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Diffstat (limited to 'lib/Analysis/PostDominators.cpp')
| -rw-r--r-- | lib/Analysis/PostDominators.cpp | 253 |
1 files changed, 253 insertions, 0 deletions
diff --git a/lib/Analysis/PostDominators.cpp b/lib/Analysis/PostDominators.cpp new file mode 100644 index 0000000000..381b03c714 --- /dev/null +++ b/lib/Analysis/PostDominators.cpp @@ -0,0 +1,253 @@ +//===- 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/Instructions.h" +#include "llvm/Support/CFG.h" +#include "llvm/ADT/DepthFirstIterator.h" +#include "llvm/ADT/SetOperations.h" +using namespace llvm; + +//===----------------------------------------------------------------------===// +// 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 (succ_begin(I) == succ_end(I)) + 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); + + +// calcIDoms - Calculate the immediate dominator mapping, given a set of +// dominators for every basic block. +void ImmediatePostDominators::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... + // + if (DS.getDominators(*I).size() == DomSetSize - 1) { + IDoms[BB] = *I; + break; + } + } + } +} + +//===----------------------------------------------------------------------===// +// 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. + // + for (DominatorSet::DomSetType::const_iterator I = Dominators.begin(), + E = Dominators.end(); I != E; ++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() { +} + |