ConstantFold.cpp revision ae3a0be92e33bc716722aa600983fc1535acb122
1//===- ConstantFold.cpp - LLVM constant folder ----------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements folding of constants for LLVM. This implements the 11// (internal) ConstantFold.h interface, which is used by the 12// ConstantExpr::get* methods to automatically fold constants when possible. 13// 14// The current constant folding implementation is implemented in two pieces: the 15// template-based folder for simple primitive constants like ConstantInt, and 16// the special case hackery that we use to symbolically evaluate expressions 17// that use ConstantExprs. 18// 19//===----------------------------------------------------------------------===// 20 21#include "ConstantFold.h" 22#include "llvm/Constants.h" 23#include "llvm/Instructions.h" 24#include "llvm/DerivedTypes.h" 25#include "llvm/Function.h" 26#include "llvm/GlobalAlias.h" 27#include "llvm/ADT/SmallVector.h" 28#include "llvm/Support/Compiler.h" 29#include "llvm/Support/GetElementPtrTypeIterator.h" 30#include "llvm/Support/ManagedStatic.h" 31#include "llvm/Support/MathExtras.h" 32#include <limits> 33using namespace llvm; 34 35//===----------------------------------------------------------------------===// 36// ConstantFold*Instruction Implementations 37//===----------------------------------------------------------------------===// 38 39/// BitCastConstantVector - Convert the specified ConstantVector node to the 40/// specified vector type. At this point, we know that the elements of the 41/// input vector constant are all simple integer or FP values. 42static Constant *BitCastConstantVector(ConstantVector *CV, 43 const VectorType *DstTy) { 44 // If this cast changes element count then we can't handle it here: 45 // doing so requires endianness information. This should be handled by 46 // Analysis/ConstantFolding.cpp 47 unsigned NumElts = DstTy->getNumElements(); 48 if (NumElts != CV->getNumOperands()) 49 return 0; 50 51 // Check to verify that all elements of the input are simple. 52 for (unsigned i = 0; i != NumElts; ++i) { 53 if (!isa<ConstantInt>(CV->getOperand(i)) && 54 !isa<ConstantFP>(CV->getOperand(i))) 55 return 0; 56 } 57 58 // Bitcast each element now. 59 std::vector<Constant*> Result; 60 const Type *DstEltTy = DstTy->getElementType(); 61 for (unsigned i = 0; i != NumElts; ++i) 62 Result.push_back(ConstantExpr::getBitCast(CV->getOperand(i), DstEltTy)); 63 return ConstantVector::get(Result); 64} 65 66/// This function determines which opcode to use to fold two constant cast 67/// expressions together. It uses CastInst::isEliminableCastPair to determine 68/// the opcode. Consequently its just a wrapper around that function. 69/// @brief Determine if it is valid to fold a cast of a cast 70static unsigned 71foldConstantCastPair( 72 unsigned opc, ///< opcode of the second cast constant expression 73 const ConstantExpr*Op, ///< the first cast constant expression 74 const Type *DstTy ///< desintation type of the first cast 75) { 76 assert(Op && Op->isCast() && "Can't fold cast of cast without a cast!"); 77 assert(DstTy && DstTy->isFirstClassType() && "Invalid cast destination type"); 78 assert(CastInst::isCast(opc) && "Invalid cast opcode"); 79 80 // The the types and opcodes for the two Cast constant expressions 81 const Type *SrcTy = Op->getOperand(0)->getType(); 82 const Type *MidTy = Op->getType(); 83 Instruction::CastOps firstOp = Instruction::CastOps(Op->getOpcode()); 84 Instruction::CastOps secondOp = Instruction::CastOps(opc); 85 86 // Let CastInst::isEliminableCastPair do the heavy lifting. 87 return CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy, DstTy, 88 Type::Int64Ty); 89} 90 91static Constant *FoldBitCast(Constant *V, const Type *DestTy) { 92 const Type *SrcTy = V->getType(); 93 if (SrcTy == DestTy) 94 return V; // no-op cast 95 96 // Check to see if we are casting a pointer to an aggregate to a pointer to 97 // the first element. If so, return the appropriate GEP instruction. 98 if (const PointerType *PTy = dyn_cast<PointerType>(V->getType())) 99 if (const PointerType *DPTy = dyn_cast<PointerType>(DestTy)) 100 if (PTy->getAddressSpace() == DPTy->getAddressSpace()) { 101 SmallVector<Value*, 8> IdxList; 102 IdxList.push_back(Constant::getNullValue(Type::Int32Ty)); 103 const Type *ElTy = PTy->getElementType(); 104 while (ElTy != DPTy->getElementType()) { 105 if (const StructType *STy = dyn_cast<StructType>(ElTy)) { 106 if (STy->getNumElements() == 0) break; 107 ElTy = STy->getElementType(0); 108 IdxList.push_back(Constant::getNullValue(Type::Int32Ty)); 109 } else if (const SequentialType *STy = 110 dyn_cast<SequentialType>(ElTy)) { 111 if (isa<PointerType>(ElTy)) break; // Can't index into pointers! 112 ElTy = STy->getElementType(); 113 IdxList.push_back(IdxList[0]); 114 } else { 115 break; 116 } 117 } 118 119 if (ElTy == DPTy->getElementType()) 120 return ConstantExpr::getGetElementPtr(V, &IdxList[0], IdxList.size()); 121 } 122 123 // Handle casts from one vector constant to another. We know that the src 124 // and dest type have the same size (otherwise its an illegal cast). 125 if (const VectorType *DestPTy = dyn_cast<VectorType>(DestTy)) { 126 if (const VectorType *SrcTy = dyn_cast<VectorType>(V->getType())) { 127 assert(DestPTy->getBitWidth() == SrcTy->getBitWidth() && 128 "Not cast between same sized vectors!"); 129 SrcTy = NULL; 130 // First, check for null. Undef is already handled. 131 if (isa<ConstantAggregateZero>(V)) 132 return Constant::getNullValue(DestTy); 133 134 if (ConstantVector *CV = dyn_cast<ConstantVector>(V)) 135 return BitCastConstantVector(CV, DestPTy); 136 } 137 138 // Canonicalize scalar-to-vector bitcasts into vector-to-vector bitcasts 139 // This allows for other simplifications (although some of them 140 // can only be handled by Analysis/ConstantFolding.cpp). 141 if (isa<ConstantInt>(V) || isa<ConstantFP>(V)) 142 return ConstantExpr::getBitCast(ConstantVector::get(&V, 1), DestPTy); 143 } 144 145 // Finally, implement bitcast folding now. The code below doesn't handle 146 // bitcast right. 147 if (isa<ConstantPointerNull>(V)) // ptr->ptr cast. 148 return ConstantPointerNull::get(cast<PointerType>(DestTy)); 149 150 // Handle integral constant input. 151 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 152 if (DestTy->isInteger()) 153 // Integral -> Integral. This is a no-op because the bit widths must 154 // be the same. Consequently, we just fold to V. 155 return V; 156 157 if (DestTy->isFloatingPoint()) 158 return ConstantFP::get(APFloat(CI->getValue(), 159 DestTy != Type::PPC_FP128Ty)); 160 161 // Otherwise, can't fold this (vector?) 162 return 0; 163 } 164 165 // Handle ConstantFP input. 166 if (const ConstantFP *FP = dyn_cast<ConstantFP>(V)) 167 // FP -> Integral. 168 return ConstantInt::get(FP->getValueAPF().bitcastToAPInt()); 169 170 return 0; 171} 172 173 174Constant *llvm::ConstantFoldCastInstruction(unsigned opc, const Constant *V, 175 const Type *DestTy) { 176 if (isa<UndefValue>(V)) { 177 // zext(undef) = 0, because the top bits will be zero. 178 // sext(undef) = 0, because the top bits will all be the same. 179 // [us]itofp(undef) = 0, because the result value is bounded. 180 if (opc == Instruction::ZExt || opc == Instruction::SExt || 181 opc == Instruction::UIToFP || opc == Instruction::SIToFP) 182 return Constant::getNullValue(DestTy); 183 return UndefValue::get(DestTy); 184 } 185 // No compile-time operations on this type yet. 186 if (V->getType() == Type::PPC_FP128Ty || DestTy == Type::PPC_FP128Ty) 187 return 0; 188 189 // If the cast operand is a constant expression, there's a few things we can 190 // do to try to simplify it. 191 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { 192 if (CE->isCast()) { 193 // Try hard to fold cast of cast because they are often eliminable. 194 if (unsigned newOpc = foldConstantCastPair(opc, CE, DestTy)) 195 return ConstantExpr::getCast(newOpc, CE->getOperand(0), DestTy); 196 } else if (CE->getOpcode() == Instruction::GetElementPtr) { 197 // If all of the indexes in the GEP are null values, there is no pointer 198 // adjustment going on. We might as well cast the source pointer. 199 bool isAllNull = true; 200 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) 201 if (!CE->getOperand(i)->isNullValue()) { 202 isAllNull = false; 203 break; 204 } 205 if (isAllNull) 206 // This is casting one pointer type to another, always BitCast 207 return ConstantExpr::getPointerCast(CE->getOperand(0), DestTy); 208 } 209 } 210 211 // We actually have to do a cast now. Perform the cast according to the 212 // opcode specified. 213 switch (opc) { 214 case Instruction::FPTrunc: 215 case Instruction::FPExt: 216 if (const ConstantFP *FPC = dyn_cast<ConstantFP>(V)) { 217 bool ignored; 218 APFloat Val = FPC->getValueAPF(); 219 Val.convert(DestTy == Type::FloatTy ? APFloat::IEEEsingle : 220 DestTy == Type::DoubleTy ? APFloat::IEEEdouble : 221 DestTy == Type::X86_FP80Ty ? APFloat::x87DoubleExtended : 222 DestTy == Type::FP128Ty ? APFloat::IEEEquad : 223 APFloat::Bogus, 224 APFloat::rmNearestTiesToEven, &ignored); 225 return ConstantFP::get(Val); 226 } 227 return 0; // Can't fold. 228 case Instruction::FPToUI: 229 case Instruction::FPToSI: 230 if (const ConstantFP *FPC = dyn_cast<ConstantFP>(V)) { 231 const APFloat &V = FPC->getValueAPF(); 232 bool ignored; 233 uint64_t x[2]; 234 uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 235 (void) V.convertToInteger(x, DestBitWidth, opc==Instruction::FPToSI, 236 APFloat::rmTowardZero, &ignored); 237 APInt Val(DestBitWidth, 2, x); 238 return ConstantInt::get(Val); 239 } 240 if (const ConstantVector *CV = dyn_cast<ConstantVector>(V)) { 241 std::vector<Constant*> res; 242 const VectorType *DestVecTy = cast<VectorType>(DestTy); 243 const Type *DstEltTy = DestVecTy->getElementType(); 244 for (unsigned i = 0, e = CV->getType()->getNumElements(); i != e; ++i) 245 res.push_back(ConstantExpr::getCast(opc, CV->getOperand(i), DstEltTy)); 246 return ConstantVector::get(DestVecTy, res); 247 } 248 return 0; // Can't fold. 249 case Instruction::IntToPtr: //always treated as unsigned 250 if (V->isNullValue()) // Is it an integral null value? 251 return ConstantPointerNull::get(cast<PointerType>(DestTy)); 252 return 0; // Other pointer types cannot be casted 253 case Instruction::PtrToInt: // always treated as unsigned 254 if (V->isNullValue()) // is it a null pointer value? 255 return ConstantInt::get(DestTy, 0); 256 return 0; // Other pointer types cannot be casted 257 case Instruction::UIToFP: 258 case Instruction::SIToFP: 259 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 260 APInt api = CI->getValue(); 261 const uint64_t zero[] = {0, 0}; 262 APFloat apf = APFloat(APInt(DestTy->getPrimitiveSizeInBits(), 263 2, zero)); 264 (void)apf.convertFromAPInt(api, 265 opc==Instruction::SIToFP, 266 APFloat::rmNearestTiesToEven); 267 return ConstantFP::get(apf); 268 } 269 if (const ConstantVector *CV = dyn_cast<ConstantVector>(V)) { 270 std::vector<Constant*> res; 271 const VectorType *DestVecTy = cast<VectorType>(DestTy); 272 const Type *DstEltTy = DestVecTy->getElementType(); 273 for (unsigned i = 0, e = CV->getType()->getNumElements(); i != e; ++i) 274 res.push_back(ConstantExpr::getCast(opc, CV->getOperand(i), DstEltTy)); 275 return ConstantVector::get(DestVecTy, res); 276 } 277 return 0; 278 case Instruction::ZExt: 279 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 280 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 281 APInt Result(CI->getValue()); 282 Result.zext(BitWidth); 283 return ConstantInt::get(Result); 284 } 285 return 0; 286 case Instruction::SExt: 287 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 288 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 289 APInt Result(CI->getValue()); 290 Result.sext(BitWidth); 291 return ConstantInt::get(Result); 292 } 293 return 0; 294 case Instruction::Trunc: 295 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 296 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 297 APInt Result(CI->getValue()); 298 Result.trunc(BitWidth); 299 return ConstantInt::get(Result); 300 } 301 return 0; 302 case Instruction::BitCast: 303 return FoldBitCast(const_cast<Constant*>(V), DestTy); 304 default: 305 assert(!"Invalid CE CastInst opcode"); 306 break; 307 } 308 309 assert(0 && "Failed to cast constant expression"); 310 return 0; 311} 312 313Constant *llvm::ConstantFoldSelectInstruction(const Constant *Cond, 314 const Constant *V1, 315 const Constant *V2) { 316 if (const ConstantInt *CB = dyn_cast<ConstantInt>(Cond)) 317 return const_cast<Constant*>(CB->getZExtValue() ? V1 : V2); 318 319 if (isa<UndefValue>(V1)) return const_cast<Constant*>(V2); 320 if (isa<UndefValue>(V2)) return const_cast<Constant*>(V1); 321 if (isa<UndefValue>(Cond)) return const_cast<Constant*>(V1); 322 if (V1 == V2) return const_cast<Constant*>(V1); 323 return 0; 324} 325 326Constant *llvm::ConstantFoldExtractElementInstruction(const Constant *Val, 327 const Constant *Idx) { 328 if (isa<UndefValue>(Val)) // ee(undef, x) -> undef 329 return UndefValue::get(cast<VectorType>(Val->getType())->getElementType()); 330 if (Val->isNullValue()) // ee(zero, x) -> zero 331 return Constant::getNullValue( 332 cast<VectorType>(Val->getType())->getElementType()); 333 334 if (const ConstantVector *CVal = dyn_cast<ConstantVector>(Val)) { 335 if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx)) { 336 return CVal->getOperand(CIdx->getZExtValue()); 337 } else if (isa<UndefValue>(Idx)) { 338 // ee({w,x,y,z}, undef) -> w (an arbitrary value). 339 return CVal->getOperand(0); 340 } 341 } 342 return 0; 343} 344 345Constant *llvm::ConstantFoldInsertElementInstruction(const Constant *Val, 346 const Constant *Elt, 347 const Constant *Idx) { 348 const ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx); 349 if (!CIdx) return 0; 350 APInt idxVal = CIdx->getValue(); 351 if (isa<UndefValue>(Val)) { 352 // Insertion of scalar constant into vector undef 353 // Optimize away insertion of undef 354 if (isa<UndefValue>(Elt)) 355 return const_cast<Constant*>(Val); 356 // Otherwise break the aggregate undef into multiple undefs and do 357 // the insertion 358 unsigned numOps = 359 cast<VectorType>(Val->getType())->getNumElements(); 360 std::vector<Constant*> Ops; 361 Ops.reserve(numOps); 362 for (unsigned i = 0; i < numOps; ++i) { 363 const Constant *Op = 364 (idxVal == i) ? Elt : UndefValue::get(Elt->getType()); 365 Ops.push_back(const_cast<Constant*>(Op)); 366 } 367 return ConstantVector::get(Ops); 368 } 369 if (isa<ConstantAggregateZero>(Val)) { 370 // Insertion of scalar constant into vector aggregate zero 371 // Optimize away insertion of zero 372 if (Elt->isNullValue()) 373 return const_cast<Constant*>(Val); 374 // Otherwise break the aggregate zero into multiple zeros and do 375 // the insertion 376 unsigned numOps = 377 cast<VectorType>(Val->getType())->getNumElements(); 378 std::vector<Constant*> Ops; 379 Ops.reserve(numOps); 380 for (unsigned i = 0; i < numOps; ++i) { 381 const Constant *Op = 382 (idxVal == i) ? Elt : Constant::getNullValue(Elt->getType()); 383 Ops.push_back(const_cast<Constant*>(Op)); 384 } 385 return ConstantVector::get(Ops); 386 } 387 if (const ConstantVector *CVal = dyn_cast<ConstantVector>(Val)) { 388 // Insertion of scalar constant into vector constant 389 std::vector<Constant*> Ops; 390 Ops.reserve(CVal->getNumOperands()); 391 for (unsigned i = 0; i < CVal->getNumOperands(); ++i) { 392 const Constant *Op = 393 (idxVal == i) ? Elt : cast<Constant>(CVal->getOperand(i)); 394 Ops.push_back(const_cast<Constant*>(Op)); 395 } 396 return ConstantVector::get(Ops); 397 } 398 399 return 0; 400} 401 402/// GetVectorElement - If C is a ConstantVector, ConstantAggregateZero or Undef 403/// return the specified element value. Otherwise return null. 404static Constant *GetVectorElement(const Constant *C, unsigned EltNo) { 405 if (const ConstantVector *CV = dyn_cast<ConstantVector>(C)) 406 return CV->getOperand(EltNo); 407 408 const Type *EltTy = cast<VectorType>(C->getType())->getElementType(); 409 if (isa<ConstantAggregateZero>(C)) 410 return Constant::getNullValue(EltTy); 411 if (isa<UndefValue>(C)) 412 return UndefValue::get(EltTy); 413 return 0; 414} 415 416Constant *llvm::ConstantFoldShuffleVectorInstruction(const Constant *V1, 417 const Constant *V2, 418 const Constant *Mask) { 419 // Undefined shuffle mask -> undefined value. 420 if (isa<UndefValue>(Mask)) return UndefValue::get(V1->getType()); 421 422 unsigned MaskNumElts = cast<VectorType>(Mask->getType())->getNumElements(); 423 unsigned SrcNumElts = cast<VectorType>(V1->getType())->getNumElements(); 424 const Type *EltTy = cast<VectorType>(V1->getType())->getElementType(); 425 426 // Loop over the shuffle mask, evaluating each element. 427 SmallVector<Constant*, 32> Result; 428 for (unsigned i = 0; i != MaskNumElts; ++i) { 429 Constant *InElt = GetVectorElement(Mask, i); 430 if (InElt == 0) return 0; 431 432 if (isa<UndefValue>(InElt)) 433 InElt = UndefValue::get(EltTy); 434 else if (ConstantInt *CI = dyn_cast<ConstantInt>(InElt)) { 435 unsigned Elt = CI->getZExtValue(); 436 if (Elt >= SrcNumElts*2) 437 InElt = UndefValue::get(EltTy); 438 else if (Elt >= SrcNumElts) 439 InElt = GetVectorElement(V2, Elt - SrcNumElts); 440 else 441 InElt = GetVectorElement(V1, Elt); 442 if (InElt == 0) return 0; 443 } else { 444 // Unknown value. 445 return 0; 446 } 447 Result.push_back(InElt); 448 } 449 450 return ConstantVector::get(&Result[0], Result.size()); 451} 452 453Constant *llvm::ConstantFoldExtractValueInstruction(const Constant *Agg, 454 const unsigned *Idxs, 455 unsigned NumIdx) { 456 // Base case: no indices, so return the entire value. 457 if (NumIdx == 0) 458 return const_cast<Constant *>(Agg); 459 460 if (isa<UndefValue>(Agg)) // ev(undef, x) -> undef 461 return UndefValue::get(ExtractValueInst::getIndexedType(Agg->getType(), 462 Idxs, 463 Idxs + NumIdx)); 464 465 if (isa<ConstantAggregateZero>(Agg)) // ev(0, x) -> 0 466 return 467 Constant::getNullValue(ExtractValueInst::getIndexedType(Agg->getType(), 468 Idxs, 469 Idxs + NumIdx)); 470 471 // Otherwise recurse. 472 return ConstantFoldExtractValueInstruction(Agg->getOperand(*Idxs), 473 Idxs+1, NumIdx-1); 474} 475 476Constant *llvm::ConstantFoldInsertValueInstruction(const Constant *Agg, 477 const Constant *Val, 478 const unsigned *Idxs, 479 unsigned NumIdx) { 480 // Base case: no indices, so replace the entire value. 481 if (NumIdx == 0) 482 return const_cast<Constant *>(Val); 483 484 if (isa<UndefValue>(Agg)) { 485 // Insertion of constant into aggregate undef 486 // Optimize away insertion of undef 487 if (isa<UndefValue>(Val)) 488 return const_cast<Constant*>(Agg); 489 // Otherwise break the aggregate undef into multiple undefs and do 490 // the insertion 491 const CompositeType *AggTy = cast<CompositeType>(Agg->getType()); 492 unsigned numOps; 493 if (const ArrayType *AR = dyn_cast<ArrayType>(AggTy)) 494 numOps = AR->getNumElements(); 495 else 496 numOps = cast<StructType>(AggTy)->getNumElements(); 497 std::vector<Constant*> Ops(numOps); 498 for (unsigned i = 0; i < numOps; ++i) { 499 const Type *MemberTy = AggTy->getTypeAtIndex(i); 500 const Constant *Op = 501 (*Idxs == i) ? 502 ConstantFoldInsertValueInstruction(UndefValue::get(MemberTy), 503 Val, Idxs+1, NumIdx-1) : 504 UndefValue::get(MemberTy); 505 Ops[i] = const_cast<Constant*>(Op); 506 } 507 if (isa<StructType>(AggTy)) 508 return ConstantStruct::get(Ops); 509 else 510 return ConstantArray::get(cast<ArrayType>(AggTy), Ops); 511 } 512 if (isa<ConstantAggregateZero>(Agg)) { 513 // Insertion of constant into aggregate zero 514 // Optimize away insertion of zero 515 if (Val->isNullValue()) 516 return const_cast<Constant*>(Agg); 517 // Otherwise break the aggregate zero into multiple zeros and do 518 // the insertion 519 const CompositeType *AggTy = cast<CompositeType>(Agg->getType()); 520 unsigned numOps; 521 if (const ArrayType *AR = dyn_cast<ArrayType>(AggTy)) 522 numOps = AR->getNumElements(); 523 else 524 numOps = cast<StructType>(AggTy)->getNumElements(); 525 std::vector<Constant*> Ops(numOps); 526 for (unsigned i = 0; i < numOps; ++i) { 527 const Type *MemberTy = AggTy->getTypeAtIndex(i); 528 const Constant *Op = 529 (*Idxs == i) ? 530 ConstantFoldInsertValueInstruction(Constant::getNullValue(MemberTy), 531 Val, Idxs+1, NumIdx-1) : 532 Constant::getNullValue(MemberTy); 533 Ops[i] = const_cast<Constant*>(Op); 534 } 535 if (isa<StructType>(AggTy)) 536 return ConstantStruct::get(Ops); 537 else 538 return ConstantArray::get(cast<ArrayType>(AggTy), Ops); 539 } 540 if (isa<ConstantStruct>(Agg) || isa<ConstantArray>(Agg)) { 541 // Insertion of constant into aggregate constant 542 std::vector<Constant*> Ops(Agg->getNumOperands()); 543 for (unsigned i = 0; i < Agg->getNumOperands(); ++i) { 544 const Constant *Op = 545 (*Idxs == i) ? 546 ConstantFoldInsertValueInstruction(Agg->getOperand(i), 547 Val, Idxs+1, NumIdx-1) : 548 Agg->getOperand(i); 549 Ops[i] = const_cast<Constant*>(Op); 550 } 551 Constant *C; 552 if (isa<StructType>(Agg->getType())) 553 C = ConstantStruct::get(Ops); 554 else 555 C = ConstantArray::get(cast<ArrayType>(Agg->getType()), Ops); 556 return C; 557 } 558 559 return 0; 560} 561 562/// EvalVectorOp - Given two vector constants and a function pointer, apply the 563/// function pointer to each element pair, producing a new ConstantVector 564/// constant. Either or both of V1 and V2 may be NULL, meaning a 565/// ConstantAggregateZero operand. 566static Constant *EvalVectorOp(const ConstantVector *V1, 567 const ConstantVector *V2, 568 const VectorType *VTy, 569 Constant *(*FP)(Constant*, Constant*)) { 570 std::vector<Constant*> Res; 571 const Type *EltTy = VTy->getElementType(); 572 for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) { 573 const Constant *C1 = V1 ? V1->getOperand(i) : Constant::getNullValue(EltTy); 574 const Constant *C2 = V2 ? V2->getOperand(i) : Constant::getNullValue(EltTy); 575 Res.push_back(FP(const_cast<Constant*>(C1), 576 const_cast<Constant*>(C2))); 577 } 578 return ConstantVector::get(Res); 579} 580 581Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, 582 const Constant *C1, 583 const Constant *C2) { 584 // No compile-time operations on this type yet. 585 if (C1->getType() == Type::PPC_FP128Ty) 586 return 0; 587 588 // Handle UndefValue up front 589 if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) { 590 switch (Opcode) { 591 case Instruction::Xor: 592 if (isa<UndefValue>(C1) && isa<UndefValue>(C2)) 593 // Handle undef ^ undef -> 0 special case. This is a common 594 // idiom (misuse). 595 return Constant::getNullValue(C1->getType()); 596 // Fallthrough 597 case Instruction::Add: 598 case Instruction::Sub: 599 return UndefValue::get(C1->getType()); 600 case Instruction::Mul: 601 case Instruction::And: 602 return Constant::getNullValue(C1->getType()); 603 case Instruction::UDiv: 604 case Instruction::SDiv: 605 case Instruction::URem: 606 case Instruction::SRem: 607 if (!isa<UndefValue>(C2)) // undef / X -> 0 608 return Constant::getNullValue(C1->getType()); 609 return const_cast<Constant*>(C2); // X / undef -> undef 610 case Instruction::Or: // X | undef -> -1 611 if (const VectorType *PTy = dyn_cast<VectorType>(C1->getType())) 612 return ConstantVector::getAllOnesValue(PTy); 613 return ConstantInt::getAllOnesValue(C1->getType()); 614 case Instruction::LShr: 615 if (isa<UndefValue>(C2) && isa<UndefValue>(C1)) 616 return const_cast<Constant*>(C1); // undef lshr undef -> undef 617 return Constant::getNullValue(C1->getType()); // X lshr undef -> 0 618 // undef lshr X -> 0 619 case Instruction::AShr: 620 if (!isa<UndefValue>(C2)) 621 return const_cast<Constant*>(C1); // undef ashr X --> undef 622 else if (isa<UndefValue>(C1)) 623 return const_cast<Constant*>(C1); // undef ashr undef -> undef 624 else 625 return const_cast<Constant*>(C1); // X ashr undef --> X 626 case Instruction::Shl: 627 // undef << X -> 0 or X << undef -> 0 628 return Constant::getNullValue(C1->getType()); 629 } 630 } 631 632 // Handle simplifications of the RHS when a constant int. 633 if (const ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) { 634 switch (Opcode) { 635 case Instruction::Add: 636 if (CI2->equalsInt(0)) return const_cast<Constant*>(C1); // X + 0 == X 637 break; 638 case Instruction::Sub: 639 if (CI2->equalsInt(0)) return const_cast<Constant*>(C1); // X - 0 == X 640 break; 641 case Instruction::Mul: 642 if (CI2->equalsInt(0)) return const_cast<Constant*>(C2); // X * 0 == 0 643 if (CI2->equalsInt(1)) 644 return const_cast<Constant*>(C1); // X * 1 == X 645 break; 646 case Instruction::UDiv: 647 case Instruction::SDiv: 648 if (CI2->equalsInt(1)) 649 return const_cast<Constant*>(C1); // X / 1 == X 650 if (CI2->equalsInt(0)) 651 return UndefValue::get(CI2->getType()); // X / 0 == undef 652 break; 653 case Instruction::URem: 654 case Instruction::SRem: 655 if (CI2->equalsInt(1)) 656 return Constant::getNullValue(CI2->getType()); // X % 1 == 0 657 if (CI2->equalsInt(0)) 658 return UndefValue::get(CI2->getType()); // X % 0 == undef 659 break; 660 case Instruction::And: 661 if (CI2->isZero()) return const_cast<Constant*>(C2); // X & 0 == 0 662 if (CI2->isAllOnesValue()) 663 return const_cast<Constant*>(C1); // X & -1 == X 664 665 if (const ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) { 666 // (zext i32 to i64) & 4294967295 -> (zext i32 to i64) 667 if (CE1->getOpcode() == Instruction::ZExt) { 668 unsigned DstWidth = CI2->getType()->getBitWidth(); 669 unsigned SrcWidth = 670 CE1->getOperand(0)->getType()->getPrimitiveSizeInBits(); 671 APInt PossiblySetBits(APInt::getLowBitsSet(DstWidth, SrcWidth)); 672 if ((PossiblySetBits & CI2->getValue()) == PossiblySetBits) 673 return const_cast<Constant*>(C1); 674 } 675 676 // If and'ing the address of a global with a constant, fold it. 677 if (CE1->getOpcode() == Instruction::PtrToInt && 678 isa<GlobalValue>(CE1->getOperand(0))) { 679 GlobalValue *GV = cast<GlobalValue>(CE1->getOperand(0)); 680 681 // Functions are at least 4-byte aligned. 682 unsigned GVAlign = GV->getAlignment(); 683 if (isa<Function>(GV)) 684 GVAlign = std::max(GVAlign, 4U); 685 686 if (GVAlign > 1) { 687 unsigned DstWidth = CI2->getType()->getBitWidth(); 688 unsigned SrcWidth = std::min(DstWidth, Log2_32(GVAlign)); 689 APInt BitsNotSet(APInt::getLowBitsSet(DstWidth, SrcWidth)); 690 691 // If checking bits we know are clear, return zero. 692 if ((CI2->getValue() & BitsNotSet) == CI2->getValue()) 693 return Constant::getNullValue(CI2->getType()); 694 } 695 } 696 } 697 break; 698 case Instruction::Or: 699 if (CI2->equalsInt(0)) return const_cast<Constant*>(C1); // X | 0 == X 700 if (CI2->isAllOnesValue()) 701 return const_cast<Constant*>(C2); // X | -1 == -1 702 break; 703 case Instruction::Xor: 704 if (CI2->equalsInt(0)) return const_cast<Constant*>(C1); // X ^ 0 == X 705 break; 706 case Instruction::AShr: 707 // ashr (zext C to Ty), C2 -> lshr (zext C, CSA), C2 708 if (const ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) 709 if (CE1->getOpcode() == Instruction::ZExt) // Top bits known zero. 710 return ConstantExpr::getLShr(const_cast<Constant*>(C1), 711 const_cast<Constant*>(C2)); 712 break; 713 } 714 } 715 716 // At this point we know neither constant is an UndefValue. 717 if (const ConstantInt *CI1 = dyn_cast<ConstantInt>(C1)) { 718 if (const ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) { 719 using namespace APIntOps; 720 const APInt &C1V = CI1->getValue(); 721 const APInt &C2V = CI2->getValue(); 722 switch (Opcode) { 723 default: 724 break; 725 case Instruction::Add: 726 return ConstantInt::get(C1V + C2V); 727 case Instruction::Sub: 728 return ConstantInt::get(C1V - C2V); 729 case Instruction::Mul: 730 return ConstantInt::get(C1V * C2V); 731 case Instruction::UDiv: 732 assert(!CI2->isNullValue() && "Div by zero handled above"); 733 return ConstantInt::get(C1V.udiv(C2V)); 734 case Instruction::SDiv: 735 assert(!CI2->isNullValue() && "Div by zero handled above"); 736 if (C2V.isAllOnesValue() && C1V.isMinSignedValue()) 737 return UndefValue::get(CI1->getType()); // MIN_INT / -1 -> undef 738 return ConstantInt::get(C1V.sdiv(C2V)); 739 case Instruction::URem: 740 assert(!CI2->isNullValue() && "Div by zero handled above"); 741 return ConstantInt::get(C1V.urem(C2V)); 742 case Instruction::SRem: 743 assert(!CI2->isNullValue() && "Div by zero handled above"); 744 if (C2V.isAllOnesValue() && C1V.isMinSignedValue()) 745 return UndefValue::get(CI1->getType()); // MIN_INT % -1 -> undef 746 return ConstantInt::get(C1V.srem(C2V)); 747 case Instruction::And: 748 return ConstantInt::get(C1V & C2V); 749 case Instruction::Or: 750 return ConstantInt::get(C1V | C2V); 751 case Instruction::Xor: 752 return ConstantInt::get(C1V ^ C2V); 753 case Instruction::Shl: { 754 uint32_t shiftAmt = C2V.getZExtValue(); 755 if (shiftAmt < C1V.getBitWidth()) 756 return ConstantInt::get(C1V.shl(shiftAmt)); 757 else 758 return UndefValue::get(C1->getType()); // too big shift is undef 759 } 760 case Instruction::LShr: { 761 uint32_t shiftAmt = C2V.getZExtValue(); 762 if (shiftAmt < C1V.getBitWidth()) 763 return ConstantInt::get(C1V.lshr(shiftAmt)); 764 else 765 return UndefValue::get(C1->getType()); // too big shift is undef 766 } 767 case Instruction::AShr: { 768 uint32_t shiftAmt = C2V.getZExtValue(); 769 if (shiftAmt < C1V.getBitWidth()) 770 return ConstantInt::get(C1V.ashr(shiftAmt)); 771 else 772 return UndefValue::get(C1->getType()); // too big shift is undef 773 } 774 } 775 } 776 } else if (const ConstantFP *CFP1 = dyn_cast<ConstantFP>(C1)) { 777 if (const ConstantFP *CFP2 = dyn_cast<ConstantFP>(C2)) { 778 APFloat C1V = CFP1->getValueAPF(); 779 APFloat C2V = CFP2->getValueAPF(); 780 APFloat C3V = C1V; // copy for modification 781 switch (Opcode) { 782 default: 783 break; 784 case Instruction::FAdd: 785 (void)C3V.add(C2V, APFloat::rmNearestTiesToEven); 786 return ConstantFP::get(C3V); 787 case Instruction::FSub: 788 (void)C3V.subtract(C2V, APFloat::rmNearestTiesToEven); 789 return ConstantFP::get(C3V); 790 case Instruction::FMul: 791 (void)C3V.multiply(C2V, APFloat::rmNearestTiesToEven); 792 return ConstantFP::get(C3V); 793 case Instruction::FDiv: 794 (void)C3V.divide(C2V, APFloat::rmNearestTiesToEven); 795 return ConstantFP::get(C3V); 796 case Instruction::FRem: 797 (void)C3V.mod(C2V, APFloat::rmNearestTiesToEven); 798 return ConstantFP::get(C3V); 799 } 800 } 801 } else if (const VectorType *VTy = dyn_cast<VectorType>(C1->getType())) { 802 const ConstantVector *CP1 = dyn_cast<ConstantVector>(C1); 803 const ConstantVector *CP2 = dyn_cast<ConstantVector>(C2); 804 if ((CP1 != NULL || isa<ConstantAggregateZero>(C1)) && 805 (CP2 != NULL || isa<ConstantAggregateZero>(C2))) { 806 switch (Opcode) { 807 default: 808 break; 809 case Instruction::Add: 810 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getAdd); 811 case Instruction::FAdd: 812 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getFAdd); 813 case Instruction::Sub: 814 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getSub); 815 case Instruction::FSub: 816 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getFSub); 817 case Instruction::Mul: 818 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getMul); 819 case Instruction::FMul: 820 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getFMul); 821 case Instruction::UDiv: 822 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getUDiv); 823 case Instruction::SDiv: 824 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getSDiv); 825 case Instruction::FDiv: 826 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getFDiv); 827 case Instruction::URem: 828 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getURem); 829 case Instruction::SRem: 830 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getSRem); 831 case Instruction::FRem: 832 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getFRem); 833 case Instruction::And: 834 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getAnd); 835 case Instruction::Or: 836 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getOr); 837 case Instruction::Xor: 838 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getXor); 839 case Instruction::LShr: 840 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getLShr); 841 case Instruction::AShr: 842 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getAShr); 843 case Instruction::Shl: 844 return EvalVectorOp(CP1, CP2, VTy, ConstantExpr::getShl); 845 } 846 } 847 } 848 849 if (isa<ConstantExpr>(C1)) { 850 // There are many possible foldings we could do here. We should probably 851 // at least fold add of a pointer with an integer into the appropriate 852 // getelementptr. This will improve alias analysis a bit. 853 } else if (isa<ConstantExpr>(C2)) { 854 // If C2 is a constant expr and C1 isn't, flop them around and fold the 855 // other way if possible. 856 switch (Opcode) { 857 case Instruction::Add: 858 case Instruction::FAdd: 859 case Instruction::Mul: 860 case Instruction::FMul: 861 case Instruction::And: 862 case Instruction::Or: 863 case Instruction::Xor: 864 // No change of opcode required. 865 return ConstantFoldBinaryInstruction(Opcode, C2, C1); 866 867 case Instruction::Shl: 868 case Instruction::LShr: 869 case Instruction::AShr: 870 case Instruction::Sub: 871 case Instruction::FSub: 872 case Instruction::SDiv: 873 case Instruction::UDiv: 874 case Instruction::FDiv: 875 case Instruction::URem: 876 case Instruction::SRem: 877 case Instruction::FRem: 878 default: // These instructions cannot be flopped around. 879 break; 880 } 881 } 882 883 // We don't know how to fold this. 884 return 0; 885} 886 887/// isZeroSizedType - This type is zero sized if its an array or structure of 888/// zero sized types. The only leaf zero sized type is an empty structure. 889static bool isMaybeZeroSizedType(const Type *Ty) { 890 if (isa<OpaqueType>(Ty)) return true; // Can't say. 891 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 892 893 // If all of elements have zero size, this does too. 894 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 895 if (!isMaybeZeroSizedType(STy->getElementType(i))) return false; 896 return true; 897 898 } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 899 return isMaybeZeroSizedType(ATy->getElementType()); 900 } 901 return false; 902} 903 904/// IdxCompare - Compare the two constants as though they were getelementptr 905/// indices. This allows coersion of the types to be the same thing. 906/// 907/// If the two constants are the "same" (after coersion), return 0. If the 908/// first is less than the second, return -1, if the second is less than the 909/// first, return 1. If the constants are not integral, return -2. 910/// 911static int IdxCompare(Constant *C1, Constant *C2, const Type *ElTy) { 912 if (C1 == C2) return 0; 913 914 // Ok, we found a different index. If they are not ConstantInt, we can't do 915 // anything with them. 916 if (!isa<ConstantInt>(C1) || !isa<ConstantInt>(C2)) 917 return -2; // don't know! 918 919 // Ok, we have two differing integer indices. Sign extend them to be the same 920 // type. Long is always big enough, so we use it. 921 if (C1->getType() != Type::Int64Ty) 922 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty); 923 924 if (C2->getType() != Type::Int64Ty) 925 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty); 926 927 if (C1 == C2) return 0; // They are equal 928 929 // If the type being indexed over is really just a zero sized type, there is 930 // no pointer difference being made here. 931 if (isMaybeZeroSizedType(ElTy)) 932 return -2; // dunno. 933 934 // If they are really different, now that they are the same type, then we 935 // found a difference! 936 if (cast<ConstantInt>(C1)->getSExtValue() < 937 cast<ConstantInt>(C2)->getSExtValue()) 938 return -1; 939 else 940 return 1; 941} 942 943/// evaluateFCmpRelation - This function determines if there is anything we can 944/// decide about the two constants provided. This doesn't need to handle simple 945/// things like ConstantFP comparisons, but should instead handle ConstantExprs. 946/// If we can determine that the two constants have a particular relation to 947/// each other, we should return the corresponding FCmpInst predicate, 948/// otherwise return FCmpInst::BAD_FCMP_PREDICATE. This is used below in 949/// ConstantFoldCompareInstruction. 950/// 951/// To simplify this code we canonicalize the relation so that the first 952/// operand is always the most "complex" of the two. We consider ConstantFP 953/// to be the simplest, and ConstantExprs to be the most complex. 954static FCmpInst::Predicate evaluateFCmpRelation(const Constant *V1, 955 const Constant *V2) { 956 assert(V1->getType() == V2->getType() && 957 "Cannot compare values of different types!"); 958 959 // No compile-time operations on this type yet. 960 if (V1->getType() == Type::PPC_FP128Ty) 961 return FCmpInst::BAD_FCMP_PREDICATE; 962 963 // Handle degenerate case quickly 964 if (V1 == V2) return FCmpInst::FCMP_OEQ; 965 966 if (!isa<ConstantExpr>(V1)) { 967 if (!isa<ConstantExpr>(V2)) { 968 // We distilled thisUse the standard constant folder for a few cases 969 ConstantInt *R = 0; 970 Constant *C1 = const_cast<Constant*>(V1); 971 Constant *C2 = const_cast<Constant*>(V2); 972 R = dyn_cast<ConstantInt>( 973 ConstantExpr::getFCmp(FCmpInst::FCMP_OEQ, C1, C2)); 974 if (R && !R->isZero()) 975 return FCmpInst::FCMP_OEQ; 976 R = dyn_cast<ConstantInt>( 977 ConstantExpr::getFCmp(FCmpInst::FCMP_OLT, C1, C2)); 978 if (R && !R->isZero()) 979 return FCmpInst::FCMP_OLT; 980 R = dyn_cast<ConstantInt>( 981 ConstantExpr::getFCmp(FCmpInst::FCMP_OGT, C1, C2)); 982 if (R && !R->isZero()) 983 return FCmpInst::FCMP_OGT; 984 985 // Nothing more we can do 986 return FCmpInst::BAD_FCMP_PREDICATE; 987 } 988 989 // If the first operand is simple and second is ConstantExpr, swap operands. 990 FCmpInst::Predicate SwappedRelation = evaluateFCmpRelation(V2, V1); 991 if (SwappedRelation != FCmpInst::BAD_FCMP_PREDICATE) 992 return FCmpInst::getSwappedPredicate(SwappedRelation); 993 } else { 994 // Ok, the LHS is known to be a constantexpr. The RHS can be any of a 995 // constantexpr or a simple constant. 996 const ConstantExpr *CE1 = cast<ConstantExpr>(V1); 997 switch (CE1->getOpcode()) { 998 case Instruction::FPTrunc: 999 case Instruction::FPExt: 1000 case Instruction::UIToFP: 1001 case Instruction::SIToFP: 1002 // We might be able to do something with these but we don't right now. 1003 break; 1004 default: 1005 break; 1006 } 1007 } 1008 // There are MANY other foldings that we could perform here. They will 1009 // probably be added on demand, as they seem needed. 1010 return FCmpInst::BAD_FCMP_PREDICATE; 1011} 1012 1013/// evaluateICmpRelation - This function determines if there is anything we can 1014/// decide about the two constants provided. This doesn't need to handle simple 1015/// things like integer comparisons, but should instead handle ConstantExprs 1016/// and GlobalValues. If we can determine that the two constants have a 1017/// particular relation to each other, we should return the corresponding ICmp 1018/// predicate, otherwise return ICmpInst::BAD_ICMP_PREDICATE. 1019/// 1020/// To simplify this code we canonicalize the relation so that the first 1021/// operand is always the most "complex" of the two. We consider simple 1022/// constants (like ConstantInt) to be the simplest, followed by 1023/// GlobalValues, followed by ConstantExpr's (the most complex). 1024/// 1025static ICmpInst::Predicate evaluateICmpRelation(const Constant *V1, 1026 const Constant *V2, 1027 bool isSigned) { 1028 assert(V1->getType() == V2->getType() && 1029 "Cannot compare different types of values!"); 1030 if (V1 == V2) return ICmpInst::ICMP_EQ; 1031 1032 if (!isa<ConstantExpr>(V1) && !isa<GlobalValue>(V1)) { 1033 if (!isa<GlobalValue>(V2) && !isa<ConstantExpr>(V2)) { 1034 // We distilled this down to a simple case, use the standard constant 1035 // folder. 1036 ConstantInt *R = 0; 1037 Constant *C1 = const_cast<Constant*>(V1); 1038 Constant *C2 = const_cast<Constant*>(V2); 1039 ICmpInst::Predicate pred = ICmpInst::ICMP_EQ; 1040 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 1041 if (R && !R->isZero()) 1042 return pred; 1043 pred = isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 1044 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 1045 if (R && !R->isZero()) 1046 return pred; 1047 pred = isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1048 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 1049 if (R && !R->isZero()) 1050 return pred; 1051 1052 // If we couldn't figure it out, bail. 1053 return ICmpInst::BAD_ICMP_PREDICATE; 1054 } 1055 1056 // If the first operand is simple, swap operands. 1057 ICmpInst::Predicate SwappedRelation = 1058 evaluateICmpRelation(V2, V1, isSigned); 1059 if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE) 1060 return ICmpInst::getSwappedPredicate(SwappedRelation); 1061 1062 } else if (const GlobalValue *CPR1 = dyn_cast<GlobalValue>(V1)) { 1063 if (isa<ConstantExpr>(V2)) { // Swap as necessary. 1064 ICmpInst::Predicate SwappedRelation = 1065 evaluateICmpRelation(V2, V1, isSigned); 1066 if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE) 1067 return ICmpInst::getSwappedPredicate(SwappedRelation); 1068 else 1069 return ICmpInst::BAD_ICMP_PREDICATE; 1070 } 1071 1072 // Now we know that the RHS is a GlobalValue or simple constant, 1073 // which (since the types must match) means that it's a ConstantPointerNull. 1074 if (const GlobalValue *CPR2 = dyn_cast<GlobalValue>(V2)) { 1075 // Don't try to decide equality of aliases. 1076 if (!isa<GlobalAlias>(CPR1) && !isa<GlobalAlias>(CPR2)) 1077 if (!CPR1->hasExternalWeakLinkage() || !CPR2->hasExternalWeakLinkage()) 1078 return ICmpInst::ICMP_NE; 1079 } else { 1080 assert(isa<ConstantPointerNull>(V2) && "Canonicalization guarantee!"); 1081 // GlobalVals can never be null. Don't try to evaluate aliases. 1082 if (!CPR1->hasExternalWeakLinkage() && !isa<GlobalAlias>(CPR1)) 1083 return ICmpInst::ICMP_NE; 1084 } 1085 } else { 1086 // Ok, the LHS is known to be a constantexpr. The RHS can be any of a 1087 // constantexpr, a CPR, or a simple constant. 1088 const ConstantExpr *CE1 = cast<ConstantExpr>(V1); 1089 const Constant *CE1Op0 = CE1->getOperand(0); 1090 1091 switch (CE1->getOpcode()) { 1092 case Instruction::Trunc: 1093 case Instruction::FPTrunc: 1094 case Instruction::FPExt: 1095 case Instruction::FPToUI: 1096 case Instruction::FPToSI: 1097 break; // We can't evaluate floating point casts or truncations. 1098 1099 case Instruction::UIToFP: 1100 case Instruction::SIToFP: 1101 case Instruction::BitCast: 1102 case Instruction::ZExt: 1103 case Instruction::SExt: 1104 // If the cast is not actually changing bits, and the second operand is a 1105 // null pointer, do the comparison with the pre-casted value. 1106 if (V2->isNullValue() && 1107 (isa<PointerType>(CE1->getType()) || CE1->getType()->isInteger())) { 1108 bool sgnd = isSigned; 1109 if (CE1->getOpcode() == Instruction::ZExt) isSigned = false; 1110 if (CE1->getOpcode() == Instruction::SExt) isSigned = true; 1111 return evaluateICmpRelation(CE1Op0, 1112 Constant::getNullValue(CE1Op0->getType()), 1113 sgnd); 1114 } 1115 1116 // If the dest type is a pointer type, and the RHS is a constantexpr cast 1117 // from the same type as the src of the LHS, evaluate the inputs. This is 1118 // important for things like "icmp eq (cast 4 to int*), (cast 5 to int*)", 1119 // which happens a lot in compilers with tagged integers. 1120 if (const ConstantExpr *CE2 = dyn_cast<ConstantExpr>(V2)) 1121 if (CE2->isCast() && isa<PointerType>(CE1->getType()) && 1122 CE1->getOperand(0)->getType() == CE2->getOperand(0)->getType() && 1123 CE1->getOperand(0)->getType()->isInteger()) { 1124 bool sgnd = isSigned; 1125 if (CE1->getOpcode() == Instruction::ZExt) isSigned = false; 1126 if (CE1->getOpcode() == Instruction::SExt) isSigned = true; 1127 return evaluateICmpRelation(CE1->getOperand(0), CE2->getOperand(0), 1128 sgnd); 1129 } 1130 break; 1131 1132 case Instruction::GetElementPtr: 1133 // Ok, since this is a getelementptr, we know that the constant has a 1134 // pointer type. Check the various cases. 1135 if (isa<ConstantPointerNull>(V2)) { 1136 // If we are comparing a GEP to a null pointer, check to see if the base 1137 // of the GEP equals the null pointer. 1138 if (const GlobalValue *GV = dyn_cast<GlobalValue>(CE1Op0)) { 1139 if (GV->hasExternalWeakLinkage()) 1140 // Weak linkage GVals could be zero or not. We're comparing that 1141 // to null pointer so its greater-or-equal 1142 return isSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; 1143 else 1144 // If its not weak linkage, the GVal must have a non-zero address 1145 // so the result is greater-than 1146 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1147 } else if (isa<ConstantPointerNull>(CE1Op0)) { 1148 // If we are indexing from a null pointer, check to see if we have any 1149 // non-zero indices. 1150 for (unsigned i = 1, e = CE1->getNumOperands(); i != e; ++i) 1151 if (!CE1->getOperand(i)->isNullValue()) 1152 // Offsetting from null, must not be equal. 1153 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1154 // Only zero indexes from null, must still be zero. 1155 return ICmpInst::ICMP_EQ; 1156 } 1157 // Otherwise, we can't really say if the first operand is null or not. 1158 } else if (const GlobalValue *CPR2 = dyn_cast<GlobalValue>(V2)) { 1159 if (isa<ConstantPointerNull>(CE1Op0)) { 1160 if (CPR2->hasExternalWeakLinkage()) 1161 // Weak linkage GVals could be zero or not. We're comparing it to 1162 // a null pointer, so its less-or-equal 1163 return isSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; 1164 else 1165 // If its not weak linkage, the GVal must have a non-zero address 1166 // so the result is less-than 1167 return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 1168 } else if (const GlobalValue *CPR1 = dyn_cast<GlobalValue>(CE1Op0)) { 1169 if (CPR1 == CPR2) { 1170 // If this is a getelementptr of the same global, then it must be 1171 // different. Because the types must match, the getelementptr could 1172 // only have at most one index, and because we fold getelementptr's 1173 // with a single zero index, it must be nonzero. 1174 assert(CE1->getNumOperands() == 2 && 1175 !CE1->getOperand(1)->isNullValue() && 1176 "Suprising getelementptr!"); 1177 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1178 } else { 1179 // If they are different globals, we don't know what the value is, 1180 // but they can't be equal. 1181 return ICmpInst::ICMP_NE; 1182 } 1183 } 1184 } else { 1185 const ConstantExpr *CE2 = cast<ConstantExpr>(V2); 1186 const Constant *CE2Op0 = CE2->getOperand(0); 1187 1188 // There are MANY other foldings that we could perform here. They will 1189 // probably be added on demand, as they seem needed. 1190 switch (CE2->getOpcode()) { 1191 default: break; 1192 case Instruction::GetElementPtr: 1193 // By far the most common case to handle is when the base pointers are 1194 // obviously to the same or different globals. 1195 if (isa<GlobalValue>(CE1Op0) && isa<GlobalValue>(CE2Op0)) { 1196 if (CE1Op0 != CE2Op0) // Don't know relative ordering, but not equal 1197 return ICmpInst::ICMP_NE; 1198 // Ok, we know that both getelementptr instructions are based on the 1199 // same global. From this, we can precisely determine the relative 1200 // ordering of the resultant pointers. 1201 unsigned i = 1; 1202 1203 // Compare all of the operands the GEP's have in common. 1204 gep_type_iterator GTI = gep_type_begin(CE1); 1205 for (;i != CE1->getNumOperands() && i != CE2->getNumOperands(); 1206 ++i, ++GTI) 1207 switch (IdxCompare(CE1->getOperand(i), CE2->getOperand(i), 1208 GTI.getIndexedType())) { 1209 case -1: return isSigned ? ICmpInst::ICMP_SLT:ICmpInst::ICMP_ULT; 1210 case 1: return isSigned ? ICmpInst::ICMP_SGT:ICmpInst::ICMP_UGT; 1211 case -2: return ICmpInst::BAD_ICMP_PREDICATE; 1212 } 1213 1214 // Ok, we ran out of things they have in common. If any leftovers 1215 // are non-zero then we have a difference, otherwise we are equal. 1216 for (; i < CE1->getNumOperands(); ++i) 1217 if (!CE1->getOperand(i)->isNullValue()) { 1218 if (isa<ConstantInt>(CE1->getOperand(i))) 1219 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1220 else 1221 return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal. 1222 } 1223 1224 for (; i < CE2->getNumOperands(); ++i) 1225 if (!CE2->getOperand(i)->isNullValue()) { 1226 if (isa<ConstantInt>(CE2->getOperand(i))) 1227 return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 1228 else 1229 return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal. 1230 } 1231 return ICmpInst::ICMP_EQ; 1232 } 1233 } 1234 } 1235 default: 1236 break; 1237 } 1238 } 1239 1240 return ICmpInst::BAD_ICMP_PREDICATE; 1241} 1242 1243Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred, 1244 const Constant *C1, 1245 const Constant *C2) { 1246 // Fold FCMP_FALSE/FCMP_TRUE unconditionally. 1247 if (pred == FCmpInst::FCMP_FALSE) { 1248 if (const VectorType *VT = dyn_cast<VectorType>(C1->getType())) 1249 return Constant::getNullValue(VectorType::getInteger(VT)); 1250 else 1251 return ConstantInt::getFalse(); 1252 } 1253 1254 if (pred == FCmpInst::FCMP_TRUE) { 1255 if (const VectorType *VT = dyn_cast<VectorType>(C1->getType())) 1256 return Constant::getAllOnesValue(VectorType::getInteger(VT)); 1257 else 1258 return ConstantInt::getTrue(); 1259 } 1260 1261 // Handle some degenerate cases first 1262 if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) { 1263 // vicmp/vfcmp -> [vector] undef 1264 if (const VectorType *VTy = dyn_cast<VectorType>(C1->getType())) 1265 return UndefValue::get(VectorType::getInteger(VTy)); 1266 1267 // icmp/fcmp -> i1 undef 1268 return UndefValue::get(Type::Int1Ty); 1269 } 1270 1271 // No compile-time operations on this type yet. 1272 if (C1->getType() == Type::PPC_FP128Ty) 1273 return 0; 1274 1275 // icmp eq/ne(null,GV) -> false/true 1276 if (C1->isNullValue()) { 1277 if (const GlobalValue *GV = dyn_cast<GlobalValue>(C2)) 1278 // Don't try to evaluate aliases. External weak GV can be null. 1279 if (!isa<GlobalAlias>(GV) && !GV->hasExternalWeakLinkage()) { 1280 if (pred == ICmpInst::ICMP_EQ) 1281 return ConstantInt::getFalse(); 1282 else if (pred == ICmpInst::ICMP_NE) 1283 return ConstantInt::getTrue(); 1284 } 1285 // icmp eq/ne(GV,null) -> false/true 1286 } else if (C2->isNullValue()) { 1287 if (const GlobalValue *GV = dyn_cast<GlobalValue>(C1)) 1288 // Don't try to evaluate aliases. External weak GV can be null. 1289 if (!isa<GlobalAlias>(GV) && !GV->hasExternalWeakLinkage()) { 1290 if (pred == ICmpInst::ICMP_EQ) 1291 return ConstantInt::getFalse(); 1292 else if (pred == ICmpInst::ICMP_NE) 1293 return ConstantInt::getTrue(); 1294 } 1295 } 1296 1297 if (isa<ConstantInt>(C1) && isa<ConstantInt>(C2)) { 1298 APInt V1 = cast<ConstantInt>(C1)->getValue(); 1299 APInt V2 = cast<ConstantInt>(C2)->getValue(); 1300 switch (pred) { 1301 default: assert(0 && "Invalid ICmp Predicate"); return 0; 1302 case ICmpInst::ICMP_EQ: return ConstantInt::get(Type::Int1Ty, V1 == V2); 1303 case ICmpInst::ICMP_NE: return ConstantInt::get(Type::Int1Ty, V1 != V2); 1304 case ICmpInst::ICMP_SLT:return ConstantInt::get(Type::Int1Ty, V1.slt(V2)); 1305 case ICmpInst::ICMP_SGT:return ConstantInt::get(Type::Int1Ty, V1.sgt(V2)); 1306 case ICmpInst::ICMP_SLE:return ConstantInt::get(Type::Int1Ty, V1.sle(V2)); 1307 case ICmpInst::ICMP_SGE:return ConstantInt::get(Type::Int1Ty, V1.sge(V2)); 1308 case ICmpInst::ICMP_ULT:return ConstantInt::get(Type::Int1Ty, V1.ult(V2)); 1309 case ICmpInst::ICMP_UGT:return ConstantInt::get(Type::Int1Ty, V1.ugt(V2)); 1310 case ICmpInst::ICMP_ULE:return ConstantInt::get(Type::Int1Ty, V1.ule(V2)); 1311 case ICmpInst::ICMP_UGE:return ConstantInt::get(Type::Int1Ty, V1.uge(V2)); 1312 } 1313 } else if (isa<ConstantFP>(C1) && isa<ConstantFP>(C2)) { 1314 APFloat C1V = cast<ConstantFP>(C1)->getValueAPF(); 1315 APFloat C2V = cast<ConstantFP>(C2)->getValueAPF(); 1316 APFloat::cmpResult R = C1V.compare(C2V); 1317 switch (pred) { 1318 default: assert(0 && "Invalid FCmp Predicate"); return 0; 1319 case FCmpInst::FCMP_FALSE: return ConstantInt::getFalse(); 1320 case FCmpInst::FCMP_TRUE: return ConstantInt::getTrue(); 1321 case FCmpInst::FCMP_UNO: 1322 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpUnordered); 1323 case FCmpInst::FCMP_ORD: 1324 return ConstantInt::get(Type::Int1Ty, R!=APFloat::cmpUnordered); 1325 case FCmpInst::FCMP_UEQ: 1326 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpUnordered || 1327 R==APFloat::cmpEqual); 1328 case FCmpInst::FCMP_OEQ: 1329 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpEqual); 1330 case FCmpInst::FCMP_UNE: 1331 return ConstantInt::get(Type::Int1Ty, R!=APFloat::cmpEqual); 1332 case FCmpInst::FCMP_ONE: 1333 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpLessThan || 1334 R==APFloat::cmpGreaterThan); 1335 case FCmpInst::FCMP_ULT: 1336 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpUnordered || 1337 R==APFloat::cmpLessThan); 1338 case FCmpInst::FCMP_OLT: 1339 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpLessThan); 1340 case FCmpInst::FCMP_UGT: 1341 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpUnordered || 1342 R==APFloat::cmpGreaterThan); 1343 case FCmpInst::FCMP_OGT: 1344 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpGreaterThan); 1345 case FCmpInst::FCMP_ULE: 1346 return ConstantInt::get(Type::Int1Ty, R!=APFloat::cmpGreaterThan); 1347 case FCmpInst::FCMP_OLE: 1348 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpLessThan || 1349 R==APFloat::cmpEqual); 1350 case FCmpInst::FCMP_UGE: 1351 return ConstantInt::get(Type::Int1Ty, R!=APFloat::cmpLessThan); 1352 case FCmpInst::FCMP_OGE: 1353 return ConstantInt::get(Type::Int1Ty, R==APFloat::cmpGreaterThan || 1354 R==APFloat::cmpEqual); 1355 } 1356 } else if (isa<VectorType>(C1->getType())) { 1357 SmallVector<Constant*, 16> C1Elts, C2Elts; 1358 C1->getVectorElements(C1Elts); 1359 C2->getVectorElements(C2Elts); 1360 1361 // If we can constant fold the comparison of each element, constant fold 1362 // the whole vector comparison. 1363 SmallVector<Constant*, 4> ResElts; 1364 const Type *InEltTy = C1Elts[0]->getType(); 1365 bool isFP = InEltTy->isFloatingPoint(); 1366 const Type *ResEltTy = InEltTy; 1367 if (isFP) 1368 ResEltTy = IntegerType::get(InEltTy->getPrimitiveSizeInBits()); 1369 1370 for (unsigned i = 0, e = C1Elts.size(); i != e; ++i) { 1371 // Compare the elements, producing an i1 result or constant expr. 1372 Constant *C; 1373 if (isFP) 1374 C = ConstantExpr::getFCmp(pred, C1Elts[i], C2Elts[i]); 1375 else 1376 C = ConstantExpr::getICmp(pred, C1Elts[i], C2Elts[i]); 1377 1378 // If it is a bool or undef result, convert to the dest type. 1379 if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) { 1380 if (CI->isZero()) 1381 ResElts.push_back(Constant::getNullValue(ResEltTy)); 1382 else 1383 ResElts.push_back(Constant::getAllOnesValue(ResEltTy)); 1384 } else if (isa<UndefValue>(C)) { 1385 ResElts.push_back(UndefValue::get(ResEltTy)); 1386 } else { 1387 break; 1388 } 1389 } 1390 1391 if (ResElts.size() == C1Elts.size()) 1392 return ConstantVector::get(&ResElts[0], ResElts.size()); 1393 } 1394 1395 if (C1->getType()->isFloatingPoint()) { 1396 int Result = -1; // -1 = unknown, 0 = known false, 1 = known true. 1397 switch (evaluateFCmpRelation(C1, C2)) { 1398 default: assert(0 && "Unknown relation!"); 1399 case FCmpInst::FCMP_UNO: 1400 case FCmpInst::FCMP_ORD: 1401 case FCmpInst::FCMP_UEQ: 1402 case FCmpInst::FCMP_UNE: 1403 case FCmpInst::FCMP_ULT: 1404 case FCmpInst::FCMP_UGT: 1405 case FCmpInst::FCMP_ULE: 1406 case FCmpInst::FCMP_UGE: 1407 case FCmpInst::FCMP_TRUE: 1408 case FCmpInst::FCMP_FALSE: 1409 case FCmpInst::BAD_FCMP_PREDICATE: 1410 break; // Couldn't determine anything about these constants. 1411 case FCmpInst::FCMP_OEQ: // We know that C1 == C2 1412 Result = (pred == FCmpInst::FCMP_UEQ || pred == FCmpInst::FCMP_OEQ || 1413 pred == FCmpInst::FCMP_ULE || pred == FCmpInst::FCMP_OLE || 1414 pred == FCmpInst::FCMP_UGE || pred == FCmpInst::FCMP_OGE); 1415 break; 1416 case FCmpInst::FCMP_OLT: // We know that C1 < C2 1417 Result = (pred == FCmpInst::FCMP_UNE || pred == FCmpInst::FCMP_ONE || 1418 pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT || 1419 pred == FCmpInst::FCMP_ULE || pred == FCmpInst::FCMP_OLE); 1420 break; 1421 case FCmpInst::FCMP_OGT: // We know that C1 > C2 1422 Result = (pred == FCmpInst::FCMP_UNE || pred == FCmpInst::FCMP_ONE || 1423 pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT || 1424 pred == FCmpInst::FCMP_UGE || pred == FCmpInst::FCMP_OGE); 1425 break; 1426 case FCmpInst::FCMP_OLE: // We know that C1 <= C2 1427 // We can only partially decide this relation. 1428 if (pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT) 1429 Result = 0; 1430 else if (pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT) 1431 Result = 1; 1432 break; 1433 case FCmpInst::FCMP_OGE: // We known that C1 >= C2 1434 // We can only partially decide this relation. 1435 if (pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT) 1436 Result = 0; 1437 else if (pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT) 1438 Result = 1; 1439 break; 1440 case ICmpInst::ICMP_NE: // We know that C1 != C2 1441 // We can only partially decide this relation. 1442 if (pred == FCmpInst::FCMP_OEQ || pred == FCmpInst::FCMP_UEQ) 1443 Result = 0; 1444 else if (pred == FCmpInst::FCMP_ONE || pred == FCmpInst::FCMP_UNE) 1445 Result = 1; 1446 break; 1447 } 1448 1449 // If we evaluated the result, return it now. 1450 if (Result != -1) { 1451 if (const VectorType *VT = dyn_cast<VectorType>(C1->getType())) { 1452 if (Result == 0) 1453 return Constant::getNullValue(VectorType::getInteger(VT)); 1454 else 1455 return Constant::getAllOnesValue(VectorType::getInteger(VT)); 1456 } 1457 return ConstantInt::get(Type::Int1Ty, Result); 1458 } 1459 1460 } else { 1461 // Evaluate the relation between the two constants, per the predicate. 1462 int Result = -1; // -1 = unknown, 0 = known false, 1 = known true. 1463 switch (evaluateICmpRelation(C1, C2, CmpInst::isSigned(pred))) { 1464 default: assert(0 && "Unknown relational!"); 1465 case ICmpInst::BAD_ICMP_PREDICATE: 1466 break; // Couldn't determine anything about these constants. 1467 case ICmpInst::ICMP_EQ: // We know the constants are equal! 1468 // If we know the constants are equal, we can decide the result of this 1469 // computation precisely. 1470 Result = (pred == ICmpInst::ICMP_EQ || 1471 pred == ICmpInst::ICMP_ULE || 1472 pred == ICmpInst::ICMP_SLE || 1473 pred == ICmpInst::ICMP_UGE || 1474 pred == ICmpInst::ICMP_SGE); 1475 break; 1476 case ICmpInst::ICMP_ULT: 1477 // If we know that C1 < C2, we can decide the result of this computation 1478 // precisely. 1479 Result = (pred == ICmpInst::ICMP_ULT || 1480 pred == ICmpInst::ICMP_NE || 1481 pred == ICmpInst::ICMP_ULE); 1482 break; 1483 case ICmpInst::ICMP_SLT: 1484 // If we know that C1 < C2, we can decide the result of this computation 1485 // precisely. 1486 Result = (pred == ICmpInst::ICMP_SLT || 1487 pred == ICmpInst::ICMP_NE || 1488 pred == ICmpInst::ICMP_SLE); 1489 break; 1490 case ICmpInst::ICMP_UGT: 1491 // If we know that C1 > C2, we can decide the result of this computation 1492 // precisely. 1493 Result = (pred == ICmpInst::ICMP_UGT || 1494 pred == ICmpInst::ICMP_NE || 1495 pred == ICmpInst::ICMP_UGE); 1496 break; 1497 case ICmpInst::ICMP_SGT: 1498 // If we know that C1 > C2, we can decide the result of this computation 1499 // precisely. 1500 Result = (pred == ICmpInst::ICMP_SGT || 1501 pred == ICmpInst::ICMP_NE || 1502 pred == ICmpInst::ICMP_SGE); 1503 break; 1504 case ICmpInst::ICMP_ULE: 1505 // If we know that C1 <= C2, we can only partially decide this relation. 1506 if (pred == ICmpInst::ICMP_UGT) Result = 0; 1507 if (pred == ICmpInst::ICMP_ULT) Result = 1; 1508 break; 1509 case ICmpInst::ICMP_SLE: 1510 // If we know that C1 <= C2, we can only partially decide this relation. 1511 if (pred == ICmpInst::ICMP_SGT) Result = 0; 1512 if (pred == ICmpInst::ICMP_SLT) Result = 1; 1513 break; 1514 1515 case ICmpInst::ICMP_UGE: 1516 // If we know that C1 >= C2, we can only partially decide this relation. 1517 if (pred == ICmpInst::ICMP_ULT) Result = 0; 1518 if (pred == ICmpInst::ICMP_UGT) Result = 1; 1519 break; 1520 case ICmpInst::ICMP_SGE: 1521 // If we know that C1 >= C2, we can only partially decide this relation. 1522 if (pred == ICmpInst::ICMP_SLT) Result = 0; 1523 if (pred == ICmpInst::ICMP_SGT) Result = 1; 1524 break; 1525 1526 case ICmpInst::ICMP_NE: 1527 // If we know that C1 != C2, we can only partially decide this relation. 1528 if (pred == ICmpInst::ICMP_EQ) Result = 0; 1529 if (pred == ICmpInst::ICMP_NE) Result = 1; 1530 break; 1531 } 1532 1533 // If we evaluated the result, return it now. 1534 if (Result != -1) { 1535 if (const VectorType *VT = dyn_cast<VectorType>(C1->getType())) { 1536 if (Result == 0) 1537 return Constant::getNullValue(VT); 1538 else 1539 return Constant::getAllOnesValue(VT); 1540 } 1541 return ConstantInt::get(Type::Int1Ty, Result); 1542 } 1543 1544 if (!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) { 1545 // If C2 is a constant expr and C1 isn't, flop them around and fold the 1546 // other way if possible. 1547 switch (pred) { 1548 case ICmpInst::ICMP_EQ: 1549 case ICmpInst::ICMP_NE: 1550 // No change of predicate required. 1551 return ConstantFoldCompareInstruction(pred, C2, C1); 1552 1553 case ICmpInst::ICMP_ULT: 1554 case ICmpInst::ICMP_SLT: 1555 case ICmpInst::ICMP_UGT: 1556 case ICmpInst::ICMP_SGT: 1557 case ICmpInst::ICMP_ULE: 1558 case ICmpInst::ICMP_SLE: 1559 case ICmpInst::ICMP_UGE: 1560 case ICmpInst::ICMP_SGE: 1561 // Change the predicate as necessary to swap the operands. 1562 pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred); 1563 return ConstantFoldCompareInstruction(pred, C2, C1); 1564 1565 default: // These predicates cannot be flopped around. 1566 break; 1567 } 1568 } 1569 } 1570 return 0; 1571} 1572 1573Constant *llvm::ConstantFoldGetElementPtr(const Constant *C, 1574 Constant* const *Idxs, 1575 unsigned NumIdx) { 1576 if (NumIdx == 0 || 1577 (NumIdx == 1 && Idxs[0]->isNullValue())) 1578 return const_cast<Constant*>(C); 1579 1580 if (isa<UndefValue>(C)) { 1581 const PointerType *Ptr = cast<PointerType>(C->getType()); 1582 const Type *Ty = GetElementPtrInst::getIndexedType(Ptr, 1583 (Value **)Idxs, 1584 (Value **)Idxs+NumIdx); 1585 assert(Ty != 0 && "Invalid indices for GEP!"); 1586 return UndefValue::get(PointerType::get(Ty, Ptr->getAddressSpace())); 1587 } 1588 1589 Constant *Idx0 = Idxs[0]; 1590 if (C->isNullValue()) { 1591 bool isNull = true; 1592 for (unsigned i = 0, e = NumIdx; i != e; ++i) 1593 if (!Idxs[i]->isNullValue()) { 1594 isNull = false; 1595 break; 1596 } 1597 if (isNull) { 1598 const PointerType *Ptr = cast<PointerType>(C->getType()); 1599 const Type *Ty = GetElementPtrInst::getIndexedType(Ptr, 1600 (Value**)Idxs, 1601 (Value**)Idxs+NumIdx); 1602 assert(Ty != 0 && "Invalid indices for GEP!"); 1603 return 1604 ConstantPointerNull::get(PointerType::get(Ty,Ptr->getAddressSpace())); 1605 } 1606 } 1607 1608 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(const_cast<Constant*>(C))) { 1609 // Combine Indices - If the source pointer to this getelementptr instruction 1610 // is a getelementptr instruction, combine the indices of the two 1611 // getelementptr instructions into a single instruction. 1612 // 1613 if (CE->getOpcode() == Instruction::GetElementPtr) { 1614 const Type *LastTy = 0; 1615 for (gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE); 1616 I != E; ++I) 1617 LastTy = *I; 1618 1619 if ((LastTy && isa<ArrayType>(LastTy)) || Idx0->isNullValue()) { 1620 SmallVector<Value*, 16> NewIndices; 1621 NewIndices.reserve(NumIdx + CE->getNumOperands()); 1622 for (unsigned i = 1, e = CE->getNumOperands()-1; i != e; ++i) 1623 NewIndices.push_back(CE->getOperand(i)); 1624 1625 // Add the last index of the source with the first index of the new GEP. 1626 // Make sure to handle the case when they are actually different types. 1627 Constant *Combined = CE->getOperand(CE->getNumOperands()-1); 1628 // Otherwise it must be an array. 1629 if (!Idx0->isNullValue()) { 1630 const Type *IdxTy = Combined->getType(); 1631 if (IdxTy != Idx0->getType()) { 1632 Constant *C1 = ConstantExpr::getSExtOrBitCast(Idx0, Type::Int64Ty); 1633 Constant *C2 = ConstantExpr::getSExtOrBitCast(Combined, 1634 Type::Int64Ty); 1635 Combined = ConstantExpr::get(Instruction::Add, C1, C2); 1636 } else { 1637 Combined = 1638 ConstantExpr::get(Instruction::Add, Idx0, Combined); 1639 } 1640 } 1641 1642 NewIndices.push_back(Combined); 1643 NewIndices.insert(NewIndices.end(), Idxs+1, Idxs+NumIdx); 1644 return ConstantExpr::getGetElementPtr(CE->getOperand(0), &NewIndices[0], 1645 NewIndices.size()); 1646 } 1647 } 1648 1649 // Implement folding of: 1650 // int* getelementptr ([2 x int]* cast ([3 x int]* %X to [2 x int]*), 1651 // long 0, long 0) 1652 // To: int* getelementptr ([3 x int]* %X, long 0, long 0) 1653 // 1654 if (CE->isCast() && NumIdx > 1 && Idx0->isNullValue()) { 1655 if (const PointerType *SPT = 1656 dyn_cast<PointerType>(CE->getOperand(0)->getType())) 1657 if (const ArrayType *SAT = dyn_cast<ArrayType>(SPT->getElementType())) 1658 if (const ArrayType *CAT = 1659 dyn_cast<ArrayType>(cast<PointerType>(C->getType())->getElementType())) 1660 if (CAT->getElementType() == SAT->getElementType()) 1661 return ConstantExpr::getGetElementPtr( 1662 (Constant*)CE->getOperand(0), Idxs, NumIdx); 1663 } 1664 1665 // Fold: getelementptr (i8* inttoptr (i64 1 to i8*), i32 -1) 1666 // Into: inttoptr (i64 0 to i8*) 1667 // This happens with pointers to member functions in C++. 1668 if (CE->getOpcode() == Instruction::IntToPtr && NumIdx == 1 && 1669 isa<ConstantInt>(CE->getOperand(0)) && isa<ConstantInt>(Idxs[0]) && 1670 cast<PointerType>(CE->getType())->getElementType() == Type::Int8Ty) { 1671 Constant *Base = CE->getOperand(0); 1672 Constant *Offset = Idxs[0]; 1673 1674 // Convert the smaller integer to the larger type. 1675 if (Offset->getType()->getPrimitiveSizeInBits() < 1676 Base->getType()->getPrimitiveSizeInBits()) 1677 Offset = ConstantExpr::getSExt(Offset, Base->getType()); 1678 else if (Base->getType()->getPrimitiveSizeInBits() < 1679 Offset->getType()->getPrimitiveSizeInBits()) 1680 Base = ConstantExpr::getZExt(Base, Offset->getType()); 1681 1682 Base = ConstantExpr::getAdd(Base, Offset); 1683 return ConstantExpr::getIntToPtr(Base, CE->getType()); 1684 } 1685 } 1686 return 0; 1687} 1688 1689