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/Analysis/OptimizationRemarkEmitter.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/GISelKnownBits.h"
22 #include "llvm/CodeGen/GlobalISel/GISelWorkList.h"
23 #include "llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h"
24 #include "llvm/CodeGen/GlobalISel/LegalizerHelper.h"
25 #include "llvm/CodeGen/GlobalISel/LostDebugLocObserver.h"
26 #include "llvm/CodeGen/GlobalISel/Utils.h"
27 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
28 #include "llvm/CodeGen/TargetPassConfig.h"
29 #include "llvm/CodeGen/TargetSubtargetInfo.h"
30 #include "llvm/InitializePasses.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/Error.h"
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 // This is a temporary hack, should be removed soon.
44 static cl::opt<bool> AllowGInsertAsArtifact(
45     "allow-ginsert-as-artifact",
46     cl::desc("Allow G_INSERT to be considered an artifact. Hack around AMDGPU "
47              "test infinite loops."),
48     cl::Optional, cl::init(true));
49 
50 enum class DebugLocVerifyLevel {
51   None,
52   Legalizations,
53   LegalizationsAndArtifactCombiners,
54 };
55 #ifndef NDEBUG
56 static cl::opt<DebugLocVerifyLevel> VerifyDebugLocs(
57     "verify-legalizer-debug-locs",
58     cl::desc("Verify that debug locations are handled"),
59     cl::values(
60         clEnumValN(DebugLocVerifyLevel::None, "none", "No verification"),
61         clEnumValN(DebugLocVerifyLevel::Legalizations, "legalizations",
62                    "Verify legalizations"),
63         clEnumValN(DebugLocVerifyLevel::LegalizationsAndArtifactCombiners,
64                    "legalizations+artifactcombiners",
65                    "Verify legalizations and artifact combines")),
66     cl::init(DebugLocVerifyLevel::Legalizations));
67 #else
68 // Always disable it for release builds by preventing the observer from being
69 // installed.
70 static const DebugLocVerifyLevel VerifyDebugLocs = DebugLocVerifyLevel::None;
71 #endif
72 
73 char Legalizer::ID = 0;
74 INITIALIZE_PASS_BEGIN(Legalizer, DEBUG_TYPE,
75                       "Legalize the Machine IR a function's Machine IR", false,
76                       false)
77 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
78 INITIALIZE_PASS_DEPENDENCY(GISelCSEAnalysisWrapperPass)
79 INITIALIZE_PASS_DEPENDENCY(GISelKnownBitsAnalysis)
80 INITIALIZE_PASS_END(Legalizer, DEBUG_TYPE,
81                     "Legalize the Machine IR a function's Machine IR", false,
82                     false)
83 
84 Legalizer::Legalizer() : MachineFunctionPass(ID) { }
85 
86 void Legalizer::getAnalysisUsage(AnalysisUsage &AU) const {
87   AU.addRequired<TargetPassConfig>();
88   AU.addRequired<GISelCSEAnalysisWrapperPass>();
89   AU.addPreserved<GISelCSEAnalysisWrapperPass>();
90   AU.addRequired<GISelKnownBitsAnalysis>();
91   AU.addPreserved<GISelKnownBitsAnalysis>();
92   getSelectionDAGFallbackAnalysisUsage(AU);
93   MachineFunctionPass::getAnalysisUsage(AU);
94 }
95 
96 void Legalizer::init(MachineFunction &MF) {
97 }
98 
99 static bool isArtifact(const MachineInstr &MI) {
100   switch (MI.getOpcode()) {
101   default:
102     return false;
103   case TargetOpcode::G_TRUNC:
104   case TargetOpcode::G_ZEXT:
105   case TargetOpcode::G_ANYEXT:
106   case TargetOpcode::G_SEXT:
107   case TargetOpcode::G_MERGE_VALUES:
108   case TargetOpcode::G_UNMERGE_VALUES:
109   case TargetOpcode::G_CONCAT_VECTORS:
110   case TargetOpcode::G_BUILD_VECTOR:
111   case TargetOpcode::G_EXTRACT:
112     return true;
113   case TargetOpcode::G_INSERT:
114     return AllowGInsertAsArtifact;
115   }
116 }
117 using InstListTy = GISelWorkList<256>;
118 using ArtifactListTy = GISelWorkList<128>;
119 
120 namespace {
121 class LegalizerWorkListManager : public GISelChangeObserver {
122   InstListTy &InstList;
123   ArtifactListTy &ArtifactList;
124 #ifndef NDEBUG
125   SmallVector<MachineInstr *, 4> NewMIs;
126 #endif
127 
128 public:
129   LegalizerWorkListManager(InstListTy &Insts, ArtifactListTy &Arts)
130       : InstList(Insts), ArtifactList(Arts) {}
131 
132   void createdOrChangedInstr(MachineInstr &MI) {
133     // Only legalize pre-isel generic instructions.
134     // Legalization process could generate Target specific pseudo
135     // instructions with generic types. Don't record them
136     if (isPreISelGenericOpcode(MI.getOpcode())) {
137       if (isArtifact(MI))
138         ArtifactList.insert(&MI);
139       else
140         InstList.insert(&MI);
141     }
142   }
143 
144   void createdInstr(MachineInstr &MI) override {
145     LLVM_DEBUG(NewMIs.push_back(&MI));
146     createdOrChangedInstr(MI);
147   }
148 
149   void printNewInstrs() {
150     LLVM_DEBUG({
151       for (const auto *MI : NewMIs)
152         dbgs() << ".. .. New MI: " << *MI;
153       NewMIs.clear();
154     });
155   }
156 
157   void erasingInstr(MachineInstr &MI) override {
158     LLVM_DEBUG(dbgs() << ".. .. Erasing: " << MI);
159     InstList.remove(&MI);
160     ArtifactList.remove(&MI);
161   }
162 
163   void changingInstr(MachineInstr &MI) override {
164     LLVM_DEBUG(dbgs() << ".. .. Changing MI: " << MI);
165   }
166 
167   void changedInstr(MachineInstr &MI) override {
168     // When insts change, we want to revisit them to legalize them again.
169     // We'll consider them the same as created.
170     LLVM_DEBUG(dbgs() << ".. .. Changed MI: " << MI);
171     createdOrChangedInstr(MI);
172   }
173 };
174 } // namespace
175 
176 Legalizer::MFResult
177 Legalizer::legalizeMachineFunction(MachineFunction &MF, const LegalizerInfo &LI,
178                                    ArrayRef<GISelChangeObserver *> AuxObservers,
179                                    LostDebugLocObserver &LocObserver,
180                                    MachineIRBuilder &MIRBuilder,
181                                    GISelKnownBits *KB) {
182   MIRBuilder.setMF(MF);
183   MachineRegisterInfo &MRI = MF.getRegInfo();
184 
185   // Populate worklists.
186   InstListTy InstList;
187   ArtifactListTy ArtifactList;
188   ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
189   // Perform legalization bottom up so we can DCE as we legalize.
190   // Traverse BB in RPOT and within each basic block, add insts top down,
191   // so when we pop_back_val in the legalization process, we traverse bottom-up.
192   for (auto *MBB : RPOT) {
193     if (MBB->empty())
194       continue;
195     for (MachineInstr &MI : *MBB) {
196       // Only legalize pre-isel generic instructions: others don't have types
197       // and are assumed to be legal.
198       if (!isPreISelGenericOpcode(MI.getOpcode()))
199         continue;
200       if (isArtifact(MI))
201         ArtifactList.deferred_insert(&MI);
202       else
203         InstList.deferred_insert(&MI);
204     }
205   }
206   ArtifactList.finalize();
207   InstList.finalize();
208 
209   // This observer keeps the worklists updated.
210   LegalizerWorkListManager WorkListObserver(InstList, ArtifactList);
211   // We want both WorkListObserver as well as all the auxiliary observers (e.g.
212   // CSEInfo) to observe all changes. Use the wrapper observer.
213   GISelObserverWrapper WrapperObserver(&WorkListObserver);
214   for (GISelChangeObserver *Observer : AuxObservers)
215     WrapperObserver.addObserver(Observer);
216 
217   // Now install the observer as the delegate to MF.
218   // This will keep all the observers notified about new insertions/deletions.
219   RAIIMFObsDelInstaller Installer(MF, WrapperObserver);
220   LegalizerHelper Helper(MF, LI, WrapperObserver, MIRBuilder, KB);
221   LegalizationArtifactCombiner ArtCombiner(MIRBuilder, MRI, LI, KB);
222   bool Changed = false;
223   SmallVector<MachineInstr *, 128> RetryList;
224   do {
225     LLVM_DEBUG(dbgs() << "=== New Iteration ===\n");
226     assert(RetryList.empty() && "Expected no instructions in RetryList");
227     unsigned NumArtifacts = ArtifactList.size();
228     while (!InstList.empty()) {
229       MachineInstr &MI = *InstList.pop_back_val();
230       assert(isPreISelGenericOpcode(MI.getOpcode()) &&
231              "Expecting generic opcode");
232       if (isTriviallyDead(MI, MRI)) {
233         salvageDebugInfo(MRI, MI);
234         eraseInstr(MI, MRI, &LocObserver);
235         continue;
236       }
237 
238       // Do the legalization for this instruction.
239       auto Res = Helper.legalizeInstrStep(MI, LocObserver);
240       // Error out if we couldn't legalize this instruction. We may want to
241       // fall back to DAG ISel instead in the future.
242       if (Res == LegalizerHelper::UnableToLegalize) {
243         // Move illegal artifacts to RetryList instead of aborting because
244         // legalizing InstList may generate artifacts that allow
245         // ArtifactCombiner to combine away them.
246         if (isArtifact(MI)) {
247           LLVM_DEBUG(dbgs() << ".. Not legalized, moving to artifacts retry\n");
248           assert(NumArtifacts == 0 &&
249                  "Artifacts are only expected in instruction list starting the "
250                  "second iteration, but each iteration starting second must "
251                  "start with an empty artifacts list");
252           (void)NumArtifacts;
253           RetryList.push_back(&MI);
254           continue;
255         }
256         Helper.MIRBuilder.stopObservingChanges();
257         return {Changed, &MI};
258       }
259       WorkListObserver.printNewInstrs();
260       LocObserver.checkpoint();
261       Changed |= Res == LegalizerHelper::Legalized;
262     }
263     // Try to combine the instructions in RetryList again if there
264     // are new artifacts. If not, stop legalizing.
265     if (!RetryList.empty()) {
266       if (!ArtifactList.empty()) {
267         while (!RetryList.empty())
268           ArtifactList.insert(RetryList.pop_back_val());
269       } else {
270         LLVM_DEBUG(dbgs() << "No new artifacts created, not retrying!\n");
271         Helper.MIRBuilder.stopObservingChanges();
272         return {Changed, RetryList.front()};
273       }
274     }
275     LocObserver.checkpoint();
276     while (!ArtifactList.empty()) {
277       MachineInstr &MI = *ArtifactList.pop_back_val();
278       assert(isPreISelGenericOpcode(MI.getOpcode()) &&
279              "Expecting generic opcode");
280       if (isTriviallyDead(MI, MRI)) {
281         salvageDebugInfo(MRI, MI);
282         eraseInstr(MI, MRI, &LocObserver);
283         continue;
284       }
285       SmallVector<MachineInstr *, 4> DeadInstructions;
286       LLVM_DEBUG(dbgs() << "Trying to combine: " << MI);
287       if (ArtCombiner.tryCombineInstruction(MI, DeadInstructions,
288                                             WrapperObserver)) {
289         WorkListObserver.printNewInstrs();
290         eraseInstrs(DeadInstructions, MRI, &LocObserver);
291         LocObserver.checkpoint(
292             VerifyDebugLocs ==
293             DebugLocVerifyLevel::LegalizationsAndArtifactCombiners);
294         Changed = true;
295         continue;
296       }
297       // If this was not an artifact (that could be combined away), this might
298       // need special handling. Add it to InstList, so when it's processed
299       // there, it has to be legal or specially handled.
300       else {
301         LLVM_DEBUG(dbgs() << ".. Not combined, moving to instructions list\n");
302         InstList.insert(&MI);
303       }
304     }
305   } while (!InstList.empty());
306 
307   return {Changed, /*FailedOn*/ nullptr};
308 }
309 
310 bool Legalizer::runOnMachineFunction(MachineFunction &MF) {
311   // If the ISel pipeline failed, do not bother running that pass.
312   if (MF.getProperties().hasProperty(
313           MachineFunctionProperties::Property::FailedISel))
314     return false;
315   LLVM_DEBUG(dbgs() << "Legalize Machine IR for: " << MF.getName() << '\n');
316   init(MF);
317   const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
318   GISelCSEAnalysisWrapper &Wrapper =
319       getAnalysis<GISelCSEAnalysisWrapperPass>().getCSEWrapper();
320   MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
321 
322   std::unique_ptr<MachineIRBuilder> MIRBuilder;
323   GISelCSEInfo *CSEInfo = nullptr;
324   bool EnableCSE = EnableCSEInLegalizer.getNumOccurrences()
325                        ? EnableCSEInLegalizer
326                        : TPC.isGISelCSEEnabled();
327   if (EnableCSE) {
328     MIRBuilder = std::make_unique<CSEMIRBuilder>();
329     CSEInfo = &Wrapper.get(TPC.getCSEConfig());
330     MIRBuilder->setCSEInfo(CSEInfo);
331   } else
332     MIRBuilder = std::make_unique<MachineIRBuilder>();
333 
334   SmallVector<GISelChangeObserver *, 1> AuxObservers;
335   if (EnableCSE && CSEInfo) {
336     // We want CSEInfo in addition to WorkListObserver to observe all changes.
337     AuxObservers.push_back(CSEInfo);
338   }
339   assert(!CSEInfo || !errorToBool(CSEInfo->verify()));
340   LostDebugLocObserver LocObserver(DEBUG_TYPE);
341   if (VerifyDebugLocs > DebugLocVerifyLevel::None)
342     AuxObservers.push_back(&LocObserver);
343 
344   // This allows Known Bits Analysis in the legalizer.
345   GISelKnownBits *KB = &getAnalysis<GISelKnownBitsAnalysis>().get(MF);
346 
347   const LegalizerInfo &LI = *MF.getSubtarget().getLegalizerInfo();
348   MFResult Result = legalizeMachineFunction(MF, LI, AuxObservers, LocObserver,
349                                             *MIRBuilder, KB);
350 
351   if (Result.FailedOn) {
352     reportGISelFailure(MF, TPC, MORE, "gisel-legalize",
353                        "unable to legalize instruction", *Result.FailedOn);
354     return false;
355   }
356 
357   if (LocObserver.getNumLostDebugLocs()) {
358     MachineOptimizationRemarkMissed R("gisel-legalize", "LostDebugLoc",
359                                       MF.getFunction().getSubprogram(),
360                                       /*MBB=*/&*MF.begin());
361     R << "lost "
362       << ore::NV("NumLostDebugLocs", LocObserver.getNumLostDebugLocs())
363       << " debug locations during pass";
364     reportGISelWarning(MF, TPC, MORE, R);
365     // Example remark:
366     // --- !Missed
367     // Pass:            gisel-legalize
368     // Name:            GISelFailure
369     // DebugLoc:        { File: '.../legalize-urem.mir', Line: 1, Column: 0 }
370     // Function:        test_urem_s32
371     // Args:
372     //   - String:          'lost '
373     //   - NumLostDebugLocs: '1'
374     //   - String:          ' debug locations during pass'
375     // ...
376   }
377 
378   // If for some reason CSE was not enabled, make sure that we invalidate the
379   // CSEInfo object (as we currently declare that the analysis is preserved).
380   // The next time get on the wrapper is called, it will force it to recompute
381   // the analysis.
382   if (!EnableCSE)
383     Wrapper.setComputed(false);
384   return Result.Changed;
385 }
386