//===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator --------*- C++ -*--=//
//
// This file defines the LoopInfo class that is used to identify natural loops
-// and determine the loop depth of various nodes of the CFG. Note that the
-// loops identified may actually be several natural loops that share the same
-// header node... not just a single natural loop.
+// and determine the loop depth of various nodes of the CFG. Note that natural
+// loops may actually be several loops that share the same header node...
+//
+// This analysis calculates the nesting structure of loops in a function. For
+// each natural loop identified, this analysis identifies natural loops
+// contained entirely within the function, the basic blocks the make up the
+// loop, the nesting depth of the loop, and the successor blocks of the loop.
+//
+// It can calculate on the fly a variety of different bits of information, such
+// as whether there is a preheader for the loop, the number of back edges to the
+// header, and whether or not a particular block branches out of the loop.
//
//===----------------------------------------------------------------------===//
class LoopInfo;
//===----------------------------------------------------------------------===//
-// Loop class - Instances of this class are used to represent loops that are
-// detected in the flow graph
-//
+/// Loop class - Instances of this class are used to represent loops that are
+/// detected in the flow graph
+///
class Loop {
Loop *ParentLoop;
- std::vector<BasicBlock *> Blocks; // First entry is the header node
std::vector<Loop*> SubLoops; // Loops contained entirely within this one
+ std::vector<BasicBlock *> Blocks; // First entry is the header node
+ std::vector<BasicBlock *> ExitBlocks; // Reachable blocks outside the loop
unsigned LoopDepth; // Nesting depth of this loop
Loop(const Loop &); // DO NOT IMPLEMENT
inline unsigned getLoopDepth() const { return LoopDepth; }
inline BasicBlock *getHeader() const { return Blocks.front(); }
+ inline Loop *getParentLoop() const { return ParentLoop; }
- // contains - Return true of the specified basic block is in this loop
+ /// contains - Return true of the specified basic block is in this loop
bool contains(const BasicBlock *BB) const;
- // getSubLoops - Return the loops contained entirely within this loop
- inline const std::vector<Loop*> &getSubLoops() const { return SubLoops; }
- inline const std::vector<BasicBlock*> &getBlocks() const { return Blocks; }
-
+ /// getSubLoops - Return the loops contained entirely within this loop
+ ///
+ const std::vector<Loop*> &getSubLoops() const { return SubLoops; }
+
+ /// getBlocks - Get a list of the basic blocks which make up this loop.
+ ///
+ const std::vector<BasicBlock*> &getBlocks() const { return Blocks; }
+
+ /// getExitBlocks - Return all of the successor blocks of this loop. These
+ /// are the blocks _outside of the current loop_ which are branched to.
+ ///
+ const std::vector<BasicBlock*> &getExitBlocks() const { return ExitBlocks; }
+
+ /// isLoopExit - True if terminator in the block can branch to another block
+ /// that is outside of the current loop. The reached block should be in the
+ /// ExitBlocks list.
+ ///
+ bool isLoopExit(const BasicBlock *BB) const;
+
+ /// getNumBackEdges - Calculate the number of back edges to the loop header
+ ///
+ unsigned getNumBackEdges() const;
+
+ /// getLoopPreheader - If there is a preheader for this loop, return it. A
+ /// loop has a preheader if there is only one edge to the header of the loop
+ /// from outside of the loop. If this is the case, the block branching to the
+ /// header of the loop is the preheader node. The "preheaders" pass can be
+ /// "Required" to ensure that there is always a preheader node for every loop.
+ ///
+ /// This method returns null if there is no preheader for the loop (either
+ /// because the loop is dead or because multiple blocks branch to the header
+ /// node of this loop).
+ ///
+ BasicBlock *getLoopPreheader() const;
+
+ /// addBasicBlockToLoop - This method is used by other analyses to update loop
+ /// information. NewBB is set to be a new member of the current loop.
+ /// Because of this, it is added as a member of all parent loops, and is added
+ /// to the specified LoopInfo object as being in the current basic block. It
+ /// is not valid to replace the loop header with this method.
+ ///
+ void addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI);
+
+ /// changeExitBlock - This method is used to update loop information. One
+ /// instance of the specified Old basic block is removed from the exit list
+ /// and replaced with New.
+ ///
+ void changeExitBlock(BasicBlock *Old, BasicBlock *New);
+
+ void print(std::ostream &O) const;
private:
friend class LoopInfo;
- inline Loop(BasicBlock *BB) { Blocks.push_back(BB); LoopDepth = 0; }
+ inline Loop(BasicBlock *BB) : ParentLoop(0) {
+ Blocks.push_back(BB); LoopDepth = 0;
+ }
~Loop() {
for (unsigned i = 0, e = SubLoops.size(); i != e; ++i)
delete SubLoops[i];
//===----------------------------------------------------------------------===//
-// LoopInfo - This class builds and contains all of the top level loop
-// structures in the specified function.
-//
+/// LoopInfo - This class builds and contains all of the top level loop
+/// structures in the specified function.
+///
class LoopInfo : public FunctionPass {
// BBMap - Mapping of basic blocks to the inner most loop they occur in
std::map<BasicBlock*, Loop*> BBMap;
std::vector<Loop*> TopLevelLoops;
+ friend class Loop;
public:
- static AnalysisID ID; // LoopInfo Analysis ID
-
- // LoopInfo ctor - Calculate the natural loop information for a CFG
- LoopInfo(AnalysisID id) { assert(id == ID); }
~LoopInfo() { releaseMemory(); }
- const char *getPassName() const { return "Natural Loop Analysis"; }
-
const std::vector<Loop*> &getTopLevelLoops() const { return TopLevelLoops; }
- // getLoopFor - Return the inner most loop that BB lives in. If a basic block
- // is in no loop (for example the entry node), null is returned.
- //
+ /// getLoopFor - Return the inner most loop that BB lives in. If a basic
+ /// block is in no loop (for example the entry node), null is returned.
+ ///
const Loop *getLoopFor(const BasicBlock *BB) const {
std::map<BasicBlock *, Loop*>::const_iterator I=BBMap.find((BasicBlock*)BB);
return I != BBMap.end() ? I->second : 0;
}
+
+ /// operator[] - same as getLoopFor...
+ ///
inline const Loop *operator[](const BasicBlock *BB) const {
return getLoopFor(BB);
}
- // getLoopDepth - Return the loop nesting level of the specified block...
+ /// getLoopDepth - Return the loop nesting level of the specified block...
+ ///
unsigned getLoopDepth(const BasicBlock *BB) const {
const Loop *L = getLoopFor(BB);
return L ? L->getLoopDepth() : 0;
}
-#if 0
// isLoopHeader - True if the block is a loop header node
bool isLoopHeader(BasicBlock *BB) const {
return getLoopFor(BB)->getHeader() == BB;
}
- // isLoopEnd - True if block jumps to loop entry
- bool isLoopEnd(BasicBlock *BB) const;
- // isLoopExit - True if block is the loop exit
- bool isLoopExit(BasicBlock *BB) const;
-#endif
- // runOnFunction - Pass framework implementation
+ /// runOnFunction - Calculate the natural loop information.
+ ///
virtual bool runOnFunction(Function &F);
virtual void releaseMemory();
+ void print(std::ostream &O) const;
- // getAnalysisUsage - Provide loop info, require dominator set
- //
+ /// getAnalysisUsage - Requires dominator sets
+ ///
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
+ static void stub(); // Noop
private:
void Calculate(const DominatorSet &DS);
Loop *ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS);
};
+
+// Make sure that any clients of this file link in LoopInfo.cpp
+static IncludeFile
+LOOP_INFO_INCLUDE_FILE((void*)&LoopInfo::stub);
+
#endif
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