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"
35 #include "llvm/ADT/SmallVector.h"
44 //===----------------------------------------------------------------------===//
45 /// Loop class - Instances of this class are used to represent loops that are
46 /// detected in the flow graph
50 std::vector<Loop*> SubLoops; // Loops contained entirely within this one
51 std::vector<BasicBlock*> Blocks; // First entry is the header node
53 Loop(const Loop &); // DO NOT IMPLEMENT
54 const Loop &operator=(const Loop &); // DO NOT IMPLEMENT
56 /// Loop ctor - This creates an empty loop.
57 Loop() : ParentLoop(0) {}
59 for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
63 unsigned getLoopDepth() const {
65 for (const Loop *CurLoop = this; CurLoop; CurLoop = CurLoop->ParentLoop)
69 BasicBlock *getHeader() const { return Blocks.front(); }
70 Loop *getParentLoop() const { return ParentLoop; }
72 /// contains - Return true of the specified basic block is in this loop
74 bool contains(const BasicBlock *BB) const;
76 /// iterator/begin/end - Return the loops contained entirely within this loop.
78 const std::vector<Loop*> &getSubLoops() const { return SubLoops; }
79 typedef std::vector<Loop*>::const_iterator iterator;
80 iterator begin() const { return SubLoops.begin(); }
81 iterator end() const { return SubLoops.end(); }
82 bool empty() const { return SubLoops.empty(); }
84 /// getBlocks - Get a list of the basic blocks which make up this loop.
86 const std::vector<BasicBlock*> &getBlocks() const { return Blocks; }
87 typedef std::vector<BasicBlock*>::const_iterator block_iterator;
88 block_iterator block_begin() const { return Blocks.begin(); }
89 block_iterator block_end() const { return Blocks.end(); }
91 /// isLoopExit - True if terminator in the block can branch to another block
92 /// that is outside of the current loop.
94 bool isLoopExit(const BasicBlock *BB) const;
96 /// getNumBackEdges - Calculate the number of back edges to the loop header
98 unsigned getNumBackEdges() const;
100 /// isLoopInvariant - Return true if the specified value is loop invariant
102 bool isLoopInvariant(Value *V) const;
104 //===--------------------------------------------------------------------===//
105 // APIs for simple analysis of the loop.
107 // Note that all of these methods can fail on general loops (ie, there may not
108 // be a preheader, etc). For best success, the loop simplification and
109 // induction variable canonicalization pass should be used to normalize loops
110 // for easy analysis. These methods assume canonical loops.
112 /// getExitingBlocks - Return all blocks inside the loop that have successors
113 /// outside of the loop. These are the blocks _inside of the current loop_
114 /// which branch out. The returned list is always unique.
116 void getExitingBlocks(SmallVectorImpl<BasicBlock *> &Blocks) const;
118 /// getExitBlocks - Return all of the successor blocks of this loop. These
119 /// are the blocks _outside of the current loop_ which are branched to.
121 void getExitBlocks(SmallVectorImpl<BasicBlock* > &Blocks) const;
123 /// getUniqueExitBlocks - Return all unique successor blocks of this loop.
124 /// These are the blocks _outside of the current loop_ which are branched to.
125 /// This assumes that loop is in canonical form.
127 void getUniqueExitBlocks(SmallVectorImpl<BasicBlock*> &ExitBlocks) const;
129 /// getLoopPreheader - If there is a preheader for this loop, return it. A
130 /// loop has a preheader if there is only one edge to the header of the loop
131 /// from outside of the loop. If this is the case, the block branching to the
132 /// header of the loop is the preheader node.
134 /// This method returns null if there is no preheader for the loop.
136 BasicBlock *getLoopPreheader() const;
138 /// getLoopLatch - If there is a latch block for this loop, return it. A
139 /// latch block is the canonical backedge for a loop. A loop header in normal
140 /// form has two edges into it: one from a preheader and one from a latch
142 BasicBlock *getLoopLatch() const;
144 /// getCanonicalInductionVariable - Check to see if the loop has a canonical
145 /// induction variable: an integer recurrence that starts at 0 and increments
146 /// by one each time through the loop. If so, return the phi node that
147 /// corresponds to it.
149 PHINode *getCanonicalInductionVariable() const;
151 /// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
152 /// the canonical induction variable value for the "next" iteration of the
153 /// loop. This always succeeds if getCanonicalInductionVariable succeeds.
155 Instruction *getCanonicalInductionVariableIncrement() const;
157 /// getTripCount - Return a loop-invariant LLVM value indicating the number of
158 /// times the loop will be executed. Note that this means that the backedge
159 /// of the loop executes N-1 times. If the trip-count cannot be determined,
160 /// this returns null.
162 Value *getTripCount() const;
164 /// isLCSSAForm - Return true if the Loop is in LCSSA form
165 bool isLCSSAForm() const;
167 //===--------------------------------------------------------------------===//
168 // APIs for updating loop information after changing the CFG
171 /// addBasicBlockToLoop - This method is used by other analyses to update loop
172 /// information. NewBB is set to be a new member of the current loop.
173 /// Because of this, it is added as a member of all parent loops, and is added
174 /// to the specified LoopInfo object as being in the current basic block. It
175 /// is not valid to replace the loop header with this method.
177 void addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI);
179 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
180 /// the OldChild entry in our children list with NewChild, and updates the
181 /// parent pointer of OldChild to be null and the NewChild to be this loop.
182 /// This updates the loop depth of the new child.
183 void replaceChildLoopWith(Loop *OldChild, Loop *NewChild);
185 /// addChildLoop - Add the specified loop to be a child of this loop. This
186 /// updates the loop depth of the new child.
188 void addChildLoop(Loop *NewChild);
190 /// removeChildLoop - This removes the specified child from being a subloop of
191 /// this loop. The loop is not deleted, as it will presumably be inserted
192 /// into another loop.
193 Loop *removeChildLoop(iterator OldChild);
195 /// addBlockEntry - This adds a basic block directly to the basic block list.
196 /// This should only be used by transformations that create new loops. Other
197 /// transformations should use addBasicBlockToLoop.
198 void addBlockEntry(BasicBlock *BB) {
199 Blocks.push_back(BB);
202 /// moveToHeader - This method is used to move BB (which must be part of this
203 /// loop) to be the loop header of the loop (the block that dominates all
205 void moveToHeader(BasicBlock *BB) {
206 if (Blocks[0] == BB) return;
207 for (unsigned i = 0; ; ++i) {
208 assert(i != Blocks.size() && "Loop does not contain BB!");
209 if (Blocks[i] == BB) {
210 Blocks[i] = Blocks[0];
217 /// removeBlockFromLoop - This removes the specified basic block from the
218 /// current loop, updating the Blocks as appropriate. This does not update
219 /// the mapping in the LoopInfo class.
220 void removeBlockFromLoop(BasicBlock *BB);
222 /// verifyLoop - Verify loop structure
223 void verifyLoop() const;
225 void print(std::ostream &O, unsigned Depth = 0) const;
226 void print(std::ostream *O, unsigned Depth = 0) const {
227 if (O) print(*O, Depth);
231 friend class LoopInfo;
232 Loop(BasicBlock *BB) : ParentLoop(0) {
233 Blocks.push_back(BB);
239 //===----------------------------------------------------------------------===//
240 /// LoopInfo - This class builds and contains all of the top level loop
241 /// structures in the specified function.
243 class LoopInfo : public FunctionPass {
244 // BBMap - Mapping of basic blocks to the inner most loop they occur in
245 std::map<BasicBlock*, Loop*> BBMap;
246 std::vector<Loop*> TopLevelLoops;
249 static char ID; // Pass identification, replacement for typeid
251 LoopInfo() : FunctionPass(intptr_t(&ID)) {}
252 ~LoopInfo() { releaseMemory(); }
254 /// iterator/begin/end - The interface to the top-level loops in the current
257 typedef std::vector<Loop*>::const_iterator iterator;
258 iterator begin() const { return TopLevelLoops.begin(); }
259 iterator end() const { return TopLevelLoops.end(); }
261 /// getLoopFor - Return the inner most loop that BB lives in. If a basic
262 /// block is in no loop (for example the entry node), null is returned.
264 Loop *getLoopFor(const BasicBlock *BB) const {
265 std::map<BasicBlock *, Loop*>::const_iterator I=
266 BBMap.find(const_cast<BasicBlock*>(BB));
267 return I != BBMap.end() ? I->second : 0;
270 /// operator[] - same as getLoopFor...
272 const Loop *operator[](const BasicBlock *BB) const {
273 return getLoopFor(BB);
276 /// getLoopDepth - Return the loop nesting level of the specified block...
278 unsigned getLoopDepth(const BasicBlock *BB) const {
279 const Loop *L = getLoopFor(BB);
280 return L ? L->getLoopDepth() : 0;
283 // isLoopHeader - True if the block is a loop header node
284 bool isLoopHeader(BasicBlock *BB) const {
285 const Loop *L = getLoopFor(BB);
286 return L && L->getHeader() == BB;
289 /// runOnFunction - Calculate the natural loop information.
291 virtual bool runOnFunction(Function &F);
293 virtual void releaseMemory();
295 void print(std::ostream &O, const Module* = 0) const;
296 void print(std::ostream *O, const Module* M = 0) const {
300 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
302 /// removeLoop - This removes the specified top-level loop from this loop info
303 /// object. The loop is not deleted, as it will presumably be inserted into
305 Loop *removeLoop(iterator I);
307 /// changeLoopFor - Change the top-level loop that contains BB to the
308 /// specified loop. This should be used by transformations that restructure
309 /// the loop hierarchy tree.
310 void changeLoopFor(BasicBlock *BB, Loop *L);
312 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
313 /// list with the indicated loop.
314 void changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop);
316 /// addTopLevelLoop - This adds the specified loop to the collection of
318 void addTopLevelLoop(Loop *New) {
319 assert(New->getParentLoop() == 0 && "Loop already in subloop!");
320 TopLevelLoops.push_back(New);
323 /// removeBlock - This method completely removes BB from all data structures,
324 /// including all of the Loop objects it is nested in and our mapping from
325 /// BasicBlocks to loops.
326 void removeBlock(BasicBlock *BB);
329 void Calculate(DominatorTree &DT);
330 Loop *ConsiderForLoop(BasicBlock *BB, DominatorTree &DT);
331 void MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent);
332 void InsertLoopInto(Loop *L, Loop *Parent);
336 // Allow clients to walk the list of nested loops...
337 template <> struct GraphTraits<const Loop*> {
338 typedef const Loop NodeType;
339 typedef std::vector<Loop*>::const_iterator ChildIteratorType;
341 static NodeType *getEntryNode(const Loop *L) { return L; }
342 static inline ChildIteratorType child_begin(NodeType *N) {
345 static inline ChildIteratorType child_end(NodeType *N) {
350 template <> struct GraphTraits<Loop*> {
351 typedef Loop NodeType;
352 typedef std::vector<Loop*>::const_iterator ChildIteratorType;
354 static NodeType *getEntryNode(Loop *L) { return L; }
355 static inline ChildIteratorType child_begin(NodeType *N) {
358 static inline ChildIteratorType child_end(NodeType *N) {
363 } // End llvm namespace
365 // Make sure that any clients of this file link in LoopInfo.cpp
366 FORCE_DEFINING_FILE_TO_BE_LINKED(LoopInfo)