lib/CompilerDriver/CompilationGraph.cpp - fp2-dev/platform/external/llvm - Gitiles

 //===--- 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&,
                                     bool ShortNames)
     {
       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(const std::string& OutputFilename) {
   std::ofstream O(OutputFilename.c_str());

   if (O.good()) {
     std::cerr << "Writing '"<< OutputFilename << "' file...";
     llvm::WriteGraph(O, this);
     std::cerr << "done.\n";
     O.close();
   }
   else {
     throw std::runtime_error("Error opening file '" + OutputFilename
                              + "' for writing!");
   }
 }

 void CompilationGraph::viewGraph() {
   llvm::ViewGraph(this, "compilation-graph");
 }
	//===--- 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&,
	bool ShortNames)
	{
	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(const std::string& OutputFilename) {
	std::ofstream O(OutputFilename.c_str());

	if (O.good()) {
	std::cerr << "Writing '"<< OutputFilename << "' file...";
	llvm::WriteGraph(O, this);
	std::cerr << "done.\n";
	O.close();
	}
	else {
	throw std::runtime_error("Error opening file '" + OutputFilename
	+ "' for writing!");
	}
	}

	void CompilationGraph::viewGraph() {
	llvm::ViewGraph(this, "compilation-graph");
	}