src/llvm/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/ConstantFolding.h"
  17 #include "llvm/Analysis/InstructionSimplify.h"
  18 using namespace llvm;
  19 using namespace PatternMatch;
  20
  21 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
  22 /// returning the kind and providing the out parameter results if we
  23 /// successfully match.
  24 static SelectPatternFlavor
  25 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
  26   SelectInst *SI = dyn_cast<SelectInst>(V);
  27   if (SI == 0) return SPF_UNKNOWN;
  28
  29   ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
  30   if (ICI == 0) return SPF_UNKNOWN;
  31
  32   LHS = ICI->getOperand(0);
  33   RHS = ICI->getOperand(1);
  34
  35   // (icmp X, Y) ? X : Y
  36   if (SI->getTrueValue() == ICI->getOperand(0) &&
  37       SI->getFalseValue() == ICI->getOperand(1)) {
  38     switch (ICI->getPredicate()) {
  39     default: return SPF_UNKNOWN; // Equality.
  40     case ICmpInst::ICMP_UGT:
  41     case ICmpInst::ICMP_UGE: return SPF_UMAX;
  42     case ICmpInst::ICMP_SGT:
  43     case ICmpInst::ICMP_SGE: return SPF_SMAX;
  44     case ICmpInst::ICMP_ULT:
  45     case ICmpInst::ICMP_ULE: return SPF_UMIN;
  46     case ICmpInst::ICMP_SLT:
  47     case ICmpInst::ICMP_SLE: return SPF_SMIN;
  48     }
  49   }
  50
  51   // (icmp X, Y) ? Y : X
  52   if (SI->getTrueValue() == ICI->getOperand(1) &&
  53       SI->getFalseValue() == ICI->getOperand(0)) {
  54     switch (ICI->getPredicate()) {
  55       default: return SPF_UNKNOWN; // Equality.
  56       case ICmpInst::ICMP_UGT:
  57       case ICmpInst::ICMP_UGE: return SPF_UMIN;
  58       case ICmpInst::ICMP_SGT:
  59       case ICmpInst::ICMP_SGE: return SPF_SMIN;
  60       case ICmpInst::ICMP_ULT:
  61       case ICmpInst::ICMP_ULE: return SPF_UMAX;
  62       case ICmpInst::ICMP_SLT:
  63       case ICmpInst::ICMP_SLE: return SPF_SMAX;
  64     }
  65   }
  66
  67   // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)
  68
  69   return SPF_UNKNOWN;
  70 }
  71
  72
  73 /// GetSelectFoldableOperands - We want to turn code that looks like this:
  74 ///   %C = or %A, %B
  75 ///   %D = select %cond, %C, %A
  76 /// into:
  77 ///   %C = select %cond, %B, 0
  78 ///   %D = or %A, %C
  79 ///
  80 /// Assuming that the specified instruction is an operand to the select, return
  81 /// a bitmask indicating which operands of this instruction are foldable if they
  82 /// equal the other incoming value of the select.
  83 ///
  84 static unsigned GetSelectFoldableOperands(Instruction *I) {
  85   switch (I->getOpcode()) {
  86   case Instruction::Add:
  87   case Instruction::Mul:
  88   case Instruction::And:
  89   case Instruction::Or:
  90   case Instruction::Xor:
  91     return 3;              // Can fold through either operand.
  92   case Instruction::Sub:   // Can only fold on the amount subtracted.
  93   case Instruction::Shl:   // Can only fold on the shift amount.
  94   case Instruction::LShr:
  95   case Instruction::AShr:
  96     return 1;
  97   default:
  98     return 0;              // Cannot fold
  99   }
 100 }
 101
 102 /// GetSelectFoldableConstant - For the same transformation as the previous
 103 /// function, return the identity constant that goes into the select.
 104 static Constant *GetSelectFoldableConstant(Instruction *I) {
 105   switch (I->getOpcode()) {
 106   default: llvm_unreachable("This cannot happen!");
 107   case Instruction::Add:
 108   case Instruction::Sub:
 109   case Instruction::Or:
 110   case Instruction::Xor:
 111   case Instruction::Shl:
 112   case Instruction::LShr:
 113   case Instruction::AShr:
 114     return Constant::getNullValue(I->getType());
 115   case Instruction::And:
 116     return Constant::getAllOnesValue(I->getType());
 117   case Instruction::Mul:
 118     return ConstantInt::get(I->getType(), 1);
 119   }
 120 }
 121
 122 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
 123 /// have the same opcode and only one use each.  Try to simplify this.
 124 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
 125                                           Instruction *FI) {
 126   if (TI->getNumOperands() == 1) {
 127     // If this is a non-volatile load or a cast from the same type,
 128     // merge.
 129     if (TI->isCast()) {
 130       if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType())
 131         return 0;
 132       // The select condition may be a vector. We may only change the operand
 133       // type if the vector width remains the same (and matches the condition).
 134       Type *CondTy = SI.getCondition()->getType();
 135       if (CondTy->isVectorTy() && CondTy->getVectorNumElements() !=
 136           FI->getOperand(0)->getType()->getVectorNumElements())
 137         return 0;
 138     } else {
 139       return 0;  // unknown unary op.
 140     }
 141
 142     // Fold this by inserting a select from the input values.
 143     Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0),
 144                                          FI->getOperand(0), SI.getName()+".v");
 145     return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
 146                             TI->getType());
 147   }
 148
 149   // Only handle binary operators here.
 150   if (!isa<BinaryOperator>(TI))
 151     return 0;
 152
 153   // Figure out if the operations have any operands in common.
 154   Value *MatchOp, *OtherOpT, *OtherOpF;
 155   bool MatchIsOpZero;
 156   if (TI->getOperand(0) == FI->getOperand(0)) {
 157     MatchOp  = TI->getOperand(0);
 158     OtherOpT = TI->getOperand(1);
 159     OtherOpF = FI->getOperand(1);
 160     MatchIsOpZero = true;
 161   } else if (TI->getOperand(1) == FI->getOperand(1)) {
 162     MatchOp  = TI->getOperand(1);
 163     OtherOpT = TI->getOperand(0);
 164     OtherOpF = FI->getOperand(0);
 165     MatchIsOpZero = false;
 166   } else if (!TI->isCommutative()) {
 167     return 0;
 168   } else if (TI->getOperand(0) == FI->getOperand(1)) {
 169     MatchOp  = TI->getOperand(0);
 170     OtherOpT = TI->getOperand(1);
 171     OtherOpF = FI->getOperand(0);
 172     MatchIsOpZero = true;
 173   } else if (TI->getOperand(1) == FI->getOperand(0)) {
 174     MatchOp  = TI->getOperand(1);
 175     OtherOpT = TI->getOperand(0);
 176     OtherOpF = FI->getOperand(1);
 177     MatchIsOpZero = true;
 178   } else {
 179     return 0;
 180   }
 181
 182   // If we reach here, they do have operations in common.
 183   Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
 184                                        OtherOpF, SI.getName()+".v");
 185
 186   if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
 187     if (MatchIsOpZero)
 188       return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
 189     else
 190       return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
 191   }
 192   llvm_unreachable("Shouldn't get here");
 193 }
 194
 195 static bool isSelect01(Constant *C1, Constant *C2) {
 196   ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
 197   if (!C1I)
 198     return false;
 199   ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
 200   if (!C2I)
 201     return false;
 202   if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
 203     return false;
 204   return C1I->isOne() || C1I->isAllOnesValue() ||
 205          C2I->isOne() || C2I->isAllOnesValue();
 206 }
 207
 208 /// FoldSelectIntoOp - Try fold the select into one of the operands to
 209 /// facilitate further optimization.
 210 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
 211                                             Value *FalseVal) {
 212   // See the comment above GetSelectFoldableOperands for a description of the
 213   // transformation we are doing here.
 214   if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
 215     if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
 216         !isa<Constant>(FalseVal)) {
 217       if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
 218         unsigned OpToFold = 0;
 219         if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
 220           OpToFold = 1;
 221         } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
 222           OpToFold = 2;
 223         }
 224
 225         if (OpToFold) {
 226           Constant *C = GetSelectFoldableConstant(TVI);
 227           Value *OOp = TVI->getOperand(2-OpToFold);
 228           // Avoid creating select between 2 constants unless it's selecting
 229           // between 0, 1 and -1.
 230           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
 231             Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C);
 232             NewSel->takeName(TVI);
 233             BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
 234             BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
 235                                                         FalseVal, NewSel);
 236             if (isa<PossiblyExactOperator>(BO))
 237               BO->setIsExact(TVI_BO->isExact());
 238             if (isa<OverflowingBinaryOperator>(BO)) {
 239               BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
 240               BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
 241             }
 242             return BO;
 243           }
 244         }
 245       }
 246     }
 247   }
 248
 249   if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
 250     if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
 251         !isa<Constant>(TrueVal)) {
 252       if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
 253         unsigned OpToFold = 0;
 254         if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
 255           OpToFold = 1;
 256         } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
 257           OpToFold = 2;
 258         }
 259
 260         if (OpToFold) {
 261           Constant *C = GetSelectFoldableConstant(FVI);
 262           Value *OOp = FVI->getOperand(2-OpToFold);
 263           // Avoid creating select between 2 constants unless it's selecting
 264           // between 0, 1 and -1.
 265           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
 266             Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp);
 267             NewSel->takeName(FVI);
 268             BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
 269             BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
 270                                                         TrueVal, NewSel);
 271             if (isa<PossiblyExactOperator>(BO))
 272               BO->setIsExact(FVI_BO->isExact());
 273             if (isa<OverflowingBinaryOperator>(BO)) {
 274               BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
 275               BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
 276             }
 277             return BO;
 278           }
 279         }
 280       }
 281     }
 282   }
 283
 284   return 0;
 285 }
 286
 287 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
 288 /// replaced with RepOp.
 289 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
 290                                      const TargetData *TD,
 291                                      const TargetLibraryInfo *TLI) {
 292   // Trivial replacement.
 293   if (V == Op)
 294     return RepOp;
 295
 296   Instruction *I = dyn_cast<Instruction>(V);
 297   if (!I)
 298     return 0;
 299
 300   // If this is a binary operator, try to simplify it with the replaced op.
 301   if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
 302     if (B->getOperand(0) == Op)
 303       return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI);
 304     if (B->getOperand(1) == Op)
 305       return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI);
 306   }
 307
 308   // Same for CmpInsts.
 309   if (CmpInst *C = dyn_cast<CmpInst>(I)) {
 310     if (C->getOperand(0) == Op)
 311       return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD,
 312                              TLI);
 313     if (C->getOperand(1) == Op)
 314       return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD,
 315                              TLI);
 316   }
 317
 318   // TODO: We could hand off more cases to instsimplify here.
 319
 320   // If all operands are constant after substituting Op for RepOp then we can
 321   // constant fold the instruction.
 322   if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
 323     // Build a list of all constant operands.
 324     SmallVector<Constant*, 8> ConstOps;
 325     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
 326       if (I->getOperand(i) == Op)
 327         ConstOps.push_back(CRepOp);
 328       else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
 329         ConstOps.push_back(COp);
 330       else
 331         break;
 332     }
 333
 334     // All operands were constants, fold it.
 335     if (ConstOps.size() == I->getNumOperands()) {
 336       if (LoadInst *LI = dyn_cast<LoadInst>(I))
 337         if (!LI->isVolatile())
 338           return ConstantFoldLoadFromConstPtr(ConstOps[0], TD);
 339
 340       return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
 341                                       ConstOps, TD, TLI);
 342     }
 343   }
 344
 345   return 0;
 346 }
 347
 348 /// visitSelectInstWithICmp - Visit a SelectInst that has an
 349 /// ICmpInst as its first operand.
 350 ///
 351 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
 352                                                    ICmpInst *ICI) {
 353   bool Changed = false;
 354   ICmpInst::Predicate Pred = ICI->getPredicate();
 355   Value *CmpLHS = ICI->getOperand(0);
 356   Value *CmpRHS = ICI->getOperand(1);
 357   Value *TrueVal = SI.getTrueValue();
 358   Value *FalseVal = SI.getFalseValue();
 359
 360   // Check cases where the comparison is with a constant that
 361   // can be adjusted to fit the min/max idiom. We may move or edit ICI
 362   // here, so make sure the select is the only user.
 363   if (ICI->hasOneUse())
 364     if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
 365       // X < MIN ? T : F  -->  F
 366       if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
 367           && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
 368         return ReplaceInstUsesWith(SI, FalseVal);
 369       // X > MAX ? T : F  -->  F
 370       else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
 371                && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
 372         return ReplaceInstUsesWith(SI, FalseVal);
 373       switch (Pred) {
 374       default: break;
 375       case ICmpInst::ICMP_ULT:
 376       case ICmpInst::ICMP_SLT:
 377       case ICmpInst::ICMP_UGT:
 378       case ICmpInst::ICMP_SGT: {
 379         // These transformations only work for selects over integers.
 380         IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
 381         if (!SelectTy)
 382           break;
 383
 384         Constant *AdjustedRHS;
 385         if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
 386           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
 387         else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
 388           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
 389
 390         // X > C ? X : C+1  -->  X < C+1 ? C+1 : X
 391         // X < C ? X : C-1  -->  X > C-1 ? C-1 : X
 392         if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
 393             (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
 394           ; // Nothing to do here. Values match without any sign/zero extension.
 395
 396         // Types do not match. Instead of calculating this with mixed types
 397         // promote all to the larger type. This enables scalar evolution to
 398         // analyze this expression.
 399         else if (CmpRHS->getType()->getScalarSizeInBits()
 400                  < SelectTy->getBitWidth()) {
 401           Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
 402
 403           // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
 404           // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
 405           // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
 406           // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
 407           if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
 408                 sextRHS == FalseVal) {
 409             CmpLHS = TrueVal;
 410             AdjustedRHS = sextRHS;
 411           } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
 412                      sextRHS == TrueVal) {
 413             CmpLHS = FalseVal;
 414             AdjustedRHS = sextRHS;
 415           } else if (ICI->isUnsigned()) {
 416             Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
 417             // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
 418             // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
 419             // zext + signed compare cannot be changed:
 420             //    0xff <s 0x00, but 0x00ff >s 0x0000
 421             if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
 422                 zextRHS == FalseVal) {
 423               CmpLHS = TrueVal;
 424               AdjustedRHS = zextRHS;
 425             } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
 426                        zextRHS == TrueVal) {
 427               CmpLHS = FalseVal;
 428               AdjustedRHS = zextRHS;
 429             } else
 430               break;
 431           } else
 432             break;
 433         } else
 434           break;
 435
 436         Pred = ICmpInst::getSwappedPredicate(Pred);
 437         CmpRHS = AdjustedRHS;
 438         std::swap(FalseVal, TrueVal);
 439         ICI->setPredicate(Pred);
 440         ICI->setOperand(0, CmpLHS);
 441         ICI->setOperand(1, CmpRHS);
 442         SI.setOperand(1, TrueVal);
 443         SI.setOperand(2, FalseVal);
 444
 445         // Move ICI instruction right before the select instruction. Otherwise
 446         // the sext/zext value may be defined after the ICI instruction uses it.
 447         ICI->moveBefore(&SI);
 448
 449         Changed = true;
 450         break;
 451       }
 452       }
 453     }
 454
 455   // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
 456   // and       (X <s  0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
 457   // FIXME: Type and constness constraints could be lifted, but we have to
 458   //        watch code size carefully. We should consider xor instead of
 459   //        sub/add when we decide to do that.
 460   if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
 461     if (TrueVal->getType() == Ty) {
 462       if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
 463         ConstantInt *C1 = NULL, *C2 = NULL;
 464         if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
 465           C1 = dyn_cast<ConstantInt>(TrueVal);
 466           C2 = dyn_cast<ConstantInt>(FalseVal);
 467         } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
 468           C1 = dyn_cast<ConstantInt>(FalseVal);
 469           C2 = dyn_cast<ConstantInt>(TrueVal);
 470         }
 471         if (C1 && C2) {
 472           // This shift results in either -1 or 0.
 473           Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
 474
 475           // Check if we can express the operation with a single or.
 476           if (C2->isAllOnesValue())
 477             return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
 478
 479           Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
 480           return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
 481         }
 482       }
 483     }
 484   }
 485
 486   // If we have an equality comparison then we know the value in one of the
 487   // arms of the select. See if substituting this value into the arm and
 488   // simplifying the result yields the same value as the other arm.
 489   if (Pred == ICmpInst::ICMP_EQ) {
 490     if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal ||
 491         SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal)
 492       return ReplaceInstUsesWith(SI, FalseVal);
 493     if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal ||
 494         SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal)
 495       return ReplaceInstUsesWith(SI, FalseVal);
 496   } else if (Pred == ICmpInst::ICMP_NE) {
 497     if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal ||
 498         SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal)
 499       return ReplaceInstUsesWith(SI, TrueVal);
 500     if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal ||
 501         SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal)
 502       return ReplaceInstUsesWith(SI, TrueVal);
 503   }
 504
 505   // NOTE: if we wanted to, this is where to detect integer MIN/MAX
 506
 507   if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
 508     if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
 509       // Transform (X == C) ? X : Y -> (X == C) ? C : Y
 510       SI.setOperand(1, CmpRHS);
 511       Changed = true;
 512     } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
 513       // Transform (X != C) ? Y : X -> (X != C) ? Y : C
 514       SI.setOperand(2, CmpRHS);
 515       Changed = true;
 516     }
 517   }
 518
 519   return Changed ? &SI : 0;
 520 }
 521
 522
 523 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
 524 /// PHI node (but the two may be in different blocks).  See if the true/false
 525 /// values (V) are live in all of the predecessor blocks of the PHI.  For
 526 /// example, cases like this cannot be mapped:
 527 ///
 528 ///   X = phi [ C1, BB1], [C2, BB2]
 529 ///   Y = add
 530 ///   Z = select X, Y, 0
 531 ///
 532 /// because Y is not live in BB1/BB2.
 533 ///
 534 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
 535                                                    const SelectInst &SI) {
 536   // If the value is a non-instruction value like a constant or argument, it
 537   // can always be mapped.
 538   const Instruction *I = dyn_cast<Instruction>(V);
 539   if (I == 0) return true;
 540
 541   // If V is a PHI node defined in the same block as the condition PHI, we can
 542   // map the arguments.
 543   const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
 544
 545   if (const PHINode *VP = dyn_cast<PHINode>(I))
 546     if (VP->getParent() == CondPHI->getParent())
 547       return true;
 548
 549   // Otherwise, if the PHI and select are defined in the same block and if V is
 550   // defined in a different block, then we can transform it.
 551   if (SI.getParent() == CondPHI->getParent() &&
 552       I->getParent() != CondPHI->getParent())
 553     return true;
 554
 555   // Otherwise we have a 'hard' case and we can't tell without doing more
 556   // detailed dominator based analysis, punt.
 557   return false;
 558 }
 559
 560 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
 561 ///   SPF2(SPF1(A, B), C)
 562 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
 563                                         SelectPatternFlavor SPF1,
 564                                         Value *A, Value *B,
 565                                         Instruction &Outer,
 566                                         SelectPatternFlavor SPF2, Value *C) {
 567   if (C == A || C == B) {
 568     // MAX(MAX(A, B), B) -> MAX(A, B)
 569     // MIN(MIN(a, b), a) -> MIN(a, b)
 570     if (SPF1 == SPF2)
 571       return ReplaceInstUsesWith(Outer, Inner);
 572
 573     // MAX(MIN(a, b), a) -> a
 574     // MIN(MAX(a, b), a) -> a
 575     if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
 576         (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
 577         (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
 578         (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
 579       return ReplaceInstUsesWith(Outer, C);
 580   }
 581
 582   // TODO: MIN(MIN(A, 23), 97)
 583   return 0;
 584 }
 585
 586
 587 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
 588 /// both be) and we have an icmp instruction with zero, and we have an 'and'
 589 /// with the non-constant value and a power of two we can turn the select
 590 /// into a shift on the result of the 'and'.
 591 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
 592                                 ConstantInt *FalseVal,
 593                                 InstCombiner::BuilderTy *Builder) {
 594   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
 595   if (!IC || !IC->isEquality())
 596     return 0;
 597
 598   if (!match(IC->getOperand(1), m_Zero()))
 599     return 0;
 600
 601   ConstantInt *AndRHS;
 602   Value *LHS = IC->getOperand(0);
 603   if (LHS->getType() != SI.getType() ||
 604       !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
 605     return 0;
 606
 607   // If both select arms are non-zero see if we have a select of the form
 608   // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
 609   // for 'x ? 2^n : 0' and fix the thing up at the end.
 610   ConstantInt *Offset = 0;
 611   if (!TrueVal->isZero() && !FalseVal->isZero()) {
 612     if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
 613       Offset = FalseVal;
 614     else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
 615       Offset = TrueVal;
 616     else
 617       return 0;
 618
 619     // Adjust TrueVal and FalseVal to the offset.
 620     TrueVal = ConstantInt::get(Builder->getContext(),
 621                                TrueVal->getValue() - Offset->getValue());
 622     FalseVal = ConstantInt::get(Builder->getContext(),
 623                                 FalseVal->getValue() - Offset->getValue());
 624   }
 625
 626   // Make sure the mask in the 'and' and one of the select arms is a power of 2.
 627   if (!AndRHS->getValue().isPowerOf2() ||
 628       (!TrueVal->getValue().isPowerOf2() &&
 629        !FalseVal->getValue().isPowerOf2()))
 630     return 0;
 631
 632   // Determine which shift is needed to transform result of the 'and' into the
 633   // desired result.
 634   ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
 635   unsigned ValZeros = ValC->getValue().logBase2();
 636   unsigned AndZeros = AndRHS->getValue().logBase2();
 637
 638   Value *V = LHS;
 639   if (ValZeros > AndZeros)
 640     V = Builder->CreateShl(V, ValZeros - AndZeros);
 641   else if (ValZeros < AndZeros)
 642     V = Builder->CreateLShr(V, AndZeros - ValZeros);
 643
 644   // Okay, now we know that everything is set up, we just don't know whether we
 645   // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
 646   bool ShouldNotVal = !TrueVal->isZero();
 647   ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
 648   if (ShouldNotVal)
 649     V = Builder->CreateXor(V, ValC);
 650
 651   // Apply an offset if needed.
 652   if (Offset)
 653     V = Builder->CreateAdd(V, Offset);
 654   return V;
 655 }
 656
 657 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
 658   Value *CondVal = SI.getCondition();
 659   Value *TrueVal = SI.getTrueValue();
 660   Value *FalseVal = SI.getFalseValue();
 661
 662   if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD))
 663     return ReplaceInstUsesWith(SI, V);
 664
 665   if (SI.getType()->isIntegerTy(1)) {
 666     if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
 667       if (C->getZExtValue()) {
 668         // Change: A = select B, true, C --> A = or B, C
 669         return BinaryOperator::CreateOr(CondVal, FalseVal);
 670       }
 671       // Change: A = select B, false, C --> A = and !B, C
 672       Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
 673       return BinaryOperator::CreateAnd(NotCond, FalseVal);
 674     } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
 675       if (C->getZExtValue() == false) {
 676         // Change: A = select B, C, false --> A = and B, C
 677         return BinaryOperator::CreateAnd(CondVal, TrueVal);
 678       }
 679       // Change: A = select B, C, true --> A = or !B, C
 680       Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
 681       return BinaryOperator::CreateOr(NotCond, TrueVal);
 682     }
 683
 684     // select a, b, a  -> a&b
 685     // select a, a, b  -> a|b
 686     if (CondVal == TrueVal)
 687       return BinaryOperator::CreateOr(CondVal, FalseVal);
 688     else if (CondVal == FalseVal)
 689       return BinaryOperator::CreateAnd(CondVal, TrueVal);
 690
 691     // select a, ~a, b -> (~a)&b
 692     // select a, b, ~a -> (~a)|b
 693     if (match(TrueVal, m_Not(m_Specific(CondVal))))
 694       return BinaryOperator::CreateAnd(TrueVal, FalseVal);
 695     else if (match(FalseVal, m_Not(m_Specific(CondVal))))
 696       return BinaryOperator::CreateOr(TrueVal, FalseVal);
 697   }
 698
 699   // Selecting between two integer constants?
 700   if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
 701     if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
 702       // select C, 1, 0 -> zext C to int
 703       if (FalseValC->isZero() && TrueValC->getValue() == 1)
 704         return new ZExtInst(CondVal, SI.getType());
 705
 706       // select C, -1, 0 -> sext C to int
 707       if (FalseValC->isZero() && TrueValC->isAllOnesValue())
 708         return new SExtInst(CondVal, SI.getType());
 709
 710       // select C, 0, 1 -> zext !C to int
 711       if (TrueValC->isZero() && FalseValC->getValue() == 1) {
 712         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
 713         return new ZExtInst(NotCond, SI.getType());
 714       }
 715
 716       // select C, 0, -1 -> sext !C to int
 717       if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
 718         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
 719         return new SExtInst(NotCond, SI.getType());
 720       }
 721
 722       if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
 723         return ReplaceInstUsesWith(SI, V);
 724     }
 725
 726   // See if we are selecting two values based on a comparison of the two values.
 727   if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
 728     if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
 729       // Transform (X == Y) ? X : Y  -> Y
 730       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
 731         // This is not safe in general for floating point:
 732         // consider X== -0, Y== +0.
 733         // It becomes safe if either operand is a nonzero constant.
 734         ConstantFP *CFPt, *CFPf;
 735         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 736               !CFPt->getValueAPF().isZero()) ||
 737             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 738              !CFPf->getValueAPF().isZero()))
 739         return ReplaceInstUsesWith(SI, FalseVal);
 740       }
 741       // Transform (X une Y) ? X : Y  -> X
 742       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
 743         // This is not safe in general for floating point:
 744         // consider X== -0, Y== +0.
 745         // It becomes safe if either operand is a nonzero constant.
 746         ConstantFP *CFPt, *CFPf;
 747         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 748               !CFPt->getValueAPF().isZero()) ||
 749             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 750              !CFPf->getValueAPF().isZero()))
 751         return ReplaceInstUsesWith(SI, TrueVal);
 752       }
 753       // NOTE: if we wanted to, this is where to detect MIN/MAX
 754
 755     } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
 756       // Transform (X == Y) ? Y : X  -> X
 757       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
 758         // This is not safe in general for floating point:
 759         // consider X== -0, Y== +0.
 760         // It becomes safe if either operand is a nonzero constant.
 761         ConstantFP *CFPt, *CFPf;
 762         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 763               !CFPt->getValueAPF().isZero()) ||
 764             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 765              !CFPf->getValueAPF().isZero()))
 766           return ReplaceInstUsesWith(SI, FalseVal);
 767       }
 768       // Transform (X une Y) ? Y : X  -> Y
 769       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
 770         // This is not safe in general for floating point:
 771         // consider X== -0, Y== +0.
 772         // It becomes safe if either operand is a nonzero constant.
 773         ConstantFP *CFPt, *CFPf;
 774         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
 775               !CFPt->getValueAPF().isZero()) ||
 776             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
 777              !CFPf->getValueAPF().isZero()))
 778           return ReplaceInstUsesWith(SI, TrueVal);
 779       }
 780       // NOTE: if we wanted to, this is where to detect MIN/MAX
 781     }
 782     // NOTE: if we wanted to, this is where to detect ABS
 783   }
 784
 785   // See if we are selecting two values based on a comparison of the two values.
 786   if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
 787     if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
 788       return Result;
 789
 790   if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
 791     if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
 792       if (TI->hasOneUse() && FI->hasOneUse()) {
 793         Instruction *AddOp = 0, *SubOp = 0;
 794
 795         // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
 796         if (TI->getOpcode() == FI->getOpcode())
 797           if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
 798             return IV;
 799
 800         // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))).  This is
 801         // even legal for FP.
 802         if ((TI->getOpcode() == Instruction::Sub &&
 803              FI->getOpcode() == Instruction::Add) ||
 804             (TI->getOpcode() == Instruction::FSub &&
 805              FI->getOpcode() == Instruction::FAdd)) {
 806           AddOp = FI; SubOp = TI;
 807         } else if ((FI->getOpcode() == Instruction::Sub &&
 808                     TI->getOpcode() == Instruction::Add) ||
 809                    (FI->getOpcode() == Instruction::FSub &&
 810                     TI->getOpcode() == Instruction::FAdd)) {
 811           AddOp = TI; SubOp = FI;
 812         }
 813
 814         if (AddOp) {
 815           Value *OtherAddOp = 0;
 816           if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
 817             OtherAddOp = AddOp->getOperand(1);
 818           } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
 819             OtherAddOp = AddOp->getOperand(0);
 820           }
 821
 822           if (OtherAddOp) {
 823             // So at this point we know we have (Y -> OtherAddOp):
 824             //        select C, (add X, Y), (sub X, Z)
 825             Value *NegVal;  // Compute -Z
 826             if (SI.getType()->isFPOrFPVectorTy()) {
 827               NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
 828             } else {
 829               NegVal = Builder->CreateNeg(SubOp->getOperand(1));
 830             }
 831
 832             Value *NewTrueOp = OtherAddOp;
 833             Value *NewFalseOp = NegVal;
 834             if (AddOp != TI)
 835               std::swap(NewTrueOp, NewFalseOp);
 836             Value *NewSel =
 837               Builder->CreateSelect(CondVal, NewTrueOp,
 838                                     NewFalseOp, SI.getName() + ".p");
 839
 840             if (SI.getType()->isFPOrFPVectorTy())
 841               return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
 842             else
 843               return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
 844           }
 845         }
 846       }
 847
 848   // See if we can fold the select into one of our operands.
 849   if (SI.getType()->isIntegerTy()) {
 850     if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
 851       return FoldI;
 852
 853     // MAX(MAX(a, b), a) -> MAX(a, b)
 854     // MIN(MIN(a, b), a) -> MIN(a, b)
 855     // MAX(MIN(a, b), a) -> a
 856     // MIN(MAX(a, b), a) -> a
 857     Value *LHS, *RHS, *LHS2, *RHS2;
 858     if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
 859       if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
 860         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
 861                                           SI, SPF, RHS))
 862           return R;
 863       if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
 864         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
 865                                           SI, SPF, LHS))
 866           return R;
 867     }
 868
 869     // TODO.
 870     // ABS(-X) -> ABS(X)
 871     // ABS(ABS(X)) -> ABS(X)
 872   }
 873
 874   // See if we can fold the select into a phi node if the condition is a select.
 875   if (isa<PHINode>(SI.getCondition()))
 876     // The true/false values have to be live in the PHI predecessor's blocks.
 877     if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
 878         CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
 879       if (Instruction *NV = FoldOpIntoPhi(SI))
 880         return NV;
 881
 882   if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
 883     if (TrueSI->getCondition() == CondVal) {
 884       if (SI.getTrueValue() == TrueSI->getTrueValue())
 885         return 0;
 886       SI.setOperand(1, TrueSI->getTrueValue());
 887       return &SI;
 888     }
 889   }
 890   if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
 891     if (FalseSI->getCondition() == CondVal) {
 892       if (SI.getFalseValue() == FalseSI->getFalseValue())
 893         return 0;
 894       SI.setOperand(2, FalseSI->getFalseValue());
 895       return &SI;
 896     }
 897   }
 898
 899   if (BinaryOperator::isNot(CondVal)) {
 900     SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
 901     SI.setOperand(1, FalseVal);
 902     SI.setOperand(2, TrueVal);
 903     return &SI;
 904   }
 905
 906   if (VectorType *VecTy = dyn_cast<VectorType>(SI.getType())) {
 907     unsigned VWidth = VecTy->getNumElements();
 908     APInt UndefElts(VWidth, 0);
 909     APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
 910     if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
 911       if (V != &SI)
 912         return ReplaceInstUsesWith(SI, V);
 913       return &SI;
 914     }
 915
 916     if (ConstantVector *CV = dyn_cast<ConstantVector>(CondVal)) {
 917       // Form a shufflevector instruction.
 918       SmallVector<Constant *, 8> Mask(VWidth);
 919       Type *Int32Ty = Type::getInt32Ty(CV->getContext());
 920       for (unsigned i = 0; i != VWidth; ++i) {
 921         Constant *Elem = cast<Constant>(CV->getOperand(i));
 922         if (ConstantInt *E = dyn_cast<ConstantInt>(Elem))
 923           Mask[i] = ConstantInt::get(Int32Ty, i + (E->isZero() ? VWidth : 0));
 924         else if (isa<UndefValue>(Elem))
 925           Mask[i] = UndefValue::get(Int32Ty);
 926         else
 927           return 0;
 928       }
 929       Constant *MaskVal = ConstantVector::get(Mask);
 930       Value *V = Builder->CreateShuffleVector(TrueVal, FalseVal, MaskVal);
 931       return ReplaceInstUsesWith(SI, V);
 932     }
 933
 934     if (isa<ConstantAggregateZero>(CondVal)) {
 935       return ReplaceInstUsesWith(SI, FalseVal);
 936     }
 937   }
 938
 939   return 0;
 940 }