lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

   1 //===- InstCombineMulDivRem.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 mul, fmul, sdiv, udiv, fdiv,
  11 // srem, urem, frem.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "InstCombine.h"
  16 #include "llvm/IntrinsicInst.h"
  17 #include "llvm/Analysis/InstructionSimplify.h"
  18 #include "llvm/Support/PatternMatch.h"
  19 using namespace llvm;
  20 using namespace PatternMatch;
  21
  22
  23 /// simplifyValueKnownNonZero - The specific integer value is used in a context
  24 /// where it is known to be non-zero.  If this allows us to simplify the
  25 /// computation, do so and return the new operand, otherwise return null.
  26 static Value *simplifyValueKnownNonZero(Value *V, InstCombiner &IC) {
  27   // If V has multiple uses, then we would have to do more analysis to determine
  28   // if this is safe.  For example, the use could be in dynamically unreached
  29   // code.
  30   if (!V->hasOneUse()) return 0;
  31
  32   bool MadeChange = false;
  33
  34   // ((1 << A) >>u B) --> (1 << (A-B))
  35   // Because V cannot be zero, we know that B is less than A.
  36   Value *A = 0, *B = 0, *PowerOf2 = 0;
  37   if (match(V, m_LShr(m_OneUse(m_Shl(m_Value(PowerOf2), m_Value(A))),
  38                       m_Value(B))) &&
  39       // The "1" can be any value known to be a power of 2.
  40       isPowerOfTwo(PowerOf2, IC.getTargetData())) {
  41     A = IC.Builder->CreateSub(A, B, "tmp");
  42     return IC.Builder->CreateShl(PowerOf2, A);
  43   }
  44
  45   // (PowerOfTwo >>u B) --> isExact since shifting out the result would make it
  46   // inexact.  Similarly for <<.
  47   if (BinaryOperator *I = dyn_cast<BinaryOperator>(V))
  48     if (I->isLogicalShift() &&
  49         isPowerOfTwo(I->getOperand(0), IC.getTargetData())) {
  50       // We know that this is an exact/nuw shift and that the input is a
  51       // non-zero context as well.
  52       if (Value *V2 = simplifyValueKnownNonZero(I->getOperand(0), IC)) {
  53         I->setOperand(0, V2);
  54         MadeChange = true;
  55       }
  56
  57       if (I->getOpcode() == Instruction::LShr && !I->isExact()) {
  58         I->setIsExact();
  59         MadeChange = true;
  60       }
  61
  62       if (I->getOpcode() == Instruction::Shl && !I->hasNoUnsignedWrap()) {
  63         I->setHasNoUnsignedWrap();
  64         MadeChange = true;
  65       }
  66     }
  67
  68   // TODO: Lots more we could do here:
  69   //    If V is a phi node, we can call this on each of its operands.
  70   //    "select cond, X, 0" can simplify to "X".
  71
  72   return MadeChange ? V : 0;
  73 }
  74
  75
  76 /// MultiplyOverflows - True if the multiply can not be expressed in an int
  77 /// this size.
  78 static bool MultiplyOverflows(ConstantInt *C1, ConstantInt *C2, bool sign) {
  79   uint32_t W = C1->getBitWidth();
  80   APInt LHSExt = C1->getValue(), RHSExt = C2->getValue();
  81   if (sign) {
  82     LHSExt = LHSExt.sext(W * 2);
  83     RHSExt = RHSExt.sext(W * 2);
  84   } else {
  85     LHSExt = LHSExt.zext(W * 2);
  86     RHSExt = RHSExt.zext(W * 2);
  87   }
  88
  89   APInt MulExt = LHSExt * RHSExt;
  90
  91   if (!sign)
  92     return MulExt.ugt(APInt::getLowBitsSet(W * 2, W));
  93
  94   APInt Min = APInt::getSignedMinValue(W).sext(W * 2);
  95   APInt Max = APInt::getSignedMaxValue(W).sext(W * 2);
  96   return MulExt.slt(Min) || MulExt.sgt(Max);
  97 }
  98
  99 Instruction *InstCombiner::visitMul(BinaryOperator &I) {
 100   bool Changed = SimplifyAssociativeOrCommutative(I);
 101   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 102
 103   if (Value *V = SimplifyMulInst(Op0, Op1, TD))
 104     return ReplaceInstUsesWith(I, V);
 105
 106   if (Value *V = SimplifyUsingDistributiveLaws(I))
 107     return ReplaceInstUsesWith(I, V);
 108
 109   if (match(Op1, m_AllOnes()))  // X * -1 == 0 - X
 110     return BinaryOperator::CreateNeg(Op0, I.getName());
 111
 112   if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
 113
 114     // ((X << C1)*C2) == (X * (C2 << C1))
 115     if (BinaryOperator *SI = dyn_cast<BinaryOperator>(Op0))
 116       if (SI->getOpcode() == Instruction::Shl)
 117         if (Constant *ShOp = dyn_cast<Constant>(SI->getOperand(1)))
 118           return BinaryOperator::CreateMul(SI->getOperand(0),
 119                                            ConstantExpr::getShl(CI, ShOp));
 120
 121     const APInt &Val = CI->getValue();
 122     if (Val.isPowerOf2()) {          // Replace X*(2^C) with X << C
 123       Constant *NewCst = ConstantInt::get(Op0->getType(), Val.logBase2());
 124       BinaryOperator *Shl = BinaryOperator::CreateShl(Op0, NewCst);
 125       if (I.hasNoSignedWrap()) Shl->setHasNoSignedWrap();
 126       if (I.hasNoUnsignedWrap()) Shl->setHasNoUnsignedWrap();
 127       return Shl;
 128     }
 129
 130     // Canonicalize (X+C1)*CI -> X*CI+C1*CI.
 131     { Value *X; ConstantInt *C1;
 132       if (Op0->hasOneUse() &&
 133           match(Op0, m_Add(m_Value(X), m_ConstantInt(C1)))) {
 134         Value *Add = Builder->CreateMul(X, CI, "tmp");
 135         return BinaryOperator::CreateAdd(Add, Builder->CreateMul(C1, CI));
 136       }
 137     }
 138
 139     // (Y - X) * (-(2**n)) -> (X - Y) * (2**n), for positive nonzero n
 140     // (Y + const) * (-(2**n)) -> (-constY) * (2**n), for positive nonzero n
 141     // The "* (2**n)" thus becomes a potential shifting opportunity.
 142     {
 143       const APInt &   Val = CI->getValue();
 144       const APInt &PosVal = Val.abs();
 145       if (Val.isNegative() && PosVal.isPowerOf2()) {
 146         Value *X = 0, *Y = 0;
 147         if (Op0->hasOneUse()) {
 148           ConstantInt *C1;
 149           Value *Sub = 0;
 150           if (match(Op0, m_Sub(m_Value(Y), m_Value(X))))
 151             Sub = Builder->CreateSub(X, Y, "suba");
 152           else if (match(Op0, m_Add(m_Value(Y), m_ConstantInt(C1))))
 153             Sub = Builder->CreateSub(Builder->CreateNeg(C1), Y, "subc");
 154           if (Sub)
 155             return
 156               BinaryOperator::CreateMul(Sub,
 157                                         ConstantInt::get(Y->getType(), PosVal));
 158         }
 159       }
 160     }
 161   }
 162
 163   // Simplify mul instructions with a constant RHS.
 164   if (isa<Constant>(Op1)) {
 165     // Try to fold constant mul into select arguments.
 166     if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
 167       if (Instruction *R = FoldOpIntoSelect(I, SI))
 168         return R;
 169
 170     if (isa<PHINode>(Op0))
 171       if (Instruction *NV = FoldOpIntoPhi(I))
 172         return NV;
 173   }
 174
 175   if (Value *Op0v = dyn_castNegVal(Op0))     // -X * -Y = X*Y
 176     if (Value *Op1v = dyn_castNegVal(Op1))
 177       return BinaryOperator::CreateMul(Op0v, Op1v);
 178
 179   // (X / Y) *  Y = X - (X % Y)
 180   // (X / Y) * -Y = (X % Y) - X
 181   {
 182     Value *Op1C = Op1;
 183     BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0);
 184     if (!BO ||
 185         (BO->getOpcode() != Instruction::UDiv &&
 186          BO->getOpcode() != Instruction::SDiv)) {
 187       Op1C = Op0;
 188       BO = dyn_cast<BinaryOperator>(Op1);
 189     }
 190     Value *Neg = dyn_castNegVal(Op1C);
 191     if (BO && BO->hasOneUse() &&
 192         (BO->getOperand(1) == Op1C || BO->getOperand(1) == Neg) &&
 193         (BO->getOpcode() == Instruction::UDiv ||
 194          BO->getOpcode() == Instruction::SDiv)) {
 195       Value *Op0BO = BO->getOperand(0), *Op1BO = BO->getOperand(1);
 196
 197       // If the division is exact, X % Y is zero, so we end up with X or -X.
 198       if (PossiblyExactOperator *SDiv = dyn_cast<PossiblyExactOperator>(BO))
 199         if (SDiv->isExact()) {
 200           if (Op1BO == Op1C)
 201             return ReplaceInstUsesWith(I, Op0BO);
 202           return BinaryOperator::CreateNeg(Op0BO);
 203         }
 204
 205       Value *Rem;
 206       if (BO->getOpcode() == Instruction::UDiv)
 207         Rem = Builder->CreateURem(Op0BO, Op1BO);
 208       else
 209         Rem = Builder->CreateSRem(Op0BO, Op1BO);
 210       Rem->takeName(BO);
 211
 212       if (Op1BO == Op1C)
 213         return BinaryOperator::CreateSub(Op0BO, Rem);
 214       return BinaryOperator::CreateSub(Rem, Op0BO);
 215     }
 216   }
 217
 218   /// i1 mul -> i1 and.
 219   if (I.getType()->isIntegerTy(1))
 220     return BinaryOperator::CreateAnd(Op0, Op1);
 221
 222   // X*(1 << Y) --> X << Y
 223   // (1 << Y)*X --> X << Y
 224   {
 225     Value *Y;
 226     if (match(Op0, m_Shl(m_One(), m_Value(Y))))
 227       return BinaryOperator::CreateShl(Op1, Y);
 228     if (match(Op1, m_Shl(m_One(), m_Value(Y))))
 229       return BinaryOperator::CreateShl(Op0, Y);
 230   }
 231
 232   // If one of the operands of the multiply is a cast from a boolean value, then
 233   // we know the bool is either zero or one, so this is a 'masking' multiply.
 234   //   X * Y (where Y is 0 or 1) -> X & (0-Y)
 235   if (!I.getType()->isVectorTy()) {
 236     // -2 is "-1 << 1" so it is all bits set except the low one.
 237     APInt Negative2(I.getType()->getPrimitiveSizeInBits(), (uint64_t)-2, true);
 238
 239     Value *BoolCast = 0, *OtherOp = 0;
 240     if (MaskedValueIsZero(Op0, Negative2))
 241       BoolCast = Op0, OtherOp = Op1;
 242     else if (MaskedValueIsZero(Op1, Negative2))
 243       BoolCast = Op1, OtherOp = Op0;
 244
 245     if (BoolCast) {
 246       Value *V = Builder->CreateSub(Constant::getNullValue(I.getType()),
 247                                     BoolCast, "tmp");
 248       return BinaryOperator::CreateAnd(V, OtherOp);
 249     }
 250   }
 251
 252   return Changed ? &I : 0;
 253 }
 254
 255 Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
 256   bool Changed = SimplifyAssociativeOrCommutative(I);
 257   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 258
 259   // Simplify mul instructions with a constant RHS...
 260   if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
 261     if (ConstantFP *Op1F = dyn_cast<ConstantFP>(Op1C)) {
 262       // "In IEEE floating point, x*1 is not equivalent to x for nans.  However,
 263       // ANSI says we can drop signals, so we can do this anyway." (from GCC)
 264       if (Op1F->isExactlyValue(1.0))
 265         return ReplaceInstUsesWith(I, Op0);  // Eliminate 'fmul double %X, 1.0'
 266     } else if (Op1C->getType()->isVectorTy()) {
 267       if (ConstantVector *Op1V = dyn_cast<ConstantVector>(Op1C)) {
 268         // As above, vector X*splat(1.0) -> X in all defined cases.
 269         if (Constant *Splat = Op1V->getSplatValue()) {
 270           if (ConstantFP *F = dyn_cast<ConstantFP>(Splat))
 271             if (F->isExactlyValue(1.0))
 272               return ReplaceInstUsesWith(I, Op0);
 273         }
 274       }
 275     }
 276
 277     // Try to fold constant mul into select arguments.
 278     if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
 279       if (Instruction *R = FoldOpIntoSelect(I, SI))
 280         return R;
 281
 282     if (isa<PHINode>(Op0))
 283       if (Instruction *NV = FoldOpIntoPhi(I))
 284         return NV;
 285   }
 286
 287   if (Value *Op0v = dyn_castFNegVal(Op0))     // -X * -Y = X*Y
 288     if (Value *Op1v = dyn_castFNegVal(Op1))
 289       return BinaryOperator::CreateFMul(Op0v, Op1v);
 290
 291   return Changed ? &I : 0;
 292 }
 293
 294 /// SimplifyDivRemOfSelect - Try to fold a divide or remainder of a select
 295 /// instruction.
 296 bool InstCombiner::SimplifyDivRemOfSelect(BinaryOperator &I) {
 297   SelectInst *SI = cast<SelectInst>(I.getOperand(1));
 298
 299   // div/rem X, (Cond ? 0 : Y) -> div/rem X, Y
 300   int NonNullOperand = -1;
 301   if (Constant *ST = dyn_cast<Constant>(SI->getOperand(1)))
 302     if (ST->isNullValue())
 303       NonNullOperand = 2;
 304   // div/rem X, (Cond ? Y : 0) -> div/rem X, Y
 305   if (Constant *ST = dyn_cast<Constant>(SI->getOperand(2)))
 306     if (ST->isNullValue())
 307       NonNullOperand = 1;
 308
 309   if (NonNullOperand == -1)
 310     return false;
 311
 312   Value *SelectCond = SI->getOperand(0);
 313
 314   // Change the div/rem to use 'Y' instead of the select.
 315   I.setOperand(1, SI->getOperand(NonNullOperand));
 316
 317   // Okay, we know we replace the operand of the div/rem with 'Y' with no
 318   // problem.  However, the select, or the condition of the select may have
 319   // multiple uses.  Based on our knowledge that the operand must be non-zero,
 320   // propagate the known value for the select into other uses of it, and
 321   // propagate a known value of the condition into its other users.
 322
 323   // If the select and condition only have a single use, don't bother with this,
 324   // early exit.
 325   if (SI->use_empty() && SelectCond->hasOneUse())
 326     return true;
 327
 328   // Scan the current block backward, looking for other uses of SI.
 329   BasicBlock::iterator BBI = &I, BBFront = I.getParent()->begin();
 330
 331   while (BBI != BBFront) {
 332     --BBI;
 333     // If we found a call to a function, we can't assume it will return, so
 334     // information from below it cannot be propagated above it.
 335     if (isa<CallInst>(BBI) && !isa<IntrinsicInst>(BBI))
 336       break;
 337
 338     // Replace uses of the select or its condition with the known values.
 339     for (Instruction::op_iterator I = BBI->op_begin(), E = BBI->op_end();
 340          I != E; ++I) {
 341       if (*I == SI) {
 342         *I = SI->getOperand(NonNullOperand);
 343         Worklist.Add(BBI);
 344       } else if (*I == SelectCond) {
 345         *I = NonNullOperand == 1 ? ConstantInt::getTrue(BBI->getContext()) :
 346                                    ConstantInt::getFalse(BBI->getContext());
 347         Worklist.Add(BBI);
 348       }
 349     }
 350
 351     // If we past the instruction, quit looking for it.
 352     if (&*BBI == SI)
 353       SI = 0;
 354     if (&*BBI == SelectCond)
 355       SelectCond = 0;
 356
 357     // If we ran out of things to eliminate, break out of the loop.
 358     if (SelectCond == 0 && SI == 0)
 359       break;
 360
 361   }
 362   return true;
 363 }
 364
 365
 366 /// This function implements the transforms common to both integer division
 367 /// instructions (udiv and sdiv). It is called by the visitors to those integer
 368 /// division instructions.
 369 /// @brief Common integer divide transforms
 370 Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) {
 371   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 372
 373   // The RHS is known non-zero.
 374   if (Value *V = simplifyValueKnownNonZero(I.getOperand(1), *this)) {
 375     I.setOperand(1, V);
 376     return &I;
 377   }
 378
 379   // Handle cases involving: [su]div X, (select Cond, Y, Z)
 380   // This does not apply for fdiv.
 381   if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
 382     return &I;
 383
 384   if (ConstantInt *RHS = dyn_cast<ConstantInt>(Op1)) {
 385     // (X / C1) / C2  -> X / (C1*C2)
 386     if (Instruction *LHS = dyn_cast<Instruction>(Op0))
 387       if (Instruction::BinaryOps(LHS->getOpcode()) == I.getOpcode())
 388         if (ConstantInt *LHSRHS = dyn_cast<ConstantInt>(LHS->getOperand(1))) {
 389           if (MultiplyOverflows(RHS, LHSRHS,
 390                                 I.getOpcode()==Instruction::SDiv))
 391             return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
 392           return BinaryOperator::Create(I.getOpcode(), LHS->getOperand(0),
 393                                         ConstantExpr::getMul(RHS, LHSRHS));
 394         }
 395
 396     if (!RHS->isZero()) { // avoid X udiv 0
 397       if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
 398         if (Instruction *R = FoldOpIntoSelect(I, SI))
 399           return R;
 400       if (isa<PHINode>(Op0))
 401         if (Instruction *NV = FoldOpIntoPhi(I))
 402           return NV;
 403     }
 404   }
 405
 406   // See if we can fold away this div instruction.
 407   if (SimplifyDemandedInstructionBits(I))
 408     return &I;
 409
 410   // (X - (X rem Y)) / Y -> X / Y; usually originates as ((X / Y) * Y) / Y
 411   Value *X = 0, *Z = 0;
 412   if (match(Op0, m_Sub(m_Value(X), m_Value(Z)))) { // (X - Z) / Y; Y = Op1
 413     bool isSigned = I.getOpcode() == Instruction::SDiv;
 414     if ((isSigned && match(Z, m_SRem(m_Specific(X), m_Specific(Op1)))) ||
 415         (!isSigned && match(Z, m_URem(m_Specific(X), m_Specific(Op1)))))
 416       return BinaryOperator::Create(I.getOpcode(), X, Op1);
 417   }
 418
 419   return 0;
 420 }
 421
 422 /// dyn_castZExtVal - Checks if V is a zext or constant that can
 423 /// be truncated to Ty without losing bits.
 424 static Value *dyn_castZExtVal(Value *V, const Type *Ty) {
 425   if (ZExtInst *Z = dyn_cast<ZExtInst>(V)) {
 426     if (Z->getSrcTy() == Ty)
 427       return Z->getOperand(0);
 428   } else if (ConstantInt *C = dyn_cast<ConstantInt>(V)) {
 429     if (C->getValue().getActiveBits() <= cast<IntegerType>(Ty)->getBitWidth())
 430       return ConstantExpr::getTrunc(C, Ty);
 431   }
 432   return 0;
 433 }
 434
 435 Instruction *InstCombiner::visitUDiv(BinaryOperator &I) {
 436   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 437
 438   if (Value *V = SimplifyUDivInst(Op0, Op1, TD))
 439     return ReplaceInstUsesWith(I, V);
 440
 441   // Handle the integer div common cases
 442   if (Instruction *Common = commonIDivTransforms(I))
 443     return Common;
 444
 445   if (ConstantInt *C = dyn_cast<ConstantInt>(Op1)) {
 446     // X udiv 2^C -> X >> C
 447     // Check to see if this is an unsigned division with an exact power of 2,
 448     // if so, convert to a right shift.
 449     if (C->getValue().isPowerOf2()) { // 0 not included in isPowerOf2
 450       BinaryOperator *LShr =
 451         BinaryOperator::CreateLShr(Op0,
 452             ConstantInt::get(Op0->getType(), C->getValue().logBase2()));
 453       if (I.isExact()) LShr->setIsExact();
 454       return LShr;
 455     }
 456
 457     // X udiv C, where C >= signbit
 458     if (C->getValue().isNegative()) {
 459       Value *IC = Builder->CreateICmpULT(Op0, C);
 460       return SelectInst::Create(IC, Constant::getNullValue(I.getType()),
 461                                 ConstantInt::get(I.getType(), 1));
 462     }
 463   }
 464
 465   // X udiv (C1 << N), where C1 is "1<<C2"  -->  X >> (N+C2)
 466   { const APInt *CI; Value *N;
 467     if (match(Op1, m_Shl(m_Power2(CI), m_Value(N)))) {
 468       if (*CI != 1)
 469         N = Builder->CreateAdd(N, ConstantInt::get(I.getType(), CI->logBase2()),
 470                                "tmp");
 471       if (I.isExact())
 472         return BinaryOperator::CreateExactLShr(Op0, N);
 473       return BinaryOperator::CreateLShr(Op0, N);
 474     }
 475   }
 476
 477   // udiv X, (Select Cond, C1, C2) --> Select Cond, (shr X, C1), (shr X, C2)
 478   // where C1&C2 are powers of two.
 479   { Value *Cond; const APInt *C1, *C2;
 480     if (match(Op1, m_Select(m_Value(Cond), m_Power2(C1), m_Power2(C2)))) {
 481       // Construct the "on true" case of the select
 482       Value *TSI = Builder->CreateLShr(Op0, C1->logBase2(), Op1->getName()+".t",
 483                                        I.isExact());
 484
 485       // Construct the "on false" case of the select
 486       Value *FSI = Builder->CreateLShr(Op0, C2->logBase2(), Op1->getName()+".f",
 487                                        I.isExact());
 488
 489       // construct the select instruction and return it.
 490       return SelectInst::Create(Cond, TSI, FSI);
 491     }
 492   }
 493
 494   // (zext A) udiv (zext B) --> zext (A udiv B)
 495   if (ZExtInst *ZOp0 = dyn_cast<ZExtInst>(Op0))
 496     if (Value *ZOp1 = dyn_castZExtVal(Op1, ZOp0->getSrcTy()))
 497       return new ZExtInst(Builder->CreateUDiv(ZOp0->getOperand(0), ZOp1, "div",
 498                                               I.isExact()),
 499                           I.getType());
 500
 501   return 0;
 502 }
 503
 504 Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
 505   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 506
 507   if (Value *V = SimplifySDivInst(Op0, Op1, TD))
 508     return ReplaceInstUsesWith(I, V);
 509
 510   // Handle the integer div common cases
 511   if (Instruction *Common = commonIDivTransforms(I))
 512     return Common;
 513
 514   if (ConstantInt *RHS = dyn_cast<ConstantInt>(Op1)) {
 515     // sdiv X, -1 == -X
 516     if (RHS->isAllOnesValue())
 517       return BinaryOperator::CreateNeg(Op0);
 518
 519     // sdiv X, C  -->  ashr exact X, log2(C)
 520     if (I.isExact() && RHS->getValue().isNonNegative() &&
 521         RHS->getValue().isPowerOf2()) {
 522       Value *ShAmt = llvm::ConstantInt::get(RHS->getType(),
 523                                             RHS->getValue().exactLogBase2());
 524       return BinaryOperator::CreateExactAShr(Op0, ShAmt, I.getName());
 525     }
 526
 527     // -X/C  -->  X/-C  provided the negation doesn't overflow.
 528     if (SubOperator *Sub = dyn_cast<SubOperator>(Op0))
 529       if (match(Sub->getOperand(0), m_Zero()) && Sub->hasNoSignedWrap())
 530         return BinaryOperator::CreateSDiv(Sub->getOperand(1),
 531                                           ConstantExpr::getNeg(RHS));
 532   }
 533
 534   // If the sign bits of both operands are zero (i.e. we can prove they are
 535   // unsigned inputs), turn this into a udiv.
 536   if (I.getType()->isIntegerTy()) {
 537     APInt Mask(APInt::getSignBit(I.getType()->getPrimitiveSizeInBits()));
 538     if (MaskedValueIsZero(Op0, Mask)) {
 539       if (MaskedValueIsZero(Op1, Mask)) {
 540         // X sdiv Y -> X udiv Y, iff X and Y don't have sign bit set
 541         return BinaryOperator::CreateUDiv(Op0, Op1, I.getName());
 542       }
 543
 544       if (match(Op1, m_Shl(m_Power2(), m_Value()))) {
 545         // X sdiv (1 << Y) -> X udiv (1 << Y) ( -> X u>> Y)
 546         // Safe because the only negative value (1 << Y) can take on is
 547         // INT_MIN, and X sdiv INT_MIN == X udiv INT_MIN == 0 if X doesn't have
 548         // the sign bit set.
 549         return BinaryOperator::CreateUDiv(Op0, Op1, I.getName());
 550       }
 551     }
 552   }
 553
 554   return 0;
 555 }
 556
 557 Instruction *InstCombiner::visitFDiv(BinaryOperator &I) {
 558   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 559
 560   if (Value *V = SimplifyFDivInst(Op0, Op1, TD))
 561     return ReplaceInstUsesWith(I, V);
 562
 563   if (ConstantFP *Op1C = dyn_cast<ConstantFP>(Op1)) {
 564     const APFloat &Op1F = Op1C->getValueAPF();
 565
 566     // If the divisor has an exact multiplicative inverse we can turn the fdiv
 567     // into a cheaper fmul.
 568     APFloat Reciprocal(Op1F.getSemantics());
 569     if (Op1F.getExactInverse(&Reciprocal)) {
 570       ConstantFP *RFP = ConstantFP::get(Builder->getContext(), Reciprocal);
 571       return BinaryOperator::CreateFMul(Op0, RFP);
 572     }
 573   }
 574
 575   return 0;
 576 }
 577
 578 /// This function implements the transforms common to both integer remainder
 579 /// instructions (urem and srem). It is called by the visitors to those integer
 580 /// remainder instructions.
 581 /// @brief Common integer remainder transforms
 582 Instruction *InstCombiner::commonIRemTransforms(BinaryOperator &I) {
 583   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 584
 585   // The RHS is known non-zero.
 586   if (Value *V = simplifyValueKnownNonZero(I.getOperand(1), *this)) {
 587     I.setOperand(1, V);
 588     return &I;
 589   }
 590
 591   // Handle cases involving: rem X, (select Cond, Y, Z)
 592   if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
 593     return &I;
 594
 595   if (isa<ConstantInt>(Op1)) {
 596     if (Instruction *Op0I = dyn_cast<Instruction>(Op0)) {
 597       if (SelectInst *SI = dyn_cast<SelectInst>(Op0I)) {
 598         if (Instruction *R = FoldOpIntoSelect(I, SI))
 599           return R;
 600       } else if (isa<PHINode>(Op0I)) {
 601         if (Instruction *NV = FoldOpIntoPhi(I))
 602           return NV;
 603       }
 604
 605       // See if we can fold away this rem instruction.
 606       if (SimplifyDemandedInstructionBits(I))
 607         return &I;
 608     }
 609   }
 610
 611   return 0;
 612 }
 613
 614 Instruction *InstCombiner::visitURem(BinaryOperator &I) {
 615   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 616
 617   if (Value *V = SimplifyURemInst(Op0, Op1, TD))
 618     return ReplaceInstUsesWith(I, V);
 619
 620   if (Instruction *common = commonIRemTransforms(I))
 621     return common;
 622
 623   // X urem C^2 -> X and C-1
 624   { const APInt *C;
 625     if (match(Op1, m_Power2(C)))
 626       return BinaryOperator::CreateAnd(Op0,
 627                                        ConstantInt::get(I.getType(), *C-1));
 628   }
 629
 630   // Turn A % (C << N), where C is 2^k, into A & ((C << N)-1)
 631   if (match(Op1, m_Shl(m_Power2(), m_Value()))) {
 632     Constant *N1 = Constant::getAllOnesValue(I.getType());
 633     Value *Add = Builder->CreateAdd(Op1, N1, "tmp");
 634     return BinaryOperator::CreateAnd(Op0, Add);
 635   }
 636
 637   // urem X, (select Cond, 2^C1, 2^C2) -->
 638   //    select Cond, (and X, C1-1), (and X, C2-1)
 639   // when C1&C2 are powers of two.
 640   { Value *Cond; const APInt *C1, *C2;
 641     if (match(Op1, m_Select(m_Value(Cond), m_Power2(C1), m_Power2(C2)))) {
 642       Value *TrueAnd = Builder->CreateAnd(Op0, *C1-1, Op1->getName()+".t");
 643       Value *FalseAnd = Builder->CreateAnd(Op0, *C2-1, Op1->getName()+".f");
 644       return SelectInst::Create(Cond, TrueAnd, FalseAnd);
 645     }
 646   }
 647
 648   // (zext A) urem (zext B) --> zext (A urem B)
 649   if (ZExtInst *ZOp0 = dyn_cast<ZExtInst>(Op0))
 650     if (Value *ZOp1 = dyn_castZExtVal(Op1, ZOp0->getSrcTy()))
 651       return new ZExtInst(Builder->CreateURem(ZOp0->getOperand(0), ZOp1),
 652                           I.getType());
 653
 654   return 0;
 655 }
 656
 657 Instruction *InstCombiner::visitSRem(BinaryOperator &I) {
 658   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 659
 660   if (Value *V = SimplifySRemInst(Op0, Op1, TD))
 661     return ReplaceInstUsesWith(I, V);
 662
 663   // Handle the integer rem common cases
 664   if (Instruction *Common = commonIRemTransforms(I))
 665     return Common;
 666
 667   if (Value *RHSNeg = dyn_castNegVal(Op1))
 668     if (!isa<Constant>(RHSNeg) ||
 669         (isa<ConstantInt>(RHSNeg) &&
 670          cast<ConstantInt>(RHSNeg)->getValue().isStrictlyPositive())) {
 671       // X % -Y -> X % Y
 672       Worklist.AddValue(I.getOperand(1));
 673       I.setOperand(1, RHSNeg);
 674       return &I;
 675     }
 676
 677   // If the sign bits of both operands are zero (i.e. we can prove they are
 678   // unsigned inputs), turn this into a urem.
 679   if (I.getType()->isIntegerTy()) {
 680     APInt Mask(APInt::getSignBit(I.getType()->getPrimitiveSizeInBits()));
 681     if (MaskedValueIsZero(Op1, Mask) && MaskedValueIsZero(Op0, Mask)) {
 682       // X srem Y -> X urem Y, iff X and Y don't have sign bit set
 683       return BinaryOperator::CreateURem(Op0, Op1, I.getName());
 684     }
 685   }
 686
 687   // If it's a constant vector, flip any negative values positive.
 688   if (ConstantVector *RHSV = dyn_cast<ConstantVector>(Op1)) {
 689     unsigned VWidth = RHSV->getNumOperands();
 690
 691     bool hasNegative = false;
 692     for (unsigned i = 0; !hasNegative && i != VWidth; ++i)
 693       if (ConstantInt *RHS = dyn_cast<ConstantInt>(RHSV->getOperand(i)))
 694         if (RHS->getValue().isNegative())
 695           hasNegative = true;
 696
 697     if (hasNegative) {
 698       std::vector<Constant *> Elts(VWidth);
 699       for (unsigned i = 0; i != VWidth; ++i) {
 700         if (ConstantInt *RHS = dyn_cast<ConstantInt>(RHSV->getOperand(i))) {
 701           if (RHS->getValue().isNegative())
 702             Elts[i] = cast<ConstantInt>(ConstantExpr::getNeg(RHS));
 703           else
 704             Elts[i] = RHS;
 705         }
 706       }
 707
 708       Constant *NewRHSV = ConstantVector::get(Elts);
 709       if (NewRHSV != RHSV) {
 710         Worklist.AddValue(I.getOperand(1));
 711         I.setOperand(1, NewRHSV);
 712         return &I;
 713       }
 714     }
 715   }
 716
 717   return 0;
 718 }
 719
 720 Instruction *InstCombiner::visitFRem(BinaryOperator &I) {
 721   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 722
 723   if (Value *V = SimplifyFRemInst(Op0, Op1, TD))
 724     return ReplaceInstUsesWith(I, V);
 725
 726   // Handle cases involving: rem X, (select Cond, Y, Z)
 727   if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
 728     return &I;
 729
 730   return 0;
 731 }