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/Operator.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Support/GetElementPtrTypeIterator.h"
26 #include "llvm/Support/MathExtras.h"
27 #include "llvm/Support/PatternMatch.h"
28 #include "llvm/ADT/SmallPtrSet.h"
31 using namespace llvm::PatternMatch
;
33 const unsigned MaxDepth
= 6;
35 /// getBitWidth - Returns the bitwidth of the given scalar or pointer type (if
36 /// unknown returns 0). For vector types, returns the element type's bitwidth.
37 static unsigned getBitWidth(const Type
*Ty
, const TargetData
*TD
) {
38 if (unsigned BitWidth
= Ty
->getScalarSizeInBits())
40 assert(isa
<PointerType
>(Ty
) && "Expected a pointer type!");
41 return TD
? TD
->getPointerSizeInBits() : 0;
44 /// ComputeMaskedBits - Determine which of the bits specified in Mask are
45 /// known to be either zero or one and return them in the KnownZero/KnownOne
46 /// bit sets. This code only analyzes bits in Mask, in order to short-circuit
48 /// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
49 /// we cannot optimize based on the assumption that it is zero without changing
50 /// it to be an explicit zero. If we don't change it to zero, other code could
51 /// optimized based on the contradictory assumption that it is non-zero.
52 /// Because instcombine aggressively folds operations with undef args anyway,
53 /// this won't lose us code quality.
55 /// This function is defined on values with integer type, values with pointer
56 /// type (but only if TD is non-null), and vectors of integers. In the case
57 /// where V is a vector, the mask, known zero, and known one values are the
58 /// same width as the vector element, and the bit is set only if it is true
59 /// for all of the elements in the vector.
60 void llvm::ComputeMaskedBits(Value
*V
, const APInt
&Mask
,
61 APInt
&KnownZero
, APInt
&KnownOne
,
62 const TargetData
*TD
, unsigned Depth
) {
63 assert(V
&& "No Value?");
64 assert(Depth
<= MaxDepth
&& "Limit Search Depth");
65 unsigned BitWidth
= Mask
.getBitWidth();
66 assert((V
->getType()->isIntOrIntVectorTy() || V
->getType()->isPointerTy())
67 && "Not integer or pointer type!");
69 TD
->getTypeSizeInBits(V
->getType()->getScalarType()) == BitWidth
) &&
70 (!V
->getType()->isIntOrIntVectorTy() ||
71 V
->getType()->getScalarSizeInBits() == BitWidth
) &&
72 KnownZero
.getBitWidth() == BitWidth
&&
73 KnownOne
.getBitWidth() == BitWidth
&&
74 "V, Mask, KnownOne and KnownZero should have same BitWidth");
76 if (ConstantInt
*CI
= dyn_cast
<ConstantInt
>(V
)) {
77 // We know all of the bits for a constant!
78 KnownOne
= CI
->getValue() & Mask
;
79 KnownZero
= ~KnownOne
& Mask
;
82 // Null and aggregate-zero are all-zeros.
83 if (isa
<ConstantPointerNull
>(V
) ||
84 isa
<ConstantAggregateZero
>(V
)) {
85 KnownOne
.clearAllBits();
89 // Handle a constant vector by taking the intersection of the known bits of
91 if (ConstantVector
*CV
= dyn_cast
<ConstantVector
>(V
)) {
92 KnownZero
.setAllBits(); KnownOne
.setAllBits();
93 for (unsigned i
= 0, e
= CV
->getNumOperands(); i
!= e
; ++i
) {
94 APInt
KnownZero2(BitWidth
, 0), KnownOne2(BitWidth
, 0);
95 ComputeMaskedBits(CV
->getOperand(i
), Mask
, KnownZero2
, KnownOne2
,
97 KnownZero
&= KnownZero2
;
98 KnownOne
&= KnownOne2
;
102 // The address of an aligned GlobalValue has trailing zeros.
103 if (GlobalValue
*GV
= dyn_cast
<GlobalValue
>(V
)) {
104 unsigned Align
= GV
->getAlignment();
105 if (Align
== 0 && TD
&& GV
->getType()->getElementType()->isSized()) {
106 const Type
*ObjectType
= GV
->getType()->getElementType();
107 // If the object is defined in the current Module, we'll be giving
108 // it the preferred alignment. Otherwise, we have to assume that it
109 // may only have the minimum ABI alignment.
110 if (!GV
->isDeclaration() && !GV
->mayBeOverridden())
111 Align
= TD
->getPrefTypeAlignment(ObjectType
);
113 Align
= TD
->getABITypeAlignment(ObjectType
);
116 KnownZero
= Mask
& APInt::getLowBitsSet(BitWidth
,
117 CountTrailingZeros_32(Align
));
119 KnownZero
.clearAllBits();
120 KnownOne
.clearAllBits();
123 // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
124 // the bits of its aliasee.
125 if (GlobalAlias
*GA
= dyn_cast
<GlobalAlias
>(V
)) {
126 if (GA
->mayBeOverridden()) {
127 KnownZero
.clearAllBits(); KnownOne
.clearAllBits();
129 ComputeMaskedBits(GA
->getAliasee(), Mask
, KnownZero
, KnownOne
,
135 KnownZero
.clearAllBits(); KnownOne
.clearAllBits(); // Start out not knowing anything.
137 if (Depth
== MaxDepth
|| Mask
== 0)
138 return; // Limit search depth.
140 Operator
*I
= dyn_cast
<Operator
>(V
);
143 APInt
KnownZero2(KnownZero
), KnownOne2(KnownOne
);
144 switch (I
->getOpcode()) {
146 case Instruction::And
: {
147 // If either the LHS or the RHS are Zero, the result is zero.
148 ComputeMaskedBits(I
->getOperand(1), Mask
, KnownZero
, KnownOne
, TD
, Depth
+1);
149 APInt
Mask2(Mask
& ~KnownZero
);
150 ComputeMaskedBits(I
->getOperand(0), Mask2
, KnownZero2
, KnownOne2
, TD
,
152 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
153 assert((KnownZero2
& KnownOne2
) == 0 && "Bits known to be one AND zero?");
155 // Output known-1 bits are only known if set in both the LHS & RHS.
156 KnownOne
&= KnownOne2
;
157 // Output known-0 are known to be clear if zero in either the LHS | RHS.
158 KnownZero
|= KnownZero2
;
161 case Instruction::Or
: {
162 ComputeMaskedBits(I
->getOperand(1), Mask
, KnownZero
, KnownOne
, TD
, Depth
+1);
163 APInt
Mask2(Mask
& ~KnownOne
);
164 ComputeMaskedBits(I
->getOperand(0), Mask2
, KnownZero2
, KnownOne2
, TD
,
166 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
167 assert((KnownZero2
& KnownOne2
) == 0 && "Bits known to be one AND zero?");
169 // Output known-0 bits are only known if clear in both the LHS & RHS.
170 KnownZero
&= KnownZero2
;
171 // Output known-1 are known to be set if set in either the LHS | RHS.
172 KnownOne
|= KnownOne2
;
175 case Instruction::Xor
: {
176 ComputeMaskedBits(I
->getOperand(1), Mask
, KnownZero
, KnownOne
, TD
, Depth
+1);
177 ComputeMaskedBits(I
->getOperand(0), Mask
, KnownZero2
, KnownOne2
, TD
,
179 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
180 assert((KnownZero2
& KnownOne2
) == 0 && "Bits known to be one AND zero?");
182 // Output known-0 bits are known if clear or set in both the LHS & RHS.
183 APInt KnownZeroOut
= (KnownZero
& KnownZero2
) | (KnownOne
& KnownOne2
);
184 // Output known-1 are known to be set if set in only one of the LHS, RHS.
185 KnownOne
= (KnownZero
& KnownOne2
) | (KnownOne
& KnownZero2
);
186 KnownZero
= KnownZeroOut
;
189 case Instruction::Mul
: {
190 APInt Mask2
= APInt::getAllOnesValue(BitWidth
);
191 ComputeMaskedBits(I
->getOperand(1), Mask2
, KnownZero
, KnownOne
, TD
,Depth
+1);
192 ComputeMaskedBits(I
->getOperand(0), Mask2
, KnownZero2
, KnownOne2
, TD
,
194 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
195 assert((KnownZero2
& KnownOne2
) == 0 && "Bits known to be one AND zero?");
197 // If low bits are zero in either operand, output low known-0 bits.
198 // Also compute a conserative estimate for high known-0 bits.
199 // More trickiness is possible, but this is sufficient for the
200 // interesting case of alignment computation.
201 KnownOne
.clearAllBits();
202 unsigned TrailZ
= KnownZero
.countTrailingOnes() +
203 KnownZero2
.countTrailingOnes();
204 unsigned LeadZ
= std::max(KnownZero
.countLeadingOnes() +
205 KnownZero2
.countLeadingOnes(),
206 BitWidth
) - BitWidth
;
208 TrailZ
= std::min(TrailZ
, BitWidth
);
209 LeadZ
= std::min(LeadZ
, BitWidth
);
210 KnownZero
= APInt::getLowBitsSet(BitWidth
, TrailZ
) |
211 APInt::getHighBitsSet(BitWidth
, LeadZ
);
215 case Instruction::UDiv
: {
216 // For the purposes of computing leading zeros we can conservatively
217 // treat a udiv as a logical right shift by the power of 2 known to
218 // be less than the denominator.
219 APInt AllOnes
= APInt::getAllOnesValue(BitWidth
);
220 ComputeMaskedBits(I
->getOperand(0),
221 AllOnes
, KnownZero2
, KnownOne2
, TD
, Depth
+1);
222 unsigned LeadZ
= KnownZero2
.countLeadingOnes();
224 KnownOne2
.clearAllBits();
225 KnownZero2
.clearAllBits();
226 ComputeMaskedBits(I
->getOperand(1),
227 AllOnes
, KnownZero2
, KnownOne2
, TD
, Depth
+1);
228 unsigned RHSUnknownLeadingOnes
= KnownOne2
.countLeadingZeros();
229 if (RHSUnknownLeadingOnes
!= BitWidth
)
230 LeadZ
= std::min(BitWidth
,
231 LeadZ
+ BitWidth
- RHSUnknownLeadingOnes
- 1);
233 KnownZero
= APInt::getHighBitsSet(BitWidth
, LeadZ
) & Mask
;
236 case Instruction::Select
:
237 ComputeMaskedBits(I
->getOperand(2), Mask
, KnownZero
, KnownOne
, TD
, Depth
+1);
238 ComputeMaskedBits(I
->getOperand(1), Mask
, KnownZero2
, KnownOne2
, TD
,
240 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
241 assert((KnownZero2
& KnownOne2
) == 0 && "Bits known to be one AND zero?");
243 // Only known if known in both the LHS and RHS.
244 KnownOne
&= KnownOne2
;
245 KnownZero
&= KnownZero2
;
247 case Instruction::FPTrunc
:
248 case Instruction::FPExt
:
249 case Instruction::FPToUI
:
250 case Instruction::FPToSI
:
251 case Instruction::SIToFP
:
252 case Instruction::UIToFP
:
253 return; // Can't work with floating point.
254 case Instruction::PtrToInt
:
255 case Instruction::IntToPtr
:
256 // We can't handle these if we don't know the pointer size.
258 // FALL THROUGH and handle them the same as zext/trunc.
259 case Instruction::ZExt
:
260 case Instruction::Trunc
: {
261 const Type
*SrcTy
= I
->getOperand(0)->getType();
263 unsigned SrcBitWidth
;
264 // Note that we handle pointer operands here because of inttoptr/ptrtoint
265 // which fall through here.
266 if (SrcTy
->isPointerTy())
267 SrcBitWidth
= TD
->getTypeSizeInBits(SrcTy
);
269 SrcBitWidth
= SrcTy
->getScalarSizeInBits();
271 APInt MaskIn
= Mask
.zextOrTrunc(SrcBitWidth
);
272 KnownZero
= KnownZero
.zextOrTrunc(SrcBitWidth
);
273 KnownOne
= KnownOne
.zextOrTrunc(SrcBitWidth
);
274 ComputeMaskedBits(I
->getOperand(0), MaskIn
, KnownZero
, KnownOne
, TD
,
276 KnownZero
= KnownZero
.zextOrTrunc(BitWidth
);
277 KnownOne
= KnownOne
.zextOrTrunc(BitWidth
);
278 // Any top bits are known to be zero.
279 if (BitWidth
> SrcBitWidth
)
280 KnownZero
|= APInt::getHighBitsSet(BitWidth
, BitWidth
- SrcBitWidth
);
283 case Instruction::BitCast
: {
284 const Type
*SrcTy
= I
->getOperand(0)->getType();
285 if ((SrcTy
->isIntegerTy() || SrcTy
->isPointerTy()) &&
286 // TODO: For now, not handling conversions like:
287 // (bitcast i64 %x to <2 x i32>)
288 !I
->getType()->isVectorTy()) {
289 ComputeMaskedBits(I
->getOperand(0), Mask
, KnownZero
, KnownOne
, TD
,
295 case Instruction::SExt
: {
296 // Compute the bits in the result that are not present in the input.
297 unsigned SrcBitWidth
= I
->getOperand(0)->getType()->getScalarSizeInBits();
299 APInt MaskIn
= Mask
.trunc(SrcBitWidth
);
300 KnownZero
= KnownZero
.trunc(SrcBitWidth
);
301 KnownOne
= KnownOne
.trunc(SrcBitWidth
);
302 ComputeMaskedBits(I
->getOperand(0), MaskIn
, KnownZero
, KnownOne
, TD
,
304 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
305 KnownZero
= KnownZero
.zext(BitWidth
);
306 KnownOne
= KnownOne
.zext(BitWidth
);
308 // If the sign bit of the input is known set or clear, then we know the
309 // top bits of the result.
310 if (KnownZero
[SrcBitWidth
-1]) // Input sign bit known zero
311 KnownZero
|= APInt::getHighBitsSet(BitWidth
, BitWidth
- SrcBitWidth
);
312 else if (KnownOne
[SrcBitWidth
-1]) // Input sign bit known set
313 KnownOne
|= APInt::getHighBitsSet(BitWidth
, BitWidth
- SrcBitWidth
);
316 case Instruction::Shl
:
317 // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
318 if (ConstantInt
*SA
= dyn_cast
<ConstantInt
>(I
->getOperand(1))) {
319 uint64_t ShiftAmt
= SA
->getLimitedValue(BitWidth
);
320 APInt
Mask2(Mask
.lshr(ShiftAmt
));
321 ComputeMaskedBits(I
->getOperand(0), Mask2
, KnownZero
, KnownOne
, TD
,
323 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
324 KnownZero
<<= ShiftAmt
;
325 KnownOne
<<= ShiftAmt
;
326 KnownZero
|= APInt::getLowBitsSet(BitWidth
, ShiftAmt
); // low bits known 0
330 case Instruction::LShr
:
331 // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
332 if (ConstantInt
*SA
= dyn_cast
<ConstantInt
>(I
->getOperand(1))) {
333 // Compute the new bits that are at the top now.
334 uint64_t ShiftAmt
= SA
->getLimitedValue(BitWidth
);
336 // Unsigned shift right.
337 APInt
Mask2(Mask
.shl(ShiftAmt
));
338 ComputeMaskedBits(I
->getOperand(0), Mask2
, KnownZero
,KnownOne
, TD
,
340 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
341 KnownZero
= APIntOps::lshr(KnownZero
, ShiftAmt
);
342 KnownOne
= APIntOps::lshr(KnownOne
, ShiftAmt
);
343 // high bits known zero.
344 KnownZero
|= APInt::getHighBitsSet(BitWidth
, ShiftAmt
);
348 case Instruction::AShr
:
349 // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
350 if (ConstantInt
*SA
= dyn_cast
<ConstantInt
>(I
->getOperand(1))) {
351 // Compute the new bits that are at the top now.
352 uint64_t ShiftAmt
= SA
->getLimitedValue(BitWidth
-1);
354 // Signed shift right.
355 APInt
Mask2(Mask
.shl(ShiftAmt
));
356 ComputeMaskedBits(I
->getOperand(0), Mask2
, KnownZero
, KnownOne
, TD
,
358 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
359 KnownZero
= APIntOps::lshr(KnownZero
, ShiftAmt
);
360 KnownOne
= APIntOps::lshr(KnownOne
, ShiftAmt
);
362 APInt
HighBits(APInt::getHighBitsSet(BitWidth
, ShiftAmt
));
363 if (KnownZero
[BitWidth
-ShiftAmt
-1]) // New bits are known zero.
364 KnownZero
|= HighBits
;
365 else if (KnownOne
[BitWidth
-ShiftAmt
-1]) // New bits are known one.
366 KnownOne
|= HighBits
;
370 case Instruction::Sub
: {
371 if (ConstantInt
*CLHS
= dyn_cast
<ConstantInt
>(I
->getOperand(0))) {
372 // We know that the top bits of C-X are clear if X contains less bits
373 // than C (i.e. no wrap-around can happen). For example, 20-X is
374 // positive if we can prove that X is >= 0 and < 16.
375 if (!CLHS
->getValue().isNegative()) {
376 unsigned NLZ
= (CLHS
->getValue()+1).countLeadingZeros();
377 // NLZ can't be BitWidth with no sign bit
378 APInt MaskV
= APInt::getHighBitsSet(BitWidth
, NLZ
+1);
379 ComputeMaskedBits(I
->getOperand(1), MaskV
, KnownZero2
, KnownOne2
,
382 // If all of the MaskV bits are known to be zero, then we know the
383 // output top bits are zero, because we now know that the output is
385 if ((KnownZero2
& MaskV
) == MaskV
) {
386 unsigned NLZ2
= CLHS
->getValue().countLeadingZeros();
387 // Top bits known zero.
388 KnownZero
= APInt::getHighBitsSet(BitWidth
, NLZ2
) & Mask
;
394 case Instruction::Add
: {
395 // If one of the operands has trailing zeros, then the bits that the
396 // other operand has in those bit positions will be preserved in the
397 // result. For an add, this works with either operand. For a subtract,
398 // this only works if the known zeros are in the right operand.
399 APInt
LHSKnownZero(BitWidth
, 0), LHSKnownOne(BitWidth
, 0);
400 APInt Mask2
= APInt::getLowBitsSet(BitWidth
,
401 BitWidth
- Mask
.countLeadingZeros());
402 ComputeMaskedBits(I
->getOperand(0), Mask2
, LHSKnownZero
, LHSKnownOne
, TD
,
404 assert((LHSKnownZero
& LHSKnownOne
) == 0 &&
405 "Bits known to be one AND zero?");
406 unsigned LHSKnownZeroOut
= LHSKnownZero
.countTrailingOnes();
408 ComputeMaskedBits(I
->getOperand(1), Mask2
, KnownZero2
, KnownOne2
, TD
,
410 assert((KnownZero2
& KnownOne2
) == 0 && "Bits known to be one AND zero?");
411 unsigned RHSKnownZeroOut
= KnownZero2
.countTrailingOnes();
413 // Determine which operand has more trailing zeros, and use that
414 // many bits from the other operand.
415 if (LHSKnownZeroOut
> RHSKnownZeroOut
) {
416 if (I
->getOpcode() == Instruction::Add
) {
417 APInt Mask
= APInt::getLowBitsSet(BitWidth
, LHSKnownZeroOut
);
418 KnownZero
|= KnownZero2
& Mask
;
419 KnownOne
|= KnownOne2
& Mask
;
421 // If the known zeros are in the left operand for a subtract,
422 // fall back to the minimum known zeros in both operands.
423 KnownZero
|= APInt::getLowBitsSet(BitWidth
,
424 std::min(LHSKnownZeroOut
,
427 } else if (RHSKnownZeroOut
>= LHSKnownZeroOut
) {
428 APInt Mask
= APInt::getLowBitsSet(BitWidth
, RHSKnownZeroOut
);
429 KnownZero
|= LHSKnownZero
& Mask
;
430 KnownOne
|= LHSKnownOne
& Mask
;
434 case Instruction::SRem
:
435 if (ConstantInt
*Rem
= dyn_cast
<ConstantInt
>(I
->getOperand(1))) {
436 APInt RA
= Rem
->getValue().abs();
437 if (RA
.isPowerOf2()) {
438 APInt LowBits
= RA
- 1;
439 APInt Mask2
= LowBits
| APInt::getSignBit(BitWidth
);
440 ComputeMaskedBits(I
->getOperand(0), Mask2
, KnownZero2
, KnownOne2
, TD
,
443 // The low bits of the first operand are unchanged by the srem.
444 KnownZero
= KnownZero2
& LowBits
;
445 KnownOne
= KnownOne2
& LowBits
;
447 // If the first operand is non-negative or has all low bits zero, then
448 // the upper bits are all zero.
449 if (KnownZero2
[BitWidth
-1] || ((KnownZero2
& LowBits
) == LowBits
))
450 KnownZero
|= ~LowBits
;
452 // If the first operand is negative and not all low bits are zero, then
453 // the upper bits are all one.
454 if (KnownOne2
[BitWidth
-1] && ((KnownOne2
& LowBits
) != 0))
455 KnownOne
|= ~LowBits
;
460 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
464 case Instruction::URem
: {
465 if (ConstantInt
*Rem
= dyn_cast
<ConstantInt
>(I
->getOperand(1))) {
466 APInt RA
= Rem
->getValue();
467 if (RA
.isPowerOf2()) {
468 APInt LowBits
= (RA
- 1);
469 APInt Mask2
= LowBits
& Mask
;
470 KnownZero
|= ~LowBits
& Mask
;
471 ComputeMaskedBits(I
->getOperand(0), Mask2
, KnownZero
, KnownOne
, TD
,
473 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
478 // Since the result is less than or equal to either operand, any leading
479 // zero bits in either operand must also exist in the result.
480 APInt AllOnes
= APInt::getAllOnesValue(BitWidth
);
481 ComputeMaskedBits(I
->getOperand(0), AllOnes
, KnownZero
, KnownOne
,
483 ComputeMaskedBits(I
->getOperand(1), AllOnes
, KnownZero2
, KnownOne2
,
486 unsigned Leaders
= std::max(KnownZero
.countLeadingOnes(),
487 KnownZero2
.countLeadingOnes());
488 KnownOne
.clearAllBits();
489 KnownZero
= APInt::getHighBitsSet(BitWidth
, Leaders
) & Mask
;
493 case Instruction::Alloca
: {
494 AllocaInst
*AI
= cast
<AllocaInst
>(V
);
495 unsigned Align
= AI
->getAlignment();
496 if (Align
== 0 && TD
)
497 Align
= TD
->getABITypeAlignment(AI
->getType()->getElementType());
500 KnownZero
= Mask
& APInt::getLowBitsSet(BitWidth
,
501 CountTrailingZeros_32(Align
));
504 case Instruction::GetElementPtr
: {
505 // Analyze all of the subscripts of this getelementptr instruction
506 // to determine if we can prove known low zero bits.
507 APInt LocalMask
= APInt::getAllOnesValue(BitWidth
);
508 APInt
LocalKnownZero(BitWidth
, 0), LocalKnownOne(BitWidth
, 0);
509 ComputeMaskedBits(I
->getOperand(0), LocalMask
,
510 LocalKnownZero
, LocalKnownOne
, TD
, Depth
+1);
511 unsigned TrailZ
= LocalKnownZero
.countTrailingOnes();
513 gep_type_iterator GTI
= gep_type_begin(I
);
514 for (unsigned i
= 1, e
= I
->getNumOperands(); i
!= e
; ++i
, ++GTI
) {
515 Value
*Index
= I
->getOperand(i
);
516 if (const StructType
*STy
= dyn_cast
<StructType
>(*GTI
)) {
517 // Handle struct member offset arithmetic.
519 const StructLayout
*SL
= TD
->getStructLayout(STy
);
520 unsigned Idx
= cast
<ConstantInt
>(Index
)->getZExtValue();
521 uint64_t Offset
= SL
->getElementOffset(Idx
);
522 TrailZ
= std::min(TrailZ
,
523 CountTrailingZeros_64(Offset
));
525 // Handle array index arithmetic.
526 const Type
*IndexedTy
= GTI
.getIndexedType();
527 if (!IndexedTy
->isSized()) return;
528 unsigned GEPOpiBits
= Index
->getType()->getScalarSizeInBits();
529 uint64_t TypeSize
= TD
? TD
->getTypeAllocSize(IndexedTy
) : 1;
530 LocalMask
= APInt::getAllOnesValue(GEPOpiBits
);
531 LocalKnownZero
= LocalKnownOne
= APInt(GEPOpiBits
, 0);
532 ComputeMaskedBits(Index
, LocalMask
,
533 LocalKnownZero
, LocalKnownOne
, TD
, Depth
+1);
534 TrailZ
= std::min(TrailZ
,
535 unsigned(CountTrailingZeros_64(TypeSize
) +
536 LocalKnownZero
.countTrailingOnes()));
540 KnownZero
= APInt::getLowBitsSet(BitWidth
, TrailZ
) & Mask
;
543 case Instruction::PHI
: {
544 PHINode
*P
= cast
<PHINode
>(I
);
545 // Handle the case of a simple two-predecessor recurrence PHI.
546 // There's a lot more that could theoretically be done here, but
547 // this is sufficient to catch some interesting cases.
548 if (P
->getNumIncomingValues() == 2) {
549 for (unsigned i
= 0; i
!= 2; ++i
) {
550 Value
*L
= P
->getIncomingValue(i
);
551 Value
*R
= P
->getIncomingValue(!i
);
552 Operator
*LU
= dyn_cast
<Operator
>(L
);
555 unsigned Opcode
= LU
->getOpcode();
556 // Check for operations that have the property that if
557 // both their operands have low zero bits, the result
558 // will have low zero bits.
559 if (Opcode
== Instruction::Add
||
560 Opcode
== Instruction::Sub
||
561 Opcode
== Instruction::And
||
562 Opcode
== Instruction::Or
||
563 Opcode
== Instruction::Mul
) {
564 Value
*LL
= LU
->getOperand(0);
565 Value
*LR
= LU
->getOperand(1);
566 // Find a recurrence.
573 // Ok, we have a PHI of the form L op= R. Check for low
575 APInt Mask2
= APInt::getAllOnesValue(BitWidth
);
576 ComputeMaskedBits(R
, Mask2
, KnownZero2
, KnownOne2
, TD
, Depth
+1);
577 Mask2
= APInt::getLowBitsSet(BitWidth
,
578 KnownZero2
.countTrailingOnes());
580 // We need to take the minimum number of known bits
581 APInt
KnownZero3(KnownZero
), KnownOne3(KnownOne
);
582 ComputeMaskedBits(L
, Mask2
, KnownZero3
, KnownOne3
, TD
, Depth
+1);
585 APInt::getLowBitsSet(BitWidth
,
586 std::min(KnownZero2
.countTrailingOnes(),
587 KnownZero3
.countTrailingOnes()));
593 // Otherwise take the unions of the known bit sets of the operands,
594 // taking conservative care to avoid excessive recursion.
595 if (Depth
< MaxDepth
- 1 && !KnownZero
&& !KnownOne
) {
596 KnownZero
= APInt::getAllOnesValue(BitWidth
);
597 KnownOne
= APInt::getAllOnesValue(BitWidth
);
598 for (unsigned i
= 0, e
= P
->getNumIncomingValues(); i
!= e
; ++i
) {
599 // Skip direct self references.
600 if (P
->getIncomingValue(i
) == P
) continue;
602 KnownZero2
= APInt(BitWidth
, 0);
603 KnownOne2
= APInt(BitWidth
, 0);
604 // Recurse, but cap the recursion to one level, because we don't
605 // want to waste time spinning around in loops.
606 ComputeMaskedBits(P
->getIncomingValue(i
), KnownZero
| KnownOne
,
607 KnownZero2
, KnownOne2
, TD
, MaxDepth
-1);
608 KnownZero
&= KnownZero2
;
609 KnownOne
&= KnownOne2
;
610 // If all bits have been ruled out, there's no need to check
612 if (!KnownZero
&& !KnownOne
)
618 case Instruction::Call
:
619 if (IntrinsicInst
*II
= dyn_cast
<IntrinsicInst
>(I
)) {
620 switch (II
->getIntrinsicID()) {
622 case Intrinsic::ctpop
:
623 case Intrinsic::ctlz
:
624 case Intrinsic::cttz
: {
625 unsigned LowBits
= Log2_32(BitWidth
)+1;
626 KnownZero
= APInt::getHighBitsSet(BitWidth
, BitWidth
- LowBits
);
635 /// ComputeSignBit - Determine whether the sign bit is known to be zero or
636 /// one. Convenience wrapper around ComputeMaskedBits.
637 void llvm::ComputeSignBit(Value
*V
, bool &KnownZero
, bool &KnownOne
,
638 const TargetData
*TD
, unsigned Depth
) {
639 unsigned BitWidth
= getBitWidth(V
->getType(), TD
);
645 APInt
ZeroBits(BitWidth
, 0);
646 APInt
OneBits(BitWidth
, 0);
647 ComputeMaskedBits(V
, APInt::getSignBit(BitWidth
), ZeroBits
, OneBits
, TD
,
649 KnownOne
= OneBits
[BitWidth
- 1];
650 KnownZero
= ZeroBits
[BitWidth
- 1];
653 /// isPowerOfTwo - Return true if the given value is known to have exactly one
654 /// bit set when defined. For vectors return true if every element is known to
655 /// be a power of two when defined. Supports values with integer or pointer
656 /// types and vectors of integers.
657 bool llvm::isPowerOfTwo(Value
*V
, const TargetData
*TD
, unsigned Depth
) {
658 if (ConstantInt
*CI
= dyn_cast
<ConstantInt
>(V
))
659 return CI
->getValue().isPowerOf2();
660 // TODO: Handle vector constants.
662 // 1 << X is clearly a power of two if the one is not shifted off the end. If
663 // it is shifted off the end then the result is undefined.
664 if (match(V
, m_Shl(m_One(), m_Value())))
667 // (signbit) >>l X is clearly a power of two if the one is not shifted off the
668 // bottom. If it is shifted off the bottom then the result is undefined.
670 if (match(V
, m_LShr(m_ConstantInt(CI
), m_Value())) &&
671 CI
->getValue().isSignBit())
674 // The remaining tests are all recursive, so bail out if we hit the limit.
675 if (Depth
++ == MaxDepth
)
678 if (ZExtInst
*ZI
= dyn_cast
<ZExtInst
>(V
))
679 return isPowerOfTwo(ZI
->getOperand(0), TD
, Depth
);
681 if (SelectInst
*SI
= dyn_cast
<SelectInst
>(V
))
682 return isPowerOfTwo(SI
->getTrueValue(), TD
, Depth
) &&
683 isPowerOfTwo(SI
->getFalseValue(), TD
, Depth
);
688 /// isKnownNonZero - Return true if the given value is known to be non-zero
689 /// when defined. For vectors return true if every element is known to be
690 /// non-zero when defined. Supports values with integer or pointer type and
691 /// vectors of integers.
692 bool llvm::isKnownNonZero(Value
*V
, const TargetData
*TD
, unsigned Depth
) {
693 if (Constant
*C
= dyn_cast
<Constant
>(V
)) {
694 if (C
->isNullValue())
696 if (isa
<ConstantInt
>(C
))
697 // Must be non-zero due to null test above.
699 // TODO: Handle vectors
703 // The remaining tests are all recursive, so bail out if we hit the limit.
704 if (Depth
++ == MaxDepth
)
707 unsigned BitWidth
= getBitWidth(V
->getType(), TD
);
709 // X | Y != 0 if X != 0 or Y != 0.
710 Value
*X
= 0, *Y
= 0;
711 if (match(V
, m_Or(m_Value(X
), m_Value(Y
))))
712 return isKnownNonZero(X
, TD
, Depth
) || isKnownNonZero(Y
, TD
, Depth
);
714 // ext X != 0 if X != 0.
715 if (isa
<SExtInst
>(V
) || isa
<ZExtInst
>(V
))
716 return isKnownNonZero(cast
<Instruction
>(V
)->getOperand(0), TD
, Depth
);
718 // shl X, Y != 0 if X is odd. Note that the value of the shift is undefined
719 // if the lowest bit is shifted off the end.
720 if (BitWidth
&& match(V
, m_Shl(m_Value(X
), m_Value(Y
)))) {
721 APInt
KnownZero(BitWidth
, 0);
722 APInt
KnownOne(BitWidth
, 0);
723 ComputeMaskedBits(X
, APInt(BitWidth
, 1), KnownZero
, KnownOne
, TD
, Depth
);
727 // shr X, Y != 0 if X is negative. Note that the value of the shift is not
728 // defined if the sign bit is shifted off the end.
729 else if (match(V
, m_Shr(m_Value(X
), m_Value(Y
)))) {
730 bool XKnownNonNegative
, XKnownNegative
;
731 ComputeSignBit(X
, XKnownNonNegative
, XKnownNegative
, TD
, Depth
);
736 else if (match(V
, m_Add(m_Value(X
), m_Value(Y
)))) {
737 bool XKnownNonNegative
, XKnownNegative
;
738 bool YKnownNonNegative
, YKnownNegative
;
739 ComputeSignBit(X
, XKnownNonNegative
, XKnownNegative
, TD
, Depth
);
740 ComputeSignBit(Y
, YKnownNonNegative
, YKnownNegative
, TD
, Depth
);
742 // If X and Y are both non-negative (as signed values) then their sum is not
743 // zero unless both X and Y are zero.
744 if (XKnownNonNegative
&& YKnownNonNegative
)
745 if (isKnownNonZero(X
, TD
, Depth
) || isKnownNonZero(Y
, TD
, Depth
))
748 // If X and Y are both negative (as signed values) then their sum is not
749 // zero unless both X and Y equal INT_MIN.
750 if (BitWidth
&& XKnownNegative
&& YKnownNegative
) {
751 APInt
KnownZero(BitWidth
, 0);
752 APInt
KnownOne(BitWidth
, 0);
753 APInt Mask
= APInt::getSignedMaxValue(BitWidth
);
754 // The sign bit of X is set. If some other bit is set then X is not equal
756 ComputeMaskedBits(X
, Mask
, KnownZero
, KnownOne
, TD
, Depth
);
757 if ((KnownOne
& Mask
) != 0)
759 // The sign bit of Y is set. If some other bit is set then Y is not equal
761 ComputeMaskedBits(Y
, Mask
, KnownZero
, KnownOne
, TD
, Depth
);
762 if ((KnownOne
& Mask
) != 0)
766 // The sum of a non-negative number and a power of two is not zero.
767 if (XKnownNonNegative
&& isPowerOfTwo(Y
, TD
, Depth
))
769 if (YKnownNonNegative
&& isPowerOfTwo(X
, TD
, Depth
))
772 // (C ? X : Y) != 0 if X != 0 and Y != 0.
773 else if (SelectInst
*SI
= dyn_cast
<SelectInst
>(V
)) {
774 if (isKnownNonZero(SI
->getTrueValue(), TD
, Depth
) &&
775 isKnownNonZero(SI
->getFalseValue(), TD
, Depth
))
779 if (!BitWidth
) return false;
780 APInt
KnownZero(BitWidth
, 0);
781 APInt
KnownOne(BitWidth
, 0);
782 ComputeMaskedBits(V
, APInt::getAllOnesValue(BitWidth
), KnownZero
, KnownOne
,
784 return KnownOne
!= 0;
787 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
788 /// this predicate to simplify operations downstream. Mask is known to be zero
789 /// for bits that V cannot have.
791 /// This function is defined on values with integer type, values with pointer
792 /// type (but only if TD is non-null), and vectors of integers. In the case
793 /// where V is a vector, the mask, known zero, and known one values are the
794 /// same width as the vector element, and the bit is set only if it is true
795 /// for all of the elements in the vector.
796 bool llvm::MaskedValueIsZero(Value
*V
, const APInt
&Mask
,
797 const TargetData
*TD
, unsigned Depth
) {
798 APInt
KnownZero(Mask
.getBitWidth(), 0), KnownOne(Mask
.getBitWidth(), 0);
799 ComputeMaskedBits(V
, Mask
, KnownZero
, KnownOne
, TD
, Depth
);
800 assert((KnownZero
& KnownOne
) == 0 && "Bits known to be one AND zero?");
801 return (KnownZero
& Mask
) == Mask
;
806 /// ComputeNumSignBits - Return the number of times the sign bit of the
807 /// register is replicated into the other bits. We know that at least 1 bit
808 /// is always equal to the sign bit (itself), but other cases can give us
809 /// information. For example, immediately after an "ashr X, 2", we know that
810 /// the top 3 bits are all equal to each other, so we return 3.
812 /// 'Op' must have a scalar integer type.
814 unsigned llvm::ComputeNumSignBits(Value
*V
, const TargetData
*TD
,
816 assert((TD
|| V
->getType()->isIntOrIntVectorTy()) &&
817 "ComputeNumSignBits requires a TargetData object to operate "
818 "on non-integer values!");
819 const Type
*Ty
= V
->getType();
820 unsigned TyBits
= TD
? TD
->getTypeSizeInBits(V
->getType()->getScalarType()) :
821 Ty
->getScalarSizeInBits();
823 unsigned FirstAnswer
= 1;
825 // Note that ConstantInt is handled by the general ComputeMaskedBits case
829 return 1; // Limit search depth.
831 Operator
*U
= dyn_cast
<Operator
>(V
);
832 switch (Operator::getOpcode(V
)) {
834 case Instruction::SExt
:
835 Tmp
= TyBits
- U
->getOperand(0)->getType()->getScalarSizeInBits();
836 return ComputeNumSignBits(U
->getOperand(0), TD
, Depth
+1) + Tmp
;
838 case Instruction::AShr
:
839 Tmp
= ComputeNumSignBits(U
->getOperand(0), TD
, Depth
+1);
840 // ashr X, C -> adds C sign bits.
841 if (ConstantInt
*C
= dyn_cast
<ConstantInt
>(U
->getOperand(1))) {
842 Tmp
+= C
->getZExtValue();
843 if (Tmp
> TyBits
) Tmp
= TyBits
;
845 // vector ashr X, <C, C, C, C> -> adds C sign bits
846 if (ConstantVector
*C
= dyn_cast
<ConstantVector
>(U
->getOperand(1))) {
847 if (ConstantInt
*CI
= dyn_cast_or_null
<ConstantInt
>(C
->getSplatValue())) {
848 Tmp
+= CI
->getZExtValue();
849 if (Tmp
> TyBits
) Tmp
= TyBits
;
853 case Instruction::Shl
:
854 if (ConstantInt
*C
= dyn_cast
<ConstantInt
>(U
->getOperand(1))) {
855 // shl destroys sign bits.
856 Tmp
= ComputeNumSignBits(U
->getOperand(0), TD
, Depth
+1);
857 if (C
->getZExtValue() >= TyBits
|| // Bad shift.
858 C
->getZExtValue() >= Tmp
) break; // Shifted all sign bits out.
859 return Tmp
- C
->getZExtValue();
862 case Instruction::And
:
863 case Instruction::Or
:
864 case Instruction::Xor
: // NOT is handled here.
865 // Logical binary ops preserve the number of sign bits at the worst.
866 Tmp
= ComputeNumSignBits(U
->getOperand(0), TD
, Depth
+1);
868 Tmp2
= ComputeNumSignBits(U
->getOperand(1), TD
, Depth
+1);
869 FirstAnswer
= std::min(Tmp
, Tmp2
);
870 // We computed what we know about the sign bits as our first
871 // answer. Now proceed to the generic code that uses
872 // ComputeMaskedBits, and pick whichever answer is better.
876 case Instruction::Select
:
877 Tmp
= ComputeNumSignBits(U
->getOperand(1), TD
, Depth
+1);
878 if (Tmp
== 1) return 1; // Early out.
879 Tmp2
= ComputeNumSignBits(U
->getOperand(2), TD
, Depth
+1);
880 return std::min(Tmp
, Tmp2
);
882 case Instruction::Add
:
883 // Add can have at most one carry bit. Thus we know that the output
884 // is, at worst, one more bit than the inputs.
885 Tmp
= ComputeNumSignBits(U
->getOperand(0), TD
, Depth
+1);
886 if (Tmp
== 1) return 1; // Early out.
888 // Special case decrementing a value (ADD X, -1):
889 if (ConstantInt
*CRHS
= dyn_cast
<ConstantInt
>(U
->getOperand(1)))
890 if (CRHS
->isAllOnesValue()) {
891 APInt
KnownZero(TyBits
, 0), KnownOne(TyBits
, 0);
892 APInt Mask
= APInt::getAllOnesValue(TyBits
);
893 ComputeMaskedBits(U
->getOperand(0), Mask
, KnownZero
, KnownOne
, TD
,
896 // If the input is known to be 0 or 1, the output is 0/-1, which is all
898 if ((KnownZero
| APInt(TyBits
, 1)) == Mask
)
901 // If we are subtracting one from a positive number, there is no carry
902 // out of the result.
903 if (KnownZero
.isNegative())
907 Tmp2
= ComputeNumSignBits(U
->getOperand(1), TD
, Depth
+1);
908 if (Tmp2
== 1) return 1;
909 return std::min(Tmp
, Tmp2
)-1;
911 case Instruction::Sub
:
912 Tmp2
= ComputeNumSignBits(U
->getOperand(1), TD
, Depth
+1);
913 if (Tmp2
== 1) return 1;
916 if (ConstantInt
*CLHS
= dyn_cast
<ConstantInt
>(U
->getOperand(0)))
917 if (CLHS
->isNullValue()) {
918 APInt
KnownZero(TyBits
, 0), KnownOne(TyBits
, 0);
919 APInt Mask
= APInt::getAllOnesValue(TyBits
);
920 ComputeMaskedBits(U
->getOperand(1), Mask
, KnownZero
, KnownOne
,
922 // If the input is known to be 0 or 1, the output is 0/-1, which is all
924 if ((KnownZero
| APInt(TyBits
, 1)) == Mask
)
927 // If the input is known to be positive (the sign bit is known clear),
928 // the output of the NEG has the same number of sign bits as the input.
929 if (KnownZero
.isNegative())
932 // Otherwise, we treat this like a SUB.
935 // Sub can have at most one carry bit. Thus we know that the output
936 // is, at worst, one more bit than the inputs.
937 Tmp
= ComputeNumSignBits(U
->getOperand(0), TD
, Depth
+1);
938 if (Tmp
== 1) return 1; // Early out.
939 return std::min(Tmp
, Tmp2
)-1;
941 case Instruction::PHI
: {
942 PHINode
*PN
= cast
<PHINode
>(U
);
943 // Don't analyze large in-degree PHIs.
944 if (PN
->getNumIncomingValues() > 4) break;
946 // Take the minimum of all incoming values. This can't infinitely loop
947 // because of our depth threshold.
948 Tmp
= ComputeNumSignBits(PN
->getIncomingValue(0), TD
, Depth
+1);
949 for (unsigned i
= 1, e
= PN
->getNumIncomingValues(); i
!= e
; ++i
) {
950 if (Tmp
== 1) return Tmp
;
952 ComputeNumSignBits(PN
->getIncomingValue(i
), TD
, Depth
+1));
957 case Instruction::Trunc
:
958 // FIXME: it's tricky to do anything useful for this, but it is an important
959 // case for targets like X86.
963 // Finally, if we can prove that the top bits of the result are 0's or 1's,
964 // use this information.
965 APInt
KnownZero(TyBits
, 0), KnownOne(TyBits
, 0);
966 APInt Mask
= APInt::getAllOnesValue(TyBits
);
967 ComputeMaskedBits(V
, Mask
, KnownZero
, KnownOne
, TD
, Depth
);
969 if (KnownZero
.isNegative()) { // sign bit is 0
971 } else if (KnownOne
.isNegative()) { // sign bit is 1;
978 // Okay, we know that the sign bit in Mask is set. Use CLZ to determine
979 // the number of identical bits in the top of the input value.
981 Mask
<<= Mask
.getBitWidth()-TyBits
;
982 // Return # leading zeros. We use 'min' here in case Val was zero before
983 // shifting. We don't want to return '64' as for an i32 "0".
984 return std::max(FirstAnswer
, std::min(TyBits
, Mask
.countLeadingZeros()));
987 /// ComputeMultiple - This function computes the integer multiple of Base that
988 /// equals V. If successful, it returns true and returns the multiple in
989 /// Multiple. If unsuccessful, it returns false. It looks
990 /// through SExt instructions only if LookThroughSExt is true.
991 bool llvm::ComputeMultiple(Value
*V
, unsigned Base
, Value
*&Multiple
,
992 bool LookThroughSExt
, unsigned Depth
) {
993 const unsigned MaxDepth
= 6;
995 assert(V
&& "No Value?");
996 assert(Depth
<= MaxDepth
&& "Limit Search Depth");
997 assert(V
->getType()->isIntegerTy() && "Not integer or pointer type!");
999 const Type
*T
= V
->getType();
1001 ConstantInt
*CI
= dyn_cast
<ConstantInt
>(V
);
1011 ConstantExpr
*CO
= dyn_cast
<ConstantExpr
>(V
);
1012 Constant
*BaseVal
= ConstantInt::get(T
, Base
);
1013 if (CO
&& CO
== BaseVal
) {
1015 Multiple
= ConstantInt::get(T
, 1);
1019 if (CI
&& CI
->getZExtValue() % Base
== 0) {
1020 Multiple
= ConstantInt::get(T
, CI
->getZExtValue() / Base
);
1024 if (Depth
== MaxDepth
) return false; // Limit search depth.
1026 Operator
*I
= dyn_cast
<Operator
>(V
);
1027 if (!I
) return false;
1029 switch (I
->getOpcode()) {
1031 case Instruction::SExt
:
1032 if (!LookThroughSExt
) return false;
1033 // otherwise fall through to ZExt
1034 case Instruction::ZExt
:
1035 return ComputeMultiple(I
->getOperand(0), Base
, Multiple
,
1036 LookThroughSExt
, Depth
+1);
1037 case Instruction::Shl
:
1038 case Instruction::Mul
: {
1039 Value
*Op0
= I
->getOperand(0);
1040 Value
*Op1
= I
->getOperand(1);
1042 if (I
->getOpcode() == Instruction::Shl
) {
1043 ConstantInt
*Op1CI
= dyn_cast
<ConstantInt
>(Op1
);
1044 if (!Op1CI
) return false;
1045 // Turn Op0 << Op1 into Op0 * 2^Op1
1046 APInt Op1Int
= Op1CI
->getValue();
1047 uint64_t BitToSet
= Op1Int
.getLimitedValue(Op1Int
.getBitWidth() - 1);
1048 APInt
API(Op1Int
.getBitWidth(), 0);
1049 API
.setBit(BitToSet
);
1050 Op1
= ConstantInt::get(V
->getContext(), API
);
1054 if (ComputeMultiple(Op0
, Base
, Mul0
, LookThroughSExt
, Depth
+1)) {
1055 if (Constant
*Op1C
= dyn_cast
<Constant
>(Op1
))
1056 if (Constant
*MulC
= dyn_cast
<Constant
>(Mul0
)) {
1057 if (Op1C
->getType()->getPrimitiveSizeInBits() <
1058 MulC
->getType()->getPrimitiveSizeInBits())
1059 Op1C
= ConstantExpr::getZExt(Op1C
, MulC
->getType());
1060 if (Op1C
->getType()->getPrimitiveSizeInBits() >
1061 MulC
->getType()->getPrimitiveSizeInBits())
1062 MulC
= ConstantExpr::getZExt(MulC
, Op1C
->getType());
1064 // V == Base * (Mul0 * Op1), so return (Mul0 * Op1)
1065 Multiple
= ConstantExpr::getMul(MulC
, Op1C
);
1069 if (ConstantInt
*Mul0CI
= dyn_cast
<ConstantInt
>(Mul0
))
1070 if (Mul0CI
->getValue() == 1) {
1071 // V == Base * Op1, so return Op1
1078 if (ComputeMultiple(Op1
, Base
, Mul1
, LookThroughSExt
, Depth
+1)) {
1079 if (Constant
*Op0C
= dyn_cast
<Constant
>(Op0
))
1080 if (Constant
*MulC
= dyn_cast
<Constant
>(Mul1
)) {
1081 if (Op0C
->getType()->getPrimitiveSizeInBits() <
1082 MulC
->getType()->getPrimitiveSizeInBits())
1083 Op0C
= ConstantExpr::getZExt(Op0C
, MulC
->getType());
1084 if (Op0C
->getType()->getPrimitiveSizeInBits() >
1085 MulC
->getType()->getPrimitiveSizeInBits())
1086 MulC
= ConstantExpr::getZExt(MulC
, Op0C
->getType());
1088 // V == Base * (Mul1 * Op0), so return (Mul1 * Op0)
1089 Multiple
= ConstantExpr::getMul(MulC
, Op0C
);
1093 if (ConstantInt
*Mul1CI
= dyn_cast
<ConstantInt
>(Mul1
))
1094 if (Mul1CI
->getValue() == 1) {
1095 // V == Base * Op0, so return Op0
1103 // We could not determine if V is a multiple of Base.
1107 /// CannotBeNegativeZero - Return true if we can prove that the specified FP
1108 /// value is never equal to -0.0.
1110 /// NOTE: this function will need to be revisited when we support non-default
1113 bool llvm::CannotBeNegativeZero(const Value
*V
, unsigned Depth
) {
1114 if (const ConstantFP
*CFP
= dyn_cast
<ConstantFP
>(V
))
1115 return !CFP
->getValueAPF().isNegZero();
1118 return 1; // Limit search depth.
1120 const Operator
*I
= dyn_cast
<Operator
>(V
);
1121 if (I
== 0) return false;
1123 // (add x, 0.0) is guaranteed to return +0.0, not -0.0.
1124 if (I
->getOpcode() == Instruction::FAdd
&&
1125 isa
<ConstantFP
>(I
->getOperand(1)) &&
1126 cast
<ConstantFP
>(I
->getOperand(1))->isNullValue())
1129 // sitofp and uitofp turn into +0.0 for zero.
1130 if (isa
<SIToFPInst
>(I
) || isa
<UIToFPInst
>(I
))
1133 if (const IntrinsicInst
*II
= dyn_cast
<IntrinsicInst
>(I
))
1134 // sqrt(-0.0) = -0.0, no other negative results are possible.
1135 if (II
->getIntrinsicID() == Intrinsic::sqrt
)
1136 return CannotBeNegativeZero(II
->getArgOperand(0), Depth
+1);
1138 if (const CallInst
*CI
= dyn_cast
<CallInst
>(I
))
1139 if (const Function
*F
= CI
->getCalledFunction()) {
1140 if (F
->isDeclaration()) {
1142 if (F
->getName() == "abs") return true;
1143 // fabs[lf](x) != -0.0
1144 if (F
->getName() == "fabs") return true;
1145 if (F
->getName() == "fabsf") return true;
1146 if (F
->getName() == "fabsl") return true;
1147 if (F
->getName() == "sqrt" || F
->getName() == "sqrtf" ||
1148 F
->getName() == "sqrtl")
1149 return CannotBeNegativeZero(CI
->getArgOperand(0), Depth
+1);
1156 /// isBytewiseValue - If the specified value can be set by repeating the same
1157 /// byte in memory, return the i8 value that it is represented with. This is
1158 /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
1159 /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
1160 /// byte store (e.g. i16 0x1234), return null.
1161 Value
*llvm::isBytewiseValue(Value
*V
) {
1162 // All byte-wide stores are splatable, even of arbitrary variables.
1163 if (V
->getType()->isIntegerTy(8)) return V
;
1165 // Constant float and double values can be handled as integer values if the
1166 // corresponding integer value is "byteable". An important case is 0.0.
1167 if (ConstantFP
*CFP
= dyn_cast
<ConstantFP
>(V
)) {
1168 if (CFP
->getType()->isFloatTy())
1169 V
= ConstantExpr::getBitCast(CFP
, Type::getInt32Ty(V
->getContext()));
1170 if (CFP
->getType()->isDoubleTy())
1171 V
= ConstantExpr::getBitCast(CFP
, Type::getInt64Ty(V
->getContext()));
1172 // Don't handle long double formats, which have strange constraints.
1175 // We can handle constant integers that are power of two in size and a
1176 // multiple of 8 bits.
1177 if (ConstantInt
*CI
= dyn_cast
<ConstantInt
>(V
)) {
1178 unsigned Width
= CI
->getBitWidth();
1179 if (isPowerOf2_32(Width
) && Width
> 8) {
1180 // We can handle this value if the recursive binary decomposition is the
1181 // same at all levels.
1182 APInt Val
= CI
->getValue();
1184 while (Val
.getBitWidth() != 8) {
1185 unsigned NextWidth
= Val
.getBitWidth()/2;
1186 Val2
= Val
.lshr(NextWidth
);
1187 Val2
= Val2
.trunc(Val
.getBitWidth()/2);
1188 Val
= Val
.trunc(Val
.getBitWidth()/2);
1190 // If the top/bottom halves aren't the same, reject it.
1194 return ConstantInt::get(V
->getContext(), Val
);
1198 // A ConstantArray is splatable if all its members are equal and also
1200 if (ConstantArray
*CA
= dyn_cast
<ConstantArray
>(V
)) {
1201 if (CA
->getNumOperands() == 0)
1204 Value
*Val
= isBytewiseValue(CA
->getOperand(0));
1208 for (unsigned I
= 1, E
= CA
->getNumOperands(); I
!= E
; ++I
)
1209 if (CA
->getOperand(I
-1) != CA
->getOperand(I
))
1215 // Conceptually, we could handle things like:
1216 // %a = zext i8 %X to i16
1217 // %b = shl i16 %a, 8
1218 // %c = or i16 %a, %b
1219 // but until there is an example that actually needs this, it doesn't seem
1220 // worth worrying about.
1225 // This is the recursive version of BuildSubAggregate. It takes a few different
1226 // arguments. Idxs is the index within the nested struct From that we are
1227 // looking at now (which is of type IndexedType). IdxSkip is the number of
1228 // indices from Idxs that should be left out when inserting into the resulting
1229 // struct. To is the result struct built so far, new insertvalue instructions
1231 static Value
*BuildSubAggregate(Value
*From
, Value
* To
, const Type
*IndexedType
,
1232 SmallVector
<unsigned, 10> &Idxs
,
1234 Instruction
*InsertBefore
) {
1235 const llvm::StructType
*STy
= llvm::dyn_cast
<llvm::StructType
>(IndexedType
);
1237 // Save the original To argument so we can modify it
1239 // General case, the type indexed by Idxs is a struct
1240 for (unsigned i
= 0, e
= STy
->getNumElements(); i
!= e
; ++i
) {
1241 // Process each struct element recursively
1244 To
= BuildSubAggregate(From
, To
, STy
->getElementType(i
), Idxs
, IdxSkip
,
1248 // Couldn't find any inserted value for this index? Cleanup
1249 while (PrevTo
!= OrigTo
) {
1250 InsertValueInst
* Del
= cast
<InsertValueInst
>(PrevTo
);
1251 PrevTo
= Del
->getAggregateOperand();
1252 Del
->eraseFromParent();
1254 // Stop processing elements
1258 // If we succesfully found a value for each of our subaggregates
1262 // Base case, the type indexed by SourceIdxs is not a struct, or not all of
1263 // the struct's elements had a value that was inserted directly. In the latter
1264 // case, perhaps we can't determine each of the subelements individually, but
1265 // we might be able to find the complete struct somewhere.
1267 // Find the value that is at that particular spot
1268 Value
*V
= FindInsertedValue(From
, Idxs
.begin(), Idxs
.end());
1273 // Insert the value in the new (sub) aggregrate
1274 return llvm::InsertValueInst::Create(To
, V
, Idxs
.begin() + IdxSkip
,
1275 Idxs
.end(), "tmp", InsertBefore
);
1278 // This helper takes a nested struct and extracts a part of it (which is again a
1279 // struct) into a new value. For example, given the struct:
1280 // { a, { b, { c, d }, e } }
1281 // and the indices "1, 1" this returns
1284 // It does this by inserting an insertvalue for each element in the resulting
1285 // struct, as opposed to just inserting a single struct. This will only work if
1286 // each of the elements of the substruct are known (ie, inserted into From by an
1287 // insertvalue instruction somewhere).
1289 // All inserted insertvalue instructions are inserted before InsertBefore
1290 static Value
*BuildSubAggregate(Value
*From
, const unsigned *idx_begin
,
1291 const unsigned *idx_end
,
1292 Instruction
*InsertBefore
) {
1293 assert(InsertBefore
&& "Must have someplace to insert!");
1294 const Type
*IndexedType
= ExtractValueInst::getIndexedType(From
->getType(),
1297 Value
*To
= UndefValue::get(IndexedType
);
1298 SmallVector
<unsigned, 10> Idxs(idx_begin
, idx_end
);
1299 unsigned IdxSkip
= Idxs
.size();
1301 return BuildSubAggregate(From
, To
, IndexedType
, Idxs
, IdxSkip
, InsertBefore
);
1304 /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
1305 /// the scalar value indexed is already around as a register, for example if it
1306 /// were inserted directly into the aggregrate.
1308 /// If InsertBefore is not null, this function will duplicate (modified)
1309 /// insertvalues when a part of a nested struct is extracted.
1310 Value
*llvm::FindInsertedValue(Value
*V
, const unsigned *idx_begin
,
1311 const unsigned *idx_end
, Instruction
*InsertBefore
) {
1312 // Nothing to index? Just return V then (this is useful at the end of our
1314 if (idx_begin
== idx_end
)
1316 // We have indices, so V should have an indexable type
1317 assert((V
->getType()->isStructTy() || V
->getType()->isArrayTy())
1318 && "Not looking at a struct or array?");
1319 assert(ExtractValueInst::getIndexedType(V
->getType(), idx_begin
, idx_end
)
1320 && "Invalid indices for type?");
1321 const CompositeType
*PTy
= cast
<CompositeType
>(V
->getType());
1323 if (isa
<UndefValue
>(V
))
1324 return UndefValue::get(ExtractValueInst::getIndexedType(PTy
,
1327 else if (isa
<ConstantAggregateZero
>(V
))
1328 return Constant::getNullValue(ExtractValueInst::getIndexedType(PTy
,
1331 else if (Constant
*C
= dyn_cast
<Constant
>(V
)) {
1332 if (isa
<ConstantArray
>(C
) || isa
<ConstantStruct
>(C
))
1333 // Recursively process this constant
1334 return FindInsertedValue(C
->getOperand(*idx_begin
), idx_begin
+ 1,
1335 idx_end
, InsertBefore
);
1336 } else if (InsertValueInst
*I
= dyn_cast
<InsertValueInst
>(V
)) {
1337 // Loop the indices for the insertvalue instruction in parallel with the
1338 // requested indices
1339 const unsigned *req_idx
= idx_begin
;
1340 for (const unsigned *i
= I
->idx_begin(), *e
= I
->idx_end();
1341 i
!= e
; ++i
, ++req_idx
) {
1342 if (req_idx
== idx_end
) {
1344 // The requested index identifies a part of a nested aggregate. Handle
1345 // this specially. For example,
1346 // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
1347 // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
1348 // %C = extractvalue {i32, { i32, i32 } } %B, 1
1349 // This can be changed into
1350 // %A = insertvalue {i32, i32 } undef, i32 10, 0
1351 // %C = insertvalue {i32, i32 } %A, i32 11, 1
1352 // which allows the unused 0,0 element from the nested struct to be
1354 return BuildSubAggregate(V
, idx_begin
, req_idx
, InsertBefore
);
1356 // We can't handle this without inserting insertvalues
1360 // This insert value inserts something else than what we are looking for.
1361 // See if the (aggregrate) value inserted into has the value we are
1362 // looking for, then.
1364 return FindInsertedValue(I
->getAggregateOperand(), idx_begin
, idx_end
,
1367 // If we end up here, the indices of the insertvalue match with those
1368 // requested (though possibly only partially). Now we recursively look at
1369 // the inserted value, passing any remaining indices.
1370 return FindInsertedValue(I
->getInsertedValueOperand(), req_idx
, idx_end
,
1372 } else if (ExtractValueInst
*I
= dyn_cast
<ExtractValueInst
>(V
)) {
1373 // If we're extracting a value from an aggregrate that was extracted from
1374 // something else, we can extract from that something else directly instead.
1375 // However, we will need to chain I's indices with the requested indices.
1377 // Calculate the number of indices required
1378 unsigned size
= I
->getNumIndices() + (idx_end
- idx_begin
);
1379 // Allocate some space to put the new indices in
1380 SmallVector
<unsigned, 5> Idxs
;
1382 // Add indices from the extract value instruction
1383 for (const unsigned *i
= I
->idx_begin(), *e
= I
->idx_end();
1387 // Add requested indices
1388 for (const unsigned *i
= idx_begin
, *e
= idx_end
; i
!= e
; ++i
)
1391 assert(Idxs
.size() == size
1392 && "Number of indices added not correct?");
1394 return FindInsertedValue(I
->getAggregateOperand(), Idxs
.begin(), Idxs
.end(),
1397 // Otherwise, we don't know (such as, extracting from a function return value
1398 // or load instruction)
1402 /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
1403 /// it can be expressed as a base pointer plus a constant offset. Return the
1404 /// base and offset to the caller.
1405 Value
*llvm::GetPointerBaseWithConstantOffset(Value
*Ptr
, int64_t &Offset
,
1406 const TargetData
&TD
) {
1407 Operator
*PtrOp
= dyn_cast
<Operator
>(Ptr
);
1408 if (PtrOp
== 0) return Ptr
;
1410 // Just look through bitcasts.
1411 if (PtrOp
->getOpcode() == Instruction::BitCast
)
1412 return GetPointerBaseWithConstantOffset(PtrOp
->getOperand(0), Offset
, TD
);
1414 // If this is a GEP with constant indices, we can look through it.
1415 GEPOperator
*GEP
= dyn_cast
<GEPOperator
>(PtrOp
);
1416 if (GEP
== 0 || !GEP
->hasAllConstantIndices()) return Ptr
;
1418 gep_type_iterator GTI
= gep_type_begin(GEP
);
1419 for (User::op_iterator I
= GEP
->idx_begin(), E
= GEP
->idx_end(); I
!= E
;
1421 ConstantInt
*OpC
= cast
<ConstantInt
>(*I
);
1422 if (OpC
->isZero()) continue;
1424 // Handle a struct and array indices which add their offset to the pointer.
1425 if (const StructType
*STy
= dyn_cast
<StructType
>(*GTI
)) {
1426 Offset
+= TD
.getStructLayout(STy
)->getElementOffset(OpC
->getZExtValue());
1428 uint64_t Size
= TD
.getTypeAllocSize(GTI
.getIndexedType());
1429 Offset
+= OpC
->getSExtValue()*Size
;
1433 // Re-sign extend from the pointer size if needed to get overflow edge cases
1435 unsigned PtrSize
= TD
.getPointerSizeInBits();
1437 Offset
= (Offset
<< (64-PtrSize
)) >> (64-PtrSize
);
1439 return GetPointerBaseWithConstantOffset(GEP
->getPointerOperand(), Offset
, TD
);
1443 /// GetConstantStringInfo - This function computes the length of a
1444 /// null-terminated C string pointed to by V. If successful, it returns true
1445 /// and returns the string in Str. If unsuccessful, it returns false.
1446 bool llvm::GetConstantStringInfo(const Value
*V
, std::string
&Str
,
1449 // If V is NULL then return false;
1450 if (V
== NULL
) return false;
1452 // Look through bitcast instructions.
1453 if (const BitCastInst
*BCI
= dyn_cast
<BitCastInst
>(V
))
1454 return GetConstantStringInfo(BCI
->getOperand(0), Str
, Offset
, StopAtNul
);
1456 // If the value is not a GEP instruction nor a constant expression with a
1457 // GEP instruction, then return false because ConstantArray can't occur
1459 const User
*GEP
= 0;
1460 if (const GetElementPtrInst
*GEPI
= dyn_cast
<GetElementPtrInst
>(V
)) {
1462 } else if (const ConstantExpr
*CE
= dyn_cast
<ConstantExpr
>(V
)) {
1463 if (CE
->getOpcode() == Instruction::BitCast
)
1464 return GetConstantStringInfo(CE
->getOperand(0), Str
, Offset
, StopAtNul
);
1465 if (CE
->getOpcode() != Instruction::GetElementPtr
)
1471 // Make sure the GEP has exactly three arguments.
1472 if (GEP
->getNumOperands() != 3)
1475 // Make sure the index-ee is a pointer to array of i8.
1476 const PointerType
*PT
= cast
<PointerType
>(GEP
->getOperand(0)->getType());
1477 const ArrayType
*AT
= dyn_cast
<ArrayType
>(PT
->getElementType());
1478 if (AT
== 0 || !AT
->getElementType()->isIntegerTy(8))
1481 // Check to make sure that the first operand of the GEP is an integer and
1482 // has value 0 so that we are sure we're indexing into the initializer.
1483 const ConstantInt
*FirstIdx
= dyn_cast
<ConstantInt
>(GEP
->getOperand(1));
1484 if (FirstIdx
== 0 || !FirstIdx
->isZero())
1487 // If the second index isn't a ConstantInt, then this is a variable index
1488 // into the array. If this occurs, we can't say anything meaningful about
1490 uint64_t StartIdx
= 0;
1491 if (const ConstantInt
*CI
= dyn_cast
<ConstantInt
>(GEP
->getOperand(2)))
1492 StartIdx
= CI
->getZExtValue();
1495 return GetConstantStringInfo(GEP
->getOperand(0), Str
, StartIdx
+Offset
,
1499 // The GEP instruction, constant or instruction, must reference a global
1500 // variable that is a constant and is initialized. The referenced constant
1501 // initializer is the array that we'll use for optimization.
1502 const GlobalVariable
* GV
= dyn_cast
<GlobalVariable
>(V
);
1503 if (!GV
|| !GV
->isConstant() || !GV
->hasDefinitiveInitializer())
1505 const Constant
*GlobalInit
= GV
->getInitializer();
1507 // Handle the ConstantAggregateZero case
1508 if (isa
<ConstantAggregateZero
>(GlobalInit
)) {
1509 // This is a degenerate case. The initializer is constant zero so the
1510 // length of the string must be zero.
1515 // Must be a Constant Array
1516 const ConstantArray
*Array
= dyn_cast
<ConstantArray
>(GlobalInit
);
1517 if (Array
== 0 || !Array
->getType()->getElementType()->isIntegerTy(8))
1520 // Get the number of elements in the array
1521 uint64_t NumElts
= Array
->getType()->getNumElements();
1523 if (Offset
> NumElts
)
1526 // Traverse the constant array from 'Offset' which is the place the GEP refers
1528 Str
.reserve(NumElts
-Offset
);
1529 for (unsigned i
= Offset
; i
!= NumElts
; ++i
) {
1530 const Constant
*Elt
= Array
->getOperand(i
);
1531 const ConstantInt
*CI
= dyn_cast
<ConstantInt
>(Elt
);
1532 if (!CI
) // This array isn't suitable, non-int initializer.
1534 if (StopAtNul
&& CI
->isZero())
1535 return true; // we found end of string, success!
1536 Str
+= (char)CI
->getZExtValue();
1539 // The array isn't null terminated, but maybe this is a memcpy, not a strcpy.
1543 // These next two are very similar to the above, but also look through PHI
1545 // TODO: See if we can integrate these two together.
1547 /// GetStringLengthH - If we can compute the length of the string pointed to by
1548 /// the specified pointer, return 'len+1'. If we can't, return 0.
1549 static uint64_t GetStringLengthH(Value
*V
, SmallPtrSet
<PHINode
*, 32> &PHIs
) {
1550 // Look through noop bitcast instructions.
1551 if (BitCastInst
*BCI
= dyn_cast
<BitCastInst
>(V
))
1552 return GetStringLengthH(BCI
->getOperand(0), PHIs
);
1554 // If this is a PHI node, there are two cases: either we have already seen it
1556 if (PHINode
*PN
= dyn_cast
<PHINode
>(V
)) {
1557 if (!PHIs
.insert(PN
))
1558 return ~0ULL; // already in the set.
1560 // If it was new, see if all the input strings are the same length.
1561 uint64_t LenSoFar
= ~0ULL;
1562 for (unsigned i
= 0, e
= PN
->getNumIncomingValues(); i
!= e
; ++i
) {
1563 uint64_t Len
= GetStringLengthH(PN
->getIncomingValue(i
), PHIs
);
1564 if (Len
== 0) return 0; // Unknown length -> unknown.
1566 if (Len
== ~0ULL) continue;
1568 if (Len
!= LenSoFar
&& LenSoFar
!= ~0ULL)
1569 return 0; // Disagree -> unknown.
1573 // Success, all agree.
1577 // strlen(select(c,x,y)) -> strlen(x) ^ strlen(y)
1578 if (SelectInst
*SI
= dyn_cast
<SelectInst
>(V
)) {
1579 uint64_t Len1
= GetStringLengthH(SI
->getTrueValue(), PHIs
);
1580 if (Len1
== 0) return 0;
1581 uint64_t Len2
= GetStringLengthH(SI
->getFalseValue(), PHIs
);
1582 if (Len2
== 0) return 0;
1583 if (Len1
== ~0ULL) return Len2
;
1584 if (Len2
== ~0ULL) return Len1
;
1585 if (Len1
!= Len2
) return 0;
1589 // If the value is not a GEP instruction nor a constant expression with a
1590 // GEP instruction, then return unknown.
1592 if (GetElementPtrInst
*GEPI
= dyn_cast
<GetElementPtrInst
>(V
)) {
1594 } else if (ConstantExpr
*CE
= dyn_cast
<ConstantExpr
>(V
)) {
1595 if (CE
->getOpcode() != Instruction::GetElementPtr
)
1602 // Make sure the GEP has exactly three arguments.
1603 if (GEP
->getNumOperands() != 3)
1606 // Check to make sure that the first operand of the GEP is an integer and
1607 // has value 0 so that we are sure we're indexing into the initializer.
1608 if (ConstantInt
*Idx
= dyn_cast
<ConstantInt
>(GEP
->getOperand(1))) {
1614 // If the second index isn't a ConstantInt, then this is a variable index
1615 // into the array. If this occurs, we can't say anything meaningful about
1617 uint64_t StartIdx
= 0;
1618 if (ConstantInt
*CI
= dyn_cast
<ConstantInt
>(GEP
->getOperand(2)))
1619 StartIdx
= CI
->getZExtValue();
1623 // The GEP instruction, constant or instruction, must reference a global
1624 // variable that is a constant and is initialized. The referenced constant
1625 // initializer is the array that we'll use for optimization.
1626 GlobalVariable
* GV
= dyn_cast
<GlobalVariable
>(GEP
->getOperand(0));
1627 if (!GV
|| !GV
->isConstant() || !GV
->hasInitializer() ||
1628 GV
->mayBeOverridden())
1630 Constant
*GlobalInit
= GV
->getInitializer();
1632 // Handle the ConstantAggregateZero case, which is a degenerate case. The
1633 // initializer is constant zero so the length of the string must be zero.
1634 if (isa
<ConstantAggregateZero
>(GlobalInit
))
1635 return 1; // Len = 0 offset by 1.
1637 // Must be a Constant Array
1638 ConstantArray
*Array
= dyn_cast
<ConstantArray
>(GlobalInit
);
1639 if (!Array
|| !Array
->getType()->getElementType()->isIntegerTy(8))
1642 // Get the number of elements in the array
1643 uint64_t NumElts
= Array
->getType()->getNumElements();
1645 // Traverse the constant array from StartIdx (derived above) which is
1646 // the place the GEP refers to in the array.
1647 for (unsigned i
= StartIdx
; i
!= NumElts
; ++i
) {
1648 Constant
*Elt
= Array
->getOperand(i
);
1649 ConstantInt
*CI
= dyn_cast
<ConstantInt
>(Elt
);
1650 if (!CI
) // This array isn't suitable, non-int initializer.
1653 return i
-StartIdx
+1; // We found end of string, success!
1656 return 0; // The array isn't null terminated, conservatively return 'unknown'.
1659 /// GetStringLength - If we can compute the length of the string pointed to by
1660 /// the specified pointer, return 'len+1'. If we can't, return 0.
1661 uint64_t llvm::GetStringLength(Value
*V
) {
1662 if (!V
->getType()->isPointerTy()) return 0;
1664 SmallPtrSet
<PHINode
*, 32> PHIs
;
1665 uint64_t Len
= GetStringLengthH(V
, PHIs
);
1666 // If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return
1667 // an empty string as a length.
1668 return Len
== ~0ULL ? 1 : Len
;
1672 llvm::GetUnderlyingObject(Value
*V
, const TargetData
*TD
, unsigned MaxLookup
) {
1673 if (!V
->getType()->isPointerTy())
1675 for (unsigned Count
= 0; MaxLookup
== 0 || Count
< MaxLookup
; ++Count
) {
1676 if (GEPOperator
*GEP
= dyn_cast
<GEPOperator
>(V
)) {
1677 V
= GEP
->getPointerOperand();
1678 } else if (Operator::getOpcode(V
) == Instruction::BitCast
) {
1679 V
= cast
<Operator
>(V
)->getOperand(0);
1680 } else if (GlobalAlias
*GA
= dyn_cast
<GlobalAlias
>(V
)) {
1681 if (GA
->mayBeOverridden())
1683 V
= GA
->getAliasee();
1685 // See if InstructionSimplify knows any relevant tricks.
1686 if (Instruction
*I
= dyn_cast
<Instruction
>(V
))
1687 // TODO: Aquire a DominatorTree and use it.
1688 if (Value
*Simplified
= SimplifyInstruction(I
, TD
, 0)) {
1695 assert(V
->getType()->isPointerTy() && "Unexpected operand type!");