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diff --git a/lib/CodeGen/LiveDebugValues.cpp b/lib/CodeGen/LiveDebugValues.cpp
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+//===------ LiveDebugValues.cpp - Tracking Debug Value MIs ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// This pass implements a data flow analysis that propagates debug location
+/// information by inserting additional DBG_VALUE instructions into the machine
+/// instruction stream. The pass internally builds debug location liveness
+/// ranges to determine the points where additional DBG_VALUEs need to be
+/// inserted.
+///
+/// This is a separate pass from DbgValueHistoryCalculator to facilitate
+/// testing and improve modularity.
+///
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
+#include <deque>
+#include <list>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "live-debug-values"
+
+STATISTIC(NumInserted, "Number of DBG_VALUE instructions inserted");
+
+namespace {
+
+class LiveDebugValues : public MachineFunctionPass {
+
+private:
+  const TargetRegisterInfo *TRI;
+  const TargetInstrInfo *TII;
+
+  typedef std::pair<const DILocalVariable *, const DILocation *>
+      InlinedVariable;
+
+  /// A potentially inlined instance of a variable.
+  struct DebugVariable {
+    const DILocalVariable *Var;
+    const DILocation *InlinedAt;
+
+    DebugVariable(const DILocalVariable *_var, const DILocation *_inlinedAt)
+        : Var(_var), InlinedAt(_inlinedAt) {}
+
+    bool operator==(const DebugVariable &DV) const {
+      return (Var == DV.Var) && (InlinedAt == DV.InlinedAt);
+    }
+  };
+
+  /// Member variables and functions for Range Extension across basic blocks.
+  struct VarLoc {
+    DebugVariable Var;
+    const MachineInstr *MI; // MachineInstr should be a DBG_VALUE instr.
+
+    VarLoc(DebugVariable _var, const MachineInstr *_mi) : Var(_var), MI(_mi) {}
+
+    bool operator==(const VarLoc &V) const;
+  };
+
+  typedef std::list<VarLoc> VarLocList;
+  typedef SmallDenseMap<const MachineBasicBlock *, VarLocList> VarLocInMBB;
+
+  bool OLChanged; // OutgoingLocs got changed for this bb.
+  bool MBBJoined; // The MBB was joined.
+
+  void transferDebugValue(MachineInstr &MI, VarLocList &OpenRanges);
+  void transferRegisterDef(MachineInstr &MI, VarLocList &OpenRanges);
+  void transferTerminatorInst(MachineInstr &MI, VarLocList &OpenRanges,
+                              VarLocInMBB &OutLocs);
+  void transfer(MachineInstr &MI, VarLocList &OpenRanges, VarLocInMBB &OutLocs);
+
+  void join(MachineBasicBlock &MBB, VarLocInMBB &OutLocs, VarLocInMBB &InLocs);
+
+  bool ExtendRanges(MachineFunction &MF);
+
+public:
+  static char ID;
+
+  /// Default construct and initialize the pass.
+  LiveDebugValues();
+
+  /// Tell the pass manager which passes we depend on and what
+  /// information we preserve.
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+
+  /// Print to ostream with a message.
+  void printVarLocInMBB(const VarLocInMBB &V, const char *msg,
+                        raw_ostream &Out) const;
+
+  /// Calculate the liveness information for the given machine function.
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+} // namespace
+
+//===----------------------------------------------------------------------===//
+//            Implementation
+//===----------------------------------------------------------------------===//
+
+char LiveDebugValues::ID = 0;
+char &llvm::LiveDebugValuesID = LiveDebugValues::ID;
+INITIALIZE_PASS(LiveDebugValues, "livedebugvalues", "Live DEBUG_VALUE analysis",
+                false, false)
+
+/// Default construct and initialize the pass.
+LiveDebugValues::LiveDebugValues() : MachineFunctionPass(ID) {
+  initializeLiveDebugValuesPass(*PassRegistry::getPassRegistry());
+}
+
+/// Tell the pass manager which passes we depend on and what information we
+/// preserve.
+void LiveDebugValues::getAnalysisUsage(AnalysisUsage &AU) const {
+  MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+// \brief If @MI is a DBG_VALUE with debug value described by a defined
+// register, returns the number of this register. In the other case, returns 0.
+static unsigned isDescribedByReg(const MachineInstr &MI) {
+  assert(MI.isDebugValue());
+  assert(MI.getNumOperands() == 4);
+  // If location of variable is described using a register (directly or
+  // indirecltly), this register is always a first operand.
+  return MI.getOperand(0).isReg() ? MI.getOperand(0).getReg() : 0;
+}
+
+// \brief This function takes two DBG_VALUE instructions and returns true
+// if their offsets are equal; otherwise returns false.
+static bool areOffsetsEqual(const MachineInstr &MI1, const MachineInstr &MI2) {
+  assert(MI1.isDebugValue());
+  assert(MI1.getNumOperands() == 4);
+
+  assert(MI2.isDebugValue());
+  assert(MI2.getNumOperands() == 4);
+
+  if (!MI1.isIndirectDebugValue() && !MI2.isIndirectDebugValue())
+    return true;
+
+  // Check if both MIs are indirect and they are equal.
+  if (MI1.isIndirectDebugValue() && MI2.isIndirectDebugValue())
+    return MI1.getOperand(1).getImm() == MI2.getOperand(1).getImm();
+
+  return false;
+}
+
+//===----------------------------------------------------------------------===//
+//            Debug Range Extension Implementation
+//===----------------------------------------------------------------------===//
+
+void LiveDebugValues::printVarLocInMBB(const VarLocInMBB &V, const char *msg,
+                                       raw_ostream &Out) const {
+  Out << "Printing " << msg << ":\n";
+  for (const auto &L : V) {
+    Out << "MBB: " << L.first->getName() << ":\n";
+    for (const auto &VLL : L.second) {
+      Out << " Var: " << VLL.Var.Var->getName();
+      Out << " MI: ";
+      (*VLL.MI).dump();
+      Out << "\n";
+    }
+  }
+  Out << "\n";
+}
+
+bool LiveDebugValues::VarLoc::operator==(const VarLoc &V) const {
+  return (Var == V.Var) && (isDescribedByReg(*MI) == isDescribedByReg(*V.MI)) &&
+         (areOffsetsEqual(*MI, *V.MI));
+}
+
+/// End all previous ranges related to @MI and start a new range from @MI
+/// if it is a DBG_VALUE instr.
+void LiveDebugValues::transferDebugValue(MachineInstr &MI,
+                                         VarLocList &OpenRanges) {
+  if (!MI.isDebugValue())
+    return;
+  const DILocalVariable *RawVar = MI.getDebugVariable();
+  assert(RawVar->isValidLocationForIntrinsic(MI.getDebugLoc()) &&
+         "Expected inlined-at fields to agree");
+  DebugVariable Var(RawVar, MI.getDebugLoc()->getInlinedAt());
+
+  // End all previous ranges of Var.
+  OpenRanges.erase(
+      std::remove_if(OpenRanges.begin(), OpenRanges.end(),
+                     [&](const VarLoc &V) { return (Var == V.Var); }),
+      OpenRanges.end());
+
+  // Add Var to OpenRanges from this DBG_VALUE.
+  // TODO: Currently handles DBG_VALUE which has only reg as location.
+  if (isDescribedByReg(MI)) {
+    VarLoc V(Var, &MI);
+    OpenRanges.push_back(std::move(V));
+  }
+}
+
+/// A definition of a register may mark the end of a range.
+void LiveDebugValues::transferRegisterDef(MachineInstr &MI,
+                                          VarLocList &OpenRanges) {
+  for (const MachineOperand &MO : MI.operands()) {
+    if (!(MO.isReg() && MO.isDef() && MO.getReg() &&
+          TRI->isPhysicalRegister(MO.getReg())))
+      continue;
+    // Remove ranges of all aliased registers.
+    for (MCRegAliasIterator RAI(MO.getReg(), TRI, true); RAI.isValid(); ++RAI)
+      OpenRanges.erase(std::remove_if(OpenRanges.begin(), OpenRanges.end(),
+                                      [&](const VarLoc &V) {
+                                        return (*RAI ==
+                                                isDescribedByReg(*V.MI));
+                                      }),
+                       OpenRanges.end());
+  }
+}
+
+/// Terminate all open ranges at the end of the current basic block.
+void LiveDebugValues::transferTerminatorInst(MachineInstr &MI,
+                                             VarLocList &OpenRanges,
+                                             VarLocInMBB &OutLocs) {
+  const MachineBasicBlock *CurMBB = MI.getParent();
+  if (!(MI.isTerminator() || (&MI == &CurMBB->instr_back())))
+    return;
+
+  if (OpenRanges.empty())
+    return;
+
+  if (OutLocs.find(CurMBB) == OutLocs.end()) {
+    // Create space for new Outgoing locs entries.
+    VarLocList VLL;
+    OutLocs.insert(std::make_pair(CurMBB, std::move(VLL)));
+  }
+  auto OL = OutLocs.find(CurMBB);
+  assert(OL != OutLocs.end());
+  VarLocList &VLL = OL->second;
+
+  for (auto OR : OpenRanges) {
+    // Copy OpenRanges to OutLocs, if not already present.
+    assert(OR.MI->isDebugValue());
+    DEBUG(dbgs() << "Add to OutLocs: "; OR.MI->dump(););
+    if (std::find_if(VLL.begin(), VLL.end(),
+                     [&](const VarLoc &V) { return (OR == V); }) == VLL.end()) {
+      VLL.push_back(std::move(OR));
+      OLChanged = true;
+    }
+  }
+  OpenRanges.clear();
+}
+
+/// This routine creates OpenRanges and OutLocs.
+void LiveDebugValues::transfer(MachineInstr &MI, VarLocList &OpenRanges,
+                               VarLocInMBB &OutLocs) {
+  transferDebugValue(MI, OpenRanges);
+  transferRegisterDef(MI, OpenRanges);
+  transferTerminatorInst(MI, OpenRanges, OutLocs);
+}
+
+/// This routine joins the analysis results of all incoming edges in @MBB by
+/// inserting a new DBG_VALUE instruction at the start of the @MBB - if the same
+/// source variable in all the predecessors of @MBB reside in the same location.
+void LiveDebugValues::join(MachineBasicBlock &MBB, VarLocInMBB &OutLocs,
+                           VarLocInMBB &InLocs) {
+  DEBUG(dbgs() << "join MBB: " << MBB.getName() << "\n");
+
+  MBBJoined = false;
+
+  VarLocList InLocsT; // Temporary incoming locations.
+
+  // For all predecessors of this MBB, find the set of VarLocs that can be
+  // joined.
+  for (auto p : MBB.predecessors()) {
+    auto OL = OutLocs.find(p);
+    // Join is null in case of empty OutLocs from any of the pred.
+    if (OL == OutLocs.end())
+      return;
+
+    // Just copy over the Out locs to incoming locs for the first predecessor.
+    if (p == *MBB.pred_begin()) {
+      InLocsT = OL->second;
+      continue;
+    }
+
+    // Join with this predecessor.
+    VarLocList &VLL = OL->second;
+    InLocsT.erase(std::remove_if(InLocsT.begin(), InLocsT.end(),
+                                 [&](VarLoc &ILT) {
+                                   return (std::find_if(VLL.begin(), VLL.end(),
+                                                        [&](const VarLoc &V) {
+                                                          return (ILT == V);
+                                                        }) == VLL.end());
+                                 }),
+                  InLocsT.end());
+  }
+
+  if (InLocsT.empty())
+    return;
+
+  if (InLocs.find(&MBB) == InLocs.end()) {
+    // Create space for new Incoming locs entries.
+    VarLocList VLL;
+    InLocs.insert(std::make_pair(&MBB, std::move(VLL)));
+  }
+  auto IL = InLocs.find(&MBB);
+  assert(IL != InLocs.end());
+  VarLocList &ILL = IL->second;
+
+  // Insert DBG_VALUE instructions, if not already inserted.
+  for (auto ILT : InLocsT) {
+    if (std::find_if(ILL.begin(), ILL.end(), [&](const VarLoc &I) {
+          return (ILT == I);
+        }) == ILL.end()) {
+      // This VarLoc is not found in InLocs i.e. it is not yet inserted. So, a
+      // new range is started for the var from the mbb's beginning by inserting
+      // a new DBG_VALUE. transfer() will end this range however appropriate.
+      const MachineInstr *DMI = ILT.MI;
+      MachineInstr *MI =
+          BuildMI(MBB, MBB.instr_begin(), DMI->getDebugLoc(), DMI->getDesc(),
+                  DMI->isIndirectDebugValue(), DMI->getOperand(0).getReg(), 0,
+                  DMI->getDebugVariable(), DMI->getDebugExpression());
+      if (DMI->isIndirectDebugValue())
+        MI->getOperand(1).setImm(DMI->getOperand(1).getImm());
+      DEBUG(dbgs() << "Inserted: "; MI->dump(););
+      ++NumInserted;
+      MBBJoined = true; // rerun transfer().
+
+      VarLoc V(ILT.Var, MI);
+      ILL.push_back(std::move(V));
+    }
+  }
+}
+
+/// Calculate the liveness information for the given machine function and
+/// extend ranges across basic blocks.
+bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
+
+  DEBUG(dbgs() << "\nDebug Range Extension\n");
+
+  bool Changed = false;
+  OLChanged = MBBJoined = false;
+
+  VarLocList OpenRanges; // Ranges that are open until end of bb.
+  VarLocInMBB OutLocs;   // Ranges that exist beyond bb.
+  VarLocInMBB InLocs;    // Ranges that are incoming after joining.
+
+  std::deque<MachineBasicBlock *> BBWorklist;
+
+  // Initialize every mbb with OutLocs.
+  for (auto &MBB : MF)
+    for (auto &MI : MBB)
+      transfer(MI, OpenRanges, OutLocs);
+  DEBUG(printVarLocInMBB(OutLocs, "OutLocs after initialization", dbgs()));
+
+  // Construct a worklist of MBBs.
+  for (auto &MBB : MF)
+    BBWorklist.push_back(&MBB);
+
+  // Perform join() and transfer() using the worklist until the ranges converge
+  // Ranges have converged when the worklist is empty.
+  while (!BBWorklist.empty()) {
+    MachineBasicBlock *MBB = BBWorklist.front();
+    BBWorklist.pop_front();
+
+    join(*MBB, OutLocs, InLocs);
+
+    if (MBBJoined) {
+      Changed = true;
+      for (auto &MI : *MBB)
+        transfer(MI, OpenRanges, OutLocs);
+      DEBUG(printVarLocInMBB(OutLocs, "OutLocs after propagating", dbgs()));
+      DEBUG(printVarLocInMBB(InLocs, "InLocs after propagating", dbgs()));
+
+      if (OLChanged) {
+        OLChanged = false;
+        for (auto s : MBB->successors())
+          if (std::find(BBWorklist.begin(), BBWorklist.end(), s) ==
+              BBWorklist.end()) // add if not already present.
+            BBWorklist.push_back(s);
+      }
+    }
+  }
+  DEBUG(printVarLocInMBB(OutLocs, "Final OutLocs", dbgs()));
+  DEBUG(printVarLocInMBB(InLocs, "Final InLocs", dbgs()));
+  return Changed;
+}
+
+bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
+  TRI = MF.getSubtarget().getRegisterInfo();
+  TII = MF.getSubtarget().getInstrInfo();
+
+  bool Changed = false;
+
+  Changed |= ExtendRanges(MF);
+
+  return Changed;
+}