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/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/GlobalVariable.h"
19 #include "llvm/GlobalAlias.h"
20 #include "llvm/IntrinsicInst.h"
21 #include "llvm/LLVMContext.h"
22 #include "llvm/Operator.h"
23 #include "llvm/Target/TargetData.h"
24 #include "llvm/Support/GetElementPtrTypeIterator.h"
25 #include "llvm/Support/MathExtras.h"
29 /// ComputeMaskedBits - Determine which of the bits specified in Mask are
30 /// known to be either zero or one and return them in the KnownZero/KnownOne
31 /// bit sets. This code only analyzes bits in Mask, in order to short-circuit
33 /// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
34 /// we cannot optimize based on the assumption that it is zero without changing
35 /// it to be an explicit zero. If we don't change it to zero, other code could
36 /// optimized based on the contradictory assumption that it is non-zero.
37 /// Because instcombine aggressively folds operations with undef args anyway,
38 /// this won't lose us code quality.
40 /// This function is defined on values with integer type, values with pointer
41 /// type (but only if TD is non-null), and vectors of integers. In the case
42 /// where V is a vector, the mask, known zero, and known one values are the
43 /// same width as the vector element, and the bit is set only if it is true
44 /// for all of the elements in the vector.
45 void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
46 APInt &KnownZero, APInt &KnownOne,
47 const TargetData *TD, unsigned Depth) {
48 const unsigned MaxDepth = 6;
49 assert(V && "No Value?");
50 assert(Depth <= MaxDepth && "Limit Search Depth");
51 unsigned BitWidth = Mask.getBitWidth();
52 assert((V->getType()->isIntOrIntVector() || isa<PointerType>(V->getType())) &&
53 "Not integer or pointer type!");
55 TD->getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
56 (!V->getType()->isIntOrIntVector() ||
57 V->getType()->getScalarSizeInBits() == BitWidth) &&
58 KnownZero.getBitWidth() == BitWidth &&
59 KnownOne.getBitWidth() == BitWidth &&
60 "V, Mask, KnownOne and KnownZero should have same BitWidth");
62 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
63 // We know all of the bits for a constant!
64 KnownOne = CI->getValue() & Mask;
65 KnownZero = ~KnownOne & Mask;
68 // Null and aggregate-zero are all-zeros.
69 if (isa<ConstantPointerNull>(V) ||
70 isa<ConstantAggregateZero>(V)) {
75 // Handle a constant vector by taking the intersection of the known bits of
77 if (ConstantVector *CV = dyn_cast<ConstantVector>(V)) {
78 KnownZero.set(); KnownOne.set();
79 for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) {
80 APInt KnownZero2(BitWidth, 0), KnownOne2(BitWidth, 0);
81 ComputeMaskedBits(CV->getOperand(i), Mask, KnownZero2, KnownOne2,
83 KnownZero &= KnownZero2;
84 KnownOne &= KnownOne2;
88 // The address of an aligned GlobalValue has trailing zeros.
89 if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
90 unsigned Align = GV->getAlignment();
91 if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) {
92 const Type *ObjectType = GV->getType()->getElementType();
93 // If the object is defined in the current Module, we'll be giving
94 // it the preferred alignment. Otherwise, we have to assume that it
95 // may only have the minimum ABI alignment.
96 if (!GV->isDeclaration() && !GV->mayBeOverridden())
97 Align = TD->getPrefTypeAlignment(ObjectType);
99 Align = TD->getABITypeAlignment(ObjectType);
102 KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
103 CountTrailingZeros_32(Align));
109 // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
110 // the bits of its aliasee.
111 if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
112 if (GA->mayBeOverridden()) {
113 KnownZero.clear(); KnownOne.clear();
115 ComputeMaskedBits(GA->getAliasee(), Mask, KnownZero, KnownOne,
121 KnownZero.clear(); KnownOne.clear(); // Start out not knowing anything.
123 if (Depth == MaxDepth || Mask == 0)
124 return; // Limit search depth.
126 Operator *I = dyn_cast<Operator>(V);
129 APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
130 switch (I->getOpcode()) {
132 case Instruction::And: {
133 // If either the LHS or the RHS are Zero, the result is zero.
134 ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
135 APInt Mask2(Mask & ~KnownZero);
136 ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
138 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
139 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
141 // Output known-1 bits are only known if set in both the LHS & RHS.
142 KnownOne &= KnownOne2;
143 // Output known-0 are known to be clear if zero in either the LHS | RHS.
144 KnownZero |= KnownZero2;
147 case Instruction::Or: {
148 ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
149 APInt Mask2(Mask & ~KnownOne);
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-0 bits are only known if clear in both the LHS & RHS.
156 KnownZero &= KnownZero2;
157 // Output known-1 are known to be set if set in either the LHS | RHS.
158 KnownOne |= KnownOne2;
161 case Instruction::Xor: {
162 ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
163 ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD,
165 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
166 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
168 // Output known-0 bits are known if clear or set in both the LHS & RHS.
169 APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
170 // Output known-1 are known to be set if set in only one of the LHS, RHS.
171 KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
172 KnownZero = KnownZeroOut;
175 case Instruction::Mul: {
176 APInt Mask2 = APInt::getAllOnesValue(BitWidth);
177 ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1);
178 ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
180 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
181 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
183 // If low bits are zero in either operand, output low known-0 bits.
184 // Also compute a conserative estimate for high known-0 bits.
185 // More trickiness is possible, but this is sufficient for the
186 // interesting case of alignment computation.
188 unsigned TrailZ = KnownZero.countTrailingOnes() +
189 KnownZero2.countTrailingOnes();
190 unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
191 KnownZero2.countLeadingOnes(),
192 BitWidth) - BitWidth;
194 TrailZ = std::min(TrailZ, BitWidth);
195 LeadZ = std::min(LeadZ, BitWidth);
196 KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
197 APInt::getHighBitsSet(BitWidth, LeadZ);
201 case Instruction::UDiv: {
202 // For the purposes of computing leading zeros we can conservatively
203 // treat a udiv as a logical right shift by the power of 2 known to
204 // be less than the denominator.
205 APInt AllOnes = APInt::getAllOnesValue(BitWidth);
206 ComputeMaskedBits(I->getOperand(0),
207 AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
208 unsigned LeadZ = KnownZero2.countLeadingOnes();
212 ComputeMaskedBits(I->getOperand(1),
213 AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
214 unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
215 if (RHSUnknownLeadingOnes != BitWidth)
216 LeadZ = std::min(BitWidth,
217 LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
219 KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
222 case Instruction::Select:
223 ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, TD, Depth+1);
224 ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, TD,
226 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
227 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
229 // Only known if known in both the LHS and RHS.
230 KnownOne &= KnownOne2;
231 KnownZero &= KnownZero2;
233 case Instruction::FPTrunc:
234 case Instruction::FPExt:
235 case Instruction::FPToUI:
236 case Instruction::FPToSI:
237 case Instruction::SIToFP:
238 case Instruction::UIToFP:
239 return; // Can't work with floating point.
240 case Instruction::PtrToInt:
241 case Instruction::IntToPtr:
242 // We can't handle these if we don't know the pointer size.
244 // FALL THROUGH and handle them the same as zext/trunc.
245 case Instruction::ZExt:
246 case Instruction::Trunc: {
247 const Type *SrcTy = I->getOperand(0)->getType();
249 unsigned SrcBitWidth;
250 // Note that we handle pointer operands here because of inttoptr/ptrtoint
251 // which fall through here.
252 if (isa<PointerType>(SrcTy))
253 SrcBitWidth = TD->getTypeSizeInBits(SrcTy);
255 SrcBitWidth = SrcTy->getScalarSizeInBits();
258 MaskIn.zextOrTrunc(SrcBitWidth);
259 KnownZero.zextOrTrunc(SrcBitWidth);
260 KnownOne.zextOrTrunc(SrcBitWidth);
261 ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
263 KnownZero.zextOrTrunc(BitWidth);
264 KnownOne.zextOrTrunc(BitWidth);
265 // Any top bits are known to be zero.
266 if (BitWidth > SrcBitWidth)
267 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
270 case Instruction::BitCast: {
271 const Type *SrcTy = I->getOperand(0)->getType();
272 if ((SrcTy->isInteger() || isa<PointerType>(SrcTy)) &&
273 // TODO: For now, not handling conversions like:
274 // (bitcast i64 %x to <2 x i32>)
275 !isa<VectorType>(I->getType())) {
276 ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD,
282 case Instruction::SExt: {
283 // Compute the bits in the result that are not present in the input.
284 unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits();
287 MaskIn.trunc(SrcBitWidth);
288 KnownZero.trunc(SrcBitWidth);
289 KnownOne.trunc(SrcBitWidth);
290 ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
292 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
293 KnownZero.zext(BitWidth);
294 KnownOne.zext(BitWidth);
296 // If the sign bit of the input is known set or clear, then we know the
297 // top bits of the result.
298 if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
299 KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
300 else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
301 KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
304 case Instruction::Shl:
305 // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
306 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
307 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
308 APInt Mask2(Mask.lshr(ShiftAmt));
309 ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
311 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
312 KnownZero <<= ShiftAmt;
313 KnownOne <<= ShiftAmt;
314 KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
318 case Instruction::LShr:
319 // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
320 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
321 // Compute the new bits that are at the top now.
322 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
324 // Unsigned shift right.
325 APInt Mask2(Mask.shl(ShiftAmt));
326 ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne, TD,
328 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
329 KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
330 KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
331 // high bits known zero.
332 KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
336 case Instruction::AShr:
337 // (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
338 if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
339 // Compute the new bits that are at the top now.
340 uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
342 // Signed shift right.
343 APInt Mask2(Mask.shl(ShiftAmt));
344 ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
346 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
347 KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
348 KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
350 APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
351 if (KnownZero[BitWidth-ShiftAmt-1]) // New bits are known zero.
352 KnownZero |= HighBits;
353 else if (KnownOne[BitWidth-ShiftAmt-1]) // New bits are known one.
354 KnownOne |= HighBits;
358 case Instruction::Sub: {
359 if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->getOperand(0))) {
360 // We know that the top bits of C-X are clear if X contains less bits
361 // than C (i.e. no wrap-around can happen). For example, 20-X is
362 // positive if we can prove that X is >= 0 and < 16.
363 if (!CLHS->getValue().isNegative()) {
364 unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
365 // NLZ can't be BitWidth with no sign bit
366 APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
367 ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2,
370 // If all of the MaskV bits are known to be zero, then we know the
371 // output top bits are zero, because we now know that the output is
373 if ((KnownZero2 & MaskV) == MaskV) {
374 unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
375 // Top bits known zero.
376 KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
382 case Instruction::Add: {
383 // If one of the operands has trailing zeros, then the bits that the
384 // other operand has in those bit positions will be preserved in the
385 // result. For an add, this works with either operand. For a subtract,
386 // this only works if the known zeros are in the right operand.
387 APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
388 APInt Mask2 = APInt::getLowBitsSet(BitWidth,
389 BitWidth - Mask.countLeadingZeros());
390 ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne, TD,
392 assert((LHSKnownZero & LHSKnownOne) == 0 &&
393 "Bits known to be one AND zero?");
394 unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes();
396 ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, TD,
398 assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
399 unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes();
401 // Determine which operand has more trailing zeros, and use that
402 // many bits from the other operand.
403 if (LHSKnownZeroOut > RHSKnownZeroOut) {
404 if (I->getOpcode() == Instruction::Add) {
405 APInt Mask = APInt::getLowBitsSet(BitWidth, LHSKnownZeroOut);
406 KnownZero |= KnownZero2 & Mask;
407 KnownOne |= KnownOne2 & Mask;
409 // If the known zeros are in the left operand for a subtract,
410 // fall back to the minimum known zeros in both operands.
411 KnownZero |= APInt::getLowBitsSet(BitWidth,
412 std::min(LHSKnownZeroOut,
415 } else if (RHSKnownZeroOut >= LHSKnownZeroOut) {
416 APInt Mask = APInt::getLowBitsSet(BitWidth, RHSKnownZeroOut);
417 KnownZero |= LHSKnownZero & Mask;
418 KnownOne |= LHSKnownOne & Mask;
422 case Instruction::SRem:
423 if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
424 APInt RA = Rem->getValue().abs();
425 if (RA.isPowerOf2()) {
426 APInt LowBits = RA - 1;
427 APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
428 ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
431 // The low bits of the first operand are unchanged by the srem.
432 KnownZero = KnownZero2 & LowBits;
433 KnownOne = KnownOne2 & LowBits;
435 // If the first operand is non-negative or has all low bits zero, then
436 // the upper bits are all zero.
437 if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
438 KnownZero |= ~LowBits;
440 // If the first operand is negative and not all low bits are zero, then
441 // the upper bits are all one.
442 if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
443 KnownOne |= ~LowBits;
448 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
452 case Instruction::URem: {
453 if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
454 APInt RA = Rem->getValue();
455 if (RA.isPowerOf2()) {
456 APInt LowBits = (RA - 1);
457 APInt Mask2 = LowBits & Mask;
458 KnownZero |= ~LowBits & Mask;
459 ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
461 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
466 // Since the result is less than or equal to either operand, any leading
467 // zero bits in either operand must also exist in the result.
468 APInt AllOnes = APInt::getAllOnesValue(BitWidth);
469 ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne,
471 ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2,
474 unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
475 KnownZero2.countLeadingOnes());
477 KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask;
481 case Instruction::Alloca: {
482 AllocaInst *AI = cast<AllocaInst>(V);
483 unsigned Align = AI->getAlignment();
484 if (Align == 0 && TD)
485 Align = TD->getABITypeAlignment(AI->getType()->getElementType());
488 KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
489 CountTrailingZeros_32(Align));
492 case Instruction::GetElementPtr: {
493 // Analyze all of the subscripts of this getelementptr instruction
494 // to determine if we can prove known low zero bits.
495 APInt LocalMask = APInt::getAllOnesValue(BitWidth);
496 APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
497 ComputeMaskedBits(I->getOperand(0), LocalMask,
498 LocalKnownZero, LocalKnownOne, TD, Depth+1);
499 unsigned TrailZ = LocalKnownZero.countTrailingOnes();
501 gep_type_iterator GTI = gep_type_begin(I);
502 for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
503 Value *Index = I->getOperand(i);
504 if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
505 // Handle struct member offset arithmetic.
507 const StructLayout *SL = TD->getStructLayout(STy);
508 unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
509 uint64_t Offset = SL->getElementOffset(Idx);
510 TrailZ = std::min(TrailZ,
511 CountTrailingZeros_64(Offset));
513 // Handle array index arithmetic.
514 const Type *IndexedTy = GTI.getIndexedType();
515 if (!IndexedTy->isSized()) return;
516 unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits();
517 uint64_t TypeSize = TD ? TD->getTypeAllocSize(IndexedTy) : 1;
518 LocalMask = APInt::getAllOnesValue(GEPOpiBits);
519 LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
520 ComputeMaskedBits(Index, LocalMask,
521 LocalKnownZero, LocalKnownOne, TD, Depth+1);
522 TrailZ = std::min(TrailZ,
523 unsigned(CountTrailingZeros_64(TypeSize) +
524 LocalKnownZero.countTrailingOnes()));
528 KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask;
531 case Instruction::PHI: {
532 PHINode *P = cast<PHINode>(I);
533 // Handle the case of a simple two-predecessor recurrence PHI.
534 // There's a lot more that could theoretically be done here, but
535 // this is sufficient to catch some interesting cases.
536 if (P->getNumIncomingValues() == 2) {
537 for (unsigned i = 0; i != 2; ++i) {
538 Value *L = P->getIncomingValue(i);
539 Value *R = P->getIncomingValue(!i);
540 Operator *LU = dyn_cast<Operator>(L);
543 unsigned Opcode = LU->getOpcode();
544 // Check for operations that have the property that if
545 // both their operands have low zero bits, the result
546 // will have low zero bits.
547 if (Opcode == Instruction::Add ||
548 Opcode == Instruction::Sub ||
549 Opcode == Instruction::And ||
550 Opcode == Instruction::Or ||
551 Opcode == Instruction::Mul) {
552 Value *LL = LU->getOperand(0);
553 Value *LR = LU->getOperand(1);
554 // Find a recurrence.
561 // Ok, we have a PHI of the form L op= R. Check for low
563 APInt Mask2 = APInt::getAllOnesValue(BitWidth);
564 ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, TD, Depth+1);
565 Mask2 = APInt::getLowBitsSet(BitWidth,
566 KnownZero2.countTrailingOnes());
568 // We need to take the minimum number of known bits
569 APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
570 ComputeMaskedBits(L, Mask2, KnownZero3, KnownOne3, TD, Depth+1);
573 APInt::getLowBitsSet(BitWidth,
574 std::min(KnownZero2.countTrailingOnes(),
575 KnownZero3.countTrailingOnes()));
581 // Otherwise take the unions of the known bit sets of the operands,
582 // taking conservative care to avoid excessive recursion.
583 if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) {
584 KnownZero = APInt::getAllOnesValue(BitWidth);
585 KnownOne = APInt::getAllOnesValue(BitWidth);
586 for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
587 // Skip direct self references.
588 if (P->getIncomingValue(i) == P) continue;
590 KnownZero2 = APInt(BitWidth, 0);
591 KnownOne2 = APInt(BitWidth, 0);
592 // Recurse, but cap the recursion to one level, because we don't
593 // want to waste time spinning around in loops.
594 ComputeMaskedBits(P->getIncomingValue(i), KnownZero | KnownOne,
595 KnownZero2, KnownOne2, TD, MaxDepth-1);
596 KnownZero &= KnownZero2;
597 KnownOne &= KnownOne2;
598 // If all bits have been ruled out, there's no need to check
600 if (!KnownZero && !KnownOne)
606 case Instruction::Call:
607 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
608 switch (II->getIntrinsicID()) {
610 case Intrinsic::ctpop:
611 case Intrinsic::ctlz:
612 case Intrinsic::cttz: {
613 unsigned LowBits = Log2_32(BitWidth)+1;
614 KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
623 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
624 /// this predicate to simplify operations downstream. Mask is known to be zero
625 /// for bits that V cannot have.
627 /// This function is defined on values with integer type, values with pointer
628 /// type (but only if TD is non-null), and vectors of integers. In the case
629 /// where V is a vector, the mask, known zero, and known one values are the
630 /// same width as the vector element, and the bit is set only if it is true
631 /// for all of the elements in the vector.
632 bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask,
633 const TargetData *TD, unsigned Depth) {
634 APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
635 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
636 assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
637 return (KnownZero & Mask) == Mask;
642 /// ComputeNumSignBits - Return the number of times the sign bit of the
643 /// register is replicated into the other bits. We know that at least 1 bit
644 /// is always equal to the sign bit (itself), but other cases can give us
645 /// information. For example, immediately after an "ashr X, 2", we know that
646 /// the top 3 bits are all equal to each other, so we return 3.
648 /// 'Op' must have a scalar integer type.
650 unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
652 assert((TD || V->getType()->isIntOrIntVector()) &&
653 "ComputeNumSignBits requires a TargetData object to operate "
654 "on non-integer values!");
655 const Type *Ty = V->getType();
656 unsigned TyBits = TD ? TD->getTypeSizeInBits(V->getType()->getScalarType()) :
657 Ty->getScalarSizeInBits();
659 unsigned FirstAnswer = 1;
661 // Note that ConstantInt is handled by the general ComputeMaskedBits case
665 return 1; // Limit search depth.
667 Operator *U = dyn_cast<Operator>(V);
668 switch (Operator::getOpcode(V)) {
670 case Instruction::SExt:
671 Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits();
672 return ComputeNumSignBits(U->getOperand(0), TD, Depth+1) + Tmp;
674 case Instruction::AShr:
675 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
676 // ashr X, C -> adds C sign bits.
677 if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
678 Tmp += C->getZExtValue();
679 if (Tmp > TyBits) Tmp = TyBits;
682 case Instruction::Shl:
683 if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
684 // shl destroys sign bits.
685 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
686 if (C->getZExtValue() >= TyBits || // Bad shift.
687 C->getZExtValue() >= Tmp) break; // Shifted all sign bits out.
688 return Tmp - C->getZExtValue();
691 case Instruction::And:
692 case Instruction::Or:
693 case Instruction::Xor: // NOT is handled here.
694 // Logical binary ops preserve the number of sign bits at the worst.
695 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
697 Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
698 FirstAnswer = std::min(Tmp, Tmp2);
699 // We computed what we know about the sign bits as our first
700 // answer. Now proceed to the generic code that uses
701 // ComputeMaskedBits, and pick whichever answer is better.
705 case Instruction::Select:
706 Tmp = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
707 if (Tmp == 1) return 1; // Early out.
708 Tmp2 = ComputeNumSignBits(U->getOperand(2), TD, Depth+1);
709 return std::min(Tmp, Tmp2);
711 case Instruction::Add:
712 // Add can have at most one carry bit. Thus we know that the output
713 // is, at worst, one more bit than the inputs.
714 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
715 if (Tmp == 1) return 1; // Early out.
717 // Special case decrementing a value (ADD X, -1):
718 if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(1)))
719 if (CRHS->isAllOnesValue()) {
720 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
721 APInt Mask = APInt::getAllOnesValue(TyBits);
722 ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, TD,
725 // If the input is known to be 0 or 1, the output is 0/-1, which is all
727 if ((KnownZero | APInt(TyBits, 1)) == Mask)
730 // If we are subtracting one from a positive number, there is no carry
731 // out of the result.
732 if (KnownZero.isNegative())
736 Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
737 if (Tmp2 == 1) return 1;
738 return std::min(Tmp, Tmp2)-1;
740 case Instruction::Sub:
741 Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1);
742 if (Tmp2 == 1) return 1;
745 if (ConstantInt *CLHS = dyn_cast<ConstantInt>(U->getOperand(0)))
746 if (CLHS->isNullValue()) {
747 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
748 APInt Mask = APInt::getAllOnesValue(TyBits);
749 ComputeMaskedBits(U->getOperand(1), Mask, KnownZero, KnownOne,
751 // If the input is known to be 0 or 1, the output is 0/-1, which is all
753 if ((KnownZero | APInt(TyBits, 1)) == Mask)
756 // If the input is known to be positive (the sign bit is known clear),
757 // the output of the NEG has the same number of sign bits as the input.
758 if (KnownZero.isNegative())
761 // Otherwise, we treat this like a SUB.
764 // Sub can have at most one carry bit. Thus we know that the output
765 // is, at worst, one more bit than the inputs.
766 Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1);
767 if (Tmp == 1) return 1; // Early out.
768 return std::min(Tmp, Tmp2)-1;
770 case Instruction::PHI: {
771 PHINode *PN = cast<PHINode>(U);
772 // Don't analyze large in-degree PHIs.
773 if (PN->getNumIncomingValues() > 4) break;
775 // Take the minimum of all incoming values. This can't infinitely loop
776 // because of our depth threshold.
777 Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1);
778 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
779 if (Tmp == 1) return Tmp;
781 ComputeNumSignBits(PN->getIncomingValue(1), TD, Depth+1));
786 case Instruction::Trunc:
787 // FIXME: it's tricky to do anything useful for this, but it is an important
788 // case for targets like X86.
792 // Finally, if we can prove that the top bits of the result are 0's or 1's,
793 // use this information.
794 APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
795 APInt Mask = APInt::getAllOnesValue(TyBits);
796 ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
798 if (KnownZero.isNegative()) { // sign bit is 0
800 } else if (KnownOne.isNegative()) { // sign bit is 1;
807 // Okay, we know that the sign bit in Mask is set. Use CLZ to determine
808 // the number of identical bits in the top of the input value.
810 Mask <<= Mask.getBitWidth()-TyBits;
811 // Return # leading zeros. We use 'min' here in case Val was zero before
812 // shifting. We don't want to return '64' as for an i32 "0".
813 return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
816 /// ComputeMultiple - This function computes the integer multiple of Base that
817 /// equals V. If successful, it returns true and returns the multiple in
818 /// Multiple. If unsuccessful, it returns false. It looks
819 /// through SExt instructions only if LookThroughSExt is true.
820 bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
821 bool LookThroughSExt, unsigned Depth) {
822 const unsigned MaxDepth = 6;
824 assert(V && "No Value?");
825 assert(Depth <= MaxDepth && "Limit Search Depth");
826 assert(V->getType()->isInteger() && "Not integer or pointer type!");
828 const Type *T = V->getType();
830 ConstantInt *CI = dyn_cast<ConstantInt>(V);
840 ConstantExpr *CO = dyn_cast<ConstantExpr>(V);
841 Constant *BaseVal = ConstantInt::get(T, Base);
842 if (CO && CO == BaseVal) {
844 Multiple = ConstantInt::get(T, 1);
848 if (CI && CI->getZExtValue() % Base == 0) {
849 Multiple = ConstantInt::get(T, CI->getZExtValue() / Base);
853 if (Depth == MaxDepth) return false; // Limit search depth.
855 Operator *I = dyn_cast<Operator>(V);
856 if (!I) return false;
858 switch (I->getOpcode()) {
860 case Instruction::SExt:
861 if (!LookThroughSExt) return false;
862 // otherwise fall through to ZExt
863 case Instruction::ZExt:
864 return ComputeMultiple(I->getOperand(0), Base, Multiple,
865 LookThroughSExt, Depth+1);
866 case Instruction::Shl:
867 case Instruction::Mul: {
868 Value *Op0 = I->getOperand(0);
869 Value *Op1 = I->getOperand(1);
871 if (I->getOpcode() == Instruction::Shl) {
872 ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1);
873 if (!Op1CI) return false;
874 // Turn Op0 << Op1 into Op0 * 2^Op1
875 APInt Op1Int = Op1CI->getValue();
876 uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1);
877 Op1 = ConstantInt::get(V->getContext(),
878 APInt(Op1Int.getBitWidth(), 0).set(BitToSet));
883 bool M0 = ComputeMultiple(Op0, Base, Mul0,
884 LookThroughSExt, Depth+1);
885 bool M1 = ComputeMultiple(Op1, Base, Mul1,
886 LookThroughSExt, Depth+1);
889 if (isa<Constant>(Op1) && isa<Constant>(Mul0)) {
890 // V == Base * (Mul0 * Op1), so return (Mul0 * Op1)
891 Multiple = ConstantExpr::getMul(cast<Constant>(Mul0),
892 cast<Constant>(Op1));
896 if (ConstantInt *Mul0CI = dyn_cast<ConstantInt>(Mul0))
897 if (Mul0CI->getValue() == 1) {
898 // V == Base * Op1, so return Op1
905 if (isa<Constant>(Op0) && isa<Constant>(Mul1)) {
906 // V == Base * (Mul1 * Op0), so return (Mul1 * Op0)
907 Multiple = ConstantExpr::getMul(cast<Constant>(Mul1),
908 cast<Constant>(Op0));
912 if (ConstantInt *Mul1CI = dyn_cast<ConstantInt>(Mul1))
913 if (Mul1CI->getValue() == 1) {
914 // V == Base * Op0, so return Op0
922 // We could not determine if V is a multiple of Base.
926 /// CannotBeNegativeZero - Return true if we can prove that the specified FP
927 /// value is never equal to -0.0.
929 /// NOTE: this function will need to be revisited when we support non-default
932 bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
933 if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
934 return !CFP->getValueAPF().isNegZero();
937 return 1; // Limit search depth.
939 const Operator *I = dyn_cast<Operator>(V);
940 if (I == 0) return false;
942 // (add x, 0.0) is guaranteed to return +0.0, not -0.0.
943 if (I->getOpcode() == Instruction::FAdd &&
944 isa<ConstantFP>(I->getOperand(1)) &&
945 cast<ConstantFP>(I->getOperand(1))->isNullValue())
948 // sitofp and uitofp turn into +0.0 for zero.
949 if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
952 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
953 // sqrt(-0.0) = -0.0, no other negative results are possible.
954 if (II->getIntrinsicID() == Intrinsic::sqrt)
955 return CannotBeNegativeZero(II->getOperand(1), Depth+1);
957 if (const CallInst *CI = dyn_cast<CallInst>(I))
958 if (const Function *F = CI->getCalledFunction()) {
959 if (F->isDeclaration()) {
961 if (F->getName() == "abs") return true;
962 // fabs[lf](x) != -0.0
963 if (F->getName() == "fabs") return true;
964 if (F->getName() == "fabsf") return true;
965 if (F->getName() == "fabsl") return true;
966 if (F->getName() == "sqrt" || F->getName() == "sqrtf" ||
967 F->getName() == "sqrtl")
968 return CannotBeNegativeZero(CI->getOperand(1), Depth+1);
976 /// GetLinearExpression - Analyze the specified value as a linear expression:
977 /// "A*V + B", where A and B are constant integers. Return the scale and offset
978 /// values as APInts and return V as a Value*. The incoming Value is known to
979 /// have IntegerType. Note that this looks through extends, so the high bits
980 /// may not be represented in the result.
981 static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
982 const TargetData *TD, unsigned Depth) {
983 assert(isa<IntegerType>(V->getType()) && "Not an integer value");
985 // Limit our recursion depth.
992 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
993 if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
994 switch (BOp->getOpcode()) {
996 case Instruction::Or:
997 // X|C == X+C if all the bits in C are unset in X. Otherwise we can't
999 if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), TD))
1002 case Instruction::Add:
1003 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, TD, Depth+1);
1004 Offset += RHSC->getValue();
1006 case Instruction::Mul:
1007 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, TD, Depth+1);
1008 Offset *= RHSC->getValue();
1009 Scale *= RHSC->getValue();
1011 case Instruction::Shl:
1012 V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, TD, Depth+1);
1013 Offset <<= RHSC->getValue().getLimitedValue();
1014 Scale <<= RHSC->getValue().getLimitedValue();
1020 // Since clients don't care about the high bits of the value, just scales and
1021 // offsets, we can look through extensions.
1022 if (isa<SExtInst>(V) || isa<ZExtInst>(V)) {
1023 Value *CastOp = cast<CastInst>(V)->getOperand(0);
1024 unsigned OldWidth = Scale.getBitWidth();
1025 unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
1026 Scale.trunc(SmallWidth);
1027 Offset.trunc(SmallWidth);
1028 Value *Result = GetLinearExpression(CastOp, Scale, Offset, TD, Depth+1);
1029 Scale.zext(OldWidth);
1030 Offset.zext(OldWidth);
1039 /// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
1040 /// into a base pointer with a constant offset and a number of scaled symbolic
1043 /// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
1044 /// the VarIndices vector) are Value*'s that are known to be scaled by the
1045 /// specified amount, but which may have other unrepresented high bits. As such,
1046 /// the gep cannot necessarily be reconstructed from its decomposed form.
1048 /// When TargetData is around, this function is capable of analyzing everything
1049 /// that Value::getUnderlyingObject() can look through. When not, it just looks
1050 /// through pointer casts.
1052 const Value *llvm::DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
1053 SmallVectorImpl<std::pair<const Value*, int64_t> > &VarIndices,
1054 const TargetData *TD) {
1055 // Limit recursion depth to limit compile time in crazy cases.
1056 unsigned MaxLookup = 6;
1060 // See if this is a bitcast or GEP.
1061 const Operator *Op = dyn_cast<Operator>(V);
1063 // The only non-operator case we can handle are GlobalAliases.
1064 if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
1065 if (!GA->mayBeOverridden()) {
1066 V = GA->getAliasee();
1073 if (Op->getOpcode() == Instruction::BitCast) {
1074 V = Op->getOperand(0);
1078 const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
1082 // Don't attempt to analyze GEPs over unsized objects.
1083 if (!cast<PointerType>(GEPOp->getOperand(0)->getType())
1084 ->getElementType()->isSized())
1087 // If we are lacking TargetData information, we can't compute the offets of
1088 // elements computed by GEPs. However, we can handle bitcast equivalent
1091 if (!GEPOp->hasAllZeroIndices())
1093 V = GEPOp->getOperand(0);
1097 // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
1098 gep_type_iterator GTI = gep_type_begin(GEPOp);
1099 for (User::const_op_iterator I = GEPOp->op_begin()+1,
1100 E = GEPOp->op_end(); I != E; ++I) {
1102 // Compute the (potentially symbolic) offset in bytes for this index.
1103 if (const StructType *STy = dyn_cast<StructType>(*GTI++)) {
1104 // For a struct, add the member offset.
1105 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
1106 if (FieldNo == 0) continue;
1108 BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo);
1112 // For an array/pointer, add the element offset, explicitly scaled.
1113 if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
1114 if (CIdx->isZero()) continue;
1115 BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
1119 uint64_t Scale = TD->getTypeAllocSize(*GTI);
1121 // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
1122 unsigned Width = cast<IntegerType>(Index->getType())->getBitWidth();
1123 APInt IndexScale(Width, 0), IndexOffset(Width, 0);
1124 Index = GetLinearExpression(Index, IndexScale, IndexOffset, TD, 0);
1126 // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
1127 // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
1128 BaseOffs += IndexOffset.getZExtValue()*Scale;
1129 Scale *= IndexScale.getZExtValue();
1132 // If we already had an occurrance of this index variable, merge this
1133 // scale into it. For example, we want to handle:
1134 // A[x][x] -> x*16 + x*4 -> x*20
1135 // This also ensures that 'x' only appears in the index list once.
1136 for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
1137 if (VarIndices[i].first == Index) {
1138 Scale += VarIndices[i].second;
1139 VarIndices.erase(VarIndices.begin()+i);
1144 // Make sure that we have a scale that makes sense for this target's
1146 if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) {
1147 Scale <<= ShiftBits;
1148 Scale >>= ShiftBits;
1152 VarIndices.push_back(std::make_pair(Index, Scale));
1155 // Analyze the base pointer next.
1156 V = GEPOp->getOperand(0);
1157 } while (--MaxLookup);
1159 // If the chain of expressions is too deep, just return early.
1164 // This is the recursive version of BuildSubAggregate. It takes a few different
1165 // arguments. Idxs is the index within the nested struct From that we are
1166 // looking at now (which is of type IndexedType). IdxSkip is the number of
1167 // indices from Idxs that should be left out when inserting into the resulting
1168 // struct. To is the result struct built so far, new insertvalue instructions
1170 static Value *BuildSubAggregate(Value *From, Value* To, const Type *IndexedType,
1171 SmallVector<unsigned, 10> &Idxs,
1173 Instruction *InsertBefore) {
1174 const llvm::StructType *STy = llvm::dyn_cast<llvm::StructType>(IndexedType);
1176 // Save the original To argument so we can modify it
1178 // General case, the type indexed by Idxs is a struct
1179 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1180 // Process each struct element recursively
1183 To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip,
1187 // Couldn't find any inserted value for this index? Cleanup
1188 while (PrevTo != OrigTo) {
1189 InsertValueInst* Del = cast<InsertValueInst>(PrevTo);
1190 PrevTo = Del->getAggregateOperand();
1191 Del->eraseFromParent();
1193 // Stop processing elements
1197 // If we succesfully found a value for each of our subaggregates
1201 // Base case, the type indexed by SourceIdxs is not a struct, or not all of
1202 // the struct's elements had a value that was inserted directly. In the latter
1203 // case, perhaps we can't determine each of the subelements individually, but
1204 // we might be able to find the complete struct somewhere.
1206 // Find the value that is at that particular spot
1207 Value *V = FindInsertedValue(From, Idxs.begin(), Idxs.end());
1212 // Insert the value in the new (sub) aggregrate
1213 return llvm::InsertValueInst::Create(To, V, Idxs.begin() + IdxSkip,
1214 Idxs.end(), "tmp", InsertBefore);
1217 // This helper takes a nested struct and extracts a part of it (which is again a
1218 // struct) into a new value. For example, given the struct:
1219 // { a, { b, { c, d }, e } }
1220 // and the indices "1, 1" this returns
1223 // It does this by inserting an insertvalue for each element in the resulting
1224 // struct, as opposed to just inserting a single struct. This will only work if
1225 // each of the elements of the substruct are known (ie, inserted into From by an
1226 // insertvalue instruction somewhere).
1228 // All inserted insertvalue instructions are inserted before InsertBefore
1229 static Value *BuildSubAggregate(Value *From, const unsigned *idx_begin,
1230 const unsigned *idx_end,
1231 Instruction *InsertBefore) {
1232 assert(InsertBefore && "Must have someplace to insert!");
1233 const Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(),
1236 Value *To = UndefValue::get(IndexedType);
1237 SmallVector<unsigned, 10> Idxs(idx_begin, idx_end);
1238 unsigned IdxSkip = Idxs.size();
1240 return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore);
1243 /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
1244 /// the scalar value indexed is already around as a register, for example if it
1245 /// were inserted directly into the aggregrate.
1247 /// If InsertBefore is not null, this function will duplicate (modified)
1248 /// insertvalues when a part of a nested struct is extracted.
1249 Value *llvm::FindInsertedValue(Value *V, const unsigned *idx_begin,
1250 const unsigned *idx_end, Instruction *InsertBefore) {
1251 // Nothing to index? Just return V then (this is useful at the end of our
1253 if (idx_begin == idx_end)
1255 // We have indices, so V should have an indexable type
1256 assert((isa<StructType>(V->getType()) || isa<ArrayType>(V->getType()))
1257 && "Not looking at a struct or array?");
1258 assert(ExtractValueInst::getIndexedType(V->getType(), idx_begin, idx_end)
1259 && "Invalid indices for type?");
1260 const CompositeType *PTy = cast<CompositeType>(V->getType());
1262 if (isa<UndefValue>(V))
1263 return UndefValue::get(ExtractValueInst::getIndexedType(PTy,
1266 else if (isa<ConstantAggregateZero>(V))
1267 return Constant::getNullValue(ExtractValueInst::getIndexedType(PTy,
1270 else if (Constant *C = dyn_cast<Constant>(V)) {
1271 if (isa<ConstantArray>(C) || isa<ConstantStruct>(C))
1272 // Recursively process this constant
1273 return FindInsertedValue(C->getOperand(*idx_begin), idx_begin + 1,
1274 idx_end, InsertBefore);
1275 } else if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) {
1276 // Loop the indices for the insertvalue instruction in parallel with the
1277 // requested indices
1278 const unsigned *req_idx = idx_begin;
1279 for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
1280 i != e; ++i, ++req_idx) {
1281 if (req_idx == idx_end) {
1283 // The requested index identifies a part of a nested aggregate. Handle
1284 // this specially. For example,
1285 // %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
1286 // %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
1287 // %C = extractvalue {i32, { i32, i32 } } %B, 1
1288 // This can be changed into
1289 // %A = insertvalue {i32, i32 } undef, i32 10, 0
1290 // %C = insertvalue {i32, i32 } %A, i32 11, 1
1291 // which allows the unused 0,0 element from the nested struct to be
1293 return BuildSubAggregate(V, idx_begin, req_idx, InsertBefore);
1295 // We can't handle this without inserting insertvalues
1299 // This insert value inserts something else than what we are looking for.
1300 // See if the (aggregrate) value inserted into has the value we are
1301 // looking for, then.
1303 return FindInsertedValue(I->getAggregateOperand(), idx_begin, idx_end,
1306 // If we end up here, the indices of the insertvalue match with those
1307 // requested (though possibly only partially). Now we recursively look at
1308 // the inserted value, passing any remaining indices.
1309 return FindInsertedValue(I->getInsertedValueOperand(), req_idx, idx_end,
1311 } else if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) {
1312 // If we're extracting a value from an aggregrate that was extracted from
1313 // something else, we can extract from that something else directly instead.
1314 // However, we will need to chain I's indices with the requested indices.
1316 // Calculate the number of indices required
1317 unsigned size = I->getNumIndices() + (idx_end - idx_begin);
1318 // Allocate some space to put the new indices in
1319 SmallVector<unsigned, 5> Idxs;
1321 // Add indices from the extract value instruction
1322 for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
1326 // Add requested indices
1327 for (const unsigned *i = idx_begin, *e = idx_end; i != e; ++i)
1330 assert(Idxs.size() == size
1331 && "Number of indices added not correct?");
1333 return FindInsertedValue(I->getAggregateOperand(), Idxs.begin(), Idxs.end(),
1336 // Otherwise, we don't know (such as, extracting from a function return value
1337 // or load instruction)
1341 /// GetConstantStringInfo - This function computes the length of a
1342 /// null-terminated C string pointed to by V. If successful, it returns true
1343 /// and returns the string in Str. If unsuccessful, it returns false.
1344 bool llvm::GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset,
1346 // If V is NULL then return false;
1347 if (V == NULL) return false;
1349 // Look through bitcast instructions.
1350 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V))
1351 return GetConstantStringInfo(BCI->getOperand(0), Str, Offset, StopAtNul);
1353 // If the value is not a GEP instruction nor a constant expression with a
1354 // GEP instruction, then return false because ConstantArray can't occur
1357 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) {
1359 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
1360 if (CE->getOpcode() == Instruction::BitCast)
1361 return GetConstantStringInfo(CE->getOperand(0), Str, Offset, StopAtNul);
1362 if (CE->getOpcode() != Instruction::GetElementPtr)
1368 // Make sure the GEP has exactly three arguments.
1369 if (GEP->getNumOperands() != 3)
1372 // Make sure the index-ee is a pointer to array of i8.
1373 const PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType());
1374 const ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType());
1375 if (AT == 0 || !AT->getElementType()->isInteger(8))
1378 // Check to make sure that the first operand of the GEP is an integer and
1379 // has value 0 so that we are sure we're indexing into the initializer.
1380 ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
1381 if (FirstIdx == 0 || !FirstIdx->isZero())
1384 // If the second index isn't a ConstantInt, then this is a variable index
1385 // into the array. If this occurs, we can't say anything meaningful about
1387 uint64_t StartIdx = 0;
1388 if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
1389 StartIdx = CI->getZExtValue();
1392 return GetConstantStringInfo(GEP->getOperand(0), Str, StartIdx+Offset,
1396 // The GEP instruction, constant or instruction, must reference a global
1397 // variable that is a constant and is initialized. The referenced constant
1398 // initializer is the array that we'll use for optimization.
1399 GlobalVariable* GV = dyn_cast<GlobalVariable>(V);
1400 if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
1402 Constant *GlobalInit = GV->getInitializer();
1404 // Handle the ConstantAggregateZero case
1405 if (isa<ConstantAggregateZero>(GlobalInit)) {
1406 // This is a degenerate case. The initializer is constant zero so the
1407 // length of the string must be zero.
1412 // Must be a Constant Array
1413 ConstantArray *Array = dyn_cast<ConstantArray>(GlobalInit);
1414 if (Array == 0 || !Array->getType()->getElementType()->isInteger(8))
1417 // Get the number of elements in the array
1418 uint64_t NumElts = Array->getType()->getNumElements();
1420 if (Offset > NumElts)
1423 // Traverse the constant array from 'Offset' which is the place the GEP refers
1425 Str.reserve(NumElts-Offset);
1426 for (unsigned i = Offset; i != NumElts; ++i) {
1427 Constant *Elt = Array->getOperand(i);
1428 ConstantInt *CI = dyn_cast<ConstantInt>(Elt);
1429 if (!CI) // This array isn't suitable, non-int initializer.
1431 if (StopAtNul && CI->isZero())
1432 return true; // we found end of string, success!
1433 Str += (char)CI->getZExtValue();
1436 // The array isn't null terminated, but maybe this is a memcpy, not a strcpy.