CodeGenSchedule.h | Explore in Territory

//===- CodeGenSchedule.h - Scheduling Machine Models ------------*- 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 defines structures to encapsulate the machine model as described in
// the target description.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_UTILS_TABLEGEN_COMMON_CODEGENSCHEDULE_H
#define LLVM_UTILS_TABLEGEN_COMMON_CODEGENSCHEDULE_H

#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/TableGen/Record.h"
#include "llvm/TableGen/SetTheory.h"
#include <cassert>
#include <string>
#include <utility>
#include <vector>

namespace llvm {

class CodeGenTarget;
class CodeGenSchedModels;
class CodeGenInstruction;

ConstRecVec;
ConstRecIter;

IdxVec;
IdxIter;

/// We have two kinds of SchedReadWrites. Explicitly defined and inferred
/// sequences.  TheDef is nonnull for explicit SchedWrites, but Sequence may or
/// may not be empty. TheDef is null for inferred sequences, and Sequence must
/// be nonempty.
///
/// IsVariadic controls whether the variants are expanded into multiple operands
/// or a sequence of writes on one operand.
struct CodeGenSchedRW { … };

/// Represent a transition between SchedClasses induced by SchedVariant.
struct CodeGenSchedTransition { … };

/// Scheduling class.
///
/// Each instruction description will be mapped to a scheduling class. There are
/// four types of classes:
///
/// 1) An explicitly defined itinerary class with ItinClassDef set.
/// Writes and ReadDefs are empty. ProcIndices contains 0 for any processor.
///
/// 2) An implied class with a list of SchedWrites and SchedReads that are
/// defined in an instruction definition and which are common across all
/// subtargets. ProcIndices contains 0 for any processor.
///
/// 3) An implied class with a list of InstRW records that map instructions to
/// SchedWrites and SchedReads per-processor. InstrClassMap should map the same
/// instructions to this class. ProcIndices contains all the processors that
/// provided InstrRW records for this class. ItinClassDef or Writes/Reads may
/// still be defined for processors with no InstRW entry.
///
/// 4) An inferred class represents a variant of another class that may be
/// resolved at runtime. ProcIndices contains the set of processors that may
/// require the class. ProcIndices are propagated through SchedClasses as
/// variants are expanded. Multiple SchedClasses may be inferred from an
/// itinerary class. Each inherits the processor index from the ItinRW record
/// that mapped the itinerary class to the variant Writes or Reads.
struct CodeGenSchedClass { … };

/// Represent the cost of allocating a register of register class RCDef.
///
/// The cost of allocating a register is equivalent to the number of physical
/// registers used by the register renamer. Register costs are defined at
/// register class granularity.
struct CodeGenRegisterCost { … };

/// A processor register file.
///
/// This class describes a processor register file. Register file information is
/// currently consumed by external tools like llvm-mca to predict dispatch
/// stalls due to register pressure.
struct CodeGenRegisterFile { … };

// Processor model.
//
// ModelName is a unique name used to name an instantiation of MCSchedModel.
//
// ModelDef is NULL for inferred Models. This happens when a processor defines
// an itinerary but no machine model. If the processor defines neither a machine
// model nor itinerary, then ModelDef remains pointing to NoModel. NoModel has
// the special "NoModel" field set to true.
//
// ItinsDef always points to a valid record definition, but may point to the
// default NoItineraries. NoItineraries has an empty list of InstrItinData
// records.
//
// ItinDefList orders this processor's InstrItinData records by SchedClass idx.
struct CodeGenProcModel { … };

/// Used to correlate instructions to MCInstPredicates specified by
/// InstructionEquivalentClass tablegen definitions.
///
/// Example: a XOR of a register with self, is a known zero-idiom for most
/// X86 processors.
///
/// Each processor can use a (potentially different) InstructionEquivalenceClass
///  definition to classify zero-idioms. That means, XORrr is likely to appear
/// in more than one equivalence class (where each class definition is
/// contributed by a different processor).
///
/// There is no guarantee that the same MCInstPredicate will be used to describe
/// equivalence classes that identify XORrr as a zero-idiom.
///
/// To be more specific, the requirements for being a zero-idiom XORrr may be
/// different for different processors.
///
/// Class PredicateInfo identifies a subset of processors that specify the same
/// requirements (i.e. same MCInstPredicate and OperandMask) for an instruction
/// opcode.
///
/// Back to the example. Field `ProcModelMask` will have one bit set for every
/// processor model that sees XORrr as a zero-idiom, and that specifies the same
/// set of constraints.
///
/// By construction, there can be multiple instances of PredicateInfo associated
/// with a same instruction opcode. For example, different processors may define
/// different constraints on the same opcode.
///
/// Field OperandMask can be used as an extra constraint.
/// It may be used to describe conditions that appy only to a subset of the
/// operands of a machine instruction, and the operands subset may not be the
/// same for all processor models.
struct PredicateInfo { … };

/// A collection of PredicateInfo objects.
///
/// There is at least one OpcodeInfo object for every opcode specified by a
/// TIPredicate definition.
class OpcodeInfo { … };

/// Used to group together tablegen instruction definitions that are subject
/// to a same set of constraints (identified by an instance of OpcodeInfo).
class OpcodeGroup { … };

/// An STIPredicateFunction descriptor used by tablegen backends to
/// auto-generate the body of a predicate function as a member of tablegen'd
/// class XXXGenSubtargetInfo.
class STIPredicateFunction { … };

ProcModelMapTy;

/// Top level container for machine model data.
class CodeGenSchedModels { … };

} // namespace llvm

#endif // LLVM_UTILS_TABLEGEN_COMMON_CODEGENSCHEDULE_H
llvm/llvm/utils/TableGen/Common/CodeGenSchedule.h
