| //===- PostDominators.cpp - Post-Dominator Calculation --------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements the post-dominator construction algorithms. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/PostDominators.h" |
| #include "llvm/iTerminators.h" |
| #include "llvm/Support/CFG.h" |
| #include "Support/DepthFirstIterator.h" |
| #include "Support/SetOperations.h" |
| |
| //===----------------------------------------------------------------------===// |
| // PostDominatorSet Implementation |
| //===----------------------------------------------------------------------===// |
| |
| static RegisterAnalysis<PostDominatorSet> |
| B("postdomset", "Post-Dominator Set Construction", true); |
| |
| // 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... |
| |
| // Scan the function looking for the root nodes of the post-dominance |
| // relationships. These blocks end with return and unwind instructions. |
| // While we are iterating over the function, we also initialize all of the |
| // domsets to empty. |
| Roots.clear(); |
| for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) { |
| Doms[I]; // Initialize to empty |
| |
| if (isa<ReturnInst>(I->getTerminator()) || |
| isa<UnwindInst>(I->getTerminator())) |
| Roots.push_back(I); |
| } |
| |
| // If there are no exit nodes for the function, postdomsets are all empty. |
| // This can happen if the function just contains an infinite loop, for |
| // example. |
| if (Roots.empty()) return false; |
| |
| // If we have more than one root, we insert an artificial "null" exit, which |
| // has "virtual edges" to each of the real exit nodes. |
| if (Roots.size() > 1) |
| Doms[0].insert(0); |
| |
| bool Changed; |
| do { |
| Changed = false; |
| |
| std::set<BasicBlock*> Visited; |
| DomSetType WorkingSet; |
| |
| for (unsigned i = 0, e = Roots.size(); i != e; ++i) |
| for (idf_ext_iterator<BasicBlock*> It = idf_ext_begin(Roots[i], Visited), |
| E = idf_ext_end(Roots[i], Visited); It != E; ++It) { |
| BasicBlock *BB = *It; |
| succ_iterator SI = succ_begin(BB), SE = succ_end(BB); |
| if (SI != SE) { // Is there SOME successor? |
| // 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[*SI].size() == 0) ++SI; |
| WorkingSet = Doms[*SI]; |
| |
| for (++SI; SI != SE; ++SI) { // Intersect all of the successor sets |
| DomSetType &SuccSet = Doms[*SI]; |
| if (SuccSet.size()) |
| set_intersect(WorkingSet, SuccSet); |
| } |
| } else { |
| // If this node has no successors, it must be one of the root nodes. |
| // We will already take care of the notion that the node |
| // post-dominates itself. The only thing we have to add is that if |
| // there are multiple root nodes, we want to insert a special "null" |
| // exit node which dominates the roots as well. |
| if (Roots.size() > 1) |
| WorkingSet.insert(0); |
| } |
| |
| 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; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // ImmediatePostDominators Implementation |
| //===----------------------------------------------------------------------===// |
| |
| static RegisterAnalysis<ImmediatePostDominators> |
| D("postidom", "Immediate Post-Dominators Construction", true); |
| |
| //===----------------------------------------------------------------------===// |
| // PostDominatorTree Implementation |
| //===----------------------------------------------------------------------===// |
| |
| static RegisterAnalysis<PostDominatorTree> |
| F("postdomtree", "Post-Dominator Tree Construction", true); |
| |
| void PostDominatorTree::calculate(const PostDominatorSet &DS) { |
| if (Roots.empty()) return; |
| BasicBlock *Root = Roots.size() == 1 ? Roots[0] : 0; |
| |
| Nodes[Root] = RootNode = new Node(Root, 0); // Add a node for the root... |
| |
| // Iterate over all nodes in depth first order... |
| for (unsigned i = 0, e = Roots.size(); i != e; ++i) |
| for (idf_iterator<BasicBlock*> I = idf_begin(Roots[i]), |
| E = idf_end(Roots[i]); I != E; ++I) { |
| BasicBlock *BB = *I; |
| const DominatorSet::DomSetType &Dominators = DS.getDominators(BB); |
| unsigned DomSetSize = Dominators.size(); |
| if (DomSetSize == 1) continue; // Root node... IDom = null |
| |
| // If we have already computed the immediate dominator for this node, |
| // don't revisit. This can happen due to nodes reachable from multiple |
| // roots, but which the idf_iterator doesn't know about. |
| if (Nodes.find(BB) != Nodes.end()) continue; |
| |
| // 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! We know that we have |
| // already added a DominatorTree node for our idom, because the idom must |
| // be a predecessor in the depth first order that we are iterating through |
| // the function. |
| // |
| 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... |
| // |
| if (DS.getDominators(*I).size() == DomSetSize - 1) { |
| // We know that the immediate dominator should already have a node, |
| // because we are traversing the CFG in depth first order! |
| // |
| Node *IDomNode = Nodes[*I]; |
| assert(IDomNode && "No node for IDOM?"); |
| |
| // Add a new tree node for this BasicBlock, and link it as a child of |
| // IDomNode |
| Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode)); |
| break; |
| } |
| } |
| } |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // PostDominanceFrontier Implementation |
| //===----------------------------------------------------------------------===// |
| |
| static RegisterAnalysis<PostDominanceFrontier> |
| H("postdomfrontier", "Post-Dominance Frontier Construction", true); |
| |
| const DominanceFrontier::DomSetType & |
| PostDominanceFrontier::calculate(const PostDominatorTree &DT, |
| const DominatorTree::Node *Node) { |
| // Loop over CFG successors to calculate DFlocal[Node] |
| BasicBlock *BB = Node->getBlock(); |
| DomSetType &S = Frontiers[BB]; // The new set to fill in... |
| if (getRoots().empty()) return S; |
| |
| if (BB) |
| for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB); |
| SI != SE; ++SI) |
| // Does Node immediately dominate this predecessor? |
| if (DT[*SI]->getIDom() != Node) |
| S.insert(*SI); |
| |
| // At this point, S is DFlocal. Now we union in DFup's of our children... |
| // Loop through and visit the nodes that Node immediately dominates (Node's |
| // children in the IDomTree) |
| // |
| for (PostDominatorTree::Node::const_iterator |
| NI = Node->begin(), NE = Node->end(); NI != NE; ++NI) { |
| DominatorTree::Node *IDominee = *NI; |
| const DomSetType &ChildDF = calculate(DT, IDominee); |
| |
| DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end(); |
| for (; CDFI != CDFE; ++CDFI) { |
| if (!Node->dominates(DT[*CDFI])) |
| S.insert(*CDFI); |
| } |
| } |
| |
| return S; |
| } |
| |
| // stub - a dummy function to make linking work ok. |
| void PostDominanceFrontier::stub() { |
| } |
