SideEffectInterfaces.h

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//===- SideEffectInterfaces.h - SideEffect in MLIR --------------*- 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
//
//===----------------------------------------------------------------------===//
//
// This file contains traits, interfaces, and utilities for defining and
// querying the side effects of an operation.
//
//===----------------------------------------------------------------------===//
 
#ifndef MLIR_INTERFACES_SIDEEFFECTINTERFACES_H
#define MLIR_INTERFACES_SIDEEFFECTINTERFACES_H
 
#include "mlir/IR/OpDefinition.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Twine.h"
#include <cstdint>
 
namespace mlir {
namespace SideEffects {
//===----------------------------------------------------------------------===//
// Effects
//===----------------------------------------------------------------------===//
 
/// This class represents a base class for a specific effect type.
class Effect {
public:
  /// This base class is used for derived effects that are non-parametric.
  template <typename DerivedEffect, typename BaseEffect = Effect>
  class Base : public BaseEffect {
  public:
    using BaseT = Base<DerivedEffect>;
 
    /// Return the unique identifier for the base effects class.
    static TypeID getEffectID() { return TypeID::get<DerivedEffect>(); }
 
    /// 'classof' used to support llvm style cast functionality.
    static bool classof(const ::mlir::SideEffects::Effect *effect) {
      return effect->getEffectID() == BaseT::getEffectID();
    }
 
    /// Returns a unique instance for the derived effect class.
    static DerivedEffect *get() {
      return BaseEffect::template get<DerivedEffect>();
    }
    using BaseEffect::get;
 
  protected:
    Base() : BaseEffect(BaseT::getEffectID()) {}
  };
 
  /// Return the unique identifier for the base effects class.
  TypeID getEffectID() const { return id; }
 
  /// Returns a unique instance for the given effect class.
  template <typename DerivedEffect>
  static DerivedEffect *get() {
    static_assert(std::is_base_of<Effect, DerivedEffect>::value,
                  "expected DerivedEffect to inherit from Effect");
 
    static DerivedEffect instance;
    return &instance;
  }
 
protected:
  Effect(TypeID id) : id(id) {}
 
private:
  /// The id of the derived effect class.
  TypeID id;
};
 
//===----------------------------------------------------------------------===//
// Resources
//===----------------------------------------------------------------------===//
 
/// This class represents a specific resource that an effect applies to. This
/// class represents an abstract interface for a given resource. Resources
/// form a hierarchy via getParent(); disjointness (isDisjointFrom) is used to
/// determine whether effects can conflict.
///
/// Scope: The resource hierarchy is for disjointness of *abstract* resources
/// (e.g. addressable memory vs. runtime state). It is deliberately *not*
/// intended for fine-grained regions with specific addresses/sizes, or for
/// alias classes / offset-based disambiguation; such concerns are out of scope
/// and should be handled by alias analysis or other mechanisms.
class Resource {
public:
  virtual ~Resource() = default;
 
  /// This base class is used for derived effects that are non-parametric.
  template <typename DerivedResource, typename BaseResource = Resource>
  class Base : public BaseResource {
  public:
    /// Use the current instantiation so get()/getResourceID() refer to this
    /// hierarchy's singleton, not Base<DerivedResource, Resource>'s.
    using BaseT = Base<DerivedResource, BaseResource>;
 
    /// Returns a unique instance for the given effect class.
    static DerivedResource *get() {
      static DerivedResource instance;
      return &instance;
    }
 
    /// Return the unique identifier for the base resource class.
    static TypeID getResourceID() { return TypeID::get<DerivedResource>(); }
 
    /// 'classof' used to support llvm style cast functionality. Returns true
    /// iff the resource is the same as or a descendant of this resource type
    /// in the hierarchy (so isa/cast work for ancestor checks).
    static bool classof(const Resource *resource) {
      return resource->isSubresourceOf(BaseT::get());
    }
 
  protected:
    Base() : BaseResource(BaseT::getResourceID()) {}
    /// Constructor for use when this type is used as a parent (BaseResource);
    /// allows the derived resource to pass its TypeID so the hierarchy is
    /// correct.
    Base(TypeID id) : BaseResource(id) {}
  };
 
  /// Return the unique identifier for the base resource class.
  TypeID getResourceID() const { return id; }
 
  /// Return a string name of the resource.
  virtual StringRef getName() const = 0;
 
  /// Return the parent resource in the hierarchy.
  virtual Resource *getParent() const;
 
  /// Returns true if this resource is addressable (effects on it can alias
  /// pointer-based memory). Default is true.
  virtual bool isAddressable() const { return true; }
 
  /// Returns true if this resource is a subresource of (or equal to) another.
  bool isSubresourceOf(const Resource *other) const {
    for (const Resource *r = this; r != nullptr; r = r->getParent()) {
#ifdef EXPENSIVE_CHECKS
      r->verifyImmediateParentAddressability();
#endif // EXPENSIVE_CHECKS
      if (r == other)
        return true;
    }
    return false;
  }
 
  /// Returns true if this resource is disjoint from another. Two resources are
  /// disjoint if neither is an ancestor of the other.
  bool isDisjointFrom(const Resource *other) const {
    return !isSubresourceOf(other) && !other->isSubresourceOf(this);
  }
 
protected:
  Resource(TypeID id) : id(id) {}
 
private:
#ifdef EXPENSIVE_CHECKS
  /// Verifies the single-link invariant: an addressable resource must not have
  /// a non-addressable parent. Used from isSubresourceOf() under
  /// EXPENSIVE_CHECKS so the invariant is checked when the hierarchy is
  /// traversed.
  void verifyImmediateParentAddressability() const {
    Resource *parent = getParent();
    if (parent && isAddressable() && !parent->isAddressable())
      llvm::report_fatal_error(
          llvm::Twine("Resource '") + getName() +
          "' is addressable but has non-addressable parent '" +
          parent->getName() + "'");
  }
#endif // EXPENSIVE_CHECKS
 
  /// The id of the derived resource class.
  TypeID id;
};
 
/// The default resource kind. It serves as the root of the resource hierarchy:
/// all resources that do not override getParent() have DefaultResource as their
/// parent.
struct DefaultResource : public Resource::Base<DefaultResource> {
  DefaultResource() = default;
  StringRef getName() const override { return "<Default>"; }
  Resource *getParent() const override { return nullptr; }
 
protected:
  /// For use when this type is the parent of another resource; allows the
  /// derived resource to pass its TypeID so the hierarchy is correct.
  DefaultResource(TypeID id) : Base(id) {}
};
 
/// All resources that do not override getParent() have DefaultResource
/// as their parent.
inline Resource *Resource::getParent() const { return DefaultResource::get(); }
 
/// An automatic allocation-scope resource that is valid in the context of a
/// parent AutomaticAllocationScope trait.
struct AutomaticAllocationScopeResource
    : public Resource::Base<AutomaticAllocationScopeResource, DefaultResource> {
  StringRef getName() const final { return "AutomaticAllocationScope"; }
  Resource *getParent() const override { return DefaultResource::get(); }
};
 
/// This class represents a specific instance of an effect. It contains the
/// effect being applied, a resource that corresponds to where the effect is
/// applied, and an optional symbol reference or value(either operand, result,
/// or region entry argument) that the effect is applied to, and an optional
/// parameters attribute further specifying the details of the effect.
template <typename EffectT>
class EffectInstance {
public:
  EffectInstance(EffectT *effect, Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), stage(0),
        effectOnFullRegion(false) {}
  EffectInstance(EffectT *effect, int stage, bool effectOnFullRegion,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), stage(stage),
        effectOnFullRegion(effectOnFullRegion) {}
  template <typename T,
            std::enable_if_t<
                llvm::is_one_of<T, OpOperand *, OpResult, BlockArgument>::value,
                bool> = true>
  EffectInstance(EffectT *effect, T value,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), value(value), stage(0),
        effectOnFullRegion(false) {
    checkResourceAllowsValue();
  }
  template <typename T,
            std::enable_if_t<
                llvm::is_one_of<T, OpOperand *, OpResult, BlockArgument>::value,
                bool> = true>
  EffectInstance(EffectT *effect, T value, int stage, bool effectOnFullRegion,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), value(value), stage(stage),
        effectOnFullRegion(effectOnFullRegion) {
    checkResourceAllowsValue();
  }
  EffectInstance(EffectT *effect, SymbolRefAttr symbol,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), value(symbol), stage(0),
        effectOnFullRegion(false) {}
  EffectInstance(EffectT *effect, SymbolRefAttr symbol, int stage,
                 bool effectOnFullRegion,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), value(symbol), stage(stage),
        effectOnFullRegion(effectOnFullRegion) {}
  EffectInstance(EffectT *effect, Attribute parameters,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), parameters(parameters), stage(0),
        effectOnFullRegion(false) {}
  EffectInstance(EffectT *effect, Attribute parameters, int stage,
                 bool effectOnFullRegion,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), parameters(parameters),
        stage(stage), effectOnFullRegion(effectOnFullRegion) {}
  template <typename T,
            std::enable_if_t<
                llvm::is_one_of<T, OpOperand *, OpResult, BlockArgument>::value,
                bool> = true>
  EffectInstance(EffectT *effect, T value, Attribute parameters,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), value(value),
        parameters(parameters), stage(0), effectOnFullRegion(false) {
    checkResourceAllowsValue();
  }
  template <typename T,
            std::enable_if_t<
                llvm::is_one_of<T, OpOperand *, OpResult, BlockArgument>::value,
                bool> = true>
  EffectInstance(EffectT *effect, T value, Attribute parameters, int stage,
                 bool effectOnFullRegion,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), value(value),
        parameters(parameters), stage(stage),
        effectOnFullRegion(effectOnFullRegion) {
    checkResourceAllowsValue();
  }
  EffectInstance(EffectT *effect, SymbolRefAttr symbol, Attribute parameters,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), value(symbol),
        parameters(parameters), stage(0), effectOnFullRegion(false) {}
  EffectInstance(EffectT *effect, SymbolRefAttr symbol, Attribute parameters,
                 int stage, bool effectOnFullRegion,
                 Resource *resource = DefaultResource::get())
      : effect(effect), resource(resource), value(symbol),
        parameters(parameters), stage(stage),
        effectOnFullRegion(effectOnFullRegion) {}
 
  /// Return the effect being applied.
  EffectT *getEffect() const { return effect; }
 
  /// Return the value the effect is applied on, or nullptr if there isn't a
  /// known value being affected.
  Value getValue() const {
    if (!value || llvm::isa_and_present<SymbolRefAttr>(value)) {
      return Value();
    }
    if (OpOperand *operand = llvm::dyn_cast_if_present<OpOperand *>(value)) {
      return operand->get();
    }
    if (OpResult result = llvm::dyn_cast_if_present<OpResult>(value)) {
      return result;
    }
    return cast_if_present<BlockArgument>(value);
  }
 
  /// Returns the OpOperand effect is applied on, or nullptr if there isn't a
  /// known value being effected.
  template <typename T,
            std::enable_if_t<
                llvm::is_one_of<T, OpOperand *, OpResult, BlockArgument>::value,
                bool> = true>
  T getEffectValue() const {
    return value ? dyn_cast_if_present<T>(value) : nullptr;
  }
 
  /// Return the symbol reference the effect is applied on, or nullptr if there
  /// isn't a known smbol being affected.
  SymbolRefAttr getSymbolRef() const {
    return value ? llvm::dyn_cast_if_present<SymbolRefAttr>(value)
                 : SymbolRefAttr();
  }
 
  /// Return the resource that the effect applies to.
  Resource *getResource() const { return resource; }
 
  /// Return the parameters of the effect, if any.
  Attribute getParameters() const { return parameters; }
 
  /// Return the effect happen stage.
  int getStage() const { return stage; }
 
  /// Return if this side effect act on every single value of resource.
  bool getEffectOnFullRegion() const { return effectOnFullRegion; }
 
private:
  /// Effect on a non-addressable resource cannot have an associated Value.
  void checkResourceAllowsValue() {
    if (value && resource && !resource->isAddressable())
      llvm::report_fatal_error(
          llvm::Twine("EffectInstance: resource '") + resource->getName() +
          "' is non-addressable and cannot have an associated Value");
  }
 
  /// The specific effect being applied.
  EffectT *effect;
 
  /// The resource that the given value resides in.
  Resource *resource;
 
  /// The Symbol, OpOperand, OpResult or BlockArgument that the effect applies
  /// to. This is optionally null.
  PointerUnion<SymbolRefAttr, OpOperand *, OpResult, BlockArgument> value;
 
  /// Additional parameters of the effect instance. An attribute is used for
  /// type-safe structured storage and context-based uniquing. Concrete effects
  /// can use this at their convenience. This is optionally null.
  Attribute parameters;
 
  // The stage side effect happen. Side effect with a lower stage
  // number happen earlier than those with a higher stage number
  int stage;
 
  // Does this side effect act on every single value of resource.
  bool effectOnFullRegion;
};
} // namespace SideEffects
 
namespace Speculation {
/// This enum is returned from the `getSpeculatability` method in the
/// `ConditionallySpeculatable` op interface.
enum class Speculatability {
  /// The Operation in question cannot be speculatively executed.  This could be
  /// because it may invoke undefined behavior or have other side effects.
  NotSpeculatable,
 
  // The Operation in question can be speculatively executed.  It does not have
  // any side effects or undefined behavior.
  Speculatable,
 
  // The Operation in question can be speculatively executed if all the
  // operations in all attached regions can also be speculatively executed.
  RecursivelySpeculatable,
};
 
constexpr auto NotSpeculatable = Speculatability::NotSpeculatable;
constexpr auto Speculatable = Speculatability::Speculatable;
constexpr auto RecursivelySpeculatable =
    Speculatability::RecursivelySpeculatable;
} // namespace Speculation
 
//===----------------------------------------------------------------------===//
// SideEffect Traits
//===----------------------------------------------------------------------===//
 
namespace OpTrait {
/// This trait indicates that the memory effects of an operation includes the
/// effects of operations nested within its regions. If the operation has no
/// derived effects interfaces, the operation itself can be assumed to have no
/// memory effects.
template <typename ConcreteType>
class HasRecursiveMemoryEffects
    : public TraitBase<ConcreteType, HasRecursiveMemoryEffects> {};
 
/// This trait marks an op (which must be tagged as implementing the
/// ConditionallySpeculatable interface) as being recursively speculatable.
/// This means that said op can be speculated only if all the instructions in
/// all the regions attached to the op can be speculated.
template <typename ConcreteType>
struct RecursivelySpeculatableImplTrait
    : public TraitBase<ConcreteType, RecursivelySpeculatableImplTrait> {
 
  Speculation::Speculatability getSpeculatability() {
    return Speculation::RecursivelySpeculatable;
  }
};
 
/// This trait marks an op (which must be tagged as implementing the
/// ConditionallySpeculatable interface) as being always speculatable.
template <typename ConcreteType>
struct AlwaysSpeculatableImplTrait
    : public TraitBase<ConcreteType, AlwaysSpeculatableImplTrait> {
 
  Speculation::Speculatability getSpeculatability() {
    return Speculation::Speculatable;
  }
};
} // namespace OpTrait
 
//===----------------------------------------------------------------------===//
// Operation Memory-Effect Modeling
//===----------------------------------------------------------------------===//
 
namespace MemoryEffects {
/// This class represents the base class used for memory effects.
struct Effect : public SideEffects::Effect {
  using SideEffects::Effect::Effect;
 
  /// A base class for memory effects that provides helper utilities.
  template <typename DerivedEffect>
  using Base = SideEffects::Effect::Base<DerivedEffect, Effect>;
 
  static bool classof(const SideEffects::Effect *effect);
};
using EffectInstance = SideEffects::EffectInstance<Effect>;
 
/// The following effect indicates that the operation allocates from some
/// resource. An 'allocate' effect implies only allocation of the resource, and
/// not any visible mutation or dereference.
struct Allocate : public Effect::Base<Allocate> {};
 
/// The following effect indicates that the operation frees some resource that
/// has been allocated. An 'allocate' effect implies only de-allocation of the
/// resource, and not any visible allocation, mutation or dereference.
struct Free : public Effect::Base<Free> {};
 
/// The following effect indicates that the operation reads from some resource.
/// A 'read' effect implies only dereferencing of the resource, and not any
/// visible mutation.
struct Read : public Effect::Base<Read> {};
 
/// The following effect indicates that the operation writes to some resource. A
/// 'write' effect implies only mutating a resource, and not any visible
/// dereference or read.
struct Write : public Effect::Base<Write> {};
} // namespace MemoryEffects
 
//===----------------------------------------------------------------------===//
// SideEffect Utilities
//===----------------------------------------------------------------------===//
 
/// Return "true" if `op` has unknown effects. I.e., the effects of the
/// operation itself are unknown and the operation does not derive its effects
/// from its nested operations. (`HasRecursiveMemoryEffects` trait is not
/// implemented or it is unknown whether it is implemented or not.)
bool hasUnknownEffects(Operation *op);
 
/// Returns "true" if `op` has only an effect of type `EffectTy`. Returns
/// "false" if `op` has unknown effects or other/additional effects. Recursive
/// effects are not taken into account.
template <typename EffectTy>
bool hasSingleEffect(Operation *op);
 
/// Returns "true" if `op` has only an effect of type `EffectTy` on `value`.
/// Returns "false" if `op` has unknown effects or other/additional effects.
/// Recursive effects are not taken into account.
template <typename EffectTy>
bool hasSingleEffect(Operation *op, Value value);
 
/// Returns "true" if `op` has only an effect of type `EffectTy` on `value` of
/// type `ValueTy`. Returns "false" if `op` has unknown effects or
/// other/additional effects. Recursive effects are not taken into account.
template <typename ValueTy, typename EffectTy>
bool hasSingleEffect(Operation *op, ValueTy value);
 
/// Returns "true" if `op` has an effect of type `EffectTy`. Returns "false" if
/// `op` has unknown effects. Recursive effects are not taken into account.
template <typename... EffectTys>
bool hasEffect(Operation *op);
 
/// Returns "true" if `op` has an effect of type `EffectTy` on `value`. Returns
/// "false" if `op` has unknown effects. Recursive effects are not taken into
/// account.
template <typename... EffectTys>
bool hasEffect(Operation *op, Value value);
 
/// Returns "true" if `op` has an effect of type `EffectTy` on `value` of type
/// `ValueTy`. Returns "false" if `op` has unknown effects. Recursive effects
/// are not taken into account.
template <typename ValueTy, typename... EffectTys>
bool hasEffect(Operation *op, ValueTy value);
 
/// Returns "true" if `op` might have an effect of type `EffectTy`. Returns
/// "true" if the op has unknown effects. Recursive effects are not taken into
/// account.
template <typename... EffectTys>
bool mightHaveEffect(Operation *op) {
  return hasUnknownEffects(op) || hasEffect<EffectTys...>(op);
}
 
/// Returns "true" if `op` might have an effect of type `EffectTy` on `value`.
/// Returns "true" if the op has unknown effects. Recursive effects are not
/// taken into account.
template <typename... EffectTys>
bool mightHaveEffect(Operation *op, Value value) {
  return hasUnknownEffects(op) || hasEffect<EffectTys...>(op, value);
}
 
/// Returns "true" if `op` might have an effect of type `EffectTy` on `value`
/// of type `ValueTy`. Returns "true" if the op has unknown effects. Recursive
/// effects are not taken into account.
template <typename ValueTy, typename... EffectTys>
bool mightHaveEffect(Operation *op, ValueTy value) {
  return hasUnknownEffects(op) || hasEffect<EffectTys...>(op, value);
}
 
/// Return true if the given operation is unused, and has no side effects on
/// memory that prevent erasing.
bool isOpTriviallyDead(Operation *op);
 
/// Return true if the given operation would be dead if unused, and has no side
/// effects on memory that would prevent erasing. This is equivalent to checking
/// `isOpTriviallyDead` if `op` was unused.
///
/// Note: Terminators and symbols are never considered to be trivially dead.
bool wouldOpBeTriviallyDead(Operation *op);
 
/// A cache for repeated deadness queries on nested operations. All changes to
/// an operation or its nested IR must invalidate that operation. Moves must
/// also invalidate the old parent. Invalidate operations before erasing them.
class DeadnessCache {
public:
  enum class State : uint8_t { Alive, Dead };
 
  /// Return true if the operation is unused and can be erased. Terminators and
  /// symbols cannot be erased. Uses are checked on every query.
  bool isOpTriviallyDead(Operation *op);
 
  /// Invalidate the operation, its descendants, and its ancestors.
  void invalidate(Operation *op);
 
  /// Invalidate the operation and its ancestors, preserving descendant entries.
  void invalidateAncestors(Operation *op);
 
private:
  DenseMap<Operation *, State> cache;
};
 
/// Returns true if the given operation is free of memory effects.
///
/// An operation is free of memory effects if its implementation of
/// `MemoryEffectOpInterface` indicates that it has no memory effects. For
/// example, it may implement `NoMemoryEffect` in ODS. Alternatively, if the
/// operation has the `HasRecursiveMemoryEffects` trait, then it is free of
/// memory effects if all of its nested operations are free of memory effects.
///
/// If the operation has both, then it is free of memory effects if both
/// conditions are satisfied.
bool isMemoryEffectFree(Operation *op);
 
/// Returns the side effects of an operation. If the operation has
/// RecursiveMemoryEffects, include all side effects of child operations.
///
/// std::nullopt indicates that an option did not have a memory effect interface
/// and so no result could be obtained. An empty vector indicates that there
/// were no memory effects found (but every operation implemented the memory
/// effect interface or has RecursiveMemoryEffects). If the vector contains
/// multiple effects, these effects may be duplicates.
std::optional<llvm::SmallVector<MemoryEffects::EffectInstance>>
getEffectsRecursively(Operation *rootOp);
 
/// Returns true if the given operation is speculatable, i.e. has no undefined
/// behavior or other side effects.
///
/// An operation can indicate that it is speculatable by implementing the
/// getSpeculatability hook in the ConditionallySpeculatable op interface.
bool isSpeculatable(Operation *op);
 
/// Returns true if the given operation is pure, i.e., is speculatable that does
/// not touch memory.
///
/// This function is the C++ equivalent of the `Pure` trait.
bool isPure(Operation *op);
 
} // namespace mlir
 
//===----------------------------------------------------------------------===//
// SideEffect Interfaces
//===----------------------------------------------------------------------===//
 
/// Include the definitions of the side effect interfaces.
#include "mlir/Interfaces/SideEffectInterfaces.h.inc"
 
#endif // MLIR_INTERFACES_SIDEEFFECTINTERFACES_H