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 #define DEBUG_TYPE "dwarfdebug"
29 
30 Optional<DbgVariableLocation>
31 DbgVariableLocation::extractFromMachineInstruction(
32     const MachineInstr &Instruction) {
33   DbgVariableLocation Location;
34   if (!Instruction.isDebugValue())
35     return None;
36   if (!Instruction.getOperand(0).isReg())
37     return None;
38   Location.Register = Instruction.getOperand(0).getReg();
39   Location.FragmentInfo.reset();
40   // We only handle expressions generated by DIExpression::appendOffset,
41   // which doesn't require a full stack machine.
42   int64_t Offset = 0;
43   const DIExpression *DIExpr = Instruction.getDebugExpression();
44   auto Op = DIExpr->expr_op_begin();
45   while (Op != DIExpr->expr_op_end()) {
46     switch (Op->getOp()) {
47     case dwarf::DW_OP_constu: {
48       int Value = Op->getArg(0);
49       ++Op;
50       if (Op != DIExpr->expr_op_end()) {
51         switch (Op->getOp()) {
52         case dwarf::DW_OP_minus:
53           Offset -= Value;
54           break;
55         case dwarf::DW_OP_plus:
56           Offset += Value;
57           break;
58         default:
59           continue;
60         }
61       }
62     } break;
63     case dwarf::DW_OP_plus_uconst:
64       Offset += Op->getArg(0);
65       break;
66     case dwarf::DW_OP_LLVM_fragment:
67       Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
68       break;
69     case dwarf::DW_OP_deref:
70       Location.LoadChain.push_back(Offset);
71       Offset = 0;
72       break;
73     default:
74       return None;
75     }
76     ++Op;
77   }
78 
79   // Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
80   // instruction.
81   // FIXME: Replace these with DIExpression.
82   if (Instruction.isIndirectDebugValue())
83     Location.LoadChain.push_back(Offset);
84 
85   return Location;
86 }
87 
88 DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
89 
90 // Each LexicalScope has first instruction and last instruction to mark
91 // beginning and end of a scope respectively. Create an inverse map that list
92 // scopes starts (and ends) with an instruction. One instruction may start (or
93 // end) multiple scopes. Ignore scopes that are not reachable.
94 void DebugHandlerBase::identifyScopeMarkers() {
95   SmallVector<LexicalScope *, 4> WorkList;
96   WorkList.push_back(LScopes.getCurrentFunctionScope());
97   while (!WorkList.empty()) {
98     LexicalScope *S = WorkList.pop_back_val();
99 
100     const SmallVectorImpl<LexicalScope *> &Children = S->getChildren();
101     if (!Children.empty())
102       WorkList.append(Children.begin(), Children.end());
103 
104     if (S->isAbstractScope())
105       continue;
106 
107     for (const InsnRange &R : S->getRanges()) {
108       assert(R.first && "InsnRange does not have first instruction!");
109       assert(R.second && "InsnRange does not have second instruction!");
110       requestLabelBeforeInsn(R.first);
111       requestLabelAfterInsn(R.second);
112     }
113   }
114 }
115 
116 // Return Label preceding the instruction.
117 MCSymbol *DebugHandlerBase::getLabelBeforeInsn(const MachineInstr *MI) {
118   MCSymbol *Label = LabelsBeforeInsn.lookup(MI);
119   assert(Label && "Didn't insert label before instruction");
120   return Label;
121 }
122 
123 // Return Label immediately following the instruction.
124 MCSymbol *DebugHandlerBase::getLabelAfterInsn(const MachineInstr *MI) {
125   return LabelsAfterInsn.lookup(MI);
126 }
127 
128 /// If this type is derived from a base type then return base type size.
129 uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
130   DIType *Ty = TyRef.resolve();
131   assert(Ty);
132   DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
133   if (!DDTy)
134     return Ty->getSizeInBits();
135 
136   unsigned Tag = DDTy->getTag();
137 
138   if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
139       Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
140       Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type)
141     return DDTy->getSizeInBits();
142 
143   DIType *BaseType = DDTy->getBaseType().resolve();
144 
145   if (!BaseType)
146     return 0;
147 
148   // If this is a derived type, go ahead and get the base type, unless it's a
149   // reference then it's just the size of the field. Pointer types have no need
150   // of this since they're a different type of qualification on the type.
151   if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
152       BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
153     return Ty->getSizeInBits();
154 
155   return getBaseTypeSize(BaseType);
156 }
157 
158 static bool hasDebugInfo(const MachineModuleInfo *MMI,
159                          const MachineFunction *MF) {
160   if (!MMI->hasDebugInfo())
161     return false;
162   auto *SP = MF->getFunction().getSubprogram();
163   if (!SP)
164     return false;
165   assert(SP->getUnit());
166   auto EK = SP->getUnit()->getEmissionKind();
167   if (EK == DICompileUnit::NoDebug)
168     return false;
169   return true;
170 }
171 
172 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
173   PrevInstBB = nullptr;
174 
175   if (!Asm || !hasDebugInfo(MMI, MF)) {
176     skippedNonDebugFunction();
177     return;
178   }
179 
180   // Grab the lexical scopes for the function, if we don't have any of those
181   // then we're not going to be able to do anything.
182   LScopes.initialize(*MF);
183   if (LScopes.empty()) {
184     beginFunctionImpl(MF);
185     return;
186   }
187 
188   // Make sure that each lexical scope will have a begin/end label.
189   identifyScopeMarkers();
190 
191   // Calculate history for local variables.
192   assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
193   assert(DbgLabels.empty() && "DbgLabels map wasn't cleaned!");
194   calculateDbgEntityHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
195                             DbgValues, DbgLabels);
196   LLVM_DEBUG(DbgValues.dump());
197 
198   // Request labels for the full history.
199   for (const auto &I : DbgValues) {
200     const auto &Ranges = I.second;
201     if (Ranges.empty())
202       continue;
203 
204     // The first mention of a function argument gets the CurrentFnBegin
205     // label, so arguments are visible when breaking at function entry.
206     const DILocalVariable *DIVar = Ranges.front().first->getDebugVariable();
207     if (DIVar->isParameter() &&
208         getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
209       LabelsBeforeInsn[Ranges.front().first] = Asm->getFunctionBegin();
210       if (Ranges.front().first->getDebugExpression()->isFragment()) {
211         // Mark all non-overlapping initial fragments.
212         for (auto I = Ranges.begin(); I != Ranges.end(); ++I) {
213           const DIExpression *Fragment = I->first->getDebugExpression();
214           if (std::all_of(Ranges.begin(), I,
215                           [&](DbgValueHistoryMap::InstrRange Pred) {
216                             return !Fragment->fragmentsOverlap(
217                                 Pred.first->getDebugExpression());
218                           }))
219             LabelsBeforeInsn[I->first] = Asm->getFunctionBegin();
220           else
221             break;
222         }
223       }
224     }
225 
226     for (const auto &Range : Ranges) {
227       requestLabelBeforeInsn(Range.first);
228       if (Range.second)
229         requestLabelAfterInsn(Range.second);
230     }
231   }
232 
233   // Ensure there is a symbol before DBG_LABEL.
234   for (const auto &I : DbgLabels) {
235     const MachineInstr *MI = I.second;
236     requestLabelBeforeInsn(MI);
237   }
238 
239   PrevInstLoc = DebugLoc();
240   PrevLabel = Asm->getFunctionBegin();
241   beginFunctionImpl(MF);
242 }
243 
244 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
245   if (!MMI->hasDebugInfo())
246     return;
247 
248   assert(CurMI == nullptr);
249   CurMI = MI;
250 
251   // Insert labels where requested.
252   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
253       LabelsBeforeInsn.find(MI);
254 
255   // No label needed.
256   if (I == LabelsBeforeInsn.end())
257     return;
258 
259   // Label already assigned.
260   if (I->second)
261     return;
262 
263   if (!PrevLabel) {
264     PrevLabel = MMI->getContext().createTempSymbol();
265     Asm->OutStreamer->EmitLabel(PrevLabel);
266   }
267   I->second = PrevLabel;
268 }
269 
270 void DebugHandlerBase::endInstruction() {
271   if (!MMI->hasDebugInfo())
272     return;
273 
274   assert(CurMI != nullptr);
275   // Don't create a new label after DBG_VALUE and other instructions that don't
276   // generate code.
277   if (!CurMI->isMetaInstruction()) {
278     PrevLabel = nullptr;
279     PrevInstBB = CurMI->getParent();
280   }
281 
282   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
283       LabelsAfterInsn.find(CurMI);
284   CurMI = nullptr;
285 
286   // No label needed.
287   if (I == LabelsAfterInsn.end())
288     return;
289 
290   // Label already assigned.
291   if (I->second)
292     return;
293 
294   // We need a label after this instruction.
295   if (!PrevLabel) {
296     PrevLabel = MMI->getContext().createTempSymbol();
297     Asm->OutStreamer->EmitLabel(PrevLabel);
298   }
299   I->second = PrevLabel;
300 }
301 
302 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
303   if (hasDebugInfo(MMI, MF))
304     endFunctionImpl(MF);
305   DbgValues.clear();
306   DbgLabels.clear();
307   LabelsBeforeInsn.clear();
308   LabelsAfterInsn.clear();
309 }
310