Reapply "[DebugInfo] Add new instruction and DIExpression operator for variadic debug values"

Rewrites test to use correct architecture triple; fixes incorrect reference in SourceLevelDebugging doc; simplifies `spillReg` behaviour so as to not be dependent on changes elsewhere in the patch stack. This reverts commit d2000b45d033c06dc7973f59909a0ad12887ff51.
2024-11-22 02:33:06 +01:00 · 2021-03-04 12:02:28 +00:00 · 2021-03-04 12:02:28 +00:00 · e0cb677eb6
commit e0cb677eb6
parent 4a1dabde23
23 changed files with 467 additions and 139 deletions
--- a/docs/LangRef.rst
+++ b/docs/LangRef.rst
@ -5324,6 +5324,14 @@ The current supported opcode vocabulary is limited:
  ``AsmPrinter`` pass when a call site parameter value
  (``DW_AT_call_site_parameter_value``) is represented as entry value
  of the parameter.
+- ``DW_OP_LLVM_arg, N`` is used in debug intrinsics that refer to more than one
+  value, such as one that calculates the sum of two registers. This is always
+  used in combination with an ordered list of values, such that
+  ``DW_OP_LLVM_arg, N`` refers to the ``N``th element in that list. For
+  example, ``!DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_minus,
+  DW_OP_stack_value)`` used with the list ``(%reg1, %reg2)`` would evaluate to
+  ``%reg1 - reg2``. This list of values should be provided by the containing
+  intrinsic/instruction.
 - ``DW_OP_breg`` (or ``DW_OP_bregx``) represents a content on the provided
  signed offset of the specified register. The opcode is only generated by the
  ``AsmPrinter`` pass to describe call site parameter value which requires an
--- a/docs/SourceLevelDebugging.rst
+++ b/docs/SourceLevelDebugging.rst
@ -576,13 +576,15 @@ the equivalent location is used.

 After MIR locations are assigned to each variable, machine pseudo-instructions
 corresponding to each ``llvm.dbg.value`` and ``llvm.dbg.addr`` intrinsic are
-inserted. These ``DBG_VALUE`` instructions appear thus:
+inserted. There are two forms of this type of instruction.
+
+The first form, ``DBG_VALUE``, appears thus:

 .. code-block:: text

  DBG_VALUE %1, $noreg, !123, !DIExpression()

-And have the following operands:
+And has the following operands:
 * The first operand can record the variable location as a register,
   a frame index, an immediate, or the base address register if the original
   debug intrinsic referred to memory. ``$noreg`` indicates the variable
@ -594,6 +596,22 @@ And have the following operands:
 * Operand 3 is the Variable field of the original debug intrinsic.
 * Operand 4 is the Expression field of the original debug intrinsic.

+The second form, ``DBG_VALUE_LIST``, appears thus:
+
+.. code-block:: text
+
+  DBG_VALUE_LIST !123, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus), %1, %2
+
+And has the following operands:
+ * The first operand is the Variable field of the original debug intrinsic.
+ * The second operand is the Expression field of the original debug intrinsic.
+ * Any number of operands, from the 3rd onwards, record a sequence of variable
+   location operands, which may take any of the same values as the first
+   operand of the ``DBG_VALUE`` instruction above. These variable location
+   operands are inserted into the final DWARF Expression in positions indicated
+   by the DW_OP_LLVM_arg operator in the `DIExpression
+   <LangRef.html#diexpression>`.
+
 The position at which the DBG_VALUEs are inserted should correspond to the
 positions of their matching ``llvm.dbg.value`` intrinsics in the IR block.  As
 with optimization, LLVM aims to preserve the order in which variable
--- a/include/llvm/BinaryFormat/Dwarf.h
+++ b/include/llvm/BinaryFormat/Dwarf.h
@ -144,6 +144,7 @@ enum LocationAtom {
  DW_OP_LLVM_tag_offset = 0x1002,       ///< Only used in LLVM metadata.
  DW_OP_LLVM_entry_value = 0x1003,      ///< Only used in LLVM metadata.
  DW_OP_LLVM_implicit_pointer = 0x1004, ///< Only used in LLVM metadata.
+  DW_OP_LLVM_arg = 0x1005,              ///< Only used in LLVM metadata.
 };

 enum TypeKind : uint8_t {
--- a/include/llvm/CodeGen/MachineInstr.h
+++ b/include/llvm/CodeGen/MachineInstr.h
@ -420,11 +420,11 @@ public:
  /// instruction is indirect; will be an invalid register if this value is
  /// not indirect, and an immediate with value 0 otherwise.
  const MachineOperand &getDebugOffset() const {
-    assert(isDebugValue() && "not a DBG_VALUE");
+    assert(isNonListDebugValue() && "not a DBG_VALUE");
    return getOperand(1);
  }
  MachineOperand &getDebugOffset() {
-    assert(isDebugValue() && "not a DBG_VALUE");
+    assert(isNonListDebugValue() && "not a DBG_VALUE");
    return getOperand(1);
  }

@ -439,6 +439,7 @@ public:

  /// Return the operand for the complex address expression referenced by
  /// this DBG_VALUE instruction.
+  const MachineOperand &getDebugExpressionOp() const;
  MachineOperand &getDebugExpressionOp();

  /// Return the complex address expression referenced by
@ -501,26 +502,43 @@ public:
    return *(debug_operands().begin() + Index);
  }

-  /// Returns a pointer to the operand corresponding to a debug use of Reg, or
-  /// nullptr if Reg is not used in any debug operand.
-  const MachineOperand *getDebugOperandForReg(Register Reg) const {
-    const MachineOperand *RegOp =
-        find_if(debug_operands(), [Reg](const MachineOperand &Op) {
-          return Op.isReg() && Op.getReg() == Reg;
-        });
-    return RegOp == adl_end(debug_operands()) ? nullptr : RegOp;
+  /// Returns whether this debug value has at least one debug operand with the
+  /// register \p Reg.
+  bool hasDebugOperandForReg(Register Reg) const {
+    return any_of(debug_operands(), [Reg](const MachineOperand &Op) {
+      return Op.isReg() && Op.getReg() == Reg;
+    });
  }
-  MachineOperand *getDebugOperandForReg(Register Reg) {
-    MachineOperand *RegOp =
-        find_if(debug_operands(), [Reg](const MachineOperand &Op) {
-          return Op.isReg() && Op.getReg() == Reg;
-        });
-    return RegOp == adl_end(debug_operands()) ? nullptr : RegOp;
+
+  /// Returns a range of all of the operands that correspond to a debug use of
+  /// \p Reg.
+  template <typename Operand, typename Instruction>
+  static iterator_range<
+      filter_iterator<Operand *, std::function<bool(Operand &Op)>>>
+  getDebugOperandsForReg(Instruction *MI, Register Reg) {
+    std::function<bool(Operand & Op)> OpUsesReg(
+        [Reg](Operand &Op) { return Op.isReg() && Op.getReg() == Reg; });
+    return make_filter_range(MI->debug_operands(), OpUsesReg);
+  }
+  iterator_range<filter_iterator<const MachineOperand *,
+                                 std::function<bool(const MachineOperand &Op)>>>
+  getDebugOperandsForReg(Register Reg) const {
+    return MachineInstr::getDebugOperandsForReg<const MachineOperand,
+                                                const MachineInstr>(this, Reg);
+  }
+  iterator_range<filter_iterator<MachineOperand *,
+                                 std::function<bool(MachineOperand &Op)>>>
+  getDebugOperandsForReg(Register Reg) {
+    return MachineInstr::getDebugOperandsForReg<MachineOperand, MachineInstr>(
+        this, Reg);
+  }
+
+  bool isDebugOperand(const MachineOperand *Op) const {
+    return Op >= adl_begin(debug_operands()) && Op <= adl_end(debug_operands());
  }

  unsigned getDebugOperandIndex(const MachineOperand *Op) const {
-    assert(Op >= adl_begin(debug_operands()) &&
-           Op <= adl_end(debug_operands()) && "Expected a debug operand.");
+    assert(isDebugOperand(Op) && "Expected a debug operand.");
    return std::distance(adl_begin(debug_operands()), Op);
  }

@ -600,12 +618,16 @@ public:
  /// location for this DBG_VALUE instruction.
  iterator_range<mop_iterator> debug_operands() {
    assert(isDebugValue() && "Must be a debug value instruction.");
-    return make_range(operands_begin(), operands_begin() + 1);
+    return isDebugValueList()
+               ? make_range(operands_begin() + 2, operands_end())
+               : make_range(operands_begin(), operands_begin() + 1);
  }
  /// \copydoc debug_operands()
  iterator_range<const_mop_iterator> debug_operands() const {
    assert(isDebugValue() && "Must be a debug value instruction.");
-    return make_range(operands_begin(), operands_begin() + 1);
+    return isDebugValueList()
+               ? make_range(operands_begin() + 2, operands_end())
+               : make_range(operands_begin(), operands_begin() + 1);
  }
  /// Returns a range over all explicit operands that are register definitions.
  /// Implicit definition are not included!
@ -1164,7 +1186,15 @@ public:
  // True if the instruction represents a position in the function.
  bool isPosition() const { return isLabel() || isCFIInstruction(); }

-  bool isDebugValue() const { return getOpcode() == TargetOpcode::DBG_VALUE; }
+  bool isNonListDebugValue() const {
+    return getOpcode() == TargetOpcode::DBG_VALUE;
+  }
+  bool isDebugValueList() const {
+    return getOpcode() == TargetOpcode::DBG_VALUE_LIST;
+  }
+  bool isDebugValue() const {
+    return isNonListDebugValue() || isDebugValueList();
+  }
  bool isDebugLabel() const { return getOpcode() == TargetOpcode::DBG_LABEL; }
  bool isDebugRef() const { return getOpcode() == TargetOpcode::DBG_INSTR_REF; }
  bool isDebugInstr() const {
@ -1174,12 +1204,14 @@ public:
    return isDebugInstr() || isPseudoProbe();
  }

-  bool isDebugOffsetImm() const { return getDebugOffset().isImm(); }
+  bool isDebugOffsetImm() const {
+    return isNonListDebugValue() && getDebugOffset().isImm();
+  }

  /// A DBG_VALUE is indirect iff the location operand is a register and
  /// the offset operand is an immediate.
  bool isIndirectDebugValue() const {
-    return isDebugValue() && getDebugOperand(0).isReg() && isDebugOffsetImm();
+    return isDebugOffsetImm() && getDebugOperand(0).isReg();
  }

  /// A DBG_VALUE is an entry value iff its debug expression contains the
@ -1189,8 +1221,13 @@ public:
  /// Return true if the instruction is a debug value which describes a part of
  /// a variable as unavailable.
  bool isUndefDebugValue() const {
-    return isDebugValue() && getDebugOperand(0).isReg() &&
-           !getDebugOperand(0).getReg().isValid();
+    if (!isDebugValue())
+      return false;
+    // If any $noreg locations are given, this DV is undef.
+    for (const MachineOperand &Op : debug_operands())
+      if (Op.isReg() && !Op.getReg().isValid())
+        return true;
+    return false;
  }

  bool isPHI() const {
@ -1265,6 +1302,7 @@ public:
    case TargetOpcode::EH_LABEL:
    case TargetOpcode::GC_LABEL:
    case TargetOpcode::DBG_VALUE:
+    case TargetOpcode::DBG_VALUE_LIST:
    case TargetOpcode::DBG_INSTR_REF:
    case TargetOpcode::DBG_LABEL:
    case TargetOpcode::LIFETIME_START:
--- a/include/llvm/CodeGen/MachineInstrBuilder.h
+++ b/include/llvm/CodeGen/MachineInstrBuilder.h
@ -451,9 +451,16 @@ MachineInstrBuilder BuildMI(MachineFunction &MF, const DebugLoc &DL,
 /// for a MachineOperand.
 MachineInstrBuilder BuildMI(MachineFunction &MF, const DebugLoc &DL,
                            const MCInstrDesc &MCID, bool IsIndirect,
-                            MachineOperand &MO, const MDNode *Variable,
+                            const MachineOperand &MO, const MDNode *Variable,
                            const MDNode *Expr);

+/// This version of the builder builds a DBG_VALUE or DBG_VALUE_LIST intrinsic
+/// for a MachineOperand.
+MachineInstrBuilder BuildMI(MachineFunction &MF, const DebugLoc &DL,
+                            const MCInstrDesc &MCID, bool IsIndirect,
+                            ArrayRef<MachineOperand> MOs,
+                            const MDNode *Variable, const MDNode *Expr);
+
 /// This version of the builder builds a DBG_VALUE intrinsic
 /// for either a value in a register or a register-indirect
 /// address and inserts it at position I.
@ -471,6 +478,14 @@ MachineInstrBuilder BuildMI(MachineBasicBlock &BB,
                            MachineOperand &MO, const MDNode *Variable,
                            const MDNode *Expr);

+/// This version of the builder builds a DBG_VALUE or DBG_VALUE_LIST intrinsic
+/// for a machine operand and inserts it at position I.
+MachineInstrBuilder BuildMI(MachineBasicBlock &BB,
+                            MachineBasicBlock::iterator I, const DebugLoc &DL,
+                            const MCInstrDesc &MCID, bool IsIndirect,
+                            ArrayRef<MachineOperand> MOs,
+                            const MDNode *Variable, const MDNode *Expr);
+
 /// Clone a DBG_VALUE whose value has been spilled to FrameIndex.
 MachineInstr *buildDbgValueForSpill(MachineBasicBlock &BB,
                                    MachineBasicBlock::iterator I,
--- a/include/llvm/IR/DebugInfoMetadata.h
+++ b/include/llvm/IR/DebugInfoMetadata.h
@ -2771,6 +2771,14 @@ public:
  static DIExpression *appendToStack(const DIExpression *Expr,
                                     ArrayRef<uint64_t> Ops);

+  /// Create a copy of \p Expr by appending the given list of \p Ops to each
+  /// instance of the operand `DW_OP_LLVM_arg, \p ArgNo`. This is used to
+  /// modify a specific location used by \p Expr, such as when salvaging that
+  /// location.
+  static DIExpression *appendOpsToArg(const DIExpression *Expr,
+                                      ArrayRef<uint64_t> Ops, unsigned ArgNo,
+                                      bool StackValue = false);
+
  /// Create a DIExpression to describe one part of an aggregate variable that
  /// is fragmented across multiple Values. The DW_OP_LLVM_fragment operation
  /// will be appended to the elements of \c Expr. If \c Expr already contains
--- a/include/llvm/Support/TargetOpcodes.def
+++ b/include/llvm/Support/TargetOpcodes.def
@ -77,6 +77,10 @@ HANDLE_TARGET_OPCODE(SUBREG_TO_REG)
 /// DBG_VALUE - a mapping of the llvm.dbg.value intrinsic
 HANDLE_TARGET_OPCODE(DBG_VALUE)

+/// DBG_VALUE - a mapping of the llvm.dbg.value intrinsic with a variadic
+/// list of locations
+HANDLE_TARGET_OPCODE(DBG_VALUE_LIST)
+
 /// DBG_INSTR_REF - A mapping of llvm.dbg.value referring to the instruction
 /// that defines the value, rather than a virtual register.
 HANDLE_TARGET_OPCODE(DBG_INSTR_REF)
--- a/include/llvm/Target/Target.td
+++ b/include/llvm/Target/Target.td
@ -1107,6 +1107,12 @@ def DBG_VALUE : StandardPseudoInstruction {
  let AsmString = "DBG_VALUE";
  let hasSideEffects = false;
 }
+def DBG_VALUE_LIST : StandardPseudoInstruction {
+  let OutOperandList = (outs);
+  let InOperandList = (ins variable_ops);
+  let AsmString = "DBG_VALUE_LIST";
+  let hasSideEffects = 0;
+}
 def DBG_INSTR_REF : StandardPseudoInstruction {
  let OutOperandList = (outs);
  let InOperandList = (ins variable_ops);
--- a/lib/BinaryFormat/Dwarf.cpp
+++ b/lib/BinaryFormat/Dwarf.cpp
@ -153,6 +153,8 @@ StringRef llvm::dwarf::OperationEncodingString(unsigned Encoding) {
    return "DW_OP_LLVM_entry_value";
  case DW_OP_LLVM_implicit_pointer:
    return "DW_OP_LLVM_implicit_pointer";
+  case DW_OP_LLVM_arg:
+    return "DW_OP_LLVM_arg";
  }
 }

@ -166,6 +168,7 @@ unsigned llvm::dwarf::getOperationEncoding(StringRef OperationEncodingString) {
      .Case("DW_OP_LLVM_tag_offset", DW_OP_LLVM_tag_offset)
      .Case("DW_OP_LLVM_entry_value", DW_OP_LLVM_entry_value)
      .Case("DW_OP_LLVM_implicit_pointer", DW_OP_LLVM_implicit_pointer)
+      .Case("DW_OP_LLVM_arg", DW_OP_LLVM_arg)
      .Default(0);
 }

--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@ -905,7 +905,7 @@ static void emitKill(const MachineInstr *MI, AsmPrinter &AP) {
 /// means the target will need to handle MI in EmitInstruction.
 static bool emitDebugValueComment(const MachineInstr *MI, AsmPrinter &AP) {
  // This code handles only the 4-operand target-independent form.
-  if (MI->getNumOperands() != 4)
+  if (MI->isNonListDebugValue() && MI->getNumOperands() != 4)
    return false;

  SmallString<128> Str;
@ -1228,6 +1228,7 @@ void AsmPrinter::emitFunctionBody() {
        emitInlineAsm(&MI);
        break;
      case TargetOpcode::DBG_VALUE:
+      case TargetOpcode::DBG_VALUE_LIST:
        if (isVerbose()) {
          if (!emitDebugValueComment(&MI, *this))
            emitInstruction(&MI);
--- a/lib/CodeGen/LiveRangeShrink.cpp
+++ b/lib/CodeGen/LiveRangeShrink.cpp
@ -235,7 +235,7 @@ bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) {
        MachineBasicBlock::iterator EndIter = std::next(MI.getIterator());
        if (MI.getOperand(0).isReg())
          for (; EndIter != MBB.end() && EndIter->isDebugValue() &&
-                 EndIter->getDebugOperandForReg(MI.getOperand(0).getReg());
+                 EndIter->hasDebugOperandForReg(MI.getOperand(0).getReg());
               ++EndIter, ++Next)
            IOM[&*EndIter] = NewOrder;
        MBB.splice(I, &MBB, MI.getIterator(), EndIter);
--- a/lib/CodeGen/MIRParser/MIParser.cpp
+++ b/lib/CodeGen/MIRParser/MIParser.cpp
@ -987,7 +987,9 @@ bool MIParser::parse(MachineInstr *&MI) {
    Optional<unsigned> TiedDefIdx;
    if (parseMachineOperandAndTargetFlags(OpCode, Operands.size(), MO, TiedDefIdx))
      return true;
-    if (OpCode == TargetOpcode::DBG_VALUE && MO.isReg())
+    if ((OpCode == TargetOpcode::DBG_VALUE ||
+         OpCode == TargetOpcode::DBG_VALUE_LIST) &&
+        MO.isReg())
      MO.setIsDebug();
    Operands.push_back(
        ParsedMachineOperand(MO, Loc, Token.location(), TiedDefIdx));
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@ -841,28 +841,35 @@ const DILabel *MachineInstr::getDebugLabel() const {
 }

 const MachineOperand &MachineInstr::getDebugVariableOp() const {
-  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE");
-  return getOperand(2);
+  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE*");
+  unsigned VariableOp = isDebugValueList() ? 0 : 2;
+  return getOperand(VariableOp);
 }

 MachineOperand &MachineInstr::getDebugVariableOp() {
-  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE");
-  return getOperand(2);
+  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE*");
+  unsigned VariableOp = isDebugValueList() ? 0 : 2;
+  return getOperand(VariableOp);
 }

 const DILocalVariable *MachineInstr::getDebugVariable() const {
-  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE");
-  return cast<DILocalVariable>(getOperand(2).getMetadata());
+  return cast<DILocalVariable>(getDebugVariableOp().getMetadata());
+}
+
+const MachineOperand &MachineInstr::getDebugExpressionOp() const {
+  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE*");
+  unsigned ExpressionOp = isDebugValueList() ? 1 : 3;
+  return getOperand(ExpressionOp);
 }

 MachineOperand &MachineInstr::getDebugExpressionOp() {
-  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE");
-  return getOperand(3);
+  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE*");
+  unsigned ExpressionOp = isDebugValueList() ? 1 : 3;
+  return getOperand(ExpressionOp);
 }

 const DIExpression *MachineInstr::getDebugExpression() const {
-  assert((isDebugValue() || isDebugRef()) && "not a DBG_VALUE");
-  return cast<DIExpression>(getOperand(3).getMetadata());
+  return cast<DIExpression>(getDebugExpressionOp().getMetadata());
 }

 bool MachineInstr::isDebugEntryValue() const {
@ -1712,7 +1719,7 @@ void MachineInstr::print(raw_ostream &OS, ModuleSlotTracker &MST,
    OS << " ";

    if (isDebugValue() && MO.isMetadata()) {
-      // Pretty print DBG_VALUE instructions.
+      // Pretty print DBG_VALUE* instructions.
      auto *DIV = dyn_cast<DILocalVariable>(MO.getMetadata());
      if (DIV && !DIV->getName().empty())
        OS << "!\"" << DIV->getName() << '\"';
@ -2116,8 +2123,8 @@ MachineInstrBuilder llvm::BuildMI(MachineFunction &MF, const DebugLoc &DL,

 MachineInstrBuilder llvm::BuildMI(MachineFunction &MF, const DebugLoc &DL,
                                  const MCInstrDesc &MCID, bool IsIndirect,
-                                  MachineOperand &MO, const MDNode *Variable,
-                                  const MDNode *Expr) {
+                                  const MachineOperand &MO,
+                                  const MDNode *Variable, const MDNode *Expr) {
  assert(isa<DILocalVariable>(Variable) && "not a variable");
  assert(cast<DIExpression>(Expr)->isValid() && "not an expression");
  assert(cast<DILocalVariable>(Variable)->isValidLocationForIntrinsic(DL) &&
@ -2131,7 +2138,28 @@ MachineInstrBuilder llvm::BuildMI(MachineFunction &MF, const DebugLoc &DL,
  else
    MIB.addReg(0U, RegState::Debug);
  return MIB.addMetadata(Variable).addMetadata(Expr);
- }
+}
+
+MachineInstrBuilder llvm::BuildMI(MachineFunction &MF, const DebugLoc &DL,
+                                  const MCInstrDesc &MCID, bool IsIndirect,
+                                  ArrayRef<MachineOperand> MOs,
+                                  const MDNode *Variable, const MDNode *Expr) {
+  assert(isa<DILocalVariable>(Variable) && "not a variable");
+  assert(cast<DIExpression>(Expr)->isValid() && "not an expression");
+  assert(cast<DILocalVariable>(Variable)->isValidLocationForIntrinsic(DL) &&
+         "Expected inlined-at fields to agree");
+  if (MCID.Opcode == TargetOpcode::DBG_VALUE)
+    return BuildMI(MF, DL, MCID, IsIndirect, MOs[0], Variable, Expr);
+
+  auto MIB = BuildMI(MF, DL, MCID);
+  MIB.addMetadata(Variable).addMetadata(Expr);
+  for (const MachineOperand &MO : MOs)
+    if (MO.isReg())
+      MIB.addReg(MO.getReg(), RegState::Debug);
+    else
+      MIB.add(MO);
+  return MIB;
+}

 MachineInstrBuilder llvm::BuildMI(MachineBasicBlock &BB,
                                  MachineBasicBlock::iterator I,
@ -2155,10 +2183,22 @@ MachineInstrBuilder llvm::BuildMI(MachineBasicBlock &BB,
  return MachineInstrBuilder(MF, *MI);
 }

+MachineInstrBuilder llvm::BuildMI(MachineBasicBlock &BB,
+                                  MachineBasicBlock::iterator I,
+                                  const DebugLoc &DL, const MCInstrDesc &MCID,
+                                  bool IsIndirect, ArrayRef<MachineOperand> MOs,
+                                  const MDNode *Variable, const MDNode *Expr) {
+  MachineFunction &MF = *BB.getParent();
+  MachineInstr *MI = BuildMI(MF, DL, MCID, IsIndirect, MOs, Variable, Expr);
+  BB.insert(I, MI);
+  return MachineInstrBuilder(MF, *MI);
+}
+
 /// Compute the new DIExpression to use with a DBG_VALUE for a spill slot.
 /// This prepends DW_OP_deref when spilling an indirect DBG_VALUE.
-static const DIExpression *computeExprForSpill(const MachineInstr &MI) {
-  assert(MI.getOperand(0).isReg() && "can't spill non-register");
+static const DIExpression *computeExprForSpill(const MachineInstr &MI,
+                                               Register SpillReg) {
+  assert(MI.hasDebugOperandForReg(SpillReg) && "Spill Reg is not used in MI.");
  assert(MI.getDebugVariable()->isValidLocationForIntrinsic(MI.getDebugLoc()) &&
         "Expected inlined-at fields to agree");

@ -2167,6 +2207,14 @@ static const DIExpression *computeExprForSpill(const MachineInstr &MI) {
    assert(MI.getDebugOffset().getImm() == 0 &&
           "DBG_VALUE with nonzero offset");
    Expr = DIExpression::prepend(Expr, DIExpression::DerefBefore);
+  } else if (MI.isDebugValueList()) {
+    // We will replace the spilled register with a frame index, so
+    // immediately deref all references to the spilled register.
+    std::array<uint64_t, 1> Ops{{dwarf::DW_OP_deref}};
+    for (const MachineOperand &Op : MI.getDebugOperandsForReg(SpillReg)) {
+      unsigned OpIdx = MI.getDebugOperandIndex(&Op);
+      Expr = DIExpression::appendOpsToArg(Expr, Ops, OpIdx);
+    }
  }
  return Expr;
 }
@ -2175,18 +2223,32 @@ MachineInstr *llvm::buildDbgValueForSpill(MachineBasicBlock &BB,
                                          MachineBasicBlock::iterator I,
                                          const MachineInstr &Orig,
                                          int FrameIndex) {
-  const DIExpression *Expr = computeExprForSpill(Orig);
-  return BuildMI(BB, I, Orig.getDebugLoc(), Orig.getDesc())
-      .addFrameIndex(FrameIndex)
-      .addImm(0U)
-      .addMetadata(Orig.getDebugVariable())
-      .addMetadata(Expr);
+  Register SpillReg = Orig.getDebugOperand(0).getReg();
+  const DIExpression *Expr = computeExprForSpill(Orig, SpillReg);
+  MachineInstrBuilder NewMI =
+      BuildMI(BB, I, Orig.getDebugLoc(), Orig.getDesc());
+  // Non-Variadic Operands: Location, Offset, Variable, Expression
+  // Variadic Operands:     Variable, Expression, Locations...
+  if (Orig.isNonListDebugValue())
+    NewMI.addFrameIndex(FrameIndex).addImm(0U);
+  NewMI.addMetadata(Orig.getDebugVariable()).addMetadata(Expr);
+  if (Orig.isDebugValueList()) {
+    for (const MachineOperand &Op : Orig.debug_operands())
+      if (Op.isReg() && Op.getReg() == SpillReg)
+        NewMI.addFrameIndex(FrameIndex);
+      else
+        NewMI.add(MachineOperand(Op));
+  }
+  return NewMI;
 }

 void llvm::updateDbgValueForSpill(MachineInstr &Orig, int FrameIndex) {
-  const DIExpression *Expr = computeExprForSpill(Orig);
-  Orig.getDebugOperand(0).ChangeToFrameIndex(FrameIndex);
-  Orig.getDebugOffset().ChangeToImmediate(0U);
+  Register SpillReg = Orig.getDebugOperand(0).getReg();
+  const DIExpression *Expr = computeExprForSpill(Orig, SpillReg);
+  if (Orig.isNonListDebugValue())
+    Orig.getDebugOffset().ChangeToImmediate(0U);
+  for (MachineOperand &Op : Orig.getDebugOperandsForReg(SpillReg))
+    Op.ChangeToFrameIndex(FrameIndex);
  Orig.getDebugExpressionOp().setMetadata(Expr);
 }

@ -2201,7 +2263,7 @@ void MachineInstr::collectDebugValues(
       DI != DE; ++DI) {
    if (!DI->isDebugValue())
      return;
-    if (DI->getDebugOperandForReg(MI.getOperand(0).getReg()))
+    if (DI->hasDebugOperandForReg(MI.getOperand(0).getReg()))
      DbgValues.push_back(&*DI);
  }
 }
@ -2219,14 +2281,15 @@ void MachineInstr::changeDebugValuesDefReg(Register Reg) {
    auto *DI = MO.getParent();
    if (!DI->isDebugValue())
      continue;
-    if (DI->getDebugOperandForReg(DefReg)) {
+    if (DI->hasDebugOperandForReg(DefReg)) {
      DbgValues.push_back(DI);
    }
  }

  // Propagate Reg to debug value instructions.
  for (auto *DBI : DbgValues)
-    DBI->getDebugOperandForReg(DefReg)->setReg(Reg);
+    for (MachineOperand &Op : DBI->getDebugOperandsForReg(DefReg))
+      Op.setReg(Reg);
 }

 using MMOList = SmallVector<const MachineMemOperand *, 2>;
--- a/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/lib/CodeGen/MachineRegisterInfo.cpp
@ -530,11 +530,11 @@ bool MachineRegisterInfo::isConstantPhysReg(MCRegister PhysReg) const {
 /// specified register as undefined which causes the DBG_VALUE to be
 /// deleted during LiveDebugVariables analysis.
 void MachineRegisterInfo::markUsesInDebugValueAsUndef(Register Reg) const {
-  // Mark any DBG_VALUE that uses Reg as undef (but don't delete it.)
+  // Mark any DBG_VALUE* that uses Reg as undef (but don't delete it.)
  // We use make_early_inc_range because setReg invalidates the iterator.
  for (MachineInstr &UseMI : llvm::make_early_inc_range(use_instructions(Reg))) {
-    if (UseMI.isDebugValue())
-      UseMI.getDebugOperandForReg(Reg)->setReg(0U);
+    if (UseMI.isDebugValue() && UseMI.hasDebugOperandForReg(Reg))
+      UseMI.setDebugValueUndef();
  }
 }

--- a/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/lib/CodeGen/PrologEpilogInserter.cpp
@ -1233,23 +1233,33 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &MF,
        // complex location that is interpreted as being a memory address.
        // This changes a pointer-valued variable to dereference that pointer,
        // which is incorrect. Fix by adding DW_OP_stack_value.
-        unsigned PrependFlags = DIExpression::ApplyOffset;
-        if (!MI.isIndirectDebugValue() && !DIExpr->isComplex())
-          PrependFlags |= DIExpression::StackValue;

-        // If we have DBG_VALUE that is indirect and has a Implicit location
-        // expression need to insert a deref before prepending a Memory
-        // location expression. Also after doing this we change the DBG_VALUE
-        // to be direct.
-        if (MI.isIndirectDebugValue() && DIExpr->isImplicit()) {
-          SmallVector<uint64_t, 2> Ops = {dwarf::DW_OP_deref_size, Size};
-          bool WithStackValue = true;
-          DIExpr = DIExpression::prependOpcodes(DIExpr, Ops, WithStackValue);
-          // Make the DBG_VALUE direct.
-          MI.getDebugOffset().ChangeToRegister(0, false);
+        if (MI.isNonListDebugValue()) {
+          unsigned PrependFlags = DIExpression::ApplyOffset;
+          if (!MI.isIndirectDebugValue() && !DIExpr->isComplex())
+            PrependFlags |= DIExpression::StackValue;
+
+          // If we have DBG_VALUE that is indirect and has a Implicit location
+          // expression need to insert a deref before prepending a Memory
+          // location expression. Also after doing this we change the DBG_VALUE
+          // to be direct.
+          if (MI.isIndirectDebugValue() && DIExpr->isImplicit()) {
+            SmallVector<uint64_t, 2> Ops = {dwarf::DW_OP_deref_size, Size};
+            bool WithStackValue = true;
+            DIExpr = DIExpression::prependOpcodes(DIExpr, Ops, WithStackValue);
+            // Make the DBG_VALUE direct.
+            MI.getDebugOffset().ChangeToRegister(0, false);
+          }
+          DIExpr = TRI.prependOffsetExpression(DIExpr, PrependFlags, Offset);
+        } else {
+          // The debug operand at DebugOpIndex was a frame index at offset
+          // `Offset`; now the operand has been replaced with the frame
+          // register, we must add Offset with `register x, plus Offset`.
+          unsigned DebugOpIndex = MI.getDebugOperandIndex(&MI.getOperand(i));
+          SmallVector<uint64_t, 3> Ops;
+          TRI.getOffsetOpcodes(Offset, Ops);
+          DIExpr = DIExpression::appendOpsToArg(DIExpr, Ops, DebugOpIndex);
        }
-
-        DIExpr = TRI.prependOffsetExpression(DIExpr, PrependFlags, Offset);
        MI.getDebugExpressionOp().setMetadata(DIExpr);
        continue;
      }
--- a/lib/CodeGen/RegAllocFast.cpp
+++ b/lib/CodeGen/RegAllocFast.cpp
@ -424,9 +424,14 @@ void RegAllocFast::spill(MachineBasicBlock::iterator Before, Register VirtReg,
    }

    // Rewrite unassigned dbg_values to use the stack slot.
-    MachineOperand &MO = DBG->getOperand(0);
-    if (MO.isReg() && MO.getReg() == 0)
-      updateDbgValueForSpill(*DBG, FI);
+    // TODO We can potentially do this for list debug values as well if we know
+    // how the dbg_values are getting unassigned.
+    if (DBG->isNonListDebugValue()) {
+      MachineOperand &MO = DBG->getDebugOperand(0);
+      if (MO.isReg() && MO.getReg() == 0) {
+        updateDbgValueForSpill(*DBG, FI);
+      }
+    }
  }
  // Now this register is spilled there is should not be any DBG_VALUE
  // pointing to this register because they are all pointing to spilled value
@ -623,8 +628,7 @@ void RegAllocFast::assignDanglingDebugValues(MachineInstr &Definition,
  SmallVectorImpl<MachineInstr*> &Dangling = UDBGValIter->second;
  for (MachineInstr *DbgValue : Dangling) {
    assert(DbgValue->isDebugValue());
-    MachineOperand &MO = DbgValue->getOperand(0);
-    if (!MO.isReg())
+    if (!DbgValue->hasDebugOperandForReg(VirtReg))
      continue;

    // Test whether the physreg survives from the definition to the DBG_VALUE.
@ -639,9 +643,11 @@ void RegAllocFast::assignDanglingDebugValues(MachineInstr &Definition,
        break;
      }
    }
-    MO.setReg(SetToReg);
-    if (SetToReg != 0)
-      MO.setIsRenamable();
+    for (MachineOperand &MO : DbgValue->getDebugOperandsForReg(VirtReg)) {
+      MO.setReg(SetToReg);
+      if (SetToReg != 0)
+        MO.setIsRenamable();
+    }
  }
  Dangling.clear();
 }
@ -1360,37 +1366,44 @@ void RegAllocFast::allocateInstruction(MachineInstr &MI) {
 }

 void RegAllocFast::handleDebugValue(MachineInstr &MI) {
-  MachineOperand &MO = MI.getDebugOperand(0);
+  SmallSet<Register, 4> SeenRegisters;
+  for (MachineOperand &MO : MI.debug_operands()) {
+    // Ignore DBG_VALUEs that aren't based on virtual registers. These are
+    // mostly constants and frame indices.
+    if (!MO.isReg())
+      continue;
+    Register Reg = MO.getReg();
+    if (!Register::isVirtualRegister(Reg))
+      continue;
+    // Only process each register once per MI, each use of that register will
+    // be updated if necessary.
+    if (!SeenRegisters.insert(Reg).second)
+      continue;

-  // Ignore DBG_VALUEs that aren't based on virtual registers. These are
-  // mostly constants and frame indices.
-  if (!MO.isReg())
-    return;
-  Register Reg = MO.getReg();
-  if (!Register::isVirtualRegister(Reg))
-    return;
+    // Already spilled to a stackslot?
+    int SS = StackSlotForVirtReg[Reg];
+    if (SS != -1) {
+      // Modify DBG_VALUE now that the value is in a spill slot.
+      updateDbgValueForSpill(MI, SS);
+      LLVM_DEBUG(dbgs() << "Rewrite DBG_VALUE for spilled memory: " << MI);
+      continue;
+    }

-  // Already spilled to a stackslot?
-  int SS = StackSlotForVirtReg[Reg];
-  if (SS != -1) {
-    // Modify DBG_VALUE now that the value is in a spill slot.
-    updateDbgValueForSpill(MI, SS);
-    LLVM_DEBUG(dbgs() << "Rewrite DBG_VALUE for spilled memory: " << MI);
-    return;
+    // See if this virtual register has already been allocated to a physical
+    // register or spilled to a stack slot.
+    LiveRegMap::iterator LRI = findLiveVirtReg(Reg);
+    if (LRI != LiveVirtRegs.end() && LRI->PhysReg) {
+      // Update every use of Reg within MI.
+      for (auto &RegMO : MI.getDebugOperandsForReg(Reg))
+        setPhysReg(MI, RegMO, LRI->PhysReg);
+    } else {
+      DanglingDbgValues[Reg].push_back(&MI);
+    }
+
+    // If Reg hasn't been spilled, put this DBG_VALUE in LiveDbgValueMap so
+    // that future spills of Reg will have DBG_VALUEs.
+    LiveDbgValueMap[Reg].push_back(&MI);
  }
-
-  // See if this virtual register has already been allocated to a physical
-  // register or spilled to a stack slot.
-  LiveRegMap::iterator LRI = findLiveVirtReg(Reg);
-  if (LRI != LiveVirtRegs.end() && LRI->PhysReg) {
-    setPhysReg(MI, MO, LRI->PhysReg);
-  } else {
-    DanglingDbgValues[Reg].push_back(&MI);
-  }
-
-  // If Reg hasn't been spilled, put this DBG_VALUE in LiveDbgValueMap so
-  // that future spills of Reg will have DBG_VALUEs.
-  LiveDbgValueMap[Reg].push_back(&MI);
 }

 void RegAllocFast::handleBundle(MachineInstr &MI) {
@ -1472,13 +1485,12 @@ void RegAllocFast::allocateBasicBlock(MachineBasicBlock &MBB) {
  for (auto &UDBGPair : DanglingDbgValues) {
    for (MachineInstr *DbgValue : UDBGPair.second) {
      assert(DbgValue->isDebugValue() && "expected DBG_VALUE");
-      MachineOperand &MO = DbgValue->getOperand(0);
      // Nothing to do if the vreg was spilled in the meantime.
-      if (!MO.isReg())
+      if (!DbgValue->hasDebugOperandForReg(UDBGPair.first))
        continue;
      LLVM_DEBUG(dbgs() << "Register did not survive for " << *DbgValue
                 << '\n');
-      MO.setReg(0);
+      DbgValue->setDebugValueUndef();
    }
  }
  DanglingDbgValues.clear();
--- a/lib/IR/DebugInfoMetadata.cpp
+++ b/lib/IR/DebugInfoMetadata.cpp
@ -1059,6 +1059,7 @@ unsigned DIExpression::ExprOperand::getSize() const {
  case dwarf::DW_OP_plus_uconst:
  case dwarf::DW_OP_LLVM_tag_offset:
  case dwarf::DW_OP_LLVM_entry_value:
+  case dwarf::DW_OP_LLVM_arg:
  case dwarf::DW_OP_regx:
    return 2;
  default:
@ -1115,6 +1116,7 @@ bool DIExpression::isValid() const {
    }
    case dwarf::DW_OP_LLVM_implicit_pointer:
    case dwarf::DW_OP_LLVM_convert:
+    case dwarf::DW_OP_LLVM_arg:
    case dwarf::DW_OP_LLVM_tag_offset:
    case dwarf::DW_OP_constu:
    case dwarf::DW_OP_plus_uconst:
@ -1270,6 +1272,30 @@ DIExpression *DIExpression::prepend(const DIExpression *Expr, uint8_t Flags,
  return prependOpcodes(Expr, Ops, StackValue, EntryValue);
 }

+DIExpression *DIExpression::appendOpsToArg(const DIExpression *Expr,
+                                           ArrayRef<uint64_t> Ops,
+                                           unsigned ArgNo, bool StackValue) {
+  assert(Expr && "Can't add ops to this expression");
+
+  // Handle non-variadic intrinsics by prepending the opcodes.
+  if (!any_of(Expr->expr_ops(),
+              [](auto Op) { return Op.getOp() == dwarf::DW_OP_LLVM_arg; })) {
+    assert(ArgNo == 0 &&
+           "Location Index must be 0 for a non-variadic expression.");
+    SmallVector<uint64_t, 8> NewOps(Ops.begin(), Ops.end());
+    return DIExpression::prependOpcodes(Expr, NewOps, StackValue);
+  }
+
+  SmallVector<uint64_t, 8> NewOps;
+  for (auto Op : Expr->expr_ops()) {
+    Op.appendToVector(NewOps);
+    if (Op.getOp() == dwarf::DW_OP_LLVM_arg && Op.getArg(0) == ArgNo)
+      NewOps.insert(NewOps.end(), Ops.begin(), Ops.end());
+  }
+
+  return DIExpression::get(Expr->getContext(), NewOps);
+}
+
 DIExpression *DIExpression::prependOpcodes(const DIExpression *Expr,
                                           SmallVectorImpl<uint64_t> &Ops,
                                           bool StackValue,
--- a/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/lib/Target/AArch64/AArch64AsmPrinter.cpp
@ -1210,7 +1210,8 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) {
    }
    break;

-  case AArch64::DBG_VALUE: {
+  case AArch64::DBG_VALUE:
+  case AArch64::DBG_VALUE_LIST: {
    if (isVerbose() && OutStreamer->hasRawTextSupport()) {
      SmallString<128> TmpStr;
      raw_svector_ostream OS(TmpStr);
@ -1231,7 +1232,7 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) {
      OutStreamer->emitCFIBKeyFrame();
      return;
    }
-  }
+    }

  // Tail calls use pseudo instructions so they have the proper code-gen
  // attributes (isCall, isReturn, etc.). We lower them to the real
--- a/lib/Target/NVPTX/NVPTXPrologEpilogPass.cpp
+++ b/lib/Target/NVPTX/NVPTXPrologEpilogPass.cpp
@ -65,16 +65,25 @@ bool NVPTXPrologEpilogPass::runOnMachineFunction(MachineFunction &MF) {
        // way with simply the frame index and offset rather than any
        // target-specific addressing mode.
        if (MI.isDebugValue()) {
-          assert(i == 0 && "Frame indices can only appear as the first "
-                           "operand of a DBG_VALUE machine instruction");
+          MachineOperand &Op = MI.getOperand(i);
+          assert(
+              MI.isDebugOperand(&Op) &&
+              "Frame indices can only appear as a debug operand in a DBG_VALUE*"
+              " machine instruction");
          Register Reg;
-          int64_t Offset =
-              TFI.getFrameIndexReference(MF, MI.getOperand(0).getIndex(), Reg)
-                  .getFixed();
-          MI.getOperand(0).ChangeToRegister(Reg, /*isDef=*/false);
-          MI.getOperand(0).setIsDebug();
-          auto *DIExpr = DIExpression::prepend(
-              MI.getDebugExpression(), DIExpression::ApplyOffset, Offset);
+          auto Offset =
+              TFI.getFrameIndexReference(MF, Op.getIndex(), Reg);
+          Op.ChangeToRegister(Reg, /*isDef=*/false);
+          Op.setIsDebug();
+          const DIExpression *DIExpr = MI.getDebugExpression();
+          if (MI.isNonListDebugValue()) {
+            DIExpr = TRI.prependOffsetExpression(MI.getDebugExpression(), DIExpression::ApplyOffset, Offset);
+          } else {
+	    SmallVector<uint64_t, 3> Ops;
+            TRI.getOffsetOpcodes(Offset, Ops);
+            unsigned OpIdx = MI.getDebugOperandIndex(&Op);
+            DIExpr = DIExpression::appendOpsToArg(DIExpr, Ops, OpIdx);
+          }
          MI.getDebugExpressionOp().setMetadata(DIExpr);
          continue;
        }
--- a/lib/Target/SystemZ/SystemZRegisterInfo.cpp
+++ b/lib/Target/SystemZ/SystemZRegisterInfo.cpp
@ -9,12 +9,13 @@
 #include "SystemZRegisterInfo.h"
 #include "SystemZInstrInfo.h"
 #include "SystemZSubtarget.h"
-#include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/ADT/SmallSet.h"
+#include "llvm/CodeGen/LiveIntervals.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/TargetFrameLowering.h"
 #include "llvm/CodeGen/VirtRegMap.h"
+#include "llvm/IR/DebugInfoMetadata.h"

 using namespace llvm;

@ -273,7 +274,16 @@ SystemZRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
  // Special handling of dbg_value instructions.
  if (MI->isDebugValue()) {
    MI->getOperand(FIOperandNum).ChangeToRegister(BasePtr, /*isDef*/ false);
-    MI->getDebugOffset().ChangeToImmediate(Offset);
+    if (MI->isNonListDebugValue()) {
+      MI->getDebugOffset().ChangeToImmediate(Offset);
+    } else {
+      unsigned OpIdx = MI->getDebugOperandIndex(&MI->getOperand(FIOperandNum));
+      SmallVector<uint64_t, 3> Ops;
+      DIExpression::appendOffset(
+          Ops, TFI->getFrameIndexReference(MF, FrameIndex, BasePtr).getFixed());
+      MI->getDebugExpressionOp().setMetadata(
+          DIExpression::appendOpsToArg(MI->getDebugExpression(), Ops, OpIdx));
+    }
    return;
  }

--- a/lib/Target/WebAssembly/WebAssemblyDebugValueManager.cpp
+++ b/lib/Target/WebAssembly/WebAssemblyDebugValueManager.cpp
@ -30,7 +30,7 @@ WebAssemblyDebugValueManager::WebAssemblyDebugValueManager(
  for (MachineBasicBlock::iterator DE = Instr->getParent()->end(); DI != DE;
       ++DI) {
    if (DI->isDebugValue() &&
-        DI->getDebugOperandForReg(Instr->getOperand(0).getReg()))
+        DI->hasDebugOperandForReg(Instr->getOperand(0).getReg()))
      DbgValues.push_back(&*DI);
  }
 }
--- a/lib/Target/X86/X86OptimizeLEAs.cpp
+++ b/lib/Target/X86/X86OptimizeLEAs.cpp
@ -295,8 +295,8 @@ private:
  /// Replace debug value MI with a new debug value instruction using register
  /// VReg with an appropriate offset and DIExpression to incorporate the
  /// address displacement AddrDispShift. Return new debug value instruction.
-  MachineInstr *replaceDebugValue(MachineInstr &MI, unsigned VReg,
-                                  int64_t AddrDispShift);
+  MachineInstr *replaceDebugValue(MachineInstr &MI, unsigned OldReg,
+                                  unsigned NewReg, int64_t AddrDispShift);

  /// Removes LEAs which calculate similar addresses.
  bool removeRedundantLEAs(MemOpMap &LEAs);
@ -576,21 +576,50 @@ bool X86OptimizeLEAPass::removeRedundantAddrCalc(MemOpMap &LEAs) {
 }

 MachineInstr *X86OptimizeLEAPass::replaceDebugValue(MachineInstr &MI,
-                                                    unsigned VReg,
+                                                    unsigned OldReg,
+                                                    unsigned NewReg,
                                                    int64_t AddrDispShift) {
  const DIExpression *Expr = MI.getDebugExpression();
-  if (AddrDispShift != 0)
-    Expr = DIExpression::prepend(Expr, DIExpression::StackValue, AddrDispShift);
+  if (AddrDispShift != 0) {
+    if (MI.isNonListDebugValue()) {
+      Expr =
+          DIExpression::prepend(Expr, DIExpression::StackValue, AddrDispShift);
+    } else {
+      // Update the Expression, appending an offset of `AddrDispShift` to the
+      // Op corresponding to `OldReg`.
+      SmallVector<uint64_t, 3> Ops;
+      DIExpression::appendOffset(Ops, AddrDispShift);
+      for (MachineOperand &Op : MI.getDebugOperandsForReg(OldReg)) {
+        unsigned OpIdx = MI.getDebugOperandIndex(&Op);
+        Expr = DIExpression::appendOpsToArg(Expr, Ops, OpIdx);
+      }
+    }
+  }

  // Replace DBG_VALUE instruction with modified version.
  MachineBasicBlock *MBB = MI.getParent();
  DebugLoc DL = MI.getDebugLoc();
  bool IsIndirect = MI.isIndirectDebugValue();
  const MDNode *Var = MI.getDebugVariable();
+  unsigned Opcode = MI.isNonListDebugValue() ? TargetOpcode::DBG_VALUE
+                                             : TargetOpcode::DBG_VALUE_LIST;
  if (IsIndirect)
-    assert(MI.getOperand(1).getImm() == 0 && "DBG_VALUE with nonzero offset");
-  return BuildMI(*MBB, MBB->erase(&MI), DL, TII->get(TargetOpcode::DBG_VALUE),
-                 IsIndirect, VReg, Var, Expr);
+    assert(MI.getDebugOffset().getImm() == 0 &&
+           "DBG_VALUE with nonzero offset");
+  SmallVector<MachineOperand, 4> NewOps;
+  // If we encounter an operand using the old register, replace it with an
+  // operand that uses the new register; otherwise keep the old operand.
+  auto replaceOldReg = [OldReg, NewReg](const MachineOperand &Op) {
+    if (Op.isReg() && Op.getReg() == OldReg)
+      return MachineOperand::CreateReg(NewReg, false, false, false, false,
+                                       false, false, false, false, 0,
+                                       /*IsRenamable*/ true);
+    return Op;
+  };
+  for (const MachineOperand &Op : MI.debug_operands())
+    NewOps.push_back(replaceOldReg(Op));
+  return BuildMI(*MBB, MBB->erase(&MI), DL, TII->get(Opcode), IsIndirect,
+                 NewOps, Var, Expr);
 }

 // Try to find similar LEAs in the list and replace one with another.
@ -635,7 +664,7 @@ bool X86OptimizeLEAPass::removeRedundantLEAs(MemOpMap &LEAs) {
            // Replace DBG_VALUE instruction with modified version using the
            // register from the replacing LEA and the address displacement
            // between the LEA instructions.
-            replaceDebugValue(MI, FirstVReg, AddrDispShift);
+            replaceDebugValue(MI, LastVReg, FirstVReg, AddrDispShift);
            continue;
          }

--- a/test/CodeGen/MIR/X86/dbg-value-list.mir
+++ b/test/CodeGen/MIR/X86/dbg-value-list.mir
@ -0,0 +1,64 @@
+# RUN: llc -march=x86-64 -run-pass machineverifier -o - %s | FileCheck %s
+# Simple round-trip test for DBG_VALUE_LIST.
+# CHECK: [[VAR_C:![0-9]+]] = !DILocalVariable(name: "c"
+# CHECK: DBG_VALUE_LIST [[VAR_C]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value), $edi, $esi, debug-location
+--- |
+  ; ModuleID = 'test.cpp'
+  source_filename = "test.cpp"
+  target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+  target triple = "x86_64-unknown-linux-gnu"
+  
+  ; Function Attrs: norecurse nounwind readnone uwtable
+  define dso_local i32 @_Z3fooii(i32 %a, i32 %b) local_unnamed_addr !dbg !7 {
+  entry:
+    call void @llvm.dbg.value(metadata i32 %a, metadata !12, metadata !DIExpression()), !dbg !15
+    call void @llvm.dbg.value(metadata i32 %b, metadata !13, metadata !DIExpression()), !dbg !15
+    call void @llvm.dbg.value(metadata i32 undef, metadata !14, metadata !DIExpression()), !dbg !15
+    %mul = mul nsw i32 %b, %a, !dbg !16
+    ret i32 %mul, !dbg !17
+  }
+  
+  ; Function Attrs: nounwind readnone speculatable willreturn
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+  
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!3, !4, !5}
+  !llvm.ident = !{!6}
+  
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 11.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+  !1 = !DIFile(filename: "test.cpp", directory: "/")
+  !2 = !{}
+  !3 = !{i32 7, !"Dwarf Version", i32 4}
+  !4 = !{i32 2, !"Debug Info Version", i32 3}
+  !5 = !{i32 1, !"wchar_size", i32 4}
+  !6 = !{!"clang version 11.0.0"}
+  !7 = distinct !DISubprogram(name: "foo", linkageName: "_Z3fooii", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+  !8 = !DISubroutineType(types: !9)
+  !9 = !{!10, !10, !10}
+  !10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !11 = !{!12, !13, !14}
+  !12 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 2, type: !10)
+  !13 = !DILocalVariable(name: "b", arg: 2, scope: !7, file: !1, line: 2, type: !10)
+  !14 = !DILocalVariable(name: "c", scope: !7, file: !1, line: 3, type: !10)
+  !15 = !DILocation(line: 0, scope: !7)
+  !16 = !DILocation(line: 4, column: 12, scope: !7)
+  !17 = !DILocation(line: 4, column: 3, scope: !7)
+
+...
+---
+name:            _Z3fooii
+body:             |
+  bb.0.entry:
+    liveins: $edi, $esi
+  
+    DBG_VALUE $edi, $noreg, !12, !DIExpression(), debug-location !15
+    DBG_VALUE $esi, $noreg, !13, !DIExpression(), debug-location !15
+    $eax = MOV32rr $edi
+    DBG_VALUE_LIST !14, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value), $edi, $esi, debug-location !15
+    DBG_VALUE $esi, $noreg, !13, !DIExpression(), debug-location !15
+    DBG_VALUE $eax, $noreg, !12, !DIExpression(), debug-location !15
+    renamable $eax = nsw IMUL32rr killed renamable $eax, killed renamable $esi, implicit-def dead $eflags, debug-location !16
+    RETQ $eax, debug-location !17
+
+...
+