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      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 MDLocation *PrevDL = nullptr;
     63     for (const auto &MInsn : MBB) {
     64       // Check if instruction has valid location information.
     65       const MDLocation *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 MDLocation *DL) {
    110   MDLocalScope *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   if (auto *File = dyn_cast<MDLexicalBlockFile>(Scope))
    117     Scope = File->getScope();
    118 
    119   if (auto *IA = DL->getInlinedAt()) {
    120     auto I = InlinedLexicalScopeMap.find(std::make_pair(Scope, IA));
    121     return I != InlinedLexicalScopeMap.end() ? &I->second : nullptr;
    122   }
    123   return findLexicalScope(Scope);
    124 }
    125 
    126 /// getOrCreateLexicalScope - Find lexical scope for the given DebugLoc. If
    127 /// not available then create new lexical scope.
    128 LexicalScope *LexicalScopes::getOrCreateLexicalScope(const MDLocalScope *Scope,
    129                                                      const MDLocation *IA) {
    130   if (IA) {
    131     // Create an abstract scope for inlined function.
    132     getOrCreateAbstractScope(Scope);
    133     // Create an inlined scope for inlined function.
    134     return getOrCreateInlinedScope(Scope, IA);
    135   }
    136 
    137   return getOrCreateRegularScope(Scope);
    138 }
    139 
    140 /// getOrCreateRegularScope - Find or create a regular lexical scope.
    141 LexicalScope *
    142 LexicalScopes::getOrCreateRegularScope(const MDLocalScope *Scope) {
    143   if (auto *File = dyn_cast<MDLexicalBlockFile>(Scope))
    144     Scope = File->getScope();
    145 
    146   auto I = LexicalScopeMap.find(Scope);
    147   if (I != LexicalScopeMap.end())
    148     return &I->second;
    149 
    150   // FIXME: Should the following dyn_cast be MDLexicalBlock?
    151   LexicalScope *Parent = nullptr;
    152   if (auto *Block = dyn_cast<MDLexicalBlockBase>(Scope))
    153     Parent = getOrCreateLexicalScope(Block->getScope());
    154   I = LexicalScopeMap.emplace(std::piecewise_construct,
    155                               std::forward_as_tuple(Scope),
    156                               std::forward_as_tuple(Parent, Scope, nullptr,
    157                                                     false)).first;
    158 
    159   if (!Parent) {
    160     assert(cast<MDSubprogram>(Scope)->describes(MF->getFunction()));
    161     assert(!CurrentFnLexicalScope);
    162     CurrentFnLexicalScope = &I->second;
    163   }
    164 
    165   return &I->second;
    166 }
    167 
    168 /// getOrCreateInlinedScope - Find or create an inlined lexical scope.
    169 LexicalScope *
    170 LexicalScopes::getOrCreateInlinedScope(const MDLocalScope *Scope,
    171                                        const MDLocation *InlinedAt) {
    172   std::pair<const MDLocalScope *, const MDLocation *> P(Scope, InlinedAt);
    173   auto I = InlinedLexicalScopeMap.find(P);
    174   if (I != InlinedLexicalScopeMap.end())
    175     return &I->second;
    176 
    177   LexicalScope *Parent;
    178   if (auto *Block = dyn_cast<MDLexicalBlockBase>(Scope))
    179     Parent = getOrCreateInlinedScope(Block->getScope(), InlinedAt);
    180   else
    181     Parent = getOrCreateLexicalScope(InlinedAt);
    182 
    183   I = InlinedLexicalScopeMap.emplace(std::piecewise_construct,
    184                                      std::forward_as_tuple(P),
    185                                      std::forward_as_tuple(Parent, Scope,
    186                                                            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 MDLocalScope *Scope) {
    194   assert(Scope && "Invalid Scope encoding!");
    195 
    196   if (auto *File = dyn_cast<MDLexicalBlockFile>(Scope))
    197     Scope = File->getScope();
    198   auto I = AbstractScopeMap.find(Scope);
    199   if (I != AbstractScopeMap.end())
    200     return &I->second;
    201 
    202   // FIXME: Should the following isa be MDLexicalBlock?
    203   LexicalScope *Parent = nullptr;
    204   if (auto *Block = dyn_cast<MDLexicalBlockBase>(Scope))
    205     Parent = getOrCreateAbstractScope(Block->getScope());
    206 
    207   I = AbstractScopeMap.emplace(std::piecewise_construct,
    208                                std::forward_as_tuple(Scope),
    209                                std::forward_as_tuple(Parent, Scope,
    210                                                      nullptr, true)).first;
    211   if (isa<MDSubprogram>(Scope))
    212     AbstractScopesList.push_back(&I->second);
    213   return &I->second;
    214 }
    215 
    216 /// constructScopeNest
    217 void LexicalScopes::constructScopeNest(LexicalScope *Scope) {
    218   assert(Scope && "Unable to calculate scope dominance graph!");
    219   SmallVector<LexicalScope *, 4> WorkStack;
    220   WorkStack.push_back(Scope);
    221   unsigned Counter = 0;
    222   while (!WorkStack.empty()) {
    223     LexicalScope *WS = WorkStack.back();
    224     const SmallVectorImpl<LexicalScope *> &Children = WS->getChildren();
    225     bool visitedChildren = false;
    226     for (SmallVectorImpl<LexicalScope *>::const_iterator SI = Children.begin(),
    227                                                          SE = Children.end();
    228          SI != SE; ++SI) {
    229       LexicalScope *ChildScope = *SI;
    230       if (!ChildScope->getDFSOut()) {
    231         WorkStack.push_back(ChildScope);
    232         visitedChildren = true;
    233         ChildScope->setDFSIn(++Counter);
    234         break;
    235       }
    236     }
    237     if (!visitedChildren) {
    238       WorkStack.pop_back();
    239       WS->setDFSOut(++Counter);
    240     }
    241   }
    242 }
    243 
    244 /// assignInstructionRanges - Find ranges of instructions covered by each
    245 /// lexical scope.
    246 void LexicalScopes::assignInstructionRanges(
    247     SmallVectorImpl<InsnRange> &MIRanges,
    248     DenseMap<const MachineInstr *, LexicalScope *> &MI2ScopeMap) {
    249 
    250   LexicalScope *PrevLexicalScope = nullptr;
    251   for (SmallVectorImpl<InsnRange>::const_iterator RI = MIRanges.begin(),
    252                                                   RE = MIRanges.end();
    253        RI != RE; ++RI) {
    254     const InsnRange &R = *RI;
    255     LexicalScope *S = MI2ScopeMap.lookup(R.first);
    256     assert(S && "Lost LexicalScope for a machine instruction!");
    257     if (PrevLexicalScope && !PrevLexicalScope->dominates(S))
    258       PrevLexicalScope->closeInsnRange(S);
    259     S->openInsnRange(R.first);
    260     S->extendInsnRange(R.second);
    261     PrevLexicalScope = S;
    262   }
    263 
    264   if (PrevLexicalScope)
    265     PrevLexicalScope->closeInsnRange();
    266 }
    267 
    268 /// getMachineBasicBlocks - Populate given set using machine basic blocks which
    269 /// have machine instructions that belong to lexical scope identified by
    270 /// DebugLoc.
    271 void LexicalScopes::getMachineBasicBlocks(
    272     const MDLocation *DL, SmallPtrSetImpl<const MachineBasicBlock *> &MBBs) {
    273   MBBs.clear();
    274   LexicalScope *Scope = getOrCreateLexicalScope(DL);
    275   if (!Scope)
    276     return;
    277 
    278   if (Scope == CurrentFnLexicalScope) {
    279     for (const auto &MBB : *MF)
    280       MBBs.insert(&MBB);
    281     return;
    282   }
    283 
    284   SmallVectorImpl<InsnRange> &InsnRanges = Scope->getRanges();
    285   for (SmallVectorImpl<InsnRange>::iterator I = InsnRanges.begin(),
    286                                             E = InsnRanges.end();
    287        I != E; ++I) {
    288     InsnRange &R = *I;
    289     MBBs.insert(R.first->getParent());
    290   }
    291 }
    292 
    293 /// dominates - Return true if DebugLoc's lexical scope dominates at least one
    294 /// machine instruction's lexical scope in a given machine basic block.
    295 bool LexicalScopes::dominates(const MDLocation *DL, MachineBasicBlock *MBB) {
    296   LexicalScope *Scope = getOrCreateLexicalScope(DL);
    297   if (!Scope)
    298     return false;
    299 
    300   // Current function scope covers all basic blocks in the function.
    301   if (Scope == CurrentFnLexicalScope && MBB->getParent() == MF)
    302     return true;
    303 
    304   bool Result = false;
    305   for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
    306        ++I) {
    307     if (const MDLocation *IDL = I->getDebugLoc())
    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