lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp - llvm-project/llvm - Git at Google

 //===-- llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp -------*- C++ -*--===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // Common functionality for different debug information format backends.
 // LLVM currently supports DWARF and CodeView.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/CodeGen/DebugHandlerBase.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/Support/CommandLine.h"

 using namespace llvm;

 #define DEBUG_TYPE "dwarfdebug"

 /// If true, we drop variable location ranges which exist entirely outside the
 /// variable's lexical scope instruction ranges.
 static cl::opt<bool> TrimVarLocs("trim-var-locs", cl::Hidden, cl::init(true));

 Optional<DbgVariableLocation>
 DbgVariableLocation::extractFromMachineInstruction(
     const MachineInstr &Instruction) {
   DbgVariableLocation Location;
   // Variables calculated from multiple locations can't be represented here.
   if (Instruction.getNumDebugOperands() != 1)
     return None;
   if (!Instruction.getDebugOperand(0).isReg())
     return None;
   Location.Register = Instruction.getDebugOperand(0).getReg();
   Location.FragmentInfo.reset();
   // We only handle expressions generated by DIExpression::appendOffset,
   // which doesn't require a full stack machine.
   int64_t Offset = 0;
   const DIExpression *DIExpr = Instruction.getDebugExpression();
   auto Op = DIExpr->expr_op_begin();
   // We can handle a DBG_VALUE_LIST iff it has exactly one location operand that
   // appears exactly once at the start of the expression.
   if (Instruction.isDebugValueList()) {
     if (Instruction.getNumDebugOperands() == 1 &&
         Op->getOp() == dwarf::DW_OP_LLVM_arg)
       ++Op;
     else
       return None;
   }
   while (Op != DIExpr->expr_op_end()) {
     switch (Op->getOp()) {
     case dwarf::DW_OP_constu: {
       int Value = Op->getArg(0);
       ++Op;
       if (Op != DIExpr->expr_op_end()) {
         switch (Op->getOp()) {
         case dwarf::DW_OP_minus:
           Offset -= Value;
           break;
         case dwarf::DW_OP_plus:
           Offset += Value;
           break;
         default:
           continue;
         }
       }
     } break;
     case dwarf::DW_OP_plus_uconst:
       Offset += Op->getArg(0);
       break;
     case dwarf::DW_OP_LLVM_fragment:
       Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
       break;
     case dwarf::DW_OP_deref:
       Location.LoadChain.push_back(Offset);
       Offset = 0;
       break;
     default:
       return None;
     }
     ++Op;
   }

   // Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
   // instruction.
   // FIXME: Replace these with DIExpression.
   if (Instruction.isIndirectDebugValue())
     Location.LoadChain.push_back(Offset);

   return Location;
 }

 DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}

 void DebugHandlerBase::beginModule(Module *M) {
   if (M->debug_compile_units().empty())
     Asm = nullptr;
 }

 // Each LexicalScope has first instruction and last instruction to mark
 // beginning and end of a scope respectively. Create an inverse map that list
 // scopes starts (and ends) with an instruction. One instruction may start (or
 // end) multiple scopes. Ignore scopes that are not reachable.
 void DebugHandlerBase::identifyScopeMarkers() {
   SmallVector<LexicalScope *, 4> WorkList;
   WorkList.push_back(LScopes.getCurrentFunctionScope());
   while (!WorkList.empty()) {
     LexicalScope *S = WorkList.pop_back_val();

     const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
     if (!Children.empty())
       WorkList.append(Children.begin(), Children.end());

     if (S->isAbstractScope())
       continue;

     for (const InsnRange &R : S->getRanges()) {
       assert(R.first && "InsnRange does not have first instruction!");
       assert(R.second && "InsnRange does not have second instruction!");
       requestLabelBeforeInsn(R.first);
       requestLabelAfterInsn(R.second);
     }
   }
 }

 // Return Label preceding the instruction.
 MCSymbol *DebugHandlerBase::getLabelBeforeInsn(const MachineInstr *MI) {
   MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
   assert(Label && "Didn't insert label before instruction");
   return Label;
 }

 // Return Label immediately following the instruction.
 MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
   return LabelsAfterInsn.lookup(MI);
 }

 /// If this type is derived from a base type then return base type size.
 uint64_t DebugHandlerBase::getBaseTypeSize(const DIType *Ty) {
   assert(Ty);
   const DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
   if (!DDTy)
     return Ty->getSizeInBits();

   unsigned Tag = DDTy->getTag();

   if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
       Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
       Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type)
     return DDTy->getSizeInBits();

   DIType *BaseType = DDTy->getBaseType();

   if (!BaseType)
     return 0;

   // If this is a derived type, go ahead and get the base type, unless it's a
   // reference then it's just the size of the field. Pointer types have no need
   // of this since they're a different type of qualification on the type.
   if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
       BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
     return Ty->getSizeInBits();

   return getBaseTypeSize(BaseType);
 }

 bool DebugHandlerBase::isUnsignedDIType(const DIType *Ty) {
   if (auto *CTy = dyn_cast<DICompositeType>(Ty)) {
     // FIXME: Enums without a fixed underlying type have unknown signedness
     // here, leading to incorrectly emitted constants.
     if (CTy->getTag() == dwarf::DW_TAG_enumeration_type)
       return false;

     // (Pieces of) aggregate types that get hacked apart by SROA may be
     // represented by a constant. Encode them as unsigned bytes.
     return true;
   }

   if (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
     dwarf::Tag T = (dwarf::Tag)Ty->getTag();
     // Encode pointer constants as unsigned bytes. This is used at least for
     // null pointer constant emission.
     // FIXME: reference and rvalue_reference /probably/ shouldn't be allowed
     // here, but accept them for now due to a bug in SROA producing bogus
     // dbg.values.
     if (T == dwarf::DW_TAG_pointer_type ||
         T == dwarf::DW_TAG_ptr_to_member_type ||
         T == dwarf::DW_TAG_reference_type ||
         T == dwarf::DW_TAG_rvalue_reference_type)
       return true;
     assert(T == dwarf::DW_TAG_typedef || T == dwarf::DW_TAG_const_type ||
            T == dwarf::DW_TAG_volatile_type ||
            T == dwarf::DW_TAG_restrict_type || T == dwarf::DW_TAG_atomic_type);
     assert(DTy->getBaseType() && "Expected valid base type");
     return isUnsignedDIType(DTy->getBaseType());
   }

   auto *BTy = cast<DIBasicType>(Ty);
   unsigned Encoding = BTy->getEncoding();
   assert((Encoding == dwarf::DW_ATE_unsigned ||
           Encoding == dwarf::DW_ATE_unsigned_char ||
           Encoding == dwarf::DW_ATE_signed ||
           Encoding == dwarf::DW_ATE_signed_char ||
           Encoding == dwarf::DW_ATE_float || Encoding == dwarf::DW_ATE_UTF ||
           Encoding == dwarf::DW_ATE_boolean ||
           (Ty->getTag() == dwarf::DW_TAG_unspecified_type &&
            Ty->getName() == "decltype(nullptr)")) &&
          "Unsupported encoding");
   return Encoding == dwarf::DW_ATE_unsigned ||
          Encoding == dwarf::DW_ATE_unsigned_char ||
          Encoding == dwarf::DW_ATE_UTF || Encoding == dwarf::DW_ATE_boolean ||
          Ty->getTag() == dwarf::DW_TAG_unspecified_type;
 }

 static bool hasDebugInfo(const MachineModuleInfo *MMI,
                          const MachineFunction *MF) {
   if (!MMI->hasDebugInfo())
     return false;
   auto *SP = MF->getFunction().getSubprogram();
   if (!SP)
     return false;
   assert(SP->getUnit());
   auto EK = SP->getUnit()->getEmissionKind();
   if (EK == DICompileUnit::NoDebug)
     return false;
   return true;
 }

 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
   PrevInstBB = nullptr;

   if (!Asm || !hasDebugInfo(MMI, MF)) {
     skippedNonDebugFunction();
     return;
   }

   // Grab the lexical scopes for the function, if we don't have any of those
   // then we're not going to be able to do anything.
   LScopes.initialize(*MF);
   if (LScopes.empty()) {
     beginFunctionImpl(MF);
     return;
   }

   // Make sure that each lexical scope will have a begin/end label.
   identifyScopeMarkers();

   // Calculate history for local variables.
   assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
   assert(DbgLabels.empty() && "DbgLabels map wasn't cleaned!");
   calculateDbgEntityHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
                             DbgValues, DbgLabels);
   InstOrdering.initialize(*MF);
   if (TrimVarLocs)
     DbgValues.trimLocationRanges(*MF, LScopes, InstOrdering);
   LLVM_DEBUG(DbgValues.dump());

   // Request labels for the full history.
   for (const auto &I : DbgValues) {
     const auto &Entries = I.second;
     if (Entries.empty())
       continue;

     auto IsDescribedByReg = [](const MachineInstr *MI) {
       return any_of(MI->debug_operands(),
                     [](auto &MO) { return MO.isReg() && MO.getReg(); });
     };

     // The first mention of a function argument gets the CurrentFnBegin label,
     // so arguments are visible when breaking at function entry.
     //
     // We do not change the label for values that are described by registers,
     // as that could place them above their defining instructions. We should
     // ideally not change the labels for constant debug values either, since
     // doing that violates the ranges that are calculated in the history map.
     // However, we currently do not emit debug values for constant arguments
     // directly at the start of the function, so this code is still useful.
     // FIXME: If the first mention of an argument is in a unique section basic
     // block, we cannot always assign the CurrentFnBeginLabel as it lies in a
     // different section.  Temporarily, we disable generating loc list
     // information or DW_AT_const_value when the block is in a different
     // section.
     const DILocalVariable *DIVar =
         Entries.front().getInstr()->getDebugVariable();
     if (DIVar->isParameter() &&
         getDISubprogram(DIVar->getScope())->describes(&MF->getFunction()) &&
         Entries.front().getInstr()->getParent()->sameSection(&MF->front())) {
       if (!IsDescribedByReg(Entries.front().getInstr()))
         LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
       if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {
         // Mark all non-overlapping initial fragments.
         for (auto I = Entries.begin(); I != Entries.end(); ++I) {
           if (!I->isDbgValue())
             continue;
           const DIExpression *Fragment = I->getInstr()->getDebugExpression();
           if (std::any_of(Entries.begin(), I,
                           [&](DbgValueHistoryMap::Entry Pred) {
                             return Pred.isDbgValue() &&
                                    Fragment->fragmentsOverlap(
                                        Pred.getInstr()->getDebugExpression());
                           }))
             break;
           // The code that generates location lists for DWARF assumes that the
           // entries' start labels are monotonically increasing, and since we
           // don't change the label for fragments that are described by
           // registers, we must bail out when encountering such a fragment.
           if (IsDescribedByReg(I->getInstr()))
             break;
           LabelsBeforeInsn[I->getInstr()] = Asm->getFunctionBegin();
         }
       }
     }

     for (const auto &Entry : Entries) {
       if (Entry.isDbgValue())
         requestLabelBeforeInsn(Entry.getInstr());
       else
         requestLabelAfterInsn(Entry.getInstr());
     }
   }

   // Ensure there is a symbol before DBG_LABEL.
   for (const auto &I : DbgLabels) {
     const MachineInstr *MI = I.second;
     requestLabelBeforeInsn(MI);
   }

   PrevInstLoc = DebugLoc();
   PrevLabel = Asm->getFunctionBegin();
   beginFunctionImpl(MF);
 }

 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
   if (!Asm || !MMI->hasDebugInfo())
     return;

   assert(CurMI == nullptr);
   CurMI = MI;

   // Insert labels where requested.
   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
       LabelsBeforeInsn.find(MI);

   // No label needed.
   if (I == LabelsBeforeInsn.end())
     return;

   // Label already assigned.
   if (I->second)
     return;

   if (!PrevLabel) {
     PrevLabel = MMI->getContext().createTempSymbol();
     Asm->OutStreamer->emitLabel(PrevLabel);
   }
   I->second = PrevLabel;
 }

 void DebugHandlerBase::endInstruction() {
   if (!Asm || !MMI->hasDebugInfo())
     return;

   assert(CurMI != nullptr);
   // Don't create a new label after DBG_VALUE and other instructions that don't
   // generate code.
   if (!CurMI->isMetaInstruction()) {
     PrevLabel = nullptr;
     PrevInstBB = CurMI->getParent();
   }

   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
       LabelsAfterInsn.find(CurMI);
   CurMI = nullptr;

   // No label needed.
   if (I == LabelsAfterInsn.end())
     return;

   // Label already assigned.
   if (I->second)
     return;

   // We need a label after this instruction.
   if (!PrevLabel) {
     PrevLabel = MMI->getContext().createTempSymbol();
     Asm->OutStreamer->emitLabel(PrevLabel);
   }
   I->second = PrevLabel;
 }

 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
   if (Asm && hasDebugInfo(MMI, MF))
     endFunctionImpl(MF);
   DbgValues.clear();
   DbgLabels.clear();
   LabelsBeforeInsn.clear();
   LabelsAfterInsn.clear();
   InstOrdering.clear();
 }

 void DebugHandlerBase::beginBasicBlock(const MachineBasicBlock &MBB) {
   if (!MBB.isBeginSection())
     return;

   PrevLabel = MBB.getSymbol();
 }

 void DebugHandlerBase::endBasicBlock(const MachineBasicBlock &MBB) {
   if (!MBB.isEndSection())
     return;

   PrevLabel = nullptr;
 }
	//===-- llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp -------- C++ ---===//
	//
	// 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
	//
	//===----------------------------------------------------------------------===//
	//
	// Common functionality for different debug information format backends.
	// LLVM currently supports DWARF and CodeView.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/CodeGen/DebugHandlerBase.h"
	#include "llvm/ADT/Optional.h"
	#include "llvm/ADT/Twine.h"
	#include "llvm/CodeGen/AsmPrinter.h"
	#include "llvm/CodeGen/MachineFunction.h"
	#include "llvm/CodeGen/MachineInstr.h"
	#include "llvm/CodeGen/MachineModuleInfo.h"
	#include "llvm/CodeGen/TargetSubtargetInfo.h"
	#include "llvm/IR/DebugInfo.h"
	#include "llvm/MC/MCStreamer.h"
	#include "llvm/Support/CommandLine.h"

	using namespace llvm;

	#define DEBUG_TYPE "dwarfdebug"

	/// If true, we drop variable location ranges which exist entirely outside the
	/// variable's lexical scope instruction ranges.
	static cl::opt<bool> TrimVarLocs("trim-var-locs", cl::Hidden, cl::init(true));

	Optional<DbgVariableLocation>
	DbgVariableLocation::extractFromMachineInstruction(
	const MachineInstr &Instruction) {
	DbgVariableLocation Location;
	// Variables calculated from multiple locations can't be represented here.
	if (Instruction.getNumDebugOperands() != 1)
	return None;
	if (!Instruction.getDebugOperand(0).isReg())
	return None;
	Location.Register = Instruction.getDebugOperand(0).getReg();
	Location.FragmentInfo.reset();
	// We only handle expressions generated by DIExpression::appendOffset,
	// which doesn't require a full stack machine.
	int64_t Offset = 0;
	const DIExpression *DIExpr = Instruction.getDebugExpression();
	auto Op = DIExpr->expr_op_begin();
	// We can handle a DBG_VALUE_LIST iff it has exactly one location operand that
	// appears exactly once at the start of the expression.
	if (Instruction.isDebugValueList()) {
	if (Instruction.getNumDebugOperands() == 1 &&
	Op->getOp() == dwarf::DW_OP_LLVM_arg)
	++Op;
	else
	return None;
	}
	while (Op != DIExpr->expr_op_end()) {
	switch (Op->getOp()) {
	case dwarf::DW_OP_constu: {
	int Value = Op->getArg(0);
	++Op;
	if (Op != DIExpr->expr_op_end()) {
	switch (Op->getOp()) {
	case dwarf::DW_OP_minus:
	Offset -= Value;
	break;
	case dwarf::DW_OP_plus:
	Offset += Value;
	break;
	default:
	continue;
	}
	}
	} break;
	case dwarf::DW_OP_plus_uconst:
	Offset += Op->getArg(0);
	break;
	case dwarf::DW_OP_LLVM_fragment:
	Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
	break;
	case dwarf::DW_OP_deref:
	Location.LoadChain.push_back(Offset);
	Offset = 0;
	break;
	default:
	return None;
	}
	++Op;
	}

	// Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
	// instruction.
	// FIXME: Replace these with DIExpression.
	if (Instruction.isIndirectDebugValue())
	Location.LoadChain.push_back(Offset);

	return Location;
	}

	DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}

	void DebugHandlerBase::beginModule(Module *M) {
	if (M->debug_compile_units().empty())
	Asm = nullptr;
	}

	// Each LexicalScope has first instruction and last instruction to mark
	// beginning and end of a scope respectively. Create an inverse map that list
	// scopes starts (and ends) with an instruction. One instruction may start (or
	// end) multiple scopes. Ignore scopes that are not reachable.
	void DebugHandlerBase::identifyScopeMarkers() {
	SmallVector<LexicalScope *, 4> WorkList;
	WorkList.push_back(LScopes.getCurrentFunctionScope());
	while (!WorkList.empty()) {
	LexicalScope *S = WorkList.pop_back_val();

	const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
	if (!Children.empty())
	WorkList.append(Children.begin(), Children.end());

	if (S->isAbstractScope())
	continue;

	for (const InsnRange &R : S->getRanges()) {
	assert(R.first && "InsnRange does not have first instruction!");
	assert(R.second && "InsnRange does not have second instruction!");
	requestLabelBeforeInsn(R.first);
	requestLabelAfterInsn(R.second);
	}
	}
	}

	// Return Label preceding the instruction.
	MCSymbol DebugHandlerBase::getLabelBeforeInsn(const MachineInstr MI) {
	MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
	assert(Label && "Didn't insert label before instruction");
	return Label;
	}

	// Return Label immediately following the instruction.
	MCSymbol DebugHandlerBase::getLabelAfterInsn(const MachineInstr MI) {
	return LabelsAfterInsn.lookup(MI);
	}

	/// If this type is derived from a base type then return base type size.
	uint64_t DebugHandlerBase::getBaseTypeSize(const DIType *Ty) {
	assert(Ty);
	const DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
	if (!DDTy)
	return Ty->getSizeInBits();

	unsigned Tag = DDTy->getTag();

	if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
	Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
	Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type)
	return DDTy->getSizeInBits();

	DIType *BaseType = DDTy->getBaseType();

	if (!BaseType)
	return 0;

	// If this is a derived type, go ahead and get the base type, unless it's a
	// reference then it's just the size of the field. Pointer types have no need
	// of this since they're a different type of qualification on the type.
	if (BaseType->getTag() == dwarf::DW_TAG_reference_type \|\|
	BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
	return Ty->getSizeInBits();

	return getBaseTypeSize(BaseType);
	}

	bool DebugHandlerBase::isUnsignedDIType(const DIType *Ty) {
	if (auto *CTy = dyn_cast<DICompositeType>(Ty)) {
	// FIXME: Enums without a fixed underlying type have unknown signedness
	// here, leading to incorrectly emitted constants.
	if (CTy->getTag() == dwarf::DW_TAG_enumeration_type)
	return false;

	// (Pieces of) aggregate types that get hacked apart by SROA may be
	// represented by a constant. Encode them as unsigned bytes.
	return true;
	}

	if (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
	dwarf::Tag T = (dwarf::Tag)Ty->getTag();
	// Encode pointer constants as unsigned bytes. This is used at least for
	// null pointer constant emission.
	// FIXME: reference and rvalue_reference /probably/ shouldn't be allowed
	// here, but accept them for now due to a bug in SROA producing bogus
	// dbg.values.
	if (T == dwarf::DW_TAG_pointer_type \|\|
	T == dwarf::DW_TAG_ptr_to_member_type \|\|
	T == dwarf::DW_TAG_reference_type \|\|
	T == dwarf::DW_TAG_rvalue_reference_type)
	return true;
	assert(T == dwarf::DW_TAG_typedef \|\| T == dwarf::DW_TAG_const_type \|\|
	T == dwarf::DW_TAG_volatile_type \|\|
	T == dwarf::DW_TAG_restrict_type \|\| T == dwarf::DW_TAG_atomic_type);
	assert(DTy->getBaseType() && "Expected valid base type");
	return isUnsignedDIType(DTy->getBaseType());
	}

	auto *BTy = cast<DIBasicType>(Ty);
	unsigned Encoding = BTy->getEncoding();
	assert((Encoding == dwarf::DW_ATE_unsigned \|\|
	Encoding == dwarf::DW_ATE_unsigned_char \|\|
	Encoding == dwarf::DW_ATE_signed \|\|
	Encoding == dwarf::DW_ATE_signed_char \|\|
	Encoding == dwarf::DW_ATE_float \|\| Encoding == dwarf::DW_ATE_UTF \|\|
	Encoding == dwarf::DW_ATE_boolean \|\|
	(Ty->getTag() == dwarf::DW_TAG_unspecified_type &&
	Ty->getName() == "decltype(nullptr)")) &&
	"Unsupported encoding");
	return Encoding == dwarf::DW_ATE_unsigned \|\|
	Encoding == dwarf::DW_ATE_unsigned_char \|\|
	Encoding == dwarf::DW_ATE_UTF \|\| Encoding == dwarf::DW_ATE_boolean \|\|
	Ty->getTag() == dwarf::DW_TAG_unspecified_type;
	}

	static bool hasDebugInfo(const MachineModuleInfo *MMI,
	const MachineFunction *MF) {
	if (!MMI->hasDebugInfo())
	return false;
	auto *SP = MF->getFunction().getSubprogram();
	if (!SP)
	return false;
	assert(SP->getUnit());
	auto EK = SP->getUnit()->getEmissionKind();
	if (EK == DICompileUnit::NoDebug)
	return false;
	return true;
	}

	void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
	PrevInstBB = nullptr;

	if (!Asm \|\| !hasDebugInfo(MMI, MF)) {
	skippedNonDebugFunction();
	return;
	}

	// Grab the lexical scopes for the function, if we don't have any of those
	// then we're not going to be able to do anything.
	LScopes.initialize(*MF);
	if (LScopes.empty()) {
	beginFunctionImpl(MF);
	return;
	}

	// Make sure that each lexical scope will have a begin/end label.
	identifyScopeMarkers();

	// Calculate history for local variables.
	assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
	assert(DbgLabels.empty() && "DbgLabels map wasn't cleaned!");
	calculateDbgEntityHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
	DbgValues, DbgLabels);
	InstOrdering.initialize(*MF);
	if (TrimVarLocs)
	DbgValues.trimLocationRanges(*MF, LScopes, InstOrdering);
	LLVM_DEBUG(DbgValues.dump());

	// Request labels for the full history.
	for (const auto &I : DbgValues) {
	const auto &Entries = I.second;
	if (Entries.empty())
	continue;

	auto IsDescribedByReg = [](const MachineInstr *MI) {
	return any_of(MI->debug_operands(),
	[](auto &MO) { return MO.isReg() && MO.getReg(); });
	};

	// The first mention of a function argument gets the CurrentFnBegin label,
	// so arguments are visible when breaking at function entry.
	//
	// We do not change the label for values that are described by registers,
	// as that could place them above their defining instructions. We should
	// ideally not change the labels for constant debug values either, since
	// doing that violates the ranges that are calculated in the history map.
	// However, we currently do not emit debug values for constant arguments
	// directly at the start of the function, so this code is still useful.
	// FIXME: If the first mention of an argument is in a unique section basic
	// block, we cannot always assign the CurrentFnBeginLabel as it lies in a
	// different section. Temporarily, we disable generating loc list
	// information or DW_AT_const_value when the block is in a different
	// section.
	const DILocalVariable *DIVar =
	Entries.front().getInstr()->getDebugVariable();
	if (DIVar->isParameter() &&
	getDISubprogram(DIVar->getScope())->describes(&MF->getFunction()) &&
	Entries.front().getInstr()->getParent()->sameSection(&MF->front())) {
	if (!IsDescribedByReg(Entries.front().getInstr()))
	LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
	if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {
	// Mark all non-overlapping initial fragments.
	for (auto I = Entries.begin(); I != Entries.end(); ++I) {
	if (!I->isDbgValue())
	continue;
	const DIExpression *Fragment = I->getInstr()->getDebugExpression();
	if (std::any_of(Entries.begin(), I,
	[&](DbgValueHistoryMap::Entry Pred) {
	return Pred.isDbgValue() &&
	Fragment->fragmentsOverlap(
	Pred.getInstr()->getDebugExpression());
	}))
	break;
	// The code that generates location lists for DWARF assumes that the
	// entries' start labels are monotonically increasing, and since we
	// don't change the label for fragments that are described by
	// registers, we must bail out when encountering such a fragment.
	if (IsDescribedByReg(I->getInstr()))
	break;
	LabelsBeforeInsn[I->getInstr()] = Asm->getFunctionBegin();
	}
	}
	}

	for (const auto &Entry : Entries) {
	if (Entry.isDbgValue())
	requestLabelBeforeInsn(Entry.getInstr());
	else
	requestLabelAfterInsn(Entry.getInstr());
	}
	}

	// Ensure there is a symbol before DBG_LABEL.
	for (const auto &I : DbgLabels) {
	const MachineInstr *MI = I.second;
	requestLabelBeforeInsn(MI);
	}

	PrevInstLoc = DebugLoc();
	PrevLabel = Asm->getFunctionBegin();
	beginFunctionImpl(MF);
	}

	void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
	if (!Asm \|\| !MMI->hasDebugInfo())
	return;

	assert(CurMI == nullptr);
	CurMI = MI;

	// Insert labels where requested.
	DenseMap<const MachineInstr , MCSymbol >::iterator I =
	LabelsBeforeInsn.find(MI);

	// No label needed.
	if (I == LabelsBeforeInsn.end())
	return;

	// Label already assigned.
	if (I->second)
	return;

	if (!PrevLabel) {
	PrevLabel = MMI->getContext().createTempSymbol();
	Asm->OutStreamer->emitLabel(PrevLabel);
	}
	I->second = PrevLabel;
	}

	void DebugHandlerBase::endInstruction() {
	if (!Asm \|\| !MMI->hasDebugInfo())
	return;

	assert(CurMI != nullptr);
	// Don't create a new label after DBG_VALUE and other instructions that don't
	// generate code.
	if (!CurMI->isMetaInstruction()) {
	PrevLabel = nullptr;
	PrevInstBB = CurMI->getParent();
	}

	DenseMap<const MachineInstr , MCSymbol >::iterator I =
	LabelsAfterInsn.find(CurMI);
	CurMI = nullptr;

	// No label needed.
	if (I == LabelsAfterInsn.end())
	return;

	// Label already assigned.
	if (I->second)
	return;

	// We need a label after this instruction.
	if (!PrevLabel) {
	PrevLabel = MMI->getContext().createTempSymbol();
	Asm->OutStreamer->emitLabel(PrevLabel);
	}
	I->second = PrevLabel;
	}

	void DebugHandlerBase::endFunction(const MachineFunction *MF) {
	if (Asm && hasDebugInfo(MMI, MF))
	endFunctionImpl(MF);
	DbgValues.clear();
	DbgLabels.clear();
	LabelsBeforeInsn.clear();
	LabelsAfterInsn.clear();
	InstOrdering.clear();
	}

	void DebugHandlerBase::beginBasicBlock(const MachineBasicBlock &MBB) {
	if (!MBB.isBeginSection())
	return;

	PrevLabel = MBB.getSymbol();
	}

	void DebugHandlerBase::endBasicBlock(const MachineBasicBlock &MBB) {
	if (!MBB.isEndSection())
	return;

	PrevLabel = nullptr;
	}