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     auto I = InlinedLexicalScopeMap.find(std::make_pair(Scope, IA));
124     return I != InlinedLexicalScopeMap.end() ? &I->second : nullptr;
125   }
126   return findLexicalScope(Scope);
127 }
128 
129 /// getOrCreateLexicalScope - Find lexical scope for the given DebugLoc. If
130 /// not available then create new lexical scope.
131 LexicalScope *LexicalScopes::getOrCreateLexicalScope(DebugLoc DL) {
132   if (DL.isUnknown())
133     return nullptr;
134   MDNode *Scope = nullptr;
135   MDNode *InlinedAt = nullptr;
136   DL.getScopeAndInlinedAt(Scope, InlinedAt, MF->getFunction()->getContext());
137 
138   if (InlinedAt) {
139     // Create an abstract scope for inlined function.
140     getOrCreateAbstractScope(Scope);
141     // Create an inlined scope for inlined function.
142     return getOrCreateInlinedScope(Scope, InlinedAt);
143   }
144 
145   return getOrCreateRegularScope(Scope);
146 }
147 
148 /// getOrCreateRegularScope - Find or create a regular lexical scope.
149 LexicalScope *LexicalScopes::getOrCreateRegularScope(MDNode *Scope) {
150   DIDescriptor D = DIDescriptor(Scope);
151   if (D.isLexicalBlockFile()) {
152     Scope = DILexicalBlockFile(Scope).getScope();
153     D = DIDescriptor(Scope);
154   }
155 
156   auto I = LexicalScopeMap.find(Scope);
157   if (I != LexicalScopeMap.end())
158     return &I->second;
159 
160   LexicalScope *Parent = nullptr;
161   if (D.isLexicalBlock())
162     Parent = getOrCreateLexicalScope(DebugLoc::getFromDILexicalBlock(Scope));
163   I = LexicalScopeMap.emplace(std::piecewise_construct,
164                               std::forward_as_tuple(Scope),
165                               std::forward_as_tuple(Parent, DIDescriptor(Scope),
166                                                     nullptr, false)).first;
167 
168   if (!Parent) {
169     assert(DIDescriptor(Scope).isSubprogram());
170     assert(DISubprogram(Scope).describes(MF->getFunction()));
171     assert(!CurrentFnLexicalScope);
172     CurrentFnLexicalScope = &I->second;
173   }
174 
175   return &I->second;
176 }
177 
178 /// getOrCreateInlinedScope - Find or create an inlined lexical scope.
179 LexicalScope *LexicalScopes::getOrCreateInlinedScope(MDNode *ScopeNode,
180                                                      MDNode *InlinedAt) {
181   std::pair<const MDNode*, const MDNode*> P(ScopeNode, InlinedAt);
182   auto I = InlinedLexicalScopeMap.find(P);
183   if (I != InlinedLexicalScopeMap.end())
184     return &I->second;
185 
186   LexicalScope *Parent;
187   DILexicalBlock Scope(ScopeNode);
188   if (Scope.isSubprogram())
189     Parent = getOrCreateLexicalScope(DebugLoc::getFromDILocation(InlinedAt));
190   else
191     Parent = getOrCreateInlinedScope(Scope.getContext(), InlinedAt);
192 
193   I = InlinedLexicalScopeMap.emplace(std::piecewise_construct,
194                                      std::forward_as_tuple(P),
195                                      std::forward_as_tuple(Parent, Scope,
196                                                            InlinedAt, false))
197           .first;
198   return &I->second;
199 }
200 
201 /// getOrCreateAbstractScope - Find or create an abstract lexical scope.
202 LexicalScope *LexicalScopes::getOrCreateAbstractScope(const MDNode *N) {
203   assert(N && "Invalid Scope encoding!");
204 
205   DIDescriptor Scope(N);
206   if (Scope.isLexicalBlockFile())
207     Scope = DILexicalBlockFile(Scope).getScope();
208   auto I = AbstractScopeMap.find(Scope);
209   if (I != AbstractScopeMap.end())
210     return &I->second;
211 
212   LexicalScope *Parent = nullptr;
213   if (Scope.isLexicalBlock()) {
214     DILexicalBlock DB(Scope);
215     DIDescriptor ParentDesc = DB.getContext();
216     Parent = getOrCreateAbstractScope(ParentDesc);
217   }
218   I = AbstractScopeMap.emplace(std::piecewise_construct,
219                                std::forward_as_tuple(Scope),
220                                std::forward_as_tuple(Parent, Scope,
221                                                      nullptr, true)).first;
222   if (Scope.isSubprogram())
223     AbstractScopesList.push_back(&I->second);
224   return &I->second;
225 }
226 
227 /// constructScopeNest
228 void LexicalScopes::constructScopeNest(LexicalScope *Scope) {
229   assert(Scope && "Unable to calculate scope dominance graph!");
230   SmallVector<LexicalScope *, 4> WorkStack;
231   WorkStack.push_back(Scope);
232   unsigned Counter = 0;
233   while (!WorkStack.empty()) {
234     LexicalScope *WS = WorkStack.back();
235     const SmallVectorImpl<LexicalScope *> &Children = WS->getChildren();
236     bool visitedChildren = false;
237     for (SmallVectorImpl<LexicalScope *>::const_iterator SI = Children.begin(),
238                                                          SE = Children.end();
239          SI != SE; ++SI) {
240       LexicalScope *ChildScope = *SI;
241       if (!ChildScope->getDFSOut()) {
242         WorkStack.push_back(ChildScope);
243         visitedChildren = true;
244         ChildScope->setDFSIn(++Counter);
245         break;
246       }
247     }
248     if (!visitedChildren) {
249       WorkStack.pop_back();
250       WS->setDFSOut(++Counter);
251     }
252   }
253 }
254 
255 /// assignInstructionRanges - Find ranges of instructions covered by each
256 /// lexical scope.
257 void LexicalScopes::assignInstructionRanges(
258     SmallVectorImpl<InsnRange> &MIRanges,
259     DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
260 
261   LexicalScope *PrevLexicalScope = nullptr;
262   for (SmallVectorImpl<InsnRange>::const_iterator RI = MIRanges.begin(),
263                                                   RE = MIRanges.end();
264        RI != RE; ++RI) {
265     const InsnRange &R = *RI;
266     LexicalScope *S = MI2ScopeMap.lookup(R.first);
267     assert(S && "Lost LexicalScope for a machine instruction!");
268     if (PrevLexicalScope && !PrevLexicalScope->dominates(S))
269       PrevLexicalScope->closeInsnRange(S);
270     S->openInsnRange(R.first);
271     S->extendInsnRange(R.second);
272     PrevLexicalScope = S;
273   }
274 
275   if (PrevLexicalScope)
276     PrevLexicalScope->closeInsnRange();
277 }
278 
279 /// getMachineBasicBlocks - Populate given set using machine basic blocks which
280 /// have machine instructions that belong to lexical scope identified by
281 /// DebugLoc.
282 void LexicalScopes::getMachineBasicBlocks(
283     DebugLoc DL, SmallPtrSetImpl<const MachineBasicBlock *> &MBBs) {
284   MBBs.clear();
285   LexicalScope *Scope = getOrCreateLexicalScope(DL);
286   if (!Scope)
287     return;
288 
289   if (Scope == CurrentFnLexicalScope) {
290     for (const auto &MBB : *MF)
291       MBBs.insert(&MBB);
292     return;
293   }
294 
295   SmallVectorImpl<InsnRange> &InsnRanges = Scope->getRanges();
296   for (SmallVectorImpl<InsnRange>::iterator I = InsnRanges.begin(),
297                                             E = InsnRanges.end();
298        I != E; ++I) {
299     InsnRange &R = *I;
300     MBBs.insert(R.first->getParent());
301   }
302 }
303 
304 /// dominates - Return true if DebugLoc's lexical scope dominates at least one
305 /// machine instruction's lexical scope in a given machine basic block.
306 bool LexicalScopes::dominates(DebugLoc DL, MachineBasicBlock *MBB) {
307   LexicalScope *Scope = getOrCreateLexicalScope(DL);
308   if (!Scope)
309     return false;
310 
311   // Current function scope covers all basic blocks in the function.
312   if (Scope == CurrentFnLexicalScope && MBB->getParent() == MF)
313     return true;
314 
315   bool Result = false;
316   for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
317        ++I) {
318     DebugLoc IDL = I->getDebugLoc();
319     if (IDL.isUnknown())
320       continue;
321     if (LexicalScope *IScope = getOrCreateLexicalScope(IDL))
322       if (Scope->dominates(IScope))
323         return true;
324   }
325   return Result;
326 }
327 
328 /// dump - Print data structures.
329 void LexicalScope::dump(unsigned Indent) const {
330 #ifndef NDEBUG
331   raw_ostream &err = dbgs();
332   err.indent(Indent);
333   err << "DFSIn: " << DFSIn << " DFSOut: " << DFSOut << "\n";
334   const MDNode *N = Desc;
335   err.indent(Indent);
336   N->dump();
337   if (AbstractScope)
338     err << std::string(Indent, ' ') << "Abstract Scope\n";
339 
340   if (!Children.empty())
341     err << std::string(Indent + 2, ' ') << "Children ...\n";
342   for (unsigned i = 0, e = Children.size(); i != e; ++i)
343     if (Children[i] != this)
344       Children[i]->dump(Indent + 2);
345 #endif
346 }
347