| //===- 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"); |
| } |
| |
| 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, |
| const TargetLibraryInfo *TLI) { |
| // 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, TLI); |
| if (B->getOperand(1) == Op) |
| return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, TD, TLI); |
| } |
| |
| // Same for CmpInsts. |
| if (CmpInst *C = dyn_cast<CmpInst>(I)) { |
| if (C->getOperand(0) == Op) |
| return SimplifyCmpInst(C->getPredicate(), RepOp, C->getOperand(1), TD, |
| TLI); |
| if (C->getOperand(1) == Op) |
| return SimplifyCmpInst(C->getPredicate(), C->getOperand(0), RepOp, TD, |
| TLI); |
| } |
| |
| // 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, TLI); |
| } |
| } |
| |
| 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, TLI) == TrueVal || |
| SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == TrueVal) |
| return ReplaceInstUsesWith(SI, FalseVal); |
| if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal || |
| SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal) |
| return ReplaceInstUsesWith(SI, FalseVal); |
| } else if (Pred == ICmpInst::ICMP_NE) { |
| if (SimplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, TD, TLI) == FalseVal || |
| SimplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, TD, TLI) == FalseVal) |
| return ReplaceInstUsesWith(SI, TrueVal); |
| if (SimplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, TD, TLI) == TrueVal || |
| SimplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, TD, TLI) == 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); |
| |
| // select a, ~a, b -> (~a)&b |
| // select a, b, ~a -> (~a)|b |
| if (match(TrueVal, m_Not(m_Specific(CondVal)))) |
| return BinaryOperator::CreateAnd(TrueVal, FalseVal); |
| else if (match(FalseVal, m_Not(m_Specific(CondVal)))) |
| return BinaryOperator::CreateOr(TrueVal, FalseVal); |
| } |
| |
| // 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; |
| } |
