InstCombineCasts.cpp revision d26c9e183e56d09f48d7074be4cacce099338316
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/// GetLeadingZeros - Compute the number of known-zero leading bits. 579static unsigned GetLeadingZeros(Value *V, const TargetData *TD) { 580 unsigned Bits = V->getType()->getScalarSizeInBits(); 581 APInt KnownZero(Bits, 0), KnownOne(Bits, 0); 582 ComputeMaskedBits(V, APInt::getAllOnesValue(Bits), KnownZero, KnownOne, TD); 583 return KnownZero.countLeadingOnes(); 584} 585 586/// CanEvaluateZExtd - Determine if the specified value can be computed in the 587/// specified wider type and produce the same low bits. If not, return -1. If 588/// it is possible, return the number of high bits that are known to be zero in 589/// the promoted value. 590static int CanEvaluateZExtd(Value *V, const Type *Ty,unsigned &NumCastsRemoved, 591 const TargetData *TD) { 592 const Type *OrigTy = V->getType(); 593 594 if (isa<Constant>(V)) { 595 unsigned Extended = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits(); 596 597 // Constants can always be zero ext'd, even if it requires a ConstantExpr. 598 if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) 599 return Extended + CI->getValue().countLeadingZeros(); 600 return Extended; 601 } 602 603 Instruction *I = dyn_cast<Instruction>(V); 604 if (!I) return -1; 605 606 // If the input is a truncate from the destination type, we can trivially 607 // eliminate it, and this will remove a cast overall. 608 if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty) { 609 // If the first operand is itself a cast, and is eliminable, do not count 610 // this as an eliminable cast. We would prefer to eliminate those two 611 // casts first. 612 if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse()) 613 ++NumCastsRemoved; 614 615 // Figure out the number of known-zero bits coming in. 616 return GetLeadingZeros(I->getOperand(0), TD); 617 } 618 619 // We can't extend or shrink something that has multiple uses: doing so would 620 // require duplicating the instruction in general, which isn't profitable. 621 if (!I->hasOneUse()) return -1; 622 623 int Tmp1, Tmp2; 624 unsigned Opc = I->getOpcode(); 625 switch (Opc) { 626 case Instruction::And: 627 Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 628 if (Tmp1 == -1) return -1; 629 Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 630 if (Tmp2 == -1) return -1; 631 return std::max(Tmp1, Tmp2); 632 case Instruction::Or: 633 case Instruction::Xor: 634 Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 635 if (Tmp1 == -1) return -1; 636 Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 637 return std::min(Tmp1, Tmp2); 638 639 case Instruction::Add: 640 case Instruction::Sub: 641 case Instruction::Mul: 642 Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 643 if (Tmp1 == -1) return -1; 644 Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 645 if (Tmp2 == -1) return -1; 646 return 0; // TODO: Could be improved. 647 648 case Instruction::Shl: 649 Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 650 if (Tmp1 == -1) return -1; 651 652 if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) 653 return Tmp1 - CI->getZExtValue(); 654 655 // Variable shift, no known zext bits. 656 Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 657 if (Tmp2 == -1) return -1; 658 return 0; 659 660 //case Instruction::LShr: 661 case Instruction::ZExt: 662 // zext(zext(x)) -> zext(x). Since we're replacing it, it isn't eliminated. 663 Tmp1 = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits(); 664 return GetLeadingZeros(I, TD)+Tmp1; 665 666 case Instruction::SExt: 667 // zext(sext(x)) -> sext(x) with no upper bits known. 668 return 0; 669 //case Instruction::Trunc: -> Could turn into AND. 670 671 case Instruction::Select: 672 Tmp1 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 673 if (Tmp1 == -1) return -1; 674 Tmp2 = CanEvaluateZExtd(I->getOperand(2), Ty, NumCastsRemoved, TD); 675 return std::min(Tmp1, Tmp2); 676 677 case Instruction::PHI: { 678 // We can change a phi if we can change all operands. Note that we never 679 // get into trouble with cyclic PHIs here because we only consider 680 // instructions with a single use. 681 PHINode *PN = cast<PHINode>(I); 682 int Result = CanEvaluateZExtd(PN->getIncomingValue(0), Ty, 683 NumCastsRemoved, TD); 684 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) { 685 if (Result == -1) return -1; 686 Tmp1 = CanEvaluateZExtd(PN->getIncomingValue(i), Ty, NumCastsRemoved, TD); 687 Result = std::min(Result, Tmp1); 688 } 689 return Result; 690 } 691 default: 692 // TODO: Can handle more cases here. 693 return -1; 694 } 695} 696 697Instruction *InstCombiner::visitZExt(ZExtInst &CI) { 698 // If one of the common conversion will work, do it. 699 if (Instruction *Result = commonCastTransforms(CI)) 700 return Result; 701 702 // See if we can simplify any instructions used by the input whose sole 703 // purpose is to compute bits we don't care about. 704 if (SimplifyDemandedInstructionBits(CI)) 705 return &CI; 706 707 Value *Src = CI.getOperand(0); 708 const Type *SrcTy = Src->getType(), *DestTy = CI.getType(); 709 710 // Attempt to extend the entire input expression tree to the destination 711 // type. Only do this if the dest type is a simple type, don't convert the 712 // expression tree to something weird like i93 unless the source is also 713 // strange. 714 if (isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) { 715 unsigned NumCastsRemoved = 0; 716 int BitsZExt = CanEvaluateZExtd(Src, DestTy, NumCastsRemoved, TD); 717 if (BitsZExt == -1) return 0; 718 719 uint32_t SrcBitSize = SrcTy->getScalarSizeInBits(); 720 uint32_t DestBitSize = DestTy->getScalarSizeInBits(); 721 722 // If this is a zero-extension, we need to do an AND to maintain the clear 723 // top-part of the computation. If we know the result will be zero 724 // extended enough already, we don't need the and. 725 if (NumCastsRemoved >= 1 || 726 unsigned(BitsZExt) >= DestBitSize-SrcBitSize) { 727 728 // Okay, we can transform this! Insert the new expression now. 729 DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" 730 " to avoid zero extend: " << CI); 731 Value *Res = EvaluateInDifferentType(Src, DestTy, false); 732 assert(Res->getType() == DestTy); 733 734 // If the high bits are already filled with zeros, just replace this 735 // cast with the result. 736 if (unsigned(BitsZExt) >= DestBitSize-SrcBitSize || 737 MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize, 738 DestBitSize-SrcBitSize))) 739 return ReplaceInstUsesWith(CI, Res); 740 741 // We need to emit an AND to clear the high bits. 742 Constant *C = ConstantInt::get(CI.getContext(), 743 APInt::getLowBitsSet(DestBitSize, SrcBitSize)); 744 return BinaryOperator::CreateAnd(Res, C); 745 } 746 } 747 748 // If this is a TRUNC followed by a ZEXT then we are dealing with integral 749 // types and if the sizes are just right we can convert this into a logical 750 // 'and' which will be much cheaper than the pair of casts. 751 if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) { // A->B->C cast 752 // Get the sizes of the types involved. We know that the intermediate type 753 // will be smaller than A or C, but don't know the relation between A and C. 754 Value *A = CSrc->getOperand(0); 755 unsigned SrcSize = A->getType()->getScalarSizeInBits(); 756 unsigned MidSize = CSrc->getType()->getScalarSizeInBits(); 757 unsigned DstSize = CI.getType()->getScalarSizeInBits(); 758 // If we're actually extending zero bits, then if 759 // SrcSize < DstSize: zext(a & mask) 760 // SrcSize == DstSize: a & mask 761 // SrcSize > DstSize: trunc(a) & mask 762 if (SrcSize < DstSize) { 763 APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize)); 764 Constant *AndConst = ConstantInt::get(A->getType(), AndValue); 765 Value *And = Builder->CreateAnd(A, AndConst, CSrc->getName()+".mask"); 766 return new ZExtInst(And, CI.getType()); 767 } 768 769 if (SrcSize == DstSize) { 770 APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize)); 771 return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(), 772 AndValue)); 773 } 774 if (SrcSize > DstSize) { 775 Value *Trunc = Builder->CreateTrunc(A, CI.getType(), "tmp"); 776 APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize)); 777 return BinaryOperator::CreateAnd(Trunc, 778 ConstantInt::get(Trunc->getType(), 779 AndValue)); 780 } 781 } 782 783 if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src)) 784 return transformZExtICmp(ICI, CI); 785 786 BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src); 787 if (SrcI && SrcI->getOpcode() == Instruction::Or) { 788 // zext (or icmp, icmp) --> or (zext icmp), (zext icmp) if at least one 789 // of the (zext icmp) will be transformed. 790 ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0)); 791 ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1)); 792 if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() && 793 (transformZExtICmp(LHS, CI, false) || 794 transformZExtICmp(RHS, CI, false))) { 795 Value *LCast = Builder->CreateZExt(LHS, CI.getType(), LHS->getName()); 796 Value *RCast = Builder->CreateZExt(RHS, CI.getType(), RHS->getName()); 797 return BinaryOperator::Create(Instruction::Or, LCast, RCast); 798 } 799 } 800 801 // zext(trunc(t) & C) -> (t & zext(C)). 802 if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse()) 803 if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1))) 804 if (TruncInst *TI = dyn_cast<TruncInst>(SrcI->getOperand(0))) { 805 Value *TI0 = TI->getOperand(0); 806 if (TI0->getType() == CI.getType()) 807 return 808 BinaryOperator::CreateAnd(TI0, 809 ConstantExpr::getZExt(C, CI.getType())); 810 } 811 812 // zext((trunc(t) & C) ^ C) -> ((t & zext(C)) ^ zext(C)). 813 if (SrcI && SrcI->getOpcode() == Instruction::Xor && SrcI->hasOneUse()) 814 if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1))) 815 if (BinaryOperator *And = dyn_cast<BinaryOperator>(SrcI->getOperand(0))) 816 if (And->getOpcode() == Instruction::And && And->hasOneUse() && 817 And->getOperand(1) == C) 818 if (TruncInst *TI = dyn_cast<TruncInst>(And->getOperand(0))) { 819 Value *TI0 = TI->getOperand(0); 820 if (TI0->getType() == CI.getType()) { 821 Constant *ZC = ConstantExpr::getZExt(C, CI.getType()); 822 Value *NewAnd = Builder->CreateAnd(TI0, ZC, "tmp"); 823 return BinaryOperator::CreateXor(NewAnd, ZC); 824 } 825 } 826 827 // zext (xor i1 X, true) to i32 --> xor (zext i1 X to i32), 1 828 Value *X; 829 if (SrcI && SrcI->hasOneUse() && SrcI->getType()->isInteger(1) && 830 match(SrcI, m_Not(m_Value(X))) && 831 (!X->hasOneUse() || !isa<CmpInst>(X))) { 832 Value *New = Builder->CreateZExt(X, CI.getType()); 833 return BinaryOperator::CreateXor(New, ConstantInt::get(CI.getType(), 1)); 834 } 835 836 return 0; 837} 838 839/// CanEvaluateSExtd - Return true if we can take the specified value 840/// and return it as type Ty without inserting any new casts and without 841/// changing the value of the common low bits. This is used by code that tries 842/// to promote integer operations to a wider types will allow us to eliminate 843/// the extension. 844/// 845/// This returns 0 if we can't do this or the number of sign bits that would be 846/// set if we can. For example, CanEvaluateSExtd(i16 1, i64) would return 63, 847/// because the computation can be extended (to "i64 1") and the resulting 848/// computation has 63 equal sign bits. 849/// 850/// This function works on both vectors and scalars. For vectors, the result is 851/// the number of bits known sign extended in each element. 852/// 853static unsigned CanEvaluateSExtd(Value *V, const Type *Ty, 854 unsigned &NumCastsRemoved, TargetData *TD) { 855 assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() && 856 "Can't sign extend type to a smaller type"); 857 // If this is a constant, return the number of sign bits the extended version 858 // of it would have. 859 if (Constant *C = dyn_cast<Constant>(V)) 860 return ComputeNumSignBits(ConstantExpr::getSExt(C, Ty), TD); 861 862 Instruction *I = dyn_cast<Instruction>(V); 863 if (!I) return 0; 864 865 // If this is a truncate from the destination type, we can trivially eliminate 866 // it, and this will remove a cast overall. 867 if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty) { 868 // If the operand of the truncate is itself a cast, and is eliminable, do 869 // not count this as an eliminable cast. We would prefer to eliminate those 870 // two casts first. 871 if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse()) 872 ++NumCastsRemoved; 873 return ComputeNumSignBits(I->getOperand(0), TD); 874 } 875 876 // We can't extend or shrink something that has multiple uses: doing so would 877 // require duplicating the instruction in general, which isn't profitable. 878 if (!I->hasOneUse()) return 0; 879 880 const Type *OrigTy = V->getType(); 881 882 unsigned Opc = I->getOpcode(); 883 unsigned Tmp1, Tmp2; 884 switch (Opc) { 885 case Instruction::And: 886 case Instruction::Or: 887 case Instruction::Xor: 888 // These operators can all arbitrarily be extended or truncated. 889 Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 890 if (Tmp1 == 0) return 0; 891 Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 892 return std::min(Tmp1, Tmp2); 893 case Instruction::Add: 894 case Instruction::Sub: 895 // Add/Sub can have at most one carry/borrow bit. 896 Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD); 897 if (Tmp1 == 0) return 0; 898 Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD); 899 if (Tmp2 == 0) return 0; 900 return std::min(Tmp1, Tmp2)-1; 901 case Instruction::Mul: 902 // These operators can all arbitrarily be extended or truncated. 903 if (!CanEvaluateSExtd(I->getOperand(0), Ty, NumCastsRemoved, TD)) 904 return 0; 905 if (!CanEvaluateSExtd(I->getOperand(1), Ty, NumCastsRemoved, TD)) 906 return 0; 907 return 1; // IMPROVE? 908 909 //case Instruction::Shl: TODO 910 //case Instruction::LShr: TODO 911 //case Instruction::Trunc: TODO 912 913 case Instruction::SExt: 914 case Instruction::ZExt: { 915 // sext(sext(x)) -> sext(x) 916 // sext(zext(x)) -> zext(x) 917 // Note that replacing a cast does not reduce the number of casts in the 918 // input. 919 unsigned InSignBits = ComputeNumSignBits(I, TD); 920 unsigned ExtBits = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits(); 921 // We'll end up extending it all the way out. 922 return InSignBits+ExtBits; 923 } 924 case Instruction::Select: { 925 SelectInst *SI = cast<SelectInst>(I); 926 Tmp1 = CanEvaluateSExtd(SI->getTrueValue(), Ty, NumCastsRemoved, TD); 927 if (Tmp1 == 0) return 0; 928 Tmp2 = CanEvaluateSExtd(SI->getFalseValue(), Ty, NumCastsRemoved,TD); 929 return std::min(Tmp1, Tmp2); 930 } 931 case Instruction::PHI: { 932 // We can change a phi if we can change all operands. Note that we never 933 // get into trouble with cyclic PHIs here because we only consider 934 // instructions with a single use. 935 PHINode *PN = cast<PHINode>(I); 936 unsigned Result = ~0U; 937 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 938 Result = std::min(Result, 939 CanEvaluateSExtd(PN->getIncomingValue(i), Ty, 940 NumCastsRemoved, TD)); 941 if (Result == 0) return 0; 942 } 943 return Result; 944 } 945 default: 946 // TODO: Can handle more cases here. 947 break; 948 } 949 950 return 0; 951} 952 953Instruction *InstCombiner::visitSExt(SExtInst &CI) { 954 if (Instruction *I = commonCastTransforms(CI)) 955 return I; 956 957 // See if we can simplify any instructions used by the input whose sole 958 // purpose is to compute bits we don't care about. 959 if (SimplifyDemandedInstructionBits(CI)) 960 return &CI; 961 962 Value *Src = CI.getOperand(0); 963 const Type *SrcTy = Src->getType(), *DestTy = CI.getType(); 964 965 // Canonicalize sign-extend from i1 to a select. 966 if (Src->getType()->isInteger(1)) 967 return SelectInst::Create(Src, 968 Constant::getAllOnesValue(CI.getType()), 969 Constant::getNullValue(CI.getType())); 970 971 // Attempt to extend the entire input expression tree to the destination 972 // type. Only do this if the dest type is a simple type, don't convert the 973 // expression tree to something weird like i93 unless the source is also 974 // strange. 975 if (isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) { 976 unsigned NumCastsRemoved = 0; 977 // Check to see if we can do this transformation, and if so, how many bits 978 // of the promoted expression will be known copies of the sign bit in the 979 // result. 980 unsigned NumBitsSExt = CanEvaluateSExtd(Src, DestTy, NumCastsRemoved, TD); 981 if (NumBitsSExt == 0) 982 return 0; 983 984 uint32_t SrcBitSize = SrcTy->getScalarSizeInBits(); 985 uint32_t DestBitSize = DestTy->getScalarSizeInBits(); 986 987 // Because this is a sign extension, we can always transform it by inserting 988 // two new shifts (to do the extension). However, this is only profitable 989 // if we've eliminated two or more casts from the input. If we know the 990 // result will be sign-extended enough to not require these shifts, we can 991 // always do the transformation. 992 if (NumCastsRemoved >= 2 || 993 NumBitsSExt > DestBitSize-SrcBitSize) { 994 // Okay, we can transform this! Insert the new expression now. 995 DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type" 996 " to avoid sign extend: " << CI); 997 Value *Res = EvaluateInDifferentType(Src, DestTy, true); 998 assert(Res->getType() == DestTy); 999 1000 // If the high bits are already filled with sign bit, just replace this 1001 // cast with the result. 1002 if (NumBitsSExt > DestBitSize - SrcBitSize || 1003 ComputeNumSignBits(Res) > DestBitSize - SrcBitSize) 1004 return ReplaceInstUsesWith(CI, Res); 1005 1006 // We need to emit a cast to truncate, then a cast to sext. 1007 return new SExtInst(Builder->CreateTrunc(Res, Src->getType()), DestTy); 1008 } 1009 } 1010 1011 // If the input is a shl/ashr pair of a same constant, then this is a sign 1012 // extension from a smaller value. If we could trust arbitrary bitwidth 1013 // integers, we could turn this into a truncate to the smaller bit and then 1014 // use a sext for the whole extension. Since we don't, look deeper and check 1015 // for a truncate. If the source and dest are the same type, eliminate the 1016 // trunc and extend and just do shifts. For example, turn: 1017 // %a = trunc i32 %i to i8 1018 // %b = shl i8 %a, 6 1019 // %c = ashr i8 %b, 6 1020 // %d = sext i8 %c to i32 1021 // into: 1022 // %a = shl i32 %i, 30 1023 // %d = ashr i32 %a, 30 1024 Value *A = 0; 1025 // TODO: Eventually this could be subsumed by EvaluateInDifferentType. 1026 ConstantInt *BA = 0, *CA = 0; 1027 if (match(Src, m_AShr(m_Shl(m_Trunc(m_Value(A)), m_ConstantInt(BA)), 1028 m_ConstantInt(CA))) && 1029 BA == CA && A->getType() == CI.getType()) { 1030 unsigned MidSize = Src->getType()->getScalarSizeInBits(); 1031 unsigned SrcDstSize = CI.getType()->getScalarSizeInBits(); 1032 unsigned ShAmt = CA->getZExtValue()+SrcDstSize-MidSize; 1033 Constant *ShAmtV = ConstantInt::get(CI.getType(), ShAmt); 1034 A = Builder->CreateShl(A, ShAmtV, CI.getName()); 1035 return BinaryOperator::CreateAShr(A, ShAmtV); 1036 } 1037 1038 return 0; 1039} 1040 1041 1042/// FitsInFPType - Return a Constant* for the specified FP constant if it fits 1043/// in the specified FP type without changing its value. 1044static Constant *FitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) { 1045 bool losesInfo; 1046 APFloat F = CFP->getValueAPF(); 1047 (void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo); 1048 if (!losesInfo) 1049 return ConstantFP::get(CFP->getContext(), F); 1050 return 0; 1051} 1052 1053/// LookThroughFPExtensions - If this is an fp extension instruction, look 1054/// through it until we get the source value. 1055static Value *LookThroughFPExtensions(Value *V) { 1056 if (Instruction *I = dyn_cast<Instruction>(V)) 1057 if (I->getOpcode() == Instruction::FPExt) 1058 return LookThroughFPExtensions(I->getOperand(0)); 1059 1060 // If this value is a constant, return the constant in the smallest FP type 1061 // that can accurately represent it. This allows us to turn 1062 // (float)((double)X+2.0) into x+2.0f. 1063 if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) { 1064 if (CFP->getType() == Type::getPPC_FP128Ty(V->getContext())) 1065 return V; // No constant folding of this. 1066 // See if the value can be truncated to float and then reextended. 1067 if (Value *V = FitsInFPType(CFP, APFloat::IEEEsingle)) 1068 return V; 1069 if (CFP->getType()->isDoubleTy()) 1070 return V; // Won't shrink. 1071 if (Value *V = FitsInFPType(CFP, APFloat::IEEEdouble)) 1072 return V; 1073 // Don't try to shrink to various long double types. 1074 } 1075 1076 return V; 1077} 1078 1079Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) { 1080 if (Instruction *I = commonCastTransforms(CI)) 1081 return I; 1082 1083 // If we have fptrunc(fadd (fpextend x), (fpextend y)), where x and y are 1084 // smaller than the destination type, we can eliminate the truncate by doing 1085 // the add as the smaller type. This applies to fadd/fsub/fmul/fdiv as well 1086 // as many builtins (sqrt, etc). 1087 BinaryOperator *OpI = dyn_cast<BinaryOperator>(CI.getOperand(0)); 1088 if (OpI && OpI->hasOneUse()) { 1089 switch (OpI->getOpcode()) { 1090 default: break; 1091 case Instruction::FAdd: 1092 case Instruction::FSub: 1093 case Instruction::FMul: 1094 case Instruction::FDiv: 1095 case Instruction::FRem: 1096 const Type *SrcTy = OpI->getType(); 1097 Value *LHSTrunc = LookThroughFPExtensions(OpI->getOperand(0)); 1098 Value *RHSTrunc = LookThroughFPExtensions(OpI->getOperand(1)); 1099 if (LHSTrunc->getType() != SrcTy && 1100 RHSTrunc->getType() != SrcTy) { 1101 unsigned DstSize = CI.getType()->getScalarSizeInBits(); 1102 // If the source types were both smaller than the destination type of 1103 // the cast, do this xform. 1104 if (LHSTrunc->getType()->getScalarSizeInBits() <= DstSize && 1105 RHSTrunc->getType()->getScalarSizeInBits() <= DstSize) { 1106 LHSTrunc = Builder->CreateFPExt(LHSTrunc, CI.getType()); 1107 RHSTrunc = Builder->CreateFPExt(RHSTrunc, CI.getType()); 1108 return BinaryOperator::Create(OpI->getOpcode(), LHSTrunc, RHSTrunc); 1109 } 1110 } 1111 break; 1112 } 1113 } 1114 return 0; 1115} 1116 1117Instruction *InstCombiner::visitFPExt(CastInst &CI) { 1118 return commonCastTransforms(CI); 1119} 1120 1121Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) { 1122 Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0)); 1123 if (OpI == 0) 1124 return commonCastTransforms(FI); 1125 1126 // fptoui(uitofp(X)) --> X 1127 // fptoui(sitofp(X)) --> X 1128 // This is safe if the intermediate type has enough bits in its mantissa to 1129 // accurately represent all values of X. For example, do not do this with 1130 // i64->float->i64. This is also safe for sitofp case, because any negative 1131 // 'X' value would cause an undefined result for the fptoui. 1132 if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) && 1133 OpI->getOperand(0)->getType() == FI.getType() && 1134 (int)FI.getType()->getScalarSizeInBits() < /*extra bit for sign */ 1135 OpI->getType()->getFPMantissaWidth()) 1136 return ReplaceInstUsesWith(FI, OpI->getOperand(0)); 1137 1138 return commonCastTransforms(FI); 1139} 1140 1141Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) { 1142 Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0)); 1143 if (OpI == 0) 1144 return commonCastTransforms(FI); 1145 1146 // fptosi(sitofp(X)) --> X 1147 // fptosi(uitofp(X)) --> X 1148 // This is safe if the intermediate type has enough bits in its mantissa to 1149 // accurately represent all values of X. For example, do not do this with 1150 // i64->float->i64. This is also safe for sitofp case, because any negative 1151 // 'X' value would cause an undefined result for the fptoui. 1152 if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) && 1153 OpI->getOperand(0)->getType() == FI.getType() && 1154 (int)FI.getType()->getScalarSizeInBits() <= 1155 OpI->getType()->getFPMantissaWidth()) 1156 return ReplaceInstUsesWith(FI, OpI->getOperand(0)); 1157 1158 return commonCastTransforms(FI); 1159} 1160 1161Instruction *InstCombiner::visitUIToFP(CastInst &CI) { 1162 return commonCastTransforms(CI); 1163} 1164 1165Instruction *InstCombiner::visitSIToFP(CastInst &CI) { 1166 return commonCastTransforms(CI); 1167} 1168 1169Instruction *InstCombiner::visitIntToPtr(IntToPtrInst &CI) { 1170 // If the source integer type is larger than the intptr_t type for 1171 // this target, do a trunc to the intptr_t type, then inttoptr of it. This 1172 // allows the trunc to be exposed to other transforms. Don't do this for 1173 // extending inttoptr's, because we don't know if the target sign or zero 1174 // extends to pointers. 1175 if (TD && CI.getOperand(0)->getType()->getScalarSizeInBits() > 1176 TD->getPointerSizeInBits()) { 1177 Value *P = Builder->CreateTrunc(CI.getOperand(0), 1178 TD->getIntPtrType(CI.getContext()), "tmp"); 1179 return new IntToPtrInst(P, CI.getType()); 1180 } 1181 1182 if (Instruction *I = commonCastTransforms(CI)) 1183 return I; 1184 1185 return 0; 1186} 1187 1188/// @brief Implement the transforms for cast of pointer (bitcast/ptrtoint) 1189Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) { 1190 Value *Src = CI.getOperand(0); 1191 1192 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) { 1193 // If casting the result of a getelementptr instruction with no offset, turn 1194 // this into a cast of the original pointer! 1195 if (GEP->hasAllZeroIndices()) { 1196 // Changing the cast operand is usually not a good idea but it is safe 1197 // here because the pointer operand is being replaced with another 1198 // pointer operand so the opcode doesn't need to change. 1199 Worklist.Add(GEP); 1200 CI.setOperand(0, GEP->getOperand(0)); 1201 return &CI; 1202 } 1203 1204 // If the GEP has a single use, and the base pointer is a bitcast, and the 1205 // GEP computes a constant offset, see if we can convert these three 1206 // instructions into fewer. This typically happens with unions and other 1207 // non-type-safe code. 1208 if (TD && GEP->hasOneUse() && isa<BitCastInst>(GEP->getOperand(0)) && 1209 GEP->hasAllConstantIndices()) { 1210 // We are guaranteed to get a constant from EmitGEPOffset. 1211 ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(GEP)); 1212 int64_t Offset = OffsetV->getSExtValue(); 1213 1214 // Get the base pointer input of the bitcast, and the type it points to. 1215 Value *OrigBase = cast<BitCastInst>(GEP->getOperand(0))->getOperand(0); 1216 const Type *GEPIdxTy = 1217 cast<PointerType>(OrigBase->getType())->getElementType(); 1218 SmallVector<Value*, 8> NewIndices; 1219 if (FindElementAtOffset(GEPIdxTy, Offset, NewIndices)) { 1220 // If we were able to index down into an element, create the GEP 1221 // and bitcast the result. This eliminates one bitcast, potentially 1222 // two. 1223 Value *NGEP = cast<GEPOperator>(GEP)->isInBounds() ? 1224 Builder->CreateInBoundsGEP(OrigBase, 1225 NewIndices.begin(), NewIndices.end()) : 1226 Builder->CreateGEP(OrigBase, NewIndices.begin(), NewIndices.end()); 1227 NGEP->takeName(GEP); 1228 1229 if (isa<BitCastInst>(CI)) 1230 return new BitCastInst(NGEP, CI.getType()); 1231 assert(isa<PtrToIntInst>(CI)); 1232 return new PtrToIntInst(NGEP, CI.getType()); 1233 } 1234 } 1235 } 1236 1237 return commonCastTransforms(CI); 1238} 1239 1240Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) { 1241 // If the destination integer type is smaller than the intptr_t type for 1242 // this target, do a ptrtoint to intptr_t then do a trunc. This allows the 1243 // trunc to be exposed to other transforms. Don't do this for extending 1244 // ptrtoint's, because we don't know if the target sign or zero extends its 1245 // pointers. 1246 if (TD && 1247 CI.getType()->getScalarSizeInBits() < TD->getPointerSizeInBits()) { 1248 Value *P = Builder->CreatePtrToInt(CI.getOperand(0), 1249 TD->getIntPtrType(CI.getContext()), 1250 "tmp"); 1251 return new TruncInst(P, CI.getType()); 1252 } 1253 1254 return commonPointerCastTransforms(CI); 1255} 1256 1257Instruction *InstCombiner::visitBitCast(BitCastInst &CI) { 1258 // If the operands are integer typed then apply the integer transforms, 1259 // otherwise just apply the common ones. 1260 Value *Src = CI.getOperand(0); 1261 const Type *SrcTy = Src->getType(); 1262 const Type *DestTy = CI.getType(); 1263 1264 // Get rid of casts from one type to the same type. These are useless and can 1265 // be replaced by the operand. 1266 if (DestTy == Src->getType()) 1267 return ReplaceInstUsesWith(CI, Src); 1268 1269 if (const PointerType *DstPTy = dyn_cast<PointerType>(DestTy)) { 1270 const PointerType *SrcPTy = cast<PointerType>(SrcTy); 1271 const Type *DstElTy = DstPTy->getElementType(); 1272 const Type *SrcElTy = SrcPTy->getElementType(); 1273 1274 // If the address spaces don't match, don't eliminate the bitcast, which is 1275 // required for changing types. 1276 if (SrcPTy->getAddressSpace() != DstPTy->getAddressSpace()) 1277 return 0; 1278 1279 // If we are casting a alloca to a pointer to a type of the same 1280 // size, rewrite the allocation instruction to allocate the "right" type. 1281 // There is no need to modify malloc calls because it is their bitcast that 1282 // needs to be cleaned up. 1283 if (AllocaInst *AI = dyn_cast<AllocaInst>(Src)) 1284 if (Instruction *V = PromoteCastOfAllocation(CI, *AI)) 1285 return V; 1286 1287 // If the source and destination are pointers, and this cast is equivalent 1288 // to a getelementptr X, 0, 0, 0... turn it into the appropriate gep. 1289 // This can enhance SROA and other transforms that want type-safe pointers. 1290 Constant *ZeroUInt = 1291 Constant::getNullValue(Type::getInt32Ty(CI.getContext())); 1292 unsigned NumZeros = 0; 1293 while (SrcElTy != DstElTy && 1294 isa<CompositeType>(SrcElTy) && !isa<PointerType>(SrcElTy) && 1295 SrcElTy->getNumContainedTypes() /* not "{}" */) { 1296 SrcElTy = cast<CompositeType>(SrcElTy)->getTypeAtIndex(ZeroUInt); 1297 ++NumZeros; 1298 } 1299 1300 // If we found a path from the src to dest, create the getelementptr now. 1301 if (SrcElTy == DstElTy) { 1302 SmallVector<Value*, 8> Idxs(NumZeros+1, ZeroUInt); 1303 return GetElementPtrInst::CreateInBounds(Src, Idxs.begin(), Idxs.end(),"", 1304 ((Instruction*)NULL)); 1305 } 1306 } 1307 1308 if (const VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) { 1309 if (DestVTy->getNumElements() == 1 && !isa<VectorType>(SrcTy)) { 1310 Value *Elem = Builder->CreateBitCast(Src, DestVTy->getElementType()); 1311 return InsertElementInst::Create(UndefValue::get(DestTy), Elem, 1312 Constant::getNullValue(Type::getInt32Ty(CI.getContext()))); 1313 // FIXME: Canonicalize bitcast(insertelement) -> insertelement(bitcast) 1314 } 1315 } 1316 1317 if (const VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) { 1318 if (SrcVTy->getNumElements() == 1 && !isa<VectorType>(DestTy)) { 1319 Value *Elem = 1320 Builder->CreateExtractElement(Src, 1321 Constant::getNullValue(Type::getInt32Ty(CI.getContext()))); 1322 return CastInst::Create(Instruction::BitCast, Elem, DestTy); 1323 } 1324 } 1325 1326 if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(Src)) { 1327 // Okay, we have (bitcast (shuffle ..)). Check to see if this is 1328 // a bitconvert to a vector with the same # elts. 1329 if (SVI->hasOneUse() && isa<VectorType>(DestTy) && 1330 cast<VectorType>(DestTy)->getNumElements() == 1331 SVI->getType()->getNumElements() && 1332 SVI->getType()->getNumElements() == 1333 cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements()) { 1334 BitCastInst *Tmp; 1335 // If either of the operands is a cast from CI.getType(), then 1336 // evaluating the shuffle in the casted destination's type will allow 1337 // us to eliminate at least one cast. 1338 if (((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(0))) && 1339 Tmp->getOperand(0)->getType() == DestTy) || 1340 ((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(1))) && 1341 Tmp->getOperand(0)->getType() == DestTy)) { 1342 Value *LHS = Builder->CreateBitCast(SVI->getOperand(0), DestTy); 1343 Value *RHS = Builder->CreateBitCast(SVI->getOperand(1), DestTy); 1344 // Return a new shuffle vector. Use the same element ID's, as we 1345 // know the vector types match #elts. 1346 return new ShuffleVectorInst(LHS, RHS, SVI->getOperand(2)); 1347 } 1348 } 1349 } 1350 1351 if (isa<PointerType>(SrcTy)) 1352 return commonPointerCastTransforms(CI); 1353 return commonCastTransforms(CI); 1354} 1355