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/LostDebugLocObserver.h" 25 #include "llvm/CodeGen/GlobalISel/Utils.h" 26 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h" 27 #include "llvm/CodeGen/MachineRegisterInfo.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 #include "llvm/Target/TargetMachine.h" 34 35 #include <iterator> 36 37 #define DEBUG_TYPE "legalizer" 38 39 using namespace llvm; 40 41 static cl::opt<bool> 42 EnableCSEInLegalizer("enable-cse-in-legalizer", 43 cl::desc("Should enable CSE in Legalizer"), 44 cl::Optional, cl::init(false)); 45 46 // This is a temporary hack, should be removed soon. 47 static cl::opt<bool> AllowGInsertAsArtifact( 48 "allow-ginsert-as-artifact", 49 cl::desc("Allow G_INSERT to be considered an artifact. Hack around AMDGPU " 50 "test infinite loops."), 51 cl::Optional, cl::init(true)); 52 53 enum class DebugLocVerifyLevel { 54 None, 55 Legalizations, 56 LegalizationsAndArtifactCombiners, 57 }; 58 #ifndef NDEBUG 59 static cl::opt<DebugLocVerifyLevel> VerifyDebugLocs( 60 "verify-legalizer-debug-locs", 61 cl::desc("Verify that debug locations are handled"), 62 cl::values( 63 clEnumValN(DebugLocVerifyLevel::None, "none", "No verification"), 64 clEnumValN(DebugLocVerifyLevel::Legalizations, "legalizations", 65 "Verify legalizations"), 66 clEnumValN(DebugLocVerifyLevel::LegalizationsAndArtifactCombiners, 67 "legalizations+artifactcombiners", 68 "Verify legalizations and artifact combines")), 69 cl::init(DebugLocVerifyLevel::Legalizations)); 70 #else 71 // Always disable it for release builds by preventing the observer from being 72 // installed. 73 static const DebugLocVerifyLevel VerifyDebugLocs = DebugLocVerifyLevel::None; 74 #endif 75 76 char Legalizer::ID = 0; 77 INITIALIZE_PASS_BEGIN(Legalizer, DEBUG_TYPE, 78 "Legalize the Machine IR a function's Machine IR", false, 79 false) 80 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig) 81 INITIALIZE_PASS_DEPENDENCY(GISelCSEAnalysisWrapperPass) 82 INITIALIZE_PASS_END(Legalizer, DEBUG_TYPE, 83 "Legalize the Machine IR a function's Machine IR", false, 84 false) 85 86 Legalizer::Legalizer() : MachineFunctionPass(ID) { } 87 88 void Legalizer::getAnalysisUsage(AnalysisUsage &AU) const { 89 AU.addRequired<TargetPassConfig>(); 90 AU.addRequired<GISelCSEAnalysisWrapperPass>(); 91 AU.addPreserved<GISelCSEAnalysisWrapperPass>(); 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 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); 220 LegalizationArtifactCombiner ArtCombiner(MIRBuilder, MRI, LI); 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 eraseInstr(MI, MRI, &LocObserver); 233 continue; 234 } 235 236 // Do the legalization for this instruction. 237 auto Res = Helper.legalizeInstrStep(MI, LocObserver); 238 // Error out if we couldn't legalize this instruction. We may want to 239 // fall back to DAG ISel instead in the future. 240 if (Res == LegalizerHelper::UnableToLegalize) { 241 // Move illegal artifacts to RetryList instead of aborting because 242 // legalizing InstList may generate artifacts that allow 243 // ArtifactCombiner to combine away them. 244 if (isArtifact(MI)) { 245 LLVM_DEBUG(dbgs() << ".. Not legalized, moving to artifacts retry\n"); 246 assert(NumArtifacts == 0 && 247 "Artifacts are only expected in instruction list starting the " 248 "second iteration, but each iteration starting second must " 249 "start with an empty artifacts list"); 250 (void)NumArtifacts; 251 RetryList.push_back(&MI); 252 continue; 253 } 254 Helper.MIRBuilder.stopObservingChanges(); 255 return {Changed, &MI}; 256 } 257 WorkListObserver.printNewInstrs(); 258 LocObserver.checkpoint(); 259 Changed |= Res == LegalizerHelper::Legalized; 260 } 261 // Try to combine the instructions in RetryList again if there 262 // are new artifacts. If not, stop legalizing. 263 if (!RetryList.empty()) { 264 if (!ArtifactList.empty()) { 265 while (!RetryList.empty()) 266 ArtifactList.insert(RetryList.pop_back_val()); 267 } else { 268 LLVM_DEBUG(dbgs() << "No new artifacts created, not retrying!\n"); 269 Helper.MIRBuilder.stopObservingChanges(); 270 return {Changed, RetryList.front()}; 271 } 272 } 273 LocObserver.checkpoint(); 274 while (!ArtifactList.empty()) { 275 MachineInstr &MI = *ArtifactList.pop_back_val(); 276 assert(isPreISelGenericOpcode(MI.getOpcode()) && 277 "Expecting generic opcode"); 278 if (isTriviallyDead(MI, MRI)) { 279 eraseInstr(MI, MRI, &LocObserver); 280 continue; 281 } 282 SmallVector<MachineInstr *, 4> DeadInstructions; 283 LLVM_DEBUG(dbgs() << "Trying to combine: " << MI); 284 if (ArtCombiner.tryCombineInstruction(MI, DeadInstructions, 285 WrapperObserver)) { 286 WorkListObserver.printNewInstrs(); 287 eraseInstrs(DeadInstructions, MRI, &LocObserver); 288 LocObserver.checkpoint( 289 VerifyDebugLocs == 290 DebugLocVerifyLevel::LegalizationsAndArtifactCombiners); 291 Changed = true; 292 continue; 293 } 294 // If this was not an artifact (that could be combined away), this might 295 // need special handling. Add it to InstList, so when it's processed 296 // there, it has to be legal or specially handled. 297 else { 298 LLVM_DEBUG(dbgs() << ".. Not combined, moving to instructions list\n"); 299 InstList.insert(&MI); 300 } 301 } 302 } while (!InstList.empty()); 303 304 return {Changed, /*FailedOn*/ nullptr}; 305 } 306 307 bool Legalizer::runOnMachineFunction(MachineFunction &MF) { 308 // If the ISel pipeline failed, do not bother running that pass. 309 if (MF.getProperties().hasProperty( 310 MachineFunctionProperties::Property::FailedISel)) 311 return false; 312 LLVM_DEBUG(dbgs() << "Legalize Machine IR for: " << MF.getName() << '\n'); 313 init(MF); 314 const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>(); 315 GISelCSEAnalysisWrapper &Wrapper = 316 getAnalysis<GISelCSEAnalysisWrapperPass>().getCSEWrapper(); 317 MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr); 318 319 const size_t NumBlocks = MF.size(); 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 const LegalizerInfo &LI = *MF.getSubtarget().getLegalizerInfo(); 344 MFResult Result = 345 legalizeMachineFunction(MF, LI, AuxObservers, LocObserver, *MIRBuilder); 346 347 if (Result.FailedOn) { 348 reportGISelFailure(MF, TPC, MORE, "gisel-legalize", 349 "unable to legalize instruction", *Result.FailedOn); 350 return false; 351 } 352 // For now don't support if new blocks are inserted - we would need to fix the 353 // outer loop for that. 354 if (MF.size() != NumBlocks) { 355 MachineOptimizationRemarkMissed R("gisel-legalize", "GISelFailure", 356 MF.getFunction().getSubprogram(), 357 /*MBB=*/nullptr); 358 R << "inserting blocks is not supported yet"; 359 reportGISelFailure(MF, TPC, MORE, R); 360 return false; 361 } 362 363 if (LocObserver.getNumLostDebugLocs()) { 364 MachineOptimizationRemarkMissed R("gisel-legalize", "LostDebugLoc", 365 MF.getFunction().getSubprogram(), 366 /*MBB=*/&*MF.begin()); 367 R << "lost " 368 << ore::NV("NumLostDebugLocs", LocObserver.getNumLostDebugLocs()) 369 << " debug locations during pass"; 370 reportGISelWarning(MF, TPC, MORE, R); 371 // Example remark: 372 // --- !Missed 373 // Pass: gisel-legalize 374 // Name: GISelFailure 375 // DebugLoc: { File: '.../legalize-urem.mir', Line: 1, Column: 0 } 376 // Function: test_urem_s32 377 // Args: 378 // - String: 'lost ' 379 // - NumLostDebugLocs: '1' 380 // - String: ' debug locations during pass' 381 // ... 382 } 383 384 // If for some reason CSE was not enabled, make sure that we invalidate the 385 // CSEInfo object (as we currently declare that the analysis is preserved). 386 // The next time get on the wrapper is called, it will force it to recompute 387 // the analysis. 388 if (!EnableCSE) 389 Wrapper.setComputed(false); 390 return Result.Changed; 391 } 392