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/ADT/SetVector.h"
16 #include "llvm/CodeGen/GlobalISel/CSEInfo.h"
17 #include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
18 #include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
19 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
20 #include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
21 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
22 #include "llvm/CodeGen/GlobalISel/Utils.h"
23 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.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 /// This class acts as the glue the joins the CombinerHelper to the overall
43 /// Combine algorithm. The CombinerHelper is intended to report the
44 /// modifications it makes to the MIR to the GISelChangeObserver and the
45 /// observer subclass will act on these events. In this case, instruction
46 /// erasure will cancel any future visits to the erased instruction and
47 /// instruction creation will schedule that instruction for a future visit.
48 /// Other Combiner implementations may require more complex behaviour from
49 /// their GISelChangeObserver subclass.
50 class Combiner::WorkListMaintainer : public GISelChangeObserver {
51   using WorkListTy = GISelWorkList<512>;
52   WorkListTy &WorkList;
53   /// The instructions that have been created but we want to report once they
54   /// have their operands. This is only maintained if debug output is requested.
55 #ifndef NDEBUG
56   SetVector<const MachineInstr *> CreatedInstrs;
57 #endif
58 
59 public:
60   WorkListMaintainer(WorkListTy &WorkList) : WorkList(WorkList) {}
61   virtual ~WorkListMaintainer() = default;
62 
63   void erasingInstr(MachineInstr &MI) override {
64     LLVM_DEBUG(dbgs() << "Erasing: " << MI << "\n");
65     WorkList.remove(&MI);
66   }
67   void createdInstr(MachineInstr &MI) override {
68     LLVM_DEBUG(dbgs() << "Creating: " << MI << "\n");
69     WorkList.insert(&MI);
70     LLVM_DEBUG(CreatedInstrs.insert(&MI));
71   }
72   void changingInstr(MachineInstr &MI) override {
73     LLVM_DEBUG(dbgs() << "Changing: " << MI << "\n");
74     WorkList.insert(&MI);
75   }
76   void changedInstr(MachineInstr &MI) override {
77     LLVM_DEBUG(dbgs() << "Changed: " << MI << "\n");
78     WorkList.insert(&MI);
79   }
80 
81   void reportFullyCreatedInstrs() {
82     LLVM_DEBUG(for (const auto *MI
83                     : CreatedInstrs) {
84       dbgs() << "Created: ";
85       MI->print(dbgs());
86     });
87     LLVM_DEBUG(CreatedInstrs.clear());
88   }
89 };
90 
91 Combiner::Combiner(MachineFunction &MF, CombinerInfo &CInfo,
92                    const TargetPassConfig *TPC, GISelKnownBits *KB,
93                    GISelCSEInfo *CSEInfo)
94     : Builder(CSEInfo ? std::make_unique<CSEMIRBuilder>()
95                       : std::make_unique<MachineIRBuilder>()),
96       WLObserver(std::make_unique<WorkListMaintainer>(WorkList)),
97       ObserverWrapper(std::make_unique<GISelObserverWrapper>()), CInfo(CInfo),
98       Observer(*ObserverWrapper), B(*Builder), MF(MF), MRI(MF.getRegInfo()),
99       KB(KB), TPC(TPC), CSEInfo(CSEInfo) {
100   (void)this->TPC; // FIXME: Remove when used.
101 
102   // Setup builder.
103   B.setMF(MF);
104   if (CSEInfo)
105     B.setCSEInfo(CSEInfo);
106 
107   // Setup observer.
108   ObserverWrapper->addObserver(WLObserver.get());
109   if (CSEInfo)
110     ObserverWrapper->addObserver(CSEInfo);
111 
112   B.setChangeObserver(*ObserverWrapper);
113 }
114 
115 Combiner::~Combiner() = default;
116 
117 bool Combiner::combineMachineInstrs() {
118   // If the ISel pipeline failed, do not bother running this pass.
119   // FIXME: Should this be here or in individual combiner passes.
120   if (MF.getProperties().hasProperty(
121           MachineFunctionProperties::Property::FailedISel))
122     return false;
123 
124   // We can't call this in the constructor because the derived class is
125   // uninitialized at that time.
126   if (!HasSetupMF) {
127     HasSetupMF = true;
128     setupMF(MF, KB);
129   }
130 
131   LLVM_DEBUG(dbgs() << "Generic MI Combiner for: " << MF.getName() << '\n');
132 
133   MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
134 
135   bool MFChanged = false;
136   bool Changed;
137 
138   do {
139     WorkList.clear();
140 
141     // Collect all instructions. Do a post order traversal for basic blocks and
142     // insert with list bottom up, so while we pop_back_val, we'll traverse top
143     // down RPOT.
144     Changed = false;
145 
146     RAIIDelegateInstaller DelInstall(MF, ObserverWrapper.get());
147     for (MachineBasicBlock *MBB : post_order(&MF)) {
148       for (MachineInstr &CurMI :
149            llvm::make_early_inc_range(llvm::reverse(*MBB))) {
150         // Erase dead insts before even adding to the list.
151         if (isTriviallyDead(CurMI, MRI)) {
152           LLVM_DEBUG(dbgs() << CurMI << "Is dead; erasing.\n");
153           llvm::salvageDebugInfo(MRI, CurMI);
154           CurMI.eraseFromParent();
155           continue;
156         }
157         WorkList.deferred_insert(&CurMI);
158       }
159     }
160     WorkList.finalize();
161     // Main Loop. Process the instructions here.
162     while (!WorkList.empty()) {
163       MachineInstr *CurrInst = WorkList.pop_back_val();
164       LLVM_DEBUG(dbgs() << "\nTry combining " << *CurrInst;);
165       Changed |= tryCombineAll(*CurrInst);
166       WLObserver->reportFullyCreatedInstrs();
167     }
168     MFChanged |= Changed;
169   } while (Changed);
170 
171 #ifndef NDEBUG
172   if (CSEInfo) {
173     if (auto E = CSEInfo->verify()) {
174       errs() << E << '\n';
175       assert(false && "CSEInfo is not consistent. Likely missing calls to "
176                       "observer on mutations.");
177     }
178   }
179 #endif
180   return MFChanged;
181 }
182