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 AnalysisID cfg::LoopInfo::ID(AnalysisID::create<cfg::LoopInfo>());
18 //===----------------------------------------------------------------------===//
19 // cfg::Loop implementation
21 bool cfg::Loop::contains(const BasicBlock *BB) const {
22 return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
26 //===----------------------------------------------------------------------===//
27 // cfg::LoopInfo implementation
29 bool cfg::LoopInfo::runOnMethod(Function *F) {
30 BBMap.clear(); // Reset internal state of analysis
31 TopLevelLoops.clear();
32 Calculate(getAnalysis<DominatorSet>()); // Update
36 void cfg::LoopInfo::Calculate(const DominatorSet &DS) {
37 const BasicBlock *RootNode = DS.getRoot();
39 for (df_iterator<const BasicBlock*> NI = df_begin(RootNode),
40 NE = df_end(RootNode); NI != NE; ++NI)
41 if (Loop *L = ConsiderForLoop(*NI, DS))
42 TopLevelLoops.push_back(L);
44 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
45 TopLevelLoops[i]->setLoopDepth(1);
48 void cfg::LoopInfo::getAnalysisUsageInfo(Pass::AnalysisSet &Required,
49 Pass::AnalysisSet &Destroyed,
50 Pass::AnalysisSet &Provided) {
51 Required.push_back(DominatorSet::ID);
52 Provided.push_back(ID);
56 cfg::Loop *cfg::LoopInfo::ConsiderForLoop(const BasicBlock *BB,
57 const DominatorSet &DS) {
58 if (BBMap.find(BB) != BBMap.end()) return 0; // Havn't processed this node?
60 std::vector<const BasicBlock *> TodoStack;
62 // Scan the predecessors of BB, checking to see if BB dominates any of
64 for (pred_const_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
65 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
66 TodoStack.push_back(*I);
68 if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
70 // Create a new loop to represent this basic block...
71 Loop *L = new Loop(BB);
74 while (!TodoStack.empty()) { // Process all the nodes in the loop
75 const BasicBlock *X = TodoStack.back();
78 if (!L->contains(X)) { // As of yet unprocessed??
79 L->Blocks.push_back(X);
81 // Add all of the predecessors of X to the end of the work stack...
82 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
86 // Add the basic blocks that comprise this loop to the BBMap so that this
87 // loop can be found for them. Also check subsidary basic blocks to see if
88 // they start subloops of their own.
90 for (std::vector<const BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
91 E = L->Blocks.rend(); I != E; ++I) {
93 // Check to see if this block starts a new loop
94 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
95 L->SubLoops.push_back(NewLoop);
96 NewLoop->ParentLoop = L;
99 if (BBMap.find(*I) == BBMap.end())
100 BBMap.insert(std::make_pair(*I, L));