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//===- 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/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/OverflowInstAnalysis.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/ConstantRange.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/InstCombiner.h"
#include <cassert>
#include <utility>
#define DEBUG_TYPE "instcombine"
#include "llvm/Transforms/Utils/InstructionWorklist.h"
using namespace llvm;
using namespace PatternMatch;
/// Replace a select operand based on an equality comparison with the identity
/// constant of a binop.
static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
const TargetLibraryInfo &TLI,
InstCombinerImpl &IC) {
// 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, IC.getDataLayout(), &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 }
return IC.replaceOperand(Sel, IsEq ? 1 : 2, Y);
}
/// 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.isZero() && !FC.isZero()) {
// 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.isZero() ? 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.isZero();
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::FAdd:
case Instruction::Mul:
case Instruction::FMul:
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::FSub:
case Instruction::FDiv: // Can only fold on the divisor amount.
case Instruction::Shl: // Can only fold on the shift amount.
case Instruction::LShr:
case Instruction::AShr:
return 1;
default:
return 0; // Cannot fold
}
}
/// We have (select c, TI, FI), and we know that TI and FI have the same opcode.
Instruction *InstCombinerImpl::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 (auto *CondVTy = dyn_cast<VectorType>(CondTy)) {
if (!FIOpndTy->isVectorTy() ||
CondVTy->getElementCount() !=
cast<VectorType>(FIOpndTy)->getElementCount())
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());
}
Value *OtherOpT, *OtherOpF;
bool MatchIsOpZero;
auto getCommonOp = [&](Instruction *TI, Instruction *FI, bool Commute,
bool Swapped = false) -> Value * {
assert(!(Commute && Swapped) &&
"Commute and Swapped can't set at the same time");
if (!Swapped) {
if (TI->getOperand(0) == FI->getOperand(0)) {
OtherOpT = TI->getOperand(1);
OtherOpF = FI->getOperand(1);
MatchIsOpZero = true;
return TI->getOperand(0);
} else if (TI->getOperand(1) == FI->getOperand(1)) {
OtherOpT = TI->getOperand(0);
OtherOpF = FI->getOperand(0);
MatchIsOpZero = false;
return TI->getOperand(1);
}
}
if (!Commute && !Swapped)
return nullptr;
// If we are allowing commute or swap of operands, then
// allow a cross-operand match. In that case, MatchIsOpZero
// means that TI's operand 0 (FI's operand 1) is the common op.
if (TI->getOperand(0) == FI->getOperand(1)) {
OtherOpT = TI->getOperand(1);
OtherOpF = FI->getOperand(0);
MatchIsOpZero = true;
return TI->getOperand(0);
} else if (TI->getOperand(1) == FI->getOperand(0)) {
OtherOpT = TI->getOperand(0);
OtherOpF = FI->getOperand(1);
MatchIsOpZero = false;
return TI->getOperand(1);
}
return nullptr;
};
if (TI->hasOneUse() || FI->hasOneUse()) {
// Cond ? -X : -Y --> -(Cond ? X : Y)
Value *X, *Y;
if (match(TI, m_FNeg(m_Value(X))) && match(FI, m_FNeg(m_Value(Y)))) {
// Intersect FMF from the fneg instructions and union those with the
// select.
FastMathFlags FMF = TI->getFastMathFlags();
FMF &= FI->getFastMathFlags();
FMF |= SI.getFastMathFlags();
Value *NewSel =
Builder.CreateSelect(Cond, X, Y, SI.getName() + ".v", &SI);
if (auto *NewSelI = dyn_cast<Instruction>(NewSel))
NewSelI->setFastMathFlags(FMF);
Instruction *NewFNeg = UnaryOperator::CreateFNeg(NewSel);
NewFNeg->setFastMathFlags(FMF);
return NewFNeg;
}
// Min/max intrinsic with a common operand can have the common operand
// pulled after the select. This is the same transform as below for binops,
// but specialized for intrinsic matching and without the restrictive uses
// clause.
auto *TII = dyn_cast<IntrinsicInst>(TI);
auto *FII = dyn_cast<IntrinsicInst>(FI);
if (TII && FII && TII->getIntrinsicID() == FII->getIntrinsicID()) {
if (match(TII, m_MaxOrMin(m_Value(), m_Value()))) {
if (Value *MatchOp = getCommonOp(TI, FI, true)) {
Value *NewSel =
Builder.CreateSelect(Cond, OtherOpT, OtherOpF, "minmaxop", &SI);
return CallInst::Create(TII->getCalledFunction(), {NewSel, MatchOp});
}
}
// select c, (ldexp v, e0), (ldexp v, e1) -> ldexp v, (select c, e0, e1)
// select c, (ldexp v0, e), (ldexp v1, e) -> ldexp (select c, v0, v1), e
//
// select c, (ldexp v0, e0), (ldexp v1, e1) ->
// ldexp (select c, v0, v1), (select c, e0, e1)
if (TII->getIntrinsicID() == Intrinsic::ldexp) {
Value *LdexpVal0 = TII->getArgOperand(0);
Value *LdexpExp0 = TII->getArgOperand(1);
Value *LdexpVal1 = FII->getArgOperand(0);
Value *LdexpExp1 = FII->getArgOperand(1);
if (LdexpExp0->getType() == LdexpExp1->getType()) {
FPMathOperator *SelectFPOp = cast<FPMathOperator>(&SI);
FastMathFlags FMF = cast<FPMathOperator>(TII)->getFastMathFlags();
FMF &= cast<FPMathOperator>(FII)->getFastMathFlags();
FMF |= SelectFPOp->getFastMathFlags();
Value *SelectVal = Builder.CreateSelect(Cond, LdexpVal0, LdexpVal1);
Value *SelectExp = Builder.CreateSelect(Cond, LdexpExp0, LdexpExp1);
CallInst *NewLdexp = Builder.CreateIntrinsic(
TII->getType(), Intrinsic::ldexp, {SelectVal, SelectExp});
NewLdexp->setFastMathFlags(FMF);
return replaceInstUsesWith(SI, NewLdexp);
}
}
}
// icmp with a common operand also can have the common operand
// pulled after the select.
ICmpInst::Predicate TPred, FPred;
if (match(TI, m_ICmp(TPred, m_Value(), m_Value())) &&
match(FI, m_ICmp(FPred, m_Value(), m_Value()))) {
if (TPred == FPred || TPred == CmpInst::getSwappedPredicate(FPred)) {
bool Swapped = TPred != FPred;
if (Value *MatchOp =
getCommonOp(TI, FI, ICmpInst::isEquality(TPred), Swapped)) {
Value *NewSel = Builder.CreateSelect(Cond, OtherOpT, OtherOpF,
SI.getName() + ".v", &SI);
return new ICmpInst(
MatchIsOpZero ? TPred : CmpInst::getSwappedPredicate(TPred),
MatchOp, 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 ||
!TI->isSameOperationAs(FI) ||
(!isa<BinaryOperator>(TI) && !isa<GetElementPtrInst>(TI)) ||
!TI->hasOneUse() || !FI->hasOneUse())
return nullptr;
// Figure out if the operations have any operands in common.
Value *MatchOp = getCommonOp(TI, FI, TI->isCommutative());
if (!MatchOp)
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 are sinking div/rem after a select, we may need to freeze the
// condition because div/rem may induce immediate UB with a poison operand.
// For example, the following transform is not safe if Cond can ever be poison
// because we can replace poison with zero and then we have div-by-zero that
// didn't exist in the original code:
// Cond ? x/y : x/z --> x / (Cond ? y : z)
auto *BO = dyn_cast<BinaryOperator>(TI);
if (BO && BO->isIntDivRem() && !isGuaranteedNotToBePoison(Cond)) {
// A udiv/urem with a common divisor is safe because UB can only occur with
// div-by-zero, and that would be present in the original code.
if (BO->getOpcode() == Instruction::SDiv ||
BO->getOpcode() == Instruction::SRem || MatchIsOpZero)
Cond = Builder.CreateFreeze(Cond);
}
// 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.isZero() && !C2I.isZero()) // One side must be zero.
return false;
return C1I.isOne() || C1I.isAllOnes() || C2I.isOne() || C2I.isAllOnes();
}
/// Try to fold the select into one of the operands to allow further
/// optimization.
Instruction *InstCombinerImpl::foldSelectIntoOp(SelectInst &SI, Value *TrueVal,
Value *FalseVal) {
// See the comment above getSelectFoldableOperands for a description of the
// transformation we are doing here.
auto TryFoldSelectIntoOp = [&](SelectInst &SI, Value *TrueVal,
Value *FalseVal,
bool Swapped) -> Instruction * {
auto *TVI = dyn_cast<BinaryOperator>(TrueVal);
if (!TVI || !TVI->hasOneUse() || isa<Constant>(FalseVal))
return nullptr;
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)
return nullptr;
// TODO: We probably ought to revisit cases where the select and FP
// instructions have different flags and add tests to ensure the
// behaviour is correct.
FastMathFlags FMF;
if (isa<FPMathOperator>(&SI))
FMF = SI.getFastMathFlags();
Constant *C = ConstantExpr::getBinOpIdentity(
TVI->getOpcode(), TVI->getType(), true, FMF.noSignedZeros());
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(C->getUniqueInteger(), *OOpC))) {
Value *NewSel = Builder.CreateSelect(SI.getCondition(), Swapped ? C : OOp,
Swapped ? OOp : C, "", &SI);
if (isa<FPMathOperator>(&SI))
cast<Instruction>(NewSel)->setFastMathFlags(FMF);
NewSel->takeName(TVI);
BinaryOperator *BO =
BinaryOperator::Create(TVI->getOpcode(), FalseVal, NewSel);
BO->copyIRFlags(TVI);
return BO;
}
return nullptr;
};
if (Instruction *R = TryFoldSelectIntoOp(SI, TrueVal, FalseVal, false))
return R;
if (Instruction *R = TryFoldSelectIntoOp(SI, FalseVal, TrueVal, true))
return R;
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))));
// The shift must be valid.
// TODO: This restricts the fold to constant shift amounts. Is there a way to
// handle variable shifts safely? PR47012
if (HasShift &&
!match(Z, m_SpecificInt_ICMP(CmpInst::ICMP_ULT,
APInt(SelType->getScalarSizeInBits(),
SelType->getScalarSizeInBits()))))
return nullptr;
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 eq (and X, C1), 0), 0, (shl [nsw/nuw] X, C2));
/// iff C1 is a mask and the number of its leading zeros is equal to C2
/// into:
/// shl X, C2
static Value *foldSelectICmpAndZeroShl(const ICmpInst *Cmp, Value *TVal,
Value *FVal,
InstCombiner::BuilderTy &Builder) {
ICmpInst::Predicate Pred;
Value *AndVal;
if (!match(Cmp, m_ICmp(Pred, m_Value(AndVal), m_Zero())))
return nullptr;
if (Pred == ICmpInst::ICMP_NE) {
Pred = ICmpInst::ICMP_EQ;
std::swap(TVal, FVal);
}
Value *X;
const APInt *C2, *C1;
if (Pred != ICmpInst::ICMP_EQ ||
!match(AndVal, m_And(m_Value(X), m_APInt(C1))) ||
!match(TVal, m_Zero()) || !match(FVal, m_Shl(m_Specific(X), m_APInt(C2))))
return nullptr;
if (!C1->isMask() ||
C1->countLeadingZeros() != static_cast<unsigned>(C2->getZExtValue()))
return nullptr;
auto *FI = dyn_cast<Instruction>(FVal);
if (!FI)
return nullptr;
FI->setHasNoSignedWrap(false);
FI->setHasNoUnsignedWrap(false);
return FVal;
}
/// 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, (BinOp Y, C2))
/// into:
/// IF C2 u>= C1
/// (BinOp Y, (shl (and X, C1), C3))
/// ELSE
/// (BinOp Y, (lshr (and X, C1), C3))
/// iff:
/// 0 on the RHS is the identity value (i.e add, xor, shl, etc...)
/// C1 and C2 are both powers of 2
/// where:
/// IF C2 u>= C1
/// C3 = Log(C2) - Log(C1)
/// ELSE
/// C3 = Log(C1) - Log(C2)
///
/// 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 *foldSelectICmpAndBinOp(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);
unsigned C1Log;
bool NeedAnd = false;
CmpInst::Predicate Pred = IC->getPredicate();
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;
C1Log = C1->logBase2();
} else {
APInt C1;
if (!decomposeBitTestICmp(CmpLHS, CmpRHS, Pred, CmpLHS, C1) ||
!C1.isPowerOf2())
return nullptr;
C1Log = C1.logBase2();
NeedAnd = true;
}
Value *Y, *V = CmpLHS;
BinaryOperator *BinOp;
const APInt *C2;
bool NeedXor;
if (match(FalseVal, m_BinOp(m_Specific(TrueVal), m_Power2(C2)))) {
Y = TrueVal;
BinOp = cast<BinaryOperator>(FalseVal);
NeedXor = Pred == ICmpInst::ICMP_NE;
} else if (match(TrueVal, m_BinOp(m_Specific(FalseVal), m_Power2(C2)))) {
Y = FalseVal;
BinOp = cast<BinaryOperator>(TrueVal);
NeedXor = Pred == ICmpInst::ICMP_EQ;
} else {
return nullptr;
}
// Check that 0 on RHS is identity value for this binop.
auto *IdentityC =
ConstantExpr::getBinOpIdentity(BinOp->getOpcode(), BinOp->getType(),
/*AllowRHSConstant*/ true);
if (IdentityC == nullptr || !IdentityC->isNullValue())
return nullptr;
unsigned C2Log = C2->logBase2();
bool NeedShift = C1Log != C2Log;
bool NeedZExtTrunc = Y->getType()->getScalarSizeInBits() !=
V->getType()->getScalarSizeInBits();
// Make sure we don't create more instructions than we save.
if ((NeedShift + NeedXor + NeedZExtTrunc + NeedAnd) >
(IC->hasOneUse() + BinOp->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.CreateBinOp(BinOp->getOpcode(), Y, V);
}
/// Canonicalize a set or clear of a masked set of constant bits to
/// select-of-constants form.
static Instruction *foldSetClearBits(SelectInst &Sel,
InstCombiner::BuilderTy &Builder) {
Value *Cond = Sel.getCondition();
Value *T = Sel.getTrueValue();
Value *F = Sel.getFalseValue();
Type *Ty = Sel.getType();
Value *X;
const APInt *NotC, *C;
// Cond ? (X & ~C) : (X | C) --> (X & ~C) | (Cond ? 0 : C)
if (match(T, m_And(m_Value(X), m_APInt(NotC))) &&
match(F, m_OneUse(m_Or(m_Specific(X), m_APInt(C)))) && *NotC == ~(*C)) {
Constant *Zero = ConstantInt::getNullValue(Ty);
Constant *OrC = ConstantInt::get(Ty, *C);
Value *NewSel = Builder.CreateSelect(Cond, Zero, OrC, "masksel", &Sel);
return BinaryOperator::CreateOr(T, NewSel);
}
// Cond ? (X | C) : (X & ~C) --> (X & ~C) | (Cond ? C : 0)
if (match(F, m_And(m_Value(X), m_APInt(NotC))) &&
match(T, m_OneUse(m_Or(m_Specific(X), m_APInt(C)))) && *NotC == ~(*C)) {
Constant *Zero = ConstantInt::getNullValue(Ty);
Constant *OrC = ConstantInt::get(Ty, *C);
Value *NewSel = Builder.CreateSelect(Cond, OrC, Zero, "masksel", &Sel);
return BinaryOperator::CreateOr(F, NewSel);
}
return nullptr;
}
// select (x == 0), 0, x * y --> freeze(y) * x
// select (y == 0), 0, x * y --> freeze(x) * y
// select (x == 0), undef, x * y --> freeze(y) * x
// select (x == undef), 0, x * y --> freeze(y) * x
// Usage of mul instead of 0 will make the result more poisonous,
// so the operand that was not checked in the condition should be frozen.
// The latter folding is applied only when a constant compared with x is
// is a vector consisting of 0 and undefs. If a constant compared with x
// is a scalar undefined value or undefined vector then an expression
// should be already folded into a constant.
static Instruction *foldSelectZeroOrMul(SelectInst &SI, InstCombinerImpl &IC) {
auto *CondVal = SI.getCondition();
auto *TrueVal = SI.getTrueValue();
auto *FalseVal = SI.getFalseValue();
Value *X, *Y;
ICmpInst::Predicate Predicate;
// Assuming that constant compared with zero is not undef (but it may be
// a vector with some undef elements). Otherwise (when a constant is undef)
// the select expression should be already simplified.
if (!match(CondVal, m_ICmp(Predicate, m_Value(X), m_Zero())) ||
!ICmpInst::isEquality(Predicate))
return nullptr;
if (Predicate == ICmpInst::ICMP_NE)
std::swap(TrueVal, FalseVal);
// Check that TrueVal is a constant instead of matching it with m_Zero()
// to handle the case when it is a scalar undef value or a vector containing
// non-zero elements that are masked by undef elements in the compare
// constant.
auto *TrueValC = dyn_cast<Constant>(TrueVal);
if (TrueValC == nullptr ||
!match(FalseVal, m_c_Mul(m_Specific(X), m_Value(Y))) ||
!isa<Instruction>(FalseVal))
return nullptr;
auto *ZeroC = cast<Constant>(cast<Instruction>(CondVal)->getOperand(1));
auto *MergedC = Constant::mergeUndefsWith(TrueValC, ZeroC);
// If X is compared with 0 then TrueVal could be either zero or undef.
// m_Zero match vectors containing some undef elements, but for scalars
// m_Undef should be used explicitly.
if (!match(MergedC, m_Zero()) && !match(MergedC, m_Undef()))
return nullptr;
auto *FalseValI = cast<Instruction>(FalseVal);
auto *FrY = IC.InsertNewInstBefore(new FreezeInst(Y, Y->getName() + ".fr"),
FalseValI->getIterator());
IC.replaceOperand(*FalseValI, FalseValI->getOperand(0) == Y ? 0 : 1, FrY);
return IC.replaceInstUsesWith(SI, FalseValI);
}
/// 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();
Value *A = ICI->getOperand(0);
Value *B = ICI->getOperand(1);
// (b > a) ? 0 : a - b -> (b <= a) ? a - b : 0
// (a == 0) ? 0 : a - 1 -> (a != 0) ? a - 1 : 0
if (match(TrueVal, m_Zero())) {
Pred = ICmpInst::getInversePredicate(Pred);
std::swap(TrueVal, FalseVal);
}
if (!match(FalseVal, m_Zero()))
return nullptr;
// ugt 0 is canonicalized to ne 0 and requires special handling
// (a != 0) ? a + -1 : 0 -> usub.sat(a, 1)
if (Pred == ICmpInst::ICMP_NE) {
if (match(B, m_Zero()) && match(TrueVal, m_Add(m_Specific(A), m_AllOnes())))
return Builder.CreateBinaryIntrinsic(Intrinsic::usub_sat, A,
ConstantInt::get(A->getType(), 1));
return nullptr;
}
if (!ICmpInst::isUnsigned(Pred))
return nullptr;
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!");
// Ensure the sub is of the form:
// (a > b) ? a - b : 0 -> usub.sat(a, b)
// (a > b) ? b - a : 0 -> -usub.sat(a, b)
// Checking for both a-b and a+(-b) as a constant.
bool IsNegative = false;
const APInt *C;
if (match(TrueVal, m_Sub(m_Specific(B), m_Specific(A))) ||
(match(A, m_APInt(C)) &&
match(TrueVal, m_Add(m_Specific(B), m_SpecificInt(-*C)))))
IsNegative = true;
else if (!match(TrueVal, m_Sub(m_Specific(A), m_Specific(B))) &&
!(match(B, m_APInt(C)) &&
match(TrueVal, m_Add(m_Specific(A), m_SpecificInt(-*C)))))
return nullptr;
// If we are adding a negate and the sub and icmp are used anywhere else, we
// would end up with more instructions.
if (IsNegative && !TrueVal->hasOneUse() && !ICI->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.
if (match(FVal, m_AllOnes())) {
std::swap(TVal, FVal);
Pred = CmpInst::getInversePredicate(Pred);
}
if (!match(TVal, m_AllOnes()))
return nullptr;
// Canonicalize predicate to less-than or less-or-equal-than.
if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE) {
std::swap(Cmp0, Cmp1);
Pred = CmpInst::getSwappedPredicate(Pred);
}
if (Pred != ICmpInst::ICMP_ULT && Pred != ICmpInst::ICMP_ULE)
return nullptr;
// Match unsigned saturated add of 2 variables with an unnecessary 'not'.
// Strictness of the comparison is irrelevant.
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.
// Strictness of the comparison is irrelevant.
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));
}
// The overflow may be detected via the add wrapping round.
// This is only valid for strict comparison!
if (Pred == ICmpInst::ICMP_ULT &&
match(Cmp0, m_c_Add(m_Specific(Cmp1), m_Value(Y))) &&
match(FVal, m_c_Add(m_Specific(Cmp1), m_Specific(Y)))) {
// ((X + Y) u< X) ? -1 : (X + Y) --> uadd.sat(X, Y)
// ((X + Y) u< Y) ? -1 : (X + Y) --> uadd.sat(X, Y)
return Builder.CreateBinaryIntrinsic(Intrinsic::uadd_sat, Cmp1, Y);
}
return nullptr;
}
/// Try to match patterns with select and subtract as absolute difference.
static Value *foldAbsDiff(ICmpInst *Cmp, Value *TVal, Value *FVal,
InstCombiner::BuilderTy &Builder) {
auto *TI = dyn_cast<Instruction>(TVal);
auto *FI = dyn_cast<Instruction>(FVal);
if (!TI || !FI)
return nullptr;
// Normalize predicate to gt/lt rather than ge/le.
ICmpInst::Predicate Pred = Cmp->getStrictPredicate();
Value *A = Cmp->getOperand(0);
Value *B = Cmp->getOperand(1);
// Normalize "A - B" as the true value of the select.
if (match(FI, m_Sub(m_Specific(A), m_Specific(B)))) {
std::swap(FI, TI);
Pred = ICmpInst::getSwappedPredicate(Pred);
}
// With any pair of no-wrap subtracts:
// (A > B) ? (A - B) : (B - A) --> abs(A - B)
if (Pred == CmpInst::ICMP_SGT &&
match(TI, m_Sub(m_Specific(A), m_Specific(B))) &&
match(FI, m_Sub(m_Specific(B), m_Specific(A))) &&
(TI->hasNoSignedWrap() || TI->hasNoUnsignedWrap()) &&
(FI->hasNoSignedWrap() || FI->hasNoUnsignedWrap())) {
// The remaining subtract is not "nuw" any more.
// If there's one use of the subtract (no other use than the use we are
// about to replace), then we know that the sub is "nsw" in this context
// even if it was only "nuw" before. If there's another use, then we can't
// add "nsw" to the existing instruction because it may not be safe in the
// other user's context.
TI->setHasNoUnsignedWrap(false);
if (!TI->hasNoSignedWrap())
TI->setHasNoSignedWrap(TI->hasOneUse());
return Builder.CreateBinaryIntrinsic(Intrinsic::abs, TI, Builder.getTrue());
}
return nullptr;
}
/// Fold the following code sequence:
/// \code
/// int a = ctlz(x & -x);
// x ? 31 - a : a;
// // or
// x ? 31 - a : 32;
/// \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);
Value *Ctlz;
if (!match(FalseVal,
m_Xor(m_Value(Ctlz), m_SpecificInt(BitWidth - 1))))
return nullptr;
if (!match(Ctlz, m_Intrinsic<Intrinsic::ctlz>()))
return nullptr;
if (TrueVal != Ctlz && !match(TrueVal, m_SpecificInt(BitWidth)))
return nullptr;
Value *X = ICI->getOperand(0);
auto *II = cast<IntrinsicInst>(Ctlz);
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_poison' 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 select condition compares a value for equality.
if (!ICI->isEquality())
return nullptr;
Value *SelectArg = FalseVal;
Value *ValueOnZero = TrueVal;
if (Pred == ICmpInst::ICMP_NE)
std::swap(SelectArg, ValueOnZero);
// Skip zero extend/truncate.
Value *Count = nullptr;
if (!match(SelectArg, m_ZExt(m_Value(Count))) &&
!match(SelectArg, m_Trunc(m_Value(Count))))
Count = SelectArg;
// 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.
Value *X;
if (!match(Count, m_Intrinsic<Intrinsic::cttz>(m_Value(X))) &&
!match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Value(X))))
return nullptr;
// (X == 0) ? BitWidth : ctz(X)
// (X == -1) ? BitWidth : ctz(~X)
if ((X != CmpLHS || !match(CmpRHS, m_Zero())) &&
(!match(X, m_Not(m_Specific(CmpLHS))) || !match(CmpRHS, m_AllOnes())))
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 'is_zero_poison' flag. It's always valid to go from
// true to false on this flag, so we can replace it for all users.
II->setArgOperand(1, ConstantInt::getFalse(II->getContext()));
return SelectArg;
}
// The ValueOnZero is not the bitwidth. But if the cttz/ctlz (and optional
// zext/trunc) have one use (ending at the select), the cttz/ctlz result will
// not be used if the input is zero. Relax to 'zero is poison' for that case.
if (II->hasOneUse() && SelectArg->hasOneUse() &&
!match(II->getArgOperand(1), m_One()))
II->setArgOperand(1, ConstantInt::getTrue(II->getContext()));
return nullptr;
}
static Instruction *canonicalizeSPF(SelectInst &Sel, ICmpInst &Cmp,
InstCombinerImpl &IC) {
Value *LHS, *RHS;
// TODO: What to do with pointer min/max patterns?
if (!Sel.getType()->isIntOrIntVectorTy())
return nullptr;
SelectPatternFlavor SPF = matchSelectPattern(&Sel, LHS, RHS).Flavor;
if (SPF == SelectPatternFlavor::SPF_ABS ||
SPF == SelectPatternFlavor::SPF_NABS) {
if (!Cmp.hasOneUse() && !RHS->hasOneUse())
return nullptr; // TODO: Relax this restriction.
// Note that NSW flag can only be propagated for normal, non-negated abs!
bool IntMinIsPoison = SPF == SelectPatternFlavor::SPF_ABS &&
match(RHS, m_NSWNeg(m_Specific(LHS)));
Constant *IntMinIsPoisonC =
ConstantInt::get(Type::getInt1Ty(Sel.getContext()), IntMinIsPoison);
Instruction *Abs =
IC.Builder.CreateBinaryIntrinsic(Intrinsic::abs, LHS, IntMinIsPoisonC);
if (SPF == SelectPatternFlavor::SPF_NABS)
return BinaryOperator::CreateNeg(Abs); // Always without NSW flag!
return IC.replaceInstUsesWith(Sel, Abs);
}
if (SelectPatternResult::isMinOrMax(SPF)) {
Intrinsic::ID IntrinsicID;
switch (SPF) {
case SelectPatternFlavor::SPF_UMIN:
IntrinsicID = Intrinsic::umin;
break;
case SelectPatternFlavor::SPF_UMAX:
IntrinsicID = Intrinsic::umax;
break;
case SelectPatternFlavor::SPF_SMIN:
IntrinsicID = Intrinsic::smin;
break;
case SelectPatternFlavor::SPF_SMAX:
IntrinsicID = Intrinsic::smax;
break;
default:
llvm_unreachable("Unexpected SPF");
}
return IC.replaceInstUsesWith(
Sel, IC.Builder.CreateBinaryIntrinsic(IntrinsicID, LHS, RHS));
}
return nullptr;
}
bool InstCombinerImpl::replaceInInstruction(Value *V, Value *Old, Value *New,
unsigned Depth) {
// Conservatively limit replacement to two instructions upwards.
if (Depth == 2)
return false;
auto *I = dyn_cast<Instruction>(V);
if (!I || !I->hasOneUse() || !isSafeToSpeculativelyExecute(I))
return false;
bool Changed = false;
for (Use &U : I->operands()) {
if (U == Old) {
replaceUse(U, New);
Worklist.add(I);
Changed = true;
} else {
Changed |= replaceInInstruction(U, Old, New, Depth + 1);
}
}
return Changed;
}
/// 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.
Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
ICmpInst &Cmp) {
if (!Cmp.isEquality())
return nullptr;
// Canonicalize the pattern to ICMP_EQ by swapping the select operands.
Value *TrueVal = Sel.getTrueValue(), *FalseVal = Sel.getFalseValue();
bool Swapped = false;
if (Cmp.getPredicate() == ICmpInst::ICMP_NE) {
std::swap(TrueVal, FalseVal);
Swapped = true;
}
// In X == Y ? f(X) : Z, try to evaluate f(Y) and replace the operand.
// Make sure Y cannot be undef though, as we might pick different values for
// undef in the icmp and in f(Y). Additionally, take care to avoid replacing
// X == Y ? X : Z with X == Y ? Y : Z, as that would lead to an infinite
// replacement cycle.
Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1);
if (TrueVal != CmpLHS &&
isGuaranteedNotToBeUndefOrPoison(CmpRHS, SQ.AC, &Sel, &DT)) {
if (Value *V = simplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, SQ,
/* AllowRefinement */ true))
return replaceOperand(Sel, Swapped ? 2 : 1, V);
// Even if TrueVal does not simplify, we can directly replace a use of
// CmpLHS with CmpRHS, as long as the instruction is not used anywhere
// else and is safe to speculatively execute (we may end up executing it
// with different operands, which should not cause side-effects or trigger
// undefined behavior). Only do this if CmpRHS is a constant, as
// profitability is not clear for other cases.
// FIXME: Support vectors.
if (match(CmpRHS, m_ImmConstant()) && !match(CmpLHS, m_ImmConstant()) &&
!Cmp.getType()->isVectorTy())
if (replaceInInstruction(TrueVal, CmpLHS, CmpRHS))
return &Sel;
}
if (TrueVal != CmpRHS &&
isGuaranteedNotToBeUndefOrPoison(CmpLHS, SQ.AC, &Sel, &DT))
if (Value *V = simplifyWithOpReplaced(TrueVal, CmpRHS, CmpLHS, SQ,
/* AllowRefinement */ true))
return replaceOperand(Sel, Swapped ? 2 : 1, V);
auto *FalseInst = dyn_cast<Instruction>(FalseVal);
if (!FalseInst)
return nullptr;
// InstSimplify already performed this fold if it was possible subject to
// current poison-generating flags. Check whether dropping poison-generating
// flags enables the transform.
// 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
SmallVector<Instruction *> DropFlags;
if (simplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, SQ,
/* AllowRefinement */ false,
&DropFlags) == TrueVal ||
simplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, SQ,
/* AllowRefinement */ false,
&DropFlags) == TrueVal) {
for (Instruction *I : DropFlags) {
I->dropPoisonGeneratingFlagsAndMetadata();
Worklist.add(I);
}
return replaceInstUsesWith(Sel, 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 Value *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;
ICmpInst::Predicate Pred0 = Cmp0.getPredicate();
Value *Cmp00 = Cmp0.getOperand(0);
Constant *C0;
if (!match(Cmp0.getOperand(1),
m_CombineAnd(m_AnyIntegralConstant(), m_Constant(C0))))
return nullptr;
if (!isa<SelectInst>(Sel1)) {
Pred0 = ICmpInst::getInversePredicate(Pred0);
std::swap(X, Sel1);
}
// Canonicalize Cmp0 into ult or uge.
// FIXME: we shouldn't care about lanes that are 'undef' in the end?
switch (Pred0) {
case ICmpInst::Predicate::ICMP_ULT:
case ICmpInst::Predicate::ICMP_UGE:
// Although icmp ult %x, 0 is an unusual thing to try and should generally
// have been simplified, it does not verify with undef inputs so ensure we
// are not in a strange state.
if (!match(C0, m_SpecificInt_ICMP(
ICmpInst::Predicate::ICMP_NE,
APInt::getZero(C0->getType()->getScalarSizeInBits()))))
return nullptr;
break; // Great!
case ICmpInst::Predicate::ICMP_ULE:
case ICmpInst::Predicate::ICMP_UGT:
// We want to canonicalize it to 'ult' or 'uge', 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::getAllOnes(C0->getType()->getScalarSizeInBits()))))
return nullptr; // Can't do, have all-ones element[s].
Pred0 = ICmpInst::getFlippedStrictnessPredicate(Pred0);
C0 = InstCombiner::AddOne(C0);
break;
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;
// If the types do not match, look through any truncs to the underlying
// instruction.
if (Cmp00->getType() != X->getType() && X->hasOneUse())
match(X, m_TruncOrSelf(m_Value(X)));
// 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(X->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 = InstCombiner::AddOne(C2);
[[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.
Pred1 = ICmpInst::Predicate::ICMP_SLT;
std::swap(ReplacementLow, ReplacementHigh);
break;
default:
return nullptr; // Unknown predicate.
}
assert(Pred1 == ICmpInst::Predicate::ICMP_SLT &&
"Unexpected predicate type.");
// The thresholds of this clamp-like pattern.
auto *ThresholdLowIncl = ConstantExpr::getNeg(C1);
auto *ThresholdHighExcl = ConstantExpr::getSub(C0, C1);
assert((Pred0 == ICmpInst::Predicate::ICMP_ULT ||
Pred0 == ICmpInst::Predicate::ICMP_UGE) &&
"Unexpected predicate type.");
if (Pred0 == ICmpInst::Predicate::ICMP_UGE)
std::swap(ThresholdLowIncl, ThresholdHighExcl);
// 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;
// If we are matching from a truncated input, we need to sext the
// ReplacementLow and ReplacementHigh values. Only do the transform if they
// are free to extend due to being constants.
if (X->getType() != Sel0.getType()) {
Constant *LowC, *HighC;
if (!match(ReplacementLow, m_ImmConstant(LowC)) ||
!match(ReplacementHigh, m_ImmConstant(HighC)))
return nullptr;
const DataLayout &DL = Sel0.getModule()->getDataLayout();
ReplacementLow =
ConstantFoldCastOperand(Instruction::SExt, LowC, X->getType(), DL);
ReplacementHigh =
ConstantFoldCastOperand(Instruction::SExt, HighC, X->getType(), DL);
assert(ReplacementLow && ReplacementHigh &&
"Constant folding of ImmConstant cannot fail");
}
// 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);
// Create the final select. If we looked through a truncate above, we will
// need to retruncate the result.
Value *MaybeReplacedHigh = Builder.CreateSelect(
ShouldReplaceHigh, ReplacementHigh, MaybeReplacedLow);
return Builder.CreateTrunc(MaybeReplacedHigh, Sel0.getType());
}
// 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,
InstCombinerImpl &IC) {
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 (!InstCombiner::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;
// ULT with 'add' of a constant is canonical. See foldICmpAddConstant().
// FIXME: Are there more magic icmp predicate+constant pairs we must avoid?
// Or should we just abandon this transform entirely?
if (Pred == CmpInst::ICMP_ULT && match(X, m_Add(m_Value(), m_Constant())))
return nullptr;
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 =
InstCombiner::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(IC.Builder);
IC.Builder.SetInsertPoint(&Sel);
Pred = ICmpInst::getSwappedPredicate(Pred); // Yes, swapped.
Value *NewCmp = IC.Builder.CreateICmp(Pred, X, FlippedStrictness->second,
Cmp.getName() + ".inv");
IC.replaceOperand(Sel, 0, NewCmp);
Sel.swapValues();
Sel.swapProfMetadata();
return &Sel;
}
static Instruction *foldSelectZeroOrOnes(ICmpInst *Cmp, Value *TVal,
Value *FVal,
InstCombiner::BuilderTy &Builder) {
if (!Cmp->hasOneUse())
return nullptr;
const APInt *CmpC;
if (!match(Cmp->getOperand(1), m_APIntAllowUndef(CmpC)))
return nullptr;
// (X u< 2) ? -X : -1 --> sext (X != 0)
Value *X = Cmp->getOperand(0);
if (Cmp->getPredicate() == ICmpInst::ICMP_ULT && *CmpC == 2 &&
match(TVal, m_Neg(m_Specific(X))) && match(FVal, m_AllOnes()))
return new SExtInst(Builder.CreateIsNotNull(X), TVal->getType());
// (X u> 1) ? -1 : -X --> sext (X != 0)
if (Cmp->getPredicate() == ICmpInst::ICMP_UGT && *CmpC == 1 &&
match(FVal, m_Neg(m_Specific(X))) && match(TVal, m_AllOnes()))
return new SExtInst(Builder.CreateIsNotNull(X), TVal->getType());
return nullptr;
}
static Value *foldSelectInstWithICmpConst(SelectInst &SI, ICmpInst *ICI,
InstCombiner::BuilderTy &Builder) {
const APInt *CmpC;
Value *V;
CmpInst::Predicate Pred;
if (!match(ICI, m_ICmp(Pred, m_Value(V), m_APInt(CmpC))))
return nullptr;
// Match clamp away from min/max value as a max/min operation.
Value *TVal = SI.getTrueValue();
Value *FVal = SI.getFalseValue();
if (Pred == ICmpInst::ICMP_EQ && V == FVal) {
// (V == UMIN) ? UMIN+1 : V --> umax(V, UMIN+1)
if (CmpC->isMinValue() && match(TVal, m_SpecificInt(*CmpC + 1)))
return Builder.CreateBinaryIntrinsic(Intrinsic::umax, V, TVal);
// (V == UMAX) ? UMAX-1 : V --> umin(V, UMAX-1)
if (CmpC->isMaxValue() && match(TVal, m_SpecificInt(*CmpC - 1)))
return Builder.CreateBinaryIntrinsic(Intrinsic::umin, V, TVal);
// (V == SMIN) ? SMIN+1 : V --> smax(V, SMIN+1)
if (CmpC->isMinSignedValue() && match(TVal, m_SpecificInt(*CmpC + 1)))
return Builder.CreateBinaryIntrinsic(Intrinsic::smax, V, TVal);
// (V == SMAX) ? SMAX-1 : V --> smin(V, SMAX-1)
if (CmpC->isMaxSignedValue() && match(TVal, m_SpecificInt(*CmpC - 1)))
return Builder.CreateBinaryIntrinsic(Intrinsic::smin, V, TVal);
}
BinaryOperator *BO;
const APInt *C;
CmpInst::Predicate CPred;
if (match(&SI, m_Select(m_Specific(ICI), m_APInt(C), m_BinOp(BO))))
CPred = ICI->getPredicate();
else if (match(&SI, m_Select(m_Specific(ICI), m_BinOp(BO), m_APInt(C))))
CPred = ICI->getInversePredicate();
else
return nullptr;
const APInt *BinOpC;
if (!match(BO, m_BinOp(m_Specific(V), m_APInt(BinOpC))))
return nullptr;
ConstantRange R = ConstantRange::makeExactICmpRegion(CPred, *CmpC)
.binaryOp(BO->getOpcode(), *BinOpC);
if (R == *C) {
BO->dropPoisonGeneratingFlags();
return BO;
}
return nullptr;
}
/// Visit a SelectInst that has an ICmpInst as its first operand.
Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
ICmpInst *ICI) {
if (Instruction *NewSel = foldSelectValueEquivalence(SI, *ICI))
return NewSel;
if (Instruction *NewSPF = canonicalizeSPF(SI, *ICI, *this))
return NewSPF;
if (Value *V = foldSelectInstWithICmpConst(SI, ICI, Builder))
return replaceInstUsesWith(SI, V);
if (Value *V = canonicalizeClampLike(SI, *ICI, Builder))
return replaceInstUsesWith(SI, V);
if (Instruction *NewSel =
tryToReuseConstantFromSelectInComparison(SI, *ICI, *this))
return NewSel;
if (Value *V = foldSelectICmpAnd(SI, ICI, Builder))
return replaceInstUsesWith(SI, V);
// NOTE: if we wanted to, this is where to detect integer MIN/MAX
bool Changed = false;
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) && !isa<Constant>(CmpLHS)) {
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;
}
}
// Canonicalize a signbit condition to use zero constant by swapping:
// (CmpLHS > -1) ? TV : FV --> (CmpLHS < 0) ? FV : TV
// To avoid conflicts (infinite loops) with other canonicalizations, this is
// not applied with any constant select arm.
if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes()) &&
!match(TrueVal, m_Constant()) && !match(FalseVal, m_Constant()) &&
ICI->hasOneUse()) {
InstCombiner::BuilderTy::InsertPointGuard Guard(Builder);
Builder.SetInsertPoint(&SI);
Value *IsNeg = Builder.CreateIsNeg(CmpLHS, ICI->getName());
replaceOperand(SI, 0, IsNeg);
SI.swapValues();
SI.swapProfMetadata();
return &SI;
}
// FIXME: This code is nearly duplicated in InstSimplify. Using/refactoring
// decomposeBitTestICmp() might help.
if (TrueVal->getType()->isIntOrIntVectorTy()) {
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 (Value *V = foldSelectICmpAndZeroShl(ICI, TrueVal, FalseVal, Builder))
return replaceInstUsesWith(SI, V);
if (Instruction *V = foldSelectCtlzToCttz(ICI, TrueVal, FalseVal, Builder))
return V;
if (Instruction *V = foldSelectZeroOrOnes(ICI, TrueVal, FalseVal, Builder))
return V;
if (Value *V = foldSelectICmpAndBinOp(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);
if (Value *V = foldAbsDiff(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 *InstCombinerImpl::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);
}
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;
}
/// Turn X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
/// And X - Y overflows ? 0 : X - Y -> usub_sat X, Y
/// Along with a number of patterns similar to:
/// X + Y overflows ? (X < 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
/// X - Y overflows ? (X > 0 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
static Instruction *
foldOverflowingAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) {
Value *CondVal = SI.getCondition();
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
WithOverflowInst *II;
if (!match(CondVal, m_ExtractValue<1>(m_WithOverflowInst(II))) ||
!match(FalseVal, m_ExtractValue<0>(m_Specific(II))))
return nullptr;
Value *X = II->getLHS();
Value *Y = II->getRHS();
auto IsSignedSaturateLimit = [&](Value *Limit, bool IsAdd) {
Type *Ty = Limit->getType();
ICmpInst::Predicate Pred;
Value *TrueVal, *FalseVal, *Op;
const APInt *C;
if (!match(Limit, m_Select(m_ICmp(Pred, m_Value(Op), m_APInt(C)),
m_Value(TrueVal), m_Value(FalseVal))))
return false;
auto IsZeroOrOne = [](const APInt &C) { return C.isZero() || C.isOne(); };
auto IsMinMax = [&](Value *Min, Value *Max) {
APInt MinVal = APInt::getSignedMinValue(Ty->getScalarSizeInBits());
APInt MaxVal = APInt::getSignedMaxValue(Ty->getScalarSizeInBits());
return match(Min, m_SpecificInt(MinVal)) &&
match(Max, m_SpecificInt(MaxVal));
};
if (Op != X && Op != Y)
return false;
if (IsAdd) {
// X + Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (X <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (Y <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (Y <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
if (Pred == ICmpInst::ICMP_SLT && IsZeroOrOne(*C) &&
IsMinMax(TrueVal, FalseVal))
return true;
// X + Y overflows ? (X >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (Y >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (Y >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
if (Pred == ICmpInst::ICMP_SGT && IsZeroOrOne(*C + 1) &&
IsMinMax(FalseVal, TrueVal))
return true;
} else {
// X - Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (X <s -1 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
if (Op == X && Pred == ICmpInst::ICMP_SLT && IsZeroOrOne(*C + 1) &&
IsMinMax(TrueVal, FalseVal))
return true;
// X - Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (X >s -2 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
if (Op == X && Pred == ICmpInst::ICMP_SGT && IsZeroOrOne(*C + 2) &&
IsMinMax(FalseVal, TrueVal))
return true;
// X - Y overflows ? (Y <s 0 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (Y <s 1 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
if (Op == Y && Pred == ICmpInst::ICMP_SLT && IsZeroOrOne(*C) &&
IsMinMax(FalseVal, TrueVal))
return true;
// X - Y overflows ? (Y >s 0 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (Y >s -1 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
if (Op == Y && Pred == ICmpInst::ICMP_SGT && IsZeroOrOne(*C + 1) &&
IsMinMax(TrueVal, FalseVal))
return true;
}
return false;
};
Intrinsic::ID NewIntrinsicID;
if (II->getIntrinsicID() == Intrinsic::uadd_with_overflow &&
match(TrueVal, m_AllOnes()))
// X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
NewIntrinsicID = Intrinsic::uadd_sat;
else if (II->getIntrinsicID() == Intrinsic::usub_with_overflow &&
match(TrueVal, m_Zero()))
// X - Y overflows ? 0 : X - Y -> usub_sat X, Y
NewIntrinsicID = Intrinsic::usub_sat;
else if (II->getIntrinsicID() == Intrinsic::sadd_with_overflow &&
IsSignedSaturateLimit(TrueVal, /*IsAdd=*/true))
// X + Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (X <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (X >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (Y <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (Y <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (Y >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
// X + Y overflows ? (Y >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
NewIntrinsicID = Intrinsic::sadd_sat;
else if (II->getIntrinsicID() == Intrinsic::ssub_with_overflow &&
IsSignedSaturateLimit(TrueVal, /*IsAdd=*/false))
// X - Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (X <s -1 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (X >s -2 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (Y <s 0 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (Y <s 1 ? INTMAX : INTMIN) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (Y >s 0 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
// X - Y overflows ? (Y >s -1 ? INTMIN : INTMAX) : X - Y --> ssub_sat X, Y
NewIntrinsicID = Intrinsic::ssub_sat;
else
return nullptr;
Function *F =
Intrinsic::getDeclaration(SI.getModule(), NewIntrinsicID, SI.getType());
return CallInst::Create(F, {X, Y});
}
Instruction *InstCombinerImpl::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 = getLosslessTrunc(C, SmallType, ExtOpcode);
if (TruncC && ExtInst->hasOneUse()) {
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);
}
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;
auto *CondValTy = dyn_cast<FixedVectorType>(CondVal->getType());
if (!CondValTy || !match(CondVal, m_Constant(CondC)))
return nullptr;
unsigned NumElts = CondValTy->getNumElements();
SmallVector<int, 16> Mask;
Mask.reserve(NumElts);
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(i);
} else if (Elt->isNullValue()) {
// If the select condition element is false, choose from the 2nd vector.
Mask.push_back(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(), 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,
InstCombinerImpl &IC) {
auto *Ty = dyn_cast<VectorType>(Sel.getType());
if (!Ty)
return nullptr;
// We can replace a single-use extract with constant index.
Value *Cond = Sel.getCondition();
if (!match(Cond, m_OneUse(m_ExtractElt(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).
return IC.replaceOperand(
Sel, 0, IC.Builder.CreateVectorSplat(Ty->getElementCount(), Cond));
}
/// 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 Value *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())
return SI.getFalseValue();
// 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())
return SI.getFalseValue();
return nullptr;
}
/// Try to reduce a funnel/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)
/// fshl32(a, b, c) --> (c == 0 ? a : ((b >> (32 - c)) | (a << c)))
/// --> call llvm.fshl.i32(a, b, c)
/// fshr32(a, b, c) --> (c == 0 ? b : ((a >> (32 - c)) | (b << c)))
/// --> call llvm.fshr.i32(a, b, c)
static Instruction *foldSelectFunnelShift(SelectInst &Sel,
InstCombiner::BuilderTy &Builder) {
// This must be a power-of-2 type for a bitmasking transform to be valid.
unsigned Width = Sel.getType()->getScalarSizeInBits();
if (!isPowerOf2_32(Width))
return nullptr;
BinaryOperator *Or0, *Or1;
if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_BinOp(Or0), m_BinOp(Or1)))))
return nullptr;
Value *SV0, *SV1, *SA0, *SA1;
if (!match(Or0, m_OneUse(m_LogicalShift(m_Value(SV0),
m_ZExtOrSelf(m_Value(SA0))))) ||
!match(Or1, m_OneUse(m_LogicalShift(m_Value(SV1),
m_ZExtOrSelf(m_Value(SA1))))) ||
Or0->getOpcode() == Or1->getOpcode())
return nullptr;
// Canonicalize to or(shl(SV0, SA0), lshr(SV1, SA1)).
if (Or0->getOpcode() == BinaryOperator::LShr) {
std::swap(Or0, Or1);
std::swap(SV0, SV1);
std::swap(SA0, SA1);
}
assert(Or0->getOpcode() == BinaryOperator::Shl &&
Or1->getOpcode() == BinaryOperator::LShr &&
"Illegal or(shift,shift) pair");
// 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;
// We should now have this pattern:
// select ?, TVal, (or (shl SV0, SA0), (lshr SV1, SA1))
// The false value of the select must be a funnel-shift of the true value:
// IsFShl -> TVal must be SV0 else TVal must be SV1.
bool IsFshl = (ShAmt == SA0);
Value *TVal = Sel.getTrueValue();
if ((IsFshl && TVal != SV0) || (!IsFshl && TVal != SV1))
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;
// If this is not a rotate then the select was blocking poison from the
// 'shift-by-zero' non-TVal, but a funnel shift won't - so freeze it.
if (SV0 != SV1) {
if (IsFshl && !llvm::isGuaranteedNotToBePoison(SV1))
SV1 = Builder.CreateFreeze(SV1);
else if (!IsFshl && !llvm::isGuaranteedNotToBePoison(SV0))
SV0 = Builder.CreateFreeze(SV0);
}
// This is a funnel/rotate that avoids shift-by-bitwidth UB in a suboptimal way.
// Convert to funnel shift intrinsic.
Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
Function *F = Intrinsic::getDeclaration(Sel.getModule(), IID, Sel.getType());
ShAmt = Builder.CreateZExt(ShAmt, Sel.getType());
return CallInst::Create(F, { SV0, SV1, ShAmt });
}
static Instruction *foldSelectToCopysign(SelectInst &Sel,
InstCombiner::BuilderTy &Builder) {
Value *Cond = Sel.getCondition();
Value *TVal = Sel.getTrueValue();
Value *FVal = Sel.getFalseValue();
Type *SelType = Sel.getType();
// Match select ?, TC, FC where the constants are equal but negated.
// TODO: Generalize to handle a negated variable operand?
const APFloat *TC, *FC;
if (!match(TVal, m_APFloatAllowUndef(TC)) ||
!match(FVal, m_APFloatAllowUndef(FC)) ||
!abs(*TC).bitwiseIsEqual(abs(*FC)))
return nullptr;
assert(TC != FC && "Expected equal select arms to simplify");
Value *X;
const APInt *C;
bool IsTrueIfSignSet;
ICmpInst::Predicate Pred;
if (!match(Cond, m_OneUse(m_ICmp(Pred, m_BitCast(m_Value(X)), m_APInt(C)))) ||
!InstCombiner::isSignBitCheck(Pred, *C, IsTrueIfSignSet) ||
X->getType() != SelType)
return nullptr;
// If needed, negate the value that will be the sign argument of the copysign:
// (bitcast X) < 0 ? -TC : TC --> copysign(TC, X)
// (bitcast X) < 0 ? TC : -TC --> copysign(TC, -X)
// (bitcast X) >= 0 ? -TC : TC --> copysign(TC, -X)
// (bitcast X) >= 0 ? TC : -TC --> copysign(TC, X)
// Note: FMF from the select can not be propagated to the new instructions.
if (IsTrueIfSignSet ^ TC->isNegative())
X = Builder.CreateFNeg(X);
// Canonicalize the magnitude argument as the positive constant since we do
// not care about its sign.
Value *MagArg = ConstantFP::get(SelType, abs(*TC));
Function *F = Intrinsic::getDeclaration(Sel.getModule(), Intrinsic::copysign,
Sel.getType());
return CallInst::Create(F, { MagArg, X });
}
Instruction *InstCombinerImpl::foldVectorSelect(SelectInst &Sel) {
if (!isa<VectorType>(Sel.getType()))
return nullptr;
Value *Cond = Sel.getCondition();
Value *TVal = Sel.getTrueValue();
Value *FVal = Sel.getFalseValue();
Value *C, *X, *Y;
if (match(Cond, m_VecReverse(m_Value(C)))) {
auto createSelReverse = [&](Value *C, Value *X, Value *Y) {
Value *V = Builder.CreateSelect(C, X, Y, Sel.getName(), &Sel);
if (auto *I = dyn_cast<Instruction>(V))
I->copyIRFlags(&Sel);
Module *M = Sel.getModule();
Function *F = Intrinsic::getDeclaration(
M, Intrinsic::experimental_vector_reverse, V->getType());
return CallInst::Create(F, V);
};
if (match(TVal, m_VecReverse(m_Value(X)))) {
// select rev(C), rev(X), rev(Y) --> rev(select C, X, Y)
if (match(FVal, m_VecReverse(m_Value(Y))) &&
(Cond->hasOneUse() || TVal->hasOneUse() || FVal->hasOneUse()))
return createSelReverse(C, X, Y);
// select rev(C), rev(X), FValSplat --> rev(select C, X, FValSplat)
if ((Cond->hasOneUse() || TVal->hasOneUse()) && isSplatValue(FVal))
return createSelReverse(C, X, FVal);
}
// select rev(C), TValSplat, rev(Y) --> rev(select C, TValSplat, Y)
else if (isSplatValue(TVal) && match(FVal, m_VecReverse(m_Value(Y))) &&
(Cond->hasOneUse() || FVal->hasOneUse()))
return createSelReverse(C, TVal, Y);
}
auto *VecTy = dyn_cast<FixedVectorType>(Sel.getType());
if (!VecTy)
return nullptr;
unsigned NumElts = VecTy->getNumElements();
APInt UndefElts(NumElts, 0);
APInt AllOnesEltMask(APInt::getAllOnes(NumElts));
if (Value *V = SimplifyDemandedVectorElts(&Sel, AllOnesEltMask, UndefElts)) {
if (V != &Sel)
return replaceInstUsesWith(Sel, V);
return &Sel;
}
// A select of a "select shuffle" with a common operand can be rearranged
// to select followed by "select shuffle". Because of poison, this only works
// in the case of a shuffle with no undefined mask elements.
ArrayRef<int> Mask;
if (match(TVal, m_OneUse(m_Shuffle(m_Value(X), m_Value(Y), m_Mask(Mask)))) &&
!is_contained(Mask, PoisonMaskElem) &&
cast<ShuffleVectorInst>(TVal)->isSelect()) {
if (X == FVal) {
// select Cond, (shuf_sel X, Y), X --> shuf_sel X, (select Cond, Y, X)
Value *NewSel = Builder.CreateSelect(Cond, Y, X, "sel", &Sel);
return new ShuffleVectorInst(X, NewSel, Mask);
}
if (Y == FVal) {
// select Cond, (shuf_sel X, Y), Y --> shuf_sel (select Cond, X, Y), Y
Value *NewSel = Builder.CreateSelect(Cond, X, Y, "sel", &Sel);
return new ShuffleVectorInst(NewSel, Y, Mask);
}
}
if (match(FVal, m_OneUse(m_Shuffle(m_Value(X), m_Value(Y), m_Mask(Mask)))) &&
!is_contained(Mask, PoisonMaskElem) &&
cast<ShuffleVectorInst>(FVal)->isSelect()) {
if (X == TVal) {
// select Cond, X, (shuf_sel X, Y) --> shuf_sel X, (select Cond, X, Y)
Value *NewSel = Builder.CreateSelect(Cond, X, Y, "sel", &Sel);
return new ShuffleVectorInst(X, NewSel, Mask);
}
if (Y == TVal) {
// select Cond, Y, (shuf_sel X, Y) --> shuf_sel (select Cond, Y, X), Y
Value *NewSel = Builder.CreateSelect(Cond, Y, X, "sel", &Sel);
return new ShuffleVectorInst(NewSel, Y, Mask);
}
}
return nullptr;
}
static Instruction *foldSelectToPhiImpl(SelectInst &Sel, BasicBlock *BB,
const DominatorTree &DT,
InstCombiner::BuilderTy &Builder) {
// Find the block's immediate dominator that ends with a conditional branch
// that matches select's condition (maybe inverted).
auto *IDomNode = DT[BB]->getIDom();
if (!IDomNode)
return nullptr;
BasicBlock *IDom = IDomNode->getBlock();
Value *Cond = Sel.getCondition();
Value *IfTrue, *IfFalse;
BasicBlock *TrueSucc, *FalseSucc;
if (match(IDom->getTerminator(),
m_Br(m_Specific(Cond), m_BasicBlock(TrueSucc),
m_BasicBlock(FalseSucc)))) {
IfTrue = Sel.getTrueValue();
IfFalse = Sel.getFalseValue();
} else if (match(IDom->getTerminator(),
m_Br(m_Not(m_Specific(Cond)), m_BasicBlock(TrueSucc),
m_BasicBlock(FalseSucc)))) {
IfTrue = Sel.getFalseValue();
IfFalse = Sel.getTrueValue();
} else
return nullptr;
// Make sure the branches are actually different.
if (TrueSucc == FalseSucc)
return nullptr;
// We want to replace select %cond, %a, %b with a phi that takes value %a
// for all incoming edges that are dominated by condition `%cond == true`,
// and value %b for edges dominated by condition `%cond == false`. If %a
// or %b are also phis from the same basic block, we can go further and take
// their incoming values from the corresponding blocks.
BasicBlockEdge TrueEdge(IDom, TrueSucc);
BasicBlockEdge FalseEdge(IDom, FalseSucc);
DenseMap<BasicBlock *, Value *> Inputs;
for (auto *Pred : predecessors(BB)) {
// Check implication.
BasicBlockEdge Incoming(Pred, BB);
if (DT.dominates(TrueEdge, Incoming))
Inputs[Pred] = IfTrue->DoPHITranslation(BB, Pred);
else if (DT.dominates(FalseEdge, Incoming))
Inputs[Pred] = IfFalse->DoPHITranslation(BB, Pred);
else
return nullptr;
// Check availability.
if (auto *Insn = dyn_cast<Instruction>(Inputs[Pred]))
if (!DT.dominates(Insn, Pred->getTerminator()))
return nullptr;
}
Builder.SetInsertPoint(BB, BB->begin());
auto *PN = Builder.CreatePHI(Sel.getType(), Inputs.size());
for (auto *Pred : predecessors(BB))
PN->addIncoming(Inputs[Pred], Pred);
PN->takeName(&Sel);
return PN;
}
static Instruction *foldSelectToPhi(SelectInst &Sel, const DominatorTree &DT,
InstCombiner::BuilderTy &Builder) {
// Try to replace this select with Phi in one of these blocks.
SmallSetVector<BasicBlock *, 4> CandidateBlocks;
CandidateBlocks.insert(Sel.getParent());
for (Value *V : Sel.operands())
if (auto *I = dyn_cast<Instruction>(V))
CandidateBlocks.insert(I->getParent());
for (BasicBlock *BB : CandidateBlocks)
if (auto *PN = foldSelectToPhiImpl(Sel, BB, DT, Builder))
return PN;
return nullptr;
}