lib/Transforms/InstCombine/InstCombineAddSub.cpp

   1 //===- InstCombineAddSub.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 add, fadd, sub, and fsub.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "InstCombine.h"
  15 #include "llvm/Analysis/InstructionSimplify.h"
  16 #include "llvm/Target/TargetData.h"
  17 #include "llvm/Support/GetElementPtrTypeIterator.h"
  18 #include "llvm/Support/PatternMatch.h"
  19 using namespace llvm;
  20 using namespace PatternMatch;
  21
  22 /// AddOne - Add one to a ConstantInt.
  23 static Constant *AddOne(Constant *C) {
  24   return ConstantExpr::getAdd(C, ConstantInt::get(C->getType(), 1));
  25 }
  26 /// SubOne - Subtract one from a ConstantInt.
  27 static Constant *SubOne(ConstantInt *C) {
  28   return ConstantInt::get(C->getContext(), C->getValue()-1);
  29 }
  30
  31
  32 // dyn_castFoldableMul - If this value is a multiply that can be folded into
  33 // other computations (because it has a constant operand), return the
  34 // non-constant operand of the multiply, and set CST to point to the multiplier.
  35 // Otherwise, return null.
  36 //
  37 static inline Value *dyn_castFoldableMul(Value *V, ConstantInt *&CST) {
  38   if (!V->hasOneUse() || !V->getType()->isIntegerTy())
  39     return 0;
  40
  41   Instruction *I = dyn_cast<Instruction>(V);
  42   if (I == 0) return 0;
  43
  44   if (I->getOpcode() == Instruction::Mul)
  45     if ((CST = dyn_cast<ConstantInt>(I->getOperand(1))))
  46       return I->getOperand(0);
  47   if (I->getOpcode() == Instruction::Shl)
  48     if ((CST = dyn_cast<ConstantInt>(I->getOperand(1)))) {
  49       // The multiplier is really 1 << CST.
  50       uint32_t BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
  51       uint32_t CSTVal = CST->getLimitedValue(BitWidth);
  52       CST = ConstantInt::get(V->getType()->getContext(),
  53                              APInt(BitWidth, 1).shl(CSTVal));
  54       return I->getOperand(0);
  55     }
  56   return 0;
  57 }
  58
  59
  60 /// WillNotOverflowSignedAdd - Return true if we can prove that:
  61 ///    (sext (add LHS, RHS))  === (add (sext LHS), (sext RHS))
  62 /// This basically requires proving that the add in the original type would not
  63 /// overflow to change the sign bit or have a carry out.
  64 bool InstCombiner::WillNotOverflowSignedAdd(Value *LHS, Value *RHS) {
  65   // There are different heuristics we can use for this.  Here are some simple
  66   // ones.
  67
  68   // Add has the property that adding any two 2's complement numbers can only
  69   // have one carry bit which can change a sign.  As such, if LHS and RHS each
  70   // have at least two sign bits, we know that the addition of the two values
  71   // will sign extend fine.
  72   if (ComputeNumSignBits(LHS) > 1 && ComputeNumSignBits(RHS) > 1)
  73     return true;
  74
  75
  76   // If one of the operands only has one non-zero bit, and if the other operand
  77   // has a known-zero bit in a more significant place than it (not including the
  78   // sign bit) the ripple may go up to and fill the zero, but won't change the
  79   // sign.  For example, (X & ~4) + 1.
  80
  81   // TODO: Implement.
  82
  83   return false;
  84 }
  85
  86 Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
  87   bool Changed = SimplifyAssociativeOrCommutative(I);
  88   Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
  89
  90   if (Value *V = SimplifyAddInst(LHS, RHS, I.hasNoSignedWrap(),
  91                                  I.hasNoUnsignedWrap(), TD))
  92     return ReplaceInstUsesWith(I, V);
  93
  94   // (A*B)+(A*C) -> A*(B+C) etc
  95   if (Value *V = SimplifyUsingDistributiveLaws(I))
  96     return ReplaceInstUsesWith(I, V);
  97
  98   if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
  99     // X + (signbit) --> X ^ signbit
 100     const APInt &Val = CI->getValue();
 101     if (Val.isSignBit())
 102       return BinaryOperator::CreateXor(LHS, RHS);
 103
 104     // See if SimplifyDemandedBits can simplify this.  This handles stuff like
 105     // (X & 254)+1 -> (X&254)|1
 106     if (SimplifyDemandedInstructionBits(I))
 107       return &I;
 108
 109     // zext(bool) + C -> bool ? C + 1 : C
 110     if (ZExtInst *ZI = dyn_cast<ZExtInst>(LHS))
 111       if (ZI->getSrcTy()->isIntegerTy(1))
 112         return SelectInst::Create(ZI->getOperand(0), AddOne(CI), CI);
 113
 114     Value *XorLHS = 0; ConstantInt *XorRHS = 0;
 115     if (match(LHS, m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS)))) {
 116       uint32_t TySizeBits = I.getType()->getScalarSizeInBits();
 117       const APInt &RHSVal = CI->getValue();
 118       unsigned ExtendAmt = 0;
 119       // If we have ADD(XOR(AND(X, 0xFF), 0x80), 0xF..F80), it's a sext.
 120       // If we have ADD(XOR(AND(X, 0xFF), 0xF..F80), 0x80), it's a sext.
 121       if (XorRHS->getValue() == -RHSVal) {
 122         if (RHSVal.isPowerOf2())
 123           ExtendAmt = TySizeBits - RHSVal.logBase2() - 1;
 124         else if (XorRHS->getValue().isPowerOf2())
 125           ExtendAmt = TySizeBits - XorRHS->getValue().logBase2() - 1;
 126       }
 127
 128       if (ExtendAmt) {
 129         APInt Mask = APInt::getHighBitsSet(TySizeBits, ExtendAmt);
 130         if (!MaskedValueIsZero(XorLHS, Mask))
 131           ExtendAmt = 0;
 132       }
 133
 134       if (ExtendAmt) {
 135         Constant *ShAmt = ConstantInt::get(I.getType(), ExtendAmt);
 136         Value *NewShl = Builder->CreateShl(XorLHS, ShAmt, "sext");
 137         return BinaryOperator::CreateAShr(NewShl, ShAmt);
 138       }
 139     }
 140   }
 141
 142   if (isa<Constant>(RHS) && isa<PHINode>(LHS))
 143     if (Instruction *NV = FoldOpIntoPhi(I))
 144       return NV;
 145
 146   if (I.getType()->isIntegerTy(1))
 147     return BinaryOperator::CreateXor(LHS, RHS);
 148
 149   // X + X --> X << 1
 150   if (LHS == RHS) {
 151     BinaryOperator *New =
 152       BinaryOperator::CreateShl(LHS, ConstantInt::get(I.getType(), 1));
 153     New->setHasNoSignedWrap(I.hasNoSignedWrap());
 154     New->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
 155     return New;
 156   }
 157
 158   // -A + B  -->  B - A
 159   // -A + -B  -->  -(A + B)
 160   if (Value *LHSV = dyn_castNegVal(LHS)) {
 161     if (Value *RHSV = dyn_castNegVal(RHS)) {
 162       Value *NewAdd = Builder->CreateAdd(LHSV, RHSV, "sum");
 163       return BinaryOperator::CreateNeg(NewAdd);
 164     }
 165
 166     return BinaryOperator::CreateSub(RHS, LHSV);
 167   }
 168
 169   // A + -B  -->  A - B
 170   if (!isa<Constant>(RHS))
 171     if (Value *V = dyn_castNegVal(RHS))
 172       return BinaryOperator::CreateSub(LHS, V);
 173
 174
 175   ConstantInt *C2;
 176   if (Value *X = dyn_castFoldableMul(LHS, C2)) {
 177     if (X == RHS)   // X*C + X --> X * (C+1)
 178       return BinaryOperator::CreateMul(RHS, AddOne(C2));
 179
 180     // X*C1 + X*C2 --> X * (C1+C2)
 181     ConstantInt *C1;
 182     if (X == dyn_castFoldableMul(RHS, C1))
 183       return BinaryOperator::CreateMul(X, ConstantExpr::getAdd(C1, C2));
 184   }
 185
 186   // X + X*C --> X * (C+1)
 187   if (dyn_castFoldableMul(RHS, C2) == LHS)
 188     return BinaryOperator::CreateMul(LHS, AddOne(C2));
 189
 190   // A+B --> A|B iff A and B have no bits set in common.
 191   if (const IntegerType *IT = dyn_cast<IntegerType>(I.getType())) {
 192     APInt Mask = APInt::getAllOnesValue(IT->getBitWidth());
 193     APInt LHSKnownOne(IT->getBitWidth(), 0);
 194     APInt LHSKnownZero(IT->getBitWidth(), 0);
 195     ComputeMaskedBits(LHS, Mask, LHSKnownZero, LHSKnownOne);
 196     if (LHSKnownZero != 0) {
 197       APInt RHSKnownOne(IT->getBitWidth(), 0);
 198       APInt RHSKnownZero(IT->getBitWidth(), 0);
 199       ComputeMaskedBits(RHS, Mask, RHSKnownZero, RHSKnownOne);
 200
 201       // No bits in common -> bitwise or.
 202       if ((LHSKnownZero|RHSKnownZero).isAllOnesValue())
 203         return BinaryOperator::CreateOr(LHS, RHS);
 204     }
 205   }
 206
 207   // W*X + Y*Z --> W * (X+Z)  iff W == Y
 208   {
 209     Value *W, *X, *Y, *Z;
 210     if (match(LHS, m_Mul(m_Value(W), m_Value(X))) &&
 211         match(RHS, m_Mul(m_Value(Y), m_Value(Z)))) {
 212       if (W != Y) {
 213         if (W == Z) {
 214           std::swap(Y, Z);
 215         } else if (Y == X) {
 216           std::swap(W, X);
 217         } else if (X == Z) {
 218           std::swap(Y, Z);
 219           std::swap(W, X);
 220         }
 221       }
 222
 223       if (W == Y) {
 224         Value *NewAdd = Builder->CreateAdd(X, Z, LHS->getName());
 225         return BinaryOperator::CreateMul(W, NewAdd);
 226       }
 227     }
 228   }
 229
 230   if (ConstantInt *CRHS = dyn_cast<ConstantInt>(RHS)) {
 231     Value *X = 0;
 232     if (match(LHS, m_Not(m_Value(X))))    // ~X + C --> (C-1) - X
 233       return BinaryOperator::CreateSub(SubOne(CRHS), X);
 234
 235     // (X & FF00) + xx00  -> (X+xx00) & FF00
 236     if (LHS->hasOneUse() &&
 237         match(LHS, m_And(m_Value(X), m_ConstantInt(C2))) &&
 238         CRHS->getValue() == (CRHS->getValue() & C2->getValue())) {
 239       // See if all bits from the first bit set in the Add RHS up are included
 240       // in the mask.  First, get the rightmost bit.
 241       const APInt &AddRHSV = CRHS->getValue();
 242
 243       // Form a mask of all bits from the lowest bit added through the top.
 244       APInt AddRHSHighBits(~((AddRHSV & -AddRHSV)-1));
 245
 246       // See if the and mask includes all of these bits.
 247       APInt AddRHSHighBitsAnd(AddRHSHighBits & C2->getValue());
 248
 249       if (AddRHSHighBits == AddRHSHighBitsAnd) {
 250         // Okay, the xform is safe.  Insert the new add pronto.
 251         Value *NewAdd = Builder->CreateAdd(X, CRHS, LHS->getName());
 252         return BinaryOperator::CreateAnd(NewAdd, C2);
 253       }
 254     }
 255
 256     // Try to fold constant add into select arguments.
 257     if (SelectInst *SI = dyn_cast<SelectInst>(LHS))
 258       if (Instruction *R = FoldOpIntoSelect(I, SI))
 259         return R;
 260   }
 261
 262   // add (select X 0 (sub n A)) A  -->  select X A n
 263   {
 264     SelectInst *SI = dyn_cast<SelectInst>(LHS);
 265     Value *A = RHS;
 266     if (!SI) {
 267       SI = dyn_cast<SelectInst>(RHS);
 268       A = LHS;
 269     }
 270     if (SI && SI->hasOneUse()) {
 271       Value *TV = SI->getTrueValue();
 272       Value *FV = SI->getFalseValue();
 273       Value *N;
 274
 275       // Can we fold the add into the argument of the select?
 276       // We check both true and false select arguments for a matching subtract.
 277       if (match(FV, m_Zero()) && match(TV, m_Sub(m_Value(N), m_Specific(A))))
 278         // Fold the add into the true select value.
 279         return SelectInst::Create(SI->getCondition(), N, A);
 280
 281       if (match(TV, m_Zero()) && match(FV, m_Sub(m_Value(N), m_Specific(A))))
 282         // Fold the add into the false select value.
 283         return SelectInst::Create(SI->getCondition(), A, N);
 284     }
 285   }
 286
 287   // Check for (add (sext x), y), see if we can merge this into an
 288   // integer add followed by a sext.
 289   if (SExtInst *LHSConv = dyn_cast<SExtInst>(LHS)) {
 290     // (add (sext x), cst) --> (sext (add x, cst'))
 291     if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS)) {
 292       Constant *CI =
 293         ConstantExpr::getTrunc(RHSC, LHSConv->getOperand(0)->getType());
 294       if (LHSConv->hasOneUse() &&
 295           ConstantExpr::getSExt(CI, I.getType()) == RHSC &&
 296           WillNotOverflowSignedAdd(LHSConv->getOperand(0), CI)) {
 297         // Insert the new, smaller add.
 298         Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0),
 299                                               CI, "addconv");
 300         return new SExtInst(NewAdd, I.getType());
 301       }
 302     }
 303
 304     // (add (sext x), (sext y)) --> (sext (add int x, y))
 305     if (SExtInst *RHSConv = dyn_cast<SExtInst>(RHS)) {
 306       // Only do this if x/y have the same type, if at last one of them has a
 307       // single use (so we don't increase the number of sexts), and if the
 308       // integer add will not overflow.
 309       if (LHSConv->getOperand(0)->getType()==RHSConv->getOperand(0)->getType()&&
 310           (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
 311           WillNotOverflowSignedAdd(LHSConv->getOperand(0),
 312                                    RHSConv->getOperand(0))) {
 313         // Insert the new integer add.
 314         Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0),
 315                                              RHSConv->getOperand(0), "addconv");
 316         return new SExtInst(NewAdd, I.getType());
 317       }
 318     }
 319   }
 320
 321   return Changed ? &I : 0;
 322 }
 323
 324 Instruction *InstCombiner::visitFAdd(BinaryOperator &I) {
 325   bool Changed = SimplifyAssociativeOrCommutative(I);
 326   Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
 327
 328   if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
 329     // X + 0 --> X
 330     if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
 331       if (CFP->isExactlyValue(ConstantFP::getNegativeZero
 332                               (I.getType())->getValueAPF()))
 333         return ReplaceInstUsesWith(I, LHS);
 334     }
 335
 336     if (isa<PHINode>(LHS))
 337       if (Instruction *NV = FoldOpIntoPhi(I))
 338         return NV;
 339   }
 340
 341   // -A + B  -->  B - A
 342   // -A + -B  -->  -(A + B)
 343   if (Value *LHSV = dyn_castFNegVal(LHS))
 344     return BinaryOperator::CreateFSub(RHS, LHSV);
 345
 346   // A + -B  -->  A - B
 347   if (!isa<Constant>(RHS))
 348     if (Value *V = dyn_castFNegVal(RHS))
 349       return BinaryOperator::CreateFSub(LHS, V);
 350
 351   // Check for X+0.0.  Simplify it to X if we know X is not -0.0.
 352   if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHS))
 353     if (CFP->getValueAPF().isPosZero() && CannotBeNegativeZero(LHS))
 354       return ReplaceInstUsesWith(I, LHS);
 355
 356   // Check for (fadd double (sitofp x), y), see if we can merge this into an
 357   // integer add followed by a promotion.
 358   if (SIToFPInst *LHSConv = dyn_cast<SIToFPInst>(LHS)) {
 359     // (fadd double (sitofp x), fpcst) --> (sitofp (add int x, intcst))
 360     // ... if the constant fits in the integer value.  This is useful for things
 361     // like (double)(x & 1234) + 4.0 -> (double)((X & 1234)+4) which no longer
 362     // requires a constant pool load, and generally allows the add to be better
 363     // instcombined.
 364     if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHS)) {
 365       Constant *CI =
 366       ConstantExpr::getFPToSI(CFP, LHSConv->getOperand(0)->getType());
 367       if (LHSConv->hasOneUse() &&
 368           ConstantExpr::getSIToFP(CI, I.getType()) == CFP &&
 369           WillNotOverflowSignedAdd(LHSConv->getOperand(0), CI)) {
 370         // Insert the new integer add.
 371         Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0),
 372                                               CI, "addconv");
 373         return new SIToFPInst(NewAdd, I.getType());
 374       }
 375     }
 376
 377     // (fadd double (sitofp x), (sitofp y)) --> (sitofp (add int x, y))
 378     if (SIToFPInst *RHSConv = dyn_cast<SIToFPInst>(RHS)) {
 379       // Only do this if x/y have the same type, if at last one of them has a
 380       // single use (so we don't increase the number of int->fp conversions),
 381       // and if the integer add will not overflow.
 382       if (LHSConv->getOperand(0)->getType()==RHSConv->getOperand(0)->getType()&&
 383           (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
 384           WillNotOverflowSignedAdd(LHSConv->getOperand(0),
 385                                    RHSConv->getOperand(0))) {
 386         // Insert the new integer add.
 387         Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0),
 388                                               RHSConv->getOperand(0),"addconv");
 389         return new SIToFPInst(NewAdd, I.getType());
 390       }
 391     }
 392   }
 393
 394   return Changed ? &I : 0;
 395 }
 396
 397
 398 /// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
 399 /// code necessary to compute the offset from the base pointer (without adding
 400 /// in the base pointer).  Return the result as a signed integer of intptr size.
 401 Value *InstCombiner::EmitGEPOffset(User *GEP) {
 402   TargetData &TD = *getTargetData();
 403   gep_type_iterator GTI = gep_type_begin(GEP);
 404   const Type *IntPtrTy = TD.getIntPtrType(GEP->getContext());
 405   Value *Result = Constant::getNullValue(IntPtrTy);
 406
 407   // If the GEP is inbounds, we know that none of the addressing operations will
 408   // overflow in an unsigned sense.
 409   bool isInBounds = cast<GEPOperator>(GEP)->isInBounds();
 410
 411   // Build a mask for high order bits.
 412   unsigned IntPtrWidth = TD.getPointerSizeInBits();
 413   uint64_t PtrSizeMask = ~0ULL >> (64-IntPtrWidth);
 414
 415   for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
 416        ++i, ++GTI) {
 417     Value *Op = *i;
 418     uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
 419     if (ConstantInt *OpC = dyn_cast<ConstantInt>(Op)) {
 420       if (OpC->isZero()) continue;
 421
 422       // Handle a struct index, which adds its field offset to the pointer.
 423       if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
 424         Size = TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
 425
 426         if (Size)
 427           Result = Builder->CreateAdd(Result, ConstantInt::get(IntPtrTy, Size),
 428                                       GEP->getName()+".offs");
 429         continue;
 430       }
 431
 432       Constant *Scale = ConstantInt::get(IntPtrTy, Size);
 433       Constant *OC =
 434               ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/);
 435       Scale = ConstantExpr::getMul(OC, Scale, isInBounds/*NUW*/);
 436       // Emit an add instruction.
 437       Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs");
 438       continue;
 439     }
 440     // Convert to correct type.
 441     if (Op->getType() != IntPtrTy)
 442       Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c");
 443     if (Size != 1) {
 444       // We'll let instcombine(mul) convert this to a shl if possible.
 445       Op = Builder->CreateMul(Op, ConstantInt::get(IntPtrTy, Size),
 446                               GEP->getName()+".idx", isInBounds /*NUW*/);
 447     }
 448
 449     // Emit an add instruction.
 450     Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs");
 451   }
 452   return Result;
 453 }
 454
 455
 456
 457
 458 /// Optimize pointer differences into the same array into a size.  Consider:
 459 ///  &A[10] - &A[0]: we should compile this to "10".  LHS/RHS are the pointer
 460 /// operands to the ptrtoint instructions for the LHS/RHS of the subtract.
 461 ///
 462 Value *InstCombiner::OptimizePointerDifference(Value *LHS, Value *RHS,
 463                                                const Type *Ty) {
 464   assert(TD && "Must have target data info for this");
 465
 466   // If LHS is a gep based on RHS or RHS is a gep based on LHS, we can optimize
 467   // this.
 468   bool Swapped = false;
 469   GetElementPtrInst *GEP = 0;
 470   ConstantExpr *CstGEP = 0;
 471
 472   // TODO: Could also optimize &A[i] - &A[j] -> "i-j", and "&A.foo[i] - &A.foo".
 473   // For now we require one side to be the base pointer "A" or a constant
 474   // expression derived from it.
 475   if (GetElementPtrInst *LHSGEP = dyn_cast<GetElementPtrInst>(LHS)) {
 476     // (gep X, ...) - X
 477     if (LHSGEP->getOperand(0) == RHS) {
 478       GEP = LHSGEP;
 479       Swapped = false;
 480     } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(RHS)) {
 481       // (gep X, ...) - (ce_gep X, ...)
 482       if (CE->getOpcode() == Instruction::GetElementPtr &&
 483           LHSGEP->getOperand(0) == CE->getOperand(0)) {
 484         CstGEP = CE;
 485         GEP = LHSGEP;
 486         Swapped = false;
 487       }
 488     }
 489   }
 490
 491   if (GetElementPtrInst *RHSGEP = dyn_cast<GetElementPtrInst>(RHS)) {
 492     // X - (gep X, ...)
 493     if (RHSGEP->getOperand(0) == LHS) {
 494       GEP = RHSGEP;
 495       Swapped = true;
 496     } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(LHS)) {
 497       // (ce_gep X, ...) - (gep X, ...)
 498       if (CE->getOpcode() == Instruction::GetElementPtr &&
 499           RHSGEP->getOperand(0) == CE->getOperand(0)) {
 500         CstGEP = CE;
 501         GEP = RHSGEP;
 502         Swapped = true;
 503       }
 504     }
 505   }
 506
 507   if (GEP == 0)
 508     return 0;
 509
 510   // Emit the offset of the GEP and an intptr_t.
 511   Value *Result = EmitGEPOffset(GEP);
 512
 513   // If we had a constant expression GEP on the other side offsetting the
 514   // pointer, subtract it from the offset we have.
 515   if (CstGEP) {
 516     Value *CstOffset = EmitGEPOffset(CstGEP);
 517     Result = Builder->CreateSub(Result, CstOffset);
 518   }
 519
 520
 521   // If we have p - gep(p, ...)  then we have to negate the result.
 522   if (Swapped)
 523     Result = Builder->CreateNeg(Result, "diff.neg");
 524
 525   return Builder->CreateIntCast(Result, Ty, true);
 526 }
 527
 528
 529 Instruction *InstCombiner::visitSub(BinaryOperator &I) {
 530   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 531
 532   if (Value *V = SimplifySubInst(Op0, Op1, I.hasNoSignedWrap(),
 533                                  I.hasNoUnsignedWrap(), TD))
 534     return ReplaceInstUsesWith(I, V);
 535
 536   // (A*B)-(A*C) -> A*(B-C) etc
 537   if (Value *V = SimplifyUsingDistributiveLaws(I))
 538     return ReplaceInstUsesWith(I, V);
 539
 540   // If this is a 'B = x-(-A)', change to B = x+A.  This preserves NSW/NUW.
 541   if (Value *V = dyn_castNegVal(Op1)) {
 542     BinaryOperator *Res = BinaryOperator::CreateAdd(Op0, V);
 543     Res->setHasNoSignedWrap(I.hasNoSignedWrap());
 544     Res->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
 545     return Res;
 546   }
 547
 548   if (I.getType()->isIntegerTy(1))
 549     return BinaryOperator::CreateXor(Op0, Op1);
 550
 551   // Replace (-1 - A) with (~A).
 552   if (match(Op0, m_AllOnes()))
 553     return BinaryOperator::CreateNot(Op1);
 554
 555   if (ConstantInt *C = dyn_cast<ConstantInt>(Op0)) {
 556     // C - ~X == X + (1+C)
 557     Value *X = 0;
 558     if (match(Op1, m_Not(m_Value(X))))
 559       return BinaryOperator::CreateAdd(X, AddOne(C));
 560
 561     // -(X >>u 31) -> (X >>s 31)
 562     // -(X >>s 31) -> (X >>u 31)
 563     if (C->isZero()) {
 564       Value *X; ConstantInt *CI;
 565       if (match(Op1, m_LShr(m_Value(X), m_ConstantInt(CI))) &&
 566           // Verify we are shifting out everything but the sign bit.
 567           CI->getValue() == I.getType()->getPrimitiveSizeInBits()-1)
 568         return BinaryOperator::CreateAShr(X, CI);
 569
 570       if (match(Op1, m_AShr(m_Value(X), m_ConstantInt(CI))) &&
 571           // Verify we are shifting out everything but the sign bit.
 572           CI->getValue() == I.getType()->getPrimitiveSizeInBits()-1)
 573         return BinaryOperator::CreateLShr(X, CI);
 574     }
 575
 576     // Try to fold constant sub into select arguments.
 577     if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
 578       if (Instruction *R = FoldOpIntoSelect(I, SI))
 579         return R;
 580
 581     // C - zext(bool) -> bool ? C - 1 : C
 582     if (ZExtInst *ZI = dyn_cast<ZExtInst>(Op1))
 583       if (ZI->getSrcTy()->isIntegerTy(1))
 584         return SelectInst::Create(ZI->getOperand(0), SubOne(C), C);
 585
 586     // C-(X+C2) --> (C-C2)-X
 587     ConstantInt *C2;
 588     if (match(Op1, m_Add(m_Value(X), m_ConstantInt(C2))))
 589       return BinaryOperator::CreateSub(ConstantExpr::getSub(C, C2), X);
 590   }
 591
 592
 593   { Value *Y;
 594     // X-(X+Y) == -Y    X-(Y+X) == -Y
 595     if (match(Op1, m_Add(m_Specific(Op0), m_Value(Y))) ||
 596         match(Op1, m_Add(m_Value(Y), m_Specific(Op0))))
 597       return BinaryOperator::CreateNeg(Y);
 598
 599     // (X-Y)-X == -Y
 600     if (match(Op0, m_Sub(m_Specific(Op1), m_Value(Y))))
 601       return BinaryOperator::CreateNeg(Y);
 602   }
 603
 604   if (Op1->hasOneUse()) {
 605     Value *X = 0, *Y = 0, *Z = 0;
 606     Constant *C = 0;
 607     ConstantInt *CI = 0;
 608
 609     // (X - (Y - Z))  -->  (X + (Z - Y)).
 610     if (match(Op1, m_Sub(m_Value(Y), m_Value(Z))))
 611       return BinaryOperator::CreateAdd(Op0,
 612                                       Builder->CreateSub(Z, Y, Op1->getName()));
 613
 614     // (X - (X & Y))   -->   (X & ~Y)
 615     //
 616     if (match(Op1, m_And(m_Value(Y), m_Specific(Op0))) ||
 617         match(Op1, m_And(m_Specific(Op0), m_Value(Y))))
 618       return BinaryOperator::CreateAnd(Op0,
 619                                   Builder->CreateNot(Y, Y->getName() + ".not"));
 620
 621     // 0 - (X sdiv C)  -> (X sdiv -C)
 622     if (match(Op1, m_SDiv(m_Value(X), m_Constant(C))) &&
 623         match(Op0, m_Zero()))
 624       return BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(C));
 625
 626     // 0 - (X << Y)  -> (-X << Y)   when X is freely negatable.
 627     if (match(Op1, m_Shl(m_Value(X), m_Value(Y))) && match(Op0, m_Zero()))
 628       if (Value *XNeg = dyn_castNegVal(X))
 629         return BinaryOperator::CreateShl(XNeg, Y);
 630
 631     // X - X*C --> X * (1-C)
 632     if (match(Op1, m_Mul(m_Specific(Op0), m_ConstantInt(CI)))) {
 633       Constant *CP1 = ConstantExpr::getSub(ConstantInt::get(I.getType(),1), CI);
 634       return BinaryOperator::CreateMul(Op0, CP1);
 635     }
 636
 637     // X - X<<C --> X * (1-(1<<C))
 638     if (match(Op1, m_Shl(m_Specific(Op0), m_ConstantInt(CI)))) {
 639       Constant *One = ConstantInt::get(I.getType(), 1);
 640       C = ConstantExpr::getSub(One, ConstantExpr::getShl(One, CI));
 641       return BinaryOperator::CreateMul(Op0, C);
 642     }
 643
 644     // X - A*-B -> X + A*B
 645     // X - -A*B -> X + A*B
 646     Value *A, *B;
 647     if (match(Op1, m_Mul(m_Value(A), m_Neg(m_Value(B)))) ||
 648         match(Op1, m_Mul(m_Neg(m_Value(A)), m_Value(B))))
 649       return BinaryOperator::CreateAdd(Op0, Builder->CreateMul(A, B));
 650
 651     // X - A*CI -> X + A*-CI
 652     // X - CI*A -> X + A*-CI
 653     if (match(Op1, m_Mul(m_Value(A), m_ConstantInt(CI))) ||
 654         match(Op1, m_Mul(m_ConstantInt(CI), m_Value(A)))) {
 655       Value *NewMul = Builder->CreateMul(A, ConstantExpr::getNeg(CI));
 656       return BinaryOperator::CreateAdd(Op0, NewMul);
 657     }
 658   }
 659
 660   ConstantInt *C1;
 661   if (Value *X = dyn_castFoldableMul(Op0, C1)) {
 662     if (X == Op1)  // X*C - X --> X * (C-1)
 663       return BinaryOperator::CreateMul(Op1, SubOne(C1));
 664
 665     ConstantInt *C2;   // X*C1 - X*C2 -> X * (C1-C2)
 666     if (X == dyn_castFoldableMul(Op1, C2))
 667       return BinaryOperator::CreateMul(X, ConstantExpr::getSub(C1, C2));
 668   }
 669
 670   // Optimize pointer differences into the same array into a size.  Consider:
 671   //  &A[10] - &A[0]: we should compile this to "10".
 672   if (TD) {
 673     Value *LHSOp, *RHSOp;
 674     if (match(Op0, m_PtrToInt(m_Value(LHSOp))) &&
 675         match(Op1, m_PtrToInt(m_Value(RHSOp))))
 676       if (Value *Res = OptimizePointerDifference(LHSOp, RHSOp, I.getType()))
 677         return ReplaceInstUsesWith(I, Res);
 678
 679     // trunc(p)-trunc(q) -> trunc(p-q)
 680     if (match(Op0, m_Trunc(m_PtrToInt(m_Value(LHSOp)))) &&
 681         match(Op1, m_Trunc(m_PtrToInt(m_Value(RHSOp)))))
 682       if (Value *Res = OptimizePointerDifference(LHSOp, RHSOp, I.getType()))
 683         return ReplaceInstUsesWith(I, Res);
 684   }
 685
 686   return 0;
 687 }
 688
 689 Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
 690   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 691
 692   // If this is a 'B = x-(-A)', change to B = x+A...
 693   if (Value *V = dyn_castFNegVal(Op1))
 694     return BinaryOperator::CreateFAdd(Op0, V);
 695
 696   return 0;
 697 }