1//===- InstCombineShifts.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 visitShl, visitLShr, and visitAShr functions. 11// 12//===----------------------------------------------------------------------===// 13 14#include "InstCombine.h" 15#include "llvm/Analysis/ConstantFolding.h" 16#include "llvm/Analysis/InstructionSimplify.h" 17#include "llvm/IR/IntrinsicInst.h" 18#include "llvm/IR/PatternMatch.h" 19using namespace llvm; 20using namespace PatternMatch; 21 22#define DEBUG_TYPE "instcombine" 23 24Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) { 25 assert(I.getOperand(1)->getType() == I.getOperand(0)->getType()); 26 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); 27 28 // See if we can fold away this shift. 29 if (SimplifyDemandedInstructionBits(I)) 30 return &I; 31 32 // Try to fold constant and into select arguments. 33 if (isa<Constant>(Op0)) 34 if (SelectInst *SI = dyn_cast<SelectInst>(Op1)) 35 if (Instruction *R = FoldOpIntoSelect(I, SI)) 36 return R; 37 38 if (Constant *CUI = dyn_cast<Constant>(Op1)) 39 if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I)) 40 return Res; 41 42 // X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2. 43 // Because shifts by negative values (which could occur if A were negative) 44 // are undefined. 45 Value *A; const APInt *B; 46 if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Power2(B)))) { 47 // FIXME: Should this get moved into SimplifyDemandedBits by saying we don't 48 // demand the sign bit (and many others) here?? 49 Value *Rem = Builder->CreateAnd(A, ConstantInt::get(I.getType(), *B-1), 50 Op1->getName()); 51 I.setOperand(1, Rem); 52 return &I; 53 } 54 55 return nullptr; 56} 57 58/// CanEvaluateShifted - See if we can compute the specified value, but shifted 59/// logically to the left or right by some number of bits. This should return 60/// true if the expression can be computed for the same cost as the current 61/// expression tree. This is used to eliminate extraneous shifting from things 62/// like: 63/// %C = shl i128 %A, 64 64/// %D = shl i128 %B, 96 65/// %E = or i128 %C, %D 66/// %F = lshr i128 %E, 64 67/// where the client will ask if E can be computed shifted right by 64-bits. If 68/// this succeeds, the GetShiftedValue function will be called to produce the 69/// value. 70static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift, 71 InstCombiner &IC) { 72 // We can always evaluate constants shifted. 73 if (isa<Constant>(V)) 74 return true; 75 76 Instruction *I = dyn_cast<Instruction>(V); 77 if (!I) return false; 78 79 // If this is the opposite shift, we can directly reuse the input of the shift 80 // if the needed bits are already zero in the input. This allows us to reuse 81 // the value which means that we don't care if the shift has multiple uses. 82 // TODO: Handle opposite shift by exact value. 83 ConstantInt *CI = nullptr; 84 if ((isLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) || 85 (!isLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) { 86 if (CI->getZExtValue() == NumBits) { 87 // TODO: Check that the input bits are already zero with MaskedValueIsZero 88#if 0 89 // If this is a truncate of a logical shr, we can truncate it to a smaller 90 // lshr iff we know that the bits we would otherwise be shifting in are 91 // already zeros. 92 uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); 93 uint32_t BitWidth = Ty->getScalarSizeInBits(); 94 if (MaskedValueIsZero(I->getOperand(0), 95 APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) && 96 CI->getLimitedValue(BitWidth) < BitWidth) { 97 return CanEvaluateTruncated(I->getOperand(0), Ty); 98 } 99#endif 100 101 } 102 } 103 104 // We can't mutate something that has multiple uses: doing so would 105 // require duplicating the instruction in general, which isn't profitable. 106 if (!I->hasOneUse()) return false; 107 108 switch (I->getOpcode()) { 109 default: return false; 110 case Instruction::And: 111 case Instruction::Or: 112 case Instruction::Xor: 113 // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted. 114 return CanEvaluateShifted(I->getOperand(0), NumBits, isLeftShift, IC) && 115 CanEvaluateShifted(I->getOperand(1), NumBits, isLeftShift, IC); 116 117 case Instruction::Shl: { 118 // We can often fold the shift into shifts-by-a-constant. 119 CI = dyn_cast<ConstantInt>(I->getOperand(1)); 120 if (!CI) return false; 121 122 // We can always fold shl(c1)+shl(c2) -> shl(c1+c2). 123 if (isLeftShift) return true; 124 125 // We can always turn shl(c)+shr(c) -> and(c2). 126 if (CI->getValue() == NumBits) return true; 127 128 unsigned TypeWidth = I->getType()->getScalarSizeInBits(); 129 130 // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't 131 // profitable unless we know the and'd out bits are already zero. 132 if (CI->getZExtValue() > NumBits) { 133 unsigned LowBits = TypeWidth - CI->getZExtValue(); 134 if (MaskedValueIsZero(I->getOperand(0), 135 APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits)) 136 return true; 137 } 138 139 return false; 140 } 141 case Instruction::LShr: { 142 // We can often fold the shift into shifts-by-a-constant. 143 CI = dyn_cast<ConstantInt>(I->getOperand(1)); 144 if (!CI) return false; 145 146 // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2). 147 if (!isLeftShift) return true; 148 149 // We can always turn lshr(c)+shl(c) -> and(c2). 150 if (CI->getValue() == NumBits) return true; 151 152 unsigned TypeWidth = I->getType()->getScalarSizeInBits(); 153 154 // We can always turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but it isn't 155 // profitable unless we know the and'd out bits are already zero. 156 if (CI->getValue().ult(TypeWidth) && CI->getZExtValue() > NumBits) { 157 unsigned LowBits = CI->getZExtValue() - NumBits; 158 if (MaskedValueIsZero(I->getOperand(0), 159 APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits)) 160 return true; 161 } 162 163 return false; 164 } 165 case Instruction::Select: { 166 SelectInst *SI = cast<SelectInst>(I); 167 return CanEvaluateShifted(SI->getTrueValue(), NumBits, isLeftShift, IC) && 168 CanEvaluateShifted(SI->getFalseValue(), NumBits, isLeftShift, IC); 169 } 170 case Instruction::PHI: { 171 // We can change a phi if we can change all operands. Note that we never 172 // get into trouble with cyclic PHIs here because we only consider 173 // instructions with a single use. 174 PHINode *PN = cast<PHINode>(I); 175 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 176 if (!CanEvaluateShifted(PN->getIncomingValue(i), NumBits, isLeftShift,IC)) 177 return false; 178 return true; 179 } 180 } 181} 182 183/// GetShiftedValue - When CanEvaluateShifted returned true for an expression, 184/// this value inserts the new computation that produces the shifted value. 185static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift, 186 InstCombiner &IC) { 187 // We can always evaluate constants shifted. 188 if (Constant *C = dyn_cast<Constant>(V)) { 189 if (isLeftShift) 190 V = IC.Builder->CreateShl(C, NumBits); 191 else 192 V = IC.Builder->CreateLShr(C, NumBits); 193 // If we got a constantexpr back, try to simplify it with TD info. 194 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 195 V = ConstantFoldConstantExpression(CE, IC.getDataLayout(), 196 IC.getTargetLibraryInfo()); 197 return V; 198 } 199 200 Instruction *I = cast<Instruction>(V); 201 IC.Worklist.Add(I); 202 203 switch (I->getOpcode()) { 204 default: llvm_unreachable("Inconsistency with CanEvaluateShifted"); 205 case Instruction::And: 206 case Instruction::Or: 207 case Instruction::Xor: 208 // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted. 209 I->setOperand(0, GetShiftedValue(I->getOperand(0), NumBits,isLeftShift,IC)); 210 I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC)); 211 return I; 212 213 case Instruction::Shl: { 214 BinaryOperator *BO = cast<BinaryOperator>(I); 215 unsigned TypeWidth = BO->getType()->getScalarSizeInBits(); 216 217 // We only accept shifts-by-a-constant in CanEvaluateShifted. 218 ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1)); 219 220 // We can always fold shl(c1)+shl(c2) -> shl(c1+c2). 221 if (isLeftShift) { 222 // If this is oversized composite shift, then unsigned shifts get 0. 223 unsigned NewShAmt = NumBits+CI->getZExtValue(); 224 if (NewShAmt >= TypeWidth) 225 return Constant::getNullValue(I->getType()); 226 227 BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt)); 228 BO->setHasNoUnsignedWrap(false); 229 BO->setHasNoSignedWrap(false); 230 return I; 231 } 232 233 // We turn shl(c)+lshr(c) -> and(c2) if the input doesn't already have 234 // zeros. 235 if (CI->getValue() == NumBits) { 236 APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits)); 237 V = IC.Builder->CreateAnd(BO->getOperand(0), 238 ConstantInt::get(BO->getContext(), Mask)); 239 if (Instruction *VI = dyn_cast<Instruction>(V)) { 240 VI->moveBefore(BO); 241 VI->takeName(BO); 242 } 243 return V; 244 } 245 246 // We turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but only when we know that 247 // the and won't be needed. 248 assert(CI->getZExtValue() > NumBits); 249 BO->setOperand(1, ConstantInt::get(BO->getType(), 250 CI->getZExtValue() - NumBits)); 251 BO->setHasNoUnsignedWrap(false); 252 BO->setHasNoSignedWrap(false); 253 return BO; 254 } 255 case Instruction::LShr: { 256 BinaryOperator *BO = cast<BinaryOperator>(I); 257 unsigned TypeWidth = BO->getType()->getScalarSizeInBits(); 258 // We only accept shifts-by-a-constant in CanEvaluateShifted. 259 ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1)); 260 261 // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2). 262 if (!isLeftShift) { 263 // If this is oversized composite shift, then unsigned shifts get 0. 264 unsigned NewShAmt = NumBits+CI->getZExtValue(); 265 if (NewShAmt >= TypeWidth) 266 return Constant::getNullValue(BO->getType()); 267 268 BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt)); 269 BO->setIsExact(false); 270 return I; 271 } 272 273 // We turn lshr(c)+shl(c) -> and(c2) if the input doesn't already have 274 // zeros. 275 if (CI->getValue() == NumBits) { 276 APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits)); 277 V = IC.Builder->CreateAnd(I->getOperand(0), 278 ConstantInt::get(BO->getContext(), Mask)); 279 if (Instruction *VI = dyn_cast<Instruction>(V)) { 280 VI->moveBefore(I); 281 VI->takeName(I); 282 } 283 return V; 284 } 285 286 // We turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but only when we know that 287 // the and won't be needed. 288 assert(CI->getZExtValue() > NumBits); 289 BO->setOperand(1, ConstantInt::get(BO->getType(), 290 CI->getZExtValue() - NumBits)); 291 BO->setIsExact(false); 292 return BO; 293 } 294 295 case Instruction::Select: 296 I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC)); 297 I->setOperand(2, GetShiftedValue(I->getOperand(2), NumBits,isLeftShift,IC)); 298 return I; 299 case Instruction::PHI: { 300 // We can change a phi if we can change all operands. Note that we never 301 // get into trouble with cyclic PHIs here because we only consider 302 // instructions with a single use. 303 PHINode *PN = cast<PHINode>(I); 304 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 305 PN->setIncomingValue(i, GetShiftedValue(PN->getIncomingValue(i), 306 NumBits, isLeftShift, IC)); 307 return PN; 308 } 309 } 310} 311 312 313 314Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1, 315 BinaryOperator &I) { 316 bool isLeftShift = I.getOpcode() == Instruction::Shl; 317 318 ConstantInt *COp1 = nullptr; 319 if (ConstantDataVector *CV = dyn_cast<ConstantDataVector>(Op1)) 320 COp1 = dyn_cast_or_null<ConstantInt>(CV->getSplatValue()); 321 else if (ConstantVector *CV = dyn_cast<ConstantVector>(Op1)) 322 COp1 = dyn_cast_or_null<ConstantInt>(CV->getSplatValue()); 323 else 324 COp1 = dyn_cast<ConstantInt>(Op1); 325 326 if (!COp1) 327 return nullptr; 328 329 // See if we can propagate this shift into the input, this covers the trivial 330 // cast of lshr(shl(x,c1),c2) as well as other more complex cases. 331 if (I.getOpcode() != Instruction::AShr && 332 CanEvaluateShifted(Op0, COp1->getZExtValue(), isLeftShift, *this)) { 333 DEBUG(dbgs() << "ICE: GetShiftedValue propagating shift through expression" 334 " to eliminate shift:\n IN: " << *Op0 << "\n SH: " << I <<"\n"); 335 336 return ReplaceInstUsesWith(I, 337 GetShiftedValue(Op0, COp1->getZExtValue(), isLeftShift, *this)); 338 } 339 340 // See if we can simplify any instructions used by the instruction whose sole 341 // purpose is to compute bits we don't care about. 342 uint32_t TypeBits = Op0->getType()->getScalarSizeInBits(); 343 344 assert(!COp1->uge(TypeBits) && 345 "Shift over the type width should have been removed already"); 346 347 // ((X*C1) << C2) == (X * (C1 << C2)) 348 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0)) 349 if (BO->getOpcode() == Instruction::Mul && isLeftShift) 350 if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1))) 351 return BinaryOperator::CreateMul(BO->getOperand(0), 352 ConstantExpr::getShl(BOOp, Op1)); 353 354 // Try to fold constant and into select arguments. 355 if (SelectInst *SI = dyn_cast<SelectInst>(Op0)) 356 if (Instruction *R = FoldOpIntoSelect(I, SI)) 357 return R; 358 if (isa<PHINode>(Op0)) 359 if (Instruction *NV = FoldOpIntoPhi(I)) 360 return NV; 361 362 // Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2)) 363 if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) { 364 Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0)); 365 // If 'shift2' is an ashr, we would have to get the sign bit into a funny 366 // place. Don't try to do this transformation in this case. Also, we 367 // require that the input operand is a shift-by-constant so that we have 368 // confidence that the shifts will get folded together. We could do this 369 // xform in more cases, but it is unlikely to be profitable. 370 if (TrOp && I.isLogicalShift() && TrOp->isShift() && 371 isa<ConstantInt>(TrOp->getOperand(1))) { 372 // Okay, we'll do this xform. Make the shift of shift. 373 Constant *ShAmt = ConstantExpr::getZExt(COp1, TrOp->getType()); 374 // (shift2 (shift1 & 0x00FF), c2) 375 Value *NSh = Builder->CreateBinOp(I.getOpcode(), TrOp, ShAmt,I.getName()); 376 377 // For logical shifts, the truncation has the effect of making the high 378 // part of the register be zeros. Emulate this by inserting an AND to 379 // clear the top bits as needed. This 'and' will usually be zapped by 380 // other xforms later if dead. 381 unsigned SrcSize = TrOp->getType()->getScalarSizeInBits(); 382 unsigned DstSize = TI->getType()->getScalarSizeInBits(); 383 APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize)); 384 385 // The mask we constructed says what the trunc would do if occurring 386 // between the shifts. We want to know the effect *after* the second 387 // shift. We know that it is a logical shift by a constant, so adjust the 388 // mask as appropriate. 389 if (I.getOpcode() == Instruction::Shl) 390 MaskV <<= COp1->getZExtValue(); 391 else { 392 assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift"); 393 MaskV = MaskV.lshr(COp1->getZExtValue()); 394 } 395 396 // shift1 & 0x00FF 397 Value *And = Builder->CreateAnd(NSh, 398 ConstantInt::get(I.getContext(), MaskV), 399 TI->getName()); 400 401 // Return the value truncated to the interesting size. 402 return new TruncInst(And, I.getType()); 403 } 404 } 405 406 if (Op0->hasOneUse()) { 407 if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) { 408 // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C) 409 Value *V1, *V2; 410 ConstantInt *CC; 411 switch (Op0BO->getOpcode()) { 412 default: break; 413 case Instruction::Add: 414 case Instruction::And: 415 case Instruction::Or: 416 case Instruction::Xor: { 417 // These operators commute. 418 // Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C) 419 if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() && 420 match(Op0BO->getOperand(1), m_Shr(m_Value(V1), 421 m_Specific(Op1)))) { 422 Value *YS = // (Y << C) 423 Builder->CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName()); 424 // (X + (Y << C)) 425 Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), YS, V1, 426 Op0BO->getOperand(1)->getName()); 427 uint32_t Op1Val = COp1->getLimitedValue(TypeBits); 428 429 APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val); 430 Constant *Mask = ConstantInt::get(I.getContext(), Bits); 431 if (VectorType *VT = dyn_cast<VectorType>(X->getType())) 432 Mask = ConstantVector::getSplat(VT->getNumElements(), Mask); 433 return BinaryOperator::CreateAnd(X, Mask); 434 } 435 436 // Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C)) 437 Value *Op0BOOp1 = Op0BO->getOperand(1); 438 if (isLeftShift && Op0BOOp1->hasOneUse() && 439 match(Op0BOOp1, 440 m_And(m_OneUse(m_Shr(m_Value(V1), m_Specific(Op1))), 441 m_ConstantInt(CC)))) { 442 Value *YS = // (Y << C) 443 Builder->CreateShl(Op0BO->getOperand(0), Op1, 444 Op0BO->getName()); 445 // X & (CC << C) 446 Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1), 447 V1->getName()+".mask"); 448 return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM); 449 } 450 } 451 452 // FALL THROUGH. 453 case Instruction::Sub: { 454 // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C) 455 if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() && 456 match(Op0BO->getOperand(0), m_Shr(m_Value(V1), 457 m_Specific(Op1)))) { 458 Value *YS = // (Y << C) 459 Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName()); 460 // (X + (Y << C)) 461 Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), V1, YS, 462 Op0BO->getOperand(0)->getName()); 463 uint32_t Op1Val = COp1->getLimitedValue(TypeBits); 464 465 APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val); 466 Constant *Mask = ConstantInt::get(I.getContext(), Bits); 467 if (VectorType *VT = dyn_cast<VectorType>(X->getType())) 468 Mask = ConstantVector::getSplat(VT->getNumElements(), Mask); 469 return BinaryOperator::CreateAnd(X, Mask); 470 } 471 472 // Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C) 473 if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() && 474 match(Op0BO->getOperand(0), 475 m_And(m_OneUse(m_Shr(m_Value(V1), m_Value(V2))), 476 m_ConstantInt(CC))) && V2 == Op1) { 477 Value *YS = // (Y << C) 478 Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName()); 479 // X & (CC << C) 480 Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1), 481 V1->getName()+".mask"); 482 483 return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS); 484 } 485 486 break; 487 } 488 } 489 490 491 // If the operand is an bitwise operator with a constant RHS, and the 492 // shift is the only use, we can pull it out of the shift. 493 if (ConstantInt *Op0C = dyn_cast<ConstantInt>(Op0BO->getOperand(1))) { 494 bool isValid = true; // Valid only for And, Or, Xor 495 bool highBitSet = false; // Transform if high bit of constant set? 496 497 switch (Op0BO->getOpcode()) { 498 default: isValid = false; break; // Do not perform transform! 499 case Instruction::Add: 500 isValid = isLeftShift; 501 break; 502 case Instruction::Or: 503 case Instruction::Xor: 504 highBitSet = false; 505 break; 506 case Instruction::And: 507 highBitSet = true; 508 break; 509 } 510 511 // If this is a signed shift right, and the high bit is modified 512 // by the logical operation, do not perform the transformation. 513 // The highBitSet boolean indicates the value of the high bit of 514 // the constant which would cause it to be modified for this 515 // operation. 516 // 517 if (isValid && I.getOpcode() == Instruction::AShr) 518 isValid = Op0C->getValue()[TypeBits-1] == highBitSet; 519 520 if (isValid) { 521 Constant *NewRHS = ConstantExpr::get(I.getOpcode(), Op0C, Op1); 522 523 Value *NewShift = 524 Builder->CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1); 525 NewShift->takeName(Op0BO); 526 527 return BinaryOperator::Create(Op0BO->getOpcode(), NewShift, 528 NewRHS); 529 } 530 } 531 } 532 } 533 534 // Find out if this is a shift of a shift by a constant. 535 BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0); 536 if (ShiftOp && !ShiftOp->isShift()) 537 ShiftOp = nullptr; 538 539 if (ShiftOp && isa<ConstantInt>(ShiftOp->getOperand(1))) { 540 541 // This is a constant shift of a constant shift. Be careful about hiding 542 // shl instructions behind bit masks. They are used to represent multiplies 543 // by a constant, and it is important that simple arithmetic expressions 544 // are still recognizable by scalar evolution. 545 // 546 // The transforms applied to shl are very similar to the transforms applied 547 // to mul by constant. We can be more aggressive about optimizing right 548 // shifts. 549 // 550 // Combinations of right and left shifts will still be optimized in 551 // DAGCombine where scalar evolution no longer applies. 552 553 ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1)); 554 uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits); 555 uint32_t ShiftAmt2 = COp1->getLimitedValue(TypeBits); 556 assert(ShiftAmt2 != 0 && "Should have been simplified earlier"); 557 if (ShiftAmt1 == 0) return nullptr; // Will be simplified in the future. 558 Value *X = ShiftOp->getOperand(0); 559 560 IntegerType *Ty = cast<IntegerType>(I.getType()); 561 562 // Check for (X << c1) << c2 and (X >> c1) >> c2 563 if (I.getOpcode() == ShiftOp->getOpcode()) { 564 uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift. 565 // If this is oversized composite shift, then unsigned shifts get 0, ashr 566 // saturates. 567 if (AmtSum >= TypeBits) { 568 if (I.getOpcode() != Instruction::AShr) 569 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); 570 AmtSum = TypeBits-1; // Saturate to 31 for i32 ashr. 571 } 572 573 return BinaryOperator::Create(I.getOpcode(), X, 574 ConstantInt::get(Ty, AmtSum)); 575 } 576 577 if (ShiftAmt1 == ShiftAmt2) { 578 // If we have ((X << C) >>u C), turn this into X & (-1 >>u C). 579 if (I.getOpcode() == Instruction::LShr && 580 ShiftOp->getOpcode() == Instruction::Shl) { 581 APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt1)); 582 return BinaryOperator::CreateAnd(X, 583 ConstantInt::get(I.getContext(), Mask)); 584 } 585 } else if (ShiftAmt1 < ShiftAmt2) { 586 uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1; 587 588 // (X >>?,exact C1) << C2 --> X << (C2-C1) 589 // The inexact version is deferred to DAGCombine so we don't hide shl 590 // behind a bit mask. 591 if (I.getOpcode() == Instruction::Shl && 592 ShiftOp->getOpcode() != Instruction::Shl && 593 ShiftOp->isExact()) { 594 assert(ShiftOp->getOpcode() == Instruction::LShr || 595 ShiftOp->getOpcode() == Instruction::AShr); 596 ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); 597 BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl, 598 X, ShiftDiffCst); 599 NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap()); 600 NewShl->setHasNoSignedWrap(I.hasNoSignedWrap()); 601 return NewShl; 602 } 603 604 // (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2) 605 if (I.getOpcode() == Instruction::LShr && 606 ShiftOp->getOpcode() == Instruction::Shl) { 607 ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); 608 // (X <<nuw C1) >>u C2 --> X >>u (C2-C1) 609 if (ShiftOp->hasNoUnsignedWrap()) { 610 BinaryOperator *NewLShr = BinaryOperator::Create(Instruction::LShr, 611 X, ShiftDiffCst); 612 NewLShr->setIsExact(I.isExact()); 613 return NewLShr; 614 } 615 Value *Shift = Builder->CreateLShr(X, ShiftDiffCst); 616 617 APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2)); 618 return BinaryOperator::CreateAnd(Shift, 619 ConstantInt::get(I.getContext(),Mask)); 620 } 621 622 // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. However, 623 // we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits. 624 if (I.getOpcode() == Instruction::AShr && 625 ShiftOp->getOpcode() == Instruction::Shl) { 626 if (ShiftOp->hasNoSignedWrap()) { 627 // (X <<nsw C1) >>s C2 --> X >>s (C2-C1) 628 ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); 629 BinaryOperator *NewAShr = BinaryOperator::Create(Instruction::AShr, 630 X, ShiftDiffCst); 631 NewAShr->setIsExact(I.isExact()); 632 return NewAShr; 633 } 634 } 635 } else { 636 assert(ShiftAmt2 < ShiftAmt1); 637 uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2; 638 639 // (X >>?exact C1) << C2 --> X >>?exact (C1-C2) 640 // The inexact version is deferred to DAGCombine so we don't hide shl 641 // behind a bit mask. 642 if (I.getOpcode() == Instruction::Shl && 643 ShiftOp->getOpcode() != Instruction::Shl && 644 ShiftOp->isExact()) { 645 ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); 646 BinaryOperator *NewShr = BinaryOperator::Create(ShiftOp->getOpcode(), 647 X, ShiftDiffCst); 648 NewShr->setIsExact(true); 649 return NewShr; 650 } 651 652 // (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2) 653 if (I.getOpcode() == Instruction::LShr && 654 ShiftOp->getOpcode() == Instruction::Shl) { 655 ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); 656 if (ShiftOp->hasNoUnsignedWrap()) { 657 // (X <<nuw C1) >>u C2 --> X <<nuw (C1-C2) 658 BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl, 659 X, ShiftDiffCst); 660 NewShl->setHasNoUnsignedWrap(true); 661 return NewShl; 662 } 663 Value *Shift = Builder->CreateShl(X, ShiftDiffCst); 664 665 APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2)); 666 return BinaryOperator::CreateAnd(Shift, 667 ConstantInt::get(I.getContext(),Mask)); 668 } 669 670 // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. However, 671 // we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits. 672 if (I.getOpcode() == Instruction::AShr && 673 ShiftOp->getOpcode() == Instruction::Shl) { 674 if (ShiftOp->hasNoSignedWrap()) { 675 // (X <<nsw C1) >>s C2 --> X <<nsw (C1-C2) 676 ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); 677 BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl, 678 X, ShiftDiffCst); 679 NewShl->setHasNoSignedWrap(true); 680 return NewShl; 681 } 682 } 683 } 684 } 685 return nullptr; 686} 687 688Instruction *InstCombiner::visitShl(BinaryOperator &I) { 689 if (Value *V = SimplifyVectorOp(I)) 690 return ReplaceInstUsesWith(I, V); 691 692 if (Value *V = SimplifyShlInst(I.getOperand(0), I.getOperand(1), 693 I.hasNoSignedWrap(), I.hasNoUnsignedWrap(), 694 DL)) 695 return ReplaceInstUsesWith(I, V); 696 697 if (Instruction *V = commonShiftTransforms(I)) 698 return V; 699 700 if (ConstantInt *Op1C = dyn_cast<ConstantInt>(I.getOperand(1))) { 701 unsigned ShAmt = Op1C->getZExtValue(); 702 703 // If the shifted-out value is known-zero, then this is a NUW shift. 704 if (!I.hasNoUnsignedWrap() && 705 MaskedValueIsZero(I.getOperand(0), 706 APInt::getHighBitsSet(Op1C->getBitWidth(), ShAmt))) { 707 I.setHasNoUnsignedWrap(); 708 return &I; 709 } 710 711 // If the shifted out value is all signbits, this is a NSW shift. 712 if (!I.hasNoSignedWrap() && 713 ComputeNumSignBits(I.getOperand(0)) > ShAmt) { 714 I.setHasNoSignedWrap(); 715 return &I; 716 } 717 } 718 719 // (C1 << A) << C2 -> (C1 << C2) << A 720 Constant *C1, *C2; 721 Value *A; 722 if (match(I.getOperand(0), m_OneUse(m_Shl(m_Constant(C1), m_Value(A)))) && 723 match(I.getOperand(1), m_Constant(C2))) 724 return BinaryOperator::CreateShl(ConstantExpr::getShl(C1, C2), A); 725 726 return nullptr; 727} 728 729Instruction *InstCombiner::visitLShr(BinaryOperator &I) { 730 if (Value *V = SimplifyVectorOp(I)) 731 return ReplaceInstUsesWith(I, V); 732 733 if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), 734 I.isExact(), DL)) 735 return ReplaceInstUsesWith(I, V); 736 737 if (Instruction *R = commonShiftTransforms(I)) 738 return R; 739 740 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); 741 742 if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { 743 unsigned ShAmt = Op1C->getZExtValue(); 744 745 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) { 746 unsigned BitWidth = Op0->getType()->getScalarSizeInBits(); 747 // ctlz.i32(x)>>5 --> zext(x == 0) 748 // cttz.i32(x)>>5 --> zext(x == 0) 749 // ctpop.i32(x)>>5 --> zext(x == -1) 750 if ((II->getIntrinsicID() == Intrinsic::ctlz || 751 II->getIntrinsicID() == Intrinsic::cttz || 752 II->getIntrinsicID() == Intrinsic::ctpop) && 753 isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == ShAmt) { 754 bool isCtPop = II->getIntrinsicID() == Intrinsic::ctpop; 755 Constant *RHS = ConstantInt::getSigned(Op0->getType(), isCtPop ? -1:0); 756 Value *Cmp = Builder->CreateICmpEQ(II->getArgOperand(0), RHS); 757 return new ZExtInst(Cmp, II->getType()); 758 } 759 } 760 761 // If the shifted-out value is known-zero, then this is an exact shift. 762 if (!I.isExact() && 763 MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt))){ 764 I.setIsExact(); 765 return &I; 766 } 767 } 768 769 return nullptr; 770} 771 772Instruction *InstCombiner::visitAShr(BinaryOperator &I) { 773 if (Value *V = SimplifyVectorOp(I)) 774 return ReplaceInstUsesWith(I, V); 775 776 if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), 777 I.isExact(), DL)) 778 return ReplaceInstUsesWith(I, V); 779 780 if (Instruction *R = commonShiftTransforms(I)) 781 return R; 782 783 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); 784 785 if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { 786 unsigned ShAmt = Op1C->getZExtValue(); 787 788 // If the input is a SHL by the same constant (ashr (shl X, C), C), then we 789 // have a sign-extend idiom. 790 Value *X; 791 if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) { 792 // If the input is an extension from the shifted amount value, e.g. 793 // %x = zext i8 %A to i32 794 // %y = shl i32 %x, 24 795 // %z = ashr %y, 24 796 // then turn this into "z = sext i8 A to i32". 797 if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) { 798 uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits(); 799 uint32_t DestBits = ZI->getType()->getScalarSizeInBits(); 800 if (Op1C->getZExtValue() == DestBits-SrcBits) 801 return new SExtInst(ZI->getOperand(0), ZI->getType()); 802 } 803 } 804 805 // If the shifted-out value is known-zero, then this is an exact shift. 806 if (!I.isExact() && 807 MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt))){ 808 I.setIsExact(); 809 return &I; 810 } 811 } 812 813 // See if we can turn a signed shr into an unsigned shr. 814 if (MaskedValueIsZero(Op0, 815 APInt::getSignBit(I.getType()->getScalarSizeInBits()))) 816 return BinaryOperator::CreateLShr(Op0, Op1); 817 818 // Arithmetic shifting an all-sign-bit value is a no-op. 819 unsigned NumSignBits = ComputeNumSignBits(Op0); 820 if (NumSignBits == Op0->getType()->getScalarSizeInBits()) 821 return ReplaceInstUsesWith(I, Op0); 822 823 return nullptr; 824} 825