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/PointerIntPair.h"
28 char LazyValueInfo::ID = 0;
29 static RegisterPass<LazyValueInfo>
30 X("lazy-value-info", "Lazy Value Information Analysis", false, true);
33 FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
37 //===----------------------------------------------------------------------===//
39 //===----------------------------------------------------------------------===//
41 /// LVILatticeVal - This is the information tracked by LazyValueInfo for each
44 /// FIXME: This is basically just for bringup, this can be made a lot more rich
50 /// undefined - This LLVM Value has no known value yet.
52 /// constant - This LLVM Value has a specific constant value.
55 /// notconstant - This LLVM value is known to not have the specified value.
58 /// overdefined - This instruction is not known to be constant, and we know
63 /// Val: This stores the current lattice value along with the Constant* for
64 /// the constant if this is a 'constant' or 'notconstant' value.
65 PointerIntPair<Constant *, 2, LatticeValueTy> Val;
68 LVILatticeVal() : Val(0, undefined) {}
70 static LVILatticeVal get(Constant *C) {
75 static LVILatticeVal getNot(Constant *C) {
77 Res.markNotConstant(C);
81 bool isUndefined() const { return Val.getInt() == undefined; }
82 bool isConstant() const { return Val.getInt() == constant; }
83 bool isNotConstant() const { return Val.getInt() == notconstant; }
84 bool isOverdefined() const { return Val.getInt() == overdefined; }
86 Constant *getConstant() const {
87 assert(isConstant() && "Cannot get the constant of a non-constant!");
88 return Val.getPointer();
91 Constant *getNotConstant() const {
92 assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
93 return Val.getPointer();
96 /// markOverdefined - Return true if this is a change in status.
97 bool markOverdefined() {
100 Val.setInt(overdefined);
104 /// markConstant - Return true if this is a change in status.
105 bool markConstant(Constant *V) {
107 assert(getConstant() == V && "Marking constant with different value");
111 assert(isUndefined());
112 Val.setInt(constant);
113 assert(V && "Marking constant with NULL");
118 /// markNotConstant - Return true if this is a change in status.
119 bool markNotConstant(Constant *V) {
120 if (isNotConstant()) {
121 assert(getNotConstant() == V && "Marking !constant with different value");
126 assert(getConstant() != V && "Marking not constant with different value");
128 assert(isUndefined());
130 Val.setInt(notconstant);
131 assert(V && "Marking constant with NULL");
136 /// mergeIn - Merge the specified lattice value into this one, updating this
137 /// one and returning true if anything changed.
138 bool mergeIn(const LVILatticeVal &RHS) {
139 if (RHS.isUndefined() || isOverdefined()) return false;
140 if (RHS.isOverdefined()) return markOverdefined();
142 if (RHS.isNotConstant()) {
143 if (isNotConstant()) {
144 if (getNotConstant() != RHS.getNotConstant())
145 return markOverdefined();
148 if (isConstant() && getConstant() != RHS.getNotConstant())
149 return markOverdefined();
150 return markNotConstant(RHS.getNotConstant());
153 // RHS must be a constant, we must be undef or constant.
154 if (isConstant() && getConstant() != RHS.getConstant())
155 return markOverdefined();
156 return markConstant(RHS.getConstant());
161 } // end anonymous namespace.
164 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
165 if (Val.isUndefined())
166 return OS << "undefined";
167 if (Val.isOverdefined())
168 return OS << "overdefined";
170 if (Val.isNotConstant())
171 return OS << "notconstant<" << *Val.getNotConstant() << '>';
172 return OS << "constant<" << *Val.getConstant() << '>';
176 //===----------------------------------------------------------------------===//
177 // LazyValueInfo Impl
178 //===----------------------------------------------------------------------===//
180 bool LazyValueInfo::runOnFunction(Function &F) {
181 TD = getAnalysisIfAvailable<TargetData>();
186 void LazyValueInfo::releaseMemory() {
190 static LVILatticeVal GetValueInBlock(Value *V, BasicBlock *BB,
191 DenseMap<BasicBlock*, LVILatticeVal> &);
193 static LVILatticeVal GetValueOnEdge(Value *V, BasicBlock *BBFrom,
195 DenseMap<BasicBlock*, LVILatticeVal> &BlockVals) {
196 // FIXME: Pull edge logic out of jump threading.
199 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
200 // If this is a conditional branch and only one successor goes to BBTo, then
201 // we maybe able to infer something from the condition.
202 if (BI->isConditional() &&
203 BI->getSuccessor(0) != BI->getSuccessor(1)) {
204 bool isTrueDest = BI->getSuccessor(0) == BBTo;
205 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
206 "BBTo isn't a successor of BBFrom");
208 // If V is the condition of the branch itself, then we know exactly what
210 if (BI->getCondition() == V)
211 return LVILatticeVal::get(ConstantInt::get(
212 Type::getInt1Ty(V->getContext()), isTrueDest));
214 // If the condition of the branch is an equality comparison, we may be
215 // able to infer the value.
216 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
217 if (ICI->isEquality() && ICI->getOperand(0) == V &&
218 isa<Constant>(ICI->getOperand(1))) {
219 // We know that V has the RHS constant if this is a true SETEQ or
221 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
222 return LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
223 return LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
228 // TODO: Info from switch.
231 // Otherwise see if the value is known in the block.
232 return GetValueInBlock(V, BBFrom, BlockVals);
235 static LVILatticeVal GetValueInBlock(Value *V, BasicBlock *BB,
236 DenseMap<BasicBlock*, LVILatticeVal> &BlockVals) {
237 // See if we already have a value for this block.
238 LVILatticeVal &BBLV = BlockVals[BB];
240 // If we've already computed this block's value, return it.
241 if (!BBLV.isUndefined())
244 // Otherwise, this is the first time we're seeing this block. Reset the
245 // lattice value to overdefined, so that cycles will terminate and be
246 // conservatively correct.
247 BBLV.markOverdefined();
249 LVILatticeVal Result; // Start Undefined.
251 // If V is live in to BB, see if our predecessors know anything about it.
252 Instruction *BBI = dyn_cast<Instruction>(V);
253 if (BBI == 0 || BBI->getParent() != BB) {
254 unsigned NumPreds = 0;
256 // Loop over all of our predecessors, merging what we know from them into
258 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
259 Result.mergeIn(GetValueOnEdge(V, *PI, BB, BlockVals));
261 // If we hit overdefined, exit early. The BlockVals entry is already set
263 if (Result.isOverdefined())
268 // If this is the entry block, we must be asking about an argument. The
269 // value is overdefined.
270 if (NumPreds == 0 && BB == &BB->getParent()->front()) {
271 assert(isa<Argument>(V) && "Unknown live-in to the entry block");
272 Result.markOverdefined();
276 // Return the merged value, which is more precise than 'overdefined'.
277 assert(!Result.isOverdefined());
278 return BlockVals[BB] = Result;
281 // If this value is defined by an instruction in this block, we have to
282 // process it here somehow or return overdefined.
283 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
285 // TODO: PHI Translation in preds.
290 Result.markOverdefined();
291 return BlockVals[BB] = Result;
295 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
296 // If already a constant, return it.
297 if (Constant *VC = dyn_cast<Constant>(V))
300 DenseMap<BasicBlock*, LVILatticeVal> BlockValues;
302 DEBUG(errs() << "Getting value " << *V << " at end of block '"
303 << BB->getName() << "'\n");
304 LVILatticeVal Result = GetValueInBlock(V, BB, BlockValues);
306 DEBUG(errs() << " Result = " << Result << "\n");
308 if (Result.isConstant())
309 return Result.getConstant();
313 /// getConstantOnEdge - Determine whether the specified value is known to be a
314 /// constant on the specified edge. Return null if not.
315 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
317 // If already a constant, return it.
318 if (Constant *VC = dyn_cast<Constant>(V))
321 DenseMap<BasicBlock*, LVILatticeVal> BlockValues;
323 DEBUG(errs() << "Getting value " << *V << " on edge from '"
324 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
325 LVILatticeVal Result = GetValueOnEdge(V, FromBB, ToBB, BlockValues);
327 DEBUG(errs() << " Result = " << Result << "\n");
329 if (Result.isConstant())
330 return Result.getConstant();
334 /// getPredicateOnEdge - Determine whether the specified value comparison
335 /// with a constant is known to be true or false on the specified CFG edge.
336 /// Pred is a CmpInst predicate.
337 LazyValueInfo::Tristate
338 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
339 BasicBlock *FromBB, BasicBlock *ToBB) {
340 LVILatticeVal Result;
342 // If already a constant, we can use constant folding.
343 if (Constant *VC = dyn_cast<Constant>(V)) {
344 Result = LVILatticeVal::get(VC);
346 DenseMap<BasicBlock*, LVILatticeVal> BlockValues;
348 DEBUG(errs() << "Getting value " << *V << " on edge from '"
349 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
350 Result = GetValueOnEdge(V, FromBB, ToBB, BlockValues);
351 DEBUG(errs() << " Result = " << Result << "\n");
354 // If we know the value is a constant, evaluate the conditional.
356 if (Result.isConstant()) {
357 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD);
358 if (ConstantInt *ResCI = dyn_cast_or_null<ConstantInt>(Res))
359 return ResCI->isZero() ? False : True;
360 } else if (Result.isNotConstant()) {
361 // If this is an equality comparison, we can try to fold it knowing that
363 if (Pred == ICmpInst::ICMP_EQ) {
364 // !C1 == C -> false iff C1 == C.
365 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
366 Result.getNotConstant(), C, TD);
367 if (Res->isNullValue())
369 } else if (Pred == ICmpInst::ICMP_NE) {
370 // !C1 != C -> true iff C1 == C.
371 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_EQ,
372 Result.getNotConstant(), C, TD);
373 if (Res->isNullValue())