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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  (void)Listed;
96  assert(Listed && "basic block is not found among incoming blocks");
97  return false;
98  }
99 
100 
101  bool isDeadBlock(const BasicBlock *BB) const {
102  return DeadBlocks.count(BB);
103  }
104 
105  bool isDeadEdge(const Use *U) const {
106  assert(dyn_cast<Instruction>(U->getUser())->isTerminator() &&
107  "edge must be operand of terminator");
108  assert(cast_or_null<BasicBlock>(U->get()) &&
109  "edge must refer to basic block");
110  assert(!isDeadBlock(dyn_cast<Instruction>(U->getUser())->getParent()) &&
111  "isDeadEdge() must be applied to edge from live block");
112  return DeadEdges.count(U);
113  }
114 
115  bool hasLiveIncomingEdges(const BasicBlock *BB) const {
116  // Check if all incoming edges are dead.
117  for (const_pred_iterator PredIt(BB), End(BB, true); PredIt != End; ++PredIt) {
118  auto &PU = PredIt.getUse();
119  const Use &U = PU.getUser()->getOperandUse(PU.getOperandNo());
120  if (!isDeadBlock(*PredIt) && !isDeadEdge(&U))
121  return true; // Found a live edge.
122  }
123  return false;
124  }
125 
126  void processFunction(const Function &F, const DominatorTree &DT) {
127  this->DT = &DT;
128 
129  // Start with all blocks unreachable from entry.
130  for (const BasicBlock &BB : F)
131  if (!DT.isReachableFromEntry(&BB))
132  DeadBlocks.insert(&BB);
133 
134  // Top-down walk of the dominator tree
136  for (const BasicBlock *BB : RPOT) {
137  const Instruction *TI = BB->getTerminator();
138  assert(TI && "blocks must be well formed");
139 
140  // For conditional branches, we can perform simple conditional propagation on
141  // the condition value itself.
142  const BranchInst *BI = dyn_cast<BranchInst>(TI);
143  if (!BI || !BI->isConditional() || !isa<Constant>(BI->getCondition()))
144  continue;
145 
146  // If a branch has two identical successors, we cannot declare either dead.
147  if (BI->getSuccessor(0) == BI->getSuccessor(1))
148  continue;
149 
151  if (!Cond)
152  continue;
153 
154  addDeadEdge(BI->getOperandUse(Cond->getZExtValue() ? 1 : 2));
155  }
156  }
157 
158 protected:
159  void addDeadBlock(const BasicBlock *BB) {
162 
163  NewDead.push_back(BB);
164  while (!NewDead.empty()) {
165  const BasicBlock *D = NewDead.pop_back_val();
166  if (isDeadBlock(D))
167  continue;
168 
169  // All blocks dominated by D are dead.
171  DT->getDescendants(const_cast<BasicBlock*>(D), Dom);
172  // Do not need to mark all in and out edges dead
173  // because BB is marked dead and this is enough
174  // to run further.
175  DeadBlocks.insert(Dom.begin(), Dom.end());
176 
177  // Figure out the dominance-frontier(D).
178  for (BasicBlock *B : Dom)
179  for (BasicBlock *S : successors(B))
180  if (!isDeadBlock(S) && !hasLiveIncomingEdges(S))
181  NewDead.push_back(S);
182  }
183  }
184 
185  void addDeadEdge(const Use &DeadEdge) {
186  if (!DeadEdges.insert(&DeadEdge))
187  return;
188 
189  BasicBlock *BB = cast_or_null<BasicBlock>(DeadEdge.get());
190  if (hasLiveIncomingEdges(BB))
191  return;
192 
193  addDeadBlock(BB);
194  }
195 };
196 } // namespace
197 
198 static void Verify(const Function &F, const DominatorTree &DT,
199  const CFGDeadness &CD);
200 
201 namespace {
202 
203 struct SafepointIRVerifier : public FunctionPass {
204  static char ID; // Pass identification, replacement for typeid
205  SafepointIRVerifier() : FunctionPass(ID) {
207  }
208 
209  bool runOnFunction(Function &F) override {
210  auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
211  CFGDeadness CD;
212  CD.processFunction(F, DT);
213  Verify(F, DT, CD);
214  return false; // no modifications
215  }
216 
217  void getAnalysisUsage(AnalysisUsage &AU) const override {
219  AU.setPreservesAll();
220  }
221 
222  StringRef getPassName() const override { return "safepoint verifier"; }
223 };
224 } // namespace
225 
227  SafepointIRVerifier pass;
228  pass.runOnFunction(F);
229 }
230 
231 char SafepointIRVerifier::ID = 0;
232 
234  return new SafepointIRVerifier();
235 }
236 
237 INITIALIZE_PASS_BEGIN(SafepointIRVerifier, "verify-safepoint-ir",
238  "Safepoint IR Verifier", false, false)
240 INITIALIZE_PASS_END(SafepointIRVerifier, "verify-safepoint-ir",
241  "Safepoint IR Verifier", false, false)
242 
243 static bool isGCPointerType(Type *T) {
244  if (auto *PT = dyn_cast<PointerType>(T))
245  // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
246  // GC managed heap. We know that a pointer into this heap needs to be
247  // updated and that no other pointer does.
248  return (1 == PT->getAddressSpace());
249  return false;
250 }
251 
252 static bool containsGCPtrType(Type *Ty) {
253  if (isGCPointerType(Ty))
254  return true;
255  if (VectorType *VT = dyn_cast<VectorType>(Ty))
256  return isGCPointerType(VT->getScalarType());
257  if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
258  return containsGCPtrType(AT->getElementType());
259  if (StructType *ST = dyn_cast<StructType>(Ty))
260  return std::any_of(ST->subtypes().begin(), ST->subtypes().end(),
262  return false;
263 }
264 
265 // Debugging aid -- prints a [Begin, End) range of values.
266 template<typename IteratorTy>
267 static void PrintValueSet(raw_ostream &OS, IteratorTy Begin, IteratorTy End) {
268  OS << "[ ";
269  while (Begin != End) {
270  OS << **Begin << " ";
271  ++Begin;
272  }
273  OS << "]";
274 }
275 
276 /// The verifier algorithm is phrased in terms of availability. The set of
277 /// values "available" at a given point in the control flow graph is the set of
278 /// correctly relocated value at that point, and is a subset of the set of
279 /// definitions dominating that point.
280 
282 
283 /// State we compute and track per basic block.
285  // Set of values available coming in, before the phi nodes
287 
288  // Set of values available going out
290 
291  // AvailableOut minus AvailableIn.
292  // All elements are Instructions
294 
295  // True if this block contains a safepoint and thus AvailableIn does not
296  // contribute to AvailableOut.
297  bool Cleared = false;
298 };
299 
300 /// A given derived pointer can have multiple base pointers through phi/selects.
301 /// This type indicates when the base pointer is exclusively constant
302 /// (ExclusivelySomeConstant), and if that constant is proven to be exclusively
303 /// null, we record that as ExclusivelyNull. In all other cases, the BaseType is
304 /// NonConstant.
305 enum BaseType {
306  NonConstant = 1, // Base pointers is not exclusively constant.
308  ExclusivelySomeConstant // Base pointers for a given derived pointer is from a
309  // set of constants, but they are not exclusively
310  // null.
311 };
312 
313 /// Return the baseType for Val which states whether Val is exclusively
314 /// derived from constant/null, or not exclusively derived from constant.
315 /// Val is exclusively derived off a constant base when all operands of phi and
316 /// selects are derived off a constant base.
317 static enum BaseType getBaseType(const Value *Val) {
318 
320  DenseSet<const Value *> Visited;
321  bool isExclusivelyDerivedFromNull = true;
322  Worklist.push_back(Val);
323  // Strip through all the bitcasts and geps to get base pointer. Also check for
324  // the exclusive value when there can be multiple base pointers (through phis
325  // or selects).
326  while(!Worklist.empty()) {
327  const Value *V = Worklist.pop_back_val();
328  if (!Visited.insert(V).second)
329  continue;
330 
331  if (const auto *CI = dyn_cast<CastInst>(V)) {
332  Worklist.push_back(CI->stripPointerCasts());
333  continue;
334  }
335  if (const auto *GEP = dyn_cast<GetElementPtrInst>(V)) {
336  Worklist.push_back(GEP->getPointerOperand());
337  continue;
338  }
339  // Push all the incoming values of phi node into the worklist for
340  // processing.
341  if (const auto *PN = dyn_cast<PHINode>(V)) {
342  for (Value *InV: PN->incoming_values())
343  Worklist.push_back(InV);
344  continue;
345  }
346  if (const auto *SI = dyn_cast<SelectInst>(V)) {
347  // Push in the true and false values
348  Worklist.push_back(SI->getTrueValue());
349  Worklist.push_back(SI->getFalseValue());
350  continue;
351  }
352  if (isa<Constant>(V)) {
353  // We found at least one base pointer which is non-null, so this derived
354  // pointer is not exclusively derived from null.
355  if (V != Constant::getNullValue(V->getType()))
356  isExclusivelyDerivedFromNull = false;
357  // Continue processing the remaining values to make sure it's exclusively
358  // constant.
359  continue;
360  }
361  // At this point, we know that the base pointer is not exclusively
362  // constant.
363  return BaseType::NonConstant;
364  }
365  // Now, we know that the base pointer is exclusively constant, but we need to
366  // differentiate between exclusive null constant and non-null constant.
367  return isExclusivelyDerivedFromNull ? BaseType::ExclusivelyNull
369 }
370 
371 static bool isNotExclusivelyConstantDerived(const Value *V) {
372  return getBaseType(V) == BaseType::NonConstant;
373 }
374 
375 namespace {
376 class InstructionVerifier;
377 
378 /// Builds BasicBlockState for each BB of the function.
379 /// It can traverse function for verification and provides all required
380 /// information.
381 ///
382 /// GC pointer may be in one of three states: relocated, unrelocated and
383 /// poisoned.
384 /// Relocated pointer may be used without any restrictions.
385 /// Unrelocated pointer cannot be dereferenced, passed as argument to any call
386 /// or returned. Unrelocated pointer may be safely compared against another
387 /// unrelocated pointer or against a pointer exclusively derived from null.
388 /// Poisoned pointers are produced when we somehow derive pointer from relocated
389 /// and unrelocated pointers (e.g. phi, select). This pointers may be safely
390 /// used in a very limited number of situations. Currently the only way to use
391 /// it is comparison against constant exclusively derived from null. All
392 /// limitations arise due to their undefined state: this pointers should be
393 /// treated as relocated and unrelocated simultaneously.
394 /// Rules of deriving:
395 /// R + U = P - that's where the poisoned pointers come from
396 /// P + X = P
397 /// U + U = U
398 /// R + R = R
399 /// X + C = X
400 /// Where "+" - any operation that somehow derive pointer, U - unrelocated,
401 /// R - relocated and P - poisoned, C - constant, X - U or R or P or C or
402 /// nothing (in case when "+" is unary operation).
403 /// Deriving of pointers by itself is always safe.
404 /// NOTE: when we are making decision on the status of instruction's result:
405 /// a) for phi we need to check status of each input *at the end of
406 /// corresponding predecessor BB*.
407 /// b) for other instructions we need to check status of each input *at the
408 /// current point*.
409 ///
410 /// FIXME: This works fairly well except one case
411 /// bb1:
412 /// p = *some GC-ptr def*
413 /// p1 = gep p, offset
414 /// / |
415 /// / |
416 /// bb2: |
417 /// safepoint |
418 /// \ |
419 /// \ |
420 /// bb3:
421 /// p2 = phi [p, bb2] [p1, bb1]
422 /// p3 = phi [p, bb2] [p, bb1]
423 /// here p and p1 is unrelocated
424 /// p2 and p3 is poisoned (though they shouldn't be)
425 ///
426 /// This leads to some weird results:
427 /// cmp eq p, p2 - illegal instruction (false-positive)
428 /// cmp eq p1, p2 - illegal instruction (false-positive)
429 /// cmp eq p, p3 - illegal instruction (false-positive)
430 /// cmp eq p, p1 - ok
431 /// To fix this we need to introduce conception of generations and be able to
432 /// check if two values belong to one generation or not. This way p2 will be
433 /// considered to be unrelocated and no false alarm will happen.
434 class GCPtrTracker {
435  const Function &F;
436  const CFGDeadness &CD;
439  // This set contains defs of unrelocated pointers that are proved to be legal
440  // and don't need verification.
441  DenseSet<const Instruction *> ValidUnrelocatedDefs;
442  // This set contains poisoned defs. They can be safely ignored during
443  // verification too.
444  DenseSet<const Value *> PoisonedDefs;
445 
446 public:
447  GCPtrTracker(const Function &F, const DominatorTree &DT,
448  const CFGDeadness &CD);
449 
450  bool hasLiveIncomingEdge(const PHINode *PN, const BasicBlock *InBB) const {
451  return CD.hasLiveIncomingEdge(PN, InBB);
452  }
453 
454  BasicBlockState *getBasicBlockState(const BasicBlock *BB);
455  const BasicBlockState *getBasicBlockState(const BasicBlock *BB) const;
456 
457  bool isValuePoisoned(const Value *V) const { return PoisonedDefs.count(V); }
458 
459  /// Traverse each BB of the function and call
460  /// InstructionVerifier::verifyInstruction for each possibly invalid
461  /// instruction.
462  /// It destructively modifies GCPtrTracker so it's passed via rvalue reference
463  /// in order to prohibit further usages of GCPtrTracker as it'll be in
464  /// inconsistent state.
465  static void verifyFunction(GCPtrTracker &&Tracker,
466  InstructionVerifier &Verifier);
467 
468  /// Returns true for reachable and live blocks.
469  bool isMapped(const BasicBlock *BB) const {
470  return BlockMap.find(BB) != BlockMap.end();
471  }
472 
473 private:
474  /// Returns true if the instruction may be safely skipped during verification.
475  bool instructionMayBeSkipped(const Instruction *I) const;
476 
477  /// Iterates over all BBs from BlockMap and recalculates AvailableIn/Out for
478  /// each of them until it converges.
479  void recalculateBBsStates();
480 
481  /// Remove from Contribution all defs that legally produce unrelocated
482  /// pointers and saves them to ValidUnrelocatedDefs.
483  /// Though Contribution should belong to BBS it is passed separately with
484  /// different const-modifier in order to emphasize (and guarantee) that only
485  /// Contribution will be changed.
486  /// Returns true if Contribution was changed otherwise false.
487  bool removeValidUnrelocatedDefs(const BasicBlock *BB,
488  const BasicBlockState *BBS,
489  AvailableValueSet &Contribution);
490 
491  /// Gather all the definitions dominating the start of BB into Result. This is
492  /// simply the defs introduced by every dominating basic block and the
493  /// function arguments.
494  void gatherDominatingDefs(const BasicBlock *BB, AvailableValueSet &Result,
495  const DominatorTree &DT);
496 
497  /// Compute the AvailableOut set for BB, based on the BasicBlockState BBS,
498  /// which is the BasicBlockState for BB.
499  /// ContributionChanged is set when the verifier runs for the first time
500  /// (in this case Contribution was changed from 'empty' to its initial state)
501  /// or when Contribution of this BB was changed since last computation.
502  static void transferBlock(const BasicBlock *BB, BasicBlockState &BBS,
503  bool ContributionChanged);
504 
505  /// Model the effect of an instruction on the set of available values.
506  static void transferInstruction(const Instruction &I, bool &Cleared,
507  AvailableValueSet &Available);
508 };
509 
510 /// It is a visitor for GCPtrTracker::verifyFunction. It decides if the
511 /// instruction (which uses heap reference) is legal or not, given our safepoint
512 /// semantics.
513 class InstructionVerifier {
514  bool AnyInvalidUses = false;
515 
516 public:
517  void verifyInstruction(const GCPtrTracker *Tracker, const Instruction &I,
518  const AvailableValueSet &AvailableSet);
519 
520  bool hasAnyInvalidUses() const { return AnyInvalidUses; }
521 
522 private:
523  void reportInvalidUse(const Value &V, const Instruction &I);
524 };
525 } // end anonymous namespace
526 
527 GCPtrTracker::GCPtrTracker(const Function &F, const DominatorTree &DT,
528  const CFGDeadness &CD) : F(F), CD(CD) {
529  // Calculate Contribution of each live BB.
530  // Allocate BB states for live blocks.
531  for (const BasicBlock &BB : F)
532  if (!CD.isDeadBlock(&BB)) {
533  BasicBlockState *BBS = new (BSAllocator.Allocate()) BasicBlockState;
534  for (const auto &I : BB)
535  transferInstruction(I, BBS->Cleared, BBS->Contribution);
536  BlockMap[&BB] = BBS;
537  }
538 
539  // Initialize AvailableIn/Out sets of each BB using only information about
540  // dominating BBs.
541  for (auto &BBI : BlockMap) {
542  gatherDominatingDefs(BBI.first, BBI.second->AvailableIn, DT);
543  transferBlock(BBI.first, *BBI.second, true);
544  }
545 
546  // Simulate the flow of defs through the CFG and recalculate AvailableIn/Out
547  // sets of each BB until it converges. If any def is proved to be an
548  // unrelocated pointer, it will be removed from all BBSs.
549  recalculateBBsStates();
550 }
551 
552 BasicBlockState *GCPtrTracker::getBasicBlockState(const BasicBlock *BB) {
553  auto it = BlockMap.find(BB);
554  return it != BlockMap.end() ? it->second : nullptr;
555 }
556 
557 const BasicBlockState *GCPtrTracker::getBasicBlockState(
558  const BasicBlock *BB) const {
559  return const_cast<GCPtrTracker *>(this)->getBasicBlockState(BB);
560 }
561 
562 bool GCPtrTracker::instructionMayBeSkipped(const Instruction *I) const {
563  // Poisoned defs are skipped since they are always safe by itself by
564  // definition (for details see comment to this class).
565  return ValidUnrelocatedDefs.count(I) || PoisonedDefs.count(I);
566 }
567 
568 void GCPtrTracker::verifyFunction(GCPtrTracker &&Tracker,
569  InstructionVerifier &Verifier) {
570  // We need RPO here to a) report always the first error b) report errors in
571  // same order from run to run.
573  for (const BasicBlock *BB : RPOT) {
574  BasicBlockState *BBS = Tracker.getBasicBlockState(BB);
575  if (!BBS)
576  continue;
577 
578  // We destructively modify AvailableIn as we traverse the block instruction
579  // by instruction.
580  AvailableValueSet &AvailableSet = BBS->AvailableIn;
581  for (const Instruction &I : *BB) {
582  if (Tracker.instructionMayBeSkipped(&I))
583  continue; // This instruction shouldn't be added to AvailableSet.
584 
585  Verifier.verifyInstruction(&Tracker, I, AvailableSet);
586 
587  // Model the effect of current instruction on AvailableSet to keep the set
588  // relevant at each point of BB.
589  bool Cleared = false;
590  transferInstruction(I, Cleared, AvailableSet);
591  (void)Cleared;
592  }
593  }
594 }
595 
596 void GCPtrTracker::recalculateBBsStates() {
598  // TODO: This order is suboptimal, it's better to replace it with priority
599  // queue where priority is RPO number of BB.
600  for (auto &BBI : BlockMap)
601  Worklist.insert(BBI.first);
602 
603  // This loop iterates the AvailableIn/Out sets until it converges.
604  // The AvailableIn and AvailableOut sets decrease as we iterate.
605  while (!Worklist.empty()) {
606  const BasicBlock *BB = Worklist.pop_back_val();
607  BasicBlockState *BBS = getBasicBlockState(BB);
608  if (!BBS)
609  continue; // Ignore dead successors.
610 
611  size_t OldInCount = BBS->AvailableIn.size();
612  for (const_pred_iterator PredIt(BB), End(BB, true); PredIt != End; ++PredIt) {
613  const BasicBlock *PBB = *PredIt;
614  BasicBlockState *PBBS = getBasicBlockState(PBB);
615  if (PBBS && !CD.isDeadEdge(&CFGDeadness::getEdge(PredIt)))
617  }
618 
619  assert(OldInCount >= BBS->AvailableIn.size() && "invariant!");
620 
621  bool InputsChanged = OldInCount != BBS->AvailableIn.size();
622  bool ContributionChanged =
623  removeValidUnrelocatedDefs(BB, BBS, BBS->Contribution);
624  if (!InputsChanged && !ContributionChanged)
625  continue;
626 
627  size_t OldOutCount = BBS->AvailableOut.size();
628  transferBlock(BB, *BBS, ContributionChanged);
629  if (OldOutCount != BBS->AvailableOut.size()) {
630  assert(OldOutCount > BBS->AvailableOut.size() && "invariant!");
631  Worklist.insert(succ_begin(BB), succ_end(BB));
632  }
633  }
634 }
635 
636 bool GCPtrTracker::removeValidUnrelocatedDefs(const BasicBlock *BB,
637  const BasicBlockState *BBS,
638  AvailableValueSet &Contribution) {
639  assert(&BBS->Contribution == &Contribution &&
640  "Passed Contribution should be from the passed BasicBlockState!");
641  AvailableValueSet AvailableSet = BBS->AvailableIn;
642  bool ContributionChanged = false;
643  // For explanation why instructions are processed this way see
644  // "Rules of deriving" in the comment to this class.
645  for (const Instruction &I : *BB) {
646  bool ValidUnrelocatedPointerDef = false;
647  bool PoisonedPointerDef = false;
648  // TODO: `select` instructions should be handled here too.
649  if (const PHINode *PN = dyn_cast<PHINode>(&I)) {
650  if (containsGCPtrType(PN->getType())) {
651  // If both is true, output is poisoned.
652  bool HasRelocatedInputs = false;
653  bool HasUnrelocatedInputs = false;
654  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
655  const BasicBlock *InBB = PN->getIncomingBlock(i);
656  if (!isMapped(InBB) ||
657  !CD.hasLiveIncomingEdge(PN, InBB))
658  continue; // Skip dead block or dead edge.
659 
660  const Value *InValue = PN->getIncomingValue(i);
661 
662  if (isNotExclusivelyConstantDerived(InValue)) {
663  if (isValuePoisoned(InValue)) {
664  // If any of inputs is poisoned, output is always poisoned too.
665  HasRelocatedInputs = true;
666  HasUnrelocatedInputs = true;
667  break;
668  }
669  if (BlockMap[InBB]->AvailableOut.count(InValue))
670  HasRelocatedInputs = true;
671  else
672  HasUnrelocatedInputs = true;
673  }
674  }
675  if (HasUnrelocatedInputs) {
676  if (HasRelocatedInputs)
677  PoisonedPointerDef = true;
678  else
679  ValidUnrelocatedPointerDef = true;
680  }
681  }
682  } else if ((isa<GetElementPtrInst>(I) || isa<BitCastInst>(I)) &&
683  containsGCPtrType(I.getType())) {
684  // GEP/bitcast of unrelocated pointer is legal by itself but this def
685  // shouldn't appear in any AvailableSet.
686  for (const Value *V : I.operands())
687  if (containsGCPtrType(V->getType()) &&
688  isNotExclusivelyConstantDerived(V) && !AvailableSet.count(V)) {
689  if (isValuePoisoned(V))
690  PoisonedPointerDef = true;
691  else
692  ValidUnrelocatedPointerDef = true;
693  break;
694  }
695  }
696  assert(!(ValidUnrelocatedPointerDef && PoisonedPointerDef) &&
697  "Value cannot be both unrelocated and poisoned!");
698  if (ValidUnrelocatedPointerDef) {
699  // Remove def of unrelocated pointer from Contribution of this BB and
700  // trigger update of all its successors.
701  Contribution.erase(&I);
702  PoisonedDefs.erase(&I);
703  ValidUnrelocatedDefs.insert(&I);
704  LLVM_DEBUG(dbgs() << "Removing urelocated " << I
705  << " from Contribution of " << BB->getName() << "\n");
706  ContributionChanged = true;
707  } else if (PoisonedPointerDef) {
708  // Mark pointer as poisoned, remove its def from Contribution and trigger
709  // update of all successors.
710  Contribution.erase(&I);
711  PoisonedDefs.insert(&I);
712  LLVM_DEBUG(dbgs() << "Removing poisoned " << I << " from Contribution of "
713  << BB->getName() << "\n");
714  ContributionChanged = true;
715  } else {
716  bool Cleared = false;
717  transferInstruction(I, Cleared, AvailableSet);
718  (void)Cleared;
719  }
720  }
721  return ContributionChanged;
722 }
723 
724 void GCPtrTracker::gatherDominatingDefs(const BasicBlock *BB,
726  const DominatorTree &DT) {
727  DomTreeNode *DTN = DT[const_cast<BasicBlock *>(BB)];
728 
729  assert(DTN && "Unreachable blocks are ignored");
730  while (DTN->getIDom()) {
731  DTN = DTN->getIDom();
732  auto BBS = getBasicBlockState(DTN->getBlock());
733  assert(BBS && "immediate dominator cannot be dead for a live block");
734  const auto &Defs = BBS->Contribution;
735  Result.insert(Defs.begin(), Defs.end());
736  // If this block is 'Cleared', then nothing LiveIn to this block can be
737  // available after this block completes. Note: This turns out to be
738  // really important for reducing memory consuption of the initial available
739  // sets and thus peak memory usage by this verifier.
740  if (BBS->Cleared)
741  return;
742  }
743 
744  for (const Argument &A : BB->getParent()->args())
745  if (containsGCPtrType(A.getType()))
746  Result.insert(&A);
747 }
748 
749 void GCPtrTracker::transferBlock(const BasicBlock *BB, BasicBlockState &BBS,
750  bool ContributionChanged) {
751  const AvailableValueSet &AvailableIn = BBS.AvailableIn;
752  AvailableValueSet &AvailableOut = BBS.AvailableOut;
753 
754  if (BBS.Cleared) {
755  // AvailableOut will change only when Contribution changed.
756  if (ContributionChanged)
757  AvailableOut = BBS.Contribution;
758  } else {
759  // Otherwise, we need to reduce the AvailableOut set by things which are no
760  // longer in our AvailableIn
761  AvailableValueSet Temp = BBS.Contribution;
762  set_union(Temp, AvailableIn);
763  AvailableOut = std::move(Temp);
764  }
765 
766  LLVM_DEBUG(dbgs() << "Transfered block " << BB->getName() << " from ";
767  PrintValueSet(dbgs(), AvailableIn.begin(), AvailableIn.end());
768  dbgs() << " to ";
769  PrintValueSet(dbgs(), AvailableOut.begin(), AvailableOut.end());
770  dbgs() << "\n";);
771 }
772 
773 void GCPtrTracker::transferInstruction(const Instruction &I, bool &Cleared,
774  AvailableValueSet &Available) {
775  if (isStatepoint(I)) {
776  Cleared = true;
777  Available.clear();
778  } else if (containsGCPtrType(I.getType()))
779  Available.insert(&I);
780 }
781 
782 void InstructionVerifier::verifyInstruction(
783  const GCPtrTracker *Tracker, const Instruction &I,
784  const AvailableValueSet &AvailableSet) {
785  if (const PHINode *PN = dyn_cast<PHINode>(&I)) {
786  if (containsGCPtrType(PN->getType()))
787  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
788  const BasicBlock *InBB = PN->getIncomingBlock(i);
789  const BasicBlockState *InBBS = Tracker->getBasicBlockState(InBB);
790  if (!InBBS ||
791  !Tracker->hasLiveIncomingEdge(PN, InBB))
792  continue; // Skip dead block or dead edge.
793 
794  const Value *InValue = PN->getIncomingValue(i);
795 
796  if (isNotExclusivelyConstantDerived(InValue) &&
797  !InBBS->AvailableOut.count(InValue))
798  reportInvalidUse(*InValue, *PN);
799  }
800  } else if (isa<CmpInst>(I) &&
802  Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
803  enum BaseType baseTyLHS = getBaseType(LHS),
804  baseTyRHS = getBaseType(RHS);
805 
806  // Returns true if LHS and RHS are unrelocated pointers and they are
807  // valid unrelocated uses.
808  auto hasValidUnrelocatedUse = [&AvailableSet, Tracker, baseTyLHS, baseTyRHS,
809  &LHS, &RHS] () {
810  // A cmp instruction has valid unrelocated pointer operands only if
811  // both operands are unrelocated pointers.
812  // In the comparison between two pointers, if one is an unrelocated
813  // use, the other *should be* an unrelocated use, for this
814  // instruction to contain valid unrelocated uses. This unrelocated
815  // use can be a null constant as well, or another unrelocated
816  // pointer.
817  if (AvailableSet.count(LHS) || AvailableSet.count(RHS))
818  return false;
819  // Constant pointers (that are not exclusively null) may have
820  // meaning in different VMs, so we cannot reorder the compare
821  // against constant pointers before the safepoint. In other words,
822  // comparison of an unrelocated use against a non-null constant
823  // maybe invalid.
824  if ((baseTyLHS == BaseType::ExclusivelySomeConstant &&
825  baseTyRHS == BaseType::NonConstant) ||
826  (baseTyLHS == BaseType::NonConstant &&
827  baseTyRHS == BaseType::ExclusivelySomeConstant))
828  return false;
829 
830  // If one of pointers is poisoned and other is not exclusively derived
831  // from null it is an invalid expression: it produces poisoned result
832  // and unless we want to track all defs (not only gc pointers) the only
833  // option is to prohibit such instructions.
834  if ((Tracker->isValuePoisoned(LHS) && baseTyRHS != ExclusivelyNull) ||
835  (Tracker->isValuePoisoned(RHS) && baseTyLHS != ExclusivelyNull))
836  return false;
837 
838  // All other cases are valid cases enumerated below:
839  // 1. Comparison between an exclusively derived null pointer and a
840  // constant base pointer.
841  // 2. Comparison between an exclusively derived null pointer and a
842  // non-constant unrelocated base pointer.
843  // 3. Comparison between 2 unrelocated pointers.
844  // 4. Comparison between a pointer exclusively derived from null and a
845  // non-constant poisoned pointer.
846  return true;
847  };
848  if (!hasValidUnrelocatedUse()) {
849  // Print out all non-constant derived pointers that are unrelocated
850  // uses, which are invalid.
851  if (baseTyLHS == BaseType::NonConstant && !AvailableSet.count(LHS))
852  reportInvalidUse(*LHS, I);
853  if (baseTyRHS == BaseType::NonConstant && !AvailableSet.count(RHS))
854  reportInvalidUse(*RHS, I);
855  }
856  } else {
857  for (const Value *V : I.operands())
858  if (containsGCPtrType(V->getType()) &&
859  isNotExclusivelyConstantDerived(V) && !AvailableSet.count(V))
860  reportInvalidUse(*V, I);
861  }
862 }
863 
864 void InstructionVerifier::reportInvalidUse(const Value &V,
865  const Instruction &I) {
866  errs() << "Illegal use of unrelocated value found!\n";
867  errs() << "Def: " << V << "\n";
868  errs() << "Use: " << I << "\n";
869  if (!PrintOnly)
870  abort();
871  AnyInvalidUses = true;
872 }
873 
874 static void Verify(const Function &F, const DominatorTree &DT,
875  const CFGDeadness &CD) {
876  LLVM_DEBUG(dbgs() << "Verifying gc pointers in function: " << F.getName()
877  << "\n");
878  if (PrintOnly)
879  dbgs() << "Verifying gc pointers in function: " << F.getName() << "\n";
880 
881  GCPtrTracker Tracker(F, DT, CD);
882 
883  // We now have all the information we need to decide if the use of a heap
884  // reference is legal or not, given our safepoint semantics.
885 
886  InstructionVerifier Verifier;
887  GCPtrTracker::verifyFunction(std::move(Tracker), Verifier);
888 
889  if (PrintOnly && !Verifier.hasAnyInvalidUses()) {
890  dbgs() << "No illegal uses found by SafepointIRVerifier in: " << F.getName()
891  << "\n";
892  }
893 }
static void PrintValueSet(raw_ostream &OS, IteratorTy Begin, IteratorTy End)
Safe Stack instrumentation pass
Definition: SafeStack.cpp:910
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:250
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:96
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
const Instruction * 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
bool isReachableFromEntry(const Use &U) const
Provide an overload for a Use.
Definition: Dominators.cpp:300
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:145
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:98
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")
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:58
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:129
std::pair< iterator, bool > insert(const ValueT &V)
Definition: DenseSet.h:188
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:1049
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:847
Module.h This file contains the declarations for the Module class.
size_type size() const
Definition: DenseSet.h:76
LLVM_NODISCARD T pop_back_val()
Definition: SmallVector.h:381
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:415
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:133
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:107
#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:4703
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:92
bool isStatepoint(ImmutableCallSite CS)
Definition: Statepoint.cpp:27
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
LLVM Value Representation.
Definition: Value.h:73
A vector that has set insertion semantics.
Definition: SetVector.h:41
succ_range successors(Instruction *I)
Definition: CFG.h:262
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:260
#define LLVM_DEBUG(X)
Definition: Debug.h:123
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:689
const BasicBlock * getParent() const
Definition: Instruction.h:67
static void Verify(const Function &F, const DominatorTree &DT, const CFGDeadness &CD)