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llvm-project/llvm/lib/CodeGen/LiveDebugValues.cpp

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//===- LiveDebugValues.cpp - Tracking Debug Value MIs ---------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// This pass implements a data flow analysis that propagates debug location
/// information by inserting additional DBG_VALUE insts into the machine
/// instruction stream. Before running, each DBG_VALUE inst corresponds to a
/// source assignment of a variable. Afterwards, a DBG_VALUE inst specifies a
/// variable location for the current basic block (see SourceLevelDebugging.rst).
///
/// This is a separate pass from DbgValueHistoryCalculator to facilitate
/// testing and improve modularity.
///
/// Each variable location is represented by a VarLoc object that identifies the
/// source variable, its current machine-location, and the DBG_VALUE inst that
/// specifies the location. Each VarLoc is indexed in the (function-scope)
/// VarLocMap, giving each VarLoc a unique index. Rather than operate directly
/// on machine locations, the dataflow analysis in this pass identifies
/// locations by their index in the VarLocMap, meaning all the variable
/// locations in a block can be described by a sparse vector of VarLocMap
/// indexes.
///
//===----------------------------------------------------------------------===//
#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/raw_ostream.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");
STATISTIC(NumRemoved, "Number of DBG_VALUE instructions removed");
// 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 Register 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() : Register();
}
/// 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();
unsigned 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>;
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.
///
/// TODO: Consider adding reserved intervals for kinds of VarLocs other than
/// RegisterKind, like SpillLocKind or EntryValueKind, to optimize iteration
/// over open locations.
struct LocIndex {
uint32_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.
uint32_t Index;
LocIndex(uint32_t Location, uint32_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<uint32_t>(ID >> 32), static_cast<uint32_t>(ID)};
}
/// 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(uint32_t Reg) {
return LocIndex(Reg, 0).getAsRawInteger();
}
};
class LiveDebugValues : public MachineFunctionPass {
private:
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
const TargetFrameLowering *TFI;
BitVector CalleeSavedRegs;
LexicalScopes LS;
VarLocSet::Allocator Alloc;
enum struct TransferKind { TransferCopy, TransferSpill, TransferRestore };
/// Keeps track of lexical scopes associated with a user value's source
/// location.
class UserValueScopes {
DebugLoc DL;
LexicalScopes &LS;
SmallPtrSet<const MachineBasicBlock *, 4> LBlocks;
public:
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);
}
};
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;
int SpillOffset;
bool operator==(const SpillLoc &Other) const {
return SpillBase == Other.SpillBase && SpillOffset == Other.SpillOffset;
}
};
/// 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;
mutable UserValueScopes UVS;
enum VarLocKind {
InvalidKind = 0,
RegisterKind,
SpillLocKind,
ImmediateKind,
EntryValueKind,
EntryValueBackupKind,
EntryValueCopyBackupKind
} Kind = InvalidKind;
/// The value location. Stored separately to avoid repeatedly
/// extracting it from MI.
union {
uint64_t RegNo;
SpillLoc SpillLocation;
uint64_t Hash;
int64_t Immediate;
const ConstantFP *FPImm;
const ConstantInt *CImm;
} Loc;
VarLoc(const MachineInstr &MI, LexicalScopes &LS)
: Var(MI.getDebugVariable(), MI.getDebugExpression(),
MI.getDebugLoc()->getInlinedAt()),
Expr(MI.getDebugExpression()), 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;
} else if (MI.getOperand(0).isImm()) {
Kind = ImmediateKind;
Loc.Immediate = MI.getOperand(0).getImm();
} else if (MI.getOperand(0).isFPImm()) {
Kind = ImmediateKind;
Loc.FPImm = MI.getOperand(0).getFPImm();
} else if (MI.getOperand(0).isCImm()) {
Kind = ImmediateKind;
Loc.CImm = MI.getOperand(0).getCImm();
}
// We create the debug entry values from the factory functions rather than
// from this ctor.
assert(Kind != EntryValueKind && !isEntryBackupLoc());
}
/// 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, unsigned Reg) {
VarLoc VL(MI, LS);
assert(VL.Kind == RegisterKind);
VL.Kind = EntryValueKind;
VL.Expr = EntryExpr;
VL.Loc.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.Kind == RegisterKind);
VL.Kind = 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,
unsigned NewReg) {
VarLoc VL(MI, LS);
assert(VL.Kind == RegisterKind);
VL.Kind = EntryValueCopyBackupKind;
VL.Expr = EntryExpr;
VL.Loc.RegNo = NewReg;
return VL;
}
/// Copy the register location in DBG_VALUE MI, updating the register to
/// be NewReg.
static VarLoc CreateCopyLoc(const MachineInstr &MI, LexicalScopes &LS,
unsigned NewReg) {
VarLoc VL(MI, LS);
assert(VL.Kind == RegisterKind);
VL.Loc.RegNo = NewReg;
return VL;
}
/// Take the variable described by DBG_VALUE MI, and create a VarLoc
/// locating it in the specified spill location.
static VarLoc CreateSpillLoc(const MachineInstr &MI, unsigned SpillBase,
int SpillOffset, LexicalScopes &LS) {
VarLoc VL(MI, LS);
assert(VL.Kind == RegisterKind);
VL.Kind = SpillLocKind;
VL.Loc.SpillLocation = {SpillBase, SpillOffset};
return VL;
}
/// 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 {
const DebugLoc &DbgLoc = MI.getDebugLoc();
bool Indirect = MI.isIndirectDebugValue();
const auto &IID = MI.getDesc();
const DILocalVariable *Var = MI.getDebugVariable();
const DIExpression *DIExpr = MI.getDebugExpression();
switch (Kind) {
case EntryValueKind:
// 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.
return BuildMI(MF, DbgLoc, IID, Indirect, MI.getOperand(0).getReg(),
Var, Expr);
case RegisterKind:
// Register locations are like the source DBG_VALUE, but with the
// register number from this VarLoc.
return BuildMI(MF, DbgLoc, IID, Indirect, Loc.RegNo, Var, DIExpr);
case 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.
auto *SpillExpr = DIExpression::prepend(
DIExpr, DIExpression::ApplyOffset, Loc.SpillLocation.SpillOffset);
unsigned Base = Loc.SpillLocation.SpillBase;
return BuildMI(MF, DbgLoc, IID, true, Base, Var, SpillExpr);
}
case ImmediateKind: {
MachineOperand MO = MI.getOperand(0);
return BuildMI(MF, DbgLoc, IID, Indirect, MO, Var, DIExpr);
}
case EntryValueBackupKind:
case EntryValueCopyBackupKind:
case InvalidKind:
llvm_unreachable(
"Tried to produce DBG_VALUE for invalid or backup VarLoc");
}
llvm_unreachable("Unrecognized LiveDebugValues.VarLoc.Kind enum");
}
/// Is the Loc field a constant or constant object?
bool isConstant() const { return Kind == ImmediateKind; }
/// Check if the Loc field is an entry backup location.
bool isEntryBackupLoc() const {
return Kind == EntryValueBackupKind || Kind == EntryValueCopyBackupKind;
}
/// If this variable is described by a register holding the entry value,
/// return it, otherwise return 0.
unsigned getEntryValueBackupReg() const {
if (Kind == EntryValueBackupKind)
return Loc.RegNo;
return 0;
}
/// If this variable is described by a register holding the copy of the
/// entry value, return it, otherwise return 0.
unsigned getEntryValueCopyBackupReg() const {
if (Kind == EntryValueCopyBackupKind)
return Loc.RegNo;
return 0;
}
/// 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)
// TRI can be null.
void dump(const TargetRegisterInfo *TRI, raw_ostream &Out = dbgs()) const {
dbgs() << "VarLoc(";
switch (Kind) {
case RegisterKind:
case EntryValueKind:
case EntryValueBackupKind:
case EntryValueCopyBackupKind:
dbgs() << printReg(Loc.RegNo, TRI);
break;
case SpillLocKind:
dbgs() << printReg(Loc.SpillLocation.SpillBase, TRI);
dbgs() << "[" << Loc.SpillLocation.SpillOffset << "]";
break;
case ImmediateKind:
dbgs() << Loc.Immediate;
break;
case InvalidKind:
llvm_unreachable("Invalid VarLoc in dump method");
}
dbgs() << ", \"" << Var.getVariable()->getName() << "\", " << *Expr
<< ", ";
if (Var.getInlinedAt())
dbgs() << "!" << Var.getInlinedAt()->getMetadataID() << ")\n";
else
dbgs() << "(null))";
if (isEntryBackupLoc())
dbgs() << " (backup loc)\n";
else
dbgs() << "\n";
}
#endif
bool operator==(const VarLoc &Other) const {
return Kind == Other.Kind && Var == Other.Var &&
Loc.Hash == Other.Loc.Hash && Expr == Other.Expr;
}
/// This operator guarantees that VarLocs are sorted by Variable first.
bool operator<(const VarLoc &Other) const {
return std::tie(Var, Kind, Loc.Hash, Expr) <
std::tie(Other.Var, Other.Kind, Other.Loc.Hash, Other.Expr);
}
};
/// VarLocMap is used for two things:
/// 1) Assigning a unique LocIndex to a VarLoc. This LocIndex 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, uint32_t> Var2Index;
/// Map a location to a vector which holds VarLocs which live in that
/// location.
SmallDenseMap<uint32_t, std::vector<VarLoc>> Loc2Vars;
public:
/// Retrieve a unique LocIndex for \p VL.
LocIndex insert(const VarLoc &VL) {
uint32_t Location = VL.isDescribedByReg();
uint32_t &Index = Var2Index[VL];
if (!Index) {
auto &Vars = Loc2Vars[Location];
Vars.push_back(VL);
Index = Vars.size();
}
return {Location, Index - 1};
}
/// 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>>;
/// 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 VarLocs;
// Map the DebugVariable to recent primary location ID.
SmallDenseMap<DebugVariable, LocIndex, 8> Vars;
// Map the DebugVariable to recent backup location ID.
SmallDenseMap<DebugVariable, LocIndex, 8> EntryValuesBackupVars;
OverlapMap &OverlappingFragments;
public:
OpenRangesSet(VarLocSet::Allocator &Alloc, OverlapMap &_OLapMap)
: VarLocs(Alloc), OverlappingFragments(_OLapMap) {}
const VarLocSet &getVarLocs() const { return VarLocs; }
/// Terminate all open ranges for VL.Var by removing it from the set.
void erase(const VarLoc &VL);
/// Terminate all open ranges listed in \c KillSet by removing
/// them from the set.
void erase(const VarLocSet &KillSet, const VarLocMap &VarLocIDs);
/// Insert a new range into the set.
void insert(LocIndex VarLocID, const VarLoc &VL);
/// Insert a set of ranges.
void insertFromLocSet(const VarLocSet &ToLoad, const VarLocMap &Map) {
for (uint64_t ID : ToLoad) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VarL = Map[Idx];
insert(Idx, VarL);
}
}
llvm::Optional<LocIndex> getEntryValueBackup(DebugVariable Var);
/// Empty the set.
void clear() {
VarLocs.clear();
Vars.clear();
EntryValuesBackupVars.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();
}
};
/// Collect all VarLoc IDs from \p CollectFrom for VarLocs of kind
/// RegisterKind which are located in any reg in \p Regs. Insert collected IDs
/// into \p Collected.
void collectIDsForRegs(VarLocSet &Collected, const DefinedRegsSet &Regs,
const VarLocSet &CollectFrom) const;
/// Get the registers which are used by VarLocs of kind RegisterKind tracked
/// by \p CollectFrom.
void getUsedRegs(const VarLocSet &CollectFrom,
SmallVectorImpl<uint32_t> &UsedRegs) const;
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,
unsigned &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,
unsigned &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,
unsigned NewReg = 0);
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,
VarLocSet &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,
VarLocInMBB &PendingInLocs);
/// 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);
public:
static char ID;
/// Default construct and initialize the pass.
LiveDebugValues();
/// Tell the pass manager which passes we depend on and what
/// information we preserve.
void getAnalysisUsage(AnalysisUsage &AU) const override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoVRegs);
}
/// 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;
INITIALIZE_PASS(LiveDebugValues, DEBUG_TYPE, "Live DEBUG_VALUE analysis",
false, false)
/// Default construct and initialize the pass.
LiveDebugValues::LiveDebugValues() : MachineFunctionPass(ID) {
initializeLiveDebugValuesPass(*PassRegistry::getPassRegistry());
}
/// Tell the pass manager which passes we depend on and what information we
/// preserve.
void LiveDebugValues::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
MachineFunctionPass::getAnalysisUsage(AU);
}
/// Erase a variable from the set of open ranges, and additionally erase any
/// fragments that may overlap it. If the VarLoc is a buckup 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 LiveDebugValues::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()) {
LocIndex ID = It->second;
VarLocs.reset(ID.getAsRawInteger());
EraseFrom->erase(It);
}
};
DebugVariable Var = VL.Var;
// Erase the variable/fragment that ends here.
DoErase(Var);
// 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) {
LiveDebugValues::OptFragmentInfo FragmentHolder;
if (!DebugVariable::isDefaultFragment(Fragment))
FragmentHolder = LiveDebugValues::OptFragmentInfo(Fragment);
DoErase({Var.getVariable(), FragmentHolder, Var.getInlinedAt()});
}
}
}
void LiveDebugValues::OpenRangesSet::erase(const VarLocSet &KillSet,
const VarLocMap &VarLocIDs) {
VarLocs.intersectWithComplement(KillSet);
for (uint64_t ID : KillSet) {
const VarLoc *VL = &VarLocIDs[LocIndex::fromRawInteger(ID)];
auto *EraseFrom = VL->isEntryBackupLoc() ? &EntryValuesBackupVars : &Vars;
EraseFrom->erase(VL->Var);
}
}
void LiveDebugValues::OpenRangesSet::insert(LocIndex VarLocID,
const VarLoc &VL) {
auto *InsertInto = VL.isEntryBackupLoc() ? &EntryValuesBackupVars : &Vars;
VarLocs.set(VarLocID.getAsRawInteger());
InsertInto->insert({VL.Var, VarLocID});
}
/// Return the Loc ID of an entry value backup location, if it exists for the
/// variable.
llvm::Optional<LocIndex>
LiveDebugValues::OpenRangesSet::getEntryValueBackup(DebugVariable Var) {
auto It = EntryValuesBackupVars.find(Var);
if (It != EntryValuesBackupVars.end())
return It->second;
return llvm::None;
}
void LiveDebugValues::collectIDsForRegs(VarLocSet &Collected,
const DefinedRegsSet &Regs,
const VarLocSet &CollectFrom) const {
assert(!Regs.empty() && "Nothing to collect");
SmallVector<uint32_t, 32> SortedRegs;
for (Register Reg : Regs)
SortedRegs.push_back(Reg);
array_pod_sort(SortedRegs.begin(), SortedRegs.end());
auto It = CollectFrom.find(LocIndex::rawIndexForReg(SortedRegs.front()));
auto End = CollectFrom.end();
for (uint32_t Reg : SortedRegs) {
// The half-open interval [FirstIndexForReg, FirstInvalidIndex) contains all
// possible VarLoc IDs for VarLocs of kind RegisterKind which live in Reg.
uint64_t FirstIndexForReg = LocIndex::rawIndexForReg(Reg);
uint64_t FirstInvalidIndex = LocIndex::rawIndexForReg(Reg + 1);
It.advanceToLowerBound(FirstIndexForReg);
// Iterate through that half-open interval and collect all the set IDs.
for (; It != End && *It < FirstInvalidIndex; ++It)
Collected.set(*It);
if (It == End)
return;
}
}
void LiveDebugValues::getUsedRegs(const VarLocSet &CollectFrom,
SmallVectorImpl<uint32_t> &UsedRegs) const {
// All register-based VarLocs are assigned indices greater than or equal to
// FirstRegIndex.
uint64_t FirstRegIndex = LocIndex::rawIndexForReg(1);
for (auto It = CollectFrom.find(FirstRegIndex), End = CollectFrom.end();
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");
UsedRegs.push_back(FoundReg);
// 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);
It.advanceToLowerBound(NextRegIndex);
}
}
//===----------------------------------------------------------------------===//
// 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) {
if (!V.count(&BB))
continue;
const VarLocSet &L = getVarLocsInMBB(&BB, V);
if (L.empty())
continue;
Out << "MBB: " << BB.getNumber() << ":\n";
for (uint64_t VLL : L) {
const VarLoc &VL = VarLocIDs[LocIndex::fromRawInteger(VLL)];
Out << " Var: " << VL.Var.getVariable()->getName();
Out << " MI: ";
VL.dump(TRI, Out);
}
}
Out << "\n";
}
#endif
LiveDebugValues::VarLoc::SpillLoc
LiveDebugValues::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();
unsigned Reg;
int 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 LiveDebugValues::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.getOperand(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.
bool TrySalvageEntryValue = false;
Register Reg = MI.getOperand(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;
TrySalvageEntryValue = true;
}
if (TrySalvageEntryValue) {
for (uint64_t ID : OpenRanges.getVarLocs()) {
const VarLoc &VL = VarLocIDs[LocIndex::fromRawInteger(ID)];
if (!VL.isEntryBackupLoc())
continue;
if (VL.getEntryValueCopyBackupReg() == Reg &&
VL.MI.getOperand(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 LiveDebugValues::transferDebugValue(const MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs) {
if (!MI.isDebugValue())
return;
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];
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));
OpenRanges.erase(EntryVL);
}
}
if (isDbgValueDescribedByReg(MI) || MI.getOperand(0).isImm() ||
MI.getOperand(0).isFPImm() || MI.getOperand(0).isCImm()) {
// Use normal VarLoc constructor for registers and immediates.
VarLoc VL(MI, LS);
// End all previous ranges of VL.Var.
OpenRanges.erase(VL);
LocIndex ID = VarLocIDs.insert(VL);
// Add the VarLoc to OpenRanges from this DBG_VALUE.
OpenRanges.insert(ID, VL);
} else if (MI.hasOneMemOperand()) {
llvm_unreachable("DBG_VALUE with mem operand encountered after regalloc?");
} else {
// This must be an undefined location. We should leave OpenRanges closed.
assert(MI.getOperand(0).isReg() && MI.getOperand(0).getReg() == 0 &&
"Unexpected non-undef DBG_VALUE encountered");
}
}
/// Turn the entry value backup locations into primary locations.
void LiveDebugValues::emitEntryValues(MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs,
TransferMap &Transfers,
VarLocSet &KillSet) {
// Do not insert entry value locations after a terminator.
if (MI.isTerminator())
return;
for (uint64_t ID : KillSet) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VL = VarLocIDs[Idx];
if (!VL.Var.getVariable()->isParameter())
continue;
auto DebugVar = VL.Var;
Optional<LocIndex> EntryValBackupID =
OpenRanges.getEntryValueBackup(DebugVar);
// If the parameter has the entry value backup, it means we should
// be able to use its entry value.
if (!EntryValBackupID)
continue;
const VarLoc &EntryVL = VarLocIDs[*EntryValBackupID];
VarLoc EntryLoc =
VarLoc::CreateEntryLoc(EntryVL.MI, LS, EntryVL.Expr, EntryVL.Loc.RegNo);
LocIndex EntryValueID = VarLocIDs.insert(EntryLoc);
Transfers.push_back({&MI, EntryValueID});
OpenRanges.insert(EntryValueID, 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 LiveDebugValues::insertTransferDebugPair(
MachineInstr &MI, OpenRangesSet &OpenRanges, TransferMap &Transfers,
VarLocMap &VarLocIDs, LocIndex OldVarID, TransferKind Kind,
unsigned NewReg) {
const MachineInstr *DebugInstr = &VarLocIDs[OldVarID].MI;
auto ProcessVarLoc = [&MI, &OpenRanges, &Transfers, &VarLocIDs](VarLoc &VL) {
LocIndex LocId = VarLocIDs.insert(VL);
// Close this variable's previous location range.
OpenRanges.erase(VL);
// Record the new location as an open range, and a postponed transfer
// inserting a DBG_VALUE for this location.
OpenRanges.insert(LocId, VL);
assert(!MI.isTerminator() && "Cannot insert DBG_VALUE after terminator");
TransferDebugPair MIP = {&MI, LocId};
Transfers.push_back(MIP);
};
// End all previous ranges of VL.Var.
OpenRanges.erase(VarLocIDs[OldVarID]);
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(*DebugInstr, LS, NewReg);
ProcessVarLoc(VL);
LLVM_DEBUG({
dbgs() << "Creating VarLoc for register copy:";
VL.dump(TRI);
});
return;
}
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(*DebugInstr, SpillLocation.SpillBase,
SpillLocation.SpillOffset, LS);
ProcessVarLoc(VL);
LLVM_DEBUG({
dbgs() << "Creating VarLoc for spill:";
VL.dump(TRI);
});
return;
}
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(*DebugInstr, LS, NewReg);
ProcessVarLoc(VL);
LLVM_DEBUG({
dbgs() << "Creating VarLoc for restore:";
VL.dump(TRI);
});
return;
}
}
llvm_unreachable("Invalid transfer kind");
}
/// A definition of a register may mark the end of a range.
void LiveDebugValues::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())
return;
MachineFunction *MF = MI.getMF();
const TargetLowering *TLI = MF->getSubtarget().getTargetLowering();
unsigned 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?
DeadRegs.insert(*RAI);
} else if (MO.isRegMask()) {
RegMasks.push_back(MO.getRegMask());
}
}
// 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<uint32_t, 32> UsedRegs;
getUsedRegs(OpenRanges.getVarLocs(), UsedRegs);
for (uint32_t Reg : UsedRegs) {
// The VarLocs residing in this register are already in the kill set.
if (DeadRegs.count(Reg))
continue;
// 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)
continue;
bool AnyRegMaskKillsReg =
any_of(RegMasks, [Reg](const uint32_t *RegMask) {
return MachineOperand::clobbersPhysReg(RegMask, Reg);
});
if (AnyRegMaskKillsReg)
DeadRegs.insert(Reg);
}
}
if (DeadRegs.empty())
return;
VarLocSet KillSet(Alloc);
collectIDsForRegs(KillSet, DeadRegs, OpenRanges.getVarLocs());
OpenRanges.erase(KillSet, VarLocIDs);
if (auto *TPC = getAnalysisIfAvailable<TargetPassConfig>()) {
auto &TM = TPC->getTM<TargetMachine>();
if (TM.Options.ShouldEmitDebugEntryValues())
emitEntryValues(MI, OpenRanges, VarLocIDs, Transfers, KillSet);
}
}
bool LiveDebugValues::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 LiveDebugValues::isLocationSpill(const MachineInstr &MI,
MachineFunction *MF, unsigned &Reg) {
if (!isSpillInstruction(MI, MF))
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)
continue;
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;
}
Optional<LiveDebugValues::VarLoc::SpillLoc>
LiveDebugValues::isRestoreInstruction(const MachineInstr &MI,
MachineFunction *MF, unsigned &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 LiveDebugValues::transferSpillOrRestoreInst(MachineInstr &MI,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs,
TransferMap &Transfers) {
MachineFunction *MF = MI.getMF();
TransferKind TKind;
unsigned 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.
VarLocSet KillSet(Alloc);
if (isSpillInstruction(MI, MF)) {
Loc = extractSpillBaseRegAndOffset(MI);
for (uint64_t ID : OpenRanges.getVarLocs()) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VL = VarLocIDs[Idx];
if (VL.Kind == VarLoc::SpillLocKind && VL.Loc.SpillLocation == *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.
KillSet.set(ID);
VarLoc UndefVL = VarLoc::CreateCopyLoc(VL.MI, LS, 0);
LocIndex UndefLocID = VarLocIDs.insert(UndefVL);
Transfers.push_back({&MI, UndefLocID});
}
}
OpenRanges.erase(KillSet, VarLocIDs);
}
// 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)))
return;
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.
for (uint64_t ID : OpenRanges.getVarLocs()) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VL = VarLocIDs[Idx];
if (TKind == TransferKind::TransferSpill && VL.isDescribedByReg() == Reg) {
LLVM_DEBUG(dbgs() << "Spilling Register " << printReg(Reg, TRI) << '('
<< VL.Var.getVariable()->getName() << ")\n");
} else if (TKind == TransferKind::TransferRestore &&
VL.Kind == VarLoc::SpillLocKind &&
VL.Loc.SpillLocation == *Loc) {
LLVM_DEBUG(dbgs() << "Restoring Register " << printReg(Reg, TRI) << '('
<< VL.Var.getVariable()->getName() << ")\n");
} else
continue;
insertTransferDebugPair(MI, OpenRanges, Transfers, VarLocIDs, Idx, TKind,
Reg);
return;
}
}
/// 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) {
auto DestSrc = TII->isCopyInstr(MI);
if (!DestSrc)
return;
const MachineOperand *DestRegOp = DestSrc->Destination;
const MachineOperand *SrcRegOp = DestSrc->Source;
if (!DestRegOp->isDef())
return;
auto isCalleeSavedReg = [&](unsigned 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))
return;
// 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.getVarLocs()) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
const VarLoc &VL = VarLocIDs[Idx];
if (VL.getEntryValueBackupReg() == 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.
OpenRanges.erase(VL);
// Start tracking the entry value copy.
LocIndex EntryValCopyLocID = VarLocIDs.insert(EntryValLocCopyBackup);
OpenRanges.insert(EntryValCopyLocID, EntryValLocCopyBackup);
break;
}
}
}
if (!SrcRegOp->isKill())
return;
for (uint64_t ID : OpenRanges.getVarLocs()) {
LocIndex Idx = LocIndex::fromRawInteger(ID);
if (VarLocIDs[Idx].isDescribedByReg() == SrcReg) {
insertTransferDebugPair(MI, OpenRanges, Transfers, VarLocIDs, Idx,
TransferKind::TransferCopy, DestReg);
return;
}
}
}
/// Terminate all open ranges at the end of the current basic block.
bool LiveDebugValues::transferTerminator(MachineBasicBlock *CurMBB,
OpenRangesSet &OpenRanges,
VarLocInMBB &OutLocs,
const VarLocMap &VarLocIDs) {
bool Changed = false;
LLVM_DEBUG(for (uint64_t ID
: OpenRanges.getVarLocs()) {
// Copy OpenRanges to OutLocs, if not already present.
dbgs() << "Add to OutLocs in MBB #" << CurMBB->getNumber() << ": ";
VarLocIDs[LocIndex::fromRawInteger(ID)].dump(TRI);
});
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();
OpenRanges.clear();
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 LiveDebugValues::accumulateFragmentMap(MachineInstr &MI,
VarToFragments &SeenFragments,
OverlapMap &OverlappingFragments) {
DebugVariable MIVar(MI.getDebugVariable(), MI.getDebugExpression(),
MI.getDebugLoc()->getInlinedAt());
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;
OneFragment.insert(ThisFragment);
SeenFragments.insert({MIVar.getVariable(), OneFragment});
OverlappingFragments.insert({{MIVar.getVariable(), ThisFragment}, {}});
return;
}
// 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)
return;
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.
ThisFragmentsOverlaps.push_back(ASeenFragment);
// 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");
ASeenFragmentsOverlaps->second.push_back(ThisFragment);
}
}
AllSeenFragments.insert(ThisFragment);
}
/// This routine creates OpenRanges.
void LiveDebugValues::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 LiveDebugValues::join(
MachineBasicBlock &MBB, VarLocInMBB &OutLocs, VarLocInMBB &InLocs,
const VarLocMap &VarLocIDs,
SmallPtrSet<const MachineBasicBlock *, 16> &Visited,
SmallPtrSetImpl<const MachineBasicBlock *> &ArtificialBlocks,
VarLocInMBB &PendingInLocs) {
LLVM_DEBUG(dbgs() << "join MBB: " << MBB.getNumber() << "\n");
bool Changed = false;
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");
continue;
}
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;
else
InLocsT &= OutLocVLS;
LLVM_DEBUG({
if (!InLocsT.empty()) {
for (uint64_t ID : InLocsT)
dbgs() << " gathered candidate incoming var: "
<< VarLocIDs[LocIndex::fromRawInteger(ID)]
.Var.getVariable()
->getName()
<< "\n";
}
});
NumVisited++;
}
// 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(MBB)) {
KillSet.set(ID);
LLVM_DEBUG({
auto Name = VarLocIDs[Idx].Var.getVariable()->getName();
dbgs() << " killing " << Name << ", it doesn't dominate MBB\n";
});
}
}
}
InLocsT.intersectWithComplement(KillSet);
// 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);
VarLocSet &Pending = getVarLocsInMBB(&MBB, PendingInLocs);
// New locations will have DBG_VALUE insts inserted at the start of the
// block, after location propagation has finished. Record the insertions
// that we need to perform in the Pending set.
VarLocSet Diff = InLocsT;
Diff.intersectWithComplement(ILS);
Pending.set(Diff);
ILS.set(Diff);
NumInserted += Diff.count();
Changed |= !Diff.empty();
// We may have lost locations by learning about a predecessor that either
// loses or moves a variable. Find any locations in ILS that are not in the
// new in-locations, and delete those.
VarLocSet Removed = ILS;
Removed.intersectWithComplement(InLocsT);
Pending.intersectWithComplement(Removed);
ILS.intersectWithComplement(Removed);
NumRemoved += Removed.count();
Changed |= !Removed.empty();
return Changed;
}
void LiveDebugValues::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();
for (uint64_t ID : Pending) {
// The ID location is live-in to MBB -- work out what kind of machine
// location it is and create a DBG_VALUE.
const VarLoc &DiffIt = VarLocIDs[LocIndex::fromRawInteger(ID)];
if (DiffIt.isEntryBackupLoc())
continue;
MachineInstr *MI = DiffIt.BuildDbgValue(*MBB.getParent());
MBB.insert(MBB.instr_begin(), MI);
(void)MI;
LLVM_DEBUG(dbgs() << "Inserted: "; MI->dump(););
}
}
}
bool LiveDebugValues::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;
// Do not consider indirect debug values (TODO: explain why).
if (MI.isIndirectDebugValue())
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.getOperand(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.getOperand(0).getReg()))
return false;
// TODO: Add support for parameters that have a pre-existing debug expressions
// (e.g. fragments, or indirect parameters using DW_OP_deref).
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)
Regs.insert(*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 LiveDebugValues::recordEntryValue(const MachineInstr &MI,
const DefinedRegsSet &DefinedRegs,
OpenRangesSet &OpenRanges,
VarLocMap &VarLocIDs) {
if (auto *TPC = getAnalysisIfAvailable<TargetPassConfig>()) {
auto &TM = TPC->getTM<TargetMachine>();
if (!TM.Options.ShouldEmitDebugEntryValues())
return;
}
DebugVariable V(MI.getDebugVariable(), MI.getDebugExpression(),
MI.getDebugLoc()->getInlinedAt());
if (!isEntryValueCandidate(MI, DefinedRegs) ||
OpenRanges.getEntryValueBackup(V))
return;
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);
LocIndex EntryValLocID = VarLocIDs.insert(EntryValLocAsBackup);
OpenRanges.insert(EntryValLocID, EntryValLocAsBackup);
}
/// 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.
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).
VarLocInMBB PendingInLocs; // Ranges that are incoming after joining, but
// that we have deferred creating DBG_VALUE insts
// for immediately.
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>>
Worklist;
std::priority_queue<unsigned int, std::vector<unsigned int>,
std::greater<unsigned int>>
Pending;
// 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) {
PendingInLocs[&MBB] = std::make_unique<VarLocSet>(Alloc);
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))
ArtificialBlocks.insert(&MBB);
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;
Worklist.push(RPONumber);
++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[Worklist.top()];
Worklist.pop();
MBBJoined = join(*MBB, OutLocs, InLocs, VarLocIDs, Visited,
ArtificialBlocks, PendingInLocs);
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, PendingInLocs),
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) {
Pending.push(BBToOrder[s]);
}
}
}
}
Worklist.swap(Pending);
// 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);
}
Transfers.clear();
// Deferred inlocs will not have had any DBG_VALUE insts created; do
// that now.
flushPendingLocs(PendingInLocs, VarLocIDs);
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() ==
DICompileUnit::NoDebug)
return false;
TRI = MF.getSubtarget().getRegisterInfo();
TII = MF.getSubtarget().getInstrInfo();
TFI = MF.getSubtarget().getFrameLowering();
TFI->getCalleeSaves(MF, CalleeSavedRegs);
LS.initialize(MF);
bool Changed = ExtendRanges(MF);
return Changed;
}
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