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"
24 using namespace llvm;
25
26 // Explicitly instantiate methods in LoopInfoImpl.h for MI-level Loops.
27 template class llvm::LoopBase<MachineBasicBlock, MachineLoop>;
28 template class llvm::LoopInfoBase<MachineBasicBlock, MachineLoop>;
29
30 char MachineLoopInfo::ID = 0;
MachineLoopInfo()31 MachineLoopInfo::MachineLoopInfo() : MachineFunctionPass(ID) {
32 initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
33 }
34 INITIALIZE_PASS_BEGIN(MachineLoopInfo, "machine-loops",
35 "Machine Natural Loop Construction", true, true)
36 INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
37 INITIALIZE_PASS_END(MachineLoopInfo, "machine-loops",
38 "Machine Natural Loop Construction", true, true)
39
40 char &llvm::MachineLoopInfoID = MachineLoopInfo::ID;
41
runOnMachineFunction(MachineFunction &)42 bool MachineLoopInfo::runOnMachineFunction(MachineFunction &) {
43 calculate(getAnalysis<MachineDominatorTree>());
44 return false;
45 }
46
calculate(MachineDominatorTree & MDT)47 void MachineLoopInfo::calculate(MachineDominatorTree &MDT) {
48 releaseMemory();
49 LI.analyze(MDT.getBase());
50 }
51
getAnalysisUsage(AnalysisUsage & AU) const52 void MachineLoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
53 AU.setPreservesAll();
54 AU.addRequired<MachineDominatorTree>();
55 MachineFunctionPass::getAnalysisUsage(AU);
56 }
57
getTopBlock()58 MachineBasicBlock *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
getBottomBlock()73 MachineBasicBlock *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
findLoopControlBlock()88 MachineBasicBlock *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
getStartLoc() const98 DebugLoc 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
114 MachineBasicBlock *
findLoopPreheader(MachineLoop * L,bool SpeculativePreheader) const115 MachineLoopInfo::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)
dump() const150 LLVM_DUMP_METHOD void MachineLoop::dump() const {
151 print(dbgs());
152 }
153 #endif
154