1 //===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
3 // This file defines the LoopInfo class that is used to identify natural loops
4 // and determine the loop depth of various nodes of the CFG. Note that the
5 // loops identified may actually be several natural loops that share the same
6 // header node... not just a single natural loop.
8 //===----------------------------------------------------------------------===//
10 #include "llvm/Analysis/LoopInfo.h"
11 #include "llvm/Analysis/Dominators.h"
12 #include "llvm/Support/CFG.h"
13 #include "llvm/Assembly/Writer.h"
14 #include "Support/DepthFirstIterator.h"
17 static RegisterAnalysis<LoopInfo>
18 X("loops", "Natural Loop Construction");
19 AnalysisID LoopInfo::ID = X;
21 //===----------------------------------------------------------------------===//
22 // Loop implementation
24 bool Loop::contains(const BasicBlock *BB) const {
25 return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
28 void Loop::print(std::ostream &OS) const {
29 OS << std::string(getLoopDepth()*2, ' ') << "Loop Containing: ";
31 for (unsigned i = 0; i < getBlocks().size(); ++i) {
33 WriteAsOperand(OS, (const Value*)getBlocks()[i]);
37 std::copy(getSubLoops().begin(), getSubLoops().end(),
38 std::ostream_iterator<const Loop*>(OS, "\n"));
41 //===----------------------------------------------------------------------===//
42 // LoopInfo implementation
45 bool LoopInfo::runOnFunction(Function &) {
47 Calculate(getAnalysis<DominatorSet>()); // Update
51 void LoopInfo::releaseMemory() {
52 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
53 E = TopLevelLoops.end(); I != E; ++I)
54 delete *I; // Delete all of the loops...
56 BBMap.clear(); // Reset internal state of analysis
57 TopLevelLoops.clear();
61 void LoopInfo::Calculate(const DominatorSet &DS) {
62 BasicBlock *RootNode = DS.getRoot();
64 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
65 NE = df_end(RootNode); NI != NE; ++NI)
66 if (Loop *L = ConsiderForLoop(*NI, DS))
67 TopLevelLoops.push_back(L);
69 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
70 TopLevelLoops[i]->setLoopDepth(1);
73 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
75 AU.addRequired(DominatorSet::ID);
79 void LoopInfo::print(std::ostream &OS) const {
80 std::copy(getTopLevelLoops().begin(), getTopLevelLoops().end(),
81 std::ostream_iterator<const Loop*>(OS, "\n"));
84 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
85 if (BBMap.find(BB) != BBMap.end()) return 0; // Havn't processed this node?
87 std::vector<BasicBlock *> TodoStack;
89 // Scan the predecessors of BB, checking to see if BB dominates any of
91 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
92 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
93 TodoStack.push_back(*I);
95 if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
97 // Create a new loop to represent this basic block...
98 Loop *L = new Loop(BB);
101 while (!TodoStack.empty()) { // Process all the nodes in the loop
102 BasicBlock *X = TodoStack.back();
103 TodoStack.pop_back();
105 if (!L->contains(X)) { // As of yet unprocessed??
106 L->Blocks.push_back(X);
108 // Add all of the predecessors of X to the end of the work stack...
109 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
113 // Add the basic blocks that comprise this loop to the BBMap so that this
114 // loop can be found for them. Also check subsidary basic blocks to see if
115 // they start subloops of their own.
117 for (std::vector<BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
118 E = L->Blocks.rend(); I != E; ++I) {
120 // Check to see if this block starts a new loop
121 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
122 L->SubLoops.push_back(NewLoop);
123 NewLoop->ParentLoop = L;
126 if (BBMap.find(*I) == BBMap.end())
127 BBMap.insert(std::make_pair(*I, L));