InstCombineCasts.cpp revision 9e390ddf91dcf7baa540330e1b9a73a0a177a2a6
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} 148 149 150 151/// EvaluateInDifferentType - Given an expression that 152/// CanEvaluateTruncated or CanEvaluateSExtd returns true for, actually 153/// insert the code to evaluate the expression. 154Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty, 155 bool isSigned) { 156 if (Constant *C = dyn_cast<Constant>(V)) { 157 C = ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/); 158 // If we got a constantexpr back, try to simplify it with TD info. 159 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 160 C = ConstantFoldConstantExpression(CE, TD); 161 return C; 162 } 163 164 // Otherwise, it must be an instruction. 165 Instruction *I = cast<Instruction>(V); 166 Instruction *Res = 0; 167 unsigned Opc = I->getOpcode(); 168 switch (Opc) { 169 case Instruction::Add: 170 case Instruction::Sub: 171 case Instruction::Mul: 172 case Instruction::And: 173 case Instruction::Or: 174 case Instruction::Xor: 175 case Instruction::AShr: 176 case Instruction::LShr: 177 case Instruction::Shl: 178 case Instruction::UDiv: 179 case Instruction::URem: { 180 Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned); 181 Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned); 182 Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS); 183 break; 184 } 185 case Instruction::Trunc: 186 case Instruction::ZExt: 187 case Instruction::SExt: 188 // If the source type of the cast is the type we're trying for then we can 189 // just return the source. There's no need to insert it because it is not 190 // new. 191 if (I->getOperand(0)->getType() == Ty) 192 return I->getOperand(0); 193 194 // Otherwise, must be the same type of cast, so just reinsert a new one. 195 Res = CastInst::Create(cast<CastInst>(I)->getOpcode(), I->getOperand(0),Ty); 196 break; 197 case Instruction::Select: { 198 Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned); 199 Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned); 200 Res = SelectInst::Create(I->getOperand(0), True, False); 201 break; 202 } 203 case Instruction::PHI: { 204 PHINode *OPN = cast<PHINode>(I); 205 PHINode *NPN = PHINode::Create(Ty); 206 for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) { 207 Value *V =EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned); 208 NPN->addIncoming(V, OPN->getIncomingBlock(i)); 209 } 210 Res = NPN; 211 break; 212 } 213 default: 214 // TODO: Can handle more cases here. 215 llvm_unreachable("Unreachable!"); 216 break; 217 } 218 219 Res->takeName(I); 220 return InsertNewInstBefore(Res, *I); 221} 222 223 224/// This function is a wrapper around CastInst::isEliminableCastPair. It 225/// simply extracts arguments and returns what that function returns. 226static Instruction::CastOps 227isEliminableCastPair( 228 const CastInst *CI, ///< The first cast instruction 229 unsigned opcode, ///< The opcode of the second cast instruction 230 const Type *DstTy, ///< The target type for the second cast instruction 231 TargetData *TD ///< The target data for pointer size 232) { 233 234 const Type *SrcTy = CI->getOperand(0)->getType(); // A from above 235 const Type *MidTy = CI->getType(); // B from above 236 237 // Get the opcodes of the two Cast instructions 238 Instruction::CastOps firstOp = Instruction::CastOps(CI->getOpcode()); 239 Instruction::CastOps secondOp = Instruction::CastOps(opcode); 240 241 unsigned Res = CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy, 242 DstTy, 243 TD ? TD->getIntPtrType(CI->getContext()) : 0); 244 245 // We don't want to form an inttoptr or ptrtoint that converts to an integer 246 // type that differs from the pointer size. 247 if ((Res == Instruction::IntToPtr && 248 (!TD || SrcTy != TD->getIntPtrType(CI->getContext()))) || 249 (Res == Instruction::PtrToInt && 250 (!TD || DstTy != TD->getIntPtrType(CI->getContext())))) 251 Res = 0; 252 253 return Instruction::CastOps(Res); 254} 255 256/// ValueRequiresCast - Return true if the cast from "V to Ty" actually results 257/// in any code being generated. It does not require codegen if V is simple 258/// enough or if the cast can be folded into other casts. 259bool InstCombiner::ValueRequiresCast(Instruction::CastOps opcode,const Value *V, 260 const Type *Ty) { 261 if (V->getType() == Ty || isa<Constant>(V)) return false; 262 263 // If this is another cast that can be eliminated, it isn't codegen either. 264 if (const CastInst *CI = dyn_cast<CastInst>(V)) 265 if (isEliminableCastPair(CI, opcode, Ty, TD)) 266 return false; 267 return true; 268} 269 270 271/// @brief Implement the transforms common to all CastInst visitors. 272Instruction *InstCombiner::commonCastTransforms(CastInst &CI) { 273 Value *Src = CI.getOperand(0); 274 275 // Many cases of "cast of a cast" are eliminable. If it's eliminable we just 276 // eliminate it now. 277 if (CastInst *CSrc = dyn_cast<CastInst>(Src)) { // A->B->C cast 278 if (Instruction::CastOps opc = 279 isEliminableCastPair(CSrc, CI.getOpcode(), CI.getType(), TD)) { 280 // The first cast (CSrc) is eliminable so we need to fix up or replace 281 // the second cast (CI). CSrc will then have a good chance of being dead. 282 return CastInst::Create(opc, CSrc->getOperand(0), CI.getType()); 283 } 284 } 285 286 // If we are casting a select then fold the cast into the select 287 if (SelectInst *SI = dyn_cast<SelectInst>(Src)) 288 if (Instruction *NV = FoldOpIntoSelect(CI, SI)) 289 return NV; 290 291 // If we are casting a PHI then fold the cast into the PHI 292 if (isa<PHINode>(Src)) { 293 // We don't do this if this would create a PHI node with an illegal type if 294 // it is currently legal. 295 if (!isa<IntegerType>(Src->getType()) || 296 !isa<IntegerType>(CI.getType()) || 297 ShouldChangeType(CI.getType(), Src->getType())) 298 if (Instruction *NV = FoldOpIntoPhi(CI)) 299 return NV; 300 } 301 302 return 0; 303} 304 305/// CanEvaluateTruncated - Return true if we can evaluate the specified 306/// expression tree as type Ty instead of its larger type, and arrive with the 307/// same value. This is used by code that tries to eliminate truncates. 308/// 309/// Ty will always be a type smaller than V. We should return true if trunc(V) 310/// can be computed by computing V in the smaller type. If V is an instruction, 311/// then trunc(inst(x,y)) can be computed as inst(trunc(x),trunc(y)), which only 312/// makes sense if x and y can be efficiently truncated. 313/// 314static bool CanEvaluateTruncated(Value *V, const Type *Ty) { 315 // We can always evaluate constants in another type. 316 if (isa<Constant>(V)) 317 return true; 318 319 Instruction *I = dyn_cast<Instruction>(V); 320 if (!I) return false; 321 322 const Type *OrigTy = V->getType(); 323 324 // If this is an extension from the dest type, we can eliminate it. 325 if ((isa<ZExtInst>(I) || isa<SExtInst>(I)) && 326 I->getOperand(0)->getType() == Ty) 327 return true; 328 329 // We can't extend or shrink something that has multiple uses: doing so would 330 // require duplicating the instruction in general, which isn't profitable. 331 if (!I->hasOneUse()) return false; 332 333 unsigned Opc = I->getOpcode(); 334 switch (Opc) { 335 case Instruction::Add: 336 case Instruction::Sub: 337 case Instruction::Mul: 338 case Instruction::And: 339 case Instruction::Or: 340 case Instruction::Xor: 341 // These operators can all arbitrarily be extended or truncated. 342 return CanEvaluateTruncated(I->getOperand(0), Ty) && 343 CanEvaluateTruncated(I->getOperand(1), Ty); 344 345 case Instruction::UDiv: 346 case Instruction::URem: { 347 // UDiv and URem can be truncated if all the truncated bits are zero. 348 uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); 349 uint32_t BitWidth = Ty->getScalarSizeInBits(); 350 if (BitWidth < OrigBitWidth) { 351 APInt Mask = APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth); 352 if (MaskedValueIsZero(I->getOperand(0), Mask) && 353 MaskedValueIsZero(I->getOperand(1), Mask)) { 354 return CanEvaluateTruncated(I->getOperand(0), Ty) && 355 CanEvaluateTruncated(I->getOperand(1), Ty); 356 } 357 } 358 break; 359 } 360 case Instruction::Shl: 361 // If we are truncating the result of this SHL, and if it's a shift of a 362 // constant amount, we can always perform a SHL in a smaller type. 363 if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) { 364 uint32_t BitWidth = Ty->getScalarSizeInBits(); 365 if (CI->getLimitedValue(BitWidth) < BitWidth) 366 return CanEvaluateTruncated(I->getOperand(0), Ty); 367 } 368 break; 369 case Instruction::LShr: 370 // If this is a truncate of a logical shr, we can truncate it to a smaller 371 // lshr iff we know that the bits we would otherwise be shifting in are 372 // already zeros. 373 if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) { 374 uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); 375 uint32_t BitWidth = Ty->getScalarSizeInBits(); 376 if (MaskedValueIsZero(I->getOperand(0), 377 APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) && 378 CI->getLimitedValue(BitWidth) < BitWidth) { 379 return CanEvaluateTruncated(I->getOperand(0), Ty); 380 } 381 } 382 break; 383 case Instruction::Trunc: 384 // trunc(trunc(x)) -> trunc(x) 385 return true; 386 case Instruction::Select: { 387 SelectInst *SI = cast<SelectInst>(I); 388 return CanEvaluateTruncated(SI->getTrueValue(), Ty) && 389 CanEvaluateTruncated(SI->getFalseValue(), Ty); 390 } 391 case Instruction::PHI: { 392 // We can change a phi if we can change all operands. Note that we never 393 // get into trouble with cyclic PHIs here because we only consider 394 // instructions with a single use. 395 PHINode *PN = cast<PHINode>(I); 396 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 397 if (!CanEvaluateTruncated(PN->getIncomingValue(i), Ty)) 398 return false; 399 return true; 400 } 401 default: 402 // TODO: Can handle more cases here. 403 break; 404 } 405 406 return false; 407} 408 409Instruction *InstCombiner::visitTrunc(TruncInst &CI) { 410 if (Instruction *Result = commonCastTransforms(CI)) 411 return Result; 412 413 // See if we can simplify any instructions used by the input whose sole 414 // purpose is to compute bits we don't care about. 415 if (SimplifyDemandedInstructionBits(CI)) 416 return &CI; 417 418 Value *Src = CI.getOperand(0); 419 const Type *DestTy = CI.getType(), *SrcTy = Src->getType(); 420 421 // Attempt to truncate the entire input expression tree to the destination 422 // type. Only do this if the dest type is a simple type, don't convert the 423 // expression tree to something weird like i93 unless the source is also 424 // strange. 425 if ((isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) && 426 CanEvaluateTruncated(Src, DestTy)) { 427 428 // If this cast is a truncate, evaluting in a different type always 429 // eliminates the cast, so it is always a win. 430 DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" 431 " to avoid cast: " << CI); 432 Value *Res = EvaluateInDifferentType(Src, DestTy, false); 433 assert(Res->getType() == DestTy); 434 return ReplaceInstUsesWith(CI, Res); 435 } 436 437 // Canonicalize trunc x to i1 -> (icmp ne (and x, 1), 0), likewise for vector. 438 if (DestTy->getScalarSizeInBits() == 1) { 439 Constant *One = ConstantInt::get(Src->getType(), 1); 440 Src = Builder->CreateAnd(Src, One, "tmp"); 441 Value *Zero = Constant::getNullValue(Src->getType()); 442 return new ICmpInst(ICmpInst::ICMP_NE, Src, Zero); 443 } 444 445 return 0; 446} 447 448/// transformZExtICmp - Transform (zext icmp) to bitwise / integer operations 449/// in order to eliminate the icmp. 450Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI, 451 bool DoXform) { 452 // If we are just checking for a icmp eq of a single bit and zext'ing it 453 // to an integer, then shift the bit to the appropriate place and then 454 // cast to integer to avoid the comparison. 455 if (ConstantInt *Op1C = dyn_cast<ConstantInt>(ICI->getOperand(1))) { 456 const APInt &Op1CV = Op1C->getValue(); 457 458 // zext (x <s 0) to i32 --> x>>u31 true if signbit set. 459 // zext (x >s -1) to i32 --> (x>>u31)^1 true if signbit clear. 460 if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV == 0) || 461 (ICI->getPredicate() == ICmpInst::ICMP_SGT &&Op1CV.isAllOnesValue())) { 462 if (!DoXform) return ICI; 463 464 Value *In = ICI->getOperand(0); 465 Value *Sh = ConstantInt::get(In->getType(), 466 In->getType()->getScalarSizeInBits()-1); 467 In = Builder->CreateLShr(In, Sh, In->getName()+".lobit"); 468 if (In->getType() != CI.getType()) 469 In = Builder->CreateIntCast(In, CI.getType(), false/*ZExt*/, "tmp"); 470 471 if (ICI->getPredicate() == ICmpInst::ICMP_SGT) { 472 Constant *One = ConstantInt::get(In->getType(), 1); 473 In = Builder->CreateXor(In, One, In->getName()+".not"); 474 } 475 476 return ReplaceInstUsesWith(CI, In); 477 } 478 479 480 481 // zext (X == 0) to i32 --> X^1 iff X has only the low bit set. 482 // zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set. 483 // zext (X == 1) to i32 --> X iff X has only the low bit set. 484 // zext (X == 2) to i32 --> X>>1 iff X has only the 2nd bit set. 485 // zext (X != 0) to i32 --> X iff X has only the low bit set. 486 // zext (X != 0) to i32 --> X>>1 iff X has only the 2nd bit set. 487 // zext (X != 1) to i32 --> X^1 iff X has only the low bit set. 488 // zext (X != 2) to i32 --> (X>>1)^1 iff X has only the 2nd bit set. 489 if ((Op1CV == 0 || Op1CV.isPowerOf2()) && 490 // This only works for EQ and NE 491 ICI->isEquality()) { 492 // If Op1C some other power of two, convert: 493 uint32_t BitWidth = Op1C->getType()->getBitWidth(); 494 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 495 APInt TypeMask(APInt::getAllOnesValue(BitWidth)); 496 ComputeMaskedBits(ICI->getOperand(0), TypeMask, KnownZero, KnownOne); 497 498 APInt KnownZeroMask(~KnownZero); 499 if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1? 500 if (!DoXform) return ICI; 501 502 bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE; 503 if (Op1CV != 0 && (Op1CV != KnownZeroMask)) { 504 // (X&4) == 2 --> false 505 // (X&4) != 2 --> true 506 Constant *Res = ConstantInt::get(Type::getInt1Ty(CI.getContext()), 507 isNE); 508 Res = ConstantExpr::getZExt(Res, CI.getType()); 509 return ReplaceInstUsesWith(CI, Res); 510 } 511 512 uint32_t ShiftAmt = KnownZeroMask.logBase2(); 513 Value *In = ICI->getOperand(0); 514 if (ShiftAmt) { 515 // Perform a logical shr by shiftamt. 516 // Insert the shift to put the result in the low bit. 517 In = Builder->CreateLShr(In, ConstantInt::get(In->getType(),ShiftAmt), 518 In->getName()+".lobit"); 519 } 520 521 if ((Op1CV != 0) == isNE) { // Toggle the low bit. 522 Constant *One = ConstantInt::get(In->getType(), 1); 523 In = Builder->CreateXor(In, One, "tmp"); 524 } 525 526 if (CI.getType() == In->getType()) 527 return ReplaceInstUsesWith(CI, In); 528 else 529 return CastInst::CreateIntegerCast(In, CI.getType(), false/*ZExt*/); 530 } 531 } 532 } 533 534 // icmp ne A, B is equal to xor A, B when A and B only really have one bit. 535 // It is also profitable to transform icmp eq into not(xor(A, B)) because that 536 // may lead to additional simplifications. 537 if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) { 538 if (const IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) { 539 uint32_t BitWidth = ITy->getBitWidth(); 540 Value *LHS = ICI->getOperand(0); 541 Value *RHS = ICI->getOperand(1); 542 543 APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0); 544 APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0); 545 APInt TypeMask(APInt::getAllOnesValue(BitWidth)); 546 ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS); 547 ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS); 548 549 if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) { 550 APInt KnownBits = KnownZeroLHS | KnownOneLHS; 551 APInt UnknownBit = ~KnownBits; 552 if (UnknownBit.countPopulation() == 1) { 553 if (!DoXform) return ICI; 554 555 Value *Result = Builder->CreateXor(LHS, RHS); 556 557 // Mask off any bits that are set and won't be shifted away. 558 if (KnownOneLHS.uge(UnknownBit)) 559 Result = Builder->CreateAnd(Result, 560 ConstantInt::get(ITy, UnknownBit)); 561 562 // Shift the bit we're testing down to the lsb. 563 Result = Builder->CreateLShr( 564 Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros())); 565 566 if (ICI->getPredicate() == ICmpInst::ICMP_EQ) 567 Result = Builder->CreateXor(Result, ConstantInt::get(ITy, 1)); 568 Result->takeName(ICI); 569 return ReplaceInstUsesWith(CI, Result); 570 } 571 } 572 } 573 } 574 575 return 0; 576} 577 578/// CanEvaluateZExtd - Determine if the specified value can be computed in the 579/// specified wider type and produce the same low bits. If not, return -1. If 580/// it is possible, return the number of high bits that are known to be zero in 581/// the promoted value. 582static bool CanEvaluateZExtd(Value *V, const Type *Ty, const TargetData *TD) { 583 if (isa<Constant>(V)) 584 return true; 585 586 Instruction *I = dyn_cast<Instruction>(V); 587 if (!I) return false; 588 589 // If the input is a truncate from the destination type, we can trivially 590 // eliminate it. 591 if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty) 592 return true; 593 594 // We can't extend or shrink something that has multiple uses: doing so would 595 // require duplicating the instruction in general, which isn't profitable. 596 if (!I->hasOneUse()) return false; 597 598 unsigned Opc = I->getOpcode(); 599 switch (Opc) { 600 case Instruction::And: 601 case Instruction::Or: 602 case Instruction::Xor: 603 case Instruction::Add: 604 case Instruction::Sub: 605 case Instruction::Mul: 606 case Instruction::Shl: 607 return CanEvaluateZExtd(I->getOperand(0), Ty, TD) && 608 CanEvaluateZExtd(I->getOperand(1), Ty, TD); 609 610 //case Instruction::LShr: 611 case Instruction::ZExt: // zext(zext(x)) -> zext(x). 612 case Instruction::SExt: // zext(sext(x)) -> sext(x). 613 return true; 614 615 case Instruction::Select: 616 return CanEvaluateZExtd(I->getOperand(1), Ty, TD) && 617 CanEvaluateZExtd(I->getOperand(2), Ty, TD); 618 619 case Instruction::PHI: { 620 // We can change a phi if we can change all operands. Note that we never 621 // get into trouble with cyclic PHIs here because we only consider 622 // instructions with a single use. 623 PHINode *PN = cast<PHINode>(I); 624 if (!CanEvaluateZExtd(PN->getIncomingValue(0), Ty, TD)) return false; 625 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) 626 if (!CanEvaluateZExtd(PN->getIncomingValue(0), Ty, TD)) return false; 627 return true; 628 } 629 default: 630 // TODO: Can handle more cases here. 631 return false; 632 } 633} 634 635Instruction *InstCombiner::visitZExt(ZExtInst &CI) { 636 // If this zero extend is only used by a truncate, let the truncate by 637 // eliminated before we try to optimize this zext. 638 if (CI.hasOneUse() && isa<TruncInst>(CI.use_back())) 639 return 0; 640 641 // If one of the common conversion will work, do it. 642 if (Instruction *Result = commonCastTransforms(CI)) 643 return Result; 644 645 // See if we can simplify any instructions used by the input whose sole 646 // purpose is to compute bits we don't care about. 647 if (SimplifyDemandedInstructionBits(CI)) 648 return &CI; 649 650 Value *Src = CI.getOperand(0); 651 const Type *SrcTy = Src->getType(), *DestTy = CI.getType(); 652 653 // Attempt to extend the entire input expression tree to the destination 654 // type. Only do this if the dest type is a simple type, don't convert the 655 // expression tree to something weird like i93 unless the source is also 656 // strange. 657 if ((isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) && 658 CanEvaluateZExtd(Src, DestTy, TD)) { 659 // Okay, we can transform this! Insert the new expression now. 660 DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" 661 " to avoid zero extend: " << CI); 662 Value *Res = EvaluateInDifferentType(Src, DestTy, false); 663 assert(Res->getType() == DestTy); 664 665 // If the high bits are already filled with zeros, just replace this 666 // cast with the result. 667 uint32_t SrcBitSize = SrcTy->getScalarSizeInBits(); 668 uint32_t DestBitSize = DestTy->getScalarSizeInBits(); 669 if (MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize, 670 DestBitSize-SrcBitSize))) 671 return ReplaceInstUsesWith(CI, Res); 672 673 // We need to emit an AND to clear the high bits. 674 Constant *C = ConstantInt::get(CI.getContext(), 675 APInt::getLowBitsSet(DestBitSize, SrcBitSize)); 676 return BinaryOperator::CreateAnd(Res, C); 677 } 678 679 // If this is a TRUNC followed by a ZEXT then we are dealing with integral 680 // types and if the sizes are just right we can convert this into a logical 681 // 'and' which will be much cheaper than the pair of casts. 682 if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) { // A->B->C cast 683 // Get the sizes of the types involved. We know that the intermediate type 684 // will be smaller than A or C, but don't know the relation between A and C. 685 Value *A = CSrc->getOperand(0); 686 unsigned SrcSize = A->getType()->getScalarSizeInBits(); 687 unsigned MidSize = CSrc->getType()->getScalarSizeInBits(); 688 unsigned DstSize = CI.getType()->getScalarSizeInBits(); 689 // If we're actually extending zero bits, then if 690 // SrcSize < DstSize: zext(a & mask) 691 // SrcSize == DstSize: a & mask 692 // SrcSize > DstSize: trunc(a) & mask 693 if (SrcSize < DstSize) { 694 APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize)); 695 Constant *AndConst = ConstantInt::get(A->getType(), AndValue); 696 Value *And = Builder->CreateAnd(A, AndConst, CSrc->getName()+".mask"); 697 return new ZExtInst(And, CI.getType()); 698 } 699 700 if (SrcSize == DstSize) { 701 APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize)); 702 return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(), 703 AndValue)); 704 } 705 if (SrcSize > DstSize) { 706 Value *Trunc = Builder->CreateTrunc(A, CI.getType(), "tmp"); 707 APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize)); 708 return BinaryOperator::CreateAnd(Trunc, 709 ConstantInt::get(Trunc->getType(), 710 AndValue)); 711 } 712 } 713 714 if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src)) 715 return transformZExtICmp(ICI, CI); 716 717 BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src); 718 if (SrcI && SrcI->getOpcode() == Instruction::Or) { 719 // zext (or icmp, icmp) --> or (zext icmp), (zext icmp) if at least one 720 // of the (zext icmp) will be transformed. 721 ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0)); 722 ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1)); 723 if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() && 724 (transformZExtICmp(LHS, CI, false) || 725 transformZExtICmp(RHS, CI, false))) { 726 Value *LCast = Builder->CreateZExt(LHS, CI.getType(), LHS->getName()); 727 Value *RCast = Builder->CreateZExt(RHS, CI.getType(), RHS->getName()); 728 return BinaryOperator::Create(Instruction::Or, LCast, RCast); 729 } 730 } 731 732 // zext(trunc(t) & C) -> (t & zext(C)). 733 if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse()) 734 if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1))) 735 if (TruncInst *TI = dyn_cast<TruncInst>(SrcI->getOperand(0))) { 736 Value *TI0 = TI->getOperand(0); 737 if (TI0->getType() == CI.getType()) 738 return 739 BinaryOperator::CreateAnd(TI0, 740 ConstantExpr::getZExt(C, CI.getType())); 741 } 742 743 // zext((trunc(t) & C) ^ C) -> ((t & zext(C)) ^ zext(C)). 744 if (SrcI && SrcI->getOpcode() == Instruction::Xor && SrcI->hasOneUse()) 745 if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1))) 746 if (BinaryOperator *And = dyn_cast<BinaryOperator>(SrcI->getOperand(0))) 747 if (And->getOpcode() == Instruction::And && And->hasOneUse() && 748 And->getOperand(1) == C) 749 if (TruncInst *TI = dyn_cast<TruncInst>(And->getOperand(0))) { 750 Value *TI0 = TI->getOperand(0); 751 if (TI0->getType() == CI.getType()) { 752 Constant *ZC = ConstantExpr::getZExt(C, CI.getType()); 753 Value *NewAnd = Builder->CreateAnd(TI0, ZC, "tmp"); 754 return BinaryOperator::CreateXor(NewAnd, ZC); 755 } 756 } 757 758 // zext (xor i1 X, true) to i32 --> xor (zext i1 X to i32), 1 759 Value *X; 760 if (SrcI && SrcI->hasOneUse() && SrcI->getType()->isInteger(1) && 761 match(SrcI, m_Not(m_Value(X))) && 762 (!X->hasOneUse() || !isa<CmpInst>(X))) { 763 Value *New = Builder->CreateZExt(X, CI.getType()); 764 return BinaryOperator::CreateXor(New, ConstantInt::get(CI.getType(), 1)); 765 } 766 767 return 0; 768} 769 770/// CanEvaluateSExtd - Return true if we can take the specified value 771/// and return it as type Ty without inserting any new casts and without 772/// changing the value of the common low bits. This is used by code that tries 773/// to promote integer operations to a wider types will allow us to eliminate 774/// the extension. 775/// 776/// This returns 0 if we can't do this or the number of sign bits that would be 777/// set if we can. For example, CanEvaluateSExtd(i16 1, i64) would return 63, 778/// because the computation can be extended (to "i64 1") and the resulting 779/// computation has 63 equal sign bits. 780/// 781/// This function works on both vectors and scalars. For vectors, the result is 782/// the number of bits known sign extended in each element. 783/// 784static unsigned CanEvaluateSExtd(Value *V, const Type *Ty, 785 unsigned &NumCastsRemoved, TargetData *TD) { 786 assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() && 787 "Can't sign extend type to a smaller type"); 788 // If this is a constant, return the number of sign bits the extended version 789 // of it would have. 790 if (Constant *C = dyn_cast<Constant>(V)) 791 return ComputeNumSignBits(ConstantExpr::getSExt(C, Ty), TD); 792 793 Instruction *I = dyn_cast<Instruction>(V); 794 if (!I) return 0; 795 796 // If this is a truncate from the destination type, we can trivially eliminate 797 // it, and this will remove a cast overall. 798 if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty) { 799 // If the operand of the truncate is itself a cast, and is eliminable, do 800 // not count this as an eliminable cast. We would prefer to eliminate those 801 // two casts first. 802 if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse()) 803 ++NumCastsRemoved; 804 return ComputeNumSignBits(I->getOperand(0), TD); 805 } 806 807 // We can't extend or shrink something that has multiple uses: doing so would 808 // require duplicating the instruction in general, which isn't profitable. 809 if (!I->hasOneUse()) return 0; 810 811 const Type *OrigTy = V->getType(); 812 813 unsigned Opc = I->getOpcode(); 814 unsigned Tmp1, Tmp2; 815 switch (Opc) { 816 case Instruction::And: 817 case Instruction::Or: 818 case Instruction::Xor: 819 // These operators can all arbitrarily be extended or truncated. 820 Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 821 if (Tmp1 == 0) return 0; 822 Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 823 return std::min(Tmp1, Tmp2); 824 case Instruction::Add: 825 case Instruction::Sub: 826 // Add/Sub can have at most one carry/borrow bit. 827 Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 828 if (Tmp1 == 0) return 0; 829 Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 830 if (Tmp2 == 0) return 0; 831 return std::min(Tmp1, Tmp2)-1; 832 case Instruction::Mul: 833 // These operators can all arbitrarily be extended or truncated. 834 if (!CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD)) 835 return 0; 836 if (!CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD)) 837 return 0; 838 return 1; // IMPROVE? 839 840 //case Instruction::Shl: TODO 841 //case Instruction::LShr: TODO 842 //case Instruction::Trunc: TODO 843 844 case Instruction::SExt: 845 case Instruction::ZExt: { 846 // sext(sext(x)) -> sext(x) 847 // sext(zext(x)) -> zext(x) 848 // Note that replacing a cast does not reduce the number of casts in the 849 // input. 850 unsigned InSignBits = ComputeNumSignBits(I, TD); 851 unsigned ExtBits = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits(); 852 // We'll end up extending it all the way out. 853 return InSignBits+ExtBits; 854 } 855 case Instruction::Select: { 856 SelectInst *SI = cast<SelectInst>(I); 857 Tmp1 = CanEvaluateSExtd(SI->getTrueValue(), Ty, NumCastsRemoved, TD); 858 if (Tmp1 == 0) return 0; 859 Tmp2 = CanEvaluateSExtd(SI->getFalseValue(), Ty, NumCastsRemoved,TD); 860 return std::min(Tmp1, Tmp2); 861 } 862 case Instruction::PHI: { 863 // We can change a phi if we can change all operands. Note that we never 864 // get into trouble with cyclic PHIs here because we only consider 865 // instructions with a single use. 866 PHINode *PN = cast<PHINode>(I); 867 unsigned Result = ~0U; 868 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 869 Result = std::min(Result, 870 CanEvaluateSExtd(PN->getIncomingValue(i), Ty, 871 NumCastsRemoved, TD)); 872 if (Result == 0) return 0; 873 } 874 return Result; 875 } 876 default: 877 // TODO: Can handle more cases here. 878 break; 879 } 880 881 return 0; 882} 883 884Instruction *InstCombiner::visitSExt(SExtInst &CI) { 885 // If this sign extend is only used by a truncate, let the truncate by 886 // eliminated before we try to optimize this zext. 887 if (CI.hasOneUse() && isa<TruncInst>(CI.use_back())) 888 return 0; 889 890 if (Instruction *I = commonCastTransforms(CI)) 891 return I; 892 893 // See if we can simplify any instructions used by the input whose sole 894 // purpose is to compute bits we don't care about. 895 if (SimplifyDemandedInstructionBits(CI)) 896 return &CI; 897 898 Value *Src = CI.getOperand(0); 899 const Type *SrcTy = Src->getType(), *DestTy = CI.getType(); 900 901 // Canonicalize sign-extend from i1 to a select. 902 if (Src->getType()->isInteger(1)) 903 return SelectInst::Create(Src, 904 Constant::getAllOnesValue(CI.getType()), 905 Constant::getNullValue(CI.getType())); 906 907 // Attempt to extend the entire input expression tree to the destination 908 // type. Only do this if the dest type is a simple type, don't convert the 909 // expression tree to something weird like i93 unless the source is also 910 // strange. 911 if (isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) { 912 unsigned NumCastsRemoved = 0; 913 // Check to see if we can do this transformation, and if so, how many bits 914 // of the promoted expression will be known copies of the sign bit in the 915 // result. 916 unsigned NumBitsSExt = CanEvaluateSExtd(Src, DestTy, NumCastsRemoved, TD); 917 if (NumBitsSExt == 0) 918 return 0; 919 920 uint32_t SrcBitSize = SrcTy->getScalarSizeInBits(); 921 uint32_t DestBitSize = DestTy->getScalarSizeInBits(); 922 923 // Because this is a sign extension, we can always transform it by inserting 924 // two new shifts (to do the extension). However, this is only profitable 925 // if we've eliminated two or more casts from the input. If we know the 926 // result will be sign-extended enough to not require these shifts, we can 927 // always do the transformation. 928 if (NumCastsRemoved >= 2 || 929 NumBitsSExt > DestBitSize-SrcBitSize) { 930 // Okay, we can transform this! Insert the new expression now. 931 DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" 932 " to avoid sign extend: " << CI); 933 Value *Res = EvaluateInDifferentType(Src, DestTy, true); 934 assert(Res->getType() == DestTy); 935 936 // If the high bits are already filled with sign bit, just replace this 937 // cast with the result. 938 if (NumBitsSExt > DestBitSize - SrcBitSize || 939 ComputeNumSignBits(Res) > DestBitSize - SrcBitSize) 940 return ReplaceInstUsesWith(CI, Res); 941 942 // We need to emit a cast to truncate, then a cast to sext. 943 return new SExtInst(Builder->CreateTrunc(Res, Src->getType()), DestTy); 944 } 945 } 946 947 // If the input is a shl/ashr pair of a same constant, then this is a sign 948 // extension from a smaller value. If we could trust arbitrary bitwidth 949 // integers, we could turn this into a truncate to the smaller bit and then 950 // use a sext for the whole extension. Since we don't, look deeper and check 951 // for a truncate. If the source and dest are the same type, eliminate the 952 // trunc and extend and just do shifts. For example, turn: 953 // %a = trunc i32 %i to i8 954 // %b = shl i8 %a, 6 955 // %c = ashr i8 %b, 6 956 // %d = sext i8 %c to i32 957 // into: 958 // %a = shl i32 %i, 30 959 // %d = ashr i32 %a, 30 960 Value *A = 0; 961 // TODO: Eventually this could be subsumed by EvaluateInDifferentType. 962 ConstantInt *BA = 0, *CA = 0; 963 if (match(Src, m_AShr(m_Shl(m_Trunc(m_Value(A)), m_ConstantInt(BA)), 964 m_ConstantInt(CA))) && 965 BA == CA && A->getType() == CI.getType()) { 966 unsigned MidSize = Src->getType()->getScalarSizeInBits(); 967 unsigned SrcDstSize = CI.getType()->getScalarSizeInBits(); 968 unsigned ShAmt = CA->getZExtValue()+SrcDstSize-MidSize; 969 Constant *ShAmtV = ConstantInt::get(CI.getType(), ShAmt); 970 A = Builder->CreateShl(A, ShAmtV, CI.getName()); 971 return BinaryOperator::CreateAShr(A, ShAmtV); 972 } 973 974 return 0; 975} 976 977 978/// FitsInFPType - Return a Constant* for the specified FP constant if it fits 979/// in the specified FP type without changing its value. 980static Constant *FitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) { 981 bool losesInfo; 982 APFloat F = CFP->getValueAPF(); 983 (void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo); 984 if (!losesInfo) 985 return ConstantFP::get(CFP->getContext(), F); 986 return 0; 987} 988 989/// LookThroughFPExtensions - If this is an fp extension instruction, look 990/// through it until we get the source value. 991static Value *LookThroughFPExtensions(Value *V) { 992 if (Instruction *I = dyn_cast<Instruction>(V)) 993 if (I->getOpcode() == Instruction::FPExt) 994 return LookThroughFPExtensions(I->getOperand(0)); 995 996 // If this value is a constant, return the constant in the smallest FP type 997 // that can accurately represent it. This allows us to turn 998 // (float)((double)X+2.0) into x+2.0f. 999 if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) { 1000 if (CFP->getType() == Type::getPPC_FP128Ty(V->getContext())) 1001 return V; // No constant folding of this. 1002 // See if the value can be truncated to float and then reextended. 1003 if (Value *V = FitsInFPType(CFP, APFloat::IEEEsingle)) 1004 return V; 1005 if (CFP->getType()->isDoubleTy()) 1006 return V; // Won't shrink. 1007 if (Value *V = FitsInFPType(CFP, APFloat::IEEEdouble)) 1008 return V; 1009 // Don't try to shrink to various long double types. 1010 } 1011 1012 return V; 1013} 1014 1015Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) { 1016 if (Instruction *I = commonCastTransforms(CI)) 1017 return I; 1018 1019 // If we have fptrunc(fadd (fpextend x), (fpextend y)), where x and y are 1020 // smaller than the destination type, we can eliminate the truncate by doing 1021 // the add as the smaller type. This applies to fadd/fsub/fmul/fdiv as well 1022 // as many builtins (sqrt, etc). 1023 BinaryOperator *OpI = dyn_cast<BinaryOperator>(CI.getOperand(0)); 1024 if (OpI && OpI->hasOneUse()) { 1025 switch (OpI->getOpcode()) { 1026 default: break; 1027 case Instruction::FAdd: 1028 case Instruction::FSub: 1029 case Instruction::FMul: 1030 case Instruction::FDiv: 1031 case Instruction::FRem: 1032 const Type *SrcTy = OpI->getType(); 1033 Value *LHSTrunc = LookThroughFPExtensions(OpI->getOperand(0)); 1034 Value *RHSTrunc = LookThroughFPExtensions(OpI->getOperand(1)); 1035 if (LHSTrunc->getType() != SrcTy && 1036 RHSTrunc->getType() != SrcTy) { 1037 unsigned DstSize = CI.getType()->getScalarSizeInBits(); 1038 // If the source types were both smaller than the destination type of 1039 // the cast, do this xform. 1040 if (LHSTrunc->getType()->getScalarSizeInBits() <= DstSize && 1041 RHSTrunc->getType()->getScalarSizeInBits() <= DstSize) { 1042 LHSTrunc = Builder->CreateFPExt(LHSTrunc, CI.getType()); 1043 RHSTrunc = Builder->CreateFPExt(RHSTrunc, CI.getType()); 1044 return BinaryOperator::Create(OpI->getOpcode(), LHSTrunc, RHSTrunc); 1045 } 1046 } 1047 break; 1048 } 1049 } 1050 return 0; 1051} 1052 1053Instruction *InstCombiner::visitFPExt(CastInst &CI) { 1054 return commonCastTransforms(CI); 1055} 1056 1057Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) { 1058 Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0)); 1059 if (OpI == 0) 1060 return commonCastTransforms(FI); 1061 1062 // fptoui(uitofp(X)) --> X 1063 // fptoui(sitofp(X)) --> X 1064 // This is safe if the intermediate type has enough bits in its mantissa to 1065 // accurately represent all values of X. For example, do not do this with 1066 // i64->float->i64. This is also safe for sitofp case, because any negative 1067 // 'X' value would cause an undefined result for the fptoui. 1068 if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) && 1069 OpI->getOperand(0)->getType() == FI.getType() && 1070 (int)FI.getType()->getScalarSizeInBits() < /*extra bit for sign */ 1071 OpI->getType()->getFPMantissaWidth()) 1072 return ReplaceInstUsesWith(FI, OpI->getOperand(0)); 1073 1074 return commonCastTransforms(FI); 1075} 1076 1077Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) { 1078 Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0)); 1079 if (OpI == 0) 1080 return commonCastTransforms(FI); 1081 1082 // fptosi(sitofp(X)) --> X 1083 // fptosi(uitofp(X)) --> X 1084 // This is safe if the intermediate type has enough bits in its mantissa to 1085 // accurately represent all values of X. For example, do not do this with 1086 // i64->float->i64. This is also safe for sitofp case, because any negative 1087 // 'X' value would cause an undefined result for the fptoui. 1088 if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) && 1089 OpI->getOperand(0)->getType() == FI.getType() && 1090 (int)FI.getType()->getScalarSizeInBits() <= 1091 OpI->getType()->getFPMantissaWidth()) 1092 return ReplaceInstUsesWith(FI, OpI->getOperand(0)); 1093 1094 return commonCastTransforms(FI); 1095} 1096 1097Instruction *InstCombiner::visitUIToFP(CastInst &CI) { 1098 return commonCastTransforms(CI); 1099} 1100 1101Instruction *InstCombiner::visitSIToFP(CastInst &CI) { 1102 return commonCastTransforms(CI); 1103} 1104 1105Instruction *InstCombiner::visitIntToPtr(IntToPtrInst &CI) { 1106 // If the source integer type is larger than the intptr_t type for 1107 // this target, do a trunc to the intptr_t type, then inttoptr of it. This 1108 // allows the trunc to be exposed to other transforms. Don't do this for 1109 // extending inttoptr's, because we don't know if the target sign or zero 1110 // extends to pointers. 1111 if (TD && CI.getOperand(0)->getType()->getScalarSizeInBits() > 1112 TD->getPointerSizeInBits()) { 1113 Value *P = Builder->CreateTrunc(CI.getOperand(0), 1114 TD->getIntPtrType(CI.getContext()), "tmp"); 1115 return new IntToPtrInst(P, CI.getType()); 1116 } 1117 1118 if (Instruction *I = commonCastTransforms(CI)) 1119 return I; 1120 1121 return 0; 1122} 1123 1124/// @brief Implement the transforms for cast of pointer (bitcast/ptrtoint) 1125Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) { 1126 Value *Src = CI.getOperand(0); 1127 1128 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) { 1129 // If casting the result of a getelementptr instruction with no offset, turn 1130 // this into a cast of the original pointer! 1131 if (GEP->hasAllZeroIndices()) { 1132 // Changing the cast operand is usually not a good idea but it is safe 1133 // here because the pointer operand is being replaced with another 1134 // pointer operand so the opcode doesn't need to change. 1135 Worklist.Add(GEP); 1136 CI.setOperand(0, GEP->getOperand(0)); 1137 return &CI; 1138 } 1139 1140 // If the GEP has a single use, and the base pointer is a bitcast, and the 1141 // GEP computes a constant offset, see if we can convert these three 1142 // instructions into fewer. This typically happens with unions and other 1143 // non-type-safe code. 1144 if (TD && GEP->hasOneUse() && isa<BitCastInst>(GEP->getOperand(0)) && 1145 GEP->hasAllConstantIndices()) { 1146 // We are guaranteed to get a constant from EmitGEPOffset. 1147 ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(GEP)); 1148 int64_t Offset = OffsetV->getSExtValue(); 1149 1150 // Get the base pointer input of the bitcast, and the type it points to. 1151 Value *OrigBase = cast<BitCastInst>(GEP->getOperand(0))->getOperand(0); 1152 const Type *GEPIdxTy = 1153 cast<PointerType>(OrigBase->getType())->getElementType(); 1154 SmallVector<Value*, 8> NewIndices; 1155 if (FindElementAtOffset(GEPIdxTy, Offset, NewIndices)) { 1156 // If we were able to index down into an element, create the GEP 1157 // and bitcast the result. This eliminates one bitcast, potentially 1158 // two. 1159 Value *NGEP = cast<GEPOperator>(GEP)->isInBounds() ? 1160 Builder->CreateInBoundsGEP(OrigBase, 1161 NewIndices.begin(), NewIndices.end()) : 1162 Builder->CreateGEP(OrigBase, NewIndices.begin(), NewIndices.end()); 1163 NGEP->takeName(GEP); 1164 1165 if (isa<BitCastInst>(CI)) 1166 return new BitCastInst(NGEP, CI.getType()); 1167 assert(isa<PtrToIntInst>(CI)); 1168 return new PtrToIntInst(NGEP, CI.getType()); 1169 } 1170 } 1171 } 1172 1173 return commonCastTransforms(CI); 1174} 1175 1176Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) { 1177 // If the destination integer type is smaller than the intptr_t type for 1178 // this target, do a ptrtoint to intptr_t then do a trunc. This allows the 1179 // trunc to be exposed to other transforms. Don't do this for extending 1180 // ptrtoint's, because we don't know if the target sign or zero extends its 1181 // pointers. 1182 if (TD && 1183 CI.getType()->getScalarSizeInBits() < TD->getPointerSizeInBits()) { 1184 Value *P = Builder->CreatePtrToInt(CI.getOperand(0), 1185 TD->getIntPtrType(CI.getContext()), 1186 "tmp"); 1187 return new TruncInst(P, CI.getType()); 1188 } 1189 1190 return commonPointerCastTransforms(CI); 1191} 1192 1193Instruction *InstCombiner::visitBitCast(BitCastInst &CI) { 1194 // If the operands are integer typed then apply the integer transforms, 1195 // otherwise just apply the common ones. 1196 Value *Src = CI.getOperand(0); 1197 const Type *SrcTy = Src->getType(); 1198 const Type *DestTy = CI.getType(); 1199 1200 // Get rid of casts from one type to the same type. These are useless and can 1201 // be replaced by the operand. 1202 if (DestTy == Src->getType()) 1203 return ReplaceInstUsesWith(CI, Src); 1204 1205 if (const PointerType *DstPTy = dyn_cast<PointerType>(DestTy)) { 1206 const PointerType *SrcPTy = cast<PointerType>(SrcTy); 1207 const Type *DstElTy = DstPTy->getElementType(); 1208 const Type *SrcElTy = SrcPTy->getElementType(); 1209 1210 // If the address spaces don't match, don't eliminate the bitcast, which is 1211 // required for changing types. 1212 if (SrcPTy->getAddressSpace() != DstPTy->getAddressSpace()) 1213 return 0; 1214 1215 // If we are casting a alloca to a pointer to a type of the same 1216 // size, rewrite the allocation instruction to allocate the "right" type. 1217 // There is no need to modify malloc calls because it is their bitcast that 1218 // needs to be cleaned up. 1219 if (AllocaInst *AI = dyn_cast<AllocaInst>(Src)) 1220 if (Instruction *V = PromoteCastOfAllocation(CI, *AI)) 1221 return V; 1222 1223 // If the source and destination are pointers, and this cast is equivalent 1224 // to a getelementptr X, 0, 0, 0... turn it into the appropriate gep. 1225 // This can enhance SROA and other transforms that want type-safe pointers. 1226 Constant *ZeroUInt = 1227 Constant::getNullValue(Type::getInt32Ty(CI.getContext())); 1228 unsigned NumZeros = 0; 1229 while (SrcElTy != DstElTy && 1230 isa<CompositeType>(SrcElTy) && !isa<PointerType>(SrcElTy) && 1231 SrcElTy->getNumContainedTypes() /* not "{}" */) { 1232 SrcElTy = cast<CompositeType>(SrcElTy)->getTypeAtIndex(ZeroUInt); 1233 ++NumZeros; 1234 } 1235 1236 // If we found a path from the src to dest, create the getelementptr now. 1237 if (SrcElTy == DstElTy) { 1238 SmallVector<Value*, 8> Idxs(NumZeros+1, ZeroUInt); 1239 return GetElementPtrInst::CreateInBounds(Src, Idxs.begin(), Idxs.end(),"", 1240 ((Instruction*)NULL)); 1241 } 1242 } 1243 1244 if (const VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) { 1245 if (DestVTy->getNumElements() == 1 && !isa<VectorType>(SrcTy)) { 1246 Value *Elem = Builder->CreateBitCast(Src, DestVTy->getElementType()); 1247 return InsertElementInst::Create(UndefValue::get(DestTy), Elem, 1248 Constant::getNullValue(Type::getInt32Ty(CI.getContext()))); 1249 // FIXME: Canonicalize bitcast(insertelement) -> insertelement(bitcast) 1250 } 1251 } 1252 1253 if (const VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) { 1254 if (SrcVTy->getNumElements() == 1 && !isa<VectorType>(DestTy)) { 1255 Value *Elem = 1256 Builder->CreateExtractElement(Src, 1257 Constant::getNullValue(Type::getInt32Ty(CI.getContext()))); 1258 return CastInst::Create(Instruction::BitCast, Elem, DestTy); 1259 } 1260 } 1261 1262 if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(Src)) { 1263 // Okay, we have (bitcast (shuffle ..)). Check to see if this is 1264 // a bitconvert to a vector with the same # elts. 1265 if (SVI->hasOneUse() && isa<VectorType>(DestTy) && 1266 cast<VectorType>(DestTy)->getNumElements() == 1267 SVI->getType()->getNumElements() && 1268 SVI->getType()->getNumElements() == 1269 cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements()) { 1270 BitCastInst *Tmp; 1271 // If either of the operands is a cast from CI.getType(), then 1272 // evaluating the shuffle in the casted destination's type will allow 1273 // us to eliminate at least one cast. 1274 if (((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(0))) && 1275 Tmp->getOperand(0)->getType() == DestTy) || 1276 ((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(1))) && 1277 Tmp->getOperand(0)->getType() == DestTy)) { 1278 Value *LHS = Builder->CreateBitCast(SVI->getOperand(0), DestTy); 1279 Value *RHS = Builder->CreateBitCast(SVI->getOperand(1), DestTy); 1280 // Return a new shuffle vector. Use the same element ID's, as we 1281 // know the vector types match #elts. 1282 return new ShuffleVectorInst(LHS, RHS, SVI->getOperand(2)); 1283 } 1284 } 1285 } 1286 1287 if (isa<PointerType>(SrcTy)) 1288 return commonPointerCastTransforms(CI); 1289 return commonCastTransforms(CI); 1290} 1291