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 LoopInfo::ID(AnalysisID::create<LoopInfo>());
18 //===----------------------------------------------------------------------===//
19 // Loop implementation
21 bool Loop::contains(BasicBlock *BB) const {
22 return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
25 void LoopInfo::releaseMemory() {
26 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
27 E = TopLevelLoops.end(); I != E; ++I)
28 delete *I; // Delete all of the loops...
30 BBMap.clear(); // Reset internal state of analysis
31 TopLevelLoops.clear();
35 //===----------------------------------------------------------------------===//
36 // LoopInfo implementation
38 bool LoopInfo::runOnFunction(Function *F) {
40 Calculate(getAnalysis<DominatorSet>()); // Update
44 void LoopInfo::Calculate(const DominatorSet &DS) {
45 BasicBlock *RootNode = DS.getRoot();
47 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
48 NE = df_end(RootNode); NI != NE; ++NI)
49 if (Loop *L = ConsiderForLoop(*NI, DS))
50 TopLevelLoops.push_back(L);
52 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
53 TopLevelLoops[i]->setLoopDepth(1);
56 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
58 AU.addRequired(DominatorSet::ID);
63 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
64 if (BBMap.find(BB) != BBMap.end()) return 0; // Havn't processed this node?
66 std::vector<BasicBlock *> TodoStack;
68 // Scan the predecessors of BB, checking to see if BB dominates any of
70 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
71 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
72 TodoStack.push_back(*I);
74 if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
76 // Create a new loop to represent this basic block...
77 Loop *L = new Loop(BB);
80 while (!TodoStack.empty()) { // Process all the nodes in the loop
81 BasicBlock *X = TodoStack.back();
84 if (!L->contains(X)) { // As of yet unprocessed??
85 L->Blocks.push_back(X);
87 // Add all of the predecessors of X to the end of the work stack...
88 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
92 // Add the basic blocks that comprise this loop to the BBMap so that this
93 // loop can be found for them. Also check subsidary basic blocks to see if
94 // they start subloops of their own.
96 for (std::vector<BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
97 E = L->Blocks.rend(); I != E; ++I) {
99 // Check to see if this block starts a new loop
100 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
101 L->SubLoops.push_back(NewLoop);
102 NewLoop->ParentLoop = L;
105 if (BBMap.find(*I) == BBMap.end())
106 BBMap.insert(std::make_pair(*I, L));