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/Support/Debug.h" 31 #include "llvm/Support/Error.h" 32 33 #define DEBUG_TYPE "legalizer" 34 35 using namespace llvm; 36 37 static cl::opt<bool> 38 EnableCSEInLegalizer("enable-cse-in-legalizer", 39 cl::desc("Should enable CSE in Legalizer"), 40 cl::Optional, cl::init(false)); 41 42 // This is a temporary hack, should be removed soon. 43 static cl::opt<bool> AllowGInsertAsArtifact( 44 "allow-ginsert-as-artifact", 45 cl::desc("Allow G_INSERT to be considered an artifact. Hack around AMDGPU " 46 "test infinite loops."), 47 cl::Optional, cl::init(true)); 48 49 enum class DebugLocVerifyLevel { 50 None, 51 Legalizations, 52 LegalizationsAndArtifactCombiners, 53 }; 54 #ifndef NDEBUG 55 static cl::opt<DebugLocVerifyLevel> VerifyDebugLocs( 56 "verify-legalizer-debug-locs", 57 cl::desc("Verify that debug locations are handled"), 58 cl::values( 59 clEnumValN(DebugLocVerifyLevel::None, "none", "No verification"), 60 clEnumValN(DebugLocVerifyLevel::Legalizations, "legalizations", 61 "Verify legalizations"), 62 clEnumValN(DebugLocVerifyLevel::LegalizationsAndArtifactCombiners, 63 "legalizations+artifactcombiners", 64 "Verify legalizations and artifact combines")), 65 cl::init(DebugLocVerifyLevel::Legalizations)); 66 #else 67 // Always disable it for release builds by preventing the observer from being 68 // installed. 69 static const DebugLocVerifyLevel VerifyDebugLocs = DebugLocVerifyLevel::None; 70 #endif 71 72 char Legalizer::ID = 0; 73 INITIALIZE_PASS_BEGIN(Legalizer, DEBUG_TYPE, 74 "Legalize the Machine IR a function's Machine IR", false, 75 false) 76 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig) 77 INITIALIZE_PASS_DEPENDENCY(GISelCSEAnalysisWrapperPass) 78 INITIALIZE_PASS_DEPENDENCY(GISelKnownBitsAnalysis) 79 INITIALIZE_PASS_END(Legalizer, DEBUG_TYPE, 80 "Legalize the Machine IR a function's Machine IR", false, 81 false) 82 83 Legalizer::Legalizer() : MachineFunctionPass(ID) { } 84 85 void Legalizer::getAnalysisUsage(AnalysisUsage &AU) const { 86 AU.addRequired<TargetPassConfig>(); 87 AU.addRequired<GISelCSEAnalysisWrapperPass>(); 88 AU.addPreserved<GISelCSEAnalysisWrapperPass>(); 89 AU.addRequired<GISelKnownBitsAnalysis>(); 90 AU.addPreserved<GISelKnownBitsAnalysis>(); 91 getSelectionDAGFallbackAnalysisUsage(AU); 92 MachineFunctionPass::getAnalysisUsage(AU); 93 } 94 95 void Legalizer::init(MachineFunction &MF) { 96 } 97 98 static bool isArtifact(const MachineInstr &MI) { 99 switch (MI.getOpcode()) { 100 default: 101 return false; 102 case TargetOpcode::G_TRUNC: 103 case TargetOpcode::G_ZEXT: 104 case TargetOpcode::G_ANYEXT: 105 case TargetOpcode::G_SEXT: 106 case TargetOpcode::G_MERGE_VALUES: 107 case TargetOpcode::G_UNMERGE_VALUES: 108 case TargetOpcode::G_CONCAT_VECTORS: 109 case TargetOpcode::G_BUILD_VECTOR: 110 case TargetOpcode::G_EXTRACT: 111 return true; 112 case TargetOpcode::G_INSERT: 113 return AllowGInsertAsArtifact; 114 } 115 } 116 using InstListTy = GISelWorkList<256>; 117 using ArtifactListTy = GISelWorkList<128>; 118 119 namespace { 120 class LegalizerWorkListManager : public GISelChangeObserver { 121 InstListTy &InstList; 122 ArtifactListTy &ArtifactList; 123 #ifndef NDEBUG 124 SmallVector<MachineInstr *, 4> NewMIs; 125 #endif 126 127 public: 128 LegalizerWorkListManager(InstListTy &Insts, ArtifactListTy &Arts) 129 : InstList(Insts), ArtifactList(Arts) {} 130 131 void createdOrChangedInstr(MachineInstr &MI) { 132 // Only legalize pre-isel generic instructions. 133 // Legalization process could generate Target specific pseudo 134 // instructions with generic types. Don't record them 135 if (isPreISelGenericOpcode(MI.getOpcode())) { 136 if (isArtifact(MI)) 137 ArtifactList.insert(&MI); 138 else 139 InstList.insert(&MI); 140 } 141 } 142 143 void createdInstr(MachineInstr &MI) override { 144 LLVM_DEBUG(NewMIs.push_back(&MI)); 145 createdOrChangedInstr(MI); 146 } 147 148 void printNewInstrs() { 149 LLVM_DEBUG({ 150 for (const auto *MI : NewMIs) 151 dbgs() << ".. .. New MI: " << *MI; 152 NewMIs.clear(); 153 }); 154 } 155 156 void erasingInstr(MachineInstr &MI) override { 157 LLVM_DEBUG(dbgs() << ".. .. Erasing: " << MI); 158 InstList.remove(&MI); 159 ArtifactList.remove(&MI); 160 } 161 162 void changingInstr(MachineInstr &MI) override { 163 LLVM_DEBUG(dbgs() << ".. .. Changing MI: " << MI); 164 } 165 166 void changedInstr(MachineInstr &MI) override { 167 // When insts change, we want to revisit them to legalize them again. 168 // We'll consider them the same as created. 169 LLVM_DEBUG(dbgs() << ".. .. Changed MI: " << MI); 170 createdOrChangedInstr(MI); 171 } 172 }; 173 } // namespace 174 175 Legalizer::MFResult 176 Legalizer::legalizeMachineFunction(MachineFunction &MF, const LegalizerInfo &LI, 177 ArrayRef<GISelChangeObserver *> AuxObservers, 178 LostDebugLocObserver &LocObserver, 179 MachineIRBuilder &MIRBuilder, 180 GISelKnownBits *KB) { 181 MIRBuilder.setMF(MF); 182 MachineRegisterInfo &MRI = MF.getRegInfo(); 183 184 // Populate worklists. 185 InstListTy InstList; 186 ArtifactListTy ArtifactList; 187 ReversePostOrderTraversal<MachineFunction *> RPOT(&MF); 188 // Perform legalization bottom up so we can DCE as we legalize. 189 // Traverse BB in RPOT and within each basic block, add insts top down, 190 // so when we pop_back_val in the legalization process, we traverse bottom-up. 191 for (auto *MBB : RPOT) { 192 if (MBB->empty()) 193 continue; 194 for (MachineInstr &MI : *MBB) { 195 // Only legalize pre-isel generic instructions: others don't have types 196 // and are assumed to be legal. 197 if (!isPreISelGenericOpcode(MI.getOpcode())) 198 continue; 199 if (isArtifact(MI)) 200 ArtifactList.deferred_insert(&MI); 201 else 202 InstList.deferred_insert(&MI); 203 } 204 } 205 ArtifactList.finalize(); 206 InstList.finalize(); 207 208 // This observer keeps the worklists updated. 209 LegalizerWorkListManager WorkListObserver(InstList, ArtifactList); 210 // We want both WorkListObserver as well as all the auxiliary observers (e.g. 211 // CSEInfo) to observe all changes. Use the wrapper observer. 212 GISelObserverWrapper WrapperObserver(&WorkListObserver); 213 for (GISelChangeObserver *Observer : AuxObservers) 214 WrapperObserver.addObserver(Observer); 215 216 // Now install the observer as the delegate to MF. 217 // This will keep all the observers notified about new insertions/deletions. 218 RAIIMFObsDelInstaller Installer(MF, WrapperObserver); 219 LegalizerHelper Helper(MF, LI, WrapperObserver, MIRBuilder, KB); 220 LegalizationArtifactCombiner ArtCombiner(MIRBuilder, MRI, LI, KB); 221 bool Changed = false; 222 SmallVector<MachineInstr *, 128> RetryList; 223 do { 224 LLVM_DEBUG(dbgs() << "=== New Iteration ===\n"); 225 assert(RetryList.empty() && "Expected no instructions in RetryList"); 226 unsigned NumArtifacts = ArtifactList.size(); 227 while (!InstList.empty()) { 228 MachineInstr &MI = *InstList.pop_back_val(); 229 assert(isPreISelGenericOpcode(MI.getOpcode()) && 230 "Expecting generic opcode"); 231 if (isTriviallyDead(MI, MRI)) { 232 salvageDebugInfo(MRI, MI); 233 eraseInstr(MI, MRI, &LocObserver); 234 continue; 235 } 236 237 // Do the legalization for this instruction. 238 auto Res = Helper.legalizeInstrStep(MI, LocObserver); 239 // Error out if we couldn't legalize this instruction. We may want to 240 // fall back to DAG ISel instead in the future. 241 if (Res == LegalizerHelper::UnableToLegalize) { 242 // Move illegal artifacts to RetryList instead of aborting because 243 // legalizing InstList may generate artifacts that allow 244 // ArtifactCombiner to combine away them. 245 if (isArtifact(MI)) { 246 LLVM_DEBUG(dbgs() << ".. Not legalized, moving to artifacts retry\n"); 247 assert(NumArtifacts == 0 && 248 "Artifacts are only expected in instruction list starting the " 249 "second iteration, but each iteration starting second must " 250 "start with an empty artifacts list"); 251 (void)NumArtifacts; 252 RetryList.push_back(&MI); 253 continue; 254 } 255 Helper.MIRBuilder.stopObservingChanges(); 256 return {Changed, &MI}; 257 } 258 WorkListObserver.printNewInstrs(); 259 LocObserver.checkpoint(); 260 Changed |= Res == LegalizerHelper::Legalized; 261 } 262 // Try to combine the instructions in RetryList again if there 263 // are new artifacts. If not, stop legalizing. 264 if (!RetryList.empty()) { 265 if (!ArtifactList.empty()) { 266 while (!RetryList.empty()) 267 ArtifactList.insert(RetryList.pop_back_val()); 268 } else { 269 LLVM_DEBUG(dbgs() << "No new artifacts created, not retrying!\n"); 270 Helper.MIRBuilder.stopObservingChanges(); 271 return {Changed, RetryList.front()}; 272 } 273 } 274 LocObserver.checkpoint(); 275 while (!ArtifactList.empty()) { 276 MachineInstr &MI = *ArtifactList.pop_back_val(); 277 assert(isPreISelGenericOpcode(MI.getOpcode()) && 278 "Expecting generic opcode"); 279 if (isTriviallyDead(MI, MRI)) { 280 salvageDebugInfo(MRI, MI); 281 eraseInstr(MI, MRI, &LocObserver); 282 continue; 283 } 284 SmallVector<MachineInstr *, 4> DeadInstructions; 285 LLVM_DEBUG(dbgs() << "Trying to combine: " << MI); 286 if (ArtCombiner.tryCombineInstruction(MI, DeadInstructions, 287 WrapperObserver)) { 288 WorkListObserver.printNewInstrs(); 289 eraseInstrs(DeadInstructions, MRI, &LocObserver); 290 LocObserver.checkpoint( 291 VerifyDebugLocs == 292 DebugLocVerifyLevel::LegalizationsAndArtifactCombiners); 293 Changed = true; 294 continue; 295 } 296 // If this was not an artifact (that could be combined away), this might 297 // need special handling. Add it to InstList, so when it's processed 298 // there, it has to be legal or specially handled. 299 else { 300 LLVM_DEBUG(dbgs() << ".. Not combined, moving to instructions list\n"); 301 InstList.insert(&MI); 302 } 303 } 304 } while (!InstList.empty()); 305 306 return {Changed, /*FailedOn*/ nullptr}; 307 } 308 309 bool Legalizer::runOnMachineFunction(MachineFunction &MF) { 310 // If the ISel pipeline failed, do not bother running that pass. 311 if (MF.getProperties().hasProperty( 312 MachineFunctionProperties::Property::FailedISel)) 313 return false; 314 LLVM_DEBUG(dbgs() << "Legalize Machine IR for: " << MF.getName() << '\n'); 315 init(MF); 316 const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>(); 317 GISelCSEAnalysisWrapper &Wrapper = 318 getAnalysis<GISelCSEAnalysisWrapperPass>().getCSEWrapper(); 319 MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr); 320 321 std::unique_ptr<MachineIRBuilder> MIRBuilder; 322 GISelCSEInfo *CSEInfo = nullptr; 323 bool EnableCSE = EnableCSEInLegalizer.getNumOccurrences() 324 ? EnableCSEInLegalizer 325 : TPC.isGISelCSEEnabled(); 326 if (EnableCSE) { 327 MIRBuilder = std::make_unique<CSEMIRBuilder>(); 328 CSEInfo = &Wrapper.get(TPC.getCSEConfig()); 329 MIRBuilder->setCSEInfo(CSEInfo); 330 } else 331 MIRBuilder = std::make_unique<MachineIRBuilder>(); 332 333 SmallVector<GISelChangeObserver *, 1> AuxObservers; 334 if (EnableCSE && CSEInfo) { 335 // We want CSEInfo in addition to WorkListObserver to observe all changes. 336 AuxObservers.push_back(CSEInfo); 337 } 338 assert(!CSEInfo || !errorToBool(CSEInfo->verify())); 339 LostDebugLocObserver LocObserver(DEBUG_TYPE); 340 if (VerifyDebugLocs > DebugLocVerifyLevel::None) 341 AuxObservers.push_back(&LocObserver); 342 343 // This allows Known Bits Analysis in the legalizer. 344 GISelKnownBits *KB = &getAnalysis<GISelKnownBitsAnalysis>().get(MF); 345 346 const LegalizerInfo &LI = *MF.getSubtarget().getLegalizerInfo(); 347 MFResult Result = legalizeMachineFunction(MF, LI, AuxObservers, LocObserver, 348 *MIRBuilder, KB); 349 350 if (Result.FailedOn) { 351 reportGISelFailure(MF, TPC, MORE, "gisel-legalize", 352 "unable to legalize instruction", *Result.FailedOn); 353 return false; 354 } 355 356 if (LocObserver.getNumLostDebugLocs()) { 357 MachineOptimizationRemarkMissed R("gisel-legalize", "LostDebugLoc", 358 MF.getFunction().getSubprogram(), 359 /*MBB=*/&*MF.begin()); 360 R << "lost " 361 << ore::NV("NumLostDebugLocs", LocObserver.getNumLostDebugLocs()) 362 << " debug locations during pass"; 363 reportGISelWarning(MF, TPC, MORE, R); 364 // Example remark: 365 // --- !Missed 366 // Pass: gisel-legalize 367 // Name: GISelFailure 368 // DebugLoc: { File: '.../legalize-urem.mir', Line: 1, Column: 0 } 369 // Function: test_urem_s32 370 // Args: 371 // - String: 'lost ' 372 // - NumLostDebugLocs: '1' 373 // - String: ' debug locations during pass' 374 // ... 375 } 376 377 // If for some reason CSE was not enabled, make sure that we invalidate the 378 // CSEInfo object (as we currently declare that the analysis is preserved). 379 // The next time get on the wrapper is called, it will force it to recompute 380 // the analysis. 381 if (!EnableCSE) 382 Wrapper.setComputed(false); 383 return Result.Changed; 384 } 385