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353 lines
13 KiB
C++
353 lines
13 KiB
C++
//===- Dominators.cpp - Dominator Calculation -----------------------------===//
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//
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// This file implements simple dominator construction algorithms for finding
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// forward dominators. Postdominators are available in libanalysis, but are not
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// included in libvmcore, because it's not needed. Forward dominators are
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// needed to support the Verifier pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Assembly/Writer.h"
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#include "Support/DepthFirstIterator.h"
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#include "Support/SetOperations.h"
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//===----------------------------------------------------------------------===//
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// DominatorSet Implementation
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//===----------------------------------------------------------------------===//
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static RegisterAnalysis<DominatorSet>
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A("domset", "Dominator Set Construction", true);
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// dominates - Return true if A dominates B. This performs the special checks
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// neccesary if A and B are in the same basic block.
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//
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bool DominatorSetBase::dominates(Instruction *A, Instruction *B) const {
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BasicBlock *BBA = A->getParent(), *BBB = B->getParent();
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if (BBA != BBB) return dominates(BBA, BBB);
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// Loop through the basic block until we find A or B.
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BasicBlock::iterator I = BBA->begin();
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for (; &*I != A && &*I != B; ++I) /*empty*/;
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// A dominates B if it is found first in the basic block...
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return &*I == A;
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}
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void DominatorSet::calculateDominatorsFromBlock(BasicBlock *RootBB) {
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bool Changed;
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Doms[RootBB].insert(RootBB); // Root always dominates itself...
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do {
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Changed = false;
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DomSetType WorkingSet;
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df_iterator<BasicBlock*> It = df_begin(RootBB), End = df_end(RootBB);
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for ( ; It != End; ++It) {
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BasicBlock *BB = *It;
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pred_iterator PI = pred_begin(BB), PEnd = pred_end(BB);
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if (PI != PEnd) { // Is there SOME predecessor?
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// Loop until we get to a predecessor 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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// except when there are unreachable blocks.
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//
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while (PI != PEnd && Doms[*PI].empty()) ++PI;
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if (PI != PEnd) { // Not unreachable code case?
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WorkingSet = Doms[*PI];
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// Intersect all of the predecessor sets
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for (++PI; PI != PEnd; ++PI) {
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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 {
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// Otherwise this block is unreachable. it doesn't really matter what
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// we use for the dominator set for the node...
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//
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WorkingSet = Doms[Root];
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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 predecessors, it
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// must be an unreachable block. Fib a bit by saying that the root node
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// dominates this unreachable node. This isn't exactly true, because
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// there is no path from the entry node to this node, but it is sorta
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// true because any paths to this node would have to go through the
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// entry node.
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//
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// This allows for dominator properties to be built for unreachable code
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// in a reasonable manner.
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//
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WorkingSet = Doms[Root];
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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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}
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// runOnFunction - This method calculates the forward dominator sets for the
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// specified function.
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//
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bool DominatorSet::runOnFunction(Function &F) {
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Root = &F.getEntryNode();
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assert(pred_begin(Root) == pred_end(Root) &&
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"Root node has predecessors in function!");
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recalculate();
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return false;
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}
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void DominatorSet::recalculate() {
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Doms.clear(); // Reset from the last time we were run...
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// Calculate dominator sets for the reachable basic blocks...
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calculateDominatorsFromBlock(Root);
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// Every basic block in the function should at least dominate themselves, and
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// thus every basic block should have an entry in Doms. The one case where we
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// miss this is when a basic block is unreachable. To get these we now do an
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// extra pass over the function, calculating dominator information for
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// unreachable blocks.
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//
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Function *F = Root->getParent();
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for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
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if (Doms[I].count(I) == 0)
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calculateDominatorsFromBlock(I);
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}
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static std::ostream &operator<<(std::ostream &o,
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const std::set<BasicBlock*> &BBs) {
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for (std::set<BasicBlock*>::const_iterator I = BBs.begin(), E = BBs.end();
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I != E; ++I) {
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o << " ";
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WriteAsOperand(o, *I, false);
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o << "\n";
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}
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return o;
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}
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void DominatorSetBase::print(std::ostream &o) const {
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for (const_iterator I = begin(), E = end(); I != E; ++I) {
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o << "=============================--------------------------------\n"
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<< "\nDominator Set For Basic Block: ";
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WriteAsOperand(o, I->first, false);
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o << "\n-------------------------------\n" << I->second << "\n";
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}
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}
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//===----------------------------------------------------------------------===//
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// ImmediateDominators Implementation
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//===----------------------------------------------------------------------===//
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static RegisterAnalysis<ImmediateDominators>
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C("idom", "Immediate 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 ImmediateDominatorsBase::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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void ImmediateDominatorsBase::print(std::ostream &o) const {
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for (const_iterator I = begin(), E = end(); I != E; ++I) {
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o << "=============================--------------------------------\n"
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<< "\nImmediate Dominator For Basic Block:";
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WriteAsOperand(o, I->first, false);
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o << " is:";
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WriteAsOperand(o, I->second, false);
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o << "\n";
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}
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}
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//===----------------------------------------------------------------------===//
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// DominatorTree Implementation
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//===----------------------------------------------------------------------===//
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static RegisterAnalysis<DominatorTree>
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E("domtree", "Dominator Tree Construction", true);
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// DominatorTreeBase::reset - Free all of the tree node memory.
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//
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void DominatorTreeBase::reset() {
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for (NodeMapType::iterator I = Nodes.begin(), E = Nodes.end(); I != E; ++I)
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delete I->second;
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Nodes.clear();
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}
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void DominatorTreeBase::Node2::setIDom(Node2 *NewIDom) {
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assert(IDom && "No immediate dominator?");
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if (IDom != NewIDom) {
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std::vector<Node*>::iterator I =
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std::find(IDom->Children.begin(), IDom->Children.end(), this);
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assert(I != IDom->Children.end() &&
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"Not in immediate dominator children set!");
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// I am no longer your child...
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IDom->Children.erase(I);
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// Switch to new dominator
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IDom = NewIDom;
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IDom->Children.push_back(this);
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}
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}
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void DominatorTree::calculate(const DominatorSet &DS) {
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Nodes[Root] = 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 (df_iterator<BasicBlock*> I = df_begin(Root), E = df_end(Root);
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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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// 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! We know that we have already added
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// a DominatorTree node for our idom, because the idom must be a
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// predecessor in the depth first order that we are iterating through the
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// function.
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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
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// elements in the dominator set indicates what level the node is at in
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// the chain. We want the node immediately above us, so it will have
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// an identical dominator set, except that BB will not dominate it...
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// therefore it's 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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static std::ostream &operator<<(std::ostream &o,
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const DominatorTreeBase::Node *Node) {
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return o << Node->getNode()
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<< "\n------------------------------------------\n";
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}
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static void PrintDomTree(const DominatorTreeBase::Node *N, std::ostream &o,
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unsigned Lev) {
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o << "Level #" << Lev << ": " << N;
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for (DominatorTreeBase::Node::const_iterator I = N->begin(), E = N->end();
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I != E; ++I) {
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PrintDomTree(*I, o, Lev+1);
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}
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}
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void DominatorTreeBase::print(std::ostream &o) const {
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o << "=============================--------------------------------\n"
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<< "Inorder Dominator Tree:\n";
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PrintDomTree(Nodes.find(getRoot())->second, o, 1);
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}
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//===----------------------------------------------------------------------===//
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// DominanceFrontier Implementation
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//===----------------------------------------------------------------------===//
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static RegisterAnalysis<DominanceFrontier>
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G("domfrontier", "Dominance Frontier Construction", true);
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const DominanceFrontier::DomSetType &
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DominanceFrontier::calculate(const DominatorTree &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->getNode();
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DomSetType &S = Frontiers[BB]; // The new set to fill in...
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for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
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SI != SE; ++SI) {
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// Does Node immediately dominate this successor?
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if (DT[*SI]->getIDom() != Node)
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S.insert(*SI);
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}
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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 (DominatorTree::Node::const_iterator NI = Node->begin(), NE = Node->end();
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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->dominates(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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void DominanceFrontierBase::print(std::ostream &o) const {
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for (const_iterator I = begin(), E = end(); I != E; ++I) {
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o << "=============================--------------------------------\n"
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<< "\nDominance Frontier For Basic Block\n";
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WriteAsOperand(o, I->first, false);
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o << " is: \n" << I->second << "\n";
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}
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}
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