| //===- InstCombineSelect.cpp ----------------------------------------------===// | |
| // | |
| // The LLVM Compiler Infrastructure | |
| // | |
| // This file is distributed under the University of Illinois Open Source | |
| // License. See LICENSE.TXT for details. | |
| // | |
| //===----------------------------------------------------------------------===// | |
| // | |
| // This file implements the visitSelect function. | |
| // | |
| //===----------------------------------------------------------------------===// | |
| #include "InstCombine.h" | |
| #include "llvm/Support/PatternMatch.h" | |
| #include "llvm/Analysis/ConstantFolding.h" | |
| #include "llvm/Analysis/InstructionSimplify.h" | |
| using namespace llvm; | |
| using namespace PatternMatch; | |
| /// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms, | |
| /// returning the kind and providing the out parameter results if we | |
| /// successfully match. | |
| static SelectPatternFlavor | |
| MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) { | |
| SelectInst *SI = dyn_cast<SelectInst>(V); | |
| if (SI == 0) return SPF_UNKNOWN; | |
| ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition()); | |
| if (ICI == 0) return SPF_UNKNOWN; | |
| LHS = ICI->getOperand(0); | |
| RHS = ICI->getOperand(1); | |
| // (icmp X, Y) ? X : Y | |
| if (SI->getTrueValue() == ICI->getOperand(0) && | |
| SI->getFalseValue() == ICI->getOperand(1)) { | |
| switch (ICI->getPredicate()) { | |
| default: return SPF_UNKNOWN; // Equality. | |
| case ICmpInst::ICMP_UGT: | |
| case ICmpInst::ICMP_UGE: return SPF_UMAX; | |
| case ICmpInst::ICMP_SGT: | |
| case ICmpInst::ICMP_SGE: return SPF_SMAX; | |
| case ICmpInst::ICMP_ULT: | |
| case ICmpInst::ICMP_ULE: return SPF_UMIN; | |
| case ICmpInst::ICMP_SLT: | |
| case ICmpInst::ICMP_SLE: return SPF_SMIN; | |
| } | |
| } | |
| // (icmp X, Y) ? Y : X | |
| if (SI->getTrueValue() == ICI->getOperand(1) && | |
| SI->getFalseValue() == ICI->getOperand(0)) { | |
| switch (ICI->getPredicate()) { | |
| default: return SPF_UNKNOWN; // Equality. | |
| case ICmpInst::ICMP_UGT: | |
| case ICmpInst::ICMP_UGE: return SPF_UMIN; | |
| case ICmpInst::ICMP_SGT: | |
| case ICmpInst::ICMP_SGE: return SPF_SMIN; | |
| case ICmpInst::ICMP_ULT: | |
| case ICmpInst::ICMP_ULE: return SPF_UMAX; | |
| case ICmpInst::ICMP_SLT: | |
| case ICmpInst::ICMP_SLE: return SPF_SMAX; | |
| } | |
| } | |
| // TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5) | |
| return SPF_UNKNOWN; | |
| } | |
| /// GetSelectFoldableOperands - We want to turn code that looks like this: | |
| /// %C = or %A, %B | |
| /// %D = select %cond, %C, %A | |
| /// into: | |
| /// %C = select %cond, %B, 0 | |
| /// %D = or %A, %C | |
| /// | |
| /// Assuming that the specified instruction is an operand to the select, return | |
| /// a bitmask indicating which operands of this instruction are foldable if they | |
| /// equal the other incoming value of the select. | |
| /// | |
| static unsigned GetSelectFoldableOperands(Instruction *I) { | |
| switch (I->getOpcode()) { | |
| case Instruction::Add: | |
| case Instruction::Mul: | |
| case Instruction::And: | |
| case Instruction::Or: | |
| case Instruction::Xor: | |
| return 3; // Can fold through either operand. | |
| case Instruction::Sub: // Can only fold on the amount subtracted. | |
| case Instruction::Shl: // Can only fold on the shift amount. | |
| case Instruction::LShr: | |
| case Instruction::AShr: | |
| return 1; | |
| default: | |
| return 0; // Cannot fold | |
| } | |
| } | |
| /// GetSelectFoldableConstant - For the same transformation as the previous | |
| /// function, return the identity constant that goes into the select. | |
| static Constant *GetSelectFoldableConstant(Instruction *I) { | |
| switch (I->getOpcode()) { | |
| default: llvm_unreachable("This cannot happen!"); | |
| case Instruction::Add: | |
| case Instruction::Sub: | |
| case Instruction::Or: | |
| case Instruction::Xor: | |
| case Instruction::Shl: | |
| case Instruction::LShr: | |
| case Instruction::AShr: | |
| return Constant::getNullValue(I->getType()); | |
| case Instruction::And: | |
| return Constant::getAllOnesValue(I->getType()); | |
| case Instruction::Mul: | |
| return ConstantInt::get(I->getType(), 1); | |
| } | |
| } | |
| /// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI | |
| /// have the same opcode and only one use each. Try to simplify this. | |
| Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI, | |
| Instruction *FI) { | |
| if (TI->getNumOperands() == 1) { | |
| // If this is a non-volatile load or a cast from the same type, | |
| // merge. | |
| if (TI->isCast()) { | |
| if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType()) | |
| return 0; | |
| } else { | |
| return 0; // unknown unary op. | |
| } | |
| // Fold this by inserting a select from the input values. | |
| Value *NewSI = Builder->CreateSelect(SI.getCondition(), TI->getOperand(0), | |
| FI->getOperand(0), SI.getName()+".v"); | |
| return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI, | |
| TI->getType()); | |
| } | |
| // Only handle binary operators here. | |
| if (!isa<BinaryOperator>(TI)) | |
| return 0; | |
| // Figure out if the operations have any operands in common. | |
| Value *MatchOp, *OtherOpT, *OtherOpF; | |
| bool MatchIsOpZero; | |
| if (TI->getOperand(0) == FI->getOperand(0)) { | |
| MatchOp = TI->getOperand(0); | |
| OtherOpT = TI->getOperand(1); | |
| OtherOpF = FI->getOperand(1); | |
| MatchIsOpZero = true; | |
| } else if (TI->getOperand(1) == FI->getOperand(1)) { | |
| MatchOp = TI->getOperand(1); | |
| OtherOpT = TI->getOperand(0); | |
| OtherOpF = FI->getOperand(0); | |
| MatchIsOpZero = false; | |
| } else if (!TI->isCommutative()) { | |
| return 0; | |
| } else if (TI->getOperand(0) == FI->getOperand(1)) { | |
| MatchOp = TI->getOperand(0); | |
| OtherOpT = TI->getOperand(1); | |
| OtherOpF = FI->getOperand(0); | |
| MatchIsOpZero = true; | |
| } else if (TI->getOperand(1) == FI->getOperand(0)) { | |
| MatchOp = TI->getOperand(1); | |
| OtherOpT = TI->getOperand(0); | |
| OtherOpF = FI->getOperand(1); | |
| MatchIsOpZero = true; | |
| } else { | |
| return 0; | |
| } | |
| // If we reach here, they do have operations in common. | |
| Value *NewSI = Builder->CreateSelect(SI.getCondition(), OtherOpT, | |
| OtherOpF, SI.getName()+".v"); | |
| if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) { | |
| if (MatchIsOpZero) | |
| return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI); | |
| else | |
| return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp); | |
| } | |
| llvm_unreachable("Shouldn't get here"); | |
| return 0; | |
| } | |
| static bool isSelect01(Constant *C1, Constant *C2) { | |
| ConstantInt *C1I = dyn_cast<ConstantInt>(C1); | |
| if (!C1I) | |
| return false; | |
| ConstantInt *C2I = dyn_cast<ConstantInt>(C2); | |
| if (!C2I) | |
| return false; | |
| if (!C1I->isZero() && !C2I->isZero()) // One side must be zero. | |
| return false; | |
| return C1I->isOne() || C1I->isAllOnesValue() || | |
| C2I->isOne() || C2I->isAllOnesValue(); | |
| } | |
| /// FoldSelectIntoOp - Try fold the select into one of the operands to | |
| /// facilitate further optimization. | |
| Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal, | |
| Value *FalseVal) { | |
| // See the comment above GetSelectFoldableOperands for a description of the | |
| // transformation we are doing here. | |
| if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) { | |
| if (TVI->hasOneUse() && TVI->getNumOperands() == 2 && | |
| !isa<Constant>(FalseVal)) { | |
| if (unsigned SFO = GetSelectFoldableOperands(TVI)) { | |
| unsigned OpToFold = 0; | |
| if ((SFO & 1) && FalseVal == TVI->getOperand(0)) { | |
| OpToFold = 1; | |
| } else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) { | |
| OpToFold = 2; | |
| } | |
| if (OpToFold) { | |
| Constant *C = GetSelectFoldableConstant(TVI); | |
| Value *OOp = TVI->getOperand(2-OpToFold); | |
| // Avoid creating select between 2 constants unless it's selecting | |
| // between 0, 1 and -1. | |
| if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { | |
| Value *NewSel = Builder->CreateSelect(SI.getCondition(), OOp, C); | |
| NewSel->takeName(TVI); | |
| BinaryOperator *TVI_BO = cast<BinaryOperator>(TVI); | |
| BinaryOperator *BO = BinaryOperator::Create(TVI_BO->getOpcode(), | |
| FalseVal, NewSel); | |
| if (isa<PossiblyExactOperator>(BO)) | |
| BO->setIsExact(TVI_BO->isExact()); | |
| if (isa<OverflowingBinaryOperator>(BO)) { | |
| BO->setHasNoUnsignedWrap(TVI_BO->hasNoUnsignedWrap()); | |
| BO->setHasNoSignedWrap(TVI_BO->hasNoSignedWrap()); | |
| } | |
| return BO; | |
| } | |
| } | |
| } | |
| } | |
| } | |
| if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) { | |
| if (FVI->hasOneUse() && FVI->getNumOperands() == 2 && | |
| !isa<Constant>(TrueVal)) { | |
| if (unsigned SFO = GetSelectFoldableOperands(FVI)) { | |
| unsigned OpToFold = 0; | |
| if ((SFO & 1) && TrueVal == FVI->getOperand(0)) { | |
| OpToFold = 1; | |
| } else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) { | |
| OpToFold = 2; | |
| } | |
| if (OpToFold) { | |
| Constant *C = GetSelectFoldableConstant(FVI); | |
| Value *OOp = FVI->getOperand(2-OpToFold); | |
| // Avoid creating select between 2 constants unless it's selecting | |
| // between 0, 1 and -1. | |
| if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { | |
| Value *NewSel = Builder->CreateSelect(SI.getCondition(), C, OOp); | |
| NewSel->takeName(FVI); | |
| BinaryOperator *FVI_BO = cast<BinaryOperator>(FVI); | |
| BinaryOperator *BO = BinaryOperator::Create(FVI_BO->getOpcode(), | |
| TrueVal, NewSel); | |
| if (isa<PossiblyExactOperator>(BO)) | |
| BO->setIsExact(FVI_BO->isExact()); | |
| if (isa<OverflowingBinaryOperator>(BO)) { | |
| BO->setHasNoUnsignedWrap(FVI_BO->hasNoUnsignedWrap()); | |
| BO->setHasNoSignedWrap(FVI_BO->hasNoSignedWrap()); | |
| } | |
| return BO; | |
| } | |
| } | |
| } | |
| } | |
| } | |
| return 0; | |
| } | |
| /// SimplifyWithOpReplaced - See if V simplifies when its operand Op is | |
| /// replaced with RepOp. | |
| static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp, | |
| const TargetData *TD) { | |
| // Trivial replacement. | |
| if (V == Op) | |
| return RepOp; | |
| Instruction *I = dyn_cast<Instruction>(V); | |
| if (!I) | |
| return 0; | |
| // If this is a binary operator, try to simplify it with the replaced op. | |
| if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) { | |
| if (B->getOperand(0) == Op) | |
| return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), TD); | |
| if (B->getOperand(1) == Op) | |
| return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD); | |
| } | |
| // Same for CmpInsts. | |
| if (CmpInst *C = dyn_cast<CmpInst>(I)) { | |
| if (C->getOperand(0) == Op) | |
| return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD); | |
| if (C->getOperand(1) == Op) | |
| return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD); | |
| } | |
| // TODO: We could hand off more cases to instsimplify here. | |
| // If all operands are constant after substituting Op for RepOp then we can | |
| // constant fold the instruction. | |
| if (Constant *CRepOp = dyn_cast<Constant>(RepOp)) { | |
| // Build a list of all constant operands. | |
| SmallVector<Constant*, 8> ConstOps; | |
| for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { | |
| if (I->getOperand(i) == Op) | |
| ConstOps.push_back(CRepOp); | |
| else if (Constant *COp = dyn_cast<Constant>(I->getOperand(i))) | |
| ConstOps.push_back(COp); | |
| else | |
| break; | |
| } | |
| // All operands were constants, fold it. | |
| if (ConstOps.size() == I->getNumOperands()) { | |
| if (LoadInst *LI = dyn_cast<LoadInst>(I)) | |
| if (!LI->isVolatile()) | |
| return ConstantFoldLoadFromConstPtr(ConstOps[0], TD); | |
| return ConstantFoldInstOperands(I->getOpcode(), I->getType(), | |
| ConstOps, TD); | |
| } | |
| } | |
| return 0; | |
| } | |
| /// visitSelectInstWithICmp - Visit a SelectInst that has an | |
| /// ICmpInst as its first operand. | |
| /// | |
| Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI, | |
| ICmpInst *ICI) { | |
| bool Changed = false; | |
| ICmpInst::Predicate Pred = ICI->getPredicate(); | |
| Value *CmpLHS = ICI->getOperand(0); | |
| Value *CmpRHS = ICI->getOperand(1); | |
| Value *TrueVal = SI.getTrueValue(); | |
| Value *FalseVal = SI.getFalseValue(); | |
| // Check cases where the comparison is with a constant that | |
| // can be adjusted to fit the min/max idiom. We may move or edit ICI | |
| // here, so make sure the select is the only user. | |
| if (ICI->hasOneUse()) | |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) { | |
| // X < MIN ? T : F --> F | |
| if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT) | |
| && CI->isMinValue(Pred == ICmpInst::ICMP_SLT)) | |
| return ReplaceInstUsesWith(SI, FalseVal); | |
| // X > MAX ? T : F --> F | |
| else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT) | |
| && CI->isMaxValue(Pred == ICmpInst::ICMP_SGT)) | |
| return ReplaceInstUsesWith(SI, FalseVal); | |
| switch (Pred) { | |
| default: break; | |
| case ICmpInst::ICMP_ULT: | |
| case ICmpInst::ICMP_SLT: | |
| case ICmpInst::ICMP_UGT: | |
| case ICmpInst::ICMP_SGT: { | |
| // These transformations only work for selects over integers. | |
| IntegerType *SelectTy = dyn_cast<IntegerType>(SI.getType()); | |
| if (!SelectTy) | |
| break; | |
| Constant *AdjustedRHS; | |
| if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT) | |
| AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1); | |
| else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) | |
| AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1); | |
| // X > C ? X : C+1 --> X < C+1 ? C+1 : X | |
| // X < C ? X : C-1 --> X > C-1 ? C-1 : X | |
| if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) || | |
| (CmpLHS == FalseVal && AdjustedRHS == TrueVal)) | |
| ; // Nothing to do here. Values match without any sign/zero extension. | |
| // Types do not match. Instead of calculating this with mixed types | |
| // promote all to the larger type. This enables scalar evolution to | |
| // analyze this expression. | |
| else if (CmpRHS->getType()->getScalarSizeInBits() | |
| < SelectTy->getBitWidth()) { | |
| Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS, SelectTy); | |
| // X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X | |
| // X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X | |
| // X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X | |
| // X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X | |
| if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && | |
| sextRHS == FalseVal) { | |
| CmpLHS = TrueVal; | |
| AdjustedRHS = sextRHS; | |
| } else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) && | |
| sextRHS == TrueVal) { | |
| CmpLHS = FalseVal; | |
| AdjustedRHS = sextRHS; | |
| } else if (ICI->isUnsigned()) { | |
| Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS, SelectTy); | |
| // X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X | |
| // X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X | |
| // zext + signed compare cannot be changed: | |
| // 0xff <s 0x00, but 0x00ff >s 0x0000 | |
| if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && | |
| zextRHS == FalseVal) { | |
| CmpLHS = TrueVal; | |
| AdjustedRHS = zextRHS; | |
| } else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) && | |
| zextRHS == TrueVal) { | |
| CmpLHS = FalseVal; | |
| AdjustedRHS = zextRHS; | |
| } else | |
| break; | |
| } else | |
| break; | |
| } else | |
| break; | |
| Pred = ICmpInst::getSwappedPredicate(Pred); | |
| CmpRHS = AdjustedRHS; | |
| std::swap(FalseVal, TrueVal); | |
| ICI->setPredicate(Pred); | |
| ICI->setOperand(0, CmpLHS); | |
| ICI->setOperand(1, CmpRHS); | |
| SI.setOperand(1, TrueVal); | |
| SI.setOperand(2, FalseVal); | |
| // Move ICI instruction right before the select instruction. Otherwise | |
| // the sext/zext value may be defined after the ICI instruction uses it. | |
| ICI->moveBefore(&SI); | |
| Changed = true; | |
| break; | |
| } | |
| } | |
| } | |
| // Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1 | |
| // and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1 | |
| // FIXME: Type and constness constraints could be lifted, but we have to | |
| // watch code size carefully. We should consider xor instead of | |
| // sub/add when we decide to do that. | |
| if (IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) { | |
| if (TrueVal->getType() == Ty) { | |
| if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) { | |
| ConstantInt *C1 = NULL, *C2 = NULL; | |
| if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) { | |
| C1 = dyn_cast<ConstantInt>(TrueVal); | |
| C2 = dyn_cast<ConstantInt>(FalseVal); | |
| } else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) { | |
| C1 = dyn_cast<ConstantInt>(FalseVal); | |
| C2 = dyn_cast<ConstantInt>(TrueVal); | |
| } | |
| if (C1 && C2) { | |
| // This shift results in either -1 or 0. | |
| Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1); | |
| // Check if we can express the operation with a single or. | |
| if (C2->isAllOnesValue()) | |
| return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1)); | |
| Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue()); | |
| return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1)); | |
| } | |
| } | |
| } | |
| } | |
| // If we have an equality comparison then we know the value in one of the | |
| // arms of the select. See if substituting this value into the arm and | |
| // simplifying the result yields the same value as the other arm. | |
| if (Pred == ICmpInst::ICMP_EQ) { | |
| if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD) == TrueVal || | |
| SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD) == TrueVal) | |
| return ReplaceInstUsesWith(SI, FalseVal); | |
| if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD) == FalseVal || | |
| SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD) == FalseVal) | |
| return ReplaceInstUsesWith(SI, FalseVal); | |
| } else if (Pred == ICmpInst::ICMP_NE) { | |
| if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD) == FalseVal || | |
| SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD) == FalseVal) | |
| return ReplaceInstUsesWith(SI, TrueVal); | |
| if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD) == TrueVal || | |
| SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD) == TrueVal) | |
| return ReplaceInstUsesWith(SI, TrueVal); | |
| } | |
| // NOTE: if we wanted to, this is where to detect integer MIN/MAX | |
| if (isa<Constant>(CmpRHS)) { | |
| if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) { | |
| // Transform (X == C) ? X : Y -> (X == C) ? C : Y | |
| SI.setOperand(1, CmpRHS); | |
| Changed = true; | |
| } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) { | |
| // Transform (X != C) ? Y : X -> (X != C) ? Y : C | |
| SI.setOperand(2, CmpRHS); | |
| Changed = true; | |
| } | |
| } | |
| return Changed ? &SI : 0; | |
| } | |
| /// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a | |
| /// PHI node (but the two may be in different blocks). See if the true/false | |
| /// values (V) are live in all of the predecessor blocks of the PHI. For | |
| /// example, cases like this cannot be mapped: | |
| /// | |
| /// X = phi [ C1, BB1], [C2, BB2] | |
| /// Y = add | |
| /// Z = select X, Y, 0 | |
| /// | |
| /// because Y is not live in BB1/BB2. | |
| /// | |
| static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V, | |
| const SelectInst &SI) { | |
| // If the value is a non-instruction value like a constant or argument, it | |
| // can always be mapped. | |
| const Instruction *I = dyn_cast<Instruction>(V); | |
| if (I == 0) return true; | |
| // If V is a PHI node defined in the same block as the condition PHI, we can | |
| // map the arguments. | |
| const PHINode *CondPHI = cast<PHINode>(SI.getCondition()); | |
| if (const PHINode *VP = dyn_cast<PHINode>(I)) | |
| if (VP->getParent() == CondPHI->getParent()) | |
| return true; | |
| // Otherwise, if the PHI and select are defined in the same block and if V is | |
| // defined in a different block, then we can transform it. | |
| if (SI.getParent() == CondPHI->getParent() && | |
| I->getParent() != CondPHI->getParent()) | |
| return true; | |
| // Otherwise we have a 'hard' case and we can't tell without doing more | |
| // detailed dominator based analysis, punt. | |
| return false; | |
| } | |
| /// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form: | |
| /// SPF2(SPF1(A, B), C) | |
| Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner, | |
| SelectPatternFlavor SPF1, | |
| Value *A, Value *B, | |
| Instruction &Outer, | |
| SelectPatternFlavor SPF2, Value *C) { | |
| if (C == A || C == B) { | |
| // MAX(MAX(A, B), B) -> MAX(A, B) | |
| // MIN(MIN(a, b), a) -> MIN(a, b) | |
| if (SPF1 == SPF2) | |
| return ReplaceInstUsesWith(Outer, Inner); | |
| // MAX(MIN(a, b), a) -> a | |
| // MIN(MAX(a, b), a) -> a | |
| if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) || | |
| (SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) || | |
| (SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) || | |
| (SPF1 == SPF_UMAX && SPF2 == SPF_UMIN)) | |
| return ReplaceInstUsesWith(Outer, C); | |
| } | |
| // TODO: MIN(MIN(A, 23), 97) | |
| return 0; | |
| } | |
| /// foldSelectICmpAnd - If one of the constants is zero (we know they can't | |
| /// both be) and we have an icmp instruction with zero, and we have an 'and' | |
| /// with the non-constant value and a power of two we can turn the select | |
| /// into a shift on the result of the 'and'. | |
| static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal, | |
| ConstantInt *FalseVal, | |
| InstCombiner::BuilderTy *Builder) { | |
| const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition()); | |
| if (!IC || !IC->isEquality()) | |
| return 0; | |
| if (!match(IC->getOperand(1), m_Zero())) | |
| return 0; | |
| ConstantInt *AndRHS; | |
| Value *LHS = IC->getOperand(0); | |
| if (LHS->getType() != SI.getType() || | |
| !match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS)))) | |
| return 0; | |
| // If both select arms are non-zero see if we have a select of the form | |
| // 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic | |
| // for 'x ? 2^n : 0' and fix the thing up at the end. | |
| ConstantInt *Offset = 0; | |
| if (!TrueVal->isZero() && !FalseVal->isZero()) { | |
| if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2()) | |
| Offset = FalseVal; | |
| else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2()) | |
| Offset = TrueVal; | |
| else | |
| return 0; | |
| // Adjust TrueVal and FalseVal to the offset. | |
| TrueVal = ConstantInt::get(Builder->getContext(), | |
| TrueVal->getValue() - Offset->getValue()); | |
| FalseVal = ConstantInt::get(Builder->getContext(), | |
| FalseVal->getValue() - Offset->getValue()); | |
| } | |
| // Make sure the mask in the 'and' and one of the select arms is a power of 2. | |
| if (!AndRHS->getValue().isPowerOf2() || | |
| (!TrueVal->getValue().isPowerOf2() && | |
| !FalseVal->getValue().isPowerOf2())) | |
| return 0; | |
| // Determine which shift is needed to transform result of the 'and' into the | |
| // desired result. | |
| ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal; | |
| unsigned ValZeros = ValC->getValue().logBase2(); | |
| unsigned AndZeros = AndRHS->getValue().logBase2(); | |
| Value *V = LHS; | |
| if (ValZeros > AndZeros) | |
| V = Builder->CreateShl(V, ValZeros - AndZeros); | |
| else if (ValZeros < AndZeros) | |
| V = Builder->CreateLShr(V, AndZeros - ValZeros); | |
| // Okay, now we know that everything is set up, we just don't know whether we | |
| // have a icmp_ne or icmp_eq and whether the true or false val is the zero. | |
| bool ShouldNotVal = !TrueVal->isZero(); | |
| ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE; | |
| if (ShouldNotVal) | |
| V = Builder->CreateXor(V, ValC); | |
| // Apply an offset if needed. | |
| if (Offset) | |
| V = Builder->CreateAdd(V, Offset); | |
| return V; | |
| } | |
| Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { | |
| Value *CondVal = SI.getCondition(); | |
| Value *TrueVal = SI.getTrueValue(); | |
| Value *FalseVal = SI.getFalseValue(); | |
| if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD)) | |
| return ReplaceInstUsesWith(SI, V); | |
| if (SI.getType()->isIntegerTy(1)) { | |
| if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) { | |
| if (C->getZExtValue()) { | |
| // Change: A = select B, true, C --> A = or B, C | |
| return BinaryOperator::CreateOr(CondVal, FalseVal); | |
| } | |
| // Change: A = select B, false, C --> A = and !B, C | |
| Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); | |
| return BinaryOperator::CreateAnd(NotCond, FalseVal); | |
| } else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) { | |
| if (C->getZExtValue() == false) { | |
| // Change: A = select B, C, false --> A = and B, C | |
| return BinaryOperator::CreateAnd(CondVal, TrueVal); | |
| } | |
| // Change: A = select B, C, true --> A = or !B, C | |
| Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); | |
| return BinaryOperator::CreateOr(NotCond, TrueVal); | |
| } | |
| // select a, b, a -> a&b | |
| // select a, a, b -> a|b | |
| if (CondVal == TrueVal) | |
| return BinaryOperator::CreateOr(CondVal, FalseVal); | |
| else if (CondVal == FalseVal) | |
| return BinaryOperator::CreateAnd(CondVal, TrueVal); | |
| } | |
| // Selecting between two integer constants? | |
| if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal)) | |
| if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) { | |
| // select C, 1, 0 -> zext C to int | |
| if (FalseValC->isZero() && TrueValC->getValue() == 1) | |
| return new ZExtInst(CondVal, SI.getType()); | |
| // select C, -1, 0 -> sext C to int | |
| if (FalseValC->isZero() && TrueValC->isAllOnesValue()) | |
| return new SExtInst(CondVal, SI.getType()); | |
| // select C, 0, 1 -> zext !C to int | |
| if (TrueValC->isZero() && FalseValC->getValue() == 1) { | |
| Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); | |
| return new ZExtInst(NotCond, SI.getType()); | |
| } | |
| // select C, 0, -1 -> sext !C to int | |
| if (TrueValC->isZero() && FalseValC->isAllOnesValue()) { | |
| Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName()); | |
| return new SExtInst(NotCond, SI.getType()); | |
| } | |
| if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder)) | |
| return ReplaceInstUsesWith(SI, V); | |
| } | |
| // See if we are selecting two values based on a comparison of the two values. | |
| if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) { | |
| if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { | |
| // Transform (X == Y) ? X : Y -> Y | |
| if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { | |
| // This is not safe in general for floating point: | |
| // consider X== -0, Y== +0. | |
| // It becomes safe if either operand is a nonzero constant. | |
| ConstantFP *CFPt, *CFPf; | |
| if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && | |
| !CFPt->getValueAPF().isZero()) || | |
| ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && | |
| !CFPf->getValueAPF().isZero())) | |
| return ReplaceInstUsesWith(SI, FalseVal); | |
| } | |
| // Transform (X une Y) ? X : Y -> X | |
| if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { | |
| // This is not safe in general for floating point: | |
| // consider X== -0, Y== +0. | |
| // It becomes safe if either operand is a nonzero constant. | |
| ConstantFP *CFPt, *CFPf; | |
| if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && | |
| !CFPt->getValueAPF().isZero()) || | |
| ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && | |
| !CFPf->getValueAPF().isZero())) | |
| return ReplaceInstUsesWith(SI, TrueVal); | |
| } | |
| // NOTE: if we wanted to, this is where to detect MIN/MAX | |
| } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ | |
| // Transform (X == Y) ? Y : X -> X | |
| if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) { | |
| // This is not safe in general for floating point: | |
| // consider X== -0, Y== +0. | |
| // It becomes safe if either operand is a nonzero constant. | |
| ConstantFP *CFPt, *CFPf; | |
| if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && | |
| !CFPt->getValueAPF().isZero()) || | |
| ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && | |
| !CFPf->getValueAPF().isZero())) | |
| return ReplaceInstUsesWith(SI, FalseVal); | |
| } | |
| // Transform (X une Y) ? Y : X -> Y | |
| if (FCI->getPredicate() == FCmpInst::FCMP_UNE) { | |
| // This is not safe in general for floating point: | |
| // consider X== -0, Y== +0. | |
| // It becomes safe if either operand is a nonzero constant. | |
| ConstantFP *CFPt, *CFPf; | |
| if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) && | |
| !CFPt->getValueAPF().isZero()) || | |
| ((CFPf = dyn_cast<ConstantFP>(FalseVal)) && | |
| !CFPf->getValueAPF().isZero())) | |
| return ReplaceInstUsesWith(SI, TrueVal); | |
| } | |
| // NOTE: if we wanted to, this is where to detect MIN/MAX | |
| } | |
| // NOTE: if we wanted to, this is where to detect ABS | |
| } | |
| // See if we are selecting two values based on a comparison of the two values. | |
| if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal)) | |
| if (Instruction *Result = visitSelectInstWithICmp(SI, ICI)) | |
| return Result; | |
| if (Instruction *TI = dyn_cast<Instruction>(TrueVal)) | |
| if (Instruction *FI = dyn_cast<Instruction>(FalseVal)) | |
| if (TI->hasOneUse() && FI->hasOneUse()) { | |
| Instruction *AddOp = 0, *SubOp = 0; | |
| // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) | |
| if (TI->getOpcode() == FI->getOpcode()) | |
| if (Instruction *IV = FoldSelectOpOp(SI, TI, FI)) | |
| return IV; | |
| // Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is | |
| // even legal for FP. | |
| if ((TI->getOpcode() == Instruction::Sub && | |
| FI->getOpcode() == Instruction::Add) || | |
| (TI->getOpcode() == Instruction::FSub && | |
| FI->getOpcode() == Instruction::FAdd)) { | |
| AddOp = FI; SubOp = TI; | |
| } else if ((FI->getOpcode() == Instruction::Sub && | |
| TI->getOpcode() == Instruction::Add) || | |
| (FI->getOpcode() == Instruction::FSub && | |
| TI->getOpcode() == Instruction::FAdd)) { | |
| AddOp = TI; SubOp = FI; | |
| } | |
| if (AddOp) { | |
| Value *OtherAddOp = 0; | |
| if (SubOp->getOperand(0) == AddOp->getOperand(0)) { | |
| OtherAddOp = AddOp->getOperand(1); | |
| } else if (SubOp->getOperand(0) == AddOp->getOperand(1)) { | |
| OtherAddOp = AddOp->getOperand(0); | |
| } | |
| if (OtherAddOp) { | |
| // So at this point we know we have (Y -> OtherAddOp): | |
| // select C, (add X, Y), (sub X, Z) | |
| Value *NegVal; // Compute -Z | |
| if (SI.getType()->isFPOrFPVectorTy()) { | |
| NegVal = Builder->CreateFNeg(SubOp->getOperand(1)); | |
| } else { | |
| NegVal = Builder->CreateNeg(SubOp->getOperand(1)); | |
| } | |
| Value *NewTrueOp = OtherAddOp; | |
| Value *NewFalseOp = NegVal; | |
| if (AddOp != TI) | |
| std::swap(NewTrueOp, NewFalseOp); | |
| Value *NewSel = | |
| Builder->CreateSelect(CondVal, NewTrueOp, | |
| NewFalseOp, SI.getName() + ".p"); | |
| if (SI.getType()->isFPOrFPVectorTy()) | |
| return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); | |
| else | |
| return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); | |
| } | |
| } | |
| } | |
| // See if we can fold the select into one of our operands. | |
| if (SI.getType()->isIntegerTy()) { | |
| if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) | |
| return FoldI; | |
| // MAX(MAX(a, b), a) -> MAX(a, b) | |
| // MIN(MIN(a, b), a) -> MIN(a, b) | |
| // MAX(MIN(a, b), a) -> a | |
| // MIN(MAX(a, b), a) -> a | |
| Value *LHS, *RHS, *LHS2, *RHS2; | |
| if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) { | |
| if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2)) | |
| if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2, | |
| SI, SPF, RHS)) | |
| return R; | |
| if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2)) | |
| if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2, | |
| SI, SPF, LHS)) | |
| return R; | |
| } | |
| // TODO. | |
| // ABS(-X) -> ABS(X) | |
| // ABS(ABS(X)) -> ABS(X) | |
| } | |
| // See if we can fold the select into a phi node if the condition is a select. | |
| if (isa<PHINode>(SI.getCondition())) | |
| // The true/false values have to be live in the PHI predecessor's blocks. | |
| if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) && | |
| CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI)) | |
| if (Instruction *NV = FoldOpIntoPhi(SI)) | |
| return NV; | |
| if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) { | |
| if (TrueSI->getCondition() == CondVal) { | |
| SI.setOperand(1, TrueSI->getTrueValue()); | |
| return &SI; | |
| } | |
| } | |
| if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) { | |
| if (FalseSI->getCondition() == CondVal) { | |
| SI.setOperand(2, FalseSI->getFalseValue()); | |
| return &SI; | |
| } | |
| } | |
| if (BinaryOperator::isNot(CondVal)) { | |
| SI.setOperand(0, BinaryOperator::getNotArgument(CondVal)); | |
| SI.setOperand(1, FalseVal); | |
| SI.setOperand(2, TrueVal); | |
| return &SI; | |
| } | |
| return 0; | |
| } |