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/ADT/DenseSet.h"
18 #include "llvm/ADT/STLExtras.h"
19 #include "llvm/Analysis/ConstantFolding.h"
20 #include "llvm/Analysis/ValueTracking.h"
21 #include "llvm/IR/Constants.h"
22 #include "llvm/IR/DataLayout.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/IntrinsicInst.h"
25 #include "llvm/Support/CFG.h"
26 #include "llvm/Support/ConstantRange.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/PatternMatch.h"
29 #include "llvm/Support/ValueHandle.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/Target/TargetLibraryInfo.h"
32 #include <map>
33 #include <stack>
34 using namespace llvm;
35 using namespace PatternMatch;
36
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)
43
44 namespace llvm {
createLazyValueInfoPass()45 FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
46 }
47
48
49 //===----------------------------------------------------------------------===//
50 // LVILatticeVal
51 //===----------------------------------------------------------------------===//
52
53 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each
54 /// value.
55 ///
56 /// FIXME: This is basically just for bringup, this can be made a lot more rich
57 /// in the future.
58 ///
59 namespace {
60 class LVILatticeVal {
61 enum LatticeValueTy {
62 /// undefined - This Value has no known value yet.
63 undefined,
64
65 /// constant - This Value has a specific constant value.
66 constant,
67 /// notconstant - This Value is known to not have the specified value.
68 notconstant,
69
70 /// constantrange - The Value falls within this range.
71 constantrange,
72
73 /// overdefined - This value is not known to be constant, and we know that
74 /// it has a value.
75 overdefined
76 };
77
78 /// Val: This stores the current lattice value along with the Constant* for
79 /// the constant if this is a 'constant' or 'notconstant' value.
80 LatticeValueTy Tag;
81 Constant *Val;
82 ConstantRange Range;
83
84 public:
LVILatticeVal()85 LVILatticeVal() : Tag(undefined), Val(0), Range(1, true) {}
86
get(Constant * C)87 static LVILatticeVal get(Constant *C) {
88 LVILatticeVal Res;
89 if (!isa<UndefValue>(C))
90 Res.markConstant(C);
91 return Res;
92 }
getNot(Constant * C)93 static LVILatticeVal getNot(Constant *C) {
94 LVILatticeVal Res;
95 if (!isa<UndefValue>(C))
96 Res.markNotConstant(C);
97 return Res;
98 }
getRange(ConstantRange CR)99 static LVILatticeVal getRange(ConstantRange CR) {
100 LVILatticeVal Res;
101 Res.markConstantRange(CR);
102 return Res;
103 }
104
isUndefined() const105 bool isUndefined() const { return Tag == undefined; }
isConstant() const106 bool isConstant() const { return Tag == constant; }
isNotConstant() const107 bool isNotConstant() const { return Tag == notconstant; }
isConstantRange() const108 bool isConstantRange() const { return Tag == constantrange; }
isOverdefined() const109 bool isOverdefined() const { return Tag == overdefined; }
110
getConstant() const111 Constant *getConstant() const {
112 assert(isConstant() && "Cannot get the constant of a non-constant!");
113 return Val;
114 }
115
getNotConstant() const116 Constant *getNotConstant() const {
117 assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
118 return Val;
119 }
120
getConstantRange() const121 ConstantRange getConstantRange() const {
122 assert(isConstantRange() &&
123 "Cannot get the constant-range of a non-constant-range!");
124 return Range;
125 }
126
127 /// markOverdefined - Return true if this is a change in status.
markOverdefined()128 bool markOverdefined() {
129 if (isOverdefined())
130 return false;
131 Tag = overdefined;
132 return true;
133 }
134
135 /// markConstant - Return true if this is a change in status.
markConstant(Constant * V)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))
141 return false;
142
143 assert((!isConstant() || getConstant() == V) &&
144 "Marking constant with different value");
145 assert(isUndefined());
146 Tag = constant;
147 Val = V;
148 return true;
149 }
150
151 /// markNotConstant - Return true if this is a change in status.
markNotConstant(Constant * V)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))
157 return false;
158
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());
164 Tag = notconstant;
165 Val = V;
166 return true;
167 }
168
169 /// markConstantRange - Return true if this is a change in status.
markConstantRange(const ConstantRange NewR)170 bool markConstantRange(const ConstantRange NewR) {
171 if (isConstantRange()) {
172 if (NewR.isEmptySet())
173 return markOverdefined();
174
175 bool changed = Range != NewR;
176 Range = NewR;
177 return changed;
178 }
179
180 assert(isUndefined());
181 if (NewR.isEmptySet())
182 return markOverdefined();
183
184 Tag = constantrange;
185 Range = NewR;
186 return true;
187 }
188
189 /// mergeIn - Merge the specified lattice value into this one, updating this
190 /// one and returning true if anything changed.
mergeIn(const LVILatticeVal & RHS)191 bool mergeIn(const LVILatticeVal &RHS) {
192 if (RHS.isUndefined() || isOverdefined()) return false;
193 if (RHS.isOverdefined()) return markOverdefined();
194
195 if (isUndefined()) {
196 Tag = RHS.Tag;
197 Val = RHS.Val;
198 Range = RHS.Range;
199 return true;
200 }
201
202 if (isConstant()) {
203 if (RHS.isConstant()) {
204 if (Val == RHS.Val)
205 return false;
206 return markOverdefined();
207 }
208
209 if (RHS.isNotConstant()) {
210 if (Val == RHS.Val)
211 return markOverdefined();
212
213 // Unless we can prove that the two Constants are different, we must
214 // move to overdefined.
215 // FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
216 if (ConstantInt *Res = dyn_cast<ConstantInt>(
217 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
218 getConstant(),
219 RHS.getNotConstant())))
220 if (Res->isOne())
221 return markNotConstant(RHS.getNotConstant());
222
223 return markOverdefined();
224 }
225
226 // RHS is a ConstantRange, LHS is a non-integer Constant.
227
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.
230
231 return markOverdefined();
232 }
233
234 if (isNotConstant()) {
235 if (RHS.isConstant()) {
236 if (Val == RHS.Val)
237 return markOverdefined();
238
239 // Unless we can prove that the two Constants are different, we must
240 // move to overdefined.
241 // FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
242 if (ConstantInt *Res = dyn_cast<ConstantInt>(
243 ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
244 getNotConstant(),
245 RHS.getConstant())))
246 if (Res->isOne())
247 return false;
248
249 return markOverdefined();
250 }
251
252 if (RHS.isNotConstant()) {
253 if (Val == RHS.Val)
254 return false;
255 return markOverdefined();
256 }
257
258 return markOverdefined();
259 }
260
261 assert(isConstantRange() && "New LVILattice type?");
262 if (!RHS.isConstantRange())
263 return markOverdefined();
264
265 ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
266 if (NewR.isFullSet())
267 return markOverdefined();
268 return markConstantRange(NewR);
269 }
270 };
271
272 } // end anonymous namespace.
273
274 namespace llvm {
275 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
276 LLVM_ATTRIBUTE_USED;
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";
282
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() << '>';
289 }
290 }
291
292 //===----------------------------------------------------------------------===//
293 // LazyValueInfoCache Decl
294 //===----------------------------------------------------------------------===//
295
296 namespace {
297 /// LVIValueHandle - A callback value handle updates the cache when
298 /// values are erased.
299 class LazyValueInfoCache;
300 struct LVIValueHandle : public CallbackVH {
301 LazyValueInfoCache *Parent;
302
LVIValueHandle__anon3633ecd40211::LVIValueHandle303 LVIValueHandle(Value *V, LazyValueInfoCache *P)
304 : CallbackVH(V), Parent(P) { }
305
306 void deleted();
allUsesReplacedWith__anon3633ecd40211::LVIValueHandle307 void allUsesReplacedWith(Value *V) {
308 deleted();
309 }
310 };
311 }
312
313 namespace {
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;
321
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;
325
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;
331
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;
335
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;
340
341 friend struct LVIValueHandle;
342
343 /// OverDefinedCacheUpdater - A helper object that ensures that the
344 /// OverDefinedCache is updated whenever solveBlockValue returns.
345 struct OverDefinedCacheUpdater {
346 LazyValueInfoCache *Parent;
347 Value *Val;
348 BasicBlock *BB;
349 LVILatticeVal &BBLV;
350
OverDefinedCacheUpdater__anon3633ecd40311::LazyValueInfoCache::OverDefinedCacheUpdater351 OverDefinedCacheUpdater(Value *V, BasicBlock *B, LVILatticeVal &LV,
352 LazyValueInfoCache *P)
353 : Parent(P), Val(V), BB(B), BBLV(LV) { }
354
markResult__anon3633ecd40311::LazyValueInfoCache::OverDefinedCacheUpdater355 bool markResult(bool changed) {
356 if (changed && BBLV.isOverdefined())
357 Parent->OverDefinedCache.insert(std::make_pair(BB, Val));
358 return changed;
359 }
360 };
361
362
363
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);
368
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);
379
380 void solve();
381
lookup(Value * V)382 ValueCacheEntryTy &lookup(Value *V) {
383 return ValueCache[LVIValueHandle(V, this)];
384 }
385
386 public:
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);
390
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);
394
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
397 /// NewSucc.
398 void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
399
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);
403
404 /// clear - Empty the cache.
clear()405 void clear() {
406 SeenBlocks.clear();
407 ValueCache.clear();
408 OverDefinedCache.clear();
409 }
410 };
411 } // end anonymous namespace
412
deleted()413 void LVIValueHandle::deleted() {
414 typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
415
416 SmallVector<OverDefinedPairTy, 4> ToErase;
417 for (DenseSet<OverDefinedPairTy>::iterator
418 I = Parent->OverDefinedCache.begin(),
419 E = Parent->OverDefinedCache.end();
420 I != E; ++I) {
421 if (I->second == getValPtr())
422 ToErase.push_back(*I);
423 }
424
425 for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
426 E = ToErase.end(); I != E; ++I)
427 Parent->OverDefinedCache.erase(*I);
428
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);
432 }
433
eraseBlock(BasicBlock * BB)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())
438 return;
439 SeenBlocks.erase(I);
440
441 SmallVector<OverDefinedPairTy, 4> ToErase;
442 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
443 E = OverDefinedCache.end(); I != E; ++I) {
444 if (I->first == BB)
445 ToErase.push_back(*I);
446 }
447
448 for (SmallVector<OverDefinedPairTy, 4>::iterator I = ToErase.begin(),
449 E = ToErase.end(); I != E; ++I)
450 OverDefinedCache.erase(*I);
451
452 for (std::map<LVIValueHandle, ValueCacheEntryTy>::iterator
453 I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
454 I->second.erase(BB);
455 }
456
solve()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();
463 }
464 }
465 }
466
hasBlockValue(Value * Val,BasicBlock * BB)467 bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
468 // If already a constant, there is nothing to compute.
469 if (isa<Constant>(Val))
470 return true;
471
472 LVIValueHandle ValHandle(Val, this);
473 std::map<LVIValueHandle, ValueCacheEntryTy>::iterator I =
474 ValueCache.find(ValHandle);
475 if (I == ValueCache.end()) return false;
476 return I->second.count(BB);
477 }
478
getBlockValue(Value * Val,BasicBlock * BB)479 LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
480 // If already a constant, there is nothing to compute.
481 if (Constant *VC = dyn_cast<Constant>(Val))
482 return LVILatticeVal::get(VC);
483
484 SeenBlocks.insert(BB);
485 return lookup(Val)[BB];
486 }
487
solveBlockValue(Value * Val,BasicBlock * BB)488 bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
489 if (isa<Constant>(Val))
490 return true;
491
492 ValueCacheEntryTy &Cache = lookup(Val);
493 SeenBlocks.insert(BB);
494 LVILatticeVal &BBLV = Cache[BB];
495
496 // OverDefinedCacheUpdater is a helper object that will update
497 // the OverDefinedCache for us when this method exits. Make sure to
498 // call markResult on it as we exist, passing a bool to indicate if the
499 // cache needs updating, i.e. if we have solve a new value or not.
500 OverDefinedCacheUpdater ODCacheUpdater(Val, BB, BBLV, this);
501
502 // If we've already computed this block's value, return it.
503 if (!BBLV.isUndefined()) {
504 DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
505
506 // Since we're reusing a cached value here, we don't need to update the
507 // OverDefinedCahce. The cache will have been properly updated
508 // whenever the cached value was inserted.
509 ODCacheUpdater.markResult(false);
510 return true;
511 }
512
513 // Otherwise, this is the first time we're seeing this block. Reset the
514 // lattice value to overdefined, so that cycles will terminate and be
515 // conservatively correct.
516 BBLV.markOverdefined();
517
518 Instruction *BBI = dyn_cast<Instruction>(Val);
519 if (BBI == 0 || BBI->getParent() != BB) {
520 return ODCacheUpdater.markResult(solveBlockValueNonLocal(BBLV, Val, BB));
521 }
522
523 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
524 return ODCacheUpdater.markResult(solveBlockValuePHINode(BBLV, PN, BB));
525 }
526
527 if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
528 BBLV = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
529 return ODCacheUpdater.markResult(true);
530 }
531
532 // We can only analyze the definitions of certain classes of instructions
533 // (integral binops and casts at the moment), so bail if this isn't one.
534 LVILatticeVal Result;
535 if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
536 !BBI->getType()->isIntegerTy()) {
537 DEBUG(dbgs() << " compute BB '" << BB->getName()
538 << "' - overdefined because inst def found.\n");
539 BBLV.markOverdefined();
540 return ODCacheUpdater.markResult(true);
541 }
542
543 // FIXME: We're currently limited to binops with a constant RHS. This should
544 // be improved.
545 BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
546 if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
547 DEBUG(dbgs() << " compute BB '" << BB->getName()
548 << "' - overdefined because inst def found.\n");
549
550 BBLV.markOverdefined();
551 return ODCacheUpdater.markResult(true);
552 }
553
554 return ODCacheUpdater.markResult(solveBlockValueConstantRange(BBLV, BBI, BB));
555 }
556
InstructionDereferencesPointer(Instruction * I,Value * Ptr)557 static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
558 if (LoadInst *L = dyn_cast<LoadInst>(I)) {
559 return L->getPointerAddressSpace() == 0 &&
560 GetUnderlyingObject(L->getPointerOperand()) == Ptr;
561 }
562 if (StoreInst *S = dyn_cast<StoreInst>(I)) {
563 return S->getPointerAddressSpace() == 0 &&
564 GetUnderlyingObject(S->getPointerOperand()) == Ptr;
565 }
566 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
567 if (MI->isVolatile()) return false;
568
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;
572
573 if (MI->getDestAddressSpace() == 0)
574 if (GetUnderlyingObject(MI->getRawDest()) == Ptr)
575 return true;
576 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
577 if (MTI->getSourceAddressSpace() == 0)
578 if (GetUnderlyingObject(MTI->getRawSource()) == Ptr)
579 return true;
580 }
581 return false;
582 }
583
solveBlockValueNonLocal(LVILatticeVal & BBLV,Value * Val,BasicBlock * BB)584 bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
585 Value *Val, BasicBlock *BB) {
586 LVILatticeVal Result; // Start Undefined.
587
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 (isKnownNonNull(Val)) {
593 NotNull = true;
594 } else {
595 Value *UnderlyingVal = GetUnderlyingObject(Val);
596 // If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
597 // inside InstructionDereferencesPointer either.
598 if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, NULL, 1)) {
599 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
600 BI != BE; ++BI) {
601 if (InstructionDereferencesPointer(BI, UnderlyingVal)) {
602 NotNull = true;
603 break;
604 }
605 }
606 }
607 }
608 }
609
610 // If this is the entry block, we must be asking about an argument. The
611 // value is overdefined.
612 if (BB == &BB->getParent()->getEntryBlock()) {
613 assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
614 if (NotNull) {
615 PointerType *PTy = cast<PointerType>(Val->getType());
616 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
617 } else {
618 Result.markOverdefined();
619 }
620 BBLV = Result;
621 return true;
622 }
623
624 // Loop over all of our predecessors, merging what we know from them into
625 // result.
626 bool EdgesMissing = false;
627 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
628 LVILatticeVal EdgeResult;
629 EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
630 if (EdgesMissing)
631 continue;
632
633 Result.mergeIn(EdgeResult);
634
635 // If we hit overdefined, exit early. The BlockVals entry is already set
636 // to overdefined.
637 if (Result.isOverdefined()) {
638 DEBUG(dbgs() << " compute BB '" << BB->getName()
639 << "' - overdefined because of pred.\n");
640 // If we previously determined that this is a pointer that can't be null
641 // then return that rather than giving up entirely.
642 if (NotNull) {
643 PointerType *PTy = cast<PointerType>(Val->getType());
644 Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
645 }
646
647 BBLV = Result;
648 return true;
649 }
650 }
651 if (EdgesMissing)
652 return false;
653
654 // Return the merged value, which is more precise than 'overdefined'.
655 assert(!Result.isOverdefined());
656 BBLV = Result;
657 return true;
658 }
659
solveBlockValuePHINode(LVILatticeVal & BBLV,PHINode * PN,BasicBlock * BB)660 bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
661 PHINode *PN, BasicBlock *BB) {
662 LVILatticeVal Result; // Start Undefined.
663
664 // Loop over all of our predecessors, merging what we know from them into
665 // result.
666 bool EdgesMissing = false;
667 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
668 BasicBlock *PhiBB = PN->getIncomingBlock(i);
669 Value *PhiVal = PN->getIncomingValue(i);
670 LVILatticeVal EdgeResult;
671 EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult);
672 if (EdgesMissing)
673 continue;
674
675 Result.mergeIn(EdgeResult);
676
677 // If we hit overdefined, exit early. The BlockVals entry is already set
678 // to overdefined.
679 if (Result.isOverdefined()) {
680 DEBUG(dbgs() << " compute BB '" << BB->getName()
681 << "' - overdefined because of pred.\n");
682
683 BBLV = Result;
684 return true;
685 }
686 }
687 if (EdgesMissing)
688 return false;
689
690 // Return the merged value, which is more precise than 'overdefined'.
691 assert(!Result.isOverdefined() && "Possible PHI in entry block?");
692 BBLV = Result;
693 return true;
694 }
695
solveBlockValueConstantRange(LVILatticeVal & BBLV,Instruction * BBI,BasicBlock * BB)696 bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
697 Instruction *BBI,
698 BasicBlock *BB) {
699 // Figure out the range of the LHS. If that fails, bail.
700 if (!hasBlockValue(BBI->getOperand(0), BB)) {
701 BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
702 return false;
703 }
704
705 LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
706 if (!LHSVal.isConstantRange()) {
707 BBLV.markOverdefined();
708 return true;
709 }
710
711 ConstantRange LHSRange = LHSVal.getConstantRange();
712 ConstantRange RHSRange(1);
713 IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
714 if (isa<BinaryOperator>(BBI)) {
715 if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
716 RHSRange = ConstantRange(RHS->getValue());
717 } else {
718 BBLV.markOverdefined();
719 return true;
720 }
721 }
722
723 // NOTE: We're currently limited by the set of operations that ConstantRange
724 // can evaluate symbolically. Enhancing that set will allows us to analyze
725 // more definitions.
726 LVILatticeVal Result;
727 switch (BBI->getOpcode()) {
728 case Instruction::Add:
729 Result.markConstantRange(LHSRange.add(RHSRange));
730 break;
731 case Instruction::Sub:
732 Result.markConstantRange(LHSRange.sub(RHSRange));
733 break;
734 case Instruction::Mul:
735 Result.markConstantRange(LHSRange.multiply(RHSRange));
736 break;
737 case Instruction::UDiv:
738 Result.markConstantRange(LHSRange.udiv(RHSRange));
739 break;
740 case Instruction::Shl:
741 Result.markConstantRange(LHSRange.shl(RHSRange));
742 break;
743 case Instruction::LShr:
744 Result.markConstantRange(LHSRange.lshr(RHSRange));
745 break;
746 case Instruction::Trunc:
747 Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
748 break;
749 case Instruction::SExt:
750 Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
751 break;
752 case Instruction::ZExt:
753 Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
754 break;
755 case Instruction::BitCast:
756 Result.markConstantRange(LHSRange);
757 break;
758 case Instruction::And:
759 Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
760 break;
761 case Instruction::Or:
762 Result.markConstantRange(LHSRange.binaryOr(RHSRange));
763 break;
764
765 // Unhandled instructions are overdefined.
766 default:
767 DEBUG(dbgs() << " compute BB '" << BB->getName()
768 << "' - overdefined because inst def found.\n");
769 Result.markOverdefined();
770 break;
771 }
772
773 BBLV = Result;
774 return true;
775 }
776
777 /// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
778 /// Val is not constrained on the edge.
getEdgeValueLocal(Value * Val,BasicBlock * BBFrom,BasicBlock * BBTo,LVILatticeVal & Result)779 static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
780 BasicBlock *BBTo, LVILatticeVal &Result) {
781 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
782 // know that v != 0.
783 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
784 // If this is a conditional branch and only one successor goes to BBTo, then
785 // we maybe able to infer something from the condition.
786 if (BI->isConditional() &&
787 BI->getSuccessor(0) != BI->getSuccessor(1)) {
788 bool isTrueDest = BI->getSuccessor(0) == BBTo;
789 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
790 "BBTo isn't a successor of BBFrom");
791
792 // If V is the condition of the branch itself, then we know exactly what
793 // it is.
794 if (BI->getCondition() == Val) {
795 Result = LVILatticeVal::get(ConstantInt::get(
796 Type::getInt1Ty(Val->getContext()), isTrueDest));
797 return true;
798 }
799
800 // If the condition of the branch is an equality comparison, we may be
801 // able to infer the value.
802 ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
803 if (ICI && isa<Constant>(ICI->getOperand(1))) {
804 if (ICI->isEquality() && ICI->getOperand(0) == Val) {
805 // We know that V has the RHS constant if this is a true SETEQ or
806 // false SETNE.
807 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
808 Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
809 else
810 Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
811 return true;
812 }
813
814 // Recognize the range checking idiom that InstCombine produces.
815 // (X-C1) u< C2 --> [C1, C1+C2)
816 ConstantInt *NegOffset = 0;
817 if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
818 match(ICI->getOperand(0), m_Add(m_Specific(Val),
819 m_ConstantInt(NegOffset)));
820
821 ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
822 if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
823 // Calculate the range of values that would satisfy the comparison.
824 ConstantRange CmpRange(CI->getValue());
825 ConstantRange TrueValues =
826 ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
827
828 if (NegOffset) // Apply the offset from above.
829 TrueValues = TrueValues.subtract(NegOffset->getValue());
830
831 // If we're interested in the false dest, invert the condition.
832 if (!isTrueDest) TrueValues = TrueValues.inverse();
833
834 Result = LVILatticeVal::getRange(TrueValues);
835 return true;
836 }
837 }
838 }
839 }
840
841 // If the edge was formed by a switch on the value, then we may know exactly
842 // what it is.
843 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
844 if (SI->getCondition() != Val)
845 return false;
846
847 bool DefaultCase = SI->getDefaultDest() == BBTo;
848 unsigned BitWidth = Val->getType()->getIntegerBitWidth();
849 ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
850
851 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
852 i != e; ++i) {
853 ConstantRange EdgeVal(i.getCaseValue()->getValue());
854 if (DefaultCase) {
855 // It is possible that the default destination is the destination of
856 // some cases. There is no need to perform difference for those cases.
857 if (i.getCaseSuccessor() != BBTo)
858 EdgesVals = EdgesVals.difference(EdgeVal);
859 } else if (i.getCaseSuccessor() == BBTo)
860 EdgesVals = EdgesVals.unionWith(EdgeVal);
861 }
862 Result = LVILatticeVal::getRange(EdgesVals);
863 return true;
864 }
865 return false;
866 }
867
868 /// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at
869 /// the basic block if the edge does not constraint Val.
getEdgeValue(Value * Val,BasicBlock * BBFrom,BasicBlock * BBTo,LVILatticeVal & Result)870 bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
871 BasicBlock *BBTo, LVILatticeVal &Result) {
872 // If already a constant, there is nothing to compute.
873 if (Constant *VC = dyn_cast<Constant>(Val)) {
874 Result = LVILatticeVal::get(VC);
875 return true;
876 }
877
878 if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
879 if (!Result.isConstantRange() ||
880 Result.getConstantRange().getSingleElement())
881 return true;
882
883 // FIXME: this check should be moved to the beginning of the function when
884 // LVI better supports recursive values. Even for the single value case, we
885 // can intersect to detect dead code (an empty range).
886 if (!hasBlockValue(Val, BBFrom)) {
887 BlockValueStack.push(std::make_pair(BBFrom, Val));
888 return false;
889 }
890
891 // Try to intersect ranges of the BB and the constraint on the edge.
892 LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
893 if (!InBlock.isConstantRange())
894 return true;
895
896 ConstantRange Range =
897 Result.getConstantRange().intersectWith(InBlock.getConstantRange());
898 Result = LVILatticeVal::getRange(Range);
899 return true;
900 }
901
902 if (!hasBlockValue(Val, BBFrom)) {
903 BlockValueStack.push(std::make_pair(BBFrom, Val));
904 return false;
905 }
906
907 // if we couldn't compute the value on the edge, use the value from the BB
908 Result = getBlockValue(Val, BBFrom);
909 return true;
910 }
911
getValueInBlock(Value * V,BasicBlock * BB)912 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
913 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
914 << BB->getName() << "'\n");
915
916 BlockValueStack.push(std::make_pair(BB, V));
917 solve();
918 LVILatticeVal Result = getBlockValue(V, BB);
919
920 DEBUG(dbgs() << " Result = " << Result << "\n");
921 return Result;
922 }
923
924 LVILatticeVal LazyValueInfoCache::
getValueOnEdge(Value * V,BasicBlock * FromBB,BasicBlock * ToBB)925 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
926 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
927 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
928
929 LVILatticeVal Result;
930 if (!getEdgeValue(V, FromBB, ToBB, Result)) {
931 solve();
932 bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result);
933 (void)WasFastQuery;
934 assert(WasFastQuery && "More work to do after problem solved?");
935 }
936
937 DEBUG(dbgs() << " Result = " << Result << "\n");
938 return Result;
939 }
940
threadEdge(BasicBlock * PredBB,BasicBlock * OldSucc,BasicBlock * NewSucc)941 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
942 BasicBlock *NewSucc) {
943 // When an edge in the graph has been threaded, values that we could not
944 // determine a value for before (i.e. were marked overdefined) may be possible
945 // to solve now. We do NOT try to proactively update these values. Instead,
946 // we clear their entries from the cache, and allow lazy updating to recompute
947 // them when needed.
948
949 // The updating process is fairly simple: we need to dropped cached info
950 // for all values that were marked overdefined in OldSucc, and for those same
951 // values in any successor of OldSucc (except NewSucc) in which they were
952 // also marked overdefined.
953 std::vector<BasicBlock*> worklist;
954 worklist.push_back(OldSucc);
955
956 DenseSet<Value*> ClearSet;
957 for (DenseSet<OverDefinedPairTy>::iterator I = OverDefinedCache.begin(),
958 E = OverDefinedCache.end(); I != E; ++I) {
959 if (I->first == OldSucc)
960 ClearSet.insert(I->second);
961 }
962
963 // Use a worklist to perform a depth-first search of OldSucc's successors.
964 // NOTE: We do not need a visited list since any blocks we have already
965 // visited will have had their overdefined markers cleared already, and we
966 // thus won't loop to their successors.
967 while (!worklist.empty()) {
968 BasicBlock *ToUpdate = worklist.back();
969 worklist.pop_back();
970
971 // Skip blocks only accessible through NewSucc.
972 if (ToUpdate == NewSucc) continue;
973
974 bool changed = false;
975 for (DenseSet<Value*>::iterator I = ClearSet.begin(), E = ClearSet.end();
976 I != E; ++I) {
977 // If a value was marked overdefined in OldSucc, and is here too...
978 DenseSet<OverDefinedPairTy>::iterator OI =
979 OverDefinedCache.find(std::make_pair(ToUpdate, *I));
980 if (OI == OverDefinedCache.end()) continue;
981
982 // Remove it from the caches.
983 ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(*I, this)];
984 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
985
986 assert(CI != Entry.end() && "Couldn't find entry to update?");
987 Entry.erase(CI);
988 OverDefinedCache.erase(OI);
989
990 // If we removed anything, then we potentially need to update
991 // blocks successors too.
992 changed = true;
993 }
994
995 if (!changed) continue;
996
997 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
998 }
999 }
1000
1001 //===----------------------------------------------------------------------===//
1002 // LazyValueInfo Impl
1003 //===----------------------------------------------------------------------===//
1004
1005 /// getCache - This lazily constructs the LazyValueInfoCache.
getCache(void * & PImpl)1006 static LazyValueInfoCache &getCache(void *&PImpl) {
1007 if (!PImpl)
1008 PImpl = new LazyValueInfoCache();
1009 return *static_cast<LazyValueInfoCache*>(PImpl);
1010 }
1011
runOnFunction(Function & F)1012 bool LazyValueInfo::runOnFunction(Function &F) {
1013 if (PImpl)
1014 getCache(PImpl).clear();
1015
1016 TD = getAnalysisIfAvailable<DataLayout>();
1017 TLI = &getAnalysis<TargetLibraryInfo>();
1018
1019 // Fully lazy.
1020 return false;
1021 }
1022
getAnalysisUsage(AnalysisUsage & AU) const1023 void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
1024 AU.setPreservesAll();
1025 AU.addRequired<TargetLibraryInfo>();
1026 }
1027
releaseMemory()1028 void LazyValueInfo::releaseMemory() {
1029 // If the cache was allocated, free it.
1030 if (PImpl) {
1031 delete &getCache(PImpl);
1032 PImpl = 0;
1033 }
1034 }
1035
getConstant(Value * V,BasicBlock * BB)1036 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
1037 LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
1038
1039 if (Result.isConstant())
1040 return Result.getConstant();
1041 if (Result.isConstantRange()) {
1042 ConstantRange CR = Result.getConstantRange();
1043 if (const APInt *SingleVal = CR.getSingleElement())
1044 return ConstantInt::get(V->getContext(), *SingleVal);
1045 }
1046 return 0;
1047 }
1048
1049 /// getConstantOnEdge - Determine whether the specified value is known to be a
1050 /// constant on the specified edge. Return null if not.
getConstantOnEdge(Value * V,BasicBlock * FromBB,BasicBlock * ToBB)1051 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
1052 BasicBlock *ToBB) {
1053 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1054
1055 if (Result.isConstant())
1056 return Result.getConstant();
1057 if (Result.isConstantRange()) {
1058 ConstantRange CR = Result.getConstantRange();
1059 if (const APInt *SingleVal = CR.getSingleElement())
1060 return ConstantInt::get(V->getContext(), *SingleVal);
1061 }
1062 return 0;
1063 }
1064
1065 /// getPredicateOnEdge - Determine whether the specified value comparison
1066 /// with a constant is known to be true or false on the specified CFG edge.
1067 /// Pred is a CmpInst predicate.
1068 LazyValueInfo::Tristate
getPredicateOnEdge(unsigned Pred,Value * V,Constant * C,BasicBlock * FromBB,BasicBlock * ToBB)1069 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
1070 BasicBlock *FromBB, BasicBlock *ToBB) {
1071 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
1072
1073 // If we know the value is a constant, evaluate the conditional.
1074 Constant *Res = 0;
1075 if (Result.isConstant()) {
1076 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD,
1077 TLI);
1078 if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
1079 return ResCI->isZero() ? False : True;
1080 return Unknown;
1081 }
1082
1083 if (Result.isConstantRange()) {
1084 ConstantInt *CI = dyn_cast<ConstantInt>(C);
1085 if (!CI) return Unknown;
1086
1087 ConstantRange CR = Result.getConstantRange();
1088 if (Pred == ICmpInst::ICMP_EQ) {
1089 if (!CR.contains(CI->getValue()))
1090 return False;
1091
1092 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1093 return True;
1094 } else if (Pred == ICmpInst::ICMP_NE) {
1095 if (!CR.contains(CI->getValue()))
1096 return True;
1097
1098 if (CR.isSingleElement() && CR.contains(CI->getValue()))
1099 return False;
1100 }
1101
1102 // Handle more complex predicates.
1103 ConstantRange TrueValues =
1104 ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
1105 if (TrueValues.contains(CR))
1106 return True;
1107 if (TrueValues.inverse().contains(CR))
1108 return False;
1109 return Unknown;
1110 }
1111
1112 if (Result.isNotConstant()) {
1113 // If this is an equality comparison, we can try to fold it knowing that
1114 // "V != C1".
1115 if (Pred == ICmpInst::ICMP_EQ) {
1116 // !C1 == C -> false iff C1 == C.
1117 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1118 Result.getNotConstant(), C, TD,
1119 TLI);
1120 if (Res->isNullValue())
1121 return False;
1122 } else if (Pred == ICmpInst::ICMP_NE) {
1123 // !C1 != C -> true iff C1 == C.
1124 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
1125 Result.getNotConstant(), C, TD,
1126 TLI);
1127 if (Res->isNullValue())
1128 return True;
1129 }
1130 return Unknown;
1131 }
1132
1133 return Unknown;
1134 }
1135
threadEdge(BasicBlock * PredBB,BasicBlock * OldSucc,BasicBlock * NewSucc)1136 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
1137 BasicBlock *NewSucc) {
1138 if (PImpl) getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);
1139 }
1140
eraseBlock(BasicBlock * BB)1141 void LazyValueInfo::eraseBlock(BasicBlock *BB) {
1142 if (PImpl) getCache(PImpl).eraseBlock(BB);
1143 }
1144