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(Value *Val, BasicBlock *BB);
227 LVILatticeVal getEdgeValue(Value *Val, BasicBlock *Pred, BasicBlock *Succ);
228 LVILatticeVal &getCachedEntryForBlock(Value *Val, ValueCacheEntryTy &Cache,
231 /************* Begin Per-Query State *************/
233 /// NewBlocks - This is a mapping of the new BasicBlocks which have been
234 /// added to cache but that are not in sorted order.
235 DenseSet<std::pair<BasicBlock*,Value*> > NewBlockInfo;
237 /// QuerySetup - An RAII helper to construct and tear-down per-query
240 LazyValueInfoCache &Owner;
241 QuerySetup(LazyValueInfoCache &O) : Owner(O) {
242 assert(Owner.NewBlockInfo.empty() && "Leaked block info!");
246 // When the query is done, insert the newly discovered facts into the
247 // cache in sorted order.
248 for (DenseSet<std::pair<BasicBlock*,Value*> >::iterator
249 I = Owner.NewBlockInfo.begin(), E = Owner.NewBlockInfo.end();
251 if (Owner.ValueCache[I->second][I->first].isOverdefined())
252 Owner.OverDefinedCache.insert(*I);
255 // Reset Per-Query State
256 Owner.NewBlockInfo.clear();
259 /************* End Per-Query State *************/
262 LazyValueInfoCache() { }
264 /// getValueInBlock - This is the query interface to determine the lattice
265 /// value for the specified Value* at the end of the specified block.
266 LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB);
268 /// getValueOnEdge - This is the query interface to determine the lattice
269 /// value for the specified Value* that is true on the specified edge.
270 LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB);
272 /// threadEdge - This is the update interface to inform the cache that an
273 /// edge from PredBB to OldSucc has been threaded to be from PredBB to
275 void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
277 } // end anonymous namespace
280 /// getCachedEntryForBlock - See if we already have a value for this block. If
281 /// so, return it, otherwise create a new entry in the Cache map to use.
283 LazyValueInfoCache::getCachedEntryForBlock(Value *Val, ValueCacheEntryTy &Cache,
285 NewBlockInfo.insert(std::make_pair(BB, Val));
290 LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
291 // See if we already have a value for this block.
292 ValueCacheEntryTy &Cache = ValueCache[Val];
293 LVILatticeVal &BBLV = getCachedEntryForBlock(Val, Cache, BB);
295 // If we've already computed this block's value, return it.
296 if (!BBLV.isUndefined()) {
297 DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
301 // Otherwise, this is the first time we're seeing this block. Reset the
302 // lattice value to overdefined, so that cycles will terminate and be
303 // conservatively correct.
304 BBLV.markOverdefined();
306 // If V is live into BB, see if our predecessors know anything about it.
307 Instruction *BBI = dyn_cast<Instruction>(Val);
308 if (BBI == 0 || BBI->getParent() != BB) {
309 LVILatticeVal Result; // Start Undefined.
310 unsigned NumPreds = 0;
312 // Loop over all of our predecessors, merging what we know from them into
314 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
315 Result.mergeIn(getEdgeValue(Val, *PI, BB));
317 // If we hit overdefined, exit early. The BlockVals entry is already set
319 if (Result.isOverdefined()) {
320 DEBUG(dbgs() << " compute BB '" << BB->getName()
321 << "' - overdefined because of pred.\n");
327 // If this is the entry block, we must be asking about an argument. The
328 // value is overdefined.
329 if (NumPreds == 0 && BB == &BB->getParent()->front()) {
330 assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
331 Result.markOverdefined();
335 // Return the merged value, which is more precise than 'overdefined'.
336 assert(!Result.isOverdefined());
337 return getCachedEntryForBlock(Val, Cache, BB) = Result;
340 // If this value is defined by an instruction in this block, we have to
341 // process it here somehow or return overdefined.
342 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
344 // TODO: PHI Translation in preds.
349 DEBUG(dbgs() << " compute BB '" << BB->getName()
350 << "' - overdefined because inst def found.\n");
352 LVILatticeVal Result;
353 Result.markOverdefined();
354 return getCachedEntryForBlock(Val, Cache, BB) = Result;
358 /// getEdgeValue - This method attempts to infer more complex
359 LVILatticeVal LazyValueInfoCache::getEdgeValue(Value *Val,
360 BasicBlock *BBFrom, BasicBlock *BBTo) {
361 // TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
363 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
364 // If this is a conditional branch and only one successor goes to BBTo, then
365 // we maybe able to infer something from the condition.
366 if (BI->isConditional() &&
367 BI->getSuccessor(0) != BI->getSuccessor(1)) {
368 bool isTrueDest = BI->getSuccessor(0) == BBTo;
369 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
370 "BBTo isn't a successor of BBFrom");
372 // If V is the condition of the branch itself, then we know exactly what
374 if (BI->getCondition() == Val)
375 return LVILatticeVal::get(ConstantInt::get(
376 Type::getInt1Ty(Val->getContext()), isTrueDest));
378 // If the condition of the branch is an equality comparison, we may be
379 // able to infer the value.
380 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
381 if (ICI->isEquality() && ICI->getOperand(0) == Val &&
382 isa<Constant>(ICI->getOperand(1))) {
383 // We know that V has the RHS constant if this is a true SETEQ or
385 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
386 return LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
387 return LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
392 // If the edge was formed by a switch on the value, then we may know exactly
394 if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
395 // If BBTo is the default destination of the switch, we don't know anything.
396 // Given a more powerful range analysis we could know stuff.
397 if (SI->getCondition() == Val && SI->getDefaultDest() != BBTo) {
398 // We only know something if there is exactly one value that goes from
400 unsigned NumEdges = 0;
401 ConstantInt *EdgeVal = 0;
402 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
403 if (SI->getSuccessor(i) != BBTo) continue;
404 if (NumEdges++) break;
405 EdgeVal = SI->getCaseValue(i);
407 assert(EdgeVal && "Missing successor?");
409 return LVILatticeVal::get(EdgeVal);
413 // Otherwise see if the value is known in the block.
414 return getBlockValue(Val, BBFrom);
417 LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
418 // If already a constant, there is nothing to compute.
419 if (Constant *VC = dyn_cast<Constant>(V))
420 return LVILatticeVal::get(VC);
422 DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
423 << BB->getName() << "'\n");
425 QuerySetup QS(*this);
426 LVILatticeVal Result = getBlockValue(V, BB);
428 DEBUG(dbgs() << " Result = " << Result << "\n");
432 LVILatticeVal LazyValueInfoCache::
433 getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
434 // If already a constant, there is nothing to compute.
435 if (Constant *VC = dyn_cast<Constant>(V))
436 return LVILatticeVal::get(VC);
438 DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
439 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
441 QuerySetup QS(*this);
442 LVILatticeVal Result = getEdgeValue(V, FromBB, ToBB);
444 DEBUG(dbgs() << " Result = " << Result << "\n");
449 void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
450 BasicBlock *NewSucc) {
451 // When an edge in the graph has been threaded, values that we could not
452 // determine a value for before (i.e. were marked overdefined) may be possible
453 // to solve now. We do NOT try to proactively update these values. Instead,
454 // we clear their entries from the cache, and allow lazy updating to recompute
457 // The updating process is fairly simple: we need to dropped cached info
458 // for all values that were marked overdefined in OldSucc, and for those same
459 // values in any successor of OldSucc (except NewSucc) in which they were
460 // also marked overdefined.
461 std::vector<BasicBlock*> worklist;
462 worklist.push_back(OldSucc);
464 DenseSet<Value*> ClearSet;
465 for (DenseSet<std::pair<BasicBlock*, Value*> >::iterator
466 I = OverDefinedCache.begin(), E = OverDefinedCache.end(); I != E; ++I) {
467 if (I->first == OldSucc)
468 ClearSet.insert(I->second);
471 // Use a worklist to perform a depth-first search of OldSucc's successors.
472 // NOTE: We do not need a visited list since any blocks we have already
473 // visited will have had their overdefined markers cleared already, and we
474 // thus won't loop to their successors.
475 while (!worklist.empty()) {
476 BasicBlock *ToUpdate = worklist.back();
479 // Skip blocks only accessible through NewSucc.
480 if (ToUpdate == NewSucc) continue;
482 bool changed = false;
483 for (DenseSet<Value*>::iterator I = ClearSet.begin(),E = ClearSet.end();
485 // If a value was marked overdefined in OldSucc, and is here too...
486 DenseSet<std::pair<BasicBlock*, Value*> >::iterator OI =
487 OverDefinedCache.find(std::make_pair(ToUpdate, *I));
488 if (OI == OverDefinedCache.end()) continue;
490 // Remove it from the caches.
491 ValueCacheEntryTy &Entry = ValueCache[*I];
492 ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
494 assert(CI != Entry.end() && "Couldn't find entry to update?");
496 OverDefinedCache.erase(OI);
498 // If we removed anything, then we potentially need to update
499 // blocks successors too.
503 if (!changed) continue;
505 worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
509 //===----------------------------------------------------------------------===//
510 // LazyValueInfo Impl
511 //===----------------------------------------------------------------------===//
513 bool LazyValueInfo::runOnFunction(Function &F) {
514 TD = getAnalysisIfAvailable<TargetData>();
519 /// getCache - This lazily constructs the LazyValueInfoCache.
520 static LazyValueInfoCache &getCache(void *&PImpl) {
522 PImpl = new LazyValueInfoCache();
523 return *static_cast<LazyValueInfoCache*>(PImpl);
526 void LazyValueInfo::releaseMemory() {
527 // If the cache was allocated, free it.
529 delete &getCache(PImpl);
534 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
535 LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
537 if (Result.isConstant())
538 return Result.getConstant();
542 /// getConstantOnEdge - Determine whether the specified value is known to be a
543 /// constant on the specified edge. Return null if not.
544 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
546 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
548 if (Result.isConstant())
549 return Result.getConstant();
553 /// getPredicateOnEdge - Determine whether the specified value comparison
554 /// with a constant is known to be true or false on the specified CFG edge.
555 /// Pred is a CmpInst predicate.
556 LazyValueInfo::Tristate
557 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
558 BasicBlock *FromBB, BasicBlock *ToBB) {
559 LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
561 // If we know the value is a constant, evaluate the conditional.
563 if (Result.isConstant()) {
564 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD);
565 if (ConstantInt *ResCI = dyn_cast_or_null<ConstantInt>(Res))
566 return ResCI->isZero() ? False : True;
570 if (Result.isNotConstant()) {
571 // If this is an equality comparison, we can try to fold it knowing that
573 if (Pred == ICmpInst::ICMP_EQ) {
574 // !C1 == C -> false iff C1 == C.
575 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
576 Result.getNotConstant(), C, TD);
577 if (Res->isNullValue())
579 } else if (Pred == ICmpInst::ICMP_NE) {
580 // !C1 != C -> true iff C1 == C.
581 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
582 Result.getNotConstant(), C, TD);
583 if (Res->isNullValue())
592 void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
593 BasicBlock* NewSucc) {
594 getCache(PImpl).threadEdge(PredBB, OldSucc, NewSucc);