutEdges.push_back(llvm::IntrusiveRefCntPtr<Edge>(Edg));
+}
+
+CompilationGraph::CompilationGraph() {
+  NodesMap["root"] = Node(this);
+}
+
+Node& CompilationGraph::getNode(const std::string& ToolName) {
+  nodes_map_type::iterator I = NodesMap.find(ToolName);
+  if (I == NodesMap.end())
+    throw std::runtime_error("Node " + ToolName + " is not in the graph");
+  return I->second;
+}
+
+const Node& CompilationGraph::getNode(const std::string& ToolName) const {
+  nodes_map_type::const_iterator I = NodesMap.find(ToolName);
+  if (I == NodesMap.end())
+    throw std::runtime_error("Node " + ToolName + " is not in the graph!");
+  return I->second;
+}
+
+// Find the tools list corresponding to the given language name.
+const CompilationGraph::tools_vector_type&
+CompilationGraph::getToolsVector(const std::string& LangName) const
+{
+  tools_map_type::const_iterator I = ToolsMap.find(LangName);
+  if (I == ToolsMap.end())
+    throw std::runtime_error("No tool corresponding to the language "
+                             + LangName + " found");
+  return I->second;
+}
+
+void CompilationGraph::insertNode(Tool* V) {
+  if (NodesMap.count(V->Name()) == 0)
+    NodesMap[V->Name()] = Node(this, V);
+}
+
+void CompilationGraph::insertEdge(const std::string& A, Edge* Edg) {
+  Node& B = getNode(Edg->ToolName());
+  if (A == "root") {
+    const char** InLangs = B.ToolPtr->InputLanguages();
+    for (;*InLangs; ++InLangs)
+      ToolsMap[*InLangs].push_back(IntrusiveRefCntPtr<Edge>(Edg));
+    NodesMap["root"].AddEdge(Edg);
+  }
+  else {
+    Node& N = getNode(A);
+    N.AddEdge(Edg);
+  }
+  // Increase the inward edge counter.
+  B.IncrInEdges();
+}
+
+// Pass input file through the chain until we bump into a Join node or
+// a node that says that it is the last.
+void CompilationGraph::PassThroughGraph (const sys::Path& InFile,
+                                         const Node* StartNode,
+                                         const InputLanguagesSet& InLangs,
+                                         const sys::Path& TempDir,
+                                         const LanguageMap& LangMap) const {
+  sys::Path In = InFile;
+  const Node* CurNode = StartNode;
+
+  while(true) {
+    Tool* CurTool = CurNode->ToolPtr.getPtr();
+
+    if (CurTool->IsJoin()) {
+      JoinTool& JT = dynamic_cast<JoinTool&>(*CurTool);
+      JT.AddToJoinList(In);
+      break;
+    }
+
+    Action CurAction = CurTool->GenerateAction(In, CurNode->HasChildren(),
+                                               TempDir, InLangs, LangMap);
+
+    if (int ret = CurAction.Execute())
+      throw error_code(ret);
+
+    if (CurAction.StopCompilation())
+      return;
+
+    CurNode = &getNode(ChooseEdge(CurNode->OutEdges,
+                                  InLangs,
+                                  CurNode->Name())->ToolName());
+    In = CurAction.OutFile();
+  }
+}
+
+// Find the head of the toolchain corresponding to the given file.
+// Also, insert an input language into InLangs.
+const Node* CompilationGraph::
+FindToolChain(const sys::Path& In, const std::string* ForceLanguage,
+              InputLanguagesSet& InLangs, const LanguageMap& LangMap) const {
+
+  // Determine the input language.
+  const std::string& InLanguage =
+    ForceLanguage ? *ForceLanguage : LangMap.GetLanguage(In);
+
+  // Add the current input language to the input language set.
+  InLangs.insert(InLanguage);
+
+  // Find the toolchain for the input language.
+  const tools_vector_type& TV = getToolsVector(InLanguage);
+  if (TV.empty())
+    throw std::runtime_error("No toolchain corresponding to language "
+                             + InLanguage + " found");
+  return &getNode(ChooseEdge(TV, InLangs)->ToolName());
+}
+
+// Helper function used by Build().
+// Traverses initial portions of the toolchains (up to the first Join node).
+// This function is also responsible for handling the -x option.
+void CompilationGraph::BuildInitial (InputLanguagesSet& InLangs,
+                                     const sys::Path& TempDir,
+                                     const LanguageMap& LangMap) {
+  // This is related to -x option handling.
+  cl::list<std::string>::const_iterator xIter = Languages.begin(),
+    xBegin = xIter, xEnd = Languages.end();
+  bool xEmpty = true;
+  const std::string* xLanguage = 0;
+  unsigned xPos = 0, xPosNext = 0, filePos = 0;
+
+  if (xIter != xEnd) {
+    xEmpty = false;
+    xPos = Languages.getPosition(xIter - xBegin);
+    cl::list<std::string>::const_iterator xNext = llvm::next(xIter);
+    xPosNext = (xNext == xEnd) ? std::numeric_limits<unsigned>::max()
+      : Languages.getPosition(xNext - xBegin);
+    xLanguage = (*xIter == "none") ? 0 : &(*xIter);
+  }
+
+  // For each input file:
+  for (cl::list<std::string>::const_iterator B = InputFilenames.begin(),
+         CB = B, E = InputFilenames.end(); B != E; ++B) {
+    sys::Path In = sys::Path(*B);
+
+    // Code for handling the -x option.
+    // Output: std::string* xLanguage (can be NULL).
+    if (!xEmpty) {
+      filePos = InputFilenames.getPosition(B - CB);
+
+      if (xPos < filePos) {
+        if (filePos < xPosNext) {
+          xLanguage = (*xIter == "none") ? 0 : &(*xIter);
+        }
+        else { // filePos >= xPosNext
+          // Skip xIters while filePos > xPosNext
+          while (filePos > xPosNext) {
+            ++xIter;
+            xPos = xPosNext;
+
+            cl::list<std::string>::const_iterator xNext = llvm::next(xIter);
+            if (xNext == xEnd)
+              xPosNext = std::numeric_limits<unsigned>::max();
+            else
+              xPosNext = Languages.getPosition(xNext - xBegin);
+            xLanguage = (*xIter == "none") ? 0 : &(*xIter);
+          }
+        }
+      }
+    }
+
+    // Find the toolchain corresponding to this file.
+    const Node* N = FindToolChain(In, xLanguage, InLangs, LangMap);
+    // Pass file through the chain starting at head.
+    PassThroughGraph(In, N, InLangs, TempDir, LangMap);
+  }
+}
+
+// Sort the nodes in topological order.
+void CompilationGraph::TopologicalSort(std::vector<const Node*>& Out) {
+  std::queue<const Node*> Q;
+  Q.push(&getNode("root"));
+
+  while (!Q.empty()) {
+    const Node* A = Q.front();
+    Q.pop();
+    Out.push_back(A);
+    for (Node::const_iterator EB = A->EdgesBegin(), EE = A->EdgesEnd();
+         EB != EE; ++EB) {
+      Node* B = &getNode((*EB)->ToolName());
+      B->DecrInEdges();
+      if (B->HasNoInEdges())
+        Q.push(B);
+    }
+  }
+}
+
+namespace {
+  bool NotJoinNode(const Node* N) {
+    return N->ToolPtr ? !N->ToolPtr->IsJoin() : true;
+  }
+}
+
+// Call TopologicalSort and filter the resulting list to include
+// only Join nodes.
+void CompilationGraph::
+TopologicalSortFilterJoinNodes(std::vector<const Node*>& Out) {
+  std::vector<const Node*> TopSorted;
+  TopologicalSort(TopSorted);
+  std::remove_copy_if(TopSorted.begin(), TopSorted.end(),
+                      std::back_inserter(Out), NotJoinNode);
+}
+
+int CompilationGraph::Build (const sys::Path& TempDir,
+                             const LanguageMap& LangMap) {
+
+  InputLanguagesSet InLangs;
+
+  // Traverse initial parts of the toolchains and fill in InLangs.
+  BuildInitial(InLangs, TempDir, LangMap);
+
+  std::vector<const Node*> JTV;
+  TopologicalSortFilterJoinNodes(JTV);
+
+  // For all join nodes in topological order:
+  for (std::vector<const Node*>::iterator B = JTV.begin(), E = JTV.end();
+       B != E; ++B) {
+
+    const Node* CurNode = *B;
+    JoinTool* JT = &dynamic_cast<JoinTool&>(*CurNode->ToolPtr.getPtr());
+
+    // Are there any files in the join list?
+    if (JT->JoinListEmpty())
+      continue;
+
+    Action CurAction = JT->GenerateAction(CurNode->HasChildren(),
+                                          TempDir, InLangs, LangMap);
+
+    if (int ret = CurAction.Execute())
+      throw error_code(ret);
+
+    if (CurAction.StopCompilation())
+      return 0;
+
+    const Node* NextNode = &getNode(ChooseEdge(CurNode->OutEdges, InLangs,
+                                               CurNode->Name())->ToolName());
+    PassThroughGraph(sys::Path(CurAction.OutFile()), NextNode,
+                     InLangs, TempDir, LangMap);
+  }
+
+  return 0;
+}
+
+int CompilationGraph::CheckLanguageNames() const {
+  int ret = 0;
+  // Check that names for output and input languages on all edges do match.
+  for (const_nodes_iterator B = this->NodesMap.begin(),
+         E = this->NodesMap.end(); B != E; ++B) {
+
+    const Node & N1 = B->second;
+    if (N1.ToolPtr) {
+      for (Node::const_iterator EB = N1.EdgesBegin(), EE = N1.EdgesEnd();
+           EB != EE; ++EB) {
+        const Node& N2 = this->getNode((*EB)->ToolName());
+
+        if (!N2.ToolPtr) {
+          ++ret;
+          std::cerr << "Error: there is an edge from '" << N1.ToolPtr->Name()
+                    << "' back to the root!\n\n";
+          continue;
+        }
+
+        const char* OutLang = N1.ToolPtr->OutputLanguage();
+        const char** InLangs = N2.ToolPtr->InputLanguages();
+        bool eq = false;
+        for (;*InLangs; ++InLangs) {
+          if (std::strcmp(OutLang, *InLangs) == 0) {
+            eq = true;
+            break;
+          }
+        }
+
+        if (!eq) {
+          ++ret;
+          std::cerr << "Error: Output->input language mismatch in the edge '" <<
+            N1.ToolPtr->Name() << "' -> '" << N2.ToolPtr->Name() << "'!\n";
+
+          std::cerr << "Expected one of { ";
+
+          InLangs = N2.ToolPtr->InputLanguages();
+          for (;*InLangs; ++InLangs) {
+            std::cerr << '\'' << *InLangs << (*(InLangs+1) ? "', " : "'");
+          }
+
+          std::cerr << " }, but got '" << OutLang << "'!\n\n";
+        }
+
+      }
+    }
+  }
+
+  return ret;
+}
+
+int CompilationGraph::CheckMultipleDefaultEdges() const {
+  int ret = 0;
+  InputLanguagesSet Dummy;
+
+  // For all nodes, just iterate over the outgoing edges and check if there is
+  // more than one edge with maximum weight.
+  for (const_nodes_iterator B = this->NodesMap.begin(),
+         E = this->NodesMap.end(); B != E; ++B) {
+    const Node& N = B->second;
+    unsigned MaxWeight = 0;
+
+    // Ignore the root node.
+    if (!N.ToolPtr)
+      continue;
+
+    for (Node::const_iterator EB = N.EdgesBegin(), EE = N.EdgesEnd();
+         EB != EE; ++EB) {
+      unsigned EdgeWeight = (*EB)->Weight(Dummy);
+      if (EdgeWeight > MaxWeight) {
+        MaxWeight = EdgeWeight;
+      }
+      else if (EdgeWeight == MaxWeight) {
+        ++ret;
+        std::cerr
+          << "Error: there are multiple maximal edges stemming from the '"
+          << N.ToolPtr->Name() << "' node!\n\n";
+        break;
+      }
+    }
+  }
+
+  return ret;
+}
+
+int CompilationGraph::CheckCycles() {
+  unsigned deleted = 0;
+  std::queue<Node*> Q;
+  Q.push(&getNode("root"));
+
+  // Try to delete all nodes that have no ingoing edges, starting from the
+  // root. If there are any nodes left after this operation, then we have a
+  // cycle. This relies on '--check-graph' not performing the topological sort.
+  while (!Q.empty()) {
+    Node* A = Q.front();
+    Q.pop();
+    ++deleted;
+
+    for (Node::iterator EB = A->EdgesBegin(), EE = A->EdgesEnd();
+         EB != EE; ++EB) {
+      Node* B = &getNode((*EB)->ToolName());
+      B->DecrInEdges();
+      if (B->HasNoInEdges())
+        Q.push(B);
+    }
+  }
+
+  if (deleted != NodesMap.size()) {
+    std::cerr << "Error: there are cycles in the compilation graph!\n"
+              << "Try inspecting the diagram produced by "
+      "'llvmc --view-graph'.\n\n";
+    return 1;
+  }
+
+  return 0;
+}
+
+int CompilationGraph::Check () {
+  // We try to catch as many errors as we can in one go.
+  int ret = 0;
+
+  // Check that output/input language names match.
+  ret += this->CheckLanguageNames();
+
+  // Check for multiple default edges.
+  ret += this->CheckMultipleDefaultEdges();
+
+  // Check for cycles.
+  ret += this->CheckCycles();
+
+  return ret;
+}
+
+// Code related to graph visualization.
+
+namespace llvm {
+  template <>
+  struct DOTGraphTraits<llvmc::CompilationGraph*>
+    : public DefaultDOTGraphTraits
+  {
+
+    template<typename GraphType>
+    static std::string getNodeLabel(const Node* N, const GraphType&)
+    {
+      if (N->ToolPtr)
+        if (N->ToolPtr->IsJoin())
+          return N->Name() + "\n (join" +
+            (N->HasChildren() ? ")"
+             : std::string(": ") + N->ToolPtr->OutputLanguage() + ')');
+        else
+          return N->Name();
+      else
+        return "root";
+    }
+
+    template<typename EdgeIter>
+    static std::string getEdgeSourceLabel(const Node* N, EdgeIter I) {
+      if (N->ToolPtr) {
+        return N->ToolPtr->OutputLanguage();
+      }
+      else {
+        const char** InLangs = I->ToolPtr->InputLanguages();
+        std::string ret;
+
+        for (; *InLangs; ++InLangs) {
+          if (*(InLangs + 1)) {
+            ret += *InLangs;
+            ret +=  ", ";
+          }
+          else {
+            ret += *InLangs;
+          }
+        }
+
+        return ret;
+      }
+    }
+  };
+
+}
+
+void CompilationGraph::writeGraph() {
+  std::ofstream O("compilation-graph.dot");
+
+  if (O.good()) {
+    llvm::WriteGraph(this, "compilation-graph");
+    O.close();
+  }
+  else {
+    throw std::runtime_error("Error opening file 'compilation-graph.dot'"
+                             " for writing!");
+  }
+}
+
+void CompilationGraph::viewGraph() {
+  llvm::ViewGraph(this, "compilation-graph");
+}