InstCombineShifts.cpp revision 226633
1202375Srdivacky//===- InstCombineShifts.cpp ----------------------------------------------===// 2202375Srdivacky// 3202375Srdivacky// The LLVM Compiler Infrastructure 4202375Srdivacky// 5202375Srdivacky// This file is distributed under the University of Illinois Open Source 6202375Srdivacky// License. See LICENSE.TXT for details. 7202375Srdivacky// 8202375Srdivacky//===----------------------------------------------------------------------===// 9202375Srdivacky// 10202375Srdivacky// This file implements the visitShl, visitLShr, and visitAShr functions. 11202375Srdivacky// 12202375Srdivacky//===----------------------------------------------------------------------===// 13202375Srdivacky 14202375Srdivacky#include "InstCombine.h" 15203954Srdivacky#include "llvm/IntrinsicInst.h" 16226633Sdim#include "llvm/Analysis/ConstantFolding.h" 17218893Sdim#include "llvm/Analysis/InstructionSimplify.h" 18202375Srdivacky#include "llvm/Support/PatternMatch.h" 19202375Srdivackyusing namespace llvm; 20202375Srdivackyusing namespace PatternMatch; 21202375Srdivacky 22202375SrdivackyInstruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) { 23202375Srdivacky assert(I.getOperand(1)->getType() == I.getOperand(0)->getType()); 24202375Srdivacky Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); 25202375Srdivacky 26202375Srdivacky // See if we can fold away this shift. 27202375Srdivacky if (SimplifyDemandedInstructionBits(I)) 28202375Srdivacky return &I; 29202375Srdivacky 30202375Srdivacky // Try to fold constant and into select arguments. 31202375Srdivacky if (isa<Constant>(Op0)) 32202375Srdivacky if (SelectInst *SI = dyn_cast<SelectInst>(Op1)) 33202375Srdivacky if (Instruction *R = FoldOpIntoSelect(I, SI)) 34202375Srdivacky return R; 35202375Srdivacky 36202375Srdivacky if (ConstantInt *CUI = dyn_cast<ConstantInt>(Op1)) 37202375Srdivacky if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I)) 38202375Srdivacky return Res; 39218893Sdim 40218893Sdim // X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2. 41218893Sdim // Because shifts by negative values (which could occur if A were negative) 42218893Sdim // are undefined. 43218893Sdim Value *A; const APInt *B; 44218893Sdim if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Power2(B)))) { 45218893Sdim // FIXME: Should this get moved into SimplifyDemandedBits by saying we don't 46218893Sdim // demand the sign bit (and many others) here?? 47218893Sdim Value *Rem = Builder->CreateAnd(A, ConstantInt::get(I.getType(), *B-1), 48218893Sdim Op1->getName()); 49218893Sdim I.setOperand(1, Rem); 50218893Sdim return &I; 51218893Sdim } 52218893Sdim 53202375Srdivacky return 0; 54202375Srdivacky} 55202375Srdivacky 56212904Sdim/// CanEvaluateShifted - See if we can compute the specified value, but shifted 57212904Sdim/// logically to the left or right by some number of bits. This should return 58212904Sdim/// true if the expression can be computed for the same cost as the current 59212904Sdim/// expression tree. This is used to eliminate extraneous shifting from things 60212904Sdim/// like: 61212904Sdim/// %C = shl i128 %A, 64 62212904Sdim/// %D = shl i128 %B, 96 63212904Sdim/// %E = or i128 %C, %D 64212904Sdim/// %F = lshr i128 %E, 64 65212904Sdim/// where the client will ask if E can be computed shifted right by 64-bits. If 66212904Sdim/// this succeeds, the GetShiftedValue function will be called to produce the 67212904Sdim/// value. 68212904Sdimstatic bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift, 69212904Sdim InstCombiner &IC) { 70212904Sdim // We can always evaluate constants shifted. 71212904Sdim if (isa<Constant>(V)) 72212904Sdim return true; 73212904Sdim 74212904Sdim Instruction *I = dyn_cast<Instruction>(V); 75212904Sdim if (!I) return false; 76212904Sdim 77212904Sdim // If this is the opposite shift, we can directly reuse the input of the shift 78212904Sdim // if the needed bits are already zero in the input. This allows us to reuse 79212904Sdim // the value which means that we don't care if the shift has multiple uses. 80212904Sdim // TODO: Handle opposite shift by exact value. 81218893Sdim ConstantInt *CI = 0; 82212904Sdim if ((isLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) || 83212904Sdim (!isLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) { 84212904Sdim if (CI->getZExtValue() == NumBits) { 85212904Sdim // TODO: Check that the input bits are already zero with MaskedValueIsZero 86212904Sdim#if 0 87212904Sdim // If this is a truncate of a logical shr, we can truncate it to a smaller 88212904Sdim // lshr iff we know that the bits we would otherwise be shifting in are 89212904Sdim // already zeros. 90212904Sdim uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); 91212904Sdim uint32_t BitWidth = Ty->getScalarSizeInBits(); 92212904Sdim if (MaskedValueIsZero(I->getOperand(0), 93212904Sdim APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) && 94212904Sdim CI->getLimitedValue(BitWidth) < BitWidth) { 95212904Sdim return CanEvaluateTruncated(I->getOperand(0), Ty); 96212904Sdim } 97212904Sdim#endif 98212904Sdim 99212904Sdim } 100212904Sdim } 101212904Sdim 102212904Sdim // We can't mutate something that has multiple uses: doing so would 103212904Sdim // require duplicating the instruction in general, which isn't profitable. 104212904Sdim if (!I->hasOneUse()) return false; 105212904Sdim 106212904Sdim switch (I->getOpcode()) { 107212904Sdim default: return false; 108212904Sdim case Instruction::And: 109212904Sdim case Instruction::Or: 110212904Sdim case Instruction::Xor: 111212904Sdim // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted. 112212904Sdim return CanEvaluateShifted(I->getOperand(0), NumBits, isLeftShift, IC) && 113212904Sdim CanEvaluateShifted(I->getOperand(1), NumBits, isLeftShift, IC); 114212904Sdim 115212904Sdim case Instruction::Shl: { 116212904Sdim // We can often fold the shift into shifts-by-a-constant. 117212904Sdim CI = dyn_cast<ConstantInt>(I->getOperand(1)); 118212904Sdim if (CI == 0) return false; 119212904Sdim 120212904Sdim // We can always fold shl(c1)+shl(c2) -> shl(c1+c2). 121212904Sdim if (isLeftShift) return true; 122212904Sdim 123212904Sdim // We can always turn shl(c)+shr(c) -> and(c2). 124212904Sdim if (CI->getValue() == NumBits) return true; 125212904Sdim 126212904Sdim unsigned TypeWidth = I->getType()->getScalarSizeInBits(); 127212904Sdim 128212904Sdim // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't 129212904Sdim // profitable unless we know the and'd out bits are already zero. 130212904Sdim if (CI->getZExtValue() > NumBits) { 131218893Sdim unsigned LowBits = TypeWidth - CI->getZExtValue(); 132212904Sdim if (MaskedValueIsZero(I->getOperand(0), 133218893Sdim APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits)) 134212904Sdim return true; 135212904Sdim } 136212904Sdim 137212904Sdim return false; 138212904Sdim } 139212904Sdim case Instruction::LShr: { 140212904Sdim // We can often fold the shift into shifts-by-a-constant. 141212904Sdim CI = dyn_cast<ConstantInt>(I->getOperand(1)); 142212904Sdim if (CI == 0) return false; 143212904Sdim 144212904Sdim // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2). 145212904Sdim if (!isLeftShift) return true; 146212904Sdim 147212904Sdim // We can always turn lshr(c)+shl(c) -> and(c2). 148212904Sdim if (CI->getValue() == NumBits) return true; 149212904Sdim 150212904Sdim unsigned TypeWidth = I->getType()->getScalarSizeInBits(); 151212904Sdim 152212904Sdim // We can always turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but it isn't 153212904Sdim // profitable unless we know the and'd out bits are already zero. 154212904Sdim if (CI->getZExtValue() > NumBits) { 155212904Sdim unsigned LowBits = CI->getZExtValue() - NumBits; 156212904Sdim if (MaskedValueIsZero(I->getOperand(0), 157218893Sdim APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits)) 158212904Sdim return true; 159212904Sdim } 160212904Sdim 161212904Sdim return false; 162212904Sdim } 163212904Sdim case Instruction::Select: { 164212904Sdim SelectInst *SI = cast<SelectInst>(I); 165212904Sdim return CanEvaluateShifted(SI->getTrueValue(), NumBits, isLeftShift, IC) && 166212904Sdim CanEvaluateShifted(SI->getFalseValue(), NumBits, isLeftShift, IC); 167212904Sdim } 168212904Sdim case Instruction::PHI: { 169212904Sdim // We can change a phi if we can change all operands. Note that we never 170212904Sdim // get into trouble with cyclic PHIs here because we only consider 171212904Sdim // instructions with a single use. 172212904Sdim PHINode *PN = cast<PHINode>(I); 173212904Sdim for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 174212904Sdim if (!CanEvaluateShifted(PN->getIncomingValue(i), NumBits, isLeftShift,IC)) 175212904Sdim return false; 176212904Sdim return true; 177212904Sdim } 178212904Sdim } 179212904Sdim} 180212904Sdim 181212904Sdim/// GetShiftedValue - When CanEvaluateShifted returned true for an expression, 182212904Sdim/// this value inserts the new computation that produces the shifted value. 183212904Sdimstatic Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift, 184212904Sdim InstCombiner &IC) { 185212904Sdim // We can always evaluate constants shifted. 186212904Sdim if (Constant *C = dyn_cast<Constant>(V)) { 187212904Sdim if (isLeftShift) 188212904Sdim V = IC.Builder->CreateShl(C, NumBits); 189212904Sdim else 190212904Sdim V = IC.Builder->CreateLShr(C, NumBits); 191212904Sdim // If we got a constantexpr back, try to simplify it with TD info. 192212904Sdim if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 193212904Sdim V = ConstantFoldConstantExpression(CE, IC.getTargetData()); 194212904Sdim return V; 195212904Sdim } 196212904Sdim 197212904Sdim Instruction *I = cast<Instruction>(V); 198212904Sdim IC.Worklist.Add(I); 199212904Sdim 200212904Sdim switch (I->getOpcode()) { 201212904Sdim default: assert(0 && "Inconsistency with CanEvaluateShifted"); 202212904Sdim case Instruction::And: 203212904Sdim case Instruction::Or: 204212904Sdim case Instruction::Xor: 205212904Sdim // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted. 206212904Sdim I->setOperand(0, GetShiftedValue(I->getOperand(0), NumBits,isLeftShift,IC)); 207212904Sdim I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC)); 208212904Sdim return I; 209212904Sdim 210212904Sdim case Instruction::Shl: { 211226633Sdim BinaryOperator *BO = cast<BinaryOperator>(I); 212226633Sdim unsigned TypeWidth = BO->getType()->getScalarSizeInBits(); 213212904Sdim 214212904Sdim // We only accept shifts-by-a-constant in CanEvaluateShifted. 215226633Sdim ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1)); 216226633Sdim 217212904Sdim // We can always fold shl(c1)+shl(c2) -> shl(c1+c2). 218212904Sdim if (isLeftShift) { 219212904Sdim // If this is oversized composite shift, then unsigned shifts get 0. 220212904Sdim unsigned NewShAmt = NumBits+CI->getZExtValue(); 221212904Sdim if (NewShAmt >= TypeWidth) 222212904Sdim return Constant::getNullValue(I->getType()); 223212904Sdim 224226633Sdim BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt)); 225226633Sdim BO->setHasNoUnsignedWrap(false); 226226633Sdim BO->setHasNoSignedWrap(false); 227212904Sdim return I; 228212904Sdim } 229212904Sdim 230212904Sdim // We turn shl(c)+lshr(c) -> and(c2) if the input doesn't already have 231212904Sdim // zeros. 232212904Sdim if (CI->getValue() == NumBits) { 233212904Sdim APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits)); 234226633Sdim V = IC.Builder->CreateAnd(BO->getOperand(0), 235226633Sdim ConstantInt::get(BO->getContext(), Mask)); 236212904Sdim if (Instruction *VI = dyn_cast<Instruction>(V)) { 237226633Sdim VI->moveBefore(BO); 238226633Sdim VI->takeName(BO); 239212904Sdim } 240212904Sdim return V; 241212904Sdim } 242212904Sdim 243212904Sdim // We turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but only when we know that 244212904Sdim // the and won't be needed. 245212904Sdim assert(CI->getZExtValue() > NumBits); 246226633Sdim BO->setOperand(1, ConstantInt::get(BO->getType(), 247226633Sdim CI->getZExtValue() - NumBits)); 248226633Sdim BO->setHasNoUnsignedWrap(false); 249226633Sdim BO->setHasNoSignedWrap(false); 250226633Sdim return BO; 251212904Sdim } 252212904Sdim case Instruction::LShr: { 253226633Sdim BinaryOperator *BO = cast<BinaryOperator>(I); 254226633Sdim unsigned TypeWidth = BO->getType()->getScalarSizeInBits(); 255212904Sdim // We only accept shifts-by-a-constant in CanEvaluateShifted. 256226633Sdim ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1)); 257212904Sdim 258212904Sdim // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2). 259212904Sdim if (!isLeftShift) { 260212904Sdim // If this is oversized composite shift, then unsigned shifts get 0. 261212904Sdim unsigned NewShAmt = NumBits+CI->getZExtValue(); 262212904Sdim if (NewShAmt >= TypeWidth) 263226633Sdim return Constant::getNullValue(BO->getType()); 264212904Sdim 265226633Sdim BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt)); 266226633Sdim BO->setIsExact(false); 267212904Sdim return I; 268212904Sdim } 269212904Sdim 270212904Sdim // We turn lshr(c)+shl(c) -> and(c2) if the input doesn't already have 271212904Sdim // zeros. 272212904Sdim if (CI->getValue() == NumBits) { 273212904Sdim APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits)); 274212904Sdim V = IC.Builder->CreateAnd(I->getOperand(0), 275226633Sdim ConstantInt::get(BO->getContext(), Mask)); 276212904Sdim if (Instruction *VI = dyn_cast<Instruction>(V)) { 277212904Sdim VI->moveBefore(I); 278212904Sdim VI->takeName(I); 279212904Sdim } 280212904Sdim return V; 281212904Sdim } 282212904Sdim 283212904Sdim // We turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but only when we know that 284212904Sdim // the and won't be needed. 285212904Sdim assert(CI->getZExtValue() > NumBits); 286226633Sdim BO->setOperand(1, ConstantInt::get(BO->getType(), 287226633Sdim CI->getZExtValue() - NumBits)); 288226633Sdim BO->setIsExact(false); 289226633Sdim return BO; 290212904Sdim } 291212904Sdim 292212904Sdim case Instruction::Select: 293212904Sdim I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC)); 294212904Sdim I->setOperand(2, GetShiftedValue(I->getOperand(2), NumBits,isLeftShift,IC)); 295212904Sdim return I; 296212904Sdim case Instruction::PHI: { 297212904Sdim // We can change a phi if we can change all operands. Note that we never 298212904Sdim // get into trouble with cyclic PHIs here because we only consider 299212904Sdim // instructions with a single use. 300212904Sdim PHINode *PN = cast<PHINode>(I); 301212904Sdim for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 302212904Sdim PN->setIncomingValue(i, GetShiftedValue(PN->getIncomingValue(i), 303212904Sdim NumBits, isLeftShift, IC)); 304212904Sdim return PN; 305212904Sdim } 306212904Sdim } 307212904Sdim} 308212904Sdim 309212904Sdim 310212904Sdim 311202375SrdivackyInstruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, 312202375Srdivacky BinaryOperator &I) { 313202375Srdivacky bool isLeftShift = I.getOpcode() == Instruction::Shl; 314212904Sdim 315212904Sdim 316212904Sdim // See if we can propagate this shift into the input, this covers the trivial 317212904Sdim // cast of lshr(shl(x,c1),c2) as well as other more complex cases. 318212904Sdim if (I.getOpcode() != Instruction::AShr && 319212904Sdim CanEvaluateShifted(Op0, Op1->getZExtValue(), isLeftShift, *this)) { 320212904Sdim DEBUG(dbgs() << "ICE: GetShiftedValue propagating shift through expression" 321212904Sdim " to eliminate shift:\n IN: " << *Op0 << "\n SH: " << I <<"\n"); 322212904Sdim 323212904Sdim return ReplaceInstUsesWith(I, 324212904Sdim GetShiftedValue(Op0, Op1->getZExtValue(), isLeftShift, *this)); 325212904Sdim } 326212904Sdim 327212904Sdim 328202375Srdivacky // See if we can simplify any instructions used by the instruction whose sole 329202375Srdivacky // purpose is to compute bits we don't care about. 330202375Srdivacky uint32_t TypeBits = Op0->getType()->getScalarSizeInBits(); 331202375Srdivacky 332202375Srdivacky // shl i32 X, 32 = 0 and srl i8 Y, 9 = 0, ... just don't eliminate 333202375Srdivacky // a signed shift. 334202375Srdivacky // 335202375Srdivacky if (Op1->uge(TypeBits)) { 336202375Srdivacky if (I.getOpcode() != Instruction::AShr) 337202375Srdivacky return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType())); 338203954Srdivacky // ashr i32 X, 32 --> ashr i32 X, 31 339203954Srdivacky I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1)); 340203954Srdivacky return &I; 341202375Srdivacky } 342202375Srdivacky 343202375Srdivacky // ((X*C1) << C2) == (X * (C1 << C2)) 344202375Srdivacky if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0)) 345202375Srdivacky if (BO->getOpcode() == Instruction::Mul && isLeftShift) 346202375Srdivacky if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1))) 347202375Srdivacky return BinaryOperator::CreateMul(BO->getOperand(0), 348202375Srdivacky ConstantExpr::getShl(BOOp, Op1)); 349202375Srdivacky 350202375Srdivacky // Try to fold constant and into select arguments. 351202375Srdivacky if (SelectInst *SI = dyn_cast<SelectInst>(Op0)) 352202375Srdivacky if (Instruction *R = FoldOpIntoSelect(I, SI)) 353202375Srdivacky return R; 354202375Srdivacky if (isa<PHINode>(Op0)) 355202375Srdivacky if (Instruction *NV = FoldOpIntoPhi(I)) 356202375Srdivacky return NV; 357202375Srdivacky 358202375Srdivacky // Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2)) 359202375Srdivacky if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) { 360202375Srdivacky Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0)); 361202375Srdivacky // If 'shift2' is an ashr, we would have to get the sign bit into a funny 362202375Srdivacky // place. Don't try to do this transformation in this case. Also, we 363202375Srdivacky // require that the input operand is a shift-by-constant so that we have 364202375Srdivacky // confidence that the shifts will get folded together. We could do this 365202375Srdivacky // xform in more cases, but it is unlikely to be profitable. 366202375Srdivacky if (TrOp && I.isLogicalShift() && TrOp->isShift() && 367202375Srdivacky isa<ConstantInt>(TrOp->getOperand(1))) { 368202375Srdivacky // Okay, we'll do this xform. Make the shift of shift. 369202375Srdivacky Constant *ShAmt = ConstantExpr::getZExt(Op1, TrOp->getType()); 370202375Srdivacky // (shift2 (shift1 & 0x00FF), c2) 371202375Srdivacky Value *NSh = Builder->CreateBinOp(I.getOpcode(), TrOp, ShAmt,I.getName()); 372202375Srdivacky 373202375Srdivacky // For logical shifts, the truncation has the effect of making the high 374202375Srdivacky // part of the register be zeros. Emulate this by inserting an AND to 375202375Srdivacky // clear the top bits as needed. This 'and' will usually be zapped by 376202375Srdivacky // other xforms later if dead. 377202375Srdivacky unsigned SrcSize = TrOp->getType()->getScalarSizeInBits(); 378202375Srdivacky unsigned DstSize = TI->getType()->getScalarSizeInBits(); 379202375Srdivacky APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize)); 380202375Srdivacky 381202375Srdivacky // The mask we constructed says what the trunc would do if occurring 382202375Srdivacky // between the shifts. We want to know the effect *after* the second 383202375Srdivacky // shift. We know that it is a logical shift by a constant, so adjust the 384202375Srdivacky // mask as appropriate. 385202375Srdivacky if (I.getOpcode() == Instruction::Shl) 386202375Srdivacky MaskV <<= Op1->getZExtValue(); 387202375Srdivacky else { 388202375Srdivacky assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift"); 389202375Srdivacky MaskV = MaskV.lshr(Op1->getZExtValue()); 390202375Srdivacky } 391202375Srdivacky 392202375Srdivacky // shift1 & 0x00FF 393202375Srdivacky Value *And = Builder->CreateAnd(NSh, 394202375Srdivacky ConstantInt::get(I.getContext(), MaskV), 395202375Srdivacky TI->getName()); 396202375Srdivacky 397202375Srdivacky // Return the value truncated to the interesting size. 398202375Srdivacky return new TruncInst(And, I.getType()); 399202375Srdivacky } 400202375Srdivacky } 401202375Srdivacky 402202375Srdivacky if (Op0->hasOneUse()) { 403202375Srdivacky if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) { 404202375Srdivacky // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C) 405202375Srdivacky Value *V1, *V2; 406202375Srdivacky ConstantInt *CC; 407202375Srdivacky switch (Op0BO->getOpcode()) { 408202375Srdivacky default: break; 409202375Srdivacky case Instruction::Add: 410202375Srdivacky case Instruction::And: 411202375Srdivacky case Instruction::Or: 412202375Srdivacky case Instruction::Xor: { 413202375Srdivacky // These operators commute. 414202375Srdivacky // Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C) 415202375Srdivacky if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() && 416202375Srdivacky match(Op0BO->getOperand(1), m_Shr(m_Value(V1), 417202375Srdivacky m_Specific(Op1)))) { 418202375Srdivacky Value *YS = // (Y << C) 419202375Srdivacky Builder->CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName()); 420202375Srdivacky // (X + (Y << C)) 421202375Srdivacky Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), YS, V1, 422202375Srdivacky Op0BO->getOperand(1)->getName()); 423202375Srdivacky uint32_t Op1Val = Op1->getLimitedValue(TypeBits); 424202375Srdivacky return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(), 425202375Srdivacky APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val))); 426202375Srdivacky } 427202375Srdivacky 428202375Srdivacky // Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C)) 429202375Srdivacky Value *Op0BOOp1 = Op0BO->getOperand(1); 430202375Srdivacky if (isLeftShift && Op0BOOp1->hasOneUse() && 431202375Srdivacky match(Op0BOOp1, 432202375Srdivacky m_And(m_Shr(m_Value(V1), m_Specific(Op1)), 433202375Srdivacky m_ConstantInt(CC))) && 434202375Srdivacky cast<BinaryOperator>(Op0BOOp1)->getOperand(0)->hasOneUse()) { 435202375Srdivacky Value *YS = // (Y << C) 436202375Srdivacky Builder->CreateShl(Op0BO->getOperand(0), Op1, 437202375Srdivacky Op0BO->getName()); 438202375Srdivacky // X & (CC << C) 439202375Srdivacky Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1), 440202375Srdivacky V1->getName()+".mask"); 441202375Srdivacky return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM); 442202375Srdivacky } 443202375Srdivacky } 444202375Srdivacky 445202375Srdivacky // FALL THROUGH. 446202375Srdivacky case Instruction::Sub: { 447202375Srdivacky // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C) 448202375Srdivacky if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() && 449202375Srdivacky match(Op0BO->getOperand(0), m_Shr(m_Value(V1), 450202375Srdivacky m_Specific(Op1)))) { 451202375Srdivacky Value *YS = // (Y << C) 452202375Srdivacky Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName()); 453202375Srdivacky // (X + (Y << C)) 454202375Srdivacky Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), V1, YS, 455202375Srdivacky Op0BO->getOperand(0)->getName()); 456202375Srdivacky uint32_t Op1Val = Op1->getLimitedValue(TypeBits); 457202375Srdivacky return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(), 458202375Srdivacky APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val))); 459202375Srdivacky } 460202375Srdivacky 461202375Srdivacky // Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C) 462202375Srdivacky if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() && 463202375Srdivacky match(Op0BO->getOperand(0), 464202375Srdivacky m_And(m_Shr(m_Value(V1), m_Value(V2)), 465202375Srdivacky m_ConstantInt(CC))) && V2 == Op1 && 466202375Srdivacky cast<BinaryOperator>(Op0BO->getOperand(0)) 467202375Srdivacky ->getOperand(0)->hasOneUse()) { 468202375Srdivacky Value *YS = // (Y << C) 469202375Srdivacky Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName()); 470202375Srdivacky // X & (CC << C) 471202375Srdivacky Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1), 472202375Srdivacky V1->getName()+".mask"); 473202375Srdivacky 474202375Srdivacky return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS); 475202375Srdivacky } 476202375Srdivacky 477202375Srdivacky break; 478202375Srdivacky } 479202375Srdivacky } 480202375Srdivacky 481202375Srdivacky 482202375Srdivacky // If the operand is an bitwise operator with a constant RHS, and the 483202375Srdivacky // shift is the only use, we can pull it out of the shift. 484202375Srdivacky if (ConstantInt *Op0C = dyn_cast<ConstantInt>(Op0BO->getOperand(1))) { 485202375Srdivacky bool isValid = true; // Valid only for And, Or, Xor 486202375Srdivacky bool highBitSet = false; // Transform if high bit of constant set? 487202375Srdivacky 488202375Srdivacky switch (Op0BO->getOpcode()) { 489202375Srdivacky default: isValid = false; break; // Do not perform transform! 490202375Srdivacky case Instruction::Add: 491202375Srdivacky isValid = isLeftShift; 492202375Srdivacky break; 493202375Srdivacky case Instruction::Or: 494202375Srdivacky case Instruction::Xor: 495202375Srdivacky highBitSet = false; 496202375Srdivacky break; 497202375Srdivacky case Instruction::And: 498202375Srdivacky highBitSet = true; 499202375Srdivacky break; 500202375Srdivacky } 501202375Srdivacky 502202375Srdivacky // If this is a signed shift right, and the high bit is modified 503202375Srdivacky // by the logical operation, do not perform the transformation. 504202375Srdivacky // The highBitSet boolean indicates the value of the high bit of 505202375Srdivacky // the constant which would cause it to be modified for this 506202375Srdivacky // operation. 507202375Srdivacky // 508202375Srdivacky if (isValid && I.getOpcode() == Instruction::AShr) 509202375Srdivacky isValid = Op0C->getValue()[TypeBits-1] == highBitSet; 510202375Srdivacky 511202375Srdivacky if (isValid) { 512202375Srdivacky Constant *NewRHS = ConstantExpr::get(I.getOpcode(), Op0C, Op1); 513202375Srdivacky 514202375Srdivacky Value *NewShift = 515202375Srdivacky Builder->CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1); 516202375Srdivacky NewShift->takeName(Op0BO); 517202375Srdivacky 518202375Srdivacky return BinaryOperator::Create(Op0BO->getOpcode(), NewShift, 519202375Srdivacky NewRHS); 520202375Srdivacky } 521202375Srdivacky } 522202375Srdivacky } 523202375Srdivacky } 524202375Srdivacky 525202375Srdivacky // Find out if this is a shift of a shift by a constant. 526202375Srdivacky BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0); 527202375Srdivacky if (ShiftOp && !ShiftOp->isShift()) 528202375Srdivacky ShiftOp = 0; 529202375Srdivacky 530202375Srdivacky if (ShiftOp && isa<ConstantInt>(ShiftOp->getOperand(1))) { 531202375Srdivacky ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1)); 532202375Srdivacky uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits); 533202375Srdivacky uint32_t ShiftAmt2 = Op1->getLimitedValue(TypeBits); 534202375Srdivacky assert(ShiftAmt2 != 0 && "Should have been simplified earlier"); 535202375Srdivacky if (ShiftAmt1 == 0) return 0; // Will be simplified in the future. 536202375Srdivacky Value *X = ShiftOp->getOperand(0); 537202375Srdivacky 538202375Srdivacky uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift. 539202375Srdivacky 540226633Sdim IntegerType *Ty = cast<IntegerType>(I.getType()); 541202375Srdivacky 542202375Srdivacky // Check for (X << c1) << c2 and (X >> c1) >> c2 543202375Srdivacky if (I.getOpcode() == ShiftOp->getOpcode()) { 544202375Srdivacky // If this is oversized composite shift, then unsigned shifts get 0, ashr 545202375Srdivacky // saturates. 546202375Srdivacky if (AmtSum >= TypeBits) { 547202375Srdivacky if (I.getOpcode() != Instruction::AShr) 548202375Srdivacky return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); 549202375Srdivacky AmtSum = TypeBits-1; // Saturate to 31 for i32 ashr. 550202375Srdivacky } 551202375Srdivacky 552202375Srdivacky return BinaryOperator::Create(I.getOpcode(), X, 553202375Srdivacky ConstantInt::get(Ty, AmtSum)); 554202375Srdivacky } 555202375Srdivacky 556202375Srdivacky if (ShiftAmt1 == ShiftAmt2) { 557202375Srdivacky // If we have ((X >>? C) << C), turn this into X & (-1 << C). 558212904Sdim if (I.getOpcode() == Instruction::Shl && 559212904Sdim ShiftOp->getOpcode() != Instruction::Shl) { 560202375Srdivacky APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt1)); 561202375Srdivacky return BinaryOperator::CreateAnd(X, 562202375Srdivacky ConstantInt::get(I.getContext(),Mask)); 563202375Srdivacky } 564202375Srdivacky // If we have ((X << C) >>u C), turn this into X & (-1 >>u C). 565212904Sdim if (I.getOpcode() == Instruction::LShr && 566212904Sdim ShiftOp->getOpcode() == Instruction::Shl) { 567202375Srdivacky APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt1)); 568202375Srdivacky return BinaryOperator::CreateAnd(X, 569202375Srdivacky ConstantInt::get(I.getContext(), Mask)); 570202375Srdivacky } 571202375Srdivacky } else if (ShiftAmt1 < ShiftAmt2) { 572202375Srdivacky uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1; 573202375Srdivacky 574202375Srdivacky // (X >>? C1) << C2 --> X << (C2-C1) & (-1 << C2) 575212904Sdim if (I.getOpcode() == Instruction::Shl && 576212904Sdim ShiftOp->getOpcode() != Instruction::Shl) { 577202375Srdivacky assert(ShiftOp->getOpcode() == Instruction::LShr || 578202375Srdivacky ShiftOp->getOpcode() == Instruction::AShr); 579202375Srdivacky Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff)); 580202375Srdivacky 581202375Srdivacky APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2)); 582202375Srdivacky return BinaryOperator::CreateAnd(Shift, 583202375Srdivacky ConstantInt::get(I.getContext(),Mask)); 584202375Srdivacky } 585202375Srdivacky 586202375Srdivacky // (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2) 587212904Sdim if (I.getOpcode() == Instruction::LShr && 588212904Sdim ShiftOp->getOpcode() == Instruction::Shl) { 589202375Srdivacky assert(ShiftOp->getOpcode() == Instruction::Shl); 590202375Srdivacky Value *Shift = Builder->CreateLShr(X, ConstantInt::get(Ty, ShiftDiff)); 591202375Srdivacky 592202375Srdivacky APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2)); 593202375Srdivacky return BinaryOperator::CreateAnd(Shift, 594202375Srdivacky ConstantInt::get(I.getContext(),Mask)); 595202375Srdivacky } 596202375Srdivacky 597202375Srdivacky // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. 598202375Srdivacky } else { 599202375Srdivacky assert(ShiftAmt2 < ShiftAmt1); 600202375Srdivacky uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2; 601202375Srdivacky 602202375Srdivacky // (X >>? C1) << C2 --> X >>? (C1-C2) & (-1 << C2) 603212904Sdim if (I.getOpcode() == Instruction::Shl && 604212904Sdim ShiftOp->getOpcode() != Instruction::Shl) { 605202375Srdivacky Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), X, 606202375Srdivacky ConstantInt::get(Ty, ShiftDiff)); 607202375Srdivacky 608202375Srdivacky APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2)); 609202375Srdivacky return BinaryOperator::CreateAnd(Shift, 610202375Srdivacky ConstantInt::get(I.getContext(),Mask)); 611202375Srdivacky } 612202375Srdivacky 613202375Srdivacky // (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2) 614212904Sdim if (I.getOpcode() == Instruction::LShr && 615212904Sdim ShiftOp->getOpcode() == Instruction::Shl) { 616202375Srdivacky Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff)); 617202375Srdivacky 618202375Srdivacky APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2)); 619202375Srdivacky return BinaryOperator::CreateAnd(Shift, 620202375Srdivacky ConstantInt::get(I.getContext(),Mask)); 621202375Srdivacky } 622202375Srdivacky 623202375Srdivacky // We can't handle (X << C1) >>a C2, it shifts arbitrary bits in. 624202375Srdivacky } 625202375Srdivacky } 626202375Srdivacky return 0; 627202375Srdivacky} 628202375Srdivacky 629202375SrdivackyInstruction *InstCombiner::visitShl(BinaryOperator &I) { 630218893Sdim if (Value *V = SimplifyShlInst(I.getOperand(0), I.getOperand(1), 631218893Sdim I.hasNoSignedWrap(), I.hasNoUnsignedWrap(), 632218893Sdim TD)) 633218893Sdim return ReplaceInstUsesWith(I, V); 634218893Sdim 635218893Sdim if (Instruction *V = commonShiftTransforms(I)) 636218893Sdim return V; 637218893Sdim 638218893Sdim if (ConstantInt *Op1C = dyn_cast<ConstantInt>(I.getOperand(1))) { 639218893Sdim unsigned ShAmt = Op1C->getZExtValue(); 640218893Sdim 641218893Sdim // If the shifted-out value is known-zero, then this is a NUW shift. 642218893Sdim if (!I.hasNoUnsignedWrap() && 643218893Sdim MaskedValueIsZero(I.getOperand(0), 644218893Sdim APInt::getHighBitsSet(Op1C->getBitWidth(), ShAmt))) { 645218893Sdim I.setHasNoUnsignedWrap(); 646218893Sdim return &I; 647218893Sdim } 648218893Sdim 649218893Sdim // If the shifted out value is all signbits, this is a NSW shift. 650218893Sdim if (!I.hasNoSignedWrap() && 651218893Sdim ComputeNumSignBits(I.getOperand(0)) > ShAmt) { 652218893Sdim I.setHasNoSignedWrap(); 653218893Sdim return &I; 654218893Sdim } 655218893Sdim } 656221345Sdim 657221345Sdim // (C1 << A) << C2 -> (C1 << C2) << A 658221345Sdim Constant *C1, *C2; 659221345Sdim Value *A; 660221345Sdim if (match(I.getOperand(0), m_OneUse(m_Shl(m_Constant(C1), m_Value(A)))) && 661221345Sdim match(I.getOperand(1), m_Constant(C2))) 662221345Sdim return BinaryOperator::CreateShl(ConstantExpr::getShl(C1, C2), A); 663221345Sdim 664218893Sdim return 0; 665202375Srdivacky} 666202375Srdivacky 667202375SrdivackyInstruction *InstCombiner::visitLShr(BinaryOperator &I) { 668218893Sdim if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), 669218893Sdim I.isExact(), TD)) 670218893Sdim return ReplaceInstUsesWith(I, V); 671218893Sdim 672203954Srdivacky if (Instruction *R = commonShiftTransforms(I)) 673203954Srdivacky return R; 674203954Srdivacky 675203954Srdivacky Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); 676203954Srdivacky 677218893Sdim if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { 678218893Sdim unsigned ShAmt = Op1C->getZExtValue(); 679218893Sdim 680203954Srdivacky if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) { 681203954Srdivacky unsigned BitWidth = Op0->getType()->getScalarSizeInBits(); 682203954Srdivacky // ctlz.i32(x)>>5 --> zext(x == 0) 683203954Srdivacky // cttz.i32(x)>>5 --> zext(x == 0) 684203954Srdivacky // ctpop.i32(x)>>5 --> zext(x == -1) 685203954Srdivacky if ((II->getIntrinsicID() == Intrinsic::ctlz || 686203954Srdivacky II->getIntrinsicID() == Intrinsic::cttz || 687203954Srdivacky II->getIntrinsicID() == Intrinsic::ctpop) && 688218893Sdim isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == ShAmt) { 689203954Srdivacky bool isCtPop = II->getIntrinsicID() == Intrinsic::ctpop; 690203954Srdivacky Constant *RHS = ConstantInt::getSigned(Op0->getType(), isCtPop ? -1:0); 691210299Sed Value *Cmp = Builder->CreateICmpEQ(II->getArgOperand(0), RHS); 692203954Srdivacky return new ZExtInst(Cmp, II->getType()); 693203954Srdivacky } 694203954Srdivacky } 695203954Srdivacky 696218893Sdim // If the shifted-out value is known-zero, then this is an exact shift. 697218893Sdim if (!I.isExact() && 698218893Sdim MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt))){ 699218893Sdim I.setIsExact(); 700218893Sdim return &I; 701218893Sdim } 702218893Sdim } 703218893Sdim 704203954Srdivacky return 0; 705202375Srdivacky} 706202375Srdivacky 707202375SrdivackyInstruction *InstCombiner::visitAShr(BinaryOperator &I) { 708218893Sdim if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), 709218893Sdim I.isExact(), TD)) 710218893Sdim return ReplaceInstUsesWith(I, V); 711218893Sdim 712202375Srdivacky if (Instruction *R = commonShiftTransforms(I)) 713202375Srdivacky return R; 714202375Srdivacky 715202375Srdivacky Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); 716218893Sdim 717202375Srdivacky if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { 718218893Sdim unsigned ShAmt = Op1C->getZExtValue(); 719218893Sdim 720202375Srdivacky // If the input is a SHL by the same constant (ashr (shl X, C), C), then we 721202878Srdivacky // have a sign-extend idiom. 722202375Srdivacky Value *X; 723202878Srdivacky if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) { 724218893Sdim // If the left shift is just shifting out partial signbits, delete the 725218893Sdim // extension. 726218893Sdim if (cast<OverflowingBinaryOperator>(Op0)->hasNoSignedWrap()) 727202878Srdivacky return ReplaceInstUsesWith(I, X); 728202878Srdivacky 729202878Srdivacky // If the input is an extension from the shifted amount value, e.g. 730202878Srdivacky // %x = zext i8 %A to i32 731202878Srdivacky // %y = shl i32 %x, 24 732202878Srdivacky // %z = ashr %y, 24 733202878Srdivacky // then turn this into "z = sext i8 A to i32". 734202878Srdivacky if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) { 735202878Srdivacky uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits(); 736202878Srdivacky uint32_t DestBits = ZI->getType()->getScalarSizeInBits(); 737202878Srdivacky if (Op1C->getZExtValue() == DestBits-SrcBits) 738202878Srdivacky return new SExtInst(ZI->getOperand(0), ZI->getType()); 739202878Srdivacky } 740202878Srdivacky } 741218893Sdim 742218893Sdim // If the shifted-out value is known-zero, then this is an exact shift. 743218893Sdim if (!I.isExact() && 744218893Sdim MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt))){ 745218893Sdim I.setIsExact(); 746218893Sdim return &I; 747218893Sdim } 748202375Srdivacky } 749202375Srdivacky 750202375Srdivacky // See if we can turn a signed shr into an unsigned shr. 751202375Srdivacky if (MaskedValueIsZero(Op0, 752202375Srdivacky APInt::getSignBit(I.getType()->getScalarSizeInBits()))) 753202375Srdivacky return BinaryOperator::CreateLShr(Op0, Op1); 754202375Srdivacky 755202375Srdivacky // Arithmetic shifting an all-sign-bit value is a no-op. 756202375Srdivacky unsigned NumSignBits = ComputeNumSignBits(Op0); 757202375Srdivacky if (NumSignBits == Op0->getType()->getScalarSizeInBits()) 758202375Srdivacky return ReplaceInstUsesWith(I, Op0); 759202375Srdivacky 760202375Srdivacky return 0; 761202375Srdivacky} 762202375Srdivacky 763