1 //===- LazyValueInfo.cpp - Value constraint analysis ----------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the interface for lazy computation of value constraint
11 // information.
12 //
13 //===----------------------------------------------------------------------===//
14
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/Support/CFG.h"
24 #include "llvm/Support/ConstantRange.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include "llvm/Support/ValueHandle.h"
28 #include "llvm/ADT/DenseMap.h"
29 #include "llvm/ADT/DenseSet.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include <map>
32 #include <stack>
33 using namespace llvm;
34
35 char LazyValueInfo::ID = 0;
36 INITIALIZE_PASS(LazyValueInfo, "lazy-value-info",
37 "Lazy Value Information Analysis", false, true)
38
39 namespace llvm {
createLazyValueInfoPass()40 FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
41 }
42
43
44 //===----------------------------------------------------------------------===//
45 // LVILatticeVal
46 //===----------------------------------------------------------------------===//
47
48 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each
49 /// value.
50 ///
51 /// FIXME: This is basically just for bringup, this can be made a lot more rich
52 /// in the future.
53 ///
54 namespace {
55 class LVILatticeVal {
56 enum LatticeValueTy {
57 /// undefined - This Value has no known value yet.
58 undefined,
59
60 /// constant - This Value has a specific constant value.
61 constant,
62 /// notconstant - This Value is known to not have the specified value.
63 notconstant,
64
65 /// constantrange - The Value falls within this range.
66 constantrange,
67
68 /// overdefined - This value is not known to be constant, and we know that
69 /// it has a value.
70 overdefined
71 };
72
73 /// Val: This stores the current lattice value along with the Constant* for
74 /// the constant if this is a 'constant' or 'notconstant' value.
75 LatticeValueTy Tag;
76 Constant *Val;
77 ConstantRange Range;
78
79 public:
LVILatticeVal()80 LVILatticeVal() : Tag(undefined), Val(0), Range(1, true) {}
81
get(Constant * C)82 static LVILatticeVal get(Constant *C) {
83 LVILatticeVal Res;
84 if (!isa<UndefValue>(C))
85 Res.markConstant(C);
86 return Res;
87 }
getNot(Constant * C)88 static LVILatticeVal getNot(Constant *C) {
89 LVILatticeVal Res;
90 if (!isa<UndefValue>(C))
91 Res.markNotConstant(C);
92 return Res;
93 }
getRange(ConstantRange CR)94 static LVILatticeVal getRange(ConstantRange CR) {
95 LVILatticeVal Res;
96 Res.markConstantRange(CR);
97 return Res;
98 }
99
isUndefined() const100 bool isUndefined() const { return Tag == undefined; }
isConstant() const101 bool isConstant() const { return Tag == constant; }
isNotConstant() const102 bool isNotConstant() const { return Tag == notconstant; }
isConstantRange() const103 bool isConstantRange() const { return Tag == constantrange; }
isOverdefined() const104 bool isOverdefined() const { return Tag == overdefined; }
105
getConstant() const106 Constant *getConstant() const {
107 assert(isConstant() && "Cannot get the constant of a non-constant!");
108 return Val;
109 }
110
getNotConstant() const111 Constant *getNotConstant() const {
112 assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
113 return Val;
114 }
115
getConstantRange() const116 ConstantRange getConstantRange() const {
117 assert(isConstantRange() &&
118 "Cannot get the constant-range of a non-constant-range!");
119 return Range;
120 }
121
122 /// markOverdefined - Return true if this is a change in status.
markOverdefined()123 bool markOverdefined() {
124 if (isOverdefined())
125 return false;
126 Tag = overdefined;
127 return true;
128 }
129
130 /// markConstant - Return true if this is a change in status.
markConstant(Constant * V)131 bool markConstant(Constant *V) {
132 assert(V && "Marking constant with NULL");
133 if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
134 return markConstantRange(ConstantRange(CI->getValue()));
135 if (isa<UndefValue>(V))
136 return false;
137
138 assert((!isConstant() || getConstant() == V) &&
139 "Marking constant with different value");
140 assert(isUndefined());
141 Tag = constant;
142 Val = V;
143 return true;
144 }
145
146 /// markNotConstant - Return true if this is a change in status.
markNotConstant(Constant * V)147 bool markNotConstant(Constant *V) {
148 assert(V && "Marking constant with NULL");
149 if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
150 return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
151 if (isa<UndefValue>(V))
152 return false;
153
154 assert((!isConstant() || getConstant() != V) &&
155 "Marking constant !constant with same value");
156 assert((!isNotConstant() || getNotConstant() == V) &&
157 "Marking !constant with different value");
158 assert(isUndefined() || isConstant());
159 Tag = notconstant;
160 Val = V;
161 return true;
162 }
163
164 /// markConstantRange - Return true if this is a change in status.
markConstantRange(const ConstantRange NewR)165 bool markConstantRange(const ConstantRange NewR) {
166 if (isConstantRange()) {
167 if (NewR.isEmptySet())
168 return markOverdefined();
169
170 bool changed = Range == NewR;
171 Range = NewR;
172 return changed;
173 }
174
175 assert(isUndefined());
176 if (NewR.isEmptySet())
177 return markOverdefined();
178
179 Tag = constantrange;
180 Range = NewR;
181 return true;
182 }
183
184 /// mergeIn - Merge the specified lattice value into this one, updating this
185 /// one and returning true if anything changed.
mergeIn(const LVILatticeVal & RHS)186 bool mergeIn(const LVILatticeVal &RHS) {
187 if (RHS.isUndefined() || isOverdefined()) return false;
188 if (RHS.isOverdefined()) return markOverdefined();
189
190 if (isUndefined()) {
191 Tag = RHS.Tag;
192 Val = RHS.Val;
193 Range = RHS.Range;
194 return true;
195 }
196
197 if (isConstant()) {
198 if (RHS.isConstant()) {
199 if (Val == RHS.Val)
200 return false;
201 return markOverdefined();
202 }
203
204 if (RHS.isNotConstant()) {
205 if (Val == RHS.Val)
206 return markOverdefined();
207
208 // Unless we can prove that the two Constants are different, we must
209 // move to overdefined.
210 // FIXME: use TargetData for smarter constant folding.
211 if (ConstantInt *Res = dyn_cast<ConstantInt>(
212 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
213 getConstant(),
214 RHS.getNotConstant())))
215 if (Res->isOne())
216 return markNotConstant(RHS.getNotConstant());
217
218 return markOverdefined();
219 }
220
221 // RHS is a ConstantRange, LHS is a non-integer Constant.
222
223 // FIXME: consider the case where RHS is a range [1, 0) and LHS is
224 // a function. The correct result is to pick up RHS.
225
226 return markOverdefined();
227 }
228
229 if (isNotConstant()) {
230 if (RHS.isConstant()) {
231 if (Val == RHS.Val)
232 return markOverdefined();
233
234 // Unless we can prove that the two Constants are different, we must
235 // move to overdefined.
236 // FIXME: use TargetData for smarter constant folding.
237 if (ConstantInt *Res = dyn_cast<ConstantInt>(
238 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
239 getNotConstant(),
240 RHS.getConstant())))
241 if (Res->isOne())
242 return false;
243
244 return markOverdefined();
245 }
246
247 if (RHS.isNotConstant()) {
248 if (Val == RHS.Val)
249 return false;
250 return markOverdefined();
251 }
252
253 return markOverdefined();
254 }
255
256 assert(isConstantRange() && "New LVILattice type?");
257 if (!RHS.isConstantRange())
258 return markOverdefined();
259
260 ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
261 if (NewR.isFullSet())
262 return markOverdefined();
263 return markConstantRange(NewR);
264 }
265 };
266
267 } // end anonymous namespace.
268
269 namespace llvm {
270 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
271 LLVM_ATTRIBUTE_USED;
operator <<(raw_ostream & OS,const LVILatticeVal & Val)272 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
273 if (Val.isUndefined())
274 return OS << "undefined";
275 if (Val.isOverdefined())
276 return OS << "overdefined";
277
278 if (Val.isNotConstant())
279 return OS << "notconstant<" << *Val.getNotConstant() << '>';
280 else if (Val.isConstantRange())
281 return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
282 << Val.getConstantRange().getUpper() << '>';
283 return OS << "constant<" << *Val.getConstant() << '>';
284 }
285 }
286
287 //===----------------------------------------------------------------------===//
288 // LazyValueInfoCache Decl
289 //===----------------------------------------------------------------------===//
290
291 namespace {
292 /// LVIValueHandle - A callback value handle update the cache when
293 /// values are erased.
294 class LazyValueInfoCache;
295 struct LVIValueHandle : public CallbackVH {
296 LazyValueInfoCache *Parent;
297
LVIValueHandle__anon033df9310211::LVIValueHandle298 LVIValueHandle(Value *V, LazyValueInfoCache *P)
299 : CallbackVH(V), Parent(P) { }
300
301 void deleted();
allUsesReplacedWith__anon033df9310211::LVIValueHandle302 void allUsesReplacedWith(Value *V) {
303 deleted();
304 }
305 };
306 }
307
308 namespace llvm {
309 template<>
310 struct DenseMapInfo<LVIValueHandle> {
311 typedef DenseMapInfo<Value*> PointerInfo;
getEmptyKeyllvm::DenseMapInfo312 static inline LVIValueHandle getEmptyKey() {
313 return LVIValueHandle(PointerInfo::getEmptyKey(),
314 static_cast<LazyValueInfoCache*>(0));
315 }
getTombstoneKeyllvm::DenseMapInfo316 static inline LVIValueHandle getTombstoneKey() {
317 return LVIValueHandle(PointerInfo::getTombstoneKey(),
318 static_cast<LazyValueInfoCache*>(0));
319 }
getHashValuellvm::DenseMapInfo320 static unsigned getHashValue(const LVIValueHandle &Val) {
321 return PointerInfo::getHashValue(Val);
322 }
isEqualllvm::DenseMapInfo323 static bool isEqual(const LVIValueHandle &LHS, const LVIValueHandle &RHS) {
324 return LHS == RHS;
325 }
326 };
327
328 template<>
329 struct DenseMapInfo<std::pair<AssertingVH<BasicBlock>, Value*> > {
330 typedef std::pair<AssertingVH<BasicBlock>, Value*> PairTy;
331 typedef DenseMapInfo<AssertingVH<BasicBlock> > APointerInfo;
332 typedef DenseMapInfo<Value*> BPointerInfo;
getEmptyKeyllvm::DenseMapInfo333 static inline PairTy getEmptyKey() {
334 return std::make_pair(APointerInfo::getEmptyKey(),
335 BPointerInfo::getEmptyKey());
336 }
getTombstoneKeyllvm::DenseMapInfo337 static inline PairTy getTombstoneKey() {
338 return std::make_pair(APointerInfo::getTombstoneKey(),
339 BPointerInfo::getTombstoneKey());
340 }
getHashValuellvm::DenseMapInfo341 static unsigned getHashValue( const PairTy &Val) {
342 return APointerInfo::getHashValue(Val.first) ^
343 BPointerInfo::getHashValue(Val.second);
344 }
isEqualllvm::DenseMapInfo345 static bool isEqual(const PairTy &LHS, const PairTy &RHS) {
346 return APointerInfo::isEqual(LHS.first, RHS.first) &&
347 BPointerInfo::isEqual(LHS.second, RHS.second);
348 }
349 };
350 }
351
352 namespace {
353 /// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
354 /// maintains information about queries across the clients' queries.
355 class LazyValueInfoCache {
356 /// ValueCacheEntryTy - This is all of the cached block information for
357 /// exactly one Value*. The entries are sorted by the BasicBlock* of the
358 /// entries, allowing us to do a lookup with a binary search.
359 typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy;
360
361 /// ValueCache - This is all of the cached information for all values,
362 /// mapped from Value* to key information.
363 DenseMap<LVIValueHandle, ValueCacheEntryTy> ValueCache;
364
365 /// OverDefinedCache - This tracks, on a per-block basis, the set of
366 /// values that are over-defined at the end of that block. This is required
367 /// for cache updating.
368 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
369 DenseSet<OverDefinedPairTy> OverDefinedCache;
370
371 /// BlockValueStack - This stack holds the state of the value solver
372 /// during a query. It basically emulates the callstack of the naive
373 /// recursive value lookup process.
374 std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
375
376 friend struct LVIValueHandle;
377
378 /// OverDefinedCacheUpdater - A helper object that ensures that the
379 /// OverDefinedCache is updated whenever solveBlockValue returns.
380 struct OverDefinedCacheUpdater {
381 LazyValueInfoCache *Parent;
382 Value *Val;
383 BasicBlock *BB;
384 LVILatticeVal &BBLV;
385
OverDefinedCacheUpdater__anon033df9310311::LazyValueInfoCache::OverDefinedCacheUpdater386 OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV,
387 LazyValueInfoCache *P)
388 : Parent(P), Val(V), BB(B), BBLV(LV) { }
389
markResult__anon033df9310311::LazyValueInfoCache::OverDefinedCacheUpdater390 bool markResult(bool changed) {
391 if (changed && BBLV.isOverdefined())
392 Parent->OverDefinedCache.insert(std::make_pair(BB, Val));
393 return changed;
394 }
395 };
396
397
398
399 LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
400 bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
401 LVILatticeVal &Result);
402 bool hasBlockValue(Value *Val, BasicBlock *BB);
403
404 // These methods process one work item and may add more. A false value
405 // returned means that the work item was not completely processed and must
406 // be revisited after going through the new items.
407 bool solveBlockValue(Value *Val, BasicBlock *BB);
408 bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
409 Value *Val, BasicBlock *BB);
410 bool solveBlockValuePHINode(LVILatticeVal &BBLV,
411 PHINode *PN, BasicBlock *BB);
412 bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
413 Instruction *BBI, BasicBlock *BB);
414
415 void solve();
416
lookup(Value * V)417 ValueCacheEntryTy &lookup(Value *V) {
418 return ValueCache[LVIValueHandle(V, this)];
419 }
420
421 public:
422 /// getValueInBlock - This is the query interface to determine the lattice
423 /// value for the specified Value* at the end of the specified block.
424 LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB);
425
426 /// getValueOnEdge - This is the query interface to determine the lattice
427 /// value for the specified Value* that is true on the specified edge.
428 LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB);
429
430 /// threadEdge - This is the update interface to inform the cache that an
431 /// edge from PredBB to OldSucc has been threaded to be from PredBB to
432 /// NewSucc.
433 void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
434
435 /// eraseBlock - This is part of the update interface to inform the cache
436 /// that a block has been deleted.
437 void eraseBlock(BasicBlock *BB);
438
439 /// clear - Empty the cache.
clear()440 void clear() {
441 ValueCache.clear();
442 OverDefinedCache.clear();
443 }
444 };
445 } // end anonymous namespace
446
deleted()447 void LVIValueHandle::deleted() {
448 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
449
450 SmallVector<OverDefinedPairTy, 4> ToErase;
451 for (DenseSet<OverDefinedPairTy>::iterator
452 I = Parent->OverDefinedCache.begin(),
453 E = Parent->OverDefinedCache.end();
454 I != E; ++I) {
455 if (I->second == getValPtr())
456 ToErase.push_back(*I);
457 }
458
459 for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
460 E = ToErase.end(); I != E; ++I)
461 Parent->OverDefinedCache.erase(*I);
462
463 // This erasure deallocates *this, so it MUST happen after we're done
464 // using any and all members of *this.
465 Parent->ValueCache.erase(*this);
466 }
467
eraseBlock(BasicBlock * BB)468 void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
469 SmallVector<OverDefinedPairTy, 4> ToErase;
470 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
471 E = OverDefinedCache.end(); I != E; ++I) {
472 if (I->first == BB)
473 ToErase.push_back(*I);
474 }
475
476 for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
477 E = ToErase.end(); I != E; ++I)
478 OverDefinedCache.erase(*I);
479
480 for (DenseMap<LVIValueHandle, ValueCacheEntryTy>::iterator
481 I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
482 I->second.erase(BB);
483 }
484
solve()485 void LazyValueInfoCache::solve() {
486 while (!BlockValueStack.empty()) {
487 std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
488 if (solveBlockValue(e.second, e.first))
489 BlockValueStack.pop();
490 }
491 }
492
hasBlockValue(Value * Val,BasicBlock * BB)493 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
494 // If already a constant, there is nothing to compute.
495 if (isa<Constant>(Val))
496 return true;
497
498 LVIValueHandle ValHandle(Val, this);
499 if (!ValueCache.count(ValHandle)) return false;
500 return ValueCache[ValHandle].count(BB);
501 }
502
getBlockValue(Value * Val,BasicBlock * BB)503 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
504 // If already a constant, there is nothing to compute.
505 if (Constant *VC = dyn_cast<Constant>(Val))
506 return LVILatticeVal::get(VC);
507
508 return lookup(Val)[BB];
509 }
510
solveBlockValue(Value * Val,BasicBlock * BB)511 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
512 if (isa<Constant>(Val))
513 return true;
514
515 ValueCacheEntryTy &Cache = lookup(Val);
516 LVILatticeVal &BBLV = Cache[BB];
517
518 // OverDefinedCacheUpdater is a helper object that will update
519 // the OverDefinedCache for us when this method exits. Make sure to
520 // call markResult on it as we exist, passing a bool to indicate if the
521 // cache needs updating, i.e. if we have solve a new value or not.
522 OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this);
523
524 // If we've already computed this block's value, return it.
525 if (!BBLV.isUndefined()) {
526 DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
527
528 // Since we're reusing a cached value here, we don't need to update the
529 // OverDefinedCahce. The cache will have been properly updated
530 // whenever the cached value was inserted.
531 ODCacheUpdater.markResult(false);
532 return true;
533 }
534
535 // Otherwise, this is the first time we're seeing this block. Reset the
536 // lattice value to overdefined, so that cycles will terminate and be
537 // conservatively correct.
538 BBLV.markOverdefined();
539
540 Instruction *BBI = dyn_cast<Instruction>(Val);
541 if (BBI == 0 || BBI->getParent() != BB) {
542 return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB));
543 }
544
545 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
546 return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB));
547 }
548
549 if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
550 BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
551 return ODCacheUpdater.markResult(true);
552 }
553
554 // We can only analyze the definitions of certain classes of instructions
555 // (integral binops and casts at the moment), so bail if this isn't one.
556 LVILatticeVal Result;
557 if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
558 !BBI->getType()->isIntegerTy()) {
559 DEBUG(dbgs() << " compute BB '" << BB->getName()
560 << "' - overdefined because inst def found.\n");
561 BBLV.markOverdefined();
562 return ODCacheUpdater.markResult(true);
563 }
564
565 // FIXME: We're currently limited to binops with a constant RHS. This should
566 // be improved.
567 BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
568 if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
569 DEBUG(dbgs() << " compute BB '" << BB->getName()
570 << "' - overdefined because inst def found.\n");
571
572 BBLV.markOverdefined();
573 return ODCacheUpdater.markResult(true);
574 }
575
576 return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB));
577 }
578
InstructionDereferencesPointer(Instruction * I,Value * Ptr)579 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
580 if (LoadInst *L = dyn_cast<LoadInst>(I)) {
581 return L->getPointerAddressSpace() == 0 &&
582 GetUnderlyingObject(L->getPointerOperand()) ==
583 GetUnderlyingObject(Ptr);
584 }
585 if (StoreInst *S = dyn_cast<StoreInst>(I)) {
586 return S->getPointerAddressSpace() == 0 &&
587 GetUnderlyingObject(S->getPointerOperand()) ==
588 GetUnderlyingObject(Ptr);
589 }
590 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
591 if (MI->isVolatile()) return false;
592
593 // FIXME: check whether it has a valuerange that excludes zero?
594 ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
595 if (!Len || Len->isZero()) return false;
596
597 if (MI->getDestAddressSpace() == 0)
598 if (MI->getRawDest() == Ptr || MI->getDest() == Ptr)
599 return true;
600 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
601 if (MTI->getSourceAddressSpace() == 0)
602 if (MTI->getRawSource() == Ptr || MTI->getSource() == Ptr)
603 return true;
604 }
605 return false;
606 }
607
solveBlockValueNonLocal(LVILatticeVal & BBLV,Value * Val,BasicBlock * BB)608 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
609 Value *Val, BasicBlock *BB) {
610 LVILatticeVal Result; // Start Undefined.
611
612 // If this is a pointer, and there's a load from that pointer in this BB,
613 // then we know that the pointer can't be NULL.
614 bool NotNull = false;
615 if (Val->getType()->isPointerTy()) {
616 if (isa<AllocaInst>(Val)) {
617 NotNull = true;
618 } else {
619 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();BI != BE;++BI){
620 if (InstructionDereferencesPointer(BI, Val)) {
621 NotNull = true;
622 break;
623 }
624 }
625 }
626 }
627
628 // If this is the entry block, we must be asking about an argument. The
629 // value is overdefined.
630 if (BB == &BB->getParent()->getEntryBlock()) {
631 assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
632 if (NotNull) {
633 PointerType *PTy = cast<PointerType>(Val->getType());
634 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
635 } else {
636 Result.markOverdefined();
637 }
638 BBLV = Result;
639 return true;
640 }
641
642 // Loop over all of our predecessors, merging what we know from them into
643 // result.
644 bool EdgesMissing = false;
645 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
646 LVILatticeVal EdgeResult;
647 EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
648 if (EdgesMissing)
649 continue;
650
651 Result.mergeIn(EdgeResult);
652
653 // If we hit overdefined, exit early. The BlockVals entry is already set
654 // to overdefined.
655 if (Result.isOverdefined()) {
656 DEBUG(dbgs() << " compute BB '" << BB->getName()
657 << "' - overdefined because of pred.\n");
658 // If we previously determined that this is a pointer that can't be null
659 // then return that rather than giving up entirely.
660 if (NotNull) {
661 PointerType *PTy = cast<PointerType>(Val->getType());
662 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
663 }
664
665 BBLV = Result;
666 return true;
667 }
668 }
669 if (EdgesMissing)
670 return false;
671
672 // Return the merged value, which is more precise than 'overdefined'.
673 assert(!Result.isOverdefined());
674 BBLV = Result;
675 return true;
676 }
677
solveBlockValuePHINode(LVILatticeVal & BBLV,PHINode * PN,BasicBlock * BB)678 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
679 PHINode *PN, BasicBlock *BB) {
680 LVILatticeVal Result; // Start Undefined.
681
682 // Loop over all of our predecessors, merging what we know from them into
683 // result.
684 bool EdgesMissing = false;
685 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
686 BasicBlock *PhiBB = PN->getIncomingBlock(i);
687 Value *PhiVal = PN->getIncomingValue(i);
688 LVILatticeVal EdgeResult;
689 EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult);
690 if (EdgesMissing)
691 continue;
692
693 Result.mergeIn(EdgeResult);
694
695 // If we hit overdefined, exit early. The BlockVals entry is already set
696 // to overdefined.
697 if (Result.isOverdefined()) {
698 DEBUG(dbgs() << " compute BB '" << BB->getName()
699 << "' - overdefined because of pred.\n");
700
701 BBLV = Result;
702 return true;
703 }
704 }
705 if (EdgesMissing)
706 return false;
707
708 // Return the merged value, which is more precise than 'overdefined'.
709 assert(!Result.isOverdefined() && "Possible PHI in entry block?");
710 BBLV = Result;
711 return true;
712 }
713
solveBlockValueConstantRange(LVILatticeVal & BBLV,Instruction * BBI,BasicBlock * BB)714 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
715 Instruction *BBI,
716 BasicBlock *BB) {
717 // Figure out the range of the LHS. If that fails, bail.
718 if (!hasBlockValue(BBI->getOperand(0), BB)) {
719 BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
720 return false;
721 }
722
723 LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
724 if (!LHSVal.isConstantRange()) {
725 BBLV.markOverdefined();
726 return true;
727 }
728
729 ConstantRange LHSRange = LHSVal.getConstantRange();
730 ConstantRange RHSRange(1);
731 IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
732 if (isa<BinaryOperator>(BBI)) {
733 if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
734 RHSRange = ConstantRange(RHS->getValue());
735 } else {
736 BBLV.markOverdefined();
737 return true;
738 }
739 }
740
741 // NOTE: We're currently limited by the set of operations that ConstantRange
742 // can evaluate symbolically. Enhancing that set will allows us to analyze
743 // more definitions.
744 LVILatticeVal Result;
745 switch (BBI->getOpcode()) {
746 case Instruction::Add:
747 Result.markConstantRange(LHSRange.add(RHSRange));
748 break;
749 case Instruction::Sub:
750 Result.markConstantRange(LHSRange.sub(RHSRange));
751 break;
752 case Instruction::Mul:
753 Result.markConstantRange(LHSRange.multiply(RHSRange));
754 break;
755 case Instruction::UDiv:
756 Result.markConstantRange(LHSRange.udiv(RHSRange));
757 break;
758 case Instruction::Shl:
759 Result.markConstantRange(LHSRange.shl(RHSRange));
760 break;
761 case Instruction::LShr:
762 Result.markConstantRange(LHSRange.lshr(RHSRange));
763 break;
764 case Instruction::Trunc:
765 Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
766 break;
767 case Instruction::SExt:
768 Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
769 break;
770 case Instruction::ZExt:
771 Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
772 break;
773 case Instruction::BitCast:
774 Result.markConstantRange(LHSRange);
775 break;
776 case Instruction::And:
777 Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
778 break;
779 case Instruction::Or:
780 Result.markConstantRange(LHSRange.binaryOr(RHSRange));
781 break;
782
783 // Unhandled instructions are overdefined.
784 default:
785 DEBUG(dbgs() << " compute BB '" << BB->getName()
786 << "' - overdefined because inst def found.\n");
787 Result.markOverdefined();
788 break;
789 }
790
791 BBLV = Result;
792 return true;
793 }
794
795 /// getEdgeValue - This method attempts to infer more complex
getEdgeValue(Value * Val,BasicBlock * BBFrom,BasicBlock * BBTo,LVILatticeVal & Result)796 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
797 BasicBlock *BBTo, LVILatticeVal &Result) {
798 // If already a constant, there is nothing to compute.
799 if (Constant *VC = dyn_cast<Constant>(Val)) {
800 Result = LVILatticeVal::get(VC);
801 return true;
802 }
803
804 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
805 // know that v != 0.
806 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
807 // If this is a conditional branch and only one successor goes to BBTo, then
808 // we maybe able to infer something from the condition.
809 if (BI->isConditional() &&
810 BI->getSuccessor(0) != BI->getSuccessor(1)) {
811 bool isTrueDest = BI->getSuccessor(0) == BBTo;
812 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
813 "BBTo isn't a successor of BBFrom");
814
815 // If V is the condition of the branch itself, then we know exactly what
816 // it is.
817 if (BI->getCondition() == Val) {
818 Result = LVILatticeVal::get(ConstantInt::get(
819 Type::getInt1Ty(Val->getContext()), isTrueDest));
820 return true;
821 }
822
823 // If the condition of the branch is an equality comparison, we may be
824 // able to infer the value.
825 ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
826 if (ICI && ICI->getOperand(0) == Val &&
827 isa<Constant>(ICI->getOperand(1))) {
828 if (ICI->isEquality()) {
829 // We know that V has the RHS constant if this is a true SETEQ or
830 // false SETNE.
831 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
832 Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
833 else
834 Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
835 return true;
836 }
837
838 if (ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
839 // Calculate the range of values that would satisfy the comparison.
840 ConstantRange CmpRange(CI->getValue(), CI->getValue()+1);
841 ConstantRange TrueValues =
842 ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
843
844 // If we're interested in the false dest, invert the condition.
845 if (!isTrueDest) TrueValues = TrueValues.inverse();
846
847 // Figure out the possible values of the query BEFORE this branch.
848 if (!hasBlockValue(Val, BBFrom)) {
849 BlockValueStack.push(std::make_pair(BBFrom, Val));
850 return false;
851 }
852
853 LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
854 if (!InBlock.isConstantRange()) {
855 Result = LVILatticeVal::getRange(TrueValues);
856 return true;
857 }
858
859 // Find all potential values that satisfy both the input and output
860 // conditions.
861 ConstantRange PossibleValues =
862 TrueValues.intersectWith(InBlock.getConstantRange());
863
864 Result = LVILatticeVal::getRange(PossibleValues);
865 return true;
866 }
867 }
868 }
869 }
870
871 // If the edge was formed by a switch on the value, then we may know exactly
872 // what it is.
873 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
874 if (SI->getCondition() == Val) {
875 // We don't know anything in the default case.
876 if (SI->getDefaultDest() == BBTo) {
877 Result.markOverdefined();
878 return true;
879 }
880
881 // We only know something if there is exactly one value that goes from
882 // BBFrom to BBTo.
883 unsigned NumEdges = 0;
884 ConstantInt *EdgeVal = 0;
885 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
886 if (SI->getSuccessor(i) != BBTo) continue;
887 if (NumEdges++) break;
888 EdgeVal = SI->getCaseValue(i);
889 }
890 assert(EdgeVal && "Missing successor?");
891 if (NumEdges == 1) {
892 Result = LVILatticeVal::get(EdgeVal);
893 return true;
894 }
895 }
896 }
897
898 // Otherwise see if the value is known in the block.
899 if (hasBlockValue(Val, BBFrom)) {
900 Result = getBlockValue(Val, BBFrom);
901 return true;
902 }
903 BlockValueStack.push(std::make_pair(BBFrom, Val));
904 return false;
905 }
906
getValueInBlock(Value * V,BasicBlock * BB)907 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
908 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
909 << BB->getName() << "'\n");
910
911 BlockValueStack.push(std::make_pair(BB, V));
912 solve();
913 LVILatticeVal Result = getBlockValue(V, BB);
914
915 DEBUG(dbgs() << " Result = " << Result << "\n");
916 return Result;
917 }
918
919 LVILatticeVal LazyValueInfoCache::
getValueOnEdge(Value * V,BasicBlock * FromBB,BasicBlock * ToBB)920 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
921 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
922 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
923
924 LVILatticeVal Result;
925 if (!getEdgeValue(V, FromBB, ToBB, Result)) {
926 solve();
927 bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result);
928 (void)WasFastQuery;
929 assert(WasFastQuery && "More work to do after problem solved?");
930 }
931
932 DEBUG(dbgs() << " Result = " << Result << "\n");
933 return Result;
934 }
935
threadEdge(BasicBlock * PredBB,BasicBlock * OldSucc,BasicBlock * NewSucc)936 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
937 BasicBlock *NewSucc) {
938 // When an edge in the graph has been threaded, values that we could not
939 // determine a value for before (i.e. were marked overdefined) may be possible
940 // to solve now. We do NOT try to proactively update these values. Instead,
941 // we clear their entries from the cache, and allow lazy updating to recompute
942 // them when needed.
943
944 // The updating process is fairly simple: we need to dropped cached info
945 // for all values that were marked overdefined in OldSucc, and for those same
946 // values in any successor of OldSucc (except NewSucc) in which they were
947 // also marked overdefined.
948 std::vector<BasicBlock*> worklist;
949 worklist.push_back(OldSucc);
950
951 DenseSet<Value*> ClearSet;
952 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
953 E = OverDefinedCache.end(); I != E; ++I) {
954 if (I->first == OldSucc)
955 ClearSet.insert(I->second);
956 }
957
958 // Use a worklist to perform a depth-first search of OldSucc's successors.
959 // NOTE: We do not need a visited list since any blocks we have already
960 // visited will have had their overdefined markers cleared already, and we
961 // thus won't loop to their successors.
962 while (!worklist.empty()) {
963 BasicBlock *ToUpdate = worklist.back();
964 worklist.pop_back();
965
966 // Skip blocks only accessible through NewSucc.
967 if (ToUpdate == NewSucc) continue;
968
969 bool changed = false;
970 for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end();
971 I != E; ++I) {
972 // If a value was marked overdefined in OldSucc, and is here too...
973 DenseSet<OverDefinedPairTy>::iterator OI =
974 OverDefinedCache.find(std::make_pair(ToUpdate, *I));
975 if (OI == OverDefinedCache.end()) continue;
976
977 // Remove it from the caches.
978 ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)];
979 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
980
981 assert(CI != Entry.end() && "Couldn't find entry to update?");
982 Entry.erase(CI);
983 OverDefinedCache.erase(OI);
984
985 // If we removed anything, then we potentially need to update
986 // blocks successors too.
987 changed = true;
988 }
989
990 if (!changed) continue;
991
992 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
993 }
994 }
995
996 //===----------------------------------------------------------------------===//
997 // LazyValueInfo Impl
998 //===----------------------------------------------------------------------===//
999
1000 /// getCache - This lazily constructs the LazyValueInfoCache.
getCache(void * & PImpl)1001 static LazyValueInfoCache &getCache(void *&PImpl) {
1002 if (!PImpl)
1003 PImpl = new LazyValueInfoCache();
1004 return *static_cast<LazyValueInfoCache*>(PImpl);
1005 }
1006
runOnFunction(Function & F)1007 bool LazyValueInfo::runOnFunction(Function &F) {
1008 if (PImpl)
1009 getCache(PImpl).clear();
1010
1011 TD = getAnalysisIfAvailable<TargetData>();
1012 // Fully lazy.
1013 return false;
1014 }
1015
releaseMemory()1016 void LazyValueInfo::releaseMemory() {
1017 // If the cache was allocated, free it.
1018 if (PImpl) {
1019 delete &getCache(PImpl);
1020 PImpl = 0;
1021 }
1022 }
1023
getConstant(Value * V,BasicBlock * BB)1024 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
1025 LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
1026
1027 if (Result.isConstant())
1028 return Result.getConstant();
1029 if (Result.isConstantRange()) {
1030 ConstantRange CR = Result.getConstantRange();
1031 if (const APInt *SingleVal = CR.getSingleElement())
1032 return ConstantInt::get(V->getContext(), *SingleVal);
1033 }
1034 return 0;
1035 }
1036
1037 /// getConstantOnEdge - Determine whether the specified value is known to be a
1038 /// constant on the specified edge. Return null if not.
getConstantOnEdge(Value * V,BasicBlock * FromBB,BasicBlock * ToBB)1039 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
1040 BasicBlock *ToBB) {
1041 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1042
1043 if (Result.isConstant())
1044 return Result.getConstant();
1045 if (Result.isConstantRange()) {
1046 ConstantRange CR = Result.getConstantRange();
1047 if (const APInt *SingleVal = CR.getSingleElement())
1048 return ConstantInt::get(V->getContext(), *SingleVal);
1049 }
1050 return 0;
1051 }
1052
1053 /// getPredicateOnEdge - Determine whether the specified value comparison
1054 /// with a constant is known to be true or false on the specified CFG edge.
1055 /// Pred is a CmpInst predicate.
1056 LazyValueInfo::Tristate
getPredicateOnEdge(unsigned Pred,Value * V,Constant * C,BasicBlock * FromBB,BasicBlock * ToBB)1057 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
1058 BasicBlock *FromBB, BasicBlock *ToBB) {
1059 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1060
1061 // If we know the value is a constant, evaluate the conditional.
1062 Constant *Res = 0;
1063 if (Result.isConstant()) {
1064 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD);
1065 if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
1066 return ResCI->isZero() ? False : True;
1067 return Unknown;
1068 }
1069
1070 if (Result.isConstantRange()) {
1071 ConstantInt *CI = dyn_cast<ConstantInt>(C);
1072 if (!CI) return Unknown;
1073
1074 ConstantRange CR = Result.getConstantRange();
1075 if (Pred == ICmpInst::ICMP_EQ) {
1076 if (!CR.contains(CI->getValue()))
1077 return False;
1078
1079 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1080 return True;
1081 } else if (Pred == ICmpInst::ICMP_NE) {
1082 if (!CR.contains(CI->getValue()))
1083 return True;
1084
1085 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1086 return False;
1087 }
1088
1089 // Handle more complex predicates.
1090 ConstantRange TrueValues =
1091 ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
1092 if (TrueValues.contains(CR))
1093 return True;
1094 if (TrueValues.inverse().contains(CR))
1095 return False;
1096 return Unknown;
1097 }
1098
1099 if (Result.isNotConstant()) {
1100 // If this is an equality comparison, we can try to fold it knowing that
1101 // "V != C1".
1102 if (Pred == ICmpInst::ICMP_EQ) {
1103 // !C1 == C -> false iff C1 == C.
1104 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1105 Result.getNotConstant(), C, TD);
1106 if (Res->isNullValue())
1107 return False;
1108 } else if (Pred == ICmpInst::ICMP_NE) {
1109 // !C1 != C -> true iff C1 == C.
1110 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1111 Result.getNotConstant(), C, TD);
1112 if (Res->isNullValue())
1113 return True;
1114 }
1115 return Unknown;
1116 }
1117
1118 return Unknown;
1119 }
1120
threadEdge(BasicBlock * PredBB,BasicBlock * OldSucc,BasicBlock * NewSucc)1121 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1122 BasicBlock *NewSucc) {
1123 if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);
1124 }
1125
eraseBlock(BasicBlock * BB)1126 void LazyValueInfo::eraseBlock(BasicBlock *BB) {
1127 if (PImpl) getCache(PImpl).eraseBlock(BB);
1128 }
1129