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   if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
 199     return false;
 200   return C1I->isOne() || C1I->isAllOnesValue() ||
 201          C2I->isOne() || C2I->isAllOnesValue();
 202 }
 203
 204 /// FoldSelectIntoOp - Try fold the select into one of the operands to
 205 /// facilitate further optimization.
 206 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
 207                                             Value *FalseVal) {
 208   // See the comment above GetSelectFoldableOperands for a description of the
 209   // transformation we are doing here.
 210   if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
 211     if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
 212         !isa<Constant>(FalseVal)) {
 213       if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
 214         unsigned OpToFold = 0;
 215         if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
 216           OpToFold = 1;
 217         } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
 218           OpToFold = 2;
 219         }
 220
 221         if (OpToFold) {
 222           Constant *C = GetSelectFoldableConstant(TVI);
 223           Value *OOp = TVI->getOperand(2-OpToFold);
 224           // Avoid creating select between 2 constants unless it's selecting
 225           // between 0, 1 and -1.
 226           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
 227             Instruction *NewSel = SelectInst::Create(SI.getCondition(), OOp, C);
 228             InsertNewInstBefore(NewSel, SI);
 229             NewSel->takeName(TVI);
 230             BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
 231             BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
 232                                                         FalseVal, NewSel);
 233             if (isa<PossiblyExactOperator>(BO))
 234               BO->setIsExact(TVI_BO->isExact());
 235             if (isa<OverflowingBinaryOperator>(BO)) {
 236               BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
 237               BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
 238             }
 239             return BO;
 240           }
 241         }
 242       }
 243     }
 244   }
 245
 246   if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
 247     if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
 248         !isa<Constant>(TrueVal)) {
 249       if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
 250         unsigned OpToFold = 0;
 251         if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
 252           OpToFold = 1;
 253         } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
 254           OpToFold = 2;
 255         }
 256
 257         if (OpToFold) {
 258           Constant *C = GetSelectFoldableConstant(FVI);
 259           Value *OOp = FVI->getOperand(2-OpToFold);
 260           // Avoid creating select between 2 constants unless it's selecting
 261           // between 0, 1 and -1.
 262           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
 263             Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp);
 264             InsertNewInstBefore(NewSel, SI);
 265             NewSel->takeName(FVI);
 266             BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
 267             BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
 268                                                         TrueVal, NewSel);
 269             if (isa<PossiblyExactOperator>(BO))
 270               BO->setIsExact(FVI_BO->isExact());
 271             if (isa<OverflowingBinaryOperator>(BO)) {
 272               BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
 273               BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
 274             }
 275             return BO;
 276           }
 277         }
 278       }
 279     }
 280   }
 281
 282   return 0;
 283 }
 284
 285 /// visitSelectInstWithICmp - Visit a SelectInst that has an
 286 /// ICmpInst as its first operand.
 287 ///
 288 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
 289                                                    ICmpInst *ICI) {
 290   bool Changed = false;
 291   ICmpInst::Predicate Pred = ICI->getPredicate();
 292   Value *CmpLHS = ICI->getOperand(0);
 293   Value *CmpRHS = ICI->getOperand(1);
 294   Value *TrueVal = SI.getTrueValue();
 295   Value *FalseVal = SI.getFalseValue();
 296
 297   // Check cases where the comparison is with a constant that
 298   // can be adjusted to fit the min/max idiom. We may move or edit ICI
 299   // here, so make sure the select is the only user.
 300   if (ICI->hasOneUse())
 301     if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
 302       // X < MIN ? T : F  -->  F
 303       if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
 304           && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
 305         return ReplaceInstUsesWith(SI, FalseVal);
 306       // X > MAX ? T : F  -->  F
 307       else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
 308                && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
 309         return ReplaceInstUsesWith(SI, FalseVal);
 310       switch (Pred) {
 311       default: break;
 312       case ICmpInst::ICMP_ULT:
 313       case ICmpInst::ICMP_SLT:
 314       case ICmpInst::ICMP_UGT:
 315       case ICmpInst::ICMP_SGT: {
 316         // These transformations only work for selects over integers.
 317         const IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
 318         if (!SelectTy)
 319           break;
 320
 321         Constant *AdjustedRHS;
 322         if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
 323           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
 324         else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
 325           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
 326
 327         // X > C ? X : C+1  -->  X < C+1 ? C+1 : X
 328         // X < C ? X : C-1  -->  X > C-1 ? C-1 : X
 329         if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
 330             (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
 331           ; // Nothing to do here. Values match without any sign/zero extension.
 332
 333         // Types do not match. Instead of calculating this with mixed types
 334         // promote all to the larger type. This enables scalar evolution to
 335         // analyze this expression.
 336         else if (CmpRHS->getType()->getScalarSizeInBits()
 337                  < SelectTy->getBitWidth()) {
 338           Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
 339
 340           // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
 341           // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
 342           // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
 343           // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
 344           if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
 345                 sextRHS == FalseVal) {
 346             CmpLHS = TrueVal;
 347             AdjustedRHS = sextRHS;
 348           } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
 349                      sextRHS == TrueVal) {
 350             CmpLHS = FalseVal;
 351             AdjustedRHS = sextRHS;
 352           } else if (ICI->isUnsigned()) {
 353             Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
 354             // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
 355             // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
 356             // zext + signed compare cannot be changed:
 357             //    0xff <s 0x00, but 0x00ff >s 0x0000
 358             if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
 359                 zextRHS == FalseVal) {
 360               CmpLHS = TrueVal;
 361               AdjustedRHS = zextRHS;
 362             } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
 363                        zextRHS == TrueVal) {
 364               CmpLHS = FalseVal;
 365               AdjustedRHS = zextRHS;
 366             } else
 367               break;
 368           } else
 369             break;
 370         } else
 371           break;
 372
 373         Pred = ICmpInst::getSwappedPredicate(Pred);
 374         CmpRHS = AdjustedRHS;
 375         std::swap(FalseVal, TrueVal);
 376         ICI->setPredicate(Pred);
 377         ICI->setOperand(0, CmpLHS);
 378         ICI->setOperand(1, CmpRHS);
 379         SI.setOperand(1, TrueVal);
 380         SI.setOperand(2, FalseVal);
 381
 382         // Move ICI instruction right before the select instruction. Otherwise
 383         // the sext/zext value may be defined after the ICI instruction uses it.
 384         ICI->moveBefore(&SI);
 385
 386         Changed = true;
 387         break;
 388       }
 389       }
 390     }
 391
 392   // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
 393   // and       (X <s  0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
 394   // FIXME: Type and constness constraints could be lifted, but we have to
 395   //        watch code size carefully. We should consider xor instead of
 396   //        sub/add when we decide to do that.
 397   if (const IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
 398     if (TrueVal->getType() == Ty) {
 399       if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
 400         ConstantInt *C1 = NULL, *C2 = NULL;
 401         if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
 402           C1 = dyn_cast<ConstantInt>(TrueVal);
 403           C2 = dyn_cast<ConstantInt>(FalseVal);
 404         } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
 405           C1 = dyn_cast<ConstantInt>(FalseVal);
 406           C2 = dyn_cast<ConstantInt>(TrueVal);
 407         }
 408         if (C1 && C2) {
 409           // This shift results in either -1 or 0.
 410           Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
 411
 412           // Check if we can express the operation with a single or.
 413           if (C2->isAllOnesValue())
 414             return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
 415
 416           Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
 417           return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
 418         }
 419       }
 420     }
 421   }
 422
 423   if (CmpLHS == TrueVal && CmpRHS == FalseVal) {
 424     // Transform (X == Y) ? X : Y  -> Y
 425     if (Pred == ICmpInst::ICMP_EQ)
 426       return ReplaceInstUsesWith(SI, FalseVal);
 427     // Transform (X != Y) ? X : Y  -> X
 428     if (Pred == ICmpInst::ICMP_NE)
 429       return ReplaceInstUsesWith(SI, TrueVal);
 430     /// NOTE: if we wanted to, this is where to detect integer MIN/MAX
 431
 432   } else if (CmpLHS == FalseVal && CmpRHS == TrueVal) {
 433     // Transform (X == Y) ? Y : X  -> X
 434     if (Pred == ICmpInst::ICMP_EQ)
 435       return ReplaceInstUsesWith(SI, FalseVal);
 436     // Transform (X != Y) ? Y : X  -> Y
 437     if (Pred == ICmpInst::ICMP_NE)
 438       return ReplaceInstUsesWith(SI, TrueVal);
 439     /// NOTE: if we wanted to, this is where to detect integer MIN/MAX
 440   }
 441
 442   if (isa<Constant>(CmpRHS)) {
 443     if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
 444       // Transform (X == C) ? X : Y -> (X == C) ? C : Y
 445       SI.setOperand(1, CmpRHS);
 446       Changed = true;
 447     } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
 448       // Transform (X != C) ? Y : X -> (X != C) ? Y : C
 449       SI.setOperand(2, CmpRHS);
 450       Changed = true;
 451     }
 452   }
 453
 454   return Changed ? &SI : 0;
 455 }
 456
 457
 458 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
 459 /// PHI node (but the two may be in different blocks).  See if the true/false
 460 /// values (V) are live in all of the predecessor blocks of the PHI.  For
 461 /// example, cases like this cannot be mapped:
 462 ///
 463 ///   X = phi [ C1, BB1], [C2, BB2]
 464 ///   Y = add
 465 ///   Z = select X, Y, 0
 466 ///
 467 /// because Y is not live in BB1/BB2.
 468 ///
 469 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
 470                                                    const SelectInst &SI) {
 471   // If the value is a non-instruction value like a constant or argument, it
 472   // can always be mapped.
 473   const Instruction *I = dyn_cast<Instruction>(V);
 474   if (I == 0) return true;
 475
 476   // If V is a PHI node defined in the same block as the condition PHI, we can
 477   // map the arguments.
 478   const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
 479
 480   if (const PHINode *VP = dyn_cast<PHINode>(I))
 481     if (VP->getParent() == CondPHI->getParent())
 482       return true;
 483
 484   // Otherwise, if the PHI and select are defined in the same block and if V is
 485   // defined in a different block, then we can transform it.
 486   if (SI.getParent() == CondPHI->getParent() &&
 487       I->getParent() != CondPHI->getParent())
 488     return true;
 489
 490   // Otherwise we have a 'hard' case and we can't tell without doing more
 491   // detailed dominator based analysis, punt.
 492   return false;
 493 }
 494
 495 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
 496 ///   SPF2(SPF1(A, B), C)
 497 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
 498                                         SelectPatternFlavor SPF1,
 499                                         Value *A, Value *B,
 500                                         Instruction &Outer,
 501                                         SelectPatternFlavor SPF2, Value *C) {
 502   if (C == A || C == B) {
 503     // MAX(MAX(A, B), B) -> MAX(A, B)
 504     // MIN(MIN(a, b), a) -> MIN(a, b)
 505     if (SPF1 == SPF2)
 506       return ReplaceInstUsesWith(Outer, Inner);
 507
 508     // MAX(MIN(a, b), a) -> a
 509     // MIN(MAX(a, b), a) -> a
 510     if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
 511         (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
 512         (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
 513         (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
 514       return ReplaceInstUsesWith(Outer, C);
 515   }
 516
 517   // TODO: MIN(MIN(A, 23), 97)
 518   return 0;
 519 }
 520
 521
 522 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
 523 /// both be) and we have an icmp instruction with zero, and we have an 'and'
 524 /// with the non-constant value and a power of two we can turn the select
 525 /// into a shift on the result of the 'and'.
 526 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
 527                                 ConstantInt *FalseVal,
 528                                 InstCombiner::BuilderTy *Builder) {
 529   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
 530   if (!IC || !IC->isEquality())
 531     return 0;
 532
 533   if (!match(IC->getOperand(1), m_Zero()))
 534     return 0;
 535
 536   ConstantInt *AndRHS;
 537   Value *LHS = IC->getOperand(0);
 538   if (LHS->getType() != SI.getType() ||
 539       !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
 540     return 0;
 541
 542   // If both select arms are non-zero see if we have a select of the form
 543   // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
 544   // for 'x ? 2^n : 0' and fix the thing up at the end.
 545   ConstantInt *Offset = 0;
 546   if (!TrueVal->isZero() && !FalseVal->isZero()) {
 547     if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
 548       Offset = FalseVal;
 549     else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
 550       Offset = TrueVal;
 551     else
 552       return 0;
 553
 554     // Adjust TrueVal and FalseVal to the offset.
 555     TrueVal = ConstantInt::get(Builder->getContext(),
 556                                TrueVal->getValue() - Offset->getValue());
 557     FalseVal = ConstantInt::get(Builder->getContext(),
 558                                 FalseVal->getValue() - Offset->getValue());
 559   }
 560
 561   // Make sure the mask in the 'and' and one of the select arms is a power of 2.
 562   if (!AndRHS->getValue().isPowerOf2() ||
 563       (!TrueVal->getValue().isPowerOf2() &&
 564        !FalseVal->getValue().isPowerOf2()))
 565     return 0;
 566
 567   // Determine which shift is needed to transform result of the 'and' into the
 568   // desired result.
 569   ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
 570   unsigned ValZeros = ValC->getValue().logBase2();
 571   unsigned AndZeros = AndRHS->getValue().logBase2();
 572
 573   Value *V = LHS;
 574   if (ValZeros > AndZeros)
 575     V = Builder->CreateShl(V, ValZeros - AndZeros);
 576   else if (ValZeros < AndZeros)
 577     V = Builder->CreateLShr(V, AndZeros - ValZeros);
 578
 579   // Okay, now we know that everything is set up, we just don't know whether we
 580   // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
 581   bool ShouldNotVal = !TrueVal->isZero();
 582   ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
 583   if (ShouldNotVal)
 584     V = Builder->CreateXor(V, ValC);
 585
 586   // Apply an offset if needed.
 587   if (Offset)
 588     V = Builder->CreateAdd(V, Offset);
 589   return V;
 590 }
 591
 592 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
 593   Value *CondVal = SI.getCondition();
 594   Value *TrueVal = SI.getTrueValue();
 595   Value *FalseVal = SI.getFalseValue();
 596
 597   if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD))
 598     return ReplaceInstUsesWith(SI, V);
 599
 600   if (SI.getType()->isIntegerTy(1)) {
 601     if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
 602       if (C->getZExtValue()) {
 603         // Change: A = select B, true, C --> A = or B, C
 604         return BinaryOperator::CreateOr(CondVal, FalseVal);
 605       }
 606       // Change: A = select B, false, C --> A = and !B, C
 607       Value *NotCond =
 608         InsertNewInstBefore(BinaryOperator::CreateNot(CondVal,
 609                                            "not."+CondVal->getName()), SI);
 610       return BinaryOperator::CreateAnd(NotCond, FalseVal);
 611     } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
 612       if (C->getZExtValue() == false) {
 613         // Change: A = select B, C, false --> A = and B, C
 614         return BinaryOperator::CreateAnd(CondVal, TrueVal);
 615       }
 616       // Change: A = select B, C, true --> A = or !B, C
 617       Value *NotCond =
 618         InsertNewInstBefore(BinaryOperator::CreateNot(CondVal,
 619                                            "not."+CondVal->getName()), SI);
 620       return BinaryOperator::CreateOr(NotCond, TrueVal);
 621     }
 622
 623     // select a, b, a  -> a&b
 624     // select a, a, b  -> a|b
 625     if (CondVal == TrueVal)
 626       return BinaryOperator::CreateOr(CondVal, FalseVal);
 627     else if (CondVal == FalseVal)
 628       return BinaryOperator::CreateAnd(CondVal, TrueVal);
 629   }
 630
 631   // Selecting between two integer constants?
 632   if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
 633     if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
 634       // select C, 1, 0 -> zext C to int
 635       if (FalseValC->isZero() && TrueValC->getValue() == 1)
 636         return new ZExtInst(CondVal, SI.getType());
 637
 638       // select C, -1, 0 -> sext C to int
 639       if (FalseValC->isZero() && TrueValC->isAllOnesValue())
 640         return new SExtInst(CondVal, SI.getType());
 641
 642       // select C, 0, 1 -> zext !C to int
 643       if (TrueValC->isZero() && FalseValC->getValue() == 1) {
 644         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
 645         return new ZExtInst(NotCond, SI.getType());
 646       }
 647
 648       // select C, 0, -1 -> sext !C to int
 649       if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
 650         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
 651         return new SExtInst(NotCond, SI.getType());
 652       }
 653
 654       if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
 655         return ReplaceInstUsesWith(SI, V);
 656     }
 657
 658   // See if we are selecting two values based on a comparison of the two values.
 659   if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
 660     if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
 661       // Transform (X == Y) ? X : Y  -> Y
 662       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
 663         // This is not safe in general for floating point:
 664         // consider X== -0, Y== +0.
 665         // It becomes safe if either operand is a nonzero constant.
 666         ConstantFP *CFPt, *CFPf;
 667         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 668               !CFPt->getValueAPF().isZero()) ||
 669             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 670              !CFPf->getValueAPF().isZero()))
 671         return ReplaceInstUsesWith(SI, FalseVal);
 672       }
 673       // Transform (X une Y) ? X : Y  -> X
 674       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
 675         // This is not safe in general for floating point:
 676         // consider X== -0, Y== +0.
 677         // It becomes safe if either operand is a nonzero constant.
 678         ConstantFP *CFPt, *CFPf;
 679         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 680               !CFPt->getValueAPF().isZero()) ||
 681             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 682              !CFPf->getValueAPF().isZero()))
 683         return ReplaceInstUsesWith(SI, TrueVal);
 684       }
 685       // NOTE: if we wanted to, this is where to detect MIN/MAX
 686
 687     } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
 688       // Transform (X == Y) ? Y : X  -> X
 689       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
 690         // This is not safe in general for floating point:
 691         // consider X== -0, Y== +0.
 692         // It becomes safe if either operand is a nonzero constant.
 693         ConstantFP *CFPt, *CFPf;
 694         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 695               !CFPt->getValueAPF().isZero()) ||
 696             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 697              !CFPf->getValueAPF().isZero()))
 698           return ReplaceInstUsesWith(SI, FalseVal);
 699       }
 700       // Transform (X une Y) ? Y : X  -> Y
 701       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
 702         // This is not safe in general for floating point:
 703         // consider X== -0, Y== +0.
 704         // It becomes safe if either operand is a nonzero constant.
 705         ConstantFP *CFPt, *CFPf;
 706         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 707               !CFPt->getValueAPF().isZero()) ||
 708             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 709              !CFPf->getValueAPF().isZero()))
 710           return ReplaceInstUsesWith(SI, TrueVal);
 711       }
 712       // NOTE: if we wanted to, this is where to detect MIN/MAX
 713     }
 714     // NOTE: if we wanted to, this is where to detect ABS
 715   }
 716
 717   // See if we are selecting two values based on a comparison of the two values.
 718   if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
 719     if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
 720       return Result;
 721
 722   if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
 723     if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
 724       if (TI->hasOneUse() && FI->hasOneUse()) {
 725         Instruction *AddOp = 0, *SubOp = 0;
 726
 727         // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
 728         if (TI->getOpcode() == FI->getOpcode())
 729           if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
 730             return IV;
 731
 732         // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))).  This is
 733         // even legal for FP.
 734         if ((TI->getOpcode() == Instruction::Sub &&
 735              FI->getOpcode() == Instruction::Add) ||
 736             (TI->getOpcode() == Instruction::FSub &&
 737              FI->getOpcode() == Instruction::FAdd)) {
 738           AddOp = FI; SubOp = TI;
 739         } else if ((FI->getOpcode() == Instruction::Sub &&
 740                     TI->getOpcode() == Instruction::Add) ||
 741                    (FI->getOpcode() == Instruction::FSub &&
 742                     TI->getOpcode() == Instruction::FAdd)) {
 743           AddOp = TI; SubOp = FI;
 744         }
 745
 746         if (AddOp) {
 747           Value *OtherAddOp = 0;
 748           if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
 749             OtherAddOp = AddOp->getOperand(1);
 750           } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
 751             OtherAddOp = AddOp->getOperand(0);
 752           }
 753
 754           if (OtherAddOp) {
 755             // So at this point we know we have (Y -> OtherAddOp):
 756             //        select C, (add X, Y), (sub X, Z)
 757             Value *NegVal;  // Compute -Z
 758             if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) {
 759               NegVal = ConstantExpr::getNeg(C);
 760             } else if (SI.getType()->isFloatingPointTy()) {
 761               NegVal = InsertNewInstBefore(
 762                     BinaryOperator::CreateFNeg(SubOp->getOperand(1),
 763                                               "tmp"), SI);
 764             } else {
 765               NegVal = InsertNewInstBefore(
 766                     BinaryOperator::CreateNeg(SubOp->getOperand(1),
 767                                               "tmp"), SI);
 768             }
 769
 770             Value *NewTrueOp = OtherAddOp;
 771             Value *NewFalseOp = NegVal;
 772             if (AddOp != TI)
 773               std::swap(NewTrueOp, NewFalseOp);
 774             Instruction *NewSel =
 775               SelectInst::Create(CondVal, NewTrueOp,
 776                                  NewFalseOp, SI.getName() + ".p");
 777
 778             NewSel = InsertNewInstBefore(NewSel, SI);
 779             if (SI.getType()->isFloatingPointTy())
 780               return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
 781             else
 782               return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
 783           }
 784         }
 785       }
 786
 787   // See if we can fold the select into one of our operands.
 788   if (SI.getType()->isIntegerTy()) {
 789     if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
 790       return FoldI;
 791
 792     // MAX(MAX(a, b), a) -> MAX(a, b)
 793     // MIN(MIN(a, b), a) -> MIN(a, b)
 794     // MAX(MIN(a, b), a) -> a
 795     // MIN(MAX(a, b), a) -> a
 796     Value *LHS, *RHS, *LHS2, *RHS2;
 797     if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
 798       if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
 799         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
 800                                           SI, SPF, RHS))
 801           return R;
 802       if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
 803         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
 804                                           SI, SPF, LHS))
 805           return R;
 806     }
 807
 808     // TODO.
 809     // ABS(-X) -> ABS(X)
 810     // ABS(ABS(X)) -> ABS(X)
 811   }
 812
 813   // See if we can fold the select into a phi node if the condition is a select.
 814   if (isa<PHINode>(SI.getCondition()))
 815     // The true/false values have to be live in the PHI predecessor's blocks.
 816     if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
 817         CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
 818       if (Instruction *NV = FoldOpIntoPhi(SI))
 819         return NV;
 820
 821   if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
 822     if (TrueSI->getCondition() == CondVal) {
 823       SI.setOperand(1, TrueSI->getTrueValue());
 824       return &SI;
 825     }
 826   }
 827   if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
 828     if (FalseSI->getCondition() == CondVal) {
 829       SI.setOperand(2, FalseSI->getFalseValue());
 830       return &SI;
 831     }
 832   }
 833
 834   if (BinaryOperator::isNot(CondVal)) {
 835     SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
 836     SI.setOperand(1, FalseVal);
 837     SI.setOperand(2, TrueVal);
 838     return &SI;
 839   }
 840
 841   return 0;
 842 }