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   assert(BaseType && "Unexpected invalid base type");
167 
168   // If this is a derived type, go ahead and get the base type, unless it's a
169   // reference then it's just the size of the field. Pointer types have no need
170   // of this since they're a different type of qualification on the type.
171   if (BaseType->getTag() == dwarf::DW_TAG_reference_type ||
172       BaseType->getTag() == dwarf::DW_TAG_rvalue_reference_type)
173     return Ty->getSizeInBits();
174 
175   return getBaseTypeSize(BaseType);
176 }
177 
178 static bool hasDebugInfo(const MachineModuleInfo *MMI,
179                          const MachineFunction *MF) {
180   if (!MMI->hasDebugInfo())
181     return false;
182   auto *SP = MF->getFunction().getSubprogram();
183   if (!SP)
184     return false;
185   assert(SP->getUnit());
186   auto EK = SP->getUnit()->getEmissionKind();
187   if (EK == DICompileUnit::NoDebug)
188     return false;
189   return true;
190 }
191 
192 void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
193   PrevInstBB = nullptr;
194 
195   if (!Asm || !hasDebugInfo(MMI, MF)) {
196     skippedNonDebugFunction();
197     return;
198   }
199 
200   // Grab the lexical scopes for the function, if we don't have any of those
201   // then we're not going to be able to do anything.
202   LScopes.initialize(*MF);
203   if (LScopes.empty()) {
204     beginFunctionImpl(MF);
205     return;
206   }
207 
208   // Make sure that each lexical scope will have a begin/end label.
209   identifyScopeMarkers();
210 
211   // Calculate history for local variables.
212   assert(DbgValues.empty() && "DbgValues map wasn't cleaned!");
213   calculateDbgValueHistory(MF, Asm->MF->getSubtarget().getRegisterInfo(),
214                            DbgValues);
215 
216   // Request labels for the full history.
217   for (const auto &I : DbgValues) {
218     const auto &Ranges = I.second;
219     if (Ranges.empty())
220       continue;
221 
222     // The first mention of a function argument gets the CurrentFnBegin
223     // label, so arguments are visible when breaking at function entry.
224     const DILocalVariable *DIVar = Ranges.front().first->getDebugVariable();
225     if (DIVar->isParameter() &&
226         getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
227       LabelsBeforeInsn[Ranges.front().first] = Asm->getFunctionBegin();
228       if (Ranges.front().first->getDebugExpression()->isFragment()) {
229         // Mark all non-overlapping initial fragments.
230         for (auto I = Ranges.begin(); I != Ranges.end(); ++I) {
231           const DIExpression *Fragment = I->first->getDebugExpression();
232           if (std::all_of(Ranges.begin(), I,
233                           [&](DbgValueHistoryMap::InstrRange Pred) {
234                             return !fragmentsOverlap(
235                                 Fragment, Pred.first->getDebugExpression());
236                           }))
237             LabelsBeforeInsn[I->first] = Asm->getFunctionBegin();
238           else
239             break;
240         }
241       }
242     }
243 
244     for (const auto &Range : Ranges) {
245       requestLabelBeforeInsn(Range.first);
246       if (Range.second)
247         requestLabelAfterInsn(Range.second);
248     }
249   }
250 
251   PrevInstLoc = DebugLoc();
252   PrevLabel = Asm->getFunctionBegin();
253   beginFunctionImpl(MF);
254 }
255 
256 void DebugHandlerBase::beginInstruction(const MachineInstr *MI) {
257   if (!MMI->hasDebugInfo())
258     return;
259 
260   assert(CurMI == nullptr);
261   CurMI = MI;
262 
263   // Insert labels where requested.
264   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
265       LabelsBeforeInsn.find(MI);
266 
267   // No label needed.
268   if (I == LabelsBeforeInsn.end())
269     return;
270 
271   // Label already assigned.
272   if (I->second)
273     return;
274 
275   if (!PrevLabel) {
276     PrevLabel = MMI->getContext().createTempSymbol();
277     Asm->OutStreamer->EmitLabel(PrevLabel);
278   }
279   I->second = PrevLabel;
280 }
281 
282 void DebugHandlerBase::endInstruction() {
283   if (!MMI->hasDebugInfo())
284     return;
285 
286   assert(CurMI != nullptr);
287   // Don't create a new label after DBG_VALUE and other instructions that don't
288   // generate code.
289   if (!CurMI->isMetaInstruction()) {
290     PrevLabel = nullptr;
291     PrevInstBB = CurMI->getParent();
292   }
293 
294   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
295       LabelsAfterInsn.find(CurMI);
296   CurMI = nullptr;
297 
298   // No label needed.
299   if (I == LabelsAfterInsn.end())
300     return;
301 
302   // Label already assigned.
303   if (I->second)
304     return;
305 
306   // We need a label after this instruction.
307   if (!PrevLabel) {
308     PrevLabel = MMI->getContext().createTempSymbol();
309     Asm->OutStreamer->EmitLabel(PrevLabel);
310   }
311   I->second = PrevLabel;
312 }
313 
314 void DebugHandlerBase::endFunction(const MachineFunction *MF) {
315   if (hasDebugInfo(MMI, MF))
316     endFunctionImpl(MF);
317   DbgValues.clear();
318   LabelsBeforeInsn.clear();
319   LabelsAfterInsn.clear();
320 }
321