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      1 //===-- llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp -------*- C++ -*--===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // Common functionality for different debug information format backends.
     11 // LLVM currently supports DWARF and CodeView.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "DebugHandlerBase.h"
     16 #include "llvm/ADT/Optional.h"
     17 #include "llvm/ADT/Twine.h"
     18 #include "llvm/CodeGen/AsmPrinter.h"
     19 #include "llvm/CodeGen/MachineFunction.h"
     20 #include "llvm/CodeGen/MachineInstr.h"
     21 #include "llvm/CodeGen/MachineModuleInfo.h"
     22 #include "llvm/CodeGen/TargetSubtargetInfo.h"
     23 #include "llvm/IR/DebugInfo.h"
     24 #include "llvm/MC/MCStreamer.h"
     25 
     26 using namespace llvm;
     27 
     28 #define DEBUG_TYPE "dwarfdebug"
     29 
     30 Optional<DbgVariableLocation>
     31 DbgVariableLocation::extractFromMachineInstruction(
     32     const MachineInstr &Instruction) {
     33   DbgVariableLocation Location;
     34   if (!Instruction.isDebugValue())
     35     return None;
     36   if (!Instruction.getOperand(0).isReg())
     37     return None;
     38   Location.Register = Instruction.getOperand(0).getReg();
     39   Location.FragmentInfo.reset();
     40   // We only handle expressions generated by DIExpression::appendOffset,
     41   // which doesn't require a full stack machine.
     42   int64_t Offset = 0;
     43   const DIExpression *DIExpr = Instruction.getDebugExpression();
     44   auto Op = DIExpr->expr_op_begin();
     45   while (Op != DIExpr->expr_op_end()) {
     46     switch (Op->getOp()) {
     47     case dwarf::DW_OP_constu: {
     48       int Value = Op->getArg(0);
     49       ++Op;
     50       if (Op != DIExpr->expr_op_end()) {
     51         switch (Op->getOp()) {
     52         case dwarf::DW_OP_minus:
     53           Offset -= Value;
     54           break;
     55         case dwarf::DW_OP_plus:
     56           Offset += Value;
     57           break;
     58         default:
     59           continue;
     60         }
     61       }
     62     } break;
     63     case dwarf::DW_OP_plus_uconst:
     64       Offset += Op->getArg(0);
     65       break;
     66     case dwarf::DW_OP_LLVM_fragment:
     67       Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
     68       break;
     69     case dwarf::DW_OP_deref:
     70       Location.LoadChain.push_back(Offset);
     71       Offset = 0;
     72       break;
     73     default:
     74       return None;
     75     }
     76     ++Op;
     77   }
     78 
     79   // Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
     80   // instruction.
     81   // FIXME: Replace these with DIExpression.
     82   if (Instruction.isIndirectDebugValue())
     83     Location.LoadChain.push_back(Offset);
     84 
     85   return Location;
     86 }
     87 
     88 DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
     89 
     90 // Each LexicalScope has first instruction and last instruction to mark
     91 // beginning and end of a scope respectively. Create an inverse map that list
     92 // scopes starts (and ends) with an instruction. One instruction may start (or
     93 // end) multiple scopes. Ignore scopes that are not reachable.
     94 void DebugHandlerBase::identifyScopeMarkers() {
     95   SmallVector<LexicalScope *, 4> WorkList;
     96   WorkList.push_back(LScopes.getCurrentFunctionScope());
     97   while (!WorkList.empty()) {
     98     LexicalScope *S = WorkList.pop_back_val();
     99 
    100     const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
    101     if (!Children.empty())
    102       WorkList.append(Children.begin(), Children.end());
    103 
    104     if (S->isAbstractScope())
    105       continue;
    106 
    107     for (const InsnRange &R : S->getRanges()) {
    108       assert(R.first && "InsnRange does not have first instruction!");
    109       assert(R.second && "InsnRange does not have second instruction!");
    110       requestLabelBeforeInsn(R.first);
    111       requestLabelAfterInsn(R.second);
    112     }
    113   }
    114 }
    115 
    116 // Return Label preceding the instruction.
    117 MCSymbol *DebugHandlerBase::getLabelBeforeInsn(const MachineInstr *MI) {
    118   MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
    119   assert(Label && "Didn't insert label before instruction");
    120   return Label;
    121 }
    122 
    123 // Return Label immediately following the instruction.
    124 MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
    125   return LabelsAfterInsn.lookup(MI);
    126 }
    127 
    128 /// If this type is derived from a base type then return base type size.
    129 uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
    130   DIType *Ty = TyRef.resolve();
    131   assert(Ty);
    132   DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
    133   if (!DDTy)
    134     return Ty->getSizeInBits();
    135 
    136   unsigned Tag = DDTy->getTag();
    137 
    138   if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
    139       Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
    140       Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type)
    141     return DDTy->getSizeInBits();
    142 
    143   DIType *BaseType = DDTy->getBaseType().resolve();
    144 
    145   if (!BaseType)
    146     return 0;
    147 
    148   // If this is a derived type, go ahead and get the base type, unless it's a
    149   // reference then it's just the size of the field. Pointer types have no need
    150   // of this since they're a different type of qualification on the type.
    151   if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
    152       BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
    153     return Ty->getSizeInBits();
    154 
    155   return getBaseTypeSize(BaseType);
    156 }
    157 
    158 static bool hasDebugInfo(const MachineModuleInfo *MMI,
    159                          const MachineFunction *MF) {
    160   if (!MMI->hasDebugInfo())
    161     return false;
    162   auto *SP = MF->getFunction().getSubprogram();
    163   if (!SP)
    164     return false;
    165   assert(SP->getUnit());
    166   auto EK = SP->getUnit()->getEmissionKind();
    167   if (EK == DICompileUnit::NoDebug)
    168     return false;
    169   return true;
    170 }
    171 
    172 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
    173   PrevInstBB = nullptr;
    174 
    175   if (!Asm || !hasDebugInfo(MMI, MF)) {
    176     skippedNonDebugFunction();
    177     return;
    178   }
    179 
    180   // Grab the lexical scopes for the function, if we don't have any of those
    181   // then we're not going to be able to do anything.
    182   LScopes.initialize(*MF);
    183   if (LScopes.empty()) {
    184     beginFunctionImpl(MF);
    185     return;
    186   }
    187 
    188   // Make sure that each lexical scope will have a begin/end label.
    189   identifyScopeMarkers();
    190 
    191   // Calculate history for local variables.
    192   assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
    193   calculateDbgValueHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
    194                            DbgValues);
    195   LLVM_DEBUG(DbgValues.dump());
    196 
    197   // Request labels for the full history.
    198   for (const auto &I : DbgValues) {
    199     const auto &Ranges = I.second;
    200     if (Ranges.empty())
    201       continue;
    202 
    203     // The first mention of a function argument gets the CurrentFnBegin
    204     // label, so arguments are visible when breaking at function entry.
    205     const DILocalVariable *DIVar = Ranges.front().first->getDebugVariable();
    206     if (DIVar->isParameter() &&
    207         getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
    208       LabelsBeforeInsn[Ranges.front().first] = Asm->getFunctionBegin();
    209       if (Ranges.front().first->getDebugExpression()->isFragment()) {
    210         // Mark all non-overlapping initial fragments.
    211         for (auto I = Ranges.begin(); I != Ranges.end(); ++I) {
    212           const DIExpression *Fragment = I->first->getDebugExpression();
    213           if (std::all_of(Ranges.begin(), I,
    214                           [&](DbgValueHistoryMap::InstrRange Pred) {
    215                             return !Fragment->fragmentsOverlap(
    216                                 Pred.first->getDebugExpression());
    217                           }))
    218             LabelsBeforeInsn[I->first] = Asm->getFunctionBegin();
    219           else
    220             break;
    221         }
    222       }
    223     }
    224 
    225     for (const auto &Range : Ranges) {
    226       requestLabelBeforeInsn(Range.first);
    227       if (Range.second)
    228         requestLabelAfterInsn(Range.second);
    229     }
    230   }
    231 
    232   PrevInstLoc = DebugLoc();
    233   PrevLabel = Asm->getFunctionBegin();
    234   beginFunctionImpl(MF);
    235 }
    236 
    237 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
    238   if (!MMI->hasDebugInfo())
    239     return;
    240 
    241   assert(CurMI == nullptr);
    242   CurMI = MI;
    243 
    244   // Insert labels where requested.
    245   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
    246       LabelsBeforeInsn.find(MI);
    247 
    248   // No label needed.
    249   if (I == LabelsBeforeInsn.end())
    250     return;
    251 
    252   // Label already assigned.
    253   if (I->second)
    254     return;
    255 
    256   if (!PrevLabel) {
    257     PrevLabel = MMI->getContext().createTempSymbol();
    258     Asm->OutStreamer->EmitLabel(PrevLabel);
    259   }
    260   I->second = PrevLabel;
    261 }
    262 
    263 void DebugHandlerBase::endInstruction() {
    264   if (!MMI->hasDebugInfo())
    265     return;
    266 
    267   assert(CurMI != nullptr);
    268   // Don't create a new label after DBG_VALUE and other instructions that don't
    269   // generate code.
    270   if (!CurMI->isMetaInstruction()) {
    271     PrevLabel = nullptr;
    272     PrevInstBB = CurMI->getParent();
    273   }
    274 
    275   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
    276       LabelsAfterInsn.find(CurMI);
    277   CurMI = nullptr;
    278 
    279   // No label needed.
    280   if (I == LabelsAfterInsn.end())
    281     return;
    282 
    283   // Label already assigned.
    284   if (I->second)
    285     return;
    286 
    287   // We need a label after this instruction.
    288   if (!PrevLabel) {
    289     PrevLabel = MMI->getContext().createTempSymbol();
    290     Asm->OutStreamer->EmitLabel(PrevLabel);
    291   }
    292   I->second = PrevLabel;
    293 }
    294 
    295 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
    296   if (hasDebugInfo(MMI, MF))
    297     endFunctionImpl(MF);
    298   DbgValues.clear();
    299   LabelsBeforeInsn.clear();
    300   LabelsAfterInsn.clear();
    301 }
    302