C++ iterator::getSinglePredecessor方法代码示例

//.........这里部分代码省略.........
      for (; (PN = dyn_cast<PHINode>(I)); ++I) {
        for (std::map<BasicBlock*, unsigned>::iterator PCI =PredCount.begin(),
             E = PredCount.end(); PCI != E; ++PCI) {
          BasicBlock *Pred     = PCI->first;
          for (unsigned NumToRemove = PCI->second; NumToRemove; --NumToRemove)
            PN->removeIncomingValue(Pred, false);
        }
      }
    }
    
    // If the loops above have made these phi nodes have 0 or 1 operand,
    // replace them with undef or the input value.  We must do this for
    // correctness, because 0-operand phis are not valid.
    PN = cast<PHINode>(NewBB->begin());
    if (PN->getNumIncomingValues() == 0) {
      BasicBlock::iterator I = NewBB->begin();
      BasicBlock::const_iterator OldI = OldBB->begin();
      while ((PN = dyn_cast<PHINode>(I++))) {
        Value *NV = UndefValue::get(PN->getType());
        PN->replaceAllUsesWith(NV);
        assert(VMap[&*OldI] == PN && "VMap mismatch");
        VMap[&*OldI] = NV;
        PN->eraseFromParent();
        ++OldI;
      }
    }
  }

  // Make a second pass over the PHINodes now that all of them have been
  // remapped into the new function, simplifying the PHINode and performing any
  // recursive simplifications exposed. This will transparently update the
  // WeakVH in the VMap. Notably, we rely on that so that if we coalesce
  // two PHINodes, the iteration over the old PHIs remains valid, and the
  // mapping will just map us to the new node (which may not even be a PHI
  // node).
  for (unsigned Idx = 0, Size = PHIToResolve.size(); Idx != Size; ++Idx)
    if (PHINode *PN = dyn_cast<PHINode>(VMap[PHIToResolve[Idx]]))
      recursivelySimplifyInstruction(PN);

  // Now that the inlined function body has been fully constructed, go through
  // and zap unconditional fall-through branches. This happens all the time when
  // specializing code: code specialization turns conditional branches into
  // uncond branches, and this code folds them.
  Function::iterator Begin = cast<BasicBlock>(VMap[StartingBB])->getIterator();
  Function::iterator I = Begin;
  while (I != NewFunc->end()) {
    // Check if this block has become dead during inlining or other
    // simplifications. Note that the first block will appear dead, as it has
    // not yet been wired up properly.
    if (I != Begin && (pred_begin(&*I) == pred_end(&*I) ||
                       I->getSinglePredecessor() == &*I)) {
      BasicBlock *DeadBB = &*I++;
      DeleteDeadBlock(DeadBB);
      continue;
    }

    // We need to simplify conditional branches and switches with a constant
    // operand. We try to prune these out when cloning, but if the
    // simplification required looking through PHI nodes, those are only
    // available after forming the full basic block. That may leave some here,
    // and we still want to prune the dead code as early as possible.
    ConstantFoldTerminator(&*I);

    BranchInst *BI = dyn_cast<BranchInst>(I->getTerminator());
    if (!BI || BI->isConditional()) { ++I; continue; }
    
    BasicBlock *Dest = BI->getSuccessor(0);
    if (!Dest->getSinglePredecessor()) {
      ++I; continue;
    }

    // We shouldn't be able to get single-entry PHI nodes here, as instsimplify
    // above should have zapped all of them..
    assert(!isa<PHINode>(Dest->begin()));

    // We know all single-entry PHI nodes in the inlined function have been
    // removed, so we just need to splice the blocks.
    BI->eraseFromParent();
    
    // Make all PHI nodes that referred to Dest now refer to I as their source.
    Dest->replaceAllUsesWith(&*I);

    // Move all the instructions in the succ to the pred.
    I->getInstList().splice(I->end(), Dest->getInstList());
    
    // Remove the dest block.
    Dest->eraseFromParent();
    
    // Do not increment I, iteratively merge all things this block branches to.
  }

  // Make a final pass over the basic blocks from the old function to gather
  // any return instructions which survived folding. We have to do this here
  // because we can iteratively remove and merge returns above.
  for (Function::iterator I = cast<BasicBlock>(VMap[StartingBB])->getIterator(),
                          E = NewFunc->end();
       I != E; ++I)
    if (ReturnInst *RI = dyn_cast<ReturnInst>(I->getTerminator()))
      Returns.push_back(RI);
}