llvm-6502/lib/VMCore/DominatorCalculation.h

//==- DominatorCalculation.h - Dominator Calculation -------------*- C++ -*-==//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by Owen Anderson and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_VMCORE_DOMINATOR_CALCULATION_H
#define LLVM_VMCORE_DOMINATOR_CALCULATION_H

#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/DominatorInternals.h"

//===----------------------------------------------------------------------===//
//
// DominatorTree construction - This pass constructs immediate dominator
// information for a flow-graph based on the algorithm described in this
// document:
//
//   A Fast Algorithm for Finding Dominators in a Flowgraph
//   T. Lengauer & R. Tarjan, ACM TOPLAS July 1979, pgs 121-141.
//
// This implements both the O(n*ack(n)) and the O(n*log(n)) versions of EVAL and
// LINK, but it turns out that the theoretically slower O(n*log(n))
// implementation is actually faster than the "efficient" algorithm (even for
// large CFGs) because the constant overheads are substantially smaller.  The
// lower-complexity version can be enabled with the following #define:
//
#define BALANCE_IDOM_TREE 0
//
//===----------------------------------------------------------------------===//

namespace llvm {
  
void DTcalculate(DominatorTree& DT, Function &F) {
  BasicBlock* Root = DT.Roots[0];

  // Add a node for the root...
  DT.DomTreeNodes[Root] = DT.RootNode = new DomTreeNode(Root, 0);

  DT.Vertex.push_back(0);

  // Step #1: Number blocks in depth-first order and initialize variables used
  // in later stages of the algorithm.
  unsigned N = DFSPass<GraphTraits<BasicBlock*> >(DT, Root, 0);

  for (unsigned i = N; i >= 2; --i) {
    BasicBlock *W = DT.Vertex[i];
    DominatorTree::InfoRec &WInfo = DT.Info[W];

    // Step #2: Calculate the semidominators of all vertices
    for (pred_iterator PI = pred_begin(W), E = pred_end(W); PI != E; ++PI)
      if (DT.Info.count(*PI)) {  // Only if this predecessor is reachable!
        unsigned SemiU = DT.Info[Eval(DT, *PI)].Semi;
        if (SemiU < WInfo.Semi)
          WInfo.Semi = SemiU;
      }

    DT.Info[DT.Vertex[WInfo.Semi]].Bucket.push_back(W);

    BasicBlock *WParent = WInfo.Parent;
    Link(DT, WParent, W, WInfo);

    // Step #3: Implicitly define the immediate dominator of vertices
    std::vector<BasicBlock*> &WParentBucket = DT.Info[WParent].Bucket;
    while (!WParentBucket.empty()) {
      BasicBlock *V = WParentBucket.back();
      WParentBucket.pop_back();
      BasicBlock *U = Eval(DT, V);
      DT.IDoms[V] = DT.Info[U].Semi < DT.Info[V].Semi ? U : WParent;
    }
  }

  // Step #4: Explicitly define the immediate dominator of each vertex
  for (unsigned i = 2; i <= N; ++i) {
    BasicBlock *W = DT.Vertex[i];
    BasicBlock *&WIDom = DT.IDoms[W];
    if (WIDom != DT.Vertex[DT.Info[W].Semi])
      WIDom = DT.IDoms[WIDom];
  }

  // Loop over all of the reachable blocks in the function...
  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
    if (BasicBlock *ImmDom = DT.getIDom(I)) {  // Reachable block.
      DomTreeNode *BBNode = DT.DomTreeNodes[I];
      if (BBNode) continue;  // Haven't calculated this node yet?

      // Get or calculate the node for the immediate dominator
      DomTreeNode *IDomNode = DT.getNodeForBlock(ImmDom);

      // Add a new tree node for this BasicBlock, and link it as a child of
      // IDomNode
      DomTreeNode *C = new DomTreeNode(I, IDomNode);
      DT.DomTreeNodes[I] = IDomNode->addChild(C);
    }

  // Free temporary memory used to construct idom's
  DT.Info.clear();
  DT.IDoms.clear();
  std::vector<BasicBlock*>().swap(DT.Vertex);

  DT.updateDFSNumbers();
}

}
#endif