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