1 //===- llvm/CodeGen/MachineLoopInfo.h - Natural Loop Calculator -*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the MachineLoopInfo class that is used to identify natural
11 // loops and determine the loop depth of various nodes of the CFG. Note that
12 // natural 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_CODEGEN_MACHINELOOPINFO_H
31 #define LLVM_CODEGEN_MACHINELOOPINFO_H
33 #include "llvm/Analysis/LoopInfo.h"
34 #include "llvm/CodeGen/MachineBasicBlock.h"
35 #include "llvm/CodeGen/MachineFunctionPass.h"
39 // Implementation in LoopInfoImpl.h
41 extern template class LoopBase<MachineBasicBlock, MachineLoop>;
43 class MachineLoop : public LoopBase<MachineBasicBlock, MachineLoop> {
47 /// Return the "top" block in the loop, which is the first block in the linear
48 /// layout, ignoring any parts of the loop not contiguous with the part that
49 /// contains the header.
50 MachineBasicBlock *getTopBlock();
52 /// Return the "bottom" block in the loop, which is the last block in the
53 /// linear layout, ignoring any parts of the loop not contiguous with the part
54 /// that contains the header.
55 MachineBasicBlock *getBottomBlock();
57 /// \brief Find the block that contains the loop control variable and the
58 /// loop test. This will return the latch block if it's one of the exiting
59 /// blocks. Otherwise, return the exiting block. Return 'null' when
60 /// multiple exiting blocks are present.
61 MachineBasicBlock *findLoopControlBlock();
63 /// Return the debug location of the start of this loop.
64 /// This looks for a BB terminating instruction with a known debug
65 /// location by looking at the preheader and header blocks. If it
66 /// cannot find a terminating instruction with location information,
67 /// it returns an unknown location.
68 DebugLoc getStartLoc() const;
73 friend class LoopInfoBase<MachineBasicBlock, MachineLoop>;
74 explicit MachineLoop(MachineBasicBlock *MBB)
75 : LoopBase<MachineBasicBlock, MachineLoop>(MBB) {}
78 // Implementation in LoopInfoImpl.h
79 extern template class LoopInfoBase<MachineBasicBlock, MachineLoop>;
81 class MachineLoopInfo : public MachineFunctionPass {
82 LoopInfoBase<MachineBasicBlock, MachineLoop> LI;
83 friend class LoopBase<MachineBasicBlock, MachineLoop>;
85 void operator=(const MachineLoopInfo &) = delete;
86 MachineLoopInfo(const MachineLoopInfo &) = delete;
89 static char ID; // Pass identification, replacement for typeid
91 MachineLoopInfo() : MachineFunctionPass(ID) {
92 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
95 LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
97 /// \brief Find the block that either is the loop preheader, or could
98 /// speculatively be used as the preheader. This is e.g. useful to place
99 /// loop setup code. Code that cannot be speculated should not be placed
100 /// here. SpeculativePreheader is controlling whether it also tries to
101 /// find the speculative preheader if the regular preheader is not present.
102 MachineBasicBlock *findLoopPreheader(MachineLoop *L,
103 bool SpeculativePreheader = false) const;
105 /// The iterator interface to the top-level loops in the current function.
106 typedef LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator iterator;
107 inline iterator begin() const { return LI.begin(); }
108 inline iterator end() const { return LI.end(); }
109 bool empty() const { return LI.empty(); }
111 /// Return the innermost loop that BB lives in. If a basic block is in no loop
112 /// (for example the entry node), null is returned.
113 inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const {
114 return LI.getLoopFor(BB);
117 /// Same as getLoopFor.
118 inline const MachineLoop *operator[](const MachineBasicBlock *BB) const {
119 return LI.getLoopFor(BB);
122 /// Return the loop nesting level of the specified block.
123 inline unsigned getLoopDepth(const MachineBasicBlock *BB) const {
124 return LI.getLoopDepth(BB);
127 /// True if the block is a loop header node.
128 inline bool isLoopHeader(const MachineBasicBlock *BB) const {
129 return LI.isLoopHeader(BB);
132 /// Calculate the natural loop information.
133 bool runOnMachineFunction(MachineFunction &F) override;
135 void releaseMemory() override { LI.releaseMemory(); }
137 void getAnalysisUsage(AnalysisUsage &AU) const override;
139 /// This removes the specified top-level loop from this loop info object. The
140 /// loop is not deleted, as it will presumably be inserted into another loop.
141 inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); }
143 /// Change the top-level loop that contains BB to the specified loop. This
144 /// should be used by transformations that restructure the loop hierarchy
146 inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) {
147 LI.changeLoopFor(BB, L);
150 /// Replace the specified loop in the top-level loops list with the indicated
152 inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) {
153 LI.changeTopLevelLoop(OldLoop, NewLoop);
156 /// This adds the specified loop to the collection of top-level loops.
157 inline void addTopLevelLoop(MachineLoop *New) {
158 LI.addTopLevelLoop(New);
161 /// This method completely removes BB from all data structures, including all
162 /// of the Loop objects it is nested in and our mapping from
163 /// MachineBasicBlocks to loops.
164 void removeBlock(MachineBasicBlock *BB) {
170 // Allow clients to walk the list of nested loops...
171 template <> struct GraphTraits<const MachineLoop*> {
172 typedef const MachineLoop *NodeRef;
173 typedef MachineLoopInfo::iterator ChildIteratorType;
175 static NodeRef getEntryNode(const MachineLoop *L) { return L; }
176 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
177 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
180 template <> struct GraphTraits<MachineLoop*> {
181 typedef MachineLoop *NodeRef;
182 typedef MachineLoopInfo::iterator ChildIteratorType;
184 static NodeRef getEntryNode(MachineLoop *L) { return L; }
185 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
186 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
189 } // End llvm namespace