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227698a9eb
llvm-mirror/lib/Transforms/InstCombine/InstCombineSelect.cpp
Neil Henning 227698a9eb [IRBuilder] Fixup CreateIntrinsic to allow specifying Types to Mangle. 
The IRBuilder CreateIntrinsic method wouldn't allow you to specify the
types that you wanted the intrinsic to be mangled with. To fix this
I've:

- Added an ArrayRef<Type *> member to both CreateIntrinsic overloads.
- Used that array to pass into the Intrinsic::getDeclaration call.
- Added a CreateUnaryIntrinsic to replace the most common use of
  CreateIntrinsic where the type was auto-deduced from operand 0.
- Added a bunch more unit tests to test Create*Intrinsic calls that
  weren't being tested (including the FMF flag that wasn't checked).

This was suggested as part of the AMDGPU specific atomic optimizer
review (https://reviews.llvm.org/D51969).

Differential Revision: https://reviews.llvm.org/D52087

llvm-svn: 343962
2018-10-08 10:32:33 +00:00

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//===- InstCombineSelect.cpp ----------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the visitSelect function.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CmpInstAnalysis.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Transforms/InstCombine/InstCombineWorklist.h"
#include <cassert>
#include <utility>
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "instcombine"
static Value *createMinMax(InstCombiner::BuilderTy &Builder,
SelectPatternFlavor SPF, Value *A, Value *B) {
CmpInst::Predicate Pred = getMinMaxPred(SPF);
assert(CmpInst::isIntPredicate(Pred) && "Expected integer predicate");
return Builder.CreateSelect(Builder.CreateICmp(Pred, A, B), A, B);
}
/// Replace a select operand based on an equality comparison with the identity
/// constant of a binop.
static Instruction *foldSelectBinOpIdentity(SelectInst &Sel,
const TargetLibraryInfo &TLI) {
// The select condition must be an equality compare with a constant operand.
Value *X;
Constant *C;
CmpInst::Predicate Pred;
if (!match(Sel.getCondition(), m_Cmp(Pred, m_Value(X), m_Constant(C))))
return nullptr;
bool IsEq;
if (ICmpInst::isEquality(Pred))
IsEq = Pred == ICmpInst::ICMP_EQ;
else if (Pred == FCmpInst::FCMP_OEQ)
IsEq = true;
else if (Pred == FCmpInst::FCMP_UNE)
IsEq = false;
else
return nullptr;
// A select operand must be a binop, and the compare constant must be the
// identity constant for that binop.
BinaryOperator *BO;
if (!match(Sel.getOperand(IsEq ? 1 : 2), m_BinOp(BO)) ||
ConstantExpr::getBinOpIdentity(BO->getOpcode(), BO->getType(), true) != C)
return nullptr;
// Last, match the compare variable operand with a binop operand.
Value *Y;
if (!BO->isCommutative() && !match(BO, m_BinOp(m_Value(Y), m_Specific(X))))
return nullptr;
if (!match(BO, m_c_BinOp(m_Value(Y), m_Specific(X))))
return nullptr;
// +0.0 compares equal to -0.0, and so it does not behave as required for this
// transform. Bail out if we can not exclude that possibility.
if (isa<FPMathOperator>(BO))
if (!BO->hasNoSignedZeros() && !CannotBeNegativeZero(Y, &TLI))
return nullptr;
// BO = binop Y, X
// S = { select (cmp eq X, C), BO, ? } or { select (cmp ne X, C), ?, BO }
// =>
// S = { select (cmp eq X, C), Y, ? } or { select (cmp ne X, C), ?, Y }
Sel.setOperand(IsEq ? 1 : 2, Y);
return &Sel;
}
/// This folds:
/// select (icmp eq (and X, C1)), TC, FC
/// iff C1 is a power 2 and the difference between TC and FC is a power-of-2.
/// To something like:
/// (shr (and (X, C1)), (log2(C1) - log2(TC-FC))) + FC
/// Or:
/// (shl (and (X, C1)), (log2(TC-FC) - log2(C1))) + FC
/// With some variations depending if FC is larger than TC, or the shift
/// isn't needed, or the bit widths don't match.
static Value *foldSelectICmpAnd(SelectInst &Sel, ICmpInst *Cmp,
InstCombiner::BuilderTy &Builder) {
const APInt *SelTC, *SelFC;
if (!match(Sel.getTrueValue(), m_APInt(SelTC)) ||
!match(Sel.getFalseValue(), m_APInt(SelFC)))
return nullptr;
// If this is a vector select, we need a vector compare.
Type *SelType = Sel.getType();
if (SelType->isVectorTy() != Cmp->getType()->isVectorTy())
return nullptr;
Value *V;
APInt AndMask;
bool CreateAnd = false;
ICmpInst::Predicate Pred = Cmp->getPredicate();
if (ICmpInst::isEquality(Pred)) {
if (!match(Cmp->getOperand(1), m_Zero()))
return nullptr;
V = Cmp->getOperand(0);
const APInt *AndRHS;
if (!match(V, m_And(m_Value(), m_Power2(AndRHS))))
return nullptr;
AndMask = *AndRHS;
} else if (decomposeBitTestICmp(Cmp->getOperand(0), Cmp->getOperand(1),
Pred, V, AndMask)) {
assert(ICmpInst::isEquality(Pred) && "Not equality test?");
if (!AndMask.isPowerOf2())
return nullptr;
CreateAnd = true;
} else {
return nullptr;
}
// In general, when both constants are non-zero, we would need an offset to
// replace the select. This would require more instructions than we started
// with. But there's one special-case that we handle here because it can
// simplify/reduce the instructions.
APInt TC = *SelTC;
APInt FC = *SelFC;
if (!TC.isNullValue() && !FC.isNullValue()) {
// If the select constants differ by exactly one bit and that's the same
// bit that is masked and checked by the select condition, the select can
// be replaced by bitwise logic to set/clear one bit of the constant result.
if (TC.getBitWidth() != AndMask.getBitWidth() || (TC ^ FC) != AndMask)
return nullptr;
if (CreateAnd) {
// If we have to create an 'and', then we must kill the cmp to not
// increase the instruction count.
if (!Cmp->hasOneUse())
return nullptr;
V = Builder.CreateAnd(V, ConstantInt::get(SelType, AndMask));
}
bool ExtraBitInTC = TC.ugt(FC);
if (Pred == ICmpInst::ICMP_EQ) {
// If the masked bit in V is clear, clear or set the bit in the result:
// (V & AndMaskC) == 0 ? TC : FC --> (V & AndMaskC) ^ TC
// (V & AndMaskC) == 0 ? TC : FC --> (V & AndMaskC) | TC
Constant *C = ConstantInt::get(SelType, TC);
return ExtraBitInTC ? Builder.CreateXor(V, C) : Builder.CreateOr(V, C);
}
if (Pred == ICmpInst::ICMP_NE) {
// If the masked bit in V is set, set or clear the bit in the result:
// (V & AndMaskC) != 0 ? TC : FC --> (V & AndMaskC) | FC
// (V & AndMaskC) != 0 ? TC : FC --> (V & AndMaskC) ^ FC
Constant *C = ConstantInt::get(SelType, FC);
return ExtraBitInTC ? Builder.CreateOr(V, C) : Builder.CreateXor(V, C);
}
llvm_unreachable("Only expecting equality predicates");
}
// Make sure one of the select arms is a power-of-2.
if (!TC.isPowerOf2() && !FC.isPowerOf2())
return nullptr;
// Determine which shift is needed to transform result of the 'and' into the
// desired result.
const APInt &ValC = !TC.isNullValue() ? TC : FC;
unsigned ValZeros = ValC.logBase2();
unsigned AndZeros = AndMask.logBase2();
// Insert the 'and' instruction on the input to the truncate.
if (CreateAnd)
V = Builder.CreateAnd(V, ConstantInt::get(V->getType(), AndMask));
// If types don't match, we can still convert the select by introducing a zext
// or a trunc of the 'and'.
if (ValZeros > AndZeros) {
V = Builder.CreateZExtOrTrunc(V, SelType);
V = Builder.CreateShl(V, ValZeros - AndZeros);
} else if (ValZeros < AndZeros) {
V = Builder.CreateLShr(V, AndZeros - ValZeros);
V = Builder.CreateZExtOrTrunc(V, SelType);
} else {
V = Builder.CreateZExtOrTrunc(V, SelType);
}
// Okay, now we know that everything is set up, we just don't know whether we
// have a icmp_ne or icmp_eq and whether the true or false val is the zero.
bool ShouldNotVal = !TC.isNullValue();
ShouldNotVal ^= Pred == ICmpInst::ICMP_NE;
if (ShouldNotVal)
V = Builder.CreateXor(V, ValC);
return V;
}
/// We want to turn code that looks like this:
/// %C = or %A, %B
/// %D = select %cond, %C, %A
/// into:
/// %C = select %cond, %B, 0
/// %D = or %A, %C
///
/// Assuming that the specified instruction is an operand to the select, return
/// a bitmask indicating which operands of this instruction are foldable if they
/// equal the other incoming value of the select.
static unsigned getSelectFoldableOperands(BinaryOperator *I) {
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
return 3; // Can fold through either operand.
case Instruction::Sub: // Can only fold on the amount subtracted.
case Instruction::Shl: // Can only fold on the shift amount.
case Instruction::LShr:
case Instruction::AShr:
return 1;
default:
return 0; // Cannot fold
}
}
/// For the same transformation as the previous function, return the identity
/// constant that goes into the select.
static APInt getSelectFoldableConstant(BinaryOperator *I) {
switch (I->getOpcode()) {
default: llvm_unreachable("This cannot happen!");
case Instruction::Add:
case Instruction::Sub:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
return APInt::getNullValue(I->getType()->getScalarSizeInBits());
case Instruction::And:
return APInt::getAllOnesValue(I->getType()->getScalarSizeInBits());
case Instruction::Mul:
return APInt(I->getType()->getScalarSizeInBits(), 1);
}
}
/// We have (select c, TI, FI), and we know that TI and FI have the same opcode.
Instruction *InstCombiner::foldSelectOpOp(SelectInst &SI, Instruction *TI,
Instruction *FI) {
// Don't break up min/max patterns. The hasOneUse checks below prevent that
// for most cases, but vector min/max with bitcasts can be transformed. If the
// one-use restrictions are eased for other patterns, we still don't want to
// obfuscate min/max.
if ((match(&SI, m_SMin(m_Value(), m_Value())) ||
match(&SI, m_SMax(m_Value(), m_Value())) ||
match(&SI, m_UMin(m_Value(), m_Value())) ||
match(&SI, m_UMax(m_Value(), m_Value()))))
return nullptr;
// If this is a cast from the same type, merge.
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).
Type *CondTy = SI.getCondition()->getType();
if (CondTy->isVectorTy()) {
if (!FIOpndTy->isVectorTy())
return nullptr;
if (CondTy->getVectorNumElements() != FIOpndTy->getVectorNumElements())
return nullptr;
// TODO: If the backend knew how to deal with casts better, we could
// remove this limitation. For now, there's too much potential to create
// worse codegen by promoting the select ahead of size-altering casts
// (PR28160).
//
// Note that ValueTracking's matchSelectPattern() looks through casts
// without checking 'hasOneUse' when it matches min/max patterns, so this
// transform may end up happening anyway.
if (TI->getOpcode() != Instruction::BitCast &&
(!TI->hasOneUse() || !FI->hasOneUse()))
return nullptr;
} else if (!TI->hasOneUse() || !FI->hasOneUse()) {
// TODO: The one-use restrictions for a scalar select could be eased if
// the fold of a select in visitLoadInst() was enhanced to match a pattern
// that includes a cast.
return nullptr;
}
// Fold this by inserting a select from the input values.
Value *NewSI =
Builder.CreateSelect(SI.getCondition(), TI->getOperand(0),
FI->getOperand(0), SI.getName() + ".v", &SI);
return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
TI->getType());
}
// Only handle binary operators (including two-operand getelementptr) with
// one-use here. As with the cast case above, it may be possible to relax the
// one-use constraint, but that needs be examined carefully since it may not
// reduce the total number of instructions.
if (TI->getNumOperands() != 2 || FI->getNumOperands() != 2 ||
(!isa<BinaryOperator>(TI) && !isa<GetElementPtrInst>(TI)) ||
!TI->hasOneUse() || !FI->hasOneUse())
return nullptr;
// Figure out if the operations have any operands in common.
Value *MatchOp, *OtherOpT, *OtherOpF;
bool MatchIsOpZero;
if (TI->getOperand(0) == FI->getOperand(0)) {
MatchOp = TI->getOperand(0);
OtherOpT = TI->getOperand(1);
OtherOpF = FI->getOperand(1);
MatchIsOpZero = true;
} else if (TI->getOperand(1) == FI->getOperand(1)) {
MatchOp = TI->getOperand(1);
OtherOpT = TI->getOperand(0);
OtherOpF = FI->getOperand(0);
MatchIsOpZero = false;
} else if (!TI->isCommutative()) {
return nullptr;
} else if (TI->getOperand(0) == FI->getOperand(1)) {
MatchOp = TI->getOperand(0);
OtherOpT = TI->getOperand(1);
OtherOpF = FI->getOperand(0);
MatchIsOpZero = true;
} else if (TI->getOperand(1) == FI->getOperand(0)) {
MatchOp = TI->getOperand(1);
OtherOpT = TI->getOperand(0);
OtherOpF = FI->getOperand(1);
MatchIsOpZero = true;
} else {
return nullptr;
}
// If the select condition is a vector, the operands of the original select's
// operands also must be vectors. This may not be the case for getelementptr
// for example.
if (SI.getCondition()->getType()->isVectorTy() &&
(!OtherOpT->getType()->isVectorTy() ||
!OtherOpF->getType()->isVectorTy()))
return nullptr;
// If we reach here, they do have operations in common.
Value *NewSI = Builder.CreateSelect(SI.getCondition(), OtherOpT, OtherOpF,
SI.getName() + ".v", &SI);
Value *Op0 = MatchIsOpZero ? MatchOp : NewSI;
Value *Op1 = MatchIsOpZero ? NewSI : MatchOp;
if (auto *BO = dyn_cast<BinaryOperator>(TI)) {
BinaryOperator *NewBO = BinaryOperator::Create(BO->getOpcode(), Op0, Op1);
NewBO->copyIRFlags(TI);
NewBO->andIRFlags(FI);
return NewBO;
}
if (auto *TGEP = dyn_cast<GetElementPtrInst>(TI)) {
auto *FGEP = cast<GetElementPtrInst>(FI);
Type *ElementType = TGEP->getResultElementType();
return TGEP->isInBounds() && FGEP->isInBounds()
? GetElementPtrInst::CreateInBounds(ElementType, Op0, {Op1})
: GetElementPtrInst::Create(ElementType, Op0, {Op1});
}
llvm_unreachable("Expected BinaryOperator or GEP");
return nullptr;
}
static bool isSelect01(const APInt &C1I, const APInt &C2I) {
if (!C1I.isNullValue() && !C2I.isNullValue()) // One side must be zero.
return false;
return C1I.isOneValue() || C1I.isAllOnesValue() ||
C2I.isOneValue() || C2I.isAllOnesValue();
}
/// Try to fold the select into one of the operands to allow further
/// optimization.
Instruction *InstCombiner::foldSelectIntoOp(SelectInst &SI, Value *TrueVal,
Value *FalseVal) {
// See the comment above GetSelectFoldableOperands for a description of the
// transformation we are doing here.
if (auto *TVI = dyn_cast<BinaryOperator>(TrueVal)) {
if (TVI->hasOneUse() && !isa<Constant>(FalseVal)) {
if (unsigned SFO = getSelectFoldableOperands(TVI)) {
unsigned OpToFold = 0;
if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
OpToFold = 1;
} else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
OpToFold = 2;
}
if (OpToFold) {
APInt CI = getSelectFoldableConstant(TVI);
Value *OOp = TVI->getOperand(2-OpToFold);
// Avoid creating select between 2 constants unless it's selecting
// between 0, 1 and -1.
const APInt *OOpC;
bool OOpIsAPInt = match(OOp, m_APInt(OOpC));
if (!isa<Constant>(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) {
Value *C = ConstantInt::get(OOp->getType(), CI);
Value *NewSel = Builder.CreateSelect(SI.getCondition(), OOp, C);
NewSel->takeName(TVI);
BinaryOperator *BO = BinaryOperator::Create(TVI->getOpcode(),
FalseVal, NewSel);
BO->copyIRFlags(TVI);
return BO;
}
}
}
}
}
if (auto *FVI = dyn_cast<BinaryOperator>(FalseVal)) {
if (FVI->hasOneUse() && !isa<Constant>(TrueVal)) {
if (unsigned SFO = getSelectFoldableOperands(FVI)) {
unsigned OpToFold = 0;
if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
OpToFold = 1;
} else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
OpToFold = 2;
}
if (OpToFold) {
APInt CI = getSelectFoldableConstant(FVI);
Value *OOp = FVI->getOperand(2-OpToFold);
// Avoid creating select between 2 constants unless it's selecting
// between 0, 1 and -1.
const APInt *OOpC;
bool OOpIsAPInt = match(OOp, m_APInt(OOpC));
if (!isa<Constant>(OOp) || (OOpIsAPInt && isSelect01(CI, *OOpC))) {
Value *C = ConstantInt::get(OOp->getType(), CI);
Value *NewSel = Builder.CreateSelect(SI.getCondition(), C, OOp);
NewSel->takeName(FVI);
BinaryOperator *BO = BinaryOperator::Create(FVI->getOpcode(),
TrueVal, NewSel);
BO->copyIRFlags(FVI);
return BO;
}
}
}
}
}
return nullptr;
}
/// We want to turn:
/// (select (icmp eq (and X, Y), 0), (and (lshr X, Z), 1), 1)
/// into:
/// zext (icmp ne i32 (and X, (or Y, (shl 1, Z))), 0)
/// Note:
/// Z may be 0 if lshr is missing.
/// Worst-case scenario is that we will replace 5 instructions with 5 different
/// instructions, but we got rid of select.
static Instruction *foldSelectICmpAndAnd(Type *SelType, const ICmpInst *Cmp,
Value *TVal, Value *FVal,
InstCombiner::BuilderTy &Builder) {
if (!(Cmp->hasOneUse() && Cmp->getOperand(0)->hasOneUse() &&
Cmp->getPredicate() == ICmpInst::ICMP_EQ &&
match(Cmp->getOperand(1), m_Zero()) && match(FVal, m_One())))
return nullptr;
// The TrueVal has general form of: and %B, 1
Value *B;
if (!match(TVal, m_OneUse(m_And(m_Value(B), m_One()))))
return nullptr;
// Where %B may be optionally shifted: lshr %X, %Z.
Value *X, *Z;
const bool HasShift = match(B, m_OneUse(m_LShr(m_Value(X), m_Value(Z))));
if (!HasShift)
X = B;
Value *Y;
if (!match(Cmp->getOperand(0), m_c_And(m_Specific(X), m_Value(Y))))
return nullptr;
// ((X & Y) == 0) ? ((X >> Z) & 1) : 1 --> (X & (Y | (1 << Z))) != 0
// ((X & Y) == 0) ? (X & 1) : 1 --> (X & (Y | 1)) != 0
Constant *One = ConstantInt::get(SelType, 1);
Value *MaskB = HasShift ? Builder.CreateShl(One, Z) : One;
Value *FullMask = Builder.CreateOr(Y, MaskB);
Value *MaskedX = Builder.CreateAnd(X, FullMask);
Value *ICmpNeZero = Builder.CreateIsNotNull(MaskedX);
return new ZExtInst(ICmpNeZero, SelType);
}
/// We want to turn:
/// (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
/// into:
/// (or (shl (and X, C1), C3), Y)
/// iff:
/// C1 and C2 are both powers of 2
/// where:
/// C3 = Log(C2) - Log(C1)
///
/// This transform handles cases where:
/// 1. The icmp predicate is inverted
/// 2. The select operands are reversed
/// 3. The magnitude of C2 and C1 are flipped
static Value *foldSelectICmpAndOr(const ICmpInst *IC, Value *TrueVal,
Value *FalseVal,
InstCombiner::BuilderTy &Builder) {
// Only handle integer compares. Also, if this is a vector select, we need a
// vector compare.
if (!TrueVal->getType()->isIntOrIntVectorTy() ||
TrueVal->getType()->isVectorTy() != IC->getType()->isVectorTy())
return nullptr;
Value *CmpLHS = IC->getOperand(0);
Value *CmpRHS = IC->getOperand(1);
Value *V;
unsigned C1Log;
bool IsEqualZero;
bool NeedAnd = false;
if (IC->isEquality()) {
if (!match(CmpRHS, m_Zero()))
return nullptr;
const APInt *C1;
if (!match(CmpLHS, m_And(m_Value(), m_Power2(C1))))
return nullptr;
V = CmpLHS;
C1Log = C1->logBase2();
IsEqualZero = IC->getPredicate() == ICmpInst::ICMP_EQ;
} else if (IC->getPredicate() == ICmpInst::ICMP_SLT ||
IC->getPredicate() == ICmpInst::ICMP_SGT) {
// We also need to recognize (icmp slt (trunc (X)), 0) and
// (icmp sgt (trunc (X)), -1).
IsEqualZero = IC->getPredicate() == ICmpInst::ICMP_SGT;
if ((IsEqualZero && !match(CmpRHS, m_AllOnes())) ||
(!IsEqualZero && !match(CmpRHS, m_Zero())))
return nullptr;
if (!match(CmpLHS, m_OneUse(m_Trunc(m_Value(V)))))
return nullptr;
C1Log = CmpLHS->getType()->getScalarSizeInBits() - 1;
NeedAnd = true;
} else {
return nullptr;
}
const APInt *C2;
bool OrOnTrueVal = false;
bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
if (!OrOnFalseVal)
OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
if (!OrOnFalseVal && !OrOnTrueVal)
return nullptr;
Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
unsigned C2Log = C2->logBase2();
bool NeedXor = (!IsEqualZero && OrOnFalseVal) || (IsEqualZero && OrOnTrueVal);
bool NeedShift = C1Log != C2Log;
bool NeedZExtTrunc = Y->getType()->getScalarSizeInBits() !=
V->getType()->getScalarSizeInBits();
// Make sure we don't create more instructions than we save.
Value *Or = OrOnFalseVal ? FalseVal : TrueVal;
if ((NeedShift + NeedXor + NeedZExtTrunc) >
(IC->hasOneUse() + Or->hasOneUse()))
return nullptr;
if (NeedAnd) {
// Insert the AND instruction on the input to the truncate.
APInt C1 = APInt::getOneBitSet(V->getType()->getScalarSizeInBits(), C1Log);
V = Builder.CreateAnd(V, ConstantInt::get(V->getType(), C1));
}
if (C2Log > C1Log) {
V = Builder.CreateZExtOrTrunc(V, Y->getType());
V = Builder.CreateShl(V, C2Log - C1Log);
} else if (C1Log > C2Log) {
V = Builder.CreateLShr(V, C1Log - C2Log);
V = Builder.CreateZExtOrTrunc(V, Y->getType());
} else
V = Builder.CreateZExtOrTrunc(V, Y->getType());
if (NeedXor)
V = Builder.CreateXor(V, *C2);
return Builder.CreateOr(V, Y);
}
/// Transform patterns such as: (a > b) ? a - b : 0
/// into: ((a > b) ? a : b) - b)
/// This produces a canonical max pattern that is more easily recognized by the
/// backend and converted into saturated subtraction instructions if those
/// exist.
/// There are 8 commuted/swapped variants of this pattern.
/// TODO: Also support a - UMIN(a,b) patterns.
static Value *canonicalizeSaturatedSubtract(const ICmpInst *ICI,
const Value *TrueVal,
const Value *FalseVal,
InstCombiner::BuilderTy &Builder) {
ICmpInst::Predicate Pred = ICI->getPredicate();
if (!ICmpInst::isUnsigned(Pred))
return nullptr;
// (b > a) ? 0 : a - b -> (b <= a) ? a - b : 0
if (match(TrueVal, m_Zero())) {
Pred = ICmpInst::getInversePredicate(Pred);
std::swap(TrueVal, FalseVal);
}
if (!match(FalseVal, m_Zero()))
return nullptr;
Value *A = ICI->getOperand(0);
Value *B = ICI->getOperand(1);
if (Pred == ICmpInst::ICMP_ULE || Pred == ICmpInst::ICMP_ULT) {
// (b < a) ? a - b : 0 -> (a > b) ? a - b : 0
std::swap(A, B);
Pred = ICmpInst::getSwappedPredicate(Pred);
}
assert((Pred == ICmpInst::ICMP_UGE || Pred == ICmpInst::ICMP_UGT) &&
"Unexpected isUnsigned predicate!");
// Account for swapped form of subtraction: ((a > b) ? b - a : 0).
bool IsNegative = false;
if (match(TrueVal, m_Sub(m_Specific(B), m_Specific(A))))
IsNegative = true;
else if (!match(TrueVal, m_Sub(m_Specific(A), m_Specific(B))))
return nullptr;
// If sub is used anywhere else, we wouldn't be able to eliminate it
// afterwards.
if (!TrueVal->hasOneUse())
return nullptr;
// All checks passed, convert to canonical unsigned saturated subtraction
// form: sub(max()).
// (a > b) ? a - b : 0 -> ((a > b) ? a : b) - b)
Value *Max = Builder.CreateSelect(Builder.CreateICmp(Pred, A, B), A, B);
return IsNegative ? Builder.CreateSub(B, Max) : Builder.CreateSub(Max, B);
}
/// Attempt to fold a cttz/ctlz followed by a icmp plus select into a single
/// call to cttz/ctlz with flag 'is_zero_undef' cleared.
///
/// For example, we can fold the following code sequence:
/// \code
/// %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
/// %1 = icmp ne i32 %x, 0
/// %2 = select i1 %1, i32 %0, i32 32
/// \code
///
/// into:
/// %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
InstCombiner::BuilderTy &Builder) {
ICmpInst::Predicate Pred = ICI->getPredicate();
Value *CmpLHS = ICI->getOperand(0);
Value *CmpRHS = ICI->getOperand(1);
// Check if the condition value compares a value for equality against zero.
if (!ICI->isEquality() || !match(CmpRHS, m_Zero()))
return nullptr;
Value *Count = FalseVal;
Value *ValueOnZero = TrueVal;
if (Pred == ICmpInst::ICMP_NE)
std::swap(Count, ValueOnZero);
// Skip zero extend/truncate.
Value *V = nullptr;
if (match(Count, m_ZExt(m_Value(V))) ||
match(Count, m_Trunc(m_Value(V))))
Count = V;
// Check 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)))
return nullptr;
// Check that 'Count' is a call to intrinsic cttz/ctlz. Also check that the
// input to the cttz/ctlz is used as LHS for the compare instruction.
if (match(Count, m_Intrinsic<Intrinsic::cttz>(m_Specific(CmpLHS))) ||
match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Specific(CmpLHS)))) {
IntrinsicInst *II = cast<IntrinsicInst>(Count);
// Explicitly clear the 'undef_on_zero' flag.
IntrinsicInst *NewI = cast<IntrinsicInst>(II->clone());
NewI->setArgOperand(1, ConstantInt::getFalse(NewI->getContext()));
Builder.Insert(NewI);
return Builder.CreateZExtOrTrunc(NewI, ValueOnZero->getType());
}
return nullptr;
}
/// Return true if we find and adjust an icmp+select pattern where the compare
/// is with a constant that can be incremented or decremented to match the
/// minimum or maximum idiom.
static bool adjustMinMax(SelectInst &Sel, ICmpInst &Cmp) {
ICmpInst::Predicate Pred = Cmp.getPredicate();
Value *CmpLHS = Cmp.getOperand(0);
Value *CmpRHS = Cmp.getOperand(1);
Value *TrueVal = Sel.getTrueValue();
Value *FalseVal = Sel.getFalseValue();
// We may move or edit the compare, so make sure the select is the only user.
const APInt *CmpC;
if (!Cmp.hasOneUse() || !match(CmpRHS, m_APInt(CmpC)))
return false;
// These transforms only work for selects of integers or vector selects of
// integer vectors.
Type *SelTy = Sel.getType();
auto *SelEltTy = dyn_cast<IntegerType>(SelTy->getScalarType());
if (!SelEltTy || SelTy->isVectorTy() != Cmp.getType()->isVectorTy())
return false;
Constant *AdjustedRHS;
if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
AdjustedRHS = ConstantInt::get(CmpRHS->getType(), *CmpC + 1);
else if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
AdjustedRHS = ConstantInt::get(CmpRHS->getType(), *CmpC - 1);
else
return false;
// X > C ? X : C+1 --> X < C+1 ? C+1 : X
// X < C ? X : C-1 --> X > C-1 ? C-1 : X
if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
(CmpLHS == FalseVal && AdjustedRHS == TrueVal)) {
; // Nothing to do here. Values match without any sign/zero extension.
}
// Types do not match. Instead of calculating this with mixed types, promote
// all to the larger type. This enables scalar evolution to analyze this
// expression.
else if (CmpRHS->getType()->getScalarSizeInBits() < SelEltTy->getBitWidth()) {
Constant *SextRHS = ConstantExpr::getSExt(AdjustedRHS, SelTy);
// X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
// X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
// X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
// X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) && SextRHS == FalseVal) {
CmpLHS = TrueVal;
AdjustedRHS = SextRHS;
} else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
SextRHS == TrueVal) {
CmpLHS = FalseVal;
AdjustedRHS = SextRHS;
} else if (Cmp.isUnsigned()) {
Constant *ZextRHS = ConstantExpr::getZExt(AdjustedRHS, SelTy);
// X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
// X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
// zext + signed compare cannot be changed:
// 0xff <s 0x00, but 0x00ff >s 0x0000
if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) && ZextRHS == FalseVal) {
CmpLHS = TrueVal;
AdjustedRHS = ZextRHS;
} else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
ZextRHS == TrueVal) {
CmpLHS = FalseVal;
AdjustedRHS = ZextRHS;
} else {
return false;
}
} else {
return false;
}
} else {
return false;
}
Pred = ICmpInst::getSwappedPredicate(Pred);
CmpRHS = AdjustedRHS;
std::swap(FalseVal, TrueVal);
Cmp.setPredicate(Pred);
Cmp.setOperand(0, CmpLHS);
Cmp.setOperand(1, CmpRHS);
Sel.setOperand(1, TrueVal);
Sel.setOperand(2, FalseVal);
Sel.swapProfMetadata();
// Move the compare instruction right before the select instruction. Otherwise
// the sext/zext value may be defined after the compare instruction uses it.
Cmp.moveBefore(&Sel);
return true;
}
/// If this is an integer min/max (icmp + select) with a constant operand,
/// create the canonical icmp for the min/max operation and canonicalize the
/// constant to the 'false' operand of the select:
/// select (icmp Pred X, C1), C2, X --> select (icmp Pred' X, C2), X, C2
/// Note: if C1 != C2, this will change the icmp constant to the existing
/// constant operand of the select.
static Instruction *
canonicalizeMinMaxWithConstant(SelectInst &Sel, ICmpInst &Cmp,
InstCombiner::BuilderTy &Builder) {
if (!Cmp.hasOneUse() || !isa<Constant>(Cmp.getOperand(1)))
return nullptr;
// Canonicalize the compare predicate based on whether we have min or max.
Value *LHS, *RHS;
SelectPatternResult SPR = matchSelectPattern(&Sel, LHS, RHS);
if (!SelectPatternResult::isMinOrMax(SPR.Flavor))
return nullptr;
// Is this already canonical?
ICmpInst::Predicate CanonicalPred = getMinMaxPred(SPR.Flavor);
if (Cmp.getOperand(0) == LHS && Cmp.getOperand(1) == RHS &&
Cmp.getPredicate() == CanonicalPred)
return nullptr;
// Create the canonical compare and plug it into the select.
Sel.setCondition(Builder.CreateICmp(CanonicalPred, LHS, RHS));
// If the select operands did not change, we're done.
if (Sel.getTrueValue() == LHS && Sel.getFalseValue() == RHS)
return &Sel;
// If we are swapping the select operands, swap the metadata too.
assert(Sel.getTrueValue() == RHS && Sel.getFalseValue() == LHS &&
"Unexpected results from matchSelectPattern");
Sel.setTrueValue(LHS);
Sel.setFalseValue(RHS);
Sel.swapProfMetadata();
return &Sel;
}
/// There are many select variants for each of ABS/NABS.
/// In matchSelectPattern(), there are different compare constants, compare
/// predicates/operands and select operands.
/// In isKnownNegation(), there are different formats of negated operands.
/// Canonicalize all these variants to 1 pattern.
/// This makes CSE more likely.
static Instruction *canonicalizeAbsNabs(SelectInst &Sel, ICmpInst &Cmp,
InstCombiner::BuilderTy &Builder) {
if (!Cmp.hasOneUse() || !isa<Constant>(Cmp.getOperand(1)))
return nullptr;
// Choose a sign-bit check for the compare (likely simpler for codegen).
// ABS: (X <s 0) ? -X : X
// NABS: (X <s 0) ? X : -X
Value *LHS, *RHS;
SelectPatternFlavor SPF = matchSelectPattern(&Sel, LHS, RHS).Flavor;
if (SPF != SelectPatternFlavor::SPF_ABS &&
SPF != SelectPatternFlavor::SPF_NABS)
return nullptr;
Value *TVal = Sel.getTrueValue();
Value *FVal = Sel.getFalseValue();
assert(isKnownNegation(TVal, FVal) &&
"Unexpected result from matchSelectPattern");
// The compare may use the negated abs()/nabs() operand, or it may use
// negation in non-canonical form such as: sub A, B.
bool CmpUsesNegatedOp = match(Cmp.getOperand(0), m_Neg(m_Specific(TVal))) ||
match(Cmp.getOperand(0), m_Neg(m_Specific(FVal)));
bool CmpCanonicalized = !CmpUsesNegatedOp &&
match(Cmp.getOperand(1), m_ZeroInt()) &&
Cmp.getPredicate() == ICmpInst::ICMP_SLT;
bool RHSCanonicalized = match(RHS, m_Neg(m_Specific(LHS)));
// Is this already canonical?
if (CmpCanonicalized && RHSCanonicalized)
return nullptr;
// If RHS is used by other instructions except compare and select, don't
// canonicalize it to not increase the instruction count.
if (!(RHS->hasOneUse() || (RHS->hasNUses(2) && CmpUsesNegatedOp)))
return nullptr;
// Create the canonical compare: icmp slt LHS 0.
if (!CmpCanonicalized) {
Cmp.setPredicate(ICmpInst::ICMP_SLT);
Cmp.setOperand(1, ConstantInt::getNullValue(Cmp.getOperand(0)->getType()));
if (CmpUsesNegatedOp)
Cmp.setOperand(0, LHS);
}
// Create the canonical RHS: RHS = sub (0, LHS).
if (!RHSCanonicalized) {
assert(RHS->hasOneUse() && "RHS use number is not right");
RHS = Builder.CreateNeg(LHS);
if (TVal == LHS) {
Sel.setFalseValue(RHS);
FVal = RHS;
} else {
Sel.setTrueValue(RHS);
TVal = RHS;
}
}
// If the select operands do not change, we're done.
if (SPF == SelectPatternFlavor::SPF_NABS) {
if (TVal == LHS)
return &Sel;
assert(FVal == LHS && "Unexpected results from matchSelectPattern");
} else {
if (FVal == LHS)
return &Sel;
assert(TVal == LHS && "Unexpected results from matchSelectPattern");
}
// We are swapping the select operands, so swap the metadata too.
Sel.setTrueValue(FVal);
Sel.setFalseValue(TVal);
Sel.swapProfMetadata();
return &Sel;
}
/// Visit a SelectInst that has an ICmpInst as its first operand.
Instruction *InstCombiner::foldSelectInstWithICmp(SelectInst &SI,
ICmpInst *ICI) {
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
if (Instruction *NewSel = canonicalizeMinMaxWithConstant(SI, *ICI, Builder))
return NewSel;
if (Instruction *NewAbs = canonicalizeAbsNabs(SI, *ICI, Builder))
return NewAbs;
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
ICmpInst::Predicate Pred = ICI->getPredicate();
Value *CmpLHS = ICI->getOperand(0);
Value *CmpRHS = ICI->getOperand(1);
if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS)) {
if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
// Transform (X == C) ? X : Y -> (X == C) ? C : Y
SI.setOperand(1, CmpRHS);
Changed = true;
} else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
// Transform (X != C) ? Y : X -> (X != C) ? Y : C
SI.setOperand(2, CmpRHS);
Changed = true;
}
}
// FIXME: This code is nearly duplicated in InstSimplify. Using/refactoring
// decomposeBitTestICmp() might help.
{
unsigned BitWidth =
DL.getTypeSizeInBits(TrueVal->getType()->getScalarType());
APInt MinSignedValue = APInt::getSignedMinValue(BitWidth);
Value *X;
const APInt *Y, *C;
bool TrueWhenUnset;
bool IsBitTest = false;
if (ICmpInst::isEquality(Pred) &&
match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) &&
match(CmpRHS, m_Zero())) {
IsBitTest = true;
TrueWhenUnset = Pred == ICmpInst::ICMP_EQ;
} else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
X = CmpLHS;
Y = &MinSignedValue;
IsBitTest = true;
TrueWhenUnset = false;
} else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
X = CmpLHS;
Y = &MinSignedValue;
IsBitTest = true;
TrueWhenUnset = true;
}
if (IsBitTest) {
Value *V = nullptr;
// (X & Y) == 0 ? X : X ^ Y --> X & ~Y
if (TrueWhenUnset && TrueVal == X &&
match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
V = Builder.CreateAnd(X, ~(*Y));
// (X & Y) != 0 ? X ^ Y : X --> X & ~Y
else if (!TrueWhenUnset && FalseVal == X &&
match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
V = Builder.CreateAnd(X, ~(*Y));
// (X & Y) == 0 ? X ^ Y : X --> X | Y
else if (TrueWhenUnset && FalseVal == X &&
match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
V = Builder.CreateOr(X, *Y);
// (X & Y) != 0 ? X : X ^ Y --> X | Y
else if (!TrueWhenUnset && TrueVal == X &&
match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
V = Builder.CreateOr(X, *Y);
if (V)
return replaceInstUsesWith(SI, V);
}
}
if (Instruction *V =
foldSelectICmpAndAnd(SI.getType(), ICI, TrueVal, FalseVal, Builder))
return V;
if (Value *V = foldSelectICmpAndOr(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);
return Changed ? &SI : nullptr;
}
/// SI is a select whose condition is a PHI node (but the two may be in
/// different blocks). See if the true/false values (V) are live in all of the
/// predecessor blocks of the PHI. For example, cases like this can't be mapped:
///
/// X = phi [ C1, BB1], [C2, BB2]
/// Y = add
/// Z = select X, Y, 0
///
/// because Y is not live in BB1/BB2.
static bool canSelectOperandBeMappingIntoPredBlock(const Value *V,
const SelectInst &SI) {
// If the value is a non-instruction value like a constant or argument, it
// can always be mapped.
const Instruction *I = dyn_cast<Instruction>(V);
if (!I) return true;
// If V is a PHI node defined in the same block as the condition PHI, we can
// map the arguments.
const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
if (const PHINode *VP = dyn_cast<PHINode>(I))
if (VP->getParent() == CondPHI->getParent())
return true;
// Otherwise, if the PHI and select are defined in the same block and if V is
// defined in a different block, then we can transform it.
if (SI.getParent() == CondPHI->getParent() &&
I->getParent() != CondPHI->getParent())
return true;
// Otherwise we have a 'hard' case and we can't tell without doing more
// detailed dominator based analysis, punt.
return false;
}
/// We have an SPF (e.g. a min or max) of an SPF of the form:
/// SPF2(SPF1(A, B), C)
Instruction *InstCombiner::foldSPFofSPF(Instruction *Inner,
SelectPatternFlavor SPF1,
Value *A, Value *B,
Instruction &Outer,
SelectPatternFlavor SPF2, Value *C) {
if (Outer.getType() != Inner->getType())
return nullptr;
if (C == A || C == B) {
// MAX(MAX(A, B), B) -> MAX(A, B)
// MIN(MIN(a, b), a) -> MIN(a, b)
// TODO: This could be done in instsimplify.
if (SPF1 == SPF2 && SelectPatternResult::isMinOrMax(SPF1))
return replaceInstUsesWith(Outer, Inner);
// MAX(MIN(a, b), a) -> a
// MIN(MAX(a, b), a) -> a
// TODO: This could be done in instsimplify.
if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
(SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
(SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
(SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
return replaceInstUsesWith(Outer, C);
}
if (SPF1 == SPF2) {
const APInt *CB, *CC;
if (match(B, m_APInt(CB)) && match(C, m_APInt(CC))) {
// MIN(MIN(A, 23), 97) -> MIN(A, 23)
// MAX(MAX(A, 97), 23) -> MAX(A, 97)
// TODO: This could be done in instsimplify.
if ((SPF1 == SPF_UMIN && CB->ule(*CC)) ||
(SPF1 == SPF_SMIN && CB->sle(*CC)) ||
(SPF1 == SPF_UMAX && CB->uge(*CC)) ||
(SPF1 == SPF_SMAX && CB->sge(*CC)))
return replaceInstUsesWith(Outer, Inner);
// MIN(MIN(A, 97), 23) -> MIN(A, 23)
// MAX(MAX(A, 23), 97) -> MAX(A, 97)
if ((SPF1 == SPF_UMIN && CB->ugt(*CC)) ||
(SPF1 == SPF_SMIN && CB->sgt(*CC)) ||
(SPF1 == SPF_UMAX && CB->ult(*CC)) ||
(SPF1 == SPF_SMAX && CB->slt(*CC))) {
Outer.replaceUsesOfWith(Inner, A);
return &Outer;
}
}
}
// ABS(ABS(X)) -> ABS(X)
// NABS(NABS(X)) -> NABS(X)
// TODO: This could be done in instsimplify.
if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
return replaceInstUsesWith(Outer, Inner);
}
// ABS(NABS(X)) -> ABS(X)
// NABS(ABS(X)) -> NABS(X)
if ((SPF1 == SPF_ABS && SPF2 == SPF_NABS) ||
(SPF1 == SPF_NABS && SPF2 == SPF_ABS)) {
SelectInst *SI = cast<SelectInst>(Inner);
Value *NewSI =
Builder.CreateSelect(SI->getCondition(), SI->getFalseValue(),
SI->getTrueValue(), SI->getName(), SI);
return replaceInstUsesWith(Outer, NewSI);
}
auto IsFreeOrProfitableToInvert =
[&](Value *V, Value *&NotV, bool &ElidesXor) {
if (match(V, m_Not(m_Value(NotV)))) {
// If V has at most 2 uses then we can get rid of the xor operation
// entirely.
ElidesXor |= !V->hasNUsesOrMore(3);
return true;
}
if (IsFreeToInvert(V, !V->hasNUsesOrMore(3))) {
NotV = nullptr;
return true;
}
return false;
};
Value *NotA, *NotB, *NotC;
bool ElidesXor = false;
// MIN(MIN(~A, ~B), ~C) == ~MAX(MAX(A, B), C)
// MIN(MAX(~A, ~B), ~C) == ~MAX(MIN(A, B), C)
// MAX(MIN(~A, ~B), ~C) == ~MIN(MAX(A, B), C)
// MAX(MAX(~A, ~B), ~C) == ~MIN(MIN(A, B), C)
//
// This transform is performance neutral if we can elide at least one xor from
// the set of three operands, since we'll be tacking on an xor at the very
// end.
if (SelectPatternResult::isMinOrMax(SPF1) &&
SelectPatternResult::isMinOrMax(SPF2) &&
IsFreeOrProfitableToInvert(A, NotA, ElidesXor) &&
IsFreeOrProfitableToInvert(B, NotB, ElidesXor) &&
IsFreeOrProfitableToInvert(C, NotC, ElidesXor) && ElidesXor) {
if (!NotA)
NotA = Builder.CreateNot(A);
if (!NotB)
NotB = Builder.CreateNot(B);
if (!NotC)
NotC = Builder.CreateNot(C);
Value *NewInner = createMinMax(Builder, getInverseMinMaxFlavor(SPF1), NotA,
NotB);
Value *NewOuter = Builder.CreateNot(
createMinMax(Builder, getInverseMinMaxFlavor(SPF2), NewInner, NotC));
return replaceInstUsesWith(Outer, NewOuter);
}
return nullptr;
}
/// Turn select C, (X + Y), (X - Y) --> (X + (select C, Y, (-Y))).
/// This is even legal for FP.
static Instruction *foldAddSubSelect(SelectInst &SI,
InstCombiner::BuilderTy &Builder) {
Value *CondVal = SI.getCondition();
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
auto *TI = dyn_cast<Instruction>(TrueVal);
auto *FI = dyn_cast<Instruction>(FalseVal);
if (!TI || !FI || !TI->hasOneUse() || !FI->hasOneUse())
return nullptr;
Instruction *AddOp = nullptr, *SubOp = nullptr;
if ((TI->getOpcode() == Instruction::Sub &&
FI->getOpcode() == Instruction::Add) ||
(TI->getOpcode() == Instruction::FSub &&
FI->getOpcode() == Instruction::FAdd)) {
AddOp = FI;
SubOp = TI;
} else if ((FI->getOpcode() == Instruction::Sub &&
TI->getOpcode() == Instruction::Add) ||
(FI->getOpcode() == Instruction::FSub &&
TI->getOpcode() == Instruction::FAdd)) {
AddOp = TI;
SubOp = FI;
}
if (AddOp) {
Value *OtherAddOp = nullptr;
if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
OtherAddOp = AddOp->getOperand(1);
} else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
OtherAddOp = AddOp->getOperand(0);
}
if (OtherAddOp) {
// So at this point we know we have (Y -> OtherAddOp):
// select C, (add X, Y), (sub X, Z)
Value *NegVal; // Compute -Z
if (SI.getType()->isFPOrFPVectorTy()) {
NegVal = Builder.CreateFNeg(SubOp->getOperand(1));
if (Instruction *NegInst = dyn_cast<Instruction>(NegVal)) {
FastMathFlags Flags = AddOp->getFastMathFlags();
Flags &= SubOp->getFastMathFlags();
NegInst->setFastMathFlags(Flags);
}
} else {
NegVal = Builder.CreateNeg(SubOp->getOperand(1));
}
Value *NewTrueOp = OtherAddOp;
Value *NewFalseOp = NegVal;
if (AddOp != TI)
std::swap(NewTrueOp, NewFalseOp);
Value *NewSel = Builder.CreateSelect(CondVal, NewTrueOp, NewFalseOp,
SI.getName() + ".p", &SI);
if (SI.getType()->isFPOrFPVectorTy()) {
Instruction *RI =
BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
FastMathFlags Flags = AddOp->getFastMathFlags();
Flags &= SubOp->getFastMathFlags();
RI->setFastMathFlags(Flags);
return RI;
} else
return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
}
}
return nullptr;
}
Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) {
Constant *C;
if (!match(Sel.getTrueValue(), m_Constant(C)) &&
!match(Sel.getFalseValue(), m_Constant(C)))
return nullptr;
Instruction *ExtInst;
if (!match(Sel.getTrueValue(), m_Instruction(ExtInst)) &&
!match(Sel.getFalseValue(), m_Instruction(ExtInst)))
return nullptr;
auto ExtOpcode = ExtInst->getOpcode();
if (ExtOpcode != Instruction::ZExt && ExtOpcode != Instruction::SExt)
return nullptr;
// If we are extending from a boolean type or if we can create a select that
// has the same size operands as its condition, try to narrow the select.
Value *X = ExtInst->getOperand(0);
Type *SmallType = X->getType();
Value *Cond = Sel.getCondition();
auto *Cmp = dyn_cast<CmpInst>(Cond);
if (!SmallType->isIntOrIntVectorTy(1) &&
(!Cmp || Cmp->getOperand(0)->getType() != SmallType))
return nullptr;
// If the constant is the same after truncation to the smaller type and
// extension to the original type, we can narrow the select.
Type *SelType = Sel.getType();
Constant *TruncC = ConstantExpr::getTrunc(C, SmallType);
Constant *ExtC = ConstantExpr::getCast(ExtOpcode, TruncC, SelType);
if (ExtC == C) {
Value *TruncCVal = cast<Value>(TruncC);
if (ExtInst == Sel.getFalseValue())
std::swap(X, TruncCVal);
// select Cond, (ext X), C --> ext(select Cond, X, C')
// select Cond, C, (ext X) --> ext(select Cond, C', X)
Value *NewSel = Builder.CreateSelect(Cond, X, TruncCVal, "narrow", &Sel);
return CastInst::Create(Instruction::CastOps(ExtOpcode), NewSel, SelType);
}
// If one arm of the select is the extend of the condition, replace that arm
// with the extension of the appropriate known bool value.
if (Cond == X) {
if (ExtInst == Sel.getTrueValue()) {
// select X, (sext X), C --> select X, -1, C
// select X, (zext X), C --> select X, 1, C
Constant *One = ConstantInt::getTrue(SmallType);
Constant *AllOnesOrOne = ConstantExpr::getCast(ExtOpcode, One, SelType);
return SelectInst::Create(Cond, AllOnesOrOne, C, "", nullptr, &Sel);
} else {
// select X, C, (sext X) --> select X, C, 0
// select X, C, (zext X) --> select X, C, 0
Constant *Zero = ConstantInt::getNullValue(SelType);
return SelectInst::Create(Cond, C, Zero, "", nullptr, &Sel);
}
}
return nullptr;
}
/// Try to transform a vector select with a constant condition vector into a
/// shuffle for easier combining with other shuffles and insert/extract.
static Instruction *canonicalizeSelectToShuffle(SelectInst &SI) {
Value *CondVal = SI.getCondition();
Constant *CondC;
if (!CondVal->getType()->isVectorTy() || !match(CondVal, m_Constant(CondC)))
return nullptr;
unsigned NumElts = CondVal->getType()->getVectorNumElements();
SmallVector<Constant *, 16> Mask;
Mask.reserve(NumElts);
Type *Int32Ty = Type::getInt32Ty(CondVal->getContext());
for (unsigned i = 0; i != NumElts; ++i) {
Constant *Elt = CondC->getAggregateElement(i);
if (!Elt)
return nullptr;
if (Elt->isOneValue()) {
// If the select condition element is true, choose from the 1st vector.
Mask.push_back(ConstantInt::get(Int32Ty, i));
} else if (Elt->isNullValue()) {
// If the select condition element is false, choose from the 2nd vector.
Mask.push_back(ConstantInt::get(Int32Ty, i + NumElts));
} else if (isa<UndefValue>(Elt)) {
// Undef in a select condition (choose one of the operands) does not mean
// the same thing as undef in a shuffle mask (any value is acceptable), so
// give up.
return nullptr;
} else {
// Bail out on a constant expression.
return nullptr;
}
}
return new ShuffleVectorInst(SI.getTrueValue(), SI.getFalseValue(),
ConstantVector::get(Mask));
}
/// Reuse bitcasted operands between a compare and select:
/// select (cmp (bitcast C), (bitcast D)), (bitcast' C), (bitcast' D) -->
/// bitcast (select (cmp (bitcast C), (bitcast D)), (bitcast C), (bitcast D))
static Instruction *foldSelectCmpBitcasts(SelectInst &Sel,
InstCombiner::BuilderTy &Builder) {
Value *Cond = Sel.getCondition();
Value *TVal = Sel.getTrueValue();
Value *FVal = Sel.getFalseValue();
CmpInst::Predicate Pred;
Value *A, *B;
if (!match(Cond, m_Cmp(Pred, m_Value(A), m_Value(B))))
return nullptr;
// The select condition is a compare instruction. If the select's true/false
// values are already the same as the compare operands, there's nothing to do.
if (TVal == A || TVal == B || FVal == A || FVal == B)
return nullptr;
Value *C, *D;
if (!match(A, m_BitCast(m_Value(C))) || !match(B, m_BitCast(m_Value(D))))
return nullptr;
// select (cmp (bitcast C), (bitcast D)), (bitcast TSrc), (bitcast FSrc)
Value *TSrc, *FSrc;
if (!match(TVal, m_BitCast(m_Value(TSrc))) ||
!match(FVal, m_BitCast(m_Value(FSrc))))
return nullptr;
// If the select true/false values are *different bitcasts* of the same source
// operands, make the select operands the same as the compare operands and
// cast the result. This is the canonical select form for min/max.
Value *NewSel;
if (TSrc == C && FSrc == D) {
// select (cmp (bitcast C), (bitcast D)), (bitcast' C), (bitcast' D) -->
// bitcast (select (cmp A, B), A, B)
NewSel = Builder.CreateSelect(Cond, A, B, "", &Sel);
} else if (TSrc == D && FSrc == C) {
// select (cmp (bitcast C), (bitcast D)), (bitcast' D), (bitcast' C) -->
// bitcast (select (cmp A, B), B, A)
NewSel = Builder.CreateSelect(Cond, B, A, "", &Sel);
} else {
return nullptr;
}
return CastInst::CreateBitOrPointerCast(NewSel, Sel.getType());
}
/// Try to eliminate select instructions that test the returned flag of cmpxchg
/// instructions.
///
/// If a select instruction tests the returned flag of a cmpxchg instruction and
/// selects between the returned value of the cmpxchg instruction its compare
/// operand, the result of the select will always be equal to its false value.
/// For example:
///
/// %0 = cmpxchg i64* %ptr, i64 %compare, i64 %new_value seq_cst seq_cst
/// %1 = extractvalue { i64, i1 } %0, 1
/// %2 = extractvalue { i64, i1 } %0, 0
/// %3 = select i1 %1, i64 %compare, i64 %2
/// ret i64 %3
///
/// The returned value of the cmpxchg instruction (%2) is the original value
/// located at %ptr prior to any update. If the cmpxchg operation succeeds, %2
/// must have been equal to %compare. Thus, the result of the select is always
/// equal to %2, and the code can be simplified to:
///
/// %0 = cmpxchg i64* %ptr, i64 %compare, i64 %new_value seq_cst seq_cst
/// %1 = extractvalue { i64, i1 } %0, 0
/// ret i64 %1
///
static Instruction *foldSelectCmpXchg(SelectInst &SI) {
// A helper that determines if V is an extractvalue instruction whose
// aggregate operand is a cmpxchg instruction and whose single index is equal
// to I. If such conditions are true, the helper returns the cmpxchg
// instruction; otherwise, a nullptr is returned.
auto isExtractFromCmpXchg = [](Value *V, unsigned I) -> AtomicCmpXchgInst * {
auto *Extract = dyn_cast<ExtractValueInst>(V);
if (!Extract)
return nullptr;
if (Extract->getIndices()[0] != I)
return nullptr;
return dyn_cast<AtomicCmpXchgInst>(Extract->getAggregateOperand());
};
// If the select has a single user, and this user is a select instruction that
// we can simplify, skip the cmpxchg simplification for now.
if (SI.hasOneUse())
if (auto *Select = dyn_cast<SelectInst>(SI.user_back()))
if (Select->getCondition() == SI.getCondition())
if (Select->getFalseValue() == SI.getTrueValue() ||
Select->getTrueValue() == SI.getFalseValue())
return nullptr;
// Ensure the select condition is the returned flag of a cmpxchg instruction.
auto *CmpXchg = isExtractFromCmpXchg(SI.getCondition(), 1);
if (!CmpXchg)
return nullptr;
// Check the true value case: The true value of the select is the returned
// value of the same cmpxchg used by the condition, and the false value is the
// cmpxchg instruction's compare operand.
if (auto *X = isExtractFromCmpXchg(SI.getTrueValue(), 0))
if (X == CmpXchg && X->getCompareOperand() == SI.getFalseValue()) {
SI.setTrueValue(SI.getFalseValue());
return &SI;
}
// Check the false value case: The false value of the select is the returned
// value of the same cmpxchg used by the condition, and the true value is the
// cmpxchg instruction's compare operand.
if (auto *X = isExtractFromCmpXchg(SI.getFalseValue(), 0))
if (X == CmpXchg && X->getCompareOperand() == SI.getTrueValue()) {
SI.setTrueValue(SI.getFalseValue());
return &SI;
}
return nullptr;
}
/// Reduce a sequence of min/max with a common operand.
static Instruction *factorizeMinMaxTree(SelectPatternFlavor SPF, Value *LHS,
Value *RHS,
InstCombiner::BuilderTy &Builder) {
assert(SelectPatternResult::isMinOrMax(SPF) && "Expected a min/max");
// TODO: Allow FP min/max with nnan/nsz.
if (!LHS->getType()->isIntOrIntVectorTy())
return nullptr;
// Match 3 of the same min/max ops. Example: umin(umin(), umin()).
Value *A, *B, *C, *D;
SelectPatternResult L = matchSelectPattern(LHS, A, B);
SelectPatternResult R = matchSelectPattern(RHS, C, D);
if (SPF != L.Flavor || L.Flavor != R.Flavor)
return nullptr;
// Look for a common operand. The use checks are different than usual because
// a min/max pattern typically has 2 uses of each op: 1 by the cmp and 1 by
// the select.
Value *MinMaxOp = nullptr;
Value *ThirdOp = nullptr;
if (!LHS->hasNUsesOrMore(3) && RHS->hasNUsesOrMore(3)) {
// If the LHS is only used in this chain and the RHS is used outside of it,
// reuse the RHS min/max because that will eliminate the LHS.
if (D == A || C == A) {
// min(min(a, b), min(c, a)) --> min(min(c, a), b)
// min(min(a, b), min(a, d)) --> min(min(a, d), b)
MinMaxOp = RHS;
ThirdOp = B;
} else if (D == B || C == B) {
// min(min(a, b), min(c, b)) --> min(min(c, b), a)
// min(min(a, b), min(b, d)) --> min(min(b, d), a)
MinMaxOp = RHS;
ThirdOp = A;
}
} else if (!RHS->hasNUsesOrMore(3)) {
// Reuse the LHS. This will eliminate the RHS.
if (D == A || D == B) {
// min(min(a, b), min(c, a)) --> min(min(a, b), c)
// min(min(a, b), min(c, b)) --> min(min(a, b), c)
MinMaxOp = LHS;
ThirdOp = C;
} else if (C == A || C == B) {
// min(min(a, b), min(b, d)) --> min(min(a, b), d)
// min(min(a, b), min(c, b)) --> min(min(a, b), d)
MinMaxOp = LHS;
ThirdOp = D;
}
}
if (!MinMaxOp || !ThirdOp)
return nullptr;
CmpInst::Predicate P = getMinMaxPred(SPF);
Value *CmpABC = Builder.CreateICmp(P, MinMaxOp, ThirdOp);
return SelectInst::Create(CmpABC, MinMaxOp, ThirdOp);
}
Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
Value *CondVal = SI.getCondition();
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
Type *SelType = SI.getType();
// FIXME: Remove this workaround when freeze related patches are done.
// For select with undef operand which feeds into an equality comparison,
// don't simplify it so loop unswitch can know the equality comparison
// may have an undef operand. This is a workaround for PR31652 caused by
// descrepancy about branch on undef between LoopUnswitch and GVN.
if (isa<UndefValue>(TrueVal) || isa<UndefValue>(FalseVal)) {
if (llvm::any_of(SI.users(), [&](User *U) {
ICmpInst *CI = dyn_cast<ICmpInst>(U);
if (CI && CI->isEquality())
return true;
return false;
})) {
return nullptr;
}
}
if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal,
SQ.getWithInstruction(&SI)))
return replaceInstUsesWith(SI, V);
if (Instruction *I = canonicalizeSelectToShuffle(SI))
return I;
// Canonicalize a one-use integer compare with a non-canonical predicate by
// inverting the predicate and swapping the select operands. This matches a
// compare canonicalization for conditional branches.
// TODO: Should we do the same for FP compares?
CmpInst::Predicate Pred;
if (match(CondVal, m_OneUse(m_ICmp(Pred, m_Value(), m_Value()))) &&
!isCanonicalPredicate(Pred)) {
// Swap true/false values and condition.
CmpInst *Cond = cast<CmpInst>(CondVal);
Cond->setPredicate(CmpInst::getInversePredicate(Pred));
SI.setOperand(1, FalseVal);
SI.setOperand(2, TrueVal);
SI.swapProfMetadata();
Worklist.Add(Cond);
return &SI;
}
if (SelType->isIntOrIntVectorTy(1) &&
TrueVal->getType() == CondVal->getType()) {
if (match(TrueVal, m_One())) {
// Change: A = select B, true, C --> A = or B, C
return BinaryOperator::CreateOr(CondVal, FalseVal);
}
if (match(TrueVal, m_Zero())) {
// Change: A = select B, false, C --> A = and !B, C
Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
return BinaryOperator::CreateAnd(NotCond, FalseVal);
}
if (match(FalseVal, m_Zero())) {
// Change: A = select B, C, false --> A = and B, C
return BinaryOperator::CreateAnd(CondVal, TrueVal);
}
if (match(FalseVal, m_One())) {
// Change: A = select B, C, true --> A = or !B, C
Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
return BinaryOperator::CreateOr(NotCond, TrueVal);
}
// select a, a, b -> a | b
// select a, b, a -> a & b
if (CondVal == TrueVal)
return BinaryOperator::CreateOr(CondVal, FalseVal);
if (CondVal == FalseVal)
return BinaryOperator::CreateAnd(CondVal, TrueVal);
// select a, ~a, b -> (~a) & b
// select a, b, ~a -> (~a) | b
if (match(TrueVal, m_Not(m_Specific(CondVal))))
return BinaryOperator::CreateAnd(TrueVal, FalseVal);
if (match(FalseVal, m_Not(m_Specific(CondVal))))
return BinaryOperator::CreateOr(TrueVal, FalseVal);
}
// Selecting between two integer or vector splat integer constants?
//
// Note that we don't handle a scalar select of vectors:
// select i1 %c, <2 x i8> <1, 1>, <2 x i8> <0, 0>
// because that may need 3 instructions to splat the condition value:
// extend, insertelement, shufflevector.
if (SelType->isIntOrIntVectorTy() &&
CondVal->getType()->isVectorTy() == SelType->isVectorTy()) {
// select C, 1, 0 -> zext C to int
if (match(TrueVal, m_One()) && match(FalseVal, m_Zero()))
return new ZExtInst(CondVal, SelType);
// select C, -1, 0 -> sext C to int
if (match(TrueVal, m_AllOnes()) && match(FalseVal, m_Zero()))
return new SExtInst(CondVal, SelType);
// select C, 0, 1 -> zext !C to int
if (match(TrueVal, m_Zero()) && match(FalseVal, m_One())) {
Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
return new ZExtInst(NotCond, SelType);
}
// select C, 0, -1 -> sext !C to int
if (match(TrueVal, m_Zero()) && match(FalseVal, m_AllOnes())) {
Value *NotCond = Builder.CreateNot(CondVal, "not." + CondVal->getName());
return new SExtInst(NotCond, SelType);
}
}
// See if we are selecting two values based on a comparison of the two values.
if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
// Transform (X == Y) ? X : Y -> Y
if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
// This is not safe in general for floating point:
// consider X== -0, Y== +0.
// It becomes safe if either operand is a nonzero constant.
ConstantFP *CFPt, *CFPf;
if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
!CFPt->getValueAPF().isZero()) ||
((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
!CFPf->getValueAPF().isZero()))
return replaceInstUsesWith(SI, FalseVal);
}
// Transform (X une Y) ? X : Y -> X
if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
// This is not safe in general for floating point:
// consider X== -0, Y== +0.
// It becomes safe if either operand is a nonzero constant.
ConstantFP *CFPt, *CFPf;
if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
!CFPt->getValueAPF().isZero()) ||
((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
!CFPf->getValueAPF().isZero()))
return replaceInstUsesWith(SI, TrueVal);
}
// Canonicalize to use ordered comparisons by swapping the select
// operands.
//
// e.g.
// (X ugt Y) ? X : Y -> (X ole Y) ? Y : X
if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
FCmpInst::Predicate InvPred = FCI->getInversePredicate();
IRBuilder<>::FastMathFlagGuard FMFG(Builder);
Builder.setFastMathFlags(FCI->getFastMathFlags());
Value *NewCond = Builder.CreateFCmp(InvPred, TrueVal, FalseVal,
FCI->getName() + ".inv");
return SelectInst::Create(NewCond, FalseVal, TrueVal,
SI.getName() + ".p");
}
// NOTE: if we wanted to, this is where to detect MIN/MAX
} else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
// Transform (X == Y) ? Y : X -> X
if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
// This is not safe in general for floating point:
// consider X== -0, Y== +0.
// It becomes safe if either operand is a nonzero constant.
ConstantFP *CFPt, *CFPf;
if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
!CFPt->getValueAPF().isZero()) ||
((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
!CFPf->getValueAPF().isZero()))
return replaceInstUsesWith(SI, FalseVal);
}
// Transform (X une Y) ? Y : X -> Y
if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
// This is not safe in general for floating point:
// consider X== -0, Y== +0.
// It becomes safe if either operand is a nonzero constant.
ConstantFP *CFPt, *CFPf;
if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
!CFPt->getValueAPF().isZero()) ||
((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
!CFPf->getValueAPF().isZero()))
return replaceInstUsesWith(SI, TrueVal);
}
// Canonicalize to use ordered comparisons by swapping the select
// operands.
//
// e.g.
// (X ugt Y) ? X : Y -> (X ole Y) ? X : Y
if (FCI->hasOneUse() && FCmpInst::isUnordered(FCI->getPredicate())) {
FCmpInst::Predicate InvPred = FCI->getInversePredicate();
IRBuilder<>::FastMathFlagGuard FMFG(Builder);
Builder.setFastMathFlags(FCI->getFastMathFlags());
Value *NewCond = Builder.CreateFCmp(InvPred, FalseVal, TrueVal,
FCI->getName() + ".inv");
return SelectInst::Create(NewCond, FalseVal, TrueVal,
SI.getName() + ".p");
}
// NOTE: if we wanted to, this is where to detect MIN/MAX
}
// Canonicalize select with fcmp to fabs(). -0.0 makes this tricky. We need
// fast-math-flags (nsz) or fsub with +0.0 (not fneg) for this to work. We
// also require nnan because we do not want to unintentionally change the
// sign of a NaN value.
Value *X = FCI->getOperand(0);
FCmpInst::Predicate Pred = FCI->getPredicate();
if (match(FCI->getOperand(1), m_AnyZeroFP()) && FCI->hasNoNaNs()) {
// (X <= +/-0.0) ? (0.0 - X) : X --> fabs(X)
// (X > +/-0.0) ? X : (0.0 - X) --> fabs(X)
if ((X == FalseVal && Pred == FCmpInst::FCMP_OLE &&
match(TrueVal, m_FSub(m_PosZeroFP(), m_Specific(X)))) ||
(X == TrueVal && Pred == FCmpInst::FCMP_OGT &&
match(FalseVal, m_FSub(m_PosZeroFP(), m_Specific(X))))) {
Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, FCI);
return replaceInstUsesWith(SI, Fabs);
}
// With nsz:
// (X < +/-0.0) ? -X : X --> fabs(X)
// (X <= +/-0.0) ? -X : X --> fabs(X)
// (X > +/-0.0) ? X : -X --> fabs(X)
// (X >= +/-0.0) ? X : -X --> fabs(X)
if (FCI->hasNoSignedZeros() &&
((X == FalseVal && match(TrueVal, m_FNeg(m_Specific(X))) &&
(Pred == FCmpInst::FCMP_OLT || Pred == FCmpInst::FCMP_OLE)) ||
(X == TrueVal && match(FalseVal, m_FNeg(m_Specific(X))) &&
(Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_OGE)))) {
Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, FCI);
return replaceInstUsesWith(SI, Fabs);
}
}
}
// See if we are selecting two values based on a comparison of the two values.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
if (Instruction *Result = foldSelectInstWithICmp(SI, ICI))
return Result;
if (Instruction *Add = foldAddSubSelect(SI, Builder))
return Add;
// Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
auto *TI = dyn_cast<Instruction>(TrueVal);
auto *FI = dyn_cast<Instruction>(FalseVal);
if (TI && FI && TI->getOpcode() == FI->getOpcode())
if (Instruction *IV = foldSelectOpOp(SI, TI, FI))
return IV;
if (Instruction *I = foldSelectExtConst(SI))
return I;
// See if we can fold the select into one of our operands.
if (SelType->isIntOrIntVectorTy() || SelType->isFPOrFPVectorTy()) {
if (Instruction *FoldI = foldSelectIntoOp(SI, TrueVal, FalseVal))
return FoldI;
Value *LHS, *RHS;
Instruction::CastOps CastOp;
SelectPatternResult SPR = matchSelectPattern(&SI, LHS, RHS, &CastOp);
auto SPF = SPR.Flavor;
if (SPF) {
Value *LHS2, *RHS2;
if (SelectPatternFlavor SPF2 = matchSelectPattern(LHS, LHS2, RHS2).Flavor)
if (Instruction *R = foldSPFofSPF(cast<Instruction>(LHS), SPF2, LHS2,
RHS2, SI, SPF, RHS))
return R;
if (SelectPatternFlavor SPF2 = matchSelectPattern(RHS, LHS2, RHS2).Flavor)
if (Instruction *R = foldSPFofSPF(cast<Instruction>(RHS), SPF2, LHS2,
RHS2, SI, SPF, LHS))
return R;
// TODO.
// ABS(-X) -> ABS(X)
}
if (SelectPatternResult::isMinOrMax(SPF)) {
// Canonicalize so that
// - type casts are outside select patterns.
// - float clamp is transformed to min/max pattern
bool IsCastNeeded = LHS->getType() != SelType;
Value *CmpLHS = cast<CmpInst>(CondVal)->getOperand(0);
Value *CmpRHS = cast<CmpInst>(CondVal)->getOperand(1);
if (IsCastNeeded ||
(LHS->getType()->isFPOrFPVectorTy() &&
((CmpLHS != LHS && CmpLHS != RHS) ||
(CmpRHS != LHS && CmpRHS != RHS)))) {
CmpInst::Predicate Pred = getMinMaxPred(SPF, SPR.Ordered);
Value *Cmp;
if (CmpInst::isIntPredicate(Pred)) {
Cmp = Builder.CreateICmp(Pred, LHS, RHS);
} else {
IRBuilder<>::FastMathFlagGuard FMFG(Builder);
auto FMF = cast<FPMathOperator>(SI.getCondition())->getFastMathFlags();
Builder.setFastMathFlags(FMF);
Cmp = Builder.CreateFCmp(Pred, LHS, RHS);
}
Value *NewSI = Builder.CreateSelect(Cmp, LHS, RHS, SI.getName(), &SI);
if (!IsCastNeeded)
return replaceInstUsesWith(SI, NewSI);
Value *NewCast = Builder.CreateCast(CastOp, NewSI, SelType);
return replaceInstUsesWith(SI, NewCast);
}
// MAX(~a, ~b) -> ~MIN(a, b)
// MAX(~a, C) -> ~MIN(a, ~C)
// MIN(~a, ~b) -> ~MAX(a, b)
// MIN(~a, C) -> ~MAX(a, ~C)
auto moveNotAfterMinMax = [&](Value *X, Value *Y,
bool Swapped) -> Instruction * {
Value *A;
if (match(X, m_Not(m_Value(A))) && !X->hasNUsesOrMore(3) &&
!IsFreeToInvert(A, A->hasOneUse()) &&
// Passing false to only consider m_Not and constants.
IsFreeToInvert(Y, false)) {
Value *B = Builder.CreateNot(Y);
Value *NewMinMax = createMinMax(Builder, getInverseMinMaxFlavor(SPF),
A, B);
// Copy the profile metadata.
if (MDNode *MD = SI.getMetadata(LLVMContext::MD_prof)) {
cast<SelectInst>(NewMinMax)->setMetadata(LLVMContext::MD_prof, MD);
// Swap the metadata if the operands are swapped.
if (Swapped) {
assert(X == SI.getFalseValue() && Y == SI.getTrueValue() &&
"Unexpected operands.");
cast<SelectInst>(NewMinMax)->swapProfMetadata();
} else {
assert(X == SI.getTrueValue() && Y == SI.getFalseValue() &&
"Unexpected operands.");
}
}
return BinaryOperator::CreateNot(NewMinMax);
}
return nullptr;
};
if (Instruction *I = moveNotAfterMinMax(LHS, RHS, /*Swapped*/false))
return I;
if (Instruction *I = moveNotAfterMinMax(RHS, LHS, /*Swapped*/true))
return I;
if (Instruction *I = factorizeMinMaxTree(SPF, LHS, RHS, Builder))
return I;
}
}
// See if we can fold the select into a phi node if the condition is a select.
if (auto *PN = dyn_cast<PHINode>(SI.getCondition()))
// The true/false values have to be live in the PHI predecessor's blocks.
if (canSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
canSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
if (Instruction *NV = foldOpIntoPhi(SI, PN))
return NV;
if (SelectInst *TrueSI = dyn_cast<SelectInst>(TrueVal)) {
if (TrueSI->getCondition()->getType() == CondVal->getType()) {
// select(C, select(C, a, b), c) -> select(C, a, c)
if (TrueSI->getCondition() == CondVal) {
if (SI.getTrueValue() == TrueSI->getTrueValue())
return nullptr;
SI.setOperand(1, TrueSI->getTrueValue());
return &SI;
}
// select(C0, select(C1, a, b), b) -> select(C0&C1, a, b)
// We choose this as normal form to enable folding on the And and shortening
// paths for the values (this helps GetUnderlyingObjects() for example).
if (TrueSI->getFalseValue() == FalseVal && TrueSI->hasOneUse()) {
Value *And = Builder.CreateAnd(CondVal, TrueSI->getCondition());
SI.setOperand(0, And);
SI.setOperand(1, TrueSI->getTrueValue());
return &SI;
}
}
}
if (SelectInst *FalseSI = dyn_cast<SelectInst>(FalseVal)) {
if (FalseSI->getCondition()->getType() == CondVal->getType()) {
// select(C, a, select(C, b, c)) -> select(C, a, c)
if (FalseSI->getCondition() == CondVal) {
if (SI.getFalseValue() == FalseSI->getFalseValue())
return nullptr;
SI.setOperand(2, FalseSI->getFalseValue());
return &SI;
}
// select(C0, a, select(C1, a, b)) -> select(C0|C1, a, b)
if (FalseSI->getTrueValue() == TrueVal && FalseSI->hasOneUse()) {
Value *Or = Builder.CreateOr(CondVal, FalseSI->getCondition());
SI.setOperand(0, Or);
SI.setOperand(2, FalseSI->getFalseValue());
return &SI;
}
}
}
auto canMergeSelectThroughBinop = [](BinaryOperator *BO) {
// The select might be preventing a division by 0.
switch (BO->getOpcode()) {
default:
return true;
case Instruction::SRem:
case Instruction::URem:
case Instruction::SDiv:
case Instruction::UDiv:
return false;
}
};
// Try to simplify a binop sandwiched between 2 selects with the same
// condition.
// select(C, binop(select(C, X, Y), W), Z) -> select(C, binop(X, W), Z)
BinaryOperator *TrueBO;
if (match(TrueVal, m_OneUse(m_BinOp(TrueBO))) &&
canMergeSelectThroughBinop(TrueBO)) {
if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(0))) {
if (TrueBOSI->getCondition() == CondVal) {
TrueBO->setOperand(0, TrueBOSI->getTrueValue());
Worklist.Add(TrueBO);
return &SI;
}
}
if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(1))) {
if (TrueBOSI->getCondition() == CondVal) {
TrueBO->setOperand(1, TrueBOSI->getTrueValue());
Worklist.Add(TrueBO);
return &SI;
}
}
}
// select(C, Z, binop(select(C, X, Y), W)) -> select(C, Z, binop(Y, W))
BinaryOperator *FalseBO;
if (match(FalseVal, m_OneUse(m_BinOp(FalseBO))) &&
canMergeSelectThroughBinop(FalseBO)) {
if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(0))) {
if (FalseBOSI->getCondition() == CondVal) {
FalseBO->setOperand(0, FalseBOSI->getFalseValue());
Worklist.Add(FalseBO);
return &SI;
}
}
if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(1))) {
if (FalseBOSI->getCondition() == CondVal) {
FalseBO->setOperand(1, FalseBOSI->getFalseValue());
Worklist.Add(FalseBO);
return &SI;
}
}
}
if (BinaryOperator::isNot(CondVal)) {
SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
SI.setOperand(1, FalseVal);
SI.setOperand(2, TrueVal);
return &SI;
}
if (VectorType *VecTy = dyn_cast<VectorType>(SelType)) {
unsigned VWidth = VecTy->getNumElements();
APInt UndefElts(VWidth, 0);
APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
if (V != &SI)
return replaceInstUsesWith(SI, V);
return &SI;
}
}
// See if we can determine the result of this select based on a dominating
// condition.
BasicBlock *Parent = SI.getParent();
if (BasicBlock *Dom = Parent->getSinglePredecessor()) {
auto *PBI = dyn_cast_or_null<BranchInst>(Dom->getTerminator());
if (PBI && PBI->isConditional() &&
PBI->getSuccessor(0) != PBI->getSuccessor(1) &&
(PBI->getSuccessor(0) == Parent || PBI->getSuccessor(1) == Parent)) {
bool CondIsTrue = PBI->getSuccessor(0) == Parent;
Optional<bool> Implication = isImpliedCondition(
PBI->getCondition(), SI.getCondition(), DL, CondIsTrue);
if (Implication) {
Value *V = *Implication ? TrueVal : FalseVal;
return replaceInstUsesWith(SI, V);
}
}
}
// If we can compute the condition, there's no need for a select.
// Like the above fold, we are attempting to reduce compile-time cost by
// putting this fold here with limitations rather than in InstSimplify.
// The motivation for this call into value tracking is to take advantage of
// the assumption cache, so make sure that is populated.
if (!CondVal->getType()->isVectorTy() && !AC.assumptions().empty()) {
KnownBits Known(1);
computeKnownBits(CondVal, Known, 0, &SI);
if (Known.One.isOneValue())
return replaceInstUsesWith(SI, TrueVal);
if (Known.Zero.isOneValue())
return replaceInstUsesWith(SI, FalseVal);
}
if (Instruction *BitCastSel = foldSelectCmpBitcasts(SI, Builder))
return BitCastSel;
// Simplify selects that test the returned flag of cmpxchg instructions.
if (Instruction *Select = foldSelectCmpXchg(SI))
return Select;
if (Instruction *Select = foldSelectBinOpIdentity(SI, TLI))
return Select;
return nullptr;
}
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