1 //===- Localizer.cpp ---------------------- Localize some instrs -*- C++ -*-==//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 /// \file
10 /// This file implements the Localizer class.
11 //===----------------------------------------------------------------------===//
12
13 #include "llvm/CodeGen/GlobalISel/Localizer.h"
14 #include "llvm/ADT/DenseMap.h"
15 #include "llvm/ADT/SmallPtrSet.h"
16 #include "llvm/CodeGen/MachineRegisterInfo.h"
17 #include "llvm/Support/Debug.h"
18
19 #define DEBUG_TYPE "localizer"
20
21 using namespace llvm;
22
23 char Localizer::ID = 0;
24 INITIALIZE_PASS(Localizer, DEBUG_TYPE,
25 "Move/duplicate certain instructions close to their use", false,
26 false)
27
Localizer()28 Localizer::Localizer() : MachineFunctionPass(ID) {
29 initializeLocalizerPass(*PassRegistry::getPassRegistry());
30 }
31
init(MachineFunction & MF)32 void Localizer::init(MachineFunction &MF) { MRI = &MF.getRegInfo(); }
33
shouldLocalize(const MachineInstr & MI)34 bool Localizer::shouldLocalize(const MachineInstr &MI) {
35 switch (MI.getOpcode()) {
36 default:
37 return false;
38 // Constants-like instructions should be close to their users.
39 // We don't want long live-ranges for them.
40 case TargetOpcode::G_CONSTANT:
41 case TargetOpcode::G_FCONSTANT:
42 case TargetOpcode::G_FRAME_INDEX:
43 return true;
44 }
45 }
46
getAnalysisUsage(AnalysisUsage & AU) const47 void Localizer::getAnalysisUsage(AnalysisUsage &AU) const {
48 getSelectionDAGFallbackAnalysisUsage(AU);
49 MachineFunctionPass::getAnalysisUsage(AU);
50 }
51
isLocalUse(MachineOperand & MOUse,const MachineInstr & Def,MachineBasicBlock * & InsertMBB)52 bool Localizer::isLocalUse(MachineOperand &MOUse, const MachineInstr &Def,
53 MachineBasicBlock *&InsertMBB) {
54 MachineInstr &MIUse = *MOUse.getParent();
55 InsertMBB = MIUse.getParent();
56 if (MIUse.isPHI())
57 InsertMBB = MIUse.getOperand(MIUse.getOperandNo(&MOUse) + 1).getMBB();
58 return InsertMBB == Def.getParent();
59 }
60
runOnMachineFunction(MachineFunction & MF)61 bool Localizer::runOnMachineFunction(MachineFunction &MF) {
62 // If the ISel pipeline failed, do not bother running that pass.
63 if (MF.getProperties().hasProperty(
64 MachineFunctionProperties::Property::FailedISel))
65 return false;
66
67 LLVM_DEBUG(dbgs() << "Localize instructions for: " << MF.getName() << '\n');
68
69 init(MF);
70
71 bool Changed = false;
72 // Keep track of the instructions we localized.
73 // We won't need to process them if we see them later in the CFG.
74 SmallPtrSet<MachineInstr *, 16> LocalizedInstrs;
75 DenseMap<std::pair<MachineBasicBlock *, unsigned>, unsigned> MBBWithLocalDef;
76 // TODO: Do bottom up traversal.
77 for (MachineBasicBlock &MBB : MF) {
78 for (MachineInstr &MI : MBB) {
79 if (LocalizedInstrs.count(&MI) || !shouldLocalize(MI))
80 continue;
81 LLVM_DEBUG(dbgs() << "Should localize: " << MI);
82 assert(MI.getDesc().getNumDefs() == 1 &&
83 "More than one definition not supported yet");
84 unsigned Reg = MI.getOperand(0).getReg();
85 // Check if all the users of MI are local.
86 // We are going to invalidation the list of use operands, so we
87 // can't use range iterator.
88 for (auto MOIt = MRI->use_begin(Reg), MOItEnd = MRI->use_end();
89 MOIt != MOItEnd;) {
90 MachineOperand &MOUse = *MOIt++;
91 // Check if the use is already local.
92 MachineBasicBlock *InsertMBB;
93 LLVM_DEBUG(MachineInstr &MIUse = *MOUse.getParent();
94 dbgs() << "Checking use: " << MIUse
95 << " #Opd: " << MIUse.getOperandNo(&MOUse) << '\n');
96 if (isLocalUse(MOUse, MI, InsertMBB))
97 continue;
98 LLVM_DEBUG(dbgs() << "Fixing non-local use\n");
99 Changed = true;
100 auto MBBAndReg = std::make_pair(InsertMBB, Reg);
101 auto NewVRegIt = MBBWithLocalDef.find(MBBAndReg);
102 if (NewVRegIt == MBBWithLocalDef.end()) {
103 // Create the localized instruction.
104 MachineInstr *LocalizedMI = MF.CloneMachineInstr(&MI);
105 LocalizedInstrs.insert(LocalizedMI);
106 // Don't try to be smart for the insertion point.
107 // There is no guarantee that the first seen use is the first
108 // use in the block.
109 InsertMBB->insert(InsertMBB->SkipPHIsAndLabels(InsertMBB->begin()),
110 LocalizedMI);
111
112 // Set a new register for the definition.
113 unsigned NewReg =
114 MRI->createGenericVirtualRegister(MRI->getType(Reg));
115 MRI->setRegClassOrRegBank(NewReg, MRI->getRegClassOrRegBank(Reg));
116 LocalizedMI->getOperand(0).setReg(NewReg);
117 NewVRegIt =
118 MBBWithLocalDef.insert(std::make_pair(MBBAndReg, NewReg)).first;
119 LLVM_DEBUG(dbgs() << "Inserted: " << *LocalizedMI);
120 }
121 LLVM_DEBUG(dbgs() << "Update use with: " << printReg(NewVRegIt->second)
122 << '\n');
123 // Update the user reg.
124 MOUse.setReg(NewVRegIt->second);
125 }
126 }
127 }
128 return Changed;
129 }
130