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/Analysis/InstructionSimplify.h"
17 #include "llvm/Constants.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/GlobalVariable.h"
20 #include "llvm/GlobalAlias.h"
21 #include "llvm/IntrinsicInst.h"
22 #include "llvm/LLVMContext.h"
23 #include "llvm/Metadata.h"
24 #include "llvm/Operator.h"
25 #include "llvm/Target/TargetData.h"
26 #include "llvm/Support/ConstantRange.h"
27 #include "llvm/Support/GetElementPtrTypeIterator.h"
28 #include "llvm/Support/MathExtras.h"
29 #include "llvm/Support/PatternMatch.h"
30 #include "llvm/ADT/SmallPtrSet.h"
33 using namespace llvm::PatternMatch;
35 const unsigned MaxDepth = 6;
37 /// getBitWidth - Returns the bitwidth of the given scalar or pointer type (if
38 /// unknown returns 0). For vector types, returns the element type's bitwidth.
39 static unsigned getBitWidth(Type *Ty, const TargetData *TD) {
40 if (unsigned BitWidth = Ty->getScalarSizeInBits())
42 assert(isa<PointerType>(Ty) && "Expected a pointer type!");
43 return TD ? TD->getPointerSizeInBits() : 0;
46 static void ComputeMaskedBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
47 APInt &KnownZero, APInt &KnownOne,
48 APInt &KnownZero2, APInt &KnownOne2,
49 const TargetData *TD, unsigned Depth) {
51 if (ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) {
52 // We know that the top bits of C-X are clear if X contains less bits
53 // than C (i.e. no wrap-around can happen). For example, 20-X is
54 // positive if we can prove that X is >= 0 and < 16.
55 if (!CLHS->getValue().isNegative()) {
56 unsigned BitWidth = KnownZero.getBitWidth();
57 unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
58 // NLZ can't be BitWidth with no sign bit
59 APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
60 llvm::ComputeMaskedBits(Op1, KnownZero2, KnownOne2, TD, Depth+1);
62 // If all of the MaskV bits are known to be zero, then we know the
63 // output top bits are zero, because we now know that the output is
65 if ((KnownZero2 & MaskV) == MaskV) {
66 unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
67 // Top bits known zero.
68 KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2);
74 unsigned BitWidth = KnownZero.getBitWidth();
76 // If one of the operands has trailing zeros, then the bits that the
77 // other operand has in those bit positions will be preserved in the
78 // result. For an add, this works with either operand. For a subtract,
79 // this only works if the known zeros are in the right operand.
80 APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
81 llvm::ComputeMaskedBits(Op0, LHSKnownZero, LHSKnownOne, TD, Depth+1);
82 assert((LHSKnownZero & LHSKnownOne) == 0 &&
83 "Bits known to be one AND zero?");
84 unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes();
86 llvm::ComputeMaskedBits(Op1, KnownZero2, KnownOne2, TD, Depth+1);
87 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
88 unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes();
90 // Determine which operand has more trailing zeros, and use that
91 // many bits from the other operand.
92 if (LHSKnownZeroOut > RHSKnownZeroOut) {
94 APInt Mask = APInt::getLowBitsSet(BitWidth, LHSKnownZeroOut);
95 KnownZero |= KnownZero2 & Mask;
96 KnownOne |= KnownOne2 & Mask;
98 // If the known zeros are in the left operand for a subtract,
99 // fall back to the minimum known zeros in both operands.
100 KnownZero |= APInt::getLowBitsSet(BitWidth,
101 std::min(LHSKnownZeroOut,
104 } else if (RHSKnownZeroOut >= LHSKnownZeroOut) {
105 APInt Mask = APInt::getLowBitsSet(BitWidth, RHSKnownZeroOut);
106 KnownZero |= LHSKnownZero & Mask;
107 KnownOne |= LHSKnownOne & Mask;
110 // Are we still trying to solve for the sign bit?
111 if (!KnownZero.isNegative() && !KnownOne.isNegative()) {
114 // Adding two positive numbers can't wrap into negative
115 if (LHSKnownZero.isNegative() && KnownZero2.isNegative())
116 KnownZero |= APInt::getSignBit(BitWidth);
117 // and adding two negative numbers can't wrap into positive.
118 else if (LHSKnownOne.isNegative() && KnownOne2.isNegative())
119 KnownOne |= APInt::getSignBit(BitWidth);
121 // Subtracting a negative number from a positive one can't wrap
122 if (LHSKnownZero.isNegative() && KnownOne2.isNegative())
123 KnownZero |= APInt::getSignBit(BitWidth);
124 // neither can subtracting a positive number from a negative one.
125 else if (LHSKnownOne.isNegative() && KnownZero2.isNegative())
126 KnownOne |= APInt::getSignBit(BitWidth);
132 static void ComputeMaskedBitsMul(Value *Op0, Value *Op1, bool NSW,
133 APInt &KnownZero, APInt &KnownOne,
134 APInt &KnownZero2, APInt &KnownOne2,
135 const TargetData *TD, unsigned Depth) {
136 unsigned BitWidth = KnownZero.getBitWidth();
137 ComputeMaskedBits(Op1, KnownZero, KnownOne, TD, Depth+1);
138 ComputeMaskedBits(Op0, KnownZero2, KnownOne2, TD, Depth+1);
139 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
140 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
142 bool isKnownNegative = false;
143 bool isKnownNonNegative = false;
144 // If the multiplication is known not to overflow, compute the sign bit.
147 // The product of a number with itself is non-negative.
148 isKnownNonNegative = true;
150 bool isKnownNonNegativeOp1 = KnownZero.isNegative();
151 bool isKnownNonNegativeOp0 = KnownZero2.isNegative();
152 bool isKnownNegativeOp1 = KnownOne.isNegative();
153 bool isKnownNegativeOp0 = KnownOne2.isNegative();
154 // The product of two numbers with the same sign is non-negative.
155 isKnownNonNegative = (isKnownNegativeOp1 && isKnownNegativeOp0) ||
156 (isKnownNonNegativeOp1 && isKnownNonNegativeOp0);
157 // The product of a negative number and a non-negative number is either
159 if (!isKnownNonNegative)
160 isKnownNegative = (isKnownNegativeOp1 && isKnownNonNegativeOp0 &&
161 isKnownNonZero(Op0, TD, Depth)) ||
162 (isKnownNegativeOp0 && isKnownNonNegativeOp1 &&
163 isKnownNonZero(Op1, TD, Depth));
167 // If low bits are zero in either operand, output low known-0 bits.
168 // Also compute a conserative estimate for high known-0 bits.
169 // More trickiness is possible, but this is sufficient for the
170 // interesting case of alignment computation.
171 KnownOne.clearAllBits();
172 unsigned TrailZ = KnownZero.countTrailingOnes() +
173 KnownZero2.countTrailingOnes();
174 unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
175 KnownZero2.countLeadingOnes(),
176 BitWidth) - BitWidth;
178 TrailZ = std::min(TrailZ, BitWidth);
179 LeadZ = std::min(LeadZ, BitWidth);
180 KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
181 APInt::getHighBitsSet(BitWidth, LeadZ);
183 // Only make use of no-wrap flags if we failed to compute the sign bit
184 // directly. This matters if the multiplication always overflows, in
185 // which case we prefer to follow the result of the direct computation,
186 // though as the program is invoking undefined behaviour we can choose
187 // whatever we like here.
188 if (isKnownNonNegative && !KnownOne.isNegative())
189 KnownZero.setBit(BitWidth - 1);
190 else if (isKnownNegative && !KnownZero.isNegative())
191 KnownOne.setBit(BitWidth - 1);
194 void llvm::computeMaskedBitsLoad(const MDNode &Ranges, APInt &KnownZero) {
195 unsigned BitWidth = KnownZero.getBitWidth();
196 unsigned NumRanges = Ranges.getNumOperands() / 2;
197 assert(NumRanges >= 1);
199 // Use the high end of the ranges to find leading zeros.
200 unsigned MinLeadingZeros = BitWidth;
201 for (unsigned i = 0; i < NumRanges; ++i) {
202 ConstantInt *Lower = cast<ConstantInt>(Ranges.getOperand(2*i + 0));
203 ConstantInt *Upper = cast<ConstantInt>(Ranges.getOperand(2*i + 1));
204 ConstantRange Range(Lower->getValue(), Upper->getValue());
205 if (Range.isWrappedSet())
206 MinLeadingZeros = 0; // -1 has no zeros
207 unsigned LeadingZeros = (Upper->getValue() - 1).countLeadingZeros();
208 MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros);
211 KnownZero = APInt::getHighBitsSet(BitWidth, MinLeadingZeros);
213 /// ComputeMaskedBits - Determine which of the bits are known to be either zero
214 /// or one and return them in the KnownZero/KnownOne bit sets.
216 /// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
217 /// we cannot optimize based on the assumption that it is zero without changing
218 /// it to be an explicit zero. If we don't change it to zero, other code could
219 /// optimized based on the contradictory assumption that it is non-zero.
220 /// Because instcombine aggressively folds operations with undef args anyway,
221 /// this won't lose us code quality.
223 /// This function is defined on values with integer type, values with pointer
224 /// type (but only if TD is non-null), and vectors of integers. In the case
225 /// where V is a vector, known zero, and known one values are the
226 /// same width as the vector element, and the bit is set only if it is true
227 /// for all of the elements in the vector.
228 void llvm::ComputeMaskedBits(Value *V, APInt &KnownZero, APInt &KnownOne,
229 const TargetData *TD, unsigned Depth) {
230 assert(V && "No Value?");
231 assert(Depth <= MaxDepth && "Limit Search Depth");
232 unsigned BitWidth = KnownZero.getBitWidth();
234 assert((V->getType()->isIntOrIntVectorTy() ||
235 V->getType()->getScalarType()->isPointerTy()) &&
236 "Not integer or pointer type!");
238 TD->getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
239 (!V->getType()->isIntOrIntVectorTy() ||
240 V->getType()->getScalarSizeInBits() == BitWidth) &&
241 KnownZero.getBitWidth() == BitWidth &&
242 KnownOne.getBitWidth() == BitWidth &&
243 "V, Mask, KnownOne and KnownZero should have same BitWidth");
245 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
246 // We know all of the bits for a constant!
247 KnownOne = CI->getValue();
248 KnownZero = ~KnownOne;
251 // Null and aggregate-zero are all-zeros.
252 if (isa<ConstantPointerNull>(V) ||
253 isa<ConstantAggregateZero>(V)) {
254 KnownOne.clearAllBits();
255 KnownZero = APInt::getAllOnesValue(BitWidth);
258 // Handle a constant vector by taking the intersection of the known bits of
259 // each element. There is no real need to handle ConstantVector here, because
260 // we don't handle undef in any particularly useful way.
261 if (ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(V)) {
262 // We know that CDS must be a vector of integers. Take the intersection of
264 KnownZero.setAllBits(); KnownOne.setAllBits();
265 APInt Elt(KnownZero.getBitWidth(), 0);
266 for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) {
267 Elt = CDS->getElementAsInteger(i);
274 // The address of an aligned GlobalValue has trailing zeros.
275 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
276 unsigned Align = GV->getAlignment();
277 if (Align == 0 && TD) {
278 if (GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV)) {
279 Type *ObjectType = GVar->getType()->getElementType();
280 if (ObjectType->isSized()) {
281 // If the object is defined in the current Module, we'll be giving
282 // it the preferred alignment. Otherwise, we have to assume that it
283 // may only have the minimum ABI alignment.
284 if (!GVar->isDeclaration() && !GVar->isWeakForLinker())
285 Align = TD->getPreferredAlignment(GVar);
287 Align = TD->getABITypeAlignment(ObjectType);
292 KnownZero = APInt::getLowBitsSet(BitWidth,
293 CountTrailingZeros_32(Align));
295 KnownZero.clearAllBits();
296 KnownOne.clearAllBits();
299 // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
300 // the bits of its aliasee.
301 if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
302 if (GA->mayBeOverridden()) {
303 KnownZero.clearAllBits(); KnownOne.clearAllBits();
305 ComputeMaskedBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth+1);
310 if (Argument *A = dyn_cast<Argument>(V)) {
313 if (A->hasByValAttr()) {
314 // Get alignment information off byval arguments if specified in the IR.
315 Align = A->getParamAlignment();
316 } else if (TD && A->hasStructRetAttr()) {
317 // An sret parameter has at least the ABI alignment of the return type.
318 Type *EltTy = cast<PointerType>(A->getType())->getElementType();
319 if (EltTy->isSized())
320 Align = TD->getABITypeAlignment(EltTy);
324 KnownZero = APInt::getLowBitsSet(BitWidth, CountTrailingZeros_32(Align));
328 // Start out not knowing anything.
329 KnownZero.clearAllBits(); KnownOne.clearAllBits();
331 if (Depth == MaxDepth)
332 return; // Limit search depth.
334 Operator *I = dyn_cast<Operator>(V);
337 APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
338 switch (I->getOpcode()) {
340 case Instruction::Load:
341 if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range))
342 computeMaskedBitsLoad(*MD, KnownZero);
344 case Instruction::And: {
345 // If either the LHS or the RHS are Zero, the result is zero.
346 ComputeMaskedBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1);
347 ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
348 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
349 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
351 // Output known-1 bits are only known if set in both the LHS & RHS.
352 KnownOne &= KnownOne2;
353 // Output known-0 are known to be clear if zero in either the LHS | RHS.
354 KnownZero |= KnownZero2;
357 case Instruction::Or: {
358 ComputeMaskedBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1);
359 ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
360 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
361 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
363 // Output known-0 bits are only known if clear in both the LHS & RHS.
364 KnownZero &= KnownZero2;
365 // Output known-1 are known to be set if set in either the LHS | RHS.
366 KnownOne |= KnownOne2;
369 case Instruction::Xor: {
370 ComputeMaskedBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1);
371 ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
372 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
373 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
375 // Output known-0 bits are known if clear or set in both the LHS & RHS.
376 APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
377 // Output known-1 are known to be set if set in only one of the LHS, RHS.
378 KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
379 KnownZero = KnownZeroOut;
382 case Instruction::Mul: {
383 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
384 ComputeMaskedBitsMul(I->getOperand(0), I->getOperand(1), NSW,
385 KnownZero, KnownOne, KnownZero2, KnownOne2, TD, Depth);
388 case Instruction::UDiv: {
389 // For the purposes of computing leading zeros we can conservatively
390 // treat a udiv as a logical right shift by the power of 2 known to
391 // be less than the denominator.
392 ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
393 unsigned LeadZ = KnownZero2.countLeadingOnes();
395 KnownOne2.clearAllBits();
396 KnownZero2.clearAllBits();
397 ComputeMaskedBits(I->getOperand(1), KnownZero2, KnownOne2, TD, Depth+1);
398 unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
399 if (RHSUnknownLeadingOnes != BitWidth)
400 LeadZ = std::min(BitWidth,
401 LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
403 KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ);
406 case Instruction::Select:
407 ComputeMaskedBits(I->getOperand(2), KnownZero, KnownOne, TD, Depth+1);
408 ComputeMaskedBits(I->getOperand(1), KnownZero2, KnownOne2, TD,
410 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
411 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
413 // Only known if known in both the LHS and RHS.
414 KnownOne &= KnownOne2;
415 KnownZero &= KnownZero2;
417 case Instruction::FPTrunc:
418 case Instruction::FPExt:
419 case Instruction::FPToUI:
420 case Instruction::FPToSI:
421 case Instruction::SIToFP:
422 case Instruction::UIToFP:
423 return; // Can't work with floating point.
424 case Instruction::PtrToInt:
425 case Instruction::IntToPtr:
426 // We can't handle these if we don't know the pointer size.
428 // FALL THROUGH and handle them the same as zext/trunc.
429 case Instruction::ZExt:
430 case Instruction::Trunc: {
431 Type *SrcTy = I->getOperand(0)->getType();
433 unsigned SrcBitWidth;
434 // Note that we handle pointer operands here because of inttoptr/ptrtoint
435 // which fall through here.
436 if (SrcTy->isPointerTy())
437 SrcBitWidth = TD->getTypeSizeInBits(SrcTy);
439 SrcBitWidth = SrcTy->getScalarSizeInBits();
441 KnownZero = KnownZero.zextOrTrunc(SrcBitWidth);
442 KnownOne = KnownOne.zextOrTrunc(SrcBitWidth);
443 ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
444 KnownZero = KnownZero.zextOrTrunc(BitWidth);
445 KnownOne = KnownOne.zextOrTrunc(BitWidth);
446 // Any top bits are known to be zero.
447 if (BitWidth > SrcBitWidth)
448 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
451 case Instruction::BitCast: {
452 Type *SrcTy = I->getOperand(0)->getType();
453 if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) &&
454 // TODO: For now, not handling conversions like:
455 // (bitcast i64 %x to <2 x i32>)
456 !I->getType()->isVectorTy()) {
457 ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
462 case Instruction::SExt: {
463 // Compute the bits in the result that are not present in the input.
464 unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits();
466 KnownZero = KnownZero.trunc(SrcBitWidth);
467 KnownOne = KnownOne.trunc(SrcBitWidth);
468 ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
469 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
470 KnownZero = KnownZero.zext(BitWidth);
471 KnownOne = KnownOne.zext(BitWidth);
473 // If the sign bit of the input is known set or clear, then we know the
474 // top bits of the result.
475 if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
476 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
477 else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
478 KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
481 case Instruction::Shl:
482 // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
483 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
484 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
485 ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
486 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
487 KnownZero <<= ShiftAmt;
488 KnownOne <<= ShiftAmt;
489 KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
493 case Instruction::LShr:
494 // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
495 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
496 // Compute the new bits that are at the top now.
497 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
499 // Unsigned shift right.
500 ComputeMaskedBits(I->getOperand(0), KnownZero,KnownOne, TD, Depth+1);
501 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
502 KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
503 KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
504 // high bits known zero.
505 KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
509 case Instruction::AShr:
510 // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
511 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
512 // Compute the new bits that are at the top now.
513 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
515 // Signed shift right.
516 ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
517 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
518 KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
519 KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
521 APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
522 if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
523 KnownZero |= HighBits;
524 else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
525 KnownOne |= HighBits;
529 case Instruction::Sub: {
530 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
531 ComputeMaskedBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW,
532 KnownZero, KnownOne, KnownZero2, KnownOne2, TD,
536 case Instruction::Add: {
537 bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
538 ComputeMaskedBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW,
539 KnownZero, KnownOne, KnownZero2, KnownOne2, TD,
543 case Instruction::SRem:
544 if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
545 APInt RA = Rem->getValue().abs();
546 if (RA.isPowerOf2()) {
547 APInt LowBits = RA - 1;
548 ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
550 // The low bits of the first operand are unchanged by the srem.
551 KnownZero = KnownZero2 & LowBits;
552 KnownOne = KnownOne2 & LowBits;
554 // If the first operand is non-negative or has all low bits zero, then
555 // the upper bits are all zero.
556 if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
557 KnownZero |= ~LowBits;
559 // If the first operand is negative and not all low bits are zero, then
560 // the upper bits are all one.
561 if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
562 KnownOne |= ~LowBits;
564 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
568 // The sign bit is the LHS's sign bit, except when the result of the
569 // remainder is zero.
570 if (KnownZero.isNonNegative()) {
571 APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
572 ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, TD,
574 // If it's known zero, our sign bit is also zero.
575 if (LHSKnownZero.isNegative())
576 KnownZero.setBit(BitWidth - 1);
580 case Instruction::URem: {
581 if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
582 APInt RA = Rem->getValue();
583 if (RA.isPowerOf2()) {
584 APInt LowBits = (RA - 1);
585 ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD,
587 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
588 KnownZero |= ~LowBits;
594 // Since the result is less than or equal to either operand, any leading
595 // zero bits in either operand must also exist in the result.
596 ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
597 ComputeMaskedBits(I->getOperand(1), KnownZero2, KnownOne2, TD, Depth+1);
599 unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
600 KnownZero2.countLeadingOnes());
601 KnownOne.clearAllBits();
602 KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
606 case Instruction::Alloca: {
607 AllocaInst *AI = cast<AllocaInst>(V);
608 unsigned Align = AI->getAlignment();
609 if (Align == 0 && TD)
610 Align = TD->getABITypeAlignment(AI->getType()->getElementType());
613 KnownZero = APInt::getLowBitsSet(BitWidth, CountTrailingZeros_32(Align));
616 case Instruction::GetElementPtr: {
617 // Analyze all of the subscripts of this getelementptr instruction
618 // to determine if we can prove known low zero bits.
619 APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
620 ComputeMaskedBits(I->getOperand(0), LocalKnownZero, LocalKnownOne, TD,
622 unsigned TrailZ = LocalKnownZero.countTrailingOnes();
624 gep_type_iterator GTI = gep_type_begin(I);
625 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
626 Value *Index = I->getOperand(i);
627 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
628 // Handle struct member offset arithmetic.
630 const StructLayout *SL = TD->getStructLayout(STy);
631 unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
632 uint64_t Offset = SL->getElementOffset(Idx);
633 TrailZ = std::min(TrailZ,
634 CountTrailingZeros_64(Offset));
636 // Handle array index arithmetic.
637 Type *IndexedTy = GTI.getIndexedType();
638 if (!IndexedTy->isSized()) return;
639 unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits();
640 uint64_t TypeSize = TD ? TD->getTypeAllocSize(IndexedTy) : 1;
641 LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
642 ComputeMaskedBits(Index, LocalKnownZero, LocalKnownOne, TD, Depth+1);
643 TrailZ = std::min(TrailZ,
644 unsigned(CountTrailingZeros_64(TypeSize) +
645 LocalKnownZero.countTrailingOnes()));
649 KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ);
652 case Instruction::PHI: {
653 PHINode *P = cast<PHINode>(I);
654 // Handle the case of a simple two-predecessor recurrence PHI.
655 // There's a lot more that could theoretically be done here, but
656 // this is sufficient to catch some interesting cases.
657 if (P->getNumIncomingValues() == 2) {
658 for (unsigned i = 0; i != 2; ++i) {
659 Value *L = P->getIncomingValue(i);
660 Value *R = P->getIncomingValue(!i);
661 Operator *LU = dyn_cast<Operator>(L);
664 unsigned Opcode = LU->getOpcode();
665 // Check for operations that have the property that if
666 // both their operands have low zero bits, the result
667 // will have low zero bits.
668 if (Opcode == Instruction::Add ||
669 Opcode == Instruction::Sub ||
670 Opcode == Instruction::And ||
671 Opcode == Instruction::Or ||
672 Opcode == Instruction::Mul) {
673 Value *LL = LU->getOperand(0);
674 Value *LR = LU->getOperand(1);
675 // Find a recurrence.
682 // Ok, we have a PHI of the form L op= R. Check for low
684 ComputeMaskedBits(R, KnownZero2, KnownOne2, TD, Depth+1);
686 // We need to take the minimum number of known bits
687 APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
688 ComputeMaskedBits(L, KnownZero3, KnownOne3, TD, Depth+1);
690 KnownZero = APInt::getLowBitsSet(BitWidth,
691 std::min(KnownZero2.countTrailingOnes(),
692 KnownZero3.countTrailingOnes()));
698 // Unreachable blocks may have zero-operand PHI nodes.
699 if (P->getNumIncomingValues() == 0)
702 // Otherwise take the unions of the known bit sets of the operands,
703 // taking conservative care to avoid excessive recursion.
704 if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) {
705 // Skip if every incoming value references to ourself.
706 if (dyn_cast_or_null<UndefValue>(P->hasConstantValue()))
709 KnownZero = APInt::getAllOnesValue(BitWidth);
710 KnownOne = APInt::getAllOnesValue(BitWidth);
711 for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
712 // Skip direct self references.
713 if (P->getIncomingValue(i) == P) continue;
715 KnownZero2 = APInt(BitWidth, 0);
716 KnownOne2 = APInt(BitWidth, 0);
717 // Recurse, but cap the recursion to one level, because we don't
718 // want to waste time spinning around in loops.
719 ComputeMaskedBits(P->getIncomingValue(i), KnownZero2, KnownOne2, TD,
721 KnownZero &= KnownZero2;
722 KnownOne &= KnownOne2;
723 // If all bits have been ruled out, there's no need to check
725 if (!KnownZero && !KnownOne)
731 case Instruction::Call:
732 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
733 switch (II->getIntrinsicID()) {
735 case Intrinsic::ctlz:
736 case Intrinsic::cttz: {
737 unsigned LowBits = Log2_32(BitWidth)+1;
738 // If this call is undefined for 0, the result will be less than 2^n.
739 if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
741 KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
744 case Intrinsic::ctpop: {
745 unsigned LowBits = Log2_32(BitWidth)+1;
746 KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
749 case Intrinsic::x86_sse42_crc32_64_8:
750 case Intrinsic::x86_sse42_crc32_64_64:
751 KnownZero = APInt::getHighBitsSet(64, 32);
756 case Instruction::ExtractValue:
757 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) {
758 ExtractValueInst *EVI = cast<ExtractValueInst>(I);
759 if (EVI->getNumIndices() != 1) break;
760 if (EVI->getIndices()[0] == 0) {
761 switch (II->getIntrinsicID()) {
763 case Intrinsic::uadd_with_overflow:
764 case Intrinsic::sadd_with_overflow:
765 ComputeMaskedBitsAddSub(true, II->getArgOperand(0),
766 II->getArgOperand(1), false, KnownZero,
767 KnownOne, KnownZero2, KnownOne2, TD, Depth);
769 case Intrinsic::usub_with_overflow:
770 case Intrinsic::ssub_with_overflow:
771 ComputeMaskedBitsAddSub(false, II->getArgOperand(0),
772 II->getArgOperand(1), false, KnownZero,
773 KnownOne, KnownZero2, KnownOne2, TD, Depth);
775 case Intrinsic::umul_with_overflow:
776 case Intrinsic::smul_with_overflow:
777 ComputeMaskedBitsMul(II->getArgOperand(0), II->getArgOperand(1),
778 false, KnownZero, KnownOne,
779 KnownZero2, KnownOne2, TD, Depth);
787 /// ComputeSignBit - Determine whether the sign bit is known to be zero or
788 /// one. Convenience wrapper around ComputeMaskedBits.
789 void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
790 const TargetData *TD, unsigned Depth) {
791 unsigned BitWidth = getBitWidth(V->getType(), TD);
797 APInt ZeroBits(BitWidth, 0);
798 APInt OneBits(BitWidth, 0);
799 ComputeMaskedBits(V, ZeroBits, OneBits, TD, Depth);
800 KnownOne = OneBits[BitWidth - 1];
801 KnownZero = ZeroBits[BitWidth - 1];
804 /// isPowerOfTwo - Return true if the given value is known to have exactly one
805 /// bit set when defined. For vectors return true if every element is known to
806 /// be a power of two when defined. Supports values with integer or pointer
807 /// types and vectors of integers.
808 bool llvm::isPowerOfTwo(Value *V, const TargetData *TD, bool OrZero,
810 if (Constant *C = dyn_cast<Constant>(V)) {
811 if (C->isNullValue())
813 if (ConstantInt *CI = dyn_cast<ConstantInt>(C))
814 return CI->getValue().isPowerOf2();
815 // TODO: Handle vector constants.
818 // 1 << X is clearly a power of two if the one is not shifted off the end. If
819 // it is shifted off the end then the result is undefined.
820 if (match(V, m_Shl(m_One(), m_Value())))
823 // (signbit) >>l X is clearly a power of two if the one is not shifted off the
824 // bottom. If it is shifted off the bottom then the result is undefined.
825 if (match(V, m_LShr(m_SignBit(), m_Value())))
828 // The remaining tests are all recursive, so bail out if we hit the limit.
829 if (Depth++ == MaxDepth)
832 Value *X = 0, *Y = 0;
833 // A shift of a power of two is a power of two or zero.
834 if (OrZero && (match(V, m_Shl(m_Value(X), m_Value())) ||
835 match(V, m_Shr(m_Value(X), m_Value()))))
836 return isPowerOfTwo(X, TD, /*OrZero*/true, Depth);
838 if (ZExtInst *ZI = dyn_cast<ZExtInst>(V))
839 return isPowerOfTwo(ZI->getOperand(0), TD, OrZero, Depth);
841 if (SelectInst *SI = dyn_cast<SelectInst>(V))
842 return isPowerOfTwo(SI->getTrueValue(), TD, OrZero, Depth) &&
843 isPowerOfTwo(SI->getFalseValue(), TD, OrZero, Depth);
845 if (OrZero && match(V, m_And(m_Value(X), m_Value(Y)))) {
846 // A power of two and'd with anything is a power of two or zero.
847 if (isPowerOfTwo(X, TD, /*OrZero*/true, Depth) ||
848 isPowerOfTwo(Y, TD, /*OrZero*/true, Depth))
850 // X & (-X) is always a power of two or zero.
851 if (match(X, m_Neg(m_Specific(Y))) || match(Y, m_Neg(m_Specific(X))))
856 // An exact divide or right shift can only shift off zero bits, so the result
857 // is a power of two only if the first operand is a power of two and not
858 // copying a sign bit (sdiv int_min, 2).
859 if (match(V, m_Exact(m_LShr(m_Value(), m_Value()))) ||
860 match(V, m_Exact(m_UDiv(m_Value(), m_Value())))) {
861 return isPowerOfTwo(cast<Operator>(V)->getOperand(0), TD, OrZero, Depth);
867 /// isKnownNonZero - Return true if the given value is known to be non-zero
868 /// when defined. For vectors return true if every element is known to be
869 /// non-zero when defined. Supports values with integer or pointer type and
870 /// vectors of integers.
871 bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
872 if (Constant *C = dyn_cast<Constant>(V)) {
873 if (C->isNullValue())
875 if (isa<ConstantInt>(C))
876 // Must be non-zero due to null test above.
878 // TODO: Handle vectors
882 // The remaining tests are all recursive, so bail out if we hit the limit.
883 if (Depth++ >= MaxDepth)
886 unsigned BitWidth = getBitWidth(V->getType(), TD);
888 // X | Y != 0 if X != 0 or Y != 0.
889 Value *X = 0, *Y = 0;
890 if (match(V, m_Or(m_Value(X), m_Value(Y))))
891 return isKnownNonZero(X, TD, Depth) || isKnownNonZero(Y, TD, Depth);
893 // ext X != 0 if X != 0.
894 if (isa<SExtInst>(V) || isa<ZExtInst>(V))
895 return isKnownNonZero(cast<Instruction>(V)->getOperand(0), TD, Depth);
897 // shl X, Y != 0 if X is odd. Note that the value of the shift is undefined
898 // if the lowest bit is shifted off the end.
899 if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
900 // shl nuw can't remove any non-zero bits.
901 OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
902 if (BO->hasNoUnsignedWrap())
903 return isKnownNonZero(X, TD, Depth);
905 APInt KnownZero(BitWidth, 0);
906 APInt KnownOne(BitWidth, 0);
907 ComputeMaskedBits(X, KnownZero, KnownOne, TD, Depth);
911 // shr X, Y != 0 if X is negative. Note that the value of the shift is not
912 // defined if the sign bit is shifted off the end.
913 else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
914 // shr exact can only shift out zero bits.
915 PossiblyExactOperator *BO = cast<PossiblyExactOperator>(V);
917 return isKnownNonZero(X, TD, Depth);
919 bool XKnownNonNegative, XKnownNegative;
920 ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
924 // div exact can only produce a zero if the dividend is zero.
925 else if (match(V, m_Exact(m_IDiv(m_Value(X), m_Value())))) {
926 return isKnownNonZero(X, TD, Depth);
929 else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
930 bool XKnownNonNegative, XKnownNegative;
931 bool YKnownNonNegative, YKnownNegative;
932 ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
933 ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, TD, Depth);
935 // If X and Y are both non-negative (as signed values) then their sum is not
936 // zero unless both X and Y are zero.
937 if (XKnownNonNegative && YKnownNonNegative)
938 if (isKnownNonZero(X, TD, Depth) || isKnownNonZero(Y, TD, Depth))
941 // If X and Y are both negative (as signed values) then their sum is not
942 // zero unless both X and Y equal INT_MIN.
943 if (BitWidth && XKnownNegative && YKnownNegative) {
944 APInt KnownZero(BitWidth, 0);
945 APInt KnownOne(BitWidth, 0);
946 APInt Mask = APInt::getSignedMaxValue(BitWidth);
947 // The sign bit of X is set. If some other bit is set then X is not equal
949 ComputeMaskedBits(X, KnownZero, KnownOne, TD, Depth);
950 if ((KnownOne & Mask) != 0)
952 // The sign bit of Y is set. If some other bit is set then Y is not equal
954 ComputeMaskedBits(Y, KnownZero, KnownOne, TD, Depth);
955 if ((KnownOne & Mask) != 0)
959 // The sum of a non-negative number and a power of two is not zero.
960 if (XKnownNonNegative && isPowerOfTwo(Y, TD, /*OrZero*/false, Depth))
962 if (YKnownNonNegative && isPowerOfTwo(X, TD, /*OrZero*/false, Depth))
966 else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) {
967 OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
968 // If X and Y are non-zero then so is X * Y as long as the multiplication
969 // does not overflow.
970 if ((BO->hasNoSignedWrap() || BO->hasNoUnsignedWrap()) &&
971 isKnownNonZero(X, TD, Depth) && isKnownNonZero(Y, TD, Depth))
974 // (C ? X : Y) != 0 if X != 0 and Y != 0.
975 else if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
976 if (isKnownNonZero(SI->getTrueValue(), TD, Depth) &&
977 isKnownNonZero(SI->getFalseValue(), TD, Depth))
981 if (!BitWidth) return false;
982 APInt KnownZero(BitWidth, 0);
983 APInt KnownOne(BitWidth, 0);
984 ComputeMaskedBits(V, KnownZero, KnownOne, TD, Depth);
985 return KnownOne != 0;
988 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
989 /// this predicate to simplify operations downstream. Mask is known to be zero
990 /// for bits that V cannot have.
992 /// This function is defined on values with integer type, values with pointer
993 /// type (but only if TD is non-null), and vectors of integers. In the case
994 /// where V is a vector, the mask, known zero, and known one values are the
995 /// same width as the vector element, and the bit is set only if it is true
996 /// for all of the elements in the vector.
997 bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask,
998 const TargetData *TD, unsigned Depth) {
999 APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
1000 ComputeMaskedBits(V, KnownZero, KnownOne, TD, Depth);
1001 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
1002 return (KnownZero & Mask) == Mask;
1007 /// ComputeNumSignBits - Return the number of times the sign bit of the
1008 /// register is replicated into the other bits. We know that at least 1 bit
1009 /// is always equal to the sign bit (itself), but other cases can give us
1010 /// information. For example, immediately after an "ashr X, 2", we know that
1011 /// the top 3 bits are all equal to each other, so we return 3.
1013 /// 'Op' must have a scalar integer type.
1015 unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
1017 assert((TD || V->getType()->isIntOrIntVectorTy()) &&
1018 "ComputeNumSignBits requires a TargetData object to operate "
1019 "on non-integer values!");
1020 Type *Ty = V->getType();
1021 unsigned TyBits = TD ? TD->getTypeSizeInBits(V->getType()->getScalarType()) :
1022 Ty->getScalarSizeInBits();
1024 unsigned FirstAnswer = 1;
1026 // Note that ConstantInt is handled by the general ComputeMaskedBits case
1030 return 1; // Limit search depth.
1032 Operator *U = dyn_cast<Operator>(V);
1033 switch (Operator::getOpcode(V)) {
1035 case Instruction::SExt:
1036 Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits();
1037 return ComputeNumSignBits(U->getOperand(0), TD, Depth+1) + Tmp;
1039 case Instruction::AShr: {
1040 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
1041 // ashr X, C -> adds C sign bits. Vectors too.
1043 if (match(U->getOperand(1), m_APInt(ShAmt))) {
1044 Tmp += ShAmt->getZExtValue();
1045 if (Tmp > TyBits) Tmp = TyBits;
1049 case Instruction::Shl: {
1051 if (match(U->getOperand(1), m_APInt(ShAmt))) {
1052 // shl destroys sign bits.
1053 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
1054 Tmp2 = ShAmt->getZExtValue();
1055 if (Tmp2 >= TyBits || // Bad shift.
1056 Tmp2 >= Tmp) break; // Shifted all sign bits out.
1061 case Instruction::And:
1062 case Instruction::Or:
1063 case Instruction::Xor: // NOT is handled here.
1064 // Logical binary ops preserve the number of sign bits at the worst.
1065 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
1067 Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
1068 FirstAnswer = std::min(Tmp, Tmp2);
1069 // We computed what we know about the sign bits as our first
1070 // answer. Now proceed to the generic code that uses
1071 // ComputeMaskedBits, and pick whichever answer is better.
1075 case Instruction::Select:
1076 Tmp = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
1077 if (Tmp == 1) return 1; // Early out.
1078 Tmp2 = ComputeNumSignBits(U->getOperand(2), TD, Depth+1);
1079 return std::min(Tmp, Tmp2);
1081 case Instruction::Add:
1082 // Add can have at most one carry bit. Thus we know that the output
1083 // is, at worst, one more bit than the inputs.
1084 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
1085 if (Tmp == 1) return 1; // Early out.
1087 // Special case decrementing a value (ADD X, -1):
1088 if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(1)))
1089 if (CRHS->isAllOnesValue()) {
1090 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
1091 ComputeMaskedBits(U->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
1093 // If the input is known to be 0 or 1, the output is 0/-1, which is all
1095 if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
1098 // If we are subtracting one from a positive number, there is no carry
1099 // out of the result.
1100 if (KnownZero.isNegative())
1104 Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
1105 if (Tmp2 == 1) return 1;
1106 return std::min(Tmp, Tmp2)-1;
1108 case Instruction::Sub:
1109 Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
1110 if (Tmp2 == 1) return 1;
1113 if (ConstantInt *CLHS = dyn_cast<ConstantInt>(U->getOperand(0)))
1114 if (CLHS->isNullValue()) {
1115 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
1116 ComputeMaskedBits(U->getOperand(1), KnownZero, KnownOne, TD, Depth+1);
1117 // If the input is known to be 0 or 1, the output is 0/-1, which is all
1119 if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
1122 // If the input is known to be positive (the sign bit is known clear),
1123 // the output of the NEG has the same number of sign bits as the input.
1124 if (KnownZero.isNegative())
1127 // Otherwise, we treat this like a SUB.
1130 // Sub can have at most one carry bit. Thus we know that the output
1131 // is, at worst, one more bit than the inputs.
1132 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
1133 if (Tmp == 1) return 1; // Early out.
1134 return std::min(Tmp, Tmp2)-1;
1136 case Instruction::PHI: {
1137 PHINode *PN = cast<PHINode>(U);
1138 // Don't analyze large in-degree PHIs.
1139 if (PN->getNumIncomingValues() > 4) break;
1141 // Take the minimum of all incoming values. This can't infinitely loop
1142 // because of our depth threshold.
1143 Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1);
1144 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
1145 if (Tmp == 1) return Tmp;
1147 ComputeNumSignBits(PN->getIncomingValue(i), TD, Depth+1));
1152 case Instruction::Trunc:
1153 // FIXME: it's tricky to do anything useful for this, but it is an important
1154 // case for targets like X86.
1158 // Finally, if we can prove that the top bits of the result are 0's or 1's,
1159 // use this information.
1160 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
1162 ComputeMaskedBits(V, KnownZero, KnownOne, TD, Depth);
1164 if (KnownZero.isNegative()) { // sign bit is 0
1166 } else if (KnownOne.isNegative()) { // sign bit is 1;
1173 // Okay, we know that the sign bit in Mask is set. Use CLZ to determine
1174 // the number of identical bits in the top of the input value.
1176 Mask <<= Mask.getBitWidth()-TyBits;
1177 // Return # leading zeros. We use 'min' here in case Val was zero before
1178 // shifting. We don't want to return '64' as for an i32 "0".
1179 return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
1182 /// ComputeMultiple - This function computes the integer multiple of Base that
1183 /// equals V. If successful, it returns true and returns the multiple in
1184 /// Multiple. If unsuccessful, it returns false. It looks
1185 /// through SExt instructions only if LookThroughSExt is true.
1186 bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
1187 bool LookThroughSExt, unsigned Depth) {
1188 const unsigned MaxDepth = 6;
1190 assert(V && "No Value?");
1191 assert(Depth <= MaxDepth && "Limit Search Depth");
1192 assert(V->getType()->isIntegerTy() && "Not integer or pointer type!");
1194 Type *T = V->getType();
1196 ConstantInt *CI = dyn_cast<ConstantInt>(V);
1206 ConstantExpr *CO = dyn_cast<ConstantExpr>(V);
1207 Constant *BaseVal = ConstantInt::get(T, Base);
1208 if (CO && CO == BaseVal) {
1210 Multiple = ConstantInt::get(T, 1);
1214 if (CI && CI->getZExtValue() % Base == 0) {
1215 Multiple = ConstantInt::get(T, CI->getZExtValue() / Base);
1219 if (Depth == MaxDepth) return false; // Limit search depth.
1221 Operator *I = dyn_cast<Operator>(V);
1222 if (!I) return false;
1224 switch (I->getOpcode()) {
1226 case Instruction::SExt:
1227 if (!LookThroughSExt) return false;
1228 // otherwise fall through to ZExt
1229 case Instruction::ZExt:
1230 return ComputeMultiple(I->getOperand(0), Base, Multiple,
1231 LookThroughSExt, Depth+1);
1232 case Instruction::Shl:
1233 case Instruction::Mul: {
1234 Value *Op0 = I->getOperand(0);
1235 Value *Op1 = I->getOperand(1);
1237 if (I->getOpcode() == Instruction::Shl) {
1238 ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1);
1239 if (!Op1CI) return false;
1240 // Turn Op0 << Op1 into Op0 * 2^Op1
1241 APInt Op1Int = Op1CI->getValue();
1242 uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1);
1243 APInt API(Op1Int.getBitWidth(), 0);
1244 API.setBit(BitToSet);
1245 Op1 = ConstantInt::get(V->getContext(), API);
1249 if (ComputeMultiple(Op0, Base, Mul0, LookThroughSExt, Depth+1)) {
1250 if (Constant *Op1C = dyn_cast<Constant>(Op1))
1251 if (Constant *MulC = dyn_cast<Constant>(Mul0)) {
1252 if (Op1C->getType()->getPrimitiveSizeInBits() <
1253 MulC->getType()->getPrimitiveSizeInBits())
1254 Op1C = ConstantExpr::getZExt(Op1C, MulC->getType());
1255 if (Op1C->getType()->getPrimitiveSizeInBits() >
1256 MulC->getType()->getPrimitiveSizeInBits())
1257 MulC = ConstantExpr::getZExt(MulC, Op1C->getType());
1259 // V == Base * (Mul0 * Op1), so return (Mul0 * Op1)
1260 Multiple = ConstantExpr::getMul(MulC, Op1C);
1264 if (ConstantInt *Mul0CI = dyn_cast<ConstantInt>(Mul0))
1265 if (Mul0CI->getValue() == 1) {
1266 // V == Base * Op1, so return Op1
1273 if (ComputeMultiple(Op1, Base, Mul1, LookThroughSExt, Depth+1)) {
1274 if (Constant *Op0C = dyn_cast<Constant>(Op0))
1275 if (Constant *MulC = dyn_cast<Constant>(Mul1)) {
1276 if (Op0C->getType()->getPrimitiveSizeInBits() <
1277 MulC->getType()->getPrimitiveSizeInBits())
1278 Op0C = ConstantExpr::getZExt(Op0C, MulC->getType());
1279 if (Op0C->getType()->getPrimitiveSizeInBits() >
1280 MulC->getType()->getPrimitiveSizeInBits())
1281 MulC = ConstantExpr::getZExt(MulC, Op0C->getType());
1283 // V == Base * (Mul1 * Op0), so return (Mul1 * Op0)
1284 Multiple = ConstantExpr::getMul(MulC, Op0C);
1288 if (ConstantInt *Mul1CI = dyn_cast<ConstantInt>(Mul1))
1289 if (Mul1CI->getValue() == 1) {
1290 // V == Base * Op0, so return Op0
1298 // We could not determine if V is a multiple of Base.
1302 /// CannotBeNegativeZero - Return true if we can prove that the specified FP
1303 /// value is never equal to -0.0.
1305 /// NOTE: this function will need to be revisited when we support non-default
1308 bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
1309 if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
1310 return !CFP->getValueAPF().isNegZero();
1313 return 1; // Limit search depth.
1315 const Operator *I = dyn_cast<Operator>(V);
1316 if (I == 0) return false;
1318 // (add x, 0.0) is guaranteed to return +0.0, not -0.0.
1319 if (I->getOpcode() == Instruction::FAdd &&
1320 isa<ConstantFP>(I->getOperand(1)) &&
1321 cast<ConstantFP>(I->getOperand(1))->isNullValue())
1324 // sitofp and uitofp turn into +0.0 for zero.
1325 if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
1328 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
1329 // sqrt(-0.0) = -0.0, no other negative results are possible.
1330 if (II->getIntrinsicID() == Intrinsic::sqrt)
1331 return CannotBeNegativeZero(II->getArgOperand(0), Depth+1);
1333 if (const CallInst *CI = dyn_cast<CallInst>(I))
1334 if (const Function *F = CI->getCalledFunction()) {
1335 if (F->isDeclaration()) {
1337 if (F->getName() == "abs") return true;
1338 // fabs[lf](x) != -0.0
1339 if (F->getName() == "fabs") return true;
1340 if (F->getName() == "fabsf") return true;
1341 if (F->getName() == "fabsl") return true;
1342 if (F->getName() == "sqrt" || F->getName() == "sqrtf" ||
1343 F->getName() == "sqrtl")
1344 return CannotBeNegativeZero(CI->getArgOperand(0), Depth+1);
1351 /// isBytewiseValue - If the specified value can be set by repeating the same
1352 /// byte in memory, return the i8 value that it is represented with. This is
1353 /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
1354 /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
1355 /// byte store (e.g. i16 0x1234), return null.
1356 Value *llvm::isBytewiseValue(Value *V) {
1357 // All byte-wide stores are splatable, even of arbitrary variables.
1358 if (V->getType()->isIntegerTy(8)) return V;
1360 // Handle 'null' ConstantArrayZero etc.
1361 if (Constant *C = dyn_cast<Constant>(V))
1362 if (C->isNullValue())
1363 return Constant::getNullValue(Type::getInt8Ty(V->getContext()));
1365 // Constant float and double values can be handled as integer values if the
1366 // corresponding integer value is "byteable". An important case is 0.0.
1367 if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
1368 if (CFP->getType()->isFloatTy())
1369 V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(V->getContext()));
1370 if (CFP->getType()->isDoubleTy())
1371 V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext()));
1372 // Don't handle long double formats, which have strange constraints.
1375 // We can handle constant integers that are power of two in size and a
1376 // multiple of 8 bits.
1377 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
1378 unsigned Width = CI->getBitWidth();
1379 if (isPowerOf2_32(Width) && Width > 8) {
1380 // We can handle this value if the recursive binary decomposition is the
1381 // same at all levels.
1382 APInt Val = CI->getValue();
1384 while (Val.getBitWidth() != 8) {
1385 unsigned NextWidth = Val.getBitWidth()/2;
1386 Val2 = Val.lshr(NextWidth);
1387 Val2 = Val2.trunc(Val.getBitWidth()/2);
1388 Val = Val.trunc(Val.getBitWidth()/2);
1390 // If the top/bottom halves aren't the same, reject it.
1394 return ConstantInt::get(V->getContext(), Val);
1398 // A ConstantDataArray/Vector is splatable if all its members are equal and
1400 if (ConstantDataSequential *CA = dyn_cast<ConstantDataSequential>(V)) {
1401 Value *Elt = CA->getElementAsConstant(0);
1402 Value *Val = isBytewiseValue(Elt);
1406 for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I)
1407 if (CA->getElementAsConstant(I) != Elt)
1413 // Conceptually, we could handle things like:
1414 // %a = zext i8 %X to i16
1415 // %b = shl i16 %a, 8
1416 // %c = or i16 %a, %b
1417 // but until there is an example that actually needs this, it doesn't seem
1418 // worth worrying about.
1423 // This is the recursive version of BuildSubAggregate. It takes a few different
1424 // arguments. Idxs is the index within the nested struct From that we are
1425 // looking at now (which is of type IndexedType). IdxSkip is the number of
1426 // indices from Idxs that should be left out when inserting into the resulting
1427 // struct. To is the result struct built so far, new insertvalue instructions
1429 static Value *BuildSubAggregate(Value *From, Value* To, Type *IndexedType,
1430 SmallVector<unsigned, 10> &Idxs,
1432 Instruction *InsertBefore) {
1433 llvm::StructType *STy = llvm::dyn_cast<llvm::StructType>(IndexedType);
1435 // Save the original To argument so we can modify it
1437 // General case, the type indexed by Idxs is a struct
1438 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1439 // Process each struct element recursively
1442 To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip,
1446 // Couldn't find any inserted value for this index? Cleanup
1447 while (PrevTo != OrigTo) {
1448 InsertValueInst* Del = cast<InsertValueInst>(PrevTo);
1449 PrevTo = Del->getAggregateOperand();
1450 Del->eraseFromParent();
1452 // Stop processing elements
1456 // If we successfully found a value for each of our subaggregates
1460 // Base case, the type indexed by SourceIdxs is not a struct, or not all of
1461 // the struct's elements had a value that was inserted directly. In the latter
1462 // case, perhaps we can't determine each of the subelements individually, but
1463 // we might be able to find the complete struct somewhere.
1465 // Find the value that is at that particular spot
1466 Value *V = FindInsertedValue(From, Idxs);
1471 // Insert the value in the new (sub) aggregrate
1472 return llvm::InsertValueInst::Create(To, V, makeArrayRef(Idxs).slice(IdxSkip),
1473 "tmp", InsertBefore);
1476 // This helper takes a nested struct and extracts a part of it (which is again a
1477 // struct) into a new value. For example, given the struct:
1478 // { a, { b, { c, d }, e } }
1479 // and the indices "1, 1" this returns
1482 // It does this by inserting an insertvalue for each element in the resulting
1483 // struct, as opposed to just inserting a single struct. This will only work if
1484 // each of the elements of the substruct are known (ie, inserted into From by an
1485 // insertvalue instruction somewhere).
1487 // All inserted insertvalue instructions are inserted before InsertBefore
1488 static Value *BuildSubAggregate(Value *From, ArrayRef<unsigned> idx_range,
1489 Instruction *InsertBefore) {
1490 assert(InsertBefore && "Must have someplace to insert!");
1491 Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(),
1493 Value *To = UndefValue::get(IndexedType);
1494 SmallVector<unsigned, 10> Idxs(idx_range.begin(), idx_range.end());
1495 unsigned IdxSkip = Idxs.size();
1497 return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore);
1500 /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
1501 /// the scalar value indexed is already around as a register, for example if it
1502 /// were inserted directly into the aggregrate.
1504 /// If InsertBefore is not null, this function will duplicate (modified)
1505 /// insertvalues when a part of a nested struct is extracted.
1506 Value *llvm::FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range,
1507 Instruction *InsertBefore) {
1508 // Nothing to index? Just return V then (this is useful at the end of our
1510 if (idx_range.empty())
1512 // We have indices, so V should have an indexable type.
1513 assert((V->getType()->isStructTy() || V->getType()->isArrayTy()) &&
1514 "Not looking at a struct or array?");
1515 assert(ExtractValueInst::getIndexedType(V->getType(), idx_range) &&
1516 "Invalid indices for type?");
1518 if (Constant *C = dyn_cast<Constant>(V)) {
1519 C = C->getAggregateElement(idx_range[0]);
1520 if (C == 0) return 0;
1521 return FindInsertedValue(C, idx_range.slice(1), InsertBefore);
1524 if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) {
1525 // Loop the indices for the insertvalue instruction in parallel with the
1526 // requested indices
1527 const unsigned *req_idx = idx_range.begin();
1528 for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
1529 i != e; ++i, ++req_idx) {
1530 if (req_idx == idx_range.end()) {
1531 // We can't handle this without inserting insertvalues
1535 // The requested index identifies a part of a nested aggregate. Handle
1536 // this specially. For example,
1537 // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
1538 // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
1539 // %C = extractvalue {i32, { i32, i32 } } %B, 1
1540 // This can be changed into
1541 // %A = insertvalue {i32, i32 } undef, i32 10, 0
1542 // %C = insertvalue {i32, i32 } %A, i32 11, 1
1543 // which allows the unused 0,0 element from the nested struct to be
1545 return BuildSubAggregate(V, makeArrayRef(idx_range.begin(), req_idx),
1549 // This insert value inserts something else than what we are looking for.
1550 // See if the (aggregrate) value inserted into has the value we are
1551 // looking for, then.
1553 return FindInsertedValue(I->getAggregateOperand(), idx_range,
1556 // If we end up here, the indices of the insertvalue match with those
1557 // requested (though possibly only partially). Now we recursively look at
1558 // the inserted value, passing any remaining indices.
1559 return FindInsertedValue(I->getInsertedValueOperand(),
1560 makeArrayRef(req_idx, idx_range.end()),
1564 if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) {
1565 // If we're extracting a value from an aggregrate that was extracted from
1566 // something else, we can extract from that something else directly instead.
1567 // However, we will need to chain I's indices with the requested indices.
1569 // Calculate the number of indices required
1570 unsigned size = I->getNumIndices() + idx_range.size();
1571 // Allocate some space to put the new indices in
1572 SmallVector<unsigned, 5> Idxs;
1574 // Add indices from the extract value instruction
1575 Idxs.append(I->idx_begin(), I->idx_end());
1577 // Add requested indices
1578 Idxs.append(idx_range.begin(), idx_range.end());
1580 assert(Idxs.size() == size
1581 && "Number of indices added not correct?");
1583 return FindInsertedValue(I->getAggregateOperand(), Idxs, InsertBefore);
1585 // Otherwise, we don't know (such as, extracting from a function return value
1586 // or load instruction)
1590 /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
1591 /// it can be expressed as a base pointer plus a constant offset. Return the
1592 /// base and offset to the caller.
1593 Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
1594 const TargetData &TD) {
1595 Operator *PtrOp = dyn_cast<Operator>(Ptr);
1596 if (PtrOp == 0 || Ptr->getType()->isVectorTy())
1599 // Just look through bitcasts.
1600 if (PtrOp->getOpcode() == Instruction::BitCast)
1601 return GetPointerBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
1603 // If this is a GEP with constant indices, we can look through it.
1604 GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
1605 if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
1607 gep_type_iterator GTI = gep_type_begin(GEP);
1608 for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
1610 ConstantInt *OpC = cast<ConstantInt>(*I);
1611 if (OpC->isZero()) continue;
1613 // Handle a struct and array indices which add their offset to the pointer.
1614 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
1615 Offset += TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
1617 uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType());
1618 Offset += OpC->getSExtValue()*Size;
1622 // Re-sign extend from the pointer size if needed to get overflow edge cases
1624 unsigned PtrSize = TD.getPointerSizeInBits();
1626 Offset = SignExtend64(Offset, PtrSize);
1628 return GetPointerBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
1632 /// getConstantStringInfo - This function computes the length of a
1633 /// null-terminated C string pointed to by V. If successful, it returns true
1634 /// and returns the string in Str. If unsuccessful, it returns false.
1635 bool llvm::getConstantStringInfo(const Value *V, StringRef &Str,
1636 uint64_t Offset, bool TrimAtNul) {
1639 // Look through bitcast instructions and geps.
1640 V = V->stripPointerCasts();
1642 // If the value is a GEP instructionor constant expression, treat it as an
1644 if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
1645 // Make sure the GEP has exactly three arguments.
1646 if (GEP->getNumOperands() != 3)
1649 // Make sure the index-ee is a pointer to array of i8.
1650 PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType());
1651 ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType());
1652 if (AT == 0 || !AT->getElementType()->isIntegerTy(8))
1655 // Check to make sure that the first operand of the GEP is an integer and
1656 // has value 0 so that we are sure we're indexing into the initializer.
1657 const ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
1658 if (FirstIdx == 0 || !FirstIdx->isZero())
1661 // If the second index isn't a ConstantInt, then this is a variable index
1662 // into the array. If this occurs, we can't say anything meaningful about
1664 uint64_t StartIdx = 0;
1665 if (const ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
1666 StartIdx = CI->getZExtValue();
1669 return getConstantStringInfo(GEP->getOperand(0), Str, StartIdx+Offset);
1672 // The GEP instruction, constant or instruction, must reference a global
1673 // variable that is a constant and is initialized. The referenced constant
1674 // initializer is the array that we'll use for optimization.
1675 const GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
1676 if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
1679 // Handle the all-zeros case
1680 if (GV->getInitializer()->isNullValue()) {
1681 // This is a degenerate case. The initializer is constant zero so the
1682 // length of the string must be zero.
1687 // Must be a Constant Array
1688 const ConstantDataArray *Array =
1689 dyn_cast<ConstantDataArray>(GV->getInitializer());
1690 if (Array == 0 || !Array->isString())
1693 // Get the number of elements in the array
1694 uint64_t NumElts = Array->getType()->getArrayNumElements();
1696 // Start out with the entire array in the StringRef.
1697 Str = Array->getAsString();
1699 if (Offset > NumElts)
1702 // Skip over 'offset' bytes.
1703 Str = Str.substr(Offset);
1706 // Trim off the \0 and anything after it. If the array is not nul
1707 // terminated, we just return the whole end of string. The client may know
1708 // some other way that the string is length-bound.
1709 Str = Str.substr(0, Str.find('\0'));
1714 // These next two are very similar to the above, but also look through PHI
1716 // TODO: See if we can integrate these two together.
1718 /// GetStringLengthH - If we can compute the length of the string pointed to by
1719 /// the specified pointer, return 'len+1'. If we can't, return 0.
1720 static uint64_t GetStringLengthH(Value *V, SmallPtrSet<PHINode*, 32> &PHIs) {
1721 // Look through noop bitcast instructions.
1722 V = V->stripPointerCasts();
1724 // If this is a PHI node, there are two cases: either we have already seen it
1726 if (PHINode *PN = dyn_cast<PHINode>(V)) {
1727 if (!PHIs.insert(PN))
1728 return ~0ULL; // already in the set.
1730 // If it was new, see if all the input strings are the same length.
1731 uint64_t LenSoFar = ~0ULL;
1732 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1733 uint64_t Len = GetStringLengthH(PN->getIncomingValue(i), PHIs);
1734 if (Len == 0) return 0; // Unknown length -> unknown.
1736 if (Len == ~0ULL) continue;
1738 if (Len != LenSoFar && LenSoFar != ~0ULL)
1739 return 0; // Disagree -> unknown.
1743 // Success, all agree.
1747 // strlen(select(c,x,y)) -> strlen(x) ^ strlen(y)
1748 if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
1749 uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs);
1750 if (Len1 == 0) return 0;
1751 uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs);
1752 if (Len2 == 0) return 0;
1753 if (Len1 == ~0ULL) return Len2;
1754 if (Len2 == ~0ULL) return Len1;
1755 if (Len1 != Len2) return 0;
1759 // Otherwise, see if we can read the string.
1761 if (!getConstantStringInfo(V, StrData))
1764 return StrData.size()+1;
1767 /// GetStringLength - If we can compute the length of the string pointed to by
1768 /// the specified pointer, return 'len+1'. If we can't, return 0.
1769 uint64_t llvm::GetStringLength(Value *V) {
1770 if (!V->getType()->isPointerTy()) return 0;
1772 SmallPtrSet<PHINode*, 32> PHIs;
1773 uint64_t Len = GetStringLengthH(V, PHIs);
1774 // If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return
1775 // an empty string as a length.
1776 return Len == ~0ULL ? 1 : Len;
1780 llvm::GetUnderlyingObject(Value *V, const TargetData *TD, unsigned MaxLookup) {
1781 if (!V->getType()->isPointerTy())
1783 for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
1784 if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
1785 V = GEP->getPointerOperand();
1786 } else if (Operator::getOpcode(V) == Instruction::BitCast) {
1787 V = cast<Operator>(V)->getOperand(0);
1788 } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
1789 if (GA->mayBeOverridden())
1791 V = GA->getAliasee();
1793 // See if InstructionSimplify knows any relevant tricks.
1794 if (Instruction *I = dyn_cast<Instruction>(V))
1795 // TODO: Acquire a DominatorTree and use it.
1796 if (Value *Simplified = SimplifyInstruction(I, TD, 0)) {
1803 assert(V->getType()->isPointerTy() && "Unexpected operand type!");
1809 llvm::GetUnderlyingObjects(Value *V,
1810 SmallVectorImpl<Value *> &Objects,
1811 const TargetData *TD,
1812 unsigned MaxLookup) {
1813 SmallPtrSet<Value *, 4> Visited;
1814 SmallVector<Value *, 4> Worklist;
1815 Worklist.push_back(V);
1817 Value *P = Worklist.pop_back_val();
1818 P = GetUnderlyingObject(P, TD, MaxLookup);
1820 if (!Visited.insert(P))
1823 if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
1824 Worklist.push_back(SI->getTrueValue());
1825 Worklist.push_back(SI->getFalseValue());
1829 if (PHINode *PN = dyn_cast<PHINode>(P)) {
1830 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
1831 Worklist.push_back(PN->getIncomingValue(i));
1835 Objects.push_back(P);
1836 } while (!Worklist.empty());
1839 /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
1840 /// are lifetime markers.
1842 bool llvm::onlyUsedByLifetimeMarkers(const Value *V) {
1843 for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
1845 const IntrinsicInst *II = dyn_cast<IntrinsicInst>(*UI);
1846 if (!II) return false;
1848 if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
1849 II->getIntrinsicID() != Intrinsic::lifetime_end)
1855 bool llvm::isSafeToSpeculativelyExecute(const Value *V,
1856 const TargetData *TD) {
1857 const Operator *Inst = dyn_cast<Operator>(V);
1861 for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
1862 if (Constant *C = dyn_cast<Constant>(Inst->getOperand(i)))
1866 switch (Inst->getOpcode()) {
1869 case Instruction::UDiv:
1870 case Instruction::URem:
1871 // x / y is undefined if y == 0, but calcuations like x / 3 are safe.
1872 return isKnownNonZero(Inst->getOperand(1), TD);
1873 case Instruction::SDiv:
1874 case Instruction::SRem: {
1875 Value *Op = Inst->getOperand(1);
1876 // x / y is undefined if y == 0
1877 if (!isKnownNonZero(Op, TD))
1879 // x / y might be undefined if y == -1
1880 unsigned BitWidth = getBitWidth(Op->getType(), TD);
1883 APInt KnownZero(BitWidth, 0);
1884 APInt KnownOne(BitWidth, 0);
1885 ComputeMaskedBits(Op, KnownZero, KnownOne, TD);
1888 case Instruction::Load: {
1889 const LoadInst *LI = cast<LoadInst>(Inst);
1890 if (!LI->isUnordered())
1892 return LI->getPointerOperand()->isDereferenceablePointer();
1894 case Instruction::Call: {
1895 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
1896 switch (II->getIntrinsicID()) {
1897 // These synthetic intrinsics have no side-effects, and just mark
1898 // information about their operands.
1899 // FIXME: There are other no-op synthetic instructions that potentially
1900 // should be considered at least *safe* to speculate...
1901 case Intrinsic::dbg_declare:
1902 case Intrinsic::dbg_value:
1905 case Intrinsic::bswap:
1906 case Intrinsic::ctlz:
1907 case Intrinsic::ctpop:
1908 case Intrinsic::cttz:
1909 case Intrinsic::objectsize:
1910 case Intrinsic::sadd_with_overflow:
1911 case Intrinsic::smul_with_overflow:
1912 case Intrinsic::ssub_with_overflow:
1913 case Intrinsic::uadd_with_overflow:
1914 case Intrinsic::umul_with_overflow:
1915 case Intrinsic::usub_with_overflow:
1917 // TODO: some fp intrinsics are marked as having the same error handling
1918 // as libm. They're safe to speculate when they won't error.
1919 // TODO: are convert_{from,to}_fp16 safe?
1920 // TODO: can we list target-specific intrinsics here?
1924 return false; // The called function could have undefined behavior or
1925 // side-effects, even if marked readnone nounwind.
1927 case Instruction::VAArg:
1928 case Instruction::Alloca:
1929 case Instruction::Invoke:
1930 case Instruction::PHI:
1931 case Instruction::Store:
1932 case Instruction::Ret:
1933 case Instruction::Br:
1934 case Instruction::IndirectBr:
1935 case Instruction::Switch:
1936 case Instruction::Unreachable:
1937 case Instruction::Fence:
1938 case Instruction::LandingPad:
1939 case Instruction::AtomicRMW:
1940 case Instruction::AtomicCmpXchg:
1941 case Instruction::Resume:
1942 return false; // Misc instructions which have effects