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 #define DEBUG_TYPE "lazy-value-info"
16 #include "llvm/Analysis/LazyValueInfo.h"
17 #include "llvm/Analysis/ValueTracking.h"
18 #include "llvm/Constants.h"
19 #include "llvm/Instructions.h"
20 #include "llvm/IntrinsicInst.h"
21 #include "llvm/Analysis/ConstantFolding.h"
22 #include "llvm/Target/TargetData.h"
23 #include "llvm/Target/TargetLibraryInfo.h"
24 #include "llvm/Support/CFG.h"
25 #include "llvm/Support/ConstantRange.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/PatternMatch.h"
28 #include "llvm/Support/raw_ostream.h"
29 #include "llvm/Support/ValueHandle.h"
30 #include "llvm/ADT/DenseSet.h"
31 #include "llvm/ADT/STLExtras.h"
35 using namespace PatternMatch;
37 char LazyValueInfo::ID = 0;
38 INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
39 "Lazy Value Information Analysis", false, true)
40 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
41 INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info",
42 "Lazy Value Information Analysis", false, true)
45 FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
49 //===----------------------------------------------------------------------===//
51 //===----------------------------------------------------------------------===//
53 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each
56 /// FIXME: This is basically just for bringup, this can be made a lot more rich
62 /// undefined - This Value has no known value yet.
65 /// constant - This Value has a specific constant value.
67 /// notconstant - This Value is known to not have the specified value.
70 /// constantrange - The Value falls within this range.
73 /// overdefined - This value is not known to be constant, and we know that
78 /// Val: This stores the current lattice value along with the Constant* for
79 /// the constant if this is a 'constant' or 'notconstant' value.
85 LVILatticeVal() : Tag(undefined), Val(0), Range(1, true) {}
87 static LVILatticeVal get(Constant *C) {
89 if (!isa<UndefValue>(C))
93 static LVILatticeVal getNot(Constant *C) {
95 if (!isa<UndefValue>(C))
96 Res.markNotConstant(C);
99 static LVILatticeVal getRange(ConstantRange CR) {
101 Res.markConstantRange(CR);
105 bool isUndefined() const { return Tag == undefined; }
106 bool isConstant() const { return Tag == constant; }
107 bool isNotConstant() const { return Tag == notconstant; }
108 bool isConstantRange() const { return Tag == constantrange; }
109 bool isOverdefined() const { return Tag == overdefined; }
111 Constant *getConstant() const {
112 assert(isConstant() && "Cannot get the constant of a non-constant!");
116 Constant *getNotConstant() const {
117 assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
121 ConstantRange getConstantRange() const {
122 assert(isConstantRange() &&
123 "Cannot get the constant-range of a non-constant-range!");
127 /// markOverdefined - Return true if this is a change in status.
128 bool markOverdefined() {
135 /// markConstant - Return true if this is a change in status.
136 bool markConstant(Constant *V) {
137 assert(V && "Marking constant with NULL");
138 if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
139 return markConstantRange(ConstantRange(CI->getValue()));
140 if (isa<UndefValue>(V))
143 assert((!isConstant() || getConstant() == V) &&
144 "Marking constant with different value");
145 assert(isUndefined());
151 /// markNotConstant - Return true if this is a change in status.
152 bool markNotConstant(Constant *V) {
153 assert(V && "Marking constant with NULL");
154 if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
155 return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
156 if (isa<UndefValue>(V))
159 assert((!isConstant() || getConstant() != V) &&
160 "Marking constant !constant with same value");
161 assert((!isNotConstant() || getNotConstant() == V) &&
162 "Marking !constant with different value");
163 assert(isUndefined() || isConstant());
169 /// markConstantRange - Return true if this is a change in status.
170 bool markConstantRange(const ConstantRange NewR) {
171 if (isConstantRange()) {
172 if (NewR.isEmptySet())
173 return markOverdefined();
175 bool changed = Range != NewR;
180 assert(isUndefined());
181 if (NewR.isEmptySet())
182 return markOverdefined();
189 /// mergeIn - Merge the specified lattice value into this one, updating this
190 /// one and returning true if anything changed.
191 bool mergeIn(const LVILatticeVal &RHS) {
192 if (RHS.isUndefined() || isOverdefined()) return false;
193 if (RHS.isOverdefined()) return markOverdefined();
203 if (RHS.isConstant()) {
206 return markOverdefined();
209 if (RHS.isNotConstant()) {
211 return markOverdefined();
213 // Unless we can prove that the two Constants are different, we must
214 // move to overdefined.
215 // FIXME: use TargetData/TargetLibraryInfo for smarter constant folding.
216 if (ConstantInt *Res = dyn_cast<ConstantInt>(
217 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
219 RHS.getNotConstant())))
221 return markNotConstant(RHS.getNotConstant());
223 return markOverdefined();
226 // RHS is a ConstantRange, LHS is a non-integer Constant.
228 // FIXME: consider the case where RHS is a range [1, 0) and LHS is
229 // a function. The correct result is to pick up RHS.
231 return markOverdefined();
234 if (isNotConstant()) {
235 if (RHS.isConstant()) {
237 return markOverdefined();
239 // Unless we can prove that the two Constants are different, we must
240 // move to overdefined.
241 // FIXME: use TargetData/TargetLibraryInfo for smarter constant folding.
242 if (ConstantInt *Res = dyn_cast<ConstantInt>(
243 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
249 return markOverdefined();
252 if (RHS.isNotConstant()) {
255 return markOverdefined();
258 return markOverdefined();
261 assert(isConstantRange() && "New LVILattice type?");
262 if (!RHS.isConstantRange())
263 return markOverdefined();
265 ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
266 if (NewR.isFullSet())
267 return markOverdefined();
268 return markConstantRange(NewR);
272 } // end anonymous namespace.
275 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
277 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
278 if (Val.isUndefined())
279 return OS << "undefined";
280 if (Val.isOverdefined())
281 return OS << "overdefined";
283 if (Val.isNotConstant())
284 return OS << "notconstant<" << *Val.getNotConstant() << '>';
285 else if (Val.isConstantRange())
286 return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
287 << Val.getConstantRange().getUpper() << '>';
288 return OS << "constant<" << *Val.getConstant() << '>';
292 //===----------------------------------------------------------------------===//
293 // LazyValueInfoCache Decl
294 //===----------------------------------------------------------------------===//
297 /// LVIValueHandle - A callback value handle update the cache when
298 /// values are erased.
299 class LazyValueInfoCache;
300 struct LVIValueHandle : public CallbackVH {
301 LazyValueInfoCache *Parent;
303 LVIValueHandle(Value *V, LazyValueInfoCache *P)
304 : CallbackVH(V), Parent(P) { }
307 void allUsesReplacedWith(Value *V) {
314 /// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
315 /// maintains information about queries across the clients' queries.
316 class LazyValueInfoCache {
317 /// ValueCacheEntryTy - This is all of the cached block information for
318 /// exactly one Value*. The entries are sorted by the BasicBlock* of the
319 /// entries, allowing us to do a lookup with a binary search.
320 typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy;
322 /// ValueCache - This is all of the cached information for all values,
323 /// mapped from Value* to key information.
324 std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache;
326 /// OverDefinedCache - This tracks, on a per-block basis, the set of
327 /// values that are over-defined at the end of that block. This is required
328 /// for cache updating.
329 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
330 DenseSet<OverDefinedPairTy> OverDefinedCache;
332 /// SeenBlocks - 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 /// BlockValueStack - This stack holds the state of the value solver
337 /// during a query. It basically emulates the callstack of the naive
338 /// recursive value lookup process.
339 std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
341 friend struct LVIValueHandle;
343 /// OverDefinedCacheUpdater - A helper object that ensures that the
344 /// OverDefinedCache is updated whenever solveBlockValue returns.
345 struct OverDefinedCacheUpdater {
346 LazyValueInfoCache *Parent;
351 OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV,
352 LazyValueInfoCache *P)
353 : Parent(P), Val(V), BB(B), BBLV(LV) { }
355 bool markResult(bool changed) {
356 if (changed && BBLV.isOverdefined())
357 Parent->OverDefinedCache.insert(std::make_pair(BB, Val));
364 LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
365 bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
366 LVILatticeVal &Result);
367 bool hasBlockValue(Value *Val, BasicBlock *BB);
369 // These methods process one work item and may add more. A false value
370 // returned means that the work item was not completely processed and must
371 // be revisited after going through the new items.
372 bool solveBlockValue(Value *Val, BasicBlock *BB);
373 bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
374 Value *Val, BasicBlock *BB);
375 bool solveBlockValuePHINode(LVILatticeVal &BBLV,
376 PHINode *PN, BasicBlock *BB);
377 bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
378 Instruction *BBI, BasicBlock *BB);
382 ValueCacheEntryTy &lookup(Value *V) {
383 return ValueCache[LVIValueHandle(V, this)];
387 /// getValueInBlock - This is the query interface to determine the lattice
388 /// value for the specified Value* at the end of the specified block.
389 LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB);
391 /// getValueOnEdge - This is the query interface to determine the lattice
392 /// value for the specified Value* that is true on the specified edge.
393 LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB);
395 /// threadEdge - This is the update interface to inform the cache that an
396 /// edge from PredBB to OldSucc has been threaded to be from PredBB to
398 void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
400 /// eraseBlock - This is part of the update interface to inform the cache
401 /// that a block has been deleted.
402 void eraseBlock(BasicBlock *BB);
404 /// clear - Empty the cache.
408 OverDefinedCache.clear();
411 } // end anonymous namespace
413 void LVIValueHandle::deleted() {
414 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
416 SmallVector<OverDefinedPairTy, 4> ToErase;
417 for (DenseSet<OverDefinedPairTy>::iterator
418 I = Parent->OverDefinedCache.begin(),
419 E = Parent->OverDefinedCache.end();
421 if (I->second == getValPtr())
422 ToErase.push_back(*I);
425 for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
426 E = ToErase.end(); I != E; ++I)
427 Parent->OverDefinedCache.erase(*I);
429 // This erasure deallocates *this, so it MUST happen after we're done
430 // using any and all members of *this.
431 Parent->ValueCache.erase(*this);
434 void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
435 // Shortcut if we have never seen this block.
436 DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
437 if (I == SeenBlocks.end())
441 SmallVector<OverDefinedPairTy, 4> ToErase;
442 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
443 E = OverDefinedCache.end(); I != E; ++I) {
445 ToErase.push_back(*I);
448 for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
449 E = ToErase.end(); I != E; ++I)
450 OverDefinedCache.erase(*I);
452 for (std::map<LVIValueHandle, ValueCacheEntryTy>::iterator
453 I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
457 void LazyValueInfoCache::solve() {
458 while (!BlockValueStack.empty()) {
459 std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
460 if (solveBlockValue(e.second, e.first)) {
461 assert(BlockValueStack.top() == e);
462 BlockValueStack.pop();
467 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
468 // If already a constant, there is nothing to compute.
469 if (isa<Constant>(Val))
472 LVIValueHandle ValHandle(Val, this);
473 if (!ValueCache.count(ValHandle)) return false;
474 return ValueCache[ValHandle].count(BB);
477 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
478 // If already a constant, there is nothing to compute.
479 if (Constant *VC = dyn_cast<Constant>(Val))
480 return LVILatticeVal::get(VC);
482 SeenBlocks.insert(BB);
483 return lookup(Val)[BB];
486 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
487 if (isa<Constant>(Val))
490 ValueCacheEntryTy &Cache = lookup(Val);
491 SeenBlocks.insert(BB);
492 LVILatticeVal &BBLV = Cache[BB];
494 // OverDefinedCacheUpdater is a helper object that will update
495 // the OverDefinedCache for us when this method exits. Make sure to
496 // call markResult on it as we exist, passing a bool to indicate if the
497 // cache needs updating, i.e. if we have solve a new value or not.
498 OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this);
500 // If we've already computed this block's value, return it.
501 if (!BBLV.isUndefined()) {
502 DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
504 // Since we're reusing a cached value here, we don't need to update the
505 // OverDefinedCahce. The cache will have been properly updated
506 // whenever the cached value was inserted.
507 ODCacheUpdater.markResult(false);
511 // Otherwise, this is the first time we're seeing this block. Reset the
512 // lattice value to overdefined, so that cycles will terminate and be
513 // conservatively correct.
514 BBLV.markOverdefined();
516 Instruction *BBI = dyn_cast<Instruction>(Val);
517 if (BBI == 0 || BBI->getParent() != BB) {
518 return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB));
521 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
522 return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB));
525 if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
526 BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
527 return ODCacheUpdater.markResult(true);
530 // We can only analyze the definitions of certain classes of instructions
531 // (integral binops and casts at the moment), so bail if this isn't one.
532 LVILatticeVal Result;
533 if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
534 !BBI->getType()->isIntegerTy()) {
535 DEBUG(dbgs() << " compute BB '" << BB->getName()
536 << "' - overdefined because inst def found.\n");
537 BBLV.markOverdefined();
538 return ODCacheUpdater.markResult(true);
541 // FIXME: We're currently limited to binops with a constant RHS. This should
543 BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
544 if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
545 DEBUG(dbgs() << " compute BB '" << BB->getName()
546 << "' - overdefined because inst def found.\n");
548 BBLV.markOverdefined();
549 return ODCacheUpdater.markResult(true);
552 return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB));
555 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
556 if (LoadInst *L = dyn_cast<LoadInst>(I)) {
557 return L->getPointerAddressSpace() == 0 &&
558 GetUnderlyingObject(L->getPointerOperand()) ==
559 GetUnderlyingObject(Ptr);
561 if (StoreInst *S = dyn_cast<StoreInst>(I)) {
562 return S->getPointerAddressSpace() == 0 &&
563 GetUnderlyingObject(S->getPointerOperand()) ==
564 GetUnderlyingObject(Ptr);
566 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
567 if (MI->isVolatile()) return false;
569 // FIXME: check whether it has a valuerange that excludes zero?
570 ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
571 if (!Len || Len->isZero()) return false;
573 if (MI->getDestAddressSpace() == 0)
574 if (MI->getRawDest() == Ptr || MI->getDest() == Ptr)
576 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
577 if (MTI->getSourceAddressSpace() == 0)
578 if (MTI->getRawSource() == Ptr || MTI->getSource() == Ptr)
584 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
585 Value *Val, BasicBlock *BB) {
586 LVILatticeVal Result; // Start Undefined.
588 // If this is a pointer, and there's a load from that pointer in this BB,
589 // then we know that the pointer can't be NULL.
590 bool NotNull = false;
591 if (Val->getType()->isPointerTy()) {
592 if (isa<AllocaInst>(Val)) {
595 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();BI != BE;++BI){
596 if (InstructionDereferencesPointer(BI, Val)) {
604 // If this is the entry block, we must be asking about an argument. The
605 // value is overdefined.
606 if (BB == &BB->getParent()->getEntryBlock()) {
607 assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
609 PointerType *PTy = cast<PointerType>(Val->getType());
610 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
612 Result.markOverdefined();
618 // Loop over all of our predecessors, merging what we know from them into
620 bool EdgesMissing = false;
621 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
622 LVILatticeVal EdgeResult;
623 EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
627 Result.mergeIn(EdgeResult);
629 // If we hit overdefined, exit early. The BlockVals entry is already set
631 if (Result.isOverdefined()) {
632 DEBUG(dbgs() << " compute BB '" << BB->getName()
633 << "' - overdefined because of pred.\n");
634 // If we previously determined that this is a pointer that can't be null
635 // then return that rather than giving up entirely.
637 PointerType *PTy = cast<PointerType>(Val->getType());
638 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
648 // Return the merged value, which is more precise than 'overdefined'.
649 assert(!Result.isOverdefined());
654 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
655 PHINode *PN, BasicBlock *BB) {
656 LVILatticeVal Result; // Start Undefined.
658 // Loop over all of our predecessors, merging what we know from them into
660 bool EdgesMissing = false;
661 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
662 BasicBlock *PhiBB = PN->getIncomingBlock(i);
663 Value *PhiVal = PN->getIncomingValue(i);
664 LVILatticeVal EdgeResult;
665 EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult);
669 Result.mergeIn(EdgeResult);
671 // If we hit overdefined, exit early. The BlockVals entry is already set
673 if (Result.isOverdefined()) {
674 DEBUG(dbgs() << " compute BB '" << BB->getName()
675 << "' - overdefined because of pred.\n");
684 // Return the merged value, which is more precise than 'overdefined'.
685 assert(!Result.isOverdefined() && "Possible PHI in entry block?");
690 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
693 // Figure out the range of the LHS. If that fails, bail.
694 if (!hasBlockValue(BBI->getOperand(0), BB)) {
695 BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
699 LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
700 if (!LHSVal.isConstantRange()) {
701 BBLV.markOverdefined();
705 ConstantRange LHSRange = LHSVal.getConstantRange();
706 ConstantRange RHSRange(1);
707 IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
708 if (isa<BinaryOperator>(BBI)) {
709 if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
710 RHSRange = ConstantRange(RHS->getValue());
712 BBLV.markOverdefined();
717 // NOTE: We're currently limited by the set of operations that ConstantRange
718 // can evaluate symbolically. Enhancing that set will allows us to analyze
720 LVILatticeVal Result;
721 switch (BBI->getOpcode()) {
722 case Instruction::Add:
723 Result.markConstantRange(LHSRange.add(RHSRange));
725 case Instruction::Sub:
726 Result.markConstantRange(LHSRange.sub(RHSRange));
728 case Instruction::Mul:
729 Result.markConstantRange(LHSRange.multiply(RHSRange));
731 case Instruction::UDiv:
732 Result.markConstantRange(LHSRange.udiv(RHSRange));
734 case Instruction::Shl:
735 Result.markConstantRange(LHSRange.shl(RHSRange));
737 case Instruction::LShr:
738 Result.markConstantRange(LHSRange.lshr(RHSRange));
740 case Instruction::Trunc:
741 Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
743 case Instruction::SExt:
744 Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
746 case Instruction::ZExt:
747 Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
749 case Instruction::BitCast:
750 Result.markConstantRange(LHSRange);
752 case Instruction::And:
753 Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
755 case Instruction::Or:
756 Result.markConstantRange(LHSRange.binaryOr(RHSRange));
759 // Unhandled instructions are overdefined.
761 DEBUG(dbgs() << " compute BB '" << BB->getName()
762 << "' - overdefined because inst def found.\n");
763 Result.markOverdefined();
771 /// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
772 /// Val is not constrained on the edge.
773 static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
774 BasicBlock *BBTo, LVILatticeVal &Result) {
775 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
777 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
778 // If this is a conditional branch and only one successor goes to BBTo, then
779 // we maybe able to infer something from the condition.
780 if (BI->isConditional() &&
781 BI->getSuccessor(0) != BI->getSuccessor(1)) {
782 bool isTrueDest = BI->getSuccessor(0) == BBTo;
783 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
784 "BBTo isn't a successor of BBFrom");
786 // If V is the condition of the branch itself, then we know exactly what
788 if (BI->getCondition() == Val) {
789 Result = LVILatticeVal::get(ConstantInt::get(
790 Type::getInt1Ty(Val->getContext()), isTrueDest));
794 // If the condition of the branch is an equality comparison, we may be
795 // able to infer the value.
796 ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
797 if (ICI && isa<Constant>(ICI->getOperand(1))) {
798 if (ICI->isEquality() && ICI->getOperand(0) == Val) {
799 // We know that V has the RHS constant if this is a true SETEQ or
801 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
802 Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
804 Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
808 // Recognize the range checking idiom that InstCombine produces.
809 // (X-C1) u< C2 --> [C1, C1+C2)
810 ConstantInt *NegOffset = 0;
811 if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
812 match(ICI->getOperand(0), m_Add(m_Specific(Val),
813 m_ConstantInt(NegOffset)));
815 ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
816 if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
817 // Calculate the range of values that would satisfy the comparison.
818 ConstantRange CmpRange(CI->getValue());
819 ConstantRange TrueValues =
820 ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
822 if (NegOffset) // Apply the offset from above.
823 TrueValues = TrueValues.subtract(NegOffset->getValue());
825 // If we're interested in the false dest, invert the condition.
826 if (!isTrueDest) TrueValues = TrueValues.inverse();
828 Result = LVILatticeVal::getRange(TrueValues);
835 // If the edge was formed by a switch on the value, then we may know exactly
837 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
838 if (SI->getCondition() != Val)
841 bool DefaultCase = SI->getDefaultDest() == BBTo;
842 unsigned BitWidth = Val->getType()->getIntegerBitWidth();
843 ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
845 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
847 ConstantRange EdgeVal(i.getCaseValue()->getValue());
849 EdgesVals = EdgesVals.difference(EdgeVal);
850 else if (i.getCaseSuccessor() == BBTo)
851 EdgesVals = EdgesVals.unionWith(EdgeVal);
853 Result = LVILatticeVal::getRange(EdgesVals);
859 /// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at
860 /// the basic block if the edge does not constraint Val.
861 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
862 BasicBlock *BBTo, LVILatticeVal &Result) {
863 // If already a constant, there is nothing to compute.
864 if (Constant *VC = dyn_cast<Constant>(Val)) {
865 Result = LVILatticeVal::get(VC);
869 if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
870 if (!Result.isConstantRange() ||
871 Result.getConstantRange().getSingleElement())
874 // FIXME: this check should be moved to the beginning of the function when
875 // LVI better supports recursive values. Even for the single value case, we
876 // can intersect to detect dead code (an empty range).
877 if (!hasBlockValue(Val, BBFrom)) {
878 BlockValueStack.push(std::make_pair(BBFrom, Val));
882 // Try to intersect ranges of the BB and the constraint on the edge.
883 LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
884 if (!InBlock.isConstantRange())
887 ConstantRange Range =
888 Result.getConstantRange().intersectWith(InBlock.getConstantRange());
889 Result = LVILatticeVal::getRange(Range);
893 if (!hasBlockValue(Val, BBFrom)) {
894 BlockValueStack.push(std::make_pair(BBFrom, Val));
898 // if we couldn't compute the value on the edge, use the value from the BB
899 Result = getBlockValue(Val, BBFrom);
903 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
904 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
905 << BB->getName() << "'\n");
907 BlockValueStack.push(std::make_pair(BB, V));
909 LVILatticeVal Result = getBlockValue(V, BB);
911 DEBUG(dbgs() << " Result = " << Result << "\n");
915 LVILatticeVal LazyValueInfoCache::
916 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
917 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
918 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
920 LVILatticeVal Result;
921 if (!getEdgeValue(V, FromBB, ToBB, Result)) {
923 bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result);
925 assert(WasFastQuery && "More work to do after problem solved?");
928 DEBUG(dbgs() << " Result = " << Result << "\n");
932 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
933 BasicBlock *NewSucc) {
934 // When an edge in the graph has been threaded, values that we could not
935 // determine a value for before (i.e. were marked overdefined) may be possible
936 // to solve now. We do NOT try to proactively update these values. Instead,
937 // we clear their entries from the cache, and allow lazy updating to recompute
940 // The updating process is fairly simple: we need to dropped cached info
941 // for all values that were marked overdefined in OldSucc, and for those same
942 // values in any successor of OldSucc (except NewSucc) in which they were
943 // also marked overdefined.
944 std::vector<BasicBlock*> worklist;
945 worklist.push_back(OldSucc);
947 DenseSet<Value*> ClearSet;
948 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
949 E = OverDefinedCache.end(); I != E; ++I) {
950 if (I->first == OldSucc)
951 ClearSet.insert(I->second);
954 // Use a worklist to perform a depth-first search of OldSucc's successors.
955 // NOTE: We do not need a visited list since any blocks we have already
956 // visited will have had their overdefined markers cleared already, and we
957 // thus won't loop to their successors.
958 while (!worklist.empty()) {
959 BasicBlock *ToUpdate = worklist.back();
962 // Skip blocks only accessible through NewSucc.
963 if (ToUpdate == NewSucc) continue;
965 bool changed = false;
966 for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end();
968 // If a value was marked overdefined in OldSucc, and is here too...
969 DenseSet<OverDefinedPairTy>::iterator OI =
970 OverDefinedCache.find(std::make_pair(ToUpdate, *I));
971 if (OI == OverDefinedCache.end()) continue;
973 // Remove it from the caches.
974 ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)];
975 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
977 assert(CI != Entry.end() && "Couldn't find entry to update?");
979 OverDefinedCache.erase(OI);
981 // If we removed anything, then we potentially need to update
982 // blocks successors too.
986 if (!changed) continue;
988 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
992 //===----------------------------------------------------------------------===//
993 // LazyValueInfo Impl
994 //===----------------------------------------------------------------------===//
996 /// getCache - This lazily constructs the LazyValueInfoCache.
997 static LazyValueInfoCache &getCache(void *&PImpl) {
999 PImpl = new LazyValueInfoCache();
1000 return *static_cast<LazyValueInfoCache*>(PImpl);
1003 bool LazyValueInfo::runOnFunction(Function &F) {
1005 getCache(PImpl).clear();
1007 TD = getAnalysisIfAvailable<TargetData>();
1008 TLI = &getAnalysis<TargetLibraryInfo>();
1014 void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
1015 AU.setPreservesAll();
1016 AU.addRequired<TargetLibraryInfo>();
1019 void LazyValueInfo::releaseMemory() {
1020 // If the cache was allocated, free it.
1022 delete &getCache(PImpl);
1027 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
1028 LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
1030 if (Result.isConstant())
1031 return Result.getConstant();
1032 if (Result.isConstantRange()) {
1033 ConstantRange CR = Result.getConstantRange();
1034 if (const APInt *SingleVal = CR.getSingleElement())
1035 return ConstantInt::get(V->getContext(), *SingleVal);
1040 /// getConstantOnEdge - Determine whether the specified value is known to be a
1041 /// constant on the specified edge. Return null if not.
1042 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
1044 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1046 if (Result.isConstant())
1047 return Result.getConstant();
1048 if (Result.isConstantRange()) {
1049 ConstantRange CR = Result.getConstantRange();
1050 if (const APInt *SingleVal = CR.getSingleElement())
1051 return ConstantInt::get(V->getContext(), *SingleVal);
1056 /// getPredicateOnEdge - Determine whether the specified value comparison
1057 /// with a constant is known to be true or false on the specified CFG edge.
1058 /// Pred is a CmpInst predicate.
1059 LazyValueInfo::Tristate
1060 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
1061 BasicBlock *FromBB, BasicBlock *ToBB) {
1062 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1064 // If we know the value is a constant, evaluate the conditional.
1066 if (Result.isConstant()) {
1067 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD,
1069 if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
1070 return ResCI->isZero() ? False : True;
1074 if (Result.isConstantRange()) {
1075 ConstantInt *CI = dyn_cast<ConstantInt>(C);
1076 if (!CI) return Unknown;
1078 ConstantRange CR = Result.getConstantRange();
1079 if (Pred == ICmpInst::ICMP_EQ) {
1080 if (!CR.contains(CI->getValue()))
1083 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1085 } else if (Pred == ICmpInst::ICMP_NE) {
1086 if (!CR.contains(CI->getValue()))
1089 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1093 // Handle more complex predicates.
1094 ConstantRange TrueValues =
1095 ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
1096 if (TrueValues.contains(CR))
1098 if (TrueValues.inverse().contains(CR))
1103 if (Result.isNotConstant()) {
1104 // If this is an equality comparison, we can try to fold it knowing that
1106 if (Pred == ICmpInst::ICMP_EQ) {
1107 // !C1 == C -> false iff C1 == C.
1108 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1109 Result.getNotConstant(), C, TD,
1111 if (Res->isNullValue())
1113 } else if (Pred == ICmpInst::ICMP_NE) {
1114 // !C1 != C -> true iff C1 == C.
1115 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1116 Result.getNotConstant(), C, TD,
1118 if (Res->isNullValue())
1127 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1128 BasicBlock *NewSucc) {
1129 if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);
1132 void LazyValueInfo::eraseBlock(BasicBlock *BB) {
1133 if (PImpl) getCache(PImpl).eraseBlock(BB);