1 //===-- llvm/CodeGen/GlobalISel/Legalizer.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 /// \file This file implements the LegalizerHelper class to legalize individual
10 /// instructions and the LegalizePass wrapper pass for the primary
11 /// legalization.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/CodeGen/GlobalISel/Legalizer.h"
16 #include "llvm/ADT/PostOrderIterator.h"
17 #include "llvm/ADT/SetVector.h"
18 #include "llvm/CodeGen/GlobalISel/CSEInfo.h"
19 #include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
20 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
21 #include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
22 #include "llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h"
23 #include "llvm/CodeGen/GlobalISel/LegalizerHelper.h"
24 #include "llvm/CodeGen/GlobalISel/Utils.h"
25 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
26 #include "llvm/CodeGen/MachineRegisterInfo.h"
27 #include "llvm/CodeGen/TargetPassConfig.h"
28 #include "llvm/CodeGen/TargetSubtargetInfo.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Target/TargetMachine.h"
31 
32 #include <iterator>
33 
34 #define DEBUG_TYPE "legalizer"
35 
36 using namespace llvm;
37 
38 static cl::opt<bool>
39     EnableCSEInLegalizer("enable-cse-in-legalizer",
40                          cl::desc("Should enable CSE in Legalizer"),
41                          cl::Optional, cl::init(false));
42 
43 char Legalizer::ID = 0;
44 INITIALIZE_PASS_BEGIN(Legalizer, DEBUG_TYPE,
45                       "Legalize the Machine IR a function's Machine IR", false,
46                       false)
47 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
48 INITIALIZE_PASS_DEPENDENCY(GISelCSEAnalysisWrapperPass)
49 INITIALIZE_PASS_END(Legalizer, DEBUG_TYPE,
50                     "Legalize the Machine IR a function's Machine IR", false,
51                     false)
52 
53 Legalizer::Legalizer() : MachineFunctionPass(ID) {
54   initializeLegalizerPass(*PassRegistry::getPassRegistry());
55 }
56 
57 void Legalizer::getAnalysisUsage(AnalysisUsage &AU) const {
58   AU.addRequired<TargetPassConfig>();
59   AU.addRequired<GISelCSEAnalysisWrapperPass>();
60   AU.addPreserved<GISelCSEAnalysisWrapperPass>();
61   getSelectionDAGFallbackAnalysisUsage(AU);
62   MachineFunctionPass::getAnalysisUsage(AU);
63 }
64 
65 void Legalizer::init(MachineFunction &MF) {
66 }
67 
68 static bool isArtifact(const MachineInstr &MI) {
69   switch (MI.getOpcode()) {
70   default:
71     return false;
72   case TargetOpcode::G_TRUNC:
73   case TargetOpcode::G_ZEXT:
74   case TargetOpcode::G_ANYEXT:
75   case TargetOpcode::G_SEXT:
76   case TargetOpcode::G_MERGE_VALUES:
77   case TargetOpcode::G_UNMERGE_VALUES:
78   case TargetOpcode::G_CONCAT_VECTORS:
79   case TargetOpcode::G_BUILD_VECTOR:
80   case TargetOpcode::G_EXTRACT:
81     return true;
82   }
83 }
84 using InstListTy = GISelWorkList<256>;
85 using ArtifactListTy = GISelWorkList<128>;
86 
87 namespace {
88 class LegalizerWorkListManager : public GISelChangeObserver {
89   InstListTy &InstList;
90   ArtifactListTy &ArtifactList;
91 #ifndef NDEBUG
92   SmallVector<MachineInstr *, 4> NewMIs;
93 #endif
94 
95 public:
96   LegalizerWorkListManager(InstListTy &Insts, ArtifactListTy &Arts)
97       : InstList(Insts), ArtifactList(Arts) {}
98 
99   void createdOrChangedInstr(MachineInstr &MI) {
100     // Only legalize pre-isel generic instructions.
101     // Legalization process could generate Target specific pseudo
102     // instructions with generic types. Don't record them
103     if (isPreISelGenericOpcode(MI.getOpcode())) {
104       if (isArtifact(MI))
105         ArtifactList.insert(&MI);
106       else
107         InstList.insert(&MI);
108     }
109   }
110 
111   void createdInstr(MachineInstr &MI) override {
112     LLVM_DEBUG(dbgs() << ".. .. New MI: " << MI);
113     LLVM_DEBUG(NewMIs.push_back(&MI));
114     createdOrChangedInstr(MI);
115   }
116 
117   void printNewInstrs() {
118     LLVM_DEBUG({
119       for (const auto *MI : NewMIs)
120         dbgs() << ".. .. New MI: " << *MI;
121       NewMIs.clear();
122     });
123   }
124 
125   void erasingInstr(MachineInstr &MI) override {
126     LLVM_DEBUG(dbgs() << ".. .. Erasing: " << MI);
127     InstList.remove(&MI);
128     ArtifactList.remove(&MI);
129   }
130 
131   void changingInstr(MachineInstr &MI) override {
132     LLVM_DEBUG(dbgs() << ".. .. Changing MI: " << MI);
133   }
134 
135   void changedInstr(MachineInstr &MI) override {
136     // When insts change, we want to revisit them to legalize them again.
137     // We'll consider them the same as created.
138     LLVM_DEBUG(dbgs() << ".. .. Changed MI: " << MI);
139     createdOrChangedInstr(MI);
140   }
141 };
142 } // namespace
143 
144 bool Legalizer::runOnMachineFunction(MachineFunction &MF) {
145   // If the ISel pipeline failed, do not bother running that pass.
146   if (MF.getProperties().hasProperty(
147           MachineFunctionProperties::Property::FailedISel))
148     return false;
149   LLVM_DEBUG(dbgs() << "Legalize Machine IR for: " << MF.getName() << '\n');
150   init(MF);
151   const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
152   GISelCSEAnalysisWrapper &Wrapper =
153       getAnalysis<GISelCSEAnalysisWrapperPass>().getCSEWrapper();
154   MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
155 
156   const size_t NumBlocks = MF.size();
157   MachineRegisterInfo &MRI = MF.getRegInfo();
158 
159   // Populate Insts
160   InstListTy InstList;
161   ArtifactListTy ArtifactList;
162   ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
163   // Perform legalization bottom up so we can DCE as we legalize.
164   // Traverse BB in RPOT and within each basic block, add insts top down,
165   // so when we pop_back_val in the legalization process, we traverse bottom-up.
166   for (auto *MBB : RPOT) {
167     if (MBB->empty())
168       continue;
169     for (MachineInstr &MI : *MBB) {
170       // Only legalize pre-isel generic instructions: others don't have types
171       // and are assumed to be legal.
172       if (!isPreISelGenericOpcode(MI.getOpcode()))
173         continue;
174       if (isArtifact(MI))
175         ArtifactList.deferred_insert(&MI);
176       else
177         InstList.deferred_insert(&MI);
178     }
179   }
180   ArtifactList.finalize();
181   InstList.finalize();
182   std::unique_ptr<MachineIRBuilder> MIRBuilder;
183   GISelCSEInfo *CSEInfo = nullptr;
184   bool EnableCSE = EnableCSEInLegalizer.getNumOccurrences()
185                        ? EnableCSEInLegalizer
186                        : TPC.isGISelCSEEnabled();
187 
188   if (EnableCSE) {
189     MIRBuilder = make_unique<CSEMIRBuilder>();
190     CSEInfo = &Wrapper.get(TPC.getCSEConfig());
191     MIRBuilder->setCSEInfo(CSEInfo);
192   } else
193     MIRBuilder = make_unique<MachineIRBuilder>();
194   // This observer keeps the worklist updated.
195   LegalizerWorkListManager WorkListObserver(InstList, ArtifactList);
196   // We want both WorkListObserver as well as CSEInfo to observe all changes.
197   // Use the wrapper observer.
198   GISelObserverWrapper WrapperObserver(&WorkListObserver);
199   if (EnableCSE && CSEInfo)
200     WrapperObserver.addObserver(CSEInfo);
201   // Now install the observer as the delegate to MF.
202   // This will keep all the observers notified about new insertions/deletions.
203   RAIIDelegateInstaller DelInstall(MF, &WrapperObserver);
204   LegalizerHelper Helper(MF, WrapperObserver, *MIRBuilder.get());
205   const LegalizerInfo &LInfo(Helper.getLegalizerInfo());
206   LegalizationArtifactCombiner ArtCombiner(*MIRBuilder.get(), MF.getRegInfo(),
207                                            LInfo);
208   auto RemoveDeadInstFromLists = [&WrapperObserver](MachineInstr *DeadMI) {
209     WrapperObserver.erasingInstr(*DeadMI);
210   };
211   bool Changed = false;
212   do {
213     while (!InstList.empty()) {
214       MachineInstr &MI = *InstList.pop_back_val();
215       assert(isPreISelGenericOpcode(MI.getOpcode()) && "Expecting generic opcode");
216       if (isTriviallyDead(MI, MRI)) {
217         LLVM_DEBUG(dbgs() << MI << "Is dead; erasing.\n");
218         MI.eraseFromParentAndMarkDBGValuesForRemoval();
219         continue;
220       }
221 
222       // Do the legalization for this instruction.
223       auto Res = Helper.legalizeInstrStep(MI);
224       // Error out if we couldn't legalize this instruction. We may want to
225       // fall back to DAG ISel instead in the future.
226       if (Res == LegalizerHelper::UnableToLegalize) {
227         Helper.MIRBuilder.stopObservingChanges();
228         reportGISelFailure(MF, TPC, MORE, "gisel-legalize",
229                            "unable to legalize instruction", MI);
230         return false;
231       }
232       WorkListObserver.printNewInstrs();
233       Changed |= Res == LegalizerHelper::Legalized;
234     }
235     while (!ArtifactList.empty()) {
236       MachineInstr &MI = *ArtifactList.pop_back_val();
237       assert(isPreISelGenericOpcode(MI.getOpcode()) && "Expecting generic opcode");
238       if (isTriviallyDead(MI, MRI)) {
239         LLVM_DEBUG(dbgs() << MI << "Is dead\n");
240         RemoveDeadInstFromLists(&MI);
241         MI.eraseFromParentAndMarkDBGValuesForRemoval();
242         continue;
243       }
244       SmallVector<MachineInstr *, 4> DeadInstructions;
245       if (ArtCombiner.tryCombineInstruction(MI, DeadInstructions,
246                                             WrapperObserver)) {
247         WorkListObserver.printNewInstrs();
248         for (auto *DeadMI : DeadInstructions) {
249           LLVM_DEBUG(dbgs() << *DeadMI << "Is dead\n");
250           RemoveDeadInstFromLists(DeadMI);
251           DeadMI->eraseFromParentAndMarkDBGValuesForRemoval();
252         }
253         Changed = true;
254         continue;
255       }
256       // If this was not an artifact (that could be combined away), this might
257       // need special handling. Add it to InstList, so when it's processed
258       // there, it has to be legal or specially handled.
259       else
260         InstList.insert(&MI);
261     }
262   } while (!InstList.empty());
263 
264   // For now don't support if new blocks are inserted - we would need to fix the
265   // outerloop for that.
266   if (MF.size() != NumBlocks) {
267     MachineOptimizationRemarkMissed R("gisel-legalize", "GISelFailure",
268                                       MF.getFunction().getSubprogram(),
269                                       /*MBB=*/nullptr);
270     R << "inserting blocks is not supported yet";
271     reportGISelFailure(MF, TPC, MORE, R);
272     return false;
273   }
274 
275   return Changed;
276 }
277