lib/Transforms/InstCombine/InstCombineSelect.cpp

   1 //===- InstCombineSelect.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 visitSelect function.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "InstCombine.h"
  15 #include "llvm/Support/PatternMatch.h"
  16 #include "llvm/Analysis/InstructionSimplify.h"
  17 using namespace llvm;
  18 using namespace PatternMatch;
  19
  20 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
  21 /// returning the kind and providing the out parameter results if we
  22 /// successfully match.
  23 static SelectPatternFlavor
  24 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
  25   SelectInst *SI = dyn_cast<SelectInst>(V);
  26   if (SI == 0) return SPF_UNKNOWN;
  27
  28   ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
  29   if (ICI == 0) return SPF_UNKNOWN;
  30
  31   LHS = ICI->getOperand(0);
  32   RHS = ICI->getOperand(1);
  33
  34   // (icmp X, Y) ? X : Y
  35   if (SI->getTrueValue() == ICI->getOperand(0) &&
  36       SI->getFalseValue() == ICI->getOperand(1)) {
  37     switch (ICI->getPredicate()) {
  38     default: return SPF_UNKNOWN; // Equality.
  39     case ICmpInst::ICMP_UGT:
  40     case ICmpInst::ICMP_UGE: return SPF_UMAX;
  41     case ICmpInst::ICMP_SGT:
  42     case ICmpInst::ICMP_SGE: return SPF_SMAX;
  43     case ICmpInst::ICMP_ULT:
  44     case ICmpInst::ICMP_ULE: return SPF_UMIN;
  45     case ICmpInst::ICMP_SLT:
  46     case ICmpInst::ICMP_SLE: return SPF_SMIN;
  47     }
  48   }
  49
  50   // (icmp X, Y) ? Y : X
  51   if (SI->getTrueValue() == ICI->getOperand(1) &&
  52       SI->getFalseValue() == ICI->getOperand(0)) {
  53     switch (ICI->getPredicate()) {
  54       default: return SPF_UNKNOWN; // Equality.
  55       case ICmpInst::ICMP_UGT:
  56       case ICmpInst::ICMP_UGE: return SPF_UMIN;
  57       case ICmpInst::ICMP_SGT:
  58       case ICmpInst::ICMP_SGE: return SPF_SMIN;
  59       case ICmpInst::ICMP_ULT:
  60       case ICmpInst::ICMP_ULE: return SPF_UMAX;
  61       case ICmpInst::ICMP_SLT:
  62       case ICmpInst::ICMP_SLE: return SPF_SMAX;
  63     }
  64   }
  65
  66   // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)
  67
  68   return SPF_UNKNOWN;
  69 }
  70
  71
  72 /// GetSelectFoldableOperands - We want to turn code that looks like this:
  73 ///   %C = or %A, %B
  74 ///   %D = select %cond, %C, %A
  75 /// into:
  76 ///   %C = select %cond, %B, 0
  77 ///   %D = or %A, %C
  78 ///
  79 /// Assuming that the specified instruction is an operand to the select, return
  80 /// a bitmask indicating which operands of this instruction are foldable if they
  81 /// equal the other incoming value of the select.
  82 ///
  83 static unsigned GetSelectFoldableOperands(Instruction *I) {
  84   switch (I->getOpcode()) {
  85   case Instruction::Add:
  86   case Instruction::Mul:
  87   case Instruction::And:
  88   case Instruction::Or:
  89   case Instruction::Xor:
  90     return 3;              // Can fold through either operand.
  91   case Instruction::Sub:   // Can only fold on the amount subtracted.
  92   case Instruction::Shl:   // Can only fold on the shift amount.
  93   case Instruction::LShr:
  94   case Instruction::AShr:
  95     return 1;
  96   default:
  97     return 0;              // Cannot fold
  98   }
  99 }
 100
 101 /// GetSelectFoldableConstant - For the same transformation as the previous
 102 /// function, return the identity constant that goes into the select.
 103 static Constant *GetSelectFoldableConstant(Instruction *I) {
 104   switch (I->getOpcode()) {
 105   default: llvm_unreachable("This cannot happen!");
 106   case Instruction::Add:
 107   case Instruction::Sub:
 108   case Instruction::Or:
 109   case Instruction::Xor:
 110   case Instruction::Shl:
 111   case Instruction::LShr:
 112   case Instruction::AShr:
 113     return Constant::getNullValue(I->getType());
 114   case Instruction::And:
 115     return Constant::getAllOnesValue(I->getType());
 116   case Instruction::Mul:
 117     return ConstantInt::get(I->getType(), 1);
 118   }
 119 }
 120
 121 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
 122 /// have the same opcode and only one use each.  Try to simplify this.
 123 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
 124                                           Instruction *FI) {
 125   if (TI->getNumOperands() == 1) {
 126     // If this is a non-volatile load or a cast from the same type,
 127     // merge.
 128     if (TI->isCast()) {
 129       if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType())
 130         return 0;
 131     } else {
 132       return 0;  // unknown unary op.
 133     }
 134
 135     // Fold this by inserting a select from the input values.
 136     SelectInst *NewSI = SelectInst::Create(SI.getCondition(), TI->getOperand(0),
 137                                           FI->getOperand(0), SI.getName()+".v");
 138     InsertNewInstBefore(NewSI, SI);
 139     return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
 140                             TI->getType());
 141   }
 142
 143   // Only handle binary operators here.
 144   if (!isa<BinaryOperator>(TI))
 145     return 0;
 146
 147   // Figure out if the operations have any operands in common.
 148   Value *MatchOp, *OtherOpT, *OtherOpF;
 149   bool MatchIsOpZero;
 150   if (TI->getOperand(0) == FI->getOperand(0)) {
 151     MatchOp  = TI->getOperand(0);
 152     OtherOpT = TI->getOperand(1);
 153     OtherOpF = FI->getOperand(1);
 154     MatchIsOpZero = true;
 155   } else if (TI->getOperand(1) == FI->getOperand(1)) {
 156     MatchOp  = TI->getOperand(1);
 157     OtherOpT = TI->getOperand(0);
 158     OtherOpF = FI->getOperand(0);
 159     MatchIsOpZero = false;
 160   } else if (!TI->isCommutative()) {
 161     return 0;
 162   } else if (TI->getOperand(0) == FI->getOperand(1)) {
 163     MatchOp  = TI->getOperand(0);
 164     OtherOpT = TI->getOperand(1);
 165     OtherOpF = FI->getOperand(0);
 166     MatchIsOpZero = true;
 167   } else if (TI->getOperand(1) == FI->getOperand(0)) {
 168     MatchOp  = TI->getOperand(1);
 169     OtherOpT = TI->getOperand(0);
 170     OtherOpF = FI->getOperand(1);
 171     MatchIsOpZero = true;
 172   } else {
 173     return 0;
 174   }
 175
 176   // If we reach here, they do have operations in common.
 177   SelectInst *NewSI = SelectInst::Create(SI.getCondition(), OtherOpT,
 178                                          OtherOpF, SI.getName()+".v");
 179   InsertNewInstBefore(NewSI, SI);
 180
 181   if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
 182     if (MatchIsOpZero)
 183       return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
 184     else
 185       return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
 186   }
 187   llvm_unreachable("Shouldn't get here");
 188   return 0;
 189 }
 190
 191 static bool isSelect01(Constant *C1, Constant *C2) {
 192   ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
 193   if (!C1I)
 194     return false;
 195   ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
 196   if (!C2I)
 197     return false;
 198   return (C1I->isZero() || C1I->isOne()) && (C2I->isZero() || C2I->isOne());
 199 }
 200
 201 /// FoldSelectIntoOp - Try fold the select into one of the operands to
 202 /// facilitate further optimization.
 203 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
 204                                             Value *FalseVal) {
 205   // See the comment above GetSelectFoldableOperands for a description of the
 206   // transformation we are doing here.
 207   if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
 208     if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
 209         !isa<Constant>(FalseVal)) {
 210       if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
 211         unsigned OpToFold = 0;
 212         if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
 213           OpToFold = 1;
 214         } else  if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
 215           OpToFold = 2;
 216         }
 217
 218         if (OpToFold) {
 219           Constant *C = GetSelectFoldableConstant(TVI);
 220           Value *OOp = TVI->getOperand(2-OpToFold);
 221           // Avoid creating select between 2 constants unless it's selecting
 222           // between 0 and 1.
 223           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
 224             Instruction *NewSel = SelectInst::Create(SI.getCondition(), OOp, C);
 225             InsertNewInstBefore(NewSel, SI);
 226             NewSel->takeName(TVI);
 227             if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TVI))
 228               return BinaryOperator::Create(BO->getOpcode(), FalseVal, NewSel);
 229             llvm_unreachable("Unknown instruction!!");
 230           }
 231         }
 232       }
 233     }
 234   }
 235
 236   if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
 237     if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
 238         !isa<Constant>(TrueVal)) {
 239       if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
 240         unsigned OpToFold = 0;
 241         if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
 242           OpToFold = 1;
 243         } else  if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
 244           OpToFold = 2;
 245         }
 246
 247         if (OpToFold) {
 248           Constant *C = GetSelectFoldableConstant(FVI);
 249           Value *OOp = FVI->getOperand(2-OpToFold);
 250           // Avoid creating select between 2 constants unless it's selecting
 251           // between 0 and 1.
 252           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
 253             Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp);
 254             InsertNewInstBefore(NewSel, SI);
 255             NewSel->takeName(FVI);
 256             if (BinaryOperator *BO = dyn_cast<BinaryOperator>(FVI))
 257               return BinaryOperator::Create(BO->getOpcode(), TrueVal, NewSel);
 258             llvm_unreachable("Unknown instruction!!");
 259           }
 260         }
 261       }
 262     }
 263   }
 264
 265   return 0;
 266 }
 267
 268 /// visitSelectInstWithICmp - Visit a SelectInst that has an
 269 /// ICmpInst as its first operand.
 270 ///
 271 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
 272                                                    ICmpInst *ICI) {
 273   bool Changed = false;
 274   ICmpInst::Predicate Pred = ICI->getPredicate();
 275   Value *CmpLHS = ICI->getOperand(0);
 276   Value *CmpRHS = ICI->getOperand(1);
 277   Value *TrueVal = SI.getTrueValue();
 278   Value *FalseVal = SI.getFalseValue();
 279
 280   // Check cases where the comparison is with a constant that
 281   // can be adjusted to fit the min/max idiom. We may edit ICI in
 282   // place here, so make sure the select is the only user.
 283   if (ICI->hasOneUse())
 284     if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
 285       switch (Pred) {
 286       default: break;
 287       case ICmpInst::ICMP_ULT:
 288       case ICmpInst::ICMP_SLT: {
 289         // X < MIN ? T : F  -->  F
 290         if (CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
 291           return ReplaceInstUsesWith(SI, FalseVal);
 292         // X < C ? X : C-1  -->  X > C-1 ? C-1 : X
 293         Constant *AdjustedRHS =
 294           ConstantInt::get(CI->getContext(), CI->getValue()-1);
 295         if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
 296             (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) {
 297           Pred = ICmpInst::getSwappedPredicate(Pred);
 298           CmpRHS = AdjustedRHS;
 299           std::swap(FalseVal, TrueVal);
 300           ICI->setPredicate(Pred);
 301           ICI->setOperand(1, CmpRHS);
 302           SI.setOperand(1, TrueVal);
 303           SI.setOperand(2, FalseVal);
 304           Changed = true;
 305         }
 306         break;
 307       }
 308       case ICmpInst::ICMP_UGT:
 309       case ICmpInst::ICMP_SGT: {
 310         // X > MAX ? T : F  -->  F
 311         if (CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
 312           return ReplaceInstUsesWith(SI, FalseVal);
 313         // X > C ? X : C+1  -->  X < C+1 ? C+1 : X
 314         Constant *AdjustedRHS =
 315           ConstantInt::get(CI->getContext(), CI->getValue()+1);
 316         if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
 317             (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) {
 318           Pred = ICmpInst::getSwappedPredicate(Pred);
 319           CmpRHS = AdjustedRHS;
 320           std::swap(FalseVal, TrueVal);
 321           ICI->setPredicate(Pred);
 322           ICI->setOperand(1, CmpRHS);
 323           SI.setOperand(1, TrueVal);
 324           SI.setOperand(2, FalseVal);
 325           Changed = true;
 326         }
 327         break;
 328       }
 329       }
 330     }
 331
 332   // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
 333   // and       (X <s  0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
 334   // FIXME: Type and constness constraints could be lifted, but we have to
 335   //        watch code size carefully. We should consider xor instead of
 336   //        sub/add when we decide to do that.
 337   if (const IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
 338     if (TrueVal->getType() == Ty) {
 339       if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
 340         ConstantInt *C1 = NULL, *C2 = NULL;
 341         if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
 342           C1 = dyn_cast<ConstantInt>(TrueVal);
 343           C2 = dyn_cast<ConstantInt>(FalseVal);
 344         } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
 345           C1 = dyn_cast<ConstantInt>(FalseVal);
 346           C2 = dyn_cast<ConstantInt>(TrueVal);
 347         }
 348         if (C1 && C2) {
 349           // This shift results in either -1 or 0.
 350           Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
 351
 352           // Check if we can express the operation with a single or.
 353           if (C2->isAllOnesValue())
 354             return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
 355
 356           Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
 357           return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
 358         }
 359       }
 360     }
 361   }
 362
 363   if (CmpLHS == TrueVal && CmpRHS == FalseVal) {
 364     // Transform (X == Y) ? X : Y  -> Y
 365     if (Pred == ICmpInst::ICMP_EQ)
 366       return ReplaceInstUsesWith(SI, FalseVal);
 367     // Transform (X != Y) ? X : Y  -> X
 368     if (Pred == ICmpInst::ICMP_NE)
 369       return ReplaceInstUsesWith(SI, TrueVal);
 370     /// NOTE: if we wanted to, this is where to detect integer MIN/MAX
 371
 372   } else if (CmpLHS == FalseVal && CmpRHS == TrueVal) {
 373     // Transform (X == Y) ? Y : X  -> X
 374     if (Pred == ICmpInst::ICMP_EQ)
 375       return ReplaceInstUsesWith(SI, FalseVal);
 376     // Transform (X != Y) ? Y : X  -> Y
 377     if (Pred == ICmpInst::ICMP_NE)
 378       return ReplaceInstUsesWith(SI, TrueVal);
 379     /// NOTE: if we wanted to, this is where to detect integer MIN/MAX
 380   }
 381   return Changed ? &SI : 0;
 382 }
 383
 384
 385 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
 386 /// PHI node (but the two may be in different blocks).  See if the true/false
 387 /// values (V) are live in all of the predecessor blocks of the PHI.  For
 388 /// example, cases like this cannot be mapped:
 389 ///
 390 ///   X = phi [ C1, BB1], [C2, BB2]
 391 ///   Y = add
 392 ///   Z = select X, Y, 0
 393 ///
 394 /// because Y is not live in BB1/BB2.
 395 ///
 396 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
 397                                                    const SelectInst &SI) {
 398   // If the value is a non-instruction value like a constant or argument, it
 399   // can always be mapped.
 400   const Instruction *I = dyn_cast<Instruction>(V);
 401   if (I == 0) return true;
 402
 403   // If V is a PHI node defined in the same block as the condition PHI, we can
 404   // map the arguments.
 405   const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
 406
 407   if (const PHINode *VP = dyn_cast<PHINode>(I))
 408     if (VP->getParent() == CondPHI->getParent())
 409       return true;
 410
 411   // Otherwise, if the PHI and select are defined in the same block and if V is
 412   // defined in a different block, then we can transform it.
 413   if (SI.getParent() == CondPHI->getParent() &&
 414       I->getParent() != CondPHI->getParent())
 415     return true;
 416
 417   // Otherwise we have a 'hard' case and we can't tell without doing more
 418   // detailed dominator based analysis, punt.
 419   return false;
 420 }
 421
 422 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
 423 ///   SPF2(SPF1(A, B), C)
 424 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
 425                                         SelectPatternFlavor SPF1,
 426                                         Value *A, Value *B,
 427                                         Instruction &Outer,
 428                                         SelectPatternFlavor SPF2, Value *C) {
 429   if (C == A || C == B) {
 430     // MAX(MAX(A, B), B) -> MAX(A, B)
 431     // MIN(MIN(a, b), a) -> MIN(a, b)
 432     if (SPF1 == SPF2)
 433       return ReplaceInstUsesWith(Outer, Inner);
 434
 435     // MAX(MIN(a, b), a) -> a
 436     // MIN(MAX(a, b), a) -> a
 437     if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
 438         (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
 439         (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
 440         (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
 441       return ReplaceInstUsesWith(Outer, C);
 442   }
 443
 444   // TODO: MIN(MIN(A, 23), 97)
 445   return 0;
 446 }
 447
 448
 449
 450
 451 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
 452   Value *CondVal = SI.getCondition();
 453   Value *TrueVal = SI.getTrueValue();
 454   Value *FalseVal = SI.getFalseValue();
 455
 456   if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD))
 457     return ReplaceInstUsesWith(SI, V);
 458
 459   if (SI.getType()->isIntegerTy(1)) {
 460     if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
 461       if (C->getZExtValue()) {
 462         // Change: A = select B, true, C --> A = or B, C
 463         return BinaryOperator::CreateOr(CondVal, FalseVal);
 464       }
 465       // Change: A = select B, false, C --> A = and !B, C
 466       Value *NotCond =
 467         InsertNewInstBefore(BinaryOperator::CreateNot(CondVal,
 468                                            "not."+CondVal->getName()), SI);
 469       return BinaryOperator::CreateAnd(NotCond, FalseVal);
 470     } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
 471       if (C->getZExtValue() == false) {
 472         // Change: A = select B, C, false --> A = and B, C
 473         return BinaryOperator::CreateAnd(CondVal, TrueVal);
 474       }
 475       // Change: A = select B, C, true --> A = or !B, C
 476       Value *NotCond =
 477         InsertNewInstBefore(BinaryOperator::CreateNot(CondVal,
 478                                            "not."+CondVal->getName()), SI);
 479       return BinaryOperator::CreateOr(NotCond, TrueVal);
 480     }
 481
 482     // select a, b, a  -> a&b
 483     // select a, a, b  -> a|b
 484     if (CondVal == TrueVal)
 485       return BinaryOperator::CreateOr(CondVal, FalseVal);
 486     else if (CondVal == FalseVal)
 487       return BinaryOperator::CreateAnd(CondVal, TrueVal);
 488   }
 489
 490   // Selecting between two integer constants?
 491   if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
 492     if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
 493       // select C, 1, 0 -> zext C to int
 494       if (FalseValC->isZero() && TrueValC->getValue() == 1)
 495         return new ZExtInst(CondVal, SI.getType());
 496
 497       // select C, -1, 0 -> sext C to int
 498       if (FalseValC->isZero() && TrueValC->isAllOnesValue())
 499         return new SExtInst(CondVal, SI.getType());
 500
 501       // select C, 0, 1 -> zext !C to int
 502       if (TrueValC->isZero() && FalseValC->getValue() == 1) {
 503         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
 504         return new ZExtInst(NotCond, SI.getType());
 505       }
 506
 507       // select C, 0, -1 -> sext !C to int
 508       if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
 509         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
 510         return new SExtInst(NotCond, SI.getType());
 511       }
 512
 513       if (ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition())) {
 514         // If one of the constants is zero (we know they can't both be) and we
 515         // have an icmp instruction with zero, and we have an 'and' with the
 516         // non-constant value, eliminate this whole mess.  This corresponds to
 517         // cases like this: ((X & 27) ? 27 : 0)
 518         if (TrueValC->isZero() || FalseValC->isZero())
 519           if (IC->isEquality() && isa<ConstantInt>(IC->getOperand(1)) &&
 520               cast<Constant>(IC->getOperand(1))->isNullValue())
 521             if (Instruction *ICA = dyn_cast<Instruction>(IC->getOperand(0)))
 522               if (ICA->getOpcode() == Instruction::And &&
 523                   isa<ConstantInt>(ICA->getOperand(1)) &&
 524                   (ICA->getOperand(1) == TrueValC ||
 525                    ICA->getOperand(1) == FalseValC) &&
 526                cast<ConstantInt>(ICA->getOperand(1))->getValue().isPowerOf2()) {
 527                 // Okay, now we know that everything is set up, we just don't
 528                 // know whether we have a icmp_ne or icmp_eq and whether the
 529                 // true or false val is the zero.
 530                 bool ShouldNotVal = !TrueValC->isZero();
 531                 ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
 532                 Value *V = ICA;
 533                 if (ShouldNotVal)
 534                   V = Builder->CreateXor(V, ICA->getOperand(1));
 535                 return ReplaceInstUsesWith(SI, V);
 536               }
 537       }
 538     }
 539
 540   // See if we are selecting two values based on a comparison of the two values.
 541   if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
 542     if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
 543       // Transform (X == Y) ? X : Y  -> Y
 544       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
 545         // This is not safe in general for floating point:
 546         // consider X== -0, Y== +0.
 547         // It becomes safe if either operand is a nonzero constant.
 548         ConstantFP *CFPt, *CFPf;
 549         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 550               !CFPt->getValueAPF().isZero()) ||
 551             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 552              !CFPf->getValueAPF().isZero()))
 553         return ReplaceInstUsesWith(SI, FalseVal);
 554       }
 555       // Transform (X une Y) ? X : Y  -> X
 556       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
 557         // This is not safe in general for floating point:
 558         // consider X== -0, Y== +0.
 559         // It becomes safe if either operand is a nonzero constant.
 560         ConstantFP *CFPt, *CFPf;
 561         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 562               !CFPt->getValueAPF().isZero()) ||
 563             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 564              !CFPf->getValueAPF().isZero()))
 565         return ReplaceInstUsesWith(SI, TrueVal);
 566       }
 567       // NOTE: if we wanted to, this is where to detect MIN/MAX
 568
 569     } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
 570       // Transform (X == Y) ? Y : X  -> X
 571       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
 572         // This is not safe in general for floating point:
 573         // consider X== -0, Y== +0.
 574         // It becomes safe if either operand is a nonzero constant.
 575         ConstantFP *CFPt, *CFPf;
 576         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 577               !CFPt->getValueAPF().isZero()) ||
 578             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 579              !CFPf->getValueAPF().isZero()))
 580           return ReplaceInstUsesWith(SI, FalseVal);
 581       }
 582       // Transform (X une Y) ? Y : X  -> Y
 583       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
 584         // This is not safe in general for floating point:
 585         // consider X== -0, Y== +0.
 586         // It becomes safe if either operand is a nonzero constant.
 587         ConstantFP *CFPt, *CFPf;
 588         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 589               !CFPt->getValueAPF().isZero()) ||
 590             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 591              !CFPf->getValueAPF().isZero()))
 592           return ReplaceInstUsesWith(SI, TrueVal);
 593       }
 594       // NOTE: if we wanted to, this is where to detect MIN/MAX
 595     }
 596     // NOTE: if we wanted to, this is where to detect ABS
 597   }
 598
 599   // See if we are selecting two values based on a comparison of the two values.
 600   if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
 601     if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
 602       return Result;
 603
 604   if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
 605     if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
 606       if (TI->hasOneUse() && FI->hasOneUse()) {
 607         Instruction *AddOp = 0, *SubOp = 0;
 608
 609         // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
 610         if (TI->getOpcode() == FI->getOpcode())
 611           if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
 612             return IV;
 613
 614         // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))).  This is
 615         // even legal for FP.
 616         if ((TI->getOpcode() == Instruction::Sub &&
 617              FI->getOpcode() == Instruction::Add) ||
 618             (TI->getOpcode() == Instruction::FSub &&
 619              FI->getOpcode() == Instruction::FAdd)) {
 620           AddOp = FI; SubOp = TI;
 621         } else if ((FI->getOpcode() == Instruction::Sub &&
 622                     TI->getOpcode() == Instruction::Add) ||
 623                    (FI->getOpcode() == Instruction::FSub &&
 624                     TI->getOpcode() == Instruction::FAdd)) {
 625           AddOp = TI; SubOp = FI;
 626         }
 627
 628         if (AddOp) {
 629           Value *OtherAddOp = 0;
 630           if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
 631             OtherAddOp = AddOp->getOperand(1);
 632           } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
 633             OtherAddOp = AddOp->getOperand(0);
 634           }
 635
 636           if (OtherAddOp) {
 637             // So at this point we know we have (Y -> OtherAddOp):
 638             //        select C, (add X, Y), (sub X, Z)
 639             Value *NegVal;  // Compute -Z
 640             if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) {
 641               NegVal = ConstantExpr::getNeg(C);
 642             } else if (SI.getType()->isFloatingPointTy()) {
 643               NegVal = InsertNewInstBefore(
 644                     BinaryOperator::CreateFNeg(SubOp->getOperand(1),
 645                                               "tmp"), SI);
 646             } else {
 647               NegVal = InsertNewInstBefore(
 648                     BinaryOperator::CreateNeg(SubOp->getOperand(1),
 649                                               "tmp"), SI);
 650             }
 651
 652             Value *NewTrueOp = OtherAddOp;
 653             Value *NewFalseOp = NegVal;
 654             if (AddOp != TI)
 655               std::swap(NewTrueOp, NewFalseOp);
 656             Instruction *NewSel =
 657               SelectInst::Create(CondVal, NewTrueOp,
 658                                  NewFalseOp, SI.getName() + ".p");
 659
 660             NewSel = InsertNewInstBefore(NewSel, SI);
 661             if (SI.getType()->isFloatingPointTy())
 662               return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
 663             else
 664               return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
 665           }
 666         }
 667       }
 668
 669   // See if we can fold the select into one of our operands.
 670   if (SI.getType()->isIntegerTy()) {
 671     if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
 672       return FoldI;
 673
 674     // MAX(MAX(a, b), a) -> MAX(a, b)
 675     // MIN(MIN(a, b), a) -> MIN(a, b)
 676     // MAX(MIN(a, b), a) -> a
 677     // MIN(MAX(a, b), a) -> a
 678     Value *LHS, *RHS, *LHS2, *RHS2;
 679     if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
 680       if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
 681         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
 682                                           SI, SPF, RHS))
 683           return R;
 684       if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
 685         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
 686                                           SI, SPF, LHS))
 687           return R;
 688     }
 689
 690     // TODO.
 691     // ABS(-X) -> ABS(X)
 692     // ABS(ABS(X)) -> ABS(X)
 693   }
 694
 695   // See if we can fold the select into a phi node if the condition is a select.
 696   if (isa<PHINode>(SI.getCondition()))
 697     // The true/false values have to be live in the PHI predecessor's blocks.
 698     if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
 699         CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
 700       if (Instruction *NV = FoldOpIntoPhi(SI))
 701         return NV;
 702
 703   if (BinaryOperator::isNot(CondVal)) {
 704     SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
 705     SI.setOperand(1, FalseVal);
 706     SI.setOperand(2, TrueVal);
 707     return &SI;
 708   }
 709
 710   return 0;
 711 }