1//===- MachineLoopInfo.cpp - Natural Loop Calculator ----------------------===//
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// the loops identified may actually be several natural loops that share the
12// same header node... not just a single natural loop.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/CodeGen/MachineLoopInfo.h"
17#include "llvm/Analysis/LoopInfoImpl.h"
18#include "llvm/CodeGen/MachineDominators.h"
19#include "llvm/CodeGen/Passes.h"
20#include "llvm/Config/llvm-config.h"
21#include "llvm/InitializePasses.h"
22#include "llvm/Support/Debug.h"
23#include "llvm/Support/raw_ostream.h"
24using namespace llvm;
25
26// Explicitly instantiate methods in LoopInfoImpl.h for MI-level Loops.
27template class llvm::LoopBase<MachineBasicBlock, MachineLoop>;
28template class llvm::LoopInfoBase<MachineBasicBlock, MachineLoop>;
29
30char MachineLoopInfo::ID = 0;
31MachineLoopInfo::MachineLoopInfo() : MachineFunctionPass(ID) {
32  initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
33}
34INITIALIZE_PASS_BEGIN(MachineLoopInfo, "machine-loops",
35                "Machine Natural Loop Construction", true, true)
36INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
37INITIALIZE_PASS_END(MachineLoopInfo, "machine-loops",
38                "Machine Natural Loop Construction", true, true)
39
40char &llvm::MachineLoopInfoID = MachineLoopInfo::ID;
41
42bool MachineLoopInfo::runOnMachineFunction(MachineFunction &) {
43  calculate(getAnalysis<MachineDominatorTree>());
44  return false;
45}
46
47void MachineLoopInfo::calculate(MachineDominatorTree &MDT) {
48  releaseMemory();
49  LI.analyze(MDT.getBase());
50}
51
52void MachineLoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
53  AU.setPreservesAll();
54  AU.addRequired<MachineDominatorTree>();
55  MachineFunctionPass::getAnalysisUsage(AU);
56}
57
58MachineBasicBlock *MachineLoop::getTopBlock() {
59  MachineBasicBlock *TopMBB = getHeader();
60  MachineFunction::iterator Begin = TopMBB->getParent()->begin();
61  if (TopMBB->getIterator() != Begin) {
62    MachineBasicBlock *PriorMBB = &*std::prev(TopMBB->getIterator());
63    while (contains(PriorMBB)) {
64      TopMBB = PriorMBB;
65      if (TopMBB->getIterator() == Begin)
66        break;
67      PriorMBB = &*std::prev(TopMBB->getIterator());
68    }
69  }
70  return TopMBB;
71}
72
73MachineBasicBlock *MachineLoop::getBottomBlock() {
74  MachineBasicBlock *BotMBB = getHeader();
75  MachineFunction::iterator End = BotMBB->getParent()->end();
76  if (BotMBB->getIterator() != std::prev(End)) {
77    MachineBasicBlock *NextMBB = &*std::next(BotMBB->getIterator());
78    while (contains(NextMBB)) {
79      BotMBB = NextMBB;
80      if (BotMBB == &*std::next(BotMBB->getIterator()))
81        break;
82      NextMBB = &*std::next(BotMBB->getIterator());
83    }
84  }
85  return BotMBB;
86}
87
88MachineBasicBlock *MachineLoop::findLoopControlBlock() {
89  if (MachineBasicBlock *Latch = getLoopLatch()) {
90    if (isLoopExiting(Latch))
91      return Latch;
92    else
93      return getExitingBlock();
94  }
95  return nullptr;
96}
97
98DebugLoc MachineLoop::getStartLoc() const {
99  // Try the pre-header first.
100  if (MachineBasicBlock *PHeadMBB = getLoopPreheader())
101    if (const BasicBlock *PHeadBB = PHeadMBB->getBasicBlock())
102      if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc())
103        return DL;
104
105  // If we have no pre-header or there are no instructions with debug
106  // info in it, try the header.
107  if (MachineBasicBlock *HeadMBB = getHeader())
108    if (const BasicBlock *HeadBB = HeadMBB->getBasicBlock())
109      return HeadBB->getTerminator()->getDebugLoc();
110
111  return DebugLoc();
112}
113
114MachineBasicBlock *
115MachineLoopInfo::findLoopPreheader(MachineLoop *L,
116                                   bool SpeculativePreheader) const {
117  if (MachineBasicBlock *PB = L->getLoopPreheader())
118    return PB;
119
120  if (!SpeculativePreheader)
121    return nullptr;
122
123  MachineBasicBlock *HB = L->getHeader(), *LB = L->getLoopLatch();
124  if (HB->pred_size() != 2 || HB->hasAddressTaken())
125    return nullptr;
126  // Find the predecessor of the header that is not the latch block.
127  MachineBasicBlock *Preheader = nullptr;
128  for (MachineBasicBlock *P : HB->predecessors()) {
129    if (P == LB)
130      continue;
131    // Sanity.
132    if (Preheader)
133      return nullptr;
134    Preheader = P;
135  }
136
137  // Check if the preheader candidate is a successor of any other loop
138  // headers. We want to avoid having two loop setups in the same block.
139  for (MachineBasicBlock *S : Preheader->successors()) {
140    if (S == HB)
141      continue;
142    MachineLoop *T = getLoopFor(S);
143    if (T && T->getHeader() == S)
144      return nullptr;
145  }
146  return Preheader;
147}
148
149#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
150LLVM_DUMP_METHOD void MachineLoop::dump() const {
151  print(dbgs());
152}
153#endif
154