1 //===- ValueTracking.cpp - Walk computations to compute properties --------===//
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 contains routines that help analyze properties that chains of
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Analysis/ValueTracking.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/Analysis/AssumptionCache.h"
18 #include "llvm/Analysis/InstructionSimplify.h"
19 #include "llvm/Analysis/MemoryBuiltins.h"
20 #include "llvm/Analysis/LoopInfo.h"
21 #include "llvm/IR/CallSite.h"
22 #include "llvm/IR/ConstantRange.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/Dominators.h"
26 #include "llvm/IR/GetElementPtrTypeIterator.h"
27 #include "llvm/IR/GlobalAlias.h"
28 #include "llvm/IR/GlobalVariable.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/IntrinsicInst.h"
31 #include "llvm/IR/LLVMContext.h"
32 #include "llvm/IR/Metadata.h"
33 #include "llvm/IR/Operator.h"
34 #include "llvm/IR/PatternMatch.h"
35 #include "llvm/IR/Statepoint.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/MathExtras.h"
40 using namespace llvm::PatternMatch;
42 const unsigned MaxDepth = 6;
44 /// Enable an experimental feature to leverage information about dominating
45 /// conditions to compute known bits. The individual options below control how
46 /// hard we search. The defaults are chosen to be fairly aggressive. If you
47 /// run into compile time problems when testing, scale them back and report
49 static cl::opt<bool> EnableDomConditions("value-tracking-dom-conditions",
50 cl::Hidden, cl::init(false));
52 // This is expensive, so we only do it for the top level query value.
53 // (TODO: evaluate cost vs profit, consider higher thresholds)
54 static cl::opt<unsigned> DomConditionsMaxDepth("dom-conditions-max-depth",
55 cl::Hidden, cl::init(1));
57 /// How many dominating blocks should be scanned looking for dominating
59 static cl::opt<unsigned> DomConditionsMaxDomBlocks("dom-conditions-dom-blocks",
63 // Controls the number of uses of the value searched for possible
64 // dominating comparisons.
65 static cl::opt<unsigned> DomConditionsMaxUses("dom-conditions-max-uses",
66 cl::Hidden, cl::init(2000));
68 // If true, don't consider only compares whose only use is a branch.
69 static cl::opt<bool> DomConditionsSingleCmpUse("dom-conditions-single-cmp-use",
70 cl::Hidden, cl::init(false));
72 /// Returns the bitwidth of the given scalar or pointer type (if unknown returns
73 /// 0). For vector types, returns the element type's bitwidth.
74 static unsigned getBitWidth(Type *Ty, const DataLayout &DL) {
75 if (unsigned BitWidth = Ty->getScalarSizeInBits())
78 return DL.getPointerTypeSizeInBits(Ty);
81 // Many of these functions have internal versions that take an assumption
82 // exclusion set. This is because of the potential for mutual recursion to
83 // cause computeKnownBits to repeatedly visit the same assume intrinsic. The
84 // classic case of this is assume(x = y), which will attempt to determine
85 // bits in x from bits in y, which will attempt to determine bits in y from
86 // bits in x, etc. Regarding the mutual recursion, computeKnownBits can call
87 // isKnownNonZero, which calls computeKnownBits and ComputeSignBit and
88 // isKnownToBeAPowerOfTwo (all of which can call computeKnownBits), and so on.
89 typedef SmallPtrSet<const Value *, 8> ExclInvsSet;
92 // Simplifying using an assume can only be done in a particular control-flow
93 // context (the context instruction provides that context). If an assume and
94 // the context instruction are not in the same block then the DT helps in
95 // figuring out if we can use it.
99 const Instruction *CxtI;
100 const DominatorTree *DT;
102 Query(AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr,
103 const DominatorTree *DT = nullptr)
104 : AC(AC), CxtI(CxtI), DT(DT) {}
106 Query(const Query &Q, const Value *NewExcl)
107 : ExclInvs(Q.ExclInvs), AC(Q.AC), CxtI(Q.CxtI), DT(Q.DT) {
108 ExclInvs.insert(NewExcl);
111 } // end anonymous namespace
113 // Given the provided Value and, potentially, a context instruction, return
114 // the preferred context instruction (if any).
115 static const Instruction *safeCxtI(const Value *V, const Instruction *CxtI) {
116 // If we've been provided with a context instruction, then use that (provided
117 // it has been inserted).
118 if (CxtI && CxtI->getParent())
121 // If the value is really an already-inserted instruction, then use that.
122 CxtI = dyn_cast<Instruction>(V);
123 if (CxtI && CxtI->getParent())
129 static void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
130 const DataLayout &DL, unsigned Depth,
133 void llvm::computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
134 const DataLayout &DL, unsigned Depth,
135 AssumptionCache *AC, const Instruction *CxtI,
136 const DominatorTree *DT) {
137 ::computeKnownBits(V, KnownZero, KnownOne, DL, Depth,
138 Query(AC, safeCxtI(V, CxtI), DT));
141 bool llvm::haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL,
142 AssumptionCache *AC, const Instruction *CxtI,
143 const DominatorTree *DT) {
144 assert(LHS->getType() == RHS->getType() &&
145 "LHS and RHS should have the same type");
146 assert(LHS->getType()->isIntOrIntVectorTy() &&
147 "LHS and RHS should be integers");
148 IntegerType *IT = cast<IntegerType>(LHS->getType()->getScalarType());
149 APInt LHSKnownZero(IT->getBitWidth(), 0), LHSKnownOne(IT->getBitWidth(), 0);
150 APInt RHSKnownZero(IT->getBitWidth(), 0), RHSKnownOne(IT->getBitWidth(), 0);
151 computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, 0, AC, CxtI, DT);
152 computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, 0, AC, CxtI, DT);
153 return (LHSKnownZero | RHSKnownZero).isAllOnesValue();
156 static void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
157 const DataLayout &DL, unsigned Depth,
160 void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
161 const DataLayout &DL, unsigned Depth,
162 AssumptionCache *AC, const Instruction *CxtI,
163 const DominatorTree *DT) {
164 ::ComputeSignBit(V, KnownZero, KnownOne, DL, Depth,
165 Query(AC, safeCxtI(V, CxtI), DT));
168 static bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
169 const Query &Q, const DataLayout &DL);
171 bool llvm::isKnownToBeAPowerOfTwo(Value *V, const DataLayout &DL, bool OrZero,
172 unsigned Depth, AssumptionCache *AC,
173 const Instruction *CxtI,
174 const DominatorTree *DT) {
175 return ::isKnownToBeAPowerOfTwo(V, OrZero, Depth,
176 Query(AC, safeCxtI(V, CxtI), DT), DL);
179 static bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth,
182 bool llvm::isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth,
183 AssumptionCache *AC, const Instruction *CxtI,
184 const DominatorTree *DT) {
185 return ::isKnownNonZero(V, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT));
188 bool llvm::isKnownNonNegative(Value *V, const DataLayout &DL, unsigned Depth,
189 AssumptionCache *AC, const Instruction *CxtI,
190 const DominatorTree *DT) {
191 bool NonNegative, Negative;
192 ComputeSignBit(V, NonNegative, Negative, DL, Depth, AC, CxtI, DT);
196 static bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
197 unsigned Depth, const Query &Q);
199 bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
200 unsigned Depth, AssumptionCache *AC,
201 const Instruction *CxtI, const DominatorTree *DT) {
202 return ::MaskedValueIsZero(V, Mask, DL, Depth,
203 Query(AC, safeCxtI(V, CxtI), DT));
206 static unsigned ComputeNumSignBits(Value *V, const DataLayout &DL,
207 unsigned Depth, const Query &Q);
209 unsigned llvm::ComputeNumSignBits(Value *V, const DataLayout &DL,
210 unsigned Depth, AssumptionCache *AC,
211 const Instruction *CxtI,
212 const DominatorTree *DT) {
213 return ::ComputeNumSignBits(V, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT));
216 static void computeKnownBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
217 APInt &KnownZero, APInt &KnownOne,
218 APInt &KnownZero2, APInt &KnownOne2,
219 const DataLayout &DL, unsigned Depth,
222 if (ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) {
223 // We know that the top bits of C-X are clear if X contains less bits
224 // than C (i.e. no wrap-around can happen). For example, 20-X is
225 // positive if we can prove that X is >= 0 and < 16.
226 if (!CLHS->getValue().isNegative()) {
227 unsigned BitWidth = KnownZero.getBitWidth();
228 unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
229 // NLZ can't be BitWidth with no sign bit
230 APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
231 computeKnownBits(Op1, KnownZero2, KnownOne2, DL, Depth + 1, Q);
233 // If all of the MaskV bits are known to be zero, then we know the
234 // output top bits are zero, because we now know that the output is
236 if ((KnownZero2 & MaskV) == MaskV) {
237 unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
238 // Top bits known zero.
239 KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2);
245 unsigned BitWidth = KnownZero.getBitWidth();
247 // If an initial sequence of bits in the result is not needed, the
248 // corresponding bits in the operands are not needed.
249 APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
250 computeKnownBits(Op0, LHSKnownZero, LHSKnownOne, DL, Depth + 1, Q);
251 computeKnownBits(Op1, KnownZero2, KnownOne2, DL, Depth + 1, Q);
253 // Carry in a 1 for a subtract, rather than a 0.
254 APInt CarryIn(BitWidth, 0);
256 // Sum = LHS + ~RHS + 1
257 std::swap(KnownZero2, KnownOne2);
261 APInt PossibleSumZero = ~LHSKnownZero + ~KnownZero2 + CarryIn;
262 APInt PossibleSumOne = LHSKnownOne + KnownOne2 + CarryIn;
264 // Compute known bits of the carry.
265 APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnownZero ^ KnownZero2);
266 APInt CarryKnownOne = PossibleSumOne ^ LHSKnownOne ^ KnownOne2;
268 // Compute set of known bits (where all three relevant bits are known).
269 APInt LHSKnown = LHSKnownZero | LHSKnownOne;
270 APInt RHSKnown = KnownZero2 | KnownOne2;
271 APInt CarryKnown = CarryKnownZero | CarryKnownOne;
272 APInt Known = LHSKnown & RHSKnown & CarryKnown;
274 assert((PossibleSumZero & Known) == (PossibleSumOne & Known) &&
275 "known bits of sum differ");
277 // Compute known bits of the result.
278 KnownZero = ~PossibleSumOne & Known;
279 KnownOne = PossibleSumOne & Known;
281 // Are we still trying to solve for the sign bit?
282 if (!Known.isNegative()) {
284 // Adding two non-negative numbers, or subtracting a negative number from
285 // a non-negative one, can't wrap into negative.
286 if (LHSKnownZero.isNegative() && KnownZero2.isNegative())
287 KnownZero |= APInt::getSignBit(BitWidth);
288 // Adding two negative numbers, or subtracting a non-negative number from
289 // a negative one, can't wrap into non-negative.
290 else if (LHSKnownOne.isNegative() && KnownOne2.isNegative())
291 KnownOne |= APInt::getSignBit(BitWidth);
296 static void computeKnownBitsMul(Value *Op0, Value *Op1, bool NSW,
297 APInt &KnownZero, APInt &KnownOne,
298 APInt &KnownZero2, APInt &KnownOne2,
299 const DataLayout &DL, unsigned Depth,
301 unsigned BitWidth = KnownZero.getBitWidth();
302 computeKnownBits(Op1, KnownZero, KnownOne, DL, Depth + 1, Q);
303 computeKnownBits(Op0, KnownZero2, KnownOne2, DL, Depth + 1, Q);
305 bool isKnownNegative = false;
306 bool isKnownNonNegative = false;
307 // If the multiplication is known not to overflow, compute the sign bit.
310 // The product of a number with itself is non-negative.
311 isKnownNonNegative = true;
313 bool isKnownNonNegativeOp1 = KnownZero.isNegative();
314 bool isKnownNonNegativeOp0 = KnownZero2.isNegative();
315 bool isKnownNegativeOp1 = KnownOne.isNegative();
316 bool isKnownNegativeOp0 = KnownOne2.isNegative();
317 // The product of two numbers with the same sign is non-negative.
318 isKnownNonNegative = (isKnownNegativeOp1 && isKnownNegativeOp0) ||
319 (isKnownNonNegativeOp1 && isKnownNonNegativeOp0);
320 // The product of a negative number and a non-negative number is either
322 if (!isKnownNonNegative)
323 isKnownNegative = (isKnownNegativeOp1 && isKnownNonNegativeOp0 &&
324 isKnownNonZero(Op0, DL, Depth, Q)) ||
325 (isKnownNegativeOp0 && isKnownNonNegativeOp1 &&
326 isKnownNonZero(Op1, DL, Depth, Q));
330 // If low bits are zero in either operand, output low known-0 bits.
331 // Also compute a conservative estimate for high known-0 bits.
332 // More trickiness is possible, but this is sufficient for the
333 // interesting case of alignment computation.
334 KnownOne.clearAllBits();
335 unsigned TrailZ = KnownZero.countTrailingOnes() +
336 KnownZero2.countTrailingOnes();
337 unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
338 KnownZero2.countLeadingOnes(),
339 BitWidth) - BitWidth;
341 TrailZ = std::min(TrailZ, BitWidth);
342 LeadZ = std::min(LeadZ, BitWidth);
343 KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
344 APInt::getHighBitsSet(BitWidth, LeadZ);
346 // Only make use of no-wrap flags if we failed to compute the sign bit
347 // directly. This matters if the multiplication always overflows, in
348 // which case we prefer to follow the result of the direct computation,
349 // though as the program is invoking undefined behaviour we can choose
350 // whatever we like here.
351 if (isKnownNonNegative && !KnownOne.isNegative())
352 KnownZero.setBit(BitWidth - 1);
353 else if (isKnownNegative && !KnownZero.isNegative())
354 KnownOne.setBit(BitWidth - 1);
357 void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
359 unsigned BitWidth = KnownZero.getBitWidth();
360 unsigned NumRanges = Ranges.getNumOperands() / 2;
361 assert(NumRanges >= 1);
363 // Use the high end of the ranges to find leading zeros.
364 unsigned MinLeadingZeros = BitWidth;
365 for (unsigned i = 0; i < NumRanges; ++i) {
367 mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 0));
369 mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 1));
370 ConstantRange Range(Lower->getValue(), Upper->getValue());
371 if (Range.isWrappedSet())
372 MinLeadingZeros = 0; // -1 has no zeros
373 unsigned LeadingZeros = (Upper->getValue() - 1).countLeadingZeros();
374 MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros);
377 KnownZero = APInt::getHighBitsSet(BitWidth, MinLeadingZeros);
380 static bool isEphemeralValueOf(Instruction *I, const Value *E) {
381 SmallVector<const Value *, 16> WorkSet(1, I);
382 SmallPtrSet<const Value *, 32> Visited;
383 SmallPtrSet<const Value *, 16> EphValues;
385 while (!WorkSet.empty()) {
386 const Value *V = WorkSet.pop_back_val();
387 if (!Visited.insert(V).second)
390 // If all uses of this value are ephemeral, then so is this value.
391 bool FoundNEUse = false;
392 for (const User *I : V->users())
393 if (!EphValues.count(I)) {
403 if (const User *U = dyn_cast<User>(V))
404 for (User::const_op_iterator J = U->op_begin(), JE = U->op_end();
406 if (isSafeToSpeculativelyExecute(*J))
407 WorkSet.push_back(*J);
415 // Is this an intrinsic that cannot be speculated but also cannot trap?
416 static bool isAssumeLikeIntrinsic(const Instruction *I) {
417 if (const CallInst *CI = dyn_cast<CallInst>(I))
418 if (Function *F = CI->getCalledFunction())
419 switch (F->getIntrinsicID()) {
421 // FIXME: This list is repeated from NoTTI::getIntrinsicCost.
422 case Intrinsic::assume:
423 case Intrinsic::dbg_declare:
424 case Intrinsic::dbg_value:
425 case Intrinsic::invariant_start:
426 case Intrinsic::invariant_end:
427 case Intrinsic::lifetime_start:
428 case Intrinsic::lifetime_end:
429 case Intrinsic::objectsize:
430 case Intrinsic::ptr_annotation:
431 case Intrinsic::var_annotation:
438 static bool isValidAssumeForContext(Value *V, const Query &Q) {
439 Instruction *Inv = cast<Instruction>(V);
441 // There are two restrictions on the use of an assume:
442 // 1. The assume must dominate the context (or the control flow must
443 // reach the assume whenever it reaches the context).
444 // 2. The context must not be in the assume's set of ephemeral values
445 // (otherwise we will use the assume to prove that the condition
446 // feeding the assume is trivially true, thus causing the removal of
450 if (Q.DT->dominates(Inv, Q.CxtI)) {
452 } else if (Inv->getParent() == Q.CxtI->getParent()) {
453 // The context comes first, but they're both in the same block. Make sure
454 // there is nothing in between that might interrupt the control flow.
455 for (BasicBlock::const_iterator I =
456 std::next(BasicBlock::const_iterator(Q.CxtI)),
457 IE(Inv); I != IE; ++I)
458 if (!isSafeToSpeculativelyExecute(I) && !isAssumeLikeIntrinsic(I))
461 return !isEphemeralValueOf(Inv, Q.CxtI);
467 // When we don't have a DT, we do a limited search...
468 if (Inv->getParent() == Q.CxtI->getParent()->getSinglePredecessor()) {
470 } else if (Inv->getParent() == Q.CxtI->getParent()) {
471 // Search forward from the assume until we reach the context (or the end
472 // of the block); the common case is that the assume will come first.
473 for (BasicBlock::iterator I = std::next(BasicBlock::iterator(Inv)),
474 IE = Inv->getParent()->end(); I != IE; ++I)
478 // The context must come first...
479 for (BasicBlock::const_iterator I =
480 std::next(BasicBlock::const_iterator(Q.CxtI)),
481 IE(Inv); I != IE; ++I)
482 if (!isSafeToSpeculativelyExecute(I) && !isAssumeLikeIntrinsic(I))
485 return !isEphemeralValueOf(Inv, Q.CxtI);
491 bool llvm::isValidAssumeForContext(const Instruction *I,
492 const Instruction *CxtI,
493 const DominatorTree *DT) {
494 return ::isValidAssumeForContext(const_cast<Instruction *>(I),
495 Query(nullptr, CxtI, DT));
498 template<typename LHS, typename RHS>
499 inline match_combine_or<CmpClass_match<LHS, RHS, ICmpInst, ICmpInst::Predicate>,
500 CmpClass_match<RHS, LHS, ICmpInst, ICmpInst::Predicate>>
501 m_c_ICmp(ICmpInst::Predicate &Pred, const LHS &L, const RHS &R) {
502 return m_CombineOr(m_ICmp(Pred, L, R), m_ICmp(Pred, R, L));
505 template<typename LHS, typename RHS>
506 inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::And>,
507 BinaryOp_match<RHS, LHS, Instruction::And>>
508 m_c_And(const LHS &L, const RHS &R) {
509 return m_CombineOr(m_And(L, R), m_And(R, L));
512 template<typename LHS, typename RHS>
513 inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::Or>,
514 BinaryOp_match<RHS, LHS, Instruction::Or>>
515 m_c_Or(const LHS &L, const RHS &R) {
516 return m_CombineOr(m_Or(L, R), m_Or(R, L));
519 template<typename LHS, typename RHS>
520 inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::Xor>,
521 BinaryOp_match<RHS, LHS, Instruction::Xor>>
522 m_c_Xor(const LHS &L, const RHS &R) {
523 return m_CombineOr(m_Xor(L, R), m_Xor(R, L));
526 /// Compute known bits in 'V' under the assumption that the condition 'Cmp' is
527 /// true (at the context instruction.) This is mostly a utility function for
528 /// the prototype dominating conditions reasoning below.
529 static void computeKnownBitsFromTrueCondition(Value *V, ICmpInst *Cmp,
532 const DataLayout &DL,
533 unsigned Depth, const Query &Q) {
534 Value *LHS = Cmp->getOperand(0);
535 Value *RHS = Cmp->getOperand(1);
536 // TODO: We could potentially be more aggressive here. This would be worth
537 // evaluating. If we can, explore commoning this code with the assume
539 if (LHS != V && RHS != V)
542 const unsigned BitWidth = KnownZero.getBitWidth();
544 switch (Cmp->getPredicate()) {
546 // We know nothing from this condition
548 // TODO: implement unsigned bound from below (known one bits)
549 // TODO: common condition check implementations with assumes
550 // TODO: implement other patterns from assume (e.g. V & B == A)
551 case ICmpInst::ICMP_SGT:
553 APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0);
554 computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q);
555 if (KnownOneTemp.isAllOnesValue() || KnownZeroTemp.isNegative()) {
556 // We know that the sign bit is zero.
557 KnownZero |= APInt::getSignBit(BitWidth);
561 case ICmpInst::ICMP_EQ:
563 APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0);
565 computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q);
567 computeKnownBits(LHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q);
569 llvm_unreachable("missing use?");
570 KnownZero |= KnownZeroTemp;
571 KnownOne |= KnownOneTemp;
574 case ICmpInst::ICMP_ULE:
576 APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0);
577 computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q);
578 // The known zero bits carry over
579 unsigned SignBits = KnownZeroTemp.countLeadingOnes();
580 KnownZero |= APInt::getHighBitsSet(BitWidth, SignBits);
583 case ICmpInst::ICMP_ULT:
585 APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0);
586 computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q);
587 // Whatever high bits in rhs are zero are known to be zero (if rhs is a
588 // power of 2, then one more).
589 unsigned SignBits = KnownZeroTemp.countLeadingOnes();
590 if (isKnownToBeAPowerOfTwo(RHS, false, Depth + 1, Query(Q, Cmp), DL))
592 KnownZero |= APInt::getHighBitsSet(BitWidth, SignBits);
598 /// Compute known bits in 'V' from conditions which are known to be true along
599 /// all paths leading to the context instruction. In particular, look for
600 /// cases where one branch of an interesting condition dominates the context
601 /// instruction. This does not do general dataflow.
602 /// NOTE: This code is EXPERIMENTAL and currently off by default.
603 static void computeKnownBitsFromDominatingCondition(Value *V, APInt &KnownZero,
605 const DataLayout &DL,
608 // Need both the dominator tree and the query location to do anything useful
609 if (!Q.DT || !Q.CxtI)
611 Instruction *Cxt = const_cast<Instruction *>(Q.CxtI);
612 // The context instruction might be in a statically unreachable block. If
613 // so, asking dominator queries may yield suprising results. (e.g. the block
614 // may not have a dom tree node)
615 if (!Q.DT->isReachableFromEntry(Cxt->getParent()))
618 // Avoid useless work
619 if (auto VI = dyn_cast<Instruction>(V))
620 if (VI->getParent() == Cxt->getParent())
623 // Note: We currently implement two options. It's not clear which of these
624 // will survive long term, we need data for that.
625 // Option 1 - Try walking the dominator tree looking for conditions which
626 // might apply. This works well for local conditions (loop guards, etc..),
627 // but not as well for things far from the context instruction (presuming a
628 // low max blocks explored). If we can set an high enough limit, this would
630 // Option 2 - We restrict out search to those conditions which are uses of
631 // the value we're interested in. This is independent of dom structure,
632 // but is slightly less powerful without looking through lots of use chains.
633 // It does handle conditions far from the context instruction (e.g. early
634 // function exits on entry) really well though.
636 // Option 1 - Search the dom tree
637 unsigned NumBlocksExplored = 0;
638 BasicBlock *Current = Cxt->getParent();
640 // Stop searching if we've gone too far up the chain
641 if (NumBlocksExplored >= DomConditionsMaxDomBlocks)
645 if (!Q.DT->getNode(Current)->getIDom())
647 Current = Q.DT->getNode(Current)->getIDom()->getBlock();
649 // found function entry
652 BranchInst *BI = dyn_cast<BranchInst>(Current->getTerminator());
653 if (!BI || BI->isUnconditional())
655 ICmpInst *Cmp = dyn_cast<ICmpInst>(BI->getCondition());
659 // We're looking for conditions that are guaranteed to hold at the context
660 // instruction. Finding a condition where one path dominates the context
661 // isn't enough because both the true and false cases could merge before
662 // the context instruction we're actually interested in. Instead, we need
663 // to ensure that the taken *edge* dominates the context instruction. We
664 // know that the edge must be reachable since we started from a reachable
666 BasicBlock *BB0 = BI->getSuccessor(0);
667 BasicBlockEdge Edge(BI->getParent(), BB0);
668 if (!Edge.isSingleEdge() || !Q.DT->dominates(Edge, Q.CxtI->getParent()))
671 computeKnownBitsFromTrueCondition(V, Cmp, KnownZero, KnownOne, DL, Depth,
675 // Option 2 - Search the other uses of V
676 unsigned NumUsesExplored = 0;
677 for (auto U : V->users()) {
678 // Avoid massive lists
679 if (NumUsesExplored >= DomConditionsMaxUses)
682 // Consider only compare instructions uniquely controlling a branch
683 ICmpInst *Cmp = dyn_cast<ICmpInst>(U);
687 if (DomConditionsSingleCmpUse && !Cmp->hasOneUse())
690 for (auto *CmpU : Cmp->users()) {
691 BranchInst *BI = dyn_cast<BranchInst>(CmpU);
692 if (!BI || BI->isUnconditional())
694 // We're looking for conditions that are guaranteed to hold at the
695 // context instruction. Finding a condition where one path dominates
696 // the context isn't enough because both the true and false cases could
697 // merge before the context instruction we're actually interested in.
698 // Instead, we need to ensure that the taken *edge* dominates the context
700 BasicBlock *BB0 = BI->getSuccessor(0);
701 BasicBlockEdge Edge(BI->getParent(), BB0);
702 if (!Edge.isSingleEdge() || !Q.DT->dominates(Edge, Q.CxtI->getParent()))
705 computeKnownBitsFromTrueCondition(V, Cmp, KnownZero, KnownOne, DL, Depth,
711 static void computeKnownBitsFromAssume(Value *V, APInt &KnownZero,
712 APInt &KnownOne, const DataLayout &DL,
713 unsigned Depth, const Query &Q) {
714 // Use of assumptions is context-sensitive. If we don't have a context, we
716 if (!Q.AC || !Q.CxtI)
719 unsigned BitWidth = KnownZero.getBitWidth();
721 for (auto &AssumeVH : Q.AC->assumptions()) {
724 CallInst *I = cast<CallInst>(AssumeVH);
725 assert(I->getParent()->getParent() == Q.CxtI->getParent()->getParent() &&
726 "Got assumption for the wrong function!");
727 if (Q.ExclInvs.count(I))
730 // Warning: This loop can end up being somewhat performance sensetive.
731 // We're running this loop for once for each value queried resulting in a
732 // runtime of ~O(#assumes * #values).
734 assert(I->getCalledFunction()->getIntrinsicID() == Intrinsic::assume &&
735 "must be an assume intrinsic");
737 Value *Arg = I->getArgOperand(0);
739 if (Arg == V && isValidAssumeForContext(I, Q)) {
740 assert(BitWidth == 1 && "assume operand is not i1?");
741 KnownZero.clearAllBits();
742 KnownOne.setAllBits();
746 // The remaining tests are all recursive, so bail out if we hit the limit.
747 if (Depth == MaxDepth)
751 auto m_V = m_CombineOr(m_Specific(V),
752 m_CombineOr(m_PtrToInt(m_Specific(V)),
753 m_BitCast(m_Specific(V))));
755 CmpInst::Predicate Pred;
758 if (match(Arg, m_c_ICmp(Pred, m_V, m_Value(A))) &&
759 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
760 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
761 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
762 KnownZero |= RHSKnownZero;
763 KnownOne |= RHSKnownOne;
765 } else if (match(Arg,
766 m_c_ICmp(Pred, m_c_And(m_V, m_Value(B)), m_Value(A))) &&
767 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
768 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
769 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
770 APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0);
771 computeKnownBits(B, MaskKnownZero, MaskKnownOne, DL, Depth+1, Query(Q, I));
773 // For those bits in the mask that are known to be one, we can propagate
774 // known bits from the RHS to V.
775 KnownZero |= RHSKnownZero & MaskKnownOne;
776 KnownOne |= RHSKnownOne & MaskKnownOne;
777 // assume(~(v & b) = a)
778 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_And(m_V, m_Value(B))),
780 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
781 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
782 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
783 APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0);
784 computeKnownBits(B, MaskKnownZero, MaskKnownOne, DL, Depth+1, Query(Q, I));
786 // For those bits in the mask that are known to be one, we can propagate
787 // inverted known bits from the RHS to V.
788 KnownZero |= RHSKnownOne & MaskKnownOne;
789 KnownOne |= RHSKnownZero & MaskKnownOne;
791 } else if (match(Arg,
792 m_c_ICmp(Pred, m_c_Or(m_V, m_Value(B)), m_Value(A))) &&
793 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
794 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
795 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
796 APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
797 computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
799 // For those bits in B that are known to be zero, we can propagate known
800 // bits from the RHS to V.
801 KnownZero |= RHSKnownZero & BKnownZero;
802 KnownOne |= RHSKnownOne & BKnownZero;
803 // assume(~(v | b) = a)
804 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Or(m_V, m_Value(B))),
806 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
807 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
808 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
809 APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
810 computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
812 // For those bits in B that are known to be zero, we can propagate
813 // inverted known bits from the RHS to V.
814 KnownZero |= RHSKnownOne & BKnownZero;
815 KnownOne |= RHSKnownZero & BKnownZero;
817 } else if (match(Arg,
818 m_c_ICmp(Pred, m_c_Xor(m_V, m_Value(B)), m_Value(A))) &&
819 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
820 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
821 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
822 APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
823 computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
825 // For those bits in B that are known to be zero, we can propagate known
826 // bits from the RHS to V. For those bits in B that are known to be one,
827 // we can propagate inverted known bits from the RHS to V.
828 KnownZero |= RHSKnownZero & BKnownZero;
829 KnownOne |= RHSKnownOne & BKnownZero;
830 KnownZero |= RHSKnownOne & BKnownOne;
831 KnownOne |= RHSKnownZero & BKnownOne;
832 // assume(~(v ^ b) = a)
833 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Xor(m_V, m_Value(B))),
835 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
836 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
837 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
838 APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
839 computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
841 // For those bits in B that are known to be zero, we can propagate
842 // inverted known bits from the RHS to V. For those bits in B that are
843 // known to be one, we can propagate known bits from the RHS to V.
844 KnownZero |= RHSKnownOne & BKnownZero;
845 KnownOne |= RHSKnownZero & BKnownZero;
846 KnownZero |= RHSKnownZero & BKnownOne;
847 KnownOne |= RHSKnownOne & BKnownOne;
848 // assume(v << c = a)
849 } else if (match(Arg, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)),
851 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
852 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
853 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
854 // For those bits in RHS that are known, we can propagate them to known
855 // bits in V shifted to the right by C.
856 KnownZero |= RHSKnownZero.lshr(C->getZExtValue());
857 KnownOne |= RHSKnownOne.lshr(C->getZExtValue());
858 // assume(~(v << c) = a)
859 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))),
861 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
862 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
863 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
864 // For those bits in RHS that are known, we can propagate them inverted
865 // to known bits in V shifted to the right by C.
866 KnownZero |= RHSKnownOne.lshr(C->getZExtValue());
867 KnownOne |= RHSKnownZero.lshr(C->getZExtValue());
868 // assume(v >> c = a)
869 } else if (match(Arg,
870 m_c_ICmp(Pred, m_CombineOr(m_LShr(m_V, m_ConstantInt(C)),
871 m_AShr(m_V, m_ConstantInt(C))),
873 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
874 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
875 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
876 // For those bits in RHS that are known, we can propagate them to known
877 // bits in V shifted to the right by C.
878 KnownZero |= RHSKnownZero << C->getZExtValue();
879 KnownOne |= RHSKnownOne << C->getZExtValue();
880 // assume(~(v >> c) = a)
881 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_CombineOr(
882 m_LShr(m_V, m_ConstantInt(C)),
883 m_AShr(m_V, m_ConstantInt(C)))),
885 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
886 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
887 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
888 // For those bits in RHS that are known, we can propagate them inverted
889 // to known bits in V shifted to the right by C.
890 KnownZero |= RHSKnownOne << C->getZExtValue();
891 KnownOne |= RHSKnownZero << C->getZExtValue();
892 // assume(v >=_s c) where c is non-negative
893 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
894 Pred == ICmpInst::ICMP_SGE && isValidAssumeForContext(I, Q)) {
895 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
896 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
898 if (RHSKnownZero.isNegative()) {
899 // We know that the sign bit is zero.
900 KnownZero |= APInt::getSignBit(BitWidth);
902 // assume(v >_s c) where c is at least -1.
903 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
904 Pred == ICmpInst::ICMP_SGT && isValidAssumeForContext(I, Q)) {
905 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
906 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
908 if (RHSKnownOne.isAllOnesValue() || RHSKnownZero.isNegative()) {
909 // We know that the sign bit is zero.
910 KnownZero |= APInt::getSignBit(BitWidth);
912 // assume(v <=_s c) where c is negative
913 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
914 Pred == ICmpInst::ICMP_SLE && isValidAssumeForContext(I, Q)) {
915 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
916 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
918 if (RHSKnownOne.isNegative()) {
919 // We know that the sign bit is one.
920 KnownOne |= APInt::getSignBit(BitWidth);
922 // assume(v <_s c) where c is non-positive
923 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
924 Pred == ICmpInst::ICMP_SLT && isValidAssumeForContext(I, Q)) {
925 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
926 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
928 if (RHSKnownZero.isAllOnesValue() || RHSKnownOne.isNegative()) {
929 // We know that the sign bit is one.
930 KnownOne |= APInt::getSignBit(BitWidth);
933 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
934 Pred == ICmpInst::ICMP_ULE && isValidAssumeForContext(I, Q)) {
935 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
936 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
938 // Whatever high bits in c are zero are known to be zero.
940 APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
942 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
943 Pred == ICmpInst::ICMP_ULT && isValidAssumeForContext(I, Q)) {
944 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
945 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
947 // Whatever high bits in c are zero are known to be zero (if c is a power
948 // of 2, then one more).
949 if (isKnownToBeAPowerOfTwo(A, false, Depth + 1, Query(Q, I), DL))
951 APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes()+1);
954 APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
959 static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero,
960 APInt &KnownOne, const DataLayout &DL,
961 unsigned Depth, const Query &Q) {
962 unsigned BitWidth = KnownZero.getBitWidth();
964 APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
965 switch (I->getOpcode()) {
967 case Instruction::Load:
968 if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range))
969 computeKnownBitsFromRangeMetadata(*MD, KnownZero);
971 case Instruction::And: {
972 // If either the LHS or the RHS are Zero, the result is zero.
973 computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q);
974 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q);
976 // Output known-1 bits are only known if set in both the LHS & RHS.
977 KnownOne &= KnownOne2;
978 // Output known-0 are known to be clear if zero in either the LHS | RHS.
979 KnownZero |= KnownZero2;
982 case Instruction::Or: {
983 computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q);
984 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q);
986 // Output known-0 bits are only known if clear in both the LHS & RHS.
987 KnownZero &= KnownZero2;
988 // Output known-1 are known to be set if set in either the LHS | RHS.
989 KnownOne |= KnownOne2;
992 case Instruction::Xor: {
993 computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q);
994 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q);
996 // Output known-0 bits are known if clear or set in both the LHS & RHS.
997 APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
998 // Output known-1 are known to be set if set in only one of the LHS, RHS.
999 KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
1000 KnownZero = KnownZeroOut;
1003 case Instruction::Mul: {
1004 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
1005 computeKnownBitsMul(I->getOperand(0), I->getOperand(1), NSW, KnownZero,
1006 KnownOne, KnownZero2, KnownOne2, DL, Depth, Q);
1009 case Instruction::UDiv: {
1010 // For the purposes of computing leading zeros we can conservatively
1011 // treat a udiv as a logical right shift by the power of 2 known to
1012 // be less than the denominator.
1013 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1014 unsigned LeadZ = KnownZero2.countLeadingOnes();
1016 KnownOne2.clearAllBits();
1017 KnownZero2.clearAllBits();
1018 computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1019 unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
1020 if (RHSUnknownLeadingOnes != BitWidth)
1021 LeadZ = std::min(BitWidth,
1022 LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
1024 KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ);
1027 case Instruction::Select:
1028 computeKnownBits(I->getOperand(2), KnownZero, KnownOne, DL, Depth + 1, Q);
1029 computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1031 // Only known if known in both the LHS and RHS.
1032 KnownOne &= KnownOne2;
1033 KnownZero &= KnownZero2;
1035 case Instruction::FPTrunc:
1036 case Instruction::FPExt:
1037 case Instruction::FPToUI:
1038 case Instruction::FPToSI:
1039 case Instruction::SIToFP:
1040 case Instruction::UIToFP:
1041 break; // Can't work with floating point.
1042 case Instruction::PtrToInt:
1043 case Instruction::IntToPtr:
1044 case Instruction::AddrSpaceCast: // Pointers could be different sizes.
1045 // FALL THROUGH and handle them the same as zext/trunc.
1046 case Instruction::ZExt:
1047 case Instruction::Trunc: {
1048 Type *SrcTy = I->getOperand(0)->getType();
1050 unsigned SrcBitWidth;
1051 // Note that we handle pointer operands here because of inttoptr/ptrtoint
1052 // which fall through here.
1053 SrcBitWidth = DL.getTypeSizeInBits(SrcTy->getScalarType());
1055 assert(SrcBitWidth && "SrcBitWidth can't be zero");
1056 KnownZero = KnownZero.zextOrTrunc(SrcBitWidth);
1057 KnownOne = KnownOne.zextOrTrunc(SrcBitWidth);
1058 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1059 KnownZero = KnownZero.zextOrTrunc(BitWidth);
1060 KnownOne = KnownOne.zextOrTrunc(BitWidth);
1061 // Any top bits are known to be zero.
1062 if (BitWidth > SrcBitWidth)
1063 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
1066 case Instruction::BitCast: {
1067 Type *SrcTy = I->getOperand(0)->getType();
1068 if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) &&
1069 // TODO: For now, not handling conversions like:
1070 // (bitcast i64 %x to <2 x i32>)
1071 !I->getType()->isVectorTy()) {
1072 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1077 case Instruction::SExt: {
1078 // Compute the bits in the result that are not present in the input.
1079 unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits();
1081 KnownZero = KnownZero.trunc(SrcBitWidth);
1082 KnownOne = KnownOne.trunc(SrcBitWidth);
1083 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1084 KnownZero = KnownZero.zext(BitWidth);
1085 KnownOne = KnownOne.zext(BitWidth);
1087 // If the sign bit of the input is known set or clear, then we know the
1088 // top bits of the result.
1089 if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
1090 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
1091 else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
1092 KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
1095 case Instruction::Shl:
1096 // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
1097 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
1098 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
1099 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1100 KnownZero <<= ShiftAmt;
1101 KnownOne <<= ShiftAmt;
1102 KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
1105 case Instruction::LShr:
1106 // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
1107 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
1108 // Compute the new bits that are at the top now.
1109 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
1111 // Unsigned shift right.
1112 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1113 KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
1114 KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
1115 // high bits known zero.
1116 KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
1119 case Instruction::AShr:
1120 // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
1121 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
1122 // Compute the new bits that are at the top now.
1123 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
1125 // Signed shift right.
1126 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1127 KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
1128 KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
1130 APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
1131 if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
1132 KnownZero |= HighBits;
1133 else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
1134 KnownOne |= HighBits;
1137 case Instruction::Sub: {
1138 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
1139 computeKnownBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW,
1140 KnownZero, KnownOne, KnownZero2, KnownOne2, DL,
1144 case Instruction::Add: {
1145 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
1146 computeKnownBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW,
1147 KnownZero, KnownOne, KnownZero2, KnownOne2, DL,
1151 case Instruction::SRem:
1152 if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
1153 APInt RA = Rem->getValue().abs();
1154 if (RA.isPowerOf2()) {
1155 APInt LowBits = RA - 1;
1156 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1,
1159 // The low bits of the first operand are unchanged by the srem.
1160 KnownZero = KnownZero2 & LowBits;
1161 KnownOne = KnownOne2 & LowBits;
1163 // If the first operand is non-negative or has all low bits zero, then
1164 // the upper bits are all zero.
1165 if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
1166 KnownZero |= ~LowBits;
1168 // If the first operand is negative and not all low bits are zero, then
1169 // the upper bits are all one.
1170 if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
1171 KnownOne |= ~LowBits;
1173 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
1177 // The sign bit is the LHS's sign bit, except when the result of the
1178 // remainder is zero.
1179 if (KnownZero.isNonNegative()) {
1180 APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
1181 computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, DL,
1183 // If it's known zero, our sign bit is also zero.
1184 if (LHSKnownZero.isNegative())
1185 KnownZero.setBit(BitWidth - 1);
1189 case Instruction::URem: {
1190 if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
1191 APInt RA = Rem->getValue();
1192 if (RA.isPowerOf2()) {
1193 APInt LowBits = (RA - 1);
1194 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1,
1196 KnownZero |= ~LowBits;
1197 KnownOne &= LowBits;
1202 // Since the result is less than or equal to either operand, any leading
1203 // zero bits in either operand must also exist in the result.
1204 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1205 computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1207 unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
1208 KnownZero2.countLeadingOnes());
1209 KnownOne.clearAllBits();
1210 KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
1214 case Instruction::Alloca: {
1215 AllocaInst *AI = cast<AllocaInst>(I);
1216 unsigned Align = AI->getAlignment();
1218 Align = DL.getABITypeAlignment(AI->getType()->getElementType());
1221 KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
1224 case Instruction::GetElementPtr: {
1225 // Analyze all of the subscripts of this getelementptr instruction
1226 // to determine if we can prove known low zero bits.
1227 APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
1228 computeKnownBits(I->getOperand(0), LocalKnownZero, LocalKnownOne, DL,
1230 unsigned TrailZ = LocalKnownZero.countTrailingOnes();
1232 gep_type_iterator GTI = gep_type_begin(I);
1233 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
1234 Value *Index = I->getOperand(i);
1235 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
1236 // Handle struct member offset arithmetic.
1238 // Handle case when index is vector zeroinitializer
1239 Constant *CIndex = cast<Constant>(Index);
1240 if (CIndex->isZeroValue())
1243 if (CIndex->getType()->isVectorTy())
1244 Index = CIndex->getSplatValue();
1246 unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
1247 const StructLayout *SL = DL.getStructLayout(STy);
1248 uint64_t Offset = SL->getElementOffset(Idx);
1249 TrailZ = std::min<unsigned>(TrailZ,
1250 countTrailingZeros(Offset));
1252 // Handle array index arithmetic.
1253 Type *IndexedTy = GTI.getIndexedType();
1254 if (!IndexedTy->isSized()) {
1258 unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits();
1259 uint64_t TypeSize = DL.getTypeAllocSize(IndexedTy);
1260 LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
1261 computeKnownBits(Index, LocalKnownZero, LocalKnownOne, DL, Depth + 1,
1263 TrailZ = std::min(TrailZ,
1264 unsigned(countTrailingZeros(TypeSize) +
1265 LocalKnownZero.countTrailingOnes()));
1269 KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ);
1272 case Instruction::PHI: {
1273 PHINode *P = cast<PHINode>(I);
1274 // Handle the case of a simple two-predecessor recurrence PHI.
1275 // There's a lot more that could theoretically be done here, but
1276 // this is sufficient to catch some interesting cases.
1277 if (P->getNumIncomingValues() == 2) {
1278 for (unsigned i = 0; i != 2; ++i) {
1279 Value *L = P->getIncomingValue(i);
1280 Value *R = P->getIncomingValue(!i);
1281 Operator *LU = dyn_cast<Operator>(L);
1284 unsigned Opcode = LU->getOpcode();
1285 // Check for operations that have the property that if
1286 // both their operands have low zero bits, the result
1287 // will have low zero bits.
1288 if (Opcode == Instruction::Add ||
1289 Opcode == Instruction::Sub ||
1290 Opcode == Instruction::And ||
1291 Opcode == Instruction::Or ||
1292 Opcode == Instruction::Mul) {
1293 Value *LL = LU->getOperand(0);
1294 Value *LR = LU->getOperand(1);
1295 // Find a recurrence.
1302 // Ok, we have a PHI of the form L op= R. Check for low
1304 computeKnownBits(R, KnownZero2, KnownOne2, DL, Depth + 1, Q);
1306 // We need to take the minimum number of known bits
1307 APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
1308 computeKnownBits(L, KnownZero3, KnownOne3, DL, Depth + 1, Q);
1310 KnownZero = APInt::getLowBitsSet(BitWidth,
1311 std::min(KnownZero2.countTrailingOnes(),
1312 KnownZero3.countTrailingOnes()));
1318 // Unreachable blocks may have zero-operand PHI nodes.
1319 if (P->getNumIncomingValues() == 0)
1322 // Otherwise take the unions of the known bit sets of the operands,
1323 // taking conservative care to avoid excessive recursion.
1324 if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) {
1325 // Skip if every incoming value references to ourself.
1326 if (dyn_cast_or_null<UndefValue>(P->hasConstantValue()))
1329 KnownZero = APInt::getAllOnesValue(BitWidth);
1330 KnownOne = APInt::getAllOnesValue(BitWidth);
1331 for (Value *IncValue : P->incoming_values()) {
1332 // Skip direct self references.
1333 if (IncValue == P) continue;
1335 KnownZero2 = APInt(BitWidth, 0);
1336 KnownOne2 = APInt(BitWidth, 0);
1337 // Recurse, but cap the recursion to one level, because we don't
1338 // want to waste time spinning around in loops.
1339 computeKnownBits(IncValue, KnownZero2, KnownOne2, DL,
1341 KnownZero &= KnownZero2;
1342 KnownOne &= KnownOne2;
1343 // If all bits have been ruled out, there's no need to check
1345 if (!KnownZero && !KnownOne)
1351 case Instruction::Call:
1352 case Instruction::Invoke:
1353 if (MDNode *MD = cast<Instruction>(I)->getMetadata(LLVMContext::MD_range))
1354 computeKnownBitsFromRangeMetadata(*MD, KnownZero);
1355 // If a range metadata is attached to this IntrinsicInst, intersect the
1356 // explicit range specified by the metadata and the implicit range of
1358 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
1359 switch (II->getIntrinsicID()) {
1361 case Intrinsic::ctlz:
1362 case Intrinsic::cttz: {
1363 unsigned LowBits = Log2_32(BitWidth)+1;
1364 // If this call is undefined for 0, the result will be less than 2^n.
1365 if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
1367 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
1370 case Intrinsic::ctpop: {
1371 unsigned LowBits = Log2_32(BitWidth)+1;
1372 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
1375 case Intrinsic::x86_sse42_crc32_64_64:
1376 KnownZero |= APInt::getHighBitsSet(64, 32);
1381 case Instruction::ExtractValue:
1382 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) {
1383 ExtractValueInst *EVI = cast<ExtractValueInst>(I);
1384 if (EVI->getNumIndices() != 1) break;
1385 if (EVI->getIndices()[0] == 0) {
1386 switch (II->getIntrinsicID()) {
1388 case Intrinsic::uadd_with_overflow:
1389 case Intrinsic::sadd_with_overflow:
1390 computeKnownBitsAddSub(true, II->getArgOperand(0),
1391 II->getArgOperand(1), false, KnownZero,
1392 KnownOne, KnownZero2, KnownOne2, DL, Depth, Q);
1394 case Intrinsic::usub_with_overflow:
1395 case Intrinsic::ssub_with_overflow:
1396 computeKnownBitsAddSub(false, II->getArgOperand(0),
1397 II->getArgOperand(1), false, KnownZero,
1398 KnownOne, KnownZero2, KnownOne2, DL, Depth, Q);
1400 case Intrinsic::umul_with_overflow:
1401 case Intrinsic::smul_with_overflow:
1402 computeKnownBitsMul(II->getArgOperand(0), II->getArgOperand(1), false,
1403 KnownZero, KnownOne, KnownZero2, KnownOne2, DL,
1412 /// Determine which bits of V are known to be either zero or one and return
1413 /// them in the KnownZero/KnownOne bit sets.
1415 /// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
1416 /// we cannot optimize based on the assumption that it is zero without changing
1417 /// it to be an explicit zero. If we don't change it to zero, other code could
1418 /// optimized based on the contradictory assumption that it is non-zero.
1419 /// Because instcombine aggressively folds operations with undef args anyway,
1420 /// this won't lose us code quality.
1422 /// This function is defined on values with integer type, values with pointer
1423 /// type, and vectors of integers. In the case
1424 /// where V is a vector, known zero, and known one values are the
1425 /// same width as the vector element, and the bit is set only if it is true
1426 /// for all of the elements in the vector.
1427 void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
1428 const DataLayout &DL, unsigned Depth, const Query &Q) {
1429 assert(V && "No Value?");
1430 assert(Depth <= MaxDepth && "Limit Search Depth");
1431 unsigned BitWidth = KnownZero.getBitWidth();
1433 assert((V->getType()->isIntOrIntVectorTy() ||
1434 V->getType()->getScalarType()->isPointerTy()) &&
1435 "Not integer or pointer type!");
1436 assert((DL.getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
1437 (!V->getType()->isIntOrIntVectorTy() ||
1438 V->getType()->getScalarSizeInBits() == BitWidth) &&
1439 KnownZero.getBitWidth() == BitWidth &&
1440 KnownOne.getBitWidth() == BitWidth &&
1441 "V, KnownOne and KnownZero should have same BitWidth");
1443 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
1444 // We know all of the bits for a constant!
1445 KnownOne = CI->getValue();
1446 KnownZero = ~KnownOne;
1449 // Null and aggregate-zero are all-zeros.
1450 if (isa<ConstantPointerNull>(V) ||
1451 isa<ConstantAggregateZero>(V)) {
1452 KnownOne.clearAllBits();
1453 KnownZero = APInt::getAllOnesValue(BitWidth);
1456 // Handle a constant vector by taking the intersection of the known bits of
1457 // each element. There is no real need to handle ConstantVector here, because
1458 // we don't handle undef in any particularly useful way.
1459 if (ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(V)) {
1460 // We know that CDS must be a vector of integers. Take the intersection of
1462 KnownZero.setAllBits(); KnownOne.setAllBits();
1463 APInt Elt(KnownZero.getBitWidth(), 0);
1464 for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) {
1465 Elt = CDS->getElementAsInteger(i);
1472 // The address of an aligned GlobalValue has trailing zeros.
1473 if (auto *GO = dyn_cast<GlobalObject>(V)) {
1474 unsigned Align = GO->getAlignment();
1476 if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
1477 Type *ObjectType = GVar->getType()->getElementType();
1478 if (ObjectType->isSized()) {
1479 // If the object is defined in the current Module, we'll be giving
1480 // it the preferred alignment. Otherwise, we have to assume that it
1481 // may only have the minimum ABI alignment.
1482 if (GVar->isStrongDefinitionForLinker())
1483 Align = DL.getPreferredAlignment(GVar);
1485 Align = DL.getABITypeAlignment(ObjectType);
1490 KnownZero = APInt::getLowBitsSet(BitWidth,
1491 countTrailingZeros(Align));
1493 KnownZero.clearAllBits();
1494 KnownOne.clearAllBits();
1498 if (Argument *A = dyn_cast<Argument>(V)) {
1499 unsigned Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0;
1501 if (!Align && A->hasStructRetAttr()) {
1502 // An sret parameter has at least the ABI alignment of the return type.
1503 Type *EltTy = cast<PointerType>(A->getType())->getElementType();
1504 if (EltTy->isSized())
1505 Align = DL.getABITypeAlignment(EltTy);
1509 KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
1511 KnownZero.clearAllBits();
1512 KnownOne.clearAllBits();
1514 // Don't give up yet... there might be an assumption that provides more
1516 computeKnownBitsFromAssume(V, KnownZero, KnownOne, DL, Depth, Q);
1518 // Or a dominating condition for that matter
1519 if (EnableDomConditions && Depth <= DomConditionsMaxDepth)
1520 computeKnownBitsFromDominatingCondition(V, KnownZero, KnownOne, DL,
1525 // Start out not knowing anything.
1526 KnownZero.clearAllBits(); KnownOne.clearAllBits();
1528 // Limit search depth.
1529 // All recursive calls that increase depth must come after this.
1530 if (Depth == MaxDepth)
1533 // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
1534 // the bits of its aliasee.
1535 if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
1536 if (!GA->mayBeOverridden())
1537 computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, DL, Depth + 1, Q);
1541 if (Operator *I = dyn_cast<Operator>(V))
1542 computeKnownBitsFromOperator(I, KnownZero, KnownOne, DL, Depth, Q);
1543 // computeKnownBitsFromAssume and computeKnownBitsFromDominatingCondition
1544 // strictly refines KnownZero and KnownOne. Therefore, we run them after
1545 // computeKnownBitsFromOperator.
1547 // Check whether a nearby assume intrinsic can determine some known bits.
1548 computeKnownBitsFromAssume(V, KnownZero, KnownOne, DL, Depth, Q);
1550 // Check whether there's a dominating condition which implies something about
1551 // this value at the given context.
1552 if (EnableDomConditions && Depth <= DomConditionsMaxDepth)
1553 computeKnownBitsFromDominatingCondition(V, KnownZero, KnownOne, DL, Depth,
1556 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
1559 /// Determine whether the sign bit is known to be zero or one.
1560 /// Convenience wrapper around computeKnownBits.
1561 void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
1562 const DataLayout &DL, unsigned Depth, const Query &Q) {
1563 unsigned BitWidth = getBitWidth(V->getType(), DL);
1569 APInt ZeroBits(BitWidth, 0);
1570 APInt OneBits(BitWidth, 0);
1571 computeKnownBits(V, ZeroBits, OneBits, DL, Depth, Q);
1572 KnownOne = OneBits[BitWidth - 1];
1573 KnownZero = ZeroBits[BitWidth - 1];
1576 /// Return true if the given value is known to have exactly one
1577 /// bit set when defined. For vectors return true if every element is known to
1578 /// be a power of two when defined. Supports values with integer or pointer
1579 /// types and vectors of integers.
1580 bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
1581 const Query &Q, const DataLayout &DL) {
1582 if (Constant *C = dyn_cast<Constant>(V)) {
1583 if (C->isNullValue())
1585 if (ConstantInt *CI = dyn_cast<ConstantInt>(C))
1586 return CI->getValue().isPowerOf2();
1587 // TODO: Handle vector constants.
1590 // 1 << X is clearly a power of two if the one is not shifted off the end. If
1591 // it is shifted off the end then the result is undefined.
1592 if (match(V, m_Shl(m_One(), m_Value())))
1595 // (signbit) >>l X is clearly a power of two if the one is not shifted off the
1596 // bottom. If it is shifted off the bottom then the result is undefined.
1597 if (match(V, m_LShr(m_SignBit(), m_Value())))
1600 // The remaining tests are all recursive, so bail out if we hit the limit.
1601 if (Depth++ == MaxDepth)
1604 Value *X = nullptr, *Y = nullptr;
1605 // A shift of a power of two is a power of two or zero.
1606 if (OrZero && (match(V, m_Shl(m_Value(X), m_Value())) ||
1607 match(V, m_Shr(m_Value(X), m_Value()))))
1608 return isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q, DL);
1610 if (ZExtInst *ZI = dyn_cast<ZExtInst>(V))
1611 return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth, Q, DL);
1613 if (SelectInst *SI = dyn_cast<SelectInst>(V))
1614 return isKnownToBeAPowerOfTwo(SI->getTrueValue(), OrZero, Depth, Q, DL) &&
1615 isKnownToBeAPowerOfTwo(SI->getFalseValue(), OrZero, Depth, Q, DL);
1617 if (OrZero && match(V, m_And(m_Value(X), m_Value(Y)))) {
1618 // A power of two and'd with anything is a power of two or zero.
1619 if (isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q, DL) ||
1620 isKnownToBeAPowerOfTwo(Y, /*OrZero*/ true, Depth, Q, DL))
1622 // X & (-X) is always a power of two or zero.
1623 if (match(X, m_Neg(m_Specific(Y))) || match(Y, m_Neg(m_Specific(X))))
1628 // Adding a power-of-two or zero to the same power-of-two or zero yields
1629 // either the original power-of-two, a larger power-of-two or zero.
1630 if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
1631 OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
1632 if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
1633 if (match(X, m_And(m_Specific(Y), m_Value())) ||
1634 match(X, m_And(m_Value(), m_Specific(Y))))
1635 if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth, Q, DL))
1637 if (match(Y, m_And(m_Specific(X), m_Value())) ||
1638 match(Y, m_And(m_Value(), m_Specific(X))))
1639 if (isKnownToBeAPowerOfTwo(X, OrZero, Depth, Q, DL))
1642 unsigned BitWidth = V->getType()->getScalarSizeInBits();
1643 APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0);
1644 computeKnownBits(X, LHSZeroBits, LHSOneBits, DL, Depth, Q);
1646 APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0);
1647 computeKnownBits(Y, RHSZeroBits, RHSOneBits, DL, Depth, Q);
1648 // If i8 V is a power of two or zero:
1649 // ZeroBits: 1 1 1 0 1 1 1 1
1650 // ~ZeroBits: 0 0 0 1 0 0 0 0
1651 if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2())
1652 // If OrZero isn't set, we cannot give back a zero result.
1653 // Make sure either the LHS or RHS has a bit set.
1654 if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue())
1659 // An exact divide or right shift can only shift off zero bits, so the result
1660 // is a power of two only if the first operand is a power of two and not
1661 // copying a sign bit (sdiv int_min, 2).
1662 if (match(V, m_Exact(m_LShr(m_Value(), m_Value()))) ||
1663 match(V, m_Exact(m_UDiv(m_Value(), m_Value())))) {
1664 return isKnownToBeAPowerOfTwo(cast<Operator>(V)->getOperand(0), OrZero,
1671 /// \brief Test whether a GEP's result is known to be non-null.
1673 /// Uses properties inherent in a GEP to try to determine whether it is known
1676 /// Currently this routine does not support vector GEPs.
1677 static bool isGEPKnownNonNull(GEPOperator *GEP, const DataLayout &DL,
1678 unsigned Depth, const Query &Q) {
1679 if (!GEP->isInBounds() || GEP->getPointerAddressSpace() != 0)
1682 // FIXME: Support vector-GEPs.
1683 assert(GEP->getType()->isPointerTy() && "We only support plain pointer GEP");
1685 // If the base pointer is non-null, we cannot walk to a null address with an
1686 // inbounds GEP in address space zero.
1687 if (isKnownNonZero(GEP->getPointerOperand(), DL, Depth, Q))
1690 // Walk the GEP operands and see if any operand introduces a non-zero offset.
1691 // If so, then the GEP cannot produce a null pointer, as doing so would
1692 // inherently violate the inbounds contract within address space zero.
1693 for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
1694 GTI != GTE; ++GTI) {
1695 // Struct types are easy -- they must always be indexed by a constant.
1696 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
1697 ConstantInt *OpC = cast<ConstantInt>(GTI.getOperand());
1698 unsigned ElementIdx = OpC->getZExtValue();
1699 const StructLayout *SL = DL.getStructLayout(STy);
1700 uint64_t ElementOffset = SL->getElementOffset(ElementIdx);
1701 if (ElementOffset > 0)
1706 // If we have a zero-sized type, the index doesn't matter. Keep looping.
1707 if (DL.getTypeAllocSize(GTI.getIndexedType()) == 0)
1710 // Fast path the constant operand case both for efficiency and so we don't
1711 // increment Depth when just zipping down an all-constant GEP.
1712 if (ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand())) {
1718 // We post-increment Depth here because while isKnownNonZero increments it
1719 // as well, when we pop back up that increment won't persist. We don't want
1720 // to recurse 10k times just because we have 10k GEP operands. We don't
1721 // bail completely out because we want to handle constant GEPs regardless
1723 if (Depth++ >= MaxDepth)
1726 if (isKnownNonZero(GTI.getOperand(), DL, Depth, Q))
1733 /// Does the 'Range' metadata (which must be a valid MD_range operand list)
1734 /// ensure that the value it's attached to is never Value? 'RangeType' is
1735 /// is the type of the value described by the range.
1736 static bool rangeMetadataExcludesValue(MDNode* Ranges,
1737 const APInt& Value) {
1738 const unsigned NumRanges = Ranges->getNumOperands() / 2;
1739 assert(NumRanges >= 1);
1740 for (unsigned i = 0; i < NumRanges; ++i) {
1741 ConstantInt *Lower =
1742 mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 0));
1743 ConstantInt *Upper =
1744 mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 1));
1745 ConstantRange Range(Lower->getValue(), Upper->getValue());
1746 if (Range.contains(Value))
1752 /// Return true if the given value is known to be non-zero when defined.
1753 /// For vectors return true if every element is known to be non-zero when
1754 /// defined. Supports values with integer or pointer type and vectors of
1756 bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth,
1758 if (Constant *C = dyn_cast<Constant>(V)) {
1759 if (C->isNullValue())
1761 if (isa<ConstantInt>(C))
1762 // Must be non-zero due to null test above.
1764 // TODO: Handle vectors
1768 if (Instruction* I = dyn_cast<Instruction>(V)) {
1769 if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) {
1770 // If the possible ranges don't contain zero, then the value is
1771 // definitely non-zero.
1772 if (IntegerType* Ty = dyn_cast<IntegerType>(V->getType())) {
1773 const APInt ZeroValue(Ty->getBitWidth(), 0);
1774 if (rangeMetadataExcludesValue(Ranges, ZeroValue))
1780 // The remaining tests are all recursive, so bail out if we hit the limit.
1781 if (Depth++ >= MaxDepth)
1784 // Check for pointer simplifications.
1785 if (V->getType()->isPointerTy()) {
1786 if (isKnownNonNull(V))
1788 if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
1789 if (isGEPKnownNonNull(GEP, DL, Depth, Q))
1793 unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), DL);
1795 // X | Y != 0 if X != 0 or Y != 0.
1796 Value *X = nullptr, *Y = nullptr;
1797 if (match(V, m_Or(m_Value(X), m_Value(Y))))
1798 return isKnownNonZero(X, DL, Depth, Q) || isKnownNonZero(Y, DL, Depth, Q);
1800 // ext X != 0 if X != 0.
1801 if (isa<SExtInst>(V) || isa<ZExtInst>(V))
1802 return isKnownNonZero(cast<Instruction>(V)->getOperand(0), DL, Depth, Q);
1804 // shl X, Y != 0 if X is odd. Note that the value of the shift is undefined
1805 // if the lowest bit is shifted off the end.
1806 if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
1807 // shl nuw can't remove any non-zero bits.
1808 OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
1809 if (BO->hasNoUnsignedWrap())
1810 return isKnownNonZero(X, DL, Depth, Q);
1812 APInt KnownZero(BitWidth, 0);
1813 APInt KnownOne(BitWidth, 0);
1814 computeKnownBits(X, KnownZero, KnownOne, DL, Depth, Q);
1818 // shr X, Y != 0 if X is negative. Note that the value of the shift is not
1819 // defined if the sign bit is shifted off the end.
1820 else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
1821 // shr exact can only shift out zero bits.
1822 PossiblyExactOperator *BO = cast<PossiblyExactOperator>(V);
1824 return isKnownNonZero(X, DL, Depth, Q);
1826 bool XKnownNonNegative, XKnownNegative;
1827 ComputeSignBit(X, XKnownNonNegative, XKnownNegative, DL, Depth, Q);
1831 // div exact can only produce a zero if the dividend is zero.
1832 else if (match(V, m_Exact(m_IDiv(m_Value(X), m_Value())))) {
1833 return isKnownNonZero(X, DL, Depth, Q);
1836 else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
1837 bool XKnownNonNegative, XKnownNegative;
1838 bool YKnownNonNegative, YKnownNegative;
1839 ComputeSignBit(X, XKnownNonNegative, XKnownNegative, DL, Depth, Q);
1840 ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, DL, Depth, Q);
1842 // If X and Y are both non-negative (as signed values) then their sum is not
1843 // zero unless both X and Y are zero.
1844 if (XKnownNonNegative && YKnownNonNegative)
1845 if (isKnownNonZero(X, DL, Depth, Q) || isKnownNonZero(Y, DL, Depth, Q))
1848 // If X and Y are both negative (as signed values) then their sum is not
1849 // zero unless both X and Y equal INT_MIN.
1850 if (BitWidth && XKnownNegative && YKnownNegative) {
1851 APInt KnownZero(BitWidth, 0);
1852 APInt KnownOne(BitWidth, 0);
1853 APInt Mask = APInt::getSignedMaxValue(BitWidth);
1854 // The sign bit of X is set. If some other bit is set then X is not equal
1856 computeKnownBits(X, KnownZero, KnownOne, DL, Depth, Q);
1857 if ((KnownOne & Mask) != 0)
1859 // The sign bit of Y is set. If some other bit is set then Y is not equal
1861 computeKnownBits(Y, KnownZero, KnownOne, DL, Depth, Q);
1862 if ((KnownOne & Mask) != 0)
1866 // The sum of a non-negative number and a power of two is not zero.
1867 if (XKnownNonNegative &&
1868 isKnownToBeAPowerOfTwo(Y, /*OrZero*/ false, Depth, Q, DL))
1870 if (YKnownNonNegative &&
1871 isKnownToBeAPowerOfTwo(X, /*OrZero*/ false, Depth, Q, DL))
1875 else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) {
1876 OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
1877 // If X and Y are non-zero then so is X * Y as long as the multiplication
1878 // does not overflow.
1879 if ((BO->hasNoSignedWrap() || BO->hasNoUnsignedWrap()) &&
1880 isKnownNonZero(X, DL, Depth, Q) && isKnownNonZero(Y, DL, Depth, Q))
1883 // (C ? X : Y) != 0 if X != 0 and Y != 0.
1884 else if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
1885 if (isKnownNonZero(SI->getTrueValue(), DL, Depth, Q) &&
1886 isKnownNonZero(SI->getFalseValue(), DL, Depth, Q))
1890 if (!BitWidth) return false;
1891 APInt KnownZero(BitWidth, 0);
1892 APInt KnownOne(BitWidth, 0);
1893 computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q);
1894 return KnownOne != 0;
1897 /// Return true if 'V & Mask' is known to be zero. We use this predicate to
1898 /// simplify operations downstream. Mask is known to be zero for bits that V
1901 /// This function is defined on values with integer type, values with pointer
1902 /// type, and vectors of integers. In the case
1903 /// where V is a vector, the mask, known zero, and known one values are the
1904 /// same width as the vector element, and the bit is set only if it is true
1905 /// for all of the elements in the vector.
1906 bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
1907 unsigned Depth, const Query &Q) {
1908 APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
1909 computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q);
1910 return (KnownZero & Mask) == Mask;
1915 /// Return the number of times the sign bit of the register is replicated into
1916 /// the other bits. We know that at least 1 bit is always equal to the sign bit
1917 /// (itself), but other cases can give us information. For example, immediately
1918 /// after an "ashr X, 2", we know that the top 3 bits are all equal to each
1919 /// other, so we return 3.
1921 /// 'Op' must have a scalar integer type.
1923 unsigned ComputeNumSignBits(Value *V, const DataLayout &DL, unsigned Depth,
1925 unsigned TyBits = DL.getTypeSizeInBits(V->getType()->getScalarType());
1927 unsigned FirstAnswer = 1;
1929 // Note that ConstantInt is handled by the general computeKnownBits case
1933 return 1; // Limit search depth.
1935 Operator *U = dyn_cast<Operator>(V);
1936 switch (Operator::getOpcode(V)) {
1938 case Instruction::SExt:
1939 Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits();
1940 return ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q) + Tmp;
1942 case Instruction::SDiv: {
1943 const APInt *Denominator;
1944 // sdiv X, C -> adds log(C) sign bits.
1945 if (match(U->getOperand(1), m_APInt(Denominator))) {
1947 // Ignore non-positive denominator.
1948 if (!Denominator->isStrictlyPositive())
1951 // Calculate the incoming numerator bits.
1952 unsigned NumBits = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1954 // Add floor(log(C)) bits to the numerator bits.
1955 return std::min(TyBits, NumBits + Denominator->logBase2());
1960 case Instruction::SRem: {
1961 const APInt *Denominator;
1962 // srem X, C -> we know that the result is within [-C+1,C) when C is a
1963 // positive constant. This let us put a lower bound on the number of sign
1965 if (match(U->getOperand(1), m_APInt(Denominator))) {
1967 // Ignore non-positive denominator.
1968 if (!Denominator->isStrictlyPositive())
1971 // Calculate the incoming numerator bits. SRem by a positive constant
1972 // can't lower the number of sign bits.
1974 ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1976 // Calculate the leading sign bit constraints by examining the
1977 // denominator. Given that the denominator is positive, there are two
1980 // 1. the numerator is positive. The result range is [0,C) and [0,C) u<
1981 // (1 << ceilLogBase2(C)).
1983 // 2. the numerator is negative. Then the result range is (-C,0] and
1984 // integers in (-C,0] are either 0 or >u (-1 << ceilLogBase2(C)).
1986 // Thus a lower bound on the number of sign bits is `TyBits -
1987 // ceilLogBase2(C)`.
1989 unsigned ResBits = TyBits - Denominator->ceilLogBase2();
1990 return std::max(NumrBits, ResBits);
1995 case Instruction::AShr: {
1996 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1997 // ashr X, C -> adds C sign bits. Vectors too.
1999 if (match(U->getOperand(1), m_APInt(ShAmt))) {
2000 Tmp += ShAmt->getZExtValue();
2001 if (Tmp > TyBits) Tmp = TyBits;
2005 case Instruction::Shl: {
2007 if (match(U->getOperand(1), m_APInt(ShAmt))) {
2008 // shl destroys sign bits.
2009 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
2010 Tmp2 = ShAmt->getZExtValue();
2011 if (Tmp2 >= TyBits || // Bad shift.
2012 Tmp2 >= Tmp) break; // Shifted all sign bits out.
2017 case Instruction::And:
2018 case Instruction::Or:
2019 case Instruction::Xor: // NOT is handled here.
2020 // Logical binary ops preserve the number of sign bits at the worst.
2021 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
2023 Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q);
2024 FirstAnswer = std::min(Tmp, Tmp2);
2025 // We computed what we know about the sign bits as our first
2026 // answer. Now proceed to the generic code that uses
2027 // computeKnownBits, and pick whichever answer is better.
2031 case Instruction::Select:
2032 Tmp = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q);
2033 if (Tmp == 1) return 1; // Early out.
2034 Tmp2 = ComputeNumSignBits(U->getOperand(2), DL, Depth + 1, Q);
2035 return std::min(Tmp, Tmp2);
2037 case Instruction::Add:
2038 // Add can have at most one carry bit. Thus we know that the output
2039 // is, at worst, one more bit than the inputs.
2040 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
2041 if (Tmp == 1) return 1; // Early out.
2043 // Special case decrementing a value (ADD X, -1):
2044 if (const auto *CRHS = dyn_cast<Constant>(U->getOperand(1)))
2045 if (CRHS->isAllOnesValue()) {
2046 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
2047 computeKnownBits(U->getOperand(0), KnownZero, KnownOne, DL, Depth + 1,
2050 // If the input is known to be 0 or 1, the output is 0/-1, which is all
2052 if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
2055 // If we are subtracting one from a positive number, there is no carry
2056 // out of the result.
2057 if (KnownZero.isNegative())
2061 Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q);
2062 if (Tmp2 == 1) return 1;
2063 return std::min(Tmp, Tmp2)-1;
2065 case Instruction::Sub:
2066 Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q);
2067 if (Tmp2 == 1) return 1;
2070 if (const auto *CLHS = dyn_cast<Constant>(U->getOperand(0)))
2071 if (CLHS->isNullValue()) {
2072 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
2073 computeKnownBits(U->getOperand(1), KnownZero, KnownOne, DL, Depth + 1,
2075 // If the input is known to be 0 or 1, the output is 0/-1, which is all
2077 if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
2080 // If the input is known to be positive (the sign bit is known clear),
2081 // the output of the NEG has the same number of sign bits as the input.
2082 if (KnownZero.isNegative())
2085 // Otherwise, we treat this like a SUB.
2088 // Sub can have at most one carry bit. Thus we know that the output
2089 // is, at worst, one more bit than the inputs.
2090 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
2091 if (Tmp == 1) return 1; // Early out.
2092 return std::min(Tmp, Tmp2)-1;
2094 case Instruction::PHI: {
2095 PHINode *PN = cast<PHINode>(U);
2096 unsigned NumIncomingValues = PN->getNumIncomingValues();
2097 // Don't analyze large in-degree PHIs.
2098 if (NumIncomingValues > 4) break;
2099 // Unreachable blocks may have zero-operand PHI nodes.
2100 if (NumIncomingValues == 0) break;
2102 // Take the minimum of all incoming values. This can't infinitely loop
2103 // because of our depth threshold.
2104 Tmp = ComputeNumSignBits(PN->getIncomingValue(0), DL, Depth + 1, Q);
2105 for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) {
2106 if (Tmp == 1) return Tmp;
2108 Tmp, ComputeNumSignBits(PN->getIncomingValue(i), DL, Depth + 1, Q));
2113 case Instruction::Trunc:
2114 // FIXME: it's tricky to do anything useful for this, but it is an important
2115 // case for targets like X86.
2119 // Finally, if we can prove that the top bits of the result are 0's or 1's,
2120 // use this information.
2121 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
2123 computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q);
2125 if (KnownZero.isNegative()) { // sign bit is 0
2127 } else if (KnownOne.isNegative()) { // sign bit is 1;
2134 // Okay, we know that the sign bit in Mask is set. Use CLZ to determine
2135 // the number of identical bits in the top of the input value.
2137 Mask <<= Mask.getBitWidth()-TyBits;
2138 // Return # leading zeros. We use 'min' here in case Val was zero before
2139 // shifting. We don't want to return '64' as for an i32 "0".
2140 return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
2143 /// This function computes the integer multiple of Base that equals V.
2144 /// If successful, it returns true and returns the multiple in
2145 /// Multiple. If unsuccessful, it returns false. It looks
2146 /// through SExt instructions only if LookThroughSExt is true.
2147 bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
2148 bool LookThroughSExt, unsigned Depth) {
2149 const unsigned MaxDepth = 6;
2151 assert(V && "No Value?");
2152 assert(Depth <= MaxDepth && "Limit Search Depth");
2153 assert(V->getType()->isIntegerTy() && "Not integer or pointer type!");
2155 Type *T = V->getType();
2157 ConstantInt *CI = dyn_cast<ConstantInt>(V);
2167 ConstantExpr *CO = dyn_cast<ConstantExpr>(V);
2168 Constant *BaseVal = ConstantInt::get(T, Base);
2169 if (CO && CO == BaseVal) {
2171 Multiple = ConstantInt::get(T, 1);
2175 if (CI && CI->getZExtValue() % Base == 0) {
2176 Multiple = ConstantInt::get(T, CI->getZExtValue() / Base);
2180 if (Depth == MaxDepth) return false; // Limit search depth.
2182 Operator *I = dyn_cast<Operator>(V);
2183 if (!I) return false;
2185 switch (I->getOpcode()) {
2187 case Instruction::SExt:
2188 if (!LookThroughSExt) return false;
2189 // otherwise fall through to ZExt
2190 case Instruction::ZExt:
2191 return ComputeMultiple(I->getOperand(0), Base, Multiple,
2192 LookThroughSExt, Depth+1);
2193 case Instruction::Shl:
2194 case Instruction::Mul: {
2195 Value *Op0 = I->getOperand(0);
2196 Value *Op1 = I->getOperand(1);
2198 if (I->getOpcode() == Instruction::Shl) {
2199 ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1);
2200 if (!Op1CI) return false;
2201 // Turn Op0 << Op1 into Op0 * 2^Op1
2202 APInt Op1Int = Op1CI->getValue();
2203 uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1);
2204 APInt API(Op1Int.getBitWidth(), 0);
2205 API.setBit(BitToSet);
2206 Op1 = ConstantInt::get(V->getContext(), API);
2209 Value *Mul0 = nullptr;
2210 if (ComputeMultiple(Op0, Base, Mul0, LookThroughSExt, Depth+1)) {
2211 if (Constant *Op1C = dyn_cast<Constant>(Op1))
2212 if (Constant *MulC = dyn_cast<Constant>(Mul0)) {
2213 if (Op1C->getType()->getPrimitiveSizeInBits() <
2214 MulC->getType()->getPrimitiveSizeInBits())
2215 Op1C = ConstantExpr::getZExt(Op1C, MulC->getType());
2216 if (Op1C->getType()->getPrimitiveSizeInBits() >
2217 MulC->getType()->getPrimitiveSizeInBits())
2218 MulC = ConstantExpr::getZExt(MulC, Op1C->getType());
2220 // V == Base * (Mul0 * Op1), so return (Mul0 * Op1)
2221 Multiple = ConstantExpr::getMul(MulC, Op1C);
2225 if (ConstantInt *Mul0CI = dyn_cast<ConstantInt>(Mul0))
2226 if (Mul0CI->getValue() == 1) {
2227 // V == Base * Op1, so return Op1
2233 Value *Mul1 = nullptr;
2234 if (ComputeMultiple(Op1, Base, Mul1, LookThroughSExt, Depth+1)) {
2235 if (Constant *Op0C = dyn_cast<Constant>(Op0))
2236 if (Constant *MulC = dyn_cast<Constant>(Mul1)) {
2237 if (Op0C->getType()->getPrimitiveSizeInBits() <
2238 MulC->getType()->getPrimitiveSizeInBits())
2239 Op0C = ConstantExpr::getZExt(Op0C, MulC->getType());
2240 if (Op0C->getType()->getPrimitiveSizeInBits() >
2241 MulC->getType()->getPrimitiveSizeInBits())
2242 MulC = ConstantExpr::getZExt(MulC, Op0C->getType());
2244 // V == Base * (Mul1 * Op0), so return (Mul1 * Op0)
2245 Multiple = ConstantExpr::getMul(MulC, Op0C);
2249 if (ConstantInt *Mul1CI = dyn_cast<ConstantInt>(Mul1))
2250 if (Mul1CI->getValue() == 1) {
2251 // V == Base * Op0, so return Op0
2259 // We could not determine if V is a multiple of Base.
2263 /// Return true if we can prove that the specified FP value is never equal to
2266 /// NOTE: this function will need to be revisited when we support non-default
2269 bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
2270 if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
2271 return !CFP->getValueAPF().isNegZero();
2273 // FIXME: Magic number! At the least, this should be given a name because it's
2274 // used similarly in CannotBeOrderedLessThanZero(). A better fix may be to
2275 // expose it as a parameter, so it can be used for testing / experimenting.
2277 return false; // Limit search depth.
2279 const Operator *I = dyn_cast<Operator>(V);
2280 if (!I) return false;
2282 // Check if the nsz fast-math flag is set
2283 if (const FPMathOperator *FPO = dyn_cast<FPMathOperator>(I))
2284 if (FPO->hasNoSignedZeros())
2287 // (add x, 0.0) is guaranteed to return +0.0, not -0.0.
2288 if (I->getOpcode() == Instruction::FAdd)
2289 if (ConstantFP *CFP = dyn_cast<ConstantFP>(I->getOperand(1)))
2290 if (CFP->isNullValue())
2293 // sitofp and uitofp turn into +0.0 for zero.
2294 if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
2297 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
2298 // sqrt(-0.0) = -0.0, no other negative results are possible.
2299 if (II->getIntrinsicID() == Intrinsic::sqrt)
2300 return CannotBeNegativeZero(II->getArgOperand(0), Depth+1);
2302 if (const CallInst *CI = dyn_cast<CallInst>(I))
2303 if (const Function *F = CI->getCalledFunction()) {
2304 if (F->isDeclaration()) {
2306 if (F->getName() == "abs") return true;
2307 // fabs[lf](x) != -0.0
2308 if (F->getName() == "fabs") return true;
2309 if (F->getName() == "fabsf") return true;
2310 if (F->getName() == "fabsl") return true;
2311 if (F->getName() == "sqrt" || F->getName() == "sqrtf" ||
2312 F->getName() == "sqrtl")
2313 return CannotBeNegativeZero(CI->getArgOperand(0), Depth+1);
2320 bool llvm::CannotBeOrderedLessThanZero(const Value *V, unsigned Depth) {
2321 if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
2322 return !CFP->getValueAPF().isNegative() || CFP->getValueAPF().isZero();
2324 // FIXME: Magic number! At the least, this should be given a name because it's
2325 // used similarly in CannotBeNegativeZero(). A better fix may be to
2326 // expose it as a parameter, so it can be used for testing / experimenting.
2328 return false; // Limit search depth.
2330 const Operator *I = dyn_cast<Operator>(V);
2331 if (!I) return false;
2333 switch (I->getOpcode()) {
2335 case Instruction::FMul:
2336 // x*x is always non-negative or a NaN.
2337 if (I->getOperand(0) == I->getOperand(1))
2340 case Instruction::FAdd:
2341 case Instruction::FDiv:
2342 case Instruction::FRem:
2343 return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1) &&
2344 CannotBeOrderedLessThanZero(I->getOperand(1), Depth+1);
2345 case Instruction::FPExt:
2346 case Instruction::FPTrunc:
2347 // Widening/narrowing never change sign.
2348 return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1);
2349 case Instruction::Call:
2350 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
2351 switch (II->getIntrinsicID()) {
2353 case Intrinsic::exp:
2354 case Intrinsic::exp2:
2355 case Intrinsic::fabs:
2356 case Intrinsic::sqrt:
2358 case Intrinsic::powi:
2359 if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
2360 // powi(x,n) is non-negative if n is even.
2361 if (CI->getBitWidth() <= 64 && CI->getSExtValue() % 2u == 0)
2364 return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1);
2365 case Intrinsic::fma:
2366 case Intrinsic::fmuladd:
2367 // x*x+y is non-negative if y is non-negative.
2368 return I->getOperand(0) == I->getOperand(1) &&
2369 CannotBeOrderedLessThanZero(I->getOperand(2), Depth+1);
2376 /// If the specified value can be set by repeating the same byte in memory,
2377 /// return the i8 value that it is represented with. This is
2378 /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
2379 /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
2380 /// byte store (e.g. i16 0x1234), return null.
2381 Value *llvm::isBytewiseValue(Value *V) {
2382 // All byte-wide stores are splatable, even of arbitrary variables.
2383 if (V->getType()->isIntegerTy(8)) return V;
2385 // Handle 'null' ConstantArrayZero etc.
2386 if (Constant *C = dyn_cast<Constant>(V))
2387 if (C->isNullValue())
2388 return Constant::getNullValue(Type::getInt8Ty(V->getContext()));
2390 // Constant float and double values can be handled as integer values if the
2391 // corresponding integer value is "byteable". An important case is 0.0.
2392 if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
2393 if (CFP->getType()->isFloatTy())
2394 V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(V->getContext()));
2395 if (CFP->getType()->isDoubleTy())
2396 V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext()));
2397 // Don't handle long double formats, which have strange constraints.
2400 // We can handle constant integers that are multiple of 8 bits.
2401 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
2402 if (CI->getBitWidth() % 8 == 0) {
2403 assert(CI->getBitWidth() > 8 && "8 bits should be handled above!");
2405 if (!CI->getValue().isSplat(8))
2407 return ConstantInt::get(V->getContext(), CI->getValue().trunc(8));
2411 // A ConstantDataArray/Vector is splatable if all its members are equal and
2413 if (ConstantDataSequential *CA = dyn_cast<ConstantDataSequential>(V)) {
2414 Value *Elt = CA->getElementAsConstant(0);
2415 Value *Val = isBytewiseValue(Elt);
2419 for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I)
2420 if (CA->getElementAsConstant(I) != Elt)
2426 // Conceptually, we could handle things like:
2427 // %a = zext i8 %X to i16
2428 // %b = shl i16 %a, 8
2429 // %c = or i16 %a, %b
2430 // but until there is an example that actually needs this, it doesn't seem
2431 // worth worrying about.
2436 // This is the recursive version of BuildSubAggregate. It takes a few different
2437 // arguments. Idxs is the index within the nested struct From that we are
2438 // looking at now (which is of type IndexedType). IdxSkip is the number of
2439 // indices from Idxs that should be left out when inserting into the resulting
2440 // struct. To is the result struct built so far, new insertvalue instructions
2442 static Value *BuildSubAggregate(Value *From, Value* To, Type *IndexedType,
2443 SmallVectorImpl<unsigned> &Idxs,
2445 Instruction *InsertBefore) {
2446 llvm::StructType *STy = dyn_cast<llvm::StructType>(IndexedType);
2448 // Save the original To argument so we can modify it
2450 // General case, the type indexed by Idxs is a struct
2451 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
2452 // Process each struct element recursively
2455 To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip,
2459 // Couldn't find any inserted value for this index? Cleanup
2460 while (PrevTo != OrigTo) {
2461 InsertValueInst* Del = cast<InsertValueInst>(PrevTo);
2462 PrevTo = Del->getAggregateOperand();
2463 Del->eraseFromParent();
2465 // Stop processing elements
2469 // If we successfully found a value for each of our subaggregates
2473 // Base case, the type indexed by SourceIdxs is not a struct, or not all of
2474 // the struct's elements had a value that was inserted directly. In the latter
2475 // case, perhaps we can't determine each of the subelements individually, but
2476 // we might be able to find the complete struct somewhere.
2478 // Find the value that is at that particular spot
2479 Value *V = FindInsertedValue(From, Idxs);
2484 // Insert the value in the new (sub) aggregrate
2485 return llvm::InsertValueInst::Create(To, V, makeArrayRef(Idxs).slice(IdxSkip),
2486 "tmp", InsertBefore);
2489 // This helper takes a nested struct and extracts a part of it (which is again a
2490 // struct) into a new value. For example, given the struct:
2491 // { a, { b, { c, d }, e } }
2492 // and the indices "1, 1" this returns
2495 // It does this by inserting an insertvalue for each element in the resulting
2496 // struct, as opposed to just inserting a single struct. This will only work if
2497 // each of the elements of the substruct are known (ie, inserted into From by an
2498 // insertvalue instruction somewhere).
2500 // All inserted insertvalue instructions are inserted before InsertBefore
2501 static Value *BuildSubAggregate(Value *From, ArrayRef<unsigned> idx_range,
2502 Instruction *InsertBefore) {
2503 assert(InsertBefore && "Must have someplace to insert!");
2504 Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(),
2506 Value *To = UndefValue::get(IndexedType);
2507 SmallVector<unsigned, 10> Idxs(idx_range.begin(), idx_range.end());
2508 unsigned IdxSkip = Idxs.size();
2510 return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore);
2513 /// Given an aggregrate and an sequence of indices, see if
2514 /// the scalar value indexed is already around as a register, for example if it
2515 /// were inserted directly into the aggregrate.
2517 /// If InsertBefore is not null, this function will duplicate (modified)
2518 /// insertvalues when a part of a nested struct is extracted.
2519 Value *llvm::FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range,
2520 Instruction *InsertBefore) {
2521 // Nothing to index? Just return V then (this is useful at the end of our
2523 if (idx_range.empty())
2525 // We have indices, so V should have an indexable type.
2526 assert((V->getType()->isStructTy() || V->getType()->isArrayTy()) &&
2527 "Not looking at a struct or array?");
2528 assert(ExtractValueInst::getIndexedType(V->getType(), idx_range) &&
2529 "Invalid indices for type?");
2531 if (Constant *C = dyn_cast<Constant>(V)) {
2532 C = C->getAggregateElement(idx_range[0]);
2533 if (!C) return nullptr;
2534 return FindInsertedValue(C, idx_range.slice(1), InsertBefore);
2537 if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) {
2538 // Loop the indices for the insertvalue instruction in parallel with the
2539 // requested indices
2540 const unsigned *req_idx = idx_range.begin();
2541 for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
2542 i != e; ++i, ++req_idx) {
2543 if (req_idx == idx_range.end()) {
2544 // We can't handle this without inserting insertvalues
2548 // The requested index identifies a part of a nested aggregate. Handle
2549 // this specially. For example,
2550 // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
2551 // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
2552 // %C = extractvalue {i32, { i32, i32 } } %B, 1
2553 // This can be changed into
2554 // %A = insertvalue {i32, i32 } undef, i32 10, 0
2555 // %C = insertvalue {i32, i32 } %A, i32 11, 1
2556 // which allows the unused 0,0 element from the nested struct to be
2558 return BuildSubAggregate(V, makeArrayRef(idx_range.begin(), req_idx),
2562 // This insert value inserts something else than what we are looking for.
2563 // See if the (aggregate) value inserted into has the value we are
2564 // looking for, then.
2566 return FindInsertedValue(I->getAggregateOperand(), idx_range,
2569 // If we end up here, the indices of the insertvalue match with those
2570 // requested (though possibly only partially). Now we recursively look at
2571 // the inserted value, passing any remaining indices.
2572 return FindInsertedValue(I->getInsertedValueOperand(),
2573 makeArrayRef(req_idx, idx_range.end()),
2577 if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) {
2578 // If we're extracting a value from an aggregate that was extracted from
2579 // something else, we can extract from that something else directly instead.
2580 // However, we will need to chain I's indices with the requested indices.
2582 // Calculate the number of indices required
2583 unsigned size = I->getNumIndices() + idx_range.size();
2584 // Allocate some space to put the new indices in
2585 SmallVector<unsigned, 5> Idxs;
2587 // Add indices from the extract value instruction
2588 Idxs.append(I->idx_begin(), I->idx_end());
2590 // Add requested indices
2591 Idxs.append(idx_range.begin(), idx_range.end());
2593 assert(Idxs.size() == size
2594 && "Number of indices added not correct?");
2596 return FindInsertedValue(I->getAggregateOperand(), Idxs, InsertBefore);
2598 // Otherwise, we don't know (such as, extracting from a function return value
2599 // or load instruction)
2603 /// Analyze the specified pointer to see if it can be expressed as a base
2604 /// pointer plus a constant offset. Return the base and offset to the caller.
2605 Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
2606 const DataLayout &DL) {
2607 unsigned BitWidth = DL.getPointerTypeSizeInBits(Ptr->getType());
2608 APInt ByteOffset(BitWidth, 0);
2610 if (Ptr->getType()->isVectorTy())
2613 if (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
2614 APInt GEPOffset(BitWidth, 0);
2615 if (!GEP->accumulateConstantOffset(DL, GEPOffset))
2618 ByteOffset += GEPOffset;
2620 Ptr = GEP->getPointerOperand();
2621 } else if (Operator::getOpcode(Ptr) == Instruction::BitCast ||
2622 Operator::getOpcode(Ptr) == Instruction::AddrSpaceCast) {
2623 Ptr = cast<Operator>(Ptr)->getOperand(0);
2624 } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
2625 if (GA->mayBeOverridden())
2627 Ptr = GA->getAliasee();
2632 Offset = ByteOffset.getSExtValue();
2637 /// This function computes the length of a null-terminated C string pointed to
2638 /// by V. If successful, it returns true and returns the string in Str.
2639 /// If unsuccessful, it returns false.
2640 bool llvm::getConstantStringInfo(const Value *V, StringRef &Str,
2641 uint64_t Offset, bool TrimAtNul) {
2644 // Look through bitcast instructions and geps.
2645 V = V->stripPointerCasts();
2647 // If the value is a GEP instruction or constant expression, treat it as an
2649 if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
2650 // Make sure the GEP has exactly three arguments.
2651 if (GEP->getNumOperands() != 3)
2654 // Make sure the index-ee is a pointer to array of i8.
2655 PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType());
2656 ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType());
2657 if (!AT || !AT->getElementType()->isIntegerTy(8))
2660 // Check to make sure that the first operand of the GEP is an integer and
2661 // has value 0 so that we are sure we're indexing into the initializer.
2662 const ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
2663 if (!FirstIdx || !FirstIdx->isZero())
2666 // If the second index isn't a ConstantInt, then this is a variable index
2667 // into the array. If this occurs, we can't say anything meaningful about
2669 uint64_t StartIdx = 0;
2670 if (const ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
2671 StartIdx = CI->getZExtValue();
2674 return getConstantStringInfo(GEP->getOperand(0), Str, StartIdx + Offset,
2678 // The GEP instruction, constant or instruction, must reference a global
2679 // variable that is a constant and is initialized. The referenced constant
2680 // initializer is the array that we'll use for optimization.
2681 const GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
2682 if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
2685 // Handle the all-zeros case
2686 if (GV->getInitializer()->isNullValue()) {
2687 // This is a degenerate case. The initializer is constant zero so the
2688 // length of the string must be zero.
2693 // Must be a Constant Array
2694 const ConstantDataArray *Array =
2695 dyn_cast<ConstantDataArray>(GV->getInitializer());
2696 if (!Array || !Array->isString())
2699 // Get the number of elements in the array
2700 uint64_t NumElts = Array->getType()->getArrayNumElements();
2702 // Start out with the entire array in the StringRef.
2703 Str = Array->getAsString();
2705 if (Offset > NumElts)
2708 // Skip over 'offset' bytes.
2709 Str = Str.substr(Offset);
2712 // Trim off the \0 and anything after it. If the array is not nul
2713 // terminated, we just return the whole end of string. The client may know
2714 // some other way that the string is length-bound.
2715 Str = Str.substr(0, Str.find('\0'));
2720 // These next two are very similar to the above, but also look through PHI
2722 // TODO: See if we can integrate these two together.
2724 /// If we can compute the length of the string pointed to by
2725 /// the specified pointer, return 'len+1'. If we can't, return 0.
2726 static uint64_t GetStringLengthH(Value *V, SmallPtrSetImpl<PHINode*> &PHIs) {
2727 // Look through noop bitcast instructions.
2728 V = V->stripPointerCasts();
2730 // If this is a PHI node, there are two cases: either we have already seen it
2732 if (PHINode *PN = dyn_cast<PHINode>(V)) {
2733 if (!PHIs.insert(PN).second)
2734 return ~0ULL; // already in the set.
2736 // If it was new, see if all the input strings are the same length.
2737 uint64_t LenSoFar = ~0ULL;
2738 for (Value *IncValue : PN->incoming_values()) {
2739 uint64_t Len = GetStringLengthH(IncValue, PHIs);
2740 if (Len == 0) return 0; // Unknown length -> unknown.
2742 if (Len == ~0ULL) continue;
2744 if (Len != LenSoFar && LenSoFar != ~0ULL)
2745 return 0; // Disagree -> unknown.
2749 // Success, all agree.
2753 // strlen(select(c,x,y)) -> strlen(x) ^ strlen(y)
2754 if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
2755 uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs);
2756 if (Len1 == 0) return 0;
2757 uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs);
2758 if (Len2 == 0) return 0;
2759 if (Len1 == ~0ULL) return Len2;
2760 if (Len2 == ~0ULL) return Len1;
2761 if (Len1 != Len2) return 0;
2765 // Otherwise, see if we can read the string.
2767 if (!getConstantStringInfo(V, StrData))
2770 return StrData.size()+1;
2773 /// If we can compute the length of the string pointed to by
2774 /// the specified pointer, return 'len+1'. If we can't, return 0.
2775 uint64_t llvm::GetStringLength(Value *V) {
2776 if (!V->getType()->isPointerTy()) return 0;
2778 SmallPtrSet<PHINode*, 32> PHIs;
2779 uint64_t Len = GetStringLengthH(V, PHIs);
2780 // If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return
2781 // an empty string as a length.
2782 return Len == ~0ULL ? 1 : Len;
2785 /// \brief \p PN defines a loop-variant pointer to an object. Check if the
2786 /// previous iteration of the loop was referring to the same object as \p PN.
2787 static bool isSameUnderlyingObjectInLoop(PHINode *PN, LoopInfo *LI) {
2788 // Find the loop-defined value.
2789 Loop *L = LI->getLoopFor(PN->getParent());
2790 if (PN->getNumIncomingValues() != 2)
2793 // Find the value from previous iteration.
2794 auto *PrevValue = dyn_cast<Instruction>(PN->getIncomingValue(0));
2795 if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L)
2796 PrevValue = dyn_cast<Instruction>(PN->getIncomingValue(1));
2797 if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L)
2800 // If a new pointer is loaded in the loop, the pointer references a different
2801 // object in every iteration. E.g.:
2805 if (auto *Load = dyn_cast<LoadInst>(PrevValue))
2806 if (!L->isLoopInvariant(Load->getPointerOperand()))
2811 Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
2812 unsigned MaxLookup) {
2813 if (!V->getType()->isPointerTy())
2815 for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
2816 if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
2817 V = GEP->getPointerOperand();
2818 } else if (Operator::getOpcode(V) == Instruction::BitCast ||
2819 Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
2820 V = cast<Operator>(V)->getOperand(0);
2821 } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
2822 if (GA->mayBeOverridden())
2824 V = GA->getAliasee();
2826 // See if InstructionSimplify knows any relevant tricks.
2827 if (Instruction *I = dyn_cast<Instruction>(V))
2828 // TODO: Acquire a DominatorTree and AssumptionCache and use them.
2829 if (Value *Simplified = SimplifyInstruction(I, DL, nullptr)) {
2836 assert(V->getType()->isPointerTy() && "Unexpected operand type!");
2841 void llvm::GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
2842 const DataLayout &DL, LoopInfo *LI,
2843 unsigned MaxLookup) {
2844 SmallPtrSet<Value *, 4> Visited;
2845 SmallVector<Value *, 4> Worklist;
2846 Worklist.push_back(V);
2848 Value *P = Worklist.pop_back_val();
2849 P = GetUnderlyingObject(P, DL, MaxLookup);
2851 if (!Visited.insert(P).second)
2854 if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
2855 Worklist.push_back(SI->getTrueValue());
2856 Worklist.push_back(SI->getFalseValue());
2860 if (PHINode *PN = dyn_cast<PHINode>(P)) {
2861 // If this PHI changes the underlying object in every iteration of the
2862 // loop, don't look through it. Consider:
2865 // Prev = Curr; // Prev = PHI (Prev_0, Curr)
2869 // Prev is tracking Curr one iteration behind so they refer to different
2870 // underlying objects.
2871 if (!LI || !LI->isLoopHeader(PN->getParent()) ||
2872 isSameUnderlyingObjectInLoop(PN, LI))
2873 for (Value *IncValue : PN->incoming_values())
2874 Worklist.push_back(IncValue);
2878 Objects.push_back(P);
2879 } while (!Worklist.empty());
2882 /// Return true if the only users of this pointer are lifetime markers.
2883 bool llvm::onlyUsedByLifetimeMarkers(const Value *V) {
2884 for (const User *U : V->users()) {
2885 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U);
2886 if (!II) return false;
2888 if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
2889 II->getIntrinsicID() != Intrinsic::lifetime_end)
2895 static bool isDereferenceableFromAttribute(const Value *BV, APInt Offset,
2896 Type *Ty, const DataLayout &DL,
2897 const Instruction *CtxI,
2898 const DominatorTree *DT,
2899 const TargetLibraryInfo *TLI) {
2900 assert(Offset.isNonNegative() && "offset can't be negative");
2901 assert(Ty->isSized() && "must be sized");
2903 APInt DerefBytes(Offset.getBitWidth(), 0);
2904 bool CheckForNonNull = false;
2905 if (const Argument *A = dyn_cast<Argument>(BV)) {
2906 DerefBytes = A->getDereferenceableBytes();
2907 if (!DerefBytes.getBoolValue()) {
2908 DerefBytes = A->getDereferenceableOrNullBytes();
2909 CheckForNonNull = true;
2911 } else if (auto CS = ImmutableCallSite(BV)) {
2912 DerefBytes = CS.getDereferenceableBytes(0);
2913 if (!DerefBytes.getBoolValue()) {
2914 DerefBytes = CS.getDereferenceableOrNullBytes(0);
2915 CheckForNonNull = true;
2917 } else if (const LoadInst *LI = dyn_cast<LoadInst>(BV)) {
2918 if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
2919 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
2920 DerefBytes = CI->getLimitedValue();
2922 if (!DerefBytes.getBoolValue()) {
2924 LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
2925 ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
2926 DerefBytes = CI->getLimitedValue();
2928 CheckForNonNull = true;
2932 if (DerefBytes.getBoolValue())
2933 if (DerefBytes.uge(Offset + DL.getTypeStoreSize(Ty)))
2934 if (!CheckForNonNull || isKnownNonNullAt(BV, CtxI, DT, TLI))
2940 static bool isDereferenceableFromAttribute(const Value *V, const DataLayout &DL,
2941 const Instruction *CtxI,
2942 const DominatorTree *DT,
2943 const TargetLibraryInfo *TLI) {
2944 Type *VTy = V->getType();
2945 Type *Ty = VTy->getPointerElementType();
2949 APInt Offset(DL.getTypeStoreSizeInBits(VTy), 0);
2950 return isDereferenceableFromAttribute(V, Offset, Ty, DL, CtxI, DT, TLI);
2953 static bool isAligned(const Value *Base, APInt Offset, unsigned Align,
2954 const DataLayout &DL) {
2955 APInt BaseAlign(Offset.getBitWidth(), 0);
2956 if (const AllocaInst *AI = dyn_cast<AllocaInst>(Base))
2957 BaseAlign = AI->getAlignment();
2958 else if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Base))
2959 BaseAlign = GV->getAlignment();
2960 else if (const Argument *A = dyn_cast<Argument>(Base))
2961 BaseAlign = A->getParamAlignment();
2962 else if (auto CS = ImmutableCallSite(Base))
2963 BaseAlign = CS.getAttributes().getParamAlignment(AttributeSet::ReturnIndex);
2966 Type *Ty = Base->getType()->getPointerElementType();
2967 BaseAlign = DL.getABITypeAlignment(Ty);
2970 APInt Alignment(Offset.getBitWidth(), Align);
2972 assert(Alignment.isPowerOf2() && "must be a power of 2!");
2973 return BaseAlign.uge(Alignment) && !(Offset & (Alignment-1));
2976 static bool isAligned(const Value *Base, unsigned Align, const DataLayout &DL) {
2977 APInt Offset(DL.getTypeStoreSizeInBits(Base->getType()), 0);
2978 return isAligned(Base, Offset, Align, DL);
2981 /// Test if V is always a pointer to allocated and suitably aligned memory for
2982 /// a simple load or store.
2983 static bool isDereferenceableAndAlignedPointer(
2984 const Value *V, unsigned Align, const DataLayout &DL,
2985 const Instruction *CtxI, const DominatorTree *DT,
2986 const TargetLibraryInfo *TLI, SmallPtrSetImpl<const Value *> &Visited) {
2987 // Note that it is not safe to speculate into a malloc'd region because
2988 // malloc may return null.
2990 // These are obviously ok if aligned.
2991 if (isa<AllocaInst>(V))
2992 return isAligned(V, Align, DL);
2994 // It's not always safe to follow a bitcast, for example:
2995 // bitcast i8* (alloca i8) to i32*
2996 // would result in a 4-byte load from a 1-byte alloca. However,
2997 // if we're casting from a pointer from a type of larger size
2998 // to a type of smaller size (or the same size), and the alignment
2999 // is at least as large as for the resulting pointer type, then
3000 // we can look through the bitcast.
3001 if (const BitCastOperator *BC = dyn_cast<BitCastOperator>(V)) {
3002 Type *STy = BC->getSrcTy()->getPointerElementType(),
3003 *DTy = BC->getDestTy()->getPointerElementType();
3004 if (STy->isSized() && DTy->isSized() &&
3005 (DL.getTypeStoreSize(STy) >= DL.getTypeStoreSize(DTy)) &&
3006 (DL.getABITypeAlignment(STy) >= DL.getABITypeAlignment(DTy)))
3007 return isDereferenceableAndAlignedPointer(BC->getOperand(0), Align, DL,
3008 CtxI, DT, TLI, Visited);
3011 // Global variables which can't collapse to null are ok.
3012 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
3013 if (!GV->hasExternalWeakLinkage())
3014 return isAligned(V, Align, DL);
3016 // byval arguments are okay.
3017 if (const Argument *A = dyn_cast<Argument>(V))
3018 if (A->hasByValAttr())
3019 return isAligned(V, Align, DL);
3021 if (isDereferenceableFromAttribute(V, DL, CtxI, DT, TLI))
3022 return isAligned(V, Align, DL);
3024 // For GEPs, determine if the indexing lands within the allocated object.
3025 if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
3026 Type *VTy = GEP->getType();
3027 Type *Ty = VTy->getPointerElementType();
3028 const Value *Base = GEP->getPointerOperand();
3030 // Conservatively require that the base pointer be fully dereferenceable
3032 if (!Visited.insert(Base).second)
3034 if (!isDereferenceableAndAlignedPointer(Base, Align, DL, CtxI, DT, TLI,
3038 APInt Offset(DL.getPointerTypeSizeInBits(VTy), 0);
3039 if (!GEP->accumulateConstantOffset(DL, Offset))
3042 // Check if the load is within the bounds of the underlying object
3043 // and offset is aligned.
3044 uint64_t LoadSize = DL.getTypeStoreSize(Ty);
3045 Type *BaseType = Base->getType()->getPointerElementType();
3046 assert(isPowerOf2_32(Align) && "must be a power of 2!");
3047 return (Offset + LoadSize).ule(DL.getTypeAllocSize(BaseType)) &&
3048 !(Offset & APInt(Offset.getBitWidth(), Align-1));
3051 // For gc.relocate, look through relocations
3052 if (const IntrinsicInst *I = dyn_cast<IntrinsicInst>(V))
3053 if (I->getIntrinsicID() == Intrinsic::experimental_gc_relocate) {
3054 GCRelocateOperands RelocateInst(I);
3055 return isDereferenceableAndAlignedPointer(
3056 RelocateInst.getDerivedPtr(), Align, DL, CtxI, DT, TLI, Visited);
3059 if (const AddrSpaceCastInst *ASC = dyn_cast<AddrSpaceCastInst>(V))
3060 return isDereferenceableAndAlignedPointer(ASC->getOperand(0), Align, DL,
3061 CtxI, DT, TLI, Visited);
3063 // If we don't know, assume the worst.
3067 bool llvm::isDereferenceableAndAlignedPointer(const Value *V, unsigned Align,
3068 const DataLayout &DL,
3069 const Instruction *CtxI,
3070 const DominatorTree *DT,
3071 const TargetLibraryInfo *TLI) {
3072 // When dereferenceability information is provided by a dereferenceable
3073 // attribute, we know exactly how many bytes are dereferenceable. If we can
3074 // determine the exact offset to the attributed variable, we can use that
3075 // information here.
3076 Type *VTy = V->getType();
3077 Type *Ty = VTy->getPointerElementType();
3079 // Require ABI alignment for loads without alignment specification
3081 Align = DL.getABITypeAlignment(Ty);
3083 if (Ty->isSized()) {
3084 APInt Offset(DL.getTypeStoreSizeInBits(VTy), 0);
3085 const Value *BV = V->stripAndAccumulateInBoundsConstantOffsets(DL, Offset);
3087 if (Offset.isNonNegative())
3088 if (isDereferenceableFromAttribute(BV, Offset, Ty, DL, CtxI, DT, TLI) &&
3089 isAligned(BV, Offset, Align, DL))
3093 SmallPtrSet<const Value *, 32> Visited;
3094 return ::isDereferenceableAndAlignedPointer(V, Align, DL, CtxI, DT, TLI,
3098 bool llvm::isDereferenceablePointer(const Value *V, const DataLayout &DL,
3099 const Instruction *CtxI,
3100 const DominatorTree *DT,
3101 const TargetLibraryInfo *TLI) {
3102 return isDereferenceableAndAlignedPointer(V, 1, DL, CtxI, DT, TLI);
3105 bool llvm::isSafeToSpeculativelyExecute(const Value *V,
3106 const Instruction *CtxI,
3107 const DominatorTree *DT,
3108 const TargetLibraryInfo *TLI) {
3109 const Operator *Inst = dyn_cast<Operator>(V);
3113 for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
3114 if (Constant *C = dyn_cast<Constant>(Inst->getOperand(i)))
3118 switch (Inst->getOpcode()) {
3121 case Instruction::UDiv:
3122 case Instruction::URem: {
3123 // x / y is undefined if y == 0.
3125 if (match(Inst->getOperand(1), m_APInt(V)))
3129 case Instruction::SDiv:
3130 case Instruction::SRem: {
3131 // x / y is undefined if y == 0 or x == INT_MIN and y == -1
3132 const APInt *Numerator, *Denominator;
3133 if (!match(Inst->getOperand(1), m_APInt(Denominator)))
3135 // We cannot hoist this division if the denominator is 0.
3136 if (*Denominator == 0)
3138 // It's safe to hoist if the denominator is not 0 or -1.
3139 if (*Denominator != -1)
3141 // At this point we know that the denominator is -1. It is safe to hoist as
3142 // long we know that the numerator is not INT_MIN.
3143 if (match(Inst->getOperand(0), m_APInt(Numerator)))
3144 return !Numerator->isMinSignedValue();
3145 // The numerator *might* be MinSignedValue.
3148 case Instruction::Load: {
3149 const LoadInst *LI = cast<LoadInst>(Inst);
3150 if (!LI->isUnordered() ||
3151 // Speculative load may create a race that did not exist in the source.
3152 LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread))
3154 const DataLayout &DL = LI->getModule()->getDataLayout();
3155 return isDereferenceableAndAlignedPointer(
3156 LI->getPointerOperand(), LI->getAlignment(), DL, CtxI, DT, TLI);
3158 case Instruction::Call: {
3159 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
3160 switch (II->getIntrinsicID()) {
3161 // These synthetic intrinsics have no side-effects and just mark
3162 // information about their operands.
3163 // FIXME: There are other no-op synthetic instructions that potentially
3164 // should be considered at least *safe* to speculate...
3165 case Intrinsic::dbg_declare:
3166 case Intrinsic::dbg_value:
3169 case Intrinsic::bswap:
3170 case Intrinsic::ctlz:
3171 case Intrinsic::ctpop:
3172 case Intrinsic::cttz:
3173 case Intrinsic::objectsize:
3174 case Intrinsic::sadd_with_overflow:
3175 case Intrinsic::smul_with_overflow:
3176 case Intrinsic::ssub_with_overflow:
3177 case Intrinsic::uadd_with_overflow:
3178 case Intrinsic::umul_with_overflow:
3179 case Intrinsic::usub_with_overflow:
3181 // Sqrt should be OK, since the llvm sqrt intrinsic isn't defined to set
3182 // errno like libm sqrt would.
3183 case Intrinsic::sqrt:
3184 case Intrinsic::fma:
3185 case Intrinsic::fmuladd:
3186 case Intrinsic::fabs:
3187 case Intrinsic::minnum:
3188 case Intrinsic::maxnum:
3190 // TODO: some fp intrinsics are marked as having the same error handling
3191 // as libm. They're safe to speculate when they won't error.
3192 // TODO: are convert_{from,to}_fp16 safe?
3193 // TODO: can we list target-specific intrinsics here?
3197 return false; // The called function could have undefined behavior or
3198 // side-effects, even if marked readnone nounwind.
3200 case Instruction::VAArg:
3201 case Instruction::Alloca:
3202 case Instruction::Invoke:
3203 case Instruction::PHI:
3204 case Instruction::Store:
3205 case Instruction::Ret:
3206 case Instruction::Br:
3207 case Instruction::IndirectBr:
3208 case Instruction::Switch:
3209 case Instruction::Unreachable:
3210 case Instruction::Fence:
3211 case Instruction::AtomicRMW:
3212 case Instruction::AtomicCmpXchg:
3213 case Instruction::LandingPad:
3214 case Instruction::Resume:
3215 case Instruction::CatchPad:
3216 case Instruction::CatchEndPad:
3217 case Instruction::CatchRet:
3218 case Instruction::CleanupPad:
3219 case Instruction::CleanupEndPad:
3220 case Instruction::CleanupRet:
3221 case Instruction::TerminatePad:
3222 return false; // Misc instructions which have effects
3226 bool llvm::mayBeMemoryDependent(const Instruction &I) {
3227 return I.mayReadOrWriteMemory() || !isSafeToSpeculativelyExecute(&I);
3230 /// Return true if we know that the specified value is never null.
3231 bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) {
3232 assert(V->getType()->isPointerTy() && "V must be pointer type");
3234 // Alloca never returns null, malloc might.
3235 if (isa<AllocaInst>(V)) return true;
3237 // A byval, inalloca, or nonnull argument is never null.
3238 if (const Argument *A = dyn_cast<Argument>(V))
3239 return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr();
3241 // A global variable in address space 0 is non null unless extern weak.
3242 // Other address spaces may have null as a valid address for a global,
3243 // so we can't assume anything.
3244 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
3245 return !GV->hasExternalWeakLinkage() &&
3246 GV->getType()->getAddressSpace() == 0;
3248 // A Load tagged w/nonnull metadata is never null.
3249 if (const LoadInst *LI = dyn_cast<LoadInst>(V))
3250 return LI->getMetadata(LLVMContext::MD_nonnull);
3252 if (auto CS = ImmutableCallSite(V))
3253 if (CS.isReturnNonNull())
3256 // operator new never returns null.
3257 if (isOperatorNewLikeFn(V, TLI, /*LookThroughBitCast=*/true))
3263 static bool isKnownNonNullFromDominatingCondition(const Value *V,
3264 const Instruction *CtxI,
3265 const DominatorTree *DT) {
3266 assert(V->getType()->isPointerTy() && "V must be pointer type");
3268 unsigned NumUsesExplored = 0;
3269 for (auto U : V->users()) {
3270 // Avoid massive lists
3271 if (NumUsesExplored >= DomConditionsMaxUses)
3274 // Consider only compare instructions uniquely controlling a branch
3275 const ICmpInst *Cmp = dyn_cast<ICmpInst>(U);
3279 if (DomConditionsSingleCmpUse && !Cmp->hasOneUse())
3282 for (auto *CmpU : Cmp->users()) {
3283 const BranchInst *BI = dyn_cast<BranchInst>(CmpU);
3287 assert(BI->isConditional() && "uses a comparison!");
3289 BasicBlock *NonNullSuccessor = nullptr;
3290 CmpInst::Predicate Pred;
3292 if (match(const_cast<ICmpInst*>(Cmp),
3293 m_c_ICmp(Pred, m_Specific(V), m_Zero()))) {
3294 if (Pred == ICmpInst::ICMP_EQ)
3295 NonNullSuccessor = BI->getSuccessor(1);
3296 else if (Pred == ICmpInst::ICMP_NE)
3297 NonNullSuccessor = BI->getSuccessor(0);
3300 if (NonNullSuccessor) {
3301 BasicBlockEdge Edge(BI->getParent(), NonNullSuccessor);
3302 if (Edge.isSingleEdge() && DT->dominates(Edge, CtxI->getParent()))
3311 bool llvm::isKnownNonNullAt(const Value *V, const Instruction *CtxI,
3312 const DominatorTree *DT, const TargetLibraryInfo *TLI) {
3313 if (isKnownNonNull(V, TLI))
3316 return CtxI ? ::isKnownNonNullFromDominatingCondition(V, CtxI, DT) : false;
3319 OverflowResult llvm::computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
3320 const DataLayout &DL,
3321 AssumptionCache *AC,
3322 const Instruction *CxtI,
3323 const DominatorTree *DT) {
3324 // Multiplying n * m significant bits yields a result of n + m significant
3325 // bits. If the total number of significant bits does not exceed the
3326 // result bit width (minus 1), there is no overflow.
3327 // This means if we have enough leading zero bits in the operands
3328 // we can guarantee that the result does not overflow.
3329 // Ref: "Hacker's Delight" by Henry Warren
3330 unsigned BitWidth = LHS->getType()->getScalarSizeInBits();
3331 APInt LHSKnownZero(BitWidth, 0);
3332 APInt LHSKnownOne(BitWidth, 0);
3333 APInt RHSKnownZero(BitWidth, 0);
3334 APInt RHSKnownOne(BitWidth, 0);
3335 computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, /*Depth=*/0, AC, CxtI,
3337 computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, /*Depth=*/0, AC, CxtI,
3339 // Note that underestimating the number of zero bits gives a more
3340 // conservative answer.
3341 unsigned ZeroBits = LHSKnownZero.countLeadingOnes() +
3342 RHSKnownZero.countLeadingOnes();
3343 // First handle the easy case: if we have enough zero bits there's
3344 // definitely no overflow.
3345 if (ZeroBits >= BitWidth)
3346 return OverflowResult::NeverOverflows;
3348 // Get the largest possible values for each operand.
3349 APInt LHSMax = ~LHSKnownZero;
3350 APInt RHSMax = ~RHSKnownZero;
3352 // We know the multiply operation doesn't overflow if the maximum values for
3353 // each operand will not overflow after we multiply them together.
3355 LHSMax.umul_ov(RHSMax, MaxOverflow);
3357 return OverflowResult::NeverOverflows;
3359 // We know it always overflows if multiplying the smallest possible values for
3360 // the operands also results in overflow.
3362 LHSKnownOne.umul_ov(RHSKnownOne, MinOverflow);
3364 return OverflowResult::AlwaysOverflows;
3366 return OverflowResult::MayOverflow;
3369 OverflowResult llvm::computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
3370 const DataLayout &DL,
3371 AssumptionCache *AC,
3372 const Instruction *CxtI,
3373 const DominatorTree *DT) {
3374 bool LHSKnownNonNegative, LHSKnownNegative;
3375 ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0,
3377 if (LHSKnownNonNegative || LHSKnownNegative) {
3378 bool RHSKnownNonNegative, RHSKnownNegative;
3379 ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0,
3382 if (LHSKnownNegative && RHSKnownNegative) {
3383 // The sign bit is set in both cases: this MUST overflow.
3384 // Create a simple add instruction, and insert it into the struct.
3385 return OverflowResult::AlwaysOverflows;
3388 if (LHSKnownNonNegative && RHSKnownNonNegative) {
3389 // The sign bit is clear in both cases: this CANNOT overflow.
3390 // Create a simple add instruction, and insert it into the struct.
3391 return OverflowResult::NeverOverflows;
3395 return OverflowResult::MayOverflow;
3398 static OverflowResult computeOverflowForSignedAdd(
3399 Value *LHS, Value *RHS, AddOperator *Add, const DataLayout &DL,
3400 AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT) {
3401 if (Add && Add->hasNoSignedWrap()) {
3402 return OverflowResult::NeverOverflows;
3405 bool LHSKnownNonNegative, LHSKnownNegative;
3406 bool RHSKnownNonNegative, RHSKnownNegative;
3407 ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0,
3409 ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0,
3412 if ((LHSKnownNonNegative && RHSKnownNegative) ||
3413 (LHSKnownNegative && RHSKnownNonNegative)) {
3414 // The sign bits are opposite: this CANNOT overflow.
3415 return OverflowResult::NeverOverflows;
3418 // The remaining code needs Add to be available. Early returns if not so.
3420 return OverflowResult::MayOverflow;
3422 // If the sign of Add is the same as at least one of the operands, this add
3423 // CANNOT overflow. This is particularly useful when the sum is
3424 // @llvm.assume'ed non-negative rather than proved so from analyzing its
3426 bool LHSOrRHSKnownNonNegative =
3427 (LHSKnownNonNegative || RHSKnownNonNegative);
3428 bool LHSOrRHSKnownNegative = (LHSKnownNegative || RHSKnownNegative);
3429 if (LHSOrRHSKnownNonNegative || LHSOrRHSKnownNegative) {
3430 bool AddKnownNonNegative, AddKnownNegative;
3431 ComputeSignBit(Add, AddKnownNonNegative, AddKnownNegative, DL,
3432 /*Depth=*/0, AC, CxtI, DT);
3433 if ((AddKnownNonNegative && LHSOrRHSKnownNonNegative) ||
3434 (AddKnownNegative && LHSOrRHSKnownNegative)) {
3435 return OverflowResult::NeverOverflows;
3439 return OverflowResult::MayOverflow;
3442 OverflowResult llvm::computeOverflowForSignedAdd(AddOperator *Add,
3443 const DataLayout &DL,
3444 AssumptionCache *AC,
3445 const Instruction *CxtI,
3446 const DominatorTree *DT) {
3447 return ::computeOverflowForSignedAdd(Add->getOperand(0), Add->getOperand(1),
3448 Add, DL, AC, CxtI, DT);
3451 OverflowResult llvm::computeOverflowForSignedAdd(Value *LHS, Value *RHS,
3452 const DataLayout &DL,
3453 AssumptionCache *AC,
3454 const Instruction *CxtI,
3455 const DominatorTree *DT) {
3456 return ::computeOverflowForSignedAdd(LHS, RHS, nullptr, DL, AC, CxtI, DT);
3459 bool llvm::isGuaranteedToTransferExecutionToSuccessor(const Instruction *I) {
3460 // FIXME: This conservative implementation can be relaxed. E.g. most
3461 // atomic operations are guaranteed to terminate on most platforms
3462 // and most functions terminate.
3464 return !I->isAtomic() && // atomics may never succeed on some platforms
3465 !isa<CallInst>(I) && // could throw and might not terminate
3466 !isa<InvokeInst>(I) && // might not terminate and could throw to
3467 // non-successor (see bug 24185 for details).
3468 !isa<ResumeInst>(I) && // has no successors
3469 !isa<ReturnInst>(I); // has no successors
3472 bool llvm::isGuaranteedToExecuteForEveryIteration(const Instruction *I,
3474 // The loop header is guaranteed to be executed for every iteration.
3476 // FIXME: Relax this constraint to cover all basic blocks that are
3477 // guaranteed to be executed at every iteration.
3478 if (I->getParent() != L->getHeader()) return false;
3480 for (const Instruction &LI : *L->getHeader()) {
3481 if (&LI == I) return true;
3482 if (!isGuaranteedToTransferExecutionToSuccessor(&LI)) return false;
3484 llvm_unreachable("Instruction not contained in its own parent basic block.");
3487 bool llvm::propagatesFullPoison(const Instruction *I) {
3488 switch (I->getOpcode()) {
3489 case Instruction::Add:
3490 case Instruction::Sub:
3491 case Instruction::Xor:
3492 case Instruction::Trunc:
3493 case Instruction::BitCast:
3494 case Instruction::AddrSpaceCast:
3495 // These operations all propagate poison unconditionally. Note that poison
3496 // is not any particular value, so xor or subtraction of poison with
3497 // itself still yields poison, not zero.
3500 case Instruction::AShr:
3501 case Instruction::SExt:
3502 // For these operations, one bit of the input is replicated across
3503 // multiple output bits. A replicated poison bit is still poison.
3506 case Instruction::Shl: {
3507 // Left shift *by* a poison value is poison. The number of
3508 // positions to shift is unsigned, so no negative values are
3509 // possible there. Left shift by zero places preserves poison. So
3510 // it only remains to consider left shift of poison by a positive
3511 // number of places.
3513 // A left shift by a positive number of places leaves the lowest order bit
3514 // non-poisoned. However, if such a shift has a no-wrap flag, then we can
3515 // make the poison operand violate that flag, yielding a fresh full-poison
3517 auto *OBO = cast<OverflowingBinaryOperator>(I);
3518 return OBO->hasNoUnsignedWrap() || OBO->hasNoSignedWrap();
3521 case Instruction::Mul: {
3522 // A multiplication by zero yields a non-poison zero result, so we need to
3523 // rule out zero as an operand. Conservatively, multiplication by a
3524 // non-zero constant is not multiplication by zero.
3526 // Multiplication by a non-zero constant can leave some bits
3527 // non-poisoned. For example, a multiplication by 2 leaves the lowest
3528 // order bit unpoisoned. So we need to consider that.
3530 // Multiplication by 1 preserves poison. If the multiplication has a
3531 // no-wrap flag, then we can make the poison operand violate that flag
3532 // when multiplied by any integer other than 0 and 1.
3533 auto *OBO = cast<OverflowingBinaryOperator>(I);
3534 if (OBO->hasNoUnsignedWrap() || OBO->hasNoSignedWrap()) {
3535 for (Value *V : OBO->operands()) {
3536 if (auto *CI = dyn_cast<ConstantInt>(V)) {
3537 // A ConstantInt cannot yield poison, so we can assume that it is
3538 // the other operand that is poison.
3539 return !CI->isZero();
3546 case Instruction::GetElementPtr:
3547 // A GEP implicitly represents a sequence of additions, subtractions,
3548 // truncations, sign extensions and multiplications. The multiplications
3549 // are by the non-zero sizes of some set of types, so we do not have to be
3550 // concerned with multiplication by zero. If the GEP is in-bounds, then
3551 // these operations are implicitly no-signed-wrap so poison is propagated
3552 // by the arguments above for Add, Sub, Trunc, SExt and Mul.
3553 return cast<GEPOperator>(I)->isInBounds();
3560 const Value *llvm::getGuaranteedNonFullPoisonOp(const Instruction *I) {
3561 switch (I->getOpcode()) {
3562 case Instruction::Store:
3563 return cast<StoreInst>(I)->getPointerOperand();
3565 case Instruction::Load:
3566 return cast<LoadInst>(I)->getPointerOperand();
3568 case Instruction::AtomicCmpXchg:
3569 return cast<AtomicCmpXchgInst>(I)->getPointerOperand();
3571 case Instruction::AtomicRMW:
3572 return cast<AtomicRMWInst>(I)->getPointerOperand();
3574 case Instruction::UDiv:
3575 case Instruction::SDiv:
3576 case Instruction::URem:
3577 case Instruction::SRem:
3578 return I->getOperand(1);
3585 bool llvm::isKnownNotFullPoison(const Instruction *PoisonI) {
3586 // We currently only look for uses of poison values within the same basic
3587 // block, as that makes it easier to guarantee that the uses will be
3588 // executed given that PoisonI is executed.
3590 // FIXME: Expand this to consider uses beyond the same basic block. To do
3591 // this, look out for the distinction between post-dominance and strong
3593 const BasicBlock *BB = PoisonI->getParent();
3595 // Set of instructions that we have proved will yield poison if PoisonI
3597 SmallSet<const Value *, 16> YieldsPoison;
3598 YieldsPoison.insert(PoisonI);
3600 for (const Instruction *I = PoisonI, *E = BB->end(); I != E;
3601 I = I->getNextNode()) {
3603 const Value *NotPoison = getGuaranteedNonFullPoisonOp(I);
3604 if (NotPoison != nullptr && YieldsPoison.count(NotPoison)) return true;
3605 if (!isGuaranteedToTransferExecutionToSuccessor(I)) return false;
3608 // Mark poison that propagates from I through uses of I.
3609 if (YieldsPoison.count(I)) {
3610 for (const User *User : I->users()) {
3611 const Instruction *UserI = cast<Instruction>(User);
3612 if (UserI->getParent() == BB && propagatesFullPoison(UserI))
3613 YieldsPoison.insert(User);
3620 static bool isKnownNonNaN(Value *V, FastMathFlags FMF) {
3624 if (auto *C = dyn_cast<ConstantFP>(V))
3629 static bool isKnownNonZero(Value *V) {
3630 if (auto *C = dyn_cast<ConstantFP>(V))
3631 return !C->isZero();
3635 static SelectPatternResult matchSelectPattern(CmpInst::Predicate Pred,
3637 Value *CmpLHS, Value *CmpRHS,
3638 Value *TrueVal, Value *FalseVal,
3639 Value *&LHS, Value *&RHS) {
3643 // If the predicate is an "or-equal" (FP) predicate, then signed zeroes may
3644 // return inconsistent results between implementations.
3645 // (0.0 <= -0.0) ? 0.0 : -0.0 // Returns 0.0
3646 // minNum(0.0, -0.0) // May return -0.0 or 0.0 (IEEE 754-2008 5.3.1)
3647 // Therefore we behave conservatively and only proceed if at least one of the
3648 // operands is known to not be zero, or if we don't care about signed zeroes.
3651 case CmpInst::FCMP_OGE: case CmpInst::FCMP_OLE:
3652 case CmpInst::FCMP_UGE: case CmpInst::FCMP_ULE:
3653 if (!FMF.noSignedZeros() && !isKnownNonZero(CmpLHS) &&
3654 !isKnownNonZero(CmpRHS))
3655 return {SPF_UNKNOWN, SPNB_NA, false};
3658 SelectPatternNaNBehavior NaNBehavior = SPNB_NA;
3659 bool Ordered = false;
3661 // When given one NaN and one non-NaN input:
3662 // - maxnum/minnum (C99 fmaxf()/fminf()) return the non-NaN input.
3663 // - A simple C99 (a < b ? a : b) construction will return 'b' (as the
3664 // ordered comparison fails), which could be NaN or non-NaN.
3665 // so here we discover exactly what NaN behavior is required/accepted.
3666 if (CmpInst::isFPPredicate(Pred)) {
3667 bool LHSSafe = isKnownNonNaN(CmpLHS, FMF);
3668 bool RHSSafe = isKnownNonNaN(CmpRHS, FMF);
3670 if (LHSSafe && RHSSafe) {
3671 // Both operands are known non-NaN.
3672 NaNBehavior = SPNB_RETURNS_ANY;
3673 } else if (CmpInst::isOrdered(Pred)) {
3674 // An ordered comparison will return false when given a NaN, so it
3678 // LHS is non-NaN, so if RHS is NaN then NaN will be returned.
3679 NaNBehavior = SPNB_RETURNS_NAN;
3681 NaNBehavior = SPNB_RETURNS_OTHER;
3683 // Completely unsafe.
3684 return {SPF_UNKNOWN, SPNB_NA, false};
3687 // An unordered comparison will return true when given a NaN, so it
3690 // LHS is non-NaN, so if RHS is NaN then non-NaN will be returned.
3691 NaNBehavior = SPNB_RETURNS_OTHER;
3693 NaNBehavior = SPNB_RETURNS_NAN;
3695 // Completely unsafe.
3696 return {SPF_UNKNOWN, SPNB_NA, false};
3700 if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
3701 std::swap(CmpLHS, CmpRHS);
3702 Pred = CmpInst::getSwappedPredicate(Pred);
3703 if (NaNBehavior == SPNB_RETURNS_NAN)
3704 NaNBehavior = SPNB_RETURNS_OTHER;
3705 else if (NaNBehavior == SPNB_RETURNS_OTHER)
3706 NaNBehavior = SPNB_RETURNS_NAN;
3710 // ([if]cmp X, Y) ? X : Y
3711 if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
3713 default: return {SPF_UNKNOWN, SPNB_NA, false}; // Equality.
3714 case ICmpInst::ICMP_UGT:
3715 case ICmpInst::ICMP_UGE: return {SPF_UMAX, SPNB_NA, false};
3716 case ICmpInst::ICMP_SGT:
3717 case ICmpInst::ICMP_SGE: return {SPF_SMAX, SPNB_NA, false};
3718 case ICmpInst::ICMP_ULT:
3719 case ICmpInst::ICMP_ULE: return {SPF_UMIN, SPNB_NA, false};
3720 case ICmpInst::ICMP_SLT:
3721 case ICmpInst::ICMP_SLE: return {SPF_SMIN, SPNB_NA, false};
3722 case FCmpInst::FCMP_UGT:
3723 case FCmpInst::FCMP_UGE:
3724 case FCmpInst::FCMP_OGT:
3725 case FCmpInst::FCMP_OGE: return {SPF_FMAXNUM, NaNBehavior, Ordered};
3726 case FCmpInst::FCMP_ULT:
3727 case FCmpInst::FCMP_ULE:
3728 case FCmpInst::FCMP_OLT:
3729 case FCmpInst::FCMP_OLE: return {SPF_FMINNUM, NaNBehavior, Ordered};
3733 if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
3734 if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
3735 (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
3737 // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
3738 // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
3739 if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) {
3740 return {(CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false};
3743 // ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
3744 // NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
3745 if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) {
3746 return {(CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false};
3750 // Y >s C ? ~Y : ~C == ~Y <s ~C ? ~Y : ~C = SMIN(~Y, ~C)
3751 if (const auto *C2 = dyn_cast<ConstantInt>(FalseVal)) {
3752 if (C1->getType() == C2->getType() && ~C1->getValue() == C2->getValue() &&
3753 (match(TrueVal, m_Not(m_Specific(CmpLHS))) ||
3754 match(CmpLHS, m_Not(m_Specific(TrueVal))))) {
3757 return {SPF_SMIN, SPNB_NA, false};
3762 // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5)
3764 return {SPF_UNKNOWN, SPNB_NA, false};
3767 static Value *lookThroughCast(CmpInst *CmpI, Value *V1, Value *V2,
3768 Instruction::CastOps *CastOp) {
3769 CastInst *CI = dyn_cast<CastInst>(V1);
3770 Constant *C = dyn_cast<Constant>(V2);
3771 CastInst *CI2 = dyn_cast<CastInst>(V2);
3774 *CastOp = CI->getOpcode();
3777 // If V1 and V2 are both the same cast from the same type, we can look
3779 if (CI2->getOpcode() == CI->getOpcode() &&
3780 CI2->getSrcTy() == CI->getSrcTy())
3781 return CI2->getOperand(0);
3787 if (isa<SExtInst>(CI) && CmpI->isSigned()) {
3788 Constant *T = ConstantExpr::getTrunc(C, CI->getSrcTy());
3789 // This is only valid if the truncated value can be sign-extended
3790 // back to the original value.
3791 if (ConstantExpr::getSExt(T, C->getType()) == C)
3795 if (isa<ZExtInst>(CI) && CmpI->isUnsigned())
3796 return ConstantExpr::getTrunc(C, CI->getSrcTy());
3798 if (isa<TruncInst>(CI))
3799 return ConstantExpr::getIntegerCast(C, CI->getSrcTy(), CmpI->isSigned());
3801 if (isa<FPToUIInst>(CI))
3802 return ConstantExpr::getUIToFP(C, CI->getSrcTy(), true);
3804 if (isa<FPToSIInst>(CI))
3805 return ConstantExpr::getSIToFP(C, CI->getSrcTy(), true);
3807 if (isa<UIToFPInst>(CI))
3808 return ConstantExpr::getFPToUI(C, CI->getSrcTy(), true);
3810 if (isa<SIToFPInst>(CI))
3811 return ConstantExpr::getFPToSI(C, CI->getSrcTy(), true);
3813 if (isa<FPTruncInst>(CI))
3814 return ConstantExpr::getFPExtend(C, CI->getSrcTy(), true);
3816 if (isa<FPExtInst>(CI))
3817 return ConstantExpr::getFPTrunc(C, CI->getSrcTy(), true);
3822 SelectPatternResult llvm::matchSelectPattern(Value *V,
3823 Value *&LHS, Value *&RHS,
3824 Instruction::CastOps *CastOp) {
3825 SelectInst *SI = dyn_cast<SelectInst>(V);
3826 if (!SI) return {SPF_UNKNOWN, SPNB_NA, false};
3828 CmpInst *CmpI = dyn_cast<CmpInst>(SI->getCondition());
3829 if (!CmpI) return {SPF_UNKNOWN, SPNB_NA, false};
3831 CmpInst::Predicate Pred = CmpI->getPredicate();
3832 Value *CmpLHS = CmpI->getOperand(0);
3833 Value *CmpRHS = CmpI->getOperand(1);
3834 Value *TrueVal = SI->getTrueValue();
3835 Value *FalseVal = SI->getFalseValue();
3837 if (isa<FPMathOperator>(CmpI))
3838 FMF = CmpI->getFastMathFlags();
3841 if (CmpI->isEquality())
3842 return {SPF_UNKNOWN, SPNB_NA, false};
3844 // Deal with type mismatches.
3845 if (CastOp && CmpLHS->getType() != TrueVal->getType()) {
3846 if (Value *C = lookThroughCast(CmpI, TrueVal, FalseVal, CastOp))
3847 return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS,
3848 cast<CastInst>(TrueVal)->getOperand(0), C,
3850 if (Value *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp))
3851 return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS,
3852 C, cast<CastInst>(FalseVal)->getOperand(0),
3855 return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, TrueVal, FalseVal,