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", 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 Loop::print(std::ostream &OS) const {
28 OS << std::string(getLoopDepth()*2, ' ') << "Loop Containing: ";
30 for (unsigned i = 0; i < getBlocks().size(); ++i) {
32 WriteAsOperand(OS, (const Value*)getBlocks()[i]);
36 std::copy(getSubLoops().begin(), getSubLoops().end(),
37 std::ostream_iterator<const Loop*>(OS, "\n"));
40 //===----------------------------------------------------------------------===//
41 // LoopInfo implementation
43 void LoopInfo::stub() {}
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>();
78 void LoopInfo::print(std::ostream &OS) const {
79 std::copy(getTopLevelLoops().begin(), getTopLevelLoops().end(),
80 std::ostream_iterator<const Loop*>(OS, "\n"));
83 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
84 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
86 std::vector<BasicBlock *> TodoStack;
88 // Scan the predecessors of BB, checking to see if BB dominates any of
90 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
91 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
92 TodoStack.push_back(*I);
94 if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
96 // Create a new loop to represent this basic block...
97 Loop *L = new Loop(BB);
100 while (!TodoStack.empty()) { // Process all the nodes in the loop
101 BasicBlock *X = TodoStack.back();
102 TodoStack.pop_back();
104 if (!L->contains(X)) { // As of yet unprocessed??
105 L->Blocks.push_back(X);
107 // Add all of the predecessors of X to the end of the work stack...
108 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
112 // Add the basic blocks that comprise this loop to the BBMap so that this
113 // loop can be found for them. Also check subsidary basic blocks to see if
114 // they start subloops of their own.
116 for (std::vector<BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
117 E = L->Blocks.rend(); I != E; ++I) {
119 // Check to see if this block starts a new loop
120 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
121 L->SubLoops.push_back(NewLoop);
122 NewLoop->ParentLoop = L;
125 if (BBMap.find(*I) == BBMap.end())
126 BBMap.insert(std::make_pair(*I, L));
132 /// getLoopPreheader - If there is a preheader for this loop, return it. A
133 /// loop has a preheader if there is only one edge to the header of the loop
134 /// from outside of the loop. If this is the case, the block branching to the
135 /// header of the loop is the preheader node. The "preheaders" pass can be
136 /// "Required" to ensure that there is always a preheader node for every loop.
138 /// This method returns null if there is no preheader for the loop (either
139 /// because the loop is dead or because multiple blocks branch to the header
140 /// node of this loop).
142 BasicBlock *Loop::getLoopPreheader() const {
143 // Keep track of nodes outside the loop branching to the header...
146 // Loop over the predecessors of the header node...
147 BasicBlock *Header = getHeader();
148 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
150 if (!contains(*PI)) { // If the block is not in the loop...
151 if (Out) return 0; // Multiple predecessors outside the loop
155 // If there is exactly one preheader, return it. If there was zero, then Out
160 /// addBasicBlockToLoop - This function is used by other analyses to update loop
161 /// information. NewBB is set to be a new member of the current loop. Because
162 /// of this, it is added as a member of all parent loops, and is added to the
163 /// specified LoopInfo object as being in the current basic block. It is not
164 /// valid to replace the loop header with this method.
166 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
167 assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
168 assert(NewBB && "Cannot add a null basic block to the loop!");
169 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
171 // Add the loop mapping to the LoopInfo object...
172 LI.BBMap[NewBB] = this;
174 // Add the basic block to this loop and all parent loops...
177 L->Blocks.push_back(NewBB);
178 L = L->getParentLoop();