C++ DomTreeNode::getChildren方法代码示例

//.........这里部分代码省略.........
  PHINode *PN;
  for (BasicBlock::iterator I = L->getHeader()->begin();
       (PN = dyn_cast<PHINode>(I++)); )
    if (Value *V = SimplifyInstruction(PN, DL, nullptr, DT, AC)) {
      if (SE) SE->forgetValue(PN);
      PN->replaceAllUsesWith(V);
      PN->eraseFromParent();
    }

  // If this loop has multiple exits and the exits all go to the same
  // block, attempt to merge the exits. This helps several passes, such
  // as LoopRotation, which do not support loops with multiple exits.
  // SimplifyCFG also does this (and this code uses the same utility
  // function), however this code is loop-aware, where SimplifyCFG is
  // not. That gives it the advantage of being able to hoist
  // loop-invariant instructions out of the way to open up more
  // opportunities, and the disadvantage of having the responsibility
  // to preserve dominator information.
  bool UniqueExit = true;
  if (!ExitBlocks.empty())
    for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i)
      if (ExitBlocks[i] != ExitBlocks[0]) {
        UniqueExit = false;
        break;
      }
  if (UniqueExit) {
    for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
      BasicBlock *ExitingBlock = ExitingBlocks[i];
      if (!ExitingBlock->getSinglePredecessor()) continue;
      BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
      if (!BI || !BI->isConditional()) continue;
      CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
      if (!CI || CI->getParent() != ExitingBlock) continue;

      // Attempt to hoist out all instructions except for the
      // comparison and the branch.
      bool AllInvariant = true;
      bool AnyInvariant = false;
      for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
        Instruction *Inst = I++;
        // Skip debug info intrinsics.
        if (isa<DbgInfoIntrinsic>(Inst))
          continue;
        if (Inst == CI)
          continue;
        if (!L->makeLoopInvariant(Inst, AnyInvariant,
                                  Preheader ? Preheader->getTerminator()
                                            : nullptr)) {
          AllInvariant = false;
          break;
        }
      }
      if (AnyInvariant) {
        Changed = true;
        // The loop disposition of all SCEV expressions that depend on any
        // hoisted values have also changed.
        if (SE)
          SE->forgetLoopDispositions(L);
      }
      if (!AllInvariant) continue;

      // The block has now been cleared of all instructions except for
      // a comparison and a conditional branch. SimplifyCFG may be able
      // to fold it now.
      if (!FoldBranchToCommonDest(BI))
        continue;

      // Success. The block is now dead, so remove it from the loop,
      // update the dominator tree and delete it.
      DEBUG(dbgs() << "LoopSimplify: Eliminating exiting block "
                   << ExitingBlock->getName() << "\n");

      // Notify ScalarEvolution before deleting this block. Currently assume the
      // parent loop doesn't change (spliting edges doesn't count). If blocks,
      // CFG edges, or other values in the parent loop change, then we need call
      // to forgetLoop() for the parent instead.
      if (SE)
        SE->forgetLoop(L);

      assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
      Changed = true;
      LI->removeBlock(ExitingBlock);

      DomTreeNode *Node = DT->getNode(ExitingBlock);
      const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
        Node->getChildren();
      while (!Children.empty()) {
        DomTreeNode *Child = Children.front();
        DT->changeImmediateDominator(Child, Node->getIDom());
      }
      DT->eraseNode(ExitingBlock);

      BI->getSuccessor(0)->removePredecessor(ExitingBlock);
      BI->getSuccessor(1)->removePredecessor(ExitingBlock);
      ExitingBlock->eraseFromParent();
    }
  }

  return Changed;
}