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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 "InstCombine.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,
00318                                      AssumptionTracker *AT) {
00319   // Trivial replacement.
00320   if (V == Op)
00321     return RepOp;
00322 
00323   Instruction *I = dyn_cast<Instruction>(V);
00324   if (!I)
00325     return nullptr;
00326 
00327   // If this is a binary operator, try to simplify it with the replaced op.
00328   if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
00329     if (B->getOperand(0) == Op)
00330       return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD, TLI);
00331     if (B->getOperand(1) == Op)
00332       return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI);
00333   }
00334 
00335   // Same for CmpInsts.
00336   if (CmpInst *C = dyn_cast<CmpInst>(I)) {
00337     if (C->getOperand(0) == Op)
00338       return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD,
00339                              TLI, DT, AT);
00340     if (C->getOperand(1) == Op)
00341       return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD,
00342                              TLI, DT, AT);
00343   }
00344 
00345   // TODO: We could hand off more cases to instsimplify here.
00346 
00347   // If all operands are constant after substituting Op for RepOp then we can
00348   // constant fold the instruction.
00349   if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) {
00350     // Build a list of all constant operands.
00351     SmallVector<Constant*, 8> ConstOps;
00352     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
00353       if (I->getOperand(i) == Op)
00354         ConstOps.push_back(CRepOp);
00355       else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i)))
00356         ConstOps.push_back(COp);
00357       else
00358         break;
00359     }
00360 
00361     // All operands were constants, fold it.
00362     if (ConstOps.size() == I->getNumOperands()) {
00363       if (CmpInst *C = dyn_cast<CmpInst>(I))
00364         return ConstantFoldCompareInstOperands(C->getPredicate(), ConstOps[0],
00365                                                ConstOps[1], TD, TLI);
00366 
00367       if (LoadInst *LI = dyn_cast<LoadInst>(I))
00368         if (!LI->isVolatile())
00369           return ConstantFoldLoadFromConstPtr(ConstOps[0], TD);
00370 
00371       return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
00372                                       ConstOps, TD, TLI);
00373     }
00374   }
00375 
00376   return nullptr;
00377 }
00378 
00379 /// foldSelectICmpAndOr - We want to turn:
00380 ///   (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
00381 /// into:
00382 ///   (or (shl (and X, C1), C3), y)
00383 /// iff:
00384 ///   C1 and C2 are both powers of 2
00385 /// where:
00386 ///   C3 = Log(C2) - Log(C1)
00387 ///
00388 /// This transform handles cases where:
00389 /// 1. The icmp predicate is inverted
00390 /// 2. The select operands are reversed
00391 /// 3. The magnitude of C2 and C1 are flipped
00392 ///
00393 /// This also tries to turn
00394 /// --- Single bit tests:
00395 /// if ((x & C) == 0) x |= C    to  x |= C
00396 /// if ((x & C) != 0) x ^= C    to  x &= ~C
00397 /// if ((x & C) == 0) x ^= C    to  x |= C
00398 /// if ((x & C) != 0) x &= ~C   to  x &= ~C
00399 /// if ((x & C) == 0) x &= ~C   to  nothing
00400 static Value *foldSelectICmpAndOr(SelectInst &SI, Value *TrueVal,
00401                                   Value *FalseVal,
00402                                   InstCombiner::BuilderTy *Builder) {
00403   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
00404   if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
00405     return nullptr;
00406 
00407   Value *CmpLHS = IC->getOperand(0);
00408   Value *CmpRHS = IC->getOperand(1);
00409 
00410   if (!match(CmpRHS, m_Zero()))
00411     return nullptr;
00412 
00413   Value *X;
00414   const APInt *C1;
00415   if (!match(CmpLHS, m_And(m_Value(X), m_Power2(C1))))
00416     return nullptr;
00417 
00418   const APInt *C2;
00419   if (match(TrueVal, m_Specific(X))) {
00420     // if ((X & C) != 0) X ^= C becomes X &= ~C
00421     if (match(FalseVal, m_Xor(m_Specific(X), m_APInt(C2))) && C1 == C2)
00422       return Builder->CreateAnd(X, ~(*C1));
00423     // if ((X & C) != 0) X &= ~C becomes X &= ~C
00424     if (match(FalseVal, m_And(m_Specific(X), m_APInt(C2))) && *C1 == ~(*C2))
00425       return FalseVal;
00426   } else if (match(FalseVal, m_Specific(X))) {
00427     // if ((X & C) == 0) X ^= C becomes X |= C
00428     if (match(TrueVal, m_Xor(m_Specific(X), m_APInt(C2))) && C1 == C2)
00429       return Builder->CreateOr(X, *C1);
00430     // if ((X & C) == 0) X &= ~C becomes nothing
00431     if (match(TrueVal, m_And(m_Specific(X), m_APInt(C2))) && *C1 == ~(*C2))
00432       return X;
00433     // if ((X & C) == 0) X |= C becomes X |= C
00434     if (match(TrueVal, m_Or(m_Specific(X), m_APInt(C2))) && C1 == C2)
00435       return TrueVal;
00436   }
00437 
00438   bool OrOnTrueVal = false;
00439   bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
00440   if (!OrOnFalseVal)
00441     OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
00442 
00443   if (!OrOnFalseVal && !OrOnTrueVal)
00444     return nullptr;
00445 
00446   Value *V = CmpLHS;
00447   Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
00448 
00449   unsigned C1Log = C1->logBase2();
00450   unsigned C2Log = C2->logBase2();
00451   if (C2Log > C1Log) {
00452     V = Builder->CreateZExtOrTrunc(V, Y->getType());
00453     V = Builder->CreateShl(V, C2Log - C1Log);
00454   } else if (C1Log > C2Log) {
00455     V = Builder->CreateLShr(V, C1Log - C2Log);
00456     V = Builder->CreateZExtOrTrunc(V, Y->getType());
00457   } else
00458     V = Builder->CreateZExtOrTrunc(V, Y->getType());
00459 
00460   ICmpInst::Predicate Pred = IC->getPredicate();
00461   if ((Pred == ICmpInst::ICMP_NE && OrOnFalseVal) ||
00462       (Pred == ICmpInst::ICMP_EQ && OrOnTrueVal))
00463     V = Builder->CreateXor(V, *C2);
00464 
00465   return Builder->CreateOr(V, Y);
00466 }
00467 
00468 /// visitSelectInstWithICmp - Visit a SelectInst that has an
00469 /// ICmpInst as its first operand.
00470 ///
00471 Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
00472                                                    ICmpInst *ICI) {
00473   bool Changed = false;
00474   ICmpInst::Predicate Pred = ICI->getPredicate();
00475   Value *CmpLHS = ICI->getOperand(0);
00476   Value *CmpRHS = ICI->getOperand(1);
00477   Value *TrueVal = SI.getTrueValue();
00478   Value *FalseVal = SI.getFalseValue();
00479 
00480   // Check cases where the comparison is with a constant that
00481   // can be adjusted to fit the min/max idiom. We may move or edit ICI
00482   // here, so make sure the select is the only user.
00483   if (ICI->hasOneUse())
00484     if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
00485       // X < MIN ? T : F  -->  F
00486       if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
00487           && CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
00488         return ReplaceInstUsesWith(SI, FalseVal);
00489       // X > MAX ? T : F  -->  F
00490       else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
00491                && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
00492         return ReplaceInstUsesWith(SI, FalseVal);
00493       switch (Pred) {
00494       default: break;
00495       case ICmpInst::ICMP_ULT:
00496       case ICmpInst::ICMP_SLT:
00497       case ICmpInst::ICMP_UGT:
00498       case ICmpInst::ICMP_SGT: {
00499         // These transformations only work for selects over integers.
00500         IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType());
00501         if (!SelectTy)
00502           break;
00503 
00504         Constant *AdjustedRHS;
00505         if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
00506           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
00507         else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
00508           AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);
00509 
00510         // X > C ? X : C+1  -->  X < C+1 ? C+1 : X
00511         // X < C ? X : C-1  -->  X > C-1 ? C-1 : X
00512         if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
00513             (CmpLHS == FalseVal && AdjustedRHS == TrueVal))
00514           ; // Nothing to do here. Values match without any sign/zero extension.
00515 
00516         // Types do not match. Instead of calculating this with mixed types
00517         // promote all to the larger type. This enables scalar evolution to
00518         // analyze this expression.
00519         else if (CmpRHS->getType()->getScalarSizeInBits()
00520                  < SelectTy->getBitWidth()) {
00521           Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy);
00522 
00523           // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
00524           // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
00525           // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
00526           // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
00527           if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
00528                 sextRHS == FalseVal) {
00529             CmpLHS = TrueVal;
00530             AdjustedRHS = sextRHS;
00531           } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
00532                      sextRHS == TrueVal) {
00533             CmpLHS = FalseVal;
00534             AdjustedRHS = sextRHS;
00535           } else if (ICI->isUnsigned()) {
00536             Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy);
00537             // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
00538             // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
00539             // zext + signed compare cannot be changed:
00540             //    0xff <s 0x00, but 0x00ff >s 0x0000
00541             if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
00542                 zextRHS == FalseVal) {
00543               CmpLHS = TrueVal;
00544               AdjustedRHS = zextRHS;
00545             } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
00546                        zextRHS == TrueVal) {
00547               CmpLHS = FalseVal;
00548               AdjustedRHS = zextRHS;
00549             } else
00550               break;
00551           } else
00552             break;
00553         } else
00554           break;
00555 
00556         Pred = ICmpInst::getSwappedPredicate(Pred);
00557         CmpRHS = AdjustedRHS;
00558         std::swap(FalseVal, TrueVal);
00559         ICI->setPredicate(Pred);
00560         ICI->setOperand(0, CmpLHS);
00561         ICI->setOperand(1, CmpRHS);
00562         SI.setOperand(1, TrueVal);
00563         SI.setOperand(2, FalseVal);
00564 
00565         // Move ICI instruction right before the select instruction. Otherwise
00566         // the sext/zext value may be defined after the ICI instruction uses it.
00567         ICI->moveBefore(&SI);
00568 
00569         Changed = true;
00570         break;
00571       }
00572       }
00573     }
00574 
00575   // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
00576   // and       (X <s  0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
00577   // FIXME: Type and constness constraints could be lifted, but we have to
00578   //        watch code size carefully. We should consider xor instead of
00579   //        sub/add when we decide to do that.
00580   if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
00581     if (TrueVal->getType() == Ty) {
00582       if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
00583         ConstantInt *C1 = nullptr, *C2 = nullptr;
00584         if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
00585           C1 = dyn_cast<ConstantInt>(TrueVal);
00586           C2 = dyn_cast<ConstantInt>(FalseVal);
00587         } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
00588           C1 = dyn_cast<ConstantInt>(FalseVal);
00589           C2 = dyn_cast<ConstantInt>(TrueVal);
00590         }
00591         if (C1 && C2) {
00592           // This shift results in either -1 or 0.
00593           Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
00594 
00595           // Check if we can express the operation with a single or.
00596           if (C2->isAllOnesValue())
00597             return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
00598 
00599           Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
00600           return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
00601         }
00602       }
00603     }
00604   }
00605 
00606   // If we have an equality comparison then we know the value in one of the
00607   // arms of the select. See if substituting this value into the arm and
00608   // simplifying the result yields the same value as the other arm.
00609   if (Pred == ICmpInst::ICMP_EQ) {
00610     if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, DL, TLI,
00611                                DT, AT) == TrueVal ||
00612         SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, DL, TLI,
00613                                DT, AT) == TrueVal)
00614       return ReplaceInstUsesWith(SI, FalseVal);
00615     if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, DL, TLI,
00616                                DT, AT) == FalseVal ||
00617         SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, DL, TLI,
00618                                DT, AT) == FalseVal)
00619       return ReplaceInstUsesWith(SI, FalseVal);
00620   } else if (Pred == ICmpInst::ICMP_NE) {
00621     if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, DL, TLI,
00622                                DT, AT) == FalseVal ||
00623         SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, DL, TLI,
00624                                DT, AT) == FalseVal)
00625       return ReplaceInstUsesWith(SI, TrueVal);
00626     if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, DL, TLI,
00627                                DT, AT) == TrueVal ||
00628         SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, DL, TLI,
00629                                DT, AT) == TrueVal)
00630       return ReplaceInstUsesWith(SI, TrueVal);
00631   }
00632 
00633   // NOTE: if we wanted to, this is where to detect integer MIN/MAX
00634 
00635   if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
00636     if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
00637       // Transform (X == C) ? X : Y -> (X == C) ? C : Y
00638       SI.setOperand(1, CmpRHS);
00639       Changed = true;
00640     } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
00641       // Transform (X != C) ? Y : X -> (X != C) ? Y : C
00642       SI.setOperand(2, CmpRHS);
00643       Changed = true;
00644     }
00645   }
00646 
00647   if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
00648     return ReplaceInstUsesWith(SI, V);
00649 
00650   return Changed ? &SI : nullptr;
00651 }
00652 
00653 
00654 /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
00655 /// PHI node (but the two may be in different blocks).  See if the true/false
00656 /// values (V) are live in all of the predecessor blocks of the PHI.  For
00657 /// example, cases like this cannot be mapped:
00658 ///
00659 ///   X = phi [ C1, BB1], [C2, BB2]
00660 ///   Y = add
00661 ///   Z = select X, Y, 0
00662 ///
00663 /// because Y is not live in BB1/BB2.
00664 ///
00665 static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
00666                                                    const SelectInst &SI) {
00667   // If the value is a non-instruction value like a constant or argument, it
00668   // can always be mapped.
00669   const Instruction *I = dyn_cast<Instruction>(V);
00670   if (!I) return true;
00671 
00672   // If V is a PHI node defined in the same block as the condition PHI, we can
00673   // map the arguments.
00674   const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
00675 
00676   if (const PHINode *VP = dyn_cast<PHINode>(I))
00677     if (VP->getParent() == CondPHI->getParent())
00678       return true;
00679 
00680   // Otherwise, if the PHI and select are defined in the same block and if V is
00681   // defined in a different block, then we can transform it.
00682   if (SI.getParent() == CondPHI->getParent() &&
00683       I->getParent() != CondPHI->getParent())
00684     return true;
00685 
00686   // Otherwise we have a 'hard' case and we can't tell without doing more
00687   // detailed dominator based analysis, punt.
00688   return false;
00689 }
00690 
00691 /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
00692 ///   SPF2(SPF1(A, B), C)
00693 Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
00694                                         SelectPatternFlavor SPF1,
00695                                         Value *A, Value *B,
00696                                         Instruction &Outer,
00697                                         SelectPatternFlavor SPF2, Value *C) {
00698   if (C == A || C == B) {
00699     // MAX(MAX(A, B), B) -> MAX(A, B)
00700     // MIN(MIN(a, b), a) -> MIN(a, b)
00701     if (SPF1 == SPF2)
00702       return ReplaceInstUsesWith(Outer, Inner);
00703 
00704     // MAX(MIN(a, b), a) -> a
00705     // MIN(MAX(a, b), a) -> a
00706     if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
00707         (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
00708         (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
00709         (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
00710       return ReplaceInstUsesWith(Outer, C);
00711   }
00712 
00713   if (SPF1 == SPF2) {
00714     if (ConstantInt *CB = dyn_cast<ConstantInt>(B)) {
00715       if (ConstantInt *CC = dyn_cast<ConstantInt>(C)) {
00716         APInt ACB = CB->getValue();
00717         APInt ACC = CC->getValue();
00718 
00719         // MIN(MIN(A, 23), 97) -> MIN(A, 23)
00720         // MAX(MAX(A, 97), 23) -> MAX(A, 97)
00721         if ((SPF1 == SPF_UMIN && ACB.ule(ACC)) ||
00722             (SPF1 == SPF_SMIN && ACB.sle(ACC)) ||
00723             (SPF1 == SPF_UMAX && ACB.uge(ACC)) ||
00724             (SPF1 == SPF_SMAX && ACB.sge(ACC)))
00725           return ReplaceInstUsesWith(Outer, Inner);
00726 
00727         // MIN(MIN(A, 97), 23) -> MIN(A, 23)
00728         // MAX(MAX(A, 23), 97) -> MAX(A, 97)
00729         if ((SPF1 == SPF_UMIN && ACB.ugt(ACC)) ||
00730             (SPF1 == SPF_SMIN && ACB.sgt(ACC)) ||
00731             (SPF1 == SPF_UMAX && ACB.ult(ACC)) ||
00732             (SPF1 == SPF_SMAX && ACB.slt(ACC))) {
00733           Outer.replaceUsesOfWith(Inner, A);
00734           return &Outer;
00735         }
00736       }
00737     }
00738   }
00739 
00740   // ABS(ABS(X)) -> ABS(X)
00741   // NABS(NABS(X)) -> NABS(X)
00742   if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
00743     return ReplaceInstUsesWith(Outer, Inner);
00744   }
00745 
00746   // ABS(NABS(X)) -> ABS(X)
00747   // NABS(ABS(X)) -> NABS(X)
00748   if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
00749       (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
00750     SelectInst *SI = cast<SelectInst>(Inner);
00751     Value *NewSI = Builder->CreateSelect(
00752         SI->getCondition(), SI->getFalseValue(), SI->getTrueValue());
00753     return ReplaceInstUsesWith(Outer, NewSI);
00754   }
00755   return nullptr;
00756 }
00757 
00758 /// foldSelectICmpAnd - If one of the constants is zero (we know they can't
00759 /// both be) and we have an icmp instruction with zero, and we have an 'and'
00760 /// with the non-constant value and a power of two we can turn the select
00761 /// into a shift on the result of the 'and'.
00762 static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
00763                                 ConstantInt *FalseVal,
00764                                 InstCombiner::BuilderTy *Builder) {
00765   const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
00766   if (!IC || !IC->isEquality() || !SI.getType()->isIntegerTy())
00767     return nullptr;
00768 
00769   if (!match(IC->getOperand(1), m_Zero()))
00770     return nullptr;
00771 
00772   ConstantInt *AndRHS;
00773   Value *LHS = IC->getOperand(0);
00774   if (!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
00775     return nullptr;
00776 
00777   // If both select arms are non-zero see if we have a select of the form
00778   // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
00779   // for 'x ? 2^n : 0' and fix the thing up at the end.
00780   ConstantInt *Offset = nullptr;
00781   if (!TrueVal->isZero() && !FalseVal->isZero()) {
00782     if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
00783       Offset = FalseVal;
00784     else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
00785       Offset = TrueVal;
00786     else
00787       return nullptr;
00788 
00789     // Adjust TrueVal and FalseVal to the offset.
00790     TrueVal = ConstantInt::get(Builder->getContext(),
00791                                TrueVal->getValue() - Offset->getValue());
00792     FalseVal = ConstantInt::get(Builder->getContext(),
00793                                 FalseVal->getValue() - Offset->getValue());
00794   }
00795 
00796   // Make sure the mask in the 'and' and one of the select arms is a power of 2.
00797   if (!AndRHS->getValue().isPowerOf2() ||
00798       (!TrueVal->getValue().isPowerOf2() &&
00799        !FalseVal->getValue().isPowerOf2()))
00800     return nullptr;
00801 
00802   // Determine which shift is needed to transform result of the 'and' into the
00803   // desired result.
00804   ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
00805   unsigned ValZeros = ValC->getValue().logBase2();
00806   unsigned AndZeros = AndRHS->getValue().logBase2();
00807 
00808   // If types don't match we can still convert the select by introducing a zext
00809   // or a trunc of the 'and'. The trunc case requires that all of the truncated
00810   // bits are zero, we can figure that out by looking at the 'and' mask.
00811   if (AndZeros >= ValC->getBitWidth())
00812     return nullptr;
00813 
00814   Value *V = Builder->CreateZExtOrTrunc(LHS, SI.getType());
00815   if (ValZeros > AndZeros)
00816     V = Builder->CreateShl(V, ValZeros - AndZeros);
00817   else if (ValZeros < AndZeros)
00818     V = Builder->CreateLShr(V, AndZeros - ValZeros);
00819 
00820   // Okay, now we know that everything is set up, we just don't know whether we
00821   // have a icmp_ne or icmp_eq and whether the true or false val is the zero.
00822   bool ShouldNotVal = !TrueVal->isZero();
00823   ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
00824   if (ShouldNotVal)
00825     V = Builder->CreateXor(V, ValC);
00826 
00827   // Apply an offset if needed.
00828   if (Offset)
00829     V = Builder->CreateAdd(V, Offset);
00830   return V;
00831 }
00832 
00833 Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
00834   Value *CondVal = SI.getCondition();
00835   Value *TrueVal = SI.getTrueValue();
00836   Value *FalseVal = SI.getFalseValue();
00837 
00838   if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, DL, TLI,
00839                                     DT, AT))
00840     return ReplaceInstUsesWith(SI, V);
00841 
00842   if (SI.getType()->isIntegerTy(1)) {
00843     if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
00844       if (C->getZExtValue()) {
00845         // Change: A = select B, true, C --> A = or B, C
00846         return BinaryOperator::CreateOr(CondVal, FalseVal);
00847       }
00848       // Change: A = select B, false, C --> A = and !B, C
00849       Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
00850       return BinaryOperator::CreateAnd(NotCond, FalseVal);
00851     }
00852     if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
00853       if (C->getZExtValue() == false) {
00854         // Change: A = select B, C, false --> A = and B, C
00855         return BinaryOperator::CreateAnd(CondVal, TrueVal);
00856       }
00857       // Change: A = select B, C, true --> A = or !B, C
00858       Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
00859       return BinaryOperator::CreateOr(NotCond, TrueVal);
00860     }
00861 
00862     // select a, b, a  -> a&b
00863     // select a, a, b  -> a|b
00864     if (CondVal == TrueVal)
00865       return BinaryOperator::CreateOr(CondVal, FalseVal);
00866     if (CondVal == FalseVal)
00867       return BinaryOperator::CreateAnd(CondVal, TrueVal);
00868 
00869     // select a, ~a, b -> (~a)&b
00870     // select a, b, ~a -> (~a)|b
00871     if (match(TrueVal, m_Not(m_Specific(CondVal))))
00872       return BinaryOperator::CreateAnd(TrueVal, FalseVal);
00873     if (match(FalseVal, m_Not(m_Specific(CondVal))))
00874       return BinaryOperator::CreateOr(TrueVal, FalseVal);
00875   }
00876 
00877   // Selecting between two integer constants?
00878   if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
00879     if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
00880       // select C, 1, 0 -> zext C to int
00881       if (FalseValC->isZero() && TrueValC->getValue() == 1)
00882         return new ZExtInst(CondVal, SI.getType());
00883 
00884       // select C, -1, 0 -> sext C to int
00885       if (FalseValC->isZero() && TrueValC->isAllOnesValue())
00886         return new SExtInst(CondVal, SI.getType());
00887 
00888       // select C, 0, 1 -> zext !C to int
00889       if (TrueValC->isZero() && FalseValC->getValue() == 1) {
00890         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
00891         return new ZExtInst(NotCond, SI.getType());
00892       }
00893 
00894       // select C, 0, -1 -> sext !C to int
00895       if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
00896         Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
00897         return new SExtInst(NotCond, SI.getType());
00898       }
00899 
00900       if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
00901         return ReplaceInstUsesWith(SI, V);
00902     }
00903 
00904   // See if we are selecting two values based on a comparison of the two values.
00905   if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
00906     if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
00907       // Transform (X == Y) ? X : Y  -> Y
00908       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
00909         // This is not safe in general for floating point:
00910         // consider X== -0, Y== +0.
00911         // It becomes safe if either operand is a nonzero constant.
00912         ConstantFP *CFPt, *CFPf;
00913         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
00914               !CFPt->getValueAPF().isZero()) ||
00915             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
00916              !CFPf->getValueAPF().isZero()))
00917         return ReplaceInstUsesWith(SI, FalseVal);
00918       }
00919       // Transform (X une Y) ? X : Y  -> X
00920       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
00921         // This is not safe in general for floating point:
00922         // consider X== -0, Y== +0.
00923         // It becomes safe if either operand is a nonzero constant.
00924         ConstantFP *CFPt, *CFPf;
00925         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
00926               !CFPt->getValueAPF().isZero()) ||
00927             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
00928              !CFPf->getValueAPF().isZero()))
00929         return ReplaceInstUsesWith(SI, TrueVal);
00930       }
00931       // NOTE: if we wanted to, this is where to detect MIN/MAX
00932 
00933     } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
00934       // Transform (X == Y) ? Y : X  -> X
00935       if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
00936         // This is not safe in general for floating point:
00937         // consider X== -0, Y== +0.
00938         // It becomes safe if either operand is a nonzero constant.
00939         ConstantFP *CFPt, *CFPf;
00940         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
00941               !CFPt->getValueAPF().isZero()) ||
00942             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
00943              !CFPf->getValueAPF().isZero()))
00944           return ReplaceInstUsesWith(SI, FalseVal);
00945       }
00946       // Transform (X une Y) ? Y : X  -> Y
00947       if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
00948         // This is not safe in general for floating point:
00949         // consider X== -0, Y== +0.
00950         // It becomes safe if either operand is a nonzero constant.
00951         ConstantFP *CFPt, *CFPf;
00952         if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
00953               !CFPt->getValueAPF().isZero()) ||
00954             ((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
00955              !CFPf->getValueAPF().isZero()))
00956           return ReplaceInstUsesWith(SI, TrueVal);
00957       }
00958       // NOTE: if we wanted to, this is where to detect MIN/MAX
00959     }
00960     // NOTE: if we wanted to, this is where to detect ABS
00961   }
00962 
00963   // See if we are selecting two values based on a comparison of the two values.
00964   if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
00965     if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
00966       return Result;
00967 
00968   if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
00969     if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
00970       if (TI->hasOneUse() && FI->hasOneUse()) {
00971         Instruction *AddOp = nullptr, *SubOp = nullptr;
00972 
00973         // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
00974         if (TI->getOpcode() == FI->getOpcode())
00975           if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
00976             return IV;
00977 
00978         // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))).  This is
00979         // even legal for FP.
00980         if ((TI->getOpcode() == Instruction::Sub &&
00981              FI->getOpcode() == Instruction::Add) ||
00982             (TI->getOpcode() == Instruction::FSub &&
00983              FI->getOpcode() == Instruction::FAdd)) {
00984           AddOp = FI; SubOp = TI;
00985         } else if ((FI->getOpcode() == Instruction::Sub &&
00986                     TI->getOpcode() == Instruction::Add) ||
00987                    (FI->getOpcode() == Instruction::FSub &&
00988                     TI->getOpcode() == Instruction::FAdd)) {
00989           AddOp = TI; SubOp = FI;
00990         }
00991 
00992         if (AddOp) {
00993           Value *OtherAddOp = nullptr;
00994           if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
00995             OtherAddOp = AddOp->getOperand(1);
00996           } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
00997             OtherAddOp = AddOp->getOperand(0);
00998           }
00999 
01000           if (OtherAddOp) {
01001             // So at this point we know we have (Y -> OtherAddOp):
01002             //        select C, (add X, Y), (sub X, Z)
01003             Value *NegVal;  // Compute -Z
01004             if (SI.getType()->isFPOrFPVectorTy()) {
01005               NegVal = Builder->CreateFNeg(SubOp->getOperand(1));
01006               if (Instruction *NegInst = dyn_cast<Instruction>(NegVal)) {
01007                 FastMathFlags Flags = AddOp->getFastMathFlags();
01008                 Flags &= SubOp->getFastMathFlags();
01009                 NegInst->setFastMathFlags(Flags);
01010               }
01011             } else {
01012               NegVal = Builder->CreateNeg(SubOp->getOperand(1));
01013             }
01014 
01015             Value *NewTrueOp = OtherAddOp;
01016             Value *NewFalseOp = NegVal;
01017             if (AddOp != TI)
01018               std::swap(NewTrueOp, NewFalseOp);
01019             Value *NewSel =
01020               Builder->CreateSelect(CondVal, NewTrueOp,
01021                                     NewFalseOp, SI.getName() + ".p");
01022 
01023             if (SI.getType()->isFPOrFPVectorTy()) {
01024               Instruction *RI =
01025                 BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
01026 
01027               FastMathFlags Flags = AddOp->getFastMathFlags();
01028               Flags &= SubOp->getFastMathFlags();
01029               RI->setFastMathFlags(Flags);
01030               return RI;
01031             } else
01032               return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
01033           }
01034         }
01035       }
01036 
01037   // See if we can fold the select into one of our operands.
01038   if (SI.getType()->isIntegerTy()) {
01039     if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
01040       return FoldI;
01041 
01042     // MAX(MAX(a, b), a) -> MAX(a, b)
01043     // MIN(MIN(a, b), a) -> MIN(a, b)
01044     // MAX(MIN(a, b), a) -> a
01045     // MIN(MAX(a, b), a) -> a
01046     Value *LHS, *RHS, *LHS2, *RHS2;
01047     if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
01048       if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
01049         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
01050                                           SI, SPF, RHS))
01051           return R;
01052       if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
01053         if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
01054                                           SI, SPF, LHS))
01055           return R;
01056     }
01057 
01058     // TODO.
01059     // ABS(-X) -> ABS(X)
01060   }
01061 
01062   // See if we can fold the select into a phi node if the condition is a select.
01063   if (isa<PHINode>(SI.getCondition()))
01064     // The true/false values have to be live in the PHI predecessor's blocks.
01065     if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
01066         CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
01067       if (Instruction *NV = FoldOpIntoPhi(SI))
01068         return NV;
01069 
01070   if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
01071     if (TrueSI->getCondition() == CondVal) {
01072       if (SI.getTrueValue() == TrueSI->getTrueValue())
01073         return nullptr;
01074       SI.setOperand(1, TrueSI->getTrueValue());
01075       return &SI;
01076     }
01077   }
01078   if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
01079     if (FalseSI->getCondition() == CondVal) {
01080       if (SI.getFalseValue() == FalseSI->getFalseValue())
01081         return nullptr;
01082       SI.setOperand(2, FalseSI->getFalseValue());
01083       return &SI;
01084     }
01085   }
01086 
01087   if (BinaryOperator::isNot(CondVal)) {
01088     SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
01089     SI.setOperand(1, FalseVal);
01090     SI.setOperand(2, TrueVal);
01091     return &SI;
01092   }
01093 
01094   if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
01095     unsigned VWidth = VecTy->getNumElements();
01096     APInt UndefElts(VWidth, 0);
01097     APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
01098     if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
01099       if (V != &SI)
01100         return ReplaceInstUsesWith(SI, V);
01101       return &SI;
01102     }
01103 
01104     if (isa<ConstantAggregateZero>(CondVal)) {
01105       return ReplaceInstUsesWith(SI, FalseVal);
01106     }
01107   }
01108 
01109   return nullptr;
01110 }