xref: /freebsd/contrib/llvm-project/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp (revision d35b039af944f68fe99bb3ad2f0c6d5ec7917096)
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/CodeGen/AsmPrinter.h"
16  #include "llvm/CodeGen/MachineFunction.h"
17  #include "llvm/CodeGen/MachineInstr.h"
18  #include "llvm/CodeGen/MachineModuleInfo.h"
19  #include "llvm/CodeGen/TargetSubtargetInfo.h"
20  #include "llvm/IR/DebugInfo.h"
21  #include "llvm/IR/Module.h"
22  #include "llvm/MC/MCStreamer.h"
23  #include "llvm/Support/CommandLine.h"
24  
25  using namespace llvm;
26  
27  #define DEBUG_TYPE "dwarfdebug"
28  
29  /// If true, we drop variable location ranges which exist entirely outside the
30  /// variable's lexical scope instruction ranges.
31  static cl::opt<bool> TrimVarLocs("trim-var-locs", cl::Hidden, cl::init(true));
32  
33  std::optional<DbgVariableLocation>
34  DbgVariableLocation::extractFromMachineInstruction(
35      const MachineInstr &Instruction) {
36    DbgVariableLocation Location;
37    // Variables calculated from multiple locations can't be represented here.
38    if (Instruction.getNumDebugOperands() != 1)
39      return std::nullopt;
40    if (!Instruction.getDebugOperand(0).isReg())
41      return std::nullopt;
42    Location.Register = Instruction.getDebugOperand(0).getReg();
43    Location.FragmentInfo.reset();
44    // We only handle expressions generated by DIExpression::appendOffset,
45    // which doesn't require a full stack machine.
46    int64_t Offset = 0;
47    const DIExpression *DIExpr = Instruction.getDebugExpression();
48    auto Op = DIExpr->expr_op_begin();
49    // We can handle a DBG_VALUE_LIST iff it has exactly one location operand that
50    // appears exactly once at the start of the expression.
51    if (Instruction.isDebugValueList()) {
52      if (Instruction.getNumDebugOperands() == 1 &&
53          Op->getOp() == dwarf::DW_OP_LLVM_arg)
54        ++Op;
55      else
56        return std::nullopt;
57    }
58    while (Op != DIExpr->expr_op_end()) {
59      switch (Op->getOp()) {
60      case dwarf::DW_OP_constu: {
61        int Value = Op->getArg(0);
62        ++Op;
63        if (Op != DIExpr->expr_op_end()) {
64          switch (Op->getOp()) {
65          case dwarf::DW_OP_minus:
66            Offset -= Value;
67            break;
68          case dwarf::DW_OP_plus:
69            Offset += Value;
70            break;
71          default:
72            continue;
73          }
74        }
75      } break;
76      case dwarf::DW_OP_plus_uconst:
77        Offset += Op->getArg(0);
78        break;
79      case dwarf::DW_OP_LLVM_fragment:
80        Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
81        break;
82      case dwarf::DW_OP_deref:
83        Location.LoadChain.push_back(Offset);
84        Offset = 0;
85        break;
86      default:
87        return std::nullopt;
88      }
89      ++Op;
90    }
91  
92    // Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
93    // instruction.
94    // FIXME: Replace these with DIExpression.
95    if (Instruction.isIndirectDebugValue())
96      Location.LoadChain.push_back(Offset);
97  
98    return Location;
99  }
100  
101  DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
102  
103  DebugHandlerBase::~DebugHandlerBase() = default;
104  
105  void DebugHandlerBase::beginModule(Module *M) {
106    if (M->debug_compile_units().empty())
107      Asm = nullptr;
108  }
109  
110  // Each LexicalScope has first instruction and last instruction to mark
111  // beginning and end of a scope respectively. Create an inverse map that list
112  // scopes starts (and ends) with an instruction. One instruction may start (or
113  // end) multiple scopes. Ignore scopes that are not reachable.
114  void DebugHandlerBase::identifyScopeMarkers() {
115    SmallVector<LexicalScope *, 4> WorkList;
116    WorkList.push_back(LScopes.getCurrentFunctionScope());
117    while (!WorkList.empty()) {
118      LexicalScope *S = WorkList.pop_back_val();
119  
120      const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
121      if (!Children.empty())
122        WorkList.append(Children.begin(), Children.end());
123  
124      if (S->isAbstractScope())
125        continue;
126  
127      for (const InsnRange &R : S->getRanges()) {
128        assert(R.first && "InsnRange does not have first instruction!");
129        assert(R.second && "InsnRange does not have second instruction!");
130        requestLabelBeforeInsn(R.first);
131        requestLabelAfterInsn(R.second);
132      }
133    }
134  }
135  
136  // Return Label preceding the instruction.
137  MCSymbol *DebugHandlerBase::getLabelBeforeInsn(const MachineInstr *MI) {
138    MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
139    assert(Label && "Didn't insert label before instruction");
140    return Label;
141  }
142  
143  // Return Label immediately following the instruction.
144  MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
145    return LabelsAfterInsn.lookup(MI);
146  }
147  
148  /// If this type is derived from a base type then return base type size.
149  uint64_t DebugHandlerBase::getBaseTypeSize(const DIType *Ty) {
150    assert(Ty);
151    const DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
152    if (!DDTy)
153      return Ty->getSizeInBits();
154  
155    unsigned Tag = DDTy->getTag();
156  
157    if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
158        Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
159        Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type &&
160        Tag != dwarf::DW_TAG_immutable_type &&
161        Tag != dwarf::DW_TAG_template_alias)
162      return DDTy->getSizeInBits();
163  
164    DIType *BaseType = DDTy->getBaseType();
165  
166    if (!BaseType)
167      return 0;
168  
169    // If this is a derived type, go ahead and get the base type, unless it's a
170    // reference then it's just the size of the field. Pointer types have no need
171    // of this since they're a different type of qualification on the type.
172    if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
173        BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
174      return Ty->getSizeInBits();
175  
176    return getBaseTypeSize(BaseType);
177  }
178  
179  bool DebugHandlerBase::isUnsignedDIType(const DIType *Ty) {
180    if (isa<DIStringType>(Ty)) {
181      // Some transformations (e.g. instcombine) may decide to turn a Fortran
182      // character object into an integer, and later ones (e.g. SROA) may
183      // further inject a constant integer in a llvm.dbg.value call to track
184      // the object's value. Here we trust the transformations are doing the
185      // right thing, and treat the constant as unsigned to preserve that value
186      // (i.e. avoid sign extension).
187      return true;
188    }
189  
190    if (auto *CTy = dyn_cast<DICompositeType>(Ty)) {
191      if (CTy->getTag() == dwarf::DW_TAG_enumeration_type) {
192        if (!(Ty = CTy->getBaseType()))
193          // FIXME: Enums without a fixed underlying type have unknown signedness
194          // here, leading to incorrectly emitted constants.
195          return false;
196      } else
197        // (Pieces of) aggregate types that get hacked apart by SROA may be
198        // represented by a constant. Encode them as unsigned bytes.
199        return true;
200    }
201  
202    if (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
203      dwarf::Tag T = (dwarf::Tag)Ty->getTag();
204      // Encode pointer constants as unsigned bytes. This is used at least for
205      // null pointer constant emission.
206      // FIXME: reference and rvalue_reference /probably/ shouldn't be allowed
207      // here, but accept them for now due to a bug in SROA producing bogus
208      // dbg.values.
209      if (T == dwarf::DW_TAG_pointer_type ||
210          T == dwarf::DW_TAG_ptr_to_member_type ||
211          T == dwarf::DW_TAG_reference_type ||
212          T == dwarf::DW_TAG_rvalue_reference_type)
213        return true;
214      assert(T == dwarf::DW_TAG_typedef || T == dwarf::DW_TAG_const_type ||
215             T == dwarf::DW_TAG_volatile_type ||
216             T == dwarf::DW_TAG_restrict_type || T == dwarf::DW_TAG_atomic_type ||
217             T == dwarf::DW_TAG_immutable_type ||
218             T == dwarf::DW_TAG_template_alias);
219      assert(DTy->getBaseType() && "Expected valid base type");
220      return isUnsignedDIType(DTy->getBaseType());
221    }
222  
223    auto *BTy = cast<DIBasicType>(Ty);
224    unsigned Encoding = BTy->getEncoding();
225    assert((Encoding == dwarf::DW_ATE_unsigned ||
226            Encoding == dwarf::DW_ATE_unsigned_char ||
227            Encoding == dwarf::DW_ATE_signed ||
228            Encoding == dwarf::DW_ATE_signed_char ||
229            Encoding == dwarf::DW_ATE_float || Encoding == dwarf::DW_ATE_UTF ||
230            Encoding == dwarf::DW_ATE_boolean ||
231            Encoding == dwarf::DW_ATE_complex_float ||
232            Encoding == dwarf::DW_ATE_signed_fixed ||
233            Encoding == dwarf::DW_ATE_unsigned_fixed ||
234            (Ty->getTag() == dwarf::DW_TAG_unspecified_type &&
235             Ty->getName() == "decltype(nullptr)")) &&
236           "Unsupported encoding");
237    return Encoding == dwarf::DW_ATE_unsigned ||
238           Encoding == dwarf::DW_ATE_unsigned_char ||
239           Encoding == dwarf::DW_ATE_UTF || Encoding == dwarf::DW_ATE_boolean ||
240           Encoding == llvm::dwarf::DW_ATE_unsigned_fixed ||
241           Ty->getTag() == dwarf::DW_TAG_unspecified_type;
242  }
243  
244  static bool hasDebugInfo(const MachineModuleInfo *MMI,
245                           const MachineFunction *MF) {
246    if (!MMI->hasDebugInfo())
247      return false;
248    auto *SP = MF->getFunction().getSubprogram();
249    if (!SP)
250      return false;
251    assert(SP->getUnit());
252    auto EK = SP->getUnit()->getEmissionKind();
253    if (EK == DICompileUnit::NoDebug)
254      return false;
255    return true;
256  }
257  
258  void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
259    PrevInstBB = nullptr;
260  
261    if (!Asm || !hasDebugInfo(MMI, MF)) {
262      skippedNonDebugFunction();
263      return;
264    }
265  
266    // Grab the lexical scopes for the function, if we don't have any of those
267    // then we're not going to be able to do anything.
268    LScopes.initialize(*MF);
269    if (LScopes.empty()) {
270      beginFunctionImpl(MF);
271      return;
272    }
273  
274    // Make sure that each lexical scope will have a begin/end label.
275    identifyScopeMarkers();
276  
277    // Calculate history for local variables.
278    assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
279    assert(DbgLabels.empty() && "DbgLabels map wasn't cleaned!");
280    calculateDbgEntityHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
281                              DbgValues, DbgLabels);
282    InstOrdering.initialize(*MF);
283    if (TrimVarLocs)
284      DbgValues.trimLocationRanges(*MF, LScopes, InstOrdering);
285    LLVM_DEBUG(DbgValues.dump(MF->getName()));
286  
287    // Request labels for the full history.
288    for (const auto &I : DbgValues) {
289      const auto &Entries = I.second;
290      if (Entries.empty())
291        continue;
292  
293      auto IsDescribedByReg = [](const MachineInstr *MI) {
294        return any_of(MI->debug_operands(),
295                      [](auto &MO) { return MO.isReg() && MO.getReg(); });
296      };
297  
298      // The first mention of a function argument gets the CurrentFnBegin label,
299      // so arguments are visible when breaking at function entry.
300      //
301      // We do not change the label for values that are described by registers,
302      // as that could place them above their defining instructions. We should
303      // ideally not change the labels for constant debug values either, since
304      // doing that violates the ranges that are calculated in the history map.
305      // However, we currently do not emit debug values for constant arguments
306      // directly at the start of the function, so this code is still useful.
307      const DILocalVariable *DIVar =
308          Entries.front().getInstr()->getDebugVariable();
309      if (DIVar->isParameter() &&
310          getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
311        if (!IsDescribedByReg(Entries.front().getInstr()))
312          LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
313        if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {
314          // Mark all non-overlapping initial fragments.
315          for (const auto *I = Entries.begin(); I != Entries.end(); ++I) {
316            if (!I->isDbgValue())
317              continue;
318            const DIExpression *Fragment = I->getInstr()->getDebugExpression();
319            if (std::any_of(Entries.begin(), I,
320                            [&](DbgValueHistoryMap::Entry Pred) {
321                              return Pred.isDbgValue() &&
322                                     Fragment->fragmentsOverlap(
323                                         Pred.getInstr()->getDebugExpression());
324                            }))
325              break;
326            // The code that generates location lists for DWARF assumes that the
327            // entries' start labels are monotonically increasing, and since we
328            // don't change the label for fragments that are described by
329            // registers, we must bail out when encountering such a fragment.
330            if (IsDescribedByReg(I->getInstr()))
331              break;
332            LabelsBeforeInsn[I->getInstr()] = Asm->getFunctionBegin();
333          }
334        }
335      }
336  
337      for (const auto &Entry : Entries) {
338        if (Entry.isDbgValue())
339          requestLabelBeforeInsn(Entry.getInstr());
340        else
341          requestLabelAfterInsn(Entry.getInstr());
342      }
343    }
344  
345    // Ensure there is a symbol before DBG_LABEL.
346    for (const auto &I : DbgLabels) {
347      const MachineInstr *MI = I.second;
348      requestLabelBeforeInsn(MI);
349    }
350  
351    PrevInstLoc = DebugLoc();
352    PrevLabel = Asm->getFunctionBegin();
353    beginFunctionImpl(MF);
354  }
355  
356  void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
357    if (!Asm || !MMI->hasDebugInfo())
358      return;
359  
360    assert(CurMI == nullptr);
361    CurMI = MI;
362  
363    // Insert labels where requested.
364    DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
365        LabelsBeforeInsn.find(MI);
366  
367    // No label needed.
368    if (I == LabelsBeforeInsn.end())
369      return;
370  
371    // Label already assigned.
372    if (I->second)
373      return;
374  
375    if (!PrevLabel) {
376      PrevLabel = MMI->getContext().createTempSymbol();
377      Asm->OutStreamer->emitLabel(PrevLabel);
378    }
379    I->second = PrevLabel;
380  }
381  
382  void DebugHandlerBase::endInstruction() {
383    if (!Asm || !MMI->hasDebugInfo())
384      return;
385  
386    assert(CurMI != nullptr);
387    // Don't create a new label after DBG_VALUE and other instructions that don't
388    // generate code.
389    if (!CurMI->isMetaInstruction()) {
390      PrevLabel = nullptr;
391      PrevInstBB = CurMI->getParent();
392    }
393  
394    DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
395        LabelsAfterInsn.find(CurMI);
396  
397    // No label needed or label already assigned.
398    if (I == LabelsAfterInsn.end() || I->second) {
399      CurMI = nullptr;
400      return;
401    }
402  
403    // We need a label after this instruction.  With basic block sections, just
404    // use the end symbol of the section if this is the last instruction of the
405    // section.  This reduces the need for an additional label and also helps
406    // merging ranges.
407    if (CurMI->getParent()->isEndSection() && CurMI->getNextNode() == nullptr) {
408      PrevLabel = CurMI->getParent()->getEndSymbol();
409    } else if (!PrevLabel) {
410      PrevLabel = MMI->getContext().createTempSymbol();
411      Asm->OutStreamer->emitLabel(PrevLabel);
412    }
413    I->second = PrevLabel;
414    CurMI = nullptr;
415  }
416  
417  void DebugHandlerBase::endFunction(const MachineFunction *MF) {
418    if (Asm && hasDebugInfo(MMI, MF))
419      endFunctionImpl(MF);
420    DbgValues.clear();
421    DbgLabels.clear();
422    LabelsBeforeInsn.clear();
423    LabelsAfterInsn.clear();
424    InstOrdering.clear();
425  }
426  
427  void DebugHandlerBase::beginBasicBlockSection(const MachineBasicBlock &MBB) {
428    EpilogBeginBlock = nullptr;
429    if (!MBB.isEntryBlock())
430      PrevLabel = MBB.getSymbol();
431  }
432  
433  void DebugHandlerBase::endBasicBlockSection(const MachineBasicBlock &MBB) {
434    PrevLabel = nullptr;
435  }
436