1 //===- RewriteStatepointsForGC.cpp - Make GC relocations explicit ---------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // Rewrite call/invoke instructions so as to make potential relocations 11 // performed by the garbage collector explicit in the IR. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Transforms/Scalar/RewriteStatepointsForGC.h" 16 17 #include "llvm/ADT/ArrayRef.h" 18 #include "llvm/ADT/DenseMap.h" 19 #include "llvm/ADT/DenseSet.h" 20 #include "llvm/ADT/MapVector.h" 21 #include "llvm/ADT/None.h" 22 #include "llvm/ADT/Optional.h" 23 #include "llvm/ADT/STLExtras.h" 24 #include "llvm/ADT/SetVector.h" 25 #include "llvm/ADT/SmallSet.h" 26 #include "llvm/ADT/SmallVector.h" 27 #include "llvm/ADT/StringRef.h" 28 #include "llvm/ADT/iterator_range.h" 29 #include "llvm/Analysis/TargetLibraryInfo.h" 30 #include "llvm/Analysis/TargetTransformInfo.h" 31 #include "llvm/Transforms/Utils/Local.h" 32 #include "llvm/IR/Argument.h" 33 #include "llvm/IR/Attributes.h" 34 #include "llvm/IR/BasicBlock.h" 35 #include "llvm/IR/CallSite.h" 36 #include "llvm/IR/CallingConv.h" 37 #include "llvm/IR/Constant.h" 38 #include "llvm/IR/Constants.h" 39 #include "llvm/IR/DataLayout.h" 40 #include "llvm/IR/DerivedTypes.h" 41 #include "llvm/IR/Dominators.h" 42 #include "llvm/IR/Function.h" 43 #include "llvm/IR/IRBuilder.h" 44 #include "llvm/IR/InstIterator.h" 45 #include "llvm/IR/InstrTypes.h" 46 #include "llvm/IR/Instruction.h" 47 #include "llvm/IR/Instructions.h" 48 #include "llvm/IR/IntrinsicInst.h" 49 #include "llvm/IR/Intrinsics.h" 50 #include "llvm/IR/LLVMContext.h" 51 #include "llvm/IR/MDBuilder.h" 52 #include "llvm/IR/Metadata.h" 53 #include "llvm/IR/Module.h" 54 #include "llvm/IR/Statepoint.h" 55 #include "llvm/IR/Type.h" 56 #include "llvm/IR/User.h" 57 #include "llvm/IR/Value.h" 58 #include "llvm/IR/ValueHandle.h" 59 #include "llvm/Pass.h" 60 #include "llvm/Support/Casting.h" 61 #include "llvm/Support/CommandLine.h" 62 #include "llvm/Support/Compiler.h" 63 #include "llvm/Support/Debug.h" 64 #include "llvm/Support/ErrorHandling.h" 65 #include "llvm/Support/raw_ostream.h" 66 #include "llvm/Transforms/Scalar.h" 67 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 68 #include "llvm/Transforms/Utils/PromoteMemToReg.h" 69 #include <algorithm> 70 #include <cassert> 71 #include <cstddef> 72 #include <cstdint> 73 #include <iterator> 74 #include <set> 75 #include <string> 76 #include <utility> 77 #include <vector> 78 79 #define DEBUG_TYPE "rewrite-statepoints-for-gc" 80 81 using namespace llvm; 82 83 // Print the liveset found at the insert location 84 static cl::opt<bool> PrintLiveSet("spp-print-liveset", cl::Hidden, 85 cl::init(false)); 86 static cl::opt<bool> PrintLiveSetSize("spp-print-liveset-size", cl::Hidden, 87 cl::init(false)); 88 89 // Print out the base pointers for debugging 90 static cl::opt<bool> PrintBasePointers("spp-print-base-pointers", cl::Hidden, 91 cl::init(false)); 92 93 // Cost threshold measuring when it is profitable to rematerialize value instead 94 // of relocating it 95 static cl::opt<unsigned> 96 RematerializationThreshold("spp-rematerialization-threshold", cl::Hidden, 97 cl::init(6)); 98 99 #ifdef EXPENSIVE_CHECKS 100 static bool ClobberNonLive = true; 101 #else 102 static bool ClobberNonLive = false; 103 #endif 104 105 static cl::opt<bool, true> ClobberNonLiveOverride("rs4gc-clobber-non-live", 106 cl::location(ClobberNonLive), 107 cl::Hidden); 108 109 static cl::opt<bool> 110 AllowStatepointWithNoDeoptInfo("rs4gc-allow-statepoint-with-no-deopt-info", 111 cl::Hidden, cl::init(true)); 112 113 /// The IR fed into RewriteStatepointsForGC may have had attributes and 114 /// metadata implying dereferenceability that are no longer valid/correct after 115 /// RewriteStatepointsForGC has run. This is because semantically, after 116 /// RewriteStatepointsForGC runs, all calls to gc.statepoint "free" the entire 117 /// heap. stripNonValidData (conservatively) restores 118 /// correctness by erasing all attributes in the module that externally imply 119 /// dereferenceability. Similar reasoning also applies to the noalias 120 /// attributes and metadata. gc.statepoint can touch the entire heap including 121 /// noalias objects. 122 /// Apart from attributes and metadata, we also remove instructions that imply 123 /// constant physical memory: llvm.invariant.start. 124 static void stripNonValidData(Module &M); 125 126 static bool shouldRewriteStatepointsIn(Function &F); 127 128 PreservedAnalyses RewriteStatepointsForGC::run(Module &M, 129 ModuleAnalysisManager &AM) { 130 bool Changed = false; 131 auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager(); 132 for (Function &F : M) { 133 // Nothing to do for declarations. 134 if (F.isDeclaration() || F.empty()) 135 continue; 136 137 // Policy choice says not to rewrite - the most common reason is that we're 138 // compiling code without a GCStrategy. 139 if (!shouldRewriteStatepointsIn(F)) 140 continue; 141 142 auto &DT = FAM.getResult<DominatorTreeAnalysis>(F); 143 auto &TTI = FAM.getResult<TargetIRAnalysis>(F); 144 auto &TLI = FAM.getResult<TargetLibraryAnalysis>(F); 145 Changed |= runOnFunction(F, DT, TTI, TLI); 146 } 147 if (!Changed) 148 return PreservedAnalyses::all(); 149 150 // stripNonValidData asserts that shouldRewriteStatepointsIn 151 // returns true for at least one function in the module. Since at least 152 // one function changed, we know that the precondition is satisfied. 153 stripNonValidData(M); 154 155 PreservedAnalyses PA; 156 PA.preserve<TargetIRAnalysis>(); 157 PA.preserve<TargetLibraryAnalysis>(); 158 return PA; 159 } 160 161 namespace { 162 163 class RewriteStatepointsForGCLegacyPass : public ModulePass { 164 RewriteStatepointsForGC Impl; 165 166 public: 167 static char ID; // Pass identification, replacement for typeid 168 169 RewriteStatepointsForGCLegacyPass() : ModulePass(ID), Impl() { 170 initializeRewriteStatepointsForGCLegacyPassPass( 171 *PassRegistry::getPassRegistry()); 172 } 173 174 bool runOnModule(Module &M) override { 175 bool Changed = false; 176 const TargetLibraryInfo &TLI = 177 getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); 178 for (Function &F : M) { 179 // Nothing to do for declarations. 180 if (F.isDeclaration() || F.empty()) 181 continue; 182 183 // Policy choice says not to rewrite - the most common reason is that 184 // we're compiling code without a GCStrategy. 185 if (!shouldRewriteStatepointsIn(F)) 186 continue; 187 188 TargetTransformInfo &TTI = 189 getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); 190 auto &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree(); 191 192 Changed |= Impl.runOnFunction(F, DT, TTI, TLI); 193 } 194 195 if (!Changed) 196 return false; 197 198 // stripNonValidData asserts that shouldRewriteStatepointsIn 199 // returns true for at least one function in the module. Since at least 200 // one function changed, we know that the precondition is satisfied. 201 stripNonValidData(M); 202 return true; 203 } 204 205 void getAnalysisUsage(AnalysisUsage &AU) const override { 206 // We add and rewrite a bunch of instructions, but don't really do much 207 // else. We could in theory preserve a lot more analyses here. 208 AU.addRequired<DominatorTreeWrapperPass>(); 209 AU.addRequired<TargetTransformInfoWrapperPass>(); 210 AU.addRequired<TargetLibraryInfoWrapperPass>(); 211 } 212 }; 213 214 } // end anonymous namespace 215 216 char RewriteStatepointsForGCLegacyPass::ID = 0; 217 218 ModulePass *llvm::createRewriteStatepointsForGCLegacyPass() { 219 return new RewriteStatepointsForGCLegacyPass(); 220 } 221 222 INITIALIZE_PASS_BEGIN(RewriteStatepointsForGCLegacyPass, 223 "rewrite-statepoints-for-gc", 224 "Make relocations explicit at statepoints", false, false) 225 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 226 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) 227 INITIALIZE_PASS_END(RewriteStatepointsForGCLegacyPass, 228 "rewrite-statepoints-for-gc", 229 "Make relocations explicit at statepoints", false, false) 230 231 namespace { 232 233 struct GCPtrLivenessData { 234 /// Values defined in this block. 235 MapVector<BasicBlock *, SetVector<Value *>> KillSet; 236 237 /// Values used in this block (and thus live); does not included values 238 /// killed within this block. 239 MapVector<BasicBlock *, SetVector<Value *>> LiveSet; 240 241 /// Values live into this basic block (i.e. used by any 242 /// instruction in this basic block or ones reachable from here) 243 MapVector<BasicBlock *, SetVector<Value *>> LiveIn; 244 245 /// Values live out of this basic block (i.e. live into 246 /// any successor block) 247 MapVector<BasicBlock *, SetVector<Value *>> LiveOut; 248 }; 249 250 // The type of the internal cache used inside the findBasePointers family 251 // of functions. From the callers perspective, this is an opaque type and 252 // should not be inspected. 253 // 254 // In the actual implementation this caches two relations: 255 // - The base relation itself (i.e. this pointer is based on that one) 256 // - The base defining value relation (i.e. before base_phi insertion) 257 // Generally, after the execution of a full findBasePointer call, only the 258 // base relation will remain. Internally, we add a mixture of the two 259 // types, then update all the second type to the first type 260 using DefiningValueMapTy = MapVector<Value *, Value *>; 261 using StatepointLiveSetTy = SetVector<Value *>; 262 using RematerializedValueMapTy = 263 MapVector<AssertingVH<Instruction>, AssertingVH<Value>>; 264 265 struct PartiallyConstructedSafepointRecord { 266 /// The set of values known to be live across this safepoint 267 StatepointLiveSetTy LiveSet; 268 269 /// Mapping from live pointers to a base-defining-value 270 MapVector<Value *, Value *> PointerToBase; 271 272 /// The *new* gc.statepoint instruction itself. This produces the token 273 /// that normal path gc.relocates and the gc.result are tied to. 274 Instruction *StatepointToken; 275 276 /// Instruction to which exceptional gc relocates are attached 277 /// Makes it easier to iterate through them during relocationViaAlloca. 278 Instruction *UnwindToken; 279 280 /// Record live values we are rematerialized instead of relocating. 281 /// They are not included into 'LiveSet' field. 282 /// Maps rematerialized copy to it's original value. 283 RematerializedValueMapTy RematerializedValues; 284 }; 285 286 } // end anonymous namespace 287 288 static ArrayRef<Use> GetDeoptBundleOperands(ImmutableCallSite CS) { 289 Optional<OperandBundleUse> DeoptBundle = 290 CS.getOperandBundle(LLVMContext::OB_deopt); 291 292 if (!DeoptBundle.hasValue()) { 293 assert(AllowStatepointWithNoDeoptInfo && 294 "Found non-leaf call without deopt info!"); 295 return None; 296 } 297 298 return DeoptBundle.getValue().Inputs; 299 } 300 301 /// Compute the live-in set for every basic block in the function 302 static void computeLiveInValues(DominatorTree &DT, Function &F, 303 GCPtrLivenessData &Data); 304 305 /// Given results from the dataflow liveness computation, find the set of live 306 /// Values at a particular instruction. 307 static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data, 308 StatepointLiveSetTy &out); 309 310 // TODO: Once we can get to the GCStrategy, this becomes 311 // Optional<bool> isGCManagedPointer(const Type *Ty) const override { 312 313 static bool isGCPointerType(Type *T) { 314 if (auto *PT = dyn_cast<PointerType>(T)) 315 // For the sake of this example GC, we arbitrarily pick addrspace(1) as our 316 // GC managed heap. We know that a pointer into this heap needs to be 317 // updated and that no other pointer does. 318 return PT->getAddressSpace() == 1; 319 return false; 320 } 321 322 // Return true if this type is one which a) is a gc pointer or contains a GC 323 // pointer and b) is of a type this code expects to encounter as a live value. 324 // (The insertion code will assert that a type which matches (a) and not (b) 325 // is not encountered.) 326 static bool isHandledGCPointerType(Type *T) { 327 // We fully support gc pointers 328 if (isGCPointerType(T)) 329 return true; 330 // We partially support vectors of gc pointers. The code will assert if it 331 // can't handle something. 332 if (auto VT = dyn_cast<VectorType>(T)) 333 if (isGCPointerType(VT->getElementType())) 334 return true; 335 return false; 336 } 337 338 #ifndef NDEBUG 339 /// Returns true if this type contains a gc pointer whether we know how to 340 /// handle that type or not. 341 static bool containsGCPtrType(Type *Ty) { 342 if (isGCPointerType(Ty)) 343 return true; 344 if (VectorType *VT = dyn_cast<VectorType>(Ty)) 345 return isGCPointerType(VT->getScalarType()); 346 if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) 347 return containsGCPtrType(AT->getElementType()); 348 if (StructType *ST = dyn_cast<StructType>(Ty)) 349 return llvm::any_of(ST->subtypes(), containsGCPtrType); 350 return false; 351 } 352 353 // Returns true if this is a type which a) is a gc pointer or contains a GC 354 // pointer and b) is of a type which the code doesn't expect (i.e. first class 355 // aggregates). Used to trip assertions. 356 static bool isUnhandledGCPointerType(Type *Ty) { 357 return containsGCPtrType(Ty) && !isHandledGCPointerType(Ty); 358 } 359 #endif 360 361 // Return the name of the value suffixed with the provided value, or if the 362 // value didn't have a name, the default value specified. 363 static std::string suffixed_name_or(Value *V, StringRef Suffix, 364 StringRef DefaultName) { 365 return V->hasName() ? (V->getName() + Suffix).str() : DefaultName.str(); 366 } 367 368 // Conservatively identifies any definitions which might be live at the 369 // given instruction. The analysis is performed immediately before the 370 // given instruction. Values defined by that instruction are not considered 371 // live. Values used by that instruction are considered live. 372 static void 373 analyzeParsePointLiveness(DominatorTree &DT, 374 GCPtrLivenessData &OriginalLivenessData, CallSite CS, 375 PartiallyConstructedSafepointRecord &Result) { 376 Instruction *Inst = CS.getInstruction(); 377 378 StatepointLiveSetTy LiveSet; 379 findLiveSetAtInst(Inst, OriginalLivenessData, LiveSet); 380 381 if (PrintLiveSet) { 382 dbgs() << "Live Variables:\n"; 383 for (Value *V : LiveSet) 384 dbgs() << " " << V->getName() << " " << *V << "\n"; 385 } 386 if (PrintLiveSetSize) { 387 dbgs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n"; 388 dbgs() << "Number live values: " << LiveSet.size() << "\n"; 389 } 390 Result.LiveSet = LiveSet; 391 } 392 393 static bool isKnownBaseResult(Value *V); 394 395 namespace { 396 397 /// A single base defining value - An immediate base defining value for an 398 /// instruction 'Def' is an input to 'Def' whose base is also a base of 'Def'. 399 /// For instructions which have multiple pointer [vector] inputs or that 400 /// transition between vector and scalar types, there is no immediate base 401 /// defining value. The 'base defining value' for 'Def' is the transitive 402 /// closure of this relation stopping at the first instruction which has no 403 /// immediate base defining value. The b.d.v. might itself be a base pointer, 404 /// but it can also be an arbitrary derived pointer. 405 struct BaseDefiningValueResult { 406 /// Contains the value which is the base defining value. 407 Value * const BDV; 408 409 /// True if the base defining value is also known to be an actual base 410 /// pointer. 411 const bool IsKnownBase; 412 413 BaseDefiningValueResult(Value *BDV, bool IsKnownBase) 414 : BDV(BDV), IsKnownBase(IsKnownBase) { 415 #ifndef NDEBUG 416 // Check consistency between new and old means of checking whether a BDV is 417 // a base. 418 bool MustBeBase = isKnownBaseResult(BDV); 419 assert(!MustBeBase || MustBeBase == IsKnownBase); 420 #endif 421 } 422 }; 423 424 } // end anonymous namespace 425 426 static BaseDefiningValueResult findBaseDefiningValue(Value *I); 427 428 /// Return a base defining value for the 'Index' element of the given vector 429 /// instruction 'I'. If Index is null, returns a BDV for the entire vector 430 /// 'I'. As an optimization, this method will try to determine when the 431 /// element is known to already be a base pointer. If this can be established, 432 /// the second value in the returned pair will be true. Note that either a 433 /// vector or a pointer typed value can be returned. For the former, the 434 /// vector returned is a BDV (and possibly a base) of the entire vector 'I'. 435 /// If the later, the return pointer is a BDV (or possibly a base) for the 436 /// particular element in 'I'. 437 static BaseDefiningValueResult 438 findBaseDefiningValueOfVector(Value *I) { 439 // Each case parallels findBaseDefiningValue below, see that code for 440 // detailed motivation. 441 442 if (isa<Argument>(I)) 443 // An incoming argument to the function is a base pointer 444 return BaseDefiningValueResult(I, true); 445 446 if (isa<Constant>(I)) 447 // Base of constant vector consists only of constant null pointers. 448 // For reasoning see similar case inside 'findBaseDefiningValue' function. 449 return BaseDefiningValueResult(ConstantAggregateZero::get(I->getType()), 450 true); 451 452 if (isa<LoadInst>(I)) 453 return BaseDefiningValueResult(I, true); 454 455 if (isa<InsertElementInst>(I)) 456 // We don't know whether this vector contains entirely base pointers or 457 // not. To be conservatively correct, we treat it as a BDV and will 458 // duplicate code as needed to construct a parallel vector of bases. 459 return BaseDefiningValueResult(I, false); 460 461 if (isa<ShuffleVectorInst>(I)) 462 // We don't know whether this vector contains entirely base pointers or 463 // not. To be conservatively correct, we treat it as a BDV and will 464 // duplicate code as needed to construct a parallel vector of bases. 465 // TODO: There a number of local optimizations which could be applied here 466 // for particular sufflevector patterns. 467 return BaseDefiningValueResult(I, false); 468 469 // The behavior of getelementptr instructions is the same for vector and 470 // non-vector data types. 471 if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) 472 return findBaseDefiningValue(GEP->getPointerOperand()); 473 474 // If the pointer comes through a bitcast of a vector of pointers to 475 // a vector of another type of pointer, then look through the bitcast 476 if (auto *BC = dyn_cast<BitCastInst>(I)) 477 return findBaseDefiningValue(BC->getOperand(0)); 478 479 // We assume that functions in the source language only return base 480 // pointers. This should probably be generalized via attributes to support 481 // both source language and internal functions. 482 if (isa<CallInst>(I) || isa<InvokeInst>(I)) 483 return BaseDefiningValueResult(I, true); 484 485 // A PHI or Select is a base defining value. The outer findBasePointer 486 // algorithm is responsible for constructing a base value for this BDV. 487 assert((isa<SelectInst>(I) || isa<PHINode>(I)) && 488 "unknown vector instruction - no base found for vector element"); 489 return BaseDefiningValueResult(I, false); 490 } 491 492 /// Helper function for findBasePointer - Will return a value which either a) 493 /// defines the base pointer for the input, b) blocks the simple search 494 /// (i.e. a PHI or Select of two derived pointers), or c) involves a change 495 /// from pointer to vector type or back. 496 static BaseDefiningValueResult findBaseDefiningValue(Value *I) { 497 assert(I->getType()->isPtrOrPtrVectorTy() && 498 "Illegal to ask for the base pointer of a non-pointer type"); 499 500 if (I->getType()->isVectorTy()) 501 return findBaseDefiningValueOfVector(I); 502 503 if (isa<Argument>(I)) 504 // An incoming argument to the function is a base pointer 505 // We should have never reached here if this argument isn't an gc value 506 return BaseDefiningValueResult(I, true); 507 508 if (isa<Constant>(I)) { 509 // We assume that objects with a constant base (e.g. a global) can't move 510 // and don't need to be reported to the collector because they are always 511 // live. Besides global references, all kinds of constants (e.g. undef, 512 // constant expressions, null pointers) can be introduced by the inliner or 513 // the optimizer, especially on dynamically dead paths. 514 // Here we treat all of them as having single null base. By doing this we 515 // trying to avoid problems reporting various conflicts in a form of 516 // "phi (const1, const2)" or "phi (const, regular gc ptr)". 517 // See constant.ll file for relevant test cases. 518 519 return BaseDefiningValueResult( 520 ConstantPointerNull::get(cast<PointerType>(I->getType())), true); 521 } 522 523 if (CastInst *CI = dyn_cast<CastInst>(I)) { 524 Value *Def = CI->stripPointerCasts(); 525 // If stripping pointer casts changes the address space there is an 526 // addrspacecast in between. 527 assert(cast<PointerType>(Def->getType())->getAddressSpace() == 528 cast<PointerType>(CI->getType())->getAddressSpace() && 529 "unsupported addrspacecast"); 530 // If we find a cast instruction here, it means we've found a cast which is 531 // not simply a pointer cast (i.e. an inttoptr). We don't know how to 532 // handle int->ptr conversion. 533 assert(!isa<CastInst>(Def) && "shouldn't find another cast here"); 534 return findBaseDefiningValue(Def); 535 } 536 537 if (isa<LoadInst>(I)) 538 // The value loaded is an gc base itself 539 return BaseDefiningValueResult(I, true); 540 541 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) 542 // The base of this GEP is the base 543 return findBaseDefiningValue(GEP->getPointerOperand()); 544 545 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { 546 switch (II->getIntrinsicID()) { 547 default: 548 // fall through to general call handling 549 break; 550 case Intrinsic::experimental_gc_statepoint: 551 llvm_unreachable("statepoints don't produce pointers"); 552 case Intrinsic::experimental_gc_relocate: 553 // Rerunning safepoint insertion after safepoints are already 554 // inserted is not supported. It could probably be made to work, 555 // but why are you doing this? There's no good reason. 556 llvm_unreachable("repeat safepoint insertion is not supported"); 557 case Intrinsic::gcroot: 558 // Currently, this mechanism hasn't been extended to work with gcroot. 559 // There's no reason it couldn't be, but I haven't thought about the 560 // implications much. 561 llvm_unreachable( 562 "interaction with the gcroot mechanism is not supported"); 563 } 564 } 565 // We assume that functions in the source language only return base 566 // pointers. This should probably be generalized via attributes to support 567 // both source language and internal functions. 568 if (isa<CallInst>(I) || isa<InvokeInst>(I)) 569 return BaseDefiningValueResult(I, true); 570 571 // TODO: I have absolutely no idea how to implement this part yet. It's not 572 // necessarily hard, I just haven't really looked at it yet. 573 assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented"); 574 575 if (isa<AtomicCmpXchgInst>(I)) 576 // A CAS is effectively a atomic store and load combined under a 577 // predicate. From the perspective of base pointers, we just treat it 578 // like a load. 579 return BaseDefiningValueResult(I, true); 580 581 assert(!isa<AtomicRMWInst>(I) && "Xchg handled above, all others are " 582 "binary ops which don't apply to pointers"); 583 584 // The aggregate ops. Aggregates can either be in the heap or on the 585 // stack, but in either case, this is simply a field load. As a result, 586 // this is a defining definition of the base just like a load is. 587 if (isa<ExtractValueInst>(I)) 588 return BaseDefiningValueResult(I, true); 589 590 // We should never see an insert vector since that would require we be 591 // tracing back a struct value not a pointer value. 592 assert(!isa<InsertValueInst>(I) && 593 "Base pointer for a struct is meaningless"); 594 595 // An extractelement produces a base result exactly when it's input does. 596 // We may need to insert a parallel instruction to extract the appropriate 597 // element out of the base vector corresponding to the input. Given this, 598 // it's analogous to the phi and select case even though it's not a merge. 599 if (isa<ExtractElementInst>(I)) 600 // Note: There a lot of obvious peephole cases here. This are deliberately 601 // handled after the main base pointer inference algorithm to make writing 602 // test cases to exercise that code easier. 603 return BaseDefiningValueResult(I, false); 604 605 // The last two cases here don't return a base pointer. Instead, they 606 // return a value which dynamically selects from among several base 607 // derived pointers (each with it's own base potentially). It's the job of 608 // the caller to resolve these. 609 assert((isa<SelectInst>(I) || isa<PHINode>(I)) && 610 "missing instruction case in findBaseDefiningValing"); 611 return BaseDefiningValueResult(I, false); 612 } 613 614 /// Returns the base defining value for this value. 615 static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &Cache) { 616 Value *&Cached = Cache[I]; 617 if (!Cached) { 618 Cached = findBaseDefiningValue(I).BDV; 619 LLVM_DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> " 620 << Cached->getName() << "\n"); 621 } 622 assert(Cache[I] != nullptr); 623 return Cached; 624 } 625 626 /// Return a base pointer for this value if known. Otherwise, return it's 627 /// base defining value. 628 static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &Cache) { 629 Value *Def = findBaseDefiningValueCached(I, Cache); 630 auto Found = Cache.find(Def); 631 if (Found != Cache.end()) { 632 // Either a base-of relation, or a self reference. Caller must check. 633 return Found->second; 634 } 635 // Only a BDV available 636 return Def; 637 } 638 639 /// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV, 640 /// is it known to be a base pointer? Or do we need to continue searching. 641 static bool isKnownBaseResult(Value *V) { 642 if (!isa<PHINode>(V) && !isa<SelectInst>(V) && 643 !isa<ExtractElementInst>(V) && !isa<InsertElementInst>(V) && 644 !isa<ShuffleVectorInst>(V)) { 645 // no recursion possible 646 return true; 647 } 648 if (isa<Instruction>(V) && 649 cast<Instruction>(V)->getMetadata("is_base_value")) { 650 // This is a previously inserted base phi or select. We know 651 // that this is a base value. 652 return true; 653 } 654 655 // We need to keep searching 656 return false; 657 } 658 659 namespace { 660 661 /// Models the state of a single base defining value in the findBasePointer 662 /// algorithm for determining where a new instruction is needed to propagate 663 /// the base of this BDV. 664 class BDVState { 665 public: 666 enum Status { Unknown, Base, Conflict }; 667 668 BDVState() : BaseValue(nullptr) {} 669 670 explicit BDVState(Status Status, Value *BaseValue = nullptr) 671 : Status(Status), BaseValue(BaseValue) { 672 assert(Status != Base || BaseValue); 673 } 674 675 explicit BDVState(Value *BaseValue) : Status(Base), BaseValue(BaseValue) {} 676 677 Status getStatus() const { return Status; } 678 Value *getBaseValue() const { return BaseValue; } 679 680 bool isBase() const { return getStatus() == Base; } 681 bool isUnknown() const { return getStatus() == Unknown; } 682 bool isConflict() const { return getStatus() == Conflict; } 683 684 bool operator==(const BDVState &Other) const { 685 return BaseValue == Other.BaseValue && Status == Other.Status; 686 } 687 688 bool operator!=(const BDVState &other) const { return !(*this == other); } 689 690 LLVM_DUMP_METHOD 691 void dump() const { 692 print(dbgs()); 693 dbgs() << '\n'; 694 } 695 696 void print(raw_ostream &OS) const { 697 switch (getStatus()) { 698 case Unknown: 699 OS << "U"; 700 break; 701 case Base: 702 OS << "B"; 703 break; 704 case Conflict: 705 OS << "C"; 706 break; 707 } 708 OS << " (" << getBaseValue() << " - " 709 << (getBaseValue() ? getBaseValue()->getName() : "nullptr") << "): "; 710 } 711 712 private: 713 Status Status = Unknown; 714 AssertingVH<Value> BaseValue; // Non-null only if Status == Base. 715 }; 716 717 } // end anonymous namespace 718 719 #ifndef NDEBUG 720 static raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) { 721 State.print(OS); 722 return OS; 723 } 724 #endif 725 726 static BDVState meetBDVStateImpl(const BDVState &LHS, const BDVState &RHS) { 727 switch (LHS.getStatus()) { 728 case BDVState::Unknown: 729 return RHS; 730 731 case BDVState::Base: 732 assert(LHS.getBaseValue() && "can't be null"); 733 if (RHS.isUnknown()) 734 return LHS; 735 736 if (RHS.isBase()) { 737 if (LHS.getBaseValue() == RHS.getBaseValue()) { 738 assert(LHS == RHS && "equality broken!"); 739 return LHS; 740 } 741 return BDVState(BDVState::Conflict); 742 } 743 assert(RHS.isConflict() && "only three states!"); 744 return BDVState(BDVState::Conflict); 745 746 case BDVState::Conflict: 747 return LHS; 748 } 749 llvm_unreachable("only three states!"); 750 } 751 752 // Values of type BDVState form a lattice, and this function implements the meet 753 // operation. 754 static BDVState meetBDVState(const BDVState &LHS, const BDVState &RHS) { 755 BDVState Result = meetBDVStateImpl(LHS, RHS); 756 assert(Result == meetBDVStateImpl(RHS, LHS) && 757 "Math is wrong: meet does not commute!"); 758 return Result; 759 } 760 761 /// For a given value or instruction, figure out what base ptr its derived from. 762 /// For gc objects, this is simply itself. On success, returns a value which is 763 /// the base pointer. (This is reliable and can be used for relocation.) On 764 /// failure, returns nullptr. 765 static Value *findBasePointer(Value *I, DefiningValueMapTy &Cache) { 766 Value *Def = findBaseOrBDV(I, Cache); 767 768 if (isKnownBaseResult(Def)) 769 return Def; 770 771 // Here's the rough algorithm: 772 // - For every SSA value, construct a mapping to either an actual base 773 // pointer or a PHI which obscures the base pointer. 774 // - Construct a mapping from PHI to unknown TOP state. Use an 775 // optimistic algorithm to propagate base pointer information. Lattice 776 // looks like: 777 // UNKNOWN 778 // b1 b2 b3 b4 779 // CONFLICT 780 // When algorithm terminates, all PHIs will either have a single concrete 781 // base or be in a conflict state. 782 // - For every conflict, insert a dummy PHI node without arguments. Add 783 // these to the base[Instruction] = BasePtr mapping. For every 784 // non-conflict, add the actual base. 785 // - For every conflict, add arguments for the base[a] of each input 786 // arguments. 787 // 788 // Note: A simpler form of this would be to add the conflict form of all 789 // PHIs without running the optimistic algorithm. This would be 790 // analogous to pessimistic data flow and would likely lead to an 791 // overall worse solution. 792 793 #ifndef NDEBUG 794 auto isExpectedBDVType = [](Value *BDV) { 795 return isa<PHINode>(BDV) || isa<SelectInst>(BDV) || 796 isa<ExtractElementInst>(BDV) || isa<InsertElementInst>(BDV) || 797 isa<ShuffleVectorInst>(BDV); 798 }; 799 #endif 800 801 // Once populated, will contain a mapping from each potentially non-base BDV 802 // to a lattice value (described above) which corresponds to that BDV. 803 // We use the order of insertion (DFS over the def/use graph) to provide a 804 // stable deterministic ordering for visiting DenseMaps (which are unordered) 805 // below. This is important for deterministic compilation. 806 MapVector<Value *, BDVState> States; 807 808 // Recursively fill in all base defining values reachable from the initial 809 // one for which we don't already know a definite base value for 810 /* scope */ { 811 SmallVector<Value*, 16> Worklist; 812 Worklist.push_back(Def); 813 States.insert({Def, BDVState()}); 814 while (!Worklist.empty()) { 815 Value *Current = Worklist.pop_back_val(); 816 assert(!isKnownBaseResult(Current) && "why did it get added?"); 817 818 auto visitIncomingValue = [&](Value *InVal) { 819 Value *Base = findBaseOrBDV(InVal, Cache); 820 if (isKnownBaseResult(Base)) 821 // Known bases won't need new instructions introduced and can be 822 // ignored safely 823 return; 824 assert(isExpectedBDVType(Base) && "the only non-base values " 825 "we see should be base defining values"); 826 if (States.insert(std::make_pair(Base, BDVState())).second) 827 Worklist.push_back(Base); 828 }; 829 if (PHINode *PN = dyn_cast<PHINode>(Current)) { 830 for (Value *InVal : PN->incoming_values()) 831 visitIncomingValue(InVal); 832 } else if (SelectInst *SI = dyn_cast<SelectInst>(Current)) { 833 visitIncomingValue(SI->getTrueValue()); 834 visitIncomingValue(SI->getFalseValue()); 835 } else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) { 836 visitIncomingValue(EE->getVectorOperand()); 837 } else if (auto *IE = dyn_cast<InsertElementInst>(Current)) { 838 visitIncomingValue(IE->getOperand(0)); // vector operand 839 visitIncomingValue(IE->getOperand(1)); // scalar operand 840 } else if (auto *SV = dyn_cast<ShuffleVectorInst>(Current)) { 841 visitIncomingValue(SV->getOperand(0)); 842 visitIncomingValue(SV->getOperand(1)); 843 } 844 else { 845 llvm_unreachable("Unimplemented instruction case"); 846 } 847 } 848 } 849 850 #ifndef NDEBUG 851 LLVM_DEBUG(dbgs() << "States after initialization:\n"); 852 for (auto Pair : States) { 853 LLVM_DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n"); 854 } 855 #endif 856 857 // Return a phi state for a base defining value. We'll generate a new 858 // base state for known bases and expect to find a cached state otherwise. 859 auto getStateForBDV = [&](Value *baseValue) { 860 if (isKnownBaseResult(baseValue)) 861 return BDVState(baseValue); 862 auto I = States.find(baseValue); 863 assert(I != States.end() && "lookup failed!"); 864 return I->second; 865 }; 866 867 bool Progress = true; 868 while (Progress) { 869 #ifndef NDEBUG 870 const size_t OldSize = States.size(); 871 #endif 872 Progress = false; 873 // We're only changing values in this loop, thus safe to keep iterators. 874 // Since this is computing a fixed point, the order of visit does not 875 // effect the result. TODO: We could use a worklist here and make this run 876 // much faster. 877 for (auto Pair : States) { 878 Value *BDV = Pair.first; 879 assert(!isKnownBaseResult(BDV) && "why did it get added?"); 880 881 // Given an input value for the current instruction, return a BDVState 882 // instance which represents the BDV of that value. 883 auto getStateForInput = [&](Value *V) mutable { 884 Value *BDV = findBaseOrBDV(V, Cache); 885 return getStateForBDV(BDV); 886 }; 887 888 BDVState NewState; 889 if (SelectInst *SI = dyn_cast<SelectInst>(BDV)) { 890 NewState = meetBDVState(NewState, getStateForInput(SI->getTrueValue())); 891 NewState = 892 meetBDVState(NewState, getStateForInput(SI->getFalseValue())); 893 } else if (PHINode *PN = dyn_cast<PHINode>(BDV)) { 894 for (Value *Val : PN->incoming_values()) 895 NewState = meetBDVState(NewState, getStateForInput(Val)); 896 } else if (auto *EE = dyn_cast<ExtractElementInst>(BDV)) { 897 // The 'meet' for an extractelement is slightly trivial, but it's still 898 // useful in that it drives us to conflict if our input is. 899 NewState = 900 meetBDVState(NewState, getStateForInput(EE->getVectorOperand())); 901 } else if (auto *IE = dyn_cast<InsertElementInst>(BDV)){ 902 // Given there's a inherent type mismatch between the operands, will 903 // *always* produce Conflict. 904 NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(0))); 905 NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(1))); 906 } else { 907 // The only instance this does not return a Conflict is when both the 908 // vector operands are the same vector. 909 auto *SV = cast<ShuffleVectorInst>(BDV); 910 NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(0))); 911 NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(1))); 912 } 913 914 BDVState OldState = States[BDV]; 915 if (OldState != NewState) { 916 Progress = true; 917 States[BDV] = NewState; 918 } 919 } 920 921 assert(OldSize == States.size() && 922 "fixed point shouldn't be adding any new nodes to state"); 923 } 924 925 #ifndef NDEBUG 926 LLVM_DEBUG(dbgs() << "States after meet iteration:\n"); 927 for (auto Pair : States) { 928 LLVM_DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n"); 929 } 930 #endif 931 932 // Insert Phis for all conflicts 933 // TODO: adjust naming patterns to avoid this order of iteration dependency 934 for (auto Pair : States) { 935 Instruction *I = cast<Instruction>(Pair.first); 936 BDVState State = Pair.second; 937 assert(!isKnownBaseResult(I) && "why did it get added?"); 938 assert(!State.isUnknown() && "Optimistic algorithm didn't complete!"); 939 940 // extractelement instructions are a bit special in that we may need to 941 // insert an extract even when we know an exact base for the instruction. 942 // The problem is that we need to convert from a vector base to a scalar 943 // base for the particular indice we're interested in. 944 if (State.isBase() && isa<ExtractElementInst>(I) && 945 isa<VectorType>(State.getBaseValue()->getType())) { 946 auto *EE = cast<ExtractElementInst>(I); 947 // TODO: In many cases, the new instruction is just EE itself. We should 948 // exploit this, but can't do it here since it would break the invariant 949 // about the BDV not being known to be a base. 950 auto *BaseInst = ExtractElementInst::Create( 951 State.getBaseValue(), EE->getIndexOperand(), "base_ee", EE); 952 BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {})); 953 States[I] = BDVState(BDVState::Base, BaseInst); 954 } 955 956 // Since we're joining a vector and scalar base, they can never be the 957 // same. As a result, we should always see insert element having reached 958 // the conflict state. 959 assert(!isa<InsertElementInst>(I) || State.isConflict()); 960 961 if (!State.isConflict()) 962 continue; 963 964 /// Create and insert a new instruction which will represent the base of 965 /// the given instruction 'I'. 966 auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* { 967 if (isa<PHINode>(I)) { 968 BasicBlock *BB = I->getParent(); 969 int NumPreds = pred_size(BB); 970 assert(NumPreds > 0 && "how did we reach here"); 971 std::string Name = suffixed_name_or(I, ".base", "base_phi"); 972 return PHINode::Create(I->getType(), NumPreds, Name, I); 973 } else if (SelectInst *SI = dyn_cast<SelectInst>(I)) { 974 // The undef will be replaced later 975 UndefValue *Undef = UndefValue::get(SI->getType()); 976 std::string Name = suffixed_name_or(I, ".base", "base_select"); 977 return SelectInst::Create(SI->getCondition(), Undef, Undef, Name, SI); 978 } else if (auto *EE = dyn_cast<ExtractElementInst>(I)) { 979 UndefValue *Undef = UndefValue::get(EE->getVectorOperand()->getType()); 980 std::string Name = suffixed_name_or(I, ".base", "base_ee"); 981 return ExtractElementInst::Create(Undef, EE->getIndexOperand(), Name, 982 EE); 983 } else if (auto *IE = dyn_cast<InsertElementInst>(I)) { 984 UndefValue *VecUndef = UndefValue::get(IE->getOperand(0)->getType()); 985 UndefValue *ScalarUndef = UndefValue::get(IE->getOperand(1)->getType()); 986 std::string Name = suffixed_name_or(I, ".base", "base_ie"); 987 return InsertElementInst::Create(VecUndef, ScalarUndef, 988 IE->getOperand(2), Name, IE); 989 } else { 990 auto *SV = cast<ShuffleVectorInst>(I); 991 UndefValue *VecUndef = UndefValue::get(SV->getOperand(0)->getType()); 992 std::string Name = suffixed_name_or(I, ".base", "base_sv"); 993 return new ShuffleVectorInst(VecUndef, VecUndef, SV->getOperand(2), 994 Name, SV); 995 } 996 }; 997 Instruction *BaseInst = MakeBaseInstPlaceholder(I); 998 // Add metadata marking this as a base value 999 BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {})); 1000 States[I] = BDVState(BDVState::Conflict, BaseInst); 1001 } 1002 1003 // Returns a instruction which produces the base pointer for a given 1004 // instruction. The instruction is assumed to be an input to one of the BDVs 1005 // seen in the inference algorithm above. As such, we must either already 1006 // know it's base defining value is a base, or have inserted a new 1007 // instruction to propagate the base of it's BDV and have entered that newly 1008 // introduced instruction into the state table. In either case, we are 1009 // assured to be able to determine an instruction which produces it's base 1010 // pointer. 1011 auto getBaseForInput = [&](Value *Input, Instruction *InsertPt) { 1012 Value *BDV = findBaseOrBDV(Input, Cache); 1013 Value *Base = nullptr; 1014 if (isKnownBaseResult(BDV)) { 1015 Base = BDV; 1016 } else { 1017 // Either conflict or base. 1018 assert(States.count(BDV)); 1019 Base = States[BDV].getBaseValue(); 1020 } 1021 assert(Base && "Can't be null"); 1022 // The cast is needed since base traversal may strip away bitcasts 1023 if (Base->getType() != Input->getType() && InsertPt) 1024 Base = new BitCastInst(Base, Input->getType(), "cast", InsertPt); 1025 return Base; 1026 }; 1027 1028 // Fixup all the inputs of the new PHIs. Visit order needs to be 1029 // deterministic and predictable because we're naming newly created 1030 // instructions. 1031 for (auto Pair : States) { 1032 Instruction *BDV = cast<Instruction>(Pair.first); 1033 BDVState State = Pair.second; 1034 1035 assert(!isKnownBaseResult(BDV) && "why did it get added?"); 1036 assert(!State.isUnknown() && "Optimistic algorithm didn't complete!"); 1037 if (!State.isConflict()) 1038 continue; 1039 1040 if (PHINode *BasePHI = dyn_cast<PHINode>(State.getBaseValue())) { 1041 PHINode *PN = cast<PHINode>(BDV); 1042 unsigned NumPHIValues = PN->getNumIncomingValues(); 1043 for (unsigned i = 0; i < NumPHIValues; i++) { 1044 Value *InVal = PN->getIncomingValue(i); 1045 BasicBlock *InBB = PN->getIncomingBlock(i); 1046 1047 // If we've already seen InBB, add the same incoming value 1048 // we added for it earlier. The IR verifier requires phi 1049 // nodes with multiple entries from the same basic block 1050 // to have the same incoming value for each of those 1051 // entries. If we don't do this check here and basephi 1052 // has a different type than base, we'll end up adding two 1053 // bitcasts (and hence two distinct values) as incoming 1054 // values for the same basic block. 1055 1056 int BlockIndex = BasePHI->getBasicBlockIndex(InBB); 1057 if (BlockIndex != -1) { 1058 Value *OldBase = BasePHI->getIncomingValue(BlockIndex); 1059 BasePHI->addIncoming(OldBase, InBB); 1060 1061 #ifndef NDEBUG 1062 Value *Base = getBaseForInput(InVal, nullptr); 1063 // In essence this assert states: the only way two values 1064 // incoming from the same basic block may be different is by 1065 // being different bitcasts of the same value. A cleanup 1066 // that remains TODO is changing findBaseOrBDV to return an 1067 // llvm::Value of the correct type (and still remain pure). 1068 // This will remove the need to add bitcasts. 1069 assert(Base->stripPointerCasts() == OldBase->stripPointerCasts() && 1070 "Sanity -- findBaseOrBDV should be pure!"); 1071 #endif 1072 continue; 1073 } 1074 1075 // Find the instruction which produces the base for each input. We may 1076 // need to insert a bitcast in the incoming block. 1077 // TODO: Need to split critical edges if insertion is needed 1078 Value *Base = getBaseForInput(InVal, InBB->getTerminator()); 1079 BasePHI->addIncoming(Base, InBB); 1080 } 1081 assert(BasePHI->getNumIncomingValues() == NumPHIValues); 1082 } else if (SelectInst *BaseSI = 1083 dyn_cast<SelectInst>(State.getBaseValue())) { 1084 SelectInst *SI = cast<SelectInst>(BDV); 1085 1086 // Find the instruction which produces the base for each input. 1087 // We may need to insert a bitcast. 1088 BaseSI->setTrueValue(getBaseForInput(SI->getTrueValue(), BaseSI)); 1089 BaseSI->setFalseValue(getBaseForInput(SI->getFalseValue(), BaseSI)); 1090 } else if (auto *BaseEE = 1091 dyn_cast<ExtractElementInst>(State.getBaseValue())) { 1092 Value *InVal = cast<ExtractElementInst>(BDV)->getVectorOperand(); 1093 // Find the instruction which produces the base for each input. We may 1094 // need to insert a bitcast. 1095 BaseEE->setOperand(0, getBaseForInput(InVal, BaseEE)); 1096 } else if (auto *BaseIE = dyn_cast<InsertElementInst>(State.getBaseValue())){ 1097 auto *BdvIE = cast<InsertElementInst>(BDV); 1098 auto UpdateOperand = [&](int OperandIdx) { 1099 Value *InVal = BdvIE->getOperand(OperandIdx); 1100 Value *Base = getBaseForInput(InVal, BaseIE); 1101 BaseIE->setOperand(OperandIdx, Base); 1102 }; 1103 UpdateOperand(0); // vector operand 1104 UpdateOperand(1); // scalar operand 1105 } else { 1106 auto *BaseSV = cast<ShuffleVectorInst>(State.getBaseValue()); 1107 auto *BdvSV = cast<ShuffleVectorInst>(BDV); 1108 auto UpdateOperand = [&](int OperandIdx) { 1109 Value *InVal = BdvSV->getOperand(OperandIdx); 1110 Value *Base = getBaseForInput(InVal, BaseSV); 1111 BaseSV->setOperand(OperandIdx, Base); 1112 }; 1113 UpdateOperand(0); // vector operand 1114 UpdateOperand(1); // vector operand 1115 } 1116 } 1117 1118 // Cache all of our results so we can cheaply reuse them 1119 // NOTE: This is actually two caches: one of the base defining value 1120 // relation and one of the base pointer relation! FIXME 1121 for (auto Pair : States) { 1122 auto *BDV = Pair.first; 1123 Value *Base = Pair.second.getBaseValue(); 1124 assert(BDV && Base); 1125 assert(!isKnownBaseResult(BDV) && "why did it get added?"); 1126 1127 LLVM_DEBUG( 1128 dbgs() << "Updating base value cache" 1129 << " for: " << BDV->getName() << " from: " 1130 << (Cache.count(BDV) ? Cache[BDV]->getName().str() : "none") 1131 << " to: " << Base->getName() << "\n"); 1132 1133 if (Cache.count(BDV)) { 1134 assert(isKnownBaseResult(Base) && 1135 "must be something we 'know' is a base pointer"); 1136 // Once we transition from the BDV relation being store in the Cache to 1137 // the base relation being stored, it must be stable 1138 assert((!isKnownBaseResult(Cache[BDV]) || Cache[BDV] == Base) && 1139 "base relation should be stable"); 1140 } 1141 Cache[BDV] = Base; 1142 } 1143 assert(Cache.count(Def)); 1144 return Cache[Def]; 1145 } 1146 1147 // For a set of live pointers (base and/or derived), identify the base 1148 // pointer of the object which they are derived from. This routine will 1149 // mutate the IR graph as needed to make the 'base' pointer live at the 1150 // definition site of 'derived'. This ensures that any use of 'derived' can 1151 // also use 'base'. This may involve the insertion of a number of 1152 // additional PHI nodes. 1153 // 1154 // preconditions: live is a set of pointer type Values 1155 // 1156 // side effects: may insert PHI nodes into the existing CFG, will preserve 1157 // CFG, will not remove or mutate any existing nodes 1158 // 1159 // post condition: PointerToBase contains one (derived, base) pair for every 1160 // pointer in live. Note that derived can be equal to base if the original 1161 // pointer was a base pointer. 1162 static void 1163 findBasePointers(const StatepointLiveSetTy &live, 1164 MapVector<Value *, Value *> &PointerToBase, 1165 DominatorTree *DT, DefiningValueMapTy &DVCache) { 1166 for (Value *ptr : live) { 1167 Value *base = findBasePointer(ptr, DVCache); 1168 assert(base && "failed to find base pointer"); 1169 PointerToBase[ptr] = base; 1170 assert((!isa<Instruction>(base) || !isa<Instruction>(ptr) || 1171 DT->dominates(cast<Instruction>(base)->getParent(), 1172 cast<Instruction>(ptr)->getParent())) && 1173 "The base we found better dominate the derived pointer"); 1174 } 1175 } 1176 1177 /// Find the required based pointers (and adjust the live set) for the given 1178 /// parse point. 1179 static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache, 1180 CallSite CS, 1181 PartiallyConstructedSafepointRecord &result) { 1182 MapVector<Value *, Value *> PointerToBase; 1183 findBasePointers(result.LiveSet, PointerToBase, &DT, DVCache); 1184 1185 if (PrintBasePointers) { 1186 errs() << "Base Pairs (w/o Relocation):\n"; 1187 for (auto &Pair : PointerToBase) { 1188 errs() << " derived "; 1189 Pair.first->printAsOperand(errs(), false); 1190 errs() << " base "; 1191 Pair.second->printAsOperand(errs(), false); 1192 errs() << "\n";; 1193 } 1194 } 1195 1196 result.PointerToBase = PointerToBase; 1197 } 1198 1199 /// Given an updated version of the dataflow liveness results, update the 1200 /// liveset and base pointer maps for the call site CS. 1201 static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData, 1202 CallSite CS, 1203 PartiallyConstructedSafepointRecord &result); 1204 1205 static void recomputeLiveInValues( 1206 Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate, 1207 MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) { 1208 // TODO-PERF: reuse the original liveness, then simply run the dataflow 1209 // again. The old values are still live and will help it stabilize quickly. 1210 GCPtrLivenessData RevisedLivenessData; 1211 computeLiveInValues(DT, F, RevisedLivenessData); 1212 for (size_t i = 0; i < records.size(); i++) { 1213 struct PartiallyConstructedSafepointRecord &info = records[i]; 1214 recomputeLiveInValues(RevisedLivenessData, toUpdate[i], info); 1215 } 1216 } 1217 1218 // When inserting gc.relocate and gc.result calls, we need to ensure there are 1219 // no uses of the original value / return value between the gc.statepoint and 1220 // the gc.relocate / gc.result call. One case which can arise is a phi node 1221 // starting one of the successor blocks. We also need to be able to insert the 1222 // gc.relocates only on the path which goes through the statepoint. We might 1223 // need to split an edge to make this possible. 1224 static BasicBlock * 1225 normalizeForInvokeSafepoint(BasicBlock *BB, BasicBlock *InvokeParent, 1226 DominatorTree &DT) { 1227 BasicBlock *Ret = BB; 1228 if (!BB->getUniquePredecessor()) 1229 Ret = SplitBlockPredecessors(BB, InvokeParent, "", &DT); 1230 1231 // Now that 'Ret' has unique predecessor we can safely remove all phi nodes 1232 // from it 1233 FoldSingleEntryPHINodes(Ret); 1234 assert(!isa<PHINode>(Ret->begin()) && 1235 "All PHI nodes should have been removed!"); 1236 1237 // At this point, we can safely insert a gc.relocate or gc.result as the first 1238 // instruction in Ret if needed. 1239 return Ret; 1240 } 1241 1242 // Create new attribute set containing only attributes which can be transferred 1243 // from original call to the safepoint. 1244 static AttributeList legalizeCallAttributes(AttributeList AL) { 1245 if (AL.isEmpty()) 1246 return AL; 1247 1248 // Remove the readonly, readnone, and statepoint function attributes. 1249 AttrBuilder FnAttrs = AL.getFnAttributes(); 1250 FnAttrs.removeAttribute(Attribute::ReadNone); 1251 FnAttrs.removeAttribute(Attribute::ReadOnly); 1252 for (Attribute A : AL.getFnAttributes()) { 1253 if (isStatepointDirectiveAttr(A)) 1254 FnAttrs.remove(A); 1255 } 1256 1257 // Just skip parameter and return attributes for now 1258 LLVMContext &Ctx = AL.getContext(); 1259 return AttributeList::get(Ctx, AttributeList::FunctionIndex, 1260 AttributeSet::get(Ctx, FnAttrs)); 1261 } 1262 1263 /// Helper function to place all gc relocates necessary for the given 1264 /// statepoint. 1265 /// Inputs: 1266 /// liveVariables - list of variables to be relocated. 1267 /// liveStart - index of the first live variable. 1268 /// basePtrs - base pointers. 1269 /// statepointToken - statepoint instruction to which relocates should be 1270 /// bound. 1271 /// Builder - Llvm IR builder to be used to construct new calls. 1272 static void CreateGCRelocates(ArrayRef<Value *> LiveVariables, 1273 const int LiveStart, 1274 ArrayRef<Value *> BasePtrs, 1275 Instruction *StatepointToken, 1276 IRBuilder<> Builder) { 1277 if (LiveVariables.empty()) 1278 return; 1279 1280 auto FindIndex = [](ArrayRef<Value *> LiveVec, Value *Val) { 1281 auto ValIt = llvm::find(LiveVec, Val); 1282 assert(ValIt != LiveVec.end() && "Val not found in LiveVec!"); 1283 size_t Index = std::distance(LiveVec.begin(), ValIt); 1284 assert(Index < LiveVec.size() && "Bug in std::find?"); 1285 return Index; 1286 }; 1287 Module *M = StatepointToken->getModule(); 1288 1289 // All gc_relocate are generated as i8 addrspace(1)* (or a vector type whose 1290 // element type is i8 addrspace(1)*). We originally generated unique 1291 // declarations for each pointer type, but this proved problematic because 1292 // the intrinsic mangling code is incomplete and fragile. Since we're moving 1293 // towards a single unified pointer type anyways, we can just cast everything 1294 // to an i8* of the right address space. A bitcast is added later to convert 1295 // gc_relocate to the actual value's type. 1296 auto getGCRelocateDecl = [&] (Type *Ty) { 1297 assert(isHandledGCPointerType(Ty)); 1298 auto AS = Ty->getScalarType()->getPointerAddressSpace(); 1299 Type *NewTy = Type::getInt8PtrTy(M->getContext(), AS); 1300 if (auto *VT = dyn_cast<VectorType>(Ty)) 1301 NewTy = VectorType::get(NewTy, VT->getNumElements()); 1302 return Intrinsic::getDeclaration(M, Intrinsic::experimental_gc_relocate, 1303 {NewTy}); 1304 }; 1305 1306 // Lazily populated map from input types to the canonicalized form mentioned 1307 // in the comment above. This should probably be cached somewhere more 1308 // broadly. 1309 DenseMap<Type*, Value*> TypeToDeclMap; 1310 1311 for (unsigned i = 0; i < LiveVariables.size(); i++) { 1312 // Generate the gc.relocate call and save the result 1313 Value *BaseIdx = 1314 Builder.getInt32(LiveStart + FindIndex(LiveVariables, BasePtrs[i])); 1315 Value *LiveIdx = Builder.getInt32(LiveStart + i); 1316 1317 Type *Ty = LiveVariables[i]->getType(); 1318 if (!TypeToDeclMap.count(Ty)) 1319 TypeToDeclMap[Ty] = getGCRelocateDecl(Ty); 1320 Value *GCRelocateDecl = TypeToDeclMap[Ty]; 1321 1322 // only specify a debug name if we can give a useful one 1323 CallInst *Reloc = Builder.CreateCall( 1324 GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx}, 1325 suffixed_name_or(LiveVariables[i], ".relocated", "")); 1326 // Trick CodeGen into thinking there are lots of free registers at this 1327 // fake call. 1328 Reloc->setCallingConv(CallingConv::Cold); 1329 } 1330 } 1331 1332 namespace { 1333 1334 /// This struct is used to defer RAUWs and `eraseFromParent` s. Using this 1335 /// avoids having to worry about keeping around dangling pointers to Values. 1336 class DeferredReplacement { 1337 AssertingVH<Instruction> Old; 1338 AssertingVH<Instruction> New; 1339 bool IsDeoptimize = false; 1340 1341 DeferredReplacement() = default; 1342 1343 public: 1344 static DeferredReplacement createRAUW(Instruction *Old, Instruction *New) { 1345 assert(Old != New && Old && New && 1346 "Cannot RAUW equal values or to / from null!"); 1347 1348 DeferredReplacement D; 1349 D.Old = Old; 1350 D.New = New; 1351 return D; 1352 } 1353 1354 static DeferredReplacement createDelete(Instruction *ToErase) { 1355 DeferredReplacement D; 1356 D.Old = ToErase; 1357 return D; 1358 } 1359 1360 static DeferredReplacement createDeoptimizeReplacement(Instruction *Old) { 1361 #ifndef NDEBUG 1362 auto *F = cast<CallInst>(Old)->getCalledFunction(); 1363 assert(F && F->getIntrinsicID() == Intrinsic::experimental_deoptimize && 1364 "Only way to construct a deoptimize deferred replacement"); 1365 #endif 1366 DeferredReplacement D; 1367 D.Old = Old; 1368 D.IsDeoptimize = true; 1369 return D; 1370 } 1371 1372 /// Does the task represented by this instance. 1373 void doReplacement() { 1374 Instruction *OldI = Old; 1375 Instruction *NewI = New; 1376 1377 assert(OldI != NewI && "Disallowed at construction?!"); 1378 assert((!IsDeoptimize || !New) && 1379 "Deoptimize intrinsics are not replaced!"); 1380 1381 Old = nullptr; 1382 New = nullptr; 1383 1384 if (NewI) 1385 OldI->replaceAllUsesWith(NewI); 1386 1387 if (IsDeoptimize) { 1388 // Note: we've inserted instructions, so the call to llvm.deoptimize may 1389 // not necessarily be followed by the matching return. 1390 auto *RI = cast<ReturnInst>(OldI->getParent()->getTerminator()); 1391 new UnreachableInst(RI->getContext(), RI); 1392 RI->eraseFromParent(); 1393 } 1394 1395 OldI->eraseFromParent(); 1396 } 1397 }; 1398 1399 } // end anonymous namespace 1400 1401 static StringRef getDeoptLowering(CallSite CS) { 1402 const char *DeoptLowering = "deopt-lowering"; 1403 if (CS.hasFnAttr(DeoptLowering)) { 1404 // FIXME: CallSite has a *really* confusing interface around attributes 1405 // with values. 1406 const AttributeList &CSAS = CS.getAttributes(); 1407 if (CSAS.hasAttribute(AttributeList::FunctionIndex, DeoptLowering)) 1408 return CSAS.getAttribute(AttributeList::FunctionIndex, DeoptLowering) 1409 .getValueAsString(); 1410 Function *F = CS.getCalledFunction(); 1411 assert(F && F->hasFnAttribute(DeoptLowering)); 1412 return F->getFnAttribute(DeoptLowering).getValueAsString(); 1413 } 1414 return "live-through"; 1415 } 1416 1417 static void 1418 makeStatepointExplicitImpl(const CallSite CS, /* to replace */ 1419 const SmallVectorImpl<Value *> &BasePtrs, 1420 const SmallVectorImpl<Value *> &LiveVariables, 1421 PartiallyConstructedSafepointRecord &Result, 1422 std::vector<DeferredReplacement> &Replacements) { 1423 assert(BasePtrs.size() == LiveVariables.size()); 1424 1425 // Then go ahead and use the builder do actually do the inserts. We insert 1426 // immediately before the previous instruction under the assumption that all 1427 // arguments will be available here. We can't insert afterwards since we may 1428 // be replacing a terminator. 1429 Instruction *InsertBefore = CS.getInstruction(); 1430 IRBuilder<> Builder(InsertBefore); 1431 1432 ArrayRef<Value *> GCArgs(LiveVariables); 1433 uint64_t StatepointID = StatepointDirectives::DefaultStatepointID; 1434 uint32_t NumPatchBytes = 0; 1435 uint32_t Flags = uint32_t(StatepointFlags::None); 1436 1437 ArrayRef<Use> CallArgs(CS.arg_begin(), CS.arg_end()); 1438 ArrayRef<Use> DeoptArgs = GetDeoptBundleOperands(CS); 1439 ArrayRef<Use> TransitionArgs; 1440 if (auto TransitionBundle = 1441 CS.getOperandBundle(LLVMContext::OB_gc_transition)) { 1442 Flags |= uint32_t(StatepointFlags::GCTransition); 1443 TransitionArgs = TransitionBundle->Inputs; 1444 } 1445 1446 // Instead of lowering calls to @llvm.experimental.deoptimize as normal calls 1447 // with a return value, we lower then as never returning calls to 1448 // __llvm_deoptimize that are followed by unreachable to get better codegen. 1449 bool IsDeoptimize = false; 1450 1451 StatepointDirectives SD = 1452 parseStatepointDirectivesFromAttrs(CS.getAttributes()); 1453 if (SD.NumPatchBytes) 1454 NumPatchBytes = *SD.NumPatchBytes; 1455 if (SD.StatepointID) 1456 StatepointID = *SD.StatepointID; 1457 1458 // Pass through the requested lowering if any. The default is live-through. 1459 StringRef DeoptLowering = getDeoptLowering(CS); 1460 if (DeoptLowering.equals("live-in")) 1461 Flags |= uint32_t(StatepointFlags::DeoptLiveIn); 1462 else { 1463 assert(DeoptLowering.equals("live-through") && "Unsupported value!"); 1464 } 1465 1466 Value *CallTarget = CS.getCalledValue(); 1467 if (Function *F = dyn_cast<Function>(CallTarget)) { 1468 if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize) { 1469 // Calls to llvm.experimental.deoptimize are lowered to calls to the 1470 // __llvm_deoptimize symbol. We want to resolve this now, since the 1471 // verifier does not allow taking the address of an intrinsic function. 1472 1473 SmallVector<Type *, 8> DomainTy; 1474 for (Value *Arg : CallArgs) 1475 DomainTy.push_back(Arg->getType()); 1476 auto *FTy = FunctionType::get(Type::getVoidTy(F->getContext()), DomainTy, 1477 /* isVarArg = */ false); 1478 1479 // Note: CallTarget can be a bitcast instruction of a symbol if there are 1480 // calls to @llvm.experimental.deoptimize with different argument types in 1481 // the same module. This is fine -- we assume the frontend knew what it 1482 // was doing when generating this kind of IR. 1483 CallTarget = 1484 F->getParent()->getOrInsertFunction("__llvm_deoptimize", FTy); 1485 1486 IsDeoptimize = true; 1487 } 1488 } 1489 1490 // Create the statepoint given all the arguments 1491 Instruction *Token = nullptr; 1492 if (CS.isCall()) { 1493 CallInst *ToReplace = cast<CallInst>(CS.getInstruction()); 1494 CallInst *Call = Builder.CreateGCStatepointCall( 1495 StatepointID, NumPatchBytes, CallTarget, Flags, CallArgs, 1496 TransitionArgs, DeoptArgs, GCArgs, "safepoint_token"); 1497 1498 Call->setTailCallKind(ToReplace->getTailCallKind()); 1499 Call->setCallingConv(ToReplace->getCallingConv()); 1500 1501 // Currently we will fail on parameter attributes and on certain 1502 // function attributes. In case if we can handle this set of attributes - 1503 // set up function attrs directly on statepoint and return attrs later for 1504 // gc_result intrinsic. 1505 Call->setAttributes(legalizeCallAttributes(ToReplace->getAttributes())); 1506 1507 Token = Call; 1508 1509 // Put the following gc_result and gc_relocate calls immediately after the 1510 // the old call (which we're about to delete) 1511 assert(ToReplace->getNextNode() && "Not a terminator, must have next!"); 1512 Builder.SetInsertPoint(ToReplace->getNextNode()); 1513 Builder.SetCurrentDebugLocation(ToReplace->getNextNode()->getDebugLoc()); 1514 } else { 1515 InvokeInst *ToReplace = cast<InvokeInst>(CS.getInstruction()); 1516 1517 // Insert the new invoke into the old block. We'll remove the old one in a 1518 // moment at which point this will become the new terminator for the 1519 // original block. 1520 InvokeInst *Invoke = Builder.CreateGCStatepointInvoke( 1521 StatepointID, NumPatchBytes, CallTarget, ToReplace->getNormalDest(), 1522 ToReplace->getUnwindDest(), Flags, CallArgs, TransitionArgs, DeoptArgs, 1523 GCArgs, "statepoint_token"); 1524 1525 Invoke->setCallingConv(ToReplace->getCallingConv()); 1526 1527 // Currently we will fail on parameter attributes and on certain 1528 // function attributes. In case if we can handle this set of attributes - 1529 // set up function attrs directly on statepoint and return attrs later for 1530 // gc_result intrinsic. 1531 Invoke->setAttributes(legalizeCallAttributes(ToReplace->getAttributes())); 1532 1533 Token = Invoke; 1534 1535 // Generate gc relocates in exceptional path 1536 BasicBlock *UnwindBlock = ToReplace->getUnwindDest(); 1537 assert(!isa<PHINode>(UnwindBlock->begin()) && 1538 UnwindBlock->getUniquePredecessor() && 1539 "can't safely insert in this block!"); 1540 1541 Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt()); 1542 Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc()); 1543 1544 // Attach exceptional gc relocates to the landingpad. 1545 Instruction *ExceptionalToken = UnwindBlock->getLandingPadInst(); 1546 Result.UnwindToken = ExceptionalToken; 1547 1548 const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx(); 1549 CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, ExceptionalToken, 1550 Builder); 1551 1552 // Generate gc relocates and returns for normal block 1553 BasicBlock *NormalDest = ToReplace->getNormalDest(); 1554 assert(!isa<PHINode>(NormalDest->begin()) && 1555 NormalDest->getUniquePredecessor() && 1556 "can't safely insert in this block!"); 1557 1558 Builder.SetInsertPoint(&*NormalDest->getFirstInsertionPt()); 1559 1560 // gc relocates will be generated later as if it were regular call 1561 // statepoint 1562 } 1563 assert(Token && "Should be set in one of the above branches!"); 1564 1565 if (IsDeoptimize) { 1566 // If we're wrapping an @llvm.experimental.deoptimize in a statepoint, we 1567 // transform the tail-call like structure to a call to a void function 1568 // followed by unreachable to get better codegen. 1569 Replacements.push_back( 1570 DeferredReplacement::createDeoptimizeReplacement(CS.getInstruction())); 1571 } else { 1572 Token->setName("statepoint_token"); 1573 if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) { 1574 StringRef Name = 1575 CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : ""; 1576 CallInst *GCResult = Builder.CreateGCResult(Token, CS.getType(), Name); 1577 GCResult->setAttributes( 1578 AttributeList::get(GCResult->getContext(), AttributeList::ReturnIndex, 1579 CS.getAttributes().getRetAttributes())); 1580 1581 // We cannot RAUW or delete CS.getInstruction() because it could be in the 1582 // live set of some other safepoint, in which case that safepoint's 1583 // PartiallyConstructedSafepointRecord will hold a raw pointer to this 1584 // llvm::Instruction. Instead, we defer the replacement and deletion to 1585 // after the live sets have been made explicit in the IR, and we no longer 1586 // have raw pointers to worry about. 1587 Replacements.emplace_back( 1588 DeferredReplacement::createRAUW(CS.getInstruction(), GCResult)); 1589 } else { 1590 Replacements.emplace_back( 1591 DeferredReplacement::createDelete(CS.getInstruction())); 1592 } 1593 } 1594 1595 Result.StatepointToken = Token; 1596 1597 // Second, create a gc.relocate for every live variable 1598 const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx(); 1599 CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, Token, Builder); 1600 } 1601 1602 // Replace an existing gc.statepoint with a new one and a set of gc.relocates 1603 // which make the relocations happening at this safepoint explicit. 1604 // 1605 // WARNING: Does not do any fixup to adjust users of the original live 1606 // values. That's the callers responsibility. 1607 static void 1608 makeStatepointExplicit(DominatorTree &DT, CallSite CS, 1609 PartiallyConstructedSafepointRecord &Result, 1610 std::vector<DeferredReplacement> &Replacements) { 1611 const auto &LiveSet = Result.LiveSet; 1612 const auto &PointerToBase = Result.PointerToBase; 1613 1614 // Convert to vector for efficient cross referencing. 1615 SmallVector<Value *, 64> BaseVec, LiveVec; 1616 LiveVec.reserve(LiveSet.size()); 1617 BaseVec.reserve(LiveSet.size()); 1618 for (Value *L : LiveSet) { 1619 LiveVec.push_back(L); 1620 assert(PointerToBase.count(L)); 1621 Value *Base = PointerToBase.find(L)->second; 1622 BaseVec.push_back(Base); 1623 } 1624 assert(LiveVec.size() == BaseVec.size()); 1625 1626 // Do the actual rewriting and delete the old statepoint 1627 makeStatepointExplicitImpl(CS, BaseVec, LiveVec, Result, Replacements); 1628 } 1629 1630 // Helper function for the relocationViaAlloca. 1631 // 1632 // It receives iterator to the statepoint gc relocates and emits a store to the 1633 // assigned location (via allocaMap) for the each one of them. It adds the 1634 // visited values into the visitedLiveValues set, which we will later use them 1635 // for sanity checking. 1636 static void 1637 insertRelocationStores(iterator_range<Value::user_iterator> GCRelocs, 1638 DenseMap<Value *, Value *> &AllocaMap, 1639 DenseSet<Value *> &VisitedLiveValues) { 1640 for (User *U : GCRelocs) { 1641 GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U); 1642 if (!Relocate) 1643 continue; 1644 1645 Value *OriginalValue = Relocate->getDerivedPtr(); 1646 assert(AllocaMap.count(OriginalValue)); 1647 Value *Alloca = AllocaMap[OriginalValue]; 1648 1649 // Emit store into the related alloca 1650 // All gc_relocates are i8 addrspace(1)* typed, and it must be bitcasted to 1651 // the correct type according to alloca. 1652 assert(Relocate->getNextNode() && 1653 "Should always have one since it's not a terminator"); 1654 IRBuilder<> Builder(Relocate->getNextNode()); 1655 Value *CastedRelocatedValue = 1656 Builder.CreateBitCast(Relocate, 1657 cast<AllocaInst>(Alloca)->getAllocatedType(), 1658 suffixed_name_or(Relocate, ".casted", "")); 1659 1660 StoreInst *Store = new StoreInst(CastedRelocatedValue, Alloca); 1661 Store->insertAfter(cast<Instruction>(CastedRelocatedValue)); 1662 1663 #ifndef NDEBUG 1664 VisitedLiveValues.insert(OriginalValue); 1665 #endif 1666 } 1667 } 1668 1669 // Helper function for the "relocationViaAlloca". Similar to the 1670 // "insertRelocationStores" but works for rematerialized values. 1671 static void insertRematerializationStores( 1672 const RematerializedValueMapTy &RematerializedValues, 1673 DenseMap<Value *, Value *> &AllocaMap, 1674 DenseSet<Value *> &VisitedLiveValues) { 1675 for (auto RematerializedValuePair: RematerializedValues) { 1676 Instruction *RematerializedValue = RematerializedValuePair.first; 1677 Value *OriginalValue = RematerializedValuePair.second; 1678 1679 assert(AllocaMap.count(OriginalValue) && 1680 "Can not find alloca for rematerialized value"); 1681 Value *Alloca = AllocaMap[OriginalValue]; 1682 1683 StoreInst *Store = new StoreInst(RematerializedValue, Alloca); 1684 Store->insertAfter(RematerializedValue); 1685 1686 #ifndef NDEBUG 1687 VisitedLiveValues.insert(OriginalValue); 1688 #endif 1689 } 1690 } 1691 1692 /// Do all the relocation update via allocas and mem2reg 1693 static void relocationViaAlloca( 1694 Function &F, DominatorTree &DT, ArrayRef<Value *> Live, 1695 ArrayRef<PartiallyConstructedSafepointRecord> Records) { 1696 #ifndef NDEBUG 1697 // record initial number of (static) allocas; we'll check we have the same 1698 // number when we get done. 1699 int InitialAllocaNum = 0; 1700 for (Instruction &I : F.getEntryBlock()) 1701 if (isa<AllocaInst>(I)) 1702 InitialAllocaNum++; 1703 #endif 1704 1705 // TODO-PERF: change data structures, reserve 1706 DenseMap<Value *, Value *> AllocaMap; 1707 SmallVector<AllocaInst *, 200> PromotableAllocas; 1708 // Used later to chack that we have enough allocas to store all values 1709 std::size_t NumRematerializedValues = 0; 1710 PromotableAllocas.reserve(Live.size()); 1711 1712 // Emit alloca for "LiveValue" and record it in "allocaMap" and 1713 // "PromotableAllocas" 1714 const DataLayout &DL = F.getParent()->getDataLayout(); 1715 auto emitAllocaFor = [&](Value *LiveValue) { 1716 AllocaInst *Alloca = new AllocaInst(LiveValue->getType(), 1717 DL.getAllocaAddrSpace(), "", 1718 F.getEntryBlock().getFirstNonPHI()); 1719 AllocaMap[LiveValue] = Alloca; 1720 PromotableAllocas.push_back(Alloca); 1721 }; 1722 1723 // Emit alloca for each live gc pointer 1724 for (Value *V : Live) 1725 emitAllocaFor(V); 1726 1727 // Emit allocas for rematerialized values 1728 for (const auto &Info : Records) 1729 for (auto RematerializedValuePair : Info.RematerializedValues) { 1730 Value *OriginalValue = RematerializedValuePair.second; 1731 if (AllocaMap.count(OriginalValue) != 0) 1732 continue; 1733 1734 emitAllocaFor(OriginalValue); 1735 ++NumRematerializedValues; 1736 } 1737 1738 // The next two loops are part of the same conceptual operation. We need to 1739 // insert a store to the alloca after the original def and at each 1740 // redefinition. We need to insert a load before each use. These are split 1741 // into distinct loops for performance reasons. 1742 1743 // Update gc pointer after each statepoint: either store a relocated value or 1744 // null (if no relocated value was found for this gc pointer and it is not a 1745 // gc_result). This must happen before we update the statepoint with load of 1746 // alloca otherwise we lose the link between statepoint and old def. 1747 for (const auto &Info : Records) { 1748 Value *Statepoint = Info.StatepointToken; 1749 1750 // This will be used for consistency check 1751 DenseSet<Value *> VisitedLiveValues; 1752 1753 // Insert stores for normal statepoint gc relocates 1754 insertRelocationStores(Statepoint->users(), AllocaMap, VisitedLiveValues); 1755 1756 // In case if it was invoke statepoint 1757 // we will insert stores for exceptional path gc relocates. 1758 if (isa<InvokeInst>(Statepoint)) { 1759 insertRelocationStores(Info.UnwindToken->users(), AllocaMap, 1760 VisitedLiveValues); 1761 } 1762 1763 // Do similar thing with rematerialized values 1764 insertRematerializationStores(Info.RematerializedValues, AllocaMap, 1765 VisitedLiveValues); 1766 1767 if (ClobberNonLive) { 1768 // As a debugging aid, pretend that an unrelocated pointer becomes null at 1769 // the gc.statepoint. This will turn some subtle GC problems into 1770 // slightly easier to debug SEGVs. Note that on large IR files with 1771 // lots of gc.statepoints this is extremely costly both memory and time 1772 // wise. 1773 SmallVector<AllocaInst *, 64> ToClobber; 1774 for (auto Pair : AllocaMap) { 1775 Value *Def = Pair.first; 1776 AllocaInst *Alloca = cast<AllocaInst>(Pair.second); 1777 1778 // This value was relocated 1779 if (VisitedLiveValues.count(Def)) { 1780 continue; 1781 } 1782 ToClobber.push_back(Alloca); 1783 } 1784 1785 auto InsertClobbersAt = [&](Instruction *IP) { 1786 for (auto *AI : ToClobber) { 1787 auto PT = cast<PointerType>(AI->getAllocatedType()); 1788 Constant *CPN = ConstantPointerNull::get(PT); 1789 StoreInst *Store = new StoreInst(CPN, AI); 1790 Store->insertBefore(IP); 1791 } 1792 }; 1793 1794 // Insert the clobbering stores. These may get intermixed with the 1795 // gc.results and gc.relocates, but that's fine. 1796 if (auto II = dyn_cast<InvokeInst>(Statepoint)) { 1797 InsertClobbersAt(&*II->getNormalDest()->getFirstInsertionPt()); 1798 InsertClobbersAt(&*II->getUnwindDest()->getFirstInsertionPt()); 1799 } else { 1800 InsertClobbersAt(cast<Instruction>(Statepoint)->getNextNode()); 1801 } 1802 } 1803 } 1804 1805 // Update use with load allocas and add store for gc_relocated. 1806 for (auto Pair : AllocaMap) { 1807 Value *Def = Pair.first; 1808 Value *Alloca = Pair.second; 1809 1810 // We pre-record the uses of allocas so that we dont have to worry about 1811 // later update that changes the user information.. 1812 1813 SmallVector<Instruction *, 20> Uses; 1814 // PERF: trade a linear scan for repeated reallocation 1815 Uses.reserve(Def->getNumUses()); 1816 for (User *U : Def->users()) { 1817 if (!isa<ConstantExpr>(U)) { 1818 // If the def has a ConstantExpr use, then the def is either a 1819 // ConstantExpr use itself or null. In either case 1820 // (recursively in the first, directly in the second), the oop 1821 // it is ultimately dependent on is null and this particular 1822 // use does not need to be fixed up. 1823 Uses.push_back(cast<Instruction>(U)); 1824 } 1825 } 1826 1827 llvm::sort(Uses.begin(), Uses.end()); 1828 auto Last = std::unique(Uses.begin(), Uses.end()); 1829 Uses.erase(Last, Uses.end()); 1830 1831 for (Instruction *Use : Uses) { 1832 if (isa<PHINode>(Use)) { 1833 PHINode *Phi = cast<PHINode>(Use); 1834 for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++) { 1835 if (Def == Phi->getIncomingValue(i)) { 1836 LoadInst *Load = new LoadInst( 1837 Alloca, "", Phi->getIncomingBlock(i)->getTerminator()); 1838 Phi->setIncomingValue(i, Load); 1839 } 1840 } 1841 } else { 1842 LoadInst *Load = new LoadInst(Alloca, "", Use); 1843 Use->replaceUsesOfWith(Def, Load); 1844 } 1845 } 1846 1847 // Emit store for the initial gc value. Store must be inserted after load, 1848 // otherwise store will be in alloca's use list and an extra load will be 1849 // inserted before it. 1850 StoreInst *Store = new StoreInst(Def, Alloca); 1851 if (Instruction *Inst = dyn_cast<Instruction>(Def)) { 1852 if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) { 1853 // InvokeInst is a TerminatorInst so the store need to be inserted 1854 // into its normal destination block. 1855 BasicBlock *NormalDest = Invoke->getNormalDest(); 1856 Store->insertBefore(NormalDest->getFirstNonPHI()); 1857 } else { 1858 assert(!Inst->isTerminator() && 1859 "The only TerminatorInst that can produce a value is " 1860 "InvokeInst which is handled above."); 1861 Store->insertAfter(Inst); 1862 } 1863 } else { 1864 assert(isa<Argument>(Def)); 1865 Store->insertAfter(cast<Instruction>(Alloca)); 1866 } 1867 } 1868 1869 assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues && 1870 "we must have the same allocas with lives"); 1871 if (!PromotableAllocas.empty()) { 1872 // Apply mem2reg to promote alloca to SSA 1873 PromoteMemToReg(PromotableAllocas, DT); 1874 } 1875 1876 #ifndef NDEBUG 1877 for (auto &I : F.getEntryBlock()) 1878 if (isa<AllocaInst>(I)) 1879 InitialAllocaNum--; 1880 assert(InitialAllocaNum == 0 && "We must not introduce any extra allocas"); 1881 #endif 1882 } 1883 1884 /// Implement a unique function which doesn't require we sort the input 1885 /// vector. Doing so has the effect of changing the output of a couple of 1886 /// tests in ways which make them less useful in testing fused safepoints. 1887 template <typename T> static void unique_unsorted(SmallVectorImpl<T> &Vec) { 1888 SmallSet<T, 8> Seen; 1889 Vec.erase(remove_if(Vec, [&](const T &V) { return !Seen.insert(V).second; }), 1890 Vec.end()); 1891 } 1892 1893 /// Insert holders so that each Value is obviously live through the entire 1894 /// lifetime of the call. 1895 static void insertUseHolderAfter(CallSite &CS, const ArrayRef<Value *> Values, 1896 SmallVectorImpl<CallInst *> &Holders) { 1897 if (Values.empty()) 1898 // No values to hold live, might as well not insert the empty holder 1899 return; 1900 1901 Module *M = CS.getInstruction()->getModule(); 1902 // Use a dummy vararg function to actually hold the values live 1903 Function *Func = cast<Function>(M->getOrInsertFunction( 1904 "__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true))); 1905 if (CS.isCall()) { 1906 // For call safepoints insert dummy calls right after safepoint 1907 Holders.push_back(CallInst::Create(Func, Values, "", 1908 &*++CS.getInstruction()->getIterator())); 1909 return; 1910 } 1911 // For invoke safepooints insert dummy calls both in normal and 1912 // exceptional destination blocks 1913 auto *II = cast<InvokeInst>(CS.getInstruction()); 1914 Holders.push_back(CallInst::Create( 1915 Func, Values, "", &*II->getNormalDest()->getFirstInsertionPt())); 1916 Holders.push_back(CallInst::Create( 1917 Func, Values, "", &*II->getUnwindDest()->getFirstInsertionPt())); 1918 } 1919 1920 static void findLiveReferences( 1921 Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate, 1922 MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) { 1923 GCPtrLivenessData OriginalLivenessData; 1924 computeLiveInValues(DT, F, OriginalLivenessData); 1925 for (size_t i = 0; i < records.size(); i++) { 1926 struct PartiallyConstructedSafepointRecord &info = records[i]; 1927 analyzeParsePointLiveness(DT, OriginalLivenessData, toUpdate[i], info); 1928 } 1929 } 1930 1931 // Helper function for the "rematerializeLiveValues". It walks use chain 1932 // starting from the "CurrentValue" until it reaches the root of the chain, i.e. 1933 // the base or a value it cannot process. Only "simple" values are processed 1934 // (currently it is GEP's and casts). The returned root is examined by the 1935 // callers of findRematerializableChainToBasePointer. Fills "ChainToBase" array 1936 // with all visited values. 1937 static Value* findRematerializableChainToBasePointer( 1938 SmallVectorImpl<Instruction*> &ChainToBase, 1939 Value *CurrentValue) { 1940 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) { 1941 ChainToBase.push_back(GEP); 1942 return findRematerializableChainToBasePointer(ChainToBase, 1943 GEP->getPointerOperand()); 1944 } 1945 1946 if (CastInst *CI = dyn_cast<CastInst>(CurrentValue)) { 1947 if (!CI->isNoopCast(CI->getModule()->getDataLayout())) 1948 return CI; 1949 1950 ChainToBase.push_back(CI); 1951 return findRematerializableChainToBasePointer(ChainToBase, 1952 CI->getOperand(0)); 1953 } 1954 1955 // We have reached the root of the chain, which is either equal to the base or 1956 // is the first unsupported value along the use chain. 1957 return CurrentValue; 1958 } 1959 1960 // Helper function for the "rematerializeLiveValues". Compute cost of the use 1961 // chain we are going to rematerialize. 1962 static unsigned 1963 chainToBasePointerCost(SmallVectorImpl<Instruction*> &Chain, 1964 TargetTransformInfo &TTI) { 1965 unsigned Cost = 0; 1966 1967 for (Instruction *Instr : Chain) { 1968 if (CastInst *CI = dyn_cast<CastInst>(Instr)) { 1969 assert(CI->isNoopCast(CI->getModule()->getDataLayout()) && 1970 "non noop cast is found during rematerialization"); 1971 1972 Type *SrcTy = CI->getOperand(0)->getType(); 1973 Cost += TTI.getCastInstrCost(CI->getOpcode(), CI->getType(), SrcTy, CI); 1974 1975 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Instr)) { 1976 // Cost of the address calculation 1977 Type *ValTy = GEP->getSourceElementType(); 1978 Cost += TTI.getAddressComputationCost(ValTy); 1979 1980 // And cost of the GEP itself 1981 // TODO: Use TTI->getGEPCost here (it exists, but appears to be not 1982 // allowed for the external usage) 1983 if (!GEP->hasAllConstantIndices()) 1984 Cost += 2; 1985 1986 } else { 1987 llvm_unreachable("unsupported instruction type during rematerialization"); 1988 } 1989 } 1990 1991 return Cost; 1992 } 1993 1994 static bool AreEquivalentPhiNodes(PHINode &OrigRootPhi, PHINode &AlternateRootPhi) { 1995 unsigned PhiNum = OrigRootPhi.getNumIncomingValues(); 1996 if (PhiNum != AlternateRootPhi.getNumIncomingValues() || 1997 OrigRootPhi.getParent() != AlternateRootPhi.getParent()) 1998 return false; 1999 // Map of incoming values and their corresponding basic blocks of 2000 // OrigRootPhi. 2001 SmallDenseMap<Value *, BasicBlock *, 8> CurrentIncomingValues; 2002 for (unsigned i = 0; i < PhiNum; i++) 2003 CurrentIncomingValues[OrigRootPhi.getIncomingValue(i)] = 2004 OrigRootPhi.getIncomingBlock(i); 2005 2006 // Both current and base PHIs should have same incoming values and 2007 // the same basic blocks corresponding to the incoming values. 2008 for (unsigned i = 0; i < PhiNum; i++) { 2009 auto CIVI = 2010 CurrentIncomingValues.find(AlternateRootPhi.getIncomingValue(i)); 2011 if (CIVI == CurrentIncomingValues.end()) 2012 return false; 2013 BasicBlock *CurrentIncomingBB = CIVI->second; 2014 if (CurrentIncomingBB != AlternateRootPhi.getIncomingBlock(i)) 2015 return false; 2016 } 2017 return true; 2018 } 2019 2020 // From the statepoint live set pick values that are cheaper to recompute then 2021 // to relocate. Remove this values from the live set, rematerialize them after 2022 // statepoint and record them in "Info" structure. Note that similar to 2023 // relocated values we don't do any user adjustments here. 2024 static void rematerializeLiveValues(CallSite CS, 2025 PartiallyConstructedSafepointRecord &Info, 2026 TargetTransformInfo &TTI) { 2027 const unsigned int ChainLengthThreshold = 10; 2028 2029 // Record values we are going to delete from this statepoint live set. 2030 // We can not di this in following loop due to iterator invalidation. 2031 SmallVector<Value *, 32> LiveValuesToBeDeleted; 2032 2033 for (Value *LiveValue: Info.LiveSet) { 2034 // For each live pointer find its defining chain 2035 SmallVector<Instruction *, 3> ChainToBase; 2036 assert(Info.PointerToBase.count(LiveValue)); 2037 Value *RootOfChain = 2038 findRematerializableChainToBasePointer(ChainToBase, 2039 LiveValue); 2040 2041 // Nothing to do, or chain is too long 2042 if ( ChainToBase.size() == 0 || 2043 ChainToBase.size() > ChainLengthThreshold) 2044 continue; 2045 2046 // Handle the scenario where the RootOfChain is not equal to the 2047 // Base Value, but they are essentially the same phi values. 2048 if (RootOfChain != Info.PointerToBase[LiveValue]) { 2049 PHINode *OrigRootPhi = dyn_cast<PHINode>(RootOfChain); 2050 PHINode *AlternateRootPhi = dyn_cast<PHINode>(Info.PointerToBase[LiveValue]); 2051 if (!OrigRootPhi || !AlternateRootPhi) 2052 continue; 2053 // PHI nodes that have the same incoming values, and belonging to the same 2054 // basic blocks are essentially the same SSA value. When the original phi 2055 // has incoming values with different base pointers, the original phi is 2056 // marked as conflict, and an additional `AlternateRootPhi` with the same 2057 // incoming values get generated by the findBasePointer function. We need 2058 // to identify the newly generated AlternateRootPhi (.base version of phi) 2059 // and RootOfChain (the original phi node itself) are the same, so that we 2060 // can rematerialize the gep and casts. This is a workaround for the 2061 // deficiency in the findBasePointer algorithm. 2062 if (!AreEquivalentPhiNodes(*OrigRootPhi, *AlternateRootPhi)) 2063 continue; 2064 // Now that the phi nodes are proved to be the same, assert that 2065 // findBasePointer's newly generated AlternateRootPhi is present in the 2066 // liveset of the call. 2067 assert(Info.LiveSet.count(AlternateRootPhi)); 2068 } 2069 // Compute cost of this chain 2070 unsigned Cost = chainToBasePointerCost(ChainToBase, TTI); 2071 // TODO: We can also account for cases when we will be able to remove some 2072 // of the rematerialized values by later optimization passes. I.e if 2073 // we rematerialized several intersecting chains. Or if original values 2074 // don't have any uses besides this statepoint. 2075 2076 // For invokes we need to rematerialize each chain twice - for normal and 2077 // for unwind basic blocks. Model this by multiplying cost by two. 2078 if (CS.isInvoke()) { 2079 Cost *= 2; 2080 } 2081 // If it's too expensive - skip it 2082 if (Cost >= RematerializationThreshold) 2083 continue; 2084 2085 // Remove value from the live set 2086 LiveValuesToBeDeleted.push_back(LiveValue); 2087 2088 // Clone instructions and record them inside "Info" structure 2089 2090 // Walk backwards to visit top-most instructions first 2091 std::reverse(ChainToBase.begin(), ChainToBase.end()); 2092 2093 // Utility function which clones all instructions from "ChainToBase" 2094 // and inserts them before "InsertBefore". Returns rematerialized value 2095 // which should be used after statepoint. 2096 auto rematerializeChain = [&ChainToBase]( 2097 Instruction *InsertBefore, Value *RootOfChain, Value *AlternateLiveBase) { 2098 Instruction *LastClonedValue = nullptr; 2099 Instruction *LastValue = nullptr; 2100 for (Instruction *Instr: ChainToBase) { 2101 // Only GEP's and casts are supported as we need to be careful to not 2102 // introduce any new uses of pointers not in the liveset. 2103 // Note that it's fine to introduce new uses of pointers which were 2104 // otherwise not used after this statepoint. 2105 assert(isa<GetElementPtrInst>(Instr) || isa<CastInst>(Instr)); 2106 2107 Instruction *ClonedValue = Instr->clone(); 2108 ClonedValue->insertBefore(InsertBefore); 2109 ClonedValue->setName(Instr->getName() + ".remat"); 2110 2111 // If it is not first instruction in the chain then it uses previously 2112 // cloned value. We should update it to use cloned value. 2113 if (LastClonedValue) { 2114 assert(LastValue); 2115 ClonedValue->replaceUsesOfWith(LastValue, LastClonedValue); 2116 #ifndef NDEBUG 2117 for (auto OpValue : ClonedValue->operand_values()) { 2118 // Assert that cloned instruction does not use any instructions from 2119 // this chain other than LastClonedValue 2120 assert(!is_contained(ChainToBase, OpValue) && 2121 "incorrect use in rematerialization chain"); 2122 // Assert that the cloned instruction does not use the RootOfChain 2123 // or the AlternateLiveBase. 2124 assert(OpValue != RootOfChain && OpValue != AlternateLiveBase); 2125 } 2126 #endif 2127 } else { 2128 // For the first instruction, replace the use of unrelocated base i.e. 2129 // RootOfChain/OrigRootPhi, with the corresponding PHI present in the 2130 // live set. They have been proved to be the same PHI nodes. Note 2131 // that the *only* use of the RootOfChain in the ChainToBase list is 2132 // the first Value in the list. 2133 if (RootOfChain != AlternateLiveBase) 2134 ClonedValue->replaceUsesOfWith(RootOfChain, AlternateLiveBase); 2135 } 2136 2137 LastClonedValue = ClonedValue; 2138 LastValue = Instr; 2139 } 2140 assert(LastClonedValue); 2141 return LastClonedValue; 2142 }; 2143 2144 // Different cases for calls and invokes. For invokes we need to clone 2145 // instructions both on normal and unwind path. 2146 if (CS.isCall()) { 2147 Instruction *InsertBefore = CS.getInstruction()->getNextNode(); 2148 assert(InsertBefore); 2149 Instruction *RematerializedValue = rematerializeChain( 2150 InsertBefore, RootOfChain, Info.PointerToBase[LiveValue]); 2151 Info.RematerializedValues[RematerializedValue] = LiveValue; 2152 } else { 2153 InvokeInst *Invoke = cast<InvokeInst>(CS.getInstruction()); 2154 2155 Instruction *NormalInsertBefore = 2156 &*Invoke->getNormalDest()->getFirstInsertionPt(); 2157 Instruction *UnwindInsertBefore = 2158 &*Invoke->getUnwindDest()->getFirstInsertionPt(); 2159 2160 Instruction *NormalRematerializedValue = rematerializeChain( 2161 NormalInsertBefore, RootOfChain, Info.PointerToBase[LiveValue]); 2162 Instruction *UnwindRematerializedValue = rematerializeChain( 2163 UnwindInsertBefore, RootOfChain, Info.PointerToBase[LiveValue]); 2164 2165 Info.RematerializedValues[NormalRematerializedValue] = LiveValue; 2166 Info.RematerializedValues[UnwindRematerializedValue] = LiveValue; 2167 } 2168 } 2169 2170 // Remove rematerializaed values from the live set 2171 for (auto LiveValue: LiveValuesToBeDeleted) { 2172 Info.LiveSet.remove(LiveValue); 2173 } 2174 } 2175 2176 static bool insertParsePoints(Function &F, DominatorTree &DT, 2177 TargetTransformInfo &TTI, 2178 SmallVectorImpl<CallSite> &ToUpdate) { 2179 #ifndef NDEBUG 2180 // sanity check the input 2181 std::set<CallSite> Uniqued; 2182 Uniqued.insert(ToUpdate.begin(), ToUpdate.end()); 2183 assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!"); 2184 2185 for (CallSite CS : ToUpdate) 2186 assert(CS.getInstruction()->getFunction() == &F); 2187 #endif 2188 2189 // When inserting gc.relocates for invokes, we need to be able to insert at 2190 // the top of the successor blocks. See the comment on 2191 // normalForInvokeSafepoint on exactly what is needed. Note that this step 2192 // may restructure the CFG. 2193 for (CallSite CS : ToUpdate) { 2194 if (!CS.isInvoke()) 2195 continue; 2196 auto *II = cast<InvokeInst>(CS.getInstruction()); 2197 normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT); 2198 normalizeForInvokeSafepoint(II->getUnwindDest(), II->getParent(), DT); 2199 } 2200 2201 // A list of dummy calls added to the IR to keep various values obviously 2202 // live in the IR. We'll remove all of these when done. 2203 SmallVector<CallInst *, 64> Holders; 2204 2205 // Insert a dummy call with all of the deopt operands we'll need for the 2206 // actual safepoint insertion as arguments. This ensures reference operands 2207 // in the deopt argument list are considered live through the safepoint (and 2208 // thus makes sure they get relocated.) 2209 for (CallSite CS : ToUpdate) { 2210 SmallVector<Value *, 64> DeoptValues; 2211 2212 for (Value *Arg : GetDeoptBundleOperands(CS)) { 2213 assert(!isUnhandledGCPointerType(Arg->getType()) && 2214 "support for FCA unimplemented"); 2215 if (isHandledGCPointerType(Arg->getType())) 2216 DeoptValues.push_back(Arg); 2217 } 2218 2219 insertUseHolderAfter(CS, DeoptValues, Holders); 2220 } 2221 2222 SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size()); 2223 2224 // A) Identify all gc pointers which are statically live at the given call 2225 // site. 2226 findLiveReferences(F, DT, ToUpdate, Records); 2227 2228 // B) Find the base pointers for each live pointer 2229 /* scope for caching */ { 2230 // Cache the 'defining value' relation used in the computation and 2231 // insertion of base phis and selects. This ensures that we don't insert 2232 // large numbers of duplicate base_phis. 2233 DefiningValueMapTy DVCache; 2234 2235 for (size_t i = 0; i < Records.size(); i++) { 2236 PartiallyConstructedSafepointRecord &info = Records[i]; 2237 findBasePointers(DT, DVCache, ToUpdate[i], info); 2238 } 2239 } // end of cache scope 2240 2241 // The base phi insertion logic (for any safepoint) may have inserted new 2242 // instructions which are now live at some safepoint. The simplest such 2243 // example is: 2244 // loop: 2245 // phi a <-- will be a new base_phi here 2246 // safepoint 1 <-- that needs to be live here 2247 // gep a + 1 2248 // safepoint 2 2249 // br loop 2250 // We insert some dummy calls after each safepoint to definitely hold live 2251 // the base pointers which were identified for that safepoint. We'll then 2252 // ask liveness for _every_ base inserted to see what is now live. Then we 2253 // remove the dummy calls. 2254 Holders.reserve(Holders.size() + Records.size()); 2255 for (size_t i = 0; i < Records.size(); i++) { 2256 PartiallyConstructedSafepointRecord &Info = Records[i]; 2257 2258 SmallVector<Value *, 128> Bases; 2259 for (auto Pair : Info.PointerToBase) 2260 Bases.push_back(Pair.second); 2261 2262 insertUseHolderAfter(ToUpdate[i], Bases, Holders); 2263 } 2264 2265 // By selecting base pointers, we've effectively inserted new uses. Thus, we 2266 // need to rerun liveness. We may *also* have inserted new defs, but that's 2267 // not the key issue. 2268 recomputeLiveInValues(F, DT, ToUpdate, Records); 2269 2270 if (PrintBasePointers) { 2271 for (auto &Info : Records) { 2272 errs() << "Base Pairs: (w/Relocation)\n"; 2273 for (auto Pair : Info.PointerToBase) { 2274 errs() << " derived "; 2275 Pair.first->printAsOperand(errs(), false); 2276 errs() << " base "; 2277 Pair.second->printAsOperand(errs(), false); 2278 errs() << "\n"; 2279 } 2280 } 2281 } 2282 2283 // It is possible that non-constant live variables have a constant base. For 2284 // example, a GEP with a variable offset from a global. In this case we can 2285 // remove it from the liveset. We already don't add constants to the liveset 2286 // because we assume they won't move at runtime and the GC doesn't need to be 2287 // informed about them. The same reasoning applies if the base is constant. 2288 // Note that the relocation placement code relies on this filtering for 2289 // correctness as it expects the base to be in the liveset, which isn't true 2290 // if the base is constant. 2291 for (auto &Info : Records) 2292 for (auto &BasePair : Info.PointerToBase) 2293 if (isa<Constant>(BasePair.second)) 2294 Info.LiveSet.remove(BasePair.first); 2295 2296 for (CallInst *CI : Holders) 2297 CI->eraseFromParent(); 2298 2299 Holders.clear(); 2300 2301 // In order to reduce live set of statepoint we might choose to rematerialize 2302 // some values instead of relocating them. This is purely an optimization and 2303 // does not influence correctness. 2304 for (size_t i = 0; i < Records.size(); i++) 2305 rematerializeLiveValues(ToUpdate[i], Records[i], TTI); 2306 2307 // We need this to safely RAUW and delete call or invoke return values that 2308 // may themselves be live over a statepoint. For details, please see usage in 2309 // makeStatepointExplicitImpl. 2310 std::vector<DeferredReplacement> Replacements; 2311 2312 // Now run through and replace the existing statepoints with new ones with 2313 // the live variables listed. We do not yet update uses of the values being 2314 // relocated. We have references to live variables that need to 2315 // survive to the last iteration of this loop. (By construction, the 2316 // previous statepoint can not be a live variable, thus we can and remove 2317 // the old statepoint calls as we go.) 2318 for (size_t i = 0; i < Records.size(); i++) 2319 makeStatepointExplicit(DT, ToUpdate[i], Records[i], Replacements); 2320 2321 ToUpdate.clear(); // prevent accident use of invalid CallSites 2322 2323 for (auto &PR : Replacements) 2324 PR.doReplacement(); 2325 2326 Replacements.clear(); 2327 2328 for (auto &Info : Records) { 2329 // These live sets may contain state Value pointers, since we replaced calls 2330 // with operand bundles with calls wrapped in gc.statepoint, and some of 2331 // those calls may have been def'ing live gc pointers. Clear these out to 2332 // avoid accidentally using them. 2333 // 2334 // TODO: We should create a separate data structure that does not contain 2335 // these live sets, and migrate to using that data structure from this point 2336 // onward. 2337 Info.LiveSet.clear(); 2338 Info.PointerToBase.clear(); 2339 } 2340 2341 // Do all the fixups of the original live variables to their relocated selves 2342 SmallVector<Value *, 128> Live; 2343 for (size_t i = 0; i < Records.size(); i++) { 2344 PartiallyConstructedSafepointRecord &Info = Records[i]; 2345 2346 // We can't simply save the live set from the original insertion. One of 2347 // the live values might be the result of a call which needs a safepoint. 2348 // That Value* no longer exists and we need to use the new gc_result. 2349 // Thankfully, the live set is embedded in the statepoint (and updated), so 2350 // we just grab that. 2351 Statepoint Statepoint(Info.StatepointToken); 2352 Live.insert(Live.end(), Statepoint.gc_args_begin(), 2353 Statepoint.gc_args_end()); 2354 #ifndef NDEBUG 2355 // Do some basic sanity checks on our liveness results before performing 2356 // relocation. Relocation can and will turn mistakes in liveness results 2357 // into non-sensical code which is must harder to debug. 2358 // TODO: It would be nice to test consistency as well 2359 assert(DT.isReachableFromEntry(Info.StatepointToken->getParent()) && 2360 "statepoint must be reachable or liveness is meaningless"); 2361 for (Value *V : Statepoint.gc_args()) { 2362 if (!isa<Instruction>(V)) 2363 // Non-instruction values trivial dominate all possible uses 2364 continue; 2365 auto *LiveInst = cast<Instruction>(V); 2366 assert(DT.isReachableFromEntry(LiveInst->getParent()) && 2367 "unreachable values should never be live"); 2368 assert(DT.dominates(LiveInst, Info.StatepointToken) && 2369 "basic SSA liveness expectation violated by liveness analysis"); 2370 } 2371 #endif 2372 } 2373 unique_unsorted(Live); 2374 2375 #ifndef NDEBUG 2376 // sanity check 2377 for (auto *Ptr : Live) 2378 assert(isHandledGCPointerType(Ptr->getType()) && 2379 "must be a gc pointer type"); 2380 #endif 2381 2382 relocationViaAlloca(F, DT, Live, Records); 2383 return !Records.empty(); 2384 } 2385 2386 // Handles both return values and arguments for Functions and CallSites. 2387 template <typename AttrHolder> 2388 static void RemoveNonValidAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH, 2389 unsigned Index) { 2390 AttrBuilder R; 2391 if (AH.getDereferenceableBytes(Index)) 2392 R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable, 2393 AH.getDereferenceableBytes(Index))); 2394 if (AH.getDereferenceableOrNullBytes(Index)) 2395 R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull, 2396 AH.getDereferenceableOrNullBytes(Index))); 2397 if (AH.getAttributes().hasAttribute(Index, Attribute::NoAlias)) 2398 R.addAttribute(Attribute::NoAlias); 2399 2400 if (!R.empty()) 2401 AH.setAttributes(AH.getAttributes().removeAttributes(Ctx, Index, R)); 2402 } 2403 2404 static void stripNonValidAttributesFromPrototype(Function &F) { 2405 LLVMContext &Ctx = F.getContext(); 2406 2407 for (Argument &A : F.args()) 2408 if (isa<PointerType>(A.getType())) 2409 RemoveNonValidAttrAtIndex(Ctx, F, 2410 A.getArgNo() + AttributeList::FirstArgIndex); 2411 2412 if (isa<PointerType>(F.getReturnType())) 2413 RemoveNonValidAttrAtIndex(Ctx, F, AttributeList::ReturnIndex); 2414 } 2415 2416 /// Certain metadata on instructions are invalid after running RS4GC. 2417 /// Optimizations that run after RS4GC can incorrectly use this metadata to 2418 /// optimize functions. We drop such metadata on the instruction. 2419 static void stripInvalidMetadataFromInstruction(Instruction &I) { 2420 if (!isa<LoadInst>(I) && !isa<StoreInst>(I)) 2421 return; 2422 // These are the attributes that are still valid on loads and stores after 2423 // RS4GC. 2424 // The metadata implying dereferenceability and noalias are (conservatively) 2425 // dropped. This is because semantically, after RewriteStatepointsForGC runs, 2426 // all calls to gc.statepoint "free" the entire heap. Also, gc.statepoint can 2427 // touch the entire heap including noalias objects. Note: The reasoning is 2428 // same as stripping the dereferenceability and noalias attributes that are 2429 // analogous to the metadata counterparts. 2430 // We also drop the invariant.load metadata on the load because that metadata 2431 // implies the address operand to the load points to memory that is never 2432 // changed once it became dereferenceable. This is no longer true after RS4GC. 2433 // Similar reasoning applies to invariant.group metadata, which applies to 2434 // loads within a group. 2435 unsigned ValidMetadataAfterRS4GC[] = {LLVMContext::MD_tbaa, 2436 LLVMContext::MD_range, 2437 LLVMContext::MD_alias_scope, 2438 LLVMContext::MD_nontemporal, 2439 LLVMContext::MD_nonnull, 2440 LLVMContext::MD_align, 2441 LLVMContext::MD_type}; 2442 2443 // Drops all metadata on the instruction other than ValidMetadataAfterRS4GC. 2444 I.dropUnknownNonDebugMetadata(ValidMetadataAfterRS4GC); 2445 } 2446 2447 static void stripNonValidDataFromBody(Function &F) { 2448 if (F.empty()) 2449 return; 2450 2451 LLVMContext &Ctx = F.getContext(); 2452 MDBuilder Builder(Ctx); 2453 2454 // Set of invariantstart instructions that we need to remove. 2455 // Use this to avoid invalidating the instruction iterator. 2456 SmallVector<IntrinsicInst*, 12> InvariantStartInstructions; 2457 2458 for (Instruction &I : instructions(F)) { 2459 // invariant.start on memory location implies that the referenced memory 2460 // location is constant and unchanging. This is no longer true after 2461 // RewriteStatepointsForGC runs because there can be calls to gc.statepoint 2462 // which frees the entire heap and the presence of invariant.start allows 2463 // the optimizer to sink the load of a memory location past a statepoint, 2464 // which is incorrect. 2465 if (auto *II = dyn_cast<IntrinsicInst>(&I)) 2466 if (II->getIntrinsicID() == Intrinsic::invariant_start) { 2467 InvariantStartInstructions.push_back(II); 2468 continue; 2469 } 2470 2471 if (MDNode *Tag = I.getMetadata(LLVMContext::MD_tbaa)) { 2472 MDNode *MutableTBAA = Builder.createMutableTBAAAccessTag(Tag); 2473 I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA); 2474 } 2475 2476 stripInvalidMetadataFromInstruction(I); 2477 2478 if (CallSite CS = CallSite(&I)) { 2479 for (int i = 0, e = CS.arg_size(); i != e; i++) 2480 if (isa<PointerType>(CS.getArgument(i)->getType())) 2481 RemoveNonValidAttrAtIndex(Ctx, CS, i + AttributeList::FirstArgIndex); 2482 if (isa<PointerType>(CS.getType())) 2483 RemoveNonValidAttrAtIndex(Ctx, CS, AttributeList::ReturnIndex); 2484 } 2485 } 2486 2487 // Delete the invariant.start instructions and RAUW undef. 2488 for (auto *II : InvariantStartInstructions) { 2489 II->replaceAllUsesWith(UndefValue::get(II->getType())); 2490 II->eraseFromParent(); 2491 } 2492 } 2493 2494 /// Returns true if this function should be rewritten by this pass. The main 2495 /// point of this function is as an extension point for custom logic. 2496 static bool shouldRewriteStatepointsIn(Function &F) { 2497 // TODO: This should check the GCStrategy 2498 if (F.hasGC()) { 2499 const auto &FunctionGCName = F.getGC(); 2500 const StringRef StatepointExampleName("statepoint-example"); 2501 const StringRef CoreCLRName("coreclr"); 2502 return (StatepointExampleName == FunctionGCName) || 2503 (CoreCLRName == FunctionGCName); 2504 } else 2505 return false; 2506 } 2507 2508 static void stripNonValidData(Module &M) { 2509 #ifndef NDEBUG 2510 assert(llvm::any_of(M, shouldRewriteStatepointsIn) && "precondition!"); 2511 #endif 2512 2513 for (Function &F : M) 2514 stripNonValidAttributesFromPrototype(F); 2515 2516 for (Function &F : M) 2517 stripNonValidDataFromBody(F); 2518 } 2519 2520 bool RewriteStatepointsForGC::runOnFunction(Function &F, DominatorTree &DT, 2521 TargetTransformInfo &TTI, 2522 const TargetLibraryInfo &TLI) { 2523 assert(!F.isDeclaration() && !F.empty() && 2524 "need function body to rewrite statepoints in"); 2525 assert(shouldRewriteStatepointsIn(F) && "mismatch in rewrite decision"); 2526 2527 auto NeedsRewrite = [&TLI](Instruction &I) { 2528 if (ImmutableCallSite CS = ImmutableCallSite(&I)) 2529 return !callsGCLeafFunction(CS, TLI) && !isStatepoint(CS); 2530 return false; 2531 }; 2532 2533 2534 // Delete any unreachable statepoints so that we don't have unrewritten 2535 // statepoints surviving this pass. This makes testing easier and the 2536 // resulting IR less confusing to human readers. 2537 DeferredDominance DD(DT); 2538 bool MadeChange = removeUnreachableBlocks(F, nullptr, &DD); 2539 DD.flush(); 2540 2541 // Gather all the statepoints which need rewritten. Be careful to only 2542 // consider those in reachable code since we need to ask dominance queries 2543 // when rewriting. We'll delete the unreachable ones in a moment. 2544 SmallVector<CallSite, 64> ParsePointNeeded; 2545 for (Instruction &I : instructions(F)) { 2546 // TODO: only the ones with the flag set! 2547 if (NeedsRewrite(I)) { 2548 // NOTE removeUnreachableBlocks() is stronger than 2549 // DominatorTree::isReachableFromEntry(). In other words 2550 // removeUnreachableBlocks can remove some blocks for which 2551 // isReachableFromEntry() returns true. 2552 assert(DT.isReachableFromEntry(I.getParent()) && 2553 "no unreachable blocks expected"); 2554 ParsePointNeeded.push_back(CallSite(&I)); 2555 } 2556 } 2557 2558 // Return early if no work to do. 2559 if (ParsePointNeeded.empty()) 2560 return MadeChange; 2561 2562 // As a prepass, go ahead and aggressively destroy single entry phi nodes. 2563 // These are created by LCSSA. They have the effect of increasing the size 2564 // of liveness sets for no good reason. It may be harder to do this post 2565 // insertion since relocations and base phis can confuse things. 2566 for (BasicBlock &BB : F) 2567 if (BB.getUniquePredecessor()) { 2568 MadeChange = true; 2569 FoldSingleEntryPHINodes(&BB); 2570 } 2571 2572 // Before we start introducing relocations, we want to tweak the IR a bit to 2573 // avoid unfortunate code generation effects. The main example is that we 2574 // want to try to make sure the comparison feeding a branch is after any 2575 // safepoints. Otherwise, we end up with a comparison of pre-relocation 2576 // values feeding a branch after relocation. This is semantically correct, 2577 // but results in extra register pressure since both the pre-relocation and 2578 // post-relocation copies must be available in registers. For code without 2579 // relocations this is handled elsewhere, but teaching the scheduler to 2580 // reverse the transform we're about to do would be slightly complex. 2581 // Note: This may extend the live range of the inputs to the icmp and thus 2582 // increase the liveset of any statepoint we move over. This is profitable 2583 // as long as all statepoints are in rare blocks. If we had in-register 2584 // lowering for live values this would be a much safer transform. 2585 auto getConditionInst = [](TerminatorInst *TI) -> Instruction* { 2586 if (auto *BI = dyn_cast<BranchInst>(TI)) 2587 if (BI->isConditional()) 2588 return dyn_cast<Instruction>(BI->getCondition()); 2589 // TODO: Extend this to handle switches 2590 return nullptr; 2591 }; 2592 for (BasicBlock &BB : F) { 2593 TerminatorInst *TI = BB.getTerminator(); 2594 if (auto *Cond = getConditionInst(TI)) 2595 // TODO: Handle more than just ICmps here. We should be able to move 2596 // most instructions without side effects or memory access. 2597 if (isa<ICmpInst>(Cond) && Cond->hasOneUse()) { 2598 MadeChange = true; 2599 Cond->moveBefore(TI); 2600 } 2601 } 2602 2603 MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded); 2604 return MadeChange; 2605 } 2606 2607 // liveness computation via standard dataflow 2608 // ------------------------------------------------------------------- 2609 2610 // TODO: Consider using bitvectors for liveness, the set of potentially 2611 // interesting values should be small and easy to pre-compute. 2612 2613 /// Compute the live-in set for the location rbegin starting from 2614 /// the live-out set of the basic block 2615 static void computeLiveInValues(BasicBlock::reverse_iterator Begin, 2616 BasicBlock::reverse_iterator End, 2617 SetVector<Value *> &LiveTmp) { 2618 for (auto &I : make_range(Begin, End)) { 2619 // KILL/Def - Remove this definition from LiveIn 2620 LiveTmp.remove(&I); 2621 2622 // Don't consider *uses* in PHI nodes, we handle their contribution to 2623 // predecessor blocks when we seed the LiveOut sets 2624 if (isa<PHINode>(I)) 2625 continue; 2626 2627 // USE - Add to the LiveIn set for this instruction 2628 for (Value *V : I.operands()) { 2629 assert(!isUnhandledGCPointerType(V->getType()) && 2630 "support for FCA unimplemented"); 2631 if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) { 2632 // The choice to exclude all things constant here is slightly subtle. 2633 // There are two independent reasons: 2634 // - We assume that things which are constant (from LLVM's definition) 2635 // do not move at runtime. For example, the address of a global 2636 // variable is fixed, even though it's contents may not be. 2637 // - Second, we can't disallow arbitrary inttoptr constants even 2638 // if the language frontend does. Optimization passes are free to 2639 // locally exploit facts without respect to global reachability. This 2640 // can create sections of code which are dynamically unreachable and 2641 // contain just about anything. (see constants.ll in tests) 2642 LiveTmp.insert(V); 2643 } 2644 } 2645 } 2646 } 2647 2648 static void computeLiveOutSeed(BasicBlock *BB, SetVector<Value *> &LiveTmp) { 2649 for (BasicBlock *Succ : successors(BB)) { 2650 for (auto &I : *Succ) { 2651 PHINode *PN = dyn_cast<PHINode>(&I); 2652 if (!PN) 2653 break; 2654 2655 Value *V = PN->getIncomingValueForBlock(BB); 2656 assert(!isUnhandledGCPointerType(V->getType()) && 2657 "support for FCA unimplemented"); 2658 if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) 2659 LiveTmp.insert(V); 2660 } 2661 } 2662 } 2663 2664 static SetVector<Value *> computeKillSet(BasicBlock *BB) { 2665 SetVector<Value *> KillSet; 2666 for (Instruction &I : *BB) 2667 if (isHandledGCPointerType(I.getType())) 2668 KillSet.insert(&I); 2669 return KillSet; 2670 } 2671 2672 #ifndef NDEBUG 2673 /// Check that the items in 'Live' dominate 'TI'. This is used as a basic 2674 /// sanity check for the liveness computation. 2675 static void checkBasicSSA(DominatorTree &DT, SetVector<Value *> &Live, 2676 TerminatorInst *TI, bool TermOkay = false) { 2677 for (Value *V : Live) { 2678 if (auto *I = dyn_cast<Instruction>(V)) { 2679 // The terminator can be a member of the LiveOut set. LLVM's definition 2680 // of instruction dominance states that V does not dominate itself. As 2681 // such, we need to special case this to allow it. 2682 if (TermOkay && TI == I) 2683 continue; 2684 assert(DT.dominates(I, TI) && 2685 "basic SSA liveness expectation violated by liveness analysis"); 2686 } 2687 } 2688 } 2689 2690 /// Check that all the liveness sets used during the computation of liveness 2691 /// obey basic SSA properties. This is useful for finding cases where we miss 2692 /// a def. 2693 static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data, 2694 BasicBlock &BB) { 2695 checkBasicSSA(DT, Data.LiveSet[&BB], BB.getTerminator()); 2696 checkBasicSSA(DT, Data.LiveOut[&BB], BB.getTerminator(), true); 2697 checkBasicSSA(DT, Data.LiveIn[&BB], BB.getTerminator()); 2698 } 2699 #endif 2700 2701 static void computeLiveInValues(DominatorTree &DT, Function &F, 2702 GCPtrLivenessData &Data) { 2703 SmallSetVector<BasicBlock *, 32> Worklist; 2704 2705 // Seed the liveness for each individual block 2706 for (BasicBlock &BB : F) { 2707 Data.KillSet[&BB] = computeKillSet(&BB); 2708 Data.LiveSet[&BB].clear(); 2709 computeLiveInValues(BB.rbegin(), BB.rend(), Data.LiveSet[&BB]); 2710 2711 #ifndef NDEBUG 2712 for (Value *Kill : Data.KillSet[&BB]) 2713 assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill"); 2714 #endif 2715 2716 Data.LiveOut[&BB] = SetVector<Value *>(); 2717 computeLiveOutSeed(&BB, Data.LiveOut[&BB]); 2718 Data.LiveIn[&BB] = Data.LiveSet[&BB]; 2719 Data.LiveIn[&BB].set_union(Data.LiveOut[&BB]); 2720 Data.LiveIn[&BB].set_subtract(Data.KillSet[&BB]); 2721 if (!Data.LiveIn[&BB].empty()) 2722 Worklist.insert(pred_begin(&BB), pred_end(&BB)); 2723 } 2724 2725 // Propagate that liveness until stable 2726 while (!Worklist.empty()) { 2727 BasicBlock *BB = Worklist.pop_back_val(); 2728 2729 // Compute our new liveout set, then exit early if it hasn't changed despite 2730 // the contribution of our successor. 2731 SetVector<Value *> LiveOut = Data.LiveOut[BB]; 2732 const auto OldLiveOutSize = LiveOut.size(); 2733 for (BasicBlock *Succ : successors(BB)) { 2734 assert(Data.LiveIn.count(Succ)); 2735 LiveOut.set_union(Data.LiveIn[Succ]); 2736 } 2737 // assert OutLiveOut is a subset of LiveOut 2738 if (OldLiveOutSize == LiveOut.size()) { 2739 // If the sets are the same size, then we didn't actually add anything 2740 // when unioning our successors LiveIn. Thus, the LiveIn of this block 2741 // hasn't changed. 2742 continue; 2743 } 2744 Data.LiveOut[BB] = LiveOut; 2745 2746 // Apply the effects of this basic block 2747 SetVector<Value *> LiveTmp = LiveOut; 2748 LiveTmp.set_union(Data.LiveSet[BB]); 2749 LiveTmp.set_subtract(Data.KillSet[BB]); 2750 2751 assert(Data.LiveIn.count(BB)); 2752 const SetVector<Value *> &OldLiveIn = Data.LiveIn[BB]; 2753 // assert: OldLiveIn is a subset of LiveTmp 2754 if (OldLiveIn.size() != LiveTmp.size()) { 2755 Data.LiveIn[BB] = LiveTmp; 2756 Worklist.insert(pred_begin(BB), pred_end(BB)); 2757 } 2758 } // while (!Worklist.empty()) 2759 2760 #ifndef NDEBUG 2761 // Sanity check our output against SSA properties. This helps catch any 2762 // missing kills during the above iteration. 2763 for (BasicBlock &BB : F) 2764 checkBasicSSA(DT, Data, BB); 2765 #endif 2766 } 2767 2768 static void findLiveSetAtInst(Instruction *Inst, GCPtrLivenessData &Data, 2769 StatepointLiveSetTy &Out) { 2770 BasicBlock *BB = Inst->getParent(); 2771 2772 // Note: The copy is intentional and required 2773 assert(Data.LiveOut.count(BB)); 2774 SetVector<Value *> LiveOut = Data.LiveOut[BB]; 2775 2776 // We want to handle the statepoint itself oddly. It's 2777 // call result is not live (normal), nor are it's arguments 2778 // (unless they're used again later). This adjustment is 2779 // specifically what we need to relocate 2780 computeLiveInValues(BB->rbegin(), ++Inst->getIterator().getReverse(), 2781 LiveOut); 2782 LiveOut.remove(Inst); 2783 Out.insert(LiveOut.begin(), LiveOut.end()); 2784 } 2785 2786 static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData, 2787 CallSite CS, 2788 PartiallyConstructedSafepointRecord &Info) { 2789 Instruction *Inst = CS.getInstruction(); 2790 StatepointLiveSetTy Updated; 2791 findLiveSetAtInst(Inst, RevisedLivenessData, Updated); 2792 2793 // We may have base pointers which are now live that weren't before. We need 2794 // to update the PointerToBase structure to reflect this. 2795 for (auto V : Updated) 2796 if (Info.PointerToBase.insert({V, V}).second) { 2797 assert(isKnownBaseResult(V) && 2798 "Can't find base for unexpected live value!"); 2799 continue; 2800 } 2801 2802 #ifndef NDEBUG 2803 for (auto V : Updated) 2804 assert(Info.PointerToBase.count(V) && 2805 "Must be able to find base for live value!"); 2806 #endif 2807 2808 // Remove any stale base mappings - this can happen since our liveness is 2809 // more precise then the one inherent in the base pointer analysis. 2810 DenseSet<Value *> ToErase; 2811 for (auto KVPair : Info.PointerToBase) 2812 if (!Updated.count(KVPair.first)) 2813 ToErase.insert(KVPair.first); 2814 2815 for (auto *V : ToErase) 2816 Info.PointerToBase.erase(V); 2817 2818 #ifndef NDEBUG 2819 for (auto KVPair : Info.PointerToBase) 2820 assert(Updated.count(KVPair.first) && "record for non-live value"); 2821 #endif 2822 2823 Info.LiveSet = Updated; 2824 } 2825