forked from OSchip/llvm-project
Rework post dominator information so that we do not have to
unify all exit nodes of a function to compute post-dominance information. This does not work with functions that have both unwind and return nodes, because we cannot unify these blocks. The new implementation is better anyway. :) llvm-svn: 8460
This commit is contained in:
Chris Lattner
parent
2dcab00d57
commit
8157505fae
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@ -5,7 +5,7 @@
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/PostDominators.h"
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#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
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#include "llvm/iTerminators.h"
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#include "llvm/Support/CFG.h"
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#include "Support/DepthFirstIterator.h"
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#include "Support/SetOperations.h"
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@ -23,75 +23,77 @@ B("postdomset", "Post-Dominator Set Construction", true);
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//
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bool PostDominatorSet::runOnFunction(Function &F) {
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Doms.clear(); // Reset from the last time we were run...
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// Since we require that the unify all exit nodes pass has been run, we know
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// that there can be at most one return instruction in the function left.
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// Get it.
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//
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Root = getAnalysis<UnifyFunctionExitNodes>().getExitNode();
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if (Root == 0) { // No exit node for the function? Postdomsets are all empty
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for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
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Doms[FI] = DomSetType();
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return false;
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// Scan the function looking for the root nodes of the post-dominance
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// relationships. These blocks end with return and unwind instructions.
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// While we are iterating over the function, we also initialize all of the
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// domsets to empty.
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Roots.clear();
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
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Doms[I]; // Initialize to empty
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if (isa<ReturnInst>(I->getTerminator()) ||
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isa<UnwindInst>(I->getTerminator()))
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Roots.push_back(I);
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}
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// If there are no exit nodes for the function, postdomsets are all empty.
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// This can happen if the function just contains an infinite loop, for
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// example.
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if (Roots.empty()) return false;
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// If we have more than one root, we insert an artificial "null" exit, which
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// has "virtual edges" to each of the real exit nodes.
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if (Roots.size() > 1)
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Doms[0].insert(0);
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bool Changed;
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do {
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Changed = false;
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std::set<const BasicBlock*> Visited;
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DomSetType WorkingSet;
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idf_iterator<BasicBlock*> It = idf_begin(Root), End = idf_end(Root);
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for ( ; It != End; ++It) {
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BasicBlock *BB = *It;
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succ_iterator PI = succ_begin(BB), PEnd = succ_end(BB);
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if (PI != PEnd) { // Is there SOME predecessor?
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// Loop until we get to a successor that has had it's dom set filled
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// in at least once. We are guaranteed to have this because we are
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// traversing the graph in DFO and have handled start nodes specially.
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//
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while (Doms[*PI].size() == 0) ++PI;
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WorkingSet = Doms[*PI];
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for (++PI; PI != PEnd; ++PI) { // Intersect all of the successor sets
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DomSetType &PredSet = Doms[*PI];
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if (PredSet.size())
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set_intersect(WorkingSet, PredSet);
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}
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} else if (BB != Root) {
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// If this isn't the root basic block and it has no successors, it must
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// be an non-returning block. Fib a bit by saying that the root node
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// postdominates this unreachable node. This isn't exactly true,
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// because there is no path from this node to the root node, but it is
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// sorta true because any paths to the exit node would have to go
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// through this node.
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//
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// This allows for postdominator properties to be built for code that
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// doesn't return in a reasonable manner.
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//
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WorkingSet = Doms[Root];
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}
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for (unsigned i = 0, e = Roots.size(); i != e; ++i)
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for (idf_iterator<BasicBlock*> It = idf_begin(Roots[i]),
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E = idf_end(Roots[i]); It != E; ++It) {
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BasicBlock *BB = *It;
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succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
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if (SI != SE) { // Is there SOME successor?
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// Loop until we get to a successor that has had it's dom set filled
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// in at least once. We are guaranteed to have this because we are
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// traversing the graph in DFO and have handled start nodes specially.
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//
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while (Doms[*SI].size() == 0) ++SI;
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WorkingSet = Doms[*SI];
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for (++SI; SI != SE; ++SI) { // Intersect all of the successor sets
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DomSetType &SuccSet = Doms[*SI];
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if (SuccSet.size())
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set_intersect(WorkingSet, SuccSet);
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}
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} else {
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// If this node has no successors, it must be one of the root nodes.
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// We will already take care of the notion that the node
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// post-dominates itself. The only thing we have to add is that if
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// there are multiple root nodes, we want to insert a special "null"
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// exit node which dominates the roots as well.
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if (Roots.size() > 1)
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WorkingSet.insert(0);
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}
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WorkingSet.insert(BB); // A block always dominates itself
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DomSetType &BBSet = Doms[BB];
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if (BBSet != WorkingSet) {
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BBSet.swap(WorkingSet); // Constant time operation!
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Changed = true; // The sets changed.
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WorkingSet.insert(BB); // A block always dominates itself
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DomSetType &BBSet = Doms[BB];
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if (BBSet != WorkingSet) {
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BBSet.swap(WorkingSet); // Constant time operation!
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Changed = true; // The sets changed.
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}
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WorkingSet.clear(); // Clear out the set for next iteration
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}
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WorkingSet.clear(); // Clear out the set for next iteration
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}
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} while (Changed);
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return false;
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}
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// getAnalysisUsage - This obviously provides a post-dominator set, but it also
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// requires the UnifyFunctionExitNodes pass.
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//
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void PostDominatorSet::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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AU.addRequired<UnifyFunctionExitNodes>();
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}
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//===----------------------------------------------------------------------===//
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// ImmediatePostDominators Implementation
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//===----------------------------------------------------------------------===//
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@ -107,17 +109,25 @@ static RegisterAnalysis<PostDominatorTree>
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F("postdomtree", "Post-Dominator Tree Construction", true);
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void PostDominatorTree::calculate(const PostDominatorSet &DS) {
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Nodes[Root] = new Node(Root, 0); // Add a node for the root...
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if (Roots.empty()) return;
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BasicBlock *Root = Roots.size() == 1 ? Roots[0] : 0;
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if (Root) {
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// Iterate over all nodes in depth first order...
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for (idf_iterator<BasicBlock*> I = idf_begin(Root), E = idf_end(Root);
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I != E; ++I) {
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Nodes[Root] = RootNode = new Node(Root, 0); // Add a node for the root...
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// Iterate over all nodes in depth first order...
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for (unsigned i = 0, e = Roots.size(); i != e; ++i)
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for (idf_iterator<BasicBlock*> I = idf_begin(Roots[i]),
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E = idf_end(Roots[i]); I != E; ++I) {
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BasicBlock *BB = *I;
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const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
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unsigned DomSetSize = Dominators.size();
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if (DomSetSize == 1) continue; // Root node... IDom = null
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// If we have already computed the immediate dominator for this node,
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// don't revisit. This can happen due to nodes reachable from multiple
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// roots, but which the idf_iterator doesn't know about.
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if (Nodes.find(BB) != Nodes.end()) continue;
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// Loop over all dominators of this node. This corresponds to looping
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// over nodes in the dominator chain, looking for a node whose dominator
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// set is equal to the current nodes, except that the current node does
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@ -130,28 +140,27 @@ void PostDominatorTree::calculate(const PostDominatorSet &DS) {
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DominatorSet::DomSetType::const_iterator I = Dominators.begin();
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DominatorSet::DomSetType::const_iterator End = Dominators.end();
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for (; I != End; ++I) { // Iterate over dominators...
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// All of our dominators should form a chain, where the number
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// of elements in the dominator set indicates what level the
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// node is at in the chain. We want the node immediately
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// above us, so it will have an identical dominator set,
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// except that BB will not dominate it... therefore it's
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// dominator set size will be one less than BB's...
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//
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if (DS.getDominators(*I).size() == DomSetSize - 1) {
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// We know that the immediate dominator should already have a node,
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// because we are traversing the CFG in depth first order!
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//
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Node *IDomNode = Nodes[*I];
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assert(IDomNode && "No node for IDOM?");
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// All of our dominators should form a chain, where the number
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// of elements in the dominator set indicates what level the
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// node is at in the chain. We want the node immediately
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// above us, so it will have an identical dominator set,
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// except that BB will not dominate it... therefore it's
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// dominator set size will be one less than BB's...
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//
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if (DS.getDominators(*I).size() == DomSetSize - 1) {
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// We know that the immediate dominator should already have a node,
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// because we are traversing the CFG in depth first order!
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//
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Node *IDomNode = Nodes[*I];
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assert(IDomNode && "No node for IDOM?");
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// Add a new tree node for this BasicBlock, and link it as a child of
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// IDomNode
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Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
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break;
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}
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// Add a new tree node for this BasicBlock, and link it as a child of
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// IDomNode
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Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
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break;
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}
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}
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}
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}
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}
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//===----------------------------------------------------------------------===//
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@ -167,14 +176,14 @@ PostDominanceFrontier::calculate(const PostDominatorTree &DT,
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// Loop over CFG successors to calculate DFlocal[Node]
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BasicBlock *BB = Node->getNode();
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DomSetType &S = Frontiers[BB]; // The new set to fill in...
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if (!Root) return S;
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if (getRoots().empty()) return S;
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for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB);
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SI != SE; ++SI) {
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// Does Node immediately dominate this predeccessor?
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if (DT[*SI]->getIDom() != Node)
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S.insert(*SI);
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}
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if (BB)
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for (pred_iterator SI = pred_begin(BB), SE = pred_end(BB);
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SI != SE; ++SI)
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// Does Node immediately dominate this predeccessor?
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if (DT[*SI]->getIDom() != Node)
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S.insert(*SI);
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// At this point, S is DFlocal. Now we union in DFup's of our children...
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// Loop through and visit the nodes that Node immediately dominates (Node's
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