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llvm-project/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
Sanjay Patel b24e2f6ef6 [InstCombine] use logical-and matcher to avoid crash 
Follow-on to:
ec0b406e16c44f1554

This should prevent crashing for example like issue #58552
by not matching a select-of-vectors-with-scalar-condition.

The test that shows a regression seems unlikely to occur
in real code.

This also picks up an optimization in the case where a real
(bitwise) logic op is used. We could already convert some
similar select ops to real logic via impliesPoison(), so
we don't see more diffs on commuted tests. Using commutative
matchers (when safe) might also handle one of the TODO tests.
2022-11-02 08:23:52 -04:00

3271 lines
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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/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/OverflowInstAnalysis.h"
#include "llvm/Analysis/ValueTracking.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, &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());
}
// 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())) {
// 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() &&
(TII->hasOneUse() || FII->hasOneUse())) {
Value *T0, *T1, *F0, *F1;
if (match(TII, m_MaxOrMin(m_Value(T0), m_Value(T1))) &&
match(FII, m_MaxOrMin(m_Value(F0), m_Value(F1)))) {
if (T0 == F0) {
Value *NewSel = Builder.CreateSelect(Cond, T1, F1, "minmaxop", &SI);
return CallInst::Create(TII->getCalledFunction(), {NewSel, T0});
}
if (T0 == F1) {
Value *NewSel = Builder.CreateSelect(Cond, T1, F0, "minmaxop", &SI);
return CallInst::Create(TII->getCalledFunction(), {NewSel, T0});
}
if (T1 == F0) {
Value *NewSel = Builder.CreateSelect(Cond, T0, F1, "minmaxop", &SI);
return CallInst::Create(TII->getCalledFunction(), {NewSel, T1});
}
if (T1 == F1) {
Value *NewSel = Builder.CreateSelect(Cond, T0, F0, "minmaxop", &SI);
return CallInst::Create(TII->getCalledFunction(), {NewSel, T1});
}
}
}
// 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, *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.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 * {
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) {
FastMathFlags FMF;
// 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.
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);
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 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);
}
/// 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);
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();
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!");
// 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;
}
/// 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_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;
}
/// 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;
}
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;
}
/// 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: The replacement could be performed recursively.
// FIXME: Support vectors.
if (match(CmpRHS, m_ImmConstant()) && !match(CmpLHS, m_ImmConstant()) &&
!Cmp.getType()->isVectorTy())
if (auto *I = dyn_cast<Instruction>(TrueVal))
if (I->hasOneUse() && isSafeToSpeculativelyExecute(I))
for (Use &U : I->operands())
if (U == CmpLHS) {
replaceUse(U, 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. Try the transform again with
// poison-generating flags temporarily dropped.
bool WasNUW = false, WasNSW = false, WasExact = false, WasInBounds = false;
if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(FalseVal)) {
WasNUW = OBO->hasNoUnsignedWrap();
WasNSW = OBO->hasNoSignedWrap();
FalseInst->setHasNoUnsignedWrap(false);
FalseInst->setHasNoSignedWrap(false);
}
if (auto *PEO = dyn_cast<PossiblyExactOperator>(FalseVal)) {
WasExact = PEO->isExact();
FalseInst->setIsExact(false);
}
if (auto *GEP = dyn_cast<GetElementPtrInst>(FalseVal)) {
WasInBounds = GEP->isInBounds();
GEP->setIsInBounds(false);
}
// 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
if (simplifyWithOpReplaced(FalseVal, CmpLHS, CmpRHS, SQ,
/* AllowRefinement */ false) == TrueVal ||
simplifyWithOpReplaced(FalseVal, CmpRHS, CmpLHS, SQ,
/* AllowRefinement */ false) == TrueVal) {
return replaceInstUsesWith(Sel, FalseVal);
}
// Restore poison-generating flags if the transform did not apply.
if (WasNUW)
FalseInst->setHasNoUnsignedWrap();
if (WasNSW)
FalseInst->setHasNoSignedWrap();
if (WasExact)
FalseInst->setIsExact();
if (WasInBounds)
cast<GetElementPtrInst>(FalseInst)->setIsInBounds();
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;
ReplacementLow = ConstantExpr::getSExt(LowC, X->getType());
ReplacementHigh = ConstantExpr::getSExt(HighC, X->getType());
}
// 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) {
const APInt *CmpC;
Value *V;
CmpInst::Predicate Pred;
if (!match(ICI, m_ICmp(Pred, m_Value(V), m_APInt(CmpC))))
return nullptr;
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))
return replaceInstUsesWith(SI, V);
if (Value *V = canonicalizeClampLike(SI, *ICI, Builder))
return replaceInstUsesWith(SI, V);
if (Instruction *NewSel =
tryToReuseConstantFromSelectInComparison(SI, *ICI, *this))
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;
}
}
// 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.
{
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 (Instruction *V = foldSelectZeroOrOnes(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 *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 = ConstantExpr::getTrunc(C, SmallType);
Constant *ExtC = ConstantExpr::getCast(ExtOpcode, TruncC, SelType);
if (ExtC == C && 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);
}
// 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;
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) {
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.
Value *Cond = Sel.getCondition();
Value *TVal = Sel.getTrueValue();
Value *FVal = Sel.getFalseValue();
Value *X, *Y;
ArrayRef<int> Mask;
if (match(TVal, m_OneUse(m_Shuffle(m_Value(X), m_Value(Y), m_Mask(Mask)))) &&
!is_contained(Mask, UndefMaskElem) &&
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, UndefMaskElem) &&
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->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;
}
static Value *foldSelectWithFrozenICmp(SelectInst &Sel, InstCombiner::BuilderTy &Builder) {
FreezeInst *FI = dyn_cast<FreezeInst>(Sel.getCondition());
if (!FI)
return nullptr;
Value *Cond = FI->getOperand(0);
Value *TrueVal = Sel.getTrueValue(), *FalseVal = Sel.getFalseValue();
// select (freeze(x == y)), x, y --> y
// select (freeze(x != y)), x, y --> x
// The freeze should be only used by this select. Otherwise, remaining uses of
// the freeze can observe a contradictory value.
// c = freeze(x == y) ; Let's assume that y = poison & x = 42; c is 0 or 1
// a = select c, x, y ;
// f(a, c) ; f(poison, 1) cannot happen, but if a is folded
// ; to y, this can happen.
CmpInst::Predicate Pred;
if (FI->hasOneUse() &&
match(Cond, m_c_ICmp(Pred, m_Specific(TrueVal), m_Specific(FalseVal))) &&
(Pred == ICmpInst::ICMP_EQ || Pred == ICmpInst::ICMP_NE)) {
return Pred == ICmpInst::ICMP_EQ ? FalseVal : TrueVal;
}
return nullptr;
}
Instruction *InstCombinerImpl::foldAndOrOfSelectUsingImpliedCond(Value *Op,
SelectInst &SI,
bool IsAnd) {
Value *CondVal = SI.getCondition();
Value *A = SI.getTrueValue();
Value *B = SI.getFalseValue();
assert(Op->getType()->isIntOrIntVectorTy(1) &&
"Op must be either i1 or vector of i1.");
Optional<bool> Res = isImpliedCondition(Op, CondVal, DL, IsAnd);
if (!Res)
return nullptr;
Value *Zero = Constant::getNullValue(A->getType());
Value *One = Constant::getAllOnesValue(A->getType());
if (*Res == true) {
if (IsAnd)
// select op, (select cond, A, B), false => select op, A, false
// and op, (select cond, A, B) => select op, A, false
// if op = true implies condval = true.
return SelectInst::Create(Op, A, Zero);
else
// select op, true, (select cond, A, B) => select op, true, A
// or op, (select cond, A, B) => select op, true, A
// if op = false implies condval = true.
return SelectInst::Create(Op, One, A);
} else {
if (IsAnd)
// select op, (select cond, A, B), false => select op, B, false
// and op, (select cond, A, B) => select op, B, false
// if op = true implies condval = false.
return SelectInst::Create(Op, B, Zero);
else
// select op, true, (select cond, A, B) => select op, true, B
// or op, (select cond, A, B) => select op, true, B
// if op = false implies condval = false.
return SelectInst::Create(Op, One, B);
}
}
// 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.
static Instruction *foldSelectWithFCmpToFabs(SelectInst &SI,
InstCombinerImpl &IC) {
Value *CondVal = SI.getCondition();
for (bool Swap : {false, true}) {
Value *TrueVal = SI.getTrueValue();
Value *X = SI.getFalseValue();
CmpInst::Predicate Pred;
if (Swap)
std::swap(TrueVal, X);
if (!match(CondVal, m_FCmp(Pred, m_Specific(X), m_AnyZeroFP())))
continue;
// fold (X <= +/-0.0) ? (0.0 - X) : X to fabs(X), when 'Swap' is false
// fold (X > +/-0.0) ? X : (0.0 - X) to fabs(X), when 'Swap' is true
if (match(TrueVal, m_FSub(m_PosZeroFP(), m_Specific(X)))) {
if (!Swap && (Pred == FCmpInst::FCMP_OLE || Pred == FCmpInst::FCMP_ULE)) {
Value *Fabs = IC.Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, &SI);
return IC.replaceInstUsesWith(SI, Fabs);
}
if (Swap && (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_UGT)) {
Value *Fabs = IC.Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, &SI);
return IC.replaceInstUsesWith(SI, Fabs);
}
}
// With nsz, when 'Swap' is false:
// fold (X < +/-0.0) ? -X : X or (X <= +/-0.0) ? -X : X to fabs(X)
// fold (X > +/-0.0) ? -X : X or (X >= +/-0.0) ? -X : X to -fabs(x)
// when 'Swap' is true:
// fold (X > +/-0.0) ? X : -X or (X >= +/-0.0) ? X : -X to fabs(X)
// fold (X < +/-0.0) ? X : -X or (X <= +/-0.0) ? X : -X to -fabs(X)
if (!match(TrueVal, m_FNeg(m_Specific(X))) || !SI.hasNoSignedZeros())
return nullptr;
if (Swap)
Pred = FCmpInst::getSwappedPredicate(Pred);
bool IsLTOrLE = Pred == FCmpInst::FCMP_OLT || Pred == FCmpInst::FCMP_OLE ||
Pred == FCmpInst::FCMP_ULT || Pred == FCmpInst::FCMP_ULE;
bool IsGTOrGE = Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_OGE ||
Pred == FCmpInst::FCMP_UGT || Pred == FCmpInst::FCMP_UGE;
if (IsLTOrLE) {
Value *Fabs = IC.Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, &SI);
return IC.replaceInstUsesWith(SI, Fabs);
}
if (IsGTOrGE) {
Value *Fabs = IC.Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, &SI);
Instruction *NewFNeg = UnaryOperator::CreateFNeg(Fabs);
NewFNeg->setFastMathFlags(SI.getFastMathFlags());
return NewFNeg;
}
}
return nullptr;
}
// Match the following IR pattern:
// %x.lowbits = and i8 %x, %lowbitmask
// %x.lowbits.are.zero = icmp eq i8 %x.lowbits, 0
// %x.biased = add i8 %x, %bias
// %x.biased.highbits = and i8 %x.biased, %highbitmask
// %x.roundedup = select i1 %x.lowbits.are.zero, i8 %x, i8 %x.biased.highbits
// Define:
// %alignment = add i8 %lowbitmask, 1
// Iff 1. an %alignment is a power-of-two (aka, %lowbitmask is a low bit mask)
// and 2. %bias is equal to either %lowbitmask or %alignment,
// and 3. %highbitmask is equal to ~%lowbitmask (aka, to -%alignment)
// then this pattern can be transformed into:
// %x.offset = add i8 %x, %lowbitmask
// %x.roundedup = and i8 %x.offset, %highbitmask
static Value *
foldRoundUpIntegerWithPow2Alignment(SelectInst &SI,
InstCombiner::BuilderTy &Builder) {
Value *Cond = SI.getCondition();
Value *X = SI.getTrueValue();
Value *XBiasedHighBits = SI.getFalseValue();
ICmpInst::Predicate Pred;
Value *XLowBits;
if (!match(Cond, m_ICmp(Pred, m_Value(XLowBits), m_ZeroInt())) ||
!ICmpInst::isEquality(Pred))
return nullptr;
if (Pred == ICmpInst::Predicate::ICMP_NE)
std::swap(X, XBiasedHighBits);
// FIXME: we could support non non-splats here.
const APInt *LowBitMaskCst;
if (!match(XLowBits, m_And(m_Specific(X), m_APIntAllowUndef(LowBitMaskCst))))
return nullptr;
// Match even if the AND and ADD are swapped.
const APInt *BiasCst, *HighBitMaskCst;
if (!match(XBiasedHighBits,
m_And(m_Add(m_Specific(X), m_APIntAllowUndef(BiasCst)),
m_APIntAllowUndef(HighBitMaskCst))) &&
!match(XBiasedHighBits,
m_Add(m_And(m_Specific(X), m_APIntAllowUndef(HighBitMaskCst)),
m_APIntAllowUndef(BiasCst))))
return nullptr;
if (!LowBitMaskCst->isMask())
return nullptr;
APInt InvertedLowBitMaskCst = ~*LowBitMaskCst;
if (InvertedLowBitMaskCst != *HighBitMaskCst)
return nullptr;
APInt AlignmentCst = *LowBitMaskCst + 1;
if (*BiasCst != AlignmentCst && *BiasCst != *LowBitMaskCst)
return nullptr;
if (!XBiasedHighBits->hasOneUse()) {
if (*BiasCst == *LowBitMaskCst)
return XBiasedHighBits;
return nullptr;
}
// FIXME: could we preserve undef's here?
Type *Ty = X->getType();
Value *XOffset = Builder.CreateAdd(X, ConstantInt::get(Ty, *LowBitMaskCst),
X->getName() + ".biased");
Value *R = Builder.CreateAnd(XOffset, ConstantInt::get(Ty, *HighBitMaskCst));
R->takeName(&SI);
return R;
}
Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) {
Value *CondVal = SI.getCondition();
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
Type *SelType = SI.getType();
// Avoid potential infinite loops by checking for non-constant condition.
// TODO: Can we assert instead by improving canonicalizeSelectToShuffle()?
// Scalar select must have simplified?
if (!SelType->isIntOrIntVectorTy(1) || isa<Constant>(CondVal) ||
TrueVal->getType() != CondVal->getType())
return nullptr;
// Folding select to and/or i1 isn't poison safe in general. impliesPoison
// checks whether folding it does not convert a well-defined value into
// poison.
if (match(TrueVal, m_One())) {
if (impliesPoison(FalseVal, CondVal)) {
// Change: A = select B, true, C --> A = or B, C
return BinaryOperator::CreateOr(CondVal, FalseVal);
}
if (auto *LHS = dyn_cast<FCmpInst>(CondVal))
if (auto *RHS = dyn_cast<FCmpInst>(FalseVal))
if (Value *V = foldLogicOfFCmps(LHS, RHS, /*IsAnd*/ false,
/*IsSelectLogical*/ true))
return replaceInstUsesWith(SI, V);
}
if (match(FalseVal, m_Zero())) {
if (impliesPoison(TrueVal, CondVal)) {
// Change: A = select B, C, false --> A = and B, C
return BinaryOperator::CreateAnd(CondVal, TrueVal);
}
if (auto *LHS = dyn_cast<FCmpInst>(CondVal))
if (auto *RHS = dyn_cast<FCmpInst>(TrueVal))
if (Value *V = foldLogicOfFCmps(LHS, RHS, /*IsAnd*/ true,
/*IsSelectLogical*/ true))
return replaceInstUsesWith(SI, V);
}
auto *One = ConstantInt::getTrue(SelType);
auto *Zero = ConstantInt::getFalse(SelType);
// We match the "full" 0 or 1 constant here to avoid a potential infinite
// loop with vectors that may have undefined/poison elements.
// select a, false, b -> select !a, b, false
if (match(TrueVal, m_Specific(Zero))) {
Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
return SelectInst::Create(NotCond, FalseVal, Zero);
}
// select a, b, true -> select !a, true, b
if (match(FalseVal, m_Specific(One))) {
Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
return SelectInst::Create(NotCond, One, TrueVal);
}
Value *A, *B;
// DeMorgan in select form: !a && !b --> !(a || b)
// select !a, !b, false --> not (select a, true, b)
if (match(&SI, m_LogicalAnd(m_Not(m_Value(A)), m_Not(m_Value(B)))) &&
(CondVal->hasOneUse() || TrueVal->hasOneUse()) &&
!match(A, m_ConstantExpr()) && !match(B, m_ConstantExpr()))
return BinaryOperator::CreateNot(Builder.CreateSelect(A, One, B));
// DeMorgan in select form: !a || !b --> !(a && b)
// select !a, true, !b --> not (select a, b, false)
if (match(&SI, m_LogicalOr(m_Not(m_Value(A)), m_Not(m_Value(B)))) &&
(CondVal->hasOneUse() || FalseVal->hasOneUse()) &&
!match(A, m_ConstantExpr()) && !match(B, m_ConstantExpr()))
return BinaryOperator::CreateNot(Builder.CreateSelect(A, B, Zero));
// select (select a, true, b), true, b -> select a, true, b
if (match(CondVal, m_Select(m_Value(A), m_One(), m_Value(B))) &&
match(TrueVal, m_One()) && match(FalseVal, m_Specific(B)))
return replaceOperand(SI, 0, A);
// select (select a, b, false), b, false -> select a, b, false
if (match(CondVal, m_Select(m_Value(A), m_Value(B), m_Zero())) &&
match(TrueVal, m_Specific(B)) && match(FalseVal, m_Zero()))
return replaceOperand(SI, 0, A);
// ~(A & B) & (A | B) --> A ^ B
if (match(&SI, m_c_LogicalAnd(m_Not(m_LogicalAnd(m_Value(A), m_Value(B))),
m_c_LogicalOr(m_Deferred(A), m_Deferred(B)))))
return BinaryOperator::CreateXor(A, B);
Value *C;
// select (~a | c), a, b -> and a, (or c, freeze(b))
if (match(CondVal, m_c_Or(m_Not(m_Specific(TrueVal)), m_Value(C))) &&
CondVal->hasOneUse()) {
FalseVal = Builder.CreateFreeze(FalseVal);
return BinaryOperator::CreateAnd(TrueVal, Builder.CreateOr(C, FalseVal));
}
// select (~c & b), a, b -> and b, (or freeze(a), c)
if (match(CondVal, m_c_And(m_Not(m_Value(C)), m_Specific(FalseVal))) &&
CondVal->hasOneUse()) {
TrueVal = Builder.CreateFreeze(TrueVal);
return BinaryOperator::CreateAnd(FalseVal, Builder.CreateOr(C, TrueVal));
}
if (match(FalseVal, m_Zero()) || match(TrueVal, m_One())) {
Use *Y = nullptr;
bool IsAnd = match(FalseVal, m_Zero()) ? true : false;
Value *Op1 = IsAnd ? TrueVal : FalseVal;
if (isCheckForZeroAndMulWithOverflow(CondVal, Op1, IsAnd, Y)) {
auto *FI = new FreezeInst(*Y, (*Y)->getName() + ".fr");
InsertNewInstBefore(FI, *cast<Instruction>(Y->getUser()));
replaceUse(*Y, FI);
return replaceInstUsesWith(SI, Op1);
}
if (auto *Op1SI = dyn_cast<SelectInst>(Op1))
if (auto *I = foldAndOrOfSelectUsingImpliedCond(CondVal, *Op1SI,
/* IsAnd */ IsAnd))
return I;
if (auto *ICmp0 = dyn_cast<ICmpInst>(CondVal))
if (auto *ICmp1 = dyn_cast<ICmpInst>(Op1))
if (auto *V = foldAndOrOfICmps(ICmp0, ICmp1, SI, IsAnd,
/* IsLogical */ true))
return replaceInstUsesWith(SI, V);
}
// select (a || b), c, false -> select a, c, false
// select c, (a || b), false -> select c, a, false
// if c implies that b is false.
if (match(CondVal, m_LogicalOr(m_Value(A), m_Value(B))) &&
match(FalseVal, m_Zero())) {
Optional<bool> Res = isImpliedCondition(TrueVal, B, DL);
if (Res && *Res == false)
return replaceOperand(SI, 0, A);
}
if (match(TrueVal, m_LogicalOr(m_Value(A), m_Value(B))) &&
match(FalseVal, m_Zero())) {
Optional<bool> Res = isImpliedCondition(CondVal, B, DL);
if (Res && *Res == false)
return replaceOperand(SI, 1, A);
}
// select c, true, (a && b) -> select c, true, a
// select (a && b), true, c -> select a, true, c
// if c = false implies that b = true
if (match(TrueVal, m_One()) &&
match(FalseVal, m_LogicalAnd(m_Value(A), m_Value(B)))) {
Optional<bool> Res = isImpliedCondition(CondVal, B, DL, false);
if (Res && *Res == true)
return replaceOperand(SI, 2, A);
}
if (match(CondVal, m_LogicalAnd(m_Value(A), m_Value(B))) &&
match(TrueVal, m_One())) {
Optional<bool> Res = isImpliedCondition(FalseVal, B, DL, false);
if (Res && *Res == true)
return replaceOperand(SI, 0, A);
}
if (match(TrueVal, m_One())) {
Value *C;
// (C && A) || (!C && B) --> sel C, A, B
// (A && C) || (!C && B) --> sel C, A, B
// (C && A) || (B && !C) --> sel C, A, B
// (A && C) || (B && !C) --> sel C, A, B (may require freeze)
if (match(FalseVal, m_c_LogicalAnd(m_Not(m_Value(C)), m_Value(B))) &&
match(CondVal, m_c_LogicalAnd(m_Specific(C), m_Value(A)))) {
auto *SelCond = dyn_cast<SelectInst>(CondVal);
auto *SelFVal = dyn_cast<SelectInst>(FalseVal);
bool MayNeedFreeze = SelCond && SelFVal &&
match(SelFVal->getTrueValue(),
m_Not(m_Specific(SelCond->getTrueValue())));
if (MayNeedFreeze)
C = Builder.CreateFreeze(C);
return SelectInst::Create(C, A, B);
}
// (!C && A) || (C && B) --> sel C, B, A
// (A && !C) || (C && B) --> sel C, B, A
// (!C && A) || (B && C) --> sel C, B, A
// (A && !C) || (B && C) --> sel C, B, A (may require freeze)
if (match(CondVal, m_c_LogicalAnd(m_Not(m_Value(C)), m_Value(A))) &&
match(FalseVal, m_c_LogicalAnd(m_Specific(C), m_Value(B)))) {
auto *SelCond = dyn_cast<SelectInst>(CondVal);
auto *SelFVal = dyn_cast<SelectInst>(FalseVal);
bool MayNeedFreeze = SelCond && SelFVal &&
match(SelCond->getTrueValue(),
m_Not(m_Specific(SelFVal->getTrueValue())));
if (MayNeedFreeze)
C = Builder.CreateFreeze(C);
return SelectInst::Create(C, B, A);
}
}
return nullptr;
}
Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
Value *CondVal = SI.getCondition();
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
Type *SelType = SI.getType();
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, *this))
return I;
// If the type of select is not an integer type or if the condition and
// the selection type are not both scalar nor both vector types, there is no
// point in attempting to match these patterns.
Type *CondType = CondVal->getType();
if (!isa<Constant>(CondVal) && SelType->isIntOrIntVectorTy() &&
CondType->isVectorTy() == SelType->isVectorTy()) {
if (Value *S = simplifyWithOpReplaced(TrueVal, CondVal,
ConstantInt::getTrue(CondType), SQ,
/* AllowRefinement */ true))
return replaceOperand(SI, 1, S);
if (Value *S = simplifyWithOpReplaced(FalseVal, CondVal,
ConstantInt::getFalse(CondType), SQ,
/* AllowRefinement */ true))
return replaceOperand(SI, 2, S);
// Handle patterns involving sext/zext + not explicitly,
// as simplifyWithOpReplaced() only looks past one instruction.
Value *NotCond;
// select a, sext(!a), b -> select !a, b, 0
// select a, zext(!a), b -> select !a, b, 0
if (match(TrueVal, m_ZExtOrSExt(m_CombineAnd(m_Value(NotCond),
m_Not(m_Specific(CondVal))))))
return SelectInst::Create(NotCond, FalseVal,
Constant::getNullValue(SelType));
// select a, b, zext(!a) -> select !a, 1, b
if (match(FalseVal, m_ZExt(m_CombineAnd(m_Value(NotCond),
m_Not(m_Specific(CondVal))))))
return SelectInst::Create(NotCond, ConstantInt::get(SelType, 1), TrueVal);
// select a, b, sext(!a) -> select !a, -1, b
if (match(FalseVal, m_SExt(m_CombineAnd(m_Value(NotCond),
m_Not(m_Specific(CondVal))))))
return SelectInst::Create(NotCond, Constant::getAllOnesValue(SelType),
TrueVal);
}
if (Instruction *R = foldSelectOfBools(SI))
return R;
// 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.
//
// Do not handle i1 TrueVal and FalseVal otherwise would result in
// zext/sext i1 to i1.
if (SelType->isIntOrIntVectorTy() && !SelType->isIntOrIntVectorTy(1) &&
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);
}
}
if (auto *FCmp = dyn_cast<FCmpInst>(CondVal)) {
Value *Cmp0 = FCmp->getOperand(0), *Cmp1 = FCmp->getOperand(1);
// Are we selecting a value based on a comparison of the two values?
if ((Cmp0 == TrueVal && Cmp1 == FalseVal) ||
(Cmp0 == FalseVal && Cmp1 == TrueVal)) {
// Canonicalize to use ordered comparisons by swapping the select
// operands.
//
// e.g.
// (X ugt Y) ? X : Y -> (X ole Y) ? Y : X
if (FCmp->hasOneUse() && FCmpInst::isUnordered(FCmp->getPredicate())) {
FCmpInst::Predicate InvPred = FCmp->getInversePredicate();
IRBuilder<>::FastMathFlagGuard FMFG(Builder);
// FIXME: The FMF should propagate from the select, not the fcmp.
Builder.setFastMathFlags(FCmp->getFastMathFlags());
Value *NewCond = Builder.CreateFCmp(InvPred, Cmp0, Cmp1,
FCmp->getName() + ".inv");
Value *NewSel = Builder.CreateSelect(NewCond, FalseVal, TrueVal);
return replaceInstUsesWith(SI, NewSel);
}
// NOTE: if we wanted to, this is where to detect MIN/MAX
}
}
// Fold selecting to fabs.
if (Instruction *Fabs = foldSelectWithFCmpToFabs(SI, *this))
return 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;
if (Instruction *Add = foldOverflowingAddSubSelect(SI, Builder))
return Add;
if (Instruction *Or = foldSetClearBits(SI, Builder))
return Or;
if (Instruction *Mul = foldSelectZeroOrMul(SI, *this))
return Mul;
// 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;
// Fold (select C, (gep Ptr, Idx), Ptr) -> (gep Ptr, (select C, Idx, 0))
// Fold (select C, Ptr, (gep Ptr, Idx)) -> (gep Ptr, (select C, 0, Idx))
auto SelectGepWithBase = [&](GetElementPtrInst *Gep, Value *Base,
bool Swap) -> GetElementPtrInst * {
Value *Ptr = Gep->getPointerOperand();
if (Gep->getNumOperands() != 2 || Gep->getPointerOperand() != Base ||
!Gep->hasOneUse())
return nullptr;
Value *Idx = Gep->getOperand(1);
if (isa<VectorType>(CondVal->getType()) && !isa<VectorType>(Idx->getType()))
return nullptr;
Type *ElementType = Gep->getResultElementType();
Value *NewT = Idx;
Value *NewF = Constant::getNullValue(Idx->getType());
if (Swap)
std::swap(NewT, NewF);
Value *NewSI =
Builder.CreateSelect(CondVal, NewT, NewF, SI.getName() + ".idx", &SI);
return GetElementPtrInst::Create(ElementType, Ptr, {NewSI});
};
if (auto *TrueGep = dyn_cast<GetElementPtrInst>(TrueVal))
if (auto *NewGep = SelectGepWithBase(TrueGep, FalseVal, false))
return NewGep;
if (auto *FalseGep = dyn_cast<GetElementPtrInst>(FalseVal))
if (auto *NewGep = SelectGepWithBase(FalseGep, TrueVal, true))
return NewGep;
// 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;
}
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);
}
}
}
// 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;
return replaceOperand(SI, 1, TrueSI->getTrueValue());
}
// 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.CreateLogicalAnd(CondVal, TrueSI->getCondition());
replaceOperand(SI, 0, And);
replaceOperand(SI, 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;
return replaceOperand(SI, 2, FalseSI->getFalseValue());
}
// select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b)
if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) {
Value *Or = Builder.CreateLogicalOr(CondVal, FalseSI->getCondition());
replaceOperand(SI, 0, Or);
replaceOperand(SI, 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) {
replaceOperand(*TrueBO, 0, TrueBOSI->getTrueValue());
Worklist.push(TrueBO);
return &SI;
}
}
if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(1))) {
if (TrueBOSI->getCondition() == CondVal) {
replaceOperand(*TrueBO, 1, TrueBOSI->getTrueValue());
Worklist.push(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) {
replaceOperand(*FalseBO, 0, FalseBOSI->getFalseValue());
Worklist.push(FalseBO);
return &SI;
}
}
if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(1))) {
if (FalseBOSI->getCondition() == CondVal) {
replaceOperand(*FalseBO, 1, FalseBOSI->getFalseValue());
Worklist.push(FalseBO);
return &SI;
}
}
}
Value *NotCond;
if (match(CondVal, m_Not(m_Value(NotCond))) &&
!InstCombiner::shouldAvoidAbsorbingNotIntoSelect(SI)) {
replaceOperand(SI, 0, NotCond);
SI.swapValues();
SI.swapProfMetadata();
return &SI;
}
if (Instruction *I = foldVectorSelect(SI))
return I;
// 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.isOne())
return replaceInstUsesWith(SI, TrueVal);
if (Known.Zero.isOne())
return replaceInstUsesWith(SI, FalseVal);
}
if (Instruction *BitCastSel = foldSelectCmpBitcasts(SI, Builder))
return BitCastSel;
// Simplify selects that test the returned flag of cmpxchg instructions.
if (Value *V = foldSelectCmpXchg(SI))
return replaceInstUsesWith(SI, V);
if (Instruction *Select = foldSelectBinOpIdentity(SI, TLI, *this))
return Select;
if (Instruction *Funnel = foldSelectFunnelShift(SI, Builder))
return Funnel;
if (Instruction *Copysign = foldSelectToCopysign(SI, Builder))
return Copysign;
if (Instruction *PN = foldSelectToPhi(SI, DT, Builder))
return replaceInstUsesWith(SI, PN);
if (Value *Fr = foldSelectWithFrozenICmp(SI, Builder))
return replaceInstUsesWith(SI, Fr);
if (Value *V = foldRoundUpIntegerWithPow2Alignment(SI, Builder))
return replaceInstUsesWith(SI, V);
// select(mask, mload(,,mask,0), 0) -> mload(,,mask,0)
// Load inst is intentionally not checked for hasOneUse()
if (match(FalseVal, m_Zero()) &&
(match(TrueVal, m_MaskedLoad(m_Value(), m_Value(), m_Specific(CondVal),
m_CombineOr(m_Undef(), m_Zero()))) ||
match(TrueVal, m_MaskedGather(m_Value(), m_Value(), m_Specific(CondVal),
m_CombineOr(m_Undef(), m_Zero()))))) {
auto *MaskedInst = cast<IntrinsicInst>(TrueVal);
if (isa<UndefValue>(MaskedInst->getArgOperand(3)))
MaskedInst->setArgOperand(3, FalseVal /* Zero */);
return replaceInstUsesWith(SI, MaskedInst);
}
Value *Mask;
if (match(TrueVal, m_Zero()) &&
(match(FalseVal, m_MaskedLoad(m_Value(), m_Value(), m_Value(Mask),
m_CombineOr(m_Undef(), m_Zero()))) ||
match(FalseVal, m_MaskedGather(m_Value(), m_Value(), m_Value(Mask),
m_CombineOr(m_Undef(), m_Zero())))) &&
(CondVal->getType() == Mask->getType())) {
// We can remove the select by ensuring the load zeros all lanes the
// select would have. We determine this by proving there is no overlap
// between the load and select masks.
// (i.e (load_mask & select_mask) == 0 == no overlap)
bool CanMergeSelectIntoLoad = false;
if (Value *V = simplifyAndInst(CondVal, Mask, SQ.getWithInstruction(&SI)))
CanMergeSelectIntoLoad = match(V, m_Zero());
if (CanMergeSelectIntoLoad) {
auto *MaskedInst = cast<IntrinsicInst>(FalseVal);
if (isa<UndefValue>(MaskedInst->getArgOperand(3)))
MaskedInst->setArgOperand(3, TrueVal /* Zero */);
return replaceInstUsesWith(SI, MaskedInst);
}
}
return nullptr;
}
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