1 //===- LazyValueInfo.cpp - Value constraint analysis ------------*- C++ -*-===//
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/AssumptionCache.h"
19 #include "llvm/Analysis/ConstantFolding.h"
20 #include "llvm/Analysis/TargetLibraryInfo.h"
21 #include "llvm/Analysis/ValueTracking.h"
22 #include "llvm/IR/CFG.h"
23 #include "llvm/IR/ConstantRange.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/DataLayout.h"
26 #include "llvm/IR/Dominators.h"
27 #include "llvm/IR/Instructions.h"
28 #include "llvm/IR/IntrinsicInst.h"
29 #include "llvm/IR/PatternMatch.h"
30 #include "llvm/IR/ValueHandle.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/raw_ostream.h"
36 using namespace PatternMatch;
38 #define DEBUG_TYPE "lazy-value-info"
40 char LazyValueInfo::ID = 0;
41 INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
42 "Lazy Value Information Analysis", false, true)
43 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
44 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
45 INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info",
46 "Lazy Value Information Analysis", false, true)
49 FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
53 //===----------------------------------------------------------------------===//
55 //===----------------------------------------------------------------------===//
57 /// This is the information tracked by LazyValueInfo for each value.
59 /// FIXME: This is basically just for bringup, this can be made a lot more rich
65 /// This Value has no known value yet.
68 /// This Value has a specific constant value.
71 /// This Value is known to not have the specified value.
74 /// The Value falls within this range.
77 /// This value is not known to be constant, and we know that it has a value.
81 /// Val: This stores the current lattice value along with the Constant* for
82 /// the constant if this is a 'constant' or 'notconstant' value.
88 LVILatticeVal() : Tag(undefined), Val(nullptr), Range(1, true) {}
90 static LVILatticeVal get(Constant *C) {
92 if (!isa<UndefValue>(C))
96 static LVILatticeVal getNot(Constant *C) {
98 if (!isa<UndefValue>(C))
99 Res.markNotConstant(C);
102 static LVILatticeVal getRange(ConstantRange CR) {
104 Res.markConstantRange(CR);
108 bool isUndefined() const { return Tag == undefined; }
109 bool isConstant() const { return Tag == constant; }
110 bool isNotConstant() const { return Tag == notconstant; }
111 bool isConstantRange() const { return Tag == constantrange; }
112 bool isOverdefined() const { return Tag == overdefined; }
114 Constant *getConstant() const {
115 assert(isConstant() && "Cannot get the constant of a non-constant!");
119 Constant *getNotConstant() const {
120 assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
124 ConstantRange getConstantRange() const {
125 assert(isConstantRange() &&
126 "Cannot get the constant-range of a non-constant-range!");
130 /// Return true if this is a change in status.
131 bool markOverdefined() {
138 /// Return true if this is a change in status.
139 bool markConstant(Constant *V) {
140 assert(V && "Marking constant with NULL");
141 if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
142 return markConstantRange(ConstantRange(CI->getValue()));
143 if (isa<UndefValue>(V))
146 assert((!isConstant() || getConstant() == V) &&
147 "Marking constant with different value");
148 assert(isUndefined());
154 /// Return true if this is a change in status.
155 bool markNotConstant(Constant *V) {
156 assert(V && "Marking constant with NULL");
157 if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
158 return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
159 if (isa<UndefValue>(V))
162 assert((!isConstant() || getConstant() != V) &&
163 "Marking constant !constant with same value");
164 assert((!isNotConstant() || getNotConstant() == V) &&
165 "Marking !constant with different value");
166 assert(isUndefined() || isConstant());
172 /// Return true if this is a change in status.
173 bool markConstantRange(const ConstantRange NewR) {
174 if (isConstantRange()) {
175 if (NewR.isEmptySet())
176 return markOverdefined();
178 bool changed = Range != NewR;
183 assert(isUndefined());
184 if (NewR.isEmptySet())
185 return markOverdefined();
192 /// Merge the specified lattice value into this one, updating this
193 /// one and returning true if anything changed.
194 bool mergeIn(const LVILatticeVal &RHS, const DataLayout &DL) {
195 if (RHS.isUndefined() || isOverdefined()) return false;
196 if (RHS.isOverdefined()) return markOverdefined();
206 if (RHS.isConstant()) {
209 return markOverdefined();
212 if (RHS.isNotConstant()) {
214 return markOverdefined();
216 // Unless we can prove that the two Constants are different, we must
217 // move to overdefined.
218 if (ConstantInt *Res =
219 dyn_cast<ConstantInt>(ConstantFoldCompareInstOperands(
220 CmpInst::ICMP_NE, getConstant(), RHS.getNotConstant(), DL)))
222 return markNotConstant(RHS.getNotConstant());
224 return markOverdefined();
227 // RHS is a ConstantRange, LHS is a non-integer Constant.
229 // FIXME: consider the case where RHS is a range [1, 0) and LHS is
230 // a function. The correct result is to pick up RHS.
232 return markOverdefined();
235 if (isNotConstant()) {
236 if (RHS.isConstant()) {
238 return markOverdefined();
240 // Unless we can prove that the two Constants are different, we must
241 // move to overdefined.
242 if (ConstantInt *Res =
243 dyn_cast<ConstantInt>(ConstantFoldCompareInstOperands(
244 CmpInst::ICMP_NE, getNotConstant(), RHS.getConstant(), DL)))
248 return markOverdefined();
251 if (RHS.isNotConstant()) {
254 return markOverdefined();
257 return markOverdefined();
260 assert(isConstantRange() && "New LVILattice type?");
261 if (!RHS.isConstantRange())
262 return markOverdefined();
264 ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
265 if (NewR.isFullSet())
266 return markOverdefined();
267 return markConstantRange(NewR);
271 } // end anonymous namespace.
274 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
276 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
277 if (Val.isUndefined())
278 return OS << "undefined";
279 if (Val.isOverdefined())
280 return OS << "overdefined";
282 if (Val.isNotConstant())
283 return OS << "notconstant<" << *Val.getNotConstant() << '>';
284 else if (Val.isConstantRange())
285 return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
286 << Val.getConstantRange().getUpper() << '>';
287 return OS << "constant<" << *Val.getConstant() << '>';
291 //===----------------------------------------------------------------------===//
292 // LazyValueInfoCache Decl
293 //===----------------------------------------------------------------------===//
296 /// A callback value handle updates the cache when values are erased.
297 class LazyValueInfoCache;
298 struct LVIValueHandle final : public CallbackVH {
299 LazyValueInfoCache *Parent;
301 LVIValueHandle(Value *V, LazyValueInfoCache *P)
302 : CallbackVH(V), Parent(P) { }
304 void deleted() override;
305 void allUsesReplacedWith(Value *V) override {
312 /// This is the cache kept by LazyValueInfo which
313 /// maintains information about queries across the clients' queries.
314 class LazyValueInfoCache {
315 /// This is all of the cached block information for exactly one Value*.
316 /// The entries are sorted by the BasicBlock* of the
317 /// entries, allowing us to do a lookup with a binary search.
318 typedef SmallDenseMap<AssertingVH<BasicBlock>, LVILatticeVal, 4>
321 /// This is all of the cached information for all values,
322 /// mapped from Value* to key information.
323 std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache;
325 /// This tracks, on a per-block basis, the set of values that are
326 /// over-defined at the end of that block. This is required
327 /// for cache updating.
328 typedef DenseMap<AssertingVH<BasicBlock>, SmallPtrSet<Value *, 4>>
330 OverDefinedCacheTy OverDefinedCache;
332 /// Keep track of all blocks that we have ever seen, so we
333 /// don't spend time removing unused blocks from our caches.
334 DenseSet<AssertingVH<BasicBlock> > SeenBlocks;
336 /// This stack holds the state of the value solver during a query.
337 /// It basically emulates the callstack of the naive
338 /// recursive value lookup process.
339 std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
341 /// Keeps track of which block-value pairs are in BlockValueStack.
342 DenseSet<std::pair<BasicBlock*, Value*> > BlockValueSet;
344 /// Push BV onto BlockValueStack unless it's already in there.
345 /// Returns true on success.
346 bool pushBlockValue(const std::pair<BasicBlock *, Value *> &BV) {
347 if (!BlockValueSet.insert(BV).second)
348 return false; // It's already in the stack.
350 BlockValueStack.push(BV);
354 AssumptionCache *AC; ///< A pointer to the cache of @llvm.assume calls.
355 const DataLayout &DL; ///< A mandatory DataLayout
356 DominatorTree *DT; ///< An optional DT pointer.
358 friend struct LVIValueHandle;
360 void insertResult(Value *Val, BasicBlock *BB, const LVILatticeVal &Result) {
361 SeenBlocks.insert(BB);
362 lookup(Val)[BB] = Result;
363 if (Result.isOverdefined())
364 OverDefinedCache[BB].insert(Val);
367 LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
368 bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
369 LVILatticeVal &Result,
370 Instruction *CxtI = nullptr);
371 bool hasBlockValue(Value *Val, BasicBlock *BB);
373 // These methods process one work item and may add more. A false value
374 // returned means that the work item was not completely processed and must
375 // be revisited after going through the new items.
376 bool solveBlockValue(Value *Val, BasicBlock *BB);
377 bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
378 Value *Val, BasicBlock *BB);
379 bool solveBlockValuePHINode(LVILatticeVal &BBLV,
380 PHINode *PN, BasicBlock *BB);
381 bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
382 Instruction *BBI, BasicBlock *BB);
383 void mergeAssumeBlockValueConstantRange(Value *Val, LVILatticeVal &BBLV,
388 ValueCacheEntryTy &lookup(Value *V) {
389 return ValueCache[LVIValueHandle(V, this)];
393 /// This is the query interface to determine the lattice
394 /// value for the specified Value* at the end of the specified block.
395 LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB,
396 Instruction *CxtI = nullptr);
398 /// This is the query interface to determine the lattice
399 /// value for the specified Value* at the specified instruction (generally
400 /// from an assume intrinsic).
401 LVILatticeVal getValueAt(Value *V, Instruction *CxtI);
403 /// This is the query interface to determine the lattice
404 /// value for the specified Value* that is true on the specified edge.
405 LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB,
406 Instruction *CxtI = nullptr);
408 /// This is the update interface to inform the cache that an edge from
409 /// PredBB to OldSucc has been threaded to be from PredBB to NewSucc.
410 void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
412 /// This is part of the update interface to inform the cache
413 /// that a block has been deleted.
414 void eraseBlock(BasicBlock *BB);
416 /// clear - Empty the cache.
420 OverDefinedCache.clear();
423 LazyValueInfoCache(AssumptionCache *AC, const DataLayout &DL,
424 DominatorTree *DT = nullptr)
425 : AC(AC), DL(DL), DT(DT) {}
427 } // end anonymous namespace
429 void LVIValueHandle::deleted() {
430 SmallVector<AssertingVH<BasicBlock>, 4> ToErase;
431 for (auto &I : Parent->OverDefinedCache) {
432 SmallPtrSetImpl<Value *> &ValueSet = I.second;
433 if (ValueSet.count(getValPtr()))
434 ValueSet.erase(getValPtr());
435 if (ValueSet.empty())
436 ToErase.push_back(I.first);
438 for (auto &BB : ToErase)
439 Parent->OverDefinedCache.erase(BB);
441 // This erasure deallocates *this, so it MUST happen after we're done
442 // using any and all members of *this.
443 Parent->ValueCache.erase(*this);
446 void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
447 // Shortcut if we have never seen this block.
448 DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
449 if (I == SeenBlocks.end())
453 auto ODI = OverDefinedCache.find(BB);
454 if (ODI != OverDefinedCache.end())
455 OverDefinedCache.erase(ODI);
457 for (auto I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
461 void LazyValueInfoCache::solve() {
462 while (!BlockValueStack.empty()) {
463 std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
464 assert(BlockValueSet.count(e) && "Stack value should be in BlockValueSet!");
466 if (solveBlockValue(e.second, e.first)) {
467 // The work item was completely processed.
468 assert(BlockValueStack.top() == e && "Nothing should have been pushed!");
469 assert(lookup(e.second).count(e.first) && "Result should be in cache!");
471 BlockValueStack.pop();
472 BlockValueSet.erase(e);
474 // More work needs to be done before revisiting.
475 assert(BlockValueStack.top() != e && "Stack should have been pushed!");
480 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
481 // If already a constant, there is nothing to compute.
482 if (isa<Constant>(Val))
485 LVIValueHandle ValHandle(Val, this);
486 auto I = ValueCache.find(ValHandle);
487 if (I == ValueCache.end()) return false;
488 return I->second.count(BB);
491 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
492 // If already a constant, there is nothing to compute.
493 if (Constant *VC = dyn_cast<Constant>(Val))
494 return LVILatticeVal::get(VC);
496 SeenBlocks.insert(BB);
497 return lookup(Val)[BB];
500 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
501 if (isa<Constant>(Val))
504 if (lookup(Val).count(BB)) {
505 // If we have a cached value, use that.
506 DEBUG(dbgs() << " reuse BB '" << BB->getName()
507 << "' val=" << lookup(Val)[BB] << '\n');
509 // Since we're reusing a cached value, we don't need to update the
510 // OverDefinedCache. The cache will have been properly updated whenever the
511 // cached value was inserted.
515 // Hold off inserting this value into the Cache in case we have to return
516 // false and come back later.
519 Instruction *BBI = dyn_cast<Instruction>(Val);
520 if (!BBI || BBI->getParent() != BB) {
521 if (!solveBlockValueNonLocal(Res, Val, BB))
523 insertResult(Val, BB, Res);
527 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
528 if (!solveBlockValuePHINode(Res, PN, BB))
530 insertResult(Val, BB, Res);
534 if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
535 Res = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
536 insertResult(Val, BB, Res);
540 // We can only analyze the definitions of certain classes of instructions
541 // (integral binops and casts at the moment), so bail if this isn't one.
542 LVILatticeVal Result;
543 if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
544 !BBI->getType()->isIntegerTy()) {
545 DEBUG(dbgs() << " compute BB '" << BB->getName()
546 << "' - overdefined because inst def found.\n");
547 Res.markOverdefined();
548 insertResult(Val, BB, Res);
552 // FIXME: We're currently limited to binops with a constant RHS. This should
554 BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
555 if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
556 DEBUG(dbgs() << " compute BB '" << BB->getName()
557 << "' - overdefined because inst def found.\n");
559 Res.markOverdefined();
560 insertResult(Val, BB, Res);
564 if (!solveBlockValueConstantRange(Res, BBI, BB))
566 insertResult(Val, BB, Res);
570 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
571 if (LoadInst *L = dyn_cast<LoadInst>(I)) {
572 return L->getPointerAddressSpace() == 0 &&
573 GetUnderlyingObject(L->getPointerOperand(),
574 L->getModule()->getDataLayout()) == Ptr;
576 if (StoreInst *S = dyn_cast<StoreInst>(I)) {
577 return S->getPointerAddressSpace() == 0 &&
578 GetUnderlyingObject(S->getPointerOperand(),
579 S->getModule()->getDataLayout()) == Ptr;
581 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
582 if (MI->isVolatile()) return false;
584 // FIXME: check whether it has a valuerange that excludes zero?
585 ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
586 if (!Len || Len->isZero()) return false;
588 if (MI->getDestAddressSpace() == 0)
589 if (GetUnderlyingObject(MI->getRawDest(),
590 MI->getModule()->getDataLayout()) == Ptr)
592 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
593 if (MTI->getSourceAddressSpace() == 0)
594 if (GetUnderlyingObject(MTI->getRawSource(),
595 MTI->getModule()->getDataLayout()) == Ptr)
601 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
602 Value *Val, BasicBlock *BB) {
603 LVILatticeVal Result; // Start Undefined.
605 // If this is a pointer, and there's a load from that pointer in this BB,
606 // then we know that the pointer can't be NULL.
607 bool NotNull = false;
608 if (Val->getType()->isPointerTy()) {
609 if (isKnownNonNull(Val)) {
612 const DataLayout &DL = BB->getModule()->getDataLayout();
613 Value *UnderlyingVal = GetUnderlyingObject(Val, DL);
614 // If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
615 // inside InstructionDereferencesPointer either.
616 if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, DL, 1)) {
617 for (Instruction &I : *BB) {
618 if (InstructionDereferencesPointer(&I, UnderlyingVal)) {
627 // If this is the entry block, we must be asking about an argument. The
628 // value is overdefined.
629 if (BB == &BB->getParent()->getEntryBlock()) {
630 assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
632 PointerType *PTy = cast<PointerType>(Val->getType());
633 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
635 Result.markOverdefined();
641 // Loop over all of our predecessors, merging what we know from them into
643 bool EdgesMissing = false;
644 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
645 LVILatticeVal EdgeResult;
646 EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
650 Result.mergeIn(EdgeResult, DL);
652 // If we hit overdefined, exit early. The BlockVals entry is already set
654 if (Result.isOverdefined()) {
655 DEBUG(dbgs() << " compute BB '" << BB->getName()
656 << "' - overdefined because of pred.\n");
657 // If we previously determined that this is a pointer that can't be null
658 // then return that rather than giving up entirely.
660 PointerType *PTy = cast<PointerType>(Val->getType());
661 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
671 // Return the merged value, which is more precise than 'overdefined'.
672 assert(!Result.isOverdefined());
677 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
678 PHINode *PN, BasicBlock *BB) {
679 LVILatticeVal Result; // Start Undefined.
681 // Loop over all of our predecessors, merging what we know from them into
683 bool EdgesMissing = false;
684 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
685 BasicBlock *PhiBB = PN->getIncomingBlock(i);
686 Value *PhiVal = PN->getIncomingValue(i);
687 LVILatticeVal EdgeResult;
688 // Note that we can provide PN as the context value to getEdgeValue, even
689 // though the results will be cached, because PN is the value being used as
690 // the cache key in the caller.
691 EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult, PN);
695 Result.mergeIn(EdgeResult, DL);
697 // If we hit overdefined, exit early. The BlockVals entry is already set
699 if (Result.isOverdefined()) {
700 DEBUG(dbgs() << " compute BB '" << BB->getName()
701 << "' - overdefined because of pred.\n");
710 // Return the merged value, which is more precise than 'overdefined'.
711 assert(!Result.isOverdefined() && "Possible PHI in entry block?");
716 static bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
717 LVILatticeVal &Result,
718 bool isTrueDest = true);
720 // If we can determine a constant range for the value Val in the context
721 // provided by the instruction BBI, then merge it into BBLV. If we did find a
722 // constant range, return true.
723 void LazyValueInfoCache::mergeAssumeBlockValueConstantRange(Value *Val,
726 BBI = BBI ? BBI : dyn_cast<Instruction>(Val);
730 for (auto &AssumeVH : AC->assumptions()) {
733 auto *I = cast<CallInst>(AssumeVH);
734 if (!isValidAssumeForContext(I, BBI, DT))
737 Value *C = I->getArgOperand(0);
738 if (ICmpInst *ICI = dyn_cast<ICmpInst>(C)) {
739 LVILatticeVal Result;
740 if (getValueFromFromCondition(Val, ICI, Result)) {
741 if (BBLV.isOverdefined())
744 BBLV.mergeIn(Result, DL);
750 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
753 // Figure out the range of the LHS. If that fails, bail.
754 if (!hasBlockValue(BBI->getOperand(0), BB)) {
755 if (pushBlockValue(std::make_pair(BB, BBI->getOperand(0))))
757 BBLV.markOverdefined();
761 LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
762 mergeAssumeBlockValueConstantRange(BBI->getOperand(0), LHSVal, BBI);
763 if (!LHSVal.isConstantRange()) {
764 BBLV.markOverdefined();
768 ConstantRange LHSRange = LHSVal.getConstantRange();
769 ConstantRange RHSRange(1);
770 IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
771 if (isa<BinaryOperator>(BBI)) {
772 if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
773 RHSRange = ConstantRange(RHS->getValue());
775 BBLV.markOverdefined();
780 // NOTE: We're currently limited by the set of operations that ConstantRange
781 // can evaluate symbolically. Enhancing that set will allows us to analyze
783 LVILatticeVal Result;
784 switch (BBI->getOpcode()) {
785 case Instruction::Add:
786 Result.markConstantRange(LHSRange.add(RHSRange));
788 case Instruction::Sub:
789 Result.markConstantRange(LHSRange.sub(RHSRange));
791 case Instruction::Mul:
792 Result.markConstantRange(LHSRange.multiply(RHSRange));
794 case Instruction::UDiv:
795 Result.markConstantRange(LHSRange.udiv(RHSRange));
797 case Instruction::Shl:
798 Result.markConstantRange(LHSRange.shl(RHSRange));
800 case Instruction::LShr:
801 Result.markConstantRange(LHSRange.lshr(RHSRange));
803 case Instruction::Trunc:
804 Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
806 case Instruction::SExt:
807 Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
809 case Instruction::ZExt:
810 Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
812 case Instruction::BitCast:
813 Result.markConstantRange(LHSRange);
815 case Instruction::And:
816 Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
818 case Instruction::Or:
819 Result.markConstantRange(LHSRange.binaryOr(RHSRange));
822 // Unhandled instructions are overdefined.
824 DEBUG(dbgs() << " compute BB '" << BB->getName()
825 << "' - overdefined because inst def found.\n");
826 Result.markOverdefined();
834 bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
835 LVILatticeVal &Result, bool isTrueDest) {
836 if (ICI && isa<Constant>(ICI->getOperand(1))) {
837 if (ICI->isEquality() && ICI->getOperand(0) == Val) {
838 // We know that V has the RHS constant if this is a true SETEQ or
840 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
841 Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
843 Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
847 // Recognize the range checking idiom that InstCombine produces.
848 // (X-C1) u< C2 --> [C1, C1+C2)
849 ConstantInt *NegOffset = nullptr;
850 if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
851 match(ICI->getOperand(0), m_Add(m_Specific(Val),
852 m_ConstantInt(NegOffset)));
854 ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
855 if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
856 // Calculate the range of values that are allowed by the comparison
857 ConstantRange CmpRange(CI->getValue());
858 ConstantRange TrueValues =
859 ConstantRange::makeAllowedICmpRegion(ICI->getPredicate(), CmpRange);
861 if (NegOffset) // Apply the offset from above.
862 TrueValues = TrueValues.subtract(NegOffset->getValue());
864 // If we're interested in the false dest, invert the condition.
865 if (!isTrueDest) TrueValues = TrueValues.inverse();
867 Result = LVILatticeVal::getRange(TrueValues);
875 /// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
876 /// Val is not constrained on the edge.
877 static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
878 BasicBlock *BBTo, LVILatticeVal &Result) {
879 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
881 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
882 // If this is a conditional branch and only one successor goes to BBTo, then
883 // we may be able to infer something from the condition.
884 if (BI->isConditional() &&
885 BI->getSuccessor(0) != BI->getSuccessor(1)) {
886 bool isTrueDest = BI->getSuccessor(0) == BBTo;
887 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
888 "BBTo isn't a successor of BBFrom");
890 // If V is the condition of the branch itself, then we know exactly what
892 if (BI->getCondition() == Val) {
893 Result = LVILatticeVal::get(ConstantInt::get(
894 Type::getInt1Ty(Val->getContext()), isTrueDest));
898 // If the condition of the branch is an equality comparison, we may be
899 // able to infer the value.
900 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
901 if (getValueFromFromCondition(Val, ICI, Result, isTrueDest))
906 // If the edge was formed by a switch on the value, then we may know exactly
908 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
909 if (SI->getCondition() != Val)
912 bool DefaultCase = SI->getDefaultDest() == BBTo;
913 unsigned BitWidth = Val->getType()->getIntegerBitWidth();
914 ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
916 for (SwitchInst::CaseIt i : SI->cases()) {
917 ConstantRange EdgeVal(i.getCaseValue()->getValue());
919 // It is possible that the default destination is the destination of
920 // some cases. There is no need to perform difference for those cases.
921 if (i.getCaseSuccessor() != BBTo)
922 EdgesVals = EdgesVals.difference(EdgeVal);
923 } else if (i.getCaseSuccessor() == BBTo)
924 EdgesVals = EdgesVals.unionWith(EdgeVal);
926 Result = LVILatticeVal::getRange(EdgesVals);
932 /// \brief Compute the value of Val on the edge BBFrom -> BBTo or the value at
933 /// the basic block if the edge does not constrain Val.
934 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
935 BasicBlock *BBTo, LVILatticeVal &Result,
937 // If already a constant, there is nothing to compute.
938 if (Constant *VC = dyn_cast<Constant>(Val)) {
939 Result = LVILatticeVal::get(VC);
943 if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
944 if (!Result.isConstantRange() ||
945 Result.getConstantRange().getSingleElement())
948 // FIXME: this check should be moved to the beginning of the function when
949 // LVI better supports recursive values. Even for the single value case, we
950 // can intersect to detect dead code (an empty range).
951 if (!hasBlockValue(Val, BBFrom)) {
952 if (pushBlockValue(std::make_pair(BBFrom, Val)))
954 Result.markOverdefined();
958 // Try to intersect ranges of the BB and the constraint on the edge.
959 LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
960 mergeAssumeBlockValueConstantRange(Val, InBlock, BBFrom->getTerminator());
961 // See note on the use of the CxtI with mergeAssumeBlockValueConstantRange,
962 // and caching, below.
963 mergeAssumeBlockValueConstantRange(Val, InBlock, CxtI);
964 if (!InBlock.isConstantRange())
967 ConstantRange Range =
968 Result.getConstantRange().intersectWith(InBlock.getConstantRange());
969 Result = LVILatticeVal::getRange(Range);
973 if (!hasBlockValue(Val, BBFrom)) {
974 if (pushBlockValue(std::make_pair(BBFrom, Val)))
976 Result.markOverdefined();
980 // If we couldn't compute the value on the edge, use the value from the BB.
981 Result = getBlockValue(Val, BBFrom);
982 mergeAssumeBlockValueConstantRange(Val, Result, BBFrom->getTerminator());
983 // We can use the context instruction (generically the ultimate instruction
984 // the calling pass is trying to simplify) here, even though the result of
985 // this function is generally cached when called from the solve* functions
986 // (and that cached result might be used with queries using a different
987 // context instruction), because when this function is called from the solve*
988 // functions, the context instruction is not provided. When called from
989 // LazyValueInfoCache::getValueOnEdge, the context instruction is provided,
990 // but then the result is not cached.
991 mergeAssumeBlockValueConstantRange(Val, Result, CxtI);
995 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB,
997 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
998 << BB->getName() << "'\n");
1000 assert(BlockValueStack.empty() && BlockValueSet.empty());
1001 pushBlockValue(std::make_pair(BB, V));
1004 LVILatticeVal Result = getBlockValue(V, BB);
1005 mergeAssumeBlockValueConstantRange(V, Result, CxtI);
1007 DEBUG(dbgs() << " Result = " << Result << "\n");
1011 LVILatticeVal LazyValueInfoCache::getValueAt(Value *V, Instruction *CxtI) {
1012 DEBUG(dbgs() << "LVI Getting value " << *V << " at '"
1013 << CxtI->getName() << "'\n");
1015 LVILatticeVal Result;
1016 mergeAssumeBlockValueConstantRange(V, Result, CxtI);
1018 DEBUG(dbgs() << " Result = " << Result << "\n");
1022 LVILatticeVal LazyValueInfoCache::
1023 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB,
1024 Instruction *CxtI) {
1025 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
1026 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
1028 LVILatticeVal Result;
1029 if (!getEdgeValue(V, FromBB, ToBB, Result, CxtI)) {
1031 bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result, CxtI);
1033 assert(WasFastQuery && "More work to do after problem solved?");
1036 DEBUG(dbgs() << " Result = " << Result << "\n");
1040 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1041 BasicBlock *NewSucc) {
1042 // When an edge in the graph has been threaded, values that we could not
1043 // determine a value for before (i.e. were marked overdefined) may be
1044 // possible to solve now. We do NOT try to proactively update these values.
1045 // Instead, we clear their entries from the cache, and allow lazy updating to
1046 // recompute them when needed.
1048 // The updating process is fairly simple: we need to drop cached info
1049 // for all values that were marked overdefined in OldSucc, and for those same
1050 // values in any successor of OldSucc (except NewSucc) in which they were
1051 // also marked overdefined.
1052 std::vector<BasicBlock*> worklist;
1053 worklist.push_back(OldSucc);
1055 auto I = OverDefinedCache.find(OldSucc);
1056 if (I == OverDefinedCache.end())
1057 return; // Nothing to process here.
1058 SmallVector<Value *, 4> ValsToClear(I->second.begin(), I->second.end());
1060 // Use a worklist to perform a depth-first search of OldSucc's successors.
1061 // NOTE: We do not need a visited list since any blocks we have already
1062 // visited will have had their overdefined markers cleared already, and we
1063 // thus won't loop to their successors.
1064 while (!worklist.empty()) {
1065 BasicBlock *ToUpdate = worklist.back();
1066 worklist.pop_back();
1068 // Skip blocks only accessible through NewSucc.
1069 if (ToUpdate == NewSucc) continue;
1071 bool changed = false;
1072 for (Value *V : ValsToClear) {
1073 // If a value was marked overdefined in OldSucc, and is here too...
1074 auto OI = OverDefinedCache.find(ToUpdate);
1075 if (OI == OverDefinedCache.end())
1077 SmallPtrSetImpl<Value *> &ValueSet = OI->second;
1078 if (!ValueSet.count(V))
1081 // Remove it from the caches.
1082 ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(V, this)];
1083 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
1085 assert(CI != Entry.end() && "Couldn't find entry to update?");
1088 if (ValueSet.empty())
1089 OverDefinedCache.erase(OI);
1091 // If we removed anything, then we potentially need to update
1092 // blocks successors too.
1096 if (!changed) continue;
1098 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
1102 //===----------------------------------------------------------------------===//
1103 // LazyValueInfo Impl
1104 //===----------------------------------------------------------------------===//
1106 /// This lazily constructs the LazyValueInfoCache.
1107 static LazyValueInfoCache &getCache(void *&PImpl, AssumptionCache *AC,
1108 const DataLayout *DL,
1109 DominatorTree *DT = nullptr) {
1111 assert(DL && "getCache() called with a null DataLayout");
1112 PImpl = new LazyValueInfoCache(AC, *DL, DT);
1114 return *static_cast<LazyValueInfoCache*>(PImpl);
1117 bool LazyValueInfo::runOnFunction(Function &F) {
1118 AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
1119 const DataLayout &DL = F.getParent()->getDataLayout();
1121 DominatorTreeWrapperPass *DTWP =
1122 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
1123 DT = DTWP ? &DTWP->getDomTree() : nullptr;
1125 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
1128 getCache(PImpl, AC, &DL, DT).clear();
1134 void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
1135 AU.setPreservesAll();
1136 AU.addRequired<AssumptionCacheTracker>();
1137 AU.addRequired<TargetLibraryInfoWrapperPass>();
1140 void LazyValueInfo::releaseMemory() {
1141 // If the cache was allocated, free it.
1143 delete &getCache(PImpl, AC, nullptr);
1148 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB,
1149 Instruction *CxtI) {
1150 const DataLayout &DL = BB->getModule()->getDataLayout();
1151 LVILatticeVal Result =
1152 getCache(PImpl, AC, &DL, DT).getValueInBlock(V, BB, CxtI);
1154 if (Result.isConstant())
1155 return Result.getConstant();
1156 if (Result.isConstantRange()) {
1157 ConstantRange CR = Result.getConstantRange();
1158 if (const APInt *SingleVal = CR.getSingleElement())
1159 return ConstantInt::get(V->getContext(), *SingleVal);
1164 /// Determine whether the specified value is known to be a
1165 /// constant on the specified edge. Return null if not.
1166 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
1168 Instruction *CxtI) {
1169 const DataLayout &DL = FromBB->getModule()->getDataLayout();
1170 LVILatticeVal Result =
1171 getCache(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
1173 if (Result.isConstant())
1174 return Result.getConstant();
1175 if (Result.isConstantRange()) {
1176 ConstantRange CR = Result.getConstantRange();
1177 if (const APInt *SingleVal = CR.getSingleElement())
1178 return ConstantInt::get(V->getContext(), *SingleVal);
1183 static LazyValueInfo::Tristate getPredicateResult(unsigned Pred, Constant *C,
1184 LVILatticeVal &Result,
1185 const DataLayout &DL,
1186 TargetLibraryInfo *TLI) {
1188 // If we know the value is a constant, evaluate the conditional.
1189 Constant *Res = nullptr;
1190 if (Result.isConstant()) {
1191 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, DL,
1193 if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
1194 return ResCI->isZero() ? LazyValueInfo::False : LazyValueInfo::True;
1195 return LazyValueInfo::Unknown;
1198 if (Result.isConstantRange()) {
1199 ConstantInt *CI = dyn_cast<ConstantInt>(C);
1200 if (!CI) return LazyValueInfo::Unknown;
1202 ConstantRange CR = Result.getConstantRange();
1203 if (Pred == ICmpInst::ICMP_EQ) {
1204 if (!CR.contains(CI->getValue()))
1205 return LazyValueInfo::False;
1207 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1208 return LazyValueInfo::True;
1209 } else if (Pred == ICmpInst::ICMP_NE) {
1210 if (!CR.contains(CI->getValue()))
1211 return LazyValueInfo::True;
1213 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1214 return LazyValueInfo::False;
1217 // Handle more complex predicates.
1218 ConstantRange TrueValues =
1219 ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
1220 if (TrueValues.contains(CR))
1221 return LazyValueInfo::True;
1222 if (TrueValues.inverse().contains(CR))
1223 return LazyValueInfo::False;
1224 return LazyValueInfo::Unknown;
1227 if (Result.isNotConstant()) {
1228 // If this is an equality comparison, we can try to fold it knowing that
1230 if (Pred == ICmpInst::ICMP_EQ) {
1231 // !C1 == C -> false iff C1 == C.
1232 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1233 Result.getNotConstant(), C, DL,
1235 if (Res->isNullValue())
1236 return LazyValueInfo::False;
1237 } else if (Pred == ICmpInst::ICMP_NE) {
1238 // !C1 != C -> true iff C1 == C.
1239 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1240 Result.getNotConstant(), C, DL,
1242 if (Res->isNullValue())
1243 return LazyValueInfo::True;
1245 return LazyValueInfo::Unknown;
1248 return LazyValueInfo::Unknown;
1251 /// Determine whether the specified value comparison with a constant is known to
1252 /// be true or false on the specified CFG edge. Pred is a CmpInst predicate.
1253 LazyValueInfo::Tristate
1254 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
1255 BasicBlock *FromBB, BasicBlock *ToBB,
1256 Instruction *CxtI) {
1257 const DataLayout &DL = FromBB->getModule()->getDataLayout();
1258 LVILatticeVal Result =
1259 getCache(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
1261 return getPredicateResult(Pred, C, Result, DL, TLI);
1264 LazyValueInfo::Tristate
1265 LazyValueInfo::getPredicateAt(unsigned Pred, Value *V, Constant *C,
1266 Instruction *CxtI) {
1267 const DataLayout &DL = CxtI->getModule()->getDataLayout();
1268 LVILatticeVal Result = getCache(PImpl, AC, &DL, DT).getValueAt(V, CxtI);
1269 Tristate Ret = getPredicateResult(Pred, C, Result, DL, TLI);
1273 // TODO: Move this logic inside getValueAt so that it can be cached rather
1274 // than re-queried on each call. This would also allow us to merge the
1275 // underlying lattice values to get more information.
1277 BasicBlock *BB = CxtI->getParent();
1279 // Function entry or an unreachable block. Bail to avoid confusing
1281 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
1285 // If V is a PHI node in the same block as the context, we need to ask
1286 // questions about the predicate as applied to the incoming value along
1287 // each edge. This is useful for eliminating cases where the predicate is
1288 // known along all incoming edges.
1289 if (auto *PHI = dyn_cast<PHINode>(V))
1290 if (PHI->getParent() == BB) {
1291 Tristate Baseline = Unknown;
1292 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i < e; i++) {
1293 Value *Incoming = PHI->getIncomingValue(i);
1294 BasicBlock *PredBB = PHI->getIncomingBlock(i);
1295 // Note that PredBB may be BB itself.
1296 Tristate Result = getPredicateOnEdge(Pred, Incoming, C, PredBB, BB,
1299 // Keep going as long as we've seen a consistent known result for
1301 Baseline = (i == 0) ? Result /* First iteration */
1302 : (Baseline == Result ? Baseline : Unknown); /* All others */
1303 if (Baseline == Unknown)
1306 if (Baseline != Unknown)
1310 // For a comparison where the V is outside this block, it's possible
1311 // that we've branched on it before. Look to see if the value is known
1312 // on all incoming edges.
1313 if (!isa<Instruction>(V) ||
1314 cast<Instruction>(V)->getParent() != BB) {
1315 // For predecessor edge, determine if the comparison is true or false
1316 // on that edge. If they're all true or all false, we can conclude
1317 // the value of the comparison in this block.
1318 Tristate Baseline = getPredicateOnEdge(Pred, V, C, *PI, BB, CxtI);
1319 if (Baseline != Unknown) {
1320 // Check that all remaining incoming values match the first one.
1321 while (++PI != PE) {
1322 Tristate Ret = getPredicateOnEdge(Pred, V, C, *PI, BB, CxtI);
1323 if (Ret != Baseline) break;
1325 // If we terminated early, then one of the values didn't match.
1335 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1336 BasicBlock *NewSucc) {
1338 const DataLayout &DL = PredBB->getModule()->getDataLayout();
1339 getCache(PImpl, AC, &DL, DT).threadEdge(PredBB, OldSucc, NewSucc);
1343 void LazyValueInfo::eraseBlock(BasicBlock *BB) {
1345 const DataLayout &DL = BB->getModule()->getDataLayout();
1346 getCache(PImpl, AC, &DL, DT).eraseBlock(BB);