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//===- LiveDebugValues.cpp - Tracking Debug Value MIs ---------------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
/// This pass implements a data flow analysis that propagates debug location
/// information by inserting additional DBG_VALUE instructions into the machine
/// instruction stream. The pass internally builds debug location liveness
/// ranges to determine the points where additional DBG_VALUEs need to be
/// inserted.
/// This is a separate pass from DbgValueHistoryCalculator to facilitate
/// testing and improve modularity.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SparseBitVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/UniqueVector.h"
#include "llvm/CodeGen/LexicalScopes.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/RegisterScavenging.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <functional>
#include <queue>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "livedebugvalues"
STATISTIC(NumInserted, "Number of DBG_VALUE instructions inserted");
// If @MI is a DBG_VALUE with debug value described by a defined
// register, returns the number of this register. In the other case, returns 0.
static unsigned isDbgValueDescribedByReg(const MachineInstr &MI) {
assert(MI.isDebugValue() && "expected a DBG_VALUE");
assert(MI.getNumOperands() == 4 && "malformed DBG_VALUE");
// If location of variable is described using a register (directly
// or indirectly), this register is always a first operand.
return MI.getOperand(0).isReg() ? MI.getOperand(0).getReg() : 0;
namespace {
class LiveDebugValues : public MachineFunctionPass {
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
const TargetFrameLowering *TFI;
BitVector CalleeSavedRegs;
LexicalScopes LS;
/// Keeps track of lexical scopes associated with a user value's source
/// location.
class UserValueScopes {
DebugLoc DL;
LexicalScopes &LS;
SmallPtrSet<const MachineBasicBlock *, 4> LBlocks;
UserValueScopes(DebugLoc D, LexicalScopes &L) : DL(std::move(D)), LS(L) {}
/// Return true if current scope dominates at least one machine
/// instruction in a given machine basic block.
bool dominates(MachineBasicBlock *MBB) {
if (LBlocks.empty())
LS.getMachineBasicBlocks(DL, LBlocks);
return LBlocks.count(MBB) != 0 || LS.dominates(DL, MBB);
/// Based on std::pair so it can be used as an index into a DenseMap.
using DebugVariableBase =
std::pair<const DILocalVariable *, const DILocation *>;
/// A potentially inlined instance of a variable.
struct DebugVariable : public DebugVariableBase {
DebugVariable(const DILocalVariable *Var, const DILocation *InlinedAt)
: DebugVariableBase(Var, InlinedAt) {}
const DILocalVariable *getVar() const { return this->first; }
const DILocation *getInlinedAt() const { return this->second; }
bool operator<(const DebugVariable &DV) const {
if (getVar() == DV.getVar())
return getInlinedAt() < DV.getInlinedAt();
return getVar() < DV.getVar();
/// A pair of debug variable and value location.
struct VarLoc {
const DebugVariable Var;
const MachineInstr &MI; ///< Only used for cloning a new DBG_VALUE.
mutable UserValueScopes UVS;
enum { InvalidKind = 0, RegisterKind } Kind = InvalidKind;
/// The value location. Stored separately to avoid repeatedly
/// extracting it from MI.
union {
uint64_t RegNo;
uint64_t Hash;
} Loc;
VarLoc(const MachineInstr &MI, LexicalScopes &LS)
: Var(MI.getDebugVariable(), MI.getDebugLoc()->getInlinedAt()), MI(MI),
UVS(MI.getDebugLoc(), LS) {
static_assert((sizeof(Loc) == sizeof(uint64_t)),
"hash does not cover all members of Loc");
assert(MI.isDebugValue() && "not a DBG_VALUE");
assert(MI.getNumOperands() == 4 && "malformed DBG_VALUE");
if (int RegNo = isDbgValueDescribedByReg(MI)) {
Kind = RegisterKind;
Loc.RegNo = RegNo;
/// If this variable is described by a register, return it,
/// otherwise return 0.
unsigned isDescribedByReg() const {
if (Kind == RegisterKind)
return Loc.RegNo;
return 0;
/// Determine whether the lexical scope of this value's debug location
/// dominates MBB.
bool dominates(MachineBasicBlock &MBB) const { return UVS.dominates(&MBB); }
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void dump() const { MI.dump(); }
bool operator==(const VarLoc &Other) const {
return Var == Other.Var && Loc.Hash == Other.Loc.Hash;
/// This operator guarantees that VarLocs are sorted by Variable first.
bool operator<(const VarLoc &Other) const {
if (Var == Other.Var)
return Loc.Hash < Other.Loc.Hash;
return Var < Other.Var;
using VarLocMap = UniqueVector<VarLoc>;
using VarLocSet = SparseBitVector<>;
using VarLocInMBB = SmallDenseMap<const MachineBasicBlock *, VarLocSet>;
struct TransferDebugPair {
MachineInstr *TransferInst;
MachineInstr *DebugInst;
using TransferMap = SmallVector<TransferDebugPair, 4>;
/// This holds the working set of currently open ranges. For fast
/// access, this is done both as a set of VarLocIDs, and a map of
/// DebugVariable to recent VarLocID. Note that a DBG_VALUE ends all
/// previous open ranges for the same variable.
class OpenRangesSet {
VarLocSet VarLocs;
SmallDenseMap<DebugVariableBase, unsigned, 8> Vars;
const VarLocSet &getVarLocs() const { return VarLocs; }
/// Terminate all open ranges for Var by removing it from the set.
void erase(DebugVariable Var) {
auto It = Vars.find(Var);
if (It != Vars.end()) {
unsigned ID = It->second;
/// Terminate all open ranges listed in \c KillSet by removing
/// them from the set.
void erase(const VarLocSet &KillSet, const VarLocMap &VarLocIDs) {
for (unsigned ID : KillSet)
/// Insert a new range into the set.
void insert(unsigned VarLocID, DebugVariableBase Var) {
Vars.insert({Var, VarLocID});
/// Empty the set.
void clear() {
/// Return whether the set is empty or not.
bool empty() const {
assert(Vars.empty() == VarLocs.empty() && "open ranges are inconsistent");
return VarLocs.empty();
bool isSpillInstruction(const MachineInstr &MI, MachineFunction *MF,
unsigned &Reg);
int extractSpillBaseRegAndOffset(const MachineInstr &MI, unsigned &Reg);
void insertTransferDebugPair(MachineInstr &MI, OpenRangesSet &OpenRanges,
TransferMap &Transfers, VarLocMap &VarLocIDs,
unsigned OldVarID, unsigned NewReg = 0);
void transferDebugValue(const MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs);
void transferSpillInst(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, TransferMap &Transfers);
void transferRegisterCopy(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, TransferMap &Transfers);
void transferRegisterDef(MachineInstr &MI, OpenRangesSet &OpenRanges,
const VarLocMap &VarLocIDs);
bool transferTerminatorInst(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocInMBB &OutLocs, const VarLocMap &VarLocIDs);
bool process(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocInMBB &OutLocs, VarLocMap &VarLocIDs,
TransferMap &Transfers, bool transferChanges);
bool join(MachineBasicBlock &MBB, VarLocInMBB &OutLocs, VarLocInMBB &InLocs,
const VarLocMap &VarLocIDs,
SmallPtrSet<const MachineBasicBlock *, 16> &Visited);
bool ExtendRanges(MachineFunction &MF);
static char ID;
/// Default construct and initialize the pass.
/// Tell the pass manager which passes we depend on and what
/// information we preserve.
void getAnalysisUsage(AnalysisUsage &AU) const override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
/// Print to ostream with a message.
void printVarLocInMBB(const MachineFunction &MF, const VarLocInMBB &V,
const VarLocMap &VarLocIDs, const char *msg,
raw_ostream &Out) const;
/// Calculate the liveness information for the given machine function.
bool runOnMachineFunction(MachineFunction &MF) override;
} // end anonymous namespace
// Implementation
char LiveDebugValues::ID = 0;
char &llvm::LiveDebugValuesID = LiveDebugValues::ID;
false, false)
/// Default construct and initialize the pass.
LiveDebugValues::LiveDebugValues() : MachineFunctionPass(ID) {
/// Tell the pass manager which passes we depend on and what information we
/// preserve.
void LiveDebugValues::getAnalysisUsage(AnalysisUsage &AU) const {
// Debug Range Extension Implementation
#ifndef NDEBUG
void LiveDebugValues::printVarLocInMBB(const MachineFunction &MF,
const VarLocInMBB &V,
const VarLocMap &VarLocIDs,
const char *msg,
raw_ostream &Out) const {
Out << '\n' << msg << '\n';
for (const MachineBasicBlock &BB : MF) {
const auto &L = V.lookup(&BB);
Out << "MBB: " << BB.getName() << ":\n";
for (unsigned VLL : L) {
const VarLoc &VL = VarLocIDs[VLL];
Out << " Var: " << VL.Var.getVar()->getName();
Out << " MI: ";
Out << "\n";
/// Given a spill instruction, extract the register and offset used to
/// address the spill location in a target independent way.
int LiveDebugValues::extractSpillBaseRegAndOffset(const MachineInstr &MI,
unsigned &Reg) {
assert(MI.hasOneMemOperand() &&
"Spill instruction does not have exactly one memory operand?");
auto MMOI = MI.memoperands_begin();
const PseudoSourceValue *PVal = (*MMOI)->getPseudoValue();
assert(PVal->kind() == PseudoSourceValue::FixedStack &&
"Inconsistent memory operand in spill instruction");
int FI = cast<FixedStackPseudoSourceValue>(PVal)->getFrameIndex();
const MachineBasicBlock *MBB = MI.getParent();
return TFI->getFrameIndexReference(*MBB->getParent(), FI, Reg);
/// End all previous ranges related to @MI and start a new range from @MI
/// if it is a DBG_VALUE instr.
void LiveDebugValues::transferDebugValue(const MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs) {
if (!MI.isDebugValue())
const DILocalVariable *Var = MI.getDebugVariable();
const DILocation *DebugLoc = MI.getDebugLoc();
const DILocation *InlinedAt = DebugLoc->getInlinedAt();
assert(Var->isValidLocationForIntrinsic(DebugLoc) &&
"Expected inlined-at fields to agree");
// End all previous ranges of Var.
DebugVariable V(Var, InlinedAt);
// Add the VarLoc to OpenRanges from this DBG_VALUE.
// TODO: Currently handles DBG_VALUE which has only reg as location.
if (isDbgValueDescribedByReg(MI)) {
VarLoc VL(MI, LS);
unsigned ID = VarLocIDs.insert(VL);
OpenRanges.insert(ID, VL.Var);
/// Create new TransferDebugPair and insert it in \p Transfers. The VarLoc
/// with \p OldVarID should be deleted form \p OpenRanges and replaced with
/// new VarLoc. If \p NewReg is different than default zero value then the
/// new location will be register location created by the copy like instruction,
/// otherwise it is variable's location on the stack.
void LiveDebugValues::insertTransferDebugPair(
MachineInstr &MI, OpenRangesSet &OpenRanges, TransferMap &Transfers,
VarLocMap &VarLocIDs, unsigned OldVarID, unsigned NewReg) {
const MachineInstr *DMI = &VarLocIDs[OldVarID].MI;
MachineFunction *MF = MI.getParent()->getParent();
MachineInstr *NewDMI;
if (NewReg) {
// Create a DBG_VALUE instruction to describe the Var in its new
// register location.
NewDMI = BuildMI(*MF, DMI->getDebugLoc(), DMI->getDesc(),
DMI->isIndirectDebugValue(), NewReg,
DMI->getDebugVariable(), DMI->getDebugExpression());
if (DMI->isIndirectDebugValue())
LLVM_DEBUG(dbgs() << "Creating DBG_VALUE inst for register copy: ";
NewDMI->print(dbgs(), false, false, false, TII));
} else {
// Create a DBG_VALUE instruction to describe the Var in its spilled
// location.
unsigned SpillBase;
int SpillOffset = extractSpillBaseRegAndOffset(MI, SpillBase);
auto *SpillExpr = DIExpression::prepend(DMI->getDebugExpression(),
DIExpression::NoDeref, SpillOffset);
NewDMI = BuildMI(*MF, DMI->getDebugLoc(), DMI->getDesc(), true, SpillBase,
DMI->getDebugVariable(), SpillExpr);
LLVM_DEBUG(dbgs() << "Creating DBG_VALUE inst for spill: ";
NewDMI->print(dbgs(), false, false, false, TII));
// The newly created DBG_VALUE instruction NewDMI must be inserted after
// MI. Keep track of the pairing.
TransferDebugPair MIP = {&MI, NewDMI};
// End all previous ranges of Var.
// Add the VarLoc to OpenRanges.
VarLoc VL(*NewDMI, LS);
unsigned LocID = VarLocIDs.insert(VL);
OpenRanges.insert(LocID, VL.Var);
/// A definition of a register may mark the end of a range.
void LiveDebugValues::transferRegisterDef(MachineInstr &MI,
OpenRangesSet &OpenRanges,
const VarLocMap &VarLocIDs) {
MachineFunction *MF = MI.getMF();
const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
unsigned SP = TLI->getStackPointerRegisterToSaveRestore();
SparseBitVector<> KillSet;
for (const MachineOperand &MO : MI.operands()) {
// Determine whether the operand is a register def. Assume that call
// instructions never clobber SP, because some backends (e.g., AArch64)
// never list SP in the regmask.
if (MO.isReg() && MO.isDef() && MO.getReg() &&
TRI->isPhysicalRegister(MO.getReg()) &&
!(MI.isCall() && MO.getReg() == SP)) {
// Remove ranges of all aliased registers.
for (MCRegAliasIterator RAI(MO.getReg(), TRI, true); RAI.isValid(); ++RAI)
for (unsigned ID : OpenRanges.getVarLocs())
if (VarLocIDs[ID].isDescribedByReg() == *RAI)
} else if (MO.isRegMask()) {
// Remove ranges of all clobbered registers. Register masks don't usually
// list SP as preserved. While the debug info may be off for an
// instruction or two around callee-cleanup calls, transferring the
// DEBUG_VALUE across the call is still a better user experience.
for (unsigned ID : OpenRanges.getVarLocs()) {
unsigned Reg = VarLocIDs[ID].isDescribedByReg();
if (Reg && Reg != SP && MO.clobbersPhysReg(Reg))
OpenRanges.erase(KillSet, VarLocIDs);
/// Decide if @MI is a spill instruction and return true if it is. We use 2
/// criteria to make this decision:
/// - Is this instruction a store to a spill slot?
/// - Is there a register operand that is both used and killed?
/// TODO: Store optimization can fold spills into other stores (including
/// other spills). We do not handle this yet (more than one memory operand).
bool LiveDebugValues::isSpillInstruction(const MachineInstr &MI,
MachineFunction *MF, unsigned &Reg) {
const MachineFrameInfo &FrameInfo = MF->getFrameInfo();
int FI;
const MachineMemOperand *MMO;
// TODO: Handle multiple stores folded into one.
if (!MI.hasOneMemOperand())
return false;
// To identify a spill instruction, use the same criteria as in AsmPrinter.
if (!((TII->isStoreToStackSlotPostFE(MI, FI) ||
TII->hasStoreToStackSlot(MI, MMO, FI)) &&
return false;
auto isKilledReg = [&](const MachineOperand MO, unsigned &Reg) {
if (!MO.isReg() || !MO.isUse()) {
Reg = 0;
return false;
Reg = MO.getReg();
return MO.isKill();
for (const MachineOperand &MO : MI.operands()) {
// In a spill instruction generated by the InlineSpiller the spilled
// register has its kill flag set.
if (isKilledReg(MO, Reg))
return true;
if (Reg != 0) {
// Check whether next instruction kills the spilled register.
// FIXME: Current solution does not cover search for killed register in
// bundles and instructions further down the chain.
auto NextI = std::next(MI.getIterator());
// Skip next instruction that points to basic block end iterator.
if (MI.getParent()->end() == NextI)
unsigned RegNext;
for (const MachineOperand &MONext : NextI->operands()) {
// Return true if we came across the register from the
// previous spill instruction that is killed in NextI.
if (isKilledReg(MONext, RegNext) && RegNext == Reg)
return true;
// Return false if we didn't find spilled register.
return false;
/// A spilled register may indicate that we have to end the current range of
/// a variable and create a new one for the spill location.
/// We don't want to insert any instructions in process(), so we just create
/// the DBG_VALUE without inserting it and keep track of it in \p Transfers.
/// It will be inserted into the BB when we're done iterating over the
/// instructions.
void LiveDebugValues::transferSpillInst(MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs,
TransferMap &Transfers) {
unsigned Reg;
MachineFunction *MF = MI.getMF();
if (!isSpillInstruction(MI, MF, Reg))
// Check if the register is the location of a debug value.
for (unsigned ID : OpenRanges.getVarLocs()) {
if (VarLocIDs[ID].isDescribedByReg() == Reg) {
LLVM_DEBUG(dbgs() << "Spilling Register " << printReg(Reg, TRI) << '('
<< VarLocIDs[ID].Var.getVar()->getName() << ")\n");
insertTransferDebugPair(MI, OpenRanges, Transfers, VarLocIDs, ID);
/// If \p MI is a register copy instruction, that copies a previously tracked
/// value from one register to another register that is callee saved, we
/// create new DBG_VALUE instruction described with copy destination register.
void LiveDebugValues::transferRegisterCopy(MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs,
TransferMap &Transfers) {
const MachineOperand *SrcRegOp, *DestRegOp;
if (!TII->isCopyInstr(MI, SrcRegOp, DestRegOp) || !SrcRegOp->isKill() ||
auto isCalleSavedReg = [&](unsigned Reg) {
for (MCRegAliasIterator RAI(Reg, TRI, true); RAI.isValid(); ++RAI)
if (CalleeSavedRegs.test(*RAI))
return true;
return false;
unsigned SrcReg = SrcRegOp->getReg();
unsigned DestReg = DestRegOp->getReg();
// We want to recognize instructions where destination register is callee
// saved register. If register that could be clobbered by the call is
// included, there would be a great chance that it is going to be clobbered
// soon. It is more likely that previous register location, which is callee
// saved, is going to stay unclobbered longer, even if it is killed.
if (!isCalleSavedReg(DestReg))
for (unsigned ID : OpenRanges.getVarLocs()) {
if (VarLocIDs[ID].isDescribedByReg() == SrcReg) {
insertTransferDebugPair(MI, OpenRanges, Transfers, VarLocIDs, ID,
/// Terminate all open ranges at the end of the current basic block.
bool LiveDebugValues::transferTerminatorInst(MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocInMBB &OutLocs,
const VarLocMap &VarLocIDs) {
bool Changed = false;
const MachineBasicBlock *CurMBB = MI.getParent();
if (!(MI.isTerminator() || (&MI == &CurMBB->back())))
return false;
if (OpenRanges.empty())
return false;
LLVM_DEBUG(for (unsigned ID
: OpenRanges.getVarLocs()) {
// Copy OpenRanges to OutLocs, if not already present.
dbgs() << "Add to OutLocs: ";
VarLocSet &VLS = OutLocs[CurMBB];
Changed = VLS |= OpenRanges.getVarLocs();
return Changed;
/// This routine creates OpenRanges and OutLocs.
bool LiveDebugValues::process(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocInMBB &OutLocs, VarLocMap &VarLocIDs,
TransferMap &Transfers, bool transferChanges) {
bool Changed = false;
transferDebugValue(MI, OpenRanges, VarLocIDs);
transferRegisterDef(MI, OpenRanges, VarLocIDs);
if (transferChanges) {
transferRegisterCopy(MI, OpenRanges, VarLocIDs, Transfers);
transferSpillInst(MI, OpenRanges, VarLocIDs, Transfers);
Changed = transferTerminatorInst(MI, OpenRanges, OutLocs, VarLocIDs);
return Changed;
/// This routine joins the analysis results of all incoming edges in @MBB by
/// inserting a new DBG_VALUE instruction at the start of the @MBB - if the same
/// source variable in all the predecessors of @MBB reside in the same location.
bool LiveDebugValues::join(MachineBasicBlock &MBB, VarLocInMBB &OutLocs,
VarLocInMBB &InLocs, const VarLocMap &VarLocIDs,
SmallPtrSet<const MachineBasicBlock *, 16> &Visited) {
LLVM_DEBUG(dbgs() << "join MBB: " << MBB.getName() << "\n");
bool Changed = false;
VarLocSet InLocsT; // Temporary incoming locations.
// For all predecessors of this MBB, find the set of VarLocs that
// can be joined.
int NumVisited = 0;
for (auto p : MBB.predecessors()) {
// Ignore unvisited predecessor blocks. As we are processing
// the blocks in reverse post-order any unvisited block can
// be considered to not remove any incoming values.
if (!Visited.count(p))
auto OL = OutLocs.find(p);
// Join is null in case of empty OutLocs from any of the pred.
if (OL == OutLocs.end())
return false;
// Just copy over the Out locs to incoming locs for the first visited
// predecessor, and for all other predecessors join the Out locs.
if (!NumVisited)
InLocsT = OL->second;
InLocsT &= OL->second;
// Filter out DBG_VALUES that are out of scope.
VarLocSet KillSet;
for (auto ID : InLocsT)
if (!VarLocIDs[ID].dominates(MBB))
// As we are processing blocks in reverse post-order we
// should have processed at least one predecessor, unless it
// is the entry block which has no predecessor.
assert((NumVisited || MBB.pred_empty()) &&
"Should have processed at least one predecessor");
if (InLocsT.empty())
return false;
VarLocSet &ILS = InLocs[&MBB];
// Insert DBG_VALUE instructions, if not already inserted.
VarLocSet Diff = InLocsT;
for (auto ID : Diff) {
// This VarLoc is not found in InLocs i.e. it is not yet inserted. So, a
// new range is started for the var from the mbb's beginning by inserting
// a new DBG_VALUE. process() will end this range however appropriate.
const VarLoc &DiffIt = VarLocIDs[ID];
const MachineInstr *DMI = &DiffIt.MI;
MachineInstr *MI =
BuildMI(MBB, MBB.instr_begin(), DMI->getDebugLoc(), DMI->getDesc(),
DMI->isIndirectDebugValue(), DMI->getOperand(0).getReg(),
DMI->getDebugVariable(), DMI->getDebugExpression());
if (DMI->isIndirectDebugValue())
LLVM_DEBUG(dbgs() << "Inserted: "; MI->dump(););
Changed = true;
return Changed;
/// Calculate the liveness information for the given machine function and
/// extend ranges across basic blocks.
bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
LLVM_DEBUG(dbgs() << "\nDebug Range Extension\n");
bool Changed = false;
bool OLChanged = false;
bool MBBJoined = false;
VarLocMap VarLocIDs; // Map VarLoc<>unique ID for use in bitvectors.
OpenRangesSet OpenRanges; // Ranges that are open until end of bb.
VarLocInMBB OutLocs; // Ranges that exist beyond bb.
VarLocInMBB InLocs; // Ranges that are incoming after joining.
TransferMap Transfers; // DBG_VALUEs associated with spills.
DenseMap<unsigned int, MachineBasicBlock *> OrderToBB;
DenseMap<MachineBasicBlock *, unsigned int> BBToOrder;
std::priority_queue<unsigned int, std::vector<unsigned int>,
std::greater<unsigned int>>
std::priority_queue<unsigned int, std::vector<unsigned int>,
std::greater<unsigned int>>
enum : bool { dontTransferChanges = false, transferChanges = true };
// Initialize every mbb with OutLocs.
// We are not looking at any spill instructions during the initial pass
// over the BBs. The LiveDebugVariables pass has already created DBG_VALUE
// instructions for spills of registers that are known to be user variables
// within the BB in which the spill occurs.
for (auto &MBB : MF)
for (auto &MI : MBB)
process(MI, OpenRanges, OutLocs, VarLocIDs, Transfers,
LLVM_DEBUG(printVarLocInMBB(MF, OutLocs, VarLocIDs,
"OutLocs after initialization", dbgs()));
ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
unsigned int RPONumber = 0;
for (auto RI = RPOT.begin(), RE = RPOT.end(); RI != RE; ++RI) {
OrderToBB[RPONumber] = *RI;
BBToOrder[*RI] = RPONumber;
// This is a standard "union of predecessor outs" dataflow problem.
// To solve it, we perform join() and process() using the two worklist method
// until the ranges converge.
// Ranges have converged when both worklists are empty.
SmallPtrSet<const MachineBasicBlock *, 16> Visited;
while (!Worklist.empty() || !Pending.empty()) {
// We track what is on the pending worklist to avoid inserting the same
// thing twice. We could avoid this with a custom priority queue, but this
// is probably not worth it.
SmallPtrSet<MachineBasicBlock *, 16> OnPending;
LLVM_DEBUG(dbgs() << "Processing Worklist\n");
while (!Worklist.empty()) {
MachineBasicBlock *MBB = OrderToBB[];
MBBJoined = join(*MBB, OutLocs, InLocs, VarLocIDs, Visited);
if (MBBJoined) {
MBBJoined = false;
Changed = true;
// Now that we have started to extend ranges across BBs we need to
// examine spill instructions to see whether they spill registers that
// correspond to user variables.
for (auto &MI : *MBB)
OLChanged |= process(MI, OpenRanges, OutLocs, VarLocIDs, Transfers,
// Add any DBG_VALUE instructions necessitated by spills.
for (auto &TR : Transfers)
LLVM_DEBUG(printVarLocInMBB(MF, OutLocs, VarLocIDs,
"OutLocs after propagating", dbgs()));
LLVM_DEBUG(printVarLocInMBB(MF, InLocs, VarLocIDs,
"InLocs after propagating", dbgs()));
if (OLChanged) {
OLChanged = false;
for (auto s : MBB->successors())
if (OnPending.insert(s).second) {
// At this point, pending must be empty, since it was just the empty
// worklist
assert(Pending.empty() && "Pending should be empty");
LLVM_DEBUG(printVarLocInMBB(MF, OutLocs, VarLocIDs, "Final OutLocs", dbgs()));
LLVM_DEBUG(printVarLocInMBB(MF, InLocs, VarLocIDs, "Final InLocs", dbgs()));
return Changed;
bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
if (!MF.getFunction().getSubprogram())
// LiveDebugValues will already have removed all DBG_VALUEs.
return false;
// Skip functions from NoDebug compilation units.
if (MF.getFunction().getSubprogram()->getUnit()->getEmissionKind() ==
return false;
TRI = MF.getSubtarget().getRegisterInfo();
TII = MF.getSubtarget().getInstrInfo();
TFI = MF.getSubtarget().getFrameLowering();
TFI->determineCalleeSaves(MF, CalleeSavedRegs,
bool Changed = ExtendRanges(MF);
return Changed;