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post-dominators. This code was written/adapted by Daniel Berlin! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25144 91177308-0d34-0410-b5e6-96231b3b80d8
317 lines
12 KiB
C++
317 lines
12 KiB
C++
//===- PostDominators.cpp - Post-Dominator Calculation --------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the post-dominator construction algorithms.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/PostDominators.h"
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#include "llvm/Instructions.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/SetOperations.h"
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using namespace llvm;
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//===----------------------------------------------------------------------===//
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// PostDominatorSet Implementation
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//===----------------------------------------------------------------------===//
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static RegisterAnalysis<PostDominatorSet>
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B("postdomset", "Post-Dominator Set Construction", true);
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// Postdominator set construction. This converts the specified function to only
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// have a single exit node (return stmt), then calculates the post dominance
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// sets for the function.
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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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// 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 (succ_begin(I) == succ_end(I))
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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<BasicBlock*> Visited;
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DomSetType WorkingSet;
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for (unsigned i = 0, e = Roots.size(); i != e; ++i)
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for (idf_ext_iterator<BasicBlock*> It = idf_ext_begin(Roots[i], Visited),
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E = idf_ext_end(Roots[i], Visited); 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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}
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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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//===----------------------------------------------------------------------===//
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// ImmediatePostDominators Implementation
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//===----------------------------------------------------------------------===//
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static RegisterAnalysis<ImmediatePostDominators>
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D("postidom", "Immediate Post-Dominators Construction", true);
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// calcIDoms - Calculate the immediate dominator mapping, given a set of
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// dominators for every basic block.
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void ImmediatePostDominators::calcIDoms(const DominatorSetBase &DS) {
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// Loop over all of the nodes that have dominators... figuring out the IDOM
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// for each node...
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//
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for (DominatorSet::const_iterator DI = DS.begin(), DEnd = DS.end();
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DI != DEnd; ++DI) {
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BasicBlock *BB = DI->first;
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const DominatorSet::DomSetType &Dominators = DI->second;
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unsigned DomSetSize = Dominators.size();
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if (DomSetSize == 1) continue; // Root node... IDom = null
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// Loop over all dominators of this node. This corresponds to looping over
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// nodes in the dominator chain, looking for a node whose dominator set is
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// equal to the current nodes, except that the current node does not exist
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// in it. This means that it is one level higher in the dom chain than the
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// current node, and it is our idom!
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//
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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 of elements
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// in the dominator set indicates what level the node is at in the chain.
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// We want the node immediately above us, so it will have an identical
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// dominator set, 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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IDoms[BB] = *I;
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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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// PostDominatorTree Implementation
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//===----------------------------------------------------------------------===//
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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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if (Roots.empty()) return;
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BasicBlock *Root = Roots.size() == 1 ? Roots[0] : 0;
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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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// not exist in it. This means that it is one level higher in the dom
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// chain than the current node, and it is our idom! We know that we have
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// already added a DominatorTree node for our idom, because the idom must
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// be a predecessor in the depth first order that we are iterating through
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// the function.
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//
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for (DominatorSet::DomSetType::const_iterator I = Dominators.begin(),
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E = Dominators.end(); I != E; ++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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// 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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// PostETForest Implementation
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//===----------------------------------------------------------------------===//
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static RegisterAnalysis<PostETForest>
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G("postetforest", "Post-ET-Forest Construction", true);
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ETNode *PostETForest::getNodeForBlock(BasicBlock *BB) {
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ETNode *&BBNode = Nodes[BB];
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if (BBNode) return BBNode;
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// Haven't calculated this node yet? Get or calculate the node for the
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// immediate dominator.
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BasicBlock *IDom = getAnalysis<ImmediatePostDominators>()[BB];
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// If we are unreachable, we may not have an immediate dominator.
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if (!IDom)
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return BBNode = new ETNode(BB);
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else {
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ETNode *IDomNode = getNodeForBlock(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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BBNode = new ETNode(BB);
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BBNode->setFather(IDomNode);
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return BBNode;
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}
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}
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void PostETForest::calculate(const ImmediatePostDominators &ID) {
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for (unsigned i = 0, e = Roots.size(); i != e; ++i)
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Nodes[Roots[i]] = new ETNode(Roots[i]); // Add a node for the root
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// Iterate over all nodes in inverse 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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ETNode *&BBNode = Nodes[BB];
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if (!BBNode) {
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ETNode *IDomNode = NULL;
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if (ID.get(BB))
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IDomNode = getNodeForBlock(ID.get(BB));
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// Add a new ETNode for this BasicBlock, and set it's parent
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// to it's immediate dominator.
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BBNode = new ETNode(BB);
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if (IDomNode)
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BBNode->setFather(IDomNode);
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}
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}
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int dfsnum = 0;
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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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if (!getNodeForBlock(*I)->hasFather())
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getNodeForBlock(*I)->assignDFSNumber(dfsnum);
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}
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DFSInfoValid = true;
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}
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//===----------------------------------------------------------------------===//
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// PostDominanceFrontier Implementation
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//===----------------------------------------------------------------------===//
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static RegisterAnalysis<PostDominanceFrontier>
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H("postdomfrontier", "Post-Dominance Frontier Construction", true);
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const DominanceFrontier::DomSetType &
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PostDominanceFrontier::calculate(const PostDominatorTree &DT,
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const DominatorTree::Node *Node) {
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// Loop over CFG successors to calculate DFlocal[Node]
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BasicBlock *BB = Node->getBlock();
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DomSetType &S = Frontiers[BB]; // The new set to fill in...
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if (getRoots().empty()) return S;
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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 predecessor?
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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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// children in the IDomTree)
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//
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for (PostDominatorTree::Node::const_iterator
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NI = Node->begin(), NE = Node->end(); NI != NE; ++NI) {
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DominatorTree::Node *IDominee = *NI;
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const DomSetType &ChildDF = calculate(DT, IDominee);
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DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
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for (; CDFI != CDFE; ++CDFI) {
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if (!Node->properlyDominates(DT[*CDFI]))
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S.insert(*CDFI);
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}
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}
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return S;
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}
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// stub - a dummy function to make linking work ok.
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void PostDominanceFrontier::stub() {
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}
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