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 "Support/DepthFirstIterator.h"
16 static RegisterAnalysis<LoopInfo>
17 X("loops", "Natural Loop Construction");
18 AnalysisID LoopInfo::ID(AnalysisID::create<LoopInfo>(), true);
20 //===----------------------------------------------------------------------===//
21 // Loop implementation
23 bool Loop::contains(const BasicBlock *BB) const {
24 return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
27 void LoopInfo::releaseMemory() {
28 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
29 E = TopLevelLoops.end(); I != E; ++I)
30 delete *I; // Delete all of the loops...
32 BBMap.clear(); // Reset internal state of analysis
33 TopLevelLoops.clear();
37 //===----------------------------------------------------------------------===//
38 // LoopInfo implementation
40 bool LoopInfo::runOnFunction(Function &) {
42 Calculate(getAnalysis<DominatorSet>()); // Update
46 void LoopInfo::Calculate(const DominatorSet &DS) {
47 BasicBlock *RootNode = DS.getRoot();
49 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
50 NE = df_end(RootNode); NI != NE; ++NI)
51 if (Loop *L = ConsiderForLoop(*NI, DS))
52 TopLevelLoops.push_back(L);
54 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
55 TopLevelLoops[i]->setLoopDepth(1);
58 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
60 AU.addRequired(DominatorSet::ID);
65 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
66 if (BBMap.find(BB) != BBMap.end()) return 0; // Havn't processed this node?
68 std::vector<BasicBlock *> TodoStack;
70 // Scan the predecessors of BB, checking to see if BB dominates any of
72 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
73 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
74 TodoStack.push_back(*I);
76 if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
78 // Create a new loop to represent this basic block...
79 Loop *L = new Loop(BB);
82 while (!TodoStack.empty()) { // Process all the nodes in the loop
83 BasicBlock *X = TodoStack.back();
86 if (!L->contains(X)) { // As of yet unprocessed??
87 L->Blocks.push_back(X);
89 // Add all of the predecessors of X to the end of the work stack...
90 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
94 // Add the basic blocks that comprise this loop to the BBMap so that this
95 // loop can be found for them. Also check subsidary basic blocks to see if
96 // they start subloops of their own.
98 for (std::vector<BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
99 E = L->Blocks.rend(); I != E; ++I) {
101 // Check to see if this block starts a new loop
102 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
103 L->SubLoops.push_back(NewLoop);
104 NewLoop->ParentLoop = L;
107 if (BBMap.find(*I) == BBMap.end())
108 BBMap.insert(std::make_pair(*I, L));