1 //===- LexicalScopes.cpp - Collecting lexical scope info ------------------===//
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 // This file implements LexicalScopes analysis.
11 //
12 // This pass collects lexical scope information and maps machine instructions
13 // to respective lexical scopes.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "llvm/CodeGen/LexicalScopes.h"
18 #include "llvm/CodeGen/MachineFunction.h"
19 #include "llvm/CodeGen/MachineInstr.h"
20 #include "llvm/IR/DebugInfo.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Support/ErrorHandling.h"
24 #include "llvm/Support/FormattedStream.h"
25 using namespace llvm;
26 
27 #define DEBUG_TYPE "lexicalscopes"
28 
29 /// reset - Reset the instance so that it's prepared for another function.
30 void LexicalScopes::reset() {
31   MF = nullptr;
32   CurrentFnLexicalScope = nullptr;
33   LexicalScopeMap.clear();
34   AbstractScopeMap.clear();
35   InlinedLexicalScopeMap.clear();
36   AbstractScopesList.clear();
37 }
38 
39 /// initialize - Scan machine function and constuct lexical scope nest.
40 void LexicalScopes::initialize(const MachineFunction &Fn) {
41   reset();
42   MF = &Fn;
43   SmallVector<InsnRange, 4> MIRanges;
44   DenseMap<const MachineInstr *, LexicalScope *> MI2ScopeMap;
45   extractLexicalScopes(MIRanges, MI2ScopeMap);
46   if (CurrentFnLexicalScope) {
47     constructScopeNest(CurrentFnLexicalScope);
48     assignInstructionRanges(MIRanges, MI2ScopeMap);
49   }
50 }
51 
52 /// extractLexicalScopes - Extract instruction ranges for each lexical scopes
53 /// for the given machine function.
54 void LexicalScopes::extractLexicalScopes(
55     SmallVectorImpl<InsnRange> &MIRanges,
56     DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
57 
58   // Scan each instruction and create scopes. First build working set of scopes.
59   for (const auto &MBB : *MF) {
60     const MachineInstr *RangeBeginMI = nullptr;
61     const MachineInstr *PrevMI = nullptr;
62     const DILocation *PrevDL = nullptr;
63     for (const auto &MInsn : MBB) {
64       // Check if instruction has valid location information.
65       const DILocation *MIDL = MInsn.getDebugLoc();
66       if (!MIDL) {
67         PrevMI = &MInsn;
68         continue;
69       }
70 
71       // If scope has not changed then skip this instruction.
72       if (MIDL == PrevDL) {
73         PrevMI = &MInsn;
74         continue;
75       }
76 
77       // Ignore DBG_VALUE. It does not contribute to any instruction in output.
78       if (MInsn.isDebugValue())
79         continue;
80 
81       if (RangeBeginMI) {
82         // If we have already seen a beginning of an instruction range and
83         // current instruction scope does not match scope of first instruction
84         // in this range then create a new instruction range.
85         InsnRange R(RangeBeginMI, PrevMI);
86         MI2ScopeMap[RangeBeginMI] = getOrCreateLexicalScope(PrevDL);
87         MIRanges.push_back(R);
88       }
89 
90       // This is a beginning of a new instruction range.
91       RangeBeginMI = &MInsn;
92 
93       // Reset previous markers.
94       PrevMI = &MInsn;
95       PrevDL = MIDL;
96     }
97 
98     // Create last instruction range.
99     if (RangeBeginMI && PrevMI && PrevDL) {
100       InsnRange R(RangeBeginMI, PrevMI);
101       MIRanges.push_back(R);
102       MI2ScopeMap[RangeBeginMI] = getOrCreateLexicalScope(PrevDL);
103     }
104   }
105 }
106 
107 /// findLexicalScope - Find lexical scope, either regular or inlined, for the
108 /// given DebugLoc. Return NULL if not found.
109 LexicalScope *LexicalScopes::findLexicalScope(const DILocation *DL) {
110   DILocalScope *Scope = DL->getScope();
111   if (!Scope)
112     return nullptr;
113 
114   // The scope that we were created with could have an extra file - which
115   // isn't what we care about in this case.
116   Scope = Scope->getNonLexicalBlockFileScope();
117 
118   if (auto *IA = DL->getInlinedAt()) {
119     auto I = InlinedLexicalScopeMap.find(std::make_pair(Scope, IA));
120     return I != InlinedLexicalScopeMap.end() ? &I->second : nullptr;
121   }
122   return findLexicalScope(Scope);
123 }
124 
125 /// getOrCreateLexicalScope - Find lexical scope for the given DebugLoc. If
126 /// not available then create new lexical scope.
127 LexicalScope *LexicalScopes::getOrCreateLexicalScope(const DILocalScope *Scope,
128                                                      const DILocation *IA) {
129   if (IA) {
130     // Create an abstract scope for inlined function.
131     getOrCreateAbstractScope(Scope);
132     // Create an inlined scope for inlined function.
133     return getOrCreateInlinedScope(Scope, IA);
134   }
135 
136   return getOrCreateRegularScope(Scope);
137 }
138 
139 /// getOrCreateRegularScope - Find or create a regular lexical scope.
140 LexicalScope *
141 LexicalScopes::getOrCreateRegularScope(const DILocalScope *Scope) {
142   assert(Scope && "Invalid Scope encoding!");
143   Scope = Scope->getNonLexicalBlockFileScope();
144 
145   auto I = LexicalScopeMap.find(Scope);
146   if (I != LexicalScopeMap.end())
147     return &I->second;
148 
149   // FIXME: Should the following dyn_cast be DILexicalBlock?
150   LexicalScope *Parent = nullptr;
151   if (auto *Block = dyn_cast<DILexicalBlockBase>(Scope))
152     Parent = getOrCreateLexicalScope(Block->getScope());
153   I = LexicalScopeMap.emplace(std::piecewise_construct,
154                               std::forward_as_tuple(Scope),
155                               std::forward_as_tuple(Parent, Scope, nullptr,
156                                                     false)).first;
157 
158   if (!Parent) {
159     assert(cast<DISubprogram>(Scope)->describes(MF->getFunction()));
160     assert(!CurrentFnLexicalScope);
161     CurrentFnLexicalScope = &I->second;
162   }
163 
164   return &I->second;
165 }
166 
167 /// getOrCreateInlinedScope - Find or create an inlined lexical scope.
168 LexicalScope *
169 LexicalScopes::getOrCreateInlinedScope(const DILocalScope *Scope,
170                                        const DILocation *InlinedAt) {
171   assert(Scope && "Invalid Scope encoding!");
172   Scope = Scope->getNonLexicalBlockFileScope();
173   std::pair<const DILocalScope *, const DILocation *> P(Scope, InlinedAt);
174   auto I = InlinedLexicalScopeMap.find(P);
175   if (I != InlinedLexicalScopeMap.end())
176     return &I->second;
177 
178   LexicalScope *Parent;
179   if (auto *Block = dyn_cast<DILexicalBlockBase>(Scope))
180     Parent = getOrCreateInlinedScope(Block->getScope(), InlinedAt);
181   else
182     Parent = getOrCreateLexicalScope(InlinedAt);
183 
184   I = InlinedLexicalScopeMap
185           .emplace(std::piecewise_construct, std::forward_as_tuple(P),
186                    std::forward_as_tuple(Parent, Scope, InlinedAt, false))
187           .first;
188   return &I->second;
189 }
190 
191 /// getOrCreateAbstractScope - Find or create an abstract lexical scope.
192 LexicalScope *
193 LexicalScopes::getOrCreateAbstractScope(const DILocalScope *Scope) {
194   assert(Scope && "Invalid Scope encoding!");
195   Scope = Scope->getNonLexicalBlockFileScope();
196   auto I = AbstractScopeMap.find(Scope);
197   if (I != AbstractScopeMap.end())
198     return &I->second;
199 
200   // FIXME: Should the following isa be DILexicalBlock?
201   LexicalScope *Parent = nullptr;
202   if (auto *Block = dyn_cast<DILexicalBlockBase>(Scope))
203     Parent = getOrCreateAbstractScope(Block->getScope());
204 
205   I = AbstractScopeMap.emplace(std::piecewise_construct,
206                                std::forward_as_tuple(Scope),
207                                std::forward_as_tuple(Parent, Scope,
208                                                      nullptr, true)).first;
209   if (isa<DISubprogram>(Scope))
210     AbstractScopesList.push_back(&I->second);
211   return &I->second;
212 }
213 
214 /// constructScopeNest
215 void LexicalScopes::constructScopeNest(LexicalScope *Scope) {
216   assert(Scope && "Unable to calculate scope dominance graph!");
217   SmallVector<LexicalScope *, 4> WorkStack;
218   WorkStack.push_back(Scope);
219   unsigned Counter = 0;
220   while (!WorkStack.empty()) {
221     LexicalScope *WS = WorkStack.back();
222     const SmallVectorImpl<LexicalScope *> &Children = WS->getChildren();
223     bool visitedChildren = false;
224     for (auto &ChildScope : Children)
225       if (!ChildScope->getDFSOut()) {
226         WorkStack.push_back(ChildScope);
227         visitedChildren = true;
228         ChildScope->setDFSIn(++Counter);
229         break;
230       }
231     if (!visitedChildren) {
232       WorkStack.pop_back();
233       WS->setDFSOut(++Counter);
234     }
235   }
236 }
237 
238 /// assignInstructionRanges - Find ranges of instructions covered by each
239 /// lexical scope.
240 void LexicalScopes::assignInstructionRanges(
241     SmallVectorImpl<InsnRange> &MIRanges,
242     DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
243 
244   LexicalScope *PrevLexicalScope = nullptr;
245   for (const auto &R : MIRanges) {
246     LexicalScope *S = MI2ScopeMap.lookup(R.first);
247     assert(S && "Lost LexicalScope for a machine instruction!");
248     if (PrevLexicalScope && !PrevLexicalScope->dominates(S))
249       PrevLexicalScope->closeInsnRange(S);
250     S->openInsnRange(R.first);
251     S->extendInsnRange(R.second);
252     PrevLexicalScope = S;
253   }
254 
255   if (PrevLexicalScope)
256     PrevLexicalScope->closeInsnRange();
257 }
258 
259 /// getMachineBasicBlocks - Populate given set using machine basic blocks which
260 /// have machine instructions that belong to lexical scope identified by
261 /// DebugLoc.
262 void LexicalScopes::getMachineBasicBlocks(
263     const DILocation *DL, SmallPtrSetImpl<const MachineBasicBlock *> &MBBs) {
264   MBBs.clear();
265   LexicalScope *Scope = getOrCreateLexicalScope(DL);
266   if (!Scope)
267     return;
268 
269   if (Scope == CurrentFnLexicalScope) {
270     for (const auto &MBB : *MF)
271       MBBs.insert(&MBB);
272     return;
273   }
274 
275   SmallVectorImpl<InsnRange> &InsnRanges = Scope->getRanges();
276   for (auto &R : InsnRanges)
277     MBBs.insert(R.first->getParent());
278 }
279 
280 /// dominates - Return true if DebugLoc's lexical scope dominates at least one
281 /// machine instruction's lexical scope in a given machine basic block.
282 bool LexicalScopes::dominates(const DILocation *DL, MachineBasicBlock *MBB) {
283   LexicalScope *Scope = getOrCreateLexicalScope(DL);
284   if (!Scope)
285     return false;
286 
287   // Current function scope covers all basic blocks in the function.
288   if (Scope == CurrentFnLexicalScope && MBB->getParent() == MF)
289     return true;
290 
291   bool Result = false;
292   for (auto &I : *MBB) {
293     if (const DILocation *IDL = I.getDebugLoc())
294       if (LexicalScope *IScope = getOrCreateLexicalScope(IDL))
295         if (Scope->dominates(IScope))
296           return true;
297   }
298   return Result;
299 }
300 
301 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
302 LLVM_DUMP_METHOD void LexicalScope::dump(unsigned Indent) const {
303   raw_ostream &err = dbgs();
304   err.indent(Indent);
305   err << "DFSIn: " << DFSIn << " DFSOut: " << DFSOut << "\n";
306   const MDNode *N = Desc;
307   err.indent(Indent);
308   N->dump();
309   if (AbstractScope)
310     err << std::string(Indent, ' ') << "Abstract Scope\n";
311 
312   if (!Children.empty())
313     err << std::string(Indent + 2, ' ') << "Children ...\n";
314   for (unsigned i = 0, e = Children.size(); i != e; ++i)
315     if (Children[i] != this)
316       Children[i]->dump(Indent + 2);
317 }
318 #endif
319