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/CodeGen/AsmPrinter.h"
17 #include "llvm/CodeGen/MachineFunction.h"
18 #include "llvm/CodeGen/MachineInstr.h"
19 #include "llvm/CodeGen/MachineModuleInfo.h"
20 #include "llvm/IR/DebugInfo.h"
21 #include "llvm/MC/MCStreamer.h"
22 #include "llvm/Target/TargetSubtargetInfo.h"
23 
24 using namespace llvm;
25 
26 bool DbgVariableLocation::extractFromMachineInstruction(
27     DbgVariableLocation &Location, const MachineInstr &Instruction) {
28   if (!Instruction.isDebugValue())
29     return false;
30   if (!Instruction.getOperand(0).isReg())
31     return false;
32   Location.Register = Instruction.getOperand(0).getReg();
33   Location.InMemory = Instruction.getOperand(1).isImm();
34   Location.Deref = false;
35   Location.FragmentInfo.reset();
36   // We only handle expressions generated by DIExpression::appendOffset,
37   // which doesn't require a full stack machine.
38   int64_t Offset = 0;
39   const DIExpression *DIExpr = Instruction.getDebugExpression();
40   auto Op = DIExpr->expr_op_begin();
41   while (Op != DIExpr->expr_op_end()) {
42     switch (Op->getOp()) {
43     case dwarf::DW_OP_constu: {
44       int Value = Op->getArg(0);
45       ++Op;
46       if (Op != DIExpr->expr_op_end()) {
47         switch (Op->getOp()) {
48         case dwarf::DW_OP_minus:
49           Offset -= Value;
50           break;
51         case dwarf::DW_OP_plus:
52           Offset += Value;
53           break;
54         default:
55           continue;
56         }
57       }
58     } break;
59     case dwarf::DW_OP_plus_uconst:
60       Offset += Op->getArg(0);
61       break;
62     case dwarf::DW_OP_LLVM_fragment:
63       Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
64       break;
65     case dwarf::DW_OP_deref:
66       Location.Deref = true;
67       break;
68     default:
69       return false;
70     }
71     ++Op;
72   }
73 
74   Location.Offset = Offset;
75   return true;
76 }
77 
78 DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
79 
80 // Each LexicalScope has first instruction and last instruction to mark
81 // beginning and end of a scope respectively. Create an inverse map that list
82 // scopes starts (and ends) with an instruction. One instruction may start (or
83 // end) multiple scopes. Ignore scopes that are not reachable.
84 void DebugHandlerBase::identifyScopeMarkers() {
85   SmallVector<LexicalScope *, 4> WorkList;
86   WorkList.push_back(LScopes.getCurrentFunctionScope());
87   while (!WorkList.empty()) {
88     LexicalScope *S = WorkList.pop_back_val();
89 
90     const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
91     if (!Children.empty())
92       WorkList.append(Children.begin(), Children.end());
93 
94     if (S->isAbstractScope())
95       continue;
96 
97     for (const InsnRange &R : S->getRanges()) {
98       assert(R.first && "InsnRange does not have first instruction!");
99       assert(R.second && "InsnRange does not have second instruction!");
100       requestLabelBeforeInsn(R.first);
101       requestLabelAfterInsn(R.second);
102     }
103   }
104 }
105 
106 // Return Label preceding the instruction.
107 MCSymbol *DebugHandlerBase::getLabelBeforeInsn(const MachineInstr *MI) {
108   MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
109   assert(Label && "Didn't insert label before instruction");
110   return Label;
111 }
112 
113 // Return Label immediately following the instruction.
114 MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
115   return LabelsAfterInsn.lookup(MI);
116 }
117 
118 int DebugHandlerBase::fragmentCmp(const DIExpression *P1,
119                                   const DIExpression *P2) {
120   auto Fragment1 = *P1->getFragmentInfo();
121   auto Fragment2 = *P2->getFragmentInfo();
122   unsigned l1 = Fragment1.OffsetInBits;
123   unsigned l2 = Fragment2.OffsetInBits;
124   unsigned r1 = l1 + Fragment1.SizeInBits;
125   unsigned r2 = l2 + Fragment2.SizeInBits;
126   if (r1 <= l2)
127     return -1;
128   else if (r2 <= l1)
129     return 1;
130   else
131     return 0;
132 }
133 
134 bool DebugHandlerBase::fragmentsOverlap(const DIExpression *P1,
135                                         const DIExpression *P2) {
136   if (!P1->isFragment() || !P2->isFragment())
137     return true;
138   return fragmentCmp(P1, P2) == 0;
139 }
140 
141 /// If this type is derived from a base type then return base type size.
142 uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
143   DIType *Ty = TyRef.resolve();
144   assert(Ty);
145   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().resolve();
157 
158   assert(BaseType && "Unexpected invalid base type");
159 
160   // If this is a derived type, go ahead and get the base type, unless it's a
161   // reference then it's just the size of the field. Pointer types have no need
162   // of this since they're a different type of qualification on the type.
163   if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
164       BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
165     return Ty->getSizeInBits();
166 
167   return getBaseTypeSize(BaseType);
168 }
169 
170 static bool hasDebugInfo(const MachineModuleInfo *MMI,
171                          const MachineFunction *MF) {
172   if (!MMI->hasDebugInfo())
173     return false;
174   auto *SP = MF->getFunction()->getSubprogram();
175   if (!SP)
176     return false;
177   assert(SP->getUnit());
178   auto EK = SP->getUnit()->getEmissionKind();
179   if (EK == DICompileUnit::NoDebug)
180     return false;
181   return true;
182 }
183 
184 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
185   PrevInstBB = nullptr;
186 
187   if (!Asm || !hasDebugInfo(MMI, MF)) {
188     skippedNonDebugFunction();
189     return;
190   }
191 
192   // Grab the lexical scopes for the function, if we don't have any of those
193   // then we're not going to be able to do anything.
194   LScopes.initialize(*MF);
195   if (LScopes.empty()) {
196     beginFunctionImpl(MF);
197     return;
198   }
199 
200   // Make sure that each lexical scope will have a begin/end label.
201   identifyScopeMarkers();
202 
203   // Calculate history for local variables.
204   assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
205   calculateDbgValueHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
206                            DbgValues);
207 
208   // Request labels for the full history.
209   for (const auto &I : DbgValues) {
210     const auto &Ranges = I.second;
211     if (Ranges.empty())
212       continue;
213 
214     // The first mention of a function argument gets the CurrentFnBegin
215     // label, so arguments are visible when breaking at function entry.
216     const DILocalVariable *DIVar = Ranges.front().first->getDebugVariable();
217     if (DIVar->isParameter() &&
218         getDISubprogram(DIVar->getScope())->describes(MF->getFunction())) {
219       LabelsBeforeInsn[Ranges.front().first] = Asm->getFunctionBegin();
220       if (Ranges.front().first->getDebugExpression()->isFragment()) {
221         // Mark all non-overlapping initial fragments.
222         for (auto I = Ranges.begin(); I != Ranges.end(); ++I) {
223           const DIExpression *Fragment = I->first->getDebugExpression();
224           if (std::all_of(Ranges.begin(), I,
225                           [&](DbgValueHistoryMap::InstrRange Pred) {
226                             return !fragmentsOverlap(
227                                 Fragment, Pred.first->getDebugExpression());
228                           }))
229             LabelsBeforeInsn[I->first] = Asm->getFunctionBegin();
230           else
231             break;
232         }
233       }
234     }
235 
236     for (const auto &Range : Ranges) {
237       requestLabelBeforeInsn(Range.first);
238       if (Range.second)
239         requestLabelAfterInsn(Range.second);
240     }
241   }
242 
243   PrevInstLoc = DebugLoc();
244   PrevLabel = Asm->getFunctionBegin();
245   beginFunctionImpl(MF);
246 }
247 
248 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
249   if (!MMI->hasDebugInfo())
250     return;
251 
252   assert(CurMI == nullptr);
253   CurMI = MI;
254 
255   // Insert labels where requested.
256   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
257       LabelsBeforeInsn.find(MI);
258 
259   // No label needed.
260   if (I == LabelsBeforeInsn.end())
261     return;
262 
263   // Label already assigned.
264   if (I->second)
265     return;
266 
267   if (!PrevLabel) {
268     PrevLabel = MMI->getContext().createTempSymbol();
269     Asm->OutStreamer->EmitLabel(PrevLabel);
270   }
271   I->second = PrevLabel;
272 }
273 
274 void DebugHandlerBase::endInstruction() {
275   if (!MMI->hasDebugInfo())
276     return;
277 
278   assert(CurMI != nullptr);
279   // Don't create a new label after DBG_VALUE and other instructions that don't
280   // generate code.
281   if (!CurMI->isMetaInstruction()) {
282     PrevLabel = nullptr;
283     PrevInstBB = CurMI->getParent();
284   }
285 
286   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
287       LabelsAfterInsn.find(CurMI);
288   CurMI = nullptr;
289 
290   // No label needed.
291   if (I == LabelsAfterInsn.end())
292     return;
293 
294   // Label already assigned.
295   if (I->second)
296     return;
297 
298   // We need a label after this instruction.
299   if (!PrevLabel) {
300     PrevLabel = MMI->getContext().createTempSymbol();
301     Asm->OutStreamer->EmitLabel(PrevLabel);
302   }
303   I->second = PrevLabel;
304 }
305 
306 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
307   if (hasDebugInfo(MMI, MF))
308     endFunctionImpl(MF);
309   DbgValues.clear();
310   LabelsBeforeInsn.clear();
311   LabelsAfterInsn.clear();
312 }
313