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     DebugLoc PrevDL;
63     for (const auto &MInsn : MBB) {
64       // Check if instruction has valid location information.
65       const DebugLoc MIDL = MInsn.getDebugLoc();
66       if (MIDL.isUnknown()) {
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.isUnknown()) {
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(DebugLoc DL) {
110   MDNode *Scope = nullptr;
111   MDNode *IA = nullptr;
112   DL.getScopeAndInlinedAt(Scope, IA, MF->getFunction()->getContext());
113   if (!Scope)
114     return nullptr;
115 
116   // The scope that we were created with could have an extra file - which
117   // isn't what we care about in this case.
118   DIDescriptor D = DIDescriptor(Scope);
119   if (D.isLexicalBlockFile())
120     Scope = DILexicalBlockFile(Scope).getScope();
121 
122   if (IA)
123     return InlinedLexicalScopeMap.lookup(DebugLoc::getFromDILocation(IA));
124   return findLexicalScope(Scope);
125 }
126 
127 /// getOrCreateLexicalScope - Find lexical scope for the given DebugLoc. If
128 /// not available then create new lexical scope.
129 LexicalScope *LexicalScopes::getOrCreateLexicalScope(DebugLoc DL) {
130   MDNode *Scope = nullptr;
131   MDNode *InlinedAt = nullptr;
132   DL.getScopeAndInlinedAt(Scope, InlinedAt, MF->getFunction()->getContext());
133 
134   if (InlinedAt) {
135     // Create an abstract scope for inlined function.
136     getOrCreateAbstractScope(Scope);
137     // Create an inlined scope for inlined function.
138     return getOrCreateInlinedScope(Scope, InlinedAt);
139   }
140 
141   return getOrCreateRegularScope(Scope);
142 }
143 
144 /// getOrCreateRegularScope - Find or create a regular lexical scope.
145 LexicalScope *LexicalScopes::getOrCreateRegularScope(MDNode *Scope) {
146   DIDescriptor D = DIDescriptor(Scope);
147   if (D.isLexicalBlockFile()) {
148     Scope = DILexicalBlockFile(Scope).getScope();
149     D = DIDescriptor(Scope);
150   }
151 
152   auto I = LexicalScopeMap.find(Scope);
153   if (I != LexicalScopeMap.end())
154     return &I->second;
155 
156   LexicalScope *Parent = nullptr;
157   if (D.isLexicalBlock())
158     Parent = getOrCreateLexicalScope(DebugLoc::getFromDILexicalBlock(Scope));
159   I = LexicalScopeMap.emplace(std::piecewise_construct,
160                               std::forward_as_tuple(Scope),
161                               std::forward_as_tuple(Parent, DIDescriptor(Scope),
162                                                     nullptr, false)).first;
163 
164   if (!Parent && DIDescriptor(Scope).isSubprogram() &&
165       DISubprogram(Scope).describes(MF->getFunction()))
166     CurrentFnLexicalScope = &I->second;
167 
168   return &I->second;
169 }
170 
171 /// getOrCreateInlinedScope - Find or create an inlined lexical scope.
172 LexicalScope *LexicalScopes::getOrCreateInlinedScope(MDNode *Scope,
173                                                      MDNode *InlinedAt) {
174   auto I = LexicalScopeMap.find(InlinedAt);
175   if (I != LexicalScopeMap.end())
176     return &I->second;
177 
178   DebugLoc InlinedLoc = DebugLoc::getFromDILocation(InlinedAt);
179   I = LexicalScopeMap.emplace(std::piecewise_construct,
180                               std::forward_as_tuple(InlinedAt),
181                               std::forward_as_tuple(
182                                   getOrCreateLexicalScope(InlinedLoc),
183                                   DIDescriptor(Scope), InlinedAt, false)).first;
184   InlinedLexicalScopeMap[InlinedLoc] = &I->second;
185   return &I->second;
186 }
187 
188 /// getOrCreateAbstractScope - Find or create an abstract lexical scope.
189 LexicalScope *LexicalScopes::getOrCreateAbstractScope(const MDNode *N) {
190   assert(N && "Invalid Scope encoding!");
191 
192   DIDescriptor Scope(N);
193   if (Scope.isLexicalBlockFile())
194     Scope = DILexicalBlockFile(Scope).getScope();
195   auto I = AbstractScopeMap.find(N);
196   if (I != AbstractScopeMap.end())
197     return &I->second;
198 
199   LexicalScope *Parent = nullptr;
200   if (Scope.isLexicalBlock()) {
201     DILexicalBlock DB(N);
202     DIDescriptor ParentDesc = DB.getContext();
203     Parent = getOrCreateAbstractScope(ParentDesc);
204   }
205   I = AbstractScopeMap.emplace(std::piecewise_construct,
206                                std::forward_as_tuple(N),
207                                std::forward_as_tuple(Parent, DIDescriptor(N),
208                                                      nullptr, true)).first;
209   if (DIDescriptor(N).isSubprogram())
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 (SmallVectorImpl<LexicalScope *>::const_iterator SI = Children.begin(),
225                                                          SE = Children.end();
226          SI != SE; ++SI) {
227       LexicalScope *ChildScope = *SI;
228       if (!ChildScope->getDFSOut()) {
229         WorkStack.push_back(ChildScope);
230         visitedChildren = true;
231         ChildScope->setDFSIn(++Counter);
232         break;
233       }
234     }
235     if (!visitedChildren) {
236       WorkStack.pop_back();
237       WS->setDFSOut(++Counter);
238     }
239   }
240 }
241 
242 /// assignInstructionRanges - Find ranges of instructions covered by each
243 /// lexical scope.
244 void LexicalScopes::assignInstructionRanges(
245     SmallVectorImpl<InsnRange> &MIRanges,
246     DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
247 
248   LexicalScope *PrevLexicalScope = nullptr;
249   for (SmallVectorImpl<InsnRange>::const_iterator RI = MIRanges.begin(),
250                                                   RE = MIRanges.end();
251        RI != RE; ++RI) {
252     const InsnRange &R = *RI;
253     LexicalScope *S = MI2ScopeMap.lookup(R.first);
254     assert(S && "Lost LexicalScope for a machine instruction!");
255     if (PrevLexicalScope && !PrevLexicalScope->dominates(S))
256       PrevLexicalScope->closeInsnRange(S);
257     S->openInsnRange(R.first);
258     S->extendInsnRange(R.second);
259     PrevLexicalScope = S;
260   }
261 
262   if (PrevLexicalScope)
263     PrevLexicalScope->closeInsnRange();
264 }
265 
266 /// getMachineBasicBlocks - Populate given set using machine basic blocks which
267 /// have machine instructions that belong to lexical scope identified by
268 /// DebugLoc.
269 void LexicalScopes::getMachineBasicBlocks(
270     DebugLoc DL, SmallPtrSet<const MachineBasicBlock *, 4> &MBBs) {
271   MBBs.clear();
272   LexicalScope *Scope = getOrCreateLexicalScope(DL);
273   if (!Scope)
274     return;
275 
276   if (Scope == CurrentFnLexicalScope) {
277     for (const auto &MBB : *MF)
278       MBBs.insert(&MBB);
279     return;
280   }
281 
282   SmallVectorImpl<InsnRange> &InsnRanges = Scope->getRanges();
283   for (SmallVectorImpl<InsnRange>::iterator I = InsnRanges.begin(),
284                                             E = InsnRanges.end();
285        I != E; ++I) {
286     InsnRange &R = *I;
287     MBBs.insert(R.first->getParent());
288   }
289 }
290 
291 /// dominates - Return true if DebugLoc's lexical scope dominates at least one
292 /// machine instruction's lexical scope in a given machine basic block.
293 bool LexicalScopes::dominates(DebugLoc DL, MachineBasicBlock *MBB) {
294   LexicalScope *Scope = getOrCreateLexicalScope(DL);
295   if (!Scope)
296     return false;
297 
298   // Current function scope covers all basic blocks in the function.
299   if (Scope == CurrentFnLexicalScope && MBB->getParent() == MF)
300     return true;
301 
302   bool Result = false;
303   for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
304        ++I) {
305     DebugLoc IDL = I->getDebugLoc();
306     if (IDL.isUnknown())
307       continue;
308     if (LexicalScope *IScope = getOrCreateLexicalScope(IDL))
309       if (Scope->dominates(IScope))
310         return true;
311   }
312   return Result;
313 }
314 
315 /// dump - Print data structures.
316 void LexicalScope::dump(unsigned Indent) const {
317 #ifndef NDEBUG
318   raw_ostream &err = dbgs();
319   err.indent(Indent);
320   err << "DFSIn: " << DFSIn << " DFSOut: " << DFSOut << "\n";
321   const MDNode *N = Desc;
322   err.indent(Indent);
323   N->dump();
324   if (AbstractScope)
325     err << std::string(Indent, ' ') << "Abstract Scope\n";
326 
327   if (!Children.empty())
328     err << std::string(Indent + 2, ' ') << "Children ...\n";
329   for (unsigned i = 0, e = Children.size(); i != e; ++i)
330     if (Children[i] != this)
331       Children[i]->dump(Indent + 2);
332 #endif
333 }
334