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 Optional<DbgVariableLocation>
29 DbgVariableLocation::extractFromMachineInstruction(
30     const MachineInstr &Instruction) {
31   DbgVariableLocation Location;
32   if (!Instruction.isDebugValue())
33     return None;
34   if (!Instruction.getOperand(0).isReg())
35     return None;
36   Location.Register = Instruction.getOperand(0).getReg();
37   Location.FragmentInfo.reset();
38   // We only handle expressions generated by DIExpression::appendOffset,
39   // which doesn't require a full stack machine.
40   int64_t Offset = 0;
41   const DIExpression *DIExpr = Instruction.getDebugExpression();
42   auto Op = DIExpr->expr_op_begin();
43   while (Op != DIExpr->expr_op_end()) {
44     switch (Op->getOp()) {
45     case dwarf::DW_OP_constu: {
46       int Value = Op->getArg(0);
47       ++Op;
48       if (Op != DIExpr->expr_op_end()) {
49         switch (Op->getOp()) {
50         case dwarf::DW_OP_minus:
51           Offset -= Value;
52           break;
53         case dwarf::DW_OP_plus:
54           Offset += Value;
55           break;
56         default:
57           continue;
58         }
59       }
60     } break;
61     case dwarf::DW_OP_plus_uconst:
62       Offset += Op->getArg(0);
63       break;
64     case dwarf::DW_OP_LLVM_fragment:
65       Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
66       break;
67     case dwarf::DW_OP_deref:
68       Location.LoadChain.push_back(Offset);
69       Offset = 0;
70       break;
71     default:
72       return None;
73     }
74     ++Op;
75   }
76 
77   // Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
78   // instruction.
79   // FIXME: Replace these with DIExpression.
80   if (Instruction.isIndirectDebugValue())
81     Location.LoadChain.push_back(Offset);
82 
83   return Location;
84 }
85 
86 DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
87 
88 // Each LexicalScope has first instruction and last instruction to mark
89 // beginning and end of a scope respectively. Create an inverse map that list
90 // scopes starts (and ends) with an instruction. One instruction may start (or
91 // end) multiple scopes. Ignore scopes that are not reachable.
92 void DebugHandlerBase::identifyScopeMarkers() {
93   SmallVector<LexicalScope *, 4> WorkList;
94   WorkList.push_back(LScopes.getCurrentFunctionScope());
95   while (!WorkList.empty()) {
96     LexicalScope *S = WorkList.pop_back_val();
97 
98     const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
99     if (!Children.empty())
100       WorkList.append(Children.begin(), Children.end());
101 
102     if (S->isAbstractScope())
103       continue;
104 
105     for (const InsnRange &R : S->getRanges()) {
106       assert(R.first && "InsnRange does not have first instruction!");
107       assert(R.second && "InsnRange does not have second instruction!");
108       requestLabelBeforeInsn(R.first);
109       requestLabelAfterInsn(R.second);
110     }
111   }
112 }
113 
114 // Return Label preceding the instruction.
115 MCSymbol *DebugHandlerBase::getLabelBeforeInsn(const MachineInstr *MI) {
116   MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
117   assert(Label && "Didn't insert label before instruction");
118   return Label;
119 }
120 
121 // Return Label immediately following the instruction.
122 MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
123   return LabelsAfterInsn.lookup(MI);
124 }
125 
126 /// If this type is derived from a base type then return base type size.
127 uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
128   DIType *Ty = TyRef.resolve();
129   assert(Ty);
130   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().resolve();
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 
156 static 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 
170 void 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   calculateDbgValueHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
192                            DbgValues);
193 
194   // Request labels for the full history.
195   for (const auto &I : DbgValues) {
196     const auto &Ranges = I.second;
197     if (Ranges.empty())
198       continue;
199 
200     // The first mention of a function argument gets the CurrentFnBegin
201     // label, so arguments are visible when breaking at function entry.
202     const DILocalVariable *DIVar = Ranges.front().first->getDebugVariable();
203     if (DIVar->isParameter() &&
204         getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
205       LabelsBeforeInsn[Ranges.front().first] = Asm->getFunctionBegin();
206       if (Ranges.front().first->getDebugExpression()->isFragment()) {
207         // Mark all non-overlapping initial fragments.
208         for (auto I = Ranges.begin(); I != Ranges.end(); ++I) {
209           const DIExpression *Fragment = I->first->getDebugExpression();
210           if (std::all_of(Ranges.begin(), I,
211                           [&](DbgValueHistoryMap::InstrRange Pred) {
212                             return !Fragment->fragmentsOverlap(
213                                 Pred.first->getDebugExpression());
214                           }))
215             LabelsBeforeInsn[I->first] = Asm->getFunctionBegin();
216           else
217             break;
218         }
219       }
220     }
221 
222     for (const auto &Range : Ranges) {
223       requestLabelBeforeInsn(Range.first);
224       if (Range.second)
225         requestLabelAfterInsn(Range.second);
226     }
227   }
228 
229   PrevInstLoc = DebugLoc();
230   PrevLabel = Asm->getFunctionBegin();
231   beginFunctionImpl(MF);
232 }
233 
234 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
235   if (!MMI->hasDebugInfo())
236     return;
237 
238   assert(CurMI == nullptr);
239   CurMI = MI;
240 
241   // Insert labels where requested.
242   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
243       LabelsBeforeInsn.find(MI);
244 
245   // No label needed.
246   if (I == LabelsBeforeInsn.end())
247     return;
248 
249   // Label already assigned.
250   if (I->second)
251     return;
252 
253   if (!PrevLabel) {
254     PrevLabel = MMI->getContext().createTempSymbol();
255     Asm->OutStreamer->EmitLabel(PrevLabel);
256   }
257   I->second = PrevLabel;
258 }
259 
260 void DebugHandlerBase::endInstruction() {
261   if (!MMI->hasDebugInfo())
262     return;
263 
264   assert(CurMI != nullptr);
265   // Don't create a new label after DBG_VALUE and other instructions that don't
266   // generate code.
267   if (!CurMI->isMetaInstruction()) {
268     PrevLabel = nullptr;
269     PrevInstBB = CurMI->getParent();
270   }
271 
272   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
273       LabelsAfterInsn.find(CurMI);
274   CurMI = nullptr;
275 
276   // No label needed.
277   if (I == LabelsAfterInsn.end())
278     return;
279 
280   // Label already assigned.
281   if (I->second)
282     return;
283 
284   // We need a label after this instruction.
285   if (!PrevLabel) {
286     PrevLabel = MMI->getContext().createTempSymbol();
287     Asm->OutStreamer->EmitLabel(PrevLabel);
288   }
289   I->second = PrevLabel;
290 }
291 
292 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
293   if (hasDebugInfo(MMI, MF))
294     endFunctionImpl(MF);
295   DbgValues.clear();
296   LabelsBeforeInsn.clear();
297   LabelsAfterInsn.clear();
298 }
299