InstCombineCasts.cpp revision c8b3fce5c5f0785b05df9cf93772a67f56bc3640
1//===- InstCombineCasts.cpp -----------------------------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements the visit functions for cast operations. 11// 12//===----------------------------------------------------------------------===// 13 14#include "InstCombine.h" 15#include "llvm/Target/TargetData.h" 16#include "llvm/Support/PatternMatch.h" 17using namespace llvm; 18using namespace PatternMatch; 19 20/// DecomposeSimpleLinearExpr - Analyze 'Val', seeing if it is a simple linear 21/// expression. If so, decompose it, returning some value X, such that Val is 22/// X*Scale+Offset. 23/// 24static Value *DecomposeSimpleLinearExpr(Value *Val, unsigned &Scale, 25 int &Offset) { 26 assert(Val->getType()->isInteger(32) && "Unexpected allocation size type!"); 27 if (ConstantInt *CI = dyn_cast<ConstantInt>(Val)) { 28 Offset = CI->getZExtValue(); 29 Scale = 0; 30 return ConstantInt::get(Type::getInt32Ty(Val->getContext()), 0); 31 } 32 33 if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) { 34 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) { 35 if (I->getOpcode() == Instruction::Shl) { 36 // This is a value scaled by '1 << the shift amt'. 37 Scale = 1U << RHS->getZExtValue(); 38 Offset = 0; 39 return I->getOperand(0); 40 } 41 42 if (I->getOpcode() == Instruction::Mul) { 43 // This value is scaled by 'RHS'. 44 Scale = RHS->getZExtValue(); 45 Offset = 0; 46 return I->getOperand(0); 47 } 48 49 if (I->getOpcode() == Instruction::Add) { 50 // We have X+C. Check to see if we really have (X*C2)+C1, 51 // where C1 is divisible by C2. 52 unsigned SubScale; 53 Value *SubVal = 54 DecomposeSimpleLinearExpr(I->getOperand(0), SubScale, Offset); 55 Offset += RHS->getZExtValue(); 56 Scale = SubScale; 57 return SubVal; 58 } 59 } 60 } 61 62 // Otherwise, we can't look past this. 63 Scale = 1; 64 Offset = 0; 65 return Val; 66} 67 68/// PromoteCastOfAllocation - If we find a cast of an allocation instruction, 69/// try to eliminate the cast by moving the type information into the alloc. 70Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI, 71 AllocaInst &AI) { 72 // This requires TargetData to get the alloca alignment and size information. 73 if (!TD) return 0; 74 75 const PointerType *PTy = cast<PointerType>(CI.getType()); 76 77 BuilderTy AllocaBuilder(*Builder); 78 AllocaBuilder.SetInsertPoint(AI.getParent(), &AI); 79 80 // Get the type really allocated and the type casted to. 81 const Type *AllocElTy = AI.getAllocatedType(); 82 const Type *CastElTy = PTy->getElementType(); 83 if (!AllocElTy->isSized() || !CastElTy->isSized()) return 0; 84 85 unsigned AllocElTyAlign = TD->getABITypeAlignment(AllocElTy); 86 unsigned CastElTyAlign = TD->getABITypeAlignment(CastElTy); 87 if (CastElTyAlign < AllocElTyAlign) return 0; 88 89 // If the allocation has multiple uses, only promote it if we are strictly 90 // increasing the alignment of the resultant allocation. If we keep it the 91 // same, we open the door to infinite loops of various kinds. (A reference 92 // from a dbg.declare doesn't count as a use for this purpose.) 93 if (!AI.hasOneUse() && !hasOneUsePlusDeclare(&AI) && 94 CastElTyAlign == AllocElTyAlign) return 0; 95 96 uint64_t AllocElTySize = TD->getTypeAllocSize(AllocElTy); 97 uint64_t CastElTySize = TD->getTypeAllocSize(CastElTy); 98 if (CastElTySize == 0 || AllocElTySize == 0) return 0; 99 100 // See if we can satisfy the modulus by pulling a scale out of the array 101 // size argument. 102 unsigned ArraySizeScale; 103 int ArrayOffset; 104 Value *NumElements = // See if the array size is a decomposable linear expr. 105 DecomposeSimpleLinearExpr(AI.getOperand(0), ArraySizeScale, ArrayOffset); 106 107 // If we can now satisfy the modulus, by using a non-1 scale, we really can 108 // do the xform. 109 if ((AllocElTySize*ArraySizeScale) % CastElTySize != 0 || 110 (AllocElTySize*ArrayOffset ) % CastElTySize != 0) return 0; 111 112 unsigned Scale = (AllocElTySize*ArraySizeScale)/CastElTySize; 113 Value *Amt = 0; 114 if (Scale == 1) { 115 Amt = NumElements; 116 } else { 117 Amt = ConstantInt::get(Type::getInt32Ty(CI.getContext()), Scale); 118 // Insert before the alloca, not before the cast. 119 Amt = AllocaBuilder.CreateMul(Amt, NumElements, "tmp"); 120 } 121 122 if (int Offset = (AllocElTySize*ArrayOffset)/CastElTySize) { 123 Value *Off = ConstantInt::get(Type::getInt32Ty(CI.getContext()), 124 Offset, true); 125 Amt = AllocaBuilder.CreateAdd(Amt, Off, "tmp"); 126 } 127 128 AllocaInst *New = AllocaBuilder.CreateAlloca(CastElTy, Amt); 129 New->setAlignment(AI.getAlignment()); 130 New->takeName(&AI); 131 132 // If the allocation has one real use plus a dbg.declare, just remove the 133 // declare. 134 if (DbgDeclareInst *DI = hasOneUsePlusDeclare(&AI)) { 135 EraseInstFromFunction(*(Instruction*)DI); 136 } 137 // If the allocation has multiple real uses, insert a cast and change all 138 // things that used it to use the new cast. This will also hack on CI, but it 139 // will die soon. 140 else if (!AI.hasOneUse()) { 141 // New is the allocation instruction, pointer typed. AI is the original 142 // allocation instruction, also pointer typed. Thus, cast to use is BitCast. 143 Value *NewCast = AllocaBuilder.CreateBitCast(New, AI.getType(), "tmpcast"); 144 AI.replaceAllUsesWith(NewCast); 145 } 146 return ReplaceInstUsesWith(CI, New); 147} 148 149 150/// CanEvaluateTruncated - Return true if we can evaluate the specified 151/// expression tree as type Ty instead of its larger type, and arrive with the 152/// same value. This is used by code that tries to eliminate truncates. 153/// 154/// Ty will always be a type smaller than V. We should return true if trunc(V) 155/// can be computed by computing V in the smaller type. If V is an instruction, 156/// then trunc(inst(x,y)) can be computed as inst(trunc(x),trunc(y)), which only 157/// makes sense if x and y can be efficiently truncated. 158/// 159static bool CanEvaluateTruncated(Value *V, const Type *Ty) { 160 // We can always evaluate constants in another type. 161 if (isa<Constant>(V)) 162 return true; 163 164 Instruction *I = dyn_cast<Instruction>(V); 165 if (!I) return false; 166 167 const Type *OrigTy = V->getType(); 168 169 // If this is an extension from the dest type, we can eliminate it. 170 if ((isa<ZExtInst>(I) || isa<SExtInst>(I)) && 171 I->getOperand(0)->getType() == Ty) 172 return true; 173 174 // We can't extend or shrink something that has multiple uses: doing so would 175 // require duplicating the instruction in general, which isn't profitable. 176 if (!I->hasOneUse()) return false; 177 178 unsigned Opc = I->getOpcode(); 179 switch (Opc) { 180 case Instruction::Add: 181 case Instruction::Sub: 182 case Instruction::Mul: 183 case Instruction::And: 184 case Instruction::Or: 185 case Instruction::Xor: 186 // These operators can all arbitrarily be extended or truncated. 187 return CanEvaluateTruncated(I->getOperand(0), Ty) && 188 CanEvaluateTruncated(I->getOperand(1), Ty); 189 190 case Instruction::UDiv: 191 case Instruction::URem: { 192 // UDiv and URem can be truncated if all the truncated bits are zero. 193 uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); 194 uint32_t BitWidth = Ty->getScalarSizeInBits(); 195 if (BitWidth < OrigBitWidth) { 196 APInt Mask = APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth); 197 if (MaskedValueIsZero(I->getOperand(0), Mask) && 198 MaskedValueIsZero(I->getOperand(1), Mask)) { 199 return CanEvaluateTruncated(I->getOperand(0), Ty) && 200 CanEvaluateTruncated(I->getOperand(1), Ty); 201 } 202 } 203 break; 204 } 205 case Instruction::Shl: 206 // If we are truncating the result of this SHL, and if it's a shift of a 207 // constant amount, we can always perform a SHL in a smaller type. 208 if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) { 209 uint32_t BitWidth = Ty->getScalarSizeInBits(); 210 if (CI->getLimitedValue(BitWidth) < BitWidth) 211 return CanEvaluateTruncated(I->getOperand(0), Ty); 212 } 213 break; 214 case Instruction::LShr: 215 // If this is a truncate of a logical shr, we can truncate it to a smaller 216 // lshr iff we know that the bits we would otherwise be shifting in are 217 // already zeros. 218 if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) { 219 uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); 220 uint32_t BitWidth = Ty->getScalarSizeInBits(); 221 if (MaskedValueIsZero(I->getOperand(0), 222 APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) && 223 CI->getLimitedValue(BitWidth) < BitWidth) { 224 return CanEvaluateTruncated(I->getOperand(0), Ty); 225 } 226 } 227 break; 228 case Instruction::Trunc: 229 // trunc(trunc(x)) -> trunc(x) 230 return true; 231 case Instruction::Select: { 232 SelectInst *SI = cast<SelectInst>(I); 233 return CanEvaluateTruncated(SI->getTrueValue(), Ty) && 234 CanEvaluateTruncated(SI->getFalseValue(), Ty); 235 } 236 case Instruction::PHI: { 237 // We can change a phi if we can change all operands. Note that we never 238 // get into trouble with cyclic PHIs here because we only consider 239 // instructions with a single use. 240 PHINode *PN = cast<PHINode>(I); 241 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 242 if (!CanEvaluateTruncated(PN->getIncomingValue(i), Ty)) 243 return false; 244 return true; 245 } 246 default: 247 // TODO: Can handle more cases here. 248 break; 249 } 250 251 return false; 252} 253 254/// GetLeadingZeros - Compute the number of known-zero leading bits. 255static unsigned GetLeadingZeros(Value *V, const TargetData *TD) { 256 unsigned Bits = V->getType()->getScalarSizeInBits(); 257 APInt KnownZero(Bits, 0), KnownOne(Bits, 0); 258 ComputeMaskedBits(V, APInt::getAllOnesValue(Bits), KnownZero, KnownOne, TD); 259 return KnownZero.countLeadingOnes(); 260} 261 262/// CanEvaluateZExtd - Determine if the specified value can be computed in the 263/// specified wider type and produce the same low bits. If not, return -1. If 264/// it is possible, return the number of high bits that are known to be zero in 265/// the promoted value. 266static int CanEvaluateZExtd(Value *V, const Type *Ty,unsigned &NumCastsRemoved, 267 const TargetData *TD) { 268 const Type *OrigTy = V->getType(); 269 270 if (isa<Constant>(V)) { 271 unsigned Extended = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits(); 272 273 // Constants can always be zero ext'd, even if it requires a ConstantExpr. 274 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) 275 return Extended + CI->getValue().countLeadingZeros(); 276 return Extended; 277 } 278 279 Instruction *I = dyn_cast<Instruction>(V); 280 if (!I) return -1; 281 282 // If the input is a truncate from the destination type, we can trivially 283 // eliminate it, and this will remove a cast overall. 284 if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty) { 285 // If the first operand is itself a cast, and is eliminable, do not count 286 // this as an eliminable cast. We would prefer to eliminate those two 287 // casts first. 288 if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse()) 289 ++NumCastsRemoved; 290 291 // Figure out the number of known-zero bits coming in. 292 return GetLeadingZeros(I->getOperand(0), TD); 293 } 294 295 // We can't extend or shrink something that has multiple uses: doing so would 296 // require duplicating the instruction in general, which isn't profitable. 297 if (!I->hasOneUse()) return -1; 298 299 int Tmp1, Tmp2; 300 unsigned Opc = I->getOpcode(); 301 switch (Opc) { 302 case Instruction::And: 303 Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 304 if (Tmp1 == -1) return -1; 305 Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 306 if (Tmp2 == -1) return -1; 307 return std::max(Tmp1, Tmp2); 308 case Instruction::Or: 309 case Instruction::Xor: 310 Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 311 if (Tmp1 == -1) return -1; 312 Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 313 return std::min(Tmp1, Tmp2); 314 315 case Instruction::Add: 316 case Instruction::Sub: 317 case Instruction::Mul: 318 Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 319 if (Tmp1 == -1) return -1; 320 Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 321 if (Tmp2 == -1) return -1; 322 return 0; 323 324 //case Instruction::Shl: 325 //case Instruction::LShr: 326 case Instruction::ZExt: 327 // zext(zext(x)) -> zext(x). Since we're replacing it, it isn't eliminated. 328 Tmp1 = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits(); 329 return GetLeadingZeros(I, TD)+Tmp1; 330 331 //case Instruction::SExt: zext(sext(x)) -> sext(x) with no upper bits known. 332 //case Instruction::Trunc: 333 case Instruction::Select: 334 Tmp1 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 335 if (Tmp1 == -1) return -1; 336 Tmp2 = CanEvaluateZExtd(I->getOperand(2), Ty, NumCastsRemoved, TD); 337 return std::min(Tmp1, Tmp2); 338 339 case Instruction::PHI: { 340 // We can change a phi if we can change all operands. Note that we never 341 // get into trouble with cyclic PHIs here because we only consider 342 // instructions with a single use. 343 PHINode *PN = cast<PHINode>(I); 344 int Result = CanEvaluateZExtd(PN->getIncomingValue(0), Ty, 345 NumCastsRemoved, TD); 346 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) { 347 if (Result == -1) return -1; 348 Tmp1 = CanEvaluateZExtd(PN->getIncomingValue(i), Ty, NumCastsRemoved, TD); 349 Result = std::min(Result, Tmp1); 350 } 351 return Result; 352 } 353 default: 354 // TODO: Can handle more cases here. 355 return -1; 356 } 357} 358 359/// CanEvaluateSExtd - Return true if we can take the specified value 360/// and return it as type Ty without inserting any new casts and without 361/// changing the value of the common low bits. This is used by code that tries 362/// to promote integer operations to a wider types will allow us to eliminate 363/// the extension. 364/// 365/// This returns 0 if we can't do this or the number of sign bits that would be 366/// set if we can. For example, CanEvaluateSExtd(i16 1, i64) would return 63, 367/// because the computation can be extended (to "i64 1") and the resulting 368/// computation has 63 equal sign bits. 369/// 370/// This function works on both vectors and scalars. For vectors, the result is 371/// the number of bits known sign extended in each element. 372/// 373static unsigned CanEvaluateSExtd(Value *V, const Type *Ty, 374 unsigned &NumCastsRemoved, TargetData *TD) { 375 assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() && 376 "Can't sign extend type to a smaller type"); 377 // If this is a constant, return the number of sign bits the extended version 378 // of it would have. 379 if (Constant *C = dyn_cast<Constant>(V)) 380 return ComputeNumSignBits(ConstantExpr::getSExt(C, Ty), TD); 381 382 Instruction *I = dyn_cast<Instruction>(V); 383 if (!I) return 0; 384 385 // If this is a truncate from the destination type, we can trivially eliminate 386 // it, and this will remove a cast overall. 387 if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty) { 388 // If the operand of the truncate is itself a cast, and is eliminable, do 389 // not count this as an eliminable cast. We would prefer to eliminate those 390 // two casts first. 391 if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse()) 392 ++NumCastsRemoved; 393 return ComputeNumSignBits(I->getOperand(0), TD); 394 } 395 396 // We can't extend or shrink something that has multiple uses: doing so would 397 // require duplicating the instruction in general, which isn't profitable. 398 if (!I->hasOneUse()) return 0; 399 400 const Type *OrigTy = V->getType(); 401 402 unsigned Opc = I->getOpcode(); 403 unsigned Tmp1, Tmp2; 404 switch (Opc) { 405 case Instruction::And: 406 case Instruction::Or: 407 case Instruction::Xor: 408 // These operators can all arbitrarily be extended or truncated. 409 Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 410 if (Tmp1 == 0) return 0; 411 Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 412 return std::min(Tmp1, Tmp2); 413 case Instruction::Add: 414 case Instruction::Sub: 415 // Add/Sub can have at most one carry/borrow bit. 416 Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 417 if (Tmp1 == 0) return 0; 418 Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 419 if (Tmp2 == 0) return 0; 420 return std::min(Tmp1, Tmp2)-1; 421 case Instruction::Mul: 422 // These operators can all arbitrarily be extended or truncated. 423 if (!CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD)) 424 return 0; 425 if (!CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD)) 426 return 0; 427 return 1; // IMPROVE? 428 429 //case Instruction::Shl: TODO 430 //case Instruction::LShr: TODO 431 //case Instruction::Trunc: TODO 432 433 case Instruction::SExt: 434 case Instruction::ZExt: { 435 // sext(sext(x)) -> sext(x) 436 // sext(zext(x)) -> zext(x) 437 // Note that replacing a cast does not reduce the number of casts in the 438 // input. 439 unsigned InSignBits = ComputeNumSignBits(I, TD); 440 unsigned ExtBits = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits(); 441 // We'll end up extending it all the way out. 442 return InSignBits+ExtBits; 443 } 444 case Instruction::Select: { 445 SelectInst *SI = cast<SelectInst>(I); 446 Tmp1 = CanEvaluateSExtd(SI->getTrueValue(), Ty, NumCastsRemoved, TD); 447 if (Tmp1 == 0) return 0; 448 Tmp2 = CanEvaluateSExtd(SI->getFalseValue(), Ty, NumCastsRemoved,TD); 449 return std::min(Tmp1, Tmp2); 450 } 451 case Instruction::PHI: { 452 // We can change a phi if we can change all operands. Note that we never 453 // get into trouble with cyclic PHIs here because we only consider 454 // instructions with a single use. 455 PHINode *PN = cast<PHINode>(I); 456 unsigned Result = ~0U; 457 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 458 Result = std::min(Result, 459 CanEvaluateSExtd(PN->getIncomingValue(i), Ty, 460 NumCastsRemoved, TD)); 461 if (Result == 0) return 0; 462 } 463 return Result; 464 } 465 default: 466 // TODO: Can handle more cases here. 467 break; 468 } 469 470 return 0; 471} 472 473 474/// EvaluateInDifferentType - Given an expression that 475/// CanEvaluateTruncated or CanEvaluateSExtd returns true for, actually 476/// insert the code to evaluate the expression. 477Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty, 478 bool isSigned) { 479 if (Constant *C = dyn_cast<Constant>(V)) { 480 C = ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/); 481 // If we got a constantexpr back, try to simplify it with TD info. 482 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 483 C = ConstantFoldConstantExpression(CE, TD); 484 return C; 485 } 486 487 // Otherwise, it must be an instruction. 488 Instruction *I = cast<Instruction>(V); 489 Instruction *Res = 0; 490 unsigned Opc = I->getOpcode(); 491 switch (Opc) { 492 case Instruction::Add: 493 case Instruction::Sub: 494 case Instruction::Mul: 495 case Instruction::And: 496 case Instruction::Or: 497 case Instruction::Xor: 498 case Instruction::AShr: 499 case Instruction::LShr: 500 case Instruction::Shl: 501 case Instruction::UDiv: 502 case Instruction::URem: { 503 Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned); 504 Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned); 505 Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS); 506 break; 507 } 508 case Instruction::Trunc: 509 case Instruction::ZExt: 510 case Instruction::SExt: 511 // If the source type of the cast is the type we're trying for then we can 512 // just return the source. There's no need to insert it because it is not 513 // new. 514 if (I->getOperand(0)->getType() == Ty) 515 return I->getOperand(0); 516 517 // Otherwise, must be the same type of cast, so just reinsert a new one. 518 Res = CastInst::Create(cast<CastInst>(I)->getOpcode(), I->getOperand(0),Ty); 519 break; 520 case Instruction::Select: { 521 Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned); 522 Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned); 523 Res = SelectInst::Create(I->getOperand(0), True, False); 524 break; 525 } 526 case Instruction::PHI: { 527 PHINode *OPN = cast<PHINode>(I); 528 PHINode *NPN = PHINode::Create(Ty); 529 for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) { 530 Value *V =EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned); 531 NPN->addIncoming(V, OPN->getIncomingBlock(i)); 532 } 533 Res = NPN; 534 break; 535 } 536 default: 537 // TODO: Can handle more cases here. 538 llvm_unreachable("Unreachable!"); 539 break; 540 } 541 542 Res->takeName(I); 543 return InsertNewInstBefore(Res, *I); 544} 545 546 547/// This function is a wrapper around CastInst::isEliminableCastPair. It 548/// simply extracts arguments and returns what that function returns. 549static Instruction::CastOps 550isEliminableCastPair( 551 const CastInst *CI, ///< The first cast instruction 552 unsigned opcode, ///< The opcode of the second cast instruction 553 const Type *DstTy, ///< The target type for the second cast instruction 554 TargetData *TD ///< The target data for pointer size 555) { 556 557 const Type *SrcTy = CI->getOperand(0)->getType(); // A from above 558 const Type *MidTy = CI->getType(); // B from above 559 560 // Get the opcodes of the two Cast instructions 561 Instruction::CastOps firstOp = Instruction::CastOps(CI->getOpcode()); 562 Instruction::CastOps secondOp = Instruction::CastOps(opcode); 563 564 unsigned Res = CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy, 565 DstTy, 566 TD ? TD->getIntPtrType(CI->getContext()) : 0); 567 568 // We don't want to form an inttoptr or ptrtoint that converts to an integer 569 // type that differs from the pointer size. 570 if ((Res == Instruction::IntToPtr && 571 (!TD || SrcTy != TD->getIntPtrType(CI->getContext()))) || 572 (Res == Instruction::PtrToInt && 573 (!TD || DstTy != TD->getIntPtrType(CI->getContext())))) 574 Res = 0; 575 576 return Instruction::CastOps(Res); 577} 578 579/// ValueRequiresCast - Return true if the cast from "V to Ty" actually results 580/// in any code being generated. It does not require codegen if V is simple 581/// enough or if the cast can be folded into other casts. 582bool InstCombiner::ValueRequiresCast(Instruction::CastOps opcode,const Value *V, 583 const Type *Ty) { 584 if (V->getType() == Ty || isa<Constant>(V)) return false; 585 586 // If this is another cast that can be eliminated, it isn't codegen either. 587 if (const CastInst *CI = dyn_cast<CastInst>(V)) 588 if (isEliminableCastPair(CI, opcode, Ty, TD)) 589 return false; 590 return true; 591} 592 593 594/// @brief Implement the transforms common to all CastInst visitors. 595Instruction *InstCombiner::commonCastTransforms(CastInst &CI) { 596 Value *Src = CI.getOperand(0); 597 598 // Many cases of "cast of a cast" are eliminable. If it's eliminable we just 599 // eliminate it now. 600 if (CastInst *CSrc = dyn_cast<CastInst>(Src)) { // A->B->C cast 601 if (Instruction::CastOps opc = 602 isEliminableCastPair(CSrc, CI.getOpcode(), CI.getType(), TD)) { 603 // The first cast (CSrc) is eliminable so we need to fix up or replace 604 // the second cast (CI). CSrc will then have a good chance of being dead. 605 return CastInst::Create(opc, CSrc->getOperand(0), CI.getType()); 606 } 607 } 608 609 // If we are casting a select then fold the cast into the select 610 if (SelectInst *SI = dyn_cast<SelectInst>(Src)) 611 if (Instruction *NV = FoldOpIntoSelect(CI, SI)) 612 return NV; 613 614 // If we are casting a PHI then fold the cast into the PHI 615 if (isa<PHINode>(Src)) { 616 // We don't do this if this would create a PHI node with an illegal type if 617 // it is currently legal. 618 if (!isa<IntegerType>(Src->getType()) || 619 !isa<IntegerType>(CI.getType()) || 620 ShouldChangeType(CI.getType(), Src->getType())) 621 if (Instruction *NV = FoldOpIntoPhi(CI)) 622 return NV; 623 } 624 625 return 0; 626} 627 628/// commonIntCastTransforms - This function implements the common transforms 629/// for trunc, zext, and sext. 630Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) { 631 if (Instruction *Result = commonCastTransforms(CI)) 632 return Result; 633 634 // See if we can simplify any instructions used by the LHS whose sole 635 // purpose is to compute bits we don't care about. 636 if (SimplifyDemandedInstructionBits(CI)) 637 return &CI; 638 639 // If the source isn't an instruction or has more than one use then we 640 // can't do anything more. 641 Instruction *Src = dyn_cast<Instruction>(CI.getOperand(0)); 642 if (!Src || !Src->hasOneUse()) 643 return 0; 644 645 // Check to see if we can eliminate the cast by changing the entire 646 // computation chain to do the computation in the result type. 647 const Type *SrcTy = Src->getType(); 648 const Type *DestTy = CI.getType(); 649 650 // Only do this if the dest type is a simple type, don't convert the 651 // expression tree to something weird like i93 unless the source is also 652 // strange. 653 if (!isa<VectorType>(DestTy) && !ShouldChangeType(SrcTy, DestTy)) 654 return 0; 655 656 uint32_t SrcBitSize = SrcTy->getScalarSizeInBits(); 657 uint32_t DestBitSize = DestTy->getScalarSizeInBits(); 658 659 // Attempt to propagate the cast into the instruction for int->int casts. 660 unsigned NumCastsRemoved = 0; 661 switch (CI.getOpcode()) { 662 default: assert(0 && "not an integer cast"); 663 case Instruction::Trunc: { 664 if (!CanEvaluateTruncated(Src, DestTy)) 665 return 0; 666 667 // If this cast is a truncate, evaluting in a different type always 668 // eliminates the cast, so it is always a win. 669 DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" 670 " to avoid cast: " << CI); 671 Value *Res = EvaluateInDifferentType(Src, DestTy, false); 672 assert(Res->getType() == DestTy); 673 return ReplaceInstUsesWith(CI, Res); 674 } 675 case Instruction::ZExt: { 676 int BitsZExt = CanEvaluateZExtd(Src, DestTy, NumCastsRemoved, TD); 677 if (BitsZExt == -1) return 0; 678 679 // If this is a zero-extension, we need to do an AND to maintain the clear 680 // top-part of the computation. If we know the result will be zero 681 // extended enough already, we don't need the and. 682 if (NumCastsRemoved < 1 && 683 unsigned(BitsZExt) < DestBitSize-SrcBitSize) 684 return 0; 685 686 // Okay, we can transform this! Insert the new expression now. 687 DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" 688 " to avoid zero extend: " << CI); 689 Value *Res = EvaluateInDifferentType(Src, DestTy, false); 690 assert(Res->getType() == DestTy); 691 692 // If the high bits are already filled with zeros, just replace this 693 // cast with the result. 694 if (unsigned(BitsZExt) >= DestBitSize-SrcBitSize || 695 MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize, 696 DestBitSize-SrcBitSize))) 697 return ReplaceInstUsesWith(CI, Res); 698 699 // We need to emit an AND to clear the high bits. 700 Constant *C = ConstantInt::get(CI.getContext(), 701 APInt::getLowBitsSet(DestBitSize, SrcBitSize)); 702 return BinaryOperator::CreateAnd(Res, C); 703 } 704 case Instruction::SExt: { 705 // Check to see if we can do this transformation, and if so, how many bits 706 // of the promoted expression will be known copies of the sign bit in the 707 // result. 708 unsigned NumBitsSExt = CanEvaluateSExtd(Src, DestTy, NumCastsRemoved, TD); 709 if (NumBitsSExt == 0) 710 return 0; 711 712 // Because this is a sign extension, we can always transform it by inserting 713 // two new shifts (to do the extension). However, this is only profitable 714 // if we've eliminated two or more casts from the input. If we know the 715 // result will be sign-extended enough to not require these shifts, we can 716 // always do the transformation. 717 if (NumCastsRemoved < 2 && 718 NumBitsSExt <= DestBitSize-SrcBitSize) 719 return 0; 720 721 // Okay, we can transform this! Insert the new expression now. 722 DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" 723 " to avoid sign extend: " << CI); 724 Value *Res = EvaluateInDifferentType(Src, DestTy, true); 725 assert(Res->getType() == DestTy); 726 727 // If the high bits are already filled with sign bit, just replace this 728 // cast with the result. 729 if (NumBitsSExt > DestBitSize - SrcBitSize || 730 ComputeNumSignBits(Res) > DestBitSize - SrcBitSize) 731 return ReplaceInstUsesWith(CI, Res); 732 733 // We need to emit a cast to truncate, then a cast to sext. 734 return new SExtInst(Builder->CreateTrunc(Res, Src->getType()), DestTy); 735 } 736 } 737} 738 739Instruction *InstCombiner::visitTrunc(TruncInst &CI) { 740 if (Instruction *Result = commonIntCastTransforms(CI)) 741 return Result; 742 743 Value *Src = CI.getOperand(0); 744 const Type *DestTy = CI.getType(); 745 746 // Canonicalize trunc x to i1 -> (icmp ne (and x, 1), 0), likewise for vector. 747 if (DestTy->getScalarSizeInBits() == 1) { 748 Constant *One = ConstantInt::get(Src->getType(), 1); 749 Src = Builder->CreateAnd(Src, One, "tmp"); 750 Value *Zero = Constant::getNullValue(Src->getType()); 751 return new ICmpInst(ICmpInst::ICMP_NE, Src, Zero); 752 } 753 754 return 0; 755} 756 757/// transformZExtICmp - Transform (zext icmp) to bitwise / integer operations 758/// in order to eliminate the icmp. 759Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI, 760 bool DoXform) { 761 // If we are just checking for a icmp eq of a single bit and zext'ing it 762 // to an integer, then shift the bit to the appropriate place and then 763 // cast to integer to avoid the comparison. 764 if (ConstantInt *Op1C = dyn_cast<ConstantInt>(ICI->getOperand(1))) { 765 const APInt &Op1CV = Op1C->getValue(); 766 767 // zext (x <s 0) to i32 --> x>>u31 true if signbit set. 768 // zext (x >s -1) to i32 --> (x>>u31)^1 true if signbit clear. 769 if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV == 0) || 770 (ICI->getPredicate() == ICmpInst::ICMP_SGT &&Op1CV.isAllOnesValue())) { 771 if (!DoXform) return ICI; 772 773 Value *In = ICI->getOperand(0); 774 Value *Sh = ConstantInt::get(In->getType(), 775 In->getType()->getScalarSizeInBits()-1); 776 In = Builder->CreateLShr(In, Sh, In->getName()+".lobit"); 777 if (In->getType() != CI.getType()) 778 In = Builder->CreateIntCast(In, CI.getType(), false/*ZExt*/, "tmp"); 779 780 if (ICI->getPredicate() == ICmpInst::ICMP_SGT) { 781 Constant *One = ConstantInt::get(In->getType(), 1); 782 In = Builder->CreateXor(In, One, In->getName()+".not"); 783 } 784 785 return ReplaceInstUsesWith(CI, In); 786 } 787 788 789 790 // zext (X == 0) to i32 --> X^1 iff X has only the low bit set. 791 // zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set. 792 // zext (X == 1) to i32 --> X iff X has only the low bit set. 793 // zext (X == 2) to i32 --> X>>1 iff X has only the 2nd bit set. 794 // zext (X != 0) to i32 --> X iff X has only the low bit set. 795 // zext (X != 0) to i32 --> X>>1 iff X has only the 2nd bit set. 796 // zext (X != 1) to i32 --> X^1 iff X has only the low bit set. 797 // zext (X != 2) to i32 --> (X>>1)^1 iff X has only the 2nd bit set. 798 if ((Op1CV == 0 || Op1CV.isPowerOf2()) && 799 // This only works for EQ and NE 800 ICI->isEquality()) { 801 // If Op1C some other power of two, convert: 802 uint32_t BitWidth = Op1C->getType()->getBitWidth(); 803 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 804 APInt TypeMask(APInt::getAllOnesValue(BitWidth)); 805 ComputeMaskedBits(ICI->getOperand(0), TypeMask, KnownZero, KnownOne); 806 807 APInt KnownZeroMask(~KnownZero); 808 if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1? 809 if (!DoXform) return ICI; 810 811 bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE; 812 if (Op1CV != 0 && (Op1CV != KnownZeroMask)) { 813 // (X&4) == 2 --> false 814 // (X&4) != 2 --> true 815 Constant *Res = ConstantInt::get(Type::getInt1Ty(CI.getContext()), 816 isNE); 817 Res = ConstantExpr::getZExt(Res, CI.getType()); 818 return ReplaceInstUsesWith(CI, Res); 819 } 820 821 uint32_t ShiftAmt = KnownZeroMask.logBase2(); 822 Value *In = ICI->getOperand(0); 823 if (ShiftAmt) { 824 // Perform a logical shr by shiftamt. 825 // Insert the shift to put the result in the low bit. 826 In = Builder->CreateLShr(In, ConstantInt::get(In->getType(),ShiftAmt), 827 In->getName()+".lobit"); 828 } 829 830 if ((Op1CV != 0) == isNE) { // Toggle the low bit. 831 Constant *One = ConstantInt::get(In->getType(), 1); 832 In = Builder->CreateXor(In, One, "tmp"); 833 } 834 835 if (CI.getType() == In->getType()) 836 return ReplaceInstUsesWith(CI, In); 837 else 838 return CastInst::CreateIntegerCast(In, CI.getType(), false/*ZExt*/); 839 } 840 } 841 } 842 843 // icmp ne A, B is equal to xor A, B when A and B only really have one bit. 844 // It is also profitable to transform icmp eq into not(xor(A, B)) because that 845 // may lead to additional simplifications. 846 if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) { 847 if (const IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) { 848 uint32_t BitWidth = ITy->getBitWidth(); 849 Value *LHS = ICI->getOperand(0); 850 Value *RHS = ICI->getOperand(1); 851 852 APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0); 853 APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0); 854 APInt TypeMask(APInt::getAllOnesValue(BitWidth)); 855 ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS); 856 ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS); 857 858 if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) { 859 APInt KnownBits = KnownZeroLHS | KnownOneLHS; 860 APInt UnknownBit = ~KnownBits; 861 if (UnknownBit.countPopulation() == 1) { 862 if (!DoXform) return ICI; 863 864 Value *Result = Builder->CreateXor(LHS, RHS); 865 866 // Mask off any bits that are set and won't be shifted away. 867 if (KnownOneLHS.uge(UnknownBit)) 868 Result = Builder->CreateAnd(Result, 869 ConstantInt::get(ITy, UnknownBit)); 870 871 // Shift the bit we're testing down to the lsb. 872 Result = Builder->CreateLShr( 873 Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros())); 874 875 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 876 Result = Builder->CreateXor(Result, ConstantInt::get(ITy, 1)); 877 Result->takeName(ICI); 878 return ReplaceInstUsesWith(CI, Result); 879 } 880 } 881 } 882 } 883 884 return 0; 885} 886 887Instruction *InstCombiner::visitZExt(ZExtInst &CI) { 888 // If one of the common conversion will work, do it. 889 if (Instruction *Result = commonIntCastTransforms(CI)) 890 return Result; 891 892 Value *Src = CI.getOperand(0); 893 894 // If this is a TRUNC followed by a ZEXT then we are dealing with integral 895 // types and if the sizes are just right we can convert this into a logical 896 // 'and' which will be much cheaper than the pair of casts. 897 if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) { // A->B->C cast 898 // Get the sizes of the types involved. We know that the intermediate type 899 // will be smaller than A or C, but don't know the relation between A and C. 900 Value *A = CSrc->getOperand(0); 901 unsigned SrcSize = A->getType()->getScalarSizeInBits(); 902 unsigned MidSize = CSrc->getType()->getScalarSizeInBits(); 903 unsigned DstSize = CI.getType()->getScalarSizeInBits(); 904 // If we're actually extending zero bits, then if 905 // SrcSize < DstSize: zext(a & mask) 906 // SrcSize == DstSize: a & mask 907 // SrcSize > DstSize: trunc(a) & mask 908 if (SrcSize < DstSize) { 909 APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize)); 910 Constant *AndConst = ConstantInt::get(A->getType(), AndValue); 911 Value *And = Builder->CreateAnd(A, AndConst, CSrc->getName()+".mask"); 912 return new ZExtInst(And, CI.getType()); 913 } 914 915 if (SrcSize == DstSize) { 916 APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize)); 917 return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(), 918 AndValue)); 919 } 920 if (SrcSize > DstSize) { 921 Value *Trunc = Builder->CreateTrunc(A, CI.getType(), "tmp"); 922 APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize)); 923 return BinaryOperator::CreateAnd(Trunc, 924 ConstantInt::get(Trunc->getType(), 925 AndValue)); 926 } 927 } 928 929 if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src)) 930 return transformZExtICmp(ICI, CI); 931 932 BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src); 933 if (SrcI && SrcI->getOpcode() == Instruction::Or) { 934 // zext (or icmp, icmp) --> or (zext icmp), (zext icmp) if at least one 935 // of the (zext icmp) will be transformed. 936 ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0)); 937 ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1)); 938 if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() && 939 (transformZExtICmp(LHS, CI, false) || 940 transformZExtICmp(RHS, CI, false))) { 941 Value *LCast = Builder->CreateZExt(LHS, CI.getType(), LHS->getName()); 942 Value *RCast = Builder->CreateZExt(RHS, CI.getType(), RHS->getName()); 943 return BinaryOperator::Create(Instruction::Or, LCast, RCast); 944 } 945 } 946 947 // zext(trunc(t) & C) -> (t & zext(C)). 948 if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse()) 949 if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1))) 950 if (TruncInst *TI = dyn_cast<TruncInst>(SrcI->getOperand(0))) { 951 Value *TI0 = TI->getOperand(0); 952 if (TI0->getType() == CI.getType()) 953 return 954 BinaryOperator::CreateAnd(TI0, 955 ConstantExpr::getZExt(C, CI.getType())); 956 } 957 958 // zext((trunc(t) & C) ^ C) -> ((t & zext(C)) ^ zext(C)). 959 if (SrcI && SrcI->getOpcode() == Instruction::Xor && SrcI->hasOneUse()) 960 if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1))) 961 if (BinaryOperator *And = dyn_cast<BinaryOperator>(SrcI->getOperand(0))) 962 if (And->getOpcode() == Instruction::And && And->hasOneUse() && 963 And->getOperand(1) == C) 964 if (TruncInst *TI = dyn_cast<TruncInst>(And->getOperand(0))) { 965 Value *TI0 = TI->getOperand(0); 966 if (TI0->getType() == CI.getType()) { 967 Constant *ZC = ConstantExpr::getZExt(C, CI.getType()); 968 Value *NewAnd = Builder->CreateAnd(TI0, ZC, "tmp"); 969 return BinaryOperator::CreateXor(NewAnd, ZC); 970 } 971 } 972 973 // zext (xor i1 X, true) to i32 --> xor (zext i1 X to i32), 1 974 Value *X; 975 if (SrcI && SrcI->hasOneUse() && SrcI->getType()->isInteger(1) && 976 match(SrcI, m_Not(m_Value(X))) && 977 (!X->hasOneUse() || !isa<CmpInst>(X))) { 978 Value *New = Builder->CreateZExt(X, CI.getType()); 979 return BinaryOperator::CreateXor(New, ConstantInt::get(CI.getType(), 1)); 980 } 981 982 return 0; 983} 984 985Instruction *InstCombiner::visitSExt(SExtInst &CI) { 986 if (Instruction *I = commonIntCastTransforms(CI)) 987 return I; 988 989 Value *Src = CI.getOperand(0); 990 991 // Canonicalize sign-extend from i1 to a select. 992 if (Src->getType()->isInteger(1)) 993 return SelectInst::Create(Src, 994 Constant::getAllOnesValue(CI.getType()), 995 Constant::getNullValue(CI.getType())); 996 997 // See if the value being truncated is already sign extended. If so, just 998 // eliminate the trunc/sext pair. 999 if (Operator::getOpcode(Src) == Instruction::Trunc) { 1000 Value *Op = cast<User>(Src)->getOperand(0); 1001 unsigned OpBits = Op->getType()->getScalarSizeInBits(); 1002 unsigned MidBits = Src->getType()->getScalarSizeInBits(); 1003 unsigned DestBits = CI.getType()->getScalarSizeInBits(); 1004 unsigned NumSignBits = ComputeNumSignBits(Op); 1005 1006 if (OpBits == DestBits) { 1007 // Op is i32, Mid is i8, and Dest is i32. If Op has more than 24 sign 1008 // bits, it is already ready. 1009 if (NumSignBits > DestBits-MidBits) 1010 return ReplaceInstUsesWith(CI, Op); 1011 } else if (OpBits < DestBits) { 1012 // Op is i32, Mid is i8, and Dest is i64. If Op has more than 24 sign 1013 // bits, just sext from i32. 1014 if (NumSignBits > OpBits-MidBits) 1015 return new SExtInst(Op, CI.getType(), "tmp"); 1016 } else { 1017 // Op is i64, Mid is i8, and Dest is i32. If Op has more than 56 sign 1018 // bits, just truncate to i32. 1019 if (NumSignBits > OpBits-MidBits) 1020 return new TruncInst(Op, CI.getType(), "tmp"); 1021 } 1022 } 1023 1024 // If the input is a shl/ashr pair of a same constant, then this is a sign 1025 // extension from a smaller value. If we could trust arbitrary bitwidth 1026 // integers, we could turn this into a truncate to the smaller bit and then 1027 // use a sext for the whole extension. Since we don't, look deeper and check 1028 // for a truncate. If the source and dest are the same type, eliminate the 1029 // trunc and extend and just do shifts. For example, turn: 1030 // %a = trunc i32 %i to i8 1031 // %b = shl i8 %a, 6 1032 // %c = ashr i8 %b, 6 1033 // %d = sext i8 %c to i32 1034 // into: 1035 // %a = shl i32 %i, 30 1036 // %d = ashr i32 %a, 30 1037 Value *A = 0; 1038 ConstantInt *BA = 0, *CA = 0; 1039 if (match(Src, m_AShr(m_Shl(m_Value(A), m_ConstantInt(BA)), 1040 m_ConstantInt(CA))) && 1041 BA == CA && isa<TruncInst>(A)) { 1042 Value *I = cast<TruncInst>(A)->getOperand(0); 1043 if (I->getType() == CI.getType()) { 1044 unsigned MidSize = Src->getType()->getScalarSizeInBits(); 1045 unsigned SrcDstSize = CI.getType()->getScalarSizeInBits(); 1046 unsigned ShAmt = CA->getZExtValue()+SrcDstSize-MidSize; 1047 Constant *ShAmtV = ConstantInt::get(CI.getType(), ShAmt); 1048 I = Builder->CreateShl(I, ShAmtV, CI.getName()); 1049 return BinaryOperator::CreateAShr(I, ShAmtV); 1050 } 1051 } 1052 1053 return 0; 1054} 1055 1056 1057/// FitsInFPType - Return a Constant* for the specified FP constant if it fits 1058/// in the specified FP type without changing its value. 1059static Constant *FitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) { 1060 bool losesInfo; 1061 APFloat F = CFP->getValueAPF(); 1062 (void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo); 1063 if (!losesInfo) 1064 return ConstantFP::get(CFP->getContext(), F); 1065 return 0; 1066} 1067 1068/// LookThroughFPExtensions - If this is an fp extension instruction, look 1069/// through it until we get the source value. 1070static Value *LookThroughFPExtensions(Value *V) { 1071 if (Instruction *I = dyn_cast<Instruction>(V)) 1072 if (I->getOpcode() == Instruction::FPExt) 1073 return LookThroughFPExtensions(I->getOperand(0)); 1074 1075 // If this value is a constant, return the constant in the smallest FP type 1076 // that can accurately represent it. This allows us to turn 1077 // (float)((double)X+2.0) into x+2.0f. 1078 if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) { 1079 if (CFP->getType() == Type::getPPC_FP128Ty(V->getContext())) 1080 return V; // No constant folding of this. 1081 // See if the value can be truncated to float and then reextended. 1082 if (Value *V = FitsInFPType(CFP, APFloat::IEEEsingle)) 1083 return V; 1084 if (CFP->getType()->isDoubleTy()) 1085 return V; // Won't shrink. 1086 if (Value *V = FitsInFPType(CFP, APFloat::IEEEdouble)) 1087 return V; 1088 // Don't try to shrink to various long double types. 1089 } 1090 1091 return V; 1092} 1093 1094Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) { 1095 if (Instruction *I = commonCastTransforms(CI)) 1096 return I; 1097 1098 // If we have fptrunc(fadd (fpextend x), (fpextend y)), where x and y are 1099 // smaller than the destination type, we can eliminate the truncate by doing 1100 // the add as the smaller type. This applies to fadd/fsub/fmul/fdiv as well 1101 // as many builtins (sqrt, etc). 1102 BinaryOperator *OpI = dyn_cast<BinaryOperator>(CI.getOperand(0)); 1103 if (OpI && OpI->hasOneUse()) { 1104 switch (OpI->getOpcode()) { 1105 default: break; 1106 case Instruction::FAdd: 1107 case Instruction::FSub: 1108 case Instruction::FMul: 1109 case Instruction::FDiv: 1110 case Instruction::FRem: 1111 const Type *SrcTy = OpI->getType(); 1112 Value *LHSTrunc = LookThroughFPExtensions(OpI->getOperand(0)); 1113 Value *RHSTrunc = LookThroughFPExtensions(OpI->getOperand(1)); 1114 if (LHSTrunc->getType() != SrcTy && 1115 RHSTrunc->getType() != SrcTy) { 1116 unsigned DstSize = CI.getType()->getScalarSizeInBits(); 1117 // If the source types were both smaller than the destination type of 1118 // the cast, do this xform. 1119 if (LHSTrunc->getType()->getScalarSizeInBits() <= DstSize && 1120 RHSTrunc->getType()->getScalarSizeInBits() <= DstSize) { 1121 LHSTrunc = Builder->CreateFPExt(LHSTrunc, CI.getType()); 1122 RHSTrunc = Builder->CreateFPExt(RHSTrunc, CI.getType()); 1123 return BinaryOperator::Create(OpI->getOpcode(), LHSTrunc, RHSTrunc); 1124 } 1125 } 1126 break; 1127 } 1128 } 1129 return 0; 1130} 1131 1132Instruction *InstCombiner::visitFPExt(CastInst &CI) { 1133 return commonCastTransforms(CI); 1134} 1135 1136Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) { 1137 Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0)); 1138 if (OpI == 0) 1139 return commonCastTransforms(FI); 1140 1141 // fptoui(uitofp(X)) --> X 1142 // fptoui(sitofp(X)) --> X 1143 // This is safe if the intermediate type has enough bits in its mantissa to 1144 // accurately represent all values of X. For example, do not do this with 1145 // i64->float->i64. This is also safe for sitofp case, because any negative 1146 // 'X' value would cause an undefined result for the fptoui. 1147 if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) && 1148 OpI->getOperand(0)->getType() == FI.getType() && 1149 (int)FI.getType()->getScalarSizeInBits() < /*extra bit for sign */ 1150 OpI->getType()->getFPMantissaWidth()) 1151 return ReplaceInstUsesWith(FI, OpI->getOperand(0)); 1152 1153 return commonCastTransforms(FI); 1154} 1155 1156Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) { 1157 Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0)); 1158 if (OpI == 0) 1159 return commonCastTransforms(FI); 1160 1161 // fptosi(sitofp(X)) --> X 1162 // fptosi(uitofp(X)) --> X 1163 // This is safe if the intermediate type has enough bits in its mantissa to 1164 // accurately represent all values of X. For example, do not do this with 1165 // i64->float->i64. This is also safe for sitofp case, because any negative 1166 // 'X' value would cause an undefined result for the fptoui. 1167 if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) && 1168 OpI->getOperand(0)->getType() == FI.getType() && 1169 (int)FI.getType()->getScalarSizeInBits() <= 1170 OpI->getType()->getFPMantissaWidth()) 1171 return ReplaceInstUsesWith(FI, OpI->getOperand(0)); 1172 1173 return commonCastTransforms(FI); 1174} 1175 1176Instruction *InstCombiner::visitUIToFP(CastInst &CI) { 1177 return commonCastTransforms(CI); 1178} 1179 1180Instruction *InstCombiner::visitSIToFP(CastInst &CI) { 1181 return commonCastTransforms(CI); 1182} 1183 1184Instruction *InstCombiner::visitIntToPtr(IntToPtrInst &CI) { 1185 // If the source integer type is larger than the intptr_t type for 1186 // this target, do a trunc to the intptr_t type, then inttoptr of it. This 1187 // allows the trunc to be exposed to other transforms. Don't do this for 1188 // extending inttoptr's, because we don't know if the target sign or zero 1189 // extends to pointers. 1190 if (TD && CI.getOperand(0)->getType()->getScalarSizeInBits() > 1191 TD->getPointerSizeInBits()) { 1192 Value *P = Builder->CreateTrunc(CI.getOperand(0), 1193 TD->getIntPtrType(CI.getContext()), "tmp"); 1194 return new IntToPtrInst(P, CI.getType()); 1195 } 1196 1197 if (Instruction *I = commonCastTransforms(CI)) 1198 return I; 1199 1200 return 0; 1201} 1202 1203/// @brief Implement the transforms for cast of pointer (bitcast/ptrtoint) 1204Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) { 1205 Value *Src = CI.getOperand(0); 1206 1207 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) { 1208 // If casting the result of a getelementptr instruction with no offset, turn 1209 // this into a cast of the original pointer! 1210 if (GEP->hasAllZeroIndices()) { 1211 // Changing the cast operand is usually not a good idea but it is safe 1212 // here because the pointer operand is being replaced with another 1213 // pointer operand so the opcode doesn't need to change. 1214 Worklist.Add(GEP); 1215 CI.setOperand(0, GEP->getOperand(0)); 1216 return &CI; 1217 } 1218 1219 // If the GEP has a single use, and the base pointer is a bitcast, and the 1220 // GEP computes a constant offset, see if we can convert these three 1221 // instructions into fewer. This typically happens with unions and other 1222 // non-type-safe code. 1223 if (TD && GEP->hasOneUse() && isa<BitCastInst>(GEP->getOperand(0)) && 1224 GEP->hasAllConstantIndices()) { 1225 // We are guaranteed to get a constant from EmitGEPOffset. 1226 ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(GEP)); 1227 int64_t Offset = OffsetV->getSExtValue(); 1228 1229 // Get the base pointer input of the bitcast, and the type it points to. 1230 Value *OrigBase = cast<BitCastInst>(GEP->getOperand(0))->getOperand(0); 1231 const Type *GEPIdxTy = 1232 cast<PointerType>(OrigBase->getType())->getElementType(); 1233 SmallVector<Value*, 8> NewIndices; 1234 if (FindElementAtOffset(GEPIdxTy, Offset, NewIndices)) { 1235 // If we were able to index down into an element, create the GEP 1236 // and bitcast the result. This eliminates one bitcast, potentially 1237 // two. 1238 Value *NGEP = cast<GEPOperator>(GEP)->isInBounds() ? 1239 Builder->CreateInBoundsGEP(OrigBase, 1240 NewIndices.begin(), NewIndices.end()) : 1241 Builder->CreateGEP(OrigBase, NewIndices.begin(), NewIndices.end()); 1242 NGEP->takeName(GEP); 1243 1244 if (isa<BitCastInst>(CI)) 1245 return new BitCastInst(NGEP, CI.getType()); 1246 assert(isa<PtrToIntInst>(CI)); 1247 return new PtrToIntInst(NGEP, CI.getType()); 1248 } 1249 } 1250 } 1251 1252 return commonCastTransforms(CI); 1253} 1254 1255Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) { 1256 // If the destination integer type is smaller than the intptr_t type for 1257 // this target, do a ptrtoint to intptr_t then do a trunc. This allows the 1258 // trunc to be exposed to other transforms. Don't do this for extending 1259 // ptrtoint's, because we don't know if the target sign or zero extends its 1260 // pointers. 1261 if (TD && 1262 CI.getType()->getScalarSizeInBits() < TD->getPointerSizeInBits()) { 1263 Value *P = Builder->CreatePtrToInt(CI.getOperand(0), 1264 TD->getIntPtrType(CI.getContext()), 1265 "tmp"); 1266 return new TruncInst(P, CI.getType()); 1267 } 1268 1269 return commonPointerCastTransforms(CI); 1270} 1271 1272Instruction *InstCombiner::visitBitCast(BitCastInst &CI) { 1273 // If the operands are integer typed then apply the integer transforms, 1274 // otherwise just apply the common ones. 1275 Value *Src = CI.getOperand(0); 1276 const Type *SrcTy = Src->getType(); 1277 const Type *DestTy = CI.getType(); 1278 1279 // Get rid of casts from one type to the same type. These are useless and can 1280 // be replaced by the operand. 1281 if (DestTy == Src->getType()) 1282 return ReplaceInstUsesWith(CI, Src); 1283 1284 if (const PointerType *DstPTy = dyn_cast<PointerType>(DestTy)) { 1285 const PointerType *SrcPTy = cast<PointerType>(SrcTy); 1286 const Type *DstElTy = DstPTy->getElementType(); 1287 const Type *SrcElTy = SrcPTy->getElementType(); 1288 1289 // If the address spaces don't match, don't eliminate the bitcast, which is 1290 // required for changing types. 1291 if (SrcPTy->getAddressSpace() != DstPTy->getAddressSpace()) 1292 return 0; 1293 1294 // If we are casting a alloca to a pointer to a type of the same 1295 // size, rewrite the allocation instruction to allocate the "right" type. 1296 // There is no need to modify malloc calls because it is their bitcast that 1297 // needs to be cleaned up. 1298 if (AllocaInst *AI = dyn_cast<AllocaInst>(Src)) 1299 if (Instruction *V = PromoteCastOfAllocation(CI, *AI)) 1300 return V; 1301 1302 // If the source and destination are pointers, and this cast is equivalent 1303 // to a getelementptr X, 0, 0, 0... turn it into the appropriate gep. 1304 // This can enhance SROA and other transforms that want type-safe pointers. 1305 Constant *ZeroUInt = 1306 Constant::getNullValue(Type::getInt32Ty(CI.getContext())); 1307 unsigned NumZeros = 0; 1308 while (SrcElTy != DstElTy && 1309 isa<CompositeType>(SrcElTy) && !isa<PointerType>(SrcElTy) && 1310 SrcElTy->getNumContainedTypes() /* not "{}" */) { 1311 SrcElTy = cast<CompositeType>(SrcElTy)->getTypeAtIndex(ZeroUInt); 1312 ++NumZeros; 1313 } 1314 1315 // If we found a path from the src to dest, create the getelementptr now. 1316 if (SrcElTy == DstElTy) { 1317 SmallVector<Value*, 8> Idxs(NumZeros+1, ZeroUInt); 1318 return GetElementPtrInst::CreateInBounds(Src, Idxs.begin(), Idxs.end(),"", 1319 ((Instruction*)NULL)); 1320 } 1321 } 1322 1323 if (const VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) { 1324 if (DestVTy->getNumElements() == 1 && !isa<VectorType>(SrcTy)) { 1325 Value *Elem = Builder->CreateBitCast(Src, DestVTy->getElementType()); 1326 return InsertElementInst::Create(UndefValue::get(DestTy), Elem, 1327 Constant::getNullValue(Type::getInt32Ty(CI.getContext()))); 1328 // FIXME: Canonicalize bitcast(insertelement) -> insertelement(bitcast) 1329 } 1330 } 1331 1332 if (const VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) { 1333 if (SrcVTy->getNumElements() == 1 && !isa<VectorType>(DestTy)) { 1334 Value *Elem = 1335 Builder->CreateExtractElement(Src, 1336 Constant::getNullValue(Type::getInt32Ty(CI.getContext()))); 1337 return CastInst::Create(Instruction::BitCast, Elem, DestTy); 1338 } 1339 } 1340 1341 if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(Src)) { 1342 // Okay, we have (bitcast (shuffle ..)). Check to see if this is 1343 // a bitconvert to a vector with the same # elts. 1344 if (SVI->hasOneUse() && isa<VectorType>(DestTy) && 1345 cast<VectorType>(DestTy)->getNumElements() == 1346 SVI->getType()->getNumElements() && 1347 SVI->getType()->getNumElements() == 1348 cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements()) { 1349 BitCastInst *Tmp; 1350 // If either of the operands is a cast from CI.getType(), then 1351 // evaluating the shuffle in the casted destination's type will allow 1352 // us to eliminate at least one cast. 1353 if (((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(0))) && 1354 Tmp->getOperand(0)->getType() == DestTy) || 1355 ((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(1))) && 1356 Tmp->getOperand(0)->getType() == DestTy)) { 1357 Value *LHS = Builder->CreateBitCast(SVI->getOperand(0), DestTy); 1358 Value *RHS = Builder->CreateBitCast(SVI->getOperand(1), DestTy); 1359 // Return a new shuffle vector. Use the same element ID's, as we 1360 // know the vector types match #elts. 1361 return new ShuffleVectorInst(LHS, RHS, SVI->getOperand(2)); 1362 } 1363 } 1364 } 1365 1366 if (isa<PointerType>(SrcTy)) 1367 return commonPointerCastTransforms(CI); 1368 return commonCastTransforms(CI); 1369} 1370