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