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InstCombineSelect.cpp
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00001 //===- InstCombineSelect.cpp ----------------------------------------------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file is distributed under the University of Illinois Open Source
00006 // License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This file implements the visitSelect function.
00011 //
00012 //===----------------------------------------------------------------------===//
00013 
00014 #include "InstCombineInternal.h"
00015 #include "llvm/Analysis/ConstantFolding.h"
00016 #include "llvm/Analysis/InstructionSimplify.h"
00017 #include "llvm/IR/PatternMatch.h"
00018 using namespace llvm;
00019 using namespace PatternMatch;
00020 
00021 #define DEBUG_TYPE "instcombine"
00022 
00023 /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
00024 /// returning the kind and providing the out parameter results if we
00025 /// successfully match.
00026 static SelectPatternFlavor
00027 MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
00028   SelectInst *SI = dyn_cast<SelectInst>(V);
00029   if (!SI) return SPF_UNKNOWN;
00030 
00031   ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
00032   if (!ICI) return SPF_UNKNOWN;
00033 
00034   ICmpInst::Predicate Pred = ICI->getPredicate();
00035   Value *CmpLHS = ICI->getOperand(0);
00036   Value *CmpRHS = ICI->getOperand(1);
00037   Value *TrueVal = SI->getTrueValue();
00038   Value *FalseVal = SI->getFalseValue();
00039 
00040   LHS = CmpLHS;
00041   RHS = CmpRHS;
00042 
00043   // (icmp X, Y) ? X : Y
00044   if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
00045     switch (Pred) {
00046     default: return SPF_UNKNOWN; // Equality.
00047     case ICmpInst::ICMP_UGT:
00048     case ICmpInst::ICMP_UGE: return SPF_UMAX;
00049     case ICmpInst::ICMP_SGT:
00050     case ICmpInst::ICMP_SGE: return SPF_SMAX;
00051     case ICmpInst::ICMP_ULT:
00052     case ICmpInst::ICMP_ULE: return SPF_UMIN;
00053     case ICmpInst::ICMP_SLT:
00054     case ICmpInst::ICMP_SLE: return SPF_SMIN;
00055     }
00056   }
00057 
00058   // (icmp X, Y) ? Y : X
00059   if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
00060     switch (Pred) {
00061     default: return SPF_UNKNOWN; // Equality.
00062     case ICmpInst::ICMP_UGT:
00063     case ICmpInst::ICMP_UGE: return SPF_UMIN;
00064     case ICmpInst::ICMP_SGT:
00065     case ICmpInst::ICMP_SGE: return SPF_SMIN;
00066     case ICmpInst::ICMP_ULT:
00067     case ICmpInst::ICMP_ULE: return SPF_UMAX;
00068     case ICmpInst::ICMP_SLT:
00069     case ICmpInst::ICMP_SLE: return SPF_SMAX;
00070     }
00071   }
00072 
00073   if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
00074     if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
00075         (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
00076 
00077       // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
00078       // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
00079       if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) {
00080         return (CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS;
00081       }
00082 
00083       // ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
00084       // NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
00085       if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) {
00086         return (CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS;
00087       }
00088     }
00089   }
00090 
00091   // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)
00092 
00093   return SPF_UNKNOWN;
00094 }
00095 
00096 
00097 /// GetSelectFoldableOperands - We want to turn code that looks like this:
00098 ///   %C = or %A, %B
00099 ///   %D = select %cond, %C, %A
00100 /// into:
00101 ///   %C = select %cond, %B, 0
00102 ///   %D = or %A, %C
00103 ///
00104 /// Assuming that the specified instruction is an operand to the select, return
00105 /// a bitmask indicating which operands of this instruction are foldable if they
00106 /// equal the other incoming value of the select.
00107 ///
00108 static unsigned GetSelectFoldableOperands(Instruction *I) {
00109   switch (I->getOpcode()) {
00110   case Instruction::Add:
00111   case Instruction::Mul:
00112   case Instruction::And:
00113   case Instruction::Or:
00114   case Instruction::Xor:
00115     return 3;              // Can fold through either operand.
00116   case Instruction::Sub:   // Can only fold on the amount subtracted.
00117   case Instruction::Shl:   // Can only fold on the shift amount.
00118   case Instruction::LShr:
00119   case Instruction::AShr:
00120     return 1;
00121   default:
00122     return 0;              // Cannot fold
00123   }
00124 }
00125 
00126 /// GetSelectFoldableConstant - For the same transformation as the previous
00127 /// function, return the identity constant that goes into the select.
00128 static Constant *GetSelectFoldableConstant(Instruction *I) {
00129   switch (I->getOpcode()) {
00130   default: llvm_unreachable("This cannot happen!");
00131   case Instruction::Add:
00132   case Instruction::Sub:
00133   case Instruction::Or:
00134   case Instruction::Xor:
00135   case Instruction::Shl:
00136   case Instruction::LShr:
00137   case Instruction::AShr:
00138     return Constant::getNullValue(I->getType());
00139   case Instruction::And:
00140     return Constant::getAllOnesValue(I->getType());
00141   case Instruction::Mul:
00142     return ConstantInt::get(I->getType(), 1);
00143   }
00144 }
00145 
00146 /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
00147 /// have the same opcode and only one use each.  Try to simplify this.
00148 Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
00149                                           Instruction *FI) {
00150   if (TI->getNumOperands() == 1) {
00151     // If this is a non-volatile load or a cast from the same type,
00152     // merge.
00153     if (TI->isCast()) {
00154       Type *FIOpndTy = FI->getOperand(0)->getType();
00155       if (TI->getOperand(0)->getType() != FIOpndTy)
00156         return nullptr;
00157       // The select condition may be a vector. We may only change the operand
00158       // type if the vector width remains the same (and matches the condition).
00159       Type *CondTy = SI.getCondition()->getType();
00160       if (CondTy->isVectorTy() && (!FIOpndTy->isVectorTy() ||
00161           CondTy->getVectorNumElements() != FIOpndTy->getVectorNumElements()))
00162         return nullptr;
00163     } else {
00164       return nullptr;  // unknown unary op.
00165     }
00166 
00167     // Fold this by inserting a select from the input values.
00168     Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0),
00169                                          FI->getOperand(0), SI.getName()+".v");
00170     return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
00171                             TI->getType());
00172   }
00173 
00174   // Only handle binary operators here.
00175   if (!isa<BinaryOperator>(TI))
00176     return nullptr;
00177 
00178   // Figure out if the operations have any operands in common.
00179   Value *MatchOp, *OtherOpT, *OtherOpF;
00180   bool MatchIsOpZero;
00181   if (TI->getOperand(0) == FI->getOperand(0)) {
00182     MatchOp  = TI->getOperand(0);
00183     OtherOpT = TI->getOperand(1);
00184     OtherOpF = FI->getOperand(1);
00185     MatchIsOpZero = true;
00186   } else if (TI->getOperand(1) == FI->getOperand(1)) {
00187     MatchOp  = TI->getOperand(1);
00188     OtherOpT = TI->getOperand(0);
00189     OtherOpF = FI->getOperand(0);
00190     MatchIsOpZero = false;
00191   } else if (!TI->isCommutative()) {
00192     return nullptr;
00193   } else if (TI->getOperand(0) == FI->getOperand(1)) {
00194     MatchOp  = TI->getOperand(0);
00195     OtherOpT = TI->getOperand(1);
00196     OtherOpF = FI->getOperand(0);
00197     MatchIsOpZero = true;
00198   } else if (TI->getOperand(1) == FI->getOperand(0)) {
00199     MatchOp  = TI->getOperand(1);
00200     OtherOpT = TI->getOperand(0);
00201     OtherOpF = FI->getOperand(1);
00202     MatchIsOpZero = true;
00203   } else {
00204     return nullptr;
00205   }
00206 
00207   // If we reach here, they do have operations in common.
00208   Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT,
00209                                        OtherOpF, SI.getName()+".v");
00210 
00211   if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
00212     if (MatchIsOpZero)
00213       return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
00214     else
00215       return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
00216   }
00217   llvm_unreachable("Shouldn't get here");
00218 }
00219 
00220 static bool isSelect01(Constant *C1, Constant *C2) {
00221   ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
00222   if (!C1I)
00223     return false;
00224   ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
00225   if (!C2I)
00226     return false;
00227   if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
00228     return false;
00229   return C1I->isOne() || C1I->isAllOnesValue() ||
00230          C2I->isOne() || C2I->isAllOnesValue();
00231 }
00232 
00233 /// FoldSelectIntoOp - Try fold the select into one of the operands to
00234 /// facilitate further optimization.
00235 Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
00236                                             Value *FalseVal) {
00237   // See the comment above GetSelectFoldableOperands for a description of the
00238   // transformation we are doing here.
00239   if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
00240     if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
00241         !isa<Constant>(FalseVal)) {
00242       if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
00243         unsigned OpToFold = 0;
00244         if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
00245           OpToFold = 1;
00246         } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
00247           OpToFold = 2;
00248         }
00249 
00250         if (OpToFold) {
00251           Constant *C = GetSelectFoldableConstant(TVI);
00252           Value *OOp = TVI->getOperand(2-OpToFold);
00253           // Avoid creating select between 2 constants unless it's selecting
00254           // between 0, 1 and -1.
00255           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
00256             Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C);
00257             NewSel->takeName(TVI);
00258             BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI);
00259             BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(),
00260                                                         FalseVal, NewSel);
00261             if (isa<PossiblyExactOperator>(BO))
00262               BO->setIsExact(TVI_BO->isExact());
00263             if (isa<OverflowingBinaryOperator>(BO)) {
00264               BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap());
00265               BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap());
00266             }
00267             return BO;
00268           }
00269         }
00270       }
00271     }
00272   }
00273 
00274   if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
00275     if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
00276         !isa<Constant>(TrueVal)) {
00277       if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
00278         unsigned OpToFold = 0;
00279         if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
00280           OpToFold = 1;
00281         } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
00282           OpToFold = 2;
00283         }
00284 
00285         if (OpToFold) {
00286           Constant *C = GetSelectFoldableConstant(FVI);
00287           Value *OOp = FVI->getOperand(2-OpToFold);
00288           // Avoid creating select between 2 constants unless it's selecting
00289           // between 0, 1 and -1.
00290           if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
00291             Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp);
00292             NewSel->takeName(FVI);
00293             BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI);
00294             BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(),
00295                                                         TrueVal, NewSel);
00296             if (isa<PossiblyExactOperator>(BO))
00297               BO->setIsExact(FVI_BO->isExact());
00298             if (isa<OverflowingBinaryOperator>(BO)) {
00299               BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap());
00300               BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap());
00301             }
00302             return BO;
00303           }
00304         }
00305       }
00306     }
00307   }
00308 
00309   return nullptr;
00310 }
00311 
00312 /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is
00313 /// replaced with RepOp.
00314 static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
00315                                      const DataLayout *TD,
00316                                      const TargetLibraryInfo *TLI,
00317                                      DominatorTree *DT, AssumptionCache *AC) {
00318   // Trivial replacement.
00319   if (V == Op)
00320     return RepOp;
00321 
00322   Instruction *I = dyn_cast<Instruction>(V);
00323   if (!I)
00324     return nullptr;
00325 
00326   // If this is a binary operator, try to simplify it with the replaced op.
00327   if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
00328     if (B->getOperand(0) == Op)
00329       return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI);
00330     if (B->getOperand(1) == Op)
00331       return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI);
00332   }
00333 
00334   // Same for CmpInsts.
00335   if (CmpInst *C = dyn_cast<CmpInst>(I)) {
00336     if (C->getOperand(0) == Op)
00337       return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD,
00338                              TLI, DT, AC);
00339     if (C->getOperand(1) == Op)
00340       return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD,
00341                              TLI, DT, AC);
00342   }
00343 
00344   // TODO: We could hand off more cases to instsimplify here.
00345 
00346   // If all operands are constant after substituting Op for RepOp then we can
00347   // constant fold the instruction.
00348   if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
00349     // Build a list of all constant operands.
00350     SmallVector<Constant*, 8> ConstOps;
00351     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
00352       if (I->getOperand(i) == Op)
00353         ConstOps.push_back(CRepOp);
00354       else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
00355         ConstOps.push_back(COp);
00356       else
00357         break;
00358     }
00359 
00360     // All operands were constants, fold it.
00361     if (ConstOps.size() == I->getNumOperands()) {
00362       if (CmpInst *C = dyn_cast<CmpInst>(I))
00363         return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
00364                                                ConstOps[1], TD, TLI);
00365 
00366       if (LoadInst *LI = dyn_cast<LoadInst>(I))
00367         if (!LI->isVolatile())
00368           return ConstantFoldLoadFromConstPtr(ConstOps[0], TD);
00369 
00370       return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
00371                                       ConstOps, TD, TLI);
00372     }
00373   }
00374 
00375   return nullptr;
00376 }
00377 
00378 /// foldSelectICmpAndOr - We want to turn:
00379 ///   (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
00380 /// into:
00381 ///   (or (shl (and X, C1), C3), y)
00382 /// iff:
00383 ///   C1 and C2 are both powers of 2
00384 /// where:
00385 ///   C3 = Log(C2) - Log(C1)
00386 ///
00387 /// This transform handles cases where:
00388 /// 1. The icmp predicate is inverted
00389 /// 2. The select operands are reversed
00390 /// 3. The magnitude of C2 and C1 are flipped
00391 static Value *foldSelectICmpAndOr(const SelectInst &SI, Value *TrueVal,
00392                                   Value *FalseVal,
00393                                   InstCombiner::BuilderTy *Builder) {
00394   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
00395   if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
00396     return nullptr;
00397 
00398   Value *CmpLHS = IC->getOperand(0);
00399   Value *CmpRHS = IC->getOperand(1);
00400 
00401   if (!match(CmpRHS, m_Zero()))
00402     return nullptr;
00403 
00404   Value *X;
00405   const APInt *C1;
00406   if (!match(CmpLHS, m_And(m_Value(X), m_Power2(C1))))
00407     return nullptr;
00408 
00409   const APInt *C2;
00410   bool OrOnTrueVal = false;
00411   bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
00412   if (!OrOnFalseVal)
00413     OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
00414 
00415   if (!OrOnFalseVal && !OrOnTrueVal)
00416     return nullptr;
00417 
00418   Value *V = CmpLHS;
00419   Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
00420 
00421   unsigned C1Log = C1->logBase2();
00422   unsigned C2Log = C2->logBase2();
00423   if (C2Log > C1Log) {
00424     V = Builder->CreateZExtOrTrunc(V, Y->getType());
00425     V = Builder->CreateShl(V, C2Log - C1Log);
00426   } else if (C1Log > C2Log) {
00427     V = Builder->CreateLShr(V, C1Log - C2Log);
00428     V = Builder->CreateZExtOrTrunc(V, Y->getType());
00429   } else
00430     V = Builder->CreateZExtOrTrunc(V, Y->getType());
00431 
00432   ICmpInst::Predicate Pred = IC->getPredicate();
00433   if ((Pred == ICmpInst::ICMP_NE && OrOnFalseVal) ||
00434       (Pred == ICmpInst::ICMP_EQ && OrOnTrueVal))
00435     V = Builder->CreateXor(V, *C2);
00436 
00437   return Builder->CreateOr(V, Y);
00438 }
00439 
00440 /// visitSelectInstWithICmp - Visit a SelectInst that has an
00441 /// ICmpInst as its first operand.
00442 ///
00443 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
00444                                                    ICmpInst *ICI) {
00445   bool Changed = false;
00446   ICmpInst::Predicate Pred = ICI->getPredicate();
00447   Value *CmpLHS = ICI->getOperand(0);
00448   Value *CmpRHS = ICI->getOperand(1);
00449   Value *TrueVal = SI.getTrueValue();
00450   Value *FalseVal = SI.getFalseValue();
00451 
00452   // Check cases where the comparison is with a constant that
00453   // can be adjusted to fit the min/max idiom. We may move or edit ICI
00454   // here, so make sure the select is the only user.
00455   if (ICI->hasOneUse())
00456     if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
00457       // X < MIN ? T : F  -->  F
00458       if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
00459           && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
00460         return ReplaceInstUsesWith(SI, FalseVal);
00461       // X > MAX ? T : F  -->  F
00462       else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
00463                && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
00464         return ReplaceInstUsesWith(SI, FalseVal);
00465       switch (Pred) {
00466       default: break;
00467       case ICmpInst::ICMP_ULT:
00468       case ICmpInst::ICMP_SLT:
00469       case ICmpInst::ICMP_UGT:
00470       case ICmpInst::ICMP_SGT: {
00471         // These transformations only work for selects over integers.
00472         IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
00473         if (!SelectTy)
00474           break;
00475 
00476         Constant *AdjustedRHS;
00477         if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
00478           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
00479         else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
00480           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
00481 
00482         // X > C ? X : C+1  -->  X < C+1 ? C+1 : X
00483         // X < C ? X : C-1  -->  X > C-1 ? C-1 : X
00484         if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
00485             (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
00486           ; // Nothing to do here. Values match without any sign/zero extension.
00487 
00488         // Types do not match. Instead of calculating this with mixed types
00489         // promote all to the larger type. This enables scalar evolution to
00490         // analyze this expression.
00491         else if (CmpRHS->getType()->getScalarSizeInBits()
00492                  < SelectTy->getBitWidth()) {
00493           Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
00494 
00495           // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
00496           // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
00497           // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
00498           // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
00499           if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
00500                 sextRHS == FalseVal) {
00501             CmpLHS = TrueVal;
00502             AdjustedRHS = sextRHS;
00503           } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
00504                      sextRHS == TrueVal) {
00505             CmpLHS = FalseVal;
00506             AdjustedRHS = sextRHS;
00507           } else if (ICI->isUnsigned()) {
00508             Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
00509             // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
00510             // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
00511             // zext + signed compare cannot be changed:
00512             //    0xff <s 0x00, but 0x00ff >s 0x0000
00513             if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
00514                 zextRHS == FalseVal) {
00515               CmpLHS = TrueVal;
00516               AdjustedRHS = zextRHS;
00517             } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
00518                        zextRHS == TrueVal) {
00519               CmpLHS = FalseVal;
00520               AdjustedRHS = zextRHS;
00521             } else
00522               break;
00523           } else
00524             break;
00525         } else
00526           break;
00527 
00528         Pred = ICmpInst::getSwappedPredicate(Pred);
00529         CmpRHS = AdjustedRHS;
00530         std::swap(FalseVal, TrueVal);
00531         ICI->setPredicate(Pred);
00532         ICI->setOperand(0, CmpLHS);
00533         ICI->setOperand(1, CmpRHS);
00534         SI.setOperand(1, TrueVal);
00535         SI.setOperand(2, FalseVal);
00536 
00537         // Move ICI instruction right before the select instruction. Otherwise
00538         // the sext/zext value may be defined after the ICI instruction uses it.
00539         ICI->moveBefore(&SI);
00540 
00541         Changed = true;
00542         break;
00543       }
00544       }
00545     }
00546 
00547   // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
00548   // and       (X <s  0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
00549   // FIXME: Type and constness constraints could be lifted, but we have to
00550   //        watch code size carefully. We should consider xor instead of
00551   //        sub/add when we decide to do that.
00552   if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
00553     if (TrueVal->getType() == Ty) {
00554       if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
00555         ConstantInt *C1 = nullptr, *C2 = nullptr;
00556         if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
00557           C1 = dyn_cast<ConstantInt>(TrueVal);
00558           C2 = dyn_cast<ConstantInt>(FalseVal);
00559         } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
00560           C1 = dyn_cast<ConstantInt>(FalseVal);
00561           C2 = dyn_cast<ConstantInt>(TrueVal);
00562         }
00563         if (C1 && C2) {
00564           // This shift results in either -1 or 0.
00565           Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
00566 
00567           // Check if we can express the operation with a single or.
00568           if (C2->isAllOnesValue())
00569             return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
00570 
00571           Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
00572           return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
00573         }
00574       }
00575     }
00576   }
00577 
00578   // If we have an equality comparison then we know the value in one of the
00579   // arms of the select. See if substituting this value into the arm and
00580   // simplifying the result yields the same value as the other arm.
00581   if (Pred == ICmpInst::ICMP_EQ) {
00582     if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, DL, TLI, DT, AC) ==
00583             TrueVal ||
00584         SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, DL, TLI, DT, AC) ==
00585             TrueVal)
00586       return ReplaceInstUsesWith(SI, FalseVal);
00587     if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, DL, TLI, DT, AC) ==
00588             FalseVal ||
00589         SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, DL, TLI, DT, AC) ==
00590             FalseVal)
00591       return ReplaceInstUsesWith(SI, FalseVal);
00592   } else if (Pred == ICmpInst::ICMP_NE) {
00593     if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, DL, TLI, DT, AC) ==
00594             FalseVal ||
00595         SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, DL, TLI, DT, AC) ==
00596             FalseVal)
00597       return ReplaceInstUsesWith(SI, TrueVal);
00598     if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, DL, TLI, DT, AC) ==
00599             TrueVal ||
00600         SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, DL, TLI, DT, AC) ==
00601             TrueVal)
00602       return ReplaceInstUsesWith(SI, TrueVal);
00603   }
00604 
00605   // NOTE: if we wanted to, this is where to detect integer MIN/MAX
00606 
00607   if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
00608     if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
00609       // Transform (X == C) ? X : Y -> (X == C) ? C : Y
00610       SI.setOperand(1, CmpRHS);
00611       Changed = true;
00612     } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
00613       // Transform (X != C) ? Y : X -> (X != C) ? Y : C
00614       SI.setOperand(2, CmpRHS);
00615       Changed = true;
00616     }
00617   }
00618 
00619   if (unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits()) {
00620     APInt MinSignedValue = APInt::getSignBit(BitWidth);
00621     Value *X;
00622     const APInt *Y, *C;
00623     bool TrueWhenUnset;
00624     bool IsBitTest = false;
00625     if (ICmpInst::isEquality(Pred) &&
00626         match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) &&
00627         match(CmpRHS, m_Zero())) {
00628       IsBitTest = true;
00629       TrueWhenUnset = Pred == ICmpInst::ICMP_EQ;
00630     } else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
00631       X = CmpLHS;
00632       Y = &MinSignedValue;
00633       IsBitTest = true;
00634       TrueWhenUnset = false;
00635     } else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
00636       X = CmpLHS;
00637       Y = &MinSignedValue;
00638       IsBitTest = true;
00639       TrueWhenUnset = true;
00640     }
00641     if (IsBitTest) {
00642       Value *V = nullptr;
00643       // (X & Y) == 0 ? X : X ^ Y  --> X & ~Y
00644       if (TrueWhenUnset && TrueVal == X &&
00645           match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
00646         V = Builder->CreateAnd(X, ~(*Y));
00647       // (X & Y) != 0 ? X ^ Y : X  --> X & ~Y
00648       else if (!TrueWhenUnset && FalseVal == X &&
00649                match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
00650         V = Builder->CreateAnd(X, ~(*Y));
00651       // (X & Y) == 0 ? X ^ Y : X  --> X | Y
00652       else if (TrueWhenUnset && FalseVal == X &&
00653                match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
00654         V = Builder->CreateOr(X, *Y);
00655       // (X & Y) != 0 ? X : X ^ Y  --> X | Y
00656       else if (!TrueWhenUnset && TrueVal == X &&
00657                match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
00658         V = Builder->CreateOr(X, *Y);
00659 
00660       if (V)
00661         return ReplaceInstUsesWith(SI, V);
00662     }
00663   }
00664 
00665   if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
00666     return ReplaceInstUsesWith(SI, V);
00667 
00668   return Changed ? &SI : nullptr;
00669 }
00670 
00671 
00672 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
00673 /// PHI node (but the two may be in different blocks).  See if the true/false
00674 /// values (V) are live in all of the predecessor blocks of the PHI.  For
00675 /// example, cases like this cannot be mapped:
00676 ///
00677 ///   X = phi [ C1, BB1], [C2, BB2]
00678 ///   Y = add
00679 ///   Z = select X, Y, 0
00680 ///
00681 /// because Y is not live in BB1/BB2.
00682 ///
00683 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
00684                                                    const SelectInst &SI) {
00685   // If the value is a non-instruction value like a constant or argument, it
00686   // can always be mapped.
00687   const Instruction *I = dyn_cast<Instruction>(V);
00688   if (!I) return true;
00689 
00690   // If V is a PHI node defined in the same block as the condition PHI, we can
00691   // map the arguments.
00692   const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
00693 
00694   if (const PHINode *VP = dyn_cast<PHINode>(I))
00695     if (VP->getParent() == CondPHI->getParent())
00696       return true;
00697 
00698   // Otherwise, if the PHI and select are defined in the same block and if V is
00699   // defined in a different block, then we can transform it.
00700   if (SI.getParent() == CondPHI->getParent() &&
00701       I->getParent() != CondPHI->getParent())
00702     return true;
00703 
00704   // Otherwise we have a 'hard' case and we can't tell without doing more
00705   // detailed dominator based analysis, punt.
00706   return false;
00707 }
00708 
00709 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
00710 ///   SPF2(SPF1(A, B), C)
00711 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
00712                                         SelectPatternFlavor SPF1,
00713                                         Value *A, Value *B,
00714                                         Instruction &Outer,
00715                                         SelectPatternFlavor SPF2, Value *C) {
00716   if (C == A || C == B) {
00717     // MAX(MAX(A, B), B) -> MAX(A, B)
00718     // MIN(MIN(a, b), a) -> MIN(a, b)
00719     if (SPF1 == SPF2)
00720       return ReplaceInstUsesWith(Outer, Inner);
00721 
00722     // MAX(MIN(a, b), a) -> a
00723     // MIN(MAX(a, b), a) -> a
00724     if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
00725         (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
00726         (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
00727         (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
00728       return ReplaceInstUsesWith(Outer, C);
00729   }
00730 
00731   if (SPF1 == SPF2) {
00732     if (ConstantInt *CB = dyn_cast<ConstantInt>(B)) {
00733       if (ConstantInt *CC = dyn_cast<ConstantInt>(C)) {
00734         APInt ACB = CB->getValue();
00735         APInt ACC = CC->getValue();
00736 
00737         // MIN(MIN(A, 23), 97) -> MIN(A, 23)
00738         // MAX(MAX(A, 97), 23) -> MAX(A, 97)
00739         if ((SPF1 == SPF_UMIN && ACB.ule(ACC)) ||
00740             (SPF1 == SPF_SMIN && ACB.sle(ACC)) ||
00741             (SPF1 == SPF_UMAX && ACB.uge(ACC)) ||
00742             (SPF1 == SPF_SMAX && ACB.sge(ACC)))
00743           return ReplaceInstUsesWith(Outer, Inner);
00744 
00745         // MIN(MIN(A, 97), 23) -> MIN(A, 23)
00746         // MAX(MAX(A, 23), 97) -> MAX(A, 97)
00747         if ((SPF1 == SPF_UMIN && ACB.ugt(ACC)) ||
00748             (SPF1 == SPF_SMIN && ACB.sgt(ACC)) ||
00749             (SPF1 == SPF_UMAX && ACB.ult(ACC)) ||
00750             (SPF1 == SPF_SMAX && ACB.slt(ACC))) {
00751           Outer.replaceUsesOfWith(Inner, A);
00752           return &Outer;
00753         }
00754       }
00755     }
00756   }
00757 
00758   // ABS(ABS(X)) -> ABS(X)
00759   // NABS(NABS(X)) -> NABS(X)
00760   if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
00761     return ReplaceInstUsesWith(Outer, Inner);
00762   }
00763 
00764   // ABS(NABS(X)) -> ABS(X)
00765   // NABS(ABS(X)) -> NABS(X)
00766   if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
00767       (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
00768     SelectInst *SI = cast<SelectInst>(Inner);
00769     Value *NewSI = Builder->CreateSelect(
00770         SI->getCondition(), SI->getFalseValue(), SI->getTrueValue());
00771     return ReplaceInstUsesWith(Outer, NewSI);
00772   }
00773   return nullptr;
00774 }
00775 
00776 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
00777 /// both be) and we have an icmp instruction with zero, and we have an 'and'
00778 /// with the non-constant value and a power of two we can turn the select
00779 /// into a shift on the result of the 'and'.
00780 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
00781                                 ConstantInt *FalseVal,
00782                                 InstCombiner::BuilderTy *Builder) {
00783   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
00784   if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
00785     return nullptr;
00786 
00787   if (!match(IC->getOperand(1), m_Zero()))
00788     return nullptr;
00789 
00790   ConstantInt *AndRHS;
00791   Value *LHS = IC->getOperand(0);
00792   if (!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
00793     return nullptr;
00794 
00795   // If both select arms are non-zero see if we have a select of the form
00796   // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
00797   // for 'x ? 2^n : 0' and fix the thing up at the end.
00798   ConstantInt *Offset = nullptr;
00799   if (!TrueVal->isZero() && !FalseVal->isZero()) {
00800     if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
00801       Offset = FalseVal;
00802     else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
00803       Offset = TrueVal;
00804     else
00805       return nullptr;
00806 
00807     // Adjust TrueVal and FalseVal to the offset.
00808     TrueVal = ConstantInt::get(Builder->getContext(),
00809                                TrueVal->getValue() - Offset->getValue());
00810     FalseVal = ConstantInt::get(Builder->getContext(),
00811                                 FalseVal->getValue() - Offset->getValue());
00812   }
00813 
00814   // Make sure the mask in the 'and' and one of the select arms is a power of 2.
00815   if (!AndRHS->getValue().isPowerOf2() ||
00816       (!TrueVal->getValue().isPowerOf2() &&
00817        !FalseVal->getValue().isPowerOf2()))
00818     return nullptr;
00819 
00820   // Determine which shift is needed to transform result of the 'and' into the
00821   // desired result.
00822   ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
00823   unsigned ValZeros = ValC->getValue().logBase2();
00824   unsigned AndZeros = AndRHS->getValue().logBase2();
00825 
00826   // If types don't match we can still convert the select by introducing a zext
00827   // or a trunc of the 'and'. The trunc case requires that all of the truncated
00828   // bits are zero, we can figure that out by looking at the 'and' mask.
00829   if (AndZeros >= ValC->getBitWidth())
00830     return nullptr;
00831 
00832   Value *V = Builder->CreateZExtOrTrunc(LHS, SI.getType());
00833   if (ValZeros > AndZeros)
00834     V = Builder->CreateShl(V, ValZeros - AndZeros);
00835   else if (ValZeros < AndZeros)
00836     V = Builder->CreateLShr(V, AndZeros - ValZeros);
00837 
00838   // Okay, now we know that everything is set up, we just don't know whether we
00839   // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
00840   bool ShouldNotVal = !TrueVal->isZero();
00841   ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
00842   if (ShouldNotVal)
00843     V = Builder->CreateXor(V, ValC);
00844 
00845   // Apply an offset if needed.
00846   if (Offset)
00847     V = Builder->CreateAdd(V, Offset);
00848   return V;
00849 }
00850 
00851 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
00852   Value *CondVal = SI.getCondition();
00853   Value *TrueVal = SI.getTrueValue();
00854   Value *FalseVal = SI.getFalseValue();
00855 
00856   if (Value *V =
00857           SimplifySelectInst(CondVal, TrueVal, FalseVal, DL, TLI, DT, AC))
00858     return ReplaceInstUsesWith(SI, V);
00859 
00860   if (SI.getType()->isIntegerTy(1)) {
00861     if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
00862       if (C->getZExtValue()) {
00863         // Change: A = select B, true, C --> A = or B, C
00864         return BinaryOperator::CreateOr(CondVal, FalseVal);
00865       }
00866       // Change: A = select B, false, C --> A = and !B, C
00867       Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
00868       return BinaryOperator::CreateAnd(NotCond, FalseVal);
00869     }
00870     if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
00871       if (C->getZExtValue() == false) {
00872         // Change: A = select B, C, false --> A = and B, C
00873         return BinaryOperator::CreateAnd(CondVal, TrueVal);
00874       }
00875       // Change: A = select B, C, true --> A = or !B, C
00876       Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
00877       return BinaryOperator::CreateOr(NotCond, TrueVal);
00878     }
00879 
00880     // select a, b, a  -> a&b
00881     // select a, a, b  -> a|b
00882     if (CondVal == TrueVal)
00883       return BinaryOperator::CreateOr(CondVal, FalseVal);
00884     if (CondVal == FalseVal)
00885       return BinaryOperator::CreateAnd(CondVal, TrueVal);
00886 
00887     // select a, ~a, b -> (~a)&b
00888     // select a, b, ~a -> (~a)|b
00889     if (match(TrueVal, m_Not(m_Specific(CondVal))))
00890       return BinaryOperator::CreateAnd(TrueVal, FalseVal);
00891     if (match(FalseVal, m_Not(m_Specific(CondVal))))
00892       return BinaryOperator::CreateOr(TrueVal, FalseVal);
00893   }
00894 
00895   // Selecting between two integer constants?
00896   if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
00897     if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
00898       // select C, 1, 0 -> zext C to int
00899       if (FalseValC->isZero() && TrueValC->getValue() == 1)
00900         return new ZExtInst(CondVal, SI.getType());
00901 
00902       // select C, -1, 0 -> sext C to int
00903       if (FalseValC->isZero() && TrueValC->isAllOnesValue())
00904         return new SExtInst(CondVal, SI.getType());
00905 
00906       // select C, 0, 1 -> zext !C to int
00907       if (TrueValC->isZero() && FalseValC->getValue() == 1) {
00908         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
00909         return new ZExtInst(NotCond, SI.getType());
00910       }
00911 
00912       // select C, 0, -1 -> sext !C to int
00913       if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
00914         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
00915         return new SExtInst(NotCond, SI.getType());
00916       }
00917 
00918       if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
00919         return ReplaceInstUsesWith(SI, V);
00920     }
00921 
00922   // See if we are selecting two values based on a comparison of the two values.
00923   if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
00924     if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
00925       // Transform (X == Y) ? X : Y  -> Y
00926       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
00927         // This is not safe in general for floating point:
00928         // consider X== -0, Y== +0.
00929         // It becomes safe if either operand is a nonzero constant.
00930         ConstantFP *CFPt, *CFPf;
00931         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
00932               !CFPt->getValueAPF().isZero()) ||
00933             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
00934              !CFPf->getValueAPF().isZero()))
00935         return ReplaceInstUsesWith(SI, FalseVal);
00936       }
00937       // Transform (X une Y) ? X : Y  -> X
00938       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
00939         // This is not safe in general for floating point:
00940         // consider X== -0, Y== +0.
00941         // It becomes safe if either operand is a nonzero constant.
00942         ConstantFP *CFPt, *CFPf;
00943         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
00944               !CFPt->getValueAPF().isZero()) ||
00945             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
00946              !CFPf->getValueAPF().isZero()))
00947         return ReplaceInstUsesWith(SI, TrueVal);
00948       }
00949 
00950       // Canonicalize to use ordered comparisons by swapping the select
00951       // operands.
00952       //
00953       // e.g.
00954       // (X ugt Y) ? X : Y -> (X ole Y) ? Y : X
00955       if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
00956         FCmpInst::Predicate InvPred = FCI->getInversePredicate();
00957         Value *NewCond = Builder->CreateFCmp(InvPred, TrueVal, FalseVal,
00958                                              FCI->getName() + ".inv");
00959 
00960         return SelectInst::Create(NewCond, FalseVal, TrueVal,
00961                                   SI.getName() + ".p");
00962       }
00963 
00964       // NOTE: if we wanted to, this is where to detect MIN/MAX
00965     } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
00966       // Transform (X == Y) ? Y : X  -> X
00967       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
00968         // This is not safe in general for floating point:
00969         // consider X== -0, Y== +0.
00970         // It becomes safe if either operand is a nonzero constant.
00971         ConstantFP *CFPt, *CFPf;
00972         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
00973               !CFPt->getValueAPF().isZero()) ||
00974             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
00975              !CFPf->getValueAPF().isZero()))
00976           return ReplaceInstUsesWith(SI, FalseVal);
00977       }
00978       // Transform (X une Y) ? Y : X  -> Y
00979       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
00980         // This is not safe in general for floating point:
00981         // consider X== -0, Y== +0.
00982         // It becomes safe if either operand is a nonzero constant.
00983         ConstantFP *CFPt, *CFPf;
00984         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
00985               !CFPt->getValueAPF().isZero()) ||
00986             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
00987              !CFPf->getValueAPF().isZero()))
00988           return ReplaceInstUsesWith(SI, TrueVal);
00989       }
00990 
00991       // Canonicalize to use ordered comparisons by swapping the select
00992       // operands.
00993       //
00994       // e.g.
00995       // (X ugt Y) ? X : Y -> (X ole Y) ? X : Y
00996       if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
00997         FCmpInst::Predicate InvPred = FCI->getInversePredicate();
00998         Value *NewCond = Builder->CreateFCmp(InvPred, FalseVal, TrueVal,
00999                                              FCI->getName() + ".inv");
01000 
01001         return SelectInst::Create(NewCond, FalseVal, TrueVal,
01002                                   SI.getName() + ".p");
01003       }
01004 
01005       // NOTE: if we wanted to, this is where to detect MIN/MAX
01006     }
01007     // NOTE: if we wanted to, this is where to detect ABS
01008   }
01009 
01010   // See if we are selecting two values based on a comparison of the two values.
01011   if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
01012     if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
01013       return Result;
01014 
01015   if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
01016     if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
01017       if (TI->hasOneUse() && FI->hasOneUse()) {
01018         Instruction *AddOp = nullptr, *SubOp = nullptr;
01019 
01020         // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
01021         if (TI->getOpcode() == FI->getOpcode())
01022           if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
01023             return IV;
01024 
01025         // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))).  This is
01026         // even legal for FP.
01027         if ((TI->getOpcode() == Instruction::Sub &&
01028              FI->getOpcode() == Instruction::Add) ||
01029             (TI->getOpcode() == Instruction::FSub &&
01030              FI->getOpcode() == Instruction::FAdd)) {
01031           AddOp = FI; SubOp = TI;
01032         } else if ((FI->getOpcode() == Instruction::Sub &&
01033                     TI->getOpcode() == Instruction::Add) ||
01034                    (FI->getOpcode() == Instruction::FSub &&
01035                     TI->getOpcode() == Instruction::FAdd)) {
01036           AddOp = TI; SubOp = FI;
01037         }
01038 
01039         if (AddOp) {
01040           Value *OtherAddOp = nullptr;
01041           if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
01042             OtherAddOp = AddOp->getOperand(1);
01043           } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
01044             OtherAddOp = AddOp->getOperand(0);
01045           }
01046 
01047           if (OtherAddOp) {
01048             // So at this point we know we have (Y -> OtherAddOp):
01049             //        select C, (add X, Y), (sub X, Z)
01050             Value *NegVal;  // Compute -Z
01051             if (SI.getType()->isFPOrFPVectorTy()) {
01052               NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
01053               if (Instruction *NegInst = dyn_cast<Instruction>(NegVal)) {
01054                 FastMathFlags Flags = AddOp->getFastMathFlags();
01055                 Flags &= SubOp->getFastMathFlags();
01056                 NegInst->setFastMathFlags(Flags);
01057               }
01058             } else {
01059               NegVal = Builder->CreateNeg(SubOp->getOperand(1));
01060             }
01061 
01062             Value *NewTrueOp = OtherAddOp;
01063             Value *NewFalseOp = NegVal;
01064             if (AddOp != TI)
01065               std::swap(NewTrueOp, NewFalseOp);
01066             Value *NewSel =
01067               Builder->CreateSelect(CondVal, NewTrueOp,
01068                                     NewFalseOp, SI.getName() + ".p");
01069 
01070             if (SI.getType()->isFPOrFPVectorTy()) {
01071               Instruction *RI =
01072                 BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
01073 
01074               FastMathFlags Flags = AddOp->getFastMathFlags();
01075               Flags &= SubOp->getFastMathFlags();
01076               RI->setFastMathFlags(Flags);
01077               return RI;
01078             } else
01079               return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
01080           }
01081         }
01082       }
01083 
01084   // See if we can fold the select into one of our operands.
01085   if (SI.getType()->isIntegerTy()) {
01086     if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
01087       return FoldI;
01088 
01089     // MAX(MAX(a, b), a) -> MAX(a, b)
01090     // MIN(MIN(a, b), a) -> MIN(a, b)
01091     // MAX(MIN(a, b), a) -> a
01092     // MIN(MAX(a, b), a) -> a
01093     Value *LHS, *RHS, *LHS2, *RHS2;
01094     if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
01095       if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
01096         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
01097                                           SI, SPF, RHS))
01098           return R;
01099       if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
01100         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
01101                                           SI, SPF, LHS))
01102           return R;
01103     }
01104 
01105     // TODO.
01106     // ABS(-X) -> ABS(X)
01107   }
01108 
01109   // See if we can fold the select into a phi node if the condition is a select.
01110   if (isa<PHINode>(SI.getCondition()))
01111     // The true/false values have to be live in the PHI predecessor's blocks.
01112     if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
01113         CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
01114       if (Instruction *NV = FoldOpIntoPhi(SI))
01115         return NV;
01116 
01117   if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
01118     if (TrueSI->getCondition() == CondVal) {
01119       if (SI.getTrueValue() == TrueSI->getTrueValue())
01120         return nullptr;
01121       SI.setOperand(1, TrueSI->getTrueValue());
01122       return &SI;
01123     }
01124   }
01125   if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
01126     if (FalseSI->getCondition() == CondVal) {
01127       if (SI.getFalseValue() == FalseSI->getFalseValue())
01128         return nullptr;
01129       SI.setOperand(2, FalseSI->getFalseValue());
01130       return &SI;
01131     }
01132   }
01133 
01134   if (BinaryOperator::isNot(CondVal)) {
01135     SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
01136     SI.setOperand(1, FalseVal);
01137     SI.setOperand(2, TrueVal);
01138     return &SI;
01139   }
01140 
01141   if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
01142     unsigned VWidth = VecTy->getNumElements();
01143     APInt UndefElts(VWidth, 0);
01144     APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
01145     if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
01146       if (V != &SI)
01147         return ReplaceInstUsesWith(SI, V);
01148       return &SI;
01149     }
01150 
01151     if (isa<ConstantAggregateZero>(CondVal)) {
01152       return ReplaceInstUsesWith(SI, FalseVal);
01153     }
01154   }
01155 
01156   return nullptr;
01157 }