//===- InstCombineSelect.cpp ----------------------------------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file implements the visitSelect function. // //===----------------------------------------------------------------------===// #include "InstCombineInternal.h" #include "llvm/ADT/APInt.h" #include "llvm/ADT/Optional.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallVector.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/CmpInstAnalysis.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/BasicBlock.h" #include "llvm/IR/Constant.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/IRBuilder.h" #include "llvm/IR/InstrTypes.h" #include "llvm/IR/Instruction.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/Intrinsics.h" #include "llvm/IR/Operator.h" #include "llvm/IR/PatternMatch.h" #include "llvm/IR/Type.h" #include "llvm/IR/User.h" #include "llvm/IR/Value.h" #include "llvm/Support/Casting.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/KnownBits.h" #include "llvm/Transforms/InstCombine/InstCombineWorklist.h" #include #include using namespace llvm; using namespace PatternMatch; #define DEBUG_TYPE "instcombine" static Value *createMinMax(InstCombiner::BuilderTy &Builder, SelectPatternFlavor SPF, Value *A, Value *B) { CmpInst::Predicate Pred = getMinMaxPred(SPF); assert(CmpInst::isIntPredicate(Pred) && "Expected integer predicate"); return Builder.CreateSelect(Builder.CreateICmp(Pred, A, B), A, B); } /// Replace a select operand based on an equality comparison with the identity /// constant of a binop. static Instruction *foldSelectBinOpIdentity(SelectInst &Sel, const TargetLibraryInfo &TLI) { // The select condition must be an equality compare with a constant operand. Value *X; Constant *C; CmpInst::Predicate Pred; if (!match(Sel.getCondition(), m_Cmp(Pred, m_Value(X), m_Constant(C)))) return nullptr; bool IsEq; if (ICmpInst::isEquality(Pred)) IsEq = Pred == ICmpInst::ICMP_EQ; else if (Pred == FCmpInst::FCMP_OEQ) IsEq = true; else if (Pred == FCmpInst::FCMP_UNE) IsEq = false; else return nullptr; // A select operand must be a binop. BinaryOperator *BO; if (!match(Sel.getOperand(IsEq ? 1 : 2), m_BinOp(BO))) return nullptr; // The compare constant must be the identity constant for that binop. // If this a floating-point compare with 0.0, any zero constant will do. Type *Ty = BO->getType(); Constant *IdC = ConstantExpr::getBinOpIdentity(BO->getOpcode(), Ty, true); if (IdC != C) { if (!IdC || !CmpInst::isFPPredicate(Pred)) return nullptr; if (!match(IdC, m_AnyZeroFP()) || !match(C, m_AnyZeroFP())) return nullptr; } // Last, match the compare variable operand with a binop operand. Value *Y; if (!BO->isCommutative() && !match(BO, m_BinOp(m_Value(Y), m_Specific(X)))) return nullptr; if (!match(BO, m_c_BinOp(m_Value(Y), m_Specific(X)))) return nullptr; // +0.0 compares equal to -0.0, and so it does not behave as required for this // transform. Bail out if we can not exclude that possibility. if (isa(BO)) if (!BO->hasNoSignedZeros() && !CannotBeNegativeZero(Y, &TLI)) return nullptr; // BO = binop Y, X // S = { select (cmp eq X, C), BO, ? } or { select (cmp ne X, C), ?, BO } // => // S = { select (cmp eq X, C), Y, ? } or { select (cmp ne X, C), ?, Y } Sel.setOperand(IsEq ? 1 : 2, Y); return &Sel; } /// This folds: /// select (icmp eq (and X, C1)), TC, FC /// iff C1 is a power 2 and the difference between TC and FC is a power-of-2. /// To something like: /// (shr (and (X, C1)), (log2(C1) - log2(TC-FC))) + FC /// Or: /// (shl (and (X, C1)), (log2(TC-FC) - log2(C1))) + FC /// With some variations depending if FC is larger than TC, or the shift /// isn't needed, or the bit widths don't match. static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp, InstCombiner::BuilderTy &Builder) { const APInt *SelTC, *SelFC; if (!match(Sel.getTrueValue(), m_APInt(SelTC)) || !match(Sel.getFalseValue(), m_APInt(SelFC))) return nullptr; // If this is a vector select, we need a vector compare. Type *SelType = Sel.getType(); if (SelType->isVectorTy() != Cmp->getType()->isVectorTy()) return nullptr; Value *V; APInt AndMask; bool CreateAnd = false; ICmpInst::Predicate Pred = Cmp->getPredicate(); if (ICmpInst::isEquality(Pred)) { if (!match(Cmp->getOperand(1), m_Zero())) return nullptr; V = Cmp->getOperand(0); const APInt *AndRHS; if (!match(V, m_And(m_Value(), m_Power2(AndRHS)))) return nullptr; AndMask = *AndRHS; } else if (decomposeBitTestICmp(Cmp->getOperand(0), Cmp->getOperand(1), Pred, V, AndMask)) { assert(ICmpInst::isEquality(Pred) && "Not equality test?"); if (!AndMask.isPowerOf2()) return nullptr; CreateAnd = true; } else { return nullptr; } // In general, when both constants are non-zero, we would need an offset to // replace the select. This would require more instructions than we started // with. But there's one special-case that we handle here because it can // simplify/reduce the instructions. APInt TC = *SelTC; APInt FC = *SelFC; if (!TC.isNullValue() && !FC.isNullValue()) { // If the select constants differ by exactly one bit and that's the same // bit that is masked and checked by the select condition, the select can // be replaced by bitwise logic to set/clear one bit of the constant result. if (TC.getBitWidth() != AndMask.getBitWidth() || (TC ^ FC) != AndMask) return nullptr; if (CreateAnd) { // If we have to create an 'and', then we must kill the cmp to not // increase the instruction count. if (!Cmp->hasOneUse()) return nullptr; V = Builder.CreateAnd(V, ConstantInt::get(SelType, AndMask)); } bool ExtraBitInTC = TC.ugt(FC); if (Pred == ICmpInst::ICMP_EQ) { // If the masked bit in V is clear, clear or set the bit in the result: // (V & AndMaskC) == 0 ? TC : FC --> (V & AndMaskC) ^ TC // (V & AndMaskC) == 0 ? TC : FC --> (V & AndMaskC) | TC Constant *C = ConstantInt::get(SelType, TC); return ExtraBitInTC ? Builder.CreateXor(V, C) : Builder.CreateOr(V, C); } if (Pred == ICmpInst::ICMP_NE) { // If the masked bit in V is set, set or clear the bit in the result: // (V & AndMaskC) != 0 ? TC : FC --> (V & AndMaskC) | FC // (V & AndMaskC) != 0 ? TC : FC --> (V & AndMaskC) ^ FC Constant *C = ConstantInt::get(SelType, FC); return ExtraBitInTC ? Builder.CreateOr(V, C) : Builder.CreateXor(V, C); } llvm_unreachable("Only expecting equality predicates"); } // Make sure one of the select arms is a power-of-2. if (!TC.isPowerOf2() && !FC.isPowerOf2()) return nullptr; // Determine which shift is needed to transform result of the 'and' into the // desired result. const APInt &ValC = !TC.isNullValue() ? TC : FC; unsigned ValZeros = ValC.logBase2(); unsigned AndZeros = AndMask.logBase2(); // Insert the 'and' instruction on the input to the truncate. if (CreateAnd) V = Builder.CreateAnd(V, ConstantInt::get(V->getType(), AndMask)); // If types don't match, we can still convert the select by introducing a zext // or a trunc of the 'and'. if (ValZeros > AndZeros) { V = Builder.CreateZExtOrTrunc(V, SelType); V = Builder.CreateShl(V, ValZeros - AndZeros); } else if (ValZeros < AndZeros) { V = Builder.CreateLShr(V, AndZeros - ValZeros); V = Builder.CreateZExtOrTrunc(V, SelType); } else { V = Builder.CreateZExtOrTrunc(V, SelType); } // 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 = !TC.isNullValue(); ShouldNotVal ^= Pred == ICmpInst::ICMP_NE; if (ShouldNotVal) V = Builder.CreateXor(V, ValC); return V; } /// 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(BinaryOperator *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 } } /// For the same transformation as the previous function, return the identity /// constant that goes into the select. static APInt getSelectFoldableConstant(BinaryOperator *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 APInt::getNullValue(I->getType()->getScalarSizeInBits()); case Instruction::And: return APInt::getAllOnesValue(I->getType()->getScalarSizeInBits()); case Instruction::Mul: return APInt(I->getType()->getScalarSizeInBits(), 1); } } /// We have (select c, TI, FI), and we know that TI and FI have the same opcode. Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI, Instruction *FI) { // Don't break up min/max patterns. The hasOneUse checks below prevent that // for most cases, but vector min/max with bitcasts can be transformed. If the // one-use restrictions are eased for other patterns, we still don't want to // obfuscate min/max. if ((match(&SI, m_SMin(m_Value(), m_Value())) || match(&SI, m_SMax(m_Value(), m_Value())) || match(&SI, m_UMin(m_Value(), m_Value())) || match(&SI, m_UMax(m_Value(), m_Value())))) return nullptr; // If this is a cast from the same type, merge. Value *Cond = SI.getCondition(); Type *CondTy = Cond->getType(); if (TI->getNumOperands() == 1 && TI->isCast()) { Type *FIOpndTy = FI->getOperand(0)->getType(); if (TI->getOperand(0)->getType() != FIOpndTy) return nullptr; // The select condition may be a vector. We may only change the operand // type if the vector width remains the same (and matches the condition). if (CondTy->isVectorTy()) { if (!FIOpndTy->isVectorTy()) return nullptr; if (CondTy->getVectorNumElements() != FIOpndTy->getVectorNumElements()) return nullptr; // TODO: If the backend knew how to deal with casts better, we could // remove this limitation. For now, there's too much potential to create // worse codegen by promoting the select ahead of size-altering casts // (PR28160). // // Note that ValueTracking's matchSelectPattern() looks through casts // without checking 'hasOneUse' when it matches min/max patterns, so this // transform may end up happening anyway. if (TI->getOpcode() != Instruction::BitCast && (!TI->hasOneUse() || !FI->hasOneUse())) return nullptr; } else if (!TI->hasOneUse() || !FI->hasOneUse()) { // TODO: The one-use restrictions for a scalar select could be eased if // the fold of a select in visitLoadInst() was enhanced to match a pattern // that includes a cast. return nullptr; } // Fold this by inserting a select from the input values. Value *NewSI = Builder.CreateSelect(Cond, TI->getOperand(0), FI->getOperand(0), SI.getName() + ".v", &SI); return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI, TI->getType()); } // Cond ? -X : -Y --> -(Cond ? X : Y) Value *X, *Y; if (match(TI, m_FNeg(m_Value(X))) && match(FI, m_FNeg(m_Value(Y))) && (TI->hasOneUse() || FI->hasOneUse())) { Value *NewSel = Builder.CreateSelect(Cond, X, Y, SI.getName() + ".v", &SI); // TODO: Remove the hack for the binop form when the unary op is optimized // properly with all IR passes. if (TI->getOpcode() != Instruction::FNeg) return BinaryOperator::CreateFNegFMF(NewSel, cast(TI)); return UnaryOperator::CreateFNeg(NewSel); } // Only handle binary operators (including two-operand getelementptr) with // one-use here. As with the cast case above, it may be possible to relax the // one-use constraint, but that needs be examined carefully since it may not // reduce the total number of instructions. if (TI->getNumOperands() != 2 || FI->getNumOperands() != 2 || (!isa(TI) && !isa(TI)) || !TI->hasOneUse() || !FI->hasOneUse()) return nullptr; // 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 nullptr; } 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 nullptr; } // If the select condition is a vector, the operands of the original select's // operands also must be vectors. This may not be the case for getelementptr // for example. if (CondTy->isVectorTy() && (!OtherOpT->getType()->isVectorTy() || !OtherOpF->getType()->isVectorTy())) return nullptr; // If we reach here, they do have operations in common. Value *NewSI = Builder.CreateSelect(Cond, OtherOpT, OtherOpF, SI.getName() + ".v", &SI); Value *Op0 = MatchIsOpZero ? MatchOp : NewSI; Value *Op1 = MatchIsOpZero ? NewSI : MatchOp; if (auto *BO = dyn_cast(TI)) { BinaryOperator *NewBO = BinaryOperator::Create(BO->getOpcode(), Op0, Op1); NewBO->copyIRFlags(TI); NewBO->andIRFlags(FI); return NewBO; } if (auto *TGEP = dyn_cast(TI)) { auto *FGEP = cast(FI); Type *ElementType = TGEP->getResultElementType(); return TGEP->isInBounds() && FGEP->isInBounds() ? GetElementPtrInst::CreateInBounds(ElementType, Op0, {Op1}) : GetElementPtrInst::Create(ElementType, Op0, {Op1}); } llvm_unreachable("Expected BinaryOperator or GEP"); return nullptr; } static bool isSelect01(const APInt &C1I, const APInt &C2I) { if (!C1I.isNullValue() && !C2I.isNullValue()) // One side must be zero. return false; return C1I.isOneValue() || C1I.isAllOnesValue() || C2I.isOneValue() || C2I.isAllOnesValue(); } /// Try to fold the select into one of the operands to allow 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 (auto *TVI = dyn_cast(TrueVal)) { if (TVI->hasOneUse() && !isa(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) { APInt CI = getSelectFoldableConstant(TVI); Value *OOp = TVI->getOperand(2-OpToFold); // Avoid creating select between 2 constants unless it's selecting // between 0, 1 and -1. const APInt *OOpC; bool OOpIsAPInt = match(OOp, m_APInt(OOpC)); if (!isa(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) { Value *C = ConstantInt::get(OOp->getType(), CI); Value *NewSel = Builder.CreateSelect(SI.getCondition(), OOp, C); NewSel->takeName(TVI); BinaryOperator *BO = BinaryOperator::Create(TVI->getOpcode(), FalseVal, NewSel); BO->copyIRFlags(TVI); return BO; } } } } } if (auto *FVI = dyn_cast(FalseVal)) { if (FVI->hasOneUse() && !isa(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) { APInt CI = getSelectFoldableConstant(FVI); Value *OOp = FVI->getOperand(2-OpToFold); // Avoid creating select between 2 constants unless it's selecting // between 0, 1 and -1. const APInt *OOpC; bool OOpIsAPInt = match(OOp, m_APInt(OOpC)); if (!isa(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) { Value *C = ConstantInt::get(OOp->getType(), CI); Value *NewSel = Builder.CreateSelect(SI.getCondition(), C, OOp); NewSel->takeName(FVI); BinaryOperator *BO = BinaryOperator::Create(FVI->getOpcode(), TrueVal, NewSel); BO->copyIRFlags(FVI); return BO; } } } } } return nullptr; } /// We want to turn: /// (select (icmp eq (and X, Y), 0), (and (lshr X, Z), 1), 1) /// into: /// zext (icmp ne i32 (and X, (or Y, (shl 1, Z))), 0) /// Note: /// Z may be 0 if lshr is missing. /// Worst-case scenario is that we will replace 5 instructions with 5 different /// instructions, but we got rid of select. static Instruction *foldSelectICmpAndAnd(Type *SelType, const ICmpInst *Cmp, Value *TVal, Value *FVal, InstCombiner::BuilderTy &Builder) { if (!(Cmp->hasOneUse() && Cmp->getOperand(0)->hasOneUse() && Cmp->getPredicate() == ICmpInst::ICMP_EQ && match(Cmp->getOperand(1), m_Zero()) && match(FVal, m_One()))) return nullptr; // The TrueVal has general form of: and %B, 1 Value *B; if (!match(TVal, m_OneUse(m_And(m_Value(B), m_One())))) return nullptr; // Where %B may be optionally shifted: lshr %X, %Z. Value *X, *Z; const bool HasShift = match(B, m_OneUse(m_LShr(m_Value(X), m_Value(Z)))); if (!HasShift) X = B; Value *Y; if (!match(Cmp->getOperand(0), m_c_And(m_Specific(X), m_Value(Y)))) return nullptr; // ((X & Y) == 0) ? ((X >> Z) & 1) : 1 --> (X & (Y | (1 << Z))) != 0 // ((X & Y) == 0) ? (X & 1) : 1 --> (X & (Y | 1)) != 0 Constant *One = ConstantInt::get(SelType, 1); Value *MaskB = HasShift ? Builder.CreateShl(One, Z) : One; Value *FullMask = Builder.CreateOr(Y, MaskB); Value *MaskedX = Builder.CreateAnd(X, FullMask); Value *ICmpNeZero = Builder.CreateIsNotNull(MaskedX); return new ZExtInst(ICmpNeZero, SelType); } /// We want to turn: /// (select (icmp sgt x, C), lshr (X, Y), ashr (X, Y)); iff C s>= -1 /// (select (icmp slt x, C), ashr (X, Y), lshr (X, Y)); iff C s>= 0 /// into: /// ashr (X, Y) static Value *foldSelectICmpLshrAshr(const ICmpInst *IC, Value *TrueVal, Value *FalseVal, InstCombiner::BuilderTy &Builder) { ICmpInst::Predicate Pred = IC->getPredicate(); Value *CmpLHS = IC->getOperand(0); Value *CmpRHS = IC->getOperand(1); if (!CmpRHS->getType()->isIntOrIntVectorTy()) return nullptr; Value *X, *Y; unsigned Bitwidth = CmpRHS->getType()->getScalarSizeInBits(); if ((Pred != ICmpInst::ICMP_SGT || !match(CmpRHS, m_SpecificInt_ICMP(ICmpInst::ICMP_SGE, APInt(Bitwidth, -1)))) && (Pred != ICmpInst::ICMP_SLT || !match(CmpRHS, m_SpecificInt_ICMP(ICmpInst::ICMP_SGE, APInt(Bitwidth, 0))))) return nullptr; // Canonicalize so that ashr is in FalseVal. if (Pred == ICmpInst::ICMP_SLT) std::swap(TrueVal, FalseVal); if (match(TrueVal, m_LShr(m_Value(X), m_Value(Y))) && match(FalseVal, m_AShr(m_Specific(X), m_Specific(Y))) && match(CmpLHS, m_Specific(X))) { const auto *Ashr = cast(FalseVal); // if lshr is not exact and ashr is, this new ashr must not be exact. bool IsExact = Ashr->isExact() && cast(TrueVal)->isExact(); return Builder.CreateAShr(X, Y, IC->getName(), IsExact); } return nullptr; } /// We want to turn: /// (select (icmp eq (and X, C1), 0), Y, (or Y, C2)) /// into: /// (or (shl (and X, C1), C3), Y) /// iff: /// C1 and C2 are both powers of 2 /// where: /// C3 = Log(C2) - Log(C1) /// /// This transform handles cases where: /// 1. The icmp predicate is inverted /// 2. The select operands are reversed /// 3. The magnitude of C2 and C1 are flipped static Value *foldSelectICmpAndOr(const ICmpInst *IC, Value *TrueVal, Value *FalseVal, InstCombiner::BuilderTy &Builder) { // Only handle integer compares. Also, if this is a vector select, we need a // vector compare. if (!TrueVal->getType()->isIntOrIntVectorTy() || TrueVal->getType()->isVectorTy() != IC->getType()->isVectorTy()) return nullptr; Value *CmpLHS = IC->getOperand(0); Value *CmpRHS = IC->getOperand(1); Value *V; unsigned C1Log; bool IsEqualZero; bool NeedAnd = false; if (IC->isEquality()) { if (!match(CmpRHS, m_Zero())) return nullptr; const APInt *C1; if (!match(CmpLHS, m_And(m_Value(), m_Power2(C1)))) return nullptr; V = CmpLHS; C1Log = C1->logBase2(); IsEqualZero = IC->getPredicate() == ICmpInst::ICMP_EQ; } else if (IC->getPredicate() == ICmpInst::ICMP_SLT || IC->getPredicate() == ICmpInst::ICMP_SGT) { // We also need to recognize (icmp slt (trunc (X)), 0) and // (icmp sgt (trunc (X)), -1). IsEqualZero = IC->getPredicate() == ICmpInst::ICMP_SGT; if ((IsEqualZero && !match(CmpRHS, m_AllOnes())) || (!IsEqualZero && !match(CmpRHS, m_Zero()))) return nullptr; if (!match(CmpLHS, m_OneUse(m_Trunc(m_Value(V))))) return nullptr; C1Log = CmpLHS->getType()->getScalarSizeInBits() - 1; NeedAnd = true; } else { return nullptr; } const APInt *C2; bool OrOnTrueVal = false; bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2))); if (!OrOnFalseVal) OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2))); if (!OrOnFalseVal && !OrOnTrueVal) return nullptr; Value *Y = OrOnFalseVal ? TrueVal : FalseVal; unsigned C2Log = C2->logBase2(); bool NeedXor = (!IsEqualZero && OrOnFalseVal) || (IsEqualZero && OrOnTrueVal); bool NeedShift = C1Log != C2Log; bool NeedZExtTrunc = Y->getType()->getScalarSizeInBits() != V->getType()->getScalarSizeInBits(); // Make sure we don't create more instructions than we save. Value *Or = OrOnFalseVal ? FalseVal : TrueVal; if ((NeedShift + NeedXor + NeedZExtTrunc) > (IC->hasOneUse() + Or->hasOneUse())) return nullptr; if (NeedAnd) { // Insert the AND instruction on the input to the truncate. APInt C1 = APInt::getOneBitSet(V->getType()->getScalarSizeInBits(), C1Log); V = Builder.CreateAnd(V, ConstantInt::get(V->getType(), C1)); } if (C2Log > C1Log) { V = Builder.CreateZExtOrTrunc(V, Y->getType()); V = Builder.CreateShl(V, C2Log - C1Log); } else if (C1Log > C2Log) { V = Builder.CreateLShr(V, C1Log - C2Log); V = Builder.CreateZExtOrTrunc(V, Y->getType()); } else V = Builder.CreateZExtOrTrunc(V, Y->getType()); if (NeedXor) V = Builder.CreateXor(V, *C2); return Builder.CreateOr(V, Y); } /// Transform patterns such as (a > b) ? a - b : 0 into usub.sat(a, b). /// There are 8 commuted/swapped variants of this pattern. /// TODO: Also support a - UMIN(a,b) patterns. static Value *canonicalizeSaturatedSubtract(const ICmpInst *ICI, const Value *TrueVal, const Value *FalseVal, InstCombiner::BuilderTy &Builder) { ICmpInst::Predicate Pred = ICI->getPredicate(); if (!ICmpInst::isUnsigned(Pred)) return nullptr; // (b > a) ? 0 : a - b -> (b <= a) ? a - b : 0 if (match(TrueVal, m_Zero())) { Pred = ICmpInst::getInversePredicate(Pred); std::swap(TrueVal, FalseVal); } if (!match(FalseVal, m_Zero())) return nullptr; Value *A = ICI->getOperand(0); Value *B = ICI->getOperand(1); if (Pred == ICmpInst::ICMP_ULE || Pred == ICmpInst::ICMP_ULT) { // (b < a) ? a - b : 0 -> (a > b) ? a - b : 0 std::swap(A, B); Pred = ICmpInst::getSwappedPredicate(Pred); } assert((Pred == ICmpInst::ICMP_UGE || Pred == ICmpInst::ICMP_UGT) && "Unexpected isUnsigned predicate!"); // Account for swapped form of subtraction: ((a > b) ? b - a : 0). bool IsNegative = false; if (match(TrueVal, m_Sub(m_Specific(B), m_Specific(A)))) IsNegative = true; else if (!match(TrueVal, m_Sub(m_Specific(A), m_Specific(B)))) return nullptr; // If sub is used anywhere else, we wouldn't be able to eliminate it // afterwards. if (!TrueVal->hasOneUse()) return nullptr; // (a > b) ? a - b : 0 -> usub.sat(a, b) // (a > b) ? b - a : 0 -> -usub.sat(a, b) Value *Result = Builder.CreateBinaryIntrinsic(Intrinsic::usub_sat, A, B); if (IsNegative) Result = Builder.CreateNeg(Result); return Result; } static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal, InstCombiner::BuilderTy &Builder) { if (!Cmp->hasOneUse()) return nullptr; // Match unsigned saturated add with constant. Value *Cmp0 = Cmp->getOperand(0); Value *Cmp1 = Cmp->getOperand(1); ICmpInst::Predicate Pred = Cmp->getPredicate(); Value *X; const APInt *C, *CmpC; if (Pred == ICmpInst::ICMP_ULT && match(TVal, m_Add(m_Value(X), m_APInt(C))) && X == Cmp0 && match(FVal, m_AllOnes()) && match(Cmp1, m_APInt(CmpC)) && *CmpC == ~*C) { // (X u< ~C) ? (X + C) : -1 --> uadd.sat(X, C) return Builder.CreateBinaryIntrinsic( Intrinsic::uadd_sat, X, ConstantInt::get(X->getType(), *C)); } // Match unsigned saturated add of 2 variables with an unnecessary 'not'. // There are 8 commuted variants. // Canonicalize -1 (saturated result) to true value of the select. Just // swapping the compare operands is legal, because the selected value is the // same in case of equality, so we can interchange u< and u<=. if (match(FVal, m_AllOnes())) { std::swap(TVal, FVal); std::swap(Cmp0, Cmp1); } if (!match(TVal, m_AllOnes())) return nullptr; // Canonicalize predicate to 'ULT'. if (Pred == ICmpInst::ICMP_UGT) { Pred = ICmpInst::ICMP_ULT; std::swap(Cmp0, Cmp1); } if (Pred != ICmpInst::ICMP_ULT) return nullptr; // Match unsigned saturated add of 2 variables with an unnecessary 'not'. Value *Y; if (match(Cmp0, m_Not(m_Value(X))) && match(FVal, m_c_Add(m_Specific(X), m_Value(Y))) && Y == Cmp1) { // (~X u< Y) ? -1 : (X + Y) --> uadd.sat(X, Y) // (~X u< Y) ? -1 : (Y + X) --> uadd.sat(X, Y) return Builder.CreateBinaryIntrinsic(Intrinsic::uadd_sat, X, Y); } // The 'not' op may be included in the sum but not the compare. X = Cmp0; Y = Cmp1; if (match(FVal, m_c_Add(m_Not(m_Specific(X)), m_Specific(Y)))) { // (X u< Y) ? -1 : (~X + Y) --> uadd.sat(~X, Y) // (X u< Y) ? -1 : (Y + ~X) --> uadd.sat(Y, ~X) BinaryOperator *BO = cast(FVal); return Builder.CreateBinaryIntrinsic( Intrinsic::uadd_sat, BO->getOperand(0), BO->getOperand(1)); } return nullptr; } /// Fold the following code sequence: /// \code /// int a = ctlz(x & -x); // x ? 31 - a : a; /// \code /// /// into: /// cttz(x) static Instruction *foldSelectCtlzToCttz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal, InstCombiner::BuilderTy &Builder) { unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits(); if (!ICI->isEquality() || !match(ICI->getOperand(1), m_Zero())) return nullptr; if (ICI->getPredicate() == ICmpInst::ICMP_NE) std::swap(TrueVal, FalseVal); if (!match(FalseVal, m_Xor(m_Deferred(TrueVal), m_SpecificInt(BitWidth - 1)))) return nullptr; if (!match(TrueVal, m_Intrinsic())) return nullptr; Value *X = ICI->getOperand(0); auto *II = cast(TrueVal); if (!match(II->getOperand(0), m_c_And(m_Specific(X), m_Neg(m_Specific(X))))) return nullptr; Function *F = Intrinsic::getDeclaration(II->getModule(), Intrinsic::cttz, II->getType()); return CallInst::Create(F, {X, II->getArgOperand(1)}); } /// Attempt to fold a cttz/ctlz followed by a icmp plus select into a single /// call to cttz/ctlz with flag 'is_zero_undef' cleared. /// /// For example, we can fold the following code sequence: /// \code /// %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true) /// %1 = icmp ne i32 %x, 0 /// %2 = select i1 %1, i32 %0, i32 32 /// \code /// /// into: /// %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 false) static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal, InstCombiner::BuilderTy &Builder) { ICmpInst::Predicate Pred = ICI->getPredicate(); Value *CmpLHS = ICI->getOperand(0); Value *CmpRHS = ICI->getOperand(1); // Check if the condition value compares a value for equality against zero. if (!ICI->isEquality() || !match(CmpRHS, m_Zero())) return nullptr; Value *Count = FalseVal; Value *ValueOnZero = TrueVal; if (Pred == ICmpInst::ICMP_NE) std::swap(Count, ValueOnZero); // Skip zero extend/truncate. Value *V = nullptr; if (match(Count, m_ZExt(m_Value(V))) || match(Count, m_Trunc(m_Value(V)))) Count = V; // Check that 'Count' is a call to intrinsic cttz/ctlz. Also check that the // input to the cttz/ctlz is used as LHS for the compare instruction. if (!match(Count, m_Intrinsic(m_Specific(CmpLHS))) && !match(Count, m_Intrinsic(m_Specific(CmpLHS)))) return nullptr; IntrinsicInst *II = cast(Count); // Check if the value propagated on zero is a constant number equal to the // sizeof in bits of 'Count'. unsigned SizeOfInBits = Count->getType()->getScalarSizeInBits(); if (match(ValueOnZero, m_SpecificInt(SizeOfInBits))) { // Explicitly clear the 'undef_on_zero' flag. IntrinsicInst *NewI = cast(II->clone()); NewI->setArgOperand(1, ConstantInt::getFalse(NewI->getContext())); Builder.Insert(NewI); return Builder.CreateZExtOrTrunc(NewI, ValueOnZero->getType()); } // If the ValueOnZero is not the bitwidth, we can at least make use of the // fact that the cttz/ctlz result will not be used if the input is zero, so // it's okay to relax it to undef for that case. if (II->hasOneUse() && !match(II->getArgOperand(1), m_One())) II->setArgOperand(1, ConstantInt::getTrue(II->getContext())); return nullptr; } /// Return true if we find and adjust an icmp+select pattern where the compare /// is with a constant that can be incremented or decremented to match the /// minimum or maximum idiom. static bool adjustMinMax(SelectInst &Sel, ICmpInst &Cmp) { ICmpInst::Predicate Pred = Cmp.getPredicate(); Value *CmpLHS = Cmp.getOperand(0); Value *CmpRHS = Cmp.getOperand(1); Value *TrueVal = Sel.getTrueValue(); Value *FalseVal = Sel.getFalseValue(); // We may move or edit the compare, so make sure the select is the only user. const APInt *CmpC; if (!Cmp.hasOneUse() || !match(CmpRHS, m_APInt(CmpC))) return false; // These transforms only work for selects of integers or vector selects of // integer vectors. Type *SelTy = Sel.getType(); auto *SelEltTy = dyn_cast(SelTy->getScalarType()); if (!SelEltTy || SelTy->isVectorTy() != Cmp.getType()->isVectorTy()) return false; Constant *AdjustedRHS; if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT) AdjustedRHS = ConstantInt::get(CmpRHS->getType(), *CmpC + 1); else if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT) AdjustedRHS = ConstantInt::get(CmpRHS->getType(), *CmpC - 1); else return false; // 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() < SelEltTy->getBitWidth()) { Constant *SextRHS = ConstantExpr::getSExt(AdjustedRHS, SelTy); // X = sext x; x >s c ? X : C+1 --> X = sext x; X X = sext x; X >s C-1 ? C-1 : X // X = sext x; x >u c ? X : C+1 --> X = sext x; X 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 (Cmp.isUnsigned()) { Constant *ZextRHS = ConstantExpr::getZExt(AdjustedRHS, SelTy); // X = zext x; x >u c ? X : C+1 --> X = zext x; X X = zext x; X >u C-1 ? C-1 : X // zext + signed compare cannot be changed: // 0xff 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 { return false; } } else { return false; } } else { return false; } Pred = ICmpInst::getSwappedPredicate(Pred); CmpRHS = AdjustedRHS; std::swap(FalseVal, TrueVal); Cmp.setPredicate(Pred); Cmp.setOperand(0, CmpLHS); Cmp.setOperand(1, CmpRHS); Sel.setOperand(1, TrueVal); Sel.setOperand(2, FalseVal); Sel.swapProfMetadata(); // Move the compare instruction right before the select instruction. Otherwise // the sext/zext value may be defined after the compare instruction uses it. Cmp.moveBefore(&Sel); return true; } /// If this is an integer min/max (icmp + select) with a constant operand, /// create the canonical icmp for the min/max operation and canonicalize the /// constant to the 'false' operand of the select: /// select (icmp Pred X, C1), C2, X --> select (icmp Pred' X, C2), X, C2 /// Note: if C1 != C2, this will change the icmp constant to the existing /// constant operand of the select. static Instruction * canonicalizeMinMaxWithConstant(SelectInst &Sel, ICmpInst &Cmp, InstCombiner::BuilderTy &Builder) { if (!Cmp.hasOneUse() || !isa(Cmp.getOperand(1))) return nullptr; // Canonicalize the compare predicate based on whether we have min or max. Value *LHS, *RHS; SelectPatternResult SPR = matchSelectPattern(&Sel, LHS, RHS); if (!SelectPatternResult::isMinOrMax(SPR.Flavor)) return nullptr; // Is this already canonical? ICmpInst::Predicate CanonicalPred = getMinMaxPred(SPR.Flavor); if (Cmp.getOperand(0) == LHS && Cmp.getOperand(1) == RHS && Cmp.getPredicate() == CanonicalPred) return nullptr; // Create the canonical compare and plug it into the select. Sel.setCondition(Builder.CreateICmp(CanonicalPred, LHS, RHS)); // If the select operands did not change, we're done. if (Sel.getTrueValue() == LHS && Sel.getFalseValue() == RHS) return &Sel; // If we are swapping the select operands, swap the metadata too. assert(Sel.getTrueValue() == RHS && Sel.getFalseValue() == LHS && "Unexpected results from matchSelectPattern"); Sel.swapValues(); Sel.swapProfMetadata(); return &Sel; } /// There are many select variants for each of ABS/NABS. /// In matchSelectPattern(), there are different compare constants, compare /// predicates/operands and select operands. /// In isKnownNegation(), there are different formats of negated operands. /// Canonicalize all these variants to 1 pattern. /// This makes CSE more likely. static Instruction *canonicalizeAbsNabs(SelectInst &Sel, ICmpInst &Cmp, InstCombiner::BuilderTy &Builder) { if (!Cmp.hasOneUse() || !isa(Cmp.getOperand(1))) return nullptr; // Choose a sign-bit check for the compare (likely simpler for codegen). // ABS: (X hasOneUse() || (RHS->hasNUses(2) && CmpUsesNegatedOp))) return nullptr; // Create the canonical compare: icmp slt LHS 0. if (!CmpCanonicalized) { Cmp.setPredicate(ICmpInst::ICMP_SLT); Cmp.setOperand(1, ConstantInt::getNullValue(Cmp.getOperand(0)->getType())); if (CmpUsesNegatedOp) Cmp.setOperand(0, LHS); } // Create the canonical RHS: RHS = sub (0, LHS). if (!RHSCanonicalized) { assert(RHS->hasOneUse() && "RHS use number is not right"); RHS = Builder.CreateNeg(LHS); if (TVal == LHS) { Sel.setFalseValue(RHS); FVal = RHS; } else { Sel.setTrueValue(RHS); TVal = RHS; } } // If the select operands do not change, we're done. if (SPF == SelectPatternFlavor::SPF_NABS) { if (TVal == LHS) return &Sel; assert(FVal == LHS && "Unexpected results from matchSelectPattern"); } else { if (FVal == LHS) return &Sel; assert(TVal == LHS && "Unexpected results from matchSelectPattern"); } // We are swapping the select operands, so swap the metadata too. Sel.swapValues(); Sel.swapProfMetadata(); return &Sel; } static Value *simplifyWithOpReplaced(Value *V, Value *Op, Value *ReplaceOp, const SimplifyQuery &Q) { // If this is a binary operator, try to simplify it with the replaced op // because we know Op and ReplaceOp are equivalant. // For example: V = X + 1, Op = X, ReplaceOp = 42 // Simplifies as: add(42, 1) --> 43 if (auto *BO = dyn_cast(V)) { if (BO->getOperand(0) == Op) return SimplifyBinOp(BO->getOpcode(), ReplaceOp, BO->getOperand(1), Q); if (BO->getOperand(1) == Op) return SimplifyBinOp(BO->getOpcode(), BO->getOperand(0), ReplaceOp, Q); } return nullptr; } /// If we have a select with an equality comparison, then we know the value in /// one of the arms of the select. See if substituting this value into an arm /// and simplifying the result yields the same value as the other arm. /// /// To make this transform safe, we must drop poison-generating flags /// (nsw, etc) if we simplified to a binop because the select may be guarding /// that poison from propagating. If the existing binop already had no /// poison-generating flags, then this transform can be done by instsimplify. /// /// Consider: /// %cmp = icmp eq i32 %x, 2147483647 /// %add = add nsw i32 %x, 1 /// %sel = select i1 %cmp, i32 -2147483648, i32 %add /// /// We can't replace %sel with %add unless we strip away the flags. /// TODO: Wrapping flags could be preserved in some cases with better analysis. static Value *foldSelectValueEquivalence(SelectInst &Sel, ICmpInst &Cmp, const SimplifyQuery &Q) { if (!Cmp.isEquality()) return nullptr; // Canonicalize the pattern to ICMP_EQ by swapping the select operands. Value *TrueVal = Sel.getTrueValue(), *FalseVal = Sel.getFalseValue(); if (Cmp.getPredicate() == ICmpInst::ICMP_NE) std::swap(TrueVal, FalseVal); // Try each equivalence substitution possibility. // We have an 'EQ' comparison, so the select's false value will propagate. // Example: // (X == 42) ? 43 : (X + 1) --> (X == 42) ? (X + 1) : (X + 1) --> X + 1 // (X == 42) ? (X + 1) : 43 --> (X == 42) ? (42 + 1) : 43 --> 43 Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1); if (simplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, Q) == TrueVal || simplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, Q) == TrueVal || simplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, Q) == FalseVal || simplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, Q) == FalseVal) { if (auto *FalseInst = dyn_cast(FalseVal)) FalseInst->dropPoisonGeneratingFlags(); return FalseVal; } return nullptr; } // See if this is a pattern like: // %old_cmp1 = icmp slt i32 %x, C2 // %old_replacement = select i1 %old_cmp1, i32 %target_low, i32 %target_high // %old_x_offseted = add i32 %x, C1 // %old_cmp0 = icmp ult i32 %old_x_offseted, C0 // %r = select i1 %old_cmp0, i32 %x, i32 %old_replacement // This can be rewritten as more canonical pattern: // %new_cmp1 = icmp slt i32 %x, -C1 // %new_cmp2 = icmp sge i32 %x, C0-C1 // %new_clamped_low = select i1 %new_cmp1, i32 %target_low, i32 %x // %r = select i1 %new_cmp2, i32 %target_high, i32 %new_clamped_low // Iff -C1 s<= C2 s<= C0-C1 // Also ULT predicate can also be UGT iff C0 != -1 (+invert result) // SLT predicate can also be SGT iff C2 != INT_MAX (+invert res.) static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0, InstCombiner::BuilderTy &Builder) { Value *X = Sel0.getTrueValue(); Value *Sel1 = Sel0.getFalseValue(); // First match the condition of the outermost select. // Said condition must be one-use. if (!Cmp0.hasOneUse()) return nullptr; Value *Cmp00 = Cmp0.getOperand(0); Constant *C0; if (!match(Cmp0.getOperand(1), m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C0)))) return nullptr; // Canonicalize Cmp0 into the form we expect. // FIXME: we shouldn't care about lanes that are 'undef' in the end? switch (Cmp0.getPredicate()) { case ICmpInst::Predicate::ICMP_ULT: break; // Great! case ICmpInst::Predicate::ICMP_ULE: // We'd have to increment C0 by one, and for that it must not have all-ones // element, but then it would have been canonicalized to 'ult' before // we get here. So we can't do anything useful with 'ule'. return nullptr; case ICmpInst::Predicate::ICMP_UGT: // We want to canonicalize it to 'ult', so we'll need to increment C0, // which again means it must not have any all-ones elements. if (!match(C0, m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_NE, APInt::getAllOnesValue( C0->getType()->getScalarSizeInBits())))) return nullptr; // Can't do, have all-ones element[s]. C0 = AddOne(C0); std::swap(X, Sel1); break; case ICmpInst::Predicate::ICMP_UGE: // The only way we'd get this predicate if this `icmp` has extra uses, // but then we won't be able to do this fold. return nullptr; default: return nullptr; // Unknown predicate. } // Now that we've canonicalized the ICmp, we know the X we expect; // the select in other hand should be one-use. if (!Sel1->hasOneUse()) return nullptr; // We now can finish matching the condition of the outermost select: // it should either be the X itself, or an addition of some constant to X. Constant *C1; if (Cmp00 == X) C1 = ConstantInt::getNullValue(Sel0.getType()); else if (!match(Cmp00, m_Add(m_Specific(X), m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C1))))) return nullptr; Value *Cmp1; ICmpInst::Predicate Pred1; Constant *C2; Value *ReplacementLow, *ReplacementHigh; if (!match(Sel1, m_Select(m_Value(Cmp1), m_Value(ReplacementLow), m_Value(ReplacementHigh))) || !match(Cmp1, m_ICmp(Pred1, m_Specific(X), m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C2))))) return nullptr; if (!Cmp1->hasOneUse() && (Cmp00 == X || !Cmp00->hasOneUse())) return nullptr; // Not enough one-use instructions for the fold. // FIXME: this restriction could be relaxed if Cmp1 can be reused as one of // two comparisons we'll need to build. // Canonicalize Cmp1 into the form we expect. // FIXME: we shouldn't care about lanes that are 'undef' in the end? switch (Pred1) { case ICmpInst::Predicate::ICMP_SLT: break; case ICmpInst::Predicate::ICMP_SLE: // We'd have to increment C2 by one, and for that it must not have signed // max element, but then it would have been canonicalized to 'slt' before // we get here. So we can't do anything useful with 'sle'. return nullptr; case ICmpInst::Predicate::ICMP_SGT: // We want to canonicalize it to 'slt', so we'll need to increment C2, // which again means it must not have any signed max elements. if (!match(C2, m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_NE, APInt::getSignedMaxValue( C2->getType()->getScalarSizeInBits())))) return nullptr; // Can't do, have signed max element[s]. C2 = AddOne(C2); LLVM_FALLTHROUGH; case ICmpInst::Predicate::ICMP_SGE: // Also non-canonical, but here we don't need to change C2, // so we don't have any restrictions on C2, so we can just handle it. std::swap(ReplacementLow, ReplacementHigh); break; default: return nullptr; // Unknown predicate. } // The thresholds of this clamp-like pattern. auto *ThresholdLowIncl = ConstantExpr::getNeg(C1); auto *ThresholdHighExcl = ConstantExpr::getSub(C0, C1); // The fold has a precondition 1: C2 s>= ThresholdLow auto *Precond1 = ConstantExpr::getICmp(ICmpInst::Predicate::ICMP_SGE, C2, ThresholdLowIncl); if (!match(Precond1, m_One())) return nullptr; // The fold has a precondition 2: C2 s<= ThresholdHigh auto *Precond2 = ConstantExpr::getICmp(ICmpInst::Predicate::ICMP_SLE, C2, ThresholdHighExcl); if (!match(Precond2, m_One())) return nullptr; // All good, finally emit the new pattern. Value *ShouldReplaceLow = Builder.CreateICmpSLT(X, ThresholdLowIncl); Value *ShouldReplaceHigh = Builder.CreateICmpSGE(X, ThresholdHighExcl); Value *MaybeReplacedLow = Builder.CreateSelect(ShouldReplaceLow, ReplacementLow, X); Instruction *MaybeReplacedHigh = SelectInst::Create(ShouldReplaceHigh, ReplacementHigh, MaybeReplacedLow); return MaybeReplacedHigh; } // If we have // %cmp = icmp [canonical predicate] i32 %x, C0 // %r = select i1 %cmp, i32 %y, i32 C1 // Where C0 != C1 and %x may be different from %y, see if the constant that we // will have if we flip the strictness of the predicate (i.e. without changing // the result) is identical to the C1 in select. If it matches we can change // original comparison to one with swapped predicate, reuse the constant, // and swap the hands of select. static Instruction * tryToReuseConstantFromSelectInComparison(SelectInst &Sel, ICmpInst &Cmp, InstCombiner::BuilderTy &Builder) { ICmpInst::Predicate Pred; Value *X; Constant *C0; if (!match(&Cmp, m_OneUse(m_ICmp( Pred, m_Value(X), m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C0)))))) return nullptr; // If comparison predicate is non-relational, we won't be able to do anything. if (ICmpInst::isEquality(Pred)) return nullptr; // If comparison predicate is non-canonical, then we certainly won't be able // to make it canonical; canonicalizeCmpWithConstant() already tried. if (!isCanonicalPredicate(Pred)) return nullptr; // If the [input] type of comparison and select type are different, lets abort // for now. We could try to compare constants with trunc/[zs]ext though. if (C0->getType() != Sel.getType()) return nullptr; // FIXME: are there any magic icmp predicate+constant pairs we must not touch? Value *SelVal0, *SelVal1; // We do not care which one is from where. match(&Sel, m_Select(m_Value(), m_Value(SelVal0), m_Value(SelVal1))); // At least one of these values we are selecting between must be a constant // else we'll never succeed. if (!match(SelVal0, m_AnyIntegralConstant()) && !match(SelVal1, m_AnyIntegralConstant())) return nullptr; // Does this constant C match any of the `select` values? auto MatchesSelectValue = [SelVal0, SelVal1](Constant *C) { return C->isElementWiseEqual(SelVal0) || C->isElementWiseEqual(SelVal1); }; // If C0 *already* matches true/false value of select, we are done. if (MatchesSelectValue(C0)) return nullptr; // Check the constant we'd have with flipped-strictness predicate. auto FlippedStrictness = getFlippedStrictnessPredicateAndConstant(Pred, C0); if (!FlippedStrictness) return nullptr; // If said constant doesn't match either, then there is no hope, if (!MatchesSelectValue(FlippedStrictness->second)) return nullptr; // It matched! Lets insert the new comparison just before select. InstCombiner::BuilderTy::InsertPointGuard Guard(Builder); Builder.SetInsertPoint(&Sel); Pred = ICmpInst::getSwappedPredicate(Pred); // Yes, swapped. Value *NewCmp = Builder.CreateICmp(Pred, X, FlippedStrictness->second, Cmp.getName() + ".inv"); Sel.setCondition(NewCmp); Sel.swapValues(); Sel.swapProfMetadata(); return &Sel; } /// Visit a SelectInst that has an ICmpInst as its first operand. Instruction *InstCombiner::foldSelectInstWithICmp(SelectInst &SI, ICmpInst *ICI) { if (Value *V = foldSelectValueEquivalence(SI, *ICI, SQ)) return replaceInstUsesWith(SI, V); if (Instruction *NewSel = canonicalizeMinMaxWithConstant(SI, *ICI, Builder)) return NewSel; if (Instruction *NewAbs = canonicalizeAbsNabs(SI, *ICI, Builder)) return NewAbs; if (Instruction *NewAbs = canonicalizeClampLike(SI, *ICI, Builder)) return NewAbs; if (Instruction *NewSel = tryToReuseConstantFromSelectInComparison(SI, *ICI, Builder)) return NewSel; bool Changed = adjustMinMax(SI, *ICI); if (Value *V = foldSelectICmpAnd(SI, ICI, Builder)) return replaceInstUsesWith(SI, V); // NOTE: if we wanted to, this is where to detect integer MIN/MAX Value *TrueVal = SI.getTrueValue(); Value *FalseVal = SI.getFalseValue(); ICmpInst::Predicate Pred = ICI->getPredicate(); Value *CmpLHS = ICI->getOperand(0); Value *CmpRHS = ICI->getOperand(1); if (CmpRHS != CmpLHS && isa(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; } } // FIXME: This code is nearly duplicated in InstSimplify. Using/refactoring // decomposeBitTestICmp() might help. { unsigned BitWidth = DL.getTypeSizeInBits(TrueVal->getType()->getScalarType()); APInt MinSignedValue = APInt::getSignedMinValue(BitWidth); Value *X; const APInt *Y, *C; bool TrueWhenUnset; bool IsBitTest = false; if (ICmpInst::isEquality(Pred) && match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) && match(CmpRHS, m_Zero())) { IsBitTest = true; TrueWhenUnset = Pred == ICmpInst::ICMP_EQ; } else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) { X = CmpLHS; Y = &MinSignedValue; IsBitTest = true; TrueWhenUnset = false; } else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) { X = CmpLHS; Y = &MinSignedValue; IsBitTest = true; TrueWhenUnset = true; } if (IsBitTest) { Value *V = nullptr; // (X & Y) == 0 ? X : X ^ Y --> X & ~Y if (TrueWhenUnset && TrueVal == X && match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C) V = Builder.CreateAnd(X, ~(*Y)); // (X & Y) != 0 ? X ^ Y : X --> X & ~Y else if (!TrueWhenUnset && FalseVal == X && match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C) V = Builder.CreateAnd(X, ~(*Y)); // (X & Y) == 0 ? X ^ Y : X --> X | Y else if (TrueWhenUnset && FalseVal == X && match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C) V = Builder.CreateOr(X, *Y); // (X & Y) != 0 ? X : X ^ Y --> X | Y else if (!TrueWhenUnset && TrueVal == X && match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C) V = Builder.CreateOr(X, *Y); if (V) return replaceInstUsesWith(SI, V); } } if (Instruction *V = foldSelectICmpAndAnd(SI.getType(), ICI, TrueVal, FalseVal, Builder)) return V; if (Instruction *V = foldSelectCtlzToCttz(ICI, TrueVal, FalseVal, Builder)) return V; if (Value *V = foldSelectICmpAndOr(ICI, TrueVal, FalseVal, Builder)) return replaceInstUsesWith(SI, V); if (Value *V = foldSelectICmpLshrAshr(ICI, TrueVal, FalseVal, Builder)) return replaceInstUsesWith(SI, V); if (Value *V = foldSelectCttzCtlz(ICI, TrueVal, FalseVal, Builder)) return replaceInstUsesWith(SI, V); if (Value *V = canonicalizeSaturatedSubtract(ICI, TrueVal, FalseVal, Builder)) return replaceInstUsesWith(SI, V); if (Value *V = canonicalizeSaturatedAdd(ICI, TrueVal, FalseVal, Builder)) return replaceInstUsesWith(SI, V); return Changed ? &SI : nullptr; } /// 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 can't 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(V); if (!I) 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(SI.getCondition()); if (const PHINode *VP = dyn_cast(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; } /// 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 (Outer.getType() != Inner->getType()) return nullptr; if (C == A || C == B) { // MAX(MAX(A, B), B) -> MAX(A, B) // MIN(MIN(a, b), a) -> MIN(a, b) // TODO: This could be done in instsimplify. if (SPF1 == SPF2 && SelectPatternResult::isMinOrMax(SPF1)) return replaceInstUsesWith(Outer, Inner); // MAX(MIN(a, b), a) -> a // MIN(MAX(a, b), a) -> a // TODO: This could be done in instsimplify. 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); } if (SPF1 == SPF2) { const APInt *CB, *CC; if (match(B, m_APInt(CB)) && match(C, m_APInt(CC))) { // MIN(MIN(A, 23), 97) -> MIN(A, 23) // MAX(MAX(A, 97), 23) -> MAX(A, 97) // TODO: This could be done in instsimplify. if ((SPF1 == SPF_UMIN && CB->ule(*CC)) || (SPF1 == SPF_SMIN && CB->sle(*CC)) || (SPF1 == SPF_UMAX && CB->uge(*CC)) || (SPF1 == SPF_SMAX && CB->sge(*CC))) return replaceInstUsesWith(Outer, Inner); // MIN(MIN(A, 97), 23) -> MIN(A, 23) // MAX(MAX(A, 23), 97) -> MAX(A, 97) if ((SPF1 == SPF_UMIN && CB->ugt(*CC)) || (SPF1 == SPF_SMIN && CB->sgt(*CC)) || (SPF1 == SPF_UMAX && CB->ult(*CC)) || (SPF1 == SPF_SMAX && CB->slt(*CC))) { Outer.replaceUsesOfWith(Inner, A); return &Outer; } } } // max(max(A, B), min(A, B)) --> max(A, B) // min(min(A, B), max(A, B)) --> min(A, B) // TODO: This could be done in instsimplify. if (SPF1 == SPF2 && ((SPF1 == SPF_UMIN && match(C, m_c_UMax(m_Specific(A), m_Specific(B)))) || (SPF1 == SPF_SMIN && match(C, m_c_SMax(m_Specific(A), m_Specific(B)))) || (SPF1 == SPF_UMAX && match(C, m_c_UMin(m_Specific(A), m_Specific(B)))) || (SPF1 == SPF_SMAX && match(C, m_c_SMin(m_Specific(A), m_Specific(B)))))) return replaceInstUsesWith(Outer, Inner); // ABS(ABS(X)) -> ABS(X) // NABS(NABS(X)) -> NABS(X) // TODO: This could be done in instsimplify. if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) { return replaceInstUsesWith(Outer, Inner); } // ABS(NABS(X)) -> ABS(X) // NABS(ABS(X)) -> NABS(X) if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) || (SPF1 == SPF_NABS && SPF2 == SPF_ABS)) { SelectInst *SI = cast(Inner); Value *NewSI = Builder.CreateSelect(SI->getCondition(), SI->getFalseValue(), SI->getTrueValue(), SI->getName(), SI); return replaceInstUsesWith(Outer, NewSI); } auto IsFreeOrProfitableToInvert = [&](Value *V, Value *&NotV, bool &ElidesXor) { if (match(V, m_Not(m_Value(NotV)))) { // If V has at most 2 uses then we can get rid of the xor operation // entirely. ElidesXor |= !V->hasNUsesOrMore(3); return true; } if (isFreeToInvert(V, !V->hasNUsesOrMore(3))) { NotV = nullptr; return true; } return false; }; Value *NotA, *NotB, *NotC; bool ElidesXor = false; // MIN(MIN(~A, ~B), ~C) == ~MAX(MAX(A, B), C) // MIN(MAX(~A, ~B), ~C) == ~MAX(MIN(A, B), C) // MAX(MIN(~A, ~B), ~C) == ~MIN(MAX(A, B), C) // MAX(MAX(~A, ~B), ~C) == ~MIN(MIN(A, B), C) // // This transform is performance neutral if we can elide at least one xor from // the set of three operands, since we'll be tacking on an xor at the very // end. if (SelectPatternResult::isMinOrMax(SPF1) && SelectPatternResult::isMinOrMax(SPF2) && IsFreeOrProfitableToInvert(A, NotA, ElidesXor) && IsFreeOrProfitableToInvert(B, NotB, ElidesXor) && IsFreeOrProfitableToInvert(C, NotC, ElidesXor) && ElidesXor) { if (!NotA) NotA = Builder.CreateNot(A); if (!NotB) NotB = Builder.CreateNot(B); if (!NotC) NotC = Builder.CreateNot(C); Value *NewInner = createMinMax(Builder, getInverseMinMaxFlavor(SPF1), NotA, NotB); Value *NewOuter = Builder.CreateNot( createMinMax(Builder, getInverseMinMaxFlavor(SPF2), NewInner, NotC)); return replaceInstUsesWith(Outer, NewOuter); } return nullptr; } /// Turn select C, (X + Y), (X - Y) --> (X + (select C, Y, (-Y))). /// This is even legal for FP. static Instruction *foldAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) { Value *CondVal = SI.getCondition(); Value *TrueVal = SI.getTrueValue(); Value *FalseVal = SI.getFalseValue(); auto *TI = dyn_cast(TrueVal); auto *FI = dyn_cast(FalseVal); if (!TI || !FI || !TI->hasOneUse() || !FI->hasOneUse()) return nullptr; Instruction *AddOp = nullptr, *SubOp = nullptr; 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 = nullptr; 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)); if (Instruction *NegInst = dyn_cast(NegVal)) { FastMathFlags Flags = AddOp->getFastMathFlags(); Flags &= SubOp->getFastMathFlags(); NegInst->setFastMathFlags(Flags); } } 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", &SI); if (SI.getType()->isFPOrFPVectorTy()) { Instruction *RI = BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel); FastMathFlags Flags = AddOp->getFastMathFlags(); Flags &= SubOp->getFastMathFlags(); RI->setFastMathFlags(Flags); return RI; } else return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel); } } return nullptr; } Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) { Constant *C; if (!match(Sel.getTrueValue(), m_Constant(C)) && !match(Sel.getFalseValue(), m_Constant(C))) return nullptr; Instruction *ExtInst; if (!match(Sel.getTrueValue(), m_Instruction(ExtInst)) && !match(Sel.getFalseValue(), m_Instruction(ExtInst))) return nullptr; auto ExtOpcode = ExtInst->getOpcode(); if (ExtOpcode != Instruction::ZExt && ExtOpcode != Instruction::SExt) return nullptr; // If we are extending from a boolean type or if we can create a select that // has the same size operands as its condition, try to narrow the select. Value *X = ExtInst->getOperand(0); Type *SmallType = X->getType(); Value *Cond = Sel.getCondition(); auto *Cmp = dyn_cast(Cond); if (!SmallType->isIntOrIntVectorTy(1) && (!Cmp || Cmp->getOperand(0)->getType() != SmallType)) return nullptr; // If the constant is the same after truncation to the smaller type and // extension to the original type, we can narrow the select. Type *SelType = Sel.getType(); Constant *TruncC = ConstantExpr::getTrunc(C, SmallType); Constant *ExtC = ConstantExpr::getCast(ExtOpcode, TruncC, SelType); if (ExtC == C) { Value *TruncCVal = cast(TruncC); if (ExtInst == Sel.getFalseValue()) std::swap(X, TruncCVal); // select Cond, (ext X), C --> ext(select Cond, X, C') // select Cond, C, (ext X) --> ext(select Cond, C', X) Value *NewSel = Builder.CreateSelect(Cond, X, TruncCVal, "narrow", &Sel); return CastInst::Create(Instruction::CastOps(ExtOpcode), NewSel, SelType); } // If one arm of the select is the extend of the condition, replace that arm // with the extension of the appropriate known bool value. if (Cond == X) { if (ExtInst == Sel.getTrueValue()) { // select X, (sext X), C --> select X, -1, C // select X, (zext X), C --> select X, 1, C Constant *One = ConstantInt::getTrue(SmallType); Constant *AllOnesOrOne = ConstantExpr::getCast(ExtOpcode, One, SelType); return SelectInst::Create(Cond, AllOnesOrOne, C, "", nullptr, &Sel); } else { // select X, C, (sext X) --> select X, C, 0 // select X, C, (zext X) --> select X, C, 0 Constant *Zero = ConstantInt::getNullValue(SelType); return SelectInst::Create(Cond, C, Zero, "", nullptr, &Sel); } } return nullptr; } /// Try to transform a vector select with a constant condition vector into a /// shuffle for easier combining with other shuffles and insert/extract. static Instruction *canonicalizeSelectToShuffle(SelectInst &SI) { Value *CondVal = SI.getCondition(); Constant *CondC; if (!CondVal->getType()->isVectorTy() || !match(CondVal, m_Constant(CondC))) return nullptr; unsigned NumElts = CondVal->getType()->getVectorNumElements(); SmallVector Mask; Mask.reserve(NumElts); Type *Int32Ty = Type::getInt32Ty(CondVal->getContext()); for (unsigned i = 0; i != NumElts; ++i) { Constant *Elt = CondC->getAggregateElement(i); if (!Elt) return nullptr; if (Elt->isOneValue()) { // If the select condition element is true, choose from the 1st vector. Mask.push_back(ConstantInt::get(Int32Ty, i)); } else if (Elt->isNullValue()) { // If the select condition element is false, choose from the 2nd vector. Mask.push_back(ConstantInt::get(Int32Ty, i + NumElts)); } else if (isa(Elt)) { // Undef in a select condition (choose one of the operands) does not mean // the same thing as undef in a shuffle mask (any value is acceptable), so // give up. return nullptr; } else { // Bail out on a constant expression. return nullptr; } } return new ShuffleVectorInst(SI.getTrueValue(), SI.getFalseValue(), ConstantVector::get(Mask)); } /// If we have a select of vectors with a scalar condition, try to convert that /// to a vector select by splatting the condition. A splat may get folded with /// other operations in IR and having all operands of a select be vector types /// is likely better for vector codegen. static Instruction *canonicalizeScalarSelectOfVecs( SelectInst &Sel, InstCombiner::BuilderTy &Builder) { Type *Ty = Sel.getType(); if (!Ty->isVectorTy()) return nullptr; // We can replace a single-use extract with constant index. Value *Cond = Sel.getCondition(); if (!match(Cond, m_OneUse(m_ExtractElement(m_Value(), m_ConstantInt())))) return nullptr; // select (extelt V, Index), T, F --> select (splat V, Index), T, F // Splatting the extracted condition reduces code (we could directly create a // splat shuffle of the source vector to eliminate the intermediate step). unsigned NumElts = Ty->getVectorNumElements(); Value *SplatCond = Builder.CreateVectorSplat(NumElts, Cond); Sel.setCondition(SplatCond); return &Sel; } /// Reuse bitcasted operands between a compare and select: /// select (cmp (bitcast C), (bitcast D)), (bitcast' C), (bitcast' D) --> /// bitcast (select (cmp (bitcast C), (bitcast D)), (bitcast C), (bitcast D)) static Instruction *foldSelectCmpBitcasts(SelectInst &Sel, InstCombiner::BuilderTy &Builder) { Value *Cond = Sel.getCondition(); Value *TVal = Sel.getTrueValue(); Value *FVal = Sel.getFalseValue(); CmpInst::Predicate Pred; Value *A, *B; if (!match(Cond, m_Cmp(Pred, m_Value(A), m_Value(B)))) return nullptr; // The select condition is a compare instruction. If the select's true/false // values are already the same as the compare operands, there's nothing to do. if (TVal == A || TVal == B || FVal == A || FVal == B) return nullptr; Value *C, *D; if (!match(A, m_BitCast(m_Value(C))) || !match(B, m_BitCast(m_Value(D)))) return nullptr; // select (cmp (bitcast C), (bitcast D)), (bitcast TSrc), (bitcast FSrc) Value *TSrc, *FSrc; if (!match(TVal, m_BitCast(m_Value(TSrc))) || !match(FVal, m_BitCast(m_Value(FSrc)))) return nullptr; // If the select true/false values are *different bitcasts* of the same source // operands, make the select operands the same as the compare operands and // cast the result. This is the canonical select form for min/max. Value *NewSel; if (TSrc == C && FSrc == D) { // select (cmp (bitcast C), (bitcast D)), (bitcast' C), (bitcast' D) --> // bitcast (select (cmp A, B), A, B) NewSel = Builder.CreateSelect(Cond, A, B, "", &Sel); } else if (TSrc == D && FSrc == C) { // select (cmp (bitcast C), (bitcast D)), (bitcast' D), (bitcast' C) --> // bitcast (select (cmp A, B), B, A) NewSel = Builder.CreateSelect(Cond, B, A, "", &Sel); } else { return nullptr; } return CastInst::CreateBitOrPointerCast(NewSel, Sel.getType()); } /// Try to eliminate select instructions that test the returned flag of cmpxchg /// instructions. /// /// If a select instruction tests the returned flag of a cmpxchg instruction and /// selects between the returned value of the cmpxchg instruction its compare /// operand, the result of the select will always be equal to its false value. /// For example: /// /// %0 = cmpxchg i64* %ptr, i64 %compare, i64 %new_value seq_cst seq_cst /// %1 = extractvalue { i64, i1 } %0, 1 /// %2 = extractvalue { i64, i1 } %0, 0 /// %3 = select i1 %1, i64 %compare, i64 %2 /// ret i64 %3 /// /// The returned value of the cmpxchg instruction (%2) is the original value /// located at %ptr prior to any update. If the cmpxchg operation succeeds, %2 /// must have been equal to %compare. Thus, the result of the select is always /// equal to %2, and the code can be simplified to: /// /// %0 = cmpxchg i64* %ptr, i64 %compare, i64 %new_value seq_cst seq_cst /// %1 = extractvalue { i64, i1 } %0, 0 /// ret i64 %1 /// static Instruction *foldSelectCmpXchg(SelectInst &SI) { // A helper that determines if V is an extractvalue instruction whose // aggregate operand is a cmpxchg instruction and whose single index is equal // to I. If such conditions are true, the helper returns the cmpxchg // instruction; otherwise, a nullptr is returned. auto isExtractFromCmpXchg = [](Value *V, unsigned I) -> AtomicCmpXchgInst * { auto *Extract = dyn_cast(V); if (!Extract) return nullptr; if (Extract->getIndices()[0] != I) return nullptr; return dyn_cast(Extract->getAggregateOperand()); }; // If the select has a single user, and this user is a select instruction that // we can simplify, skip the cmpxchg simplification for now. if (SI.hasOneUse()) if (auto *Select = dyn_cast(SI.user_back())) if (Select->getCondition() == SI.getCondition()) if (Select->getFalseValue() == SI.getTrueValue() || Select->getTrueValue() == SI.getFalseValue()) return nullptr; // Ensure the select condition is the returned flag of a cmpxchg instruction. auto *CmpXchg = isExtractFromCmpXchg(SI.getCondition(), 1); if (!CmpXchg) return nullptr; // Check the true value case: The true value of the select is the returned // value of the same cmpxchg used by the condition, and the false value is the // cmpxchg instruction's compare operand. if (auto *X = isExtractFromCmpXchg(SI.getTrueValue(), 0)) if (X == CmpXchg && X->getCompareOperand() == SI.getFalseValue()) { SI.setTrueValue(SI.getFalseValue()); return &SI; } // Check the false value case: The false value of the select is the returned // value of the same cmpxchg used by the condition, and the true value is the // cmpxchg instruction's compare operand. if (auto *X = isExtractFromCmpXchg(SI.getFalseValue(), 0)) if (X == CmpXchg && X->getCompareOperand() == SI.getTrueValue()) { SI.setTrueValue(SI.getFalseValue()); return &SI; } return nullptr; } static Instruction *moveAddAfterMinMax(SelectPatternFlavor SPF, Value *X, Value *Y, InstCombiner::BuilderTy &Builder) { assert(SelectPatternResult::isMinOrMax(SPF) && "Expected min/max pattern"); bool IsUnsigned = SPF == SelectPatternFlavor::SPF_UMIN || SPF == SelectPatternFlavor::SPF_UMAX; // TODO: If InstSimplify could fold all cases where C2 <= C1, we could change // the constant value check to an assert. Value *A; const APInt *C1, *C2; if (IsUnsigned && match(X, m_NUWAdd(m_Value(A), m_APInt(C1))) && match(Y, m_APInt(C2)) && C2->uge(*C1) && X->hasNUses(2)) { // umin (add nuw A, C1), C2 --> add nuw (umin A, C2 - C1), C1 // umax (add nuw A, C1), C2 --> add nuw (umax A, C2 - C1), C1 Value *NewMinMax = createMinMax(Builder, SPF, A, ConstantInt::get(X->getType(), *C2 - *C1)); return BinaryOperator::CreateNUW(BinaryOperator::Add, NewMinMax, ConstantInt::get(X->getType(), *C1)); } if (!IsUnsigned && match(X, m_NSWAdd(m_Value(A), m_APInt(C1))) && match(Y, m_APInt(C2)) && X->hasNUses(2)) { bool Overflow; APInt Diff = C2->ssub_ov(*C1, Overflow); if (!Overflow) { // smin (add nsw A, C1), C2 --> add nsw (smin A, C2 - C1), C1 // smax (add nsw A, C1), C2 --> add nsw (smax A, C2 - C1), C1 Value *NewMinMax = createMinMax(Builder, SPF, A, ConstantInt::get(X->getType(), Diff)); return BinaryOperator::CreateNSW(BinaryOperator::Add, NewMinMax, ConstantInt::get(X->getType(), *C1)); } } return nullptr; } /// Match a sadd_sat or ssub_sat which is using min/max to clamp the value. Instruction *InstCombiner::matchSAddSubSat(SelectInst &MinMax1) { Type *Ty = MinMax1.getType(); // We are looking for a tree of: // max(INT_MIN, min(INT_MAX, add(sext(A), sext(B)))) // Where the min and max could be reversed Instruction *MinMax2; BinaryOperator *AddSub; const APInt *MinValue, *MaxValue; if (match(&MinMax1, m_SMin(m_Instruction(MinMax2), m_APInt(MaxValue)))) { if (!match(MinMax2, m_SMax(m_BinOp(AddSub), m_APInt(MinValue)))) return nullptr; } else if (match(&MinMax1, m_SMax(m_Instruction(MinMax2), m_APInt(MinValue)))) { if (!match(MinMax2, m_SMin(m_BinOp(AddSub), m_APInt(MaxValue)))) return nullptr; } else return nullptr; // Check that the constants clamp a saturate, and that the new type would be // sensible to convert to. if (!(*MaxValue + 1).isPowerOf2() || -*MinValue != *MaxValue + 1) return nullptr; // In what bitwidth can this be treated as saturating arithmetics? unsigned NewBitWidth = (*MaxValue + 1).logBase2() + 1; // FIXME: This isn't quite right for vectors, but using the scalar type is a // good first approximation for what should be done there. if (!shouldChangeType(Ty->getScalarType()->getIntegerBitWidth(), NewBitWidth)) return nullptr; // Also make sure that the number of uses is as expected. The "3"s are for the // the two items of min/max (the compare and the select). if (MinMax2->hasNUsesOrMore(3) || AddSub->hasNUsesOrMore(3)) return nullptr; // Create the new type (which can be a vector type) Type *NewTy = Ty->getWithNewBitWidth(NewBitWidth); // Match the two extends from the add/sub Value *A, *B; if(!match(AddSub, m_BinOp(m_SExt(m_Value(A)), m_SExt(m_Value(B))))) return nullptr; // And check the incoming values are of a type smaller than or equal to the // size of the saturation. Otherwise the higher bits can cause different // results. if (A->getType()->getScalarSizeInBits() > NewBitWidth || B->getType()->getScalarSizeInBits() > NewBitWidth) return nullptr; Intrinsic::ID IntrinsicID; if (AddSub->getOpcode() == Instruction::Add) IntrinsicID = Intrinsic::sadd_sat; else if (AddSub->getOpcode() == Instruction::Sub) IntrinsicID = Intrinsic::ssub_sat; else return nullptr; // Finally create and return the sat intrinsic, truncated to the new type Function *F = Intrinsic::getDeclaration(MinMax1.getModule(), IntrinsicID, NewTy); Value *AT = Builder.CreateSExt(A, NewTy); Value *BT = Builder.CreateSExt(B, NewTy); Value *Sat = Builder.CreateCall(F, {AT, BT}); return CastInst::Create(Instruction::SExt, Sat, Ty); } /// Reduce a sequence of min/max with a common operand. static Instruction *factorizeMinMaxTree(SelectPatternFlavor SPF, Value *LHS, Value *RHS, InstCombiner::BuilderTy &Builder) { assert(SelectPatternResult::isMinOrMax(SPF) && "Expected a min/max"); // TODO: Allow FP min/max with nnan/nsz. if (!LHS->getType()->isIntOrIntVectorTy()) return nullptr; // Match 3 of the same min/max ops. Example: umin(umin(), umin()). Value *A, *B, *C, *D; SelectPatternResult L = matchSelectPattern(LHS, A, B); SelectPatternResult R = matchSelectPattern(RHS, C, D); if (SPF != L.Flavor || L.Flavor != R.Flavor) return nullptr; // Look for a common operand. The use checks are different than usual because // a min/max pattern typically has 2 uses of each op: 1 by the cmp and 1 by // the select. Value *MinMaxOp = nullptr; Value *ThirdOp = nullptr; if (!LHS->hasNUsesOrMore(3) && RHS->hasNUsesOrMore(3)) { // If the LHS is only used in this chain and the RHS is used outside of it, // reuse the RHS min/max because that will eliminate the LHS. if (D == A || C == A) { // min(min(a, b), min(c, a)) --> min(min(c, a), b) // min(min(a, b), min(a, d)) --> min(min(a, d), b) MinMaxOp = RHS; ThirdOp = B; } else if (D == B || C == B) { // min(min(a, b), min(c, b)) --> min(min(c, b), a) // min(min(a, b), min(b, d)) --> min(min(b, d), a) MinMaxOp = RHS; ThirdOp = A; } } else if (!RHS->hasNUsesOrMore(3)) { // Reuse the LHS. This will eliminate the RHS. if (D == A || D == B) { // min(min(a, b), min(c, a)) --> min(min(a, b), c) // min(min(a, b), min(c, b)) --> min(min(a, b), c) MinMaxOp = LHS; ThirdOp = C; } else if (C == A || C == B) { // min(min(a, b), min(b, d)) --> min(min(a, b), d) // min(min(a, b), min(c, b)) --> min(min(a, b), d) MinMaxOp = LHS; ThirdOp = D; } } if (!MinMaxOp || !ThirdOp) return nullptr; CmpInst::Predicate P = getMinMaxPred(SPF); Value *CmpABC = Builder.CreateICmp(P, MinMaxOp, ThirdOp); return SelectInst::Create(CmpABC, MinMaxOp, ThirdOp); } /// Try to reduce a rotate pattern that includes a compare and select into a /// funnel shift intrinsic. Example: /// rotl32(a, b) --> (b == 0 ? a : ((a >> (32 - b)) | (a << b))) /// --> call llvm.fshl.i32(a, a, b) static Instruction *foldSelectRotate(SelectInst &Sel) { // The false value of the select must be a rotate of the true value. Value *Or0, *Or1; if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1))))) return nullptr; Value *TVal = Sel.getTrueValue(); Value *SA0, *SA1; if (!match(Or0, m_OneUse(m_LogicalShift(m_Specific(TVal), m_Value(SA0)))) || !match(Or1, m_OneUse(m_LogicalShift(m_Specific(TVal), m_Value(SA1))))) return nullptr; auto ShiftOpcode0 = cast(Or0)->getOpcode(); auto ShiftOpcode1 = cast(Or1)->getOpcode(); if (ShiftOpcode0 == ShiftOpcode1) return nullptr; // We have one of these patterns so far: // select ?, TVal, (or (lshr TVal, SA0), (shl TVal, SA1)) // select ?, TVal, (or (shl TVal, SA0), (lshr TVal, SA1)) // This must be a power-of-2 rotate for a bitmasking transform to be valid. unsigned Width = Sel.getType()->getScalarSizeInBits(); if (!isPowerOf2_32(Width)) return nullptr; // Check the shift amounts to see if they are an opposite pair. Value *ShAmt; if (match(SA1, m_OneUse(m_Sub(m_SpecificInt(Width), m_Specific(SA0))))) ShAmt = SA0; else if (match(SA0, m_OneUse(m_Sub(m_SpecificInt(Width), m_Specific(SA1))))) ShAmt = SA1; else return nullptr; // Finally, see if the select is filtering out a shift-by-zero. Value *Cond = Sel.getCondition(); ICmpInst::Predicate Pred; if (!match(Cond, m_OneUse(m_ICmp(Pred, m_Specific(ShAmt), m_ZeroInt()))) || Pred != ICmpInst::ICMP_EQ) return nullptr; // This is a rotate that avoids shift-by-bitwidth UB in a suboptimal way. // Convert to funnel shift intrinsic. bool IsFshl = (ShAmt == SA0 && ShiftOpcode0 == BinaryOperator::Shl) || (ShAmt == SA1 && ShiftOpcode1 == BinaryOperator::Shl); Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr; Function *F = Intrinsic::getDeclaration(Sel.getModule(), IID, Sel.getType()); return IntrinsicInst::Create(F, { TVal, TVal, ShAmt }); } Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { Value *CondVal = SI.getCondition(); Value *TrueVal = SI.getTrueValue(); Value *FalseVal = SI.getFalseValue(); Type *SelType = SI.getType(); // FIXME: Remove this workaround when freeze related patches are done. // For select with undef operand which feeds into an equality comparison, // don't simplify it so loop unswitch can know the equality comparison // may have an undef operand. This is a workaround for PR31652 caused by // descrepancy about branch on undef between LoopUnswitch and GVN. if (isa(TrueVal) || isa(FalseVal)) { if (llvm::any_of(SI.users(), [&](User *U) { ICmpInst *CI = dyn_cast(U); if (CI && CI->isEquality()) return true; return false; })) { return nullptr; } } if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, SQ.getWithInstruction(&SI))) return replaceInstUsesWith(SI, V); if (Instruction *I = canonicalizeSelectToShuffle(SI)) return I; if (Instruction *I = canonicalizeScalarSelectOfVecs(SI, Builder)) return I; // Canonicalize a one-use integer compare with a non-canonical predicate by // inverting the predicate and swapping the select operands. This matches a // compare canonicalization for conditional branches. // TODO: Should we do the same for FP compares? CmpInst::Predicate Pred; if (match(CondVal, m_OneUse(m_ICmp(Pred, m_Value(), m_Value()))) && !isCanonicalPredicate(Pred)) { // Swap true/false values and condition. CmpInst *Cond = cast(CondVal); Cond->setPredicate(CmpInst::getInversePredicate(Pred)); SI.setOperand(1, FalseVal); SI.setOperand(2, TrueVal); SI.swapProfMetadata(); Worklist.Add(Cond); return &SI; } if (SelType->isIntOrIntVectorTy(1) && TrueVal->getType() == CondVal->getType()) { if (match(TrueVal, m_One())) { // Change: A = select B, true, C --> A = or B, C return BinaryOperator::CreateOr(CondVal, FalseVal); } if (match(TrueVal, m_Zero())) { // Change: A = select B, false, C --> A = and !B, C Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName()); return BinaryOperator::CreateAnd(NotCond, FalseVal); } if (match(FalseVal, m_Zero())) { // Change: A = select B, C, false --> A = and B, C return BinaryOperator::CreateAnd(CondVal, TrueVal); } if (match(FalseVal, m_One())) { // 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, a, b -> a | b // select a, b, a -> a & b if (CondVal == TrueVal) return BinaryOperator::CreateOr(CondVal, FalseVal); 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); if (match(FalseVal, m_Not(m_Specific(CondVal)))) return BinaryOperator::CreateOr(TrueVal, FalseVal); } // Selecting between two integer or vector splat integer constants? // // Note that we don't handle a scalar select of vectors: // select i1 %c, <2 x i8> <1, 1>, <2 x i8> <0, 0> // because that may need 3 instructions to splat the condition value: // extend, insertelement, shufflevector. if (SelType->isIntOrIntVectorTy() && CondVal->getType()->isVectorTy() == SelType->isVectorTy()) { // select C, 1, 0 -> zext C to int if (match(TrueVal, m_One()) && match(FalseVal, m_Zero())) return new ZExtInst(CondVal, SelType); // select C, -1, 0 -> sext C to int if (match(TrueVal, m_AllOnes()) && match(FalseVal, m_Zero())) return new SExtInst(CondVal, SelType); // select C, 0, 1 -> zext !C to int if (match(TrueVal, m_Zero()) && match(FalseVal, m_One())) { Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName()); return new ZExtInst(NotCond, SelType); } // select C, 0, -1 -> sext !C to int if (match(TrueVal, m_Zero()) && match(FalseVal, m_AllOnes())) { Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName()); return new SExtInst(NotCond, SelType); } } // See if we are selecting two values based on a comparison of the two values. if (FCmpInst *FCI = dyn_cast(CondVal)) { if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) { // Canonicalize to use ordered comparisons by swapping the select // operands. // // e.g. // (X ugt Y) ? X : Y -> (X ole Y) ? Y : X if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) { FCmpInst::Predicate InvPred = FCI->getInversePredicate(); IRBuilder<>::FastMathFlagGuard FMFG(Builder); Builder.setFastMathFlags(FCI->getFastMathFlags()); Value *NewCond = Builder.CreateFCmp(InvPred, TrueVal, FalseVal, FCI->getName() + ".inv"); return SelectInst::Create(NewCond, FalseVal, TrueVal, SI.getName() + ".p"); } // NOTE: if we wanted to, this is where to detect MIN/MAX } else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){ // Canonicalize to use ordered comparisons by swapping the select // operands. // // e.g. // (X ugt Y) ? X : Y -> (X ole Y) ? X : Y if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) { FCmpInst::Predicate InvPred = FCI->getInversePredicate(); IRBuilder<>::FastMathFlagGuard FMFG(Builder); Builder.setFastMathFlags(FCI->getFastMathFlags()); Value *NewCond = Builder.CreateFCmp(InvPred, FalseVal, TrueVal, FCI->getName() + ".inv"); return SelectInst::Create(NewCond, FalseVal, TrueVal, SI.getName() + ".p"); } // NOTE: if we wanted to, this is where to detect MIN/MAX } } // Canonicalize select with fcmp to fabs(). -0.0 makes this tricky. We need // fast-math-flags (nsz) or fsub with +0.0 (not fneg) for this to work. We // also require nnan because we do not want to unintentionally change the // sign of a NaN value. // FIXME: These folds should test/propagate FMF from the select, not the // fsub or fneg. // (X <= +/-0.0) ? (0.0 - X) : X --> fabs(X) Instruction *FSub; if (match(CondVal, m_FCmp(Pred, m_Specific(FalseVal), m_AnyZeroFP())) && match(TrueVal, m_FSub(m_PosZeroFP(), m_Specific(FalseVal))) && match(TrueVal, m_Instruction(FSub)) && FSub->hasNoNaNs() && (Pred == FCmpInst::FCMP_OLE || Pred == FCmpInst::FCMP_ULE)) { Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, FalseVal, FSub); return replaceInstUsesWith(SI, Fabs); } // (X > +/-0.0) ? X : (0.0 - X) --> fabs(X) if (match(CondVal, m_FCmp(Pred, m_Specific(TrueVal), m_AnyZeroFP())) && match(FalseVal, m_FSub(m_PosZeroFP(), m_Specific(TrueVal))) && match(FalseVal, m_Instruction(FSub)) && FSub->hasNoNaNs() && (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_UGT)) { Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, TrueVal, FSub); return replaceInstUsesWith(SI, Fabs); } // With nnan and nsz: // (X < +/-0.0) ? -X : X --> fabs(X) // (X <= +/-0.0) ? -X : X --> fabs(X) Instruction *FNeg; if (match(CondVal, m_FCmp(Pred, m_Specific(FalseVal), m_AnyZeroFP())) && match(TrueVal, m_FNeg(m_Specific(FalseVal))) && match(TrueVal, m_Instruction(FNeg)) && FNeg->hasNoNaNs() && FNeg->hasNoSignedZeros() && (Pred == FCmpInst::FCMP_OLT || Pred == FCmpInst::FCMP_OLE || Pred == FCmpInst::FCMP_ULT || Pred == FCmpInst::FCMP_ULE)) { Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, FalseVal, FNeg); return replaceInstUsesWith(SI, Fabs); } // With nnan and nsz: // (X > +/-0.0) ? X : -X --> fabs(X) // (X >= +/-0.0) ? X : -X --> fabs(X) if (match(CondVal, m_FCmp(Pred, m_Specific(TrueVal), m_AnyZeroFP())) && match(FalseVal, m_FNeg(m_Specific(TrueVal))) && match(FalseVal, m_Instruction(FNeg)) && FNeg->hasNoNaNs() && FNeg->hasNoSignedZeros() && (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_OGE || Pred == FCmpInst::FCMP_UGT || Pred == FCmpInst::FCMP_UGE)) { Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, TrueVal, FNeg); return replaceInstUsesWith(SI, Fabs); } // See if we are selecting two values based on a comparison of the two values. if (ICmpInst *ICI = dyn_cast(CondVal)) if (Instruction *Result = foldSelectInstWithICmp(SI, ICI)) return Result; if (Instruction *Add = foldAddSubSelect(SI, Builder)) return Add; // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z)) auto *TI = dyn_cast(TrueVal); auto *FI = dyn_cast(FalseVal); if (TI && FI && TI->getOpcode() == FI->getOpcode()) if (Instruction *IV = foldSelectOpOp(SI, TI, FI)) return IV; if (Instruction *I = foldSelectExtConst(SI)) return I; // See if we can fold the select into one of our operands. if (SelType->isIntOrIntVectorTy() || SelType->isFPOrFPVectorTy()) { if (Instruction *FoldI = foldSelectIntoOp(SI, TrueVal, FalseVal)) return FoldI; Value *LHS, *RHS; Instruction::CastOps CastOp; SelectPatternResult SPR = matchSelectPattern(&SI, LHS, RHS, &CastOp); auto SPF = SPR.Flavor; if (SPF) { Value *LHS2, *RHS2; if (SelectPatternFlavor SPF2 = matchSelectPattern(LHS, LHS2, RHS2).Flavor) if (Instruction *R = foldSPFofSPF(cast(LHS), SPF2, LHS2, RHS2, SI, SPF, RHS)) return R; if (SelectPatternFlavor SPF2 = matchSelectPattern(RHS, LHS2, RHS2).Flavor) if (Instruction *R = foldSPFofSPF(cast(RHS), SPF2, LHS2, RHS2, SI, SPF, LHS)) return R; // TODO. // ABS(-X) -> ABS(X) } if (SelectPatternResult::isMinOrMax(SPF)) { // Canonicalize so that // - type casts are outside select patterns. // - float clamp is transformed to min/max pattern bool IsCastNeeded = LHS->getType() != SelType; Value *CmpLHS = cast(CondVal)->getOperand(0); Value *CmpRHS = cast(CondVal)->getOperand(1); if (IsCastNeeded || (LHS->getType()->isFPOrFPVectorTy() && ((CmpLHS != LHS && CmpLHS != RHS) || (CmpRHS != LHS && CmpRHS != RHS)))) { CmpInst::Predicate MinMaxPred = getMinMaxPred(SPF, SPR.Ordered); Value *Cmp; if (CmpInst::isIntPredicate(MinMaxPred)) { Cmp = Builder.CreateICmp(MinMaxPred, LHS, RHS); } else { IRBuilder<>::FastMathFlagGuard FMFG(Builder); auto FMF = cast(SI.getCondition())->getFastMathFlags(); Builder.setFastMathFlags(FMF); Cmp = Builder.CreateFCmp(MinMaxPred, LHS, RHS); } Value *NewSI = Builder.CreateSelect(Cmp, LHS, RHS, SI.getName(), &SI); if (!IsCastNeeded) return replaceInstUsesWith(SI, NewSI); Value *NewCast = Builder.CreateCast(CastOp, NewSI, SelType); return replaceInstUsesWith(SI, NewCast); } // MAX(~a, ~b) -> ~MIN(a, b) // MAX(~a, C) -> ~MIN(a, ~C) // MIN(~a, ~b) -> ~MAX(a, b) // MIN(~a, C) -> ~MAX(a, ~C) auto moveNotAfterMinMax = [&](Value *X, Value *Y) -> Instruction * { Value *A; if (match(X, m_Not(m_Value(A))) && !X->hasNUsesOrMore(3) && !isFreeToInvert(A, A->hasOneUse()) && // Passing false to only consider m_Not and constants. isFreeToInvert(Y, false)) { Value *B = Builder.CreateNot(Y); Value *NewMinMax = createMinMax(Builder, getInverseMinMaxFlavor(SPF), A, B); // Copy the profile metadata. if (MDNode *MD = SI.getMetadata(LLVMContext::MD_prof)) { cast(NewMinMax)->setMetadata(LLVMContext::MD_prof, MD); // Swap the metadata if the operands are swapped. if (X == SI.getFalseValue() && Y == SI.getTrueValue()) cast(NewMinMax)->swapProfMetadata(); } return BinaryOperator::CreateNot(NewMinMax); } return nullptr; }; if (Instruction *I = moveNotAfterMinMax(LHS, RHS)) return I; if (Instruction *I = moveNotAfterMinMax(RHS, LHS)) return I; if (Instruction *I = moveAddAfterMinMax(SPF, LHS, RHS, Builder)) return I; if (Instruction *I = factorizeMinMaxTree(SPF, LHS, RHS, Builder)) return I; if (Instruction *I = matchSAddSubSat(SI)) return I; } } // Canonicalize select of FP values where NaN and -0.0 are not valid as // minnum/maxnum intrinsics. if (isa(SI) && SI.hasNoNaNs() && SI.hasNoSignedZeros()) { Value *X, *Y; if (match(&SI, m_OrdFMax(m_Value(X), m_Value(Y)))) return replaceInstUsesWith( SI, Builder.CreateBinaryIntrinsic(Intrinsic::maxnum, X, Y, &SI)); if (match(&SI, m_OrdFMin(m_Value(X), m_Value(Y)))) return replaceInstUsesWith( SI, Builder.CreateBinaryIntrinsic(Intrinsic::minnum, X, Y, &SI)); } // See if we can fold the select into a phi node if the condition is a select. if (auto *PN = dyn_cast(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, PN)) return NV; if (SelectInst *TrueSI = dyn_cast(TrueVal)) { if (TrueSI->getCondition()->getType() == CondVal->getType()) { // select(C, select(C, a, b), c) -> select(C, a, c) if (TrueSI->getCondition() == CondVal) { if (SI.getTrueValue() == TrueSI->getTrueValue()) return nullptr; SI.setOperand(1, TrueSI->getTrueValue()); return &SI; } // select(C0, select(C1, a, b), b) -> select(C0&C1, a, b) // We choose this as normal form to enable folding on the And and shortening // paths for the values (this helps GetUnderlyingObjects() for example). if (TrueSI->getFalseValue() == FalseVal && TrueSI->hasOneUse()) { Value *And = Builder.CreateAnd(CondVal, TrueSI->getCondition()); SI.setOperand(0, And); SI.setOperand(1, TrueSI->getTrueValue()); return &SI; } } } if (SelectInst *FalseSI = dyn_cast(FalseVal)) { if (FalseSI->getCondition()->getType() == CondVal->getType()) { // select(C, a, select(C, b, c)) -> select(C, a, c) if (FalseSI->getCondition() == CondVal) { if (SI.getFalseValue() == FalseSI->getFalseValue()) return nullptr; SI.setOperand(2, FalseSI->getFalseValue()); return &SI; } // select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b) if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) { Value *Or = Builder.CreateOr(CondVal, FalseSI->getCondition()); SI.setOperand(0, Or); SI.setOperand(2, FalseSI->getFalseValue()); return &SI; } } } auto canMergeSelectThroughBinop = [](BinaryOperator *BO) { // The select might be preventing a division by 0. switch (BO->getOpcode()) { default: return true; case Instruction::SRem: case Instruction::URem: case Instruction::SDiv: case Instruction::UDiv: return false; } }; // Try to simplify a binop sandwiched between 2 selects with the same // condition. // select(C, binop(select(C, X, Y), W), Z) -> select(C, binop(X, W), Z) BinaryOperator *TrueBO; if (match(TrueVal, m_OneUse(m_BinOp(TrueBO))) && canMergeSelectThroughBinop(TrueBO)) { if (auto *TrueBOSI = dyn_cast(TrueBO->getOperand(0))) { if (TrueBOSI->getCondition() == CondVal) { TrueBO->setOperand(0, TrueBOSI->getTrueValue()); Worklist.Add(TrueBO); return &SI; } } if (auto *TrueBOSI = dyn_cast(TrueBO->getOperand(1))) { if (TrueBOSI->getCondition() == CondVal) { TrueBO->setOperand(1, TrueBOSI->getTrueValue()); Worklist.Add(TrueBO); return &SI; } } } // select(C, Z, binop(select(C, X, Y), W)) -> select(C, Z, binop(Y, W)) BinaryOperator *FalseBO; if (match(FalseVal, m_OneUse(m_BinOp(FalseBO))) && canMergeSelectThroughBinop(FalseBO)) { if (auto *FalseBOSI = dyn_cast(FalseBO->getOperand(0))) { if (FalseBOSI->getCondition() == CondVal) { FalseBO->setOperand(0, FalseBOSI->getFalseValue()); Worklist.Add(FalseBO); return &SI; } } if (auto *FalseBOSI = dyn_cast(FalseBO->getOperand(1))) { if (FalseBOSI->getCondition() == CondVal) { FalseBO->setOperand(1, FalseBOSI->getFalseValue()); Worklist.Add(FalseBO); return &SI; } } } Value *NotCond; if (match(CondVal, m_Not(m_Value(NotCond)))) { SI.setOperand(0, NotCond); SI.setOperand(1, FalseVal); SI.setOperand(2, TrueVal); SI.swapProfMetadata(); return &SI; } if (VectorType *VecTy = dyn_cast(SelType)) { unsigned VWidth = VecTy->getNumElements(); APInt UndefElts(VWidth, 0); APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth)); if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) { if (V != &SI) return replaceInstUsesWith(SI, V); return &SI; } } // If we can compute the condition, there's no need for a select. // Like the above fold, we are attempting to reduce compile-time cost by // putting this fold here with limitations rather than in InstSimplify. // The motivation for this call into value tracking is to take advantage of // the assumption cache, so make sure that is populated. if (!CondVal->getType()->isVectorTy() && !AC.assumptions().empty()) { KnownBits Known(1); computeKnownBits(CondVal, Known, 0, &SI); if (Known.One.isOneValue()) return replaceInstUsesWith(SI, TrueVal); if (Known.Zero.isOneValue()) return replaceInstUsesWith(SI, FalseVal); } if (Instruction *BitCastSel = foldSelectCmpBitcasts(SI, Builder)) return BitCastSel; // Simplify selects that test the returned flag of cmpxchg instructions. if (Instruction *Select = foldSelectCmpXchg(SI)) return Select; if (Instruction *Select = foldSelectBinOpIdentity(SI, TLI)) return Select; if (Instruction *Rot = foldSelectRotate(SI)) return Rot; return nullptr; }