Combiner.cpp revision 355940 
1//===-- lib/CodeGen/GlobalISel/Combiner.cpp -------------------------------===//
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 constains common code to combine machine functions at generic
10// level.
11//===----------------------------------------------------------------------===//
12
13#include "llvm/CodeGen/GlobalISel/Combiner.h"
14#include "llvm/ADT/PostOrderIterator.h"
15#include "llvm/CodeGen/GlobalISel/CSEInfo.h"
16#include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
17#include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
18#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
19#include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
20#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
21#include "llvm/CodeGen/GlobalISel/Utils.h"
22#include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
23#include "llvm/CodeGen/MachineRegisterInfo.h"
24#include "llvm/Support/Debug.h"
25
26#define DEBUG_TYPE "gi-combiner"
27
28using namespace llvm;
29
30namespace {
31/// This class acts as the glue the joins the CombinerHelper to the overall
32/// Combine algorithm. The CombinerHelper is intended to report the
33/// modifications it makes to the MIR to the GISelChangeObserver and the
34/// observer subclass will act on these events. In this case, instruction
35/// erasure will cancel any future visits to the erased instruction and
36/// instruction creation will schedule that instruction for a future visit.
37/// Other Combiner implementations may require more complex behaviour from
38/// their GISelChangeObserver subclass.
39class WorkListMaintainer : public GISelChangeObserver {
40  using WorkListTy = GISelWorkList<512>;
41  WorkListTy &WorkList;
42  /// The instructions that have been created but we want to report once they
43  /// have their operands. This is only maintained if debug output is requested.
44  SmallPtrSet<const MachineInstr *, 4> CreatedInstrs;
45
46public:
47  WorkListMaintainer(WorkListTy &WorkList)
48      : GISelChangeObserver(), WorkList(WorkList) {}
49  virtual ~WorkListMaintainer() {
50  }
51
52  void erasingInstr(MachineInstr &MI) override {
53    LLVM_DEBUG(dbgs() << "Erasing: " << MI << "\n");
54    WorkList.remove(&MI);
55  }
56  void createdInstr(MachineInstr &MI) override {
57    LLVM_DEBUG(dbgs() << "Creating: " << MI << "\n");
58    WorkList.insert(&MI);
59    LLVM_DEBUG(CreatedInstrs.insert(&MI));
60  }
61  void changingInstr(MachineInstr &MI) override {
62    LLVM_DEBUG(dbgs() << "Changing: " << MI << "\n");
63    WorkList.insert(&MI);
64  }
65  void changedInstr(MachineInstr &MI) override {
66    LLVM_DEBUG(dbgs() << "Changed: " << MI << "\n");
67    WorkList.insert(&MI);
68  }
69
70  void reportFullyCreatedInstrs() {
71    LLVM_DEBUG(for (const auto *MI
72                    : CreatedInstrs) {
73      dbgs() << "Created: ";
74      MI->print(dbgs());
75    });
76    LLVM_DEBUG(CreatedInstrs.clear());
77  }
78};
79}
80
81Combiner::Combiner(CombinerInfo &Info, const TargetPassConfig *TPC)
82    : CInfo(Info), TPC(TPC) {
83  (void)this->TPC; // FIXME: Remove when used.
84}
85
86bool Combiner::combineMachineInstrs(MachineFunction &MF,
87                                    GISelCSEInfo *CSEInfo) {
88  // If the ISel pipeline failed, do not bother running this pass.
89  // FIXME: Should this be here or in individual combiner passes.
90  if (MF.getProperties().hasProperty(
91          MachineFunctionProperties::Property::FailedISel))
92    return false;
93
94  Builder =
95      CSEInfo ? make_unique<CSEMIRBuilder>() : make_unique<MachineIRBuilder>();
96  MRI = &MF.getRegInfo();
97  Builder->setMF(MF);
98  if (CSEInfo)
99    Builder->setCSEInfo(CSEInfo);
100
101  LLVM_DEBUG(dbgs() << "Generic MI Combiner for: " << MF.getName() << '\n');
102
103  MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
104
105  bool MFChanged = false;
106  bool Changed;
107  MachineIRBuilder &B = *Builder.get();
108
109  do {
110    // Collect all instructions. Do a post order traversal for basic blocks and
111    // insert with list bottom up, so while we pop_back_val, we'll traverse top
112    // down RPOT.
113    Changed = false;
114    GISelWorkList<512> WorkList;
115    WorkListMaintainer Observer(WorkList);
116    GISelObserverWrapper WrapperObserver(&Observer);
117    if (CSEInfo)
118      WrapperObserver.addObserver(CSEInfo);
119    RAIIDelegateInstaller DelInstall(MF, &WrapperObserver);
120    for (MachineBasicBlock *MBB : post_order(&MF)) {
121      if (MBB->empty())
122        continue;
123      for (auto MII = MBB->rbegin(), MIE = MBB->rend(); MII != MIE;) {
124        MachineInstr *CurMI = &*MII;
125        ++MII;
126        // Erase dead insts before even adding to the list.
127        if (isTriviallyDead(*CurMI, *MRI)) {
128          LLVM_DEBUG(dbgs() << *CurMI << "Is dead; erasing.\n");
129          CurMI->eraseFromParentAndMarkDBGValuesForRemoval();
130          continue;
131        }
132        WorkList.deferred_insert(CurMI);
133      }
134    }
135    WorkList.finalize();
136    // Main Loop. Process the instructions here.
137    while (!WorkList.empty()) {
138      MachineInstr *CurrInst = WorkList.pop_back_val();
139      LLVM_DEBUG(dbgs() << "\nTry combining " << *CurrInst;);
140      Changed |= CInfo.combine(WrapperObserver, *CurrInst, B);
141      Observer.reportFullyCreatedInstrs();
142    }
143    MFChanged |= Changed;
144  } while (Changed);
145
146  return MFChanged;
147}
148