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"
36 #include "llvm/IR/DebugLoc.h"
37 #include "llvm/Pass.h"
41 // Implementation in LoopInfoImpl.h
43 extern template class LoopBase<MachineBasicBlock, MachineLoop>;
45 class MachineLoop : public LoopBase<MachineBasicBlock, MachineLoop> {
49 /// Return the "top" block in the loop, which is the first block in the linear
50 /// layout, ignoring any parts of the loop not contiguous with the part that
51 /// contains the header.
52 MachineBasicBlock *getTopBlock();
54 /// Return the "bottom" block in the loop, which is the last block in the
55 /// linear layout, ignoring any parts of the loop not contiguous with the part
56 /// that contains the header.
57 MachineBasicBlock *getBottomBlock();
59 /// \brief Find the block that contains the loop control variable and the
60 /// loop test. This will return the latch block if it's one of the exiting
61 /// blocks. Otherwise, return the exiting block. Return 'null' when
62 /// multiple exiting blocks are present.
63 MachineBasicBlock *findLoopControlBlock();
65 /// Return the debug location of the start of this loop.
66 /// This looks for a BB terminating instruction with a known debug
67 /// location by looking at the preheader and header blocks. If it
68 /// cannot find a terminating instruction with location information,
69 /// it returns an unknown location.
70 DebugLoc getStartLoc() const;
75 friend class LoopInfoBase<MachineBasicBlock, MachineLoop>;
77 explicit MachineLoop(MachineBasicBlock *MBB)
78 : LoopBase<MachineBasicBlock, MachineLoop>(MBB) {}
81 // Implementation in LoopInfoImpl.h
82 extern template class LoopInfoBase<MachineBasicBlock, MachineLoop>;
84 class MachineLoopInfo : public MachineFunctionPass {
85 friend class LoopBase<MachineBasicBlock, MachineLoop>;
87 LoopInfoBase<MachineBasicBlock, MachineLoop> LI;
90 static char ID; // Pass identification, replacement for typeid
92 MachineLoopInfo() : MachineFunctionPass(ID) {
93 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
95 MachineLoopInfo(const MachineLoopInfo &) = delete;
96 MachineLoopInfo &operator=(const MachineLoopInfo &) = delete;
98 LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
100 /// \brief Find the block that either is the loop preheader, or could
101 /// speculatively be used as the preheader. This is e.g. useful to place
102 /// loop setup code. Code that cannot be speculated should not be placed
103 /// here. SpeculativePreheader is controlling whether it also tries to
104 /// find the speculative preheader if the regular preheader is not present.
105 MachineBasicBlock *findLoopPreheader(MachineLoop *L,
106 bool SpeculativePreheader = false) const;
108 /// The iterator interface to the top-level loops in the current function.
109 using iterator = LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator;
110 inline iterator begin() const { return LI.begin(); }
111 inline iterator end() const { return LI.end(); }
112 bool empty() const { return LI.empty(); }
114 /// Return the innermost loop that BB lives in. If a basic block is in no loop
115 /// (for example the entry node), null is returned.
116 inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const {
117 return LI.getLoopFor(BB);
120 /// Same as getLoopFor.
121 inline const MachineLoop *operator[](const MachineBasicBlock *BB) const {
122 return LI.getLoopFor(BB);
125 /// Return the loop nesting level of the specified block.
126 inline unsigned getLoopDepth(const MachineBasicBlock *BB) const {
127 return LI.getLoopDepth(BB);
130 /// True if the block is a loop header node.
131 inline bool isLoopHeader(const MachineBasicBlock *BB) const {
132 return LI.isLoopHeader(BB);
135 /// Calculate the natural loop information.
136 bool runOnMachineFunction(MachineFunction &F) override;
138 void releaseMemory() override { LI.releaseMemory(); }
140 void getAnalysisUsage(AnalysisUsage &AU) const override;
142 /// This removes the specified top-level loop from this loop info object. The
143 /// loop is not deleted, as it will presumably be inserted into another loop.
144 inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); }
146 /// Change the top-level loop that contains BB to the specified loop. This
147 /// should be used by transformations that restructure the loop hierarchy
149 inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) {
150 LI.changeLoopFor(BB, L);
153 /// Replace the specified loop in the top-level loops list with the indicated
155 inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) {
156 LI.changeTopLevelLoop(OldLoop, NewLoop);
159 /// This adds the specified loop to the collection of top-level loops.
160 inline void addTopLevelLoop(MachineLoop *New) {
161 LI.addTopLevelLoop(New);
164 /// This method completely removes BB from all data structures, including all
165 /// of the Loop objects it is nested in and our mapping from
166 /// MachineBasicBlocks to loops.
167 void removeBlock(MachineBasicBlock *BB) {
172 // Allow clients to walk the list of nested loops...
173 template <> struct GraphTraits<const MachineLoop*> {
174 using NodeRef = const MachineLoop *;
175 using ChildIteratorType = MachineLoopInfo::iterator;
177 static NodeRef getEntryNode(const MachineLoop *L) { return L; }
178 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
179 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
182 template <> struct GraphTraits<MachineLoop*> {
183 using NodeRef = MachineLoop *;
184 using ChildIteratorType = MachineLoopInfo::iterator;
186 static NodeRef getEntryNode(MachineLoop *L) { return L; }
187 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
188 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
191 } // end namespace llvm
193 #endif // LLVM_CODEGEN_MACHINELOOPINFO_H