1 //===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator -------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the LoopInfo class that is used to identify natural loops
11 // and determine the loop depth of various nodes of the CFG. Note that natural
12 // loops may actually be several loops that share the same header node.
14 // This analysis calculates the nesting structure of loops in a function. For
15 // each natural loop identified, this analysis identifies natural loops
16 // contained entirely within the loop and the basic blocks the make up the loop.
18 // It can calculate on the fly various bits of information, for example:
20 // * whether there is a preheader for the loop
21 // * the number of back edges to the header
22 // * whether or not a particular block branches out of the loop
23 // * the successor blocks of the loop
28 //===----------------------------------------------------------------------===//
30 #ifndef LLVM_ANALYSIS_LOOP_INFO_H
31 #define LLVM_ANALYSIS_LOOP_INFO_H
33 #include "llvm/Pass.h"
34 #include "llvm/ADT/GraphTraits.h"
43 //===----------------------------------------------------------------------===//
44 /// Loop class - Instances of this class are used to represent loops that are
45 /// detected in the flow graph
49 std::vector<Loop*> SubLoops; // Loops contained entirely within this one
50 std::vector<BasicBlock*> Blocks; // First entry is the header node
52 Loop(const Loop &); // DO NOT IMPLEMENT
53 const Loop &operator=(const Loop &); // DO NOT IMPLEMENT
55 /// Loop ctor - This creates an empty loop.
56 Loop() : ParentLoop(0) {}
58 for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
62 unsigned getLoopDepth() const {
64 for (const Loop *CurLoop = this; CurLoop; CurLoop = CurLoop->ParentLoop)
68 BasicBlock *getHeader() const { return Blocks.front(); }
69 Loop *getParentLoop() const { return ParentLoop; }
71 /// contains - Return true of the specified basic block is in this loop
73 bool contains(const BasicBlock *BB) const;
75 /// iterator/begin/end - Return the loops contained entirely within this loop.
77 const std::vector<Loop*> &getSubLoops() const { return SubLoops; }
78 typedef std::vector<Loop*>::const_iterator iterator;
79 iterator begin() const { return SubLoops.begin(); }
80 iterator end() const { return SubLoops.end(); }
82 /// getBlocks - Get a list of the basic blocks which make up this loop.
84 const std::vector<BasicBlock*> &getBlocks() const { return Blocks; }
85 typedef std::vector<BasicBlock*>::const_iterator block_iterator;
86 block_iterator block_begin() const { return Blocks.begin(); }
87 block_iterator block_end() const { return Blocks.end(); }
89 /// isLoopExit - True if terminator in the block can branch to another block
90 /// that is outside of the current loop.
92 bool isLoopExit(const BasicBlock *BB) const;
94 /// getNumBackEdges - Calculate the number of back edges to the loop header
96 unsigned getNumBackEdges() const;
98 /// isLoopInvariant - Return true if the specified value is loop invariant
100 bool isLoopInvariant(Value *V) const;
102 //===--------------------------------------------------------------------===//
103 // APIs for simple analysis of the loop.
105 // Note that all of these methods can fail on general loops (ie, there may not
106 // be a preheader, etc). For best success, the loop simplification and
107 // induction variable canonicalization pass should be used to normalize loops
108 // for easy analysis. These methods assume canonical loops.
110 /// getExitBlocks - Return all of the successor blocks of this loop. These
111 /// are the blocks _outside of the current loop_ which are branched to.
113 void getExitBlocks(std::vector<BasicBlock*> &Blocks) const;
115 /// getLoopPreheader - If there is a preheader for this loop, return it. A
116 /// loop has a preheader if there is only one edge to the header of the loop
117 /// from outside of the loop. If this is the case, the block branching to the
118 /// header of the loop is the preheader node.
120 /// This method returns null if there is no preheader for the loop.
122 BasicBlock *getLoopPreheader() const;
124 /// getLoopLatch - If there is a latch block for this loop, return it. A
125 /// latch block is the canonical backedge for a loop. A loop header in normal
126 /// form has two edges into it: one from a preheader and one from a latch
128 BasicBlock *getLoopLatch() const;
130 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
131 /// induction variable: an integer recurrence that starts at 0 and increments
132 /// by one each time through the loop. If so, return the phi node that
133 /// corresponds to it.
135 PHINode *getCanonicalInductionVariable() const;
137 /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
138 /// the canonical induction variable value for the "next" iteration of the
139 /// loop. This always succeeds if getCanonicalInductionVariable succeeds.
141 Instruction *getCanonicalInductionVariableIncrement() const;
143 /// getTripCount - Return a loop-invariant LLVM value indicating the number of
144 /// times the loop will be executed. Note that this means that the backedge
145 /// of the loop executes N-1 times. If the trip-count cannot be determined,
146 /// this returns null.
148 Value *getTripCount() const;
150 //===--------------------------------------------------------------------===//
151 // APIs for updating loop information after changing the CFG
154 /// addBasicBlockToLoop - This method is used by other analyses to update loop
155 /// information. NewBB is set to be a new member of the current loop.
156 /// Because of this, it is added as a member of all parent loops, and is added
157 /// to the specified LoopInfo object as being in the current basic block. It
158 /// is not valid to replace the loop header with this method.
160 void addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI);
162 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
163 /// the OldChild entry in our children list with NewChild, and updates the
164 /// parent pointer of OldChild to be null and the NewChild to be this loop.
165 /// This updates the loop depth of the new child.
166 void replaceChildLoopWith(Loop *OldChild, Loop *NewChild);
168 /// addChildLoop - Add the specified loop to be a child of this loop. This
169 /// updates the loop depth of the new child.
171 void addChildLoop(Loop *NewChild);
173 /// removeChildLoop - This removes the specified child from being a subloop of
174 /// this loop. The loop is not deleted, as it will presumably be inserted
175 /// into another loop.
176 Loop *removeChildLoop(iterator OldChild);
178 /// addBlockEntry - This adds a basic block directly to the basic block list.
179 /// This should only be used by transformations that create new loops. Other
180 /// transformations should use addBasicBlockToLoop.
181 void addBlockEntry(BasicBlock *BB) {
182 Blocks.push_back(BB);
185 /// moveToHeader - This method is used to move BB (which must be part of this
186 /// loop) to be the loop header of the loop (the block that dominates all
188 void moveToHeader(BasicBlock *BB) {
189 if (Blocks[0] == BB) return;
190 for (unsigned i = 0; ; ++i) {
191 assert(i != Blocks.size() && "Loop does not contain BB!");
192 if (Blocks[i] == BB) {
193 Blocks[i] = Blocks[0];
200 /// removeBlockFromLoop - This removes the specified basic block from the
201 /// current loop, updating the Blocks as appropriate. This does not update
202 /// the mapping in the LoopInfo class.
203 void removeBlockFromLoop(BasicBlock *BB);
205 void print(std::ostream &O, unsigned Depth = 0) const;
208 friend class LoopInfo;
209 Loop(BasicBlock *BB) : ParentLoop(0) {
210 Blocks.push_back(BB);
216 //===----------------------------------------------------------------------===//
217 /// LoopInfo - This class builds and contains all of the top level loop
218 /// structures in the specified function.
220 class LoopInfo : public FunctionPass {
221 // BBMap - Mapping of basic blocks to the inner most loop they occur in
222 std::map<BasicBlock*, Loop*> BBMap;
223 std::vector<Loop*> TopLevelLoops;
226 ~LoopInfo() { releaseMemory(); }
228 /// iterator/begin/end - The interface to the top-level loops in the current
231 typedef std::vector<Loop*>::const_iterator iterator;
232 iterator begin() const { return TopLevelLoops.begin(); }
233 iterator end() const { return TopLevelLoops.end(); }
235 /// getLoopFor - Return the inner most loop that BB lives in. If a basic
236 /// block is in no loop (for example the entry node), null is returned.
238 Loop *getLoopFor(const BasicBlock *BB) const {
239 std::map<BasicBlock *, Loop*>::const_iterator I=
240 BBMap.find(const_cast<BasicBlock*>(BB));
241 return I != BBMap.end() ? I->second : 0;
244 /// operator[] - same as getLoopFor...
246 const Loop *operator[](const BasicBlock *BB) const {
247 return getLoopFor(BB);
250 /// getLoopDepth - Return the loop nesting level of the specified block...
252 unsigned getLoopDepth(const BasicBlock *BB) const {
253 const Loop *L = getLoopFor(BB);
254 return L ? L->getLoopDepth() : 0;
257 // isLoopHeader - True if the block is a loop header node
258 bool isLoopHeader(BasicBlock *BB) const {
259 const Loop *L = getLoopFor(BB);
260 return L && L->getHeader() == BB;
263 /// runOnFunction - Calculate the natural loop information.
265 virtual bool runOnFunction(Function &F);
267 virtual void releaseMemory();
268 void print(std::ostream &O, const Module* = 0) const;
270 /// getAnalysisUsage - Requires dominator sets
272 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
274 /// removeLoop - This removes the specified top-level loop from this loop info
275 /// object. The loop is not deleted, as it will presumably be inserted into
277 Loop *removeLoop(iterator I);
279 /// changeLoopFor - Change the top-level loop that contains BB to the
280 /// specified loop. This should be used by transformations that restructure
281 /// the loop hierarchy tree.
282 void changeLoopFor(BasicBlock *BB, Loop *L);
284 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
285 /// list with the indicated loop.
286 void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop);
288 /// addTopLevelLoop - This adds the specified loop to the collection of
290 void addTopLevelLoop(Loop *New) {
291 assert(New->getParentLoop() == 0 && "Loop already in subloop!");
292 TopLevelLoops.push_back(New);
295 /// removeBlock - This method completely removes BB from all data structures,
296 /// including all of the Loop objects it is nested in and our mapping from
297 /// BasicBlocks to loops.
298 void removeBlock(BasicBlock *BB);
300 static void stub(); // Noop
302 void Calculate(const DominatorSet &DS);
303 Loop *ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS);
304 void MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent);
305 void InsertLoopInto(Loop *L, Loop *Parent);
309 // Make sure that any clients of this file link in LoopInfo.cpp
311 LOOP_INFO_INCLUDE_FILE((void*)(&LoopInfo::stub));
313 // Allow clients to walk the list of nested loops...
314 template <> struct GraphTraits<const Loop*> {
315 typedef const Loop NodeType;
316 typedef std::vector<Loop*>::const_iterator ChildIteratorType;
318 static NodeType *getEntryNode(const Loop *L) { return L; }
319 static inline ChildIteratorType child_begin(NodeType *N) {
322 static inline ChildIteratorType child_end(NodeType *N) {
327 template <> struct GraphTraits<Loop*> {
328 typedef Loop NodeType;
329 typedef std::vector<Loop*>::const_iterator ChildIteratorType;
331 static NodeType *getEntryNode(Loop *L) { return L; }
332 static inline ChildIteratorType child_begin(NodeType *N) {
335 static inline ChildIteratorType child_end(NodeType *N) {
340 } // End llvm namespace