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/Constants.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/Analysis/ConstantFolding.h"
20 #include "llvm/Target/TargetData.h"
21 #include "llvm/Support/CFG.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Support/raw_ostream.h"
24 #include "llvm/ADT/DenseMap.h"
25 #include "llvm/ADT/DenseSet.h"
26 #include "llvm/ADT/PointerIntPair.h"
27 #include "llvm/ADT/STLExtras.h"
30 char LazyValueInfo::ID = 0;
31 INITIALIZE_PASS(LazyValueInfo, "lazy-value-info",
32 "Lazy Value Information Analysis", false, true);
35 FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
39 //===----------------------------------------------------------------------===//
41 //===----------------------------------------------------------------------===//
43 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each
46 /// FIXME: This is basically just for bringup, this can be made a lot more rich
52 /// undefined - This LLVM Value has no known value yet.
54 /// constant - This LLVM Value has a specific constant value.
57 /// notconstant - This LLVM value is known to not have the specified value.
60 /// overdefined - This instruction is not known to be constant, and we know
65 /// Val: This stores the current lattice value along with the Constant* for
66 /// the constant if this is a 'constant' or 'notconstant' value.
67 PointerIntPair<Constant *, 2, LatticeValueTy> Val;
70 LVILatticeVal() : Val(0, undefined) {}
72 static LVILatticeVal get(Constant *C) {
77 static LVILatticeVal getNot(Constant *C) {
79 Res.markNotConstant(C);
83 bool isUndefined() const { return Val.getInt() == undefined; }
84 bool isConstant() const { return Val.getInt() == constant; }
85 bool isNotConstant() const { return Val.getInt() == notconstant; }
86 bool isOverdefined() const { return Val.getInt() == overdefined; }
88 Constant *getConstant() const {
89 assert(isConstant() && "Cannot get the constant of a non-constant!");
90 return Val.getPointer();
93 Constant *getNotConstant() const {
94 assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
95 return Val.getPointer();
98 /// markOverdefined - Return true if this is a change in status.
99 bool markOverdefined() {
102 Val.setInt(overdefined);
106 /// markConstant - Return true if this is a change in status.
107 bool markConstant(Constant *V) {
109 assert(getConstant() == V && "Marking constant with different value");
113 assert(isUndefined());
114 Val.setInt(constant);
115 assert(V && "Marking constant with NULL");
120 /// markNotConstant - Return true if this is a change in status.
121 bool markNotConstant(Constant *V) {
122 if (isNotConstant()) {
123 assert(getNotConstant() == V && "Marking !constant with different value");
128 assert(getConstant() != V && "Marking not constant with different value");
130 assert(isUndefined());
132 Val.setInt(notconstant);
133 assert(V && "Marking constant with NULL");
138 /// mergeIn - Merge the specified lattice value into this one, updating this
139 /// one and returning true if anything changed.
140 bool mergeIn(const LVILatticeVal &RHS) {
141 if (RHS.isUndefined() || isOverdefined()) return false;
142 if (RHS.isOverdefined()) return markOverdefined();
144 if (RHS.isNotConstant()) {
145 if (isNotConstant()) {
146 if (getNotConstant() != RHS.getNotConstant() ||
147 isa<ConstantExpr>(getNotConstant()) ||
148 isa<ConstantExpr>(RHS.getNotConstant()))
149 return markOverdefined();
153 if (getConstant() == RHS.getNotConstant() ||
154 isa<ConstantExpr>(RHS.getNotConstant()) ||
155 isa<ConstantExpr>(getConstant()))
156 return markOverdefined();
157 return markNotConstant(RHS.getNotConstant());
160 assert(isUndefined() && "Unexpected lattice");
161 return markNotConstant(RHS.getNotConstant());
164 // RHS must be a constant, we must be undef, constant, or notconstant.
166 return markConstant(RHS.getConstant());
169 if (getConstant() != RHS.getConstant())
170 return markOverdefined();
174 // If we are known "!=4" and RHS is "==5", stay at "!=4".
175 if (getNotConstant() == RHS.getConstant() ||
176 isa<ConstantExpr>(getNotConstant()) ||
177 isa<ConstantExpr>(RHS.getConstant()))
178 return markOverdefined();
184 } // end anonymous namespace.
187 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
188 if (Val.isUndefined())
189 return OS << "undefined";
190 if (Val.isOverdefined())
191 return OS << "overdefined";
193 if (Val.isNotConstant())
194 return OS << "notconstant<" << *Val.getNotConstant() << '>';
195 return OS << "constant<" << *Val.getConstant() << '>';
199 //===----------------------------------------------------------------------===//
200 // LazyValueInfoCache Decl
201 //===----------------------------------------------------------------------===//
204 /// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
205 /// maintains information about queries across the clients' queries.
206 class LazyValueInfoCache {
208 /// BlockCacheEntryTy - This is a computed lattice value at the end of the
209 /// specified basic block for a Value* that depends on context.
210 typedef std::pair<BasicBlock*, LVILatticeVal> BlockCacheEntryTy;
212 /// ValueCacheEntryTy - This is all of the cached block information for
213 /// exactly one Value*. The entries are sorted by the BasicBlock* of the
214 /// entries, allowing us to do a lookup with a binary search.
215 typedef DenseMap<BasicBlock*, LVILatticeVal> ValueCacheEntryTy;
217 /// ValueCache - This is all of the cached information for all values,
218 /// mapped from Value* to key information.
219 DenseMap<Value*, ValueCacheEntryTy> ValueCache;
221 /// OverDefinedCache - This tracks, on a per-block basis, the set of
222 /// values that are over-defined at the end of that block. This is required
223 /// for cache updating.
224 DenseSet<std::pair<BasicBlock*, Value*> > OverDefinedCache;
226 LVILatticeVal getBlockValue(ValueCacheEntryTy &Cache, BasicBlock *BB);
227 LVILatticeVal getEdgeValue(ValueCacheEntryTy &Cache,
228 BasicBlock *Pred, BasicBlock *Succ);
229 LVILatticeVal &getCachedEntryForBlock(ValueCacheEntryTy &Cache,
232 /************* Begin Per-Query State *************/
233 /// This is the current value being queried for.
236 /// This is all of the cached information about this value.
237 //ValueCacheEntryTy *Cache;
239 /// NewBlocks - This is a mapping of the new BasicBlocks which have been
240 /// added to cache but that are not in sorted order.
241 DenseSet<BasicBlock*> NewBlockInfo;
243 /// QuerySetup - An RAII helper to construct and tear-down per-query
246 LazyValueInfoCache &Owner;
247 QuerySetup(LazyValueInfoCache &O, Value* Val) : Owner(O) {
248 assert(!Owner.Val && "Per-query info not cleared?");
250 assert(Owner.NewBlockInfo.empty() && "Leaked block info!");
254 // When the query is done, insert the newly discovered facts into the
255 // cache in sorted order.
256 LazyValueInfoCache::ValueCacheEntryTy Cache =
257 Owner.ValueCache[Owner.Val];
258 for (DenseSet<BasicBlock*>::iterator I = Owner.NewBlockInfo.begin(),
259 E = Owner.NewBlockInfo.end(); I != E; ++I) {
260 if (Cache[*I].isOverdefined())
261 Owner.OverDefinedCache.insert(std::make_pair(*I, Owner.Val));
264 // Reset Per-Query State
266 Owner.NewBlockInfo.clear();
269 /************* End Per-Query State *************/
272 LazyValueInfoCache() : Val(0) { }
274 /// getValueInBlock - This is the query interface to determine the lattice
275 /// value for the specified Value* at the end of the specified block.
276 LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB);
278 /// getValueOnEdge - This is the query interface to determine the lattice
279 /// value for the specified Value* that is true on the specified edge.
280 LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB);
282 /// threadEdge - This is the update interface to inform the cache that an
283 /// edge from PredBB to OldSucc has been threaded to be from PredBB to
285 void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
287 } // end anonymous namespace
290 /// getCachedEntryForBlock - See if we already have a value for this block. If
291 /// so, return it, otherwise create a new entry in the Cache map to use.
293 LazyValueInfoCache::getCachedEntryForBlock(ValueCacheEntryTy &Cache,
295 NewBlockInfo.insert(BB);
300 LazyValueInfoCache::getBlockValue(ValueCacheEntryTy &Cache, BasicBlock *BB) {
301 // See if we already have a value for this block.
302 LVILatticeVal &BBLV = getCachedEntryForBlock(Cache, BB);
304 // If we've already computed this block's value, return it.
305 if (!BBLV.isUndefined()) {
306 DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
310 // Otherwise, this is the first time we're seeing this block. Reset the
311 // lattice value to overdefined, so that cycles will terminate and be
312 // conservatively correct.
313 BBLV.markOverdefined();
315 // If V is live into BB, see if our predecessors know anything about it.
316 Instruction *BBI = dyn_cast<Instruction>(Val);
317 if (BBI == 0 || BBI->getParent() != BB) {
318 LVILatticeVal Result; // Start Undefined.
319 unsigned NumPreds = 0;
321 // Loop over all of our predecessors, merging what we know from them into
323 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
324 Result.mergeIn(getEdgeValue(Cache, *PI, BB));
326 // If we hit overdefined, exit early. The BlockVals entry is already set
328 if (Result.isOverdefined()) {
329 DEBUG(dbgs() << " compute BB '" << BB->getName()
330 << "' - overdefined because of pred.\n");
336 // If this is the entry block, we must be asking about an argument. The
337 // value is overdefined.
338 if (NumPreds == 0 && BB == &BB->getParent()->front()) {
339 assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
340 Result.markOverdefined();
344 // Return the merged value, which is more precise than 'overdefined'.
345 assert(!Result.isOverdefined());
346 return getCachedEntryForBlock(Cache, BB) = Result;
349 // If this value is defined by an instruction in this block, we have to
350 // process it here somehow or return overdefined.
351 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
353 // TODO: PHI Translation in preds.
358 DEBUG(dbgs() << " compute BB '" << BB->getName()
359 << "' - overdefined because inst def found.\n");
361 LVILatticeVal Result;
362 Result.markOverdefined();
363 return getCachedEntryForBlock(Cache, BB) = Result;
367 /// getEdgeValue - This method attempts to infer more complex
368 LVILatticeVal LazyValueInfoCache::getEdgeValue(ValueCacheEntryTy &Cache,
369 BasicBlock *BBFrom, BasicBlock *BBTo) {
370 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
372 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
373 // If this is a conditional branch and only one successor goes to BBTo, then
374 // we maybe able to infer something from the condition.
375 if (BI->isConditional() &&
376 BI->getSuccessor(0) != BI->getSuccessor(1)) {
377 bool isTrueDest = BI->getSuccessor(0) == BBTo;
378 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
379 "BBTo isn't a successor of BBFrom");
381 // If V is the condition of the branch itself, then we know exactly what
383 if (BI->getCondition() == Val)
384 return LVILatticeVal::get(ConstantInt::get(
385 Type::getInt1Ty(Val->getContext()), isTrueDest));
387 // If the condition of the branch is an equality comparison, we may be
388 // able to infer the value.
389 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
390 if (ICI->isEquality() && ICI->getOperand(0) == Val &&
391 isa<Constant>(ICI->getOperand(1))) {
392 // We know that V has the RHS constant if this is a true SETEQ or
394 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
395 return LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
396 return LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
401 // If the edge was formed by a switch on the value, then we may know exactly
403 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
404 // If BBTo is the default destination of the switch, we don't know anything.
405 // Given a more powerful range analysis we could know stuff.
406 if (SI->getCondition() == Val && SI->getDefaultDest() != BBTo) {
407 // We only know something if there is exactly one value that goes from
409 unsigned NumEdges = 0;
410 ConstantInt *EdgeVal = 0;
411 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
412 if (SI->getSuccessor(i) != BBTo) continue;
413 if (NumEdges++) break;
414 EdgeVal = SI->getCaseValue(i);
416 assert(EdgeVal && "Missing successor?");
418 return LVILatticeVal::get(EdgeVal);
422 // Otherwise see if the value is known in the block.
423 return getBlockValue(Cache, BBFrom);
426 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
427 // If already a constant, there is nothing to compute.
428 if (Constant *VC = dyn_cast<Constant>(V))
429 return LVILatticeVal::get(VC);
431 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
432 << BB->getName() << "'\n");
434 QuerySetup QS(*this, V);
435 ValueCacheEntryTy &Cache = ValueCache[V];
436 LVILatticeVal Result = getBlockValue(Cache, BB);
438 DEBUG(dbgs() << " Result = " << Result << "\n");
442 LVILatticeVal LazyValueInfoCache::
443 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
444 // If already a constant, there is nothing to compute.
445 if (Constant *VC = dyn_cast<Constant>(V))
446 return LVILatticeVal::get(VC);
448 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
449 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
451 QuerySetup QS(*this, V);
452 ValueCacheEntryTy &Cache = ValueCache[V];
453 LVILatticeVal Result = getEdgeValue(Cache, FromBB, ToBB);
455 DEBUG(dbgs() << " Result = " << Result << "\n");
460 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
461 BasicBlock *NewSucc) {
462 // When an edge in the graph has been threaded, values that we could not
463 // determine a value for before (i.e. were marked overdefined) may be possible
464 // to solve now. We do NOT try to proactively update these values. Instead,
465 // we clear their entries from the cache, and allow lazy updating to recompute
468 // The updating process is fairly simple: we need to dropped cached info
469 // for all values that were marked overdefined in OldSucc, and for those same
470 // values in any successor of OldSucc (except NewSucc) in which they were
471 // also marked overdefined.
472 std::vector<BasicBlock*> worklist;
473 worklist.push_back(OldSucc);
475 DenseSet<Value*> ClearSet;
476 for (DenseSet<std::pair<BasicBlock*, Value*> >::iterator
477 I = OverDefinedCache.begin(), E = OverDefinedCache.end(); I != E; ++I) {
478 if (I->first == OldSucc)
479 ClearSet.insert(I->second);
482 // Use a worklist to perform a depth-first search of OldSucc's successors.
483 // NOTE: We do not need a visited list since any blocks we have already
484 // visited will have had their overdefined markers cleared already, and we
485 // thus won't loop to their successors.
486 while (!worklist.empty()) {
487 BasicBlock *ToUpdate = worklist.back();
490 // Skip blocks only accessible through NewSucc.
491 if (ToUpdate == NewSucc) continue;
493 bool changed = false;
494 for (DenseSet<Value*>::iterator I = ClearSet.begin(),E = ClearSet.end();
496 // If a value was marked overdefined in OldSucc, and is here too...
497 DenseSet<std::pair<BasicBlock*, Value*> >::iterator OI =
498 OverDefinedCache.find(std::make_pair(ToUpdate, *I));
499 if (OI == OverDefinedCache.end()) continue;
501 // Remove it from the caches.
502 ValueCacheEntryTy &Entry = ValueCache[*I];
503 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
505 assert(CI != Entry.end() && "Couldn't find entry to update?");
507 OverDefinedCache.erase(OI);
509 // If we removed anything, then we potentially need to update
510 // blocks successors too.
514 if (!changed) continue;
516 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
520 //===----------------------------------------------------------------------===//
521 // LazyValueInfo Impl
522 //===----------------------------------------------------------------------===//
524 bool LazyValueInfo::runOnFunction(Function &F) {
525 TD = getAnalysisIfAvailable<TargetData>();
530 /// getCache - This lazily constructs the LazyValueInfoCache.
531 static LazyValueInfoCache &getCache(void *&PImpl) {
533 PImpl = new LazyValueInfoCache();
534 return *static_cast<LazyValueInfoCache*>(PImpl);
537 void LazyValueInfo::releaseMemory() {
538 // If the cache was allocated, free it.
540 delete &getCache(PImpl);
545 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
546 LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
548 if (Result.isConstant())
549 return Result.getConstant();
553 /// getConstantOnEdge - Determine whether the specified value is known to be a
554 /// constant on the specified edge. Return null if not.
555 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
557 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
559 if (Result.isConstant())
560 return Result.getConstant();
564 /// getPredicateOnEdge - Determine whether the specified value comparison
565 /// with a constant is known to be true or false on the specified CFG edge.
566 /// Pred is a CmpInst predicate.
567 LazyValueInfo::Tristate
568 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
569 BasicBlock *FromBB, BasicBlock *ToBB) {
570 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
572 // If we know the value is a constant, evaluate the conditional.
574 if (Result.isConstant()) {
575 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD);
576 if (ConstantInt *ResCI = dyn_cast_or_null<ConstantInt>(Res))
577 return ResCI->isZero() ? False : True;
581 if (Result.isNotConstant()) {
582 // If this is an equality comparison, we can try to fold it knowing that
584 if (Pred == ICmpInst::ICMP_EQ) {
585 // !C1 == C -> false iff C1 == C.
586 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
587 Result.getNotConstant(), C, TD);
588 if (Res->isNullValue())
590 } else if (Pred == ICmpInst::ICMP_NE) {
591 // !C1 != C -> true iff C1 == C.
592 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
593 Result.getNotConstant(), C, TD);
594 if (Res->isNullValue())
603 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
604 BasicBlock* NewSucc) {
605 getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);