ConstantFold.cpp revision b8f74793b9d161bc666fe27fc92fe112b6ec169b
1//===- ConstantFold.cpp - LLVM constant folder ----------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source 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/ADT/SmallVector.h" 27#include "llvm/Support/Compiler.h" 28#include "llvm/Support/GetElementPtrTypeIterator.h" 29#include "llvm/Support/ManagedStatic.h" 30#include "llvm/Support/MathExtras.h" 31#include <limits> 32using namespace llvm; 33 34//===----------------------------------------------------------------------===// 35// ConstantFold*Instruction Implementations 36//===----------------------------------------------------------------------===// 37 38/// CastConstantVector - Convert the specified ConstantVector node to the 39/// specified vector type. At this point, we know that the elements of the 40/// input vector constant are all simple integer or FP values. 41static Constant *CastConstantVector(ConstantVector *CV, 42 const VectorType *DstTy) { 43 unsigned SrcNumElts = CV->getType()->getNumElements(); 44 unsigned DstNumElts = DstTy->getNumElements(); 45 const Type *SrcEltTy = CV->getType()->getElementType(); 46 const Type *DstEltTy = DstTy->getElementType(); 47 48 // If both vectors have the same number of elements (thus, the elements 49 // are the same size), perform the conversion now. 50 if (SrcNumElts == DstNumElts) { 51 std::vector<Constant*> Result; 52 53 // If the src and dest elements are both integers, or both floats, we can 54 // just BitCast each element because the elements are the same size. 55 if ((SrcEltTy->isInteger() && DstEltTy->isInteger()) || 56 (SrcEltTy->isFloatingPoint() && DstEltTy->isFloatingPoint())) { 57 for (unsigned i = 0; i != SrcNumElts; ++i) 58 Result.push_back( 59 ConstantExpr::getBitCast(CV->getOperand(i), DstEltTy)); 60 return ConstantVector::get(Result); 61 } 62 63 // If this is an int-to-fp cast .. 64 if (SrcEltTy->isInteger()) { 65 // Ensure that it is int-to-fp cast 66 assert(DstEltTy->isFloatingPoint()); 67 if (DstEltTy->getTypeID() == Type::DoubleTyID) { 68 for (unsigned i = 0; i != SrcNumElts; ++i) { 69 ConstantInt *CI = cast<ConstantInt>(CV->getOperand(i)); 70 double V = CI->getValue().bitsToDouble(); 71 Result.push_back(ConstantFP::get(Type::DoubleTy, V)); 72 } 73 return ConstantVector::get(Result); 74 } 75 assert(DstEltTy == Type::FloatTy && "Unknown fp type!"); 76 for (unsigned i = 0; i != SrcNumElts; ++i) { 77 ConstantInt *CI = cast<ConstantInt>(CV->getOperand(i)); 78 float V = CI->getValue().bitsToFloat(); 79 Result.push_back(ConstantFP::get(Type::FloatTy, V)); 80 } 81 return ConstantVector::get(Result); 82 } 83 84 // Otherwise, this is an fp-to-int cast. 85 assert(SrcEltTy->isFloatingPoint() && DstEltTy->isInteger()); 86 87 if (SrcEltTy->getTypeID() == Type::DoubleTyID) { 88 for (unsigned i = 0; i != SrcNumElts; ++i) { 89 uint64_t V = 90 DoubleToBits(cast<ConstantFP>(CV->getOperand(i))->getValue()); 91 Constant *C = ConstantInt::get(Type::Int64Ty, V); 92 Result.push_back(ConstantExpr::getBitCast(C, DstEltTy )); 93 } 94 return ConstantVector::get(Result); 95 } 96 97 assert(SrcEltTy->getTypeID() == Type::FloatTyID); 98 for (unsigned i = 0; i != SrcNumElts; ++i) { 99 uint32_t V = FloatToBits(cast<ConstantFP>(CV->getOperand(i))->getValue()); 100 Constant *C = ConstantInt::get(Type::Int32Ty, V); 101 Result.push_back(ConstantExpr::getBitCast(C, DstEltTy)); 102 } 103 return ConstantVector::get(Result); 104 } 105 106 // Otherwise, this is a cast that changes element count and size. Handle 107 // casts which shrink the elements here. 108 109 // FIXME: We need to know endianness to do this! 110 111 return 0; 112} 113 114/// This function determines which opcode to use to fold two constant cast 115/// expressions together. It uses CastInst::isEliminableCastPair to determine 116/// the opcode. Consequently its just a wrapper around that function. 117/// @brief Determine if it is valid to fold a cast of a cast 118static unsigned 119foldConstantCastPair( 120 unsigned opc, ///< opcode of the second cast constant expression 121 const ConstantExpr*Op, ///< the first cast constant expression 122 const Type *DstTy ///< desintation type of the first cast 123) { 124 assert(Op && Op->isCast() && "Can't fold cast of cast without a cast!"); 125 assert(DstTy && DstTy->isFirstClassType() && "Invalid cast destination type"); 126 assert(CastInst::isCast(opc) && "Invalid cast opcode"); 127 128 // The the types and opcodes for the two Cast constant expressions 129 const Type *SrcTy = Op->getOperand(0)->getType(); 130 const Type *MidTy = Op->getType(); 131 Instruction::CastOps firstOp = Instruction::CastOps(Op->getOpcode()); 132 Instruction::CastOps secondOp = Instruction::CastOps(opc); 133 134 // Let CastInst::isEliminableCastPair do the heavy lifting. 135 return CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy, DstTy, 136 Type::Int64Ty); 137} 138 139Constant *llvm::ConstantFoldCastInstruction(unsigned opc, const Constant *V, 140 const Type *DestTy) { 141 const Type *SrcTy = V->getType(); 142 143 if (isa<UndefValue>(V)) { 144 // zext(undef) = 0, because the top bits will be zero. 145 // sext(undef) = 0, because the top bits will all be the same. 146 if (opc == Instruction::ZExt || opc == Instruction::SExt) 147 return Constant::getNullValue(DestTy); 148 return UndefValue::get(DestTy); 149 } 150 151 // If the cast operand is a constant expression, there's a few things we can 152 // do to try to simplify it. 153 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { 154 if (CE->isCast()) { 155 // Try hard to fold cast of cast because they are often eliminable. 156 if (unsigned newOpc = foldConstantCastPair(opc, CE, DestTy)) 157 return ConstantExpr::getCast(newOpc, CE->getOperand(0), DestTy); 158 } else if (CE->getOpcode() == Instruction::GetElementPtr) { 159 // If all of the indexes in the GEP are null values, there is no pointer 160 // adjustment going on. We might as well cast the source pointer. 161 bool isAllNull = true; 162 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) 163 if (!CE->getOperand(i)->isNullValue()) { 164 isAllNull = false; 165 break; 166 } 167 if (isAllNull) 168 // This is casting one pointer type to another, always BitCast 169 return ConstantExpr::getPointerCast(CE->getOperand(0), DestTy); 170 } 171 } 172 173 // We actually have to do a cast now. Perform the cast according to the 174 // opcode specified. 175 switch (opc) { 176 case Instruction::FPTrunc: 177 case Instruction::FPExt: 178 if (const ConstantFP *FPC = dyn_cast<ConstantFP>(V)) 179 return ConstantFP::get(DestTy, FPC->getValue()); 180 return 0; // Can't fold. 181 case Instruction::FPToUI: 182 if (const ConstantFP *FPC = dyn_cast<ConstantFP>(V)) { 183 uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 184 APInt Val(APIntOps::RoundDoubleToAPInt(FPC->getValue(), DestBitWidth)); 185 return ConstantInt::get(Val); 186 } 187 return 0; // Can't fold. 188 case Instruction::FPToSI: 189 if (const ConstantFP *FPC = dyn_cast<ConstantFP>(V)) { 190 uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 191 APInt Val(APIntOps::RoundDoubleToAPInt(FPC->getValue(), DestBitWidth)); 192 return ConstantInt::get(Val); 193 } 194 return 0; // Can't fold. 195 case Instruction::IntToPtr: //always treated as unsigned 196 if (V->isNullValue()) // Is it an integral null value? 197 return ConstantPointerNull::get(cast<PointerType>(DestTy)); 198 return 0; // Other pointer types cannot be casted 199 case Instruction::PtrToInt: // always treated as unsigned 200 if (V->isNullValue()) // is it a null pointer value? 201 return ConstantInt::get(DestTy, 0); 202 return 0; // Other pointer types cannot be casted 203 case Instruction::UIToFP: 204 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) 205 return ConstantFP::get(DestTy, CI->getValue().roundToDouble()); 206 return 0; 207 case Instruction::SIToFP: 208 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) 209 return ConstantFP::get(DestTy, CI->getValue().signedRoundToDouble()); 210 return 0; 211 case Instruction::ZExt: 212 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 213 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 214 APInt Result(CI->getValue()); 215 Result.zext(BitWidth); 216 return ConstantInt::get(Result); 217 } 218 return 0; 219 case Instruction::SExt: 220 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 221 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 222 APInt Result(CI->getValue()); 223 Result.sext(BitWidth); 224 return ConstantInt::get(Result); 225 } 226 return 0; 227 case Instruction::Trunc: 228 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 229 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 230 APInt Result(CI->getValue()); 231 Result.trunc(BitWidth); 232 return ConstantInt::get(Result); 233 } 234 return 0; 235 case Instruction::BitCast: 236 if (SrcTy == DestTy) 237 return (Constant*)V; // no-op cast 238 239 // Check to see if we are casting a pointer to an aggregate to a pointer to 240 // the first element. If so, return the appropriate GEP instruction. 241 if (const PointerType *PTy = dyn_cast<PointerType>(V->getType())) 242 if (const PointerType *DPTy = dyn_cast<PointerType>(DestTy)) { 243 SmallVector<Value*, 8> IdxList; 244 IdxList.push_back(Constant::getNullValue(Type::Int32Ty)); 245 const Type *ElTy = PTy->getElementType(); 246 while (ElTy != DPTy->getElementType()) { 247 if (const StructType *STy = dyn_cast<StructType>(ElTy)) { 248 if (STy->getNumElements() == 0) break; 249 ElTy = STy->getElementType(0); 250 IdxList.push_back(Constant::getNullValue(Type::Int32Ty)); 251 } else if (const SequentialType *STy = 252 dyn_cast<SequentialType>(ElTy)) { 253 if (isa<PointerType>(ElTy)) break; // Can't index into pointers! 254 ElTy = STy->getElementType(); 255 IdxList.push_back(IdxList[0]); 256 } else { 257 break; 258 } 259 } 260 261 if (ElTy == DPTy->getElementType()) 262 return ConstantExpr::getGetElementPtr( 263 const_cast<Constant*>(V), &IdxList[0], IdxList.size()); 264 } 265 266 // Handle casts from one vector constant to another. We know that the src 267 // and dest type have the same size (otherwise its an illegal cast). 268 if (const VectorType *DestPTy = dyn_cast<VectorType>(DestTy)) { 269 if (const VectorType *SrcTy = dyn_cast<VectorType>(V->getType())) { 270 assert(DestPTy->getBitWidth() == SrcTy->getBitWidth() && 271 "Not cast between same sized vectors!"); 272 // First, check for null and undef 273 if (isa<ConstantAggregateZero>(V)) 274 return Constant::getNullValue(DestTy); 275 if (isa<UndefValue>(V)) 276 return UndefValue::get(DestTy); 277 278 if (const ConstantVector *CV = dyn_cast<ConstantVector>(V)) { 279 // This is a cast from a ConstantVector of one type to a 280 // ConstantVector of another type. Check to see if all elements of 281 // the input are simple. 282 bool AllSimpleConstants = true; 283 for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) { 284 if (!isa<ConstantInt>(CV->getOperand(i)) && 285 !isa<ConstantFP>(CV->getOperand(i))) { 286 AllSimpleConstants = false; 287 break; 288 } 289 } 290 291 // If all of the elements are simple constants, we can fold this. 292 if (AllSimpleConstants) 293 return CastConstantVector(const_cast<ConstantVector*>(CV), DestPTy); 294 } 295 } 296 } 297 298 // Finally, implement bitcast folding now. The code below doesn't handle 299 // bitcast right. 300 if (isa<ConstantPointerNull>(V)) // ptr->ptr cast. 301 return ConstantPointerNull::get(cast<PointerType>(DestTy)); 302 303 // Handle integral constant input. 304 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 305 if (DestTy->isInteger()) 306 // Integral -> Integral. This is a no-op because the bit widths must 307 // be the same. Consequently, we just fold to V. 308 return const_cast<Constant*>(V); 309 310 if (DestTy->isFloatingPoint()) { 311 if (DestTy == Type::FloatTy) 312 return ConstantFP::get(DestTy, CI->getValue().bitsToFloat()); 313 assert(DestTy == Type::DoubleTy && "Unknown FP type!"); 314 return ConstantFP::get(DestTy, CI->getValue().bitsToDouble()); 315 } 316 // Otherwise, can't fold this (vector?) 317 return 0; 318 } 319 320 // Handle ConstantFP input. 321 if (const ConstantFP *FP = dyn_cast<ConstantFP>(V)) { 322 // FP -> Integral. 323 if (DestTy == Type::Int32Ty) { 324 APInt Val(32, 0); 325 return ConstantInt::get(Val.floatToBits(FP->getValue())); 326 } else { 327 assert(DestTy == Type::Int64Ty && "only support f32/f64 for now!"); 328 APInt Val(64, 0); 329 return ConstantInt::get(Val.doubleToBits(FP->getValue())); 330 } 331 } 332 return 0; 333 default: 334 assert(!"Invalid CE CastInst opcode"); 335 break; 336 } 337 338 assert(0 && "Failed to cast constant expression"); 339 return 0; 340} 341 342Constant *llvm::ConstantFoldSelectInstruction(const Constant *Cond, 343 const Constant *V1, 344 const Constant *V2) { 345 if (const ConstantInt *CB = dyn_cast<ConstantInt>(Cond)) 346 return const_cast<Constant*>(CB->getZExtValue() ? V1 : V2); 347 348 if (isa<UndefValue>(V1)) return const_cast<Constant*>(V2); 349 if (isa<UndefValue>(V2)) return const_cast<Constant*>(V1); 350 if (isa<UndefValue>(Cond)) return const_cast<Constant*>(V1); 351 if (V1 == V2) return const_cast<Constant*>(V1); 352 return 0; 353} 354 355Constant *llvm::ConstantFoldExtractElementInstruction(const Constant *Val, 356 const Constant *Idx) { 357 if (isa<UndefValue>(Val)) // ee(undef, x) -> undef 358 return UndefValue::get(cast<VectorType>(Val->getType())->getElementType()); 359 if (Val->isNullValue()) // ee(zero, x) -> zero 360 return Constant::getNullValue( 361 cast<VectorType>(Val->getType())->getElementType()); 362 363 if (const ConstantVector *CVal = dyn_cast<ConstantVector>(Val)) { 364 if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx)) { 365 return const_cast<Constant*>(CVal->getOperand(CIdx->getZExtValue())); 366 } else if (isa<UndefValue>(Idx)) { 367 // ee({w,x,y,z}, undef) -> w (an arbitrary value). 368 return const_cast<Constant*>(CVal->getOperand(0)); 369 } 370 } 371 return 0; 372} 373 374Constant *llvm::ConstantFoldInsertElementInstruction(const Constant *Val, 375 const Constant *Elt, 376 const Constant *Idx) { 377 const ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx); 378 if (!CIdx) return 0; 379 APInt idxVal = CIdx->getValue(); 380 if (isa<UndefValue>(Val)) { 381 // Insertion of scalar constant into vector undef 382 // Optimize away insertion of undef 383 if (isa<UndefValue>(Elt)) 384 return const_cast<Constant*>(Val); 385 // Otherwise break the aggregate undef into multiple undefs and do 386 // the insertion 387 unsigned numOps = 388 cast<VectorType>(Val->getType())->getNumElements(); 389 std::vector<Constant*> Ops; 390 Ops.reserve(numOps); 391 for (unsigned i = 0; i < numOps; ++i) { 392 const Constant *Op = 393 (idxVal == i) ? Elt : UndefValue::get(Elt->getType()); 394 Ops.push_back(const_cast<Constant*>(Op)); 395 } 396 return ConstantVector::get(Ops); 397 } 398 if (isa<ConstantAggregateZero>(Val)) { 399 // Insertion of scalar constant into vector aggregate zero 400 // Optimize away insertion of zero 401 if (Elt->isNullValue()) 402 return const_cast<Constant*>(Val); 403 // Otherwise break the aggregate zero into multiple zeros and do 404 // the insertion 405 unsigned numOps = 406 cast<VectorType>(Val->getType())->getNumElements(); 407 std::vector<Constant*> Ops; 408 Ops.reserve(numOps); 409 for (unsigned i = 0; i < numOps; ++i) { 410 const Constant *Op = 411 (idxVal == i) ? Elt : Constant::getNullValue(Elt->getType()); 412 Ops.push_back(const_cast<Constant*>(Op)); 413 } 414 return ConstantVector::get(Ops); 415 } 416 if (const ConstantVector *CVal = dyn_cast<ConstantVector>(Val)) { 417 // Insertion of scalar constant into vector constant 418 std::vector<Constant*> Ops; 419 Ops.reserve(CVal->getNumOperands()); 420 for (unsigned i = 0; i < CVal->getNumOperands(); ++i) { 421 const Constant *Op = 422 (idxVal == i) ? Elt : cast<Constant>(CVal->getOperand(i)); 423 Ops.push_back(const_cast<Constant*>(Op)); 424 } 425 return ConstantVector::get(Ops); 426 } 427 return 0; 428} 429 430Constant *llvm::ConstantFoldShuffleVectorInstruction(const Constant *V1, 431 const Constant *V2, 432 const Constant *Mask) { 433 // TODO: 434 return 0; 435} 436 437/// EvalVectorOp - Given two vector constants and a function pointer, apply the 438/// function pointer to each element pair, producing a new ConstantVector 439/// constant. 440static Constant *EvalVectorOp(const ConstantVector *V1, 441 const ConstantVector *V2, 442 Constant *(*FP)(Constant*, Constant*)) { 443 std::vector<Constant*> Res; 444 for (unsigned i = 0, e = V1->getNumOperands(); i != e; ++i) 445 Res.push_back(FP(const_cast<Constant*>(V1->getOperand(i)), 446 const_cast<Constant*>(V2->getOperand(i)))); 447 return ConstantVector::get(Res); 448} 449 450Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, 451 const Constant *C1, 452 const Constant *C2) { 453 // Handle UndefValue up front 454 if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) { 455 switch (Opcode) { 456 case Instruction::Add: 457 case Instruction::Sub: 458 case Instruction::Xor: 459 return UndefValue::get(C1->getType()); 460 case Instruction::Mul: 461 case Instruction::And: 462 return Constant::getNullValue(C1->getType()); 463 case Instruction::UDiv: 464 case Instruction::SDiv: 465 case Instruction::FDiv: 466 case Instruction::URem: 467 case Instruction::SRem: 468 case Instruction::FRem: 469 if (!isa<UndefValue>(C2)) // undef / X -> 0 470 return Constant::getNullValue(C1->getType()); 471 return const_cast<Constant*>(C2); // X / undef -> undef 472 case Instruction::Or: // X | undef -> -1 473 if (const VectorType *PTy = dyn_cast<VectorType>(C1->getType())) 474 return ConstantVector::getAllOnesValue(PTy); 475 return ConstantInt::getAllOnesValue(C1->getType()); 476 case Instruction::LShr: 477 if (isa<UndefValue>(C2) && isa<UndefValue>(C1)) 478 return const_cast<Constant*>(C1); // undef lshr undef -> undef 479 return Constant::getNullValue(C1->getType()); // X lshr undef -> 0 480 // undef lshr X -> 0 481 case Instruction::AShr: 482 if (!isa<UndefValue>(C2)) 483 return const_cast<Constant*>(C1); // undef ashr X --> undef 484 else if (isa<UndefValue>(C1)) 485 return const_cast<Constant*>(C1); // undef ashr undef -> undef 486 else 487 return const_cast<Constant*>(C1); // X ashr undef --> X 488 case Instruction::Shl: 489 // undef << X -> 0 or X << undef -> 0 490 return Constant::getNullValue(C1->getType()); 491 } 492 } 493 494 if (const ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) { 495 if (isa<ConstantExpr>(C2)) { 496 // There are many possible foldings we could do here. We should probably 497 // at least fold add of a pointer with an integer into the appropriate 498 // getelementptr. This will improve alias analysis a bit. 499 } else { 500 // Just implement a couple of simple identities. 501 switch (Opcode) { 502 case Instruction::Add: 503 if (C2->isNullValue()) return const_cast<Constant*>(C1); // X + 0 == X 504 break; 505 case Instruction::Sub: 506 if (C2->isNullValue()) return const_cast<Constant*>(C1); // X - 0 == X 507 break; 508 case Instruction::Mul: 509 if (C2->isNullValue()) return const_cast<Constant*>(C2); // X * 0 == 0 510 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 511 if (CI->equalsInt(1)) 512 return const_cast<Constant*>(C1); // X * 1 == X 513 break; 514 case Instruction::UDiv: 515 case Instruction::SDiv: 516 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 517 if (CI->equalsInt(1)) 518 return const_cast<Constant*>(C1); // X / 1 == X 519 break; 520 case Instruction::URem: 521 case Instruction::SRem: 522 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 523 if (CI->equalsInt(1)) 524 return Constant::getNullValue(CI->getType()); // X % 1 == 0 525 break; 526 case Instruction::And: 527 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) { 528 if (CI->isZero()) return const_cast<Constant*>(C2); // X & 0 == 0 529 if (CI->isAllOnesValue()) 530 return const_cast<Constant*>(C1); // X & -1 == X 531 532 // (zext i32 to i64) & 4294967295 -> (zext i32 to i64) 533 if (CE1->getOpcode() == Instruction::ZExt) { 534 APInt PossiblySetBits 535 = cast<IntegerType>(CE1->getOperand(0)->getType())->getMask(); 536 PossiblySetBits.zext(C1->getType()->getPrimitiveSizeInBits()); 537 if ((PossiblySetBits & CI->getValue()) == PossiblySetBits) 538 return const_cast<Constant*>(C1); 539 } 540 } 541 if (CE1->isCast() && isa<GlobalValue>(CE1->getOperand(0))) { 542 GlobalValue *CPR = cast<GlobalValue>(CE1->getOperand(0)); 543 544 // Functions are at least 4-byte aligned. If and'ing the address of a 545 // function with a constant < 4, fold it to zero. 546 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 547 if (CI->getValue().ult(APInt(CI->getType()->getBitWidth(),4)) && 548 isa<Function>(CPR)) 549 return Constant::getNullValue(CI->getType()); 550 } 551 break; 552 case Instruction::Or: 553 if (C2->isNullValue()) return const_cast<Constant*>(C1); // X | 0 == X 554 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 555 if (CI->isAllOnesValue()) 556 return const_cast<Constant*>(C2); // X | -1 == -1 557 break; 558 case Instruction::Xor: 559 if (C2->isNullValue()) return const_cast<Constant*>(C1); // X ^ 0 == X 560 break; 561 case Instruction::AShr: 562 // ashr (zext C to Ty), C2 -> lshr (zext C, CSA), C2 563 if (CE1->getOpcode() == Instruction::ZExt) // Top bits known zero. 564 return ConstantExpr::getLShr(const_cast<Constant*>(C1), 565 const_cast<Constant*>(C2)); 566 break; 567 } 568 } 569 } else if (isa<ConstantExpr>(C2)) { 570 // If C2 is a constant expr and C1 isn't, flop them around and fold the 571 // other way if possible. 572 switch (Opcode) { 573 case Instruction::Add: 574 case Instruction::Mul: 575 case Instruction::And: 576 case Instruction::Or: 577 case Instruction::Xor: 578 // No change of opcode required. 579 return ConstantFoldBinaryInstruction(Opcode, C2, C1); 580 581 case Instruction::Shl: 582 case Instruction::LShr: 583 case Instruction::AShr: 584 case Instruction::Sub: 585 case Instruction::SDiv: 586 case Instruction::UDiv: 587 case Instruction::FDiv: 588 case Instruction::URem: 589 case Instruction::SRem: 590 case Instruction::FRem: 591 default: // These instructions cannot be flopped around. 592 return 0; 593 } 594 } 595 596 // At this point we know neither constant is an UndefValue nor a ConstantExpr 597 // so look at directly computing the value. 598 if (const ConstantInt *CI1 = dyn_cast<ConstantInt>(C1)) { 599 if (const ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) { 600 using namespace APIntOps; 601 APInt C1V = CI1->getValue(); 602 APInt C2V = CI2->getValue(); 603 switch (Opcode) { 604 default: 605 break; 606 case Instruction::Add: 607 return ConstantInt::get(C1V + C2V); 608 case Instruction::Sub: 609 return ConstantInt::get(C1V - C2V); 610 case Instruction::Mul: 611 return ConstantInt::get(C1V * C2V); 612 case Instruction::UDiv: 613 if (CI2->isNullValue()) 614 return 0; // X / 0 -> can't fold 615 return ConstantInt::get(C1V.udiv(C2V)); 616 case Instruction::SDiv: 617 if (CI2->isNullValue()) 618 return 0; // X / 0 -> can't fold 619 if (C2V.isAllOnesValue() && C1V.isMinSignedValue()) 620 return 0; // MIN_INT / -1 -> overflow 621 return ConstantInt::get(C1V.sdiv(C2V)); 622 case Instruction::URem: 623 if (C2->isNullValue()) 624 return 0; // X / 0 -> can't fold 625 return ConstantInt::get(C1V.urem(C2V)); 626 case Instruction::SRem: 627 if (CI2->isNullValue()) 628 return 0; // X % 0 -> can't fold 629 if (C2V.isAllOnesValue() && C1V.isMinSignedValue()) 630 return 0; // MIN_INT % -1 -> overflow 631 return ConstantInt::get(C1V.srem(C2V)); 632 case Instruction::And: 633 return ConstantInt::get(C1V & C2V); 634 case Instruction::Or: 635 return ConstantInt::get(C1V | C2V); 636 case Instruction::Xor: 637 return ConstantInt::get(C1V ^ C2V); 638 case Instruction::Shl: 639 if (uint32_t shiftAmt = C2V.getZExtValue()) 640 if (shiftAmt < C1V.getBitWidth()) 641 return ConstantInt::get(C1V.shl(shiftAmt)); 642 else 643 return UndefValue::get(C1->getType()); // too big shift is undef 644 return const_cast<ConstantInt*>(CI1); // Zero shift is identity 645 case Instruction::LShr: 646 if (uint32_t shiftAmt = C2V.getZExtValue()) 647 if (shiftAmt < C1V.getBitWidth()) 648 return ConstantInt::get(C1V.lshr(shiftAmt)); 649 else 650 return UndefValue::get(C1->getType()); // too big shift is undef 651 return const_cast<ConstantInt*>(CI1); // Zero shift is identity 652 case Instruction::AShr: 653 if (uint32_t shiftAmt = C2V.getZExtValue()) 654 if (shiftAmt < C1V.getBitWidth()) 655 return ConstantInt::get(C1V.ashr(shiftAmt)); 656 else 657 return UndefValue::get(C1->getType()); // too big shift is undef 658 return const_cast<ConstantInt*>(CI1); // Zero shift is identity 659 } 660 } 661 } else if (const ConstantFP *CFP1 = dyn_cast<ConstantFP>(C1)) { 662 if (const ConstantFP *CFP2 = dyn_cast<ConstantFP>(C2)) { 663 double C1Val = CFP1->getValue(); 664 double C2Val = CFP2->getValue(); 665 switch (Opcode) { 666 default: 667 break; 668 case Instruction::Add: 669 return ConstantFP::get(CFP1->getType(), C1Val + C2Val); 670 case Instruction::Sub: 671 return ConstantFP::get(CFP1->getType(), C1Val - C2Val); 672 case Instruction::Mul: 673 return ConstantFP::get(CFP1->getType(), C1Val * C2Val); 674 case Instruction::FDiv: 675 if (CFP2->isExactlyValue(0.0) || CFP2->isExactlyValue(-0.0)) 676 if (CFP1->isExactlyValue(0.0) || CFP1->isExactlyValue(-0.0)) 677 // IEEE 754, Section 7.1, #4 678 return ConstantFP::get(CFP1->getType(), 679 std::numeric_limits<double>::quiet_NaN()); 680 else if (CFP2->isExactlyValue(-0.0) || C1Val < 0.0) 681 // IEEE 754, Section 7.2, negative infinity case 682 return ConstantFP::get(CFP1->getType(), 683 -std::numeric_limits<double>::infinity()); 684 else 685 // IEEE 754, Section 7.2, positive infinity case 686 return ConstantFP::get(CFP1->getType(), 687 std::numeric_limits<double>::infinity()); 688 return ConstantFP::get(CFP1->getType(), C1Val / C2Val); 689 case Instruction::FRem: 690 if (CFP2->isExactlyValue(0.0) || CFP2->isExactlyValue(-0.0)) 691 // IEEE 754, Section 7.1, #5 692 return ConstantFP::get(CFP1->getType(), 693 std::numeric_limits<double>::quiet_NaN()); 694 return ConstantFP::get(CFP1->getType(), std::fmod(C1Val, C2Val)); 695 696 } 697 } 698 } else if (const ConstantVector *CP1 = dyn_cast<ConstantVector>(C1)) { 699 if (const ConstantVector *CP2 = dyn_cast<ConstantVector>(C2)) { 700 switch (Opcode) { 701 default: 702 break; 703 case Instruction::Add: 704 return EvalVectorOp(CP1, CP2, ConstantExpr::getAdd); 705 case Instruction::Sub: 706 return EvalVectorOp(CP1, CP2, ConstantExpr::getSub); 707 case Instruction::Mul: 708 return EvalVectorOp(CP1, CP2, ConstantExpr::getMul); 709 case Instruction::UDiv: 710 return EvalVectorOp(CP1, CP2, ConstantExpr::getUDiv); 711 case Instruction::SDiv: 712 return EvalVectorOp(CP1, CP2, ConstantExpr::getSDiv); 713 case Instruction::FDiv: 714 return EvalVectorOp(CP1, CP2, ConstantExpr::getFDiv); 715 case Instruction::URem: 716 return EvalVectorOp(CP1, CP2, ConstantExpr::getURem); 717 case Instruction::SRem: 718 return EvalVectorOp(CP1, CP2, ConstantExpr::getSRem); 719 case Instruction::FRem: 720 return EvalVectorOp(CP1, CP2, ConstantExpr::getFRem); 721 case Instruction::And: 722 return EvalVectorOp(CP1, CP2, ConstantExpr::getAnd); 723 case Instruction::Or: 724 return EvalVectorOp(CP1, CP2, ConstantExpr::getOr); 725 case Instruction::Xor: 726 return EvalVectorOp(CP1, CP2, ConstantExpr::getXor); 727 } 728 } 729 } 730 731 // We don't know how to fold this 732 return 0; 733} 734 735/// isZeroSizedType - This type is zero sized if its an array or structure of 736/// zero sized types. The only leaf zero sized type is an empty structure. 737static bool isMaybeZeroSizedType(const Type *Ty) { 738 if (isa<OpaqueType>(Ty)) return true; // Can't say. 739 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 740 741 // If all of elements have zero size, this does too. 742 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 743 if (!isMaybeZeroSizedType(STy->getElementType(i))) return false; 744 return true; 745 746 } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 747 return isMaybeZeroSizedType(ATy->getElementType()); 748 } 749 return false; 750} 751 752/// IdxCompare - Compare the two constants as though they were getelementptr 753/// indices. This allows coersion of the types to be the same thing. 754/// 755/// If the two constants are the "same" (after coersion), return 0. If the 756/// first is less than the second, return -1, if the second is less than the 757/// first, return 1. If the constants are not integral, return -2. 758/// 759static int IdxCompare(Constant *C1, Constant *C2, const Type *ElTy) { 760 if (C1 == C2) return 0; 761 762 // Ok, we found a different index. If they are not ConstantInt, we can't do 763 // anything with them. 764 if (!isa<ConstantInt>(C1) || !isa<ConstantInt>(C2)) 765 return -2; // don't know! 766 767 // Ok, we have two differing integer indices. Sign extend them to be the same 768 // type. Long is always big enough, so we use it. 769 if (C1->getType() != Type::Int64Ty) 770 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty); 771 772 if (C2->getType() != Type::Int64Ty) 773 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty); 774 775 if (C1 == C2) return 0; // They are equal 776 777 // If the type being indexed over is really just a zero sized type, there is 778 // no pointer difference being made here. 779 if (isMaybeZeroSizedType(ElTy)) 780 return -2; // dunno. 781 782 // If they are really different, now that they are the same type, then we 783 // found a difference! 784 if (cast<ConstantInt>(C1)->getSExtValue() < 785 cast<ConstantInt>(C2)->getSExtValue()) 786 return -1; 787 else 788 return 1; 789} 790 791/// evaluateFCmpRelation - This function determines if there is anything we can 792/// decide about the two constants provided. This doesn't need to handle simple 793/// things like ConstantFP comparisons, but should instead handle ConstantExprs. 794/// If we can determine that the two constants have a particular relation to 795/// each other, we should return the corresponding FCmpInst predicate, 796/// otherwise return FCmpInst::BAD_FCMP_PREDICATE. This is used below in 797/// ConstantFoldCompareInstruction. 798/// 799/// To simplify this code we canonicalize the relation so that the first 800/// operand is always the most "complex" of the two. We consider ConstantFP 801/// to be the simplest, and ConstantExprs to be the most complex. 802static FCmpInst::Predicate evaluateFCmpRelation(const Constant *V1, 803 const Constant *V2) { 804 assert(V1->getType() == V2->getType() && 805 "Cannot compare values of different types!"); 806 // Handle degenerate case quickly 807 if (V1 == V2) return FCmpInst::FCMP_OEQ; 808 809 if (!isa<ConstantExpr>(V1)) { 810 if (!isa<ConstantExpr>(V2)) { 811 // We distilled thisUse the standard constant folder for a few cases 812 ConstantInt *R = 0; 813 Constant *C1 = const_cast<Constant*>(V1); 814 Constant *C2 = const_cast<Constant*>(V2); 815 R = dyn_cast<ConstantInt>( 816 ConstantExpr::getFCmp(FCmpInst::FCMP_OEQ, C1, C2)); 817 if (R && !R->isZero()) 818 return FCmpInst::FCMP_OEQ; 819 R = dyn_cast<ConstantInt>( 820 ConstantExpr::getFCmp(FCmpInst::FCMP_OLT, C1, C2)); 821 if (R && !R->isZero()) 822 return FCmpInst::FCMP_OLT; 823 R = dyn_cast<ConstantInt>( 824 ConstantExpr::getFCmp(FCmpInst::FCMP_OGT, C1, C2)); 825 if (R && !R->isZero()) 826 return FCmpInst::FCMP_OGT; 827 828 // Nothing more we can do 829 return FCmpInst::BAD_FCMP_PREDICATE; 830 } 831 832 // If the first operand is simple and second is ConstantExpr, swap operands. 833 FCmpInst::Predicate SwappedRelation = evaluateFCmpRelation(V2, V1); 834 if (SwappedRelation != FCmpInst::BAD_FCMP_PREDICATE) 835 return FCmpInst::getSwappedPredicate(SwappedRelation); 836 } else { 837 // Ok, the LHS is known to be a constantexpr. The RHS can be any of a 838 // constantexpr or a simple constant. 839 const ConstantExpr *CE1 = cast<ConstantExpr>(V1); 840 switch (CE1->getOpcode()) { 841 case Instruction::FPTrunc: 842 case Instruction::FPExt: 843 case Instruction::UIToFP: 844 case Instruction::SIToFP: 845 // We might be able to do something with these but we don't right now. 846 break; 847 default: 848 break; 849 } 850 } 851 // There are MANY other foldings that we could perform here. They will 852 // probably be added on demand, as they seem needed. 853 return FCmpInst::BAD_FCMP_PREDICATE; 854} 855 856/// evaluateICmpRelation - This function determines if there is anything we can 857/// decide about the two constants provided. This doesn't need to handle simple 858/// things like integer comparisons, but should instead handle ConstantExprs 859/// and GlobalValues. If we can determine that the two constants have a 860/// particular relation to each other, we should return the corresponding ICmp 861/// predicate, otherwise return ICmpInst::BAD_ICMP_PREDICATE. 862/// 863/// To simplify this code we canonicalize the relation so that the first 864/// operand is always the most "complex" of the two. We consider simple 865/// constants (like ConstantInt) to be the simplest, followed by 866/// GlobalValues, followed by ConstantExpr's (the most complex). 867/// 868static ICmpInst::Predicate evaluateICmpRelation(const Constant *V1, 869 const Constant *V2, 870 bool isSigned) { 871 assert(V1->getType() == V2->getType() && 872 "Cannot compare different types of values!"); 873 if (V1 == V2) return ICmpInst::ICMP_EQ; 874 875 if (!isa<ConstantExpr>(V1) && !isa<GlobalValue>(V1)) { 876 if (!isa<GlobalValue>(V2) && !isa<ConstantExpr>(V2)) { 877 // We distilled this down to a simple case, use the standard constant 878 // folder. 879 ConstantInt *R = 0; 880 Constant *C1 = const_cast<Constant*>(V1); 881 Constant *C2 = const_cast<Constant*>(V2); 882 ICmpInst::Predicate pred = ICmpInst::ICMP_EQ; 883 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 884 if (R && !R->isZero()) 885 return pred; 886 pred = isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 887 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 888 if (R && !R->isZero()) 889 return pred; 890 pred = isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 891 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 892 if (R && !R->isZero()) 893 return pred; 894 895 // If we couldn't figure it out, bail. 896 return ICmpInst::BAD_ICMP_PREDICATE; 897 } 898 899 // If the first operand is simple, swap operands. 900 ICmpInst::Predicate SwappedRelation = 901 evaluateICmpRelation(V2, V1, isSigned); 902 if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE) 903 return ICmpInst::getSwappedPredicate(SwappedRelation); 904 905 } else if (const GlobalValue *CPR1 = dyn_cast<GlobalValue>(V1)) { 906 if (isa<ConstantExpr>(V2)) { // Swap as necessary. 907 ICmpInst::Predicate SwappedRelation = 908 evaluateICmpRelation(V2, V1, isSigned); 909 if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE) 910 return ICmpInst::getSwappedPredicate(SwappedRelation); 911 else 912 return ICmpInst::BAD_ICMP_PREDICATE; 913 } 914 915 // Now we know that the RHS is a GlobalValue or simple constant, 916 // which (since the types must match) means that it's a ConstantPointerNull. 917 if (const GlobalValue *CPR2 = dyn_cast<GlobalValue>(V2)) { 918 if (!CPR1->hasExternalWeakLinkage() || !CPR2->hasExternalWeakLinkage()) 919 return ICmpInst::ICMP_NE; 920 } else { 921 // GlobalVals can never be null. 922 assert(isa<ConstantPointerNull>(V2) && "Canonicalization guarantee!"); 923 if (!CPR1->hasExternalWeakLinkage()) 924 return ICmpInst::ICMP_NE; 925 } 926 } else { 927 // Ok, the LHS is known to be a constantexpr. The RHS can be any of a 928 // constantexpr, a CPR, or a simple constant. 929 const ConstantExpr *CE1 = cast<ConstantExpr>(V1); 930 const Constant *CE1Op0 = CE1->getOperand(0); 931 932 switch (CE1->getOpcode()) { 933 case Instruction::Trunc: 934 case Instruction::FPTrunc: 935 case Instruction::FPExt: 936 case Instruction::FPToUI: 937 case Instruction::FPToSI: 938 break; // We can't evaluate floating point casts or truncations. 939 940 case Instruction::UIToFP: 941 case Instruction::SIToFP: 942 case Instruction::IntToPtr: 943 case Instruction::BitCast: 944 case Instruction::ZExt: 945 case Instruction::SExt: 946 case Instruction::PtrToInt: 947 // If the cast is not actually changing bits, and the second operand is a 948 // null pointer, do the comparison with the pre-casted value. 949 if (V2->isNullValue() && 950 (isa<PointerType>(CE1->getType()) || CE1->getType()->isInteger())) { 951 bool sgnd = CE1->getOpcode() == Instruction::ZExt ? false : 952 (CE1->getOpcode() == Instruction::SExt ? true : 953 (CE1->getOpcode() == Instruction::PtrToInt ? false : isSigned)); 954 return evaluateICmpRelation( 955 CE1Op0, Constant::getNullValue(CE1Op0->getType()), sgnd); 956 } 957 958 // If the dest type is a pointer type, and the RHS is a constantexpr cast 959 // from the same type as the src of the LHS, evaluate the inputs. This is 960 // important for things like "icmp eq (cast 4 to int*), (cast 5 to int*)", 961 // which happens a lot in compilers with tagged integers. 962 if (const ConstantExpr *CE2 = dyn_cast<ConstantExpr>(V2)) 963 if (CE2->isCast() && isa<PointerType>(CE1->getType()) && 964 CE1->getOperand(0)->getType() == CE2->getOperand(0)->getType() && 965 CE1->getOperand(0)->getType()->isInteger()) { 966 bool sgnd = CE1->getOpcode() == Instruction::ZExt ? false : 967 (CE1->getOpcode() == Instruction::SExt ? true : 968 (CE1->getOpcode() == Instruction::PtrToInt ? false : isSigned)); 969 return evaluateICmpRelation(CE1->getOperand(0), CE2->getOperand(0), 970 sgnd); 971 } 972 break; 973 974 case Instruction::GetElementPtr: 975 // Ok, since this is a getelementptr, we know that the constant has a 976 // pointer type. Check the various cases. 977 if (isa<ConstantPointerNull>(V2)) { 978 // If we are comparing a GEP to a null pointer, check to see if the base 979 // of the GEP equals the null pointer. 980 if (const GlobalValue *GV = dyn_cast<GlobalValue>(CE1Op0)) { 981 if (GV->hasExternalWeakLinkage()) 982 // Weak linkage GVals could be zero or not. We're comparing that 983 // to null pointer so its greater-or-equal 984 return isSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; 985 else 986 // If its not weak linkage, the GVal must have a non-zero address 987 // so the result is greater-than 988 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 989 } else if (isa<ConstantPointerNull>(CE1Op0)) { 990 // If we are indexing from a null pointer, check to see if we have any 991 // non-zero indices. 992 for (unsigned i = 1, e = CE1->getNumOperands(); i != e; ++i) 993 if (!CE1->getOperand(i)->isNullValue()) 994 // Offsetting from null, must not be equal. 995 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 996 // Only zero indexes from null, must still be zero. 997 return ICmpInst::ICMP_EQ; 998 } 999 // Otherwise, we can't really say if the first operand is null or not. 1000 } else if (const GlobalValue *CPR2 = dyn_cast<GlobalValue>(V2)) { 1001 if (isa<ConstantPointerNull>(CE1Op0)) { 1002 if (CPR2->hasExternalWeakLinkage()) 1003 // Weak linkage GVals could be zero or not. We're comparing it to 1004 // a null pointer, so its less-or-equal 1005 return isSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; 1006 else 1007 // If its not weak linkage, the GVal must have a non-zero address 1008 // so the result is less-than 1009 return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 1010 } else if (const GlobalValue *CPR1 = dyn_cast<GlobalValue>(CE1Op0)) { 1011 if (CPR1 == CPR2) { 1012 // If this is a getelementptr of the same global, then it must be 1013 // different. Because the types must match, the getelementptr could 1014 // only have at most one index, and because we fold getelementptr's 1015 // with a single zero index, it must be nonzero. 1016 assert(CE1->getNumOperands() == 2 && 1017 !CE1->getOperand(1)->isNullValue() && 1018 "Suprising getelementptr!"); 1019 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1020 } else { 1021 // If they are different globals, we don't know what the value is, 1022 // but they can't be equal. 1023 return ICmpInst::ICMP_NE; 1024 } 1025 } 1026 } else { 1027 const ConstantExpr *CE2 = cast<ConstantExpr>(V2); 1028 const Constant *CE2Op0 = CE2->getOperand(0); 1029 1030 // There are MANY other foldings that we could perform here. They will 1031 // probably be added on demand, as they seem needed. 1032 switch (CE2->getOpcode()) { 1033 default: break; 1034 case Instruction::GetElementPtr: 1035 // By far the most common case to handle is when the base pointers are 1036 // obviously to the same or different globals. 1037 if (isa<GlobalValue>(CE1Op0) && isa<GlobalValue>(CE2Op0)) { 1038 if (CE1Op0 != CE2Op0) // Don't know relative ordering, but not equal 1039 return ICmpInst::ICMP_NE; 1040 // Ok, we know that both getelementptr instructions are based on the 1041 // same global. From this, we can precisely determine the relative 1042 // ordering of the resultant pointers. 1043 unsigned i = 1; 1044 1045 // Compare all of the operands the GEP's have in common. 1046 gep_type_iterator GTI = gep_type_begin(CE1); 1047 for (;i != CE1->getNumOperands() && i != CE2->getNumOperands(); 1048 ++i, ++GTI) 1049 switch (IdxCompare(CE1->getOperand(i), CE2->getOperand(i), 1050 GTI.getIndexedType())) { 1051 case -1: return isSigned ? ICmpInst::ICMP_SLT:ICmpInst::ICMP_ULT; 1052 case 1: return isSigned ? ICmpInst::ICMP_SGT:ICmpInst::ICMP_UGT; 1053 case -2: return ICmpInst::BAD_ICMP_PREDICATE; 1054 } 1055 1056 // Ok, we ran out of things they have in common. If any leftovers 1057 // are non-zero then we have a difference, otherwise we are equal. 1058 for (; i < CE1->getNumOperands(); ++i) 1059 if (!CE1->getOperand(i)->isNullValue()) 1060 if (isa<ConstantInt>(CE1->getOperand(i))) 1061 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1062 else 1063 return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal. 1064 1065 for (; i < CE2->getNumOperands(); ++i) 1066 if (!CE2->getOperand(i)->isNullValue()) 1067 if (isa<ConstantInt>(CE2->getOperand(i))) 1068 return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 1069 else 1070 return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal. 1071 return ICmpInst::ICMP_EQ; 1072 } 1073 } 1074 } 1075 default: 1076 break; 1077 } 1078 } 1079 1080 return ICmpInst::BAD_ICMP_PREDICATE; 1081} 1082 1083Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred, 1084 const Constant *C1, 1085 const Constant *C2) { 1086 1087 // Handle some degenerate cases first 1088 if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) 1089 return UndefValue::get(Type::Int1Ty); 1090 1091 // icmp eq/ne(null,GV) -> false/true 1092 if (C1->isNullValue()) { 1093 if (const GlobalValue *GV = dyn_cast<GlobalValue>(C2)) 1094 if (!GV->hasExternalWeakLinkage()) // External weak GV can be null 1095 if (pred == ICmpInst::ICMP_EQ) 1096 return ConstantInt::getFalse(); 1097 else if (pred == ICmpInst::ICMP_NE) 1098 return ConstantInt::getTrue(); 1099 // icmp eq/ne(GV,null) -> false/true 1100 } else if (C2->isNullValue()) { 1101 if (const GlobalValue *GV = dyn_cast<GlobalValue>(C1)) 1102 if (!GV->hasExternalWeakLinkage()) // External weak GV can be null 1103 if (pred == ICmpInst::ICMP_EQ) 1104 return ConstantInt::getFalse(); 1105 else if (pred == ICmpInst::ICMP_NE) 1106 return ConstantInt::getTrue(); 1107 } 1108 1109 if (isa<ConstantInt>(C1) && isa<ConstantInt>(C2)) { 1110 APInt V1 = cast<ConstantInt>(C1)->getValue(); 1111 APInt V2 = cast<ConstantInt>(C2)->getValue(); 1112 switch (pred) { 1113 default: assert(0 && "Invalid ICmp Predicate"); return 0; 1114 case ICmpInst::ICMP_EQ: return ConstantInt::get(Type::Int1Ty, V1 == V2); 1115 case ICmpInst::ICMP_NE: return ConstantInt::get(Type::Int1Ty, V1 != V2); 1116 case ICmpInst::ICMP_SLT:return ConstantInt::get(Type::Int1Ty, V1.slt(V2)); 1117 case ICmpInst::ICMP_SGT:return ConstantInt::get(Type::Int1Ty, V1.sgt(V2)); 1118 case ICmpInst::ICMP_SLE:return ConstantInt::get(Type::Int1Ty, V1.sle(V2)); 1119 case ICmpInst::ICMP_SGE:return ConstantInt::get(Type::Int1Ty, V1.sge(V2)); 1120 case ICmpInst::ICMP_ULT:return ConstantInt::get(Type::Int1Ty, V1.ult(V2)); 1121 case ICmpInst::ICMP_UGT:return ConstantInt::get(Type::Int1Ty, V1.ugt(V2)); 1122 case ICmpInst::ICMP_ULE:return ConstantInt::get(Type::Int1Ty, V1.ule(V2)); 1123 case ICmpInst::ICMP_UGE:return ConstantInt::get(Type::Int1Ty, V1.uge(V2)); 1124 } 1125 } else if (isa<ConstantFP>(C1) && isa<ConstantFP>(C2)) { 1126 double C1Val = cast<ConstantFP>(C1)->getValue(); 1127 double C2Val = cast<ConstantFP>(C2)->getValue(); 1128 switch (pred) { 1129 default: assert(0 && "Invalid FCmp Predicate"); return 0; 1130 case FCmpInst::FCMP_FALSE: return ConstantInt::getFalse(); 1131 case FCmpInst::FCMP_TRUE: return ConstantInt::getTrue(); 1132 case FCmpInst::FCMP_UNO: 1133 return ConstantInt::get(Type::Int1Ty, C1Val != C1Val || C2Val != C2Val); 1134 case FCmpInst::FCMP_ORD: 1135 return ConstantInt::get(Type::Int1Ty, C1Val == C1Val && C2Val == C2Val); 1136 case FCmpInst::FCMP_UEQ: 1137 if (C1Val != C1Val || C2Val != C2Val) 1138 return ConstantInt::getTrue(); 1139 /* FALL THROUGH */ 1140 case FCmpInst::FCMP_OEQ: 1141 return ConstantInt::get(Type::Int1Ty, C1Val == C2Val); 1142 case FCmpInst::FCMP_UNE: 1143 if (C1Val != C1Val || C2Val != C2Val) 1144 return ConstantInt::getTrue(); 1145 /* FALL THROUGH */ 1146 case FCmpInst::FCMP_ONE: 1147 return ConstantInt::get(Type::Int1Ty, C1Val != C2Val); 1148 case FCmpInst::FCMP_ULT: 1149 if (C1Val != C1Val || C2Val != C2Val) 1150 return ConstantInt::getTrue(); 1151 /* FALL THROUGH */ 1152 case FCmpInst::FCMP_OLT: 1153 return ConstantInt::get(Type::Int1Ty, C1Val < C2Val); 1154 case FCmpInst::FCMP_UGT: 1155 if (C1Val != C1Val || C2Val != C2Val) 1156 return ConstantInt::getTrue(); 1157 /* FALL THROUGH */ 1158 case FCmpInst::FCMP_OGT: 1159 return ConstantInt::get(Type::Int1Ty, C1Val > C2Val); 1160 case FCmpInst::FCMP_ULE: 1161 if (C1Val != C1Val || C2Val != C2Val) 1162 return ConstantInt::getTrue(); 1163 /* FALL THROUGH */ 1164 case FCmpInst::FCMP_OLE: 1165 return ConstantInt::get(Type::Int1Ty, C1Val <= C2Val); 1166 case FCmpInst::FCMP_UGE: 1167 if (C1Val != C1Val || C2Val != C2Val) 1168 return ConstantInt::getTrue(); 1169 /* FALL THROUGH */ 1170 case FCmpInst::FCMP_OGE: 1171 return ConstantInt::get(Type::Int1Ty, C1Val >= C2Val); 1172 } 1173 } else if (const ConstantVector *CP1 = dyn_cast<ConstantVector>(C1)) { 1174 if (const ConstantVector *CP2 = dyn_cast<ConstantVector>(C2)) { 1175 if (pred == FCmpInst::FCMP_OEQ || pred == FCmpInst::FCMP_UEQ) { 1176 for (unsigned i = 0, e = CP1->getNumOperands(); i != e; ++i) { 1177 Constant *C= ConstantExpr::getFCmp(FCmpInst::FCMP_OEQ, 1178 const_cast<Constant*>(CP1->getOperand(i)), 1179 const_cast<Constant*>(CP2->getOperand(i))); 1180 if (ConstantInt *CB = dyn_cast<ConstantInt>(C)) 1181 return CB; 1182 } 1183 // Otherwise, could not decide from any element pairs. 1184 return 0; 1185 } else if (pred == ICmpInst::ICMP_EQ) { 1186 for (unsigned i = 0, e = CP1->getNumOperands(); i != e; ++i) { 1187 Constant *C = ConstantExpr::getICmp(ICmpInst::ICMP_EQ, 1188 const_cast<Constant*>(CP1->getOperand(i)), 1189 const_cast<Constant*>(CP2->getOperand(i))); 1190 if (ConstantInt *CB = dyn_cast<ConstantInt>(C)) 1191 return CB; 1192 } 1193 // Otherwise, could not decide from any element pairs. 1194 return 0; 1195 } 1196 } 1197 } 1198 1199 if (C1->getType()->isFloatingPoint()) { 1200 switch (evaluateFCmpRelation(C1, C2)) { 1201 default: assert(0 && "Unknown relation!"); 1202 case FCmpInst::FCMP_UNO: 1203 case FCmpInst::FCMP_ORD: 1204 case FCmpInst::FCMP_UEQ: 1205 case FCmpInst::FCMP_UNE: 1206 case FCmpInst::FCMP_ULT: 1207 case FCmpInst::FCMP_UGT: 1208 case FCmpInst::FCMP_ULE: 1209 case FCmpInst::FCMP_UGE: 1210 case FCmpInst::FCMP_TRUE: 1211 case FCmpInst::FCMP_FALSE: 1212 case FCmpInst::BAD_FCMP_PREDICATE: 1213 break; // Couldn't determine anything about these constants. 1214 case FCmpInst::FCMP_OEQ: // We know that C1 == C2 1215 return ConstantInt::get(Type::Int1Ty, 1216 pred == FCmpInst::FCMP_UEQ || pred == FCmpInst::FCMP_OEQ || 1217 pred == FCmpInst::FCMP_ULE || pred == FCmpInst::FCMP_OLE || 1218 pred == FCmpInst::FCMP_UGE || pred == FCmpInst::FCMP_OGE); 1219 case FCmpInst::FCMP_OLT: // We know that C1 < C2 1220 return ConstantInt::get(Type::Int1Ty, 1221 pred == FCmpInst::FCMP_UNE || pred == FCmpInst::FCMP_ONE || 1222 pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT || 1223 pred == FCmpInst::FCMP_ULE || pred == FCmpInst::FCMP_OLE); 1224 case FCmpInst::FCMP_OGT: // We know that C1 > C2 1225 return ConstantInt::get(Type::Int1Ty, 1226 pred == FCmpInst::FCMP_UNE || pred == FCmpInst::FCMP_ONE || 1227 pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT || 1228 pred == FCmpInst::FCMP_UGE || pred == FCmpInst::FCMP_OGE); 1229 case FCmpInst::FCMP_OLE: // We know that C1 <= C2 1230 // We can only partially decide this relation. 1231 if (pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT) 1232 return ConstantInt::getFalse(); 1233 if (pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT) 1234 return ConstantInt::getTrue(); 1235 break; 1236 case FCmpInst::FCMP_OGE: // We known that C1 >= C2 1237 // We can only partially decide this relation. 1238 if (pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT) 1239 return ConstantInt::getFalse(); 1240 if (pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT) 1241 return ConstantInt::getTrue(); 1242 break; 1243 case ICmpInst::ICMP_NE: // We know that C1 != C2 1244 // We can only partially decide this relation. 1245 if (pred == FCmpInst::FCMP_OEQ || pred == FCmpInst::FCMP_UEQ) 1246 return ConstantInt::getFalse(); 1247 if (pred == FCmpInst::FCMP_ONE || pred == FCmpInst::FCMP_UNE) 1248 return ConstantInt::getTrue(); 1249 break; 1250 } 1251 } else { 1252 // Evaluate the relation between the two constants, per the predicate. 1253 switch (evaluateICmpRelation(C1, C2, CmpInst::isSigned(pred))) { 1254 default: assert(0 && "Unknown relational!"); 1255 case ICmpInst::BAD_ICMP_PREDICATE: 1256 break; // Couldn't determine anything about these constants. 1257 case ICmpInst::ICMP_EQ: // We know the constants are equal! 1258 // If we know the constants are equal, we can decide the result of this 1259 // computation precisely. 1260 return ConstantInt::get(Type::Int1Ty, 1261 pred == ICmpInst::ICMP_EQ || 1262 pred == ICmpInst::ICMP_ULE || 1263 pred == ICmpInst::ICMP_SLE || 1264 pred == ICmpInst::ICMP_UGE || 1265 pred == ICmpInst::ICMP_SGE); 1266 case ICmpInst::ICMP_ULT: 1267 // If we know that C1 < C2, we can decide the result of this computation 1268 // precisely. 1269 return ConstantInt::get(Type::Int1Ty, 1270 pred == ICmpInst::ICMP_ULT || 1271 pred == ICmpInst::ICMP_NE || 1272 pred == ICmpInst::ICMP_ULE); 1273 case ICmpInst::ICMP_SLT: 1274 // If we know that C1 < C2, we can decide the result of this computation 1275 // precisely. 1276 return ConstantInt::get(Type::Int1Ty, 1277 pred == ICmpInst::ICMP_SLT || 1278 pred == ICmpInst::ICMP_NE || 1279 pred == ICmpInst::ICMP_SLE); 1280 case ICmpInst::ICMP_UGT: 1281 // If we know that C1 > C2, we can decide the result of this computation 1282 // precisely. 1283 return ConstantInt::get(Type::Int1Ty, 1284 pred == ICmpInst::ICMP_UGT || 1285 pred == ICmpInst::ICMP_NE || 1286 pred == ICmpInst::ICMP_UGE); 1287 case ICmpInst::ICMP_SGT: 1288 // If we know that C1 > C2, we can decide the result of this computation 1289 // precisely. 1290 return ConstantInt::get(Type::Int1Ty, 1291 pred == ICmpInst::ICMP_SGT || 1292 pred == ICmpInst::ICMP_NE || 1293 pred == ICmpInst::ICMP_SGE); 1294 case ICmpInst::ICMP_ULE: 1295 // If we know that C1 <= C2, we can only partially decide this relation. 1296 if (pred == ICmpInst::ICMP_UGT) return ConstantInt::getFalse(); 1297 if (pred == ICmpInst::ICMP_ULT) return ConstantInt::getTrue(); 1298 break; 1299 case ICmpInst::ICMP_SLE: 1300 // If we know that C1 <= C2, we can only partially decide this relation. 1301 if (pred == ICmpInst::ICMP_SGT) return ConstantInt::getFalse(); 1302 if (pred == ICmpInst::ICMP_SLT) return ConstantInt::getTrue(); 1303 break; 1304 1305 case ICmpInst::ICMP_UGE: 1306 // If we know that C1 >= C2, we can only partially decide this relation. 1307 if (pred == ICmpInst::ICMP_ULT) return ConstantInt::getFalse(); 1308 if (pred == ICmpInst::ICMP_UGT) return ConstantInt::getTrue(); 1309 break; 1310 case ICmpInst::ICMP_SGE: 1311 // If we know that C1 >= C2, we can only partially decide this relation. 1312 if (pred == ICmpInst::ICMP_SLT) return ConstantInt::getFalse(); 1313 if (pred == ICmpInst::ICMP_SGT) return ConstantInt::getTrue(); 1314 break; 1315 1316 case ICmpInst::ICMP_NE: 1317 // If we know that C1 != C2, we can only partially decide this relation. 1318 if (pred == ICmpInst::ICMP_EQ) return ConstantInt::getFalse(); 1319 if (pred == ICmpInst::ICMP_NE) return ConstantInt::getTrue(); 1320 break; 1321 } 1322 1323 if (!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) { 1324 // If C2 is a constant expr and C1 isn't, flop them around and fold the 1325 // other way if possible. 1326 switch (pred) { 1327 case ICmpInst::ICMP_EQ: 1328 case ICmpInst::ICMP_NE: 1329 // No change of predicate required. 1330 return ConstantFoldCompareInstruction(pred, C2, C1); 1331 1332 case ICmpInst::ICMP_ULT: 1333 case ICmpInst::ICMP_SLT: 1334 case ICmpInst::ICMP_UGT: 1335 case ICmpInst::ICMP_SGT: 1336 case ICmpInst::ICMP_ULE: 1337 case ICmpInst::ICMP_SLE: 1338 case ICmpInst::ICMP_UGE: 1339 case ICmpInst::ICMP_SGE: 1340 // Change the predicate as necessary to swap the operands. 1341 pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred); 1342 return ConstantFoldCompareInstruction(pred, C2, C1); 1343 1344 default: // These predicates cannot be flopped around. 1345 break; 1346 } 1347 } 1348 } 1349 return 0; 1350} 1351 1352Constant *llvm::ConstantFoldGetElementPtr(const Constant *C, 1353 Constant* const *Idxs, 1354 unsigned NumIdx) { 1355 if (NumIdx == 0 || 1356 (NumIdx == 1 && Idxs[0]->isNullValue())) 1357 return const_cast<Constant*>(C); 1358 1359 if (isa<UndefValue>(C)) { 1360 const Type *Ty = GetElementPtrInst::getIndexedType(C->getType(), 1361 (Value **)Idxs, 1362 (Value **)Idxs+NumIdx, 1363 true); 1364 assert(Ty != 0 && "Invalid indices for GEP!"); 1365 return UndefValue::get(PointerType::get(Ty)); 1366 } 1367 1368 Constant *Idx0 = Idxs[0]; 1369 if (C->isNullValue()) { 1370 bool isNull = true; 1371 for (unsigned i = 0, e = NumIdx; i != e; ++i) 1372 if (!Idxs[i]->isNullValue()) { 1373 isNull = false; 1374 break; 1375 } 1376 if (isNull) { 1377 const Type *Ty = GetElementPtrInst::getIndexedType(C->getType(), 1378 (Value**)Idxs, 1379 (Value**)Idxs+NumIdx, 1380 true); 1381 assert(Ty != 0 && "Invalid indices for GEP!"); 1382 return ConstantPointerNull::get(PointerType::get(Ty)); 1383 } 1384 } 1385 1386 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(const_cast<Constant*>(C))) { 1387 // Combine Indices - If the source pointer to this getelementptr instruction 1388 // is a getelementptr instruction, combine the indices of the two 1389 // getelementptr instructions into a single instruction. 1390 // 1391 if (CE->getOpcode() == Instruction::GetElementPtr) { 1392 const Type *LastTy = 0; 1393 for (gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE); 1394 I != E; ++I) 1395 LastTy = *I; 1396 1397 if ((LastTy && isa<ArrayType>(LastTy)) || Idx0->isNullValue()) { 1398 SmallVector<Value*, 16> NewIndices; 1399 NewIndices.reserve(NumIdx + CE->getNumOperands()); 1400 for (unsigned i = 1, e = CE->getNumOperands()-1; i != e; ++i) 1401 NewIndices.push_back(CE->getOperand(i)); 1402 1403 // Add the last index of the source with the first index of the new GEP. 1404 // Make sure to handle the case when they are actually different types. 1405 Constant *Combined = CE->getOperand(CE->getNumOperands()-1); 1406 // Otherwise it must be an array. 1407 if (!Idx0->isNullValue()) { 1408 const Type *IdxTy = Combined->getType(); 1409 if (IdxTy != Idx0->getType()) { 1410 Constant *C1 = ConstantExpr::getSExtOrBitCast(Idx0, Type::Int64Ty); 1411 Constant *C2 = ConstantExpr::getSExtOrBitCast(Combined, 1412 Type::Int64Ty); 1413 Combined = ConstantExpr::get(Instruction::Add, C1, C2); 1414 } else { 1415 Combined = 1416 ConstantExpr::get(Instruction::Add, Idx0, Combined); 1417 } 1418 } 1419 1420 NewIndices.push_back(Combined); 1421 NewIndices.insert(NewIndices.end(), Idxs+1, Idxs+NumIdx); 1422 return ConstantExpr::getGetElementPtr(CE->getOperand(0), &NewIndices[0], 1423 NewIndices.size()); 1424 } 1425 } 1426 1427 // Implement folding of: 1428 // int* getelementptr ([2 x int]* cast ([3 x int]* %X to [2 x int]*), 1429 // long 0, long 0) 1430 // To: int* getelementptr ([3 x int]* %X, long 0, long 0) 1431 // 1432 if (CE->isCast() && NumIdx > 1 && Idx0->isNullValue()) { 1433 if (const PointerType *SPT = 1434 dyn_cast<PointerType>(CE->getOperand(0)->getType())) 1435 if (const ArrayType *SAT = dyn_cast<ArrayType>(SPT->getElementType())) 1436 if (const ArrayType *CAT = 1437 dyn_cast<ArrayType>(cast<PointerType>(C->getType())->getElementType())) 1438 if (CAT->getElementType() == SAT->getElementType()) 1439 return ConstantExpr::getGetElementPtr( 1440 (Constant*)CE->getOperand(0), Idxs, NumIdx); 1441 } 1442 1443 // Fold: getelementptr (i8* inttoptr (i64 1 to i8*), i32 -1) 1444 // Into: inttoptr (i64 0 to i8*) 1445 // This happens with pointers to member functions in C++. 1446 if (CE->getOpcode() == Instruction::IntToPtr && NumIdx == 1 && 1447 isa<ConstantInt>(CE->getOperand(0)) && isa<ConstantInt>(Idxs[0]) && 1448 cast<PointerType>(CE->getType())->getElementType() == Type::Int8Ty) { 1449 Constant *Base = CE->getOperand(0); 1450 Constant *Offset = Idxs[0]; 1451 1452 // Convert the smaller integer to the larger type. 1453 if (Offset->getType()->getPrimitiveSizeInBits() < 1454 Base->getType()->getPrimitiveSizeInBits()) 1455 Offset = ConstantExpr::getSExt(Offset, Base->getType()); 1456 else if (Base->getType()->getPrimitiveSizeInBits() < 1457 Offset->getType()->getPrimitiveSizeInBits()) 1458 Base = ConstantExpr::getZExt(Base, Base->getType()); 1459 1460 Base = ConstantExpr::getAdd(Base, Offset); 1461 return ConstantExpr::getIntToPtr(Base, CE->getType()); 1462 } 1463 } 1464 return 0; 1465} 1466 1467