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 isa<ConstantExpr>(getNotConstant()) ||
146 isa<ConstantExpr>(RHS.getNotConstant()))
147 return markOverdefined();
151 if (getConstant() == RHS.getNotConstant() ||
152 isa<ConstantExpr>(RHS.getNotConstant()) ||
153 isa<ConstantExpr>(getConstant()))
154 return markOverdefined();
155 return markNotConstant(RHS.getNotConstant());
158 assert(isUndefined() && "Unexpected lattice");
159 return markNotConstant(RHS.getNotConstant());
162 // RHS must be a constant, we must be undef, constant, or notconstant.
164 return markConstant(RHS.getConstant());
167 if (getConstant() != RHS.getConstant())
168 return markOverdefined();
172 // If we are known "!=4" and RHS is "==5", stay at "!=4".
173 if (getNotConstant() == RHS.getConstant() ||
174 isa<ConstantExpr>(getNotConstant()) ||
175 isa<ConstantExpr>(RHS.getConstant()))
176 return markOverdefined();
182 } // end anonymous namespace.
185 raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
186 if (Val.isUndefined())
187 return OS << "undefined";
188 if (Val.isOverdefined())
189 return OS << "overdefined";
191 if (Val.isNotConstant())
192 return OS << "notconstant<" << *Val.getNotConstant() << '>';
193 return OS << "constant<" << *Val.getConstant() << '>';
197 //===----------------------------------------------------------------------===//
198 // LazyValueInfo Impl
199 //===----------------------------------------------------------------------===//
201 bool LazyValueInfo::runOnFunction(Function &F) {
202 TD = getAnalysisIfAvailable<TargetData>();
207 void LazyValueInfo::releaseMemory() {
211 static LVILatticeVal GetValueInBlock(Value *V, BasicBlock *BB,
212 DenseMap<BasicBlock*, LVILatticeVal> &);
214 static LVILatticeVal GetValueOnEdge(Value *V, BasicBlock *BBFrom,
216 DenseMap<BasicBlock*, LVILatticeVal> &BlockVals) {
217 // FIXME: Pull edge logic out of jump threading.
220 if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
221 // If this is a conditional branch and only one successor goes to BBTo, then
222 // we maybe able to infer something from the condition.
223 if (BI->isConditional() &&
224 BI->getSuccessor(0) != BI->getSuccessor(1)) {
225 bool isTrueDest = BI->getSuccessor(0) == BBTo;
226 assert(BI->getSuccessor(!isTrueDest) == BBTo &&
227 "BBTo isn't a successor of BBFrom");
229 // If V is the condition of the branch itself, then we know exactly what
231 if (BI->getCondition() == V)
232 return LVILatticeVal::get(ConstantInt::get(
233 Type::getInt1Ty(V->getContext()), isTrueDest));
235 // If the condition of the branch is an equality comparison, we may be
236 // able to infer the value.
237 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
238 if (ICI->isEquality() && ICI->getOperand(0) == V &&
239 isa<Constant>(ICI->getOperand(1))) {
240 // We know that V has the RHS constant if this is a true SETEQ or
242 if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
243 return LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
244 return LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
249 // TODO: Info from switch.
252 // Otherwise see if the value is known in the block.
253 return GetValueInBlock(V, BBFrom, BlockVals);
256 static LVILatticeVal GetValueInBlock(Value *V, BasicBlock *BB,
257 DenseMap<BasicBlock*, LVILatticeVal> &BlockVals) {
258 // See if we already have a value for this block.
259 LVILatticeVal &BBLV = BlockVals[BB];
261 // If we've already computed this block's value, return it.
262 if (!BBLV.isUndefined())
265 // Otherwise, this is the first time we're seeing this block. Reset the
266 // lattice value to overdefined, so that cycles will terminate and be
267 // conservatively correct.
268 BBLV.markOverdefined();
270 LVILatticeVal Result; // Start Undefined.
272 // If V is live in to BB, see if our predecessors know anything about it.
273 Instruction *BBI = dyn_cast<Instruction>(V);
274 if (BBI == 0 || BBI->getParent() != BB) {
275 unsigned NumPreds = 0;
277 // Loop over all of our predecessors, merging what we know from them into
279 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
280 Result.mergeIn(GetValueOnEdge(V, *PI, BB, BlockVals));
282 // If we hit overdefined, exit early. The BlockVals entry is already set
284 if (Result.isOverdefined())
289 // If this is the entry block, we must be asking about an argument. The
290 // value is overdefined.
291 if (NumPreds == 0 && BB == &BB->getParent()->front()) {
292 assert(isa<Argument>(V) && "Unknown live-in to the entry block");
293 Result.markOverdefined();
297 // Return the merged value, which is more precise than 'overdefined'.
298 assert(!Result.isOverdefined());
299 return BlockVals[BB] = Result;
302 // If this value is defined by an instruction in this block, we have to
303 // process it here somehow or return overdefined.
304 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
306 // TODO: PHI Translation in preds.
311 Result.markOverdefined();
312 return BlockVals[BB] = Result;
316 Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
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 << " at end of block '"
324 << BB->getName() << "'\n");
325 LVILatticeVal Result = GetValueInBlock(V, BB, BlockValues);
327 DEBUG(errs() << " Result = " << Result << "\n");
329 if (Result.isConstant())
330 return Result.getConstant();
334 /// getConstantOnEdge - Determine whether the specified value is known to be a
335 /// constant on the specified edge. Return null if not.
336 Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
338 // If already a constant, return it.
339 if (Constant *VC = dyn_cast<Constant>(V))
342 DenseMap<BasicBlock*, LVILatticeVal> BlockValues;
344 DEBUG(errs() << "Getting value " << *V << " on edge from '"
345 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
346 LVILatticeVal Result = GetValueOnEdge(V, FromBB, ToBB, BlockValues);
348 DEBUG(errs() << " Result = " << Result << "\n");
350 if (Result.isConstant())
351 return Result.getConstant();
355 /// getPredicateOnEdge - Determine whether the specified value comparison
356 /// with a constant is known to be true or false on the specified CFG edge.
357 /// Pred is a CmpInst predicate.
358 LazyValueInfo::Tristate
359 LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
360 BasicBlock *FromBB, BasicBlock *ToBB) {
361 LVILatticeVal Result;
363 // If already a constant, we can use constant folding.
364 if (Constant *VC = dyn_cast<Constant>(V)) {
365 Result = LVILatticeVal::get(VC);
367 DenseMap<BasicBlock*, LVILatticeVal> BlockValues;
369 DEBUG(errs() << "Getting value " << *V << " on edge from '"
370 << FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
371 Result = GetValueOnEdge(V, FromBB, ToBB, BlockValues);
372 DEBUG(errs() << " Result = " << Result << "\n");
375 // If we know the value is a constant, evaluate the conditional.
377 if (Result.isConstant()) {
378 Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD);
379 if (ConstantInt *ResCI = dyn_cast_or_null<ConstantInt>(Res))
380 return ResCI->isZero() ? False : True;
381 } else if (Result.isNotConstant()) {
382 // If this is an equality comparison, we can try to fold it knowing that
384 if (Pred == ICmpInst::ICMP_EQ) {
385 // !C1 == C -> false iff C1 == C.
386 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
387 Result.getNotConstant(), C, TD);
388 if (Res->isNullValue())
390 } else if (Pred == ICmpInst::ICMP_NE) {
391 // !C1 != C -> true iff C1 == C.
392 Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_EQ,
393 Result.getNotConstant(), C, TD);
394 if (Res->isNullValue())