diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 45462da..438ba03 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1311,7 +1311,7 @@
 void AsmPrinter::processDebugLoc(DebugLoc DL) {
   if (TAI->doesSupportDebugInformation() && DW->ShouldEmitDwarfDebug()) {
     if (!DL.isUnknown()) {
-      static DebugLocTuple PrevDLT(0, ~0U, ~0U);
+      static DebugLocTuple PrevDLT(0, DebugScope::getInvalid(), ~0U, ~0U);
       DebugLocTuple CurDLT = MF->getDebugLocTuple(DL);
 
       if (CurDLT.CompileUnit != 0 && PrevDLT != CurDLT)
diff --git a/lib/CodeGen/DebugLoc.cpp b/lib/CodeGen/DebugLoc.cpp
new file mode 100644
index 0000000..bc1a5b1
--- /dev/null
+++ b/lib/CodeGen/DebugLoc.cpp
@@ -0,0 +1,38 @@
+//===-- DebugLoc.cpp ------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Implementation for DebugScopeTracker.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/DebugLoc.h"
+#include "llvm/CodeGen/MachineFunction.h"
+using namespace llvm;
+
+/// EnterDebugScope - Start a new debug scope. ScopeGV can be a DISubprogram
+/// or a DIBlock.
+void DebugScopeTracker::EnterDebugScope(GlobalVariable *ScopeGV,
+                                        MachineFunction &MF) {
+  assert(ScopeGV && "GlobalVariable for scope is null!");
+  CurScope = MF.CreateDebugScope(ScopeGV, CurScope);
+}
+
+/// ExitDebugScope - "Pop" a DISubprogram or a DIBlock.
+void DebugScopeTracker::ExitDebugScope(GlobalVariable *ScopeGV,
+                                       MachineFunction &MF) {
+  assert(ScopeGV && "GlobalVariable for scope is null!");
+  assert(!CurScope.isInvalid() && "Mismatched region.end ?");
+  // We may have skipped a region.end because it was in an unreachable block.
+  // Go up the scope chain until we reach the scope that ScopeGV points to.
+  DebugScopeInfo DSI;
+  do {
+    DSI =  MF.getDebugScopeInfo(CurScope);
+    CurScope = DSI.Parent;
+  } while (!DSI.Parent.isInvalid() && DSI.GV != ScopeGV);
+}
diff --git a/lib/CodeGen/MachineFunction.cpp b/lib/CodeGen/MachineFunction.cpp
index cacfed1..d1d782c 100644
--- a/lib/CodeGen/MachineFunction.cpp
+++ b/lib/CodeGen/MachineFunction.cpp
@@ -403,8 +403,9 @@
 /// source file, line, and column. If none currently exists, create a new
 /// DebugLocTuple, and insert it into the DebugIdMap.
 unsigned MachineFunction::getOrCreateDebugLocID(GlobalVariable *CompileUnit,
+                                                DebugScope Scope,
                                                 unsigned Line, unsigned Col) {
-  DebugLocTuple Tuple(CompileUnit, Line, Col);
+  DebugLocTuple Tuple(CompileUnit, Scope, Line, Col);
   DenseMap<DebugLocTuple, unsigned>::iterator II
     = DebugLocInfo.DebugIdMap.find(Tuple);
   if (II != DebugLocInfo.DebugIdMap.end())
@@ -424,6 +425,21 @@
   return DebugLocInfo.DebugLocations[Idx];
 }
 
+/// CreateDebugScope - Create a new debug scope.
+DebugScope MachineFunction::CreateDebugScope(GlobalVariable *ScopeGV,
+                                             DebugScope Parent) {
+  DbgScopeInfos.push_back(DebugScopeInfo(ScopeGV, Parent));
+  return DebugScope::get(DbgScopeInfos.size() - 1);
+}
+
+/// getDebugScopeInfo - Get the DebugScopeInfo for a given DebugScope object.
+const DebugScopeInfo &MachineFunction::getDebugScopeInfo(DebugScope DS) const {
+  unsigned Idx = DS.getIndex();
+  assert(Idx < DbgScopeInfos.size() && "Invalid index into debug scopes!");
+  return DbgScopeInfos[Idx];
+}
+
+
 //===----------------------------------------------------------------------===//
 //  MachineFrameInfo implementation
 //===----------------------------------------------------------------------===//
diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index 367cf4c..1c05b0a 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -331,17 +331,22 @@
       DICompileUnit CU(cast<GlobalVariable>(SPI->getContext()));
       unsigned Line = SPI->getLine();
       unsigned Col = SPI->getColumn();
-      unsigned Idx = MF.getOrCreateDebugLocID(CU.getGV(), Line, Col);
+      unsigned Idx = MF.getOrCreateDebugLocID(CU.getGV(),
+                                              DbgScopeTrack.getCurScope(),
+                                              Line, Col);
       setCurDebugLoc(DebugLoc::get(Idx));
     }
     return true;
   }
   case Intrinsic::dbg_region_start: {
     DbgRegionStartInst *RSI = cast<DbgRegionStartInst>(I);
-    if (DIDescriptor::ValidDebugInfo(RSI->getContext(), CodeGenOpt::None) &&
-        DW && DW->ShouldEmitDwarfDebug()) {
-      unsigned ID = 
-        DW->RecordRegionStart(cast<GlobalVariable>(RSI->getContext()));
+    if (!DIDescriptor::ValidDebugInfo(RSI->getContext(), CodeGenOpt::None))
+      return true;
+
+    GlobalVariable *Rgn = cast<GlobalVariable>(RSI->getContext());
+    DbgScopeTrack.EnterDebugScope(Rgn, MF);
+    if (DW && DW->ShouldEmitDwarfDebug()) {
+      unsigned ID = DW->RecordRegionStart(Rgn);
       const TargetInstrDesc &II = TII.get(TargetInstrInfo::DBG_LABEL);
       BuildMI(MBB, DL, II).addImm(ID);
     }
@@ -349,10 +354,14 @@
   }
   case Intrinsic::dbg_region_end: {
     DbgRegionEndInst *REI = cast<DbgRegionEndInst>(I);
-    if (DIDescriptor::ValidDebugInfo(REI->getContext(), CodeGenOpt::None) &&
-        DW && DW->ShouldEmitDwarfDebug()) {
+    if (!DIDescriptor::ValidDebugInfo(REI->getContext(), CodeGenOpt::None))
+      return true;
+
+    GlobalVariable *Rgn = cast<GlobalVariable>(REI->getContext());
+    DbgScopeTrack.ExitDebugScope(Rgn, MF);
+    if (DW && DW->ShouldEmitDwarfDebug()) {
      unsigned ID = 0;
-     DISubprogram Subprogram(cast<GlobalVariable>(REI->getContext()));
+     DISubprogram Subprogram(Rgn);
      if (!Subprogram.isNull() && !Subprogram.describes(MF.getFunction())) {
         // This is end of an inlined function.
         const TargetInstrDesc &II = TII.get(TargetInstrInfo::DBG_LABEL);
@@ -382,6 +391,7 @@
     DebugLoc PrevLoc = DL;
     DISubprogram Subprogram(cast<GlobalVariable>(SP));
     DICompileUnit CompileUnit = Subprogram.getCompileUnit();
+    DbgScopeTrack.EnterDebugScope(Subprogram.getGV(), MF);
 
     if (!Subprogram.describes(MF.getFunction())) {
       // This is a beginning of an inlined function.
@@ -393,8 +403,10 @@
         return true;
       // Record the source line.
       unsigned Line = Subprogram.getLineNumber();
-      setCurDebugLoc(DebugLoc::get(MF.getOrCreateDebugLocID(
-                                              CompileUnit.getGV(), Line, 0)));
+      setCurDebugLoc(
+        DebugLoc::get(MF.getOrCreateDebugLocID(CompileUnit.getGV(),
+                                               DbgScopeTrack.getCurScope(),
+                                               Line, 0)));
 
       if (DW && DW->ShouldEmitDwarfDebug()) {
         DebugLocTuple PrevLocTpl = MF.getDebugLocTuple(PrevLoc);
@@ -408,8 +420,10 @@
     } else {
       // Record the source line.
       unsigned Line = Subprogram.getLineNumber();
-      MF.setDefaultDebugLoc(DebugLoc::get(MF.getOrCreateDebugLocID(
-                                              CompileUnit.getGV(), Line, 0)));
+      MF.setDefaultDebugLoc(
+        DebugLoc::get(MF.getOrCreateDebugLocID(CompileUnit.getGV(),
+                                               DbgScopeTrack.getCurScope(),
+                                               Line, 0)));
       if (DW && DW->ShouldEmitDwarfDebug()) {
         // llvm.dbg.func_start also defines beginning of function scope.
         DW->RecordRegionStart(cast<GlobalVariable>(FSI->getSubprogram()));
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
index 430dcfd..f0b1ec8 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuild.cpp
@@ -312,6 +312,17 @@
             !StaticAllocaMap.count(cast<AllocaInst>(I)))
           InitializeRegForValue(I);
 
+  // FIXME: PHI instructions currently get an invalid scope. This is because
+  // tracking of debug scopes is done through a simple mechanism where
+  // "entering" a scope implies that the scope is entered for the first time.
+  // If we keep track of debug scopes for the following loop, the PHI
+  // instructions would get scopes that will not be used again later by the
+  // instruction selectors.
+  // Either provide a mechanism to re-enter a previously created scope or wait
+  // for when the DebugLoc is retrieved from Instruction, in which case the
+  // current debug scope tracking mechanism will be obsolete.
+  DebugScope DbgScope;
+
   // Create an initial MachineBasicBlock for each LLVM BasicBlock in F.  This
   // also creates the initial PHI MachineInstrs, though none of the input
   // operands are populated.
@@ -337,6 +348,7 @@
                                              CodeGenOpt::Default)) {
               DICompileUnit CU(cast<GlobalVariable>(SPI->getContext()));
               unsigned idx = MF->getOrCreateDebugLocID(CU.getGV(),
+                                                       DbgScope,
                                                        SPI->getLine(),
                                                        SPI->getColumn());
               DL = DebugLoc::get(idx);
@@ -352,7 +364,7 @@
               DISubprogram Subprogram(cast<GlobalVariable>(SP));
               DICompileUnit CU(Subprogram.getCompileUnit());
               unsigned Line = Subprogram.getLineNumber();
-              DL = DebugLoc::get(MF->getOrCreateDebugLocID(CU.getGV(),
+              DL = DebugLoc::get(MF->getOrCreateDebugLocID(CU.getGV(), DbgScope,
                                                            Line, 0));
             }
 
@@ -3909,7 +3921,9 @@
       MachineFunction &MF = DAG.getMachineFunction();
       DICompileUnit CU(cast<GlobalVariable>(SPI.getContext()));
       DebugLoc Loc = DebugLoc::get(MF.getOrCreateDebugLocID(CU.getGV(),
-                                              SPI.getLine(), SPI.getColumn()));
+                                                 DbgScopeTrack.getCurScope(),
+                                                           SPI.getLine(),
+                                                           SPI.getColumn()));
       setCurDebugLoc(Loc);
       
       if (OptLevel == CodeGenOpt::None)
@@ -3923,11 +3937,14 @@
   case Intrinsic::dbg_region_start: {
     DwarfWriter *DW = DAG.getDwarfWriter();
     DbgRegionStartInst &RSI = cast<DbgRegionStartInst>(I);
+    if (!DIDescriptor::ValidDebugInfo(RSI.getContext(), OptLevel))
+      return 0;
 
-    if (DIDescriptor::ValidDebugInfo(RSI.getContext(), OptLevel) &&
-        DW && DW->ShouldEmitDwarfDebug()) {
-      unsigned LabelID =
-        DW->RecordRegionStart(cast<GlobalVariable>(RSI.getContext()));
+    MachineFunction &MF = DAG.getMachineFunction();
+    GlobalVariable *Rgn = cast<GlobalVariable>(RSI.getContext());
+    DbgScopeTrack.EnterDebugScope(Rgn, MF);
+    if (DW && DW->ShouldEmitDwarfDebug()) {
+      unsigned LabelID = DW->RecordRegionStart(Rgn);
       DAG.setRoot(DAG.getLabel(ISD::DBG_LABEL, getCurDebugLoc(),
                                getRoot(), LabelID));
     }
@@ -3937,11 +3954,14 @@
   case Intrinsic::dbg_region_end: {
     DwarfWriter *DW = DAG.getDwarfWriter();
     DbgRegionEndInst &REI = cast<DbgRegionEndInst>(I);
+    if (!DIDescriptor::ValidDebugInfo(REI.getContext(), OptLevel))
+      return 0;
 
-    if (DIDescriptor::ValidDebugInfo(REI.getContext(), OptLevel) &&
-        DW && DW->ShouldEmitDwarfDebug()) {
-      MachineFunction &MF = DAG.getMachineFunction();
-      DISubprogram Subprogram(cast<GlobalVariable>(REI.getContext()));
+    MachineFunction &MF = DAG.getMachineFunction();
+    GlobalVariable *Rgn = cast<GlobalVariable>(REI.getContext());
+    DbgScopeTrack.ExitDebugScope(Rgn, MF);
+    if (DW && DW->ShouldEmitDwarfDebug()) {
+      DISubprogram Subprogram(Rgn);
 
       if (Subprogram.isNull() || Subprogram.describes(MF.getFunction())) {
         unsigned LabelID =
@@ -3974,6 +3994,7 @@
       return 0;
 
     MachineFunction &MF = DAG.getMachineFunction();
+    DbgScopeTrack.EnterDebugScope(cast<GlobalVariable>(SP), MF);
     if (OptLevel == CodeGenOpt::None) {
       // llvm.dbg.func.start implicitly defines a dbg_stoppoint which is what
       // (most?) gdb expects.
@@ -3993,7 +4014,9 @@
         // Record the source line.
         unsigned Line = Subprogram.getLineNumber();
         setCurDebugLoc(DebugLoc::get(
-                     MF.getOrCreateDebugLocID(CompileUnit.getGV(), Line, 0)));
+                     MF.getOrCreateDebugLocID(CompileUnit.getGV(),
+                                              DbgScopeTrack.getCurScope(),
+                                              Line, 0)));
 
         if (DW && DW->ShouldEmitDwarfDebug()) {
           DebugLocTuple PrevLocTpl = MF.getDebugLocTuple(PrevLoc);
@@ -4008,7 +4031,9 @@
         // Record the source line.
         unsigned Line = Subprogram.getLineNumber();
         MF.setDefaultDebugLoc(DebugLoc::get(
-                     MF.getOrCreateDebugLocID(CompileUnit.getGV(), Line, 0)));
+                     MF.getOrCreateDebugLocID(CompileUnit.getGV(),
+                                              DbgScopeTrack.getCurScope(),
+                                              Line, 0)));
         if (DW && DW->ShouldEmitDwarfDebug()) {
           // llvm.dbg.func_start also defines beginning of function scope.
           DW->RecordRegionStart(cast<GlobalVariable>(FSI.getSubprogram()));
@@ -4035,7 +4060,9 @@
       // create a label if this is a beginning of inlined function.
       unsigned Line = Subprogram.getLineNumber();
       setCurDebugLoc(DebugLoc::get(
-                     MF.getOrCreateDebugLocID(CompileUnit.getGV(), Line, 0)));
+                     MF.getOrCreateDebugLocID(CompileUnit.getGV(),
+                                              DbgScopeTrack.getCurScope(),
+                                              Line, 0)));
       // FIXME -  Start new region because llvm.dbg.func_start also defines
       // beginning of function scope.
     }
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuild.h b/lib/CodeGen/SelectionDAG/SelectionDAGBuild.h
index 578aa591..0c9b317 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuild.h
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuild.h
@@ -169,6 +169,8 @@
   /// CurDebugLoc - current file + line number.  Changes as we build the DAG.
   DebugLoc CurDebugLoc;
 
+  DebugScopeTracker DbgScopeTrack;
+
   DenseMap<const Value*, SDValue> NodeMap;
 
   /// PendingLoads - Loads are not emitted to the program immediately.  We bunch