1 //===- LazyValueInfo.cpp - Value constraint analysis ----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the interface for lazy computation of value constraint
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Analysis/LazyValueInfo.h"
16 #include "llvm/ADT/DenseSet.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/Analysis/AssumptionTracker.h"
19 #include "llvm/Analysis/ConstantFolding.h"
20 #include "llvm/Analysis/ValueTracking.h"
21 #include "llvm/IR/CFG.h"
22 #include "llvm/IR/ConstantRange.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/Dominators.h"
26 #include "llvm/IR/Instructions.h"
27 #include "llvm/IR/IntrinsicInst.h"
28 #include "llvm/IR/PatternMatch.h"
29 #include "llvm/IR/ValueHandle.h"
30 #include "llvm/Support/CommandLine.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/raw_ostream.h"
33 #include "llvm/Target/TargetLibraryInfo.h"
37 using namespace PatternMatch;
39 #define DEBUG_TYPE "lazy-value-info"
41 // Experimentally derived threshold for the number of basic blocks lowered for
42 // lattice value overdefined.
43 static cl::opt<unsigned>
44 OverdefinedBBThreshold("lvi-overdefined-BB-threshold",
45 cl::init(1500), cl::Hidden,
46 cl::desc("Threshold of the number of basic blocks lowered for lattice value"
49 // Experimentally derived threshold for additional lowering lattice values
50 // overdefined per block.
51 static cl::opt<unsigned>
52 OverdefinedThreshold("lvi-overdefined-threshold", cl::init(10), cl::Hidden,
53 cl::desc("Threshold of lowering lattice value 'overdefined'."));
55 char LazyValueInfo::ID = 0;
56 INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
57 "Lazy Value Information Analysis", false, true)
58 INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
59 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
60 INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info",
61 "Lazy Value Information Analysis", false, true)
64 FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
68 //===----------------------------------------------------------------------===//
70 //===----------------------------------------------------------------------===//
72 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each
75 /// FIXME: This is basically just for bringup, this can be made a lot more rich
81 /// undefined - This Value has no known value yet.
84 /// constant - This Value has a specific constant value.
86 /// notconstant - This Value is known to not have the specified value.
89 /// constantrange - The Value falls within this range.
92 /// overdefined - This value is not known to be constant, and we know that
97 /// Val: This stores the current lattice value along with the Constant* for
98 /// the constant if this is a 'constant' or 'notconstant' value.
104 LVILatticeVal() : Tag(undefined), Val(nullptr), Range(1, true) {}
106 static LVILatticeVal get(Constant *C) {
108 if (!isa<UndefValue>(C))
112 static LVILatticeVal getNot(Constant *C) {
114 if (!isa<UndefValue>(C))
115 Res.markNotConstant(C);
118 static LVILatticeVal getRange(ConstantRange CR) {
120 Res.markConstantRange(CR);
124 bool isUndefined() const { return Tag == undefined; }
125 bool isConstant() const { return Tag == constant; }
126 bool isNotConstant() const { return Tag == notconstant; }
127 bool isConstantRange() const { return Tag == constantrange; }
128 bool isOverdefined() const { return Tag == overdefined; }
130 Constant *getConstant() const {
131 assert(isConstant() && "Cannot get the constant of a non-constant!");
135 Constant *getNotConstant() const {
136 assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
140 ConstantRange getConstantRange() const {
141 assert(isConstantRange() &&
142 "Cannot get the constant-range of a non-constant-range!");
146 /// markOverdefined - Return true if this is a change in status.
147 bool markOverdefined() {
154 /// markConstant - Return true if this is a change in status.
155 bool markConstant(Constant *V) {
156 assert(V && "Marking constant with NULL");
157 if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
158 return markConstantRange(ConstantRange(CI->getValue()));
159 if (isa<UndefValue>(V))
162 assert((!isConstant() || getConstant() == V) &&
163 "Marking constant with different value");
164 assert(isUndefined());
170 /// markNotConstant - Return true if this is a change in status.
171 bool markNotConstant(Constant *V) {
172 assert(V && "Marking constant with NULL");
173 if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
174 return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
175 if (isa<UndefValue>(V))
178 assert((!isConstant() || getConstant() != V) &&
179 "Marking constant !constant with same value");
180 assert((!isNotConstant() || getNotConstant() == V) &&
181 "Marking !constant with different value");
182 assert(isUndefined() || isConstant());
188 /// markConstantRange - Return true if this is a change in status.
189 bool markConstantRange(const ConstantRange NewR) {
190 if (isConstantRange()) {
191 if (NewR.isEmptySet())
192 return markOverdefined();
194 bool changed = Range != NewR;
199 assert(isUndefined());
200 if (NewR.isEmptySet())
201 return markOverdefined();
208 /// mergeIn - Merge the specified lattice value into this one, updating this
209 /// one and returning true if anything changed.
210 bool mergeIn(const LVILatticeVal &RHS) {
211 if (RHS.isUndefined() || isOverdefined()) return false;
212 if (RHS.isOverdefined()) return markOverdefined();
222 if (RHS.isConstant()) {
225 return markOverdefined();
228 if (RHS.isNotConstant()) {
230 return markOverdefined();
232 // Unless we can prove that the two Constants are different, we must
233 // move to overdefined.
234 // FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
235 if (ConstantInt *Res = dyn_cast<ConstantInt>(
236 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
238 RHS.getNotConstant())))
240 return markNotConstant(RHS.getNotConstant());
242 return markOverdefined();
245 // RHS is a ConstantRange, LHS is a non-integer Constant.
247 // FIXME: consider the case where RHS is a range [1, 0) and LHS is
248 // a function. The correct result is to pick up RHS.
250 return markOverdefined();
253 if (isNotConstant()) {
254 if (RHS.isConstant()) {
256 return markOverdefined();
258 // Unless we can prove that the two Constants are different, we must
259 // move to overdefined.
260 // FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
261 if (ConstantInt *Res = dyn_cast<ConstantInt>(
262 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
268 return markOverdefined();
271 if (RHS.isNotConstant()) {
274 return markOverdefined();
277 return markOverdefined();
280 assert(isConstantRange() && "New LVILattice type?");
281 if (!RHS.isConstantRange())
282 return markOverdefined();
284 ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
285 if (NewR.isFullSet())
286 return markOverdefined();
287 return markConstantRange(NewR);
291 } // end anonymous namespace.
294 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
296 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
297 if (Val.isUndefined())
298 return OS << "undefined";
299 if (Val.isOverdefined())
300 return OS << "overdefined";
302 if (Val.isNotConstant())
303 return OS << "notconstant<" << *Val.getNotConstant() << '>';
304 else if (Val.isConstantRange())
305 return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
306 << Val.getConstantRange().getUpper() << '>';
307 return OS << "constant<" << *Val.getConstant() << '>';
311 //===----------------------------------------------------------------------===//
312 // LazyValueInfoCache Decl
313 //===----------------------------------------------------------------------===//
316 /// LVIValueHandle - A callback value handle updates the cache when
317 /// values are erased.
318 class LazyValueInfoCache;
319 struct LVIValueHandle : public CallbackVH {
320 LazyValueInfoCache *Parent;
322 LVIValueHandle(Value *V, LazyValueInfoCache *P)
323 : CallbackVH(V), Parent(P) { }
325 void deleted() override;
326 void allUsesReplacedWith(Value *V) override {
333 /// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
334 /// maintains information about queries across the clients' queries.
335 class LazyValueInfoCache {
336 /// ValueCacheEntryTy - This is all of the cached block information for
337 /// exactly one Value*. The entries are sorted by the BasicBlock* of the
338 /// entries, allowing us to do a lookup with a binary search.
339 typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy;
341 /// ValueCache - This is all of the cached information for all values,
342 /// mapped from Value* to key information.
343 std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache;
345 /// OverDefinedCache - This tracks, on a per-block basis, the set of
346 /// values that are over-defined at the end of that block. This is required
347 /// for cache updating.
348 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
349 DenseSet<OverDefinedPairTy> OverDefinedCache;
351 /// SeenBlocks - Keep track of all blocks that we have ever seen, so we
352 /// don't spend time removing unused blocks from our caches.
353 DenseSet<AssertingVH<BasicBlock> > SeenBlocks;
355 /// BlockValueStack - This stack holds the state of the value solver
356 /// during a query. It basically emulates the callstack of the naive
357 /// recursive value lookup process.
358 std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
360 /// A pointer to the cache of @llvm.assume calls.
361 AssumptionTracker *AT;
362 /// An optional DL pointer.
363 const DataLayout *DL;
364 /// An optional DT pointer.
366 /// A counter to record how many times Overdefined has been tried to be
368 DenseMap<BasicBlock *, unsigned> LoweringOverdefinedTimes;
370 friend struct LVIValueHandle;
372 /// OverDefinedCacheUpdater - A helper object that ensures that the
373 /// OverDefinedCache is updated whenever solveBlockValue returns.
374 struct OverDefinedCacheUpdater {
375 LazyValueInfoCache *Parent;
380 OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV,
381 LazyValueInfoCache *P)
382 : Parent(P), Val(V), BB(B), BBLV(LV) { }
384 bool markResult(bool changed) {
385 if (changed && BBLV.isOverdefined())
386 Parent->OverDefinedCache.insert(std::make_pair(BB, Val));
393 LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
394 bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
395 LVILatticeVal &Result,
396 Instruction *CxtI = nullptr);
397 bool hasBlockValue(Value *Val, BasicBlock *BB);
399 // These methods process one work item and may add more. A false value
400 // returned means that the work item was not completely processed and must
401 // be revisited after going through the new items.
402 bool solveBlockValue(Value *Val, BasicBlock *BB);
403 bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
404 Value *Val, BasicBlock *BB);
405 bool solveBlockValuePHINode(LVILatticeVal &BBLV,
406 PHINode *PN, BasicBlock *BB);
407 bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
408 Instruction *BBI, BasicBlock *BB);
409 void mergeAssumeBlockValueConstantRange(Value *Val, LVILatticeVal &BBLV,
414 ValueCacheEntryTy &lookup(Value *V) {
415 return ValueCache[LVIValueHandle(V, this)];
419 /// getValueInBlock - This is the query interface to determine the lattice
420 /// value for the specified Value* at the end of the specified block.
421 LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB,
422 Instruction *CxtI = nullptr);
424 /// getValueAt - This is the query interface to determine the lattice
425 /// value for the specified Value* at the specified instruction (generally
426 /// from an assume intrinsic).
427 LVILatticeVal getValueAt(Value *V, Instruction *CxtI);
429 /// getValueOnEdge - This is the query interface to determine the lattice
430 /// value for the specified Value* that is true on the specified edge.
431 LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB,
432 Instruction *CxtI = nullptr);
434 /// threadEdge - This is the update interface to inform the cache that an
435 /// edge from PredBB to OldSucc has been threaded to be from PredBB to
437 void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
439 /// eraseBlock - This is part of the update interface to inform the cache
440 /// that a block has been deleted.
441 void eraseBlock(BasicBlock *BB);
443 /// clear - Empty the cache.
447 OverDefinedCache.clear();
450 LazyValueInfoCache(AssumptionTracker *AT,
451 const DataLayout *DL = nullptr,
452 DominatorTree *DT = nullptr) : AT(AT), DL(DL), DT(DT) {}
454 } // end anonymous namespace
456 void LVIValueHandle::deleted() {
457 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
459 SmallVector<OverDefinedPairTy, 4> ToErase;
460 for (DenseSet<OverDefinedPairTy>::iterator
461 I = Parent->OverDefinedCache.begin(),
462 E = Parent->OverDefinedCache.end();
464 if (I->second == getValPtr())
465 ToErase.push_back(*I);
468 for (SmallVectorImpl<OverDefinedPairTy>::iterator I = ToErase.begin(),
469 E = ToErase.end(); I != E; ++I)
470 Parent->OverDefinedCache.erase(*I);
472 // This erasure deallocates *this, so it MUST happen after we're done
473 // using any and all members of *this.
474 Parent->ValueCache.erase(*this);
477 void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
478 // Shortcut if we have never seen this block.
479 DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
480 if (I == SeenBlocks.end())
484 SmallVector<OverDefinedPairTy, 4> ToErase;
485 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
486 E = OverDefinedCache.end(); I != E; ++I) {
488 ToErase.push_back(*I);
491 for (SmallVectorImpl<OverDefinedPairTy>::iterator I = ToErase.begin(),
492 E = ToErase.end(); I != E; ++I)
493 OverDefinedCache.erase(*I);
495 for (std::map<LVIValueHandle, ValueCacheEntryTy>::iterator
496 I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
500 void LazyValueInfoCache::solve() {
501 // Reset the counter of lowering overdefined value.
502 LoweringOverdefinedTimes.clear();
504 while (!BlockValueStack.empty()) {
505 std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
506 if (solveBlockValue(e.second, e.first)) {
507 assert(BlockValueStack.top() == e);
508 BlockValueStack.pop();
513 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
514 // If already a constant, there is nothing to compute.
515 if (isa<Constant>(Val))
518 LVIValueHandle ValHandle(Val, this);
519 std::map<LVIValueHandle, ValueCacheEntryTy>::iterator I =
520 ValueCache.find(ValHandle);
521 if (I == ValueCache.end()) return false;
522 return I->second.count(BB);
525 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
526 // If already a constant, there is nothing to compute.
527 if (Constant *VC = dyn_cast<Constant>(Val))
528 return LVILatticeVal::get(VC);
530 SeenBlocks.insert(BB);
531 return lookup(Val)[BB];
534 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
535 if (isa<Constant>(Val))
538 ValueCacheEntryTy &Cache = lookup(Val);
539 SeenBlocks.insert(BB);
540 LVILatticeVal &BBLV = Cache[BB];
542 // OverDefinedCacheUpdater is a helper object that will update
543 // the OverDefinedCache for us when this method exits. Make sure to
544 // call markResult on it as we exist, passing a bool to indicate if the
545 // cache needs updating, i.e. if we have solve a new value or not.
546 OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this);
548 // Once this BB is encountered, Val's value for this BB will not be Undefined
549 // any longer. When we encounter this BB again, if Val's value is Overdefined,
550 // we need to compute its value again.
552 // For example, considering this control flow,
553 // BB1->BB2, BB1->BB3, BB2->BB3, BB2->BB4
555 // Suppose we have "icmp slt %v, 0" in BB1, and "icmp sgt %v, 0" in BB3. At
556 // the very beginning, when analyzing edge BB2->BB3, we don't know %v's value
557 // in BB2, and the data flow algorithm tries to compute BB2's predecessors, so
558 // then we know %v has negative value on edge BB1->BB2. And then we return to
559 // check BB2 again, and at this moment BB2 has Overdefined value for %v in
560 // BB2. So we should have to follow data flow propagation algorithm to get the
561 // value on edge BB1->BB2 propagated to BB2, and finally %v on BB2 has a
562 // constant range describing a negative value.
564 // In the mean time, limit the number of additional lowering lattice value to
565 // avoid unjustified memory grows.
567 if (LoweringOverdefinedTimes.count(BB) == 0)
568 LoweringOverdefinedTimes.insert(std::make_pair(BB, 0));
569 if ((!BBLV.isUndefined() && !BBLV.isOverdefined()) ||
570 (BBLV.isOverdefined() &&
571 (LoweringOverdefinedTimes[BB] > OverdefinedThreshold ||
572 LoweringOverdefinedTimes.size() > OverdefinedBBThreshold))) {
573 DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
575 // Since we're reusing a cached value here, we don't need to update the
576 // OverDefinedCahce. The cache will have been properly updated
577 // whenever the cached value was inserted.
578 ODCacheUpdater.markResult(false);
582 // Otherwise, this is the first time we're seeing this block. Reset the
583 // lattice value to overdefined, so that cycles will terminate and be
584 // conservatively correct.
585 BBLV.markOverdefined();
586 ++LoweringOverdefinedTimes[BB];
588 Instruction *BBI = dyn_cast<Instruction>(Val);
589 if (!BBI || BBI->getParent() != BB) {
590 return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB));
593 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
594 return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB));
597 if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
598 BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
599 return ODCacheUpdater.markResult(true);
602 // We can only analyze the definitions of certain classes of instructions
603 // (integral binops and casts at the moment), so bail if this isn't one.
604 LVILatticeVal Result;
605 if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
606 !BBI->getType()->isIntegerTy()) {
607 DEBUG(dbgs() << " compute BB '" << BB->getName()
608 << "' - overdefined because inst def found.\n");
609 BBLV.markOverdefined();
610 return ODCacheUpdater.markResult(true);
613 // FIXME: We're currently limited to binops with a constant RHS. This should
615 BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
616 if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
617 DEBUG(dbgs() << " compute BB '" << BB->getName()
618 << "' - overdefined because inst def found.\n");
620 BBLV.markOverdefined();
621 return ODCacheUpdater.markResult(true);
624 return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB));
627 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
628 if (LoadInst *L = dyn_cast<LoadInst>(I)) {
629 return L->getPointerAddressSpace() == 0 &&
630 GetUnderlyingObject(L->getPointerOperand()) == Ptr;
632 if (StoreInst *S = dyn_cast<StoreInst>(I)) {
633 return S->getPointerAddressSpace() == 0 &&
634 GetUnderlyingObject(S->getPointerOperand()) == Ptr;
636 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
637 if (MI->isVolatile()) return false;
639 // FIXME: check whether it has a valuerange that excludes zero?
640 ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
641 if (!Len || Len->isZero()) return false;
643 if (MI->getDestAddressSpace() == 0)
644 if (GetUnderlyingObject(MI->getRawDest()) == Ptr)
646 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
647 if (MTI->getSourceAddressSpace() == 0)
648 if (GetUnderlyingObject(MTI->getRawSource()) == Ptr)
654 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
655 Value *Val, BasicBlock *BB) {
656 LVILatticeVal Result; // Start Undefined.
658 // If this is a pointer, and there's a load from that pointer in this BB,
659 // then we know that the pointer can't be NULL.
660 bool NotNull = false;
661 if (Val->getType()->isPointerTy()) {
662 if (isKnownNonNull(Val)) {
665 Value *UnderlyingVal = GetUnderlyingObject(Val);
666 // If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
667 // inside InstructionDereferencesPointer either.
668 if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, nullptr, 1)) {
669 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
671 if (InstructionDereferencesPointer(BI, UnderlyingVal)) {
680 // If this is the entry block, we must be asking about an argument. The
681 // value is overdefined.
682 if (BB == &BB->getParent()->getEntryBlock()) {
683 assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
685 PointerType *PTy = cast<PointerType>(Val->getType());
686 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
688 Result.markOverdefined();
694 // Loop over all of our predecessors, merging what we know from them into
696 bool EdgesMissing = false;
697 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
698 LVILatticeVal EdgeResult;
699 EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
703 Result.mergeIn(EdgeResult);
705 // If we hit overdefined, exit early. The BlockVals entry is already set
707 if (Result.isOverdefined()) {
708 DEBUG(dbgs() << " compute BB '" << BB->getName()
709 << "' - overdefined because of pred.\n");
710 // If we previously determined that this is a pointer that can't be null
711 // then return that rather than giving up entirely.
713 PointerType *PTy = cast<PointerType>(Val->getType());
714 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
724 // Return the merged value, which is more precise than 'overdefined'.
725 assert(!Result.isOverdefined());
730 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
731 PHINode *PN, BasicBlock *BB) {
732 LVILatticeVal Result; // Start Undefined.
734 // Loop over all of our predecessors, merging what we know from them into
736 bool EdgesMissing = false;
737 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
738 BasicBlock *PhiBB = PN->getIncomingBlock(i);
739 Value *PhiVal = PN->getIncomingValue(i);
740 LVILatticeVal EdgeResult;
741 EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult, PN);
745 Result.mergeIn(EdgeResult);
747 // If we hit overdefined, exit early. The BlockVals entry is already set
749 if (Result.isOverdefined()) {
750 DEBUG(dbgs() << " compute BB '" << BB->getName()
751 << "' - overdefined because of pred.\n");
760 // Return the merged value, which is more precise than 'overdefined'.
761 assert(!Result.isOverdefined() && "Possible PHI in entry block?");
766 static bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
767 LVILatticeVal &Result,
768 bool isTrueDest = true);
770 // If we can determine a constant range for the value Val at the context
771 // provided by the instruction BBI, then merge it into BBLV. If we did find a
772 // constant range, return true.
773 void LazyValueInfoCache::mergeAssumeBlockValueConstantRange(
774 Value *Val, LVILatticeVal &BBLV, Instruction *BBI) {
775 BBI = BBI ? BBI : dyn_cast<Instruction>(Val);
779 for (auto &I : AT->assumptions(BBI->getParent()->getParent())) {
780 if (!isValidAssumeForContext(I, BBI, DL, DT))
783 Value *C = I->getArgOperand(0);
784 if (ICmpInst *ICI = dyn_cast<ICmpInst>(C)) {
785 LVILatticeVal Result;
786 if (getValueFromFromCondition(Val, ICI, Result)) {
787 if (BBLV.isOverdefined())
790 BBLV.mergeIn(Result);
796 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
799 // Figure out the range of the LHS. If that fails, bail.
800 if (!hasBlockValue(BBI->getOperand(0), BB)) {
801 BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
805 LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
806 mergeAssumeBlockValueConstantRange(BBI->getOperand(0), LHSVal, BBI);
807 if (!LHSVal.isConstantRange()) {
808 BBLV.markOverdefined();
812 ConstantRange LHSRange = LHSVal.getConstantRange();
813 ConstantRange RHSRange(1);
814 IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
815 if (isa<BinaryOperator>(BBI)) {
816 if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
817 RHSRange = ConstantRange(RHS->getValue());
819 BBLV.markOverdefined();
824 // NOTE: We're currently limited by the set of operations that ConstantRange
825 // can evaluate symbolically. Enhancing that set will allows us to analyze
827 LVILatticeVal Result;
828 switch (BBI->getOpcode()) {
829 case Instruction::Add:
830 Result.markConstantRange(LHSRange.add(RHSRange));
832 case Instruction::Sub:
833 Result.markConstantRange(LHSRange.sub(RHSRange));
835 case Instruction::Mul:
836 Result.markConstantRange(LHSRange.multiply(RHSRange));
838 case Instruction::UDiv:
839 Result.markConstantRange(LHSRange.udiv(RHSRange));
841 case Instruction::Shl:
842 Result.markConstantRange(LHSRange.shl(RHSRange));
844 case Instruction::LShr:
845 Result.markConstantRange(LHSRange.lshr(RHSRange));
847 case Instruction::Trunc:
848 Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
850 case Instruction::SExt:
851 Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
853 case Instruction::ZExt:
854 Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
856 case Instruction::BitCast:
857 Result.markConstantRange(LHSRange);
859 case Instruction::And:
860 Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
862 case Instruction::Or:
863 Result.markConstantRange(LHSRange.binaryOr(RHSRange));
866 // Unhandled instructions are overdefined.
868 DEBUG(dbgs() << " compute BB '" << BB->getName()
869 << "' - overdefined because inst def found.\n");
870 Result.markOverdefined();
878 bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
879 LVILatticeVal &Result, bool isTrueDest) {
880 if (ICI && isa<Constant>(ICI->getOperand(1))) {
881 if (ICI->isEquality() && ICI->getOperand(0) == Val) {
882 // We know that V has the RHS constant if this is a true SETEQ or
884 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
885 Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
887 Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
891 // Recognize the range checking idiom that InstCombine produces.
892 // (X-C1) u< C2 --> [C1, C1+C2)
893 ConstantInt *NegOffset = nullptr;
894 if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
895 match(ICI->getOperand(0), m_Add(m_Specific(Val),
896 m_ConstantInt(NegOffset)));
898 ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
899 if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
900 // Calculate the range of values that would satisfy the comparison.
901 ConstantRange CmpRange(CI->getValue());
902 ConstantRange TrueValues =
903 ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
905 if (NegOffset) // Apply the offset from above.
906 TrueValues = TrueValues.subtract(NegOffset->getValue());
908 // If we're interested in the false dest, invert the condition.
909 if (!isTrueDest) TrueValues = TrueValues.inverse();
911 Result = LVILatticeVal::getRange(TrueValues);
919 /// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
920 /// Val is not constrained on the edge.
921 static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
922 BasicBlock *BBTo, LVILatticeVal &Result) {
923 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
925 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
926 // If this is a conditional branch and only one successor goes to BBTo, then
927 // we maybe able to infer something from the condition.
928 if (BI->isConditional() &&
929 BI->getSuccessor(0) != BI->getSuccessor(1)) {
930 bool isTrueDest = BI->getSuccessor(0) == BBTo;
931 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
932 "BBTo isn't a successor of BBFrom");
934 // If V is the condition of the branch itself, then we know exactly what
936 if (BI->getCondition() == Val) {
937 Result = LVILatticeVal::get(ConstantInt::get(
938 Type::getInt1Ty(Val->getContext()), isTrueDest));
942 // If the condition of the branch is an equality comparison, we may be
943 // able to infer the value.
944 ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
945 if (getValueFromFromCondition(Val, ICI, Result, isTrueDest))
950 // If the edge was formed by a switch on the value, then we may know exactly
952 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
953 if (SI->getCondition() != Val)
956 bool DefaultCase = SI->getDefaultDest() == BBTo;
957 unsigned BitWidth = Val->getType()->getIntegerBitWidth();
958 ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
960 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
962 ConstantRange EdgeVal(i.getCaseValue()->getValue());
964 // It is possible that the default destination is the destination of
965 // some cases. There is no need to perform difference for those cases.
966 if (i.getCaseSuccessor() != BBTo)
967 EdgesVals = EdgesVals.difference(EdgeVal);
968 } else if (i.getCaseSuccessor() == BBTo)
969 EdgesVals = EdgesVals.unionWith(EdgeVal);
971 Result = LVILatticeVal::getRange(EdgesVals);
977 /// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at
978 /// the basic block if the edge does not constraint Val.
979 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
980 BasicBlock *BBTo, LVILatticeVal &Result,
982 // If already a constant, there is nothing to compute.
983 if (Constant *VC = dyn_cast<Constant>(Val)) {
984 Result = LVILatticeVal::get(VC);
988 if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
989 if (!Result.isConstantRange() ||
990 Result.getConstantRange().getSingleElement())
993 // FIXME: this check should be moved to the beginning of the function when
994 // LVI better supports recursive values. Even for the single value case, we
995 // can intersect to detect dead code (an empty range).
996 if (!hasBlockValue(Val, BBFrom)) {
997 BlockValueStack.push(std::make_pair(BBFrom, Val));
1001 // Try to intersect ranges of the BB and the constraint on the edge.
1002 LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
1003 mergeAssumeBlockValueConstantRange(Val, InBlock, CxtI);
1004 if (!InBlock.isConstantRange())
1007 ConstantRange Range =
1008 Result.getConstantRange().intersectWith(InBlock.getConstantRange());
1009 Result = LVILatticeVal::getRange(Range);
1013 if (!hasBlockValue(Val, BBFrom)) {
1014 BlockValueStack.push(std::make_pair(BBFrom, Val));
1018 // if we couldn't compute the value on the edge, use the value from the BB
1019 Result = getBlockValue(Val, BBFrom);
1020 mergeAssumeBlockValueConstantRange(Val, Result, CxtI);
1024 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB,
1025 Instruction *CxtI) {
1026 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
1027 << BB->getName() << "'\n");
1029 BlockValueStack.push(std::make_pair(BB, V));
1031 LVILatticeVal Result = getBlockValue(V, BB);
1032 mergeAssumeBlockValueConstantRange(V, Result, CxtI);
1034 DEBUG(dbgs() << " Result = " << Result << "\n");
1038 LVILatticeVal LazyValueInfoCache::getValueAt(Value *V, Instruction *CxtI) {
1039 DEBUG(dbgs() << "LVI Getting value " << *V << " at '"
1040 << CxtI->getName() << "'\n");
1042 LVILatticeVal Result;
1043 mergeAssumeBlockValueConstantRange(V, Result, CxtI);
1045 DEBUG(dbgs() << " Result = " << Result << "\n");
1049 LVILatticeVal LazyValueInfoCache::
1050 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB,
1051 Instruction *CxtI) {
1052 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
1053 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
1055 LVILatticeVal Result;
1056 if (!getEdgeValue(V, FromBB, ToBB, Result, CxtI)) {
1058 bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result, CxtI);
1060 assert(WasFastQuery && "More work to do after problem solved?");
1063 DEBUG(dbgs() << " Result = " << Result << "\n");
1067 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1068 BasicBlock *NewSucc) {
1069 // When an edge in the graph has been threaded, values that we could not
1070 // determine a value for before (i.e. were marked overdefined) may be possible
1071 // to solve now. We do NOT try to proactively update these values. Instead,
1072 // we clear their entries from the cache, and allow lazy updating to recompute
1073 // them when needed.
1075 // The updating process is fairly simple: we need to dropped cached info
1076 // for all values that were marked overdefined in OldSucc, and for those same
1077 // values in any successor of OldSucc (except NewSucc) in which they were
1078 // also marked overdefined.
1079 std::vector<BasicBlock*> worklist;
1080 worklist.push_back(OldSucc);
1082 DenseSet<Value*> ClearSet;
1083 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
1084 E = OverDefinedCache.end(); I != E; ++I) {
1085 if (I->first == OldSucc)
1086 ClearSet.insert(I->second);
1089 // Use a worklist to perform a depth-first search of OldSucc's successors.
1090 // NOTE: We do not need a visited list since any blocks we have already
1091 // visited will have had their overdefined markers cleared already, and we
1092 // thus won't loop to their successors.
1093 while (!worklist.empty()) {
1094 BasicBlock *ToUpdate = worklist.back();
1095 worklist.pop_back();
1097 // Skip blocks only accessible through NewSucc.
1098 if (ToUpdate == NewSucc) continue;
1100 bool changed = false;
1101 for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end();
1103 // If a value was marked overdefined in OldSucc, and is here too...
1104 DenseSet<OverDefinedPairTy>::iterator OI =
1105 OverDefinedCache.find(std::make_pair(ToUpdate, *I));
1106 if (OI == OverDefinedCache.end()) continue;
1108 // Remove it from the caches.
1109 ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)];
1110 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
1112 assert(CI != Entry.end() && "Couldn't find entry to update?");
1114 OverDefinedCache.erase(OI);
1116 // If we removed anything, then we potentially need to update
1117 // blocks successors too.
1121 if (!changed) continue;
1123 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
1127 //===----------------------------------------------------------------------===//
1128 // LazyValueInfo Impl
1129 //===----------------------------------------------------------------------===//
1131 /// getCache - This lazily constructs the LazyValueInfoCache.
1132 static LazyValueInfoCache &getCache(void *&PImpl,
1133 AssumptionTracker *AT,
1134 const DataLayout *DL = nullptr,
1135 DominatorTree *DT = nullptr) {
1137 PImpl = new LazyValueInfoCache(AT, DL, DT);
1138 return *static_cast<LazyValueInfoCache*>(PImpl);
1141 bool LazyValueInfo::runOnFunction(Function &F) {
1142 AT = &getAnalysis<AssumptionTracker>();
1144 DominatorTreeWrapperPass *DTWP =
1145 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
1146 DT = DTWP ? &DTWP->getDomTree() : nullptr;
1148 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
1149 DL = DLP ? &DLP->getDataLayout() : nullptr;
1150 TLI = &getAnalysis<TargetLibraryInfo>();
1153 getCache(PImpl, AT, DL, DT).clear();
1159 void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
1160 AU.setPreservesAll();
1161 AU.addRequired<AssumptionTracker>();
1162 AU.addRequired<TargetLibraryInfo>();
1165 void LazyValueInfo::releaseMemory() {
1166 // If the cache was allocated, free it.
1168 delete &getCache(PImpl, AT);
1173 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB,
1174 Instruction *CxtI) {
1175 LVILatticeVal Result =
1176 getCache(PImpl, AT, DL, DT).getValueInBlock(V, BB, CxtI);
1178 if (Result.isConstant())
1179 return Result.getConstant();
1180 if (Result.isConstantRange()) {
1181 ConstantRange CR = Result.getConstantRange();
1182 if (const APInt *SingleVal = CR.getSingleElement())
1183 return ConstantInt::get(V->getContext(), *SingleVal);
1188 /// getConstantOnEdge - Determine whether the specified value is known to be a
1189 /// constant on the specified edge. Return null if not.
1190 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
1192 Instruction *CxtI) {
1193 LVILatticeVal Result =
1194 getCache(PImpl, AT, DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
1196 if (Result.isConstant())
1197 return Result.getConstant();
1198 if (Result.isConstantRange()) {
1199 ConstantRange CR = Result.getConstantRange();
1200 if (const APInt *SingleVal = CR.getSingleElement())
1201 return ConstantInt::get(V->getContext(), *SingleVal);
1206 static LazyValueInfo::Tristate
1207 getPredicateResult(unsigned Pred, Constant *C, LVILatticeVal &Result,
1208 const DataLayout *DL, TargetLibraryInfo *TLI) {
1210 // If we know the value is a constant, evaluate the conditional.
1211 Constant *Res = nullptr;
1212 if (Result.isConstant()) {
1213 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, DL,
1215 if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
1216 return ResCI->isZero() ? LazyValueInfo::False : LazyValueInfo::True;
1217 return LazyValueInfo::Unknown;
1220 if (Result.isConstantRange()) {
1221 ConstantInt *CI = dyn_cast<ConstantInt>(C);
1222 if (!CI) return LazyValueInfo::Unknown;
1224 ConstantRange CR = Result.getConstantRange();
1225 if (Pred == ICmpInst::ICMP_EQ) {
1226 if (!CR.contains(CI->getValue()))
1227 return LazyValueInfo::False;
1229 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1230 return LazyValueInfo::True;
1231 } else if (Pred == ICmpInst::ICMP_NE) {
1232 if (!CR.contains(CI->getValue()))
1233 return LazyValueInfo::True;
1235 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1236 return LazyValueInfo::False;
1239 // Handle more complex predicates.
1240 ConstantRange TrueValues =
1241 ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
1242 if (TrueValues.contains(CR))
1243 return LazyValueInfo::True;
1244 if (TrueValues.inverse().contains(CR))
1245 return LazyValueInfo::False;
1246 return LazyValueInfo::Unknown;
1249 if (Result.isNotConstant()) {
1250 // If this is an equality comparison, we can try to fold it knowing that
1252 if (Pred == ICmpInst::ICMP_EQ) {
1253 // !C1 == C -> false iff C1 == C.
1254 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1255 Result.getNotConstant(), C, DL,
1257 if (Res->isNullValue())
1258 return LazyValueInfo::False;
1259 } else if (Pred == ICmpInst::ICMP_NE) {
1260 // !C1 != C -> true iff C1 == C.
1261 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1262 Result.getNotConstant(), C, DL,
1264 if (Res->isNullValue())
1265 return LazyValueInfo::True;
1267 return LazyValueInfo::Unknown;
1270 return LazyValueInfo::Unknown;
1273 /// getPredicateOnEdge - Determine whether the specified value comparison
1274 /// with a constant is known to be true or false on the specified CFG edge.
1275 /// Pred is a CmpInst predicate.
1276 LazyValueInfo::Tristate
1277 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
1278 BasicBlock *FromBB, BasicBlock *ToBB,
1279 Instruction *CxtI) {
1280 LVILatticeVal Result =
1281 getCache(PImpl, AT, DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
1283 return getPredicateResult(Pred, C, Result, DL, TLI);
1286 LazyValueInfo::Tristate
1287 LazyValueInfo::getPredicateAt(unsigned Pred, Value *V, Constant *C,
1288 Instruction *CxtI) {
1289 LVILatticeVal Result =
1290 getCache(PImpl, AT, DL, DT).getValueAt(V, CxtI);
1292 return getPredicateResult(Pred, C, Result, DL, TLI);
1295 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1296 BasicBlock *NewSucc) {
1297 if (PImpl) getCache(PImpl, AT, DL, DT).threadEdge(PredBB, OldSucc, NewSucc);
1300 void LazyValueInfo::eraseBlock(BasicBlock *BB) {
1301 if (PImpl) getCache(PImpl, AT, DL, DT).eraseBlock(BB);