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Diffstat (limited to 'llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp')
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp | 2666 |
1 files changed, 2666 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp new file mode 100644 index 000000000000..9fc871e49b30 --- /dev/null +++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -0,0 +1,2666 @@ +//===- 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 <cassert> +#include <utility> + +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<FPMathOperator>(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<BinaryOperator>(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<BinaryOperator>(TI) && !isa<GetElementPtrInst>(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<BinaryOperator>(TI)) { + BinaryOperator *NewBO = BinaryOperator::Create(BO->getOpcode(), Op0, Op1); + NewBO->copyIRFlags(TI); + NewBO->andIRFlags(FI); + return NewBO; + } + if (auto *TGEP = dyn_cast<GetElementPtrInst>(TI)) { + auto *FGEP = cast<GetElementPtrInst>(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<BinaryOperator>(TrueVal)) { + if (TVI->hasOneUse() && !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) { + 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<Constant>(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<BinaryOperator>(FalseVal)) { + if (FVI->hasOneUse() && !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) { + 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<Constant>(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<Instruction>(FalseVal); + // if lshr is not exact and ashr is, this new ashr must not be exact. + bool IsExact = Ashr->isExact() && cast<Instruction>(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<BinaryOperator>(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<Intrinsic::ctlz>())) + return nullptr; + + Value *X = ICI->getOperand(0); + auto *II = cast<IntrinsicInst>(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<Intrinsic::cttz>(m_Specific(CmpLHS))) && + !match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Specific(CmpLHS)))) + return nullptr; + + IntrinsicInst *II = cast<IntrinsicInst>(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<IntrinsicInst>(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<IntegerType>(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 <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 (Cmp.isUnsigned()) { + Constant *ZextRHS = ConstantExpr::getZExt(AdjustedRHS, SelTy); + // 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 { + 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<Constant>(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<Constant>(Cmp.getOperand(1))) + return nullptr; + + // Choose a sign-bit check for the compare (likely simpler for codegen). + // ABS: (X <s 0) ? -X : X + // NABS: (X <s 0) ? X : -X + Value *LHS, *RHS; + SelectPatternFlavor SPF = matchSelectPattern(&Sel, LHS, RHS).Flavor; + if (SPF != SelectPatternFlavor::SPF_ABS && + SPF != SelectPatternFlavor::SPF_NABS) + return nullptr; + + Value *TVal = Sel.getTrueValue(); + Value *FVal = Sel.getFalseValue(); + assert(isKnownNegation(TVal, FVal) && + "Unexpected result from matchSelectPattern"); + + // The compare may use the negated abs()/nabs() operand, or it may use + // negation in non-canonical form such as: sub A, B. + bool CmpUsesNegatedOp = match(Cmp.getOperand(0), m_Neg(m_Specific(TVal))) || + match(Cmp.getOperand(0), m_Neg(m_Specific(FVal))); + + bool CmpCanonicalized = !CmpUsesNegatedOp && + match(Cmp.getOperand(1), m_ZeroInt()) && + Cmp.getPredicate() == ICmpInst::ICMP_SLT; + bool RHSCanonicalized = match(RHS, m_Neg(m_Specific(LHS))); + + // Is this already canonical? + if (CmpCanonicalized && RHSCanonicalized) + return nullptr; + + // If RHS is used by other instructions except compare and select, don't + // canonicalize it to not increase the instruction count. + if (!(RHS->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<BinaryOperator>(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<Instruction>(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<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; + } + } + + // 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<Instruction>(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<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; +} + +/// 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<SelectInst>(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<Instruction>(TrueVal); + auto *FI = dyn_cast<Instruction>(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<Instruction>(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<CmpInst>(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<Value>(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<Constant *, 16> 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<UndefValue>(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<ExtractValueInst>(V); + if (!Extract) + return nullptr; + if (Extract->getIndices()[0] != I) + return nullptr; + return dyn_cast<AtomicCmpXchgInst>(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<SelectInst>(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<BinaryOperator>(Or0)->getOpcode(); + auto ShiftOpcode1 = cast<BinaryOperator>(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<UndefValue>(TrueVal) || isa<UndefValue>(FalseVal)) { + if (llvm::any_of(SI.users(), [&](User *U) { + ICmpInst *CI = dyn_cast<ICmpInst>(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<CmpInst>(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<FCmpInst>(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<ICmpInst>(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<Instruction>(TrueVal); + auto *FI = dyn_cast<Instruction>(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<Instruction>(LHS), SPF2, LHS2, + RHS2, SI, SPF, RHS)) + return R; + if (SelectPatternFlavor SPF2 = matchSelectPattern(RHS, LHS2, RHS2).Flavor) + if (Instruction *R = foldSPFofSPF(cast<Instruction>(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<CmpInst>(CondVal)->getOperand(0); + Value *CmpRHS = cast<CmpInst>(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<FPMathOperator>(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<SelectInst>(NewMinMax)->setMetadata(LLVMContext::MD_prof, MD); + // Swap the metadata if the operands are swapped. + if (X == SI.getFalseValue() && Y == SI.getTrueValue()) + cast<SelectInst>(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<FPMathOperator>(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<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, PN)) + return NV; + + if (SelectInst *TrueSI = dyn_cast<SelectInst>(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<SelectInst>(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<SelectInst>(TrueBO->getOperand(0))) { + if (TrueBOSI->getCondition() == CondVal) { + TrueBO->setOperand(0, TrueBOSI->getTrueValue()); + Worklist.Add(TrueBO); + return &SI; + } + } + if (auto *TrueBOSI = dyn_cast<SelectInst>(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<SelectInst>(FalseBO->getOperand(0))) { + if (FalseBOSI->getCondition() == CondVal) { + FalseBO->setOperand(0, FalseBOSI->getFalseValue()); + Worklist.Add(FalseBO); + return &SI; + } + } + if (auto *FalseBOSI = dyn_cast<SelectInst>(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<VectorType>(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; +} |