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//===- LiveDebugVariables.cpp - Tracking debug info variables -------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the LiveDebugVariables analysis.
// Remove all DBG_VALUE instructions referencing virtual registers and replace
// them with a data structure tracking where live user variables are kept - in a
// virtual register or in a stack slot.
// Allow the data structure to be updated during register allocation when values
// are moved between registers and stack slots. Finally emit new DBG_VALUE
// instructions after register allocation is complete.
#include "llvm/CodeGen/LiveDebugVariables.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/IntervalMap.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/CodeGen/LexicalScopes.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <iterator>
#include <map>
#include <memory>
#include <optional>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "livedebugvars"
static cl::opt<bool>
EnableLDV("live-debug-variables", cl::init(true),
cl::desc("Enable the live debug variables pass"), cl::Hidden);
STATISTIC(NumInsertedDebugValues, "Number of DBG_VALUEs inserted");
STATISTIC(NumInsertedDebugLabels, "Number of DBG_LABELs inserted");
char LiveDebugVariables::ID = 0;
"Debug Variable Analysis", false, false)
"Debug Variable Analysis", false, false)
void LiveDebugVariables::getAnalysisUsage(AnalysisUsage &AU) const {
LiveDebugVariables::LiveDebugVariables() : MachineFunctionPass(ID) {
enum : unsigned { UndefLocNo = ~0U };
namespace {
/// Describes a debug variable value by location number and expression along
/// with some flags about the original usage of the location.
class DbgVariableValue {
DbgVariableValue(ArrayRef<unsigned> NewLocs, bool WasIndirect, bool WasList,
const DIExpression &Expr)
: WasIndirect(WasIndirect), WasList(WasList), Expression(&Expr) {
assert(!(WasIndirect && WasList) &&
"DBG_VALUE_LISTs should not be indirect.");
SmallVector<unsigned> LocNoVec;
for (unsigned LocNo : NewLocs) {
auto It = find(LocNoVec, LocNo);
if (It == LocNoVec.end())
else {
// Loc duplicates an element in LocNos; replace references to Op
// with references to the duplicating element.
unsigned OpIdx = LocNoVec.size();
unsigned DuplicatingIdx = std::distance(LocNoVec.begin(), It);
Expression =
DIExpression::replaceArg(Expression, OpIdx, DuplicatingIdx);
// FIXME: Debug values referencing 64+ unique machine locations are rare and
// currently unsupported for performance reasons. If we can verify that
// performance is acceptable for such debug values, we can increase the
// bit-width of LocNoCount to 14 to enable up to 16384 unique machine
// locations. We will also need to verify that this does not cause issues
// with LiveDebugVariables' use of IntervalMap.
if (LocNoVec.size() < 64) {
LocNoCount = LocNoVec.size();
if (LocNoCount > 0) {
LocNos = std::make_unique<unsigned[]>(LocNoCount);
std::copy(LocNoVec.begin(), LocNoVec.end(), loc_nos_begin());
} else {
LLVM_DEBUG(dbgs() << "Found debug value with 64+ unique machine "
"locations, dropping...\n");
LocNoCount = 1;
// Turn this into an undef debug value list; right now, the simplest form
// of this is an expression with one arg, and an undef debug operand.
Expression =
DIExpression::get(Expr.getContext(), {dwarf::DW_OP_LLVM_arg, 0});
if (auto FragmentInfoOpt = Expr.getFragmentInfo())
Expression = *DIExpression::createFragmentExpression(
Expression, FragmentInfoOpt->OffsetInBits,
LocNos = std::make_unique<unsigned[]>(LocNoCount);
LocNos[0] = UndefLocNo;
DbgVariableValue() : LocNoCount(0), WasIndirect(false), WasList(false) {}
DbgVariableValue(const DbgVariableValue &Other)
: LocNoCount(Other.LocNoCount), WasIndirect(Other.getWasIndirect()),
WasList(Other.getWasList()), Expression(Other.getExpression()) {
if (Other.getLocNoCount()) {
LocNos.reset(new unsigned[Other.getLocNoCount()]);
std::copy(Other.loc_nos_begin(), Other.loc_nos_end(), loc_nos_begin());
DbgVariableValue &operator=(const DbgVariableValue &Other) {
if (this == &Other)
return *this;
if (Other.getLocNoCount()) {
LocNos.reset(new unsigned[Other.getLocNoCount()]);
std::copy(Other.loc_nos_begin(), Other.loc_nos_end(), loc_nos_begin());
} else {
LocNoCount = Other.getLocNoCount();
WasIndirect = Other.getWasIndirect();
WasList = Other.getWasList();
Expression = Other.getExpression();
return *this;
const DIExpression *getExpression() const { return Expression; }
uint8_t getLocNoCount() const { return LocNoCount; }
bool containsLocNo(unsigned LocNo) const {
return is_contained(loc_nos(), LocNo);
bool getWasIndirect() const { return WasIndirect; }
bool getWasList() const { return WasList; }
bool isUndef() const { return LocNoCount == 0 || containsLocNo(UndefLocNo); }
DbgVariableValue decrementLocNosAfterPivot(unsigned Pivot) const {
SmallVector<unsigned, 4> NewLocNos;
for (unsigned LocNo : loc_nos())
NewLocNos.push_back(LocNo != UndefLocNo && LocNo > Pivot ? LocNo - 1
: LocNo);
return DbgVariableValue(NewLocNos, WasIndirect, WasList, *Expression);
DbgVariableValue remapLocNos(ArrayRef<unsigned> LocNoMap) const {
SmallVector<unsigned> NewLocNos;
for (unsigned LocNo : loc_nos())
// Undef values don't exist in locations (and thus not in LocNoMap
// either) so skip over them. See getLocationNo().
NewLocNos.push_back(LocNo == UndefLocNo ? UndefLocNo : LocNoMap[LocNo]);
return DbgVariableValue(NewLocNos, WasIndirect, WasList, *Expression);
DbgVariableValue changeLocNo(unsigned OldLocNo, unsigned NewLocNo) const {
SmallVector<unsigned> NewLocNos;
NewLocNos.assign(loc_nos_begin(), loc_nos_end());
auto OldLocIt = find(NewLocNos, OldLocNo);
assert(OldLocIt != NewLocNos.end() && "Old location must be present.");
*OldLocIt = NewLocNo;
return DbgVariableValue(NewLocNos, WasIndirect, WasList, *Expression);
bool hasLocNoGreaterThan(unsigned LocNo) const {
return any_of(loc_nos(),
[LocNo](unsigned ThisLocNo) { return ThisLocNo > LocNo; });
void printLocNos(llvm::raw_ostream &OS) const {
for (const unsigned &Loc : loc_nos())
OS << (&Loc == loc_nos_begin() ? " " : ", ") << Loc;
friend inline bool operator==(const DbgVariableValue &LHS,
const DbgVariableValue &RHS) {
if (std::tie(LHS.LocNoCount, LHS.WasIndirect, LHS.WasList,
LHS.Expression) !=
std::tie(RHS.LocNoCount, RHS.WasIndirect, RHS.WasList, RHS.Expression))
return false;
return std::equal(LHS.loc_nos_begin(), LHS.loc_nos_end(),
friend inline bool operator!=(const DbgVariableValue &LHS,
const DbgVariableValue &RHS) {
return !(LHS == RHS);
unsigned *loc_nos_begin() { return LocNos.get(); }
const unsigned *loc_nos_begin() const { return LocNos.get(); }
unsigned *loc_nos_end() { return LocNos.get() + LocNoCount; }
const unsigned *loc_nos_end() const { return LocNos.get() + LocNoCount; }
ArrayRef<unsigned> loc_nos() const {
return ArrayRef<unsigned>(LocNos.get(), LocNoCount);
// IntervalMap requires the value object to be very small, to the extent
// that we do not have enough room for an std::vector. Using a C-style array
// (with a unique_ptr wrapper for convenience) allows us to optimize for this
// specific case by packing the array size into only 6 bits (it is highly
// unlikely that any debug value will need 64+ locations).
std::unique_ptr<unsigned[]> LocNos;
uint8_t LocNoCount : 6;
bool WasIndirect : 1;
bool WasList : 1;
const DIExpression *Expression = nullptr;
} // namespace
/// Map of where a user value is live to that value.
using LocMap = IntervalMap<SlotIndex, DbgVariableValue, 4>;
/// Map of stack slot offsets for spilled locations.
/// Non-spilled locations are not added to the map.
using SpillOffsetMap = DenseMap<unsigned, unsigned>;
/// Cache to save the location where it can be used as the starting
/// position as input for calling MachineBasicBlock::SkipPHIsLabelsAndDebug.
/// This is to prevent MachineBasicBlock::SkipPHIsLabelsAndDebug from
/// repeatedly searching the same set of PHIs/Labels/Debug instructions
/// if it is called many times for the same block.
using BlockSkipInstsMap =
DenseMap<MachineBasicBlock *, MachineBasicBlock::iterator>;
namespace {
class LDVImpl;
/// A user value is a part of a debug info user variable.
/// A DBG_VALUE instruction notes that (a sub-register of) a virtual register
/// holds part of a user variable. The part is identified by a byte offset.
/// UserValues are grouped into equivalence classes for easier searching. Two
/// user values are related if they are held by the same virtual register. The
/// equivalence class is the transitive closure of that relation.
class UserValue {
const DILocalVariable *Variable; ///< The debug info variable we are part of.
/// The part of the variable we describe.
const std::optional<DIExpression::FragmentInfo> Fragment;
DebugLoc dl; ///< The debug location for the variable. This is
///< used by dwarf writer to find lexical scope.
UserValue *leader; ///< Equivalence class leader.
UserValue *next = nullptr; ///< Next value in equivalence class, or null.
/// Numbered locations referenced by locmap.
SmallVector<MachineOperand, 4> locations;
/// Map of slot indices where this value is live.
LocMap locInts;
/// Set of interval start indexes that have been trimmed to the
/// lexical scope.
SmallSet<SlotIndex, 2> trimmedDefs;
/// Insert a DBG_VALUE into MBB at Idx for DbgValue.
void insertDebugValue(MachineBasicBlock *MBB, SlotIndex StartIdx,
SlotIndex StopIdx, DbgVariableValue DbgValue,
ArrayRef<bool> LocSpills,
ArrayRef<unsigned> SpillOffsets, LiveIntervals &LIS,
const TargetInstrInfo &TII,
const TargetRegisterInfo &TRI,
BlockSkipInstsMap &BBSkipInstsMap);
/// Replace OldLocNo ranges with NewRegs ranges where NewRegs
/// is live. Returns true if any changes were made.
bool splitLocation(unsigned OldLocNo, ArrayRef<Register> NewRegs,
LiveIntervals &LIS);
/// Create a new UserValue.
UserValue(const DILocalVariable *var,
std::optional<DIExpression::FragmentInfo> Fragment, DebugLoc L,
LocMap::Allocator &alloc)
: Variable(var), Fragment(Fragment), dl(std::move(L)), leader(this),
locInts(alloc) {}
/// Get the leader of this value's equivalence class.
UserValue *getLeader() {
UserValue *l = leader;
while (l != l->leader)
l = l->leader;
return leader = l;
/// Return the next UserValue in the equivalence class.
UserValue *getNext() const { return next; }
/// Merge equivalence classes.
static UserValue *merge(UserValue *L1, UserValue *L2) {
L2 = L2->getLeader();
if (!L1)
return L2;
L1 = L1->getLeader();
if (L1 == L2)
return L1;
// Splice L2 before L1's members.
UserValue *End = L2;
while (End->next) {
End->leader = L1;
End = End->next;
End->leader = L1;
End->next = L1->next;
L1->next = L2;
return L1;
/// Return the location number that matches Loc.
/// For undef values we always return location number UndefLocNo without
/// inserting anything in locations. Since locations is a vector and the
/// location number is the position in the vector and UndefLocNo is ~0,
/// we would need a very big vector to put the value at the right position.
unsigned getLocationNo(const MachineOperand &LocMO) {
if (LocMO.isReg()) {
if (LocMO.getReg() == 0)
return UndefLocNo;
// For register locations we dont care about use/def and other flags.
for (unsigned i = 0, e = locations.size(); i != e; ++i)
if (locations[i].isReg() &&
locations[i].getReg() == LocMO.getReg() &&
locations[i].getSubReg() == LocMO.getSubReg())
return i;
} else
for (unsigned i = 0, e = locations.size(); i != e; ++i)
if (LocMO.isIdenticalTo(locations[i]))
return i;
// We are storing a MachineOperand outside a MachineInstr.
// Don't store def operands.
if (locations.back().isReg()) {
if (locations.back().isDef())
return locations.size() - 1;
/// Remove (recycle) a location number. If \p LocNo still is used by the
/// locInts nothing is done.
void removeLocationIfUnused(unsigned LocNo) {
// Bail out if LocNo still is used.
for (LocMap::const_iterator I = locInts.begin(); I.valid(); ++I) {
const DbgVariableValue &DbgValue = I.value();
if (DbgValue.containsLocNo(LocNo))
// Remove the entry in the locations vector, and adjust all references to
// location numbers above the removed entry.
locations.erase(locations.begin() + LocNo);
for (LocMap::iterator I = locInts.begin(); I.valid(); ++I) {
const DbgVariableValue &DbgValue = I.value();
if (DbgValue.hasLocNoGreaterThan(LocNo))
/// Ensure that all virtual register locations are mapped.
void mapVirtRegs(LDVImpl *LDV);
/// Add a definition point to this user value.
void addDef(SlotIndex Idx, ArrayRef<MachineOperand> LocMOs, bool IsIndirect,
bool IsList, const DIExpression &Expr) {
SmallVector<unsigned> Locs;
for (const MachineOperand &Op : LocMOs)
DbgVariableValue DbgValue(Locs, IsIndirect, IsList, Expr);
// Add a singular (Idx,Idx) -> value mapping.
LocMap::iterator I = locInts.find(Idx);
if (!I.valid() || I.start() != Idx)
I.insert(Idx, Idx.getNextSlot(), std::move(DbgValue));
// A later DBG_VALUE at the same SlotIndex overrides the old location.
/// Extend the current definition as far as possible down.
/// Stop when meeting an existing def or when leaving the live
/// range of VNI. End points where VNI is no longer live are added to Kills.
/// We only propagate DBG_VALUES locally here. LiveDebugValues performs a
/// data-flow analysis to propagate them beyond basic block boundaries.
/// \param Idx Starting point for the definition.
/// \param DbgValue value to propagate.
/// \param LiveIntervalInfo For each location number key in this map,
/// restricts liveness to where the LiveRange has the value equal to the\
/// VNInfo.
/// \param [out] Kills Append end points of VNI's live range to Kills.
/// \param LIS Live intervals analysis.
extendDef(SlotIndex Idx, DbgVariableValue DbgValue,
SmallDenseMap<unsigned, std::pair<LiveRange *, const VNInfo *>>
std::optional<std::pair<SlotIndex, SmallVector<unsigned>>> &Kills,
LiveIntervals &LIS);
/// The value in LI may be copies to other registers. Determine if
/// any of the copies are available at the kill points, and add defs if
/// possible.
/// \param DbgValue Location number of LI->reg, and DIExpression.
/// \param LocIntervals Scan for copies of the value for each location in the
/// corresponding LiveInterval->reg.
/// \param KilledAt The point where the range of DbgValue could be extended.
/// \param [in,out] NewDefs Append (Idx, DbgValue) of inserted defs here.
void addDefsFromCopies(
DbgVariableValue DbgValue,
SmallVectorImpl<std::pair<unsigned, LiveInterval *>> &LocIntervals,
SlotIndex KilledAt,
SmallVectorImpl<std::pair<SlotIndex, DbgVariableValue>> &NewDefs,
MachineRegisterInfo &MRI, LiveIntervals &LIS);
/// Compute the live intervals of all locations after collecting all their
/// def points.
void computeIntervals(MachineRegisterInfo &MRI, const TargetRegisterInfo &TRI,
LiveIntervals &LIS, LexicalScopes &LS);
/// Replace OldReg ranges with NewRegs ranges where NewRegs is
/// live. Returns true if any changes were made.
bool splitRegister(Register OldReg, ArrayRef<Register> NewRegs,
LiveIntervals &LIS);
/// Rewrite virtual register locations according to the provided virtual
/// register map. Record the stack slot offsets for the locations that
/// were spilled.
void rewriteLocations(VirtRegMap &VRM, const MachineFunction &MF,
const TargetInstrInfo &TII,
const TargetRegisterInfo &TRI,
SpillOffsetMap &SpillOffsets);
/// Recreate DBG_VALUE instruction from data structures.
void emitDebugValues(VirtRegMap *VRM, LiveIntervals &LIS,
const TargetInstrInfo &TII,
const TargetRegisterInfo &TRI,
const SpillOffsetMap &SpillOffsets,
BlockSkipInstsMap &BBSkipInstsMap);
/// Return DebugLoc of this UserValue.
const DebugLoc &getDebugLoc() { return dl; }
void print(raw_ostream &, const TargetRegisterInfo *);
/// A user label is a part of a debug info user label.
class UserLabel {
const DILabel *Label; ///< The debug info label we are part of.
DebugLoc dl; ///< The debug location for the label. This is
///< used by dwarf writer to find lexical scope.
SlotIndex loc; ///< Slot used by the debug label.
/// Insert a DBG_LABEL into MBB at Idx.
void insertDebugLabel(MachineBasicBlock *MBB, SlotIndex Idx,
LiveIntervals &LIS, const TargetInstrInfo &TII,
BlockSkipInstsMap &BBSkipInstsMap);
/// Create a new UserLabel.
UserLabel(const DILabel *label, DebugLoc L, SlotIndex Idx)
: Label(label), dl(std::move(L)), loc(Idx) {}
/// Does this UserLabel match the parameters?
bool matches(const DILabel *L, const DILocation *IA,
const SlotIndex Index) const {
return Label == L && dl->getInlinedAt() == IA && loc == Index;
/// Recreate DBG_LABEL instruction from data structures.
void emitDebugLabel(LiveIntervals &LIS, const TargetInstrInfo &TII,
BlockSkipInstsMap &BBSkipInstsMap);
/// Return DebugLoc of this UserLabel.
const DebugLoc &getDebugLoc() { return dl; }
void print(raw_ostream &, const TargetRegisterInfo *);
/// Implementation of the LiveDebugVariables pass.
class LDVImpl {
LiveDebugVariables &pass;
LocMap::Allocator allocator;
MachineFunction *MF = nullptr;
LiveIntervals *LIS;
const TargetRegisterInfo *TRI;
/// Position and VReg of a PHI instruction during register allocation.
struct PHIValPos {
SlotIndex SI; /// Slot where this PHI occurs.
Register Reg; /// VReg this PHI occurs in.
unsigned SubReg; /// Qualifiying subregister for Reg.
/// Map from debug instruction number to PHI position during allocation.
std::map<unsigned, PHIValPos> PHIValToPos;
/// Index of, for each VReg, which debug instruction numbers and corresponding
/// PHIs are sensitive to splitting. Each VReg may have multiple PHI defs,
/// at different positions.
DenseMap<Register, std::vector<unsigned>> RegToPHIIdx;
/// Record for any debug instructions unlinked from their blocks during
/// regalloc. Stores the instr and it's location, so that they can be
/// re-inserted after regalloc is over.
struct InstrPos {
MachineInstr *MI; ///< Debug instruction, unlinked from it's block.
SlotIndex Idx; ///< Slot position where MI should be re-inserted.
MachineBasicBlock *MBB; ///< Block that MI was in.
/// Collection of stored debug instructions, preserved until after regalloc.
SmallVector<InstrPos, 32> StashedDebugInstrs;
/// Whether emitDebugValues is called.
bool EmitDone = false;
/// Whether the machine function is modified during the pass.
bool ModifiedMF = false;
/// All allocated UserValue instances.
SmallVector<std::unique_ptr<UserValue>, 8> userValues;
/// All allocated UserLabel instances.
SmallVector<std::unique_ptr<UserLabel>, 2> userLabels;
/// Map virtual register to eq class leader.
using VRMap = DenseMap<unsigned, UserValue *>;
VRMap virtRegToEqClass;
/// Map to find existing UserValue instances.
using UVMap = DenseMap<DebugVariable, UserValue *>;
UVMap userVarMap;
/// Find or create a UserValue.
UserValue *getUserValue(const DILocalVariable *Var,
std::optional<DIExpression::FragmentInfo> Fragment,
const DebugLoc &DL);
/// Find the EC leader for VirtReg or null.
UserValue *lookupVirtReg(Register VirtReg);
/// Add DBG_VALUE instruction to our maps.
/// \param MI DBG_VALUE instruction
/// \param Idx Last valid SLotIndex before instruction.
/// \returns True if the DBG_VALUE instruction should be deleted.
bool handleDebugValue(MachineInstr &MI, SlotIndex Idx);
/// Track variable location debug instructions while using the instruction
/// referencing implementation. Such debug instructions do not need to be
/// updated during regalloc because they identify instructions rather than
/// register locations. However, they needs to be removed from the
/// MachineFunction during regalloc, then re-inserted later, to avoid
/// disrupting the allocator.
/// \param MI Any DBG_VALUE / DBG_INSTR_REF / DBG_PHI instruction
/// \param Idx Last valid SlotIndex before instruction
/// \returns Iterator to continue processing from after unlinking.
MachineBasicBlock::iterator handleDebugInstr(MachineInstr &MI, SlotIndex Idx);
/// Add DBG_LABEL instruction to UserLabel.
/// \param MI DBG_LABEL instruction
/// \param Idx Last valid SlotIndex before instruction.
/// \returns True if the DBG_LABEL instruction should be deleted.
bool handleDebugLabel(MachineInstr &MI, SlotIndex Idx);
/// Collect and erase all DBG_VALUE instructions, adding a UserValue def
/// for each instruction.
/// \param mf MachineFunction to be scanned.
/// \param InstrRef Whether to operate in instruction referencing mode. If
/// true, most of LiveDebugVariables doesn't run.
/// \returns True if any debug values were found.
bool collectDebugValues(MachineFunction &mf, bool InstrRef);
/// Compute the live intervals of all user values after collecting all
/// their def points.
void computeIntervals();
LDVImpl(LiveDebugVariables *ps) : pass(*ps) {}
bool runOnMachineFunction(MachineFunction &mf, bool InstrRef);
/// Release all memory.
void clear() {
MF = nullptr;
// Make sure we call emitDebugValues if the machine function was modified.
assert((!ModifiedMF || EmitDone) &&
"Dbg values are not emitted in LDV");
EmitDone = false;
ModifiedMF = false;
/// Map virtual register to an equivalence class.
void mapVirtReg(Register VirtReg, UserValue *EC);
/// Replace any PHI referring to OldReg with its corresponding NewReg, if
/// present.
void splitPHIRegister(Register OldReg, ArrayRef<Register> NewRegs);
/// Replace all references to OldReg with NewRegs.
void splitRegister(Register OldReg, ArrayRef<Register> NewRegs);
/// Recreate DBG_VALUE instruction from data structures.
void emitDebugValues(VirtRegMap *VRM);
void print(raw_ostream&);
} // end anonymous namespace
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
static void printDebugLoc(const DebugLoc &DL, raw_ostream &CommentOS,
const LLVMContext &Ctx) {
if (!DL)
auto *Scope = cast<DIScope>(DL.getScope());
// Omit the directory, because it's likely to be long and uninteresting.
CommentOS << Scope->getFilename();
CommentOS << ':' << DL.getLine();
if (DL.getCol() != 0)
CommentOS << ':' << DL.getCol();
DebugLoc InlinedAtDL = DL.getInlinedAt();
if (!InlinedAtDL)
CommentOS << " @[ ";
printDebugLoc(InlinedAtDL, CommentOS, Ctx);
CommentOS << " ]";
static void printExtendedName(raw_ostream &OS, const DINode *Node,
const DILocation *DL) {
const LLVMContext &Ctx = Node->getContext();
StringRef Res;
unsigned Line = 0;
if (const auto *V = dyn_cast<const DILocalVariable>(Node)) {
Res = V->getName();
Line = V->getLine();
} else if (const auto *L = dyn_cast<const DILabel>(Node)) {
Res = L->getName();
Line = L->getLine();
if (!Res.empty())
OS << Res << "," << Line;
auto *InlinedAt = DL ? DL->getInlinedAt() : nullptr;
if (InlinedAt) {
if (DebugLoc InlinedAtDL = InlinedAt) {
OS << " @[";
printDebugLoc(InlinedAtDL, OS, Ctx);
OS << "]";
void UserValue::print(raw_ostream &OS, const TargetRegisterInfo *TRI) {
OS << "!\"";
printExtendedName(OS, Variable, dl);
OS << "\"\t";
for (LocMap::const_iterator I = locInts.begin(); I.valid(); ++I) {
OS << " [" << I.start() << ';' << I.stop() << "):";
if (I.value().isUndef())
OS << " undef";
else {
if (I.value().getWasIndirect())
OS << " ind";
else if (I.value().getWasList())
OS << " list";
for (unsigned i = 0, e = locations.size(); i != e; ++i) {
OS << " Loc" << i << '=';
locations[i].print(OS, TRI);
OS << '\n';
void UserLabel::print(raw_ostream &OS, const TargetRegisterInfo *TRI) {
OS << "!\"";
printExtendedName(OS, Label, dl);
OS << "\"\t";
OS << loc;
OS << '\n';
void LDVImpl::print(raw_ostream &OS) {
OS << "********** DEBUG VARIABLES **********\n";
for (auto &userValue : userValues)
userValue->print(OS, TRI);
OS << "********** DEBUG LABELS **********\n";
for (auto &userLabel : userLabels)
userLabel->print(OS, TRI);
void UserValue::mapVirtRegs(LDVImpl *LDV) {
for (unsigned i = 0, e = locations.size(); i != e; ++i)
if (locations[i].isReg() && locations[i].getReg().isVirtual())
LDV->mapVirtReg(locations[i].getReg(), this);
UserValue *
LDVImpl::getUserValue(const DILocalVariable *Var,
std::optional<DIExpression::FragmentInfo> Fragment,
const DebugLoc &DL) {
// FIXME: Handle partially overlapping fragments. See
DebugVariable ID(Var, Fragment, DL->getInlinedAt());
UserValue *&UV = userVarMap[ID];
if (!UV) {
std::make_unique<UserValue>(Var, Fragment, DL, allocator));
UV = userValues.back().get();
return UV;
void LDVImpl::mapVirtReg(Register VirtReg, UserValue *EC) {
assert(VirtReg.isVirtual() && "Only map VirtRegs");
UserValue *&Leader = virtRegToEqClass[VirtReg];
Leader = UserValue::merge(Leader, EC);
UserValue *LDVImpl::lookupVirtReg(Register VirtReg) {
if (UserValue *UV = virtRegToEqClass.lookup(VirtReg))
return UV->getLeader();
return nullptr;
bool LDVImpl::handleDebugValue(MachineInstr &MI, SlotIndex Idx) {
// DBG_VALUE loc, offset, variable, expr
// DBG_VALUE_LIST variable, expr, locs...
if (!MI.isDebugValue()) {
LLVM_DEBUG(dbgs() << "Can't handle non-DBG_VALUE*: " << MI);
return false;
if (!MI.getDebugVariableOp().isMetadata()) {
LLVM_DEBUG(dbgs() << "Can't handle DBG_VALUE* with invalid variable: "
<< MI);
return false;
if (MI.isNonListDebugValue() &&
(MI.getNumOperands() != 4 ||
!(MI.getDebugOffset().isImm() || MI.getDebugOffset().isReg()))) {
LLVM_DEBUG(dbgs() << "Can't handle malformed DBG_VALUE: " << MI);
return false;
// Detect invalid DBG_VALUE instructions, with a debug-use of a virtual
// register that hasn't been defined yet. If we do not remove those here, then
// the re-insertion of the DBG_VALUE instruction after register allocation
// will be incorrect.
bool Discard = false;
for (const MachineOperand &Op : MI.debug_operands()) {
if (Op.isReg() && Op.getReg().isVirtual()) {
const Register Reg = Op.getReg();
if (!LIS->hasInterval(Reg)) {
// The DBG_VALUE is described by a virtual register that does not have a
// live interval. Discard the DBG_VALUE.
Discard = true;
LLVM_DEBUG(dbgs() << "Discarding debug info (no LIS interval): " << Idx
<< " " << MI);
} else {
// The DBG_VALUE is only valid if either Reg is live out from Idx, or
// Reg is defined dead at Idx (where Idx is the slot index for the
// instruction preceding the DBG_VALUE).
const LiveInterval &LI = LIS->getInterval(Reg);
LiveQueryResult LRQ = LI.Query(Idx);
if (!LRQ.valueOutOrDead()) {
// We have found a DBG_VALUE with the value in a virtual register that
// is not live. Discard the DBG_VALUE.
Discard = true;
LLVM_DEBUG(dbgs() << "Discarding debug info (reg not live): " << Idx
<< " " << MI);
// Get or create the UserValue for (variable,offset) here.
bool IsIndirect = MI.isDebugOffsetImm();
if (IsIndirect)
assert(MI.getDebugOffset().getImm() == 0 &&
"DBG_VALUE with nonzero offset");
bool IsList = MI.isDebugValueList();
const DILocalVariable *Var = MI.getDebugVariable();
const DIExpression *Expr = MI.getDebugExpression();
UserValue *UV = getUserValue(Var, Expr->getFragmentInfo(), MI.getDebugLoc());
if (!Discard)
IsIndirect, IsList, *Expr);
else {
MachineOperand MO = MachineOperand::CreateReg(0U, false);
// We should still pass a list the same size as MI.debug_operands() even if
// all MOs are undef, so that DbgVariableValue can correctly adjust the
// expression while removing the duplicated undefs.
SmallVector<MachineOperand, 4> UndefMOs(MI.getNumDebugOperands(), MO);
UV->addDef(Idx, UndefMOs, false, IsList, *Expr);
return true;
MachineBasicBlock::iterator LDVImpl::handleDebugInstr(MachineInstr &MI,
SlotIndex Idx) {
assert(MI.isDebugValueLike() || MI.isDebugPHI());
// In instruction referencing mode, there should be no DBG_VALUE instructions
// that refer to virtual registers. They might still refer to constants.
if (MI.isDebugValueLike())
[](const MachineOperand &MO) {
return MO.isReg() && MO.getReg().isVirtual();
}) &&
"MIs should not refer to Virtual Registers in InstrRef mode.");
// Unlink the instruction, store it in the debug instructions collection.
auto NextInst = std::next(MI.getIterator());
auto *MBB = MI.getParent();
StashedDebugInstrs.push_back({&MI, Idx, MBB});
return NextInst;
bool LDVImpl::handleDebugLabel(MachineInstr &MI, SlotIndex Idx) {
// DBG_LABEL label
if (MI.getNumOperands() != 1 || !MI.getOperand(0).isMetadata()) {
LLVM_DEBUG(dbgs() << "Can't handle " << MI);
return false;
// Get or create the UserLabel for label here.
const DILabel *Label = MI.getDebugLabel();
const DebugLoc &DL = MI.getDebugLoc();
bool Found = false;
for (auto const &L : userLabels) {
if (L->matches(Label, DL->getInlinedAt(), Idx)) {
Found = true;
if (!Found)
userLabels.push_back(std::make_unique<UserLabel>(Label, DL, Idx));
return true;
bool LDVImpl::collectDebugValues(MachineFunction &mf, bool InstrRef) {
bool Changed = false;
for (MachineBasicBlock &MBB : mf) {
for (MachineBasicBlock::iterator MBBI = MBB.begin(), MBBE = MBB.end();
MBBI != MBBE;) {
// Use the first debug instruction in the sequence to get a SlotIndex
// for following consecutive debug instructions.
if (!MBBI->isDebugOrPseudoInstr()) {
// Debug instructions has no slot index. Use the previous
// non-debug instruction's SlotIndex as its SlotIndex.
SlotIndex Idx =
MBBI == MBB.begin()
? LIS->getMBBStartIdx(&MBB)
: LIS->getInstructionIndex(*std::prev(MBBI)).getRegSlot();
// Handle consecutive debug instructions with the same slot index.
do {
// In instruction referencing mode, pass each instr to handleDebugInstr
// to be unlinked. Ignore DBG_VALUE_LISTs -- they refer to vregs, and
// need to go through the normal live interval splitting process.
if (InstrRef && (MBBI->isNonListDebugValue() || MBBI->isDebugPHI() ||
MBBI->isDebugRef())) {
MBBI = handleDebugInstr(*MBBI, Idx);
Changed = true;
// In normal debug mode, use the dedicated DBG_VALUE / DBG_LABEL handler
// to track things through register allocation, and erase the instr.
} else if ((MBBI->isDebugValue() && handleDebugValue(*MBBI, Idx)) ||
(MBBI->isDebugLabel() && handleDebugLabel(*MBBI, Idx))) {
MBBI = MBB.erase(MBBI);
Changed = true;
} else
} while (MBBI != MBBE && MBBI->isDebugOrPseudoInstr());
return Changed;
void UserValue::extendDef(
SlotIndex Idx, DbgVariableValue DbgValue,
SmallDenseMap<unsigned, std::pair<LiveRange *, const VNInfo *>>
std::optional<std::pair<SlotIndex, SmallVector<unsigned>>> &Kills,
LiveIntervals &LIS) {
SlotIndex Start = Idx;
MachineBasicBlock *MBB = LIS.getMBBFromIndex(Start);
SlotIndex Stop = LIS.getMBBEndIdx(MBB);
LocMap::iterator I = locInts.find(Start);
// Limit to the intersection of the VNIs' live ranges.
for (auto &LII : LiveIntervalInfo) {
LiveRange *LR = LII.second.first;
assert(LR && LII.second.second && "Missing range info for Idx.");
LiveInterval::Segment *Segment = LR->getSegmentContaining(Start);
assert(Segment && Segment->valno == LII.second.second &&
"Invalid VNInfo for Idx given?");
if (Segment->end < Stop) {
Stop = Segment->end;
Kills = {Stop, {LII.first}};
} else if (Segment->end == Stop && Kills) {
// If multiple locations end at the same place, track all of them in
// Kills.
// There could already be a short def at Start.
if (I.valid() && I.start() <= Start) {
// Stop when meeting a different location or an already extended interval.
Start = Start.getNextSlot();
if (I.value() != DbgValue || I.stop() != Start) {
// Clear `Kills`, as we have a new def available.
Kills = std::nullopt;
// This is a one-slot placeholder. Just skip it.
// Limited by the next def.
if (I.valid() && I.start() < Stop) {
Stop = I.start();
// Clear `Kills`, as we have a new def available.
Kills = std::nullopt;
if (Start < Stop) {
DbgVariableValue ExtDbgValue(DbgValue);
I.insert(Start, Stop, std::move(ExtDbgValue));
void UserValue::addDefsFromCopies(
DbgVariableValue DbgValue,
SmallVectorImpl<std::pair<unsigned, LiveInterval *>> &LocIntervals,
SlotIndex KilledAt,
SmallVectorImpl<std::pair<SlotIndex, DbgVariableValue>> &NewDefs,
MachineRegisterInfo &MRI, LiveIntervals &LIS) {
// Don't track copies from physregs, there are too many uses.
if (any_of(LocIntervals,
[](auto LocI) { return !LocI.second->reg().isVirtual(); }))
// Collect all the (vreg, valno) pairs that are copies of LI.
SmallVector<std::pair<LiveInterval *, const VNInfo *>, 4>>
for (auto &LocInterval : LocIntervals) {
unsigned LocNo = LocInterval.first;
LiveInterval *LI = LocInterval.second;
for (MachineOperand &MO : MRI.use_nodbg_operands(LI->reg())) {
MachineInstr *MI = MO.getParent();
// Copies of the full value.
if (MO.getSubReg() || !MI->isCopy())
Register DstReg = MI->getOperand(0).getReg();
// Don't follow copies to physregs. These are usually setting up call
// arguments, and the argument registers are always call clobbered. We are
// better off in the source register which could be a callee-saved
// register, or it could be spilled.
if (!DstReg.isVirtual())
// Is the value extended to reach this copy? If not, another def may be
// blocking it, or we are looking at a wrong value of LI.
SlotIndex Idx = LIS.getInstructionIndex(*MI);
LocMap::iterator I = locInts.find(Idx.getRegSlot(true));
if (!I.valid() || I.value() != DbgValue)
if (!LIS.hasInterval(DstReg))
LiveInterval *DstLI = &LIS.getInterval(DstReg);
const VNInfo *DstVNI = DstLI->getVNInfoAt(Idx.getRegSlot());
assert(DstVNI && DstVNI->def == Idx.getRegSlot() && "Bad copy value");
CopyValues[LocNo].push_back(std::make_pair(DstLI, DstVNI));
if (CopyValues.empty())
#if !defined(NDEBUG)
for (auto &LocInterval : LocIntervals)
LLVM_DEBUG(dbgs() << "Got " << CopyValues[LocInterval.first].size()
<< " copies of " << *LocInterval.second << '\n');
// Try to add defs of the copied values for the kill point. Check that there
// isn't already a def at Idx.
LocMap::iterator I = locInts.find(KilledAt);
if (I.valid() && I.start() <= KilledAt)
DbgVariableValue NewValue(DbgValue);
for (auto &LocInterval : LocIntervals) {
unsigned LocNo = LocInterval.first;
bool FoundCopy = false;
for (auto &LIAndVNI : CopyValues[LocNo]) {
LiveInterval *DstLI = LIAndVNI.first;
const VNInfo *DstVNI = LIAndVNI.second;
if (DstLI->getVNInfoAt(KilledAt) != DstVNI)
LLVM_DEBUG(dbgs() << "Kill at " << KilledAt << " covered by valno #"
<< DstVNI->id << " in " << *DstLI << '\n');
MachineInstr *CopyMI = LIS.getInstructionFromIndex(DstVNI->def);
assert(CopyMI && CopyMI->isCopy() && "Bad copy value");
unsigned NewLocNo = getLocationNo(CopyMI->getOperand(0));
NewValue = NewValue.changeLocNo(LocNo, NewLocNo);
FoundCopy = true;
// If there are any killed locations we can't find a copy for, we can't
// extend the variable value.
if (!FoundCopy)
I.insert(KilledAt, KilledAt.getNextSlot(), NewValue);
NewDefs.push_back(std::make_pair(KilledAt, NewValue));
void UserValue::computeIntervals(MachineRegisterInfo &MRI,
const TargetRegisterInfo &TRI,
LiveIntervals &LIS, LexicalScopes &LS) {
SmallVector<std::pair<SlotIndex, DbgVariableValue>, 16> Defs;
// Collect all defs to be extended (Skipping undefs).
for (LocMap::const_iterator I = locInts.begin(); I.valid(); ++I)
if (!I.value().isUndef())
Defs.push_back(std::make_pair(I.start(), I.value()));
// Extend all defs, and possibly add new ones along the way.
for (unsigned i = 0; i != Defs.size(); ++i) {
SlotIndex Idx = Defs[i].first;
DbgVariableValue DbgValue = Defs[i].second;
SmallDenseMap<unsigned, std::pair<LiveRange *, const VNInfo *>> LIs;
SmallVector<const VNInfo *, 4> VNIs;
bool ShouldExtendDef = false;
for (unsigned LocNo : DbgValue.loc_nos()) {
const MachineOperand &LocMO = locations[LocNo];
if (!LocMO.isReg() || !LocMO.getReg().isVirtual()) {
ShouldExtendDef |= !LocMO.isReg();
ShouldExtendDef = true;
LiveInterval *LI = nullptr;
const VNInfo *VNI = nullptr;
if (LIS.hasInterval(LocMO.getReg())) {
LI = &LIS.getInterval(LocMO.getReg());
VNI = LI->getVNInfoAt(Idx);
if (LI && VNI)
LIs[LocNo] = {LI, VNI};
if (ShouldExtendDef) {
std::optional<std::pair<SlotIndex, SmallVector<unsigned>>> Kills;
extendDef(Idx, DbgValue, LIs, Kills, LIS);
if (Kills) {
SmallVector<std::pair<unsigned, LiveInterval *>, 2> KilledLocIntervals;
bool AnySubreg = false;
for (unsigned LocNo : Kills->second) {
const MachineOperand &LocMO = this->locations[LocNo];
if (LocMO.getSubReg()) {
AnySubreg = true;
LiveInterval *LI = &LIS.getInterval(LocMO.getReg());
KilledLocIntervals.push_back({LocNo, LI});
// FIXME: Handle sub-registers in addDefsFromCopies. The problem is that
// if the original location for example is %vreg0:sub_hi, and we find a
// full register copy in addDefsFromCopies (at the moment it only
// handles full register copies), then we must add the sub1 sub-register
// index to the new location. However, that is only possible if the new
// virtual register is of the same regclass (or if there is an
// equivalent sub-register in that regclass). For now, simply skip
// handling copies if a sub-register is involved.
if (!AnySubreg)
addDefsFromCopies(DbgValue, KilledLocIntervals, Kills->first, Defs,
// For physregs, we only mark the start slot idx. DwarfDebug will see it
// as if the DBG_VALUE is valid up until the end of the basic block, or
// the next def of the physical register. So we do not need to extend the
// range. It might actually happen that the DBG_VALUE is the last use of
// the physical register (e.g. if this is an unused input argument to a
// function).
// The computed intervals may extend beyond the range of the debug
// location's lexical scope. In this case, splitting of an interval
// can result in an interval outside of the scope being created,
// causing extra unnecessary DBG_VALUEs to be emitted. To prevent
// this, trim the intervals to the lexical scope in the case of inlined
// variables, since heavy inlining may cause production of dramatically big
// number of DBG_VALUEs to be generated.
if (!dl.getInlinedAt())
LexicalScope *Scope = LS.findLexicalScope(dl);
if (!Scope)
SlotIndex PrevEnd;
LocMap::iterator I = locInts.begin();
// Iterate over the lexical scope ranges. Each time round the loop
// we check the intervals for overlap with the end of the previous
// range and the start of the next. The first range is handled as
// a special case where there is no PrevEnd.
for (const InsnRange &Range : Scope->getRanges()) {
SlotIndex RStart = LIS.getInstructionIndex(*Range.first);
SlotIndex REnd = LIS.getInstructionIndex(*Range.second);
// Variable locations at the first instruction of a block should be
// based on the block's SlotIndex, not the first instruction's index.
if (Range.first == Range.first->getParent()->begin())
RStart = LIS.getSlotIndexes()->getIndexBefore(*Range.first);
// At the start of each iteration I has been advanced so that
// I.stop() >= PrevEnd. Check for overlap.
if (PrevEnd && I.start() < PrevEnd) {
SlotIndex IStop = I.stop();
DbgVariableValue DbgValue = I.value();
// Stop overlaps previous end - trim the end of the interval to
// the scope range.
// If the interval also overlaps the start of the "next" (i.e.
// current) range create a new interval for the remainder (which
// may be further trimmed).
if (RStart < IStop)
I.insert(RStart, IStop, DbgValue);
// Advance I so that I.stop() >= RStart, and check for overlap.
if (!I.valid())
if (I.start() < RStart) {
// Interval start overlaps range - trim to the scope range.
// Remember that this interval was trimmed.
// The end of a lexical scope range is the last instruction in the
// range. To convert to an interval we need the index of the
// instruction after it.
REnd = REnd.getNextIndex();
// Advance I to first interval outside current range.
if (!I.valid())
PrevEnd = REnd;
// Check for overlap with end of final range.
if (PrevEnd && I.start() < PrevEnd)
void LDVImpl::computeIntervals() {
LexicalScopes LS;
for (unsigned i = 0, e = userValues.size(); i != e; ++i) {
userValues[i]->computeIntervals(MF->getRegInfo(), *TRI, *LIS, LS);
bool LDVImpl::runOnMachineFunction(MachineFunction &mf, bool InstrRef) {
MF = &mf;
LIS = &pass.getAnalysis<LiveIntervals>();
TRI = mf.getSubtarget().getRegisterInfo();
<< mf.getName() << " **********\n");
bool Changed = collectDebugValues(mf, InstrRef);
// Collect the set of VReg / SlotIndexs where PHIs occur; index the sensitive
// VRegs too, for when we're notified of a range split.
SlotIndexes *Slots = LIS->getSlotIndexes();
for (const auto &PHIIt : MF->DebugPHIPositions) {
const MachineFunction::DebugPHIRegallocPos &Position = PHIIt.second;
MachineBasicBlock *MBB = Position.MBB;
Register Reg = Position.Reg;
unsigned SubReg = Position.SubReg;
SlotIndex SI = Slots->getMBBStartIdx(MBB);
PHIValPos VP = {SI, Reg, SubReg};
PHIValToPos.insert(std::make_pair(PHIIt.first, VP));
ModifiedMF = Changed;
return Changed;
static void removeDebugInstrs(MachineFunction &mf) {
for (MachineBasicBlock &MBB : mf) {
for (MachineInstr &MI : llvm::make_early_inc_range(MBB))
if (MI.isDebugInstr())
bool LiveDebugVariables::runOnMachineFunction(MachineFunction &mf) {
if (!EnableLDV)
return false;
if (!mf.getFunction().getSubprogram()) {
return false;
// Have we been asked to track variable locations using instruction
// referencing?
bool InstrRef = mf.useDebugInstrRef();
if (!pImpl)
pImpl = new LDVImpl(this);
return static_cast<LDVImpl *>(pImpl)->runOnMachineFunction(mf, InstrRef);
void LiveDebugVariables::releaseMemory() {
if (pImpl)
LiveDebugVariables::~LiveDebugVariables() {
if (pImpl)
delete static_cast<LDVImpl*>(pImpl);
// Live Range Splitting
UserValue::splitLocation(unsigned OldLocNo, ArrayRef<Register> NewRegs,
LiveIntervals& LIS) {
dbgs() << "Splitting Loc" << OldLocNo << '\t';
print(dbgs(), nullptr);
bool DidChange = false;
LocMap::iterator LocMapI;
for (Register NewReg : NewRegs) {
LiveInterval *LI = &LIS.getInterval(NewReg);
if (LI->empty())
// Don't allocate the new LocNo until it is needed.
unsigned NewLocNo = UndefLocNo;
// Iterate over the overlaps between locInts and LI.
if (!LocMapI.valid())
LiveInterval::iterator LII = LI->advanceTo(LI->begin(), LocMapI.start());
LiveInterval::iterator LIE = LI->end();
while (LocMapI.valid() && LII != LIE) {
// At this point, we know that LocMapI.stop() > LII->start.
LII = LI->advanceTo(LII, LocMapI.start());
if (LII == LIE)
// Now LII->end > LocMapI.start(). Do we have an overlap?
if (LocMapI.value().containsLocNo(OldLocNo) &&
LII->start < LocMapI.stop()) {
// Overlapping correct location. Allocate NewLocNo now.
if (NewLocNo == UndefLocNo) {
MachineOperand MO = MachineOperand::CreateReg(LI->reg(), false);
NewLocNo = getLocationNo(MO);
DidChange = true;
SlotIndex LStart = LocMapI.start();
SlotIndex LStop = LocMapI.stop();
DbgVariableValue OldDbgValue = LocMapI.value();
// Trim LocMapI down to the LII overlap.
if (LStart < LII->start)
if (LStop > LII->end)
// Change the value in the overlap. This may trigger coalescing.
LocMapI.setValue(OldDbgValue.changeLocNo(OldLocNo, NewLocNo));
// Re-insert any removed OldDbgValue ranges.
if (LStart < LocMapI.start()) {
LocMapI.insert(LStart, LocMapI.start(), OldDbgValue);
assert(LocMapI.valid() && "Unexpected coalescing");
if (LStop > LocMapI.stop()) {
LocMapI.insert(LII->end, LStop, OldDbgValue);
// Advance to the next overlap.
if (LII->end < LocMapI.stop()) {
if (++LII == LIE)
} else {
if (!LocMapI.valid())
LII = LI->advanceTo(LII, LocMapI.start());
// Finally, remove OldLocNo unless it is still used by some interval in the
// locInts map. One case when OldLocNo still is in use is when the register
// has been spilled. In such situations the spilled register is kept as a
// location until rewriteLocations is called (VirtRegMap is mapping the old
// register to the spill slot). So for a while we can have locations that map
// to virtual registers that have been removed from both the MachineFunction
// and from LiveIntervals.
// We may also just be using the location for a value with a different
// expression.
dbgs() << "Split result: \t";
print(dbgs(), nullptr);
return DidChange;
UserValue::splitRegister(Register OldReg, ArrayRef<Register> NewRegs,
LiveIntervals &LIS) {
bool DidChange = false;
// Split locations referring to OldReg. Iterate backwards so splitLocation can
// safely erase unused locations.
for (unsigned i = locations.size(); i ; --i) {
unsigned LocNo = i-1;
const MachineOperand *Loc = &locations[LocNo];
if (!Loc->isReg() || Loc->getReg() != OldReg)
DidChange |= splitLocation(LocNo, NewRegs, LIS);
return DidChange;
void LDVImpl::splitPHIRegister(Register OldReg, ArrayRef<Register> NewRegs) {
auto RegIt = RegToPHIIdx.find(OldReg);
if (RegIt == RegToPHIIdx.end())
std::vector<std::pair<Register, unsigned>> NewRegIdxes;
// Iterate over all the debug instruction numbers affected by this split.
for (unsigned InstrID : RegIt->second) {
auto PHIIt = PHIValToPos.find(InstrID);
assert(PHIIt != PHIValToPos.end());
const SlotIndex &Slot = PHIIt->second.SI;
assert(OldReg == PHIIt->second.Reg);
// Find the new register that covers this position.
for (auto NewReg : NewRegs) {
const LiveInterval &LI = LIS->getInterval(NewReg);
auto LII = LI.find(Slot);
if (LII != LI.end() && LII->start <= Slot) {
// This new register covers this PHI position, record this for indexing.
NewRegIdxes.push_back(std::make_pair(NewReg, InstrID));
// Record that this value lives in a different VReg now.
PHIIt->second.Reg = NewReg;
// If we do not find a new register covering this PHI, then register
// allocation has dropped its location, for example because it's not live.
// The old VReg will not be mapped to a physreg, and the instruction
// number will have been optimized out.
// Re-create register index using the new register numbers.
for (auto &RegAndInstr : NewRegIdxes)
void LDVImpl::splitRegister(Register OldReg, ArrayRef<Register> NewRegs) {
// Consider whether this split range affects any PHI locations.
splitPHIRegister(OldReg, NewRegs);
// Check whether any intervals mapped by a DBG_VALUE were split and need
// updating.
bool DidChange = false;
for (UserValue *UV = lookupVirtReg(OldReg); UV; UV = UV->getNext())
DidChange |= UV->splitRegister(OldReg, NewRegs, *LIS);
if (!DidChange)
// Map all of the new virtual registers.
UserValue *UV = lookupVirtReg(OldReg);
for (Register NewReg : NewRegs)
mapVirtReg(NewReg, UV);
void LiveDebugVariables::
splitRegister(Register OldReg, ArrayRef<Register> NewRegs, LiveIntervals &LIS) {
if (pImpl)
static_cast<LDVImpl*>(pImpl)->splitRegister(OldReg, NewRegs);
void UserValue::rewriteLocations(VirtRegMap &VRM, const MachineFunction &MF,
const TargetInstrInfo &TII,
const TargetRegisterInfo &TRI,
SpillOffsetMap &SpillOffsets) {
// Build a set of new locations with new numbers so we can coalesce our
// IntervalMap if two vreg intervals collapse to the same physical location.
// Use MapVector instead of SetVector because MapVector::insert returns the
// position of the previously or newly inserted element. The boolean value
// tracks if the location was produced by a spill.
// FIXME: This will be problematic if we ever support direct and indirect
// frame index locations, i.e. expressing both variables in memory and
// 'int x, *px = &x'. The "spilled" bit must become part of the location.
MapVector<MachineOperand, std::pair<bool, unsigned>> NewLocations;
SmallVector<unsigned, 4> LocNoMap(locations.size());
for (unsigned I = 0, E = locations.size(); I != E; ++I) {
bool Spilled = false;
unsigned SpillOffset = 0;
MachineOperand Loc = locations[I];
// Only virtual registers are rewritten.
if (Loc.isReg() && Loc.getReg() && Loc.getReg().isVirtual()) {
Register VirtReg = Loc.getReg();
if (VRM.isAssignedReg(VirtReg) &&
Register::isPhysicalRegister(VRM.getPhys(VirtReg))) {
// This can create a %noreg operand in rare cases when the sub-register
// index is no longer available. That means the user value is in a
// non-existent sub-register, and %noreg is exactly what we want.
Loc.substPhysReg(VRM.getPhys(VirtReg), TRI);
} else if (VRM.getStackSlot(VirtReg) != VirtRegMap::NO_STACK_SLOT) {
// Retrieve the stack slot offset.
unsigned SpillSize;
const MachineRegisterInfo &MRI = MF.getRegInfo();
const TargetRegisterClass *TRC = MRI.getRegClass(VirtReg);
bool Success = TII.getStackSlotRange(TRC, Loc.getSubReg(), SpillSize,
SpillOffset, MF);
// FIXME: Invalidate the location if the offset couldn't be calculated.
Loc = MachineOperand::CreateFI(VRM.getStackSlot(VirtReg));
Spilled = true;
} else {
// Insert this location if it doesn't already exist and record a mapping
// from the old number to the new number.
auto InsertResult = NewLocations.insert({Loc, {Spilled, SpillOffset}});
unsigned NewLocNo = std::distance(NewLocations.begin(), InsertResult.first);
LocNoMap[I] = NewLocNo;
// Rewrite the locations and record the stack slot offsets for spills.
for (auto &Pair : NewLocations) {
bool Spilled;
unsigned SpillOffset;
std::tie(Spilled, SpillOffset) = Pair.second;
if (Spilled) {
unsigned NewLocNo = std::distance(&*NewLocations.begin(), &Pair);
SpillOffsets[NewLocNo] = SpillOffset;
// Update the interval map, but only coalesce left, since intervals to the
// right use the old location numbers. This should merge two contiguous
// DBG_VALUE intervals with different vregs that were allocated to the same
// physical register.
for (LocMap::iterator I = locInts.begin(); I.valid(); ++I) {
/// Find an iterator for inserting a DBG_VALUE instruction.
static MachineBasicBlock::iterator
findInsertLocation(MachineBasicBlock *MBB, SlotIndex Idx, LiveIntervals &LIS,
BlockSkipInstsMap &BBSkipInstsMap) {
SlotIndex Start = LIS.getMBBStartIdx(MBB);
Idx = Idx.getBaseIndex();
// Try to find an insert location by going backwards from Idx.
MachineInstr *MI;
while (!(MI = LIS.getInstructionFromIndex(Idx))) {
// We've reached the beginning of MBB.
if (Idx == Start) {
// Retrieve the last PHI/Label/Debug location found when calling
// SkipPHIsLabelsAndDebug last time. Start searching from there.
// Note the iterator kept in BBSkipInstsMap is one step back based
// on the iterator returned by SkipPHIsLabelsAndDebug last time.
// One exception is when SkipPHIsLabelsAndDebug returns MBB->begin(),
// BBSkipInstsMap won't save it. This is to consider the case that
// new instructions may be inserted at the beginning of MBB after
// last call of SkipPHIsLabelsAndDebug. If we save MBB->begin() in
// BBSkipInstsMap, after new non-phi/non-label/non-debug instructions
// are inserted at the beginning of the MBB, the iterator in
// BBSkipInstsMap won't point to the beginning of the MBB anymore.
// Therefore The next search in SkipPHIsLabelsAndDebug will skip those
// newly added instructions and that is unwanted.
MachineBasicBlock::iterator BeginIt;
auto MapIt = BBSkipInstsMap.find(MBB);
if (MapIt == BBSkipInstsMap.end())
BeginIt = MBB->begin();
BeginIt = std::next(MapIt->second);
auto I = MBB->SkipPHIsLabelsAndDebug(BeginIt);
if (I != BeginIt)
BBSkipInstsMap[MBB] = std::prev(I);
return I;
Idx = Idx.getPrevIndex();
// Don't insert anything after the first terminator, though.
return MI->isTerminator() ? MBB->getFirstTerminator() :
/// Find an iterator for inserting the next DBG_VALUE instruction
/// (or end if no more insert locations found).
static MachineBasicBlock::iterator
findNextInsertLocation(MachineBasicBlock *MBB, MachineBasicBlock::iterator I,
SlotIndex StopIdx, ArrayRef<MachineOperand> LocMOs,
LiveIntervals &LIS, const TargetRegisterInfo &TRI) {
SmallVector<Register, 4> Regs;
for (const MachineOperand &LocMO : LocMOs)
if (LocMO.isReg())
if (Regs.empty())
return MBB->instr_end();
// Find the next instruction in the MBB that define the register Reg.
while (I != MBB->end() && !I->isTerminator()) {
if (!LIS.isNotInMIMap(*I) &&
SlotIndex::isEarlierEqualInstr(StopIdx, LIS.getInstructionIndex(*I)))
if (any_of(Regs, [&I, &TRI](Register &Reg) {
return I->definesRegister(Reg, &TRI);
// The insert location is directly after the instruction/bundle.
return std::next(I);
return MBB->end();
void UserValue::insertDebugValue(MachineBasicBlock *MBB, SlotIndex StartIdx,
SlotIndex StopIdx, DbgVariableValue DbgValue,
ArrayRef<bool> LocSpills,
ArrayRef<unsigned> SpillOffsets,
LiveIntervals &LIS, const TargetInstrInfo &TII,
const TargetRegisterInfo &TRI,
BlockSkipInstsMap &BBSkipInstsMap) {
SlotIndex MBBEndIdx = LIS.getMBBEndIdx(&*MBB);
// Only search within the current MBB.
StopIdx = (MBBEndIdx < StopIdx) ? MBBEndIdx : StopIdx;
MachineBasicBlock::iterator I =
findInsertLocation(MBB, StartIdx, LIS, BBSkipInstsMap);
// Undef values don't exist in locations so create new "noreg" register MOs
// for them. See getLocationNo().
SmallVector<MachineOperand, 8> MOs;
if (DbgValue.isUndef()) {
/* Reg */ 0, /* isDef */ false, /* isImp */ false,
/* isKill */ false, /* isDead */ false,
/* isUndef */ false, /* isEarlyClobber */ false,
/* SubReg */ 0, /* isDebug */ true));
} else {
for (unsigned LocNo : DbgValue.loc_nos())
->isValidLocationForIntrinsic(getDebugLoc()) &&
"Expected inlined-at fields to agree");
// If the location was spilled, the new DBG_VALUE will be indirect. If the
// original DBG_VALUE was indirect, we need to add DW_OP_deref to indicate
// that the original virtual register was a pointer. Also, add the stack slot
// offset for the spilled register to the expression.
const DIExpression *Expr = DbgValue.getExpression();
bool IsIndirect = DbgValue.getWasIndirect();
bool IsList = DbgValue.getWasList();
for (unsigned I = 0, E = LocSpills.size(); I != E; ++I) {
if (LocSpills[I]) {
if (!IsList) {
uint8_t DIExprFlags = DIExpression::ApplyOffset;
if (IsIndirect)
DIExprFlags |= DIExpression::DerefAfter;
Expr = DIExpression::prepend(Expr, DIExprFlags, SpillOffsets[I]);
IsIndirect = true;
} else {
SmallVector<uint64_t, 4> Ops;
DIExpression::appendOffset(Ops, SpillOffsets[I]);
Expr = DIExpression::appendOpsToArg(Expr, Ops, I);
assert((!LocSpills[I] || MOs[I].isFI()) &&
"a spilled location must be a frame index");
unsigned DbgValueOpcode =
IsList ? TargetOpcode::DBG_VALUE_LIST : TargetOpcode::DBG_VALUE;
do {
BuildMI(*MBB, I, getDebugLoc(), TII.get(DbgValueOpcode), IsIndirect, MOs,
Variable, Expr);
// Continue and insert DBG_VALUES after every redefinition of a register
// associated with the debug value within the range
I = findNextInsertLocation(MBB, I, StopIdx, MOs, LIS, TRI);
} while (I != MBB->end());
void UserLabel::insertDebugLabel(MachineBasicBlock *MBB, SlotIndex Idx,
LiveIntervals &LIS, const TargetInstrInfo &TII,
BlockSkipInstsMap &BBSkipInstsMap) {
MachineBasicBlock::iterator I =
findInsertLocation(MBB, Idx, LIS, BBSkipInstsMap);
BuildMI(*MBB, I, getDebugLoc(), TII.get(TargetOpcode::DBG_LABEL))
void UserValue::emitDebugValues(VirtRegMap *VRM, LiveIntervals &LIS,
const TargetInstrInfo &TII,
const TargetRegisterInfo &TRI,
const SpillOffsetMap &SpillOffsets,
BlockSkipInstsMap &BBSkipInstsMap) {
MachineFunction::iterator MFEnd = VRM->getMachineFunction().end();
for (LocMap::const_iterator I = locInts.begin(); I.valid();) {
SlotIndex Start = I.start();
SlotIndex Stop = I.stop();
DbgVariableValue DbgValue = I.value();
SmallVector<bool> SpilledLocs;
SmallVector<unsigned> LocSpillOffsets;
for (unsigned LocNo : DbgValue.loc_nos()) {
auto SpillIt =
!DbgValue.isUndef() ? SpillOffsets.find(LocNo) : SpillOffsets.end();
bool Spilled = SpillIt != SpillOffsets.end();
LocSpillOffsets.push_back(Spilled ? SpillIt->second : 0);
// If the interval start was trimmed to the lexical scope insert the
// DBG_VALUE at the previous index (otherwise it appears after the
// first instruction in the range).
if (trimmedDefs.count(Start))
Start = Start.getPrevIndex();
LLVM_DEBUG(auto &dbg = dbgs(); dbg << "\t[" << Start << ';' << Stop << "):";
MachineFunction::iterator MBB = LIS.getMBBFromIndex(Start)->getIterator();
SlotIndex MBBEnd = LIS.getMBBEndIdx(&*MBB);
LLVM_DEBUG(dbgs() << ' ' << printMBBReference(*MBB) << '-' << MBBEnd);
insertDebugValue(&*MBB, Start, Stop, DbgValue, SpilledLocs, LocSpillOffsets,
LIS, TII, TRI, BBSkipInstsMap);
// This interval may span multiple basic blocks.
// Insert a DBG_VALUE into each one.
while (Stop > MBBEnd) {
// Move to the next block.
Start = MBBEnd;
if (++MBB == MFEnd)
MBBEnd = LIS.getMBBEndIdx(&*MBB);
LLVM_DEBUG(dbgs() << ' ' << printMBBReference(*MBB) << '-' << MBBEnd);
insertDebugValue(&*MBB, Start, Stop, DbgValue, SpilledLocs,
LocSpillOffsets, LIS, TII, TRI, BBSkipInstsMap);
LLVM_DEBUG(dbgs() << '\n');
if (MBB == MFEnd)
void UserLabel::emitDebugLabel(LiveIntervals &LIS, const TargetInstrInfo &TII,
BlockSkipInstsMap &BBSkipInstsMap) {
LLVM_DEBUG(dbgs() << "\t" << loc);
MachineFunction::iterator MBB = LIS.getMBBFromIndex(loc)->getIterator();
LLVM_DEBUG(dbgs() << ' ' << printMBBReference(*MBB));
insertDebugLabel(&*MBB, loc, LIS, TII, BBSkipInstsMap);
LLVM_DEBUG(dbgs() << '\n');
void LDVImpl::emitDebugValues(VirtRegMap *VRM) {
LLVM_DEBUG(dbgs() << "********** EMITTING LIVE DEBUG VARIABLES **********\n");
if (!MF)
BlockSkipInstsMap BBSkipInstsMap;
const TargetInstrInfo *TII = MF->getSubtarget().getInstrInfo();
SpillOffsetMap SpillOffsets;
for (auto &userValue : userValues) {
LLVM_DEBUG(userValue->print(dbgs(), TRI));
userValue->rewriteLocations(*VRM, *MF, *TII, *TRI, SpillOffsets);
userValue->emitDebugValues(VRM, *LIS, *TII, *TRI, SpillOffsets,
LLVM_DEBUG(dbgs() << "********** EMITTING LIVE DEBUG LABELS **********\n");
for (auto &userLabel : userLabels) {
LLVM_DEBUG(userLabel->print(dbgs(), TRI));
userLabel->emitDebugLabel(*LIS, *TII, BBSkipInstsMap);
LLVM_DEBUG(dbgs() << "********** EMITTING DEBUG PHIS **********\n");
auto Slots = LIS->getSlotIndexes();
for (auto &It : PHIValToPos) {
// For each ex-PHI, identify its physreg location or stack slot, and emit
// a DBG_PHI for it.
unsigned InstNum = It.first;
auto Slot = It.second.SI;
Register Reg = It.second.Reg;
unsigned SubReg = It.second.SubReg;
MachineBasicBlock *OrigMBB = Slots->getMBBFromIndex(Slot);
if (VRM->isAssignedReg(Reg) &&
Register::isPhysicalRegister(VRM->getPhys(Reg))) {
unsigned PhysReg = VRM->getPhys(Reg);
if (SubReg != 0)
PhysReg = TRI->getSubReg(PhysReg, SubReg);
auto Builder = BuildMI(*OrigMBB, OrigMBB->begin(), DebugLoc(),
} else if (VRM->getStackSlot(Reg) != VirtRegMap::NO_STACK_SLOT) {
const MachineRegisterInfo &MRI = MF->getRegInfo();
const TargetRegisterClass *TRC = MRI.getRegClass(Reg);
unsigned SpillSize, SpillOffset;
unsigned regSizeInBits = TRI->getRegSizeInBits(*TRC);
if (SubReg)
regSizeInBits = TRI->getSubRegIdxSize(SubReg);
// Test whether this location is legal with the given subreg. If the
// subregister has a nonzero offset, drop this location, it's too complex
// to describe. (TODO: future work).
bool Success =
TII->getStackSlotRange(TRC, SubReg, SpillSize, SpillOffset, *MF);
if (Success && SpillOffset == 0) {
auto Builder = BuildMI(*OrigMBB, OrigMBB->begin(), DebugLoc(),
// Record how large the original value is. The stack slot might be
// merged and altered during optimisation, but we will want to know how
// large the value is, at this DBG_PHI.
if (SpillOffset != 0) {
dbgs() << "DBG_PHI for Vreg " << Reg << " subreg " << SubReg <<
" has nonzero offset\n";
// If there was no mapping for a value ID, it's optimized out. Create no
// DBG_PHI, and any variables using this value will become optimized out.
LLVM_DEBUG(dbgs() << "********** EMITTING INSTR REFERENCES **********\n");
// Re-insert any debug instrs back in the position they were. We must
// re-insert in the same order to ensure that debug instructions don't swap,
// which could re-order assignments. Do so in a batch -- once we find the
// insert position, insert all instructions at the same SlotIdx. They are
// guaranteed to appear in-sequence in StashedDebugInstrs because we insert
// them in order.
for (auto *StashIt = StashedDebugInstrs.begin();
StashIt != StashedDebugInstrs.end(); ++StashIt) {
SlotIndex Idx = StashIt->Idx;
MachineBasicBlock *MBB = StashIt->MBB;
MachineInstr *MI = StashIt->MI;
auto EmitInstsHere = [this, &StashIt, MBB, Idx,
MI](MachineBasicBlock::iterator InsertPos) {
// Insert this debug instruction.
MBB->insert(InsertPos, MI);
// Look at subsequent stashed debug instructions: if they're at the same
// index, insert those too.
auto NextItem = std::next(StashIt);
while (NextItem != StashedDebugInstrs.end() && NextItem->Idx == Idx) {
assert(NextItem->MBB == MBB && "Instrs with same slot index should be"
"in the same block");
MBB->insert(InsertPos, NextItem->MI);
StashIt = NextItem;
NextItem = std::next(StashIt);
// Start block index: find the first non-debug instr in the block, and
// insert before it.
if (Idx == Slots->getMBBStartIdx(MBB)) {
MachineBasicBlock::iterator InsertPos =
findInsertLocation(MBB, Idx, *LIS, BBSkipInstsMap);
if (MachineInstr *Pos = Slots->getInstructionFromIndex(Idx)) {
// Insert at the end of any debug instructions.
auto PostDebug = std::next(Pos->getIterator());
PostDebug = skipDebugInstructionsForward(PostDebug, MBB->instr_end());
} else {
// Insert position disappeared; walk forwards through slots until we
// find a new one.
SlotIndex End = Slots->getMBBEndIdx(MBB);
for (; Idx < End; Idx = Slots->getNextNonNullIndex(Idx)) {
Pos = Slots->getInstructionFromIndex(Idx);
if (Pos) {
// We have reached the end of the block and didn't find anywhere to
// insert! It's not safe to discard any debug instructions; place them
// in front of the first terminator, or in front of end().
if (Idx >= End) {
auto TermIt = MBB->getFirstTerminator();
EmitDone = true;
void LiveDebugVariables::emitDebugValues(VirtRegMap *VRM) {
if (pImpl)
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void LiveDebugVariables::dump() const {
if (pImpl)