C++ AllocaInst::use_empty方法代码示例

void PromoteMem2Reg::run() {
  Function &F = *DF.getRoot()->getParent();

  if (AST) PointerAllocaValues.resize(Allocas.size());
  AllocaDbgDeclares.resize(Allocas.size());

  AllocaInfo Info;
  LargeBlockInfo LBI;

  for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
    AllocaInst *AI = Allocas[AllocaNum];

    assert(isAllocaPromotable(AI) &&
           "Cannot promote non-promotable alloca!");
    assert(AI->getParent()->getParent() == &F &&
           "All allocas should be in the same function, which is same as DF!");

    if (AI->use_empty()) {
      // If there are no uses of the alloca, just delete it now.
      if (AST) AST->deleteValue(AI);
      AI->eraseFromParent();

      // Remove the alloca from the Allocas list, since it has been processed
      RemoveFromAllocasList(AllocaNum);
      ++NumDeadAlloca;
      continue;
    }
    
    // Calculate the set of read and write-locations for each alloca.  This is
    // analogous to finding the 'uses' and 'definitions' of each variable.
    Info.AnalyzeAlloca(AI);

    // If there is only a single store to this value, replace any loads of
    // it that are directly dominated by the definition with the value stored.
    if (Info.DefiningBlocks.size() == 1) {
      RewriteSingleStoreAlloca(AI, Info, LBI);

      // Finally, after the scan, check to see if the store is all that is left.
      if (Info.UsingBlocks.empty()) {
        // Record debuginfo for the store and remove the declaration's debuginfo.
        if (DbgDeclareInst *DDI = Info.DbgDeclare) {
          ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore);
          DDI->eraseFromParent();
        }
        // Remove the (now dead) store and alloca.
        Info.OnlyStore->eraseFromParent();
        LBI.deleteValue(Info.OnlyStore);

        if (AST) AST->deleteValue(AI);
        AI->eraseFromParent();
        LBI.deleteValue(AI);
        
        // The alloca has been processed, move on.
        RemoveFromAllocasList(AllocaNum);
        
        ++NumSingleStore;
        continue;
      }
    }
    
    // If the alloca is only read and written in one basic block, just perform a
    // linear sweep over the block to eliminate it.
    if (Info.OnlyUsedInOneBlock) {
      PromoteSingleBlockAlloca(AI, Info, LBI);
      
      // Finally, after the scan, check to see if the stores are all that is
      // left.
      if (Info.UsingBlocks.empty()) {
        
        // Remove the (now dead) stores and alloca.
        while (!AI->use_empty()) {
          StoreInst *SI = cast<StoreInst>(AI->use_back());
          // Record debuginfo for the store before removing it.
          if (DbgDeclareInst *DDI = Info.DbgDeclare)
            ConvertDebugDeclareToDebugValue(DDI, SI);
          SI->eraseFromParent();
          LBI.deleteValue(SI);
        }
        
        if (AST) AST->deleteValue(AI);
        AI->eraseFromParent();
        LBI.deleteValue(AI);
        
        // The alloca has been processed, move on.
        RemoveFromAllocasList(AllocaNum);
        
        // The alloca's debuginfo can be removed as well.
        if (DbgDeclareInst *DDI = Info.DbgDeclare)
          DDI->eraseFromParent();

        ++NumLocalPromoted;
        continue;
      }
    }
    
    // If we haven't computed a numbering for the BB's in the function, do so
    // now.
    if (BBNumbers.empty()) {
      unsigned ID = 0;
      for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
//.........这里部分代码省略.........

//.........这里部分代码省略.........

    // We want the inliner to prune the code as it copies.  We would LOVE to
    // have no dead or constant instructions leftover after inlining occurs
    // (which can happen, e.g., because an argument was constant), but we'll be
    // happy with whatever the cloner can do.
    CloneAndPruneFunctionInto(Caller, CalledFunc, VMap, 
                              /*ModuleLevelChanges=*/false, Returns, ".i",
                              &InlinedFunctionInfo, IFI.TD, TheCall);

    // Remember the first block that is newly cloned over.
    FirstNewBlock = LastBlock; ++FirstNewBlock;

    // Update the callgraph if requested.
    if (IFI.CG)
      UpdateCallGraphAfterInlining(CS, FirstNewBlock, VMap, IFI);

    // Update inlined instructions' line number information.
    fixupLineNumbers(Caller, FirstNewBlock, TheCall);
  }

  // If there are any alloca instructions in the block that used to be the entry
  // block for the callee, move them to the entry block of the caller.  First
  // calculate which instruction they should be inserted before.  We insert the
  // instructions at the end of the current alloca list.
  {
    BasicBlock::iterator InsertPoint = Caller->begin()->begin();
    for (BasicBlock::iterator I = FirstNewBlock->begin(),
         E = FirstNewBlock->end(); I != E; ) {
      AllocaInst *AI = dyn_cast<AllocaInst>(I++);
      if (AI == 0) continue;
      
      // If the alloca is now dead, remove it.  This often occurs due to code
      // specialization.
      if (AI->use_empty()) {
        AI->eraseFromParent();
        continue;
      }

      if (!isa<Constant>(AI->getArraySize()))
        continue;
      
      // Keep track of the static allocas that we inline into the caller.
      IFI.StaticAllocas.push_back(AI);
      
      // Scan for the block of allocas that we can move over, and move them
      // all at once.
      while (isa<AllocaInst>(I) &&
             isa<Constant>(cast<AllocaInst>(I)->getArraySize())) {
        IFI.StaticAllocas.push_back(cast<AllocaInst>(I));
        ++I;
      }

      // Transfer all of the allocas over in a block.  Using splice means
      // that the instructions aren't removed from the symbol table, then
      // reinserted.
      Caller->getEntryBlock().getInstList().splice(InsertPoint,
                                                   FirstNewBlock->getInstList(),
                                                   AI, I);
    }
  }

  // Leave lifetime markers for the static alloca's, scoping them to the
  // function we just inlined.
  if (InsertLifetime && !IFI.StaticAllocas.empty()) {
    IRBuilder<> builder(FirstNewBlock->begin());
    for (unsigned ai = 0, ae = IFI.StaticAllocas.size(); ai != ae; ++ai) {

void PromoteMem2Reg::run() {
  Function &F = *DT.getRoot()->getParent();

  AllocaDbgDeclares.resize(Allocas.size());

  AllocaInfo Info;
  LargeBlockInfo LBI;
  ForwardIDFCalculator IDF(DT);

  for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
    AllocaInst *AI = Allocas[AllocaNum];

    assert(isAllocaPromotable(AI) && "Cannot promote non-promotable alloca!");
    assert(AI->getParent()->getParent() == &F &&
           "All allocas should be in the same function, which is same as DF!");

    removeLifetimeIntrinsicUsers(AI);

    if (AI->use_empty()) {
      // If there are no uses of the alloca, just delete it now.
      AI->eraseFromParent();

      // Remove the alloca from the Allocas list, since it has been processed
      RemoveFromAllocasList(AllocaNum);
      ++NumDeadAlloca;
      continue;
    }

    // Calculate the set of read and write-locations for each alloca.  This is
    // analogous to finding the 'uses' and 'definitions' of each variable.
    Info.AnalyzeAlloca(AI);

    // If there is only a single store to this value, replace any loads of
    // it that are directly dominated by the definition with the value stored.
    if (Info.DefiningBlocks.size() == 1) {
      if (rewriteSingleStoreAlloca(AI, Info, LBI, SQ.DL, DT, AC)) {
        // The alloca has been processed, move on.
        RemoveFromAllocasList(AllocaNum);
        ++NumSingleStore;
        continue;
      }
    }

    // If the alloca is only read and written in one basic block, just perform a
    // linear sweep over the block to eliminate it.
    if (Info.OnlyUsedInOneBlock &&
        promoteSingleBlockAlloca(AI, Info, LBI, SQ.DL, DT, AC)) {
      // The alloca has been processed, move on.
      RemoveFromAllocasList(AllocaNum);
      continue;
    }

    // If we haven't computed a numbering for the BB's in the function, do so
    // now.
    if (BBNumbers.empty()) {
      unsigned ID = 0;
      for (auto &BB : F)
        BBNumbers[&BB] = ID++;
    }

    // Remember the dbg.declare intrinsic describing this alloca, if any.
    if (!Info.DbgDeclares.empty())
      AllocaDbgDeclares[AllocaNum] = Info.DbgDeclares;

    // Keep the reverse mapping of the 'Allocas' array for the rename pass.
    AllocaLookup[Allocas[AllocaNum]] = AllocaNum;

    // At this point, we're committed to promoting the alloca using IDF's, and
    // the standard SSA construction algorithm.  Determine which blocks need PHI
    // nodes and see if we can optimize out some work by avoiding insertion of
    // dead phi nodes.

    // Unique the set of defining blocks for efficient lookup.
    SmallPtrSet<BasicBlock *, 32> DefBlocks;
    DefBlocks.insert(Info.DefiningBlocks.begin(), Info.DefiningBlocks.end());

    // Determine which blocks the value is live in.  These are blocks which lead
    // to uses.
    SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
    ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks);

    // At this point, we're committed to promoting the alloca using IDF's, and
    // the standard SSA construction algorithm.  Determine which blocks need phi
    // nodes and see if we can optimize out some work by avoiding insertion of
    // dead phi nodes.
    IDF.setLiveInBlocks(LiveInBlocks);
    IDF.setDefiningBlocks(DefBlocks);
    SmallVector<BasicBlock *, 32> PHIBlocks;
    IDF.calculate(PHIBlocks);
    if (PHIBlocks.size() > 1)
      llvm::sort(PHIBlocks, [this](BasicBlock *A, BasicBlock *B) {
        return BBNumbers.lookup(A) < BBNumbers.lookup(B);
      });

    unsigned CurrentVersion = 0;
    for (BasicBlock *BB : PHIBlocks)
      QueuePhiNode(BB, AllocaNum, CurrentVersion);
  }

  if (Allocas.empty())
//.........这里部分代码省略.........

//.........这里部分代码省略.........

      VMap[I] = ActualArg;
    }

    // We want the inliner to prune the code as it copies.  We would LOVE to
    // have no dead or constant instructions leftover after inlining occurs
    // (which can happen, e.g., because an argument was constant), but we'll be
    // happy with whatever the cloner can do.
    CloneAndPruneFunctionInto(Caller, CalledFunc, VMap, Returns, ".i",
                              &InlinedFunctionInfo, IFI.TD, TheCall);

    // Remember the first block that is newly cloned over.
    FirstNewBlock = LastBlock; ++FirstNewBlock;

    // Update the callgraph if requested.
    if (IFI.CG)
      UpdateCallGraphAfterInlining(CS, FirstNewBlock, VMap, IFI);
  }

  // If there are any alloca instructions in the block that used to be the entry
  // block for the callee, move them to the entry block of the caller.  First
  // calculate which instruction they should be inserted before.  We insert the
  // instructions at the end of the current alloca list.
  //
  {
    BasicBlock::iterator InsertPoint = Caller->begin()->begin();
    for (BasicBlock::iterator I = FirstNewBlock->begin(),
         E = FirstNewBlock->end(); I != E; ) {
      AllocaInst *AI = dyn_cast<AllocaInst>(I++);
      if (AI == 0) continue;
      
      // If the alloca is now dead, remove it.  This often occurs due to code
      // specialization.
      if (AI->use_empty()) {
        AI->eraseFromParent();
        continue;
      }

      if (!isa<Constant>(AI->getArraySize()))
        continue;
      
      // Keep track of the static allocas that we inline into the caller if the
      // StaticAllocas pointer is non-null.
      IFI.StaticAllocas.push_back(AI);
      
      // Scan for the block of allocas that we can move over, and move them
      // all at once.
      while (isa<AllocaInst>(I) &&
             isa<Constant>(cast<AllocaInst>(I)->getArraySize())) {
        IFI.StaticAllocas.push_back(cast<AllocaInst>(I));
        ++I;
      }

      // Transfer all of the allocas over in a block.  Using splice means
      // that the instructions aren't removed from the symbol table, then
      // reinserted.
      Caller->getEntryBlock().getInstList().splice(InsertPoint,
                                                   FirstNewBlock->getInstList(),
                                                   AI, I);
    }
  }

  // If the inlined code contained dynamic alloca instructions, wrap the inlined
  // code with llvm.stacksave/llvm.stackrestore intrinsics.
  if (InlinedFunctionInfo.ContainsDynamicAllocas) {
    Module *M = Caller->getParent();