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 DIType *Ty) {
 144   assert(Ty);
 145   const DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
 146   if (!DDTy)
 147     return Ty->getSizeInBits();
 148
 149   unsigned Tag = DDTy->getTag();
 150
 151   if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
 152       Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
 153       Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type)
 154     return DDTy->getSizeInBits();
 155
 156   DIType *BaseType = DDTy->getBaseType();
 157
 158   if (!BaseType)
 159     return 0;
 160
 161   // If this is a derived type, go ahead and get the base type, unless it's a
 162   // reference then it's just the size of the field. Pointer types have no need
 163   // of this since they're a different type of qualification on the type.
 164   if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
 165       BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
 166     return Ty->getSizeInBits();
 167
 168   return getBaseTypeSize(BaseType);
 169 }
 170
 171 static bool hasDebugInfo(const MachineModuleInfo *MMI,
 172                          const MachineFunction *MF) {
 173   if (!MMI->hasDebugInfo())
 174     return false;
 175   auto *SP = MF->getFunction().getSubprogram();
 176   if (!SP)
 177     return false;
 178   assert(SP->getUnit());
 179   auto EK = SP->getUnit()->getEmissionKind();
 180   if (EK == DICompileUnit::NoDebug)
 181     return false;
 182   return true;
 183 }
 184
 185 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
 186   PrevInstBB = nullptr;
 187
 188   if (!Asm || !hasDebugInfo(MMI, MF)) {
 189     skippedNonDebugFunction();
 190     return;
 191   }
 192
 193   // Grab the lexical scopes for the function, if we don't have any of those
 194   // then we're not going to be able to do anything.
 195   LScopes.initialize(*MF);
 196   if (LScopes.empty()) {
 197     beginFunctionImpl(MF);
 198     return;
 199   }
 200
 201   // Make sure that each lexical scope will have a begin/end label.
 202   identifyScopeMarkers();
 203
 204   // Calculate history for local variables.
 205   assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
 206   assert(DbgLabels.empty() && "DbgLabels map wasn't cleaned!");
 207   calculateDbgEntityHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
 208                             DbgValues, DbgLabels);
 209   LLVM_DEBUG(DbgValues.dump());
 210
 211   // Request labels for the full history.
 212   for (const auto &I : DbgValues) {
 213     const auto &Entries = I.second;
 214     if (Entries.empty())
 215       continue;
 216
 217     auto IsDescribedByReg = [](const MachineInstr *MI) {
 218       return MI->getOperand(0).isReg() && MI->getOperand(0).getReg();
 219     };
 220
 221     // The first mention of a function argument gets the CurrentFnBegin label,
 222     // so arguments are visible when breaking at function entry.
 223     //
 224     // We do not change the label for values that are described by registers,
 225     // as that could place them above their defining instructions. We should
 226     // ideally not change the labels for constant debug values either, since
 227     // doing that violates the ranges that are calculated in the history map.
 228     // However, we currently do not emit debug values for constant arguments
 229     // directly at the start of the function, so this code is still useful.
 230     const DILocalVariable *DIVar =
 231         Entries.front().getInstr()->getDebugVariable();
 232     if (DIVar->isParameter() &&
 233         getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
 234       if (!IsDescribedByReg(Entries.front().getInstr()))
 235         LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
 236       if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {
 237         // Mark all non-overlapping initial fragments.
 238         for (auto I = Entries.begin(); I != Entries.end(); ++I) {
 239           if (!I->isDbgValue())
 240             continue;
 241           const DIExpression *Fragment = I->getInstr()->getDebugExpression();
 242           if (std::any_of(Entries.begin(), I,
 243                           [&](DbgValueHistoryMap::Entry Pred) {
 244                             return Pred.isDbgValue() &&
 245                                    Fragment->fragmentsOverlap(
 246                                        Pred.getInstr()->getDebugExpression());
 247                           }))
 248             break;
 249           // The code that generates location lists for DWARF assumes that the
 250           // entries' start labels are monotonically increasing, and since we
 251           // don't change the label for fragments that are described by
 252           // registers, we must bail out when encountering such a fragment.
 253           if (IsDescribedByReg(I->getInstr()))
 254             break;
 255           LabelsBeforeInsn[I->getInstr()] = Asm->getFunctionBegin();
 256         }
 257       }
 258     }
 259
 260     for (const auto &Entry : Entries) {
 261       if (Entry.isDbgValue())
 262         requestLabelBeforeInsn(Entry.getInstr());
 263       else
 264         requestLabelAfterInsn(Entry.getInstr());
 265     }
 266   }
 267
 268   // Ensure there is a symbol before DBG_LABEL.
 269   for (const auto &I : DbgLabels) {
 270     const MachineInstr *MI = I.second;
 271     requestLabelBeforeInsn(MI);
 272   }
 273
 274   PrevInstLoc = DebugLoc();
 275   PrevLabel = Asm->getFunctionBegin();
 276   beginFunctionImpl(MF);
 277 }
 278
 279 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
 280   if (!MMI->hasDebugInfo())
 281     return;
 282
 283   assert(CurMI == nullptr);
 284   CurMI = MI;
 285
 286   // Insert labels where requested.
 287   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
 288       LabelsBeforeInsn.find(MI);
 289
 290   // No label needed.
 291   if (I == LabelsBeforeInsn.end())
 292     return;
 293
 294   // Label already assigned.
 295   if (I->second)
 296     return;
 297
 298   if (!PrevLabel) {
 299     PrevLabel = MMI->getContext().createTempSymbol();
 300     Asm->OutStreamer->EmitLabel(PrevLabel);
 301   }
 302   I->second = PrevLabel;
 303 }
 304
 305 void DebugHandlerBase::endInstruction() {
 306   if (!MMI->hasDebugInfo())
 307     return;
 308
 309   assert(CurMI != nullptr);
 310   // Don't create a new label after DBG_VALUE and other instructions that don't
 311   // generate code.
 312   if (!CurMI->isMetaInstruction()) {
 313     PrevLabel = nullptr;
 314     PrevInstBB = CurMI->getParent();
 315   }
 316
 317   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
 318       LabelsAfterInsn.find(CurMI);
 319   CurMI = nullptr;
 320
 321   // No label needed.
 322   if (I == LabelsAfterInsn.end())
 323     return;
 324
 325   // Label already assigned.
 326   if (I->second)
 327     return;
 328
 329   // We need a label after this instruction.
 330   if (!PrevLabel) {
 331     PrevLabel = MMI->getContext().createTempSymbol();
 332     Asm->OutStreamer->EmitLabel(PrevLabel);
 333   }
 334   I->second = PrevLabel;
 335 }
 336
 337 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
 338   if (hasDebugInfo(MMI, MF))
 339     endFunctionImpl(MF);
 340   DbgValues.clear();
 341   DbgLabels.clear();
 342   LabelsBeforeInsn.clear();
 343   LabelsAfterInsn.clear();
 344 }