1 //===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
2 //
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.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "llvm/Analysis/LoopInfo.h"
11 #include "llvm/Analysis/Dominators.h"
12 #include "llvm/Support/CFG.h"
13 #include "Support/DepthFirstIterator.h"
14 #include <algorithm>
15 
16 AnalysisID LoopInfo::ID(AnalysisID::create<LoopInfo>(), true);
17 
18 //===----------------------------------------------------------------------===//
19 // Loop implementation
20 //
21 bool Loop::contains(BasicBlock *BB) const {
22   return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
23 }
24 
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...
29 
30   BBMap.clear();                             // Reset internal state of analysis
31   TopLevelLoops.clear();
32 }
33 
34 
35 //===----------------------------------------------------------------------===//
36 // LoopInfo implementation
37 //
38 bool LoopInfo::runOnFunction(Function *F) {
39   releaseMemory();
40   Calculate(getAnalysis<DominatorSet>());    // Update
41   return false;
42 }
43 
44 void LoopInfo::Calculate(const DominatorSet &DS) {
45   BasicBlock *RootNode = DS.getRoot();
46 
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);
51 
52   for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
53     TopLevelLoops[i]->setLoopDepth(1);
54 }
55 
56 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
57   AU.setPreservesAll();
58   AU.addRequired(DominatorSet::ID);
59   AU.addProvided(ID);
60 }
61 
62 
63 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
64   if (BBMap.find(BB) != BBMap.end()) return 0;   // Havn't processed this node?
65 
66   std::vector<BasicBlock *> TodoStack;
67 
68   // Scan the predecessors of BB, checking to see if BB dominates any of
69   // them.
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);
73 
74   if (TodoStack.empty()) return 0;  // Doesn't dominate any predecessors...
75 
76   // Create a new loop to represent this basic block...
77   Loop *L = new Loop(BB);
78   BBMap[BB] = L;
79 
80   while (!TodoStack.empty()) {  // Process all the nodes in the loop
81     BasicBlock *X = TodoStack.back();
82     TodoStack.pop_back();
83 
84     if (!L->contains(X)) {                  // As of yet unprocessed??
85       L->Blocks.push_back(X);
86 
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));
89     }
90   }
91 
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.
95   //
96   for (std::vector<BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
97 	 E = L->Blocks.rend(); I != E; ++I) {
98 
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;
103     }
104 
105     if (BBMap.find(*I) == BBMap.end())
106       BBMap.insert(std::make_pair(*I, L));
107   }
108 
109   return L;
110 }
111