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
28 using namespace llvm;
29
30 namespace llvm {
31 cl::OptionCategory GICombinerOptionCategory(
32 "GlobalISel Combiner",
33 "Control the rules which are enabled. These options all take a comma "
34 "separated list of rules to disable and may be specified by number "
35 "or number range (e.g. 1-10)."
36 #ifndef NDEBUG
37 " They may also be specified by name."
38 #endif
39 );
40 } // end namespace llvm
41
42 namespace {
43 /// This class acts as the glue the joins the CombinerHelper to the overall
44 /// Combine algorithm. The CombinerHelper is intended to report the
45 /// modifications it makes to the MIR to the GISelChangeObserver and the
46 /// observer subclass will act on these events. In this case, instruction
47 /// erasure will cancel any future visits to the erased instruction and
48 /// instruction creation will schedule that instruction for a future visit.
49 /// Other Combiner implementations may require more complex behaviour from
50 /// their GISelChangeObserver subclass.
51 class WorkListMaintainer : public GISelChangeObserver {
52 using WorkListTy = GISelWorkList<512>;
53 WorkListTy &WorkList;
54 /// The instructions that have been created but we want to report once they
55 /// have their operands. This is only maintained if debug output is requested.
56 SmallPtrSet<const MachineInstr *, 4> CreatedInstrs;
57
58 public:
WorkListMaintainer(WorkListTy & WorkList)59 WorkListMaintainer(WorkListTy &WorkList)
60 : GISelChangeObserver(), WorkList(WorkList) {}
~WorkListMaintainer()61 virtual ~WorkListMaintainer() {
62 }
63
erasingInstr(MachineInstr & MI)64 void erasingInstr(MachineInstr &MI) override {
65 LLVM_DEBUG(dbgs() << "Erasing: " << MI << "\n");
66 WorkList.remove(&MI);
67 }
createdInstr(MachineInstr & MI)68 void createdInstr(MachineInstr &MI) override {
69 LLVM_DEBUG(dbgs() << "Creating: " << MI << "\n");
70 WorkList.insert(&MI);
71 LLVM_DEBUG(CreatedInstrs.insert(&MI));
72 }
changingInstr(MachineInstr & MI)73 void changingInstr(MachineInstr &MI) override {
74 LLVM_DEBUG(dbgs() << "Changing: " << MI << "\n");
75 WorkList.insert(&MI);
76 }
changedInstr(MachineInstr & MI)77 void changedInstr(MachineInstr &MI) override {
78 LLVM_DEBUG(dbgs() << "Changed: " << MI << "\n");
79 WorkList.insert(&MI);
80 }
81
reportFullyCreatedInstrs()82 void reportFullyCreatedInstrs() {
83 LLVM_DEBUG(for (const auto *MI
84 : CreatedInstrs) {
85 dbgs() << "Created: ";
86 MI->print(dbgs());
87 });
88 LLVM_DEBUG(CreatedInstrs.clear());
89 }
90 };
91 }
92
Combiner(CombinerInfo & Info,const TargetPassConfig * TPC)93 Combiner::Combiner(CombinerInfo &Info, const TargetPassConfig *TPC)
94 : CInfo(Info), TPC(TPC) {
95 (void)this->TPC; // FIXME: Remove when used.
96 }
97
combineMachineInstrs(MachineFunction & MF,GISelCSEInfo * CSEInfo)98 bool Combiner::combineMachineInstrs(MachineFunction &MF,
99 GISelCSEInfo *CSEInfo) {
100 // If the ISel pipeline failed, do not bother running this pass.
101 // FIXME: Should this be here or in individual combiner passes.
102 if (MF.getProperties().hasProperty(
103 MachineFunctionProperties::Property::FailedISel))
104 return false;
105
106 Builder =
107 CSEInfo ? std::make_unique<CSEMIRBuilder>() : std::make_unique<MachineIRBuilder>();
108 MRI = &MF.getRegInfo();
109 Builder->setMF(MF);
110 if (CSEInfo)
111 Builder->setCSEInfo(CSEInfo);
112
113 LLVM_DEBUG(dbgs() << "Generic MI Combiner for: " << MF.getName() << '\n');
114
115 MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
116
117 bool MFChanged = false;
118 bool Changed;
119 MachineIRBuilder &B = *Builder.get();
120
121 do {
122 // Collect all instructions. Do a post order traversal for basic blocks and
123 // insert with list bottom up, so while we pop_back_val, we'll traverse top
124 // down RPOT.
125 Changed = false;
126 GISelWorkList<512> WorkList;
127 WorkListMaintainer Observer(WorkList);
128 GISelObserverWrapper WrapperObserver(&Observer);
129 if (CSEInfo)
130 WrapperObserver.addObserver(CSEInfo);
131 RAIIDelegateInstaller DelInstall(MF, &WrapperObserver);
132 for (MachineBasicBlock *MBB : post_order(&MF)) {
133 if (MBB->empty())
134 continue;
135 for (auto MII = MBB->rbegin(), MIE = MBB->rend(); MII != MIE;) {
136 MachineInstr *CurMI = &*MII;
137 ++MII;
138 // Erase dead insts before even adding to the list.
139 if (isTriviallyDead(*CurMI, *MRI)) {
140 LLVM_DEBUG(dbgs() << *CurMI << "Is dead; erasing.\n");
141 CurMI->eraseFromParentAndMarkDBGValuesForRemoval();
142 continue;
143 }
144 WorkList.deferred_insert(CurMI);
145 }
146 }
147 WorkList.finalize();
148 // Main Loop. Process the instructions here.
149 while (!WorkList.empty()) {
150 MachineInstr *CurrInst = WorkList.pop_back_val();
151 LLVM_DEBUG(dbgs() << "\nTry combining " << *CurrInst;);
152 Changed |= CInfo.combine(WrapperObserver, *CurrInst, B);
153 Observer.reportFullyCreatedInstrs();
154 }
155 MFChanged |= Changed;
156 } while (Changed);
157
158 return MFChanged;
159 }
160