ConstantFold.cpp revision 4ada00d166b1d265fa4e751b63d7f869c7541f1b
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 packed 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/// @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 return UndefValue::get(DestTy); 145 146 // If the cast operand is a constant expression, there's a few things we can 147 // do to try to simplify it. 148 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { 149 if (CE->isCast()) { 150 // Try hard to fold cast of cast because they are often eliminable. 151 if (unsigned newOpc = foldConstantCastPair(opc, CE, DestTy)) 152 return ConstantExpr::getCast(newOpc, CE->getOperand(0), DestTy); 153 } else if (CE->getOpcode() == Instruction::GetElementPtr) { 154 // If all of the indexes in the GEP are null values, there is no pointer 155 // adjustment going on. We might as well cast the source pointer. 156 bool isAllNull = true; 157 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i) 158 if (!CE->getOperand(i)->isNullValue()) { 159 isAllNull = false; 160 break; 161 } 162 if (isAllNull) 163 // This is casting one pointer type to another, always BitCast 164 return ConstantExpr::getPointerCast(CE->getOperand(0), DestTy); 165 } 166 } 167 168 // We actually have to do a cast now. Perform the cast according to the 169 // opcode specified. 170 switch (opc) { 171 case Instruction::FPTrunc: 172 case Instruction::FPExt: 173 if (const ConstantFP *FPC = dyn_cast<ConstantFP>(V)) 174 return ConstantFP::get(DestTy, FPC->getValue()); 175 return 0; // Can't fold. 176 case Instruction::FPToUI: 177 if (const ConstantFP *FPC = dyn_cast<ConstantFP>(V)) { 178 uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 179 APInt Val(APIntOps::RoundDoubleToAPInt(FPC->getValue(), DestBitWidth)); 180 return ConstantInt::get(Val); 181 } 182 return 0; // Can't fold. 183 case Instruction::FPToSI: 184 if (const ConstantFP *FPC = dyn_cast<ConstantFP>(V)) { 185 uint32_t DestBitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 186 APInt Val(APIntOps::RoundDoubleToAPInt(FPC->getValue(), DestBitWidth)); 187 return ConstantInt::get(Val); 188 } 189 return 0; // Can't fold. 190 case Instruction::IntToPtr: //always treated as unsigned 191 if (V->isNullValue()) // Is it an integral null value? 192 return ConstantPointerNull::get(cast<PointerType>(DestTy)); 193 return 0; // Other pointer types cannot be casted 194 case Instruction::PtrToInt: // always treated as unsigned 195 if (V->isNullValue()) // is it a null pointer value? 196 return ConstantInt::get(DestTy, 0); 197 return 0; // Other pointer types cannot be casted 198 case Instruction::UIToFP: 199 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) 200 return ConstantFP::get(DestTy, CI->getValue().roundToDouble()); 201 return 0; 202 case Instruction::SIToFP: 203 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) 204 return ConstantFP::get(DestTy, CI->getValue().signedRoundToDouble()); 205 return 0; 206 case Instruction::ZExt: 207 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 208 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 209 APInt Result(CI->getValue()); 210 Result.zext(BitWidth); 211 return ConstantInt::get(Result); 212 } 213 return 0; 214 case Instruction::SExt: 215 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 216 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 217 APInt Result(CI->getValue()); 218 Result.sext(BitWidth); 219 return ConstantInt::get(Result); 220 } 221 return 0; 222 case Instruction::Trunc: 223 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 224 uint32_t BitWidth = cast<IntegerType>(DestTy)->getBitWidth(); 225 APInt Result(CI->getValue()); 226 Result.trunc(BitWidth); 227 return ConstantInt::get(Result); 228 } 229 return 0; 230 case Instruction::BitCast: 231 if (SrcTy == DestTy) 232 return (Constant*)V; // no-op cast 233 234 // Check to see if we are casting a pointer to an aggregate to a pointer to 235 // the first element. If so, return the appropriate GEP instruction. 236 if (const PointerType *PTy = dyn_cast<PointerType>(V->getType())) 237 if (const PointerType *DPTy = dyn_cast<PointerType>(DestTy)) { 238 SmallVector<Value*, 8> IdxList; 239 IdxList.push_back(Constant::getNullValue(Type::Int32Ty)); 240 const Type *ElTy = PTy->getElementType(); 241 while (ElTy != DPTy->getElementType()) { 242 if (const StructType *STy = dyn_cast<StructType>(ElTy)) { 243 if (STy->getNumElements() == 0) break; 244 ElTy = STy->getElementType(0); 245 IdxList.push_back(Constant::getNullValue(Type::Int32Ty)); 246 } else if (const SequentialType *STy = 247 dyn_cast<SequentialType>(ElTy)) { 248 if (isa<PointerType>(ElTy)) break; // Can't index into pointers! 249 ElTy = STy->getElementType(); 250 IdxList.push_back(IdxList[0]); 251 } else { 252 break; 253 } 254 } 255 256 if (ElTy == DPTy->getElementType()) 257 return ConstantExpr::getGetElementPtr( 258 const_cast<Constant*>(V), &IdxList[0], IdxList.size()); 259 } 260 261 // Handle casts from one packed constant to another. We know that the src 262 // and dest type have the same size (otherwise its an illegal cast). 263 if (const VectorType *DestPTy = dyn_cast<VectorType>(DestTy)) { 264 if (const VectorType *SrcTy = dyn_cast<VectorType>(V->getType())) { 265 assert(DestPTy->getBitWidth() == SrcTy->getBitWidth() && 266 "Not cast between same sized vectors!"); 267 // First, check for null and undef 268 if (isa<ConstantAggregateZero>(V)) 269 return Constant::getNullValue(DestTy); 270 if (isa<UndefValue>(V)) 271 return UndefValue::get(DestTy); 272 273 if (const ConstantVector *CV = dyn_cast<ConstantVector>(V)) { 274 // This is a cast from a ConstantVector of one type to a 275 // ConstantVector of another type. Check to see if all elements of 276 // the input are simple. 277 bool AllSimpleConstants = true; 278 for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) { 279 if (!isa<ConstantInt>(CV->getOperand(i)) && 280 !isa<ConstantFP>(CV->getOperand(i))) { 281 AllSimpleConstants = false; 282 break; 283 } 284 } 285 286 // If all of the elements are simple constants, we can fold this. 287 if (AllSimpleConstants) 288 return CastConstantVector(const_cast<ConstantVector*>(CV), DestPTy); 289 } 290 } 291 } 292 293 // Finally, implement bitcast folding now. The code below doesn't handle 294 // bitcast right. 295 if (isa<ConstantPointerNull>(V)) // ptr->ptr cast. 296 return ConstantPointerNull::get(cast<PointerType>(DestTy)); 297 298 // Handle integral constant input. 299 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V)) { 300 if (DestTy->isInteger()) 301 // Integral -> Integral. This is a no-op because the bit widths must 302 // be the same. Consequently, we just fold to V. 303 return const_cast<Constant*>(V); 304 305 if (DestTy->isFloatingPoint()) { 306 if (DestTy == Type::FloatTy) 307 return ConstantFP::get(DestTy, CI->getValue().bitsToFloat()); 308 assert(DestTy == Type::DoubleTy && "Unknown FP type!"); 309 return ConstantFP::get(DestTy, CI->getValue().bitsToDouble()); 310 } 311 // Otherwise, can't fold this (packed?) 312 return 0; 313 } 314 315 // Handle ConstantFP input. 316 if (const ConstantFP *FP = dyn_cast<ConstantFP>(V)) { 317 // FP -> Integral. 318 if (DestTy == Type::Int32Ty) { 319 APInt Val(32, 0); 320 return ConstantInt::get(Val.floatToBits(FP->getValue())); 321 } else { 322 assert(DestTy == Type::Int64Ty && "only support f32/f64 for now!"); 323 APInt Val(64, 0); 324 return ConstantInt::get(Val.doubleToBits(FP->getValue())); 325 } 326 } 327 return 0; 328 default: 329 assert(!"Invalid CE CastInst opcode"); 330 break; 331 } 332 333 assert(0 && "Failed to cast constant expression"); 334 return 0; 335} 336 337Constant *llvm::ConstantFoldSelectInstruction(const Constant *Cond, 338 const Constant *V1, 339 const Constant *V2) { 340 if (const ConstantInt *CB = dyn_cast<ConstantInt>(Cond)) 341 return const_cast<Constant*>(CB->getZExtValue() ? V1 : V2); 342 343 if (isa<UndefValue>(V1)) return const_cast<Constant*>(V2); 344 if (isa<UndefValue>(V2)) return const_cast<Constant*>(V1); 345 if (isa<UndefValue>(Cond)) return const_cast<Constant*>(V1); 346 if (V1 == V2) return const_cast<Constant*>(V1); 347 return 0; 348} 349 350Constant *llvm::ConstantFoldExtractElementInstruction(const Constant *Val, 351 const Constant *Idx) { 352 if (isa<UndefValue>(Val)) // ee(undef, x) -> undef 353 return UndefValue::get(cast<VectorType>(Val->getType())->getElementType()); 354 if (Val->isNullValue()) // ee(zero, x) -> zero 355 return Constant::getNullValue( 356 cast<VectorType>(Val->getType())->getElementType()); 357 358 if (const ConstantVector *CVal = dyn_cast<ConstantVector>(Val)) { 359 if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx)) { 360 return const_cast<Constant*>(CVal->getOperand(CIdx->getZExtValue())); 361 } else if (isa<UndefValue>(Idx)) { 362 // ee({w,x,y,z}, undef) -> w (an arbitrary value). 363 return const_cast<Constant*>(CVal->getOperand(0)); 364 } 365 } 366 return 0; 367} 368 369Constant *llvm::ConstantFoldInsertElementInstruction(const Constant *Val, 370 const Constant *Elt, 371 const Constant *Idx) { 372 const ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx); 373 if (!CIdx) return 0; 374 APInt idxVal = CIdx->getValue(); 375 if (isa<UndefValue>(Val)) { 376 // Insertion of scalar constant into packed undef 377 // Optimize away insertion of undef 378 if (isa<UndefValue>(Elt)) 379 return const_cast<Constant*>(Val); 380 // Otherwise break the aggregate undef into multiple undefs and do 381 // the insertion 382 unsigned numOps = 383 cast<VectorType>(Val->getType())->getNumElements(); 384 std::vector<Constant*> Ops; 385 Ops.reserve(numOps); 386 for (unsigned i = 0; i < numOps; ++i) { 387 const Constant *Op = 388 (idxVal == i) ? Elt : UndefValue::get(Elt->getType()); 389 Ops.push_back(const_cast<Constant*>(Op)); 390 } 391 return ConstantVector::get(Ops); 392 } 393 if (isa<ConstantAggregateZero>(Val)) { 394 // Insertion of scalar constant into packed aggregate zero 395 // Optimize away insertion of zero 396 if (Elt->isNullValue()) 397 return const_cast<Constant*>(Val); 398 // Otherwise break the aggregate zero into multiple zeros and do 399 // the insertion 400 unsigned numOps = 401 cast<VectorType>(Val->getType())->getNumElements(); 402 std::vector<Constant*> Ops; 403 Ops.reserve(numOps); 404 for (unsigned i = 0; i < numOps; ++i) { 405 const Constant *Op = 406 (idxVal == i) ? Elt : Constant::getNullValue(Elt->getType()); 407 Ops.push_back(const_cast<Constant*>(Op)); 408 } 409 return ConstantVector::get(Ops); 410 } 411 if (const ConstantVector *CVal = dyn_cast<ConstantVector>(Val)) { 412 // Insertion of scalar constant into packed constant 413 std::vector<Constant*> Ops; 414 Ops.reserve(CVal->getNumOperands()); 415 for (unsigned i = 0; i < CVal->getNumOperands(); ++i) { 416 const Constant *Op = 417 (idxVal == i) ? Elt : cast<Constant>(CVal->getOperand(i)); 418 Ops.push_back(const_cast<Constant*>(Op)); 419 } 420 return ConstantVector::get(Ops); 421 } 422 return 0; 423} 424 425Constant *llvm::ConstantFoldShuffleVectorInstruction(const Constant *V1, 426 const Constant *V2, 427 const Constant *Mask) { 428 // TODO: 429 return 0; 430} 431 432/// EvalVectorOp - Given two packed constants and a function pointer, apply the 433/// function pointer to each element pair, producing a new ConstantVector 434/// constant. 435static Constant *EvalVectorOp(const ConstantVector *V1, 436 const ConstantVector *V2, 437 Constant *(*FP)(Constant*, Constant*)) { 438 std::vector<Constant*> Res; 439 for (unsigned i = 0, e = V1->getNumOperands(); i != e; ++i) 440 Res.push_back(FP(const_cast<Constant*>(V1->getOperand(i)), 441 const_cast<Constant*>(V2->getOperand(i)))); 442 return ConstantVector::get(Res); 443} 444 445Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, 446 const Constant *C1, 447 const Constant *C2) { 448 // Handle UndefValue up front 449 if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) { 450 switch (Opcode) { 451 case Instruction::Add: 452 case Instruction::Sub: 453 case Instruction::Xor: 454 return UndefValue::get(C1->getType()); 455 case Instruction::Mul: 456 case Instruction::And: 457 return Constant::getNullValue(C1->getType()); 458 case Instruction::UDiv: 459 case Instruction::SDiv: 460 case Instruction::FDiv: 461 case Instruction::URem: 462 case Instruction::SRem: 463 case Instruction::FRem: 464 if (!isa<UndefValue>(C2)) // undef / X -> 0 465 return Constant::getNullValue(C1->getType()); 466 return const_cast<Constant*>(C2); // X / undef -> undef 467 case Instruction::Or: // X | undef -> -1 468 if (const VectorType *PTy = dyn_cast<VectorType>(C1->getType())) 469 return ConstantVector::getAllOnesValue(PTy); 470 return ConstantInt::getAllOnesValue(C1->getType()); 471 case Instruction::LShr: 472 if (isa<UndefValue>(C2) && isa<UndefValue>(C1)) 473 return const_cast<Constant*>(C1); // undef lshr undef -> undef 474 return Constant::getNullValue(C1->getType()); // X lshr undef -> 0 475 // undef lshr X -> 0 476 case Instruction::AShr: 477 if (!isa<UndefValue>(C2)) 478 return const_cast<Constant*>(C1); // undef ashr X --> undef 479 else if (isa<UndefValue>(C1)) 480 return const_cast<Constant*>(C1); // undef ashr undef -> undef 481 else 482 return const_cast<Constant*>(C1); // X ashr undef --> X 483 case Instruction::Shl: 484 // undef << X -> 0 or X << undef -> 0 485 return Constant::getNullValue(C1->getType()); 486 } 487 } 488 489 if (const ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) { 490 if (isa<ConstantExpr>(C2)) { 491 // There are many possible foldings we could do here. We should probably 492 // at least fold add of a pointer with an integer into the appropriate 493 // getelementptr. This will improve alias analysis a bit. 494 } else { 495 // Just implement a couple of simple identities. 496 switch (Opcode) { 497 case Instruction::Add: 498 if (C2->isNullValue()) return const_cast<Constant*>(C1); // X + 0 == X 499 break; 500 case Instruction::Sub: 501 if (C2->isNullValue()) return const_cast<Constant*>(C1); // X - 0 == X 502 break; 503 case Instruction::Mul: 504 if (C2->isNullValue()) return const_cast<Constant*>(C2); // X * 0 == 0 505 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 506 if (CI->equalsInt(1)) 507 return const_cast<Constant*>(C1); // X * 1 == X 508 break; 509 case Instruction::UDiv: 510 case Instruction::SDiv: 511 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 512 if (CI->equalsInt(1)) 513 return const_cast<Constant*>(C1); // X / 1 == X 514 break; 515 case Instruction::URem: 516 case Instruction::SRem: 517 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 518 if (CI->equalsInt(1)) 519 return Constant::getNullValue(CI->getType()); // X % 1 == 0 520 break; 521 case Instruction::And: 522 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) { 523 if (CI->isZero()) return const_cast<Constant*>(C2); // X & 0 == 0 524 if (CI->isAllOnesValue()) 525 return const_cast<Constant*>(C1); // X & -1 == X 526 527 // (zext i32 to i64) & 4294967295 -> (zext i32 to i64) 528 if (CE1->getOpcode() == Instruction::ZExt) { 529 APInt PossiblySetBits 530 = cast<IntegerType>(CE1->getOperand(0)->getType())->getMask(); 531 PossiblySetBits.zext(C1->getType()->getPrimitiveSizeInBits()); 532 if ((PossiblySetBits & CI->getValue()) == PossiblySetBits) 533 return const_cast<Constant*>(C1); 534 } 535 } 536 if (CE1->isCast() && isa<GlobalValue>(CE1->getOperand(0))) { 537 GlobalValue *CPR = cast<GlobalValue>(CE1->getOperand(0)); 538 539 // Functions are at least 4-byte aligned. If and'ing the address of a 540 // function with a constant < 4, fold it to zero. 541 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 542 if (CI->getValue().ult(APInt(CI->getType()->getBitWidth(),4)) && 543 isa<Function>(CPR)) 544 return Constant::getNullValue(CI->getType()); 545 } 546 break; 547 case Instruction::Or: 548 if (C2->isNullValue()) return const_cast<Constant*>(C1); // X | 0 == X 549 if (const ConstantInt *CI = dyn_cast<ConstantInt>(C2)) 550 if (CI->isAllOnesValue()) 551 return const_cast<Constant*>(C2); // X | -1 == -1 552 break; 553 case Instruction::Xor: 554 if (C2->isNullValue()) return const_cast<Constant*>(C1); // X ^ 0 == X 555 break; 556 case Instruction::AShr: 557 // ashr (zext C to Ty), C2 -> lshr (zext C, CSA), C2 558 if (CE1->getOpcode() == Instruction::ZExt) // Top bits known zero. 559 return ConstantExpr::getLShr(const_cast<Constant*>(C1), 560 const_cast<Constant*>(C2)); 561 break; 562 } 563 } 564 } else if (isa<ConstantExpr>(C2)) { 565 // If C2 is a constant expr and C1 isn't, flop them around and fold the 566 // other way if possible. 567 switch (Opcode) { 568 case Instruction::Add: 569 case Instruction::Mul: 570 case Instruction::And: 571 case Instruction::Or: 572 case Instruction::Xor: 573 // No change of opcode required. 574 return ConstantFoldBinaryInstruction(Opcode, C2, C1); 575 576 case Instruction::Shl: 577 case Instruction::LShr: 578 case Instruction::AShr: 579 case Instruction::Sub: 580 case Instruction::SDiv: 581 case Instruction::UDiv: 582 case Instruction::FDiv: 583 case Instruction::URem: 584 case Instruction::SRem: 585 case Instruction::FRem: 586 default: // These instructions cannot be flopped around. 587 return 0; 588 } 589 } 590 591 // At this point we know neither constant is an UndefValue nor a ConstantExpr 592 // so look at directly computing the value. 593 if (const ConstantInt *CI1 = dyn_cast<ConstantInt>(C1)) { 594 if (const ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) { 595 using namespace APIntOps; 596 APInt C1V = CI1->getValue(); 597 APInt C2V = CI2->getValue(); 598 switch (Opcode) { 599 default: 600 break; 601 case Instruction::Add: 602 return ConstantInt::get(C1V + C2V); 603 case Instruction::Sub: 604 return ConstantInt::get(C1V - C2V); 605 case Instruction::Mul: 606 return ConstantInt::get(C1V * C2V); 607 case Instruction::UDiv: 608 if (CI2->isNullValue()) 609 return 0; // X / 0 -> can't fold 610 return ConstantInt::get(C1V.udiv(C2V)); 611 case Instruction::SDiv: 612 if (CI2->isNullValue()) 613 return 0; // X / 0 -> can't fold 614 if (C2V.isAllOnesValue() && C1V.isMinSignedValue()) 615 return 0; // MIN_INT / -1 -> overflow 616 return ConstantInt::get(C1V.sdiv(C2V)); 617 case Instruction::URem: 618 if (C2->isNullValue()) 619 return 0; // X / 0 -> can't fold 620 return ConstantInt::get(C1V.urem(C2V)); 621 case Instruction::SRem: 622 if (CI2->isNullValue()) 623 return 0; // X % 0 -> can't fold 624 if (C2V.isAllOnesValue() && C1V.isMinSignedValue()) 625 return 0; // MIN_INT % -1 -> overflow 626 return ConstantInt::get(C1V.srem(C2V)); 627 case Instruction::And: 628 return ConstantInt::get(C1V & C2V); 629 case Instruction::Or: 630 return ConstantInt::get(C1V | C2V); 631 case Instruction::Xor: 632 return ConstantInt::get(C1V ^ C2V); 633 case Instruction::Shl: 634 if (uint32_t shiftAmt = C2V.getZExtValue()) 635 if (shiftAmt < C1V.getBitWidth()) 636 return ConstantInt::get(C1V.shl(shiftAmt)); 637 else 638 return UndefValue::get(C1->getType()); // too big shift is undef 639 return const_cast<ConstantInt*>(CI1); // Zero shift is identity 640 case Instruction::LShr: 641 if (uint32_t shiftAmt = C2V.getZExtValue()) 642 if (shiftAmt < C1V.getBitWidth()) 643 return ConstantInt::get(C1V.lshr(shiftAmt)); 644 else 645 return UndefValue::get(C1->getType()); // too big shift is undef 646 return const_cast<ConstantInt*>(CI1); // Zero shift is identity 647 case Instruction::AShr: 648 if (uint32_t shiftAmt = C2V.getZExtValue()) 649 if (shiftAmt < C1V.getBitWidth()) 650 return ConstantInt::get(C1V.ashr(shiftAmt)); 651 else 652 return UndefValue::get(C1->getType()); // too big shift is undef 653 return const_cast<ConstantInt*>(CI1); // Zero shift is identity 654 } 655 } 656 } else if (const ConstantFP *CFP1 = dyn_cast<ConstantFP>(C1)) { 657 if (const ConstantFP *CFP2 = dyn_cast<ConstantFP>(C2)) { 658 double C1Val = CFP1->getValue(); 659 double C2Val = CFP2->getValue(); 660 switch (Opcode) { 661 default: 662 break; 663 case Instruction::Add: 664 return ConstantFP::get(CFP1->getType(), C1Val + C2Val); 665 case Instruction::Sub: 666 return ConstantFP::get(CFP1->getType(), C1Val - C2Val); 667 case Instruction::Mul: 668 return ConstantFP::get(CFP1->getType(), C1Val * C2Val); 669 case Instruction::FDiv: 670 if (CFP2->isExactlyValue(0.0) || CFP2->isExactlyValue(-0.0)) 671 if (CFP1->isExactlyValue(0.0) || CFP1->isExactlyValue(-0.0)) 672 // IEEE 754, Section 7.1, #4 673 return ConstantFP::get(CFP1->getType(), 674 std::numeric_limits<double>::quiet_NaN()); 675 else if (CFP2->isExactlyValue(-0.0) || C1Val < 0.0) 676 // IEEE 754, Section 7.2, negative infinity case 677 return ConstantFP::get(CFP1->getType(), 678 -std::numeric_limits<double>::infinity()); 679 else 680 // IEEE 754, Section 7.2, positive infinity case 681 return ConstantFP::get(CFP1->getType(), 682 std::numeric_limits<double>::infinity()); 683 return ConstantFP::get(CFP1->getType(), C1Val / C2Val); 684 case Instruction::FRem: 685 if (CFP2->isExactlyValue(0.0) || CFP2->isExactlyValue(-0.0)) 686 // IEEE 754, Section 7.1, #5 687 return ConstantFP::get(CFP1->getType(), 688 std::numeric_limits<double>::quiet_NaN()); 689 return ConstantFP::get(CFP1->getType(), std::fmod(C1Val, C2Val)); 690 691 } 692 } 693 } else if (const ConstantVector *CP1 = dyn_cast<ConstantVector>(C1)) { 694 if (const ConstantVector *CP2 = dyn_cast<ConstantVector>(C2)) { 695 switch (Opcode) { 696 default: 697 break; 698 case Instruction::Add: 699 return EvalVectorOp(CP1, CP2, ConstantExpr::getAdd); 700 case Instruction::Sub: 701 return EvalVectorOp(CP1, CP2, ConstantExpr::getSub); 702 case Instruction::Mul: 703 return EvalVectorOp(CP1, CP2, ConstantExpr::getMul); 704 case Instruction::UDiv: 705 return EvalVectorOp(CP1, CP2, ConstantExpr::getUDiv); 706 case Instruction::SDiv: 707 return EvalVectorOp(CP1, CP2, ConstantExpr::getSDiv); 708 case Instruction::FDiv: 709 return EvalVectorOp(CP1, CP2, ConstantExpr::getFDiv); 710 case Instruction::URem: 711 return EvalVectorOp(CP1, CP2, ConstantExpr::getURem); 712 case Instruction::SRem: 713 return EvalVectorOp(CP1, CP2, ConstantExpr::getSRem); 714 case Instruction::FRem: 715 return EvalVectorOp(CP1, CP2, ConstantExpr::getFRem); 716 case Instruction::And: 717 return EvalVectorOp(CP1, CP2, ConstantExpr::getAnd); 718 case Instruction::Or: 719 return EvalVectorOp(CP1, CP2, ConstantExpr::getOr); 720 case Instruction::Xor: 721 return EvalVectorOp(CP1, CP2, ConstantExpr::getXor); 722 } 723 } 724 } 725 726 // We don't know how to fold this 727 return 0; 728} 729 730/// isZeroSizedType - This type is zero sized if its an array or structure of 731/// zero sized types. The only leaf zero sized type is an empty structure. 732static bool isMaybeZeroSizedType(const Type *Ty) { 733 if (isa<OpaqueType>(Ty)) return true; // Can't say. 734 if (const StructType *STy = dyn_cast<StructType>(Ty)) { 735 736 // If all of elements have zero size, this does too. 737 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 738 if (!isMaybeZeroSizedType(STy->getElementType(i))) return false; 739 return true; 740 741 } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) { 742 return isMaybeZeroSizedType(ATy->getElementType()); 743 } 744 return false; 745} 746 747/// IdxCompare - Compare the two constants as though they were getelementptr 748/// indices. This allows coersion of the types to be the same thing. 749/// 750/// If the two constants are the "same" (after coersion), return 0. If the 751/// first is less than the second, return -1, if the second is less than the 752/// first, return 1. If the constants are not integral, return -2. 753/// 754static int IdxCompare(Constant *C1, Constant *C2, const Type *ElTy) { 755 if (C1 == C2) return 0; 756 757 // Ok, we found a different index. If they are not ConstantInt, we can't do 758 // anything with them. 759 if (!isa<ConstantInt>(C1) || !isa<ConstantInt>(C2)) 760 return -2; // don't know! 761 762 // Ok, we have two differing integer indices. Sign extend them to be the same 763 // type. Long is always big enough, so we use it. 764 if (C1->getType() != Type::Int64Ty) 765 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty); 766 767 if (C2->getType() != Type::Int64Ty) 768 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty); 769 770 if (C1 == C2) return 0; // They are equal 771 772 // If the type being indexed over is really just a zero sized type, there is 773 // no pointer difference being made here. 774 if (isMaybeZeroSizedType(ElTy)) 775 return -2; // dunno. 776 777 // If they are really different, now that they are the same type, then we 778 // found a difference! 779 if (cast<ConstantInt>(C1)->getSExtValue() < 780 cast<ConstantInt>(C2)->getSExtValue()) 781 return -1; 782 else 783 return 1; 784} 785 786/// evaluateFCmpRelation - This function determines if there is anything we can 787/// decide about the two constants provided. This doesn't need to handle simple 788/// things like ConstantFP comparisons, but should instead handle ConstantExprs. 789/// If we can determine that the two constants have a particular relation to 790/// each other, we should return the corresponding FCmpInst predicate, 791/// otherwise return FCmpInst::BAD_FCMP_PREDICATE. This is used below in 792/// ConstantFoldCompareInstruction. 793/// 794/// To simplify this code we canonicalize the relation so that the first 795/// operand is always the most "complex" of the two. We consider ConstantFP 796/// to be the simplest, and ConstantExprs to be the most complex. 797static FCmpInst::Predicate evaluateFCmpRelation(const Constant *V1, 798 const Constant *V2) { 799 assert(V1->getType() == V2->getType() && 800 "Cannot compare values of different types!"); 801 // Handle degenerate case quickly 802 if (V1 == V2) return FCmpInst::FCMP_OEQ; 803 804 if (!isa<ConstantExpr>(V1)) { 805 if (!isa<ConstantExpr>(V2)) { 806 // We distilled thisUse the standard constant folder for a few cases 807 ConstantInt *R = 0; 808 Constant *C1 = const_cast<Constant*>(V1); 809 Constant *C2 = const_cast<Constant*>(V2); 810 R = dyn_cast<ConstantInt>( 811 ConstantExpr::getFCmp(FCmpInst::FCMP_OEQ, C1, C2)); 812 if (R && !R->isZero()) 813 return FCmpInst::FCMP_OEQ; 814 R = dyn_cast<ConstantInt>( 815 ConstantExpr::getFCmp(FCmpInst::FCMP_OLT, C1, C2)); 816 if (R && !R->isZero()) 817 return FCmpInst::FCMP_OLT; 818 R = dyn_cast<ConstantInt>( 819 ConstantExpr::getFCmp(FCmpInst::FCMP_OGT, C1, C2)); 820 if (R && !R->isZero()) 821 return FCmpInst::FCMP_OGT; 822 823 // Nothing more we can do 824 return FCmpInst::BAD_FCMP_PREDICATE; 825 } 826 827 // If the first operand is simple and second is ConstantExpr, swap operands. 828 FCmpInst::Predicate SwappedRelation = evaluateFCmpRelation(V2, V1); 829 if (SwappedRelation != FCmpInst::BAD_FCMP_PREDICATE) 830 return FCmpInst::getSwappedPredicate(SwappedRelation); 831 } else { 832 // Ok, the LHS is known to be a constantexpr. The RHS can be any of a 833 // constantexpr or a simple constant. 834 const ConstantExpr *CE1 = cast<ConstantExpr>(V1); 835 switch (CE1->getOpcode()) { 836 case Instruction::FPTrunc: 837 case Instruction::FPExt: 838 case Instruction::UIToFP: 839 case Instruction::SIToFP: 840 // We might be able to do something with these but we don't right now. 841 break; 842 default: 843 break; 844 } 845 } 846 // There are MANY other foldings that we could perform here. They will 847 // probably be added on demand, as they seem needed. 848 return FCmpInst::BAD_FCMP_PREDICATE; 849} 850 851/// evaluateICmpRelation - This function determines if there is anything we can 852/// decide about the two constants provided. This doesn't need to handle simple 853/// things like integer comparisons, but should instead handle ConstantExprs 854/// and GlobalValues. If we can determine that the two constants have a 855/// particular relation to each other, we should return the corresponding ICmp 856/// predicate, otherwise return ICmpInst::BAD_ICMP_PREDICATE. 857/// 858/// To simplify this code we canonicalize the relation so that the first 859/// operand is always the most "complex" of the two. We consider simple 860/// constants (like ConstantInt) to be the simplest, followed by 861/// GlobalValues, followed by ConstantExpr's (the most complex). 862/// 863static ICmpInst::Predicate evaluateICmpRelation(const Constant *V1, 864 const Constant *V2, 865 bool isSigned) { 866 assert(V1->getType() == V2->getType() && 867 "Cannot compare different types of values!"); 868 if (V1 == V2) return ICmpInst::ICMP_EQ; 869 870 if (!isa<ConstantExpr>(V1) && !isa<GlobalValue>(V1)) { 871 if (!isa<GlobalValue>(V2) && !isa<ConstantExpr>(V2)) { 872 // We distilled this down to a simple case, use the standard constant 873 // folder. 874 ConstantInt *R = 0; 875 Constant *C1 = const_cast<Constant*>(V1); 876 Constant *C2 = const_cast<Constant*>(V2); 877 ICmpInst::Predicate pred = ICmpInst::ICMP_EQ; 878 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 879 if (R && !R->isZero()) 880 return pred; 881 pred = isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 882 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 883 if (R && !R->isZero()) 884 return pred; 885 pred = isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 886 R = dyn_cast<ConstantInt>(ConstantExpr::getICmp(pred, C1, C2)); 887 if (R && !R->isZero()) 888 return pred; 889 890 // If we couldn't figure it out, bail. 891 return ICmpInst::BAD_ICMP_PREDICATE; 892 } 893 894 // If the first operand is simple, swap operands. 895 ICmpInst::Predicate SwappedRelation = 896 evaluateICmpRelation(V2, V1, isSigned); 897 if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE) 898 return ICmpInst::getSwappedPredicate(SwappedRelation); 899 900 } else if (const GlobalValue *CPR1 = dyn_cast<GlobalValue>(V1)) { 901 if (isa<ConstantExpr>(V2)) { // Swap as necessary. 902 ICmpInst::Predicate SwappedRelation = 903 evaluateICmpRelation(V2, V1, isSigned); 904 if (SwappedRelation != ICmpInst::BAD_ICMP_PREDICATE) 905 return ICmpInst::getSwappedPredicate(SwappedRelation); 906 else 907 return ICmpInst::BAD_ICMP_PREDICATE; 908 } 909 910 // Now we know that the RHS is a GlobalValue or simple constant, 911 // which (since the types must match) means that it's a ConstantPointerNull. 912 if (const GlobalValue *CPR2 = dyn_cast<GlobalValue>(V2)) { 913 if (!CPR1->hasExternalWeakLinkage() || !CPR2->hasExternalWeakLinkage()) 914 return ICmpInst::ICMP_NE; 915 } else { 916 // GlobalVals can never be null. 917 assert(isa<ConstantPointerNull>(V2) && "Canonicalization guarantee!"); 918 if (!CPR1->hasExternalWeakLinkage()) 919 return ICmpInst::ICMP_NE; 920 } 921 } else { 922 // Ok, the LHS is known to be a constantexpr. The RHS can be any of a 923 // constantexpr, a CPR, or a simple constant. 924 const ConstantExpr *CE1 = cast<ConstantExpr>(V1); 925 const Constant *CE1Op0 = CE1->getOperand(0); 926 927 switch (CE1->getOpcode()) { 928 case Instruction::Trunc: 929 case Instruction::FPTrunc: 930 case Instruction::FPExt: 931 case Instruction::FPToUI: 932 case Instruction::FPToSI: 933 break; // We can't evaluate floating point casts or truncations. 934 935 case Instruction::UIToFP: 936 case Instruction::SIToFP: 937 case Instruction::IntToPtr: 938 case Instruction::BitCast: 939 case Instruction::ZExt: 940 case Instruction::SExt: 941 case Instruction::PtrToInt: 942 // If the cast is not actually changing bits, and the second operand is a 943 // null pointer, do the comparison with the pre-casted value. 944 if (V2->isNullValue() && 945 (isa<PointerType>(CE1->getType()) || CE1->getType()->isInteger())) { 946 bool sgnd = CE1->getOpcode() == Instruction::ZExt ? false : 947 (CE1->getOpcode() == Instruction::SExt ? true : 948 (CE1->getOpcode() == Instruction::PtrToInt ? false : isSigned)); 949 return evaluateICmpRelation( 950 CE1Op0, Constant::getNullValue(CE1Op0->getType()), sgnd); 951 } 952 953 // If the dest type is a pointer type, and the RHS is a constantexpr cast 954 // from the same type as the src of the LHS, evaluate the inputs. This is 955 // important for things like "icmp eq (cast 4 to int*), (cast 5 to int*)", 956 // which happens a lot in compilers with tagged integers. 957 if (const ConstantExpr *CE2 = dyn_cast<ConstantExpr>(V2)) 958 if (CE2->isCast() && isa<PointerType>(CE1->getType()) && 959 CE1->getOperand(0)->getType() == CE2->getOperand(0)->getType() && 960 CE1->getOperand(0)->getType()->isInteger()) { 961 bool sgnd = CE1->getOpcode() == Instruction::ZExt ? false : 962 (CE1->getOpcode() == Instruction::SExt ? true : 963 (CE1->getOpcode() == Instruction::PtrToInt ? false : isSigned)); 964 return evaluateICmpRelation(CE1->getOperand(0), CE2->getOperand(0), 965 sgnd); 966 } 967 break; 968 969 case Instruction::GetElementPtr: 970 // Ok, since this is a getelementptr, we know that the constant has a 971 // pointer type. Check the various cases. 972 if (isa<ConstantPointerNull>(V2)) { 973 // If we are comparing a GEP to a null pointer, check to see if the base 974 // of the GEP equals the null pointer. 975 if (const GlobalValue *GV = dyn_cast<GlobalValue>(CE1Op0)) { 976 if (GV->hasExternalWeakLinkage()) 977 // Weak linkage GVals could be zero or not. We're comparing that 978 // to null pointer so its greater-or-equal 979 return isSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; 980 else 981 // If its not weak linkage, the GVal must have a non-zero address 982 // so the result is greater-than 983 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 984 } else if (isa<ConstantPointerNull>(CE1Op0)) { 985 // If we are indexing from a null pointer, check to see if we have any 986 // non-zero indices. 987 for (unsigned i = 1, e = CE1->getNumOperands(); i != e; ++i) 988 if (!CE1->getOperand(i)->isNullValue()) 989 // Offsetting from null, must not be equal. 990 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 991 // Only zero indexes from null, must still be zero. 992 return ICmpInst::ICMP_EQ; 993 } 994 // Otherwise, we can't really say if the first operand is null or not. 995 } else if (const GlobalValue *CPR2 = dyn_cast<GlobalValue>(V2)) { 996 if (isa<ConstantPointerNull>(CE1Op0)) { 997 if (CPR2->hasExternalWeakLinkage()) 998 // Weak linkage GVals could be zero or not. We're comparing it to 999 // a null pointer, so its less-or-equal 1000 return isSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; 1001 else 1002 // If its not weak linkage, the GVal must have a non-zero address 1003 // so the result is less-than 1004 return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 1005 } else if (const GlobalValue *CPR1 = dyn_cast<GlobalValue>(CE1Op0)) { 1006 if (CPR1 == CPR2) { 1007 // If this is a getelementptr of the same global, then it must be 1008 // different. Because the types must match, the getelementptr could 1009 // only have at most one index, and because we fold getelementptr's 1010 // with a single zero index, it must be nonzero. 1011 assert(CE1->getNumOperands() == 2 && 1012 !CE1->getOperand(1)->isNullValue() && 1013 "Suprising getelementptr!"); 1014 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1015 } else { 1016 // If they are different globals, we don't know what the value is, 1017 // but they can't be equal. 1018 return ICmpInst::ICMP_NE; 1019 } 1020 } 1021 } else { 1022 const ConstantExpr *CE2 = cast<ConstantExpr>(V2); 1023 const Constant *CE2Op0 = CE2->getOperand(0); 1024 1025 // There are MANY other foldings that we could perform here. They will 1026 // probably be added on demand, as they seem needed. 1027 switch (CE2->getOpcode()) { 1028 default: break; 1029 case Instruction::GetElementPtr: 1030 // By far the most common case to handle is when the base pointers are 1031 // obviously to the same or different globals. 1032 if (isa<GlobalValue>(CE1Op0) && isa<GlobalValue>(CE2Op0)) { 1033 if (CE1Op0 != CE2Op0) // Don't know relative ordering, but not equal 1034 return ICmpInst::ICMP_NE; 1035 // Ok, we know that both getelementptr instructions are based on the 1036 // same global. From this, we can precisely determine the relative 1037 // ordering of the resultant pointers. 1038 unsigned i = 1; 1039 1040 // Compare all of the operands the GEP's have in common. 1041 gep_type_iterator GTI = gep_type_begin(CE1); 1042 for (;i != CE1->getNumOperands() && i != CE2->getNumOperands(); 1043 ++i, ++GTI) 1044 switch (IdxCompare(CE1->getOperand(i), CE2->getOperand(i), 1045 GTI.getIndexedType())) { 1046 case -1: return isSigned ? ICmpInst::ICMP_SLT:ICmpInst::ICMP_ULT; 1047 case 1: return isSigned ? ICmpInst::ICMP_SGT:ICmpInst::ICMP_UGT; 1048 case -2: return ICmpInst::BAD_ICMP_PREDICATE; 1049 } 1050 1051 // Ok, we ran out of things they have in common. If any leftovers 1052 // are non-zero then we have a difference, otherwise we are equal. 1053 for (; i < CE1->getNumOperands(); ++i) 1054 if (!CE1->getOperand(i)->isNullValue()) 1055 if (isa<ConstantInt>(CE1->getOperand(i))) 1056 return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; 1057 else 1058 return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal. 1059 1060 for (; i < CE2->getNumOperands(); ++i) 1061 if (!CE2->getOperand(i)->isNullValue()) 1062 if (isa<ConstantInt>(CE2->getOperand(i))) 1063 return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; 1064 else 1065 return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal. 1066 return ICmpInst::ICMP_EQ; 1067 } 1068 } 1069 } 1070 default: 1071 break; 1072 } 1073 } 1074 1075 return ICmpInst::BAD_ICMP_PREDICATE; 1076} 1077 1078Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred, 1079 const Constant *C1, 1080 const Constant *C2) { 1081 1082 // Handle some degenerate cases first 1083 if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) 1084 return UndefValue::get(Type::Int1Ty); 1085 1086 // icmp eq/ne(null,GV) -> false/true 1087 if (C1->isNullValue()) { 1088 if (const GlobalValue *GV = dyn_cast<GlobalValue>(C2)) 1089 if (!GV->hasExternalWeakLinkage()) // External weak GV can be null 1090 if (pred == ICmpInst::ICMP_EQ) 1091 return ConstantInt::getFalse(); 1092 else if (pred == ICmpInst::ICMP_NE) 1093 return ConstantInt::getTrue(); 1094 // icmp eq/ne(GV,null) -> false/true 1095 } else if (C2->isNullValue()) { 1096 if (const GlobalValue *GV = dyn_cast<GlobalValue>(C1)) 1097 if (!GV->hasExternalWeakLinkage()) // External weak GV can be null 1098 if (pred == ICmpInst::ICMP_EQ) 1099 return ConstantInt::getFalse(); 1100 else if (pred == ICmpInst::ICMP_NE) 1101 return ConstantInt::getTrue(); 1102 } 1103 1104 if (isa<ConstantInt>(C1) && isa<ConstantInt>(C2)) { 1105 APInt V1 = cast<ConstantInt>(C1)->getValue(); 1106 APInt V2 = cast<ConstantInt>(C2)->getValue(); 1107 switch (pred) { 1108 default: assert(0 && "Invalid ICmp Predicate"); return 0; 1109 case ICmpInst::ICMP_EQ: return ConstantInt::get(Type::Int1Ty, V1 == V2); 1110 case ICmpInst::ICMP_NE: return ConstantInt::get(Type::Int1Ty, V1 != V2); 1111 case ICmpInst::ICMP_SLT:return ConstantInt::get(Type::Int1Ty, V1.slt(V2)); 1112 case ICmpInst::ICMP_SGT:return ConstantInt::get(Type::Int1Ty, V1.sgt(V2)); 1113 case ICmpInst::ICMP_SLE:return ConstantInt::get(Type::Int1Ty, V1.sle(V2)); 1114 case ICmpInst::ICMP_SGE:return ConstantInt::get(Type::Int1Ty, V1.sge(V2)); 1115 case ICmpInst::ICMP_ULT:return ConstantInt::get(Type::Int1Ty, V1.ult(V2)); 1116 case ICmpInst::ICMP_UGT:return ConstantInt::get(Type::Int1Ty, V1.ugt(V2)); 1117 case ICmpInst::ICMP_ULE:return ConstantInt::get(Type::Int1Ty, V1.ule(V2)); 1118 case ICmpInst::ICMP_UGE:return ConstantInt::get(Type::Int1Ty, V1.uge(V2)); 1119 } 1120 } else if (isa<ConstantFP>(C1) && isa<ConstantFP>(C2)) { 1121 double C1Val = cast<ConstantFP>(C1)->getValue(); 1122 double C2Val = cast<ConstantFP>(C2)->getValue(); 1123 switch (pred) { 1124 default: assert(0 && "Invalid FCmp Predicate"); return 0; 1125 case FCmpInst::FCMP_FALSE: return ConstantInt::getFalse(); 1126 case FCmpInst::FCMP_TRUE: return ConstantInt::getTrue(); 1127 case FCmpInst::FCMP_UNO: 1128 return ConstantInt::get(Type::Int1Ty, C1Val != C1Val || C2Val != C2Val); 1129 case FCmpInst::FCMP_ORD: 1130 return ConstantInt::get(Type::Int1Ty, C1Val == C1Val && C2Val == C2Val); 1131 case FCmpInst::FCMP_UEQ: 1132 if (C1Val != C1Val || C2Val != C2Val) 1133 return ConstantInt::getTrue(); 1134 /* FALL THROUGH */ 1135 case FCmpInst::FCMP_OEQ: 1136 return ConstantInt::get(Type::Int1Ty, C1Val == C2Val); 1137 case FCmpInst::FCMP_UNE: 1138 if (C1Val != C1Val || C2Val != C2Val) 1139 return ConstantInt::getTrue(); 1140 /* FALL THROUGH */ 1141 case FCmpInst::FCMP_ONE: 1142 return ConstantInt::get(Type::Int1Ty, C1Val != C2Val); 1143 case FCmpInst::FCMP_ULT: 1144 if (C1Val != C1Val || C2Val != C2Val) 1145 return ConstantInt::getTrue(); 1146 /* FALL THROUGH */ 1147 case FCmpInst::FCMP_OLT: 1148 return ConstantInt::get(Type::Int1Ty, C1Val < C2Val); 1149 case FCmpInst::FCMP_UGT: 1150 if (C1Val != C1Val || C2Val != C2Val) 1151 return ConstantInt::getTrue(); 1152 /* FALL THROUGH */ 1153 case FCmpInst::FCMP_OGT: 1154 return ConstantInt::get(Type::Int1Ty, C1Val > C2Val); 1155 case FCmpInst::FCMP_ULE: 1156 if (C1Val != C1Val || C2Val != C2Val) 1157 return ConstantInt::getTrue(); 1158 /* FALL THROUGH */ 1159 case FCmpInst::FCMP_OLE: 1160 return ConstantInt::get(Type::Int1Ty, C1Val <= C2Val); 1161 case FCmpInst::FCMP_UGE: 1162 if (C1Val != C1Val || C2Val != C2Val) 1163 return ConstantInt::getTrue(); 1164 /* FALL THROUGH */ 1165 case FCmpInst::FCMP_OGE: 1166 return ConstantInt::get(Type::Int1Ty, C1Val >= C2Val); 1167 } 1168 } else if (const ConstantVector *CP1 = dyn_cast<ConstantVector>(C1)) { 1169 if (const ConstantVector *CP2 = dyn_cast<ConstantVector>(C2)) { 1170 if (pred == FCmpInst::FCMP_OEQ || pred == FCmpInst::FCMP_UEQ) { 1171 for (unsigned i = 0, e = CP1->getNumOperands(); i != e; ++i) { 1172 Constant *C= ConstantExpr::getFCmp(FCmpInst::FCMP_OEQ, 1173 const_cast<Constant*>(CP1->getOperand(i)), 1174 const_cast<Constant*>(CP2->getOperand(i))); 1175 if (ConstantInt *CB = dyn_cast<ConstantInt>(C)) 1176 return CB; 1177 } 1178 // Otherwise, could not decide from any element pairs. 1179 return 0; 1180 } else if (pred == ICmpInst::ICMP_EQ) { 1181 for (unsigned i = 0, e = CP1->getNumOperands(); i != e; ++i) { 1182 Constant *C = ConstantExpr::getICmp(ICmpInst::ICMP_EQ, 1183 const_cast<Constant*>(CP1->getOperand(i)), 1184 const_cast<Constant*>(CP2->getOperand(i))); 1185 if (ConstantInt *CB = dyn_cast<ConstantInt>(C)) 1186 return CB; 1187 } 1188 // Otherwise, could not decide from any element pairs. 1189 return 0; 1190 } 1191 } 1192 } 1193 1194 if (C1->getType()->isFloatingPoint()) { 1195 switch (evaluateFCmpRelation(C1, C2)) { 1196 default: assert(0 && "Unknown relation!"); 1197 case FCmpInst::FCMP_UNO: 1198 case FCmpInst::FCMP_ORD: 1199 case FCmpInst::FCMP_UEQ: 1200 case FCmpInst::FCMP_UNE: 1201 case FCmpInst::FCMP_ULT: 1202 case FCmpInst::FCMP_UGT: 1203 case FCmpInst::FCMP_ULE: 1204 case FCmpInst::FCMP_UGE: 1205 case FCmpInst::FCMP_TRUE: 1206 case FCmpInst::FCMP_FALSE: 1207 case FCmpInst::BAD_FCMP_PREDICATE: 1208 break; // Couldn't determine anything about these constants. 1209 case FCmpInst::FCMP_OEQ: // We know that C1 == C2 1210 return ConstantInt::get(Type::Int1Ty, 1211 pred == FCmpInst::FCMP_UEQ || pred == FCmpInst::FCMP_OEQ || 1212 pred == FCmpInst::FCMP_ULE || pred == FCmpInst::FCMP_OLE || 1213 pred == FCmpInst::FCMP_UGE || pred == FCmpInst::FCMP_OGE); 1214 case FCmpInst::FCMP_OLT: // We know that C1 < C2 1215 return ConstantInt::get(Type::Int1Ty, 1216 pred == FCmpInst::FCMP_UNE || pred == FCmpInst::FCMP_ONE || 1217 pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT || 1218 pred == FCmpInst::FCMP_ULE || pred == FCmpInst::FCMP_OLE); 1219 case FCmpInst::FCMP_OGT: // We know that C1 > C2 1220 return ConstantInt::get(Type::Int1Ty, 1221 pred == FCmpInst::FCMP_UNE || pred == FCmpInst::FCMP_ONE || 1222 pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT || 1223 pred == FCmpInst::FCMP_UGE || pred == FCmpInst::FCMP_OGE); 1224 case FCmpInst::FCMP_OLE: // We know that C1 <= C2 1225 // We can only partially decide this relation. 1226 if (pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT) 1227 return ConstantInt::getFalse(); 1228 if (pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT) 1229 return ConstantInt::getTrue(); 1230 break; 1231 case FCmpInst::FCMP_OGE: // We known that C1 >= C2 1232 // We can only partially decide this relation. 1233 if (pred == FCmpInst::FCMP_ULT || pred == FCmpInst::FCMP_OLT) 1234 return ConstantInt::getFalse(); 1235 if (pred == FCmpInst::FCMP_UGT || pred == FCmpInst::FCMP_OGT) 1236 return ConstantInt::getTrue(); 1237 break; 1238 case ICmpInst::ICMP_NE: // We know that C1 != C2 1239 // We can only partially decide this relation. 1240 if (pred == FCmpInst::FCMP_OEQ || pred == FCmpInst::FCMP_UEQ) 1241 return ConstantInt::getFalse(); 1242 if (pred == FCmpInst::FCMP_ONE || pred == FCmpInst::FCMP_UNE) 1243 return ConstantInt::getTrue(); 1244 break; 1245 } 1246 } else { 1247 // Evaluate the relation between the two constants, per the predicate. 1248 switch (evaluateICmpRelation(C1, C2, CmpInst::isSigned(pred))) { 1249 default: assert(0 && "Unknown relational!"); 1250 case ICmpInst::BAD_ICMP_PREDICATE: 1251 break; // Couldn't determine anything about these constants. 1252 case ICmpInst::ICMP_EQ: // We know the constants are equal! 1253 // If we know the constants are equal, we can decide the result of this 1254 // computation precisely. 1255 return ConstantInt::get(Type::Int1Ty, 1256 pred == ICmpInst::ICMP_EQ || 1257 pred == ICmpInst::ICMP_ULE || 1258 pred == ICmpInst::ICMP_SLE || 1259 pred == ICmpInst::ICMP_UGE || 1260 pred == ICmpInst::ICMP_SGE); 1261 case ICmpInst::ICMP_ULT: 1262 // If we know that C1 < C2, we can decide the result of this computation 1263 // precisely. 1264 return ConstantInt::get(Type::Int1Ty, 1265 pred == ICmpInst::ICMP_ULT || 1266 pred == ICmpInst::ICMP_NE || 1267 pred == ICmpInst::ICMP_ULE); 1268 case ICmpInst::ICMP_SLT: 1269 // If we know that C1 < C2, we can decide the result of this computation 1270 // precisely. 1271 return ConstantInt::get(Type::Int1Ty, 1272 pred == ICmpInst::ICMP_SLT || 1273 pred == ICmpInst::ICMP_NE || 1274 pred == ICmpInst::ICMP_SLE); 1275 case ICmpInst::ICMP_UGT: 1276 // If we know that C1 > C2, we can decide the result of this computation 1277 // precisely. 1278 return ConstantInt::get(Type::Int1Ty, 1279 pred == ICmpInst::ICMP_UGT || 1280 pred == ICmpInst::ICMP_NE || 1281 pred == ICmpInst::ICMP_UGE); 1282 case ICmpInst::ICMP_SGT: 1283 // If we know that C1 > C2, we can decide the result of this computation 1284 // precisely. 1285 return ConstantInt::get(Type::Int1Ty, 1286 pred == ICmpInst::ICMP_SGT || 1287 pred == ICmpInst::ICMP_NE || 1288 pred == ICmpInst::ICMP_SGE); 1289 case ICmpInst::ICMP_ULE: 1290 // If we know that C1 <= C2, we can only partially decide this relation. 1291 if (pred == ICmpInst::ICMP_UGT) return ConstantInt::getFalse(); 1292 if (pred == ICmpInst::ICMP_ULT) return ConstantInt::getTrue(); 1293 break; 1294 case ICmpInst::ICMP_SLE: 1295 // If we know that C1 <= C2, we can only partially decide this relation. 1296 if (pred == ICmpInst::ICMP_SGT) return ConstantInt::getFalse(); 1297 if (pred == ICmpInst::ICMP_SLT) return ConstantInt::getTrue(); 1298 break; 1299 1300 case ICmpInst::ICMP_UGE: 1301 // If we know that C1 >= C2, we can only partially decide this relation. 1302 if (pred == ICmpInst::ICMP_ULT) return ConstantInt::getFalse(); 1303 if (pred == ICmpInst::ICMP_UGT) return ConstantInt::getTrue(); 1304 break; 1305 case ICmpInst::ICMP_SGE: 1306 // If we know that C1 >= C2, we can only partially decide this relation. 1307 if (pred == ICmpInst::ICMP_SLT) return ConstantInt::getFalse(); 1308 if (pred == ICmpInst::ICMP_SGT) return ConstantInt::getTrue(); 1309 break; 1310 1311 case ICmpInst::ICMP_NE: 1312 // If we know that C1 != C2, we can only partially decide this relation. 1313 if (pred == ICmpInst::ICMP_EQ) return ConstantInt::getFalse(); 1314 if (pred == ICmpInst::ICMP_NE) return ConstantInt::getTrue(); 1315 break; 1316 } 1317 1318 if (!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) { 1319 // If C2 is a constant expr and C1 isn't, flop them around and fold the 1320 // other way if possible. 1321 switch (pred) { 1322 case ICmpInst::ICMP_EQ: 1323 case ICmpInst::ICMP_NE: 1324 // No change of predicate required. 1325 return ConstantFoldCompareInstruction(pred, C2, C1); 1326 1327 case ICmpInst::ICMP_ULT: 1328 case ICmpInst::ICMP_SLT: 1329 case ICmpInst::ICMP_UGT: 1330 case ICmpInst::ICMP_SGT: 1331 case ICmpInst::ICMP_ULE: 1332 case ICmpInst::ICMP_SLE: 1333 case ICmpInst::ICMP_UGE: 1334 case ICmpInst::ICMP_SGE: 1335 // Change the predicate as necessary to swap the operands. 1336 pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred); 1337 return ConstantFoldCompareInstruction(pred, C2, C1); 1338 1339 default: // These predicates cannot be flopped around. 1340 break; 1341 } 1342 } 1343 } 1344 return 0; 1345} 1346 1347Constant *llvm::ConstantFoldGetElementPtr(const Constant *C, 1348 Constant* const *Idxs, 1349 unsigned NumIdx) { 1350 if (NumIdx == 0 || 1351 (NumIdx == 1 && Idxs[0]->isNullValue())) 1352 return const_cast<Constant*>(C); 1353 1354 if (isa<UndefValue>(C)) { 1355 const Type *Ty = GetElementPtrInst::getIndexedType(C->getType(), 1356 (Value**)Idxs, NumIdx, 1357 true); 1358 assert(Ty != 0 && "Invalid indices for GEP!"); 1359 return UndefValue::get(PointerType::get(Ty)); 1360 } 1361 1362 Constant *Idx0 = Idxs[0]; 1363 if (C->isNullValue()) { 1364 bool isNull = true; 1365 for (unsigned i = 0, e = NumIdx; i != e; ++i) 1366 if (!Idxs[i]->isNullValue()) { 1367 isNull = false; 1368 break; 1369 } 1370 if (isNull) { 1371 const Type *Ty = GetElementPtrInst::getIndexedType(C->getType(), 1372 (Value**)Idxs, NumIdx, 1373 true); 1374 assert(Ty != 0 && "Invalid indices for GEP!"); 1375 return ConstantPointerNull::get(PointerType::get(Ty)); 1376 } 1377 } 1378 1379 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(const_cast<Constant*>(C))) { 1380 // Combine Indices - If the source pointer to this getelementptr instruction 1381 // is a getelementptr instruction, combine the indices of the two 1382 // getelementptr instructions into a single instruction. 1383 // 1384 if (CE->getOpcode() == Instruction::GetElementPtr) { 1385 const Type *LastTy = 0; 1386 for (gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE); 1387 I != E; ++I) 1388 LastTy = *I; 1389 1390 if ((LastTy && isa<ArrayType>(LastTy)) || Idx0->isNullValue()) { 1391 SmallVector<Value*, 16> NewIndices; 1392 NewIndices.reserve(NumIdx + CE->getNumOperands()); 1393 for (unsigned i = 1, e = CE->getNumOperands()-1; i != e; ++i) 1394 NewIndices.push_back(CE->getOperand(i)); 1395 1396 // Add the last index of the source with the first index of the new GEP. 1397 // Make sure to handle the case when they are actually different types. 1398 Constant *Combined = CE->getOperand(CE->getNumOperands()-1); 1399 // Otherwise it must be an array. 1400 if (!Idx0->isNullValue()) { 1401 const Type *IdxTy = Combined->getType(); 1402 if (IdxTy != Idx0->getType()) { 1403 Constant *C1 = ConstantExpr::getSExtOrBitCast(Idx0, Type::Int64Ty); 1404 Constant *C2 = ConstantExpr::getSExtOrBitCast(Combined, 1405 Type::Int64Ty); 1406 Combined = ConstantExpr::get(Instruction::Add, C1, C2); 1407 } else { 1408 Combined = 1409 ConstantExpr::get(Instruction::Add, Idx0, Combined); 1410 } 1411 } 1412 1413 NewIndices.push_back(Combined); 1414 NewIndices.insert(NewIndices.end(), Idxs+1, Idxs+NumIdx); 1415 return ConstantExpr::getGetElementPtr(CE->getOperand(0), &NewIndices[0], 1416 NewIndices.size()); 1417 } 1418 } 1419 1420 // Implement folding of: 1421 // int* getelementptr ([2 x int]* cast ([3 x int]* %X to [2 x int]*), 1422 // long 0, long 0) 1423 // To: int* getelementptr ([3 x int]* %X, long 0, long 0) 1424 // 1425 if (CE->isCast() && NumIdx > 1 && Idx0->isNullValue()) 1426 if (const PointerType *SPT = 1427 dyn_cast<PointerType>(CE->getOperand(0)->getType())) 1428 if (const ArrayType *SAT = dyn_cast<ArrayType>(SPT->getElementType())) 1429 if (const ArrayType *CAT = 1430 dyn_cast<ArrayType>(cast<PointerType>(C->getType())->getElementType())) 1431 if (CAT->getElementType() == SAT->getElementType()) 1432 return ConstantExpr::getGetElementPtr( 1433 (Constant*)CE->getOperand(0), Idxs, NumIdx); 1434 } 1435 return 0; 1436} 1437 1438