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//===- VarLocBasedImpl.cpp - Tracking Debug Value MIs with VarLoc class----===//
// 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
/// \file VarLocBasedImpl.cpp
/// LiveDebugValues is an optimistic "available expressions" dataflow
/// algorithm. The set of expressions is the set of machine locations
/// (registers, spill slots, constants) that a variable fragment might be
/// located, qualified by a DIExpression and indirect-ness flag, while each
/// variable is identified by a DebugVariable object. The availability of an
/// expression begins when a DBG_VALUE instruction specifies the location of a
/// DebugVariable, and continues until that location is clobbered or
/// re-specified by a different DBG_VALUE for the same DebugVariable.
/// The output of LiveDebugValues is additional DBG_VALUE instructions,
/// placed to extend variable locations as far they're available. This file
/// and the VarLocBasedLDV class is an implementation that explicitly tracks
/// locations, using the VarLoc class.
/// The canonical "available expressions" problem doesn't have expression
/// clobbering, instead when a variable is re-assigned, any expressions using
/// that variable get invalidated. LiveDebugValues can map onto "available
/// expressions" by having every register represented by a variable, which is
/// used in an expression that becomes available at a DBG_VALUE instruction.
/// When the register is clobbered, its variable is effectively reassigned, and
/// expressions computed from it become unavailable. A similar construct is
/// needed when a DebugVariable has its location re-specified, to invalidate
/// all other locations for that DebugVariable.
/// Using the dataflow analysis to compute the available expressions, we create
/// a DBG_VALUE at the beginning of each block where the expression is
/// live-in. This propagates variable locations into every basic block where
/// the location can be determined, rather than only having DBG_VALUEs in blocks
/// where locations are specified due to an assignment or some optimization.
/// Movements of values between registers and spill slots are annotated with
/// DBG_VALUEs too to track variable values bewteen locations. All this allows
/// DbgEntityHistoryCalculator to focus on only the locations within individual
/// blocks, facilitating testing and improving modularity.
/// We follow an optimisic dataflow approach, with this lattice:
/// \verbatim
/// ┬ "Unknown"
/// |
/// v
/// True
/// |
/// v
/// ⊥ False
/// \endverbatim With "True" signifying that the expression is available (and
/// thus a DebugVariable's location is the corresponding register), while
/// "False" signifies that the expression is unavailable. "Unknown"s never
/// survive to the end of the analysis (see below).
/// Formally, all DebugVariable locations that are live-out of a block are
/// initialized to \top. A blocks live-in values take the meet of the lattice
/// value for every predecessors live-outs, except for the entry block, where
/// all live-ins are \bot. The usual dataflow propagation occurs: the transfer
/// function for a block assigns an expression for a DebugVariable to be "True"
/// if a DBG_VALUE in the block specifies it; "False" if the location is
/// clobbered; or the live-in value if it is unaffected by the block. We
/// visit each block in reverse post order until a fixedpoint is reached. The
/// solution produced is maximal.
/// Intuitively, we start by assuming that every expression / variable location
/// is at least "True", and then propagate "False" from the entry block and any
/// clobbers until there are no more changes to make. This gives us an accurate
/// solution because all incorrect locations will have a "False" propagated into
/// them. It also gives us a solution that copes well with loops by assuming
/// that variable locations are live-through every loop, and then removing those
/// that are not through dataflow.
/// Within LiveDebugValues: each variable location is represented by a
/// VarLoc object that identifies the source variable, the set of
/// machine-locations that currently describe it (a single location for
/// DBG_VALUE or multiple for DBG_VALUE_LIST), and the DBG_VALUE inst that
/// specifies the location. Each VarLoc is indexed in the (function-scope) \p
/// VarLocMap, giving each VarLoc a set of unique indexes, each of which
/// corresponds to one of the VarLoc's machine-locations and can be used to
/// lookup the VarLoc in the VarLocMap. Rather than operate directly on machine
/// locations, the dataflow analysis in this pass identifies locations by their
/// indices in the VarLocMap, meaning all the variable locations in a block can
/// be described by a sparse vector of VarLocMap indicies.
/// All the storage for the dataflow analysis is local to the ExtendRanges
/// method and passed down to helper methods. "OutLocs" and "InLocs" record the
/// in and out lattice values for each block. "OpenRanges" maintains a list of
/// variable locations and, with the "process" method, evaluates the transfer
/// function of each block. "flushPendingLocs" installs debug value instructions
/// for each live-in location at the start of blocks, while "Transfers" records
/// transfers of values between machine-locations.
/// We avoid explicitly representing the "Unknown" (\top) lattice value in the
/// implementation. Instead, unvisited blocks implicitly have all lattice
/// values set as "Unknown". After being visited, there will be path back to
/// the entry block where the lattice value is "False", and as the transfer
/// function cannot make new "Unknown" locations, there are no scenarios where
/// a block can have an "Unknown" location after being visited. Similarly, we
/// don't enumerate all possible variable locations before exploring the
/// function: when a new location is discovered, all blocks previously explored
/// were implicitly "False" but unrecorded, and become explicitly "False" when
/// a new VarLoc is created with its bit not set in predecessor InLocs or
/// OutLocs.
#include "LiveDebugValues.h"
#include "llvm/ADT/CoalescingBitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.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/RegisterScavenging.h"
#include "llvm/CodeGen/TargetFrameLowering.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.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/TypeSize.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <functional>
#include <queue>
#include <tuple>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "livedebugvalues"
STATISTIC(NumInserted, "Number of DBG_VALUE instructions inserted");
// Options to prevent pathological compile-time behavior. If InputBBLimit and
// InputDbgValueLimit are both exceeded, range extension is disabled.
static cl::opt<unsigned> InputBBLimit(
cl::desc("Maximum input basic blocks before DBG_VALUE limit applies"),
cl::init(10000), cl::Hidden);
static cl::opt<unsigned> InputDbgValueLimit(
"Maximum input DBG_VALUE insts supported by debug range extension"),
cl::init(50000), cl::Hidden);
/// If \p Op is a stack or frame register return true, otherwise return false.
/// This is used to avoid basing the debug entry values on the registers, since
/// we do not support it at the moment.
static bool isRegOtherThanSPAndFP(const MachineOperand &Op,
const MachineInstr &MI,
const TargetRegisterInfo *TRI) {
if (!Op.isReg())
return false;
const MachineFunction *MF = MI.getParent()->getParent();
const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
Register SP = TLI->getStackPointerRegisterToSaveRestore();
Register FP = TRI->getFrameRegister(*MF);
Register Reg = Op.getReg();
return Reg && Reg != SP && Reg != FP;
namespace {
// Max out the number of statically allocated elements in DefinedRegsSet, as
// this prevents fallback to std::set::count() operations.
using DefinedRegsSet = SmallSet<Register, 32>;
// The IDs in this set correspond to MachineLocs in VarLocs, as well as VarLocs
// that represent Entry Values; every VarLoc in the set will also appear
// exactly once at Location=0.
// As a result, each VarLoc may appear more than once in this "set", but each
// range corresponding to a Reg, SpillLoc, or EntryValue type will still be a
// "true" set (i.e. each VarLoc may appear only once), and the range Location=0
// is the set of all VarLocs.
using VarLocSet = CoalescingBitVector<uint64_t>;
/// A type-checked pair of {Register Location (or 0), Index}, used to index
/// into a \ref VarLocMap. This can be efficiently converted to a 64-bit int
/// for insertion into a \ref VarLocSet, and efficiently converted back. The
/// type-checker helps ensure that the conversions aren't lossy.
/// Why encode a location /into/ the VarLocMap index? This makes it possible
/// to find the open VarLocs killed by a register def very quickly. This is a
/// performance-critical operation for LiveDebugValues.
struct LocIndex {
using u32_location_t = uint32_t;
using u32_index_t = uint32_t;
u32_location_t Location; // Physical registers live in the range [1;2^30) (see
// \ref MCRegister), so we have plenty of range left
// here to encode non-register locations.
u32_index_t Index;
/// The location that has an entry for every VarLoc in the map.
static constexpr u32_location_t kUniversalLocation = 0;
/// The first location that is reserved for VarLocs with locations of kind
/// RegisterKind.
static constexpr u32_location_t kFirstRegLocation = 1;
/// The first location greater than 0 that is not reserved for VarLocs with
/// locations of kind RegisterKind.
static constexpr u32_location_t kFirstInvalidRegLocation = 1 << 30;
/// A special location reserved for VarLocs with locations of kind
/// SpillLocKind.
static constexpr u32_location_t kSpillLocation = kFirstInvalidRegLocation;
/// A special location reserved for VarLocs of kind EntryValueBackupKind and
/// EntryValueCopyBackupKind.
static constexpr u32_location_t kEntryValueBackupLocation =
kFirstInvalidRegLocation + 1;
LocIndex(u32_location_t Location, u32_index_t Index)
: Location(Location), Index(Index) {}
uint64_t getAsRawInteger() const {
return (static_cast<uint64_t>(Location) << 32) | Index;
template<typename IntT> static LocIndex fromRawInteger(IntT ID) {
static_assert(std::is_unsigned<IntT>::value &&
sizeof(ID) == sizeof(uint64_t),
"Cannot convert raw integer to LocIndex");
return {static_cast<u32_location_t>(ID >> 32),
/// Get the start of the interval reserved for VarLocs of kind RegisterKind
/// which reside in \p Reg. The end is at rawIndexForReg(Reg+1)-1.
static uint64_t rawIndexForReg(Register Reg) {
return LocIndex(Reg, 0).getAsRawInteger();
/// Return a range covering all set indices in the interval reserved for
/// \p Location in \p Set.
static auto indexRangeForLocation(const VarLocSet &Set,
u32_location_t Location) {
uint64_t Start = LocIndex(Location, 0).getAsRawInteger();
uint64_t End = LocIndex(Location + 1, 0).getAsRawInteger();
return Set.half_open_range(Start, End);
// Simple Set for storing all the VarLoc Indices at a Location bucket.
using VarLocsInRange = SmallSet<LocIndex::u32_index_t, 32>;
// Vector of all `LocIndex`s for a given VarLoc; the same Location should not
// appear in any two of these, as each VarLoc appears at most once in any
// Location bucket.
using LocIndices = SmallVector<LocIndex, 2>;
class VarLocBasedLDV : public LDVImpl {
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
const TargetFrameLowering *TFI;
TargetPassConfig *TPC;
BitVector CalleeSavedRegs;
LexicalScopes LS;
VarLocSet::Allocator Alloc;
enum struct TransferKind { TransferCopy, TransferSpill, TransferRestore };
using FragmentInfo = DIExpression::FragmentInfo;
using OptFragmentInfo = Optional<DIExpression::FragmentInfo>;
/// A pair of debug variable and value location.
struct VarLoc {
// The location at which a spilled variable resides. It consists of a
// register and an offset.
struct SpillLoc {
unsigned SpillBase;
StackOffset SpillOffset;
bool operator==(const SpillLoc &Other) const {
return SpillBase == Other.SpillBase && SpillOffset == Other.SpillOffset;
bool operator!=(const SpillLoc &Other) const {
return !(*this == Other);
/// Identity of the variable at this location.
const DebugVariable Var;
/// The expression applied to this location.
const DIExpression *Expr;
/// DBG_VALUE to clone var/expr information from if this location
/// is moved.
const MachineInstr &MI;
enum class MachineLocKind {
InvalidKind = 0,
enum class EntryValueLocKind {
NonEntryValueKind = 0,
} EVKind;
/// The value location. Stored separately to avoid repeatedly
/// extracting it from MI.
union MachineLocValue {
uint64_t RegNo;
SpillLoc SpillLocation;
uint64_t Hash;
int64_t Immediate;
const ConstantFP *FPImm;
const ConstantInt *CImm;
MachineLocValue() : Hash(0) {}
/// A single machine location; its Kind is either a register, spill
/// location, or immediate value.
/// If the VarLoc is not a NonEntryValueKind, then it will use only a
/// single MachineLoc of RegisterKind.
struct MachineLoc {
MachineLocKind Kind;
MachineLocValue Value;
bool operator==(const MachineLoc &Other) const {
if (Kind != Other.Kind)
return false;
switch (Kind) {
case MachineLocKind::SpillLocKind:
return Value.SpillLocation == Other.Value.SpillLocation;
case MachineLocKind::RegisterKind:
case MachineLocKind::ImmediateKind:
return Value.Hash == Other.Value.Hash;
llvm_unreachable("Invalid kind");
bool operator<(const MachineLoc &Other) const {
switch (Kind) {
case MachineLocKind::SpillLocKind:
return std::make_tuple(
Kind, Value.SpillLocation.SpillBase,
Value.SpillLocation.SpillOffset.getScalable()) <
Other.Kind, Other.Value.SpillLocation.SpillBase,
case MachineLocKind::RegisterKind:
case MachineLocKind::ImmediateKind:
return std::tie(Kind, Value.Hash) <
std::tie(Other.Kind, Other.Value.Hash);
llvm_unreachable("Invalid kind");
/// The set of machine locations used to determine the variable's value, in
/// conjunction with Expr. Initially populated with MI's debug operands,
/// but may be transformed independently afterwards.
SmallVector<MachineLoc, 8> Locs;
/// Used to map the index of each location in Locs back to the index of its
/// original debug operand in MI. Used when multiple location operands are
/// coalesced and the original MI's operands need to be accessed while
/// emitting a debug value.
SmallVector<unsigned, 8> OrigLocMap;
VarLoc(const MachineInstr &MI, LexicalScopes &LS)
: Var(MI.getDebugVariable(), MI.getDebugExpression(),
Expr(MI.getDebugExpression()), MI(MI),
EVKind(EntryValueLocKind::NonEntryValueKind) {
assert(MI.isDebugValue() && "not a DBG_VALUE");
assert((MI.isDebugValueList() || MI.getNumOperands() == 4) &&
"malformed DBG_VALUE");
for (const MachineOperand &Op : MI.debug_operands()) {
MachineLoc ML = GetLocForOp(Op);
auto It = find(Locs, ML);
if (It == Locs.end()) {
} else {
// ML duplicates an element in Locs; replace references to Op
// with references to the duplicating element.
unsigned OpIdx = Locs.size();
unsigned DuplicatingIdx = std::distance(Locs.begin(), It);
Expr = DIExpression::replaceArg(Expr, OpIdx, DuplicatingIdx);
// We create the debug entry values from the factory functions rather
// than from this ctor.
assert(EVKind != EntryValueLocKind::EntryValueKind &&
static MachineLoc GetLocForOp(const MachineOperand &Op) {
MachineLocKind Kind;
MachineLocValue Loc;
if (Op.isReg()) {
Kind = MachineLocKind::RegisterKind;
Loc.RegNo = Op.getReg();
} else if (Op.isImm()) {
Kind = MachineLocKind::ImmediateKind;
Loc.Immediate = Op.getImm();
} else if (Op.isFPImm()) {
Kind = MachineLocKind::ImmediateKind;
Loc.FPImm = Op.getFPImm();
} else if (Op.isCImm()) {
Kind = MachineLocKind::ImmediateKind;
Loc.CImm = Op.getCImm();
} else
llvm_unreachable("Invalid Op kind for MachineLoc.");
return {Kind, Loc};
/// Take the variable and machine-location in DBG_VALUE MI, and build an
/// entry location using the given expression.
static VarLoc CreateEntryLoc(const MachineInstr &MI, LexicalScopes &LS,
const DIExpression *EntryExpr, Register Reg) {
VarLoc VL(MI, LS);
assert(VL.Locs.size() == 1 &&
VL.Locs[0].Kind == MachineLocKind::RegisterKind);
VL.EVKind = EntryValueLocKind::EntryValueKind;
VL.Expr = EntryExpr;
VL.Locs[0].Value.RegNo = Reg;
return VL;
/// Take the variable and machine-location from the DBG_VALUE (from the
/// function entry), and build an entry value backup location. The backup
/// location will turn into the normal location if the backup is valid at
/// the time of the primary location clobbering.
static VarLoc CreateEntryBackupLoc(const MachineInstr &MI,
LexicalScopes &LS,
const DIExpression *EntryExpr) {
VarLoc VL(MI, LS);
assert(VL.Locs.size() == 1 &&
VL.Locs[0].Kind == MachineLocKind::RegisterKind);
VL.EVKind = EntryValueLocKind::EntryValueBackupKind;
VL.Expr = EntryExpr;
return VL;
/// Take the variable and machine-location from the DBG_VALUE (from the
/// function entry), and build a copy of an entry value backup location by
/// setting the register location to NewReg.
static VarLoc CreateEntryCopyBackupLoc(const MachineInstr &MI,
LexicalScopes &LS,
const DIExpression *EntryExpr,
Register NewReg) {
VarLoc VL(MI, LS);
assert(VL.Locs.size() == 1 &&
VL.Locs[0].Kind == MachineLocKind::RegisterKind);
VL.EVKind = EntryValueLocKind::EntryValueCopyBackupKind;
VL.Expr = EntryExpr;
VL.Locs[0].Value.RegNo = NewReg;
return VL;
/// Copy the register location in DBG_VALUE MI, updating the register to
/// be NewReg.
static VarLoc CreateCopyLoc(const VarLoc &OldVL, const MachineLoc &OldML,
Register NewReg) {
VarLoc VL = OldVL;
for (size_t I = 0, E = VL.Locs.size(); I < E; ++I)
if (VL.Locs[I] == OldML) {
VL.Locs[I].Kind = MachineLocKind::RegisterKind;
VL.Locs[I].Value.RegNo = NewReg;
return VL;
llvm_unreachable("Should have found OldML in new VarLoc.");
/// Take the variable described by DBG_VALUE* MI, and create a VarLoc
/// locating it in the specified spill location.
static VarLoc CreateSpillLoc(const VarLoc &OldVL, const MachineLoc &OldML,
unsigned SpillBase, StackOffset SpillOffset) {
VarLoc VL = OldVL;
for (int I = 0, E = VL.Locs.size(); I < E; ++I)
if (VL.Locs[I] == OldML) {
VL.Locs[I].Kind = MachineLocKind::SpillLocKind;
VL.Locs[I].Value.SpillLocation = {SpillBase, SpillOffset};
return VL;
llvm_unreachable("Should have found OldML in new VarLoc.");
/// Create a DBG_VALUE representing this VarLoc in the given function.
/// Copies variable-specific information such as DILocalVariable and
/// inlining information from the original DBG_VALUE instruction, which may
/// have been several transfers ago.
MachineInstr *BuildDbgValue(MachineFunction &MF) const {
assert(!isEntryBackupLoc() &&
"Tried to produce DBG_VALUE for backup VarLoc");
const DebugLoc &DbgLoc = MI.getDebugLoc();
bool Indirect = MI.isIndirectDebugValue();
const auto &IID = MI.getDesc();
const DILocalVariable *Var = MI.getDebugVariable();
const DIExpression *DIExpr = Expr;
SmallVector<MachineOperand, 8> MOs;
for (unsigned I = 0, E = Locs.size(); I < E; ++I) {
MachineLocKind LocKind = Locs[I].Kind;
MachineLocValue Loc = Locs[I].Value;
const MachineOperand &Orig = MI.getDebugOperand(OrigLocMap[I]);
switch (LocKind) {
case MachineLocKind::RegisterKind:
// An entry value is a register location -- but with an updated
// expression. The register location of such DBG_VALUE is always the
// one from the entry DBG_VALUE, it does not matter if the entry value
// was copied in to another register due to some optimizations.
// Non-entry value register locations are like the source
// DBG_VALUE, but with the register number from this VarLoc.
EVKind == EntryValueLocKind::EntryValueKind ? Orig.getReg()
: Register(Loc.RegNo),
case MachineLocKind::SpillLocKind: {
// Spills are indirect DBG_VALUEs, with a base register and offset.
// Use the original DBG_VALUEs expression to build the spilt location
// on top of. FIXME: spill locations created before this pass runs
// are not recognized, and not handled here.
unsigned Base = Loc.SpillLocation.SpillBase;
auto *TRI = MF.getSubtarget().getRegisterInfo();
if (MI.isNonListDebugValue()) {
DIExpr =
TRI->prependOffsetExpression(DIExpr, DIExpression::ApplyOffset,
Indirect = true;
} else {
SmallVector<uint64_t, 4> Ops;
TRI->getOffsetOpcodes(Loc.SpillLocation.SpillOffset, Ops);
DIExpr = DIExpression::appendOpsToArg(DIExpr, Ops, I);
MOs.push_back(MachineOperand::CreateReg(Base, false));
case MachineLocKind::ImmediateKind: {
case MachineLocKind::InvalidKind:
llvm_unreachable("Tried to produce DBG_VALUE for invalid VarLoc");
return BuildMI(MF, DbgLoc, IID, Indirect, MOs, Var, DIExpr);
/// Is the Loc field a constant or constant object?
bool isConstant(MachineLocKind Kind) const {
return Kind == MachineLocKind::ImmediateKind;
/// Check if the Loc field is an entry backup location.
bool isEntryBackupLoc() const {
return EVKind == EntryValueLocKind::EntryValueBackupKind ||
EVKind == EntryValueLocKind::EntryValueCopyBackupKind;
/// If this variable is described by register \p Reg holding the entry
/// value, return true.
bool isEntryValueBackupReg(Register Reg) const {
return EVKind == EntryValueLocKind::EntryValueBackupKind && usesReg(Reg);
/// If this variable is described by register \p Reg holding a copy of the
/// entry value, return true.
bool isEntryValueCopyBackupReg(Register Reg) const {
return EVKind == EntryValueLocKind::EntryValueCopyBackupKind &&
/// If this variable is described in whole or part by \p Reg, return true.
bool usesReg(Register Reg) const {
MachineLoc RegML;
RegML.Kind = MachineLocKind::RegisterKind;
RegML.Value.RegNo = Reg;
return is_contained(Locs, RegML);
/// If this variable is described in whole or part by \p Reg, return true.
unsigned getRegIdx(Register Reg) const {
for (unsigned Idx = 0; Idx < Locs.size(); ++Idx)
if (Locs[Idx].Kind == MachineLocKind::RegisterKind &&
Locs[Idx].Value.RegNo == Reg)
return Idx;
llvm_unreachable("Could not find given Reg in Locs");
/// If this variable is described in whole or part by 1 or more registers,
/// add each of them to \p Regs and return true.
bool getDescribingRegs(SmallVectorImpl<uint32_t> &Regs) const {
bool AnyRegs = false;
for (auto Loc : Locs)
if (Loc.Kind == MachineLocKind::RegisterKind) {
AnyRegs = true;
return AnyRegs;
bool containsSpillLocs() const {
return any_of(Locs, [](VarLoc::MachineLoc ML) {
return ML.Kind == VarLoc::MachineLocKind::SpillLocKind;
/// If this variable is described in whole or part by \p SpillLocation,
/// return true.
bool usesSpillLoc(SpillLoc SpillLocation) const {
MachineLoc SpillML;
SpillML.Kind = MachineLocKind::SpillLocKind;
SpillML.Value.SpillLocation = SpillLocation;
return is_contained(Locs, SpillML);
/// If this variable is described in whole or part by \p SpillLocation,
/// return the index .
unsigned getSpillLocIdx(SpillLoc SpillLocation) const {
for (unsigned Idx = 0; Idx < Locs.size(); ++Idx)
if (Locs[Idx].Kind == MachineLocKind::SpillLocKind &&
Locs[Idx].Value.SpillLocation == SpillLocation)
return Idx;
llvm_unreachable("Could not find given SpillLoc in Locs");
/// Determine whether the lexical scope of this value's debug location
/// dominates MBB.
bool dominates(LexicalScopes &LS, MachineBasicBlock &MBB) const {
return LS.dominates(MI.getDebugLoc().get(), &MBB);
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
// TRI can be null.
void dump(const TargetRegisterInfo *TRI, raw_ostream &Out = dbgs()) const {
Out << "VarLoc(";
for (const MachineLoc &MLoc : Locs) {
if (Locs.begin() != &MLoc)
Out << ", ";
switch (MLoc.Kind) {
case MachineLocKind::RegisterKind:
Out << printReg(MLoc.Value.RegNo, TRI);
case MachineLocKind::SpillLocKind:
Out << printReg(MLoc.Value.SpillLocation.SpillBase, TRI);
Out << "[" << MLoc.Value.SpillLocation.SpillOffset.getFixed() << " + "
<< MLoc.Value.SpillLocation.SpillOffset.getScalable()
<< "x vscale"
<< "]";
case MachineLocKind::ImmediateKind:
Out << MLoc.Value.Immediate;
case MachineLocKind::InvalidKind:
llvm_unreachable("Invalid VarLoc in dump method");
Out << ", \"" << Var.getVariable()->getName() << "\", " << *Expr << ", ";
if (Var.getInlinedAt())
Out << "!" << Var.getInlinedAt()->getMetadataID() << ")\n";
Out << "(null))";
if (isEntryBackupLoc())
Out << " (backup loc)\n";
Out << "\n";
bool operator==(const VarLoc &Other) const {
return std::tie(EVKind, Var, Expr, Locs) ==
std::tie(Other.EVKind, Other.Var, Other.Expr, Other.Locs);
/// This operator guarantees that VarLocs are sorted by Variable first.
bool operator<(const VarLoc &Other) const {
return std::tie(Var, EVKind, Locs, Expr) <
std::tie(Other.Var, Other.EVKind, Other.Locs, Other.Expr);
#ifndef NDEBUG
using VarVec = SmallVector<VarLoc, 32>;
/// VarLocMap is used for two things:
/// 1) Assigning LocIndices to a VarLoc. The LocIndices can be used to
/// virtually insert a VarLoc into a VarLocSet.
/// 2) Given a LocIndex, look up the unique associated VarLoc.
class VarLocMap {
/// Map a VarLoc to an index within the vector reserved for its location
/// within Loc2Vars.
std::map<VarLoc, LocIndices> Var2Indices;
/// Map a location to a vector which holds VarLocs which live in that
/// location.
SmallDenseMap<LocIndex::u32_location_t, std::vector<VarLoc>> Loc2Vars;
/// Retrieve LocIndices for \p VL.
LocIndices insert(const VarLoc &VL) {
LocIndices &Indices = Var2Indices[VL];
// If Indices is not empty, VL is already in the map.
if (!Indices.empty())
return Indices;
SmallVector<LocIndex::u32_location_t, 4> Locations;
// LocIndices are determined by EVKind and MLs; each Register has a
// unique location, while all SpillLocs use a single bucket, and any EV
// VarLocs use only the Backup bucket or none at all (except the
// compulsory entry at the universal location index). LocIndices will
// always have an index at the universal location index as the last index.
if (VL.EVKind == VarLoc::EntryValueLocKind::NonEntryValueKind) {
[](auto RegNo) {
return RegNo < LocIndex::kFirstInvalidRegLocation;
}) &&
"Physreg out of range?");
if (VL.containsSpillLocs()) {
LocIndex::u32_location_t Loc = LocIndex::kSpillLocation;
} else if (VL.EVKind != VarLoc::EntryValueLocKind::EntryValueKind) {
LocIndex::u32_location_t Loc = LocIndex::kEntryValueBackupLocation;
for (LocIndex::u32_location_t Location : Locations) {
auto &Vars = Loc2Vars[Location];
{Location, static_cast<LocIndex::u32_index_t>(Vars.size())});
return Indices;
LocIndices getAllIndices(const VarLoc &VL) const {
auto IndIt = Var2Indices.find(VL);
assert(IndIt != Var2Indices.end() && "VarLoc not tracked");
return IndIt->second;
/// Retrieve the unique VarLoc associated with \p ID.
const VarLoc &operator[](LocIndex ID) const {
auto LocIt = Loc2Vars.find(ID.Location);
assert(LocIt != Loc2Vars.end() && "Location not tracked");
return LocIt->second[ID.Index];
using VarLocInMBB =
SmallDenseMap<const MachineBasicBlock *, std::unique_ptr<VarLocSet>>;
struct TransferDebugPair {
MachineInstr *TransferInst; ///< Instruction where this transfer occurs.
LocIndex LocationID; ///< Location number for the transfer dest.
using TransferMap = SmallVector<TransferDebugPair, 4>;
// Types for recording sets of variable fragments that overlap. For a given
// local variable, we record all other fragments of that variable that could
// overlap it, to reduce search time.
using FragmentOfVar =
std::pair<const DILocalVariable *, DIExpression::FragmentInfo>;
using OverlapMap =
DenseMap<FragmentOfVar, SmallVector<DIExpression::FragmentInfo, 1>>;
// Helper while building OverlapMap, a map of all fragments seen for a given
// DILocalVariable.
using VarToFragments =
DenseMap<const DILocalVariable *, SmallSet<FragmentInfo, 4>>;
/// Collects all VarLocs from \p CollectFrom. Each unique VarLoc is added
/// to \p Collected once, in order of insertion into \p VarLocIDs.
static void collectAllVarLocs(SmallVectorImpl<VarLoc> &Collected,
const VarLocSet &CollectFrom,
const VarLocMap &VarLocIDs);
/// Get the registers which are used by VarLocs of kind RegisterKind tracked
/// by \p CollectFrom.
void getUsedRegs(const VarLocSet &CollectFrom,
SmallVectorImpl<Register> &UsedRegs) const;
/// 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. In addition, we keep
/// two different maps (Vars/EntryValuesBackupVars), so erase/insert
/// methods act differently depending on whether a VarLoc is primary
/// location or backup one. In the case the VarLoc is backup location
/// we will erase/insert from the EntryValuesBackupVars map, otherwise
/// we perform the operation on the Vars.
class OpenRangesSet {
VarLocSet::Allocator &Alloc;
VarLocSet VarLocs;
// Map the DebugVariable to recent primary location ID.
SmallDenseMap<DebugVariable, LocIndices, 8> Vars;
// Map the DebugVariable to recent backup location ID.
SmallDenseMap<DebugVariable, LocIndices, 8> EntryValuesBackupVars;
OverlapMap &OverlappingFragments;
OpenRangesSet(VarLocSet::Allocator &Alloc, OverlapMap &_OLapMap)
: Alloc(Alloc), VarLocs(Alloc), OverlappingFragments(_OLapMap) {}
const VarLocSet &getVarLocs() const { return VarLocs; }
// Fetches all VarLocs in \p VarLocIDs and inserts them into \p Collected.
// This method is needed to get every VarLoc once, as each VarLoc may have
// multiple indices in a VarLocMap (corresponding to each applicable
// location), but all VarLocs appear exactly once at the universal location
// index.
void getUniqueVarLocs(SmallVectorImpl<VarLoc> &Collected,
const VarLocMap &VarLocIDs) const {
collectAllVarLocs(Collected, VarLocs, VarLocIDs);
/// Terminate all open ranges for VL.Var by removing it from the set.
void erase(const VarLoc &VL);
/// Terminate all open ranges listed as indices in \c KillSet with
/// \c Location by removing them from the set.
void erase(const VarLocsInRange &KillSet, const VarLocMap &VarLocIDs,
LocIndex::u32_location_t Location);
/// Insert a new range into the set.
void insert(LocIndices VarLocIDs, const VarLoc &VL);
/// Insert a set of ranges.
void insertFromLocSet(const VarLocSet &ToLoad, const VarLocMap &Map);
llvm::Optional<LocIndices> getEntryValueBackup(DebugVariable Var);
/// Empty the set.
void clear() {
/// Return whether the set is empty or not.
bool empty() const {
assert(Vars.empty() == EntryValuesBackupVars.empty() &&
Vars.empty() == VarLocs.empty() &&
"open ranges are inconsistent");
return VarLocs.empty();
/// Get an empty range of VarLoc IDs.
auto getEmptyVarLocRange() const {
return iterator_range<VarLocSet::const_iterator>(getVarLocs().end(),
/// Get all set IDs for VarLocs with MLs of kind RegisterKind in \p Reg.
auto getRegisterVarLocs(Register Reg) const {
return LocIndex::indexRangeForLocation(getVarLocs(), Reg);
/// Get all set IDs for VarLocs with MLs of kind SpillLocKind.
auto getSpillVarLocs() const {
return LocIndex::indexRangeForLocation(getVarLocs(),
/// Get all set IDs for VarLocs of EVKind EntryValueBackupKind or
/// EntryValueCopyBackupKind.
auto getEntryValueBackupVarLocs() const {
return LocIndex::indexRangeForLocation(
getVarLocs(), LocIndex::kEntryValueBackupLocation);
/// Collect all VarLoc IDs from \p CollectFrom for VarLocs with MLs of kind
/// RegisterKind which are located in any reg in \p Regs. The IDs for each
/// VarLoc correspond to entries in the universal location bucket, which every
/// VarLoc has exactly 1 entry for. Insert collected IDs into \p Collected.
static void collectIDsForRegs(VarLocsInRange &Collected,
const DefinedRegsSet &Regs,
const VarLocSet &CollectFrom,
const VarLocMap &VarLocIDs);
VarLocSet &getVarLocsInMBB(const MachineBasicBlock *MBB, VarLocInMBB &Locs) {
std::unique_ptr<VarLocSet> &VLS = Locs[MBB];
if (!VLS)
VLS = std::make_unique<VarLocSet>(Alloc);
return *VLS.get();
const VarLocSet &getVarLocsInMBB(const MachineBasicBlock *MBB,
const VarLocInMBB &Locs) const {
auto It = Locs.find(MBB);
assert(It != Locs.end() && "MBB not in map");
return *It->second.get();
/// Tests whether this instruction is a spill to a stack location.
bool isSpillInstruction(const MachineInstr &MI, MachineFunction *MF);
/// 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 isLocationSpill(const MachineInstr &MI, MachineFunction *MF,
Register &Reg);
/// Returns true if the given machine instruction is a debug value which we
/// can emit entry values for.
/// Currently, we generate debug entry values only for parameters that are
/// unmodified throughout the function and located in a register.
bool isEntryValueCandidate(const MachineInstr &MI,
const DefinedRegsSet &Regs) const;
/// If a given instruction is identified as a spill, return the spill location
/// and set \p Reg to the spilled register.
Optional<VarLoc::SpillLoc> isRestoreInstruction(const MachineInstr &MI,
MachineFunction *MF,
Register &Reg);
/// Given a spill instruction, extract the register and offset used to
/// address the spill location in a target independent way.
VarLoc::SpillLoc extractSpillBaseRegAndOffset(const MachineInstr &MI);
void insertTransferDebugPair(MachineInstr &MI, OpenRangesSet &OpenRanges,
TransferMap &Transfers, VarLocMap &VarLocIDs,
LocIndex OldVarID, TransferKind Kind,
const VarLoc::MachineLoc &OldLoc,
Register NewReg = Register());
void transferDebugValue(const MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs);
void transferSpillOrRestoreInst(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, TransferMap &Transfers);
bool removeEntryValue(const MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, const VarLoc &EntryVL);
void emitEntryValues(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, TransferMap &Transfers,
VarLocsInRange &KillSet);
void recordEntryValue(const MachineInstr &MI,
const DefinedRegsSet &DefinedRegs,
OpenRangesSet &OpenRanges, VarLocMap &VarLocIDs);
void transferRegisterCopy(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, TransferMap &Transfers);
void transferRegisterDef(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, TransferMap &Transfers);
bool transferTerminator(MachineBasicBlock *MBB, OpenRangesSet &OpenRanges,
VarLocInMBB &OutLocs, const VarLocMap &VarLocIDs);
void process(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, TransferMap &Transfers);
void accumulateFragmentMap(MachineInstr &MI, VarToFragments &SeenFragments,
OverlapMap &OLapMap);
bool join(MachineBasicBlock &MBB, VarLocInMBB &OutLocs, VarLocInMBB &InLocs,
const VarLocMap &VarLocIDs,
SmallPtrSet<const MachineBasicBlock *, 16> &Visited,
SmallPtrSetImpl<const MachineBasicBlock *> &ArtificialBlocks);
/// Create DBG_VALUE insts for inlocs that have been propagated but
/// had their instruction creation deferred.
void flushPendingLocs(VarLocInMBB &PendingInLocs, VarLocMap &VarLocIDs);
bool ExtendRanges(MachineFunction &MF, TargetPassConfig *TPC) override;
/// Default construct and initialize the pass.
/// Print to ostream with a message.
void printVarLocInMBB(const MachineFunction &MF, const VarLocInMBB &V,
const VarLocMap &VarLocIDs, const char *msg,
raw_ostream &Out) const;
} // end anonymous namespace
// Implementation
VarLocBasedLDV::VarLocBasedLDV() { }
VarLocBasedLDV::~VarLocBasedLDV() { }
/// Erase a variable from the set of open ranges, and additionally erase any
/// fragments that may overlap it. If the VarLoc is a backup location, erase
/// the variable from the EntryValuesBackupVars set, indicating we should stop
/// tracking its backup entry location. Otherwise, if the VarLoc is primary
/// location, erase the variable from the Vars set.
void VarLocBasedLDV::OpenRangesSet::erase(const VarLoc &VL) {
// Erasure helper.
auto DoErase = [VL, this](DebugVariable VarToErase) {
auto *EraseFrom = VL.isEntryBackupLoc() ? &EntryValuesBackupVars : &Vars;
auto It = EraseFrom->find(VarToErase);
if (It != EraseFrom->end()) {
LocIndices IDs = It->second;
for (LocIndex ID : IDs)
DebugVariable Var = VL.Var;
// Erase the variable/fragment that ends here.
// Extract the fragment. Interpret an empty fragment as one that covers all
// possible bits.
FragmentInfo ThisFragment = Var.getFragmentOrDefault();
// There may be fragments that overlap the designated fragment. Look them up
// in the pre-computed overlap map, and erase them too.
auto MapIt = OverlappingFragments.find({Var.getVariable(), ThisFragment});
if (MapIt != OverlappingFragments.end()) {
for (auto Fragment : MapIt->second) {
VarLocBasedLDV::OptFragmentInfo FragmentHolder;
if (!DebugVariable::isDefaultFragment(Fragment))
FragmentHolder = VarLocBasedLDV::OptFragmentInfo(Fragment);
DoErase({Var.getVariable(), FragmentHolder, Var.getInlinedAt()});
void VarLocBasedLDV::OpenRangesSet::erase(const VarLocsInRange &KillSet,
const VarLocMap &VarLocIDs,
LocIndex::u32_location_t Location) {
VarLocSet RemoveSet(Alloc);
for (LocIndex::u32_index_t ID : KillSet) {
const VarLoc &VL = VarLocIDs[LocIndex(Location, ID)];
auto *EraseFrom = VL.isEntryBackupLoc() ? &EntryValuesBackupVars : &Vars;
LocIndices VLI = VarLocIDs.getAllIndices(VL);
for (LocIndex ID : VLI)
void VarLocBasedLDV::OpenRangesSet::insertFromLocSet(const VarLocSet &ToLoad,
const VarLocMap &Map) {
VarLocsInRange UniqueVarLocIDs;
DefinedRegsSet Regs;
collectIDsForRegs(UniqueVarLocIDs, Regs, ToLoad, Map);
for (uint64_t ID : UniqueVarLocIDs) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VarL = Map[Idx];
const LocIndices Indices = Map.getAllIndices(VarL);
insert(Indices, VarL);
void VarLocBasedLDV::OpenRangesSet::insert(LocIndices VarLocIDs,
const VarLoc &VL) {
auto *InsertInto = VL.isEntryBackupLoc() ? &EntryValuesBackupVars : &Vars;
for (LocIndex ID : VarLocIDs)
InsertInto->insert({VL.Var, VarLocIDs});
/// Return the Loc ID of an entry value backup location, if it exists for the
/// variable.
VarLocBasedLDV::OpenRangesSet::getEntryValueBackup(DebugVariable Var) {
auto It = EntryValuesBackupVars.find(Var);
if (It != EntryValuesBackupVars.end())
return It->second;
return llvm::None;
void VarLocBasedLDV::collectIDsForRegs(VarLocsInRange &Collected,
const DefinedRegsSet &Regs,
const VarLocSet &CollectFrom,
const VarLocMap &VarLocIDs) {
assert(!Regs.empty() && "Nothing to collect");
SmallVector<Register, 32> SortedRegs;
append_range(SortedRegs, Regs);
array_pod_sort(SortedRegs.begin(), SortedRegs.end());
auto It = CollectFrom.find(LocIndex::rawIndexForReg(SortedRegs.front()));
auto End = CollectFrom.end();
for (Register Reg : SortedRegs) {
// The half-open interval [FirstIndexForReg, FirstInvalidIndex) contains
// all possible VarLoc IDs for VarLocs with MLs of kind RegisterKind which
// live in Reg.
uint64_t FirstIndexForReg = LocIndex::rawIndexForReg(Reg);
uint64_t FirstInvalidIndex = LocIndex::rawIndexForReg(Reg + 1);
// Iterate through that half-open interval and collect all the set IDs.
for (; It != End && *It < FirstInvalidIndex; ++It) {
LocIndex ItIdx = LocIndex::fromRawInteger(*It);
const VarLoc &VL = VarLocIDs[ItIdx];
LocIndices LI = VarLocIDs.getAllIndices(VL);
// For now, the back index is always the universal location index.
assert(LI.back().Location == LocIndex::kUniversalLocation &&
"Unexpected order of LocIndices for VarLoc; was it inserted into "
"the VarLocMap correctly?");
if (It == End)
void VarLocBasedLDV::getUsedRegs(const VarLocSet &CollectFrom,
SmallVectorImpl<Register> &UsedRegs) const {
// All register-based VarLocs are assigned indices greater than or equal to
// FirstRegIndex.
uint64_t FirstRegIndex =
uint64_t FirstInvalidIndex =
for (auto It = CollectFrom.find(FirstRegIndex),
End = CollectFrom.find(FirstInvalidIndex);
It != End;) {
// We found a VarLoc ID for a VarLoc that lives in a register. Figure out
// which register and add it to UsedRegs.
uint32_t FoundReg = LocIndex::fromRawInteger(*It).Location;
assert((UsedRegs.empty() || FoundReg != UsedRegs.back()) &&
"Duplicate used reg");
// Skip to the next /set/ register. Note that this finds a lower bound, so
// even if there aren't any VarLocs living in `FoundReg+1`, we're still
// guaranteed to move on to the next register (or to end()).
uint64_t NextRegIndex = LocIndex::rawIndexForReg(FoundReg + 1);
// Debug Range Extension Implementation
#ifndef NDEBUG
void VarLocBasedLDV::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) {
if (!V.count(&BB))
const VarLocSet &L = getVarLocsInMBB(&BB, V);
if (L.empty())
SmallVector<VarLoc, 32> VarLocs;
collectAllVarLocs(VarLocs, L, VarLocIDs);
Out << "MBB: " << BB.getNumber() << ":\n";
for (const VarLoc &VL : VarLocs) {
Out << " Var: " << VL.Var.getVariable()->getName();
Out << " MI: ";
VL.dump(TRI, Out);
Out << "\n";
VarLocBasedLDV::extractSpillBaseRegAndOffset(const MachineInstr &MI) {
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();
Register Reg;
StackOffset Offset = TFI->getFrameIndexReference(*MBB->getParent(), FI, Reg);
return {Reg, Offset};
/// Try to salvage the debug entry value if we encounter a new debug value
/// describing the same parameter, otherwise stop tracking the value. Return
/// true if we should stop tracking the entry value, otherwise return false.
bool VarLocBasedLDV::removeEntryValue(const MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs,
const VarLoc &EntryVL) {
// Skip the DBG_VALUE which is the debug entry value itself.
if (MI.isIdenticalTo(EntryVL.MI))
return false;
// If the parameter's location is not register location, we can not track
// the entry value any more. In addition, if the debug expression from the
// DBG_VALUE is not empty, we can assume the parameter's value has changed
// indicating that we should stop tracking its entry value as well.
if (!MI.getDebugOperand(0).isReg() ||
MI.getDebugExpression()->getNumElements() != 0)
return true;
// If the DBG_VALUE comes from a copy instruction that copies the entry value,
// it means the parameter's value has not changed and we should be able to use
// its entry value.
Register Reg = MI.getDebugOperand(0).getReg();
auto I = std::next(MI.getReverseIterator());
const MachineOperand *SrcRegOp, *DestRegOp;
if (I != MI.getParent()->rend()) {
// TODO: Try to keep tracking of an entry value if we encounter a propagated
// DBG_VALUE describing the copy of the entry value. (Propagated entry value
// does not indicate the parameter modification.)
auto DestSrc = TII->isCopyInstr(*I);
if (!DestSrc)
return true;
SrcRegOp = DestSrc->Source;
DestRegOp = DestSrc->Destination;
if (Reg != DestRegOp->getReg())
return true;
for (uint64_t ID : OpenRanges.getEntryValueBackupVarLocs()) {
const VarLoc &VL = VarLocIDs[LocIndex::fromRawInteger(ID)];
if (VL.isEntryValueCopyBackupReg(Reg) &&
// Entry Values should not be variadic.
VL.MI.getDebugOperand(0).getReg() == SrcRegOp->getReg())
return false;
return true;
/// End all previous ranges related to @MI and start a new range from @MI
/// if it is a DBG_VALUE instr.
void VarLocBasedLDV::transferDebugValue(const MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs) {
if (!MI.isDebugValue())
const DILocalVariable *Var = MI.getDebugVariable();
const DIExpression *Expr = MI.getDebugExpression();
const DILocation *DebugLoc = MI.getDebugLoc();
const DILocation *InlinedAt = DebugLoc->getInlinedAt();
assert(Var->isValidLocationForIntrinsic(DebugLoc) &&
"Expected inlined-at fields to agree");
DebugVariable V(Var, Expr, InlinedAt);
// Check if this DBG_VALUE indicates a parameter's value changing.
// If that is the case, we should stop tracking its entry value.
auto EntryValBackupID = OpenRanges.getEntryValueBackup(V);
if (Var->isParameter() && EntryValBackupID) {
const VarLoc &EntryVL = VarLocIDs[EntryValBackupID->back()];
if (removeEntryValue(MI, OpenRanges, VarLocIDs, EntryVL)) {
LLVM_DEBUG(dbgs() << "Deleting a DBG entry value because of: ";
MI.print(dbgs(), /*IsStandalone*/ false,
/*SkipOpers*/ false, /*SkipDebugLoc*/ false,
/*AddNewLine*/ true, TII));
if (all_of(MI.debug_operands(), [](const MachineOperand &MO) {
return (MO.isReg() && MO.getReg()) || MO.isImm() || MO.isFPImm() ||
})) {
// Use normal VarLoc constructor for registers and immediates.
VarLoc VL(MI, LS);
// End all previous ranges of VL.Var.
LocIndices IDs = VarLocIDs.insert(VL);
// Add the VarLoc to OpenRanges from this DBG_VALUE.
OpenRanges.insert(IDs, VL);
} else if (MI.memoperands().size() > 0) {
llvm_unreachable("DBG_VALUE with mem operand encountered after regalloc?");
} else {
// This must be an undefined location. If it has an open range, erase it.
assert(MI.isUndefDebugValue() &&
"Unexpected non-undef DBG_VALUE encountered");
VarLoc VL(MI, LS);
// This should be removed later, doesn't fit the new design.
void VarLocBasedLDV::collectAllVarLocs(SmallVectorImpl<VarLoc> &Collected,
const VarLocSet &CollectFrom,
const VarLocMap &VarLocIDs) {
// The half-open interval [FirstIndexForReg, FirstInvalidIndex) contains all
// possible VarLoc IDs for VarLocs with MLs of kind RegisterKind which live
// in Reg.
uint64_t FirstIndex = LocIndex::rawIndexForReg(LocIndex::kUniversalLocation);
uint64_t FirstInvalidIndex =
LocIndex::rawIndexForReg(LocIndex::kUniversalLocation + 1);
// Iterate through that half-open interval and collect all the set IDs.
for (auto It = CollectFrom.find(FirstIndex), End = CollectFrom.end();
It != End && *It < FirstInvalidIndex; ++It) {
LocIndex RegIdx = LocIndex::fromRawInteger(*It);
/// Turn the entry value backup locations into primary locations.
void VarLocBasedLDV::emitEntryValues(MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs,
TransferMap &Transfers,
VarLocsInRange &KillSet) {
// Do not insert entry value locations after a terminator.
if (MI.isTerminator())
for (uint32_t ID : KillSet) {
// The KillSet IDs are indices for the universal location bucket.
LocIndex Idx = LocIndex(LocIndex::kUniversalLocation, ID);
const VarLoc &VL = VarLocIDs[Idx];
if (!VL.Var.getVariable()->isParameter())
auto DebugVar = VL.Var;
Optional<LocIndices> EntryValBackupIDs =
// If the parameter has the entry value backup, it means we should
// be able to use its entry value.
if (!EntryValBackupIDs)
const VarLoc &EntryVL = VarLocIDs[EntryValBackupIDs->back()];
VarLoc EntryLoc = VarLoc::CreateEntryLoc(EntryVL.MI, LS, EntryVL.Expr,
LocIndices EntryValueIDs = VarLocIDs.insert(EntryLoc);
Transfers.push_back({&MI, EntryValueIDs.back()});
OpenRanges.insert(EntryValueIDs, EntryLoc);
/// 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 VarLocBasedLDV::insertTransferDebugPair(
MachineInstr &MI, OpenRangesSet &OpenRanges, TransferMap &Transfers,
VarLocMap &VarLocIDs, LocIndex OldVarID, TransferKind Kind,
const VarLoc::MachineLoc &OldLoc, Register NewReg) {
const VarLoc &OldVarLoc = VarLocIDs[OldVarID];
auto ProcessVarLoc = [&MI, &OpenRanges, &Transfers, &VarLocIDs](VarLoc &VL) {
LocIndices LocIds = VarLocIDs.insert(VL);
// Close this variable's previous location range.
// Record the new location as an open range, and a postponed transfer
// inserting a DBG_VALUE for this location.
OpenRanges.insert(LocIds, VL);
assert(!MI.isTerminator() && "Cannot insert DBG_VALUE after terminator");
TransferDebugPair MIP = {&MI, LocIds.back()};
// End all previous ranges of VL.Var.
switch (Kind) {
case TransferKind::TransferCopy: {
assert(NewReg &&
"No register supplied when handling a copy of a debug value");
// Create a DBG_VALUE instruction to describe the Var in its new
// register location.
VarLoc VL = VarLoc::CreateCopyLoc(OldVarLoc, OldLoc, NewReg);
dbgs() << "Creating VarLoc for register copy:";
case TransferKind::TransferSpill: {
// Create a DBG_VALUE instruction to describe the Var in its spilled
// location.
VarLoc::SpillLoc SpillLocation = extractSpillBaseRegAndOffset(MI);
VarLoc VL = VarLoc::CreateSpillLoc(
OldVarLoc, OldLoc, SpillLocation.SpillBase, SpillLocation.SpillOffset);
dbgs() << "Creating VarLoc for spill:";
case TransferKind::TransferRestore: {
assert(NewReg &&
"No register supplied when handling a restore of a debug value");
// DebugInstr refers to the pre-spill location, therefore we can reuse
// its expression.
VarLoc VL = VarLoc::CreateCopyLoc(OldVarLoc, OldLoc, NewReg);
dbgs() << "Creating VarLoc for restore:";
llvm_unreachable("Invalid transfer kind");
/// A definition of a register may mark the end of a range.
void VarLocBasedLDV::transferRegisterDef(
MachineInstr &MI, OpenRangesSet &OpenRanges, VarLocMap &VarLocIDs,
TransferMap &Transfers) {
// Meta Instructions do not affect the debug liveness of any register they
// define.
if (MI.isMetaInstruction())
MachineFunction *MF = MI.getMF();
const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
Register SP = TLI->getStackPointerRegisterToSaveRestore();
// Find the regs killed by MI, and find regmasks of preserved regs.
DefinedRegsSet DeadRegs;
SmallVector<const uint32_t *, 4> RegMasks;
for (const MachineOperand &MO : MI.operands()) {
// Determine whether the operand is a register def.
if (MO.isReg() && MO.isDef() && MO.getReg() &&
Register::isPhysicalRegister(MO.getReg()) &&
!(MI.isCall() && MO.getReg() == SP)) {
// Remove ranges of all aliased registers.
for (MCRegAliasIterator RAI(MO.getReg(), TRI, true); RAI.isValid(); ++RAI)
// FIXME: Can we break out of this loop early if no insertion occurs?
} else if (MO.isRegMask()) {
// Erase VarLocs which reside in one of the dead registers. For performance
// reasons, it's critical to not iterate over the full set of open VarLocs.
// Iterate over the set of dying/used regs instead.
if (!RegMasks.empty()) {
SmallVector<Register, 32> UsedRegs;
getUsedRegs(OpenRanges.getVarLocs(), UsedRegs);
for (Register Reg : UsedRegs) {
// Remove ranges of all clobbered registers. Register masks don't usually
// list SP as preserved. Assume that call instructions never clobber SP,
// because some backends (e.g., AArch64) never list SP in the regmask.
// 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.
if (Reg == SP)
bool AnyRegMaskKillsReg =
any_of(RegMasks, [Reg](const uint32_t *RegMask) {
return MachineOperand::clobbersPhysReg(RegMask, Reg);
if (AnyRegMaskKillsReg)
if (DeadRegs.empty())
VarLocsInRange KillSet;
collectIDsForRegs(KillSet, DeadRegs, OpenRanges.getVarLocs(), VarLocIDs);
OpenRanges.erase(KillSet, VarLocIDs, LocIndex::kUniversalLocation);
if (TPC) {
auto &TM = TPC->getTM<TargetMachine>();
if (TM.Options.ShouldEmitDebugEntryValues())
emitEntryValues(MI, OpenRanges, VarLocIDs, Transfers, KillSet);
bool VarLocBasedLDV::isSpillInstruction(const MachineInstr &MI,
MachineFunction *MF) {
// TODO: Handle multiple stores folded into one.
if (!MI.hasOneMemOperand())
return false;
if (!MI.getSpillSize(TII) && !MI.getFoldedSpillSize(TII))
return false; // This is not a spill instruction, since no valid size was
// returned from either function.
return true;
bool VarLocBasedLDV::isLocationSpill(const MachineInstr &MI,
MachineFunction *MF, Register &Reg) {
if (!isSpillInstruction(MI, MF))
return false;
auto isKilledReg = [&](const MachineOperand MO, Register &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)
Register 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;
VarLocBasedLDV::isRestoreInstruction(const MachineInstr &MI,
MachineFunction *MF, Register &Reg) {
if (!MI.hasOneMemOperand())
return None;
// FIXME: Handle folded restore instructions with more than one memory
// operand.
if (MI.getRestoreSize(TII)) {
Reg = MI.getOperand(0).getReg();
return extractSpillBaseRegAndOffset(MI);
return None;
/// 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.
/// A restored register may indicate the reverse situation.
/// 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 VarLocBasedLDV::transferSpillOrRestoreInst(MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs,
TransferMap &Transfers) {
MachineFunction *MF = MI.getMF();
TransferKind TKind;
Register Reg;
Optional<VarLoc::SpillLoc> Loc;
LLVM_DEBUG(dbgs() << "Examining instruction: "; MI.dump(););
// First, if there are any DBG_VALUEs pointing at a spill slot that is
// written to, then close the variable location. The value in memory
// will have changed.
VarLocsInRange KillSet;
if (isSpillInstruction(MI, MF)) {
Loc = extractSpillBaseRegAndOffset(MI);
for (uint64_t ID : OpenRanges.getSpillVarLocs()) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VL = VarLocIDs[Idx];
assert(VL.containsSpillLocs() && "Broken VarLocSet?");
if (VL.usesSpillLoc(*Loc)) {
// This location is overwritten by the current instruction -- terminate
// the open range, and insert an explicit DBG_VALUE $noreg.
// Doing this at a later stage would require re-interpreting all
// DBG_VALUes and DIExpressions to identify whether they point at
// memory, and then analysing all memory writes to see if they
// overwrite that memory, which is expensive.
// At this stage, we already know which DBG_VALUEs are for spills and
// where they are located; it's best to fix handle overwrites now.
unsigned SpillLocIdx = VL.getSpillLocIdx(*Loc);
VarLoc::MachineLoc OldLoc = VL.Locs[SpillLocIdx];
VarLoc UndefVL = VarLoc::CreateCopyLoc(VL, OldLoc, 0);
LocIndices UndefLocIDs = VarLocIDs.insert(UndefVL);
Transfers.push_back({&MI, UndefLocIDs.back()});
OpenRanges.erase(KillSet, VarLocIDs, LocIndex::kSpillLocation);
// Try to recognise spill and restore instructions that may create a new
// variable location.
if (isLocationSpill(MI, MF, Reg)) {
TKind = TransferKind::TransferSpill;
LLVM_DEBUG(dbgs() << "Recognized as spill: "; MI.dump(););
LLVM_DEBUG(dbgs() << "Register: " << Reg << " " << printReg(Reg, TRI)
<< "\n");
} else {
if (!(Loc = isRestoreInstruction(MI, MF, Reg)))
TKind = TransferKind::TransferRestore;
LLVM_DEBUG(dbgs() << "Recognized as restore: "; MI.dump(););
LLVM_DEBUG(dbgs() << "Register: " << Reg << " " << printReg(Reg, TRI)
<< "\n");
// Check if the register or spill location is the location of a debug value.
auto TransferCandidates = OpenRanges.getEmptyVarLocRange();
if (TKind == TransferKind::TransferSpill)
TransferCandidates = OpenRanges.getRegisterVarLocs(Reg);
else if (TKind == TransferKind::TransferRestore)
TransferCandidates = OpenRanges.getSpillVarLocs();
for (uint64_t ID : TransferCandidates) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VL = VarLocIDs[Idx];
unsigned LocIdx;
if (TKind == TransferKind::TransferSpill) {
assert(VL.usesReg(Reg) && "Broken VarLocSet?");
LLVM_DEBUG(dbgs() << "Spilling Register " << printReg(Reg, TRI) << '('
<< VL.Var.getVariable()->getName() << ")\n");
LocIdx = VL.getRegIdx(Reg);
} else {
assert(TKind == TransferKind::TransferRestore && VL.containsSpillLocs() &&
"Broken VarLocSet?");
if (!VL.usesSpillLoc(*Loc))
// The spill location is not the location of a debug value.
LLVM_DEBUG(dbgs() << "Restoring Register " << printReg(Reg, TRI) << '('
<< VL.Var.getVariable()->getName() << ")\n");
LocIdx = VL.getSpillLocIdx(*Loc);
VarLoc::MachineLoc MLoc = VL.Locs[LocIdx];
insertTransferDebugPair(MI, OpenRanges, Transfers, VarLocIDs, Idx, TKind,
MLoc, Reg);
// FIXME: A comment should explain why it's correct to return early here,
// if that is in fact correct.
/// 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 VarLocBasedLDV::transferRegisterCopy(MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs,
TransferMap &Transfers) {
auto DestSrc = TII->isCopyInstr(MI);
if (!DestSrc)
const MachineOperand *DestRegOp = DestSrc->Destination;
const MachineOperand *SrcRegOp = DestSrc->Source;
if (!DestRegOp->isDef())
auto isCalleeSavedReg = [&](Register Reg) {
for (MCRegAliasIterator RAI(Reg, TRI, true); RAI.isValid(); ++RAI)
if (CalleeSavedRegs.test(*RAI))
return true;
return false;
Register SrcReg = SrcRegOp->getReg();
Register 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 (!isCalleeSavedReg(DestReg))
// Remember an entry value movement. If we encounter a new debug value of
// a parameter describing only a moving of the value around, rather then
// modifying it, we are still able to use the entry value if needed.
if (isRegOtherThanSPAndFP(*DestRegOp, MI, TRI)) {
for (uint64_t ID : OpenRanges.getEntryValueBackupVarLocs()) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VL = VarLocIDs[Idx];
if (VL.isEntryValueBackupReg(SrcReg)) {
LLVM_DEBUG(dbgs() << "Copy of the entry value: "; MI.dump(););
VarLoc EntryValLocCopyBackup =
VarLoc::CreateEntryCopyBackupLoc(VL.MI, LS, VL.Expr, DestReg);
// Stop tracking the original entry value.
// Start tracking the entry value copy.
LocIndices EntryValCopyLocIDs = VarLocIDs.insert(EntryValLocCopyBackup);
OpenRanges.insert(EntryValCopyLocIDs, EntryValLocCopyBackup);
if (!SrcRegOp->isKill())
for (uint64_t ID : OpenRanges.getRegisterVarLocs(SrcReg)) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
assert(VarLocIDs[Idx].usesReg(SrcReg) && "Broken VarLocSet?");
VarLoc::MachineLocValue Loc;
Loc.RegNo = SrcReg;
VarLoc::MachineLoc MLoc{VarLoc::MachineLocKind::RegisterKind, Loc};
insertTransferDebugPair(MI, OpenRanges, Transfers, VarLocIDs, Idx,
TransferKind::TransferCopy, MLoc, DestReg);
// FIXME: A comment should explain why it's correct to return early here,
// if that is in fact correct.
/// Terminate all open ranges at the end of the current basic block.
bool VarLocBasedLDV::transferTerminator(MachineBasicBlock *CurMBB,
OpenRangesSet &OpenRanges,
VarLocInMBB &OutLocs,
const VarLocMap &VarLocIDs) {
bool Changed = false;
VarVec VarLocs;
OpenRanges.getUniqueVarLocs(VarLocs, VarLocIDs);
for (VarLoc &VL : VarLocs) {
// Copy OpenRanges to OutLocs, if not already present.
dbgs() << "Add to OutLocs in MBB #" << CurMBB->getNumber() << ": ";
VarLocSet &VLS = getVarLocsInMBB(CurMBB, OutLocs);
Changed = VLS != OpenRanges.getVarLocs();
// New OutLocs set may be different due to spill, restore or register
// copy instruction processing.
if (Changed)
VLS = OpenRanges.getVarLocs();
return Changed;
/// Accumulate a mapping between each DILocalVariable fragment and other
/// fragments of that DILocalVariable which overlap. This reduces work during
/// the data-flow stage from "Find any overlapping fragments" to "Check if the
/// known-to-overlap fragments are present".
/// \param MI A previously unprocessed DEBUG_VALUE instruction to analyze for
/// fragment usage.
/// \param SeenFragments Map from DILocalVariable to all fragments of that
/// Variable which are known to exist.
/// \param OverlappingFragments The overlap map being constructed, from one
/// Var/Fragment pair to a vector of fragments known to overlap.
void VarLocBasedLDV::accumulateFragmentMap(MachineInstr &MI,
VarToFragments &SeenFragments,
OverlapMap &OverlappingFragments) {
DebugVariable MIVar(MI.getDebugVariable(), MI.getDebugExpression(),
FragmentInfo ThisFragment = MIVar.getFragmentOrDefault();
// If this is the first sighting of this variable, then we are guaranteed
// there are currently no overlapping fragments either. Initialize the set
// of seen fragments, record no overlaps for the current one, and return.
auto SeenIt = SeenFragments.find(MIVar.getVariable());
if (SeenIt == SeenFragments.end()) {
SmallSet<FragmentInfo, 4> OneFragment;
SeenFragments.insert({MIVar.getVariable(), OneFragment});
OverlappingFragments.insert({{MIVar.getVariable(), ThisFragment}, {}});
// If this particular Variable/Fragment pair already exists in the overlap
// map, it has already been accounted for.
auto IsInOLapMap =
OverlappingFragments.insert({{MIVar.getVariable(), ThisFragment}, {}});
if (!IsInOLapMap.second)
auto &ThisFragmentsOverlaps = IsInOLapMap.first->second;
auto &AllSeenFragments = SeenIt->second;
// Otherwise, examine all other seen fragments for this variable, with "this"
// fragment being a previously unseen fragment. Record any pair of
// overlapping fragments.
for (auto &ASeenFragment : AllSeenFragments) {
// Does this previously seen fragment overlap?
if (DIExpression::fragmentsOverlap(ThisFragment, ASeenFragment)) {
// Yes: Mark the current fragment as being overlapped.
// Mark the previously seen fragment as being overlapped by the current
// one.
auto ASeenFragmentsOverlaps =
OverlappingFragments.find({MIVar.getVariable(), ASeenFragment});
assert(ASeenFragmentsOverlaps != OverlappingFragments.end() &&
"Previously seen var fragment has no vector of overlaps");
/// This routine creates OpenRanges.
void VarLocBasedLDV::process(MachineInstr &MI, OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs, TransferMap &Transfers) {
transferDebugValue(MI, OpenRanges, VarLocIDs);
transferRegisterDef(MI, OpenRanges, VarLocIDs, Transfers);
transferRegisterCopy(MI, OpenRanges, VarLocIDs, Transfers);
transferSpillOrRestoreInst(MI, OpenRanges, VarLocIDs, Transfers);
/// 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 VarLocBasedLDV::join(
MachineBasicBlock &MBB, VarLocInMBB &OutLocs, VarLocInMBB &InLocs,
const VarLocMap &VarLocIDs,
SmallPtrSet<const MachineBasicBlock *, 16> &Visited,
SmallPtrSetImpl<const MachineBasicBlock *> &ArtificialBlocks) {
LLVM_DEBUG(dbgs() << "join MBB: " << MBB.getNumber() << "\n");
VarLocSet InLocsT(Alloc); // 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 backedges if we have not visited the predecessor yet. As the
// predecessor hasn't yet had locations propagated into it, most locations
// will not yet be valid, so treat them as all being uninitialized and
// potentially valid. If a location guessed to be correct here is
// invalidated later, we will remove it when we revisit this block.
if (!Visited.count(p)) {
LLVM_DEBUG(dbgs() << " ignoring unvisited pred MBB: " << p->getNumber()
<< "\n");
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.
VarLocSet &OutLocVLS = *OL->second.get();
if (!NumVisited)
InLocsT = OutLocVLS;
InLocsT &= OutLocVLS;
if (!InLocsT.empty()) {
VarVec VarLocs;
collectAllVarLocs(VarLocs, InLocsT, VarLocIDs);
for (const VarLoc &VL : VarLocs)
dbgs() << " gathered candidate incoming var: "
<< VL.Var.getVariable()->getName() << "\n";
// Filter out DBG_VALUES that are out of scope.
VarLocSet KillSet(Alloc);
bool IsArtificial = ArtificialBlocks.count(&MBB);
if (!IsArtificial) {
for (uint64_t ID : InLocsT) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
if (!VarLocIDs[Idx].dominates(LS, MBB)) {
auto Name = VarLocIDs[Idx].Var.getVariable()->getName();
dbgs() << " killing " << Name << ", it doesn't dominate MBB\n";
// 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");
VarLocSet &ILS = getVarLocsInMBB(&MBB, InLocs);
bool Changed = false;
if (ILS != InLocsT) {
ILS = InLocsT;
Changed = true;
return Changed;
void VarLocBasedLDV::flushPendingLocs(VarLocInMBB &PendingInLocs,
VarLocMap &VarLocIDs) {
// PendingInLocs records all locations propagated into blocks, which have
// not had DBG_VALUE insts created. Go through and create those insts now.
for (auto &Iter : PendingInLocs) {
// Map is keyed on a constant pointer, unwrap it so we can insert insts.
auto &MBB = const_cast<MachineBasicBlock &>(*Iter.first);
VarLocSet &Pending = *Iter.second.get();
SmallVector<VarLoc, 32> VarLocs;
collectAllVarLocs(VarLocs, Pending, VarLocIDs);
for (VarLoc DiffIt : VarLocs) {
// The ID location is live-in to MBB -- work out what kind of machine
// location it is and create a DBG_VALUE.
if (DiffIt.isEntryBackupLoc())
MachineInstr *MI = DiffIt.BuildDbgValue(*MBB.getParent());
MBB.insert(MBB.instr_begin(), MI);
LLVM_DEBUG(dbgs() << "Inserted: "; MI->dump(););
bool VarLocBasedLDV::isEntryValueCandidate(
const MachineInstr &MI, const DefinedRegsSet &DefinedRegs) const {
assert(MI.isDebugValue() && "This must be DBG_VALUE.");
// TODO: Add support for local variables that are expressed in terms of
// parameters entry values.
// TODO: Add support for modified arguments that can be expressed
// by using its entry value.
auto *DIVar = MI.getDebugVariable();
if (!DIVar->isParameter())
return false;
// Do not consider parameters that belong to an inlined function.
if (MI.getDebugLoc()->getInlinedAt())
return false;
// Only consider parameters that are described using registers. Parameters
// that are passed on the stack are not yet supported, so ignore debug
// values that are described by the frame or stack pointer.
if (!isRegOtherThanSPAndFP(MI.getDebugOperand(0), MI, TRI))
return false;
// If a parameter's value has been propagated from the caller, then the
// parameter's DBG_VALUE may be described using a register defined by some
// instruction in the entry block, in which case we shouldn't create an
// entry value.
if (DefinedRegs.count(MI.getDebugOperand(0).getReg()))
return false;
// TODO: Add support for parameters that have a pre-existing debug expressions
// (e.g. fragments).
if (MI.getDebugExpression()->getNumElements() > 0)
return false;
return true;
/// Collect all register defines (including aliases) for the given instruction.
static void collectRegDefs(const MachineInstr &MI, DefinedRegsSet &Regs,
const TargetRegisterInfo *TRI) {
for (const MachineOperand &MO : MI.operands())
if (MO.isReg() && MO.isDef() && MO.getReg())
for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid(); ++AI)
/// This routine records the entry values of function parameters. The values
/// could be used as backup values. If we loose the track of some unmodified
/// parameters, the backup values will be used as a primary locations.
void VarLocBasedLDV::recordEntryValue(const MachineInstr &MI,
const DefinedRegsSet &DefinedRegs,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs) {
if (TPC) {
auto &TM = TPC->getTM<TargetMachine>();
if (!TM.Options.ShouldEmitDebugEntryValues())
DebugVariable V(MI.getDebugVariable(), MI.getDebugExpression(),
if (!isEntryValueCandidate(MI, DefinedRegs) ||
LLVM_DEBUG(dbgs() << "Creating the backup entry location: "; MI.dump(););
// Create the entry value and use it as a backup location until it is
// valid. It is valid until a parameter is not changed.
DIExpression *NewExpr =
DIExpression::prepend(MI.getDebugExpression(), DIExpression::EntryValue);
VarLoc EntryValLocAsBackup = VarLoc::CreateEntryBackupLoc(MI, LS, NewExpr);
LocIndices EntryValLocIDs = VarLocIDs.insert(EntryValLocAsBackup);
OpenRanges.insert(EntryValLocIDs, EntryValLocAsBackup);
/// Calculate the liveness information for the given machine function and
/// extend ranges across basic blocks.
bool VarLocBasedLDV::ExtendRanges(MachineFunction &MF, TargetPassConfig *TPC) {
LLVM_DEBUG(dbgs() << "\nDebug Range Extension\n");
if (!MF.getFunction().getSubprogram())
// VarLocBaseLDV 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->getCalleeSaves(MF, CalleeSavedRegs);
this->TPC = TPC;
bool Changed = false;
bool OLChanged = false;
bool MBBJoined = false;
VarLocMap VarLocIDs; // Map VarLoc<>unique ID for use in bitvectors.
OverlapMap OverlapFragments; // Map of overlapping variable fragments.
OpenRangesSet OpenRanges(Alloc, OverlapFragments);
// 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 transfers (such as
// spills, copies and restores).
VarToFragments SeenFragments;
// Blocks which are artificial, i.e. blocks which exclusively contain
// instructions without locations, or with line 0 locations.
SmallPtrSet<const MachineBasicBlock *, 16> ArtificialBlocks;
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>>
// Set of register defines that are seen when traversing the entry block
// looking for debug entry value candidates.
DefinedRegsSet DefinedRegs;
// Only in the case of entry MBB collect DBG_VALUEs representing
// function parameters in order to generate debug entry values for them.
MachineBasicBlock &First_MBB = *(MF.begin());
for (auto &MI : First_MBB) {
collectRegDefs(MI, DefinedRegs, TRI);
if (MI.isDebugValue())
recordEntryValue(MI, DefinedRegs, OpenRanges, VarLocIDs);
// Initialize per-block structures and scan for fragment overlaps.
for (auto &MBB : MF)
for (auto &MI : MBB)
if (MI.isDebugValue())
accumulateFragmentMap(MI, SeenFragments, OverlapFragments);
auto hasNonArtificialLocation = [](const MachineInstr &MI) -> bool {
if (const DebugLoc &DL = MI.getDebugLoc())
return DL.getLine() != 0;
return false;
for (auto &MBB : MF)
if (none_of(MBB.instrs(), hasNonArtificialLocation))
LLVM_DEBUG(printVarLocInMBB(MF, OutLocs, VarLocIDs,
"OutLocs after initialization", dbgs()));
ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
unsigned int RPONumber = 0;
for (MachineBasicBlock *MBB : RPOT) {
OrderToBB[RPONumber] = MBB;
BBToOrder[MBB] = RPONumber;
if (RPONumber > InputBBLimit) {
unsigned NumInputDbgValues = 0;
for (auto &MBB : MF)
for (auto &MI : MBB)
if (MI.isDebugValue())
if (NumInputDbgValues > InputDbgValueLimit) {
LLVM_DEBUG(dbgs() << "Disabling VarLocBasedLDV: " << MF.getName()
<< " has " << RPONumber << " basic blocks and "
<< NumInputDbgValues
<< " input DBG_VALUEs, exceeding limits.\n");
return false;
// 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,
MBBJoined |= Visited.insert(MBB).second;
if (MBBJoined) {
MBBJoined = false;
Changed = true;
// Now that we have started to extend ranges across BBs we need to
// examine spill, copy and restore instructions to see whether they
// operate with registers that correspond to user variables.
// First load any pending inlocs.
OpenRanges.insertFromLocSet(getVarLocsInMBB(MBB, InLocs), VarLocIDs);
for (auto &MI : *MBB)
process(MI, OpenRanges, VarLocIDs, Transfers);
OLChanged |= transferTerminator(MBB, OpenRanges, OutLocs, VarLocIDs);
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");
// Add any DBG_VALUE instructions created by location transfers.
for (auto &TR : Transfers) {
assert(!TR.TransferInst->isTerminator() &&
"Cannot insert DBG_VALUE after terminator");
MachineBasicBlock *MBB = TR.TransferInst->getParent();
const VarLoc &VL = VarLocIDs[TR.LocationID];
MachineInstr *MI = VL.BuildDbgValue(MF);
MBB->insertAfterBundle(TR.TransferInst->getIterator(), MI);
// Deferred inlocs will not have had any DBG_VALUE insts created; do
// that now.
flushPendingLocs(InLocs, VarLocIDs);
LLVM_DEBUG(printVarLocInMBB(MF, OutLocs, VarLocIDs, "Final OutLocs", dbgs()));
LLVM_DEBUG(printVarLocInMBB(MF, InLocs, VarLocIDs, "Final InLocs", dbgs()));
return Changed;
LDVImpl *
return new VarLocBasedLDV();