1//===- llvm/CodeGen/MachineLoopInfo.h - Natural Loop Calculator -*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines the MachineLoopInfo class that is used to identify natural
10// loops and determine the loop depth of various nodes of the CFG. Note that
11// natural loops may actually be several loops that share the same header node.
12//
13// This analysis calculates the nesting structure of loops in a function. For
14// each natural loop identified, this analysis identifies natural loops
15// contained entirely within the loop and the basic blocks the make up the loop.
16//
17// It can calculate on the fly various bits of information, for example:
18//
19// * whether there is a preheader for the loop
20// * the number of back edges to the header
21// * whether or not a particular block branches out of the loop
22// * the successor blocks of the loop
23// * the loop depth
24// * the trip count
25// * etc...
26//
27//===----------------------------------------------------------------------===//
28
29#ifndef LLVM_CODEGEN_MACHINELOOPINFO_H
30#define LLVM_CODEGEN_MACHINELOOPINFO_H
31
32#include "llvm/CodeGen/MachineBasicBlock.h"
33#include "llvm/CodeGen/MachineFunctionPass.h"
34#include "llvm/IR/CFG.h"
35#include "llvm/IR/DebugLoc.h"
36#include "llvm/Support/GenericLoopInfo.h"
37
38namespace llvm {
39
40class MachineDominatorTree;
41// Implementation in LoopInfoImpl.h
42class MachineLoop;
43extern template class LoopBase<MachineBasicBlock, MachineLoop>;
44
45class MachineLoop : public LoopBase<MachineBasicBlock, MachineLoop> {
46public:
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();
51
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();
56
57 /// 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() const;
62
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;
69
70 /// Find the llvm.loop metadata for this loop.
71 /// If each branch to the header of this loop contains the same llvm.loop
72 /// metadata, then this metadata node is returned. Otherwise, if any
73 /// latch instruction does not contain the llvm.loop metadata or
74 /// multiple latch instructions contain different llvm.loop metadata nodes,
75 /// then null is returned.
76 MDNode *getLoopID() const;
77
78 /// Returns true if the instruction is loop invariant.
79 /// I.e., all virtual register operands are defined outside of the loop,
80 /// physical registers aren't accessed explicitly, and there are no side
81 /// effects that aren't captured by the operands or other flags.
82 /// ExcludeReg can be used to exclude the given register from the check
83 /// i.e. when we're considering hoisting it's definition but not hoisted it
84 /// yet
85 bool isLoopInvariant(MachineInstr &I, const Register ExcludeReg = 0) const;
86
87 void dump() const;
88
89private:
90 friend class LoopInfoBase<MachineBasicBlock, MachineLoop>;
91
92 /// Returns true if the given physreg has no defs inside the loop.
93 bool isLoopInvariantImplicitPhysReg(Register Reg) const;
94
95 explicit MachineLoop(MachineBasicBlock *MBB)
96 : LoopBase<MachineBasicBlock, MachineLoop>(MBB) {}
97
98 MachineLoop() = default;
99};
100
101// Implementation in LoopInfoImpl.h
102extern template class LoopInfoBase<MachineBasicBlock, MachineLoop>;
103
104class MachineLoopInfo : public MachineFunctionPass {
105 friend class LoopBase<MachineBasicBlock, MachineLoop>;
106
107 LoopInfoBase<MachineBasicBlock, MachineLoop> LI;
108
109public:
110 static char ID; // Pass identification, replacement for typeid
111
112 MachineLoopInfo();
113 explicit MachineLoopInfo(MachineDominatorTree &MDT)
114 : MachineFunctionPass(ID) {
115 calculate(MDT);
116 }
117 MachineLoopInfo(const MachineLoopInfo &) = delete;
118 MachineLoopInfo &operator=(const MachineLoopInfo &) = delete;
119
120 LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
121
122 /// Find the block that either is the loop preheader, or could
123 /// speculatively be used as the preheader. This is e.g. useful to place
124 /// loop setup code. Code that cannot be speculated should not be placed
125 /// here. SpeculativePreheader is controlling whether it also tries to
126 /// find the speculative preheader if the regular preheader is not present.
127 /// With FindMultiLoopPreheader = false, nullptr will be returned if the found
128 /// preheader is the preheader of multiple loops.
129 MachineBasicBlock *
130 findLoopPreheader(MachineLoop *L, bool SpeculativePreheader = false,
131 bool FindMultiLoopPreheader = false) const;
132
133 /// The iterator interface to the top-level loops in the current function.
134 using iterator = LoopInfoBase<MachineBasicBlock, MachineLoop>::iterator;
135 inline iterator begin() const { return LI.begin(); }
136 inline iterator end() const { return LI.end(); }
137 bool empty() const { return LI.empty(); }
138
139 /// Return the innermost loop that BB lives in. If a basic block is in no loop
140 /// (for example the entry node), null is returned.
141 inline MachineLoop *getLoopFor(const MachineBasicBlock *BB) const {
142 return LI.getLoopFor(BB);
143 }
144
145 /// Same as getLoopFor.
146 inline const MachineLoop *operator[](const MachineBasicBlock *BB) const {
147 return LI.getLoopFor(BB);
148 }
149
150 /// Return the loop nesting level of the specified block.
151 inline unsigned getLoopDepth(const MachineBasicBlock *BB) const {
152 return LI.getLoopDepth(BB);
153 }
154
155 /// True if the block is a loop header node.
156 inline bool isLoopHeader(const MachineBasicBlock *BB) const {
157 return LI.isLoopHeader(BB);
158 }
159
160 /// Calculate the natural loop information.
161 bool runOnMachineFunction(MachineFunction &F) override;
162 void calculate(MachineDominatorTree &MDT);
163
164 void releaseMemory() override { LI.releaseMemory(); }
165
166 void getAnalysisUsage(AnalysisUsage &AU) const override;
167
168 /// This removes the specified top-level loop from this loop info object. The
169 /// loop is not deleted, as it will presumably be inserted into another loop.
170 inline MachineLoop *removeLoop(iterator I) { return LI.removeLoop(I); }
171
172 /// Change the top-level loop that contains BB to the specified loop. This
173 /// should be used by transformations that restructure the loop hierarchy
174 /// tree.
175 inline void changeLoopFor(MachineBasicBlock *BB, MachineLoop *L) {
176 LI.changeLoopFor(BB, L);
177 }
178
179 /// Replace the specified loop in the top-level loops list with the indicated
180 /// loop.
181 inline void changeTopLevelLoop(MachineLoop *OldLoop, MachineLoop *NewLoop) {
182 LI.changeTopLevelLoop(OldLoop, NewLoop);
183 }
184
185 /// This adds the specified loop to the collection of top-level loops.
186 inline void addTopLevelLoop(MachineLoop *New) {
187 LI.addTopLevelLoop(New);
188 }
189
190 /// This method completely removes BB from all data structures, including all
191 /// of the Loop objects it is nested in and our mapping from
192 /// MachineBasicBlocks to loops.
193 void removeBlock(MachineBasicBlock *BB) {
194 LI.removeBlock(BB);
195 }
196};
197
198// Allow clients to walk the list of nested loops...
199template <> struct GraphTraits<const MachineLoop*> {
200 using NodeRef = const MachineLoop *;
201 using ChildIteratorType = MachineLoopInfo::iterator;
202
203 static NodeRef getEntryNode(const MachineLoop *L) { return L; }
204 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
205 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
206};
207
208template <> struct GraphTraits<MachineLoop*> {
209 using NodeRef = MachineLoop *;
210 using ChildIteratorType = MachineLoopInfo::iterator;
211
212 static NodeRef getEntryNode(MachineLoop *L) { return L; }
213 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
214 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
215};
216
217} // end namespace llvm
218
219#endif // LLVM_CODEGEN_MACHINELOOPINFO_H
220

source code of llvm/include/llvm/CodeGen/MachineLoopInfo.h