path: root/lib/Analysis/PostDominators.cpp

//===- DominatorSet.cpp - Dominator Set Calculation --------------*- C++ -*--=//
//
// This file provides a simple class to calculate the dominator set of a
// function.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/Dominators.h"
#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
#include "llvm/Support/CFG.h"
#include "llvm/Assembly/Writer.h"
#include "Support/DepthFirstIterator.h"
#include "Support/STLExtras.h"
#include "Support/SetOperations.h"
#include <algorithm>
using std::set;

//===----------------------------------------------------------------------===//
//  DominatorSet Implementation
//===----------------------------------------------------------------------===//

static RegisterAnalysis<DominatorSet>
A("domset", "Dominator Set Construction");
static RegisterAnalysis<PostDominatorSet>
B("postdomset", "Post-Dominator Set Construction");

AnalysisID DominatorSet::ID = A;
AnalysisID PostDominatorSet::ID = B;

// dominates - Return true if A dominates B.  This performs the special checks
// neccesary if A and B are in the same basic block.
//
bool DominatorSetBase::dominates(Instruction *A, Instruction *B) const {
  BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
  if (BBA != BBB) return dominates(BBA, BBB);
  
  // Loop through the basic block until we find A or B.
  BasicBlock::iterator I = BBA->begin();
  for (; &*I != A && &*I != B; ++I) /*empty*/;
  
  // A dominates B if it is found first in the basic block...
  return &*I == A;
}

// runOnFunction - This method calculates the forward dominator sets for the
// specified function.
//
bool DominatorSet::runOnFunction(Function &F) {
  Doms.clear();   // Reset from the last time we were run...
  Root = &F.getEntryNode();
  assert(pred_begin(Root) == pred_end(Root) &&
	 "Root node has predecessors in function!");

  bool Changed;
  do {
    Changed = false;

    DomSetType WorkingSet;
    df_iterator<Function*> It = df_begin(&F), End = df_end(&F);
    for ( ; It != End; ++It) {
      BasicBlock *BB = *It;
      pred_iterator PI = pred_begin(BB), PEnd = pred_end(BB);
      if (PI != PEnd) {                // Is there SOME predecessor?
	// Loop until we get to a predecessor that has had it's dom set filled
	// in at least once.  We are guaranteed to have this because we are
	// traversing the graph in DFO and have handled start nodes specially.
	//
	while (Doms[*PI].size() == 0) ++PI;
	WorkingSet = Doms[*PI];

	for (++PI; PI != PEnd; ++PI) { // Intersect all of the predecessor sets
	  DomSetType &PredSet = Doms[*PI];
	  if (PredSet.size())
	    set_intersect(WorkingSet, PredSet);
	}
      }
	
      WorkingSet.insert(BB);           // A block always dominates itself
      DomSetType &BBSet = Doms[BB];
      if (BBSet != WorkingSet) {
	BBSet.swap(WorkingSet);        // Constant time operation!
	Changed = true;                // The sets changed.
      }
      WorkingSet.clear();              // Clear out the set for next iteration
    }
  } while (Changed);
  return false;
}


// Postdominator set construction.  This converts the specified function to only
// have a single exit node (return stmt), then calculates the post dominance
// sets for the function.
//
bool PostDominatorSet::runOnFunction(Function &F) {
  Doms.clear();   // Reset from the last time we were run...
  // Since we require that the unify all exit nodes pass has been run, we know
  // that there can be at most one return instruction in the function left.
  // Get it.
  //
  Root = getAnalysis<UnifyFunctionExitNodes>().getExitNode();

  if (Root == 0) {  // No exit node for the function?  Postdomsets are all empty
    for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
      Doms[FI] = DomSetType();
    return false;
  }

  bool Changed;
  do {
    Changed = false;

    set<const BasicBlock*> Visited;
    DomSetType WorkingSet;
    idf_iterator<BasicBlock*> It = idf_begin(Root), End = idf_end(Root);
    for ( ; It != End; ++It) {
      BasicBlock *BB = *It;
      succ_iterator PI = succ_begin(BB), PEnd = succ_end(BB);
      if (PI != PEnd) {                // Is there SOME predecessor?
	// Loop until we get to a successor that has had it's dom set filled
	// in at least once.  We are guaranteed to have this because we are
	// traversing the graph in DFO and have handled start nodes specially.
	//
	while (Doms[*PI].size() == 0) ++PI;
	WorkingSet = Doms[*PI];

	for (++PI; PI != PEnd; ++PI) { // Intersect all of the successor sets
	  DomSetType &PredSet = Doms[*PI];
	  if (PredSet.size())
	    set_intersect(WorkingSet, PredSet);
	}
      }
	
      WorkingSet.insert(BB);           // A block always dominates itself
      DomSetType &BBSet = Doms[BB];
      if (BBSet != WorkingSet) {
	BBSet.swap(WorkingSet);        // Constant time operation!
	Changed = true;                // The sets changed.
      }
      WorkingSet.clear();              // Clear out the set for next iteration
    }
  } while (Changed);
  return false;
}

// getAnalysisUsage - This obviously provides a post-dominator set, but it also
// requires the UnifyFunctionExitNodes pass.
//
void PostDominatorSet::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.setPreservesAll();
  AU.addRequired(UnifyFunctionExitNodes::ID);
}

static ostream &operator<<(ostream &o, const set<BasicBlock*> &BBs) {
  for (set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
       I != E; ++I) {
    o << "  ";
    WriteAsOperand(o, *I, false);
    o << "\n";
   }
  return o;
}

void DominatorSetBase::print(std::ostream &o) const {
  for (const_iterator I = begin(), E = end(); I != E; ++I)
    o << "=============================--------------------------------\n"
      << "\nDominator Set For Basic Block\n" << I->first
      << "-------------------------------\n" << I->second << "\n";
}

//===----------------------------------------------------------------------===//
//  ImmediateDominators Implementation
//===----------------------------------------------------------------------===//

static RegisterAnalysis<ImmediateDominators>
C("idom", "Immediate Dominators Construction");
static RegisterAnalysis<ImmediatePostDominators>
D("postidom", "Immediate Post-Dominators Construction");

AnalysisID ImmediateDominators::ID = C;
AnalysisID ImmediatePostDominators::ID = D;

// calcIDoms - Calculate the immediate dominator mapping, given a set of
// dominators for every basic block.
void ImmediateDominatorsBase::calcIDoms(const DominatorSetBase &DS) {
  // Loop over all of the nodes that have dominators... figuring out the IDOM
  // for each node...
  //
  for (DominatorSet::const_iterator DI = DS.begin(), DEnd = DS.end(); 
       DI != DEnd; ++DI) {
    BasicBlock *BB = DI->first;
    const DominatorSet::DomSetType &Dominators = DI->second;
    unsigned DomSetSize = Dominators.size();
    if (DomSetSize == 1) continue;  // Root node... IDom = null

    // Loop over all dominators of this node.  This corresponds to looping over
    // nodes in the dominator chain, looking for a node whose dominator set is
    // equal to the current nodes, except that the current node does not exist
    // in it.  This means that it is one level higher in the dom chain than the
    // current node, and it is our idom!
    //
    DominatorSet::DomSetType::const_iterator I = Dominators.begin();
    DominatorSet::DomSetType::const_iterator End = Dominators.end();
    for (; I != End; ++I) {   // Iterate over dominators...
      // All of our dominators should form a chain, where the number of elements
      // in the dominator set indicates what level the node is at in the chain.
      // We want the node immediately above us, so it will have an identical 
      // dominator set, except that BB will not dominate it... therefore it's
      // dominator set size will be one less than BB's...
      //