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SafepointIRVerifier.cpp
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1 //===-- SafepointIRVerifier.cpp - Verify gc.statepoint invariants ---------===//
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 // Run a sanity check on the IR to ensure that Safepoints - if they've been
11 // inserted - were inserted correctly. In particular, look for use of
12 // non-relocated values after a safepoint. It's primary use is to check the
13 // correctness of safepoint insertion immediately after insertion, but it can
14 // also be used to verify that later transforms have not found a way to break
15 // safepoint semenatics.
16 //
17 // In its current form, this verify checks a property which is sufficient, but
18 // not neccessary for correctness. There are some cases where an unrelocated
19 // pointer can be used after the safepoint. Consider this example:
20 //
21 // a = ...
22 // b = ...
23 // (a',b') = safepoint(a,b)
24 // c = cmp eq a b
25 // br c, ..., ....
26 //
27 // Because it is valid to reorder 'c' above the safepoint, this is legal. In
28 // practice, this is a somewhat uncommon transform, but CodeGenPrep does create
29 // idioms like this. The verifier knows about these cases and avoids reporting
30 // false positives.
31 //
32 //===----------------------------------------------------------------------===//
33 
34 #include "llvm/ADT/DenseSet.h"
36 #include "llvm/ADT/SetOperations.h"
37 #include "llvm/ADT/SetVector.h"
38 #include "llvm/IR/BasicBlock.h"
39 #include "llvm/IR/Dominators.h"
40 #include "llvm/IR/Function.h"
41 #include "llvm/IR/Instructions.h"
42 #include "llvm/IR/Intrinsics.h"
43 #include "llvm/IR/IntrinsicInst.h"
44 #include "llvm/IR/Module.h"
45 #include "llvm/IR/Value.h"
47 #include "llvm/IR/Statepoint.h"
48 #include "llvm/Support/Debug.h"
51 
52 #define DEBUG_TYPE "safepoint-ir-verifier"
53 
54 using namespace llvm;
55 
56 /// This option is used for writing test cases. Instead of crashing the program
57 /// when verification fails, report a message to the console (for FileCheck
58 /// usage) and continue execution as if nothing happened.
59 static cl::opt<bool> PrintOnly("safepoint-ir-verifier-print-only",
60  cl::init(false));
61 
62 namespace {
63 
64 /// This CFG Deadness finds dead blocks and edges. Algorithm starts with a set
65 /// of blocks unreachable from entry then propagates deadness using foldable
66 /// conditional branches without modifying CFG. So GVN does but it changes CFG
67 /// by splitting critical edges. In most cases passes rely on SimplifyCFG to
68 /// clean up dead blocks, but in some cases, like verification or loop passes
69 /// it's not possible.
70 class CFGDeadness {
71  const DominatorTree *DT = nullptr;
73  SetVector<const Use *> DeadEdges; // Contains all dead edges from live blocks.
74 
75 public:
76  /// Return the edge that coresponds to the predecessor.
77  static const Use& getEdge(const_pred_iterator &PredIt) {
78  auto &PU = PredIt.getUse();
79  return PU.getUser()->getOperandUse(PU.getOperandNo());
80  }
81 
82  /// Return true if there is at least one live edge that corresponds to the
83  /// basic block InBB listed in the phi node.
84  bool hasLiveIncomingEdge(const PHINode *PN, const BasicBlock *InBB) const {
85  assert(!isDeadBlock(InBB) && "block must be live");
86  const BasicBlock* BB = PN->getParent();
87  bool Listed = false;
88  for (const_pred_iterator PredIt(BB), End(BB, true); PredIt != End; ++PredIt) {
89  if (InBB == *PredIt) {
90  if (!isDeadEdge(&getEdge(PredIt)))
91  return true;
92  Listed = true;
93  }
94  }
95  assert(Listed && "basic block is not found among incoming blocks");
96  return false;
97  }
98 
99 
100  bool isDeadBlock(const BasicBlock *BB) const {
101  return DeadBlocks.count(BB);
102  }
103 
104  bool isDeadEdge(const Use *U) const {
105  assert(dyn_cast<Instruction>(U->getUser())->isTerminator() &&
106  "edge must be operand of terminator");
107  assert(cast_or_null<BasicBlock>(U->get()) &&
108  "edge must refer to basic block");
109  assert(!isDeadBlock(dyn_cast<Instruction>(U->getUser())->getParent()) &&
110  "isDeadEdge() must be applied to edge from live block");
111  return DeadEdges.count(U);
112  }
113 
114  bool hasLiveIncomingEdges(const BasicBlock *BB) const {
115  // Check if all incoming edges are dead.
116  for (const_pred_iterator PredIt(BB), End(BB, true); PredIt != End; ++PredIt) {
117  auto &PU = PredIt.getUse();
118  const Use &U = PU.getUser()->getOperandUse(PU.getOperandNo());
119  if (!isDeadBlock(*PredIt) && !isDeadEdge(&U))
120  return true; // Found a live edge.
121  }
122  return false;
123  }
124 
125  void processFunction(const Function &F, const DominatorTree &DT) {
126  this->DT = &DT;
127 
128  // Start with all blocks unreachable from entry.
129  for (const BasicBlock &BB : F)
130  if (!DT.isReachableFromEntry(&BB))
131  DeadBlocks.insert(&BB);
132 
133  // Top-down walk of the dominator tree
135  for (const BasicBlock *BB : RPOT) {
136  const TerminatorInst *TI = BB->getTerminator();
137  assert(TI && "blocks must be well formed");
138 
139  // For conditional branches, we can perform simple conditional propagation on
140  // the condition value itself.
141  const BranchInst *BI = dyn_cast<BranchInst>(TI);
142  if (!BI || !BI->isConditional() || !isa<Constant>(BI->getCondition()))
143  continue;
144 
145  // If a branch has two identical successors, we cannot declare either dead.
146  if (BI->getSuccessor(0) == BI->getSuccessor(1))
147  continue;
148 
150  if (!Cond)
151  continue;
152 
153  addDeadEdge(BI->getOperandUse(Cond->getZExtValue() ? 1 : 2));
154  }
155  }
156 
157 protected:
158  void addDeadBlock(const BasicBlock *BB) {
161 
162  NewDead.push_back(BB);
163  while (!NewDead.empty()) {
164  const BasicBlock *D = NewDead.pop_back_val();
165  if (isDeadBlock(D))
166  continue;
167 
168  // All blocks dominated by D are dead.
170  DT->getDescendants(const_cast<BasicBlock*>(D), Dom);
171  // Do not need to mark all in and out edges dead
172  // because BB is marked dead and this is enough
173  // to run further.
174  DeadBlocks.insert(Dom.begin(), Dom.end());
175 
176  // Figure out the dominance-frontier(D).
177  for (BasicBlock *B : Dom)
178  for (BasicBlock *S : successors(B))
179  if (!isDeadBlock(S) && !hasLiveIncomingEdges(S))
180  NewDead.push_back(S);
181  }
182  }
183 
184  void addDeadEdge(const Use &DeadEdge) {
185  if (!DeadEdges.insert(&DeadEdge))
186  return;
187 
188  BasicBlock *BB = cast_or_null<BasicBlock>(DeadEdge.get());
189  if (hasLiveIncomingEdges(BB))
190  return;
191 
192  addDeadBlock(BB);
193  }
194 };
195 } // namespace
196 
197 static void Verify(const Function &F, const DominatorTree &DT,
198  const CFGDeadness &CD);
199 
200 namespace {
201 
202 struct SafepointIRVerifier : public FunctionPass {
203  static char ID; // Pass identification, replacement for typeid
204  SafepointIRVerifier() : FunctionPass(ID) {
206  }
207 
208  bool runOnFunction(Function &F) override {
209  auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
210  CFGDeadness CD;
211  CD.processFunction(F, DT);
212  Verify(F, DT, CD);
213  return false; // no modifications
214  }
215 
216  void getAnalysisUsage(AnalysisUsage &AU) const override {
218  AU.setPreservesAll();
219  }
220 
221  StringRef getPassName() const override { return "safepoint verifier"; }
222 };
223 } // namespace
224 
226  SafepointIRVerifier pass;
227  pass.runOnFunction(F);
228 }
229 
230 char SafepointIRVerifier::ID = 0;
231 
233  return new SafepointIRVerifier();
234 }
235 
236 INITIALIZE_PASS_BEGIN(SafepointIRVerifier, "verify-safepoint-ir",
237  "Safepoint IR Verifier", false, false)
239 INITIALIZE_PASS_END(SafepointIRVerifier, "verify-safepoint-ir",
240  "Safepoint IR Verifier", false, false)
241 
242 static bool isGCPointerType(Type *T) {
243  if (auto *PT = dyn_cast<PointerType>(T))
244  // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
245  // GC managed heap. We know that a pointer into this heap needs to be
246  // updated and that no other pointer does.
247  return (1 == PT->getAddressSpace());
248  return false;
249 }
250 
251 static bool containsGCPtrType(Type *Ty) {
252  if (isGCPointerType(Ty))
253  return true;
254  if (VectorType *VT = dyn_cast<VectorType>(Ty))
255  return isGCPointerType(VT->getScalarType());
256  if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
257  return containsGCPtrType(AT->getElementType());
258  if (StructType *ST = dyn_cast<StructType>(Ty))
259  return std::any_of(ST->subtypes().begin(), ST->subtypes().end(),
261  return false;
262 }
263 
264 // Debugging aid -- prints a [Begin, End) range of values.
265 template<typename IteratorTy>
266 static void PrintValueSet(raw_ostream &OS, IteratorTy Begin, IteratorTy End) {
267  OS << "[ ";
268  while (Begin != End) {
269  OS << **Begin << " ";
270  ++Begin;
271  }
272  OS << "]";
273 }
274 
275 /// The verifier algorithm is phrased in terms of availability. The set of
276 /// values "available" at a given point in the control flow graph is the set of
277 /// correctly relocated value at that point, and is a subset of the set of
278 /// definitions dominating that point.
279 
281 
282 /// State we compute and track per basic block.
284  // Set of values available coming in, before the phi nodes
286 
287  // Set of values available going out
289 
290  // AvailableOut minus AvailableIn.
291  // All elements are Instructions
293 
294  // True if this block contains a safepoint and thus AvailableIn does not
295  // contribute to AvailableOut.
296  bool Cleared = false;
297 };
298 
299 /// A given derived pointer can have multiple base pointers through phi/selects.
300 /// This type indicates when the base pointer is exclusively constant
301 /// (ExclusivelySomeConstant), and if that constant is proven to be exclusively
302 /// null, we record that as ExclusivelyNull. In all other cases, the BaseType is
303 /// NonConstant.
304 enum BaseType {
305  NonConstant = 1, // Base pointers is not exclusively constant.
307  ExclusivelySomeConstant // Base pointers for a given derived pointer is from a
308  // set of constants, but they are not exclusively
309  // null.
310 };
311 
312 /// Return the baseType for Val which states whether Val is exclusively
313 /// derived from constant/null, or not exclusively derived from constant.
314 /// Val is exclusively derived off a constant base when all operands of phi and
315 /// selects are derived off a constant base.
316 static enum BaseType getBaseType(const Value *Val) {
317 
319  DenseSet<const Value *> Visited;
320  bool isExclusivelyDerivedFromNull = true;
321  Worklist.push_back(Val);
322  // Strip through all the bitcasts and geps to get base pointer. Also check for
323  // the exclusive value when there can be multiple base pointers (through phis
324  // or selects).
325  while(!Worklist.empty()) {
326  const Value *V = Worklist.pop_back_val();
327  if (!Visited.insert(V).second)
328  continue;
329 
330  if (const auto *CI = dyn_cast<CastInst>(V)) {
331  Worklist.push_back(CI->stripPointerCasts());
332  continue;
333  }
334  if (const auto *GEP = dyn_cast<GetElementPtrInst>(V)) {
335  Worklist.push_back(GEP->getPointerOperand());
336  continue;
337  }
338  // Push all the incoming values of phi node into the worklist for
339  // processing.
340  if (const auto *PN = dyn_cast<PHINode>(V)) {
341  for (Value *InV: PN->incoming_values())
342  Worklist.push_back(InV);
343  continue;
344  }
345  if (const auto *SI = dyn_cast<SelectInst>(V)) {
346  // Push in the true and false values
347  Worklist.push_back(SI->getTrueValue());
348  Worklist.push_back(SI->getFalseValue());
349  continue;
350  }
351  if (isa<Constant>(V)) {
352  // We found at least one base pointer which is non-null, so this derived
353  // pointer is not exclusively derived from null.
354  if (V != Constant::getNullValue(V->getType()))
355  isExclusivelyDerivedFromNull = false;
356  // Continue processing the remaining values to make sure it's exclusively
357  // constant.
358  continue;
359  }
360  // At this point, we know that the base pointer is not exclusively
361  // constant.
362  return BaseType::NonConstant;
363  }
364  // Now, we know that the base pointer is exclusively constant, but we need to
365  // differentiate between exclusive null constant and non-null constant.
366  return isExclusivelyDerivedFromNull ? BaseType::ExclusivelyNull
368 }
369 
370 static bool isNotExclusivelyConstantDerived(const Value *V) {
371  return getBaseType(V) == BaseType::NonConstant;
372 }
373 
374 namespace {
375 class InstructionVerifier;
376 
377 /// Builds BasicBlockState for each BB of the function.
378 /// It can traverse function for verification and provides all required
379 /// information.
380 ///
381 /// GC pointer may be in one of three states: relocated, unrelocated and
382 /// poisoned.
383 /// Relocated pointer may be used without any restrictions.
384 /// Unrelocated pointer cannot be dereferenced, passed as argument to any call
385 /// or returned. Unrelocated pointer may be safely compared against another
386 /// unrelocated pointer or against a pointer exclusively derived from null.
387 /// Poisoned pointers are produced when we somehow derive pointer from relocated
388 /// and unrelocated pointers (e.g. phi, select). This pointers may be safely
389 /// used in a very limited number of situations. Currently the only way to use
390 /// it is comparison against constant exclusively derived from null. All
391 /// limitations arise due to their undefined state: this pointers should be
392 /// treated as relocated and unrelocated simultaneously.
393 /// Rules of deriving:
394 /// R + U = P - that's where the poisoned pointers come from
395 /// P + X = P
396 /// U + U = U
397 /// R + R = R
398 /// X + C = X
399 /// Where "+" - any operation that somehow derive pointer, U - unrelocated,
400 /// R - relocated and P - poisoned, C - constant, X - U or R or P or C or
401 /// nothing (in case when "+" is unary operation).
402 /// Deriving of pointers by itself is always safe.
403 /// NOTE: when we are making decision on the status of instruction's result:
404 /// a) for phi we need to check status of each input *at the end of
405 /// corresponding predecessor BB*.
406 /// b) for other instructions we need to check status of each input *at the
407 /// current point*.
408 ///
409 /// FIXME: This works fairly well except one case
410 /// bb1:
411 /// p = *some GC-ptr def*
412 /// p1 = gep p, offset
413 /// / |
414 /// / |
415 /// bb2: |
416 /// safepoint |
417 /// \ |
418 /// \ |
419 /// bb3:
420 /// p2 = phi [p, bb2] [p1, bb1]
421 /// p3 = phi [p, bb2] [p, bb1]
422 /// here p and p1 is unrelocated
423 /// p2 and p3 is poisoned (though they shouldn't be)
424 ///
425 /// This leads to some weird results:
426 /// cmp eq p, p2 - illegal instruction (false-positive)
427 /// cmp eq p1, p2 - illegal instruction (false-positive)
428 /// cmp eq p, p3 - illegal instruction (false-positive)
429 /// cmp eq p, p1 - ok
430 /// To fix this we need to introduce conception of generations and be able to
431 /// check if two values belong to one generation or not. This way p2 will be
432 /// considered to be unrelocated and no false alarm will happen.
433 class GCPtrTracker {
434  const Function &F;
435  const CFGDeadness &CD;
438  // This set contains defs of unrelocated pointers that are proved to be legal
439  // and don't need verification.
440  DenseSet<const Instruction *> ValidUnrelocatedDefs;
441  // This set contains poisoned defs. They can be safely ignored during
442  // verification too.
443  DenseSet<const Value *> PoisonedDefs;
444 
445 public:
446  GCPtrTracker(const Function &F, const DominatorTree &DT,
447  const CFGDeadness &CD);
448 
449  bool hasLiveIncomingEdge(const PHINode *PN, const BasicBlock *InBB) const {
450  return CD.hasLiveIncomingEdge(PN, InBB);
451  }
452 
453  BasicBlockState *getBasicBlockState(const BasicBlock *BB);
454  const BasicBlockState *getBasicBlockState(const BasicBlock *BB) const;
455 
456  bool isValuePoisoned(const Value *V) const { return PoisonedDefs.count(V); }
457 
458  /// Traverse each BB of the function and call
459  /// InstructionVerifier::verifyInstruction for each possibly invalid
460  /// instruction.
461  /// It destructively modifies GCPtrTracker so it's passed via rvalue reference
462  /// in order to prohibit further usages of GCPtrTracker as it'll be in
463  /// inconsistent state.
464  static void verifyFunction(GCPtrTracker &&Tracker,
465  InstructionVerifier &Verifier);
466 
467  /// Returns true for reachable and live blocks.
468  bool isMapped(const BasicBlock *BB) const {
469  return BlockMap.find(BB) != BlockMap.end();
470  }
471 
472 private:
473  /// Returns true if the instruction may be safely skipped during verification.
474  bool instructionMayBeSkipped(const Instruction *I) const;
475 
476  /// Iterates over all BBs from BlockMap and recalculates AvailableIn/Out for
477  /// each of them until it converges.
478  void recalculateBBsStates();
479 
480  /// Remove from Contribution all defs that legally produce unrelocated
481  /// pointers and saves them to ValidUnrelocatedDefs.
482  /// Though Contribution should belong to BBS it is passed separately with
483  /// different const-modifier in order to emphasize (and guarantee) that only
484  /// Contribution will be changed.
485  /// Returns true if Contribution was changed otherwise false.
486  bool removeValidUnrelocatedDefs(const BasicBlock *BB,
487  const BasicBlockState *BBS,
488  AvailableValueSet &Contribution);
489 
490  /// Gather all the definitions dominating the start of BB into Result. This is
491  /// simply the defs introduced by every dominating basic block and the
492  /// function arguments.
493  void gatherDominatingDefs(const BasicBlock *BB, AvailableValueSet &Result,
494  const DominatorTree &DT);
495 
496  /// Compute the AvailableOut set for BB, based on the BasicBlockState BBS,
497  /// which is the BasicBlockState for BB.
498  /// ContributionChanged is set when the verifier runs for the first time
499  /// (in this case Contribution was changed from 'empty' to its initial state)
500  /// or when Contribution of this BB was changed since last computation.
501  static void transferBlock(const BasicBlock *BB, BasicBlockState &BBS,
502  bool ContributionChanged);
503 
504  /// Model the effect of an instruction on the set of available values.
505  static void transferInstruction(const Instruction &I, bool &Cleared,
506  AvailableValueSet &Available);
507 };
508 
509 /// It is a visitor for GCPtrTracker::verifyFunction. It decides if the
510 /// instruction (which uses heap reference) is legal or not, given our safepoint
511 /// semantics.
512 class InstructionVerifier {
513  bool AnyInvalidUses = false;
514 
515 public:
516  void verifyInstruction(const GCPtrTracker *Tracker, const Instruction &I,
517  const AvailableValueSet &AvailableSet);
518 
519  bool hasAnyInvalidUses() const { return AnyInvalidUses; }
520 
521 private:
522  void reportInvalidUse(const Value &V, const Instruction &I);
523 };
524 } // end anonymous namespace
525 
526 GCPtrTracker::GCPtrTracker(const Function &F, const DominatorTree &DT,
527  const CFGDeadness &CD) : F(F), CD(CD) {
528  // Calculate Contribution of each live BB.
529  // Allocate BB states for live blocks.
530  for (const BasicBlock &BB : F)
531  if (!CD.isDeadBlock(&BB)) {
532  BasicBlockState *BBS = new (BSAllocator.Allocate()) BasicBlockState;
533  for (const auto &I : BB)
534  transferInstruction(I, BBS->Cleared, BBS->Contribution);
535  BlockMap[&BB] = BBS;
536  }
537 
538  // Initialize AvailableIn/Out sets of each BB using only information about
539  // dominating BBs.
540  for (auto &BBI : BlockMap) {
541  gatherDominatingDefs(BBI.first, BBI.second->AvailableIn, DT);
542  transferBlock(BBI.first, *BBI.second, true);
543  }
544 
545  // Simulate the flow of defs through the CFG and recalculate AvailableIn/Out
546  // sets of each BB until it converges. If any def is proved to be an
547  // unrelocated pointer, it will be removed from all BBSs.
548  recalculateBBsStates();
549 }
550 
551 BasicBlockState *GCPtrTracker::getBasicBlockState(const BasicBlock *BB) {
552  auto it = BlockMap.find(BB);
553  return it != BlockMap.end() ? it->second : nullptr;
554 }
555 
556 const BasicBlockState *GCPtrTracker::getBasicBlockState(
557  const BasicBlock *BB) const {
558  return const_cast<GCPtrTracker *>(this)->getBasicBlockState(BB);
559 }
560 
561 bool GCPtrTracker::instructionMayBeSkipped(const Instruction *I) const {
562  // Poisoned defs are skipped since they are always safe by itself by
563  // definition (for details see comment to this class).
564  return ValidUnrelocatedDefs.count(I) || PoisonedDefs.count(I);
565 }
566 
567 void GCPtrTracker::verifyFunction(GCPtrTracker &&Tracker,
568  InstructionVerifier &Verifier) {
569  // We need RPO here to a) report always the first error b) report errors in
570  // same order from run to run.
572  for (const BasicBlock *BB : RPOT) {
573  BasicBlockState *BBS = Tracker.getBasicBlockState(BB);
574  if (!BBS)
575  continue;
576 
577  // We destructively modify AvailableIn as we traverse the block instruction
578  // by instruction.
579  AvailableValueSet &AvailableSet = BBS->AvailableIn;
580  for (const Instruction &I : *BB) {
581  if (Tracker.instructionMayBeSkipped(&I))
582  continue; // This instruction shouldn't be added to AvailableSet.
583 
584  Verifier.verifyInstruction(&Tracker, I, AvailableSet);
585 
586  // Model the effect of current instruction on AvailableSet to keep the set
587  // relevant at each point of BB.
588  bool Cleared = false;
589  transferInstruction(I, Cleared, AvailableSet);
590  (void)Cleared;
591  }
592  }
593 }
594 
595 void GCPtrTracker::recalculateBBsStates() {
597  // TODO: This order is suboptimal, it's better to replace it with priority
598  // queue where priority is RPO number of BB.
599  for (auto &BBI : BlockMap)
600  Worklist.insert(BBI.first);
601 
602  // This loop iterates the AvailableIn/Out sets until it converges.
603  // The AvailableIn and AvailableOut sets decrease as we iterate.
604  while (!Worklist.empty()) {
605  const BasicBlock *BB = Worklist.pop_back_val();
606  BasicBlockState *BBS = getBasicBlockState(BB);
607  if (!BBS)
608  continue; // Ignore dead successors.
609 
610  size_t OldInCount = BBS->AvailableIn.size();
611  for (const_pred_iterator PredIt(BB), End(BB, true); PredIt != End; ++PredIt) {
612  const BasicBlock *PBB = *PredIt;
613  BasicBlockState *PBBS = getBasicBlockState(PBB);
614  if (PBBS && !CD.isDeadEdge(&CFGDeadness::getEdge(PredIt)))
616  }
617 
618  assert(OldInCount >= BBS->AvailableIn.size() && "invariant!");
619 
620  bool InputsChanged = OldInCount != BBS->AvailableIn.size();
621  bool ContributionChanged =
622  removeValidUnrelocatedDefs(BB, BBS, BBS->Contribution);
623  if (!InputsChanged && !ContributionChanged)
624  continue;
625 
626  size_t OldOutCount = BBS->AvailableOut.size();
627  transferBlock(BB, *BBS, ContributionChanged);
628  if (OldOutCount != BBS->AvailableOut.size()) {
629  assert(OldOutCount > BBS->AvailableOut.size() && "invariant!");
630  Worklist.insert(succ_begin(BB), succ_end(BB));
631  }
632  }
633 }
634 
635 bool GCPtrTracker::removeValidUnrelocatedDefs(const BasicBlock *BB,
636  const BasicBlockState *BBS,
637  AvailableValueSet &Contribution) {
638  assert(&BBS->Contribution == &Contribution &&
639  "Passed Contribution should be from the passed BasicBlockState!");
640  AvailableValueSet AvailableSet = BBS->AvailableIn;
641  bool ContributionChanged = false;
642  // For explanation why instructions are processed this way see
643  // "Rules of deriving" in the comment to this class.
644  for (const Instruction &I : *BB) {
645  bool ValidUnrelocatedPointerDef = false;
646  bool PoisonedPointerDef = false;
647  // TODO: `select` instructions should be handled here too.
648  if (const PHINode *PN = dyn_cast<PHINode>(&I)) {
649  if (containsGCPtrType(PN->getType())) {
650  // If both is true, output is poisoned.
651  bool HasRelocatedInputs = false;
652  bool HasUnrelocatedInputs = false;
653  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
654  const BasicBlock *InBB = PN->getIncomingBlock(i);
655  if (!isMapped(InBB) ||
656  !CD.hasLiveIncomingEdge(PN, InBB))
657  continue; // Skip dead block or dead edge.
658 
659  const Value *InValue = PN->getIncomingValue(i);
660 
661  if (isNotExclusivelyConstantDerived(InValue)) {
662  if (isValuePoisoned(InValue)) {
663  // If any of inputs is poisoned, output is always poisoned too.
664  HasRelocatedInputs = true;
665  HasUnrelocatedInputs = true;
666  break;
667  }
668  if (BlockMap[InBB]->AvailableOut.count(InValue))
669  HasRelocatedInputs = true;
670  else
671  HasUnrelocatedInputs = true;
672  }
673  }
674  if (HasUnrelocatedInputs) {
675  if (HasRelocatedInputs)
676  PoisonedPointerDef = true;
677  else
678  ValidUnrelocatedPointerDef = true;
679  }
680  }
681  } else if ((isa<GetElementPtrInst>(I) || isa<BitCastInst>(I)) &&
682  containsGCPtrType(I.getType())) {
683  // GEP/bitcast of unrelocated pointer is legal by itself but this def
684  // shouldn't appear in any AvailableSet.
685  for (const Value *V : I.operands())
686  if (containsGCPtrType(V->getType()) &&
687  isNotExclusivelyConstantDerived(V) && !AvailableSet.count(V)) {
688  if (isValuePoisoned(V))
689  PoisonedPointerDef = true;
690  else
691  ValidUnrelocatedPointerDef = true;
692  break;
693  }
694  }
695  assert(!(ValidUnrelocatedPointerDef && PoisonedPointerDef) &&
696  "Value cannot be both unrelocated and poisoned!");
697  if (ValidUnrelocatedPointerDef) {
698  // Remove def of unrelocated pointer from Contribution of this BB and
699  // trigger update of all its successors.
700  Contribution.erase(&I);
701  PoisonedDefs.erase(&I);
702  ValidUnrelocatedDefs.insert(&I);
703  LLVM_DEBUG(dbgs() << "Removing urelocated " << I
704  << " from Contribution of " << BB->getName() << "\n");
705  ContributionChanged = true;
706  } else if (PoisonedPointerDef) {
707  // Mark pointer as poisoned, remove its def from Contribution and trigger
708  // update of all successors.
709  Contribution.erase(&I);
710  PoisonedDefs.insert(&I);
711  LLVM_DEBUG(dbgs() << "Removing poisoned " << I << " from Contribution of "
712  << BB->getName() << "\n");
713  ContributionChanged = true;
714  } else {
715  bool Cleared = false;
716  transferInstruction(I, Cleared, AvailableSet);
717  (void)Cleared;
718  }
719  }
720  return ContributionChanged;
721 }
722 
723 void GCPtrTracker::gatherDominatingDefs(const BasicBlock *BB,
725  const DominatorTree &DT) {
726  DomTreeNode *DTN = DT[const_cast<BasicBlock *>(BB)];
727 
728  assert(DTN && "Unreachable blocks are ignored");
729  while (DTN->getIDom()) {
730  DTN = DTN->getIDom();
731  auto BBS = getBasicBlockState(DTN->getBlock());
732  assert(BBS && "immediate dominator cannot be dead for a live block");
733  const auto &Defs = BBS->Contribution;
734  Result.insert(Defs.begin(), Defs.end());
735  // If this block is 'Cleared', then nothing LiveIn to this block can be
736  // available after this block completes. Note: This turns out to be
737  // really important for reducing memory consuption of the initial available
738  // sets and thus peak memory usage by this verifier.
739  if (BBS->Cleared)
740  return;
741  }
742 
743  for (const Argument &A : BB->getParent()->args())
744  if (containsGCPtrType(A.getType()))
745  Result.insert(&A);
746 }
747 
748 void GCPtrTracker::transferBlock(const BasicBlock *BB, BasicBlockState &BBS,
749  bool ContributionChanged) {
750  const AvailableValueSet &AvailableIn = BBS.AvailableIn;
751  AvailableValueSet &AvailableOut = BBS.AvailableOut;
752 
753  if (BBS.Cleared) {
754  // AvailableOut will change only when Contribution changed.
755  if (ContributionChanged)
756  AvailableOut = BBS.Contribution;
757  } else {
758  // Otherwise, we need to reduce the AvailableOut set by things which are no
759  // longer in our AvailableIn
760  AvailableValueSet Temp = BBS.Contribution;
761  set_union(Temp, AvailableIn);
762  AvailableOut = std::move(Temp);
763  }
764 
765  LLVM_DEBUG(dbgs() << "Transfered block " << BB->getName() << " from ";
766  PrintValueSet(dbgs(), AvailableIn.begin(), AvailableIn.end());
767  dbgs() << " to ";
768  PrintValueSet(dbgs(), AvailableOut.begin(), AvailableOut.end());
769  dbgs() << "\n";);
770 }
771 
772 void GCPtrTracker::transferInstruction(const Instruction &I, bool &Cleared,
773  AvailableValueSet &Available) {
774  if (isStatepoint(I)) {
775  Cleared = true;
776  Available.clear();
777  } else if (containsGCPtrType(I.getType()))
778  Available.insert(&I);
779 }
780 
781 void InstructionVerifier::verifyInstruction(
782  const GCPtrTracker *Tracker, const Instruction &I,
783  const AvailableValueSet &AvailableSet) {
784  if (const PHINode *PN = dyn_cast<PHINode>(&I)) {
785  if (containsGCPtrType(PN->getType()))
786  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
787  const BasicBlock *InBB = PN->getIncomingBlock(i);
788  const BasicBlockState *InBBS = Tracker->getBasicBlockState(InBB);
789  if (!InBBS ||
790  !Tracker->hasLiveIncomingEdge(PN, InBB))
791  continue; // Skip dead block or dead edge.
792 
793  const Value *InValue = PN->getIncomingValue(i);
794 
795  if (isNotExclusivelyConstantDerived(InValue) &&
796  !InBBS->AvailableOut.count(InValue))
797  reportInvalidUse(*InValue, *PN);
798  }
799  } else if (isa<CmpInst>(I) &&
801  Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
802  enum BaseType baseTyLHS = getBaseType(LHS),
803  baseTyRHS = getBaseType(RHS);
804 
805  // Returns true if LHS and RHS are unrelocated pointers and they are
806  // valid unrelocated uses.
807  auto hasValidUnrelocatedUse = [&AvailableSet, Tracker, baseTyLHS, baseTyRHS,
808  &LHS, &RHS] () {
809  // A cmp instruction has valid unrelocated pointer operands only if
810  // both operands are unrelocated pointers.
811  // In the comparison between two pointers, if one is an unrelocated
812  // use, the other *should be* an unrelocated use, for this
813  // instruction to contain valid unrelocated uses. This unrelocated
814  // use can be a null constant as well, or another unrelocated
815  // pointer.
816  if (AvailableSet.count(LHS) || AvailableSet.count(RHS))
817  return false;
818  // Constant pointers (that are not exclusively null) may have
819  // meaning in different VMs, so we cannot reorder the compare
820  // against constant pointers before the safepoint. In other words,
821  // comparison of an unrelocated use against a non-null constant
822  // maybe invalid.
823  if ((baseTyLHS == BaseType::ExclusivelySomeConstant &&
824  baseTyRHS == BaseType::NonConstant) ||
825  (baseTyLHS == BaseType::NonConstant &&
826  baseTyRHS == BaseType::ExclusivelySomeConstant))
827  return false;
828 
829  // If one of pointers is poisoned and other is not exclusively derived
830  // from null it is an invalid expression: it produces poisoned result
831  // and unless we want to track all defs (not only gc pointers) the only
832  // option is to prohibit such instructions.
833  if ((Tracker->isValuePoisoned(LHS) && baseTyRHS != ExclusivelyNull) ||
834  (Tracker->isValuePoisoned(RHS) && baseTyLHS != ExclusivelyNull))
835  return false;
836 
837  // All other cases are valid cases enumerated below:
838  // 1. Comparison between an exclusively derived null pointer and a
839  // constant base pointer.
840  // 2. Comparison between an exclusively derived null pointer and a
841  // non-constant unrelocated base pointer.
842  // 3. Comparison between 2 unrelocated pointers.
843  // 4. Comparison between a pointer exclusively derived from null and a
844  // non-constant poisoned pointer.
845  return true;
846  };
847  if (!hasValidUnrelocatedUse()) {
848  // Print out all non-constant derived pointers that are unrelocated
849  // uses, which are invalid.
850  if (baseTyLHS == BaseType::NonConstant && !AvailableSet.count(LHS))
851  reportInvalidUse(*LHS, I);
852  if (baseTyRHS == BaseType::NonConstant && !AvailableSet.count(RHS))
853  reportInvalidUse(*RHS, I);
854  }
855  } else {
856  for (const Value *V : I.operands())
857  if (containsGCPtrType(V->getType()) &&
858  isNotExclusivelyConstantDerived(V) && !AvailableSet.count(V))
859  reportInvalidUse(*V, I);
860  }
861 }
862 
863 void InstructionVerifier::reportInvalidUse(const Value &V,
864  const Instruction &I) {
865  errs() << "Illegal use of unrelocated value found!\n";
866  errs() << "Def: " << V << "\n";
867  errs() << "Use: " << I << "\n";
868  if (!PrintOnly)
869  abort();
870  AnyInvalidUses = true;
871 }
872 
873 static void Verify(const Function &F, const DominatorTree &DT,
874  const CFGDeadness &CD) {
875  LLVM_DEBUG(dbgs() << "Verifying gc pointers in function: " << F.getName()
876  << "\n");
877  if (PrintOnly)
878  dbgs() << "Verifying gc pointers in function: " << F.getName() << "\n";
879 
880  GCPtrTracker Tracker(F, DT, CD);
881 
882  // We now have all the information we need to decide if the use of a heap
883  // reference is legal or not, given our safepoint semantics.
884 
885  InstructionVerifier Verifier;
886  GCPtrTracker::verifyFunction(std::move(Tracker), Verifier);
887 
888  if (PrintOnly && !Verifier.hasAnyInvalidUses()) {
889  dbgs() << "No illegal uses found by SafepointIRVerifier in: " << F.getName()
890  << "\n";
891  }
892 }
static void PrintValueSet(raw_ostream &OS, IteratorTy Begin, IteratorTy End)
Safe Stack instrumentation pass
Definition: SafeStack.cpp:900
raw_ostream & errs()
This returns a reference to a raw_ostream for standard error.
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
This class represents an incoming formal argument to a Function.
Definition: Argument.h:30
LLVM_NODISCARD T pop_back_val()
Definition: SetVector.h:228
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
void initializeSafepointIRVerifierPass(PassRegistry &)
Implements a dense probed hash-table based set.
Definition: DenseSet.h:221
static enum BaseType getBaseType(const Value *Val)
Return the baseType for Val which states whether Val is exclusively derived from constant/null, or not exclusively derived from constant.
bool erase(const ValueT &V)
Definition: DenseSet.h:95
const Use & getOperandUse(unsigned i) const
Definition: User.h:183
BasicBlock * getSuccessor(unsigned i) const
F(f)
static bool isNotExclusivelyConstantDerived(const Value *V)
Hexagon Common GEP
Value * getCondition() const
bool isReachableFromEntry(const Use &U) const
Provide an overload for a Use.
Definition: Dominators.cpp:295
Value * get() const
Definition: Use.h:108
static Constant * getNullValue(Type *Ty)
Constructor to create a &#39;0&#39; constant of arbitrary type.
Definition: Constants.cpp:268
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:51
AvailableValueSet AvailableIn
Class to represent struct types.
Definition: DerivedTypes.h:201
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
Interval::succ_iterator succ_begin(Interval *I)
succ_begin/succ_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:103
User * getUser() const LLVM_READONLY
Returns the User that contains this Use.
Definition: Use.cpp:41
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
bool insert(const value_type &X)
Insert a new element into the SetVector.
Definition: SetVector.h:142
Class to represent array types.
Definition: DerivedTypes.h:369
verify safepoint Safepoint IR static false bool isGCPointerType(Type *T)
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:142
Value * getOperand(unsigned i) const
Definition: User.h:170
size_type count(const key_type &key) const
Count the number of elements of a given key in the SetVector.
Definition: SetVector.h:211
Interval::succ_iterator succ_end(Interval *I)
Definition: Interval.h:106
Use & getUse() const
getUse - Return the operand Use in the predecessor&#39;s terminator of the successor. ...
Definition: CFG.h:88
AvailableValueSet Contribution
State we compute and track per basic block.
NodeT * getBlock() const
static bool runOnFunction(Function &F, bool PostInlining)
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:410
void verifySafepointIR(Function &F)
Run the safepoint verifier over a single function. Crashes on failure.
uint64_t getZExtValue() const
Return the constant as a 64-bit unsigned integer value after it has been zero extended as appropriate...
Definition: Constants.h:149
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:55
FunctionPass * createSafepointIRVerifierPass()
Create an instance of the safepoint verifier pass which can be added to a pass pipeline to check for ...
void set_intersect(S1Ty &S1, const S2Ty &S2)
set_intersect(A, B) - Compute A := A ^ B Identical to set_intersection, except that it works on set<>...
Definition: SetOperations.h:40
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:46
Conditional or Unconditional Branch instruction.
void getDescendants(NodeT *R, SmallVectorImpl< NodeT *> &Result) const
Get all nodes dominated by R, including R itself.
DomTreeNodeBase * getIDom() const
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator begin()
Definition: SmallVector.h:124
std::pair< iterator, bool > insert(const ValueT &V)
Definition: DenseSet.h:187
static bool containsGCPtrType(Type *Ty)
Represent the analysis usage information of a pass.
bool any_of(R &&Range, UnaryPredicate P)
Provide wrappers to std::any_of which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:928
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:285
op_range operands()
Definition: User.h:238
Value * getIncomingValue(unsigned i) const
Return incoming value number x.
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
bool verify(const TargetRegisterInfo &TRI) const
Check that information hold by this instance make sense for the given TRI.
BaseType
A given derived pointer can have multiple base pointers through phi/selects.
A SetVector that performs no allocations if smaller than a certain size.
Definition: SetVector.h:298
This is the shared class of boolean and integer constants.
Definition: Constants.h:84
AnalysisUsage & addRequiredID(const void *ID)
Definition: Pass.cpp:299
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:841
Module.h This file contains the declarations for the Module class.
size_type size() const
Definition: DenseSet.h:75
LLVM_NODISCARD T pop_back_val()
Definition: SmallVector.h:376
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
bool isConditional() const
unsigned getNumIncomingValues() const
Return the number of incoming edges.
A BumpPtrAllocator that allows only elements of a specific type to be allocated.
Definition: Allocator.h:387
AvailableValueSet AvailableOut
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:133
Class to represent vector types.
Definition: DerivedTypes.h:393
void setPreservesAll()
Set by analyses that do not transform their input at all.
INITIALIZE_PASS_BEGIN(SafepointIRVerifier, "verify-safepoint-ir", "Safepoint IR Verifier", false, false) INITIALIZE_PASS_END(SafepointIRVerifier
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator end()
Definition: SmallVector.h:128
static cl::opt< bool > PrintOnly("safepoint-ir-verifier-print-only", cl::init(false))
This option is used for writing test cases.
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:56
verify safepoint Safepoint IR Verifier
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:224
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:108
#define I(x, y, z)
Definition: MD5.cpp:58
bool empty() const
Determine if the SetVector is empty or not.
Definition: SetVector.h:73
bool verifyFunction(const Function &F, raw_ostream *OS=nullptr)
Check a function for errors, useful for use when debugging a pass.
Definition: Verifier.cpp:4669
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:323
size_type count(const_arg_type_t< ValueT > V) const
Return 1 if the specified key is in the set, 0 otherwise.
Definition: DenseSet.h:91
bool isStatepoint(ImmutableCallSite CS)
Definition: Statepoint.cpp:27
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
LLVM Value Representation.
Definition: Value.h:73
succ_range successors(BasicBlock *BB)
Definition: CFG.h:149
A vector that has set insertion semantics.
Definition: SetVector.h:41
verify safepoint ir
static const Function * getParent(const Value *V)
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:46
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:49
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:254
const TerminatorInst * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:138
#define LLVM_DEBUG(X)
Definition: Debug.h:119
op_range incoming_values()
bool set_union(S1Ty &S1, const S2Ty &S2)
set_union(A, B) - Compute A := A u B, return whether A changed.
Definition: SetOperations.h:23
Statically lint checks LLVM IR
Definition: Lint.cpp:193
iterator_range< arg_iterator > args()
Definition: Function.h:675
const BasicBlock * getParent() const
Definition: Instruction.h:67
static void Verify(const Function &F, const DominatorTree &DT, const CFGDeadness &CD)