diff --git a/include/llvm/CodeGen/LexicalScopes.h b/include/llvm/CodeGen/LexicalScopes.h
new file mode 100644
index 0000000..554ae8a
--- /dev/null
+++ b/include/llvm/CodeGen/LexicalScopes.h
@@ -0,0 +1,247 @@
+//===- LexicalScopes.cpp - Collecting lexical scope info -*- C++ -*--------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements LexicalScopes analysis.
+//
+// This pass collects lexical scope information and maps machine instructions
+// to respective lexical scopes.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_LEXICALSCOPES_H
+#define LLVM_CODEGEN_LEXICALSCOPES_H
+
+#include "llvm/Metadata.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/DebugLoc.h"
+#include "llvm/Support/ValueHandle.h"
+#include <utility>
+namespace llvm {
+
+class MachineInstr;
+class MachineBasicBlock;
+class MachineFunction;
+class LexicalScope;
+
+//===----------------------------------------------------------------------===//
+/// InsnRange - This is used to track range of instructions with identical
+/// lexical scope.
+///
+typedef std::pair<const MachineInstr *, const MachineInstr *> InsnRange;
+
+//===----------------------------------------------------------------------===//
+/// LexicalScopes -  This class provides interface to collect and use lexical
+/// scoping information from machine instruction.
+///
+class LexicalScopes {
+public:
+  LexicalScopes() : MF(NULL),  CurrentFnLexicalScope(NULL) { }
+  ~LexicalScopes();
+
+  /// initialize - Scan machine function and constuct lexical scope nest.
+  virtual void initialize(const MachineFunction &);
+
+  /// releaseMemory - release memory.
+  virtual void releaseMemory();
+  
+  /// empty - Return true if there is any lexical scope information available.
+  bool empty() { return CurrentFnLexicalScope == NULL; }
+
+  /// isCurrentFunctionScope - Return true if given lexical scope represents 
+  /// current function.
+  bool isCurrentFunctionScope(const LexicalScope *LS) { 
+    return LS == CurrentFnLexicalScope;
+  }
+
+  /// getCurrentFunctionScope - Return lexical scope for the current function.
+  LexicalScope *getCurrentFunctionScope() const { return CurrentFnLexicalScope;}
+
+  /// getMachineBasicBlocks - Populate given set using machine basic blocks which
+  /// have machine instructions that belong to lexical scope identified by 
+  /// DebugLoc.
+  void getMachineBasicBlocks(DebugLoc DL,
+                             SmallPtrSet<const MachineBasicBlock*, 4> &MBBs);
+
+  /// dominates - Return true if DebugLoc's lexical scope dominates at least one
+  /// machine instruction's lexical scope in a given machine basic block.
+  bool dominates(DebugLoc DL, MachineBasicBlock *MBB);
+
+  /// findLexicalScope - Find lexical scope, either regular or inlined, for the
+  /// given DebugLoc. Return NULL if not found.
+  LexicalScope *findLexicalScope(DebugLoc DL);
+
+  /// getAbstractScopesList - Return a reference to list of abstract scopes.
+  SmallVector<LexicalScope *, 4> &getAbstractScopesList() {
+    return AbstractScopesList;
+  }
+
+  /// findAbstractScope - Find an abstract scope or return NULL.
+  LexicalScope *findAbstractScope(const MDNode *N) {
+    return AbstractScopeMap.lookup(N);
+  }
+
+  /// findInlinedScope - Find an inlined scope for the given DebugLoc or return
+  /// NULL.
+  LexicalScope *findInlinedScope(DebugLoc DL) {
+    return InlinedLexicalScopeMap.lookup(DL);
+  }
+
+  /// findLexicalScope - Find regular lexical scope or return NULL.
+  LexicalScope *findLexicalScope(const MDNode *N) {
+    return LexicalScopeMap.lookup(N);
+  }
+
+  /// dump - Print data structures to dbgs().
+  void dump();
+
+private:
+
+  /// getOrCreateLexicalScope - Find lexical scope for the given DebugLoc. If
+  /// not available then create new lexical scope.
+  LexicalScope *getOrCreateLexicalScope(DebugLoc DL);
+
+  /// getOrCreateRegularScope - Find or create a regular lexical scope.
+  LexicalScope *getOrCreateRegularScope(MDNode *Scope);
+
+  /// getOrCreateInlinedScope - Find or create an inlined lexical scope.
+  LexicalScope *getOrCreateInlinedScope(MDNode *Scope, MDNode *InlinedAt);
+
+  /// getOrCreateAbstractScope - Find or create an abstract lexical scope.
+  LexicalScope *getOrCreateAbstractScope(const MDNode *N);
+
+  /// extractLexicalScopes - Extract instruction ranges for each lexical scopes
+  /// for the given machine function.
+  void extractLexicalScopes(SmallVectorImpl<InsnRange> &MIRanges,
+                            DenseMap<const MachineInstr *, LexicalScope *> &M);
+  void constructScopeNest(LexicalScope *Scope);
+  void assignInstructionRanges(SmallVectorImpl<InsnRange> &MIRanges,
+                             DenseMap<const MachineInstr *, LexicalScope *> &M);
+
+private:
+  const MachineFunction *MF;
+
+  /// LexicalScopeMap - Tracks the scopes in the current function.  Owns the
+  /// contained LexicalScope*s.
+  DenseMap<const MDNode *, LexicalScope *> LexicalScopeMap;
+
+  /// InlinedLexicalScopeMap - Tracks inlined function scopes in current function.
+  DenseMap<DebugLoc, LexicalScope *> InlinedLexicalScopeMap;
+
+  /// AbstractScopeMap - These scopes are  not included LexicalScopeMap.  
+  /// AbstractScopes owns its LexicalScope*s.
+  DenseMap<const MDNode *, LexicalScope *> AbstractScopeMap;
+
+  /// AbstractScopesList - Tracks abstract scopes constructed while processing
+  /// a function. 
+  SmallVector<LexicalScope *, 4>AbstractScopesList;
+
+  /// CurrentFnLexicalScope - Top level scope for the current function.
+  ///
+  LexicalScope *CurrentFnLexicalScope;
+};
+
+//===----------------------------------------------------------------------===//
+/// LexicalScope - This class is used to track scope information.
+///
+class LexicalScope {
+
+public:
+  LexicalScope(LexicalScope *P, const MDNode *D, const MDNode *I, bool A)
+    : Parent(P), Desc(D), InlinedAtLocation(I), AbstractScope(A),
+      LastInsn(0), FirstInsn(0), DFSIn(0), DFSOut(0), IndentLevel(0) {
+    if (Parent)
+      Parent->addChild(this);
+  }
+
+  virtual ~LexicalScope() {}
+
+  // Accessors.
+  LexicalScope *getParent() const               { return Parent; }
+  const MDNode *getDesc() const                 { return Desc; }
+  const MDNode *getInlinedAt() const            { return InlinedAtLocation; }
+  const MDNode *getScopeNode() const            { return Desc; }
+  bool isAbstractScope() const                  { return AbstractScope; }
+  SmallVector<LexicalScope *, 4> &getChildren() { return Children; }
+  SmallVector<InsnRange, 4> &getRanges()        { return Ranges; }
+
+  /// addChild - Add a child scope.
+  void addChild(LexicalScope *S) { Children.push_back(S); }
+
+  /// openInsnRange - This scope covers instruction range starting from MI.
+  void openInsnRange(const MachineInstr *MI) {
+    if (!FirstInsn)
+      FirstInsn = MI;
+
+    if (Parent)
+      Parent->openInsnRange(MI);
+  }
+
+  /// extendInsnRange - Extend the current instruction range covered by
+  /// this scope.
+  void extendInsnRange(const MachineInstr *MI) {
+    assert (FirstInsn && "MI Range is not open!");
+    LastInsn = MI;
+    if (Parent)
+      Parent->extendInsnRange(MI);
+  }
+
+  /// closeInsnRange - Create a range based on FirstInsn and LastInsn collected
+  /// until now. This is used when a new scope is encountered while walking
+  /// machine instructions.
+  void closeInsnRange(LexicalScope *NewScope = NULL) {
+    assert (LastInsn && "Last insn missing!");
+    Ranges.push_back(InsnRange(FirstInsn, LastInsn));
+    FirstInsn = NULL;
+    LastInsn = NULL;
+    // If Parent dominates NewScope then do not close Parent's instruction
+    // range.
+    if (Parent && (!NewScope || !Parent->dominates(NewScope)))
+      Parent->closeInsnRange(NewScope);
+  }
+
+  /// dominates - Return true if current scope dominsates given lexical scope.
+  bool dominates(const LexicalScope *S) {
+    if (S == this)
+      return true;
+    if (DFSIn < S->getDFSIn() && DFSOut > S->getDFSOut())
+      return true;
+    return false;
+  }
+
+  // Depth First Search support to walk and manipulate LexicalScope hierarchy.
+  unsigned getDFSOut() const            { return DFSOut; }
+  void setDFSOut(unsigned O)            { DFSOut = O; }
+  unsigned getDFSIn() const             { return DFSIn; }
+  void setDFSIn(unsigned I)             { DFSIn = I; }
+
+  /// dump - print lexical scope.
+  void dump() const;
+
+private:
+  LexicalScope *Parent;                          // Parent to this scope.
+  AssertingVH<const MDNode> Desc;                // Debug info descriptor.
+  AssertingVH<const MDNode> InlinedAtLocation;   // Location at which this 
+                                                 // scope is inlined.
+  bool AbstractScope;                            // Abstract Scope
+  SmallVector<LexicalScope *, 4> Children;       // Scopes defined in scope.  
+                                                 // Contents not owned.
+  SmallVector<InsnRange, 4> Ranges;
+
+  const MachineInstr *LastInsn;       // Last instruction of this scope.
+  const MachineInstr *FirstInsn;      // First instruction of this scope.
+  unsigned DFSIn, DFSOut;             // In & Out Depth use to determine
+                                      // scope nesting.
+  mutable unsigned IndentLevel;       // Private state for dump()
+};
+
+} // end llvm namespace
+
+#endif
diff --git a/lib/CodeGen/CMakeLists.txt b/lib/CodeGen/CMakeLists.txt
index 9cbb25c..af0f7f5 100644
--- a/lib/CodeGen/CMakeLists.txt
+++ b/lib/CodeGen/CMakeLists.txt
@@ -23,6 +23,7 @@
   IntrinsicLowering.cpp
   LLVMTargetMachine.cpp
   LatencyPriorityQueue.cpp
+  LexicalScopes.cpp
   LiveDebugVariables.cpp
   LiveInterval.cpp
   LiveIntervalAnalysis.cpp
diff --git a/lib/CodeGen/LexicalScopes.cpp b/lib/CodeGen/LexicalScopes.cpp
new file mode 100644
index 0000000..2276004
--- /dev/null
+++ b/lib/CodeGen/LexicalScopes.cpp
@@ -0,0 +1,305 @@
+//===- LexicalScopes.cpp - Collecting lexical scope info ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements LexicalScopes analysis.
+//
+// This pass collects lexical scope information and maps machine instructions
+// to respective lexical scopes.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "lexicalscopes"
+#include "llvm/CodeGen/LexicalScopes.h"
+#include "llvm/Function.h"
+#include "llvm/Analysis/DebugInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FormattedStream.h"
+using namespace llvm;
+
+LexicalScopes::~LexicalScopes() {
+  releaseMemory();
+}
+
+/// releaseMemory - release memory.
+void LexicalScopes::releaseMemory() {
+  MF = NULL;
+  CurrentFnLexicalScope = NULL;
+  DeleteContainerSeconds(LexicalScopeMap);
+  DeleteContainerSeconds(AbstractScopeMap);
+  InlinedLexicalScopeMap.clear();
+  AbstractScopesList.clear();
+}
+
+/// initialize - Scan machine function and constuct lexical scope nest.
+void LexicalScopes::initialize(const MachineFunction &Fn) {
+  releaseMemory();
+  MF = &Fn;
+  SmallVector<InsnRange, 4> MIRanges;
+  DenseMap<const MachineInstr *, LexicalScope *> MI2ScopeMap;
+  extractLexicalScopes(MIRanges, MI2ScopeMap);
+  if (CurrentFnLexicalScope) {
+    constructScopeNest(CurrentFnLexicalScope);
+    assignInstructionRanges(MIRanges, MI2ScopeMap);
+  }
+}
+
+/// extractLexicalScopes - Extract instruction ranges for each lexical scopes
+/// for the given machine function.
+void LexicalScopes::
+extractLexicalScopes(SmallVectorImpl<InsnRange> &MIRanges,
+                  DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
+
+  // Scan each instruction and create scopes. First build working set of scopes.
+  for (MachineFunction::const_iterator I = MF->begin(), E = MF->end();
+       I != E; ++I) {
+    const MachineInstr *RangeBeginMI = NULL;
+    const MachineInstr *PrevMI = NULL;
+    DebugLoc PrevDL;
+    for (MachineBasicBlock::const_iterator II = I->begin(), IE = I->end();
+         II != IE; ++II) {
+      const MachineInstr *MInsn = II;
+
+      // Check if instruction has valid location information.
+      const DebugLoc MIDL = MInsn->getDebugLoc();
+      if (MIDL.isUnknown()) {
+        PrevMI = MInsn;
+        continue;
+      }
+
+      // If scope has not changed then skip this instruction.
+      if (MIDL == PrevDL) {
+        PrevMI = MInsn;
+        continue;
+      }
+
+      // Ignore DBG_VALUE. It does not contribute to any instruction in output.
+      if (MInsn->isDebugValue())
+        continue;
+
+      if (RangeBeginMI) {
+        // If we have already seen a beginning of an instruction range and
+        // current instruction scope does not match scope of first instruction
+        // in this range then create a new instruction range.
+        InsnRange R(RangeBeginMI, PrevMI);
+        MI2ScopeMap[RangeBeginMI] = getOrCreateLexicalScope(PrevDL);
+        MIRanges.push_back(R);
+      }
+
+      // This is a beginning of a new instruction range.
+      RangeBeginMI = MInsn;
+
+      // Reset previous markers.
+      PrevMI = MInsn;
+      PrevDL = MIDL;
+    }
+
+    // Create last instruction range.
+    if (RangeBeginMI && PrevMI && !PrevDL.isUnknown()) {
+      InsnRange R(RangeBeginMI, PrevMI);
+      MIRanges.push_back(R);
+      MI2ScopeMap[RangeBeginMI] = getOrCreateLexicalScope(PrevDL);
+    }
+  }
+}
+
+/// findLexicalScope - Find lexical scope, either regular or inlined, for the
+/// given DebugLoc. Return NULL if not found.
+LexicalScope *LexicalScopes::findLexicalScope(DebugLoc DL) {
+  MDNode *Scope = NULL;
+  MDNode *IA = NULL;
+  DL.getScopeAndInlinedAt(Scope, IA, MF->getFunction()->getContext());
+  if (!Scope) return NULL;
+  if (IA)
+    return InlinedLexicalScopeMap.lookup(DebugLoc::getFromDILocation(IA));
+  return LexicalScopeMap.lookup(DL.getScope(Scope->getContext()));
+}
+
+/// getOrCreateLexicalScope - Find lexical scope for the given DebugLoc. If
+/// not available then create new lexical scope.
+LexicalScope *LexicalScopes::getOrCreateLexicalScope(DebugLoc DL) {
+  MDNode *Scope = NULL;
+  MDNode *InlinedAt = NULL;
+  DL.getScopeAndInlinedAt(Scope, InlinedAt, MF->getFunction()->getContext());
+  if (InlinedAt) {
+    // Create an abstract scope for inlined function.
+    getOrCreateAbstractScope(Scope);
+    // Create an inlined scope for inlined function.
+    return getOrCreateInlinedScope(Scope, InlinedAt);
+  }
+   
+  return getOrCreateRegularScope(Scope);
+}
+
+/// getOrCreateRegularScope - Find or create a regular lexical scope.
+LexicalScope *LexicalScopes::getOrCreateRegularScope(MDNode *Scope) {
+  LexicalScope *WScope = LexicalScopeMap.lookup(Scope);
+  if (WScope)
+    return WScope;
+
+  LexicalScope *Parent = NULL;
+  if (DIDescriptor(Scope).isLexicalBlock())
+    Parent = getOrCreateLexicalScope(DebugLoc::getFromDILexicalBlock(Scope));
+  WScope = new LexicalScope(Parent, DIDescriptor(Scope), NULL, false);
+  LexicalScopeMap.insert(std::make_pair(Scope, WScope));
+  if (!Parent && DIDescriptor(Scope).isSubprogram()
+      && DISubprogram(Scope).describes(MF->getFunction()))
+    CurrentFnLexicalScope = WScope;
+  
+  return WScope;
+}
+
+/// getOrCreateInlinedScope - Find or create an inlined lexical scope.
+LexicalScope *LexicalScopes::getOrCreateInlinedScope(MDNode *Scope, 
+                                                     MDNode *InlinedAt) {
+  LexicalScope *InlinedScope = LexicalScopeMap.lookup(InlinedAt);
+  if (InlinedScope)
+    return InlinedScope;
+
+  DebugLoc InlinedLoc = DebugLoc::getFromDILocation(InlinedAt);
+  InlinedScope = new LexicalScope(getOrCreateLexicalScope(InlinedLoc),
+                                  DIDescriptor(Scope), InlinedAt, false);
+  InlinedLexicalScopeMap[InlinedLoc] = InlinedScope;
+  LexicalScopeMap[InlinedAt] = InlinedScope;
+  return InlinedScope;
+}
+
+/// getOrCreateAbstractScope - Find or create an abstract lexical scope.
+LexicalScope *LexicalScopes::getOrCreateAbstractScope(const MDNode *N) {
+  assert(N && "Invalid Scope encoding!");
+
+  LexicalScope *AScope = AbstractScopeMap.lookup(N);
+  if (AScope)
+    return AScope;
+
+  LexicalScope *Parent = NULL;
+  DIDescriptor Scope(N);
+  if (Scope.isLexicalBlock()) {
+    DILexicalBlock DB(N);
+    DIDescriptor ParentDesc = DB.getContext();
+    Parent = getOrCreateAbstractScope(ParentDesc);
+  }
+  AScope = new LexicalScope(Parent, DIDescriptor(N), NULL, true);
+  AbstractScopeMap[N] = AScope;
+  if (DIDescriptor(N).isSubprogram())
+    AbstractScopesList.push_back(AScope);
+  return AScope;
+}
+
+/// constructScopeNest
+void LexicalScopes::constructScopeNest(LexicalScope *Scope) {
+  assert (Scope && "Unable to calculate scop edominance graph!");
+  SmallVector<LexicalScope *, 4> WorkStack;
+  WorkStack.push_back(Scope);
+  unsigned Counter = 0;
+  while (!WorkStack.empty()) {
+    LexicalScope *WS = WorkStack.back();
+    const SmallVector<LexicalScope *, 4> &Children = WS->getChildren();
+    bool visitedChildren = false;
+    for (SmallVector<LexicalScope *, 4>::const_iterator SI = Children.begin(),
+           SE = Children.end(); SI != SE; ++SI) {
+      LexicalScope *ChildScope = *SI;
+      if (!ChildScope->getDFSOut()) {
+        WorkStack.push_back(ChildScope);
+        visitedChildren = true;
+        ChildScope->setDFSIn(++Counter);
+        break;
+      }
+    }
+    if (!visitedChildren) {
+      WorkStack.pop_back();
+      WS->setDFSOut(++Counter);
+    }
+  }
+}
+
+/// assignInstructionRanges - Find ranges of instructions covered by each lexical 
+/// scope.
+void LexicalScopes::
+assignInstructionRanges(SmallVectorImpl<InsnRange> &MIRanges,
+                    DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
+  
+  LexicalScope *PrevLexicalScope = NULL;
+  for (SmallVectorImpl<InsnRange>::const_iterator RI = MIRanges.begin(),
+         RE = MIRanges.end(); RI != RE; ++RI) {
+    const InsnRange &R = *RI;
+    LexicalScope *S = MI2ScopeMap.lookup(R.first);
+    assert (S && "Lost LexicalScope for a machine instruction!");
+    if (PrevLexicalScope && !PrevLexicalScope->dominates(S))
+      PrevLexicalScope->closeInsnRange(S);
+    S->openInsnRange(R.first);
+    S->extendInsnRange(R.second);
+    PrevLexicalScope = S;
+  }
+
+  if (PrevLexicalScope)
+    PrevLexicalScope->closeInsnRange();
+}
+
+/// getMachineBasicBlocks - Populate given set using machine basic blocks which
+/// have machine instructions that belong to lexical scope identified by 
+/// DebugLoc.
+void LexicalScopes::
+getMachineBasicBlocks(DebugLoc DL, SmallPtrSet<const MachineBasicBlock*, 4> &MBBs) {
+  MBBs.clear();
+  LexicalScope *Scope = getOrCreateLexicalScope(DL);
+  if (!Scope)
+    return;
+  
+  SmallVector<InsnRange, 4> &InsnRanges = Scope->getRanges();
+  for (SmallVector<InsnRange, 4>::iterator I = InsnRanges.begin(),
+         E = InsnRanges.end(); I != E; ++I) {
+    InsnRange &R = *I;
+    MBBs.insert(R.first->getParent());
+  }
+}
+
+/// dominates - Return true if DebugLoc's lexical scope dominates at least one
+/// machine instruction's lexical scope in a given machine basic block.
+bool LexicalScopes::dominates(DebugLoc DL, MachineBasicBlock *MBB) {
+  LexicalScope *Scope = getOrCreateLexicalScope(DL);
+  if (!Scope)
+    return false;
+  bool Result = false;
+  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
+       I != E; ++I) {
+    DebugLoc IDL = I->getDebugLoc();
+    if (IDL.isUnknown())
+      continue;
+    if (LexicalScope *IScope = getOrCreateLexicalScope(IDL))
+      if (Scope->dominates(IScope))
+        return true;
+  }
+  return Result;
+}
+
+/// dump - Print data structures.
+void LexicalScope::dump() const {
+#ifndef NDEBUG
+  raw_ostream &err = dbgs();
+  err.indent(IndentLevel);
+  err << "DFSIn: " << DFSIn << " DFSOut: " << DFSOut << "\n";
+  const MDNode *N = Desc;
+  N->dump();
+  if (AbstractScope)
+    err << "Abstract Scope\n";
+
+  IndentLevel += 2;
+  if (!Children.empty())
+    err << "Children ...\n";
+  for (unsigned i = 0, e = Children.size(); i != e; ++i)
+    if (Children[i] != this)
+      Children[i]->dump();
+
+  IndentLevel -= 2;
+#endif
+}
+