llvm/lib/Transforms/Vectorize/SLPVectorizer/SLPUtils.h

//===- SLPUtils.h - SLP Vectorizer free utility helpers --------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Internal header used by SLPVectorizer.cpp. It declares free helper
// functions that do not depend on BoUpSLP, InstructionsState, or any other
// SLP-private type. Splitting them out keeps SLPVectorizer.cpp focused on
// the build / legality / cost / codegen pipeline.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIB_TRANSFORMS_VECTORIZE_SLPVECTORIZER_SLPUTILS_H
#define LLVM_LIB_TRANSFORMS_VECTORIZE_SLPVECTORIZER_SLPUTILS_H

#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Intrinsics.h"

#include <optional>
#include <string>

namespace llvm {
class Constant;
class DataLayout;
class Instruction;
class TargetLibraryInfo;
class Type;
class Value;
} // namespace llvm

namespace llvm::slpvectorizer {

/// Limit of the number of uses for potentially transformed instructions/values,
/// used in checks to avoid compile-time explode.
inline constexpr int UsesLimit = 64;

/// \returns True if the value is a constant (but not globals/constant
/// expressions).
bool isConstant(Value *V);

/// \returns True if \p V is the integer identity constant for binary \p Opcode
/// (e.g. 0 for add, 1 for mul, all-ones for and). Floating-point identities are
/// excluded: a ConstantInt never matches the ConstantFP getBinOpIdentity()
/// returns for FAdd/FMul, whose identity fast-math may break anyway.
bool isBinOpIdentityConstant(const Value *V, unsigned Opcode);

/// \returns the opcode of the combines emitted for a reassociated node:
/// subtract chains regroup their positive and negative operand columns with
/// plain adds.
unsigned getReassocCombineOpcode(unsigned Opcode);

/// \returns True if \p I can be a link of a flattenable binary chain:
/// subtracts flatten as adds of a negated leaf, float subtracts need reassoc
/// to allow the regrouping.
bool isReassocChainLink(const Instruction *I);

/// Checks if \p V is one of vector-like instructions, i.e. undef,
/// insertelement/extractelement with constant indices for fixed vector type
/// or extractvalue instruction.
bool isVectorLikeInstWithConstOps(Value *V);

/// \returns the number of elements for Ty.
unsigned getNumElements(Type *Ty);

/// Returns power-of-2 number of elements in a single register (part), given
/// the total number of elements \p Size and number of registers (parts) \p
/// NumParts.
unsigned getPartNumElems(unsigned Size, unsigned NumParts);

/// Returns correct remaining number of elements, considering total amount
/// \p Size, (power-of-2 number) of elements in a single register
/// \p PartNumElems and current register (part) \p Part.
unsigned getNumElems(unsigned Size, unsigned PartNumElems, unsigned Part);

#if !defined(NDEBUG)
/// Print a short descriptor of the instruction bundle suitable for debug
/// output.
std::string shortBundleName(ArrayRef<Value *> VL, int Idx = -1);
#endif

/// \returns True if all of the instructions in \p VL are in the same block.
bool allSameBlock(ArrayRef<Value *> VL);

/// \returns True if all of the values in \p VL are constants (but not
/// globals/constant expressions).
bool allConstant(ArrayRef<Value *> VL);

/// \returns True if all of the values in \p VL are identical or some of them
/// are UndefValue.
bool isSplat(ArrayRef<Value *> VL);

/// Checks if \p LHS and \p RHS are the same intrinsic, or one is llvm.fma
/// and the other is llvm.fmuladd, since both lower to the same fused
/// vector operation.
/// \returns the intrinsic ID to use for the pair (\p RHS if the IDs match,
/// otherwise Intrinsic::fma), or Intrinsic::not_intrinsic if they are not
/// equivalent.
Intrinsic::ID isEquivalentIntrinsicID(Intrinsic::ID LHS, Intrinsic::ID RHS);

/// \returns True if \p I is commutative, handles CmpInst and BinaryOperator.
/// For BinaryOperator, it also checks if \p ValWithUses is used in specific
/// patterns that make it effectively commutative (like equality comparisons
/// with zero).
/// In most cases, users should not call this function directly (since \p I and
/// \p ValWithUses are the same). However, when analyzing interchangeable
/// instructions, we need to use the converted opcode along with the original
/// uses.
/// \param I The instruction to check for commutativity
/// \param ValWithUses The value whose uses are analyzed for special
/// patterns
bool isCommutative(const Instruction *I, const Value *ValWithUses,
                   bool IsCopyable = false);

/// This is a helper function to check whether \p I is commutative.
/// This is a convenience wrapper that calls the two-parameter version of
/// isCommutative with the same instruction for both parameters. This is
/// the common case where the instruction being checked for commutativity
/// is the same as the instruction whose uses are analyzed for special
/// patterns (see the two-parameter version above for details).
/// \param I The instruction to check for commutativity
/// \returns true if the instruction is commutative, false otherwise
bool isCommutative(const Instruction *I);

/// Checks if the operand is commutative. In commutative operations, not all
/// operands might commutable, e.g. for fmuladd only 2 first operands are
/// commutable.
bool isCommutableOperand(const Instruction *I, Value *ValWithUses, unsigned Op,
                         bool IsCopyable = false);

/// \returns number of operands of \p I, considering commutativity. Returns 2
/// for commutative intrinsics.
/// \param I The instruction to check for commutativity
unsigned getNumberOfPotentiallyCommutativeOps(Instruction *I);

/// \returns inserting or extracting index of InsertElement, ExtractElement
/// or InsertValue instruction, using \p Offset as base offset for index.
/// \returns std::nullopt if the index is not an immediate.
std::optional<unsigned> getElementIndex(const Value *Inst, unsigned Offset = 0);

/// \returns True if all of the values in \p VL use the same opcode.
/// For comparison instructions, also checks if predicates match.
/// PoisonValues are considered matching. Interchangeable instructions are
/// not considered.
bool allSameOpcode(ArrayRef<Value *> VL);

/// \returns Optional element Idx for Extract{Value,Element} instructions.
std::optional<unsigned> getExtractIndex(const Instruction *E);

/// Compute the inverse permutation \p Mask of \p Indices.
void inversePermutation(ArrayRef<unsigned> Indices, SmallVectorImpl<int> &Mask);

/// Reorders the list of scalars in accordance with the given \p Mask.
void reorderScalars(SmallVectorImpl<Value *> &Scalars, ArrayRef<int> Mask);

/// \returns True iff every value in \p VL has the same Type as the first.
bool allSameType(ArrayRef<Value *> VL);

/// Checks if the provided value does not require scheduling. It does not
/// require scheduling if this is not an instruction or it is an instruction
/// that does not read/write memory and all operands are either not
/// instructions or phi nodes or instructions from different blocks.
bool areAllOperandsNonInsts(Value *V);

/// Checks if the provided value does not require scheduling. It does not
/// require scheduling if this is not an instruction or it is an instruction
/// that does not read/write memory and all users are phi nodes or
/// instructions from different blocks.
bool isUsedOutsideBlock(Value *V);

/// Checks if the specified value does not require scheduling. It does not
/// require scheduling if all operands and all users do not need to be
/// scheduled in the current basic block.
bool doesNotNeedToBeScheduled(Value *V);

/// Checks if the specified array of instructions does not require scheduling.
/// It is so if all either instructions have operands that do not require
/// scheduling or their users do not require scheduling since they are phis or
/// in other basic blocks.
bool doesNotNeedToSchedule(ArrayRef<Value *> VL);

/// \returns inserting or extracting index of InsertElement / ExtractElement
/// instruction, using \p Offset as base offset for index. Only instantiated
/// for InsertElementInst and ExtractElementInst (see SLPUtils.cpp).
template <typename T>
std::optional<unsigned> getInsertExtractIndex(const Value *Inst,
                                              unsigned Offset);

void transformScalarShuffleIndiciesToVector(unsigned VecTyNumElements,
                                            SmallVectorImpl<int> &Mask);

/// \returns the number of groups of shufflevector
/// A group has the following features
/// 1. All of value in a group are shufflevector.
/// 2. The mask of all shufflevector is isExtractSubvectorMask.
/// 3. The mask of all shufflevector uses all of the elements of the source.
/// e.g., it is 1 group (%0)
/// %1 = shufflevector <16 x i8> %0, <16 x i8> poison,
///    <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
/// %2 = shufflevector <16 x i8> %0, <16 x i8> poison,
///    <8 x i32> <i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15>
/// it is 2 groups (%3 and %4)
/// %5 = shufflevector <8 x i16> %3, <8 x i16> poison,
///    <4 x i32> <i32 0, i32 1, i32 2, i32 3>
/// %6 = shufflevector <8 x i16> %3, <8 x i16> poison,
///    <4 x i32> <i32 4, i32 5, i32 6, i32 7>
/// %7 = shufflevector <8 x i16> %4, <8 x i16> poison,
///    <4 x i32> <i32 0, i32 1, i32 2, i32 3>
/// %8 = shufflevector <8 x i16> %4, <8 x i16> poison,
///    <4 x i32> <i32 4, i32 5, i32 6, i32 7>
/// it is 0 group
/// %12 = shufflevector <8 x i16> %10, <8 x i16> poison,
///     <4 x i32> <i32 0, i32 1, i32 2, i32 3>
/// %13 = shufflevector <8 x i16> %11, <8 x i16> poison,
///     <4 x i32> <i32 0, i32 1, i32 2, i32 3>
unsigned getShufflevectorNumGroups(ArrayRef<Value *> VL);

/// \returns a shufflevector mask which is used to vectorize shufflevectors
/// e.g.,
/// %5 = shufflevector <8 x i16> %3, <8 x i16> poison,
///    <4 x i32> <i32 0, i32 1, i32 2, i32 3>
/// %6 = shufflevector <8 x i16> %3, <8 x i16> poison,
///    <4 x i32> <i32 4, i32 5, i32 6, i32 7>
/// %7 = shufflevector <8 x i16> %4, <8 x i16> poison,
///    <4 x i32> <i32 0, i32 1, i32 2, i32 3>
/// %8 = shufflevector <8 x i16> %4, <8 x i16> poison,
///    <4 x i32> <i32 4, i32 5, i32 6, i32 7>
/// the result is
/// <0, 1, 2, 3, 12, 13, 14, 15, 16, 17, 18, 19, 28, 29, 30, 31>
SmallVector<int> calculateShufflevectorMask(ArrayRef<Value *> VL);

/// Specifies the way the mask should be analyzed for undefs/poisonous elements
/// in the shuffle mask.
enum class UseMask {
  FirstArg,  ///< The mask is expected to be for permutation of 1-2 vectors,
             ///< check for the mask elements for the first argument (mask
             ///< indices are in range [0:VF)).
  SecondArg, ///< The mask is expected to be for permutation of 2 vectors, check
             ///< for the mask elements for the second argument (mask indices
             ///< are in range [VF:2*VF))
  UndefsAsMask ///< Consider undef mask elements (-1) as placeholders for
               ///< future shuffle elements and mark them as ones as being used
               ///< in future. Non-undef elements are considered as unused since
               ///< they're already marked as used in the mask.
};

/// Prepares a use bitset for the given mask either for the first argument or
/// for the second.
SmallBitVector buildUseMask(int VF, ArrayRef<int> Mask, UseMask MaskArg);

/// Checks if the given value is actually an undefined constant vector.
/// Also, if the \p UseMask is not empty, tries to check if the non-masked
/// elements actually mask the insertelement buildvector, if any.
template <bool IsPoisonOnly = false>
SmallBitVector isUndefVector(const Value *V,
                             const SmallBitVector &UseMask = {});

/// \returns True if in-tree use also needs extract. This refers to
/// possible scalar operand in vectorized instruction.
bool doesInTreeUserNeedToExtract(Value *Scalar, Instruction *UserInst,
                                 TargetLibraryInfo *TLI,
                                 const TargetTransformInfo *TTI);

/// \returns the AA location that is being access by the instruction.
MemoryLocation getLocation(Instruction *I);

/// \returns True if the instruction is not a volatile or atomic load/store.
bool isSimple(Instruction *I);

/// Checks if the loads with scalar type \p ScalarTy and pointer operands
/// \p PointerOps are each (optionally via a constant-offset GEP) a
/// `select Cond, A, B` picking between the same two base pointers A/B on
/// every lane - the shape a fully unrolled `x = cond ? A[i] : B[i]` takes. On
/// success \p TrueBase / \p FalseBase are the candidate bases and
/// \p Conditions holds each lane's `select` condition, used to build the
/// blend mask. Lane \p Idx must be at `Base + Idx * sizeof(ScalarTy)`; only
/// dense, natural lane order starting at the base is recognized (reordered or
/// partial groups fall back to Gather/Scatter).
bool isSelectedBaseLoad(Type *ScalarTy, ArrayRef<Value *> PointerOps,
                        const DataLayout &DL, Value *&TrueBase,
                        Value *&FalseBase,
                        SmallVectorImpl<Value *> &Conditions);

/// Shuffles \p Mask in accordance with the given \p SubMask.
/// \param ExtendingManyInputs Supports reshuffling of the mask with not only
/// one but two input vectors.
void addMask(SmallVectorImpl<int> &Mask, ArrayRef<int> SubMask,
             bool ExtendingManyInputs = false);

/// Order may have elements assigned special value (size) which is out of
/// bounds. Such indices only appear on places which correspond to undef values
/// (see canReuseExtract for details) and used in order to avoid undef values
/// have effect on operands ordering.
/// The first loop below simply finds all unused indices and then the next loop
/// nest assigns these indices for undef values positions.
/// As an example below Order has two undef positions and they have assigned
/// values 3 and 7 respectively:
/// before:  6 9 5 4 9 2 1 0
/// after:   6 3 5 4 7 2 1 0
void fixupOrderingIndices(MutableArrayRef<unsigned> Order);

/// \returns a bitset for selecting opcodes. false for Opcode0 and true for
/// Opcode1.
SmallBitVector getAltInstrMask(ArrayRef<Value *> VL, Type *ScalarTy,
                               unsigned Opcode0, unsigned Opcode1);

/// Replicates the given \p Val \p VF times.
SmallVector<Constant *> replicateMask(ArrayRef<Constant *> Val, unsigned VF);

/// \returns the masked division/remainder intrinsic corresponding to \p
/// Opcode. Disabled lanes of these intrinsics are poison rather than UB,
/// unlike the plain opcode.
Intrinsic::ID getMaskedDivRemIntrinsic(unsigned Opcode);

/// Returns true if \p I forms a vectorizable bundle on its own and its single
/// user does not tear the vector apart. Loads and addresses are excluded: the
/// tree is built without the users, so it does not pay off the extracts. A
/// cast, feeding a multi-used cast, is excluded for the same reason, such a
/// user stays scalar. The fp-to-int conversions move the result to the other
/// register domain, so the extracts are paid on top of the repacking. The
/// values, feeding the inserts, are vectorized together with them by the
/// dedicated attempt.
bool isOnceUsedSeed(const Instruction *I);

/// If \p V is a single-use fpext of a single-use fptrunc forming a round-trip
/// back to the type of \p V, returns the fptrunc; the round-trip source is its
/// operand, always an instruction of the same type as \p V. If
/// \p MustBeElidable, matches only when the intermediate rounding may be
/// removed: both casts must allow contraction and the widening cast cannot
/// produce nan/inf.
Instruction *lookThroughCastRoundTrip(Value *V, bool MustBeElidable);

/// Narrow reduction leaf: the value, the shift applied after widening and
/// the mask applied in the narrow type before widening, clearing the bits
/// the absorbed narrow shls shift out and applying the absorbed narrow
/// and-masks. Lossless narrow shls contribute their known-zero bits to the
/// mask so matching lanes can form a splat. All-ones mask means nothing
/// was absorbed and no 'and' is needed.
struct NarrowedLeafInfo {
  NarrowedLeafInfo(Value *V, unsigned Shift, APInt Mask)
      : V(V), Shift(Shift), Mask(std::move(Mask)) {}

  Value *V;
  unsigned Shift;
  APInt Mask;
};

/// Recursively collects the narrow leaves of the widened reduction value
/// \p V. zext is looked through directly, same-kind binops per operand,
/// shl of a zext - only if no bits are shifted out in the current type,
/// shls in narrower types fold into the shift and ands with a constant into
/// the mask applied in the narrow type. Also collects the looked-through
/// instructions into \p ChainInsts.
void collectNarrowedLeaves(Value *V, unsigned RdxOpcode, unsigned WideBW,
                           unsigned MaxDepth,
                           SmallVectorImpl<NarrowedLeafInfo> &Leaves,
                           SmallVectorImpl<Instruction *> &ChainInsts);

TargetTransformInfo::TargetCostKind getSLPCostKind(const Function *F);

} // namespace llvm::slpvectorizer

#endif // LLVM_LIB_TRANSFORMS_VECTORIZE_SLPVECTORIZER_SLPUTILS_H