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 int DebugHandlerBase::fragmentCmp(const DIExpression *P1,
127                                   const DIExpression *P2) {
128   auto Fragment1 = *P1->getFragmentInfo();
129   auto Fragment2 = *P2->getFragmentInfo();
130   unsigned l1 = Fragment1.OffsetInBits;
131   unsigned l2 = Fragment2.OffsetInBits;
132   unsigned r1 = l1 + Fragment1.SizeInBits;
133   unsigned r2 = l2 + Fragment2.SizeInBits;
134   if (r1 <= l2)
135     return -1;
136   else if (r2 <= l1)
137     return 1;
138   else
139     return 0;
140 }
141 
142 bool DebugHandlerBase::fragmentsOverlap(const DIExpression *P1,
143                                         const DIExpression *P2) {
144   if (!P1->isFragment() || !P2->isFragment())
145     return true;
146   return fragmentCmp(P1, P2) == 0;
147 }
148 
149 /// If this type is derived from a base type then return base type size.
150 uint64_t DebugHandlerBase::getBaseTypeSize(const DITypeRef TyRef) {
151   DIType *Ty = TyRef.resolve();
152   assert(Ty);
153   DIDerivedType *DDTy = dyn_cast<DIDerivedType>(Ty);
154   if (!DDTy)
155     return Ty->getSizeInBits();
156 
157   unsigned Tag = DDTy->getTag();
158 
159   if (Tag != dwarf::DW_TAG_member && Tag != dwarf::DW_TAG_typedef &&
160       Tag != dwarf::DW_TAG_const_type && Tag != dwarf::DW_TAG_volatile_type &&
161       Tag != dwarf::DW_TAG_restrict_type && Tag != dwarf::DW_TAG_atomic_type)
162     return DDTy->getSizeInBits();
163 
164   DIType *BaseType = DDTy->getBaseType().resolve();
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 static bool hasDebugInfo(const MachineModuleInfo *MMI,
180                          const MachineFunction *MF) {
181   if (!MMI->hasDebugInfo())
182     return false;
183   auto *SP = MF->getFunction().getSubprogram();
184   if (!SP)
185     return false;
186   assert(SP->getUnit());
187   auto EK = SP->getUnit()->getEmissionKind();
188   if (EK == DICompileUnit::NoDebug)
189     return false;
190   return true;
191 }
192 
193 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
194   PrevInstBB = nullptr;
195 
196   if (!Asm || !hasDebugInfo(MMI, MF)) {
197     skippedNonDebugFunction();
198     return;
199   }
200 
201   // Grab the lexical scopes for the function, if we don't have any of those
202   // then we're not going to be able to do anything.
203   LScopes.initialize(*MF);
204   if (LScopes.empty()) {
205     beginFunctionImpl(MF);
206     return;
207   }
208 
209   // Make sure that each lexical scope will have a begin/end label.
210   identifyScopeMarkers();
211 
212   // Calculate history for local variables.
213   assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
214   calculateDbgValueHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
215                            DbgValues);
216 
217   // Request labels for the full history.
218   for (const auto &I : DbgValues) {
219     const auto &Ranges = I.second;
220     if (Ranges.empty())
221       continue;
222 
223     // The first mention of a function argument gets the CurrentFnBegin
224     // label, so arguments are visible when breaking at function entry.
225     const DILocalVariable *DIVar = Ranges.front().first->getDebugVariable();
226     if (DIVar->isParameter() &&
227         getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
228       LabelsBeforeInsn[Ranges.front().first] = Asm->getFunctionBegin();
229       if (Ranges.front().first->getDebugExpression()->isFragment()) {
230         // Mark all non-overlapping initial fragments.
231         for (auto I = Ranges.begin(); I != Ranges.end(); ++I) {
232           const DIExpression *Fragment = I->first->getDebugExpression();
233           if (std::all_of(Ranges.begin(), I,
234                           [&](DbgValueHistoryMap::InstrRange Pred) {
235                             return !fragmentsOverlap(
236                                 Fragment, Pred.first->getDebugExpression());
237                           }))
238             LabelsBeforeInsn[I->first] = Asm->getFunctionBegin();
239           else
240             break;
241         }
242       }
243     }
244 
245     for (const auto &Range : Ranges) {
246       requestLabelBeforeInsn(Range.first);
247       if (Range.second)
248         requestLabelAfterInsn(Range.second);
249     }
250   }
251 
252   PrevInstLoc = DebugLoc();
253   PrevLabel = Asm->getFunctionBegin();
254   beginFunctionImpl(MF);
255 }
256 
257 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
258   if (!MMI->hasDebugInfo())
259     return;
260 
261   assert(CurMI == nullptr);
262   CurMI = MI;
263 
264   // Insert labels where requested.
265   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
266       LabelsBeforeInsn.find(MI);
267 
268   // No label needed.
269   if (I == LabelsBeforeInsn.end())
270     return;
271 
272   // Label already assigned.
273   if (I->second)
274     return;
275 
276   if (!PrevLabel) {
277     PrevLabel = MMI->getContext().createTempSymbol();
278     Asm->OutStreamer->EmitLabel(PrevLabel);
279   }
280   I->second = PrevLabel;
281 }
282 
283 void DebugHandlerBase::endInstruction() {
284   if (!MMI->hasDebugInfo())
285     return;
286 
287   assert(CurMI != nullptr);
288   // Don't create a new label after DBG_VALUE and other instructions that don't
289   // generate code.
290   if (!CurMI->isMetaInstruction()) {
291     PrevLabel = nullptr;
292     PrevInstBB = CurMI->getParent();
293   }
294 
295   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
296       LabelsAfterInsn.find(CurMI);
297   CurMI = nullptr;
298 
299   // No label needed.
300   if (I == LabelsAfterInsn.end())
301     return;
302 
303   // Label already assigned.
304   if (I->second)
305     return;
306 
307   // We need a label after this instruction.
308   if (!PrevLabel) {
309     PrevLabel = MMI->getContext().createTempSymbol();
310     Asm->OutStreamer->EmitLabel(PrevLabel);
311   }
312   I->second = PrevLabel;
313 }
314 
315 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
316   if (hasDebugInfo(MMI, MF))
317     endFunctionImpl(MF);
318   DbgValues.clear();
319   LabelsBeforeInsn.clear();
320   LabelsAfterInsn.clear();
321 }
322