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/IR/CallSite.h"
21 #include "llvm/IR/ConstantRange.h"
22 #include "llvm/IR/Constants.h"
23 #include "llvm/IR/DataLayout.h"
24 #include "llvm/IR/Dominators.h"
25 #include "llvm/IR/GetElementPtrTypeIterator.h"
26 #include "llvm/IR/GlobalAlias.h"
27 #include "llvm/IR/GlobalVariable.h"
28 #include "llvm/IR/Instructions.h"
29 #include "llvm/IR/IntrinsicInst.h"
30 #include "llvm/IR/LLVMContext.h"
31 #include "llvm/IR/Metadata.h"
32 #include "llvm/IR/Operator.h"
33 #include "llvm/IR/PatternMatch.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/MathExtras.h"
38 using namespace llvm::PatternMatch;
40 const unsigned MaxDepth = 6;
42 /// Enable an experimental feature to leverage information about dominating
43 /// conditions to compute known bits. The individual options below control how
44 /// hard we search. The defaults are choosen to be fairly aggressive. If you
45 /// run into compile time problems when testing, scale them back and report
47 static cl::opt<bool> EnableDomConditions("value-tracking-dom-conditions",
48 cl::Hidden, cl::init(false));
50 // This is expensive, so we only do it for the top level query value.
51 // (TODO: evaluate cost vs profit, consider higher thresholds)
52 static cl::opt<unsigned> DomConditionsMaxDepth("dom-conditions-max-depth",
53 cl::Hidden, cl::init(1));
55 /// How many dominating blocks should be scanned looking for dominating
57 static cl::opt<unsigned> DomConditionsMaxDomBlocks("dom-conditions-dom-blocks",
61 // Controls the number of uses of the value searched for possible
62 // dominating comparisons.
63 static cl::opt<unsigned> DomConditionsMaxUses("dom-conditions-max-uses",
64 cl::Hidden, cl::init(2000));
66 // If true, don't consider only compares whose only use is a branch.
67 static cl::opt<bool> DomConditionsSingleCmpUse("dom-conditions-single-cmp-use",
68 cl::Hidden, cl::init(false));
70 /// Returns the bitwidth of the given scalar or pointer type (if unknown returns
71 /// 0). For vector types, returns the element type's bitwidth.
72 static unsigned getBitWidth(Type *Ty, const DataLayout &DL) {
73 if (unsigned BitWidth = Ty->getScalarSizeInBits())
76 return DL.getPointerTypeSizeInBits(Ty);
79 // Many of these functions have internal versions that take an assumption
80 // exclusion set. This is because of the potential for mutual recursion to
81 // cause computeKnownBits to repeatedly visit the same assume intrinsic. The
82 // classic case of this is assume(x = y), which will attempt to determine
83 // bits in x from bits in y, which will attempt to determine bits in y from
84 // bits in x, etc. Regarding the mutual recursion, computeKnownBits can call
85 // isKnownNonZero, which calls computeKnownBits and ComputeSignBit and
86 // isKnownToBeAPowerOfTwo (all of which can call computeKnownBits), and so on.
87 typedef SmallPtrSet<const Value *, 8> ExclInvsSet;
90 // Simplifying using an assume can only be done in a particular control-flow
91 // context (the context instruction provides that context). If an assume and
92 // the context instruction are not in the same block then the DT helps in
93 // figuring out if we can use it.
97 const Instruction *CxtI;
98 const DominatorTree *DT;
100 Query(AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr,
101 const DominatorTree *DT = nullptr)
102 : AC(AC), CxtI(CxtI), DT(DT) {}
104 Query(const Query &Q, const Value *NewExcl)
105 : ExclInvs(Q.ExclInvs), AC(Q.AC), CxtI(Q.CxtI), DT(Q.DT) {
106 ExclInvs.insert(NewExcl);
109 } // end anonymous namespace
111 // Given the provided Value and, potentially, a context instruction, return
112 // the preferred context instruction (if any).
113 static const Instruction *safeCxtI(const Value *V, const Instruction *CxtI) {
114 // If we've been provided with a context instruction, then use that (provided
115 // it has been inserted).
116 if (CxtI && CxtI->getParent())
119 // If the value is really an already-inserted instruction, then use that.
120 CxtI = dyn_cast<Instruction>(V);
121 if (CxtI && CxtI->getParent())
127 static void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
128 const DataLayout &DL, unsigned Depth,
131 void llvm::computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
132 const DataLayout &DL, unsigned Depth,
133 AssumptionCache *AC, const Instruction *CxtI,
134 const DominatorTree *DT) {
135 ::computeKnownBits(V, KnownZero, KnownOne, DL, Depth,
136 Query(AC, safeCxtI(V, CxtI), DT));
139 static void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
140 const DataLayout &DL, unsigned Depth,
143 void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
144 const DataLayout &DL, unsigned Depth,
145 AssumptionCache *AC, const Instruction *CxtI,
146 const DominatorTree *DT) {
147 ::ComputeSignBit(V, KnownZero, KnownOne, DL, Depth,
148 Query(AC, safeCxtI(V, CxtI), DT));
151 static bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
152 const Query &Q, const DataLayout &DL);
154 bool llvm::isKnownToBeAPowerOfTwo(Value *V, const DataLayout &DL, bool OrZero,
155 unsigned Depth, AssumptionCache *AC,
156 const Instruction *CxtI,
157 const DominatorTree *DT) {
158 return ::isKnownToBeAPowerOfTwo(V, OrZero, Depth,
159 Query(AC, safeCxtI(V, CxtI), DT), DL);
162 static bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth,
165 bool llvm::isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth,
166 AssumptionCache *AC, const Instruction *CxtI,
167 const DominatorTree *DT) {
168 return ::isKnownNonZero(V, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT));
171 static bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
172 unsigned Depth, const Query &Q);
174 bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
175 unsigned Depth, AssumptionCache *AC,
176 const Instruction *CxtI, const DominatorTree *DT) {
177 return ::MaskedValueIsZero(V, Mask, DL, Depth,
178 Query(AC, safeCxtI(V, CxtI), DT));
181 static unsigned ComputeNumSignBits(Value *V, const DataLayout &DL,
182 unsigned Depth, const Query &Q);
184 unsigned llvm::ComputeNumSignBits(Value *V, const DataLayout &DL,
185 unsigned Depth, AssumptionCache *AC,
186 const Instruction *CxtI,
187 const DominatorTree *DT) {
188 return ::ComputeNumSignBits(V, DL, Depth, Query(AC, safeCxtI(V, CxtI), DT));
191 static void computeKnownBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
192 APInt &KnownZero, APInt &KnownOne,
193 APInt &KnownZero2, APInt &KnownOne2,
194 const DataLayout &DL, unsigned Depth,
197 if (ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) {
198 // We know that the top bits of C-X are clear if X contains less bits
199 // than C (i.e. no wrap-around can happen). For example, 20-X is
200 // positive if we can prove that X is >= 0 and < 16.
201 if (!CLHS->getValue().isNegative()) {
202 unsigned BitWidth = KnownZero.getBitWidth();
203 unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
204 // NLZ can't be BitWidth with no sign bit
205 APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
206 computeKnownBits(Op1, KnownZero2, KnownOne2, DL, Depth + 1, Q);
208 // If all of the MaskV bits are known to be zero, then we know the
209 // output top bits are zero, because we now know that the output is
211 if ((KnownZero2 & MaskV) == MaskV) {
212 unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
213 // Top bits known zero.
214 KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2);
220 unsigned BitWidth = KnownZero.getBitWidth();
222 // If an initial sequence of bits in the result is not needed, the
223 // corresponding bits in the operands are not needed.
224 APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
225 computeKnownBits(Op0, LHSKnownZero, LHSKnownOne, DL, Depth + 1, Q);
226 computeKnownBits(Op1, KnownZero2, KnownOne2, DL, Depth + 1, Q);
228 // Carry in a 1 for a subtract, rather than a 0.
229 APInt CarryIn(BitWidth, 0);
231 // Sum = LHS + ~RHS + 1
232 std::swap(KnownZero2, KnownOne2);
236 APInt PossibleSumZero = ~LHSKnownZero + ~KnownZero2 + CarryIn;
237 APInt PossibleSumOne = LHSKnownOne + KnownOne2 + CarryIn;
239 // Compute known bits of the carry.
240 APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnownZero ^ KnownZero2);
241 APInt CarryKnownOne = PossibleSumOne ^ LHSKnownOne ^ KnownOne2;
243 // Compute set of known bits (where all three relevant bits are known).
244 APInt LHSKnown = LHSKnownZero | LHSKnownOne;
245 APInt RHSKnown = KnownZero2 | KnownOne2;
246 APInt CarryKnown = CarryKnownZero | CarryKnownOne;
247 APInt Known = LHSKnown & RHSKnown & CarryKnown;
249 assert((PossibleSumZero & Known) == (PossibleSumOne & Known) &&
250 "known bits of sum differ");
252 // Compute known bits of the result.
253 KnownZero = ~PossibleSumOne & Known;
254 KnownOne = PossibleSumOne & Known;
256 // Are we still trying to solve for the sign bit?
257 if (!Known.isNegative()) {
259 // Adding two non-negative numbers, or subtracting a negative number from
260 // a non-negative one, can't wrap into negative.
261 if (LHSKnownZero.isNegative() && KnownZero2.isNegative())
262 KnownZero |= APInt::getSignBit(BitWidth);
263 // Adding two negative numbers, or subtracting a non-negative number from
264 // a negative one, can't wrap into non-negative.
265 else if (LHSKnownOne.isNegative() && KnownOne2.isNegative())
266 KnownOne |= APInt::getSignBit(BitWidth);
271 static void computeKnownBitsMul(Value *Op0, Value *Op1, bool NSW,
272 APInt &KnownZero, APInt &KnownOne,
273 APInt &KnownZero2, APInt &KnownOne2,
274 const DataLayout &DL, unsigned Depth,
276 unsigned BitWidth = KnownZero.getBitWidth();
277 computeKnownBits(Op1, KnownZero, KnownOne, DL, Depth + 1, Q);
278 computeKnownBits(Op0, KnownZero2, KnownOne2, DL, Depth + 1, Q);
280 bool isKnownNegative = false;
281 bool isKnownNonNegative = false;
282 // If the multiplication is known not to overflow, compute the sign bit.
285 // The product of a number with itself is non-negative.
286 isKnownNonNegative = true;
288 bool isKnownNonNegativeOp1 = KnownZero.isNegative();
289 bool isKnownNonNegativeOp0 = KnownZero2.isNegative();
290 bool isKnownNegativeOp1 = KnownOne.isNegative();
291 bool isKnownNegativeOp0 = KnownOne2.isNegative();
292 // The product of two numbers with the same sign is non-negative.
293 isKnownNonNegative = (isKnownNegativeOp1 && isKnownNegativeOp0) ||
294 (isKnownNonNegativeOp1 && isKnownNonNegativeOp0);
295 // The product of a negative number and a non-negative number is either
297 if (!isKnownNonNegative)
298 isKnownNegative = (isKnownNegativeOp1 && isKnownNonNegativeOp0 &&
299 isKnownNonZero(Op0, DL, Depth, Q)) ||
300 (isKnownNegativeOp0 && isKnownNonNegativeOp1 &&
301 isKnownNonZero(Op1, DL, Depth, Q));
305 // If low bits are zero in either operand, output low known-0 bits.
306 // Also compute a conserative estimate for high known-0 bits.
307 // More trickiness is possible, but this is sufficient for the
308 // interesting case of alignment computation.
309 KnownOne.clearAllBits();
310 unsigned TrailZ = KnownZero.countTrailingOnes() +
311 KnownZero2.countTrailingOnes();
312 unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
313 KnownZero2.countLeadingOnes(),
314 BitWidth) - BitWidth;
316 TrailZ = std::min(TrailZ, BitWidth);
317 LeadZ = std::min(LeadZ, BitWidth);
318 KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
319 APInt::getHighBitsSet(BitWidth, LeadZ);
321 // Only make use of no-wrap flags if we failed to compute the sign bit
322 // directly. This matters if the multiplication always overflows, in
323 // which case we prefer to follow the result of the direct computation,
324 // though as the program is invoking undefined behaviour we can choose
325 // whatever we like here.
326 if (isKnownNonNegative && !KnownOne.isNegative())
327 KnownZero.setBit(BitWidth - 1);
328 else if (isKnownNegative && !KnownZero.isNegative())
329 KnownOne.setBit(BitWidth - 1);
332 void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
334 unsigned BitWidth = KnownZero.getBitWidth();
335 unsigned NumRanges = Ranges.getNumOperands() / 2;
336 assert(NumRanges >= 1);
338 // Use the high end of the ranges to find leading zeros.
339 unsigned MinLeadingZeros = BitWidth;
340 for (unsigned i = 0; i < NumRanges; ++i) {
342 mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 0));
344 mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 1));
345 ConstantRange Range(Lower->getValue(), Upper->getValue());
346 if (Range.isWrappedSet())
347 MinLeadingZeros = 0; // -1 has no zeros
348 unsigned LeadingZeros = (Upper->getValue() - 1).countLeadingZeros();
349 MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros);
352 KnownZero = APInt::getHighBitsSet(BitWidth, MinLeadingZeros);
355 static bool isEphemeralValueOf(Instruction *I, const Value *E) {
356 SmallVector<const Value *, 16> WorkSet(1, I);
357 SmallPtrSet<const Value *, 32> Visited;
358 SmallPtrSet<const Value *, 16> EphValues;
360 while (!WorkSet.empty()) {
361 const Value *V = WorkSet.pop_back_val();
362 if (!Visited.insert(V).second)
365 // If all uses of this value are ephemeral, then so is this value.
366 bool FoundNEUse = false;
367 for (const User *I : V->users())
368 if (!EphValues.count(I)) {
378 if (const User *U = dyn_cast<User>(V))
379 for (User::const_op_iterator J = U->op_begin(), JE = U->op_end();
381 if (isSafeToSpeculativelyExecute(*J))
382 WorkSet.push_back(*J);
390 // Is this an intrinsic that cannot be speculated but also cannot trap?
391 static bool isAssumeLikeIntrinsic(const Instruction *I) {
392 if (const CallInst *CI = dyn_cast<CallInst>(I))
393 if (Function *F = CI->getCalledFunction())
394 switch (F->getIntrinsicID()) {
396 // FIXME: This list is repeated from NoTTI::getIntrinsicCost.
397 case Intrinsic::assume:
398 case Intrinsic::dbg_declare:
399 case Intrinsic::dbg_value:
400 case Intrinsic::invariant_start:
401 case Intrinsic::invariant_end:
402 case Intrinsic::lifetime_start:
403 case Intrinsic::lifetime_end:
404 case Intrinsic::objectsize:
405 case Intrinsic::ptr_annotation:
406 case Intrinsic::var_annotation:
413 static bool isValidAssumeForContext(Value *V, const Query &Q) {
414 Instruction *Inv = cast<Instruction>(V);
416 // There are two restrictions on the use of an assume:
417 // 1. The assume must dominate the context (or the control flow must
418 // reach the assume whenever it reaches the context).
419 // 2. The context must not be in the assume's set of ephemeral values
420 // (otherwise we will use the assume to prove that the condition
421 // feeding the assume is trivially true, thus causing the removal of
425 if (Q.DT->dominates(Inv, Q.CxtI)) {
427 } else if (Inv->getParent() == Q.CxtI->getParent()) {
428 // The context comes first, but they're both in the same block. Make sure
429 // there is nothing in between that might interrupt the control flow.
430 for (BasicBlock::const_iterator I =
431 std::next(BasicBlock::const_iterator(Q.CxtI)),
432 IE(Inv); I != IE; ++I)
433 if (!isSafeToSpeculativelyExecute(I) && !isAssumeLikeIntrinsic(I))
436 return !isEphemeralValueOf(Inv, Q.CxtI);
442 // When we don't have a DT, we do a limited search...
443 if (Inv->getParent() == Q.CxtI->getParent()->getSinglePredecessor()) {
445 } else if (Inv->getParent() == Q.CxtI->getParent()) {
446 // Search forward from the assume until we reach the context (or the end
447 // of the block); the common case is that the assume will come first.
448 for (BasicBlock::iterator I = std::next(BasicBlock::iterator(Inv)),
449 IE = Inv->getParent()->end(); I != IE; ++I)
453 // The context must come first...
454 for (BasicBlock::const_iterator I =
455 std::next(BasicBlock::const_iterator(Q.CxtI)),
456 IE(Inv); I != IE; ++I)
457 if (!isSafeToSpeculativelyExecute(I) && !isAssumeLikeIntrinsic(I))
460 return !isEphemeralValueOf(Inv, Q.CxtI);
466 bool llvm::isValidAssumeForContext(const Instruction *I,
467 const Instruction *CxtI,
468 const DominatorTree *DT) {
469 return ::isValidAssumeForContext(const_cast<Instruction *>(I),
470 Query(nullptr, CxtI, DT));
473 template<typename LHS, typename RHS>
474 inline match_combine_or<CmpClass_match<LHS, RHS, ICmpInst, ICmpInst::Predicate>,
475 CmpClass_match<RHS, LHS, ICmpInst, ICmpInst::Predicate>>
476 m_c_ICmp(ICmpInst::Predicate &Pred, const LHS &L, const RHS &R) {
477 return m_CombineOr(m_ICmp(Pred, L, R), m_ICmp(Pred, R, L));
480 template<typename LHS, typename RHS>
481 inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::And>,
482 BinaryOp_match<RHS, LHS, Instruction::And>>
483 m_c_And(const LHS &L, const RHS &R) {
484 return m_CombineOr(m_And(L, R), m_And(R, L));
487 template<typename LHS, typename RHS>
488 inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::Or>,
489 BinaryOp_match<RHS, LHS, Instruction::Or>>
490 m_c_Or(const LHS &L, const RHS &R) {
491 return m_CombineOr(m_Or(L, R), m_Or(R, L));
494 template<typename LHS, typename RHS>
495 inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::Xor>,
496 BinaryOp_match<RHS, LHS, Instruction::Xor>>
497 m_c_Xor(const LHS &L, const RHS &R) {
498 return m_CombineOr(m_Xor(L, R), m_Xor(R, L));
501 /// Compute known bits in 'V' under the assumption that the condition 'Cmp' is
502 /// true (at the context instruction.) This is mostly a utility function for
503 /// the prototype dominating conditions reasoning below.
504 static void computeKnownBitsFromTrueCondition(Value *V, ICmpInst *Cmp,
507 const DataLayout &DL,
508 unsigned Depth, const Query &Q) {
509 Value *LHS = Cmp->getOperand(0);
510 Value *RHS = Cmp->getOperand(1);
511 // TODO: We could potentially be more aggressive here. This would be worth
512 // evaluating. If we can, explore commoning this code with the assume
514 if (LHS != V && RHS != V)
517 const unsigned BitWidth = KnownZero.getBitWidth();
519 switch (Cmp->getPredicate()) {
521 // We know nothing from this condition
523 // TODO: implement unsigned bound from below (known one bits)
524 // TODO: common condition check implementations with assumes
525 // TODO: implement other patterns from assume (e.g. V & B == A)
526 case ICmpInst::ICMP_SGT:
528 APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0);
529 computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q);
530 if (KnownOneTemp.isAllOnesValue() || KnownZeroTemp.isNegative()) {
531 // We know that the sign bit is zero.
532 KnownZero |= APInt::getSignBit(BitWidth);
536 case ICmpInst::ICMP_EQ:
538 computeKnownBits(RHS, KnownZero, KnownOne, DL, Depth + 1, Q);
540 computeKnownBits(LHS, KnownZero, KnownOne, DL, Depth + 1, Q);
542 llvm_unreachable("missing use?");
544 case ICmpInst::ICMP_ULE:
546 APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0);
547 computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q);
548 // The known zero bits carry over
549 unsigned SignBits = KnownZeroTemp.countLeadingOnes();
550 KnownZero |= APInt::getHighBitsSet(BitWidth, SignBits);
553 case ICmpInst::ICMP_ULT:
555 APInt KnownZeroTemp(BitWidth, 0), KnownOneTemp(BitWidth, 0);
556 computeKnownBits(RHS, KnownZeroTemp, KnownOneTemp, DL, Depth + 1, Q);
557 // Whatever high bits in rhs are zero are known to be zero (if rhs is a
558 // power of 2, then one more).
559 unsigned SignBits = KnownZeroTemp.countLeadingOnes();
560 if (isKnownToBeAPowerOfTwo(RHS, false, Depth + 1, Query(Q, Cmp), DL))
562 KnownZero |= APInt::getHighBitsSet(BitWidth, SignBits);
568 /// Compute known bits in 'V' from conditions which are known to be true along
569 /// all paths leading to the context instruction. In particular, look for
570 /// cases where one branch of an interesting condition dominates the context
571 /// instruction. This does not do general dataflow.
572 /// NOTE: This code is EXPERIMENTAL and currently off by default.
573 static void computeKnownBitsFromDominatingCondition(Value *V, APInt &KnownZero,
575 const DataLayout &DL,
578 // Need both the dominator tree and the query location to do anything useful
579 if (!Q.DT || !Q.CxtI)
581 Instruction *Cxt = const_cast<Instruction *>(Q.CxtI);
583 // Avoid useless work
584 if (auto VI = dyn_cast<Instruction>(V))
585 if (VI->getParent() == Cxt->getParent())
588 // Note: We currently implement two options. It's not clear which of these
589 // will survive long term, we need data for that.
590 // Option 1 - Try walking the dominator tree looking for conditions which
591 // might apply. This works well for local conditions (loop guards, etc..),
592 // but not as well for things far from the context instruction (presuming a
593 // low max blocks explored). If we can set an high enough limit, this would
595 // Option 2 - We restrict out search to those conditions which are uses of
596 // the value we're interested in. This is independent of dom structure,
597 // but is slightly less powerful without looking through lots of use chains.
598 // It does handle conditions far from the context instruction (e.g. early
599 // function exits on entry) really well though.
601 // Option 1 - Search the dom tree
602 unsigned NumBlocksExplored = 0;
603 BasicBlock *Current = Cxt->getParent();
605 // Stop searching if we've gone too far up the chain
606 if (NumBlocksExplored >= DomConditionsMaxDomBlocks)
610 if (!Q.DT->getNode(Current)->getIDom())
612 Current = Q.DT->getNode(Current)->getIDom()->getBlock();
614 // found function entry
617 BranchInst *BI = dyn_cast<BranchInst>(Current->getTerminator());
618 if (!BI || BI->isUnconditional())
620 ICmpInst *Cmp = dyn_cast<ICmpInst>(BI->getCondition());
624 // We're looking for conditions that are guaranteed to hold at the context
625 // instruction. Finding a condition where one path dominates the context
626 // isn't enough because both the true and false cases could merge before
627 // the context instruction we're actually interested in. Instead, we need
628 // to ensure that the taken *edge* dominates the context instruction.
629 BasicBlock *BB0 = BI->getSuccessor(0);
630 BasicBlockEdge Edge(BI->getParent(), BB0);
631 if (!Edge.isSingleEdge() || !Q.DT->dominates(Edge, Q.CxtI->getParent()))
634 computeKnownBitsFromTrueCondition(V, Cmp, KnownZero, KnownOne, DL, Depth,
638 // Option 2 - Search the other uses of V
639 unsigned NumUsesExplored = 0;
640 for (auto U : V->users()) {
641 // Avoid massive lists
642 if (NumUsesExplored >= DomConditionsMaxUses)
645 // Consider only compare instructions uniquely controlling a branch
646 ICmpInst *Cmp = dyn_cast<ICmpInst>(U);
650 if (DomConditionsSingleCmpUse && !Cmp->hasOneUse())
653 for (auto *CmpU : Cmp->users()) {
654 BranchInst *BI = dyn_cast<BranchInst>(CmpU);
655 if (!BI || BI->isUnconditional())
657 // We're looking for conditions that are guaranteed to hold at the
658 // context instruction. Finding a condition where one path dominates
659 // the context isn't enough because both the true and false cases could
660 // merge before the context instruction we're actually interested in.
661 // Instead, we need to ensure that the taken *edge* dominates the context
663 BasicBlock *BB0 = BI->getSuccessor(0);
664 BasicBlockEdge Edge(BI->getParent(), BB0);
665 if (!Edge.isSingleEdge() || !Q.DT->dominates(Edge, Q.CxtI->getParent()))
668 computeKnownBitsFromTrueCondition(V, Cmp, KnownZero, KnownOne, DL, Depth,
674 static void computeKnownBitsFromAssume(Value *V, APInt &KnownZero,
675 APInt &KnownOne, const DataLayout &DL,
676 unsigned Depth, const Query &Q) {
677 // Use of assumptions is context-sensitive. If we don't have a context, we
679 if (!Q.AC || !Q.CxtI)
682 unsigned BitWidth = KnownZero.getBitWidth();
684 for (auto &AssumeVH : Q.AC->assumptions()) {
687 CallInst *I = cast<CallInst>(AssumeVH);
688 assert(I->getParent()->getParent() == Q.CxtI->getParent()->getParent() &&
689 "Got assumption for the wrong function!");
690 if (Q.ExclInvs.count(I))
693 // Warning: This loop can end up being somewhat performance sensetive.
694 // We're running this loop for once for each value queried resulting in a
695 // runtime of ~O(#assumes * #values).
697 assert(I->getCalledFunction()->getIntrinsicID() == Intrinsic::assume &&
698 "must be an assume intrinsic");
700 Value *Arg = I->getArgOperand(0);
702 if (Arg == V && isValidAssumeForContext(I, Q)) {
703 assert(BitWidth == 1 && "assume operand is not i1?");
704 KnownZero.clearAllBits();
705 KnownOne.setAllBits();
709 // The remaining tests are all recursive, so bail out if we hit the limit.
710 if (Depth == MaxDepth)
714 auto m_V = m_CombineOr(m_Specific(V),
715 m_CombineOr(m_PtrToInt(m_Specific(V)),
716 m_BitCast(m_Specific(V))));
718 CmpInst::Predicate Pred;
721 if (match(Arg, m_c_ICmp(Pred, m_V, m_Value(A))) &&
722 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
723 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
724 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
725 KnownZero |= RHSKnownZero;
726 KnownOne |= RHSKnownOne;
728 } else if (match(Arg,
729 m_c_ICmp(Pred, m_c_And(m_V, m_Value(B)), m_Value(A))) &&
730 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
731 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
732 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
733 APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0);
734 computeKnownBits(B, MaskKnownZero, MaskKnownOne, DL, Depth+1, Query(Q, I));
736 // For those bits in the mask that are known to be one, we can propagate
737 // known bits from the RHS to V.
738 KnownZero |= RHSKnownZero & MaskKnownOne;
739 KnownOne |= RHSKnownOne & MaskKnownOne;
740 // assume(~(v & b) = a)
741 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_And(m_V, m_Value(B))),
743 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
744 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
745 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
746 APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0);
747 computeKnownBits(B, MaskKnownZero, MaskKnownOne, DL, Depth+1, Query(Q, I));
749 // For those bits in the mask that are known to be one, we can propagate
750 // inverted known bits from the RHS to V.
751 KnownZero |= RHSKnownOne & MaskKnownOne;
752 KnownOne |= RHSKnownZero & MaskKnownOne;
754 } else if (match(Arg,
755 m_c_ICmp(Pred, m_c_Or(m_V, m_Value(B)), m_Value(A))) &&
756 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
757 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
758 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
759 APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
760 computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
762 // For those bits in B that are known to be zero, we can propagate known
763 // bits from the RHS to V.
764 KnownZero |= RHSKnownZero & BKnownZero;
765 KnownOne |= RHSKnownOne & BKnownZero;
766 // assume(~(v | b) = a)
767 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Or(m_V, m_Value(B))),
769 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
770 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
771 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
772 APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
773 computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
775 // For those bits in B that are known to be zero, we can propagate
776 // inverted known bits from the RHS to V.
777 KnownZero |= RHSKnownOne & BKnownZero;
778 KnownOne |= RHSKnownZero & BKnownZero;
780 } else if (match(Arg,
781 m_c_ICmp(Pred, m_c_Xor(m_V, m_Value(B)), m_Value(A))) &&
782 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
783 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
784 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
785 APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
786 computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
788 // For those bits in B that are known to be zero, we can propagate known
789 // bits from the RHS to V. For those bits in B that are known to be one,
790 // we can propagate inverted known bits from the RHS to V.
791 KnownZero |= RHSKnownZero & BKnownZero;
792 KnownOne |= RHSKnownOne & BKnownZero;
793 KnownZero |= RHSKnownOne & BKnownOne;
794 KnownOne |= RHSKnownZero & BKnownOne;
795 // assume(~(v ^ b) = a)
796 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Xor(m_V, m_Value(B))),
798 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
799 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
800 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
801 APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
802 computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
804 // For those bits in B that are known to be zero, we can propagate
805 // inverted known bits from the RHS to V. For those bits in B that are
806 // known to be one, we can propagate known bits from the RHS to V.
807 KnownZero |= RHSKnownOne & BKnownZero;
808 KnownOne |= RHSKnownZero & BKnownZero;
809 KnownZero |= RHSKnownZero & BKnownOne;
810 KnownOne |= RHSKnownOne & BKnownOne;
811 // assume(v << c = a)
812 } else if (match(Arg, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)),
814 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
815 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
816 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
817 // For those bits in RHS that are known, we can propagate them to known
818 // bits in V shifted to the right by C.
819 KnownZero |= RHSKnownZero.lshr(C->getZExtValue());
820 KnownOne |= RHSKnownOne.lshr(C->getZExtValue());
821 // assume(~(v << c) = a)
822 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))),
824 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
825 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
826 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
827 // For those bits in RHS that are known, we can propagate them inverted
828 // to known bits in V shifted to the right by C.
829 KnownZero |= RHSKnownOne.lshr(C->getZExtValue());
830 KnownOne |= RHSKnownZero.lshr(C->getZExtValue());
831 // assume(v >> c = a)
832 } else if (match(Arg,
833 m_c_ICmp(Pred, m_CombineOr(m_LShr(m_V, m_ConstantInt(C)),
834 m_AShr(m_V, m_ConstantInt(C))),
836 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
837 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
838 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
839 // For those bits in RHS that are known, we can propagate them to known
840 // bits in V shifted to the right by C.
841 KnownZero |= RHSKnownZero << C->getZExtValue();
842 KnownOne |= RHSKnownOne << C->getZExtValue();
843 // assume(~(v >> c) = a)
844 } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_CombineOr(
845 m_LShr(m_V, m_ConstantInt(C)),
846 m_AShr(m_V, m_ConstantInt(C)))),
848 Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q)) {
849 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
850 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
851 // For those bits in RHS that are known, we can propagate them inverted
852 // to known bits in V shifted to the right by C.
853 KnownZero |= RHSKnownOne << C->getZExtValue();
854 KnownOne |= RHSKnownZero << C->getZExtValue();
855 // assume(v >=_s c) where c is non-negative
856 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
857 Pred == ICmpInst::ICMP_SGE && isValidAssumeForContext(I, Q)) {
858 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
859 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
861 if (RHSKnownZero.isNegative()) {
862 // We know that the sign bit is zero.
863 KnownZero |= APInt::getSignBit(BitWidth);
865 // assume(v >_s c) where c is at least -1.
866 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
867 Pred == ICmpInst::ICMP_SGT && isValidAssumeForContext(I, Q)) {
868 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
869 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
871 if (RHSKnownOne.isAllOnesValue() || RHSKnownZero.isNegative()) {
872 // We know that the sign bit is zero.
873 KnownZero |= APInt::getSignBit(BitWidth);
875 // assume(v <=_s c) where c is negative
876 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
877 Pred == ICmpInst::ICMP_SLE && isValidAssumeForContext(I, Q)) {
878 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
879 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
881 if (RHSKnownOne.isNegative()) {
882 // We know that the sign bit is one.
883 KnownOne |= APInt::getSignBit(BitWidth);
885 // assume(v <_s c) where c is non-positive
886 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
887 Pred == ICmpInst::ICMP_SLT && isValidAssumeForContext(I, Q)) {
888 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
889 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
891 if (RHSKnownZero.isAllOnesValue() || RHSKnownOne.isNegative()) {
892 // We know that the sign bit is one.
893 KnownOne |= APInt::getSignBit(BitWidth);
896 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
897 Pred == ICmpInst::ICMP_ULE && isValidAssumeForContext(I, Q)) {
898 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
899 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
901 // Whatever high bits in c are zero are known to be zero.
903 APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
905 } else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
906 Pred == ICmpInst::ICMP_ULT && isValidAssumeForContext(I, Q)) {
907 APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
908 computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
910 // Whatever high bits in c are zero are known to be zero (if c is a power
911 // of 2, then one more).
912 if (isKnownToBeAPowerOfTwo(A, false, Depth + 1, Query(Q, I), DL))
914 APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes()+1);
917 APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
922 /// Determine which bits of V are known to be either zero or one and return
923 /// them in the KnownZero/KnownOne bit sets.
925 /// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
926 /// we cannot optimize based on the assumption that it is zero without changing
927 /// it to be an explicit zero. If we don't change it to zero, other code could
928 /// optimized based on the contradictory assumption that it is non-zero.
929 /// Because instcombine aggressively folds operations with undef args anyway,
930 /// this won't lose us code quality.
932 /// This function is defined on values with integer type, values with pointer
933 /// type, and vectors of integers. In the case
934 /// where V is a vector, known zero, and known one values are the
935 /// same width as the vector element, and the bit is set only if it is true
936 /// for all of the elements in the vector.
937 void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
938 const DataLayout &DL, unsigned Depth, const Query &Q) {
939 assert(V && "No Value?");
940 assert(Depth <= MaxDepth && "Limit Search Depth");
941 unsigned BitWidth = KnownZero.getBitWidth();
943 assert((V->getType()->isIntOrIntVectorTy() ||
944 V->getType()->getScalarType()->isPointerTy()) &&
945 "Not integer or pointer type!");
946 assert((DL.getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
947 (!V->getType()->isIntOrIntVectorTy() ||
948 V->getType()->getScalarSizeInBits() == BitWidth) &&
949 KnownZero.getBitWidth() == BitWidth &&
950 KnownOne.getBitWidth() == BitWidth &&
951 "V, KnownOne and KnownZero should have same BitWidth");
953 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
954 // We know all of the bits for a constant!
955 KnownOne = CI->getValue();
956 KnownZero = ~KnownOne;
959 // Null and aggregate-zero are all-zeros.
960 if (isa<ConstantPointerNull>(V) ||
961 isa<ConstantAggregateZero>(V)) {
962 KnownOne.clearAllBits();
963 KnownZero = APInt::getAllOnesValue(BitWidth);
966 // Handle a constant vector by taking the intersection of the known bits of
967 // each element. There is no real need to handle ConstantVector here, because
968 // we don't handle undef in any particularly useful way.
969 if (ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(V)) {
970 // We know that CDS must be a vector of integers. Take the intersection of
972 KnownZero.setAllBits(); KnownOne.setAllBits();
973 APInt Elt(KnownZero.getBitWidth(), 0);
974 for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) {
975 Elt = CDS->getElementAsInteger(i);
982 // The address of an aligned GlobalValue has trailing zeros.
983 if (auto *GO = dyn_cast<GlobalObject>(V)) {
984 unsigned Align = GO->getAlignment();
986 if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
987 Type *ObjectType = GVar->getType()->getElementType();
988 if (ObjectType->isSized()) {
989 // If the object is defined in the current Module, we'll be giving
990 // it the preferred alignment. Otherwise, we have to assume that it
991 // may only have the minimum ABI alignment.
992 if (!GVar->isDeclaration() && !GVar->isWeakForLinker())
993 Align = DL.getPreferredAlignment(GVar);
995 Align = DL.getABITypeAlignment(ObjectType);
1000 KnownZero = APInt::getLowBitsSet(BitWidth,
1001 countTrailingZeros(Align));
1003 KnownZero.clearAllBits();
1004 KnownOne.clearAllBits();
1008 if (Argument *A = dyn_cast<Argument>(V)) {
1009 unsigned Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0;
1011 if (!Align && A->hasStructRetAttr()) {
1012 // An sret parameter has at least the ABI alignment of the return type.
1013 Type *EltTy = cast<PointerType>(A->getType())->getElementType();
1014 if (EltTy->isSized())
1015 Align = DL.getABITypeAlignment(EltTy);
1019 KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
1021 KnownZero.clearAllBits();
1022 KnownOne.clearAllBits();
1024 // Don't give up yet... there might be an assumption that provides more
1026 computeKnownBitsFromAssume(V, KnownZero, KnownOne, DL, Depth, Q);
1028 // Or a dominating condition for that matter
1029 if (EnableDomConditions && Depth <= DomConditionsMaxDepth)
1030 computeKnownBitsFromDominatingCondition(V, KnownZero, KnownOne, DL,
1035 // Start out not knowing anything.
1036 KnownZero.clearAllBits(); KnownOne.clearAllBits();
1038 // Limit search depth.
1039 // All recursive calls that increase depth must come after this.
1040 if (Depth == MaxDepth)
1043 // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
1044 // the bits of its aliasee.
1045 if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
1046 if (!GA->mayBeOverridden())
1047 computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, DL, Depth + 1, Q);
1051 // Check whether a nearby assume intrinsic can determine some known bits.
1052 computeKnownBitsFromAssume(V, KnownZero, KnownOne, DL, Depth, Q);
1054 // Check whether there's a dominating condition which implies something about
1055 // this value at the given context.
1056 if (EnableDomConditions && Depth <= DomConditionsMaxDepth)
1057 computeKnownBitsFromDominatingCondition(V, KnownZero, KnownOne, DL, Depth,
1060 Operator *I = dyn_cast<Operator>(V);
1063 APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
1064 switch (I->getOpcode()) {
1066 case Instruction::Load:
1067 if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range))
1068 computeKnownBitsFromRangeMetadata(*MD, KnownZero);
1070 case Instruction::And: {
1071 // If either the LHS or the RHS are Zero, the result is zero.
1072 computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q);
1073 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1075 // Output known-1 bits are only known if set in both the LHS & RHS.
1076 KnownOne &= KnownOne2;
1077 // Output known-0 are known to be clear if zero in either the LHS | RHS.
1078 KnownZero |= KnownZero2;
1081 case Instruction::Or: {
1082 computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q);
1083 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1085 // Output known-0 bits are only known if clear in both the LHS & RHS.
1086 KnownZero &= KnownZero2;
1087 // Output known-1 are known to be set if set in either the LHS | RHS.
1088 KnownOne |= KnownOne2;
1091 case Instruction::Xor: {
1092 computeKnownBits(I->getOperand(1), KnownZero, KnownOne, DL, Depth + 1, Q);
1093 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1095 // Output known-0 bits are known if clear or set in both the LHS & RHS.
1096 APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
1097 // Output known-1 are known to be set if set in only one of the LHS, RHS.
1098 KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
1099 KnownZero = KnownZeroOut;
1102 case Instruction::Mul: {
1103 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
1104 computeKnownBitsMul(I->getOperand(0), I->getOperand(1), NSW, KnownZero,
1105 KnownOne, KnownZero2, KnownOne2, DL, Depth, Q);
1108 case Instruction::UDiv: {
1109 // For the purposes of computing leading zeros we can conservatively
1110 // treat a udiv as a logical right shift by the power of 2 known to
1111 // be less than the denominator.
1112 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1113 unsigned LeadZ = KnownZero2.countLeadingOnes();
1115 KnownOne2.clearAllBits();
1116 KnownZero2.clearAllBits();
1117 computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1118 unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
1119 if (RHSUnknownLeadingOnes != BitWidth)
1120 LeadZ = std::min(BitWidth,
1121 LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
1123 KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ);
1126 case Instruction::Select:
1127 computeKnownBits(I->getOperand(2), KnownZero, KnownOne, DL, Depth + 1, Q);
1128 computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1130 // Only known if known in both the LHS and RHS.
1131 KnownOne &= KnownOne2;
1132 KnownZero &= KnownZero2;
1134 case Instruction::FPTrunc:
1135 case Instruction::FPExt:
1136 case Instruction::FPToUI:
1137 case Instruction::FPToSI:
1138 case Instruction::SIToFP:
1139 case Instruction::UIToFP:
1140 break; // Can't work with floating point.
1141 case Instruction::PtrToInt:
1142 case Instruction::IntToPtr:
1143 case Instruction::AddrSpaceCast: // Pointers could be different sizes.
1144 // FALL THROUGH and handle them the same as zext/trunc.
1145 case Instruction::ZExt:
1146 case Instruction::Trunc: {
1147 Type *SrcTy = I->getOperand(0)->getType();
1149 unsigned SrcBitWidth;
1150 // Note that we handle pointer operands here because of inttoptr/ptrtoint
1151 // which fall through here.
1152 SrcBitWidth = DL.getTypeSizeInBits(SrcTy->getScalarType());
1154 assert(SrcBitWidth && "SrcBitWidth can't be zero");
1155 KnownZero = KnownZero.zextOrTrunc(SrcBitWidth);
1156 KnownOne = KnownOne.zextOrTrunc(SrcBitWidth);
1157 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1158 KnownZero = KnownZero.zextOrTrunc(BitWidth);
1159 KnownOne = KnownOne.zextOrTrunc(BitWidth);
1160 // Any top bits are known to be zero.
1161 if (BitWidth > SrcBitWidth)
1162 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
1165 case Instruction::BitCast: {
1166 Type *SrcTy = I->getOperand(0)->getType();
1167 if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) &&
1168 // TODO: For now, not handling conversions like:
1169 // (bitcast i64 %x to <2 x i32>)
1170 !I->getType()->isVectorTy()) {
1171 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1176 case Instruction::SExt: {
1177 // Compute the bits in the result that are not present in the input.
1178 unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits();
1180 KnownZero = KnownZero.trunc(SrcBitWidth);
1181 KnownOne = KnownOne.trunc(SrcBitWidth);
1182 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1183 KnownZero = KnownZero.zext(BitWidth);
1184 KnownOne = KnownOne.zext(BitWidth);
1186 // If the sign bit of the input is known set or clear, then we know the
1187 // top bits of the result.
1188 if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
1189 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
1190 else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
1191 KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
1194 case Instruction::Shl:
1195 // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
1196 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
1197 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
1198 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1199 KnownZero <<= ShiftAmt;
1200 KnownOne <<= ShiftAmt;
1201 KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
1204 case Instruction::LShr:
1205 // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
1206 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
1207 // Compute the new bits that are at the top now.
1208 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
1210 // Unsigned shift right.
1211 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1212 KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
1213 KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
1214 // high bits known zero.
1215 KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
1218 case Instruction::AShr:
1219 // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
1220 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
1221 // Compute the new bits that are at the top now.
1222 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
1224 // Signed shift right.
1225 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1226 KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
1227 KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
1229 APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
1230 if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
1231 KnownZero |= HighBits;
1232 else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
1233 KnownOne |= HighBits;
1236 case Instruction::Sub: {
1237 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
1238 computeKnownBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW,
1239 KnownZero, KnownOne, KnownZero2, KnownOne2, DL,
1243 case Instruction::Add: {
1244 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
1245 computeKnownBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW,
1246 KnownZero, KnownOne, KnownZero2, KnownOne2, DL,
1250 case Instruction::SRem:
1251 if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
1252 APInt RA = Rem->getValue().abs();
1253 if (RA.isPowerOf2()) {
1254 APInt LowBits = RA - 1;
1255 computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, DL, Depth + 1,
1258 // The low bits of the first operand are unchanged by the srem.
1259 KnownZero = KnownZero2 & LowBits;
1260 KnownOne = KnownOne2 & LowBits;
1262 // If the first operand is non-negative or has all low bits zero, then
1263 // the upper bits are all zero.
1264 if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
1265 KnownZero |= ~LowBits;
1267 // If the first operand is negative and not all low bits are zero, then
1268 // the upper bits are all one.
1269 if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
1270 KnownOne |= ~LowBits;
1272 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
1276 // The sign bit is the LHS's sign bit, except when the result of the
1277 // remainder is zero.
1278 if (KnownZero.isNonNegative()) {
1279 APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
1280 computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, DL,
1282 // If it's known zero, our sign bit is also zero.
1283 if (LHSKnownZero.isNegative())
1284 KnownZero.setBit(BitWidth - 1);
1288 case Instruction::URem: {
1289 if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
1290 APInt RA = Rem->getValue();
1291 if (RA.isPowerOf2()) {
1292 APInt LowBits = (RA - 1);
1293 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1,
1295 KnownZero |= ~LowBits;
1296 KnownOne &= LowBits;
1301 // Since the result is less than or equal to either operand, any leading
1302 // zero bits in either operand must also exist in the result.
1303 computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
1304 computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q);
1306 unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
1307 KnownZero2.countLeadingOnes());
1308 KnownOne.clearAllBits();
1309 KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
1313 case Instruction::Alloca: {
1314 AllocaInst *AI = cast<AllocaInst>(V);
1315 unsigned Align = AI->getAlignment();
1317 Align = DL.getABITypeAlignment(AI->getType()->getElementType());
1320 KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
1323 case Instruction::GetElementPtr: {
1324 // Analyze all of the subscripts of this getelementptr instruction
1325 // to determine if we can prove known low zero bits.
1326 APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
1327 computeKnownBits(I->getOperand(0), LocalKnownZero, LocalKnownOne, DL,
1329 unsigned TrailZ = LocalKnownZero.countTrailingOnes();
1331 gep_type_iterator GTI = gep_type_begin(I);
1332 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
1333 Value *Index = I->getOperand(i);
1334 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
1335 // Handle struct member offset arithmetic.
1337 // Handle case when index is vector zeroinitializer
1338 Constant *CIndex = cast<Constant>(Index);
1339 if (CIndex->isZeroValue())
1342 if (CIndex->getType()->isVectorTy())
1343 Index = CIndex->getSplatValue();
1345 unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
1346 const StructLayout *SL = DL.getStructLayout(STy);
1347 uint64_t Offset = SL->getElementOffset(Idx);
1348 TrailZ = std::min<unsigned>(TrailZ,
1349 countTrailingZeros(Offset));
1351 // Handle array index arithmetic.
1352 Type *IndexedTy = GTI.getIndexedType();
1353 if (!IndexedTy->isSized()) {
1357 unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits();
1358 uint64_t TypeSize = DL.getTypeAllocSize(IndexedTy);
1359 LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
1360 computeKnownBits(Index, LocalKnownZero, LocalKnownOne, DL, Depth + 1,
1362 TrailZ = std::min(TrailZ,
1363 unsigned(countTrailingZeros(TypeSize) +
1364 LocalKnownZero.countTrailingOnes()));
1368 KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ);
1371 case Instruction::PHI: {
1372 PHINode *P = cast<PHINode>(I);
1373 // Handle the case of a simple two-predecessor recurrence PHI.
1374 // There's a lot more that could theoretically be done here, but
1375 // this is sufficient to catch some interesting cases.
1376 if (P->getNumIncomingValues() == 2) {
1377 for (unsigned i = 0; i != 2; ++i) {
1378 Value *L = P->getIncomingValue(i);
1379 Value *R = P->getIncomingValue(!i);
1380 Operator *LU = dyn_cast<Operator>(L);
1383 unsigned Opcode = LU->getOpcode();
1384 // Check for operations that have the property that if
1385 // both their operands have low zero bits, the result
1386 // will have low zero bits.
1387 if (Opcode == Instruction::Add ||
1388 Opcode == Instruction::Sub ||
1389 Opcode == Instruction::And ||
1390 Opcode == Instruction::Or ||
1391 Opcode == Instruction::Mul) {
1392 Value *LL = LU->getOperand(0);
1393 Value *LR = LU->getOperand(1);
1394 // Find a recurrence.
1401 // Ok, we have a PHI of the form L op= R. Check for low
1403 computeKnownBits(R, KnownZero2, KnownOne2, DL, Depth + 1, Q);
1405 // We need to take the minimum number of known bits
1406 APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
1407 computeKnownBits(L, KnownZero3, KnownOne3, DL, Depth + 1, Q);
1409 KnownZero = APInt::getLowBitsSet(BitWidth,
1410 std::min(KnownZero2.countTrailingOnes(),
1411 KnownZero3.countTrailingOnes()));
1417 // Unreachable blocks may have zero-operand PHI nodes.
1418 if (P->getNumIncomingValues() == 0)
1421 // Otherwise take the unions of the known bit sets of the operands,
1422 // taking conservative care to avoid excessive recursion.
1423 if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) {
1424 // Skip if every incoming value references to ourself.
1425 if (dyn_cast_or_null<UndefValue>(P->hasConstantValue()))
1428 KnownZero = APInt::getAllOnesValue(BitWidth);
1429 KnownOne = APInt::getAllOnesValue(BitWidth);
1430 for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
1431 // Skip direct self references.
1432 if (P->getIncomingValue(i) == P) continue;
1434 KnownZero2 = APInt(BitWidth, 0);
1435 KnownOne2 = APInt(BitWidth, 0);
1436 // Recurse, but cap the recursion to one level, because we don't
1437 // want to waste time spinning around in loops.
1438 computeKnownBits(P->getIncomingValue(i), KnownZero2, KnownOne2, DL,
1440 KnownZero &= KnownZero2;
1441 KnownOne &= KnownOne2;
1442 // If all bits have been ruled out, there's no need to check
1444 if (!KnownZero && !KnownOne)
1450 case Instruction::Call:
1451 case Instruction::Invoke:
1452 if (MDNode *MD = cast<Instruction>(I)->getMetadata(LLVMContext::MD_range))
1453 computeKnownBitsFromRangeMetadata(*MD, KnownZero);
1454 // If a range metadata is attached to this IntrinsicInst, intersect the
1455 // explicit range specified by the metadata and the implicit range of
1457 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
1458 switch (II->getIntrinsicID()) {
1460 case Intrinsic::ctlz:
1461 case Intrinsic::cttz: {
1462 unsigned LowBits = Log2_32(BitWidth)+1;
1463 // If this call is undefined for 0, the result will be less than 2^n.
1464 if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
1466 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
1469 case Intrinsic::ctpop: {
1470 unsigned LowBits = Log2_32(BitWidth)+1;
1471 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
1474 case Intrinsic::x86_sse42_crc32_64_64:
1475 KnownZero |= APInt::getHighBitsSet(64, 32);
1480 case Instruction::ExtractValue:
1481 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) {
1482 ExtractValueInst *EVI = cast<ExtractValueInst>(I);
1483 if (EVI->getNumIndices() != 1) break;
1484 if (EVI->getIndices()[0] == 0) {
1485 switch (II->getIntrinsicID()) {
1487 case Intrinsic::uadd_with_overflow:
1488 case Intrinsic::sadd_with_overflow:
1489 computeKnownBitsAddSub(true, II->getArgOperand(0),
1490 II->getArgOperand(1), false, KnownZero,
1491 KnownOne, KnownZero2, KnownOne2, DL, Depth, Q);
1493 case Intrinsic::usub_with_overflow:
1494 case Intrinsic::ssub_with_overflow:
1495 computeKnownBitsAddSub(false, II->getArgOperand(0),
1496 II->getArgOperand(1), false, KnownZero,
1497 KnownOne, KnownZero2, KnownOne2, DL, Depth, Q);
1499 case Intrinsic::umul_with_overflow:
1500 case Intrinsic::smul_with_overflow:
1501 computeKnownBitsMul(II->getArgOperand(0), II->getArgOperand(1), false,
1502 KnownZero, KnownOne, KnownZero2, KnownOne2, DL,
1510 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
1513 /// Determine whether the sign bit is known to be zero or one.
1514 /// Convenience wrapper around computeKnownBits.
1515 void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
1516 const DataLayout &DL, unsigned Depth, const Query &Q) {
1517 unsigned BitWidth = getBitWidth(V->getType(), DL);
1523 APInt ZeroBits(BitWidth, 0);
1524 APInt OneBits(BitWidth, 0);
1525 computeKnownBits(V, ZeroBits, OneBits, DL, Depth, Q);
1526 KnownOne = OneBits[BitWidth - 1];
1527 KnownZero = ZeroBits[BitWidth - 1];
1530 /// Return true if the given value is known to have exactly one
1531 /// bit set when defined. For vectors return true if every element is known to
1532 /// be a power of two when defined. Supports values with integer or pointer
1533 /// types and vectors of integers.
1534 bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
1535 const Query &Q, const DataLayout &DL) {
1536 if (Constant *C = dyn_cast<Constant>(V)) {
1537 if (C->isNullValue())
1539 if (ConstantInt *CI = dyn_cast<ConstantInt>(C))
1540 return CI->getValue().isPowerOf2();
1541 // TODO: Handle vector constants.
1544 // 1 << X is clearly a power of two if the one is not shifted off the end. If
1545 // it is shifted off the end then the result is undefined.
1546 if (match(V, m_Shl(m_One(), m_Value())))
1549 // (signbit) >>l X is clearly a power of two if the one is not shifted off the
1550 // bottom. If it is shifted off the bottom then the result is undefined.
1551 if (match(V, m_LShr(m_SignBit(), m_Value())))
1554 // The remaining tests are all recursive, so bail out if we hit the limit.
1555 if (Depth++ == MaxDepth)
1558 Value *X = nullptr, *Y = nullptr;
1559 // A shift of a power of two is a power of two or zero.
1560 if (OrZero && (match(V, m_Shl(m_Value(X), m_Value())) ||
1561 match(V, m_Shr(m_Value(X), m_Value()))))
1562 return isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q, DL);
1564 if (ZExtInst *ZI = dyn_cast<ZExtInst>(V))
1565 return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth, Q, DL);
1567 if (SelectInst *SI = dyn_cast<SelectInst>(V))
1568 return isKnownToBeAPowerOfTwo(SI->getTrueValue(), OrZero, Depth, Q, DL) &&
1569 isKnownToBeAPowerOfTwo(SI->getFalseValue(), OrZero, Depth, Q, DL);
1571 if (OrZero && match(V, m_And(m_Value(X), m_Value(Y)))) {
1572 // A power of two and'd with anything is a power of two or zero.
1573 if (isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q, DL) ||
1574 isKnownToBeAPowerOfTwo(Y, /*OrZero*/ true, Depth, Q, DL))
1576 // X & (-X) is always a power of two or zero.
1577 if (match(X, m_Neg(m_Specific(Y))) || match(Y, m_Neg(m_Specific(X))))
1582 // Adding a power-of-two or zero to the same power-of-two or zero yields
1583 // either the original power-of-two, a larger power-of-two or zero.
1584 if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
1585 OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
1586 if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
1587 if (match(X, m_And(m_Specific(Y), m_Value())) ||
1588 match(X, m_And(m_Value(), m_Specific(Y))))
1589 if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth, Q, DL))
1591 if (match(Y, m_And(m_Specific(X), m_Value())) ||
1592 match(Y, m_And(m_Value(), m_Specific(X))))
1593 if (isKnownToBeAPowerOfTwo(X, OrZero, Depth, Q, DL))
1596 unsigned BitWidth = V->getType()->getScalarSizeInBits();
1597 APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0);
1598 computeKnownBits(X, LHSZeroBits, LHSOneBits, DL, Depth, Q);
1600 APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0);
1601 computeKnownBits(Y, RHSZeroBits, RHSOneBits, DL, Depth, Q);
1602 // If i8 V is a power of two or zero:
1603 // ZeroBits: 1 1 1 0 1 1 1 1
1604 // ~ZeroBits: 0 0 0 1 0 0 0 0
1605 if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2())
1606 // If OrZero isn't set, we cannot give back a zero result.
1607 // Make sure either the LHS or RHS has a bit set.
1608 if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue())
1613 // An exact divide or right shift can only shift off zero bits, so the result
1614 // is a power of two only if the first operand is a power of two and not
1615 // copying a sign bit (sdiv int_min, 2).
1616 if (match(V, m_Exact(m_LShr(m_Value(), m_Value()))) ||
1617 match(V, m_Exact(m_UDiv(m_Value(), m_Value())))) {
1618 return isKnownToBeAPowerOfTwo(cast<Operator>(V)->getOperand(0), OrZero,
1625 /// \brief Test whether a GEP's result is known to be non-null.
1627 /// Uses properties inherent in a GEP to try to determine whether it is known
1630 /// Currently this routine does not support vector GEPs.
1631 static bool isGEPKnownNonNull(GEPOperator *GEP, const DataLayout &DL,
1632 unsigned Depth, const Query &Q) {
1633 if (!GEP->isInBounds() || GEP->getPointerAddressSpace() != 0)
1636 // FIXME: Support vector-GEPs.
1637 assert(GEP->getType()->isPointerTy() && "We only support plain pointer GEP");
1639 // If the base pointer is non-null, we cannot walk to a null address with an
1640 // inbounds GEP in address space zero.
1641 if (isKnownNonZero(GEP->getPointerOperand(), DL, Depth, Q))
1644 // Walk the GEP operands and see if any operand introduces a non-zero offset.
1645 // If so, then the GEP cannot produce a null pointer, as doing so would
1646 // inherently violate the inbounds contract within address space zero.
1647 for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
1648 GTI != GTE; ++GTI) {
1649 // Struct types are easy -- they must always be indexed by a constant.
1650 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
1651 ConstantInt *OpC = cast<ConstantInt>(GTI.getOperand());
1652 unsigned ElementIdx = OpC->getZExtValue();
1653 const StructLayout *SL = DL.getStructLayout(STy);
1654 uint64_t ElementOffset = SL->getElementOffset(ElementIdx);
1655 if (ElementOffset > 0)
1660 // If we have a zero-sized type, the index doesn't matter. Keep looping.
1661 if (DL.getTypeAllocSize(GTI.getIndexedType()) == 0)
1664 // Fast path the constant operand case both for efficiency and so we don't
1665 // increment Depth when just zipping down an all-constant GEP.
1666 if (ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand())) {
1672 // We post-increment Depth here because while isKnownNonZero increments it
1673 // as well, when we pop back up that increment won't persist. We don't want
1674 // to recurse 10k times just because we have 10k GEP operands. We don't
1675 // bail completely out because we want to handle constant GEPs regardless
1677 if (Depth++ >= MaxDepth)
1680 if (isKnownNonZero(GTI.getOperand(), DL, Depth, Q))
1687 /// Does the 'Range' metadata (which must be a valid MD_range operand list)
1688 /// ensure that the value it's attached to is never Value? 'RangeType' is
1689 /// is the type of the value described by the range.
1690 static bool rangeMetadataExcludesValue(MDNode* Ranges,
1691 const APInt& Value) {
1692 const unsigned NumRanges = Ranges->getNumOperands() / 2;
1693 assert(NumRanges >= 1);
1694 for (unsigned i = 0; i < NumRanges; ++i) {
1695 ConstantInt *Lower =
1696 mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 0));
1697 ConstantInt *Upper =
1698 mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 1));
1699 ConstantRange Range(Lower->getValue(), Upper->getValue());
1700 if (Range.contains(Value))
1706 /// Return true if the given value is known to be non-zero when defined.
1707 /// For vectors return true if every element is known to be non-zero when
1708 /// defined. Supports values with integer or pointer type and vectors of
1710 bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth,
1712 if (Constant *C = dyn_cast<Constant>(V)) {
1713 if (C->isNullValue())
1715 if (isa<ConstantInt>(C))
1716 // Must be non-zero due to null test above.
1718 // TODO: Handle vectors
1722 if (Instruction* I = dyn_cast<Instruction>(V)) {
1723 if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) {
1724 // If the possible ranges don't contain zero, then the value is
1725 // definitely non-zero.
1726 if (IntegerType* Ty = dyn_cast<IntegerType>(V->getType())) {
1727 const APInt ZeroValue(Ty->getBitWidth(), 0);
1728 if (rangeMetadataExcludesValue(Ranges, ZeroValue))
1734 // The remaining tests are all recursive, so bail out if we hit the limit.
1735 if (Depth++ >= MaxDepth)
1738 // Check for pointer simplifications.
1739 if (V->getType()->isPointerTy()) {
1740 if (isKnownNonNull(V))
1742 if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
1743 if (isGEPKnownNonNull(GEP, DL, Depth, Q))
1747 unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), DL);
1749 // X | Y != 0 if X != 0 or Y != 0.
1750 Value *X = nullptr, *Y = nullptr;
1751 if (match(V, m_Or(m_Value(X), m_Value(Y))))
1752 return isKnownNonZero(X, DL, Depth, Q) || isKnownNonZero(Y, DL, Depth, Q);
1754 // ext X != 0 if X != 0.
1755 if (isa<SExtInst>(V) || isa<ZExtInst>(V))
1756 return isKnownNonZero(cast<Instruction>(V)->getOperand(0), DL, Depth, Q);
1758 // shl X, Y != 0 if X is odd. Note that the value of the shift is undefined
1759 // if the lowest bit is shifted off the end.
1760 if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
1761 // shl nuw can't remove any non-zero bits.
1762 OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
1763 if (BO->hasNoUnsignedWrap())
1764 return isKnownNonZero(X, DL, Depth, Q);
1766 APInt KnownZero(BitWidth, 0);
1767 APInt KnownOne(BitWidth, 0);
1768 computeKnownBits(X, KnownZero, KnownOne, DL, Depth, Q);
1772 // shr X, Y != 0 if X is negative. Note that the value of the shift is not
1773 // defined if the sign bit is shifted off the end.
1774 else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
1775 // shr exact can only shift out zero bits.
1776 PossiblyExactOperator *BO = cast<PossiblyExactOperator>(V);
1778 return isKnownNonZero(X, DL, Depth, Q);
1780 bool XKnownNonNegative, XKnownNegative;
1781 ComputeSignBit(X, XKnownNonNegative, XKnownNegative, DL, Depth, Q);
1785 // div exact can only produce a zero if the dividend is zero.
1786 else if (match(V, m_Exact(m_IDiv(m_Value(X), m_Value())))) {
1787 return isKnownNonZero(X, DL, Depth, Q);
1790 else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
1791 bool XKnownNonNegative, XKnownNegative;
1792 bool YKnownNonNegative, YKnownNegative;
1793 ComputeSignBit(X, XKnownNonNegative, XKnownNegative, DL, Depth, Q);
1794 ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, DL, Depth, Q);
1796 // If X and Y are both non-negative (as signed values) then their sum is not
1797 // zero unless both X and Y are zero.
1798 if (XKnownNonNegative && YKnownNonNegative)
1799 if (isKnownNonZero(X, DL, Depth, Q) || isKnownNonZero(Y, DL, Depth, Q))
1802 // If X and Y are both negative (as signed values) then their sum is not
1803 // zero unless both X and Y equal INT_MIN.
1804 if (BitWidth && XKnownNegative && YKnownNegative) {
1805 APInt KnownZero(BitWidth, 0);
1806 APInt KnownOne(BitWidth, 0);
1807 APInt Mask = APInt::getSignedMaxValue(BitWidth);
1808 // The sign bit of X is set. If some other bit is set then X is not equal
1810 computeKnownBits(X, KnownZero, KnownOne, DL, Depth, Q);
1811 if ((KnownOne & Mask) != 0)
1813 // The sign bit of Y is set. If some other bit is set then Y is not equal
1815 computeKnownBits(Y, KnownZero, KnownOne, DL, Depth, Q);
1816 if ((KnownOne & Mask) != 0)
1820 // The sum of a non-negative number and a power of two is not zero.
1821 if (XKnownNonNegative &&
1822 isKnownToBeAPowerOfTwo(Y, /*OrZero*/ false, Depth, Q, DL))
1824 if (YKnownNonNegative &&
1825 isKnownToBeAPowerOfTwo(X, /*OrZero*/ false, Depth, Q, DL))
1829 else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) {
1830 OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
1831 // If X and Y are non-zero then so is X * Y as long as the multiplication
1832 // does not overflow.
1833 if ((BO->hasNoSignedWrap() || BO->hasNoUnsignedWrap()) &&
1834 isKnownNonZero(X, DL, Depth, Q) && isKnownNonZero(Y, DL, Depth, Q))
1837 // (C ? X : Y) != 0 if X != 0 and Y != 0.
1838 else if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
1839 if (isKnownNonZero(SI->getTrueValue(), DL, Depth, Q) &&
1840 isKnownNonZero(SI->getFalseValue(), DL, Depth, Q))
1844 if (!BitWidth) return false;
1845 APInt KnownZero(BitWidth, 0);
1846 APInt KnownOne(BitWidth, 0);
1847 computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q);
1848 return KnownOne != 0;
1851 /// Return true if 'V & Mask' is known to be zero. We use this predicate to
1852 /// simplify operations downstream. Mask is known to be zero for bits that V
1855 /// This function is defined on values with integer type, values with pointer
1856 /// type, and vectors of integers. In the case
1857 /// where V is a vector, the mask, known zero, and known one values are the
1858 /// same width as the vector element, and the bit is set only if it is true
1859 /// for all of the elements in the vector.
1860 bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
1861 unsigned Depth, const Query &Q) {
1862 APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
1863 computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q);
1864 return (KnownZero & Mask) == Mask;
1869 /// Return the number of times the sign bit of the register is replicated into
1870 /// the other bits. We know that at least 1 bit is always equal to the sign bit
1871 /// (itself), but other cases can give us information. For example, immediately
1872 /// after an "ashr X, 2", we know that the top 3 bits are all equal to each
1873 /// other, so we return 3.
1875 /// 'Op' must have a scalar integer type.
1877 unsigned ComputeNumSignBits(Value *V, const DataLayout &DL, unsigned Depth,
1879 unsigned TyBits = DL.getTypeSizeInBits(V->getType()->getScalarType());
1881 unsigned FirstAnswer = 1;
1883 // Note that ConstantInt is handled by the general computeKnownBits case
1887 return 1; // Limit search depth.
1889 Operator *U = dyn_cast<Operator>(V);
1890 switch (Operator::getOpcode(V)) {
1892 case Instruction::SExt:
1893 Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits();
1894 return ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q) + Tmp;
1896 case Instruction::SDiv: {
1897 const APInt *Denominator;
1898 // sdiv X, C -> adds log(C) sign bits.
1899 if (match(U->getOperand(1), m_APInt(Denominator))) {
1901 // Ignore non-positive denominator.
1902 if (!Denominator->isStrictlyPositive())
1905 // Calculate the incoming numerator bits.
1906 unsigned NumBits = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1908 // Add floor(log(C)) bits to the numerator bits.
1909 return std::min(TyBits, NumBits + Denominator->logBase2());
1914 case Instruction::SRem: {
1915 const APInt *Denominator;
1916 // srem X, C -> we know that the result is within [-C+1,C) when C is a
1917 // positive constant. This let us put a lower bound on the number of sign
1919 if (match(U->getOperand(1), m_APInt(Denominator))) {
1921 // Ignore non-positive denominator.
1922 if (!Denominator->isStrictlyPositive())
1925 // Calculate the incoming numerator bits. SRem by a positive constant
1926 // can't lower the number of sign bits.
1928 ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1930 // Calculate the leading sign bit constraints by examining the
1931 // denominator. Given that the denominator is positive, there are two
1934 // 1. the numerator is positive. The result range is [0,C) and [0,C) u<
1935 // (1 << ceilLogBase2(C)).
1937 // 2. the numerator is negative. Then the result range is (-C,0] and
1938 // integers in (-C,0] are either 0 or >u (-1 << ceilLogBase2(C)).
1940 // Thus a lower bound on the number of sign bits is `TyBits -
1941 // ceilLogBase2(C)`.
1943 unsigned ResBits = TyBits - Denominator->ceilLogBase2();
1944 return std::max(NumrBits, ResBits);
1949 case Instruction::AShr: {
1950 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1951 // ashr X, C -> adds C sign bits. Vectors too.
1953 if (match(U->getOperand(1), m_APInt(ShAmt))) {
1954 Tmp += ShAmt->getZExtValue();
1955 if (Tmp > TyBits) Tmp = TyBits;
1959 case Instruction::Shl: {
1961 if (match(U->getOperand(1), m_APInt(ShAmt))) {
1962 // shl destroys sign bits.
1963 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1964 Tmp2 = ShAmt->getZExtValue();
1965 if (Tmp2 >= TyBits || // Bad shift.
1966 Tmp2 >= Tmp) break; // Shifted all sign bits out.
1971 case Instruction::And:
1972 case Instruction::Or:
1973 case Instruction::Xor: // NOT is handled here.
1974 // Logical binary ops preserve the number of sign bits at the worst.
1975 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1977 Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q);
1978 FirstAnswer = std::min(Tmp, Tmp2);
1979 // We computed what we know about the sign bits as our first
1980 // answer. Now proceed to the generic code that uses
1981 // computeKnownBits, and pick whichever answer is better.
1985 case Instruction::Select:
1986 Tmp = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q);
1987 if (Tmp == 1) return 1; // Early out.
1988 Tmp2 = ComputeNumSignBits(U->getOperand(2), DL, Depth + 1, Q);
1989 return std::min(Tmp, Tmp2);
1991 case Instruction::Add:
1992 // Add can have at most one carry bit. Thus we know that the output
1993 // is, at worst, one more bit than the inputs.
1994 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
1995 if (Tmp == 1) return 1; // Early out.
1997 // Special case decrementing a value (ADD X, -1):
1998 if (const auto *CRHS = dyn_cast<Constant>(U->getOperand(1)))
1999 if (CRHS->isAllOnesValue()) {
2000 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
2001 computeKnownBits(U->getOperand(0), KnownZero, KnownOne, DL, Depth + 1,
2004 // If the input is known to be 0 or 1, the output is 0/-1, which is all
2006 if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
2009 // If we are subtracting one from a positive number, there is no carry
2010 // out of the result.
2011 if (KnownZero.isNegative())
2015 Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q);
2016 if (Tmp2 == 1) return 1;
2017 return std::min(Tmp, Tmp2)-1;
2019 case Instruction::Sub:
2020 Tmp2 = ComputeNumSignBits(U->getOperand(1), DL, Depth + 1, Q);
2021 if (Tmp2 == 1) return 1;
2024 if (const auto *CLHS = dyn_cast<Constant>(U->getOperand(0)))
2025 if (CLHS->isNullValue()) {
2026 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
2027 computeKnownBits(U->getOperand(1), KnownZero, KnownOne, DL, Depth + 1,
2029 // If the input is known to be 0 or 1, the output is 0/-1, which is all
2031 if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
2034 // If the input is known to be positive (the sign bit is known clear),
2035 // the output of the NEG has the same number of sign bits as the input.
2036 if (KnownZero.isNegative())
2039 // Otherwise, we treat this like a SUB.
2042 // Sub can have at most one carry bit. Thus we know that the output
2043 // is, at worst, one more bit than the inputs.
2044 Tmp = ComputeNumSignBits(U->getOperand(0), DL, Depth + 1, Q);
2045 if (Tmp == 1) return 1; // Early out.
2046 return std::min(Tmp, Tmp2)-1;
2048 case Instruction::PHI: {
2049 PHINode *PN = cast<PHINode>(U);
2050 unsigned NumIncomingValues = PN->getNumIncomingValues();
2051 // Don't analyze large in-degree PHIs.
2052 if (NumIncomingValues > 4) break;
2053 // Unreachable blocks may have zero-operand PHI nodes.
2054 if (NumIncomingValues == 0) break;
2056 // Take the minimum of all incoming values. This can't infinitely loop
2057 // because of our depth threshold.
2058 Tmp = ComputeNumSignBits(PN->getIncomingValue(0), DL, Depth + 1, Q);
2059 for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) {
2060 if (Tmp == 1) return Tmp;
2062 Tmp, ComputeNumSignBits(PN->getIncomingValue(i), DL, Depth + 1, Q));
2067 case Instruction::Trunc:
2068 // FIXME: it's tricky to do anything useful for this, but it is an important
2069 // case for targets like X86.
2073 // Finally, if we can prove that the top bits of the result are 0's or 1's,
2074 // use this information.
2075 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
2077 computeKnownBits(V, KnownZero, KnownOne, DL, Depth, Q);
2079 if (KnownZero.isNegative()) { // sign bit is 0
2081 } else if (KnownOne.isNegative()) { // sign bit is 1;
2088 // Okay, we know that the sign bit in Mask is set. Use CLZ to determine
2089 // the number of identical bits in the top of the input value.
2091 Mask <<= Mask.getBitWidth()-TyBits;
2092 // Return # leading zeros. We use 'min' here in case Val was zero before
2093 // shifting. We don't want to return '64' as for an i32 "0".
2094 return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
2097 /// This function computes the integer multiple of Base that equals V.
2098 /// If successful, it returns true and returns the multiple in
2099 /// Multiple. If unsuccessful, it returns false. It looks
2100 /// through SExt instructions only if LookThroughSExt is true.
2101 bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
2102 bool LookThroughSExt, unsigned Depth) {
2103 const unsigned MaxDepth = 6;
2105 assert(V && "No Value?");
2106 assert(Depth <= MaxDepth && "Limit Search Depth");
2107 assert(V->getType()->isIntegerTy() && "Not integer or pointer type!");
2109 Type *T = V->getType();
2111 ConstantInt *CI = dyn_cast<ConstantInt>(V);
2121 ConstantExpr *CO = dyn_cast<ConstantExpr>(V);
2122 Constant *BaseVal = ConstantInt::get(T, Base);
2123 if (CO && CO == BaseVal) {
2125 Multiple = ConstantInt::get(T, 1);
2129 if (CI && CI->getZExtValue() % Base == 0) {
2130 Multiple = ConstantInt::get(T, CI->getZExtValue() / Base);
2134 if (Depth == MaxDepth) return false; // Limit search depth.
2136 Operator *I = dyn_cast<Operator>(V);
2137 if (!I) return false;
2139 switch (I->getOpcode()) {
2141 case Instruction::SExt:
2142 if (!LookThroughSExt) return false;
2143 // otherwise fall through to ZExt
2144 case Instruction::ZExt:
2145 return ComputeMultiple(I->getOperand(0), Base, Multiple,
2146 LookThroughSExt, Depth+1);
2147 case Instruction::Shl:
2148 case Instruction::Mul: {
2149 Value *Op0 = I->getOperand(0);
2150 Value *Op1 = I->getOperand(1);
2152 if (I->getOpcode() == Instruction::Shl) {
2153 ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1);
2154 if (!Op1CI) return false;
2155 // Turn Op0 << Op1 into Op0 * 2^Op1
2156 APInt Op1Int = Op1CI->getValue();
2157 uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1);
2158 APInt API(Op1Int.getBitWidth(), 0);
2159 API.setBit(BitToSet);
2160 Op1 = ConstantInt::get(V->getContext(), API);
2163 Value *Mul0 = nullptr;
2164 if (ComputeMultiple(Op0, Base, Mul0, LookThroughSExt, Depth+1)) {
2165 if (Constant *Op1C = dyn_cast<Constant>(Op1))
2166 if (Constant *MulC = dyn_cast<Constant>(Mul0)) {
2167 if (Op1C->getType()->getPrimitiveSizeInBits() <
2168 MulC->getType()->getPrimitiveSizeInBits())
2169 Op1C = ConstantExpr::getZExt(Op1C, MulC->getType());
2170 if (Op1C->getType()->getPrimitiveSizeInBits() >
2171 MulC->getType()->getPrimitiveSizeInBits())
2172 MulC = ConstantExpr::getZExt(MulC, Op1C->getType());
2174 // V == Base * (Mul0 * Op1), so return (Mul0 * Op1)
2175 Multiple = ConstantExpr::getMul(MulC, Op1C);
2179 if (ConstantInt *Mul0CI = dyn_cast<ConstantInt>(Mul0))
2180 if (Mul0CI->getValue() == 1) {
2181 // V == Base * Op1, so return Op1
2187 Value *Mul1 = nullptr;
2188 if (ComputeMultiple(Op1, Base, Mul1, LookThroughSExt, Depth+1)) {
2189 if (Constant *Op0C = dyn_cast<Constant>(Op0))
2190 if (Constant *MulC = dyn_cast<Constant>(Mul1)) {
2191 if (Op0C->getType()->getPrimitiveSizeInBits() <
2192 MulC->getType()->getPrimitiveSizeInBits())
2193 Op0C = ConstantExpr::getZExt(Op0C, MulC->getType());
2194 if (Op0C->getType()->getPrimitiveSizeInBits() >
2195 MulC->getType()->getPrimitiveSizeInBits())
2196 MulC = ConstantExpr::getZExt(MulC, Op0C->getType());
2198 // V == Base * (Mul1 * Op0), so return (Mul1 * Op0)
2199 Multiple = ConstantExpr::getMul(MulC, Op0C);
2203 if (ConstantInt *Mul1CI = dyn_cast<ConstantInt>(Mul1))
2204 if (Mul1CI->getValue() == 1) {
2205 // V == Base * Op0, so return Op0
2213 // We could not determine if V is a multiple of Base.
2217 /// Return true if we can prove that the specified FP value is never equal to
2220 /// NOTE: this function will need to be revisited when we support non-default
2223 bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
2224 if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
2225 return !CFP->getValueAPF().isNegZero();
2227 // FIXME: Magic number! At the least, this should be given a name because it's
2228 // used similarly in CannotBeOrderedLessThanZero(). A better fix may be to
2229 // expose it as a parameter, so it can be used for testing / experimenting.
2231 return false; // Limit search depth.
2233 const Operator *I = dyn_cast<Operator>(V);
2234 if (!I) return false;
2236 // Check if the nsz fast-math flag is set
2237 if (const FPMathOperator *FPO = dyn_cast<FPMathOperator>(I))
2238 if (FPO->hasNoSignedZeros())
2241 // (add x, 0.0) is guaranteed to return +0.0, not -0.0.
2242 if (I->getOpcode() == Instruction::FAdd)
2243 if (ConstantFP *CFP = dyn_cast<ConstantFP>(I->getOperand(1)))
2244 if (CFP->isNullValue())
2247 // sitofp and uitofp turn into +0.0 for zero.
2248 if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
2251 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
2252 // sqrt(-0.0) = -0.0, no other negative results are possible.
2253 if (II->getIntrinsicID() == Intrinsic::sqrt)
2254 return CannotBeNegativeZero(II->getArgOperand(0), Depth+1);
2256 if (const CallInst *CI = dyn_cast<CallInst>(I))
2257 if (const Function *F = CI->getCalledFunction()) {
2258 if (F->isDeclaration()) {
2260 if (F->getName() == "abs") return true;
2261 // fabs[lf](x) != -0.0
2262 if (F->getName() == "fabs") return true;
2263 if (F->getName() == "fabsf") return true;
2264 if (F->getName() == "fabsl") return true;
2265 if (F->getName() == "sqrt" || F->getName() == "sqrtf" ||
2266 F->getName() == "sqrtl")
2267 return CannotBeNegativeZero(CI->getArgOperand(0), Depth+1);
2274 bool llvm::CannotBeOrderedLessThanZero(const Value *V, unsigned Depth) {
2275 if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
2276 return !CFP->getValueAPF().isNegative() || CFP->getValueAPF().isZero();
2278 // FIXME: Magic number! At the least, this should be given a name because it's
2279 // used similarly in CannotBeNegativeZero(). A better fix may be to
2280 // expose it as a parameter, so it can be used for testing / experimenting.
2282 return false; // Limit search depth.
2284 const Operator *I = dyn_cast<Operator>(V);
2285 if (!I) return false;
2287 switch (I->getOpcode()) {
2289 case Instruction::FMul:
2290 // x*x is always non-negative or a NaN.
2291 if (I->getOperand(0) == I->getOperand(1))
2294 case Instruction::FAdd:
2295 case Instruction::FDiv:
2296 case Instruction::FRem:
2297 return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1) &&
2298 CannotBeOrderedLessThanZero(I->getOperand(1), Depth+1);
2299 case Instruction::FPExt:
2300 case Instruction::FPTrunc:
2301 // Widening/narrowing never change sign.
2302 return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1);
2303 case Instruction::Call:
2304 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
2305 switch (II->getIntrinsicID()) {
2307 case Intrinsic::exp:
2308 case Intrinsic::exp2:
2309 case Intrinsic::fabs:
2310 case Intrinsic::sqrt:
2312 case Intrinsic::powi:
2313 if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
2314 // powi(x,n) is non-negative if n is even.
2315 if (CI->getBitWidth() <= 64 && CI->getSExtValue() % 2u == 0)
2318 return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1);
2319 case Intrinsic::fma:
2320 case Intrinsic::fmuladd:
2321 // x*x+y is non-negative if y is non-negative.
2322 return I->getOperand(0) == I->getOperand(1) &&
2323 CannotBeOrderedLessThanZero(I->getOperand(2), Depth+1);
2330 /// If the specified value can be set by repeating the same byte in memory,
2331 /// return the i8 value that it is represented with. This is
2332 /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
2333 /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
2334 /// byte store (e.g. i16 0x1234), return null.
2335 Value *llvm::isBytewiseValue(Value *V) {
2336 // All byte-wide stores are splatable, even of arbitrary variables.
2337 if (V->getType()->isIntegerTy(8)) return V;
2339 // Handle 'null' ConstantArrayZero etc.
2340 if (Constant *C = dyn_cast<Constant>(V))
2341 if (C->isNullValue())
2342 return Constant::getNullValue(Type::getInt8Ty(V->getContext()));
2344 // Constant float and double values can be handled as integer values if the
2345 // corresponding integer value is "byteable". An important case is 0.0.
2346 if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
2347 if (CFP->getType()->isFloatTy())
2348 V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(V->getContext()));
2349 if (CFP->getType()->isDoubleTy())
2350 V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext()));
2351 // Don't handle long double formats, which have strange constraints.
2354 // We can handle constant integers that are multiple of 8 bits.
2355 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
2356 if (CI->getBitWidth() % 8 == 0) {
2357 assert(CI->getBitWidth() > 8 && "8 bits should be handled above!");
2359 if (!CI->getValue().isSplat(8))
2361 return ConstantInt::get(V->getContext(), CI->getValue().trunc(8));
2365 // A ConstantDataArray/Vector is splatable if all its members are equal and
2367 if (ConstantDataSequential *CA = dyn_cast<ConstantDataSequential>(V)) {
2368 Value *Elt = CA->getElementAsConstant(0);
2369 Value *Val = isBytewiseValue(Elt);
2373 for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I)
2374 if (CA->getElementAsConstant(I) != Elt)
2380 // Conceptually, we could handle things like:
2381 // %a = zext i8 %X to i16
2382 // %b = shl i16 %a, 8
2383 // %c = or i16 %a, %b
2384 // but until there is an example that actually needs this, it doesn't seem
2385 // worth worrying about.
2390 // This is the recursive version of BuildSubAggregate. It takes a few different
2391 // arguments. Idxs is the index within the nested struct From that we are
2392 // looking at now (which is of type IndexedType). IdxSkip is the number of
2393 // indices from Idxs that should be left out when inserting into the resulting
2394 // struct. To is the result struct built so far, new insertvalue instructions
2396 static Value *BuildSubAggregate(Value *From, Value* To, Type *IndexedType,
2397 SmallVectorImpl<unsigned> &Idxs,
2399 Instruction *InsertBefore) {
2400 llvm::StructType *STy = dyn_cast<llvm::StructType>(IndexedType);
2402 // Save the original To argument so we can modify it
2404 // General case, the type indexed by Idxs is a struct
2405 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
2406 // Process each struct element recursively
2409 To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip,
2413 // Couldn't find any inserted value for this index? Cleanup
2414 while (PrevTo != OrigTo) {
2415 InsertValueInst* Del = cast<InsertValueInst>(PrevTo);
2416 PrevTo = Del->getAggregateOperand();
2417 Del->eraseFromParent();
2419 // Stop processing elements
2423 // If we successfully found a value for each of our subaggregates
2427 // Base case, the type indexed by SourceIdxs is not a struct, or not all of
2428 // the struct's elements had a value that was inserted directly. In the latter
2429 // case, perhaps we can't determine each of the subelements individually, but
2430 // we might be able to find the complete struct somewhere.
2432 // Find the value that is at that particular spot
2433 Value *V = FindInsertedValue(From, Idxs);
2438 // Insert the value in the new (sub) aggregrate
2439 return llvm::InsertValueInst::Create(To, V, makeArrayRef(Idxs).slice(IdxSkip),
2440 "tmp", InsertBefore);
2443 // This helper takes a nested struct and extracts a part of it (which is again a
2444 // struct) into a new value. For example, given the struct:
2445 // { a, { b, { c, d }, e } }
2446 // and the indices "1, 1" this returns
2449 // It does this by inserting an insertvalue for each element in the resulting
2450 // struct, as opposed to just inserting a single struct. This will only work if
2451 // each of the elements of the substruct are known (ie, inserted into From by an
2452 // insertvalue instruction somewhere).
2454 // All inserted insertvalue instructions are inserted before InsertBefore
2455 static Value *BuildSubAggregate(Value *From, ArrayRef<unsigned> idx_range,
2456 Instruction *InsertBefore) {
2457 assert(InsertBefore && "Must have someplace to insert!");
2458 Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(),
2460 Value *To = UndefValue::get(IndexedType);
2461 SmallVector<unsigned, 10> Idxs(idx_range.begin(), idx_range.end());
2462 unsigned IdxSkip = Idxs.size();
2464 return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore);
2467 /// Given an aggregrate and an sequence of indices, see if
2468 /// the scalar value indexed is already around as a register, for example if it
2469 /// were inserted directly into the aggregrate.
2471 /// If InsertBefore is not null, this function will duplicate (modified)
2472 /// insertvalues when a part of a nested struct is extracted.
2473 Value *llvm::FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range,
2474 Instruction *InsertBefore) {
2475 // Nothing to index? Just return V then (this is useful at the end of our
2477 if (idx_range.empty())
2479 // We have indices, so V should have an indexable type.
2480 assert((V->getType()->isStructTy() || V->getType()->isArrayTy()) &&
2481 "Not looking at a struct or array?");
2482 assert(ExtractValueInst::getIndexedType(V->getType(), idx_range) &&
2483 "Invalid indices for type?");
2485 if (Constant *C = dyn_cast<Constant>(V)) {
2486 C = C->getAggregateElement(idx_range[0]);
2487 if (!C) return nullptr;
2488 return FindInsertedValue(C, idx_range.slice(1), InsertBefore);
2491 if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) {
2492 // Loop the indices for the insertvalue instruction in parallel with the
2493 // requested indices
2494 const unsigned *req_idx = idx_range.begin();
2495 for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
2496 i != e; ++i, ++req_idx) {
2497 if (req_idx == idx_range.end()) {
2498 // We can't handle this without inserting insertvalues
2502 // The requested index identifies a part of a nested aggregate. Handle
2503 // this specially. For example,
2504 // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
2505 // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
2506 // %C = extractvalue {i32, { i32, i32 } } %B, 1
2507 // This can be changed into
2508 // %A = insertvalue {i32, i32 } undef, i32 10, 0
2509 // %C = insertvalue {i32, i32 } %A, i32 11, 1
2510 // which allows the unused 0,0 element from the nested struct to be
2512 return BuildSubAggregate(V, makeArrayRef(idx_range.begin(), req_idx),
2516 // This insert value inserts something else than what we are looking for.
2517 // See if the (aggregrate) value inserted into has the value we are
2518 // looking for, then.
2520 return FindInsertedValue(I->getAggregateOperand(), idx_range,
2523 // If we end up here, the indices of the insertvalue match with those
2524 // requested (though possibly only partially). Now we recursively look at
2525 // the inserted value, passing any remaining indices.
2526 return FindInsertedValue(I->getInsertedValueOperand(),
2527 makeArrayRef(req_idx, idx_range.end()),
2531 if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) {
2532 // If we're extracting a value from an aggregrate that was extracted from
2533 // something else, we can extract from that something else directly instead.
2534 // However, we will need to chain I's indices with the requested indices.
2536 // Calculate the number of indices required
2537 unsigned size = I->getNumIndices() + idx_range.size();
2538 // Allocate some space to put the new indices in
2539 SmallVector<unsigned, 5> Idxs;
2541 // Add indices from the extract value instruction
2542 Idxs.append(I->idx_begin(), I->idx_end());
2544 // Add requested indices
2545 Idxs.append(idx_range.begin(), idx_range.end());
2547 assert(Idxs.size() == size
2548 && "Number of indices added not correct?");
2550 return FindInsertedValue(I->getAggregateOperand(), Idxs, InsertBefore);
2552 // Otherwise, we don't know (such as, extracting from a function return value
2553 // or load instruction)
2557 /// Analyze the specified pointer to see if it can be expressed as a base
2558 /// pointer plus a constant offset. Return the base and offset to the caller.
2559 Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
2560 const DataLayout &DL) {
2561 unsigned BitWidth = DL.getPointerTypeSizeInBits(Ptr->getType());
2562 APInt ByteOffset(BitWidth, 0);
2564 if (Ptr->getType()->isVectorTy())
2567 if (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
2568 APInt GEPOffset(BitWidth, 0);
2569 if (!GEP->accumulateConstantOffset(DL, GEPOffset))
2572 ByteOffset += GEPOffset;
2574 Ptr = GEP->getPointerOperand();
2575 } else if (Operator::getOpcode(Ptr) == Instruction::BitCast ||
2576 Operator::getOpcode(Ptr) == Instruction::AddrSpaceCast) {
2577 Ptr = cast<Operator>(Ptr)->getOperand(0);
2578 } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
2579 if (GA->mayBeOverridden())
2581 Ptr = GA->getAliasee();
2586 Offset = ByteOffset.getSExtValue();
2591 /// This function computes the length of a null-terminated C string pointed to
2592 /// by V. If successful, it returns true and returns the string in Str.
2593 /// If unsuccessful, it returns false.
2594 bool llvm::getConstantStringInfo(const Value *V, StringRef &Str,
2595 uint64_t Offset, bool TrimAtNul) {
2598 // Look through bitcast instructions and geps.
2599 V = V->stripPointerCasts();
2601 // If the value is a GEP instruction or constant expression, treat it as an
2603 if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
2604 // Make sure the GEP has exactly three arguments.
2605 if (GEP->getNumOperands() != 3)
2608 // Make sure the index-ee is a pointer to array of i8.
2609 PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType());
2610 ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType());
2611 if (!AT || !AT->getElementType()->isIntegerTy(8))
2614 // Check to make sure that the first operand of the GEP is an integer and
2615 // has value 0 so that we are sure we're indexing into the initializer.
2616 const ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
2617 if (!FirstIdx || !FirstIdx->isZero())
2620 // If the second index isn't a ConstantInt, then this is a variable index
2621 // into the array. If this occurs, we can't say anything meaningful about
2623 uint64_t StartIdx = 0;
2624 if (const ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
2625 StartIdx = CI->getZExtValue();
2628 return getConstantStringInfo(GEP->getOperand(0), Str, StartIdx + Offset,
2632 // The GEP instruction, constant or instruction, must reference a global
2633 // variable that is a constant and is initialized. The referenced constant
2634 // initializer is the array that we'll use for optimization.
2635 const GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
2636 if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
2639 // Handle the all-zeros case
2640 if (GV->getInitializer()->isNullValue()) {
2641 // This is a degenerate case. The initializer is constant zero so the
2642 // length of the string must be zero.
2647 // Must be a Constant Array
2648 const ConstantDataArray *Array =
2649 dyn_cast<ConstantDataArray>(GV->getInitializer());
2650 if (!Array || !Array->isString())
2653 // Get the number of elements in the array
2654 uint64_t NumElts = Array->getType()->getArrayNumElements();
2656 // Start out with the entire array in the StringRef.
2657 Str = Array->getAsString();
2659 if (Offset > NumElts)
2662 // Skip over 'offset' bytes.
2663 Str = Str.substr(Offset);
2666 // Trim off the \0 and anything after it. If the array is not nul
2667 // terminated, we just return the whole end of string. The client may know
2668 // some other way that the string is length-bound.
2669 Str = Str.substr(0, Str.find('\0'));
2674 // These next two are very similar to the above, but also look through PHI
2676 // TODO: See if we can integrate these two together.
2678 /// If we can compute the length of the string pointed to by
2679 /// the specified pointer, return 'len+1'. If we can't, return 0.
2680 static uint64_t GetStringLengthH(Value *V, SmallPtrSetImpl<PHINode*> &PHIs) {
2681 // Look through noop bitcast instructions.
2682 V = V->stripPointerCasts();
2684 // If this is a PHI node, there are two cases: either we have already seen it
2686 if (PHINode *PN = dyn_cast<PHINode>(V)) {
2687 if (!PHIs.insert(PN).second)
2688 return ~0ULL; // already in the set.
2690 // If it was new, see if all the input strings are the same length.
2691 uint64_t LenSoFar = ~0ULL;
2692 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
2693 uint64_t Len = GetStringLengthH(PN->getIncomingValue(i), PHIs);
2694 if (Len == 0) return 0; // Unknown length -> unknown.
2696 if (Len == ~0ULL) continue;
2698 if (Len != LenSoFar && LenSoFar != ~0ULL)
2699 return 0; // Disagree -> unknown.
2703 // Success, all agree.
2707 // strlen(select(c,x,y)) -> strlen(x) ^ strlen(y)
2708 if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
2709 uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs);
2710 if (Len1 == 0) return 0;
2711 uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs);
2712 if (Len2 == 0) return 0;
2713 if (Len1 == ~0ULL) return Len2;
2714 if (Len2 == ~0ULL) return Len1;
2715 if (Len1 != Len2) return 0;
2719 // Otherwise, see if we can read the string.
2721 if (!getConstantStringInfo(V, StrData))
2724 return StrData.size()+1;
2727 /// If we can compute the length of the string pointed to by
2728 /// the specified pointer, return 'len+1'. If we can't, return 0.
2729 uint64_t llvm::GetStringLength(Value *V) {
2730 if (!V->getType()->isPointerTy()) return 0;
2732 SmallPtrSet<PHINode*, 32> PHIs;
2733 uint64_t Len = GetStringLengthH(V, PHIs);
2734 // If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return
2735 // an empty string as a length.
2736 return Len == ~0ULL ? 1 : Len;
2739 Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
2740 unsigned MaxLookup) {
2741 if (!V->getType()->isPointerTy())
2743 for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
2744 if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
2745 V = GEP->getPointerOperand();
2746 } else if (Operator::getOpcode(V) == Instruction::BitCast ||
2747 Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
2748 V = cast<Operator>(V)->getOperand(0);
2749 } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
2750 if (GA->mayBeOverridden())
2752 V = GA->getAliasee();
2754 // See if InstructionSimplify knows any relevant tricks.
2755 if (Instruction *I = dyn_cast<Instruction>(V))
2756 // TODO: Acquire a DominatorTree and AssumptionCache and use them.
2757 if (Value *Simplified = SimplifyInstruction(I, DL, nullptr)) {
2764 assert(V->getType()->isPointerTy() && "Unexpected operand type!");
2769 void llvm::GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
2770 const DataLayout &DL, unsigned MaxLookup) {
2771 SmallPtrSet<Value *, 4> Visited;
2772 SmallVector<Value *, 4> Worklist;
2773 Worklist.push_back(V);
2775 Value *P = Worklist.pop_back_val();
2776 P = GetUnderlyingObject(P, DL, MaxLookup);
2778 if (!Visited.insert(P).second)
2781 if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
2782 Worklist.push_back(SI->getTrueValue());
2783 Worklist.push_back(SI->getFalseValue());
2787 if (PHINode *PN = dyn_cast<PHINode>(P)) {
2788 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
2789 Worklist.push_back(PN->getIncomingValue(i));
2793 Objects.push_back(P);
2794 } while (!Worklist.empty());
2797 /// Return true if the only users of this pointer are lifetime markers.
2798 bool llvm::onlyUsedByLifetimeMarkers(const Value *V) {
2799 for (const User *U : V->users()) {
2800 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U);
2801 if (!II) return false;
2803 if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
2804 II->getIntrinsicID() != Intrinsic::lifetime_end)
2810 bool llvm::isSafeToSpeculativelyExecute(const Value *V) {
2811 const Operator *Inst = dyn_cast<Operator>(V);
2815 for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
2816 if (Constant *C = dyn_cast<Constant>(Inst->getOperand(i)))
2820 switch (Inst->getOpcode()) {
2823 case Instruction::UDiv:
2824 case Instruction::URem: {
2825 // x / y is undefined if y == 0.
2827 if (match(Inst->getOperand(1), m_APInt(V)))
2831 case Instruction::SDiv:
2832 case Instruction::SRem: {
2833 // x / y is undefined if y == 0 or x == INT_MIN and y == -1
2834 const APInt *Numerator, *Denominator;
2835 if (!match(Inst->getOperand(1), m_APInt(Denominator)))
2837 // We cannot hoist this division if the denominator is 0.
2838 if (*Denominator == 0)
2840 // It's safe to hoist if the denominator is not 0 or -1.
2841 if (*Denominator != -1)
2843 // At this point we know that the denominator is -1. It is safe to hoist as
2844 // long we know that the numerator is not INT_MIN.
2845 if (match(Inst->getOperand(0), m_APInt(Numerator)))
2846 return !Numerator->isMinSignedValue();
2847 // The numerator *might* be MinSignedValue.
2850 case Instruction::Load: {
2851 const LoadInst *LI = cast<LoadInst>(Inst);
2852 if (!LI->isUnordered() ||
2853 // Speculative load may create a race that did not exist in the source.
2854 LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread))
2856 const DataLayout &DL = LI->getModule()->getDataLayout();
2857 return LI->getPointerOperand()->isDereferenceablePointer(DL);
2859 case Instruction::Call: {
2860 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
2861 switch (II->getIntrinsicID()) {
2862 // These synthetic intrinsics have no side-effects and just mark
2863 // information about their operands.
2864 // FIXME: There are other no-op synthetic instructions that potentially
2865 // should be considered at least *safe* to speculate...
2866 case Intrinsic::dbg_declare:
2867 case Intrinsic::dbg_value:
2870 case Intrinsic::bswap:
2871 case Intrinsic::ctlz:
2872 case Intrinsic::ctpop:
2873 case Intrinsic::cttz:
2874 case Intrinsic::objectsize:
2875 case Intrinsic::sadd_with_overflow:
2876 case Intrinsic::smul_with_overflow:
2877 case Intrinsic::ssub_with_overflow:
2878 case Intrinsic::uadd_with_overflow:
2879 case Intrinsic::umul_with_overflow:
2880 case Intrinsic::usub_with_overflow:
2882 // Sqrt should be OK, since the llvm sqrt intrinsic isn't defined to set
2883 // errno like libm sqrt would.
2884 case Intrinsic::sqrt:
2885 case Intrinsic::fma:
2886 case Intrinsic::fmuladd:
2887 case Intrinsic::fabs:
2888 case Intrinsic::minnum:
2889 case Intrinsic::maxnum:
2891 // TODO: some fp intrinsics are marked as having the same error handling
2892 // as libm. They're safe to speculate when they won't error.
2893 // TODO: are convert_{from,to}_fp16 safe?
2894 // TODO: can we list target-specific intrinsics here?
2898 return false; // The called function could have undefined behavior or
2899 // side-effects, even if marked readnone nounwind.
2901 case Instruction::VAArg:
2902 case Instruction::Alloca:
2903 case Instruction::Invoke:
2904 case Instruction::PHI:
2905 case Instruction::Store:
2906 case Instruction::Ret:
2907 case Instruction::Br:
2908 case Instruction::IndirectBr:
2909 case Instruction::Switch:
2910 case Instruction::Unreachable:
2911 case Instruction::Fence:
2912 case Instruction::LandingPad:
2913 case Instruction::AtomicRMW:
2914 case Instruction::AtomicCmpXchg:
2915 case Instruction::Resume:
2916 return false; // Misc instructions which have effects
2920 /// Return true if we know that the specified value is never null.
2921 bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) {
2922 // Alloca never returns null, malloc might.
2923 if (isa<AllocaInst>(V)) return true;
2925 // A byval, inalloca, or nonnull argument is never null.
2926 if (const Argument *A = dyn_cast<Argument>(V))
2927 return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr();
2929 // Global values are not null unless extern weak.
2930 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
2931 return !GV->hasExternalWeakLinkage();
2933 // A Load tagged w/nonnull metadata is never null.
2934 if (const LoadInst *LI = dyn_cast<LoadInst>(V))
2935 return LI->getMetadata(LLVMContext::MD_nonnull);
2937 if (auto CS = ImmutableCallSite(V))
2938 if (CS.isReturnNonNull())
2941 // operator new never returns null.
2942 if (isOperatorNewLikeFn(V, TLI, /*LookThroughBitCast=*/true))
2948 OverflowResult llvm::computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
2949 const DataLayout &DL,
2950 AssumptionCache *AC,
2951 const Instruction *CxtI,
2952 const DominatorTree *DT) {
2953 // Multiplying n * m significant bits yields a result of n + m significant
2954 // bits. If the total number of significant bits does not exceed the
2955 // result bit width (minus 1), there is no overflow.
2956 // This means if we have enough leading zero bits in the operands
2957 // we can guarantee that the result does not overflow.
2958 // Ref: "Hacker's Delight" by Henry Warren
2959 unsigned BitWidth = LHS->getType()->getScalarSizeInBits();
2960 APInt LHSKnownZero(BitWidth, 0);
2961 APInt LHSKnownOne(BitWidth, 0);
2962 APInt RHSKnownZero(BitWidth, 0);
2963 APInt RHSKnownOne(BitWidth, 0);
2964 computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, /*Depth=*/0, AC, CxtI,
2966 computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, /*Depth=*/0, AC, CxtI,
2968 // Note that underestimating the number of zero bits gives a more
2969 // conservative answer.
2970 unsigned ZeroBits = LHSKnownZero.countLeadingOnes() +
2971 RHSKnownZero.countLeadingOnes();
2972 // First handle the easy case: if we have enough zero bits there's
2973 // definitely no overflow.
2974 if (ZeroBits >= BitWidth)
2975 return OverflowResult::NeverOverflows;
2977 // Get the largest possible values for each operand.
2978 APInt LHSMax = ~LHSKnownZero;
2979 APInt RHSMax = ~RHSKnownZero;
2981 // We know the multiply operation doesn't overflow if the maximum values for
2982 // each operand will not overflow after we multiply them together.
2984 LHSMax.umul_ov(RHSMax, MaxOverflow);
2986 return OverflowResult::NeverOverflows;
2988 // We know it always overflows if multiplying the smallest possible values for
2989 // the operands also results in overflow.
2991 LHSKnownOne.umul_ov(RHSKnownOne, MinOverflow);
2993 return OverflowResult::AlwaysOverflows;
2995 return OverflowResult::MayOverflow;
2998 OverflowResult llvm::computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
2999 const DataLayout &DL,
3000 AssumptionCache *AC,
3001 const Instruction *CxtI,
3002 const DominatorTree *DT) {
3003 bool LHSKnownNonNegative, LHSKnownNegative;
3004 ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0,
3006 if (LHSKnownNonNegative || LHSKnownNegative) {
3007 bool RHSKnownNonNegative, RHSKnownNegative;
3008 ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0,
3011 if (LHSKnownNegative && RHSKnownNegative) {
3012 // The sign bit is set in both cases: this MUST overflow.
3013 // Create a simple add instruction, and insert it into the struct.
3014 return OverflowResult::AlwaysOverflows;
3017 if (LHSKnownNonNegative && RHSKnownNonNegative) {
3018 // The sign bit is clear in both cases: this CANNOT overflow.
3019 // Create a simple add instruction, and insert it into the struct.
3020 return OverflowResult::NeverOverflows;
3024 return OverflowResult::MayOverflow;