lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

   1 //===-- llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp -------*- C++ -*--===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // Common functionality for different debug information format backends.
  10 // LLVM currently supports DWARF and CodeView.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/CodeGen/DebugHandlerBase.h"
  15 #include "llvm/ADT/Optional.h"
  16 #include "llvm/ADT/Twine.h"
  17 #include "llvm/CodeGen/AsmPrinter.h"
  18 #include "llvm/CodeGen/MachineFunction.h"
  19 #include "llvm/CodeGen/MachineInstr.h"
  20 #include "llvm/CodeGen/MachineModuleInfo.h"
  21 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  22 #include "llvm/IR/DebugInfo.h"
  23 #include "llvm/MC/MCStreamer.h"
  24
  25 using namespace llvm;
  26
  27 #define DEBUG_TYPE "dwarfdebug"
  28
  29 Optional<DbgVariableLocation>
  30 DbgVariableLocation::extractFromMachineInstruction(
  31     const MachineInstr &Instruction) {
  32   DbgVariableLocation Location;
  33   if (!Instruction.isDebugValue())
  34     return None;
  35   if (!Instruction.getOperand(0).isReg())
  36     return None;
  37   Location.Register = Instruction.getOperand(0).getReg();
  38   Location.FragmentInfo.reset();
  39   // We only handle expressions generated by DIExpression::appendOffset,
  40   // which doesn't require a full stack machine.
  41   int64_t Offset = 0;
  42   const DIExpression *DIExpr = Instruction.getDebugExpression();
  43   auto Op = DIExpr->expr_op_begin();
  44   while (Op != DIExpr->expr_op_end()) {
  45     switch (Op->getOp()) {
  46     case dwarf::DW_OP_constu: {
  47       int Value = Op->getArg(0);
  48       ++Op;
  49       if (Op != DIExpr->expr_op_end()) {
  50         switch (Op->getOp()) {
  51         case dwarf::DW_OP_minus:
  52           Offset -= Value;
  53           break;
  54         case dwarf::DW_OP_plus:
  55           Offset += Value;
  56           break;
  57         default:
  58           continue;
  59         }
  60       }
  61     } break;
  62     case dwarf::DW_OP_plus_uconst:
  63       Offset += Op->getArg(0);
  64       break;
  65     case dwarf::DW_OP_LLVM_fragment:
  66       Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
  67       break;
  68     case dwarf::DW_OP_deref:
  69       Location.LoadChain.push_back(Offset);
  70       Offset = 0;
  71       break;
  72     default:
  73       return None;
  74     }
  75     ++Op;
  76   }
  77
  78   // Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
  79   // instruction.
  80   // FIXME: Replace these with DIExpression.
  81   if (Instruction.isIndirectDebugValue())
  82     Location.LoadChain.push_back(Offset);
  83
  84   return Location;
  85 }
  86
  87 DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
  88
  89 // Each LexicalScope has first instruction and last instruction to mark
  90 // beginning and end of a scope respectively. Create an inverse map that list
  91 // scopes starts (and ends) with an instruction. One instruction may start (or
  92 // end) multiple scopes. Ignore scopes that are not reachable.
  93 void DebugHandlerBase::identifyScopeMarkers() {
  94   SmallVector<LexicalScope *, 4> WorkList;
  95   WorkList.push_back(LScopes.getCurrentFunctionScope());
  96   while (!WorkList.empty()) {
  97     LexicalScope *S = WorkList.pop_back_val();
  98
  99     const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
 100     if (!Children.empty())
 101       WorkList.append(Children.begin(), Children.end());
 102
 103     if (S->isAbstractScope())
 104       continue;
 105
 106     for (const InsnRange &R : S->getRanges()) {
 107       assert(R.first && "InsnRange does not have first instruction!");
 108       assert(R.second && "InsnRange does not have second instruction!");
 109       requestLabelBeforeInsn(R.first);
 110       requestLabelAfterInsn(R.second);
 111     }
 112   }
 113 }
 114
 115 // Return Label preceding the instruction.
 116 MCSymbol *DebugHandlerBase::getLabelBeforeInsn(const MachineInstr *MI) {
 117   MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
 118   assert(Label && "Didn't insert label before instruction");
 119   return Label;
 120 }
 121
 122 // Return Label immediately following the instruction.
 123 MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
 124   return LabelsAfterInsn.lookup(MI);
 125 }
 126
 127 // Return the function-local offset of an instruction.
 128 const MCExpr *
 129 DebugHandlerBase::getFunctionLocalOffsetAfterInsn(const MachineInstr *MI) {
 130   MCContext &MC = Asm->OutContext;
 131
 132   MCSymbol *Start = Asm->getFunctionBegin();
 133   const auto *StartRef = MCSymbolRefExpr::create(Start, MC);
 134
 135   MCSymbol *AfterInsn = getLabelAfterInsn(MI);
 136   assert(AfterInsn && "Expected label after instruction");
 137   const auto *AfterRef = MCSymbolRefExpr::create(AfterInsn, MC);
 138
 139   return MCBinaryExpr::createSub(AfterRef, StartRef, MC);
 140 }
 141
 142 /// If this type is derived from a base type then return base type size.
 143 uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
 144   DIType *Ty = TyRef.resolve();
 145   assert(Ty);
 146   DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
 147   if (!DDTy)
 148     return Ty->getSizeInBits();
 149
 150   unsigned Tag = DDTy->getTag();
 151
 152   if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
 153       Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
 154       Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type)
 155     return DDTy->getSizeInBits();
 156
 157   DIType *BaseType = DDTy->getBaseType().resolve();
 158
 159   if (!BaseType)
 160     return 0;
 161
 162   // If this is a derived type, go ahead and get the base type, unless it's a
 163   // reference then it's just the size of the field. Pointer types have no need
 164   // of this since they're a different type of qualification on the type.
 165   if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
 166       BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
 167     return Ty->getSizeInBits();
 168
 169   return getBaseTypeSize(BaseType);
 170 }
 171
 172 static bool hasDebugInfo(const MachineModuleInfo *MMI,
 173                          const MachineFunction *MF) {
 174   if (!MMI->hasDebugInfo())
 175     return false;
 176   auto *SP = MF->getFunction().getSubprogram();
 177   if (!SP)
 178     return false;
 179   assert(SP->getUnit());
 180   auto EK = SP->getUnit()->getEmissionKind();
 181   if (EK == DICompileUnit::NoDebug)
 182     return false;
 183   return true;
 184 }
 185
 186 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
 187   PrevInstBB = nullptr;
 188
 189   if (!Asm || !hasDebugInfo(MMI, MF)) {
 190     skippedNonDebugFunction();
 191     return;
 192   }
 193
 194   // Grab the lexical scopes for the function, if we don't have any of those
 195   // then we're not going to be able to do anything.
 196   LScopes.initialize(*MF);
 197   if (LScopes.empty()) {
 198     beginFunctionImpl(MF);
 199     return;
 200   }
 201
 202   // Make sure that each lexical scope will have a begin/end label.
 203   identifyScopeMarkers();
 204
 205   // Calculate history for local variables.
 206   assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
 207   assert(DbgLabels.empty() && "DbgLabels map wasn't cleaned!");
 208   calculateDbgEntityHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
 209                             DbgValues, DbgLabels);
 210   LLVM_DEBUG(DbgValues.dump());
 211
 212   // Request labels for the full history.
 213   for (const auto &I : DbgValues) {
 214     const auto &Ranges = I.second;
 215     if (Ranges.empty())
 216       continue;
 217
 218     auto IsDescribedByReg = [](const MachineInstr *MI) {
 219       return MI->getOperand(0).isReg() && MI->getOperand(0).getReg();
 220     };
 221
 222     // The first mention of a function argument gets the CurrentFnBegin label,
 223     // so arguments are visible when breaking at function entry.
 224     //
 225     // We do not change the label for values that are described by registers,
 226     // as that could place them above their defining instructions. We should
 227     // ideally not change the labels for constant debug values either, since
 228     // doing that violates the ranges that are calculated in the history map.
 229     // However, we currently do not emit debug values for constant arguments
 230     // directly at the start of the function, so this code is still useful.
 231     const DILocalVariable *DIVar = Ranges.front().first->getDebugVariable();
 232     if (DIVar->isParameter() &&
 233         getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
 234       if (!IsDescribedByReg(Ranges.front().first))
 235         LabelsBeforeInsn[Ranges.front().first] = Asm->getFunctionBegin();
 236       if (Ranges.front().first->getDebugExpression()->isFragment()) {
 237         // Mark all non-overlapping initial fragments.
 238         for (auto I = Ranges.begin(); I != Ranges.end(); ++I) {
 239           const DIExpression *Fragment = I->first->getDebugExpression();
 240           if (std::any_of(Ranges.begin(), I,
 241                           [&](DbgValueHistoryMap::InstrRange Pred) {
 242                             return Fragment->fragmentsOverlap(
 243                                 Pred.first->getDebugExpression());
 244                           }))
 245             break;
 246           if (!IsDescribedByReg(I->first))
 247             LabelsBeforeInsn[I->first] = Asm->getFunctionBegin();
 248         }
 249       }
 250     }
 251
 252     for (const auto &Range : Ranges) {
 253       requestLabelBeforeInsn(Range.first);
 254       if (Range.second)
 255         requestLabelAfterInsn(Range.second);
 256     }
 257   }
 258
 259   // Ensure there is a symbol before DBG_LABEL.
 260   for (const auto &I : DbgLabels) {
 261     const MachineInstr *MI = I.second;
 262     requestLabelBeforeInsn(MI);
 263   }
 264
 265   PrevInstLoc = DebugLoc();
 266   PrevLabel = Asm->getFunctionBegin();
 267   beginFunctionImpl(MF);
 268 }
 269
 270 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
 271   if (!MMI->hasDebugInfo())
 272     return;
 273
 274   assert(CurMI == nullptr);
 275   CurMI = MI;
 276
 277   // Insert labels where requested.
 278   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
 279       LabelsBeforeInsn.find(MI);
 280
 281   // No label needed.
 282   if (I == LabelsBeforeInsn.end())
 283     return;
 284
 285   // Label already assigned.
 286   if (I->second)
 287     return;
 288
 289   if (!PrevLabel) {
 290     PrevLabel = MMI->getContext().createTempSymbol();
 291     Asm->OutStreamer->EmitLabel(PrevLabel);
 292   }
 293   I->second = PrevLabel;
 294 }
 295
 296 void DebugHandlerBase::endInstruction() {
 297   if (!MMI->hasDebugInfo())
 298     return;
 299
 300   assert(CurMI != nullptr);
 301   // Don't create a new label after DBG_VALUE and other instructions that don't
 302   // generate code.
 303   if (!CurMI->isMetaInstruction()) {
 304     PrevLabel = nullptr;
 305     PrevInstBB = CurMI->getParent();
 306   }
 307
 308   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
 309       LabelsAfterInsn.find(CurMI);
 310   CurMI = nullptr;
 311
 312   // No label needed.
 313   if (I == LabelsAfterInsn.end())
 314     return;
 315
 316   // Label already assigned.
 317   if (I->second)
 318     return;
 319
 320   // We need a label after this instruction.
 321   if (!PrevLabel) {
 322     PrevLabel = MMI->getContext().createTempSymbol();
 323     Asm->OutStreamer->EmitLabel(PrevLabel);
 324   }
 325   I->second = PrevLabel;
 326 }
 327
 328 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
 329   if (hasDebugInfo(MMI, MF))
 330     endFunctionImpl(MF);
 331   DbgValues.clear();
 332   DbgLabels.clear();
 333   LabelsBeforeInsn.clear();
 334   LabelsAfterInsn.clear();
 335 }