1 //===- Localizer.cpp ---------------------- Localize some instrs -*- 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 /// \file
9 /// This file implements the Localizer class.
10 //===----------------------------------------------------------------------===//
11 
12 #include "llvm/CodeGen/GlobalISel/Localizer.h"
13 #include "llvm/ADT/DenseMap.h"
14 #include "llvm/ADT/STLExtras.h"
15 #include "llvm/Analysis/TargetTransformInfo.h"
16 #include "llvm/CodeGen/GlobalISel/Utils.h"
17 #include "llvm/CodeGen/MachineRegisterInfo.h"
18 #include "llvm/CodeGen/TargetLowering.h"
19 #include "llvm/InitializePasses.h"
20 #include "llvm/Support/Debug.h"
21 
22 #define DEBUG_TYPE "localizer"
23 
24 using namespace llvm;
25 
26 char Localizer::ID = 0;
27 INITIALIZE_PASS_BEGIN(Localizer, DEBUG_TYPE,
28                       "Move/duplicate certain instructions close to their use",
29                       false, false)
30 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
31 INITIALIZE_PASS_END(Localizer, DEBUG_TYPE,
32                     "Move/duplicate certain instructions close to their use",
33                     false, false)
34 
35 Localizer::Localizer(std::function<bool(const MachineFunction &)> F)
36     : MachineFunctionPass(ID), DoNotRunPass(F) {}
37 
38 Localizer::Localizer()
39     : Localizer([](const MachineFunction &) { return false; }) {}
40 
41 void Localizer::init(MachineFunction &MF) {
42   MRI = &MF.getRegInfo();
43   TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(MF.getFunction());
44 }
45 
46 void Localizer::getAnalysisUsage(AnalysisUsage &AU) const {
47   AU.addRequired<TargetTransformInfoWrapperPass>();
48   getSelectionDAGFallbackAnalysisUsage(AU);
49   MachineFunctionPass::getAnalysisUsage(AU);
50 }
51 
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 
61 bool Localizer::isNonUniquePhiValue(MachineOperand &Op) const {
62   MachineInstr *MI = Op.getParent();
63   if (!MI->isPHI())
64     return false;
65 
66   Register SrcReg = Op.getReg();
67   for (unsigned Idx = 1; Idx < MI->getNumOperands(); Idx += 2) {
68     auto &MO = MI->getOperand(Idx);
69     if (&MO != &Op && MO.isReg() && MO.getReg() == SrcReg)
70       return true;
71   }
72   return false;
73 }
74 
75 bool Localizer::localizeInterBlock(MachineFunction &MF,
76                                    LocalizedSetVecT &LocalizedInstrs) {
77   bool Changed = false;
78   DenseMap<std::pair<MachineBasicBlock *, unsigned>, unsigned> MBBWithLocalDef;
79 
80   // Since the IRTranslator only emits constants into the entry block, and the
81   // rest of the GISel pipeline generally emits constants close to their users,
82   // we only localize instructions in the entry block here. This might change if
83   // we start doing CSE across blocks.
84   auto &MBB = MF.front();
85   auto &TL = *MF.getSubtarget().getTargetLowering();
86   for (MachineInstr &MI : llvm::reverse(MBB)) {
87     if (!TL.shouldLocalize(MI, TTI))
88       continue;
89     LLVM_DEBUG(dbgs() << "Should localize: " << MI);
90     assert(MI.getDesc().getNumDefs() == 1 &&
91            "More than one definition not supported yet");
92     Register Reg = MI.getOperand(0).getReg();
93     // Check if all the users of MI are local.
94     // We are going to invalidation the list of use operands, so we
95     // can't use range iterator.
96     for (MachineOperand &MOUse :
97          llvm::make_early_inc_range(MRI->use_operands(Reg))) {
98       // Check if the use is already local.
99       MachineBasicBlock *InsertMBB;
100       LLVM_DEBUG(MachineInstr &MIUse = *MOUse.getParent();
101                  dbgs() << "Checking use: " << MIUse
102                         << " #Opd: " << MIUse.getOperandNo(&MOUse) << '\n');
103       if (isLocalUse(MOUse, MI, InsertMBB)) {
104         // Even if we're in the same block, if the block is very large we could
105         // still have many long live ranges. Try to do intra-block localization
106         // too.
107         LocalizedInstrs.insert(&MI);
108         continue;
109       }
110 
111       // If the use is a phi operand that's not unique, don't try to localize.
112       // If we do, we can cause unnecessary instruction bloat by duplicating
113       // into each predecessor block, when the existing one is sufficient and
114       // allows for easier optimization later.
115       if (isNonUniquePhiValue(MOUse))
116         continue;
117 
118       LLVM_DEBUG(dbgs() << "Fixing non-local use\n");
119       Changed = true;
120       auto MBBAndReg = std::make_pair(InsertMBB, Reg);
121       auto NewVRegIt = MBBWithLocalDef.find(MBBAndReg);
122       if (NewVRegIt == MBBWithLocalDef.end()) {
123         // Create the localized instruction.
124         MachineInstr *LocalizedMI = MF.CloneMachineInstr(&MI);
125         LocalizedInstrs.insert(LocalizedMI);
126         MachineInstr &UseMI = *MOUse.getParent();
127         if (MRI->hasOneUse(Reg) && !UseMI.isPHI())
128           InsertMBB->insert(UseMI, LocalizedMI);
129         else
130           InsertMBB->insert(InsertMBB->SkipPHIsAndLabels(InsertMBB->begin()),
131                             LocalizedMI);
132 
133         // Set a new register for the definition.
134         Register NewReg = MRI->cloneVirtualRegister(Reg);
135         LocalizedMI->getOperand(0).setReg(NewReg);
136         NewVRegIt =
137             MBBWithLocalDef.insert(std::make_pair(MBBAndReg, NewReg)).first;
138         LLVM_DEBUG(dbgs() << "Inserted: " << *LocalizedMI);
139       }
140       LLVM_DEBUG(dbgs() << "Update use with: " << printReg(NewVRegIt->second)
141                         << '\n');
142       // Update the user reg.
143       MOUse.setReg(NewVRegIt->second);
144     }
145   }
146   return Changed;
147 }
148 
149 bool Localizer::localizeIntraBlock(LocalizedSetVecT &LocalizedInstrs) {
150   bool Changed = false;
151 
152   // For each already-localized instruction which has multiple users, then we
153   // scan the block top down from the current position until we hit one of them.
154 
155   // FIXME: Consider doing inst duplication if live ranges are very long due to
156   // many users, but this case may be better served by regalloc improvements.
157 
158   for (MachineInstr *MI : LocalizedInstrs) {
159     Register Reg = MI->getOperand(0).getReg();
160     MachineBasicBlock &MBB = *MI->getParent();
161     // All of the user MIs of this reg.
162     SmallPtrSet<MachineInstr *, 32> Users;
163     for (MachineInstr &UseMI : MRI->use_nodbg_instructions(Reg)) {
164       if (!UseMI.isPHI())
165         Users.insert(&UseMI);
166     }
167     // If all the users were PHIs then they're not going to be in our block,
168     // don't try to move this instruction.
169     if (Users.empty())
170       continue;
171 
172     MachineBasicBlock::iterator II(MI);
173     ++II;
174     while (II != MBB.end() && !Users.count(&*II))
175       ++II;
176 
177     assert(II != MBB.end() && "Didn't find the user in the MBB");
178     LLVM_DEBUG(dbgs() << "Intra-block: moving " << *MI << " before " << *II
179                       << '\n');
180 
181     MI->removeFromParent();
182     MBB.insert(II, MI);
183     Changed = true;
184 
185     // If the instruction (constant) being localized has single user, we can
186     // propagate debug location from user.
187     if (Users.size() == 1) {
188       const auto &DefDL = MI->getDebugLoc();
189       const auto &UserDL = (*Users.begin())->getDebugLoc();
190 
191       if ((!DefDL || DefDL.getLine() == 0) && UserDL && UserDL.getLine() != 0) {
192         MI->setDebugLoc(UserDL);
193       }
194     }
195   }
196   return Changed;
197 }
198 
199 bool Localizer::runOnMachineFunction(MachineFunction &MF) {
200   // If the ISel pipeline failed, do not bother running that pass.
201   if (MF.getProperties().hasProperty(
202           MachineFunctionProperties::Property::FailedISel))
203     return false;
204 
205   // Don't run the pass if the target asked so.
206   if (DoNotRunPass(MF))
207     return false;
208 
209   LLVM_DEBUG(dbgs() << "Localize instructions for: " << MF.getName() << '\n');
210 
211   init(MF);
212 
213   // Keep track of the instructions we localized. We'll do a second pass of
214   // intra-block localization to further reduce live ranges.
215   LocalizedSetVecT LocalizedInstrs;
216 
217   bool Changed = localizeInterBlock(MF, LocalizedInstrs);
218   Changed |= localizeIntraBlock(LocalizedInstrs);
219   return Changed;
220 }
221