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
25using namespace llvm;
26
27#define DEBUG_TYPE "dwarfdebug"
28
29Optional<DbgVariableLocation>
30DbgVariableLocation::extractFromMachineInstruction(
31    const MachineInstr &Instruction) {
32  DbgVariableLocation Location;
33  if (!Instruction.isDebugValue())
34    return None;
35  if (!Instruction.getDebugOperand(0).isReg())
36    return None;
37  Location.Register = Instruction.getDebugOperand(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
87DebugHandlerBase::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.
93void 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.
116MCSymbol *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.
123MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
124  return LabelsAfterInsn.lookup(MI);
125}
126
127/// If this type is derived from a base type then return base type size.
128uint64_t DebugHandlerBase::getBaseTypeSize(const DIType *Ty) {
129  assert(Ty);
130  const DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
131  if (!DDTy)
132    return Ty->getSizeInBits();
133
134  unsigned Tag = DDTy->getTag();
135
136  if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
137      Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
138      Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type)
139    return DDTy->getSizeInBits();
140
141  DIType *BaseType = DDTy->getBaseType();
142
143  if (!BaseType)
144    return 0;
145
146  // If this is a derived type, go ahead and get the base type, unless it's a
147  // reference then it's just the size of the field. Pointer types have no need
148  // of this since they're a different type of qualification on the type.
149  if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
150      BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
151    return Ty->getSizeInBits();
152
153  return getBaseTypeSize(BaseType);
154}
155
156static bool hasDebugInfo(const MachineModuleInfo *MMI,
157                         const MachineFunction *MF) {
158  if (!MMI->hasDebugInfo())
159    return false;
160  auto *SP = MF->getFunction().getSubprogram();
161  if (!SP)
162    return false;
163  assert(SP->getUnit());
164  auto EK = SP->getUnit()->getEmissionKind();
165  if (EK == DICompileUnit::NoDebug)
166    return false;
167  return true;
168}
169
170void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
171  PrevInstBB = nullptr;
172
173  if (!Asm || !hasDebugInfo(MMI, MF)) {
174    skippedNonDebugFunction();
175    return;
176  }
177
178  // Grab the lexical scopes for the function, if we don't have any of those
179  // then we're not going to be able to do anything.
180  LScopes.initialize(*MF);
181  if (LScopes.empty()) {
182    beginFunctionImpl(MF);
183    return;
184  }
185
186  // Make sure that each lexical scope will have a begin/end label.
187  identifyScopeMarkers();
188
189  // Calculate history for local variables.
190  assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
191  assert(DbgLabels.empty() && "DbgLabels map wasn't cleaned!");
192  calculateDbgEntityHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
193                            DbgValues, DbgLabels);
194  LLVM_DEBUG(DbgValues.dump());
195
196  // Request labels for the full history.
197  for (const auto &I : DbgValues) {
198    const auto &Entries = I.second;
199    if (Entries.empty())
200      continue;
201
202    auto IsDescribedByReg = [](const MachineInstr *MI) {
203      return MI->getDebugOperand(0).isReg() && MI->getDebugOperand(0).getReg();
204    };
205
206    // The first mention of a function argument gets the CurrentFnBegin label,
207    // so arguments are visible when breaking at function entry.
208    //
209    // We do not change the label for values that are described by registers,
210    // as that could place them above their defining instructions. We should
211    // ideally not change the labels for constant debug values either, since
212    // doing that violates the ranges that are calculated in the history map.
213    // However, we currently do not emit debug values for constant arguments
214    // directly at the start of the function, so this code is still useful.
215    const DILocalVariable *DIVar =
216        Entries.front().getInstr()->getDebugVariable();
217    if (DIVar->isParameter() &&
218        getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
219      if (!IsDescribedByReg(Entries.front().getInstr()))
220        LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
221      if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {
222        // Mark all non-overlapping initial fragments.
223        for (auto I = Entries.begin(); I != Entries.end(); ++I) {
224          if (!I->isDbgValue())
225            continue;
226          const DIExpression *Fragment = I->getInstr()->getDebugExpression();
227          if (std::any_of(Entries.begin(), I,
228                          [&](DbgValueHistoryMap::Entry Pred) {
229                            return Pred.isDbgValue() &&
230                                   Fragment->fragmentsOverlap(
231                                       Pred.getInstr()->getDebugExpression());
232                          }))
233            break;
234          // The code that generates location lists for DWARF assumes that the
235          // entries' start labels are monotonically increasing, and since we
236          // don't change the label for fragments that are described by
237          // registers, we must bail out when encountering such a fragment.
238          if (IsDescribedByReg(I->getInstr()))
239            break;
240          LabelsBeforeInsn[I->getInstr()] = Asm->getFunctionBegin();
241        }
242      }
243    }
244
245    for (const auto &Entry : Entries) {
246      if (Entry.isDbgValue())
247        requestLabelBeforeInsn(Entry.getInstr());
248      else
249        requestLabelAfterInsn(Entry.getInstr());
250    }
251  }
252
253  // Ensure there is a symbol before DBG_LABEL.
254  for (const auto &I : DbgLabels) {
255    const MachineInstr *MI = I.second;
256    requestLabelBeforeInsn(MI);
257  }
258
259  PrevInstLoc = DebugLoc();
260  PrevLabel = Asm->getFunctionBegin();
261  beginFunctionImpl(MF);
262}
263
264void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
265  if (!MMI->hasDebugInfo())
266    return;
267
268  assert(CurMI == nullptr);
269  CurMI = MI;
270
271  // Insert labels where requested.
272  DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
273      LabelsBeforeInsn.find(MI);
274
275  // No label needed.
276  if (I == LabelsBeforeInsn.end())
277    return;
278
279  // Label already assigned.
280  if (I->second)
281    return;
282
283  if (!PrevLabel) {
284    PrevLabel = MMI->getContext().createTempSymbol();
285    Asm->OutStreamer->emitLabel(PrevLabel);
286  }
287  I->second = PrevLabel;
288}
289
290void DebugHandlerBase::endInstruction() {
291  if (!MMI->hasDebugInfo())
292    return;
293
294  assert(CurMI != nullptr);
295  // Don't create a new label after DBG_VALUE and other instructions that don't
296  // generate code.
297  if (!CurMI->isMetaInstruction()) {
298    PrevLabel = nullptr;
299    PrevInstBB = CurMI->getParent();
300  }
301
302  DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
303      LabelsAfterInsn.find(CurMI);
304  CurMI = nullptr;
305
306  // No label needed.
307  if (I == LabelsAfterInsn.end())
308    return;
309
310  // Label already assigned.
311  if (I->second)
312    return;
313
314  // We need a label after this instruction.
315  if (!PrevLabel) {
316    PrevLabel = MMI->getContext().createTempSymbol();
317    Asm->OutStreamer->emitLabel(PrevLabel);
318  }
319  I->second = PrevLabel;
320}
321
322void DebugHandlerBase::endFunction(const MachineFunction *MF) {
323  if (hasDebugInfo(MMI, MF))
324    endFunctionImpl(MF);
325  DbgValues.clear();
326  DbgLabels.clear();
327  LabelsBeforeInsn.clear();
328  LabelsAfterInsn.clear();
329}
330
331void DebugHandlerBase::beginBasicBlock(const MachineBasicBlock &MBB) {
332  if (!MBB.isBeginSection())
333    return;
334
335  PrevLabel = MBB.getSymbol();
336}
337
338void DebugHandlerBase::endBasicBlock(const MachineBasicBlock &MBB) {
339  if (!MBB.isEndSection())
340    return;
341
342  PrevLabel = nullptr;
343}
344